Building for Sustainable Ventilation and Air Quality

*Mikael Björling*

#### **Abstract**

Most legislations concerning ventilation are based on perceived air quality criteria, but ventilation is also important for the health of the occupants. The perceived air quality criteria can be viewed as a pragmatic tool to achieve an adequate ventilation for precautionary health measures. From a comfort and health perspective, the ventilation rate and an efficient air distribution are both important for achieving a healthy and comfortable indoor environment. Yet, most legislative requirements focus on the ventilation rate. This is not enough, and it is recommended that legislation also address the air distribution with the same zeal. In particular, the efficient distribution of fresh air to the occupied zones or lowering the concentrations of pollutants in the occupied zones. Because there are clear links between ventilation and health, it is extremely worrying that the "energy efficiency first" principle advocated in the Energy Performance of Buildings Directive (EPBD) has led to decreasing ventilation requirements in the European Union legislations, at the same time as the objective is to aggressively tighten the envelopes of the building stock. A second consequence of EPBD is probably that many naturally ventilated buildings will be retrofitted with mechanical ventilation systems. It is not clear that this would be the more sustainable solution in the long run.

**Keywords:** ventilation requirements, ventilation rates, air distribution, air change rate, local mean age of air, air change efficiency, indoor air quality, EPBD, natural ventilation

#### **1. Introduction**

The purpose of buildings is to protect the occupants from a harsh outdoor climate, but also to provide a comfortable and healthy indoor environment. The latter two objectives are intimately related to building ventilation, i.e. the exchange of indoor air with outdoor air. However, 40% of the total consumption of energy resources in the European Union (EU) can be traced to building use [1]. A large part of the consumption is due to the need to condition the indoor air for the thermal comfort of the occupants, i.e. heating or cooling depending on the outdoor climate. In these situations, exchanging the conditioned indoor air for unconditioned outdoor air obviously raises the energy consumption. On the other hand, striving for more energy efficient buildings without a clear strategy for adequate ventilation is likely to lead to more

toxic and hazardous indoor environments. In a wider perspective, the relative projected societal costs for the occupants of a building, compared to the energy use in that building, are probably nine to one [2]. Compromising public health in the name of "energy efficiency" can therefore lead to a considerable economic backlash for society. In a larger perspective, many indoor sources of pollutants in the world have been identified as major causes of premature mortality, e.g. combustion of biomass fuels for cooking, burning incense or mosquito coils and parental smoking [3, 4]. In addition, if the occupants perceive the indoor environment to be unhealthy or uncomfortable, they are likely to take actions (e.g. use air cleaners or increase ventilation flows) that will increase the energy use in buildings [5].

After the energy crisis in 1973, new and renovated buildings have been built with increasingly tighter envelopes to stop uncontrolled air exchanges through cracks and leaks in the construction and to improve energy efficiency. In 1974, the "Passivhaus"-concept combined three energy-saving measures: adequate thermal insulation, a tight envelope, and heat recovery into the idea of a building requiring no, or very little, energy use after it was built [6]. After a few serious backlashes in the early days, the building technologies used to achieve energy efficiency in nearly zero energy (NZE) buildings are currently more mature, but the efficiency of the corresponding ventilation strategies have not been given the same attention. There are several examples of inadequate ventilation in NZE buildings [7]. After the EU Energy Performance in Buildings Directive (EPBD) in 2010 [1], stipulating that all new building should meet the NZE requirements, a majority of EU ventilation experts were worried that EPBD would lead to a worse indoor air quality as compared to the current state [8].

The EPBD is an integral part of the European Green Deal: an action plan to reach a "climate neutral" EU economy [9]. The European Green Deal outlines a more sustainable path for economic and societal development to "transform the EU into a fair and prosperous society, with a modern, resource-efficient and competitive economy" [9]. The European Green Deal addresses many issues: a toxic-free environment; preserving and restoring ecosystems and biodiversity; circular economy; a fair, healthy and environmentally friendly food system; but much focus is devoted to an energy transition to reach zero net emissions of greenhouse gases in the EU by 2050 at the latest [9]. Zero net emissions means that there should be a balance, between the actual emissions of greenhouse gases and the absorption of greenhouse gases by nature (or other processes), in some bookkeeping system like the Emission Trading System [9, 10]. This goal of net zero emissions by 2050 will be legally binding for the member states if the proposal for an EU Climate Law is ratified [11]. Renewable energy sources as well as moving to more energy efficient and sustainable solutions play essential roles in the European Green Deal [9]. The EPBD is the result of the European Commission's resolve to "rigorously enforce legislation related to the energy performance of buildings" [9].

Another issue addressed in EPBD (and its amendments as well as in the European Green Deal) is that 85% of the present building stock in the EU is built before 2001, and most of those buildings are not considered energy efficient [12, 13]. More importantly, at the current rate of renewal (1%), 85–95% of the buildings that will be standing in 2050 are already built [9, 12, 13]. Increasing the rate of renovation of the existing building stock to NZE standard should therefore be strongly encouraged in order to reach "climate neutrality" [12]. Recently, the European Commission also proposed to triple the building renewal rate to 3% coupled with an even more aggressive renovation strategy to kick-start the EU economy after Covid-19 [14].

Adapting existing buildings to NZE are much more complex tasks than to build a NZE-building from scratch. It requires a considerable knowledge-base of old building

#### *Building for Sustainable Ventilation and Air Quality DOI: http://dx.doi.org/10.5772/intechopen.97719*

techniques, old installations, and the consequences that may arise when NZE technologies are retrofitted to these older structures. In addition, 25% of the existing buildings are historic and will require respect for aesthetics, conservations principles and architectural craftsmanship [15]. In fact, the craftsmanship in many older buildings, although non-historic, deserve the same respect. However, the guiding principle of EPBD: "Energy efficiency first", clearly states that the energy aspect will be given a high weight in a decision conflict [14]. Even though the EPBD states that indoor environments should be healthy or that cultural heritage should be safeguarded and preserved, it is obvious that these incentives will be pushed towards the minimum legal requirements when they are in conflict with the efforts to achieve energy efficiency [12].

In the decision conflict between energy efficiency in buildings and adequate ventilation, EPBD has put an increasing pressure on governmental agencies in the member states to lower the standards for ventilation and air quality in existing building codes and ventilation regulations (see discussion in Section 2.3) [12]. From a ventilation perspective, the standards for air quality should rather become more stringent when the buildings become tighter. There is a balance between the existing ventilation regulations in a country and the air leakages in its building stock because these air leakages contribute to the indoor ventilation, albeit uncontrollably. Legislative regulations on the performance of ventilation systems are also important counter balances to the quest for energy efficiency in buildings. The pressing question is *what* must, or should, be regulated to ensure an adequate indoor environment that is comfortable and healthy for the occupants. The aim of Section 2 of this chapter is to investigate possible answers to this question and put them in a wider perspective.

Another effect, of the coming EPBD renovation wave, is probably that the number of buildings with natural ventilation systems will decrease [8]. Many of the older buildings have some kind of natural ventilation system, whereas most new buildings have mechanical ventilation systems. Because heat recovery is such an important ingredient in NZE buildings, mechanical ventilation systems will be chosen more frequently in spite of the fact that some of the energy recovered will be offset by the energy used by the fans. In a milder climate, a balanced mechanical ventilation system with heat recovery will probably save very little energy and would be costly from a life cycle perspective [16]. Fully functional older buildings with natural ventilation systems will perhaps be retrofitted with mechanical ventilation systems and lose some of their aesthetical or cultural heritage values. On the other side of the spectrum, if such a building cannot satisfy the building code regulations, it may be declared unfit for use and demolished [17]. It would naively appear that natural ventilation, where natural driving forces for air flows are used to ventilate the building, is a more sustainable solution than mechanical ventilation, where electrical energy is used to power fans that generate air flows with high pressures. While even the older natural ventilation systems have many advantages regarding occupant satisfaction, they have some difficulties to compete with the mechanical systems when it comes to predictability, controllability, and heat recovery [16, 18]. Nevertheless, natural ventilation systems are considered the more sustainable options in many research initiatives [19–22].

From this perspective, a revival of the use of natural ventilation systems, rather than the projected decline outlined above, would be desired. There are a number of new promising innovations and old, forgotten, know-how is rediscovered, e.g. wind towers, evaporative cooling, solar chimneys and box windows to name a few [23]. The thermal performances of many ancient buildings, with natural ventilation systems, are far superior to many modern buildings, with mechanical ventilation systems. The list could probably be made very long, but some selected examples are: the "baadgir" in the Dolatabaad garden in Yazd, Iran, that uses several of the mentioned techniques [24]; the Villas at Costozza, Italy, use cool air from nearby caves; the Palazzo Pitti in Florence, Italy, use the cooler air from the Boboli gardens and further cool it underground; the cloister Palazzo Marchese in Palermo, Italy, cool the air underground and augment the effect using underground rivers [23]. Natural ventilation systems thus display many good properties, but their drawbacks will prevent them from fulfilling all ventilation needs. The future of sustainable ventilation will probably be centered on optimal combinations of natural and mechanical ventilation techniques instead, i.e. hybrid ventilation systems.

While there are many good modern examples of buildings with natural and hybrid ventilation systems [21], there are at least three important hurdles to cross. One hurdle is that the local building codes and the ventilation regulations in many instances are written with mechanical ventilation systems in mind, which makes it difficult for natural ventilation systems to comply. The second hurdle is that architects and builders may consider natural ventilation systems as a more risky option than mechanical ventilation systems. Describing the low pressure systems of natural ventilation is inherently more difficult than to describe the high pressure systems of mechanical ventilation. The most diligent Computational Fluid Dynamics (CFD) description of natural ventilation can be completely transformed when occupants are moving or closing doors. To cross this hurdle, better tools for design of larger buildings with natural or hybrid ventilation are needed [16, 25]. The third hurdle is urbanization. Many effects of urbanization: pollution, "heat islands", and wind obstruction, favor the use of mechanical ventilation systems [20]. Ventilation requires the outdoor air to be healthy, otherwise it must be cleaned at a considerable cost of energy. There are many issues concerning natural ventilation to discuss, but in this chapter, there is only a brief discussion (at the end of Section 2) on the hurdles for natural ventilation systems in the local building codes and ventilation regulations.

#### **2. Requirements for ventilation**

The purpose of building ventilation is to provide a healthy and comfortable environment for the occupants. However, the human perception of the conditions that constitute a healthy and comfortable environment depends on many factors [26, 27]. The section starts with a historical perspective on the evolution of different ideas concerning the relationship between ventilation and human health and comfort. This is followed by a theoretical treatment of ventilation that hopefully will give the reader some insights into how a good ventilation system performance may be specified. The section finishes with a critical examination of how legislative regulations of ventilation are specified and some suggestions on how it may be modified to facilitate the use of natural and hybrid ventilation systems.

#### **2.1 A short history of ventilation and health effects**

The notion that "bad air" leads to health problems has a long history. The name for the disease malaria is derived from the Italian *mala aria* that literally means "bad air". The origin of the word, used in the sense that the surrounding air in wet, and swampy locations is a cause of disease, can be traced back as far as the ancient Greeks and Romans. Another word for "bad air", first used in 1655, is "miasma" that is derived from the Greek *minainein* "to pollute". In the advent of urbanization in the late

#### *Building for Sustainable Ventilation and Air Quality DOI: http://dx.doi.org/10.5772/intechopen.97719*

eighteen hundreds, medical doctors observed that diseases were more common in the poorer areas of cities. These areas were often overcrowded and situated in unsuitable damp areas. Two battling theories were put forth: the *miasma*-theory preached that diseases were caused by locally generated emissions (or antropotoxins); the *contagium*-theory preached that diseases were caused by poisonous particles that were transferred between humans. The father of ventilation science, Max von Pettenkofer, was a front figure for the *miasma*-theory and suggested increased air flows into the dwellings to remove the locally generated emissions [28]. A leader of the *contagium*theory (from Latin *contagio* "contact"), i.e. the father of clinical microbiology Robert Koch, instead suggested measures to limit the spread of the supposed *contagium*: isolation, quarantine, and border control [29]. The scientific battle was infected by political undertones. The latter measures were unpopular among the trade-friendly industrialists that were politically opposed to the more isolation-friendly local land owners at this time [30]. It was a heated battle, where von Pettenkofer scored some political points when he in 1892 drank a cocktail of cholera bacteria without catching the disease [31]. He was probably immune [30]. By 1900, bacteria were firmly established as the *contagium*-vehicle. It was a landslide victory to the point where most of von Pettenkofers academic contributions were practically erased. He continued to maintain that *miasma* ought to be an aiding factor in the spread of diseases, until he killed himself with a pistol head shot in 1901 [30].

Today this issue may not be altogether black or white. Ventilation and overcrowding have been shown to indirectly influence the spread of diseases [32]. It becomes difficult to conduct good scientific work when political polarization and strong emotions enter the scientific discussion. The historical lessons are not so easy to adopt, as evidenced by more recent heated scientific battles such as global warming or the present Covid-19 battles (see for example [33]).

A remaining *miasma*-related question concerned the rising sense of discomfort experienced by humans in overcrowded rooms. It was well known at the time that enclosing people in a room with very little ventilation lead to symptoms like headache, nausea and dizziness. In severe cases it could even lead to unconsciousness and death. The father of chemistry, Antoine Lavoisier, in cooperation with Laplace had demonstrated in 1783 that the cause of death could not be attributed to lack of oxygen molecules, but probably to an excess of carbon dioxide [34]. Exhaled air of humans contain approximately 44 000 ppm of metabolic CO2 [35]. This means that the excess CO2 in the blood cannot be expelled at exposures to CO2 concentrations above that. Accumulation of CO2 in the blood cause the pH to progressively decrease, and in turn this leads to a series of bodily malfunctions. Death by drowning is caused by the increasing acidity of the blood (acidosis) as the CO2 concentration accumulates and not by too few oxygen molecules in the lungs. Exposure to 20 000 ppm CO2 leads to headache and shortness of breath after a few hours. Exposure to 70 000–100 000 ppm CO2 leads to unconsciousness after a few minutes. Exposure to >170 000 ppm CO2 causes death in humans within one minute from first inhalation [36]. To illustrate how high these concentrations are: a human hermetically enclosed in a 2.5 m3 box would probably still be barely conscious after 24 hours, assuming an exhalation rate equivalent to 0.018 m3 h<sup>1</sup> pure CO2 [35]. Pettenkofer had dismissed CO2 as the cause of diseases, but had developed simple methods to measure it and suggested that the concentration of CO2 could be used as a proxy for the supposed antropotoxins. While investigating public venues in Munich, he had found values as high as 7100 ppm CO2 [31]. Pettenkofer noticed that human odours were clearly perceptible around 1000 ppm CO2 (now known as the Pettenkofer number) and proposed this as a "safe" target to strive for.

The final blow to the *miasma*-theories was dealt by Carl Flügge in 1905 [37]. He devised a series of experiments enclosing humans in glass boxes. The air supply to the breathing zone and to the rest of the box could be controlled separately, as well as other parameters such as temperature and relative humidity. Among other parameters, Flügge varied the odors in the air supply, e.g. air from sewage etc. He found that only the appetite of the subjects was adversely affected, otherwise the subjects adapted to the foul smells. The only "contaminant" that had any adverse effect on the comfort of the subjects was temperature [38]. These experiments totally obliterated the contemporary ventilation philosophy and turned it on its head. There appeared to be no evidence for regulating ventilation from a chemical perspective, as long as the physical parameters (like temperature and relative humidity) were within acceptable comfort-limits. The purpose of a window quickly changed from letting fresh air in to letting heat out. However, some practitioners argued (on the basis of proven experience) that it might be wise to retain some ventilation flows into buildings [30]. It took several years before new ventilation standards were proposed [38, 39].

The need for ventilation, and the chemical perspective, slowly crept back via odorcontrol. The human nose is in fact very sensitive to certain indoor odors. From an evolutionary perspective, it appears to have been advantageous for humans to judge a dwelling by its smell. While the human nose may adapt, people were not comfortable with entering a room with foul smells. This angle provided an incentive for new and fruitful experiments on ventilation requirements. In 1936, Yaglou et al. [40] extended some experiments performed by Lehmberg et al. [41] the year before. They conducted a series of experiments on a group of people to determine their subjective acceptance of the perceived air quality upon entering a test chamber. By varying a number of parameters in the test chamber, Yaglou et al. demonstrated a correlation between the degree of acceptance, the pollution load, and the ventilation air flow into the test chamber. Their results were immediately, but cautiously, adopted by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) [38].

**Figure 1** (inspired by Awbi [35]) shows a compilation of the ventilation requirements historically recommended by ASHRAE, including its predecessors [38]. The

#### **Figure 1.**

*Ventilation requirements recommended by ASHRAE and predecessors. From 1936 and forward (grey) the required flow per person in a standard office is shown. The earlier values (blue) are per room. The red shows the unadopted ASHRAE 62 (1981).*

#### *Building for Sustainable Ventilation and Air Quality DOI: http://dx.doi.org/10.5772/intechopen.97719*

news of Flügge's experiments hit like a bomb when it was presented at the ASHRAE 1911-meeting [30]. All previously accepted ventilation requirements were for all practical purposes under reevaluation until 1936 [37]. (The reason why the old high ventilation requirements were maintained for some time (as shown in **Figure 1**) had to do with the fact that the previous requirements were included in many state laws [37]). Yaglou also studied the ventilation requirements in relation to environmental tobacco smoke (ETS) [42]. As non-smokers are very sensitive to any remaining smoke odor, he found that very high ventilation rates were required to reach acceptance (from them). Smoking was very common at the time. In 1965, 43% of U.S. adults were regular smokers [43]. As health concerns in U.S.A. regarding smoking and indoor ETS were starting to be officially recognized from 1964 and onwards, the question of ventilation requirements started to become a hot topic again [43]. In the ASHRAE Standard 62 (1981), two ventilation requirements for offices were proposed (shown in red in **Figure 1**). The lower one applied to offices without smokers and the higher one to offices where smoking was allowed. This was immediately perceived as a business threat by the tobacco industry. A memorandum circulated at Philip Morris concludes that adopting and enforcing this standard would at least double the maintenance costs for a workplace that allow smoking [44]. In the end, neither the American National Standards Institute (ANSI), nor the Building and Official Code Administrators adopted the 1981 standard as it was considered "controversial". Therefore, the standard was never enforced. In the next "revised" standard that was accepted by ANSI, i.e. ASHRAE 62 (1989), the lower ventilation requirement was retained and moderate smoking was allowed [44]. The tobacco industry succeeded to block the enforcement of new ASHRAE standards until 2000 [44]. The recent decreases in the recommended ventilation requirements, shown in **Figure 1**, can probably also be interpreted as energy-saving measures.

Note that the lower limit proposed in ASHRAE Standard 62 (1981) (red in **Figure 1**) essentially is a revocation to the lowest ventilation requirements proposed in 1836. The guidelines for ventilation requirements are in fact influenced by a number societal parameters. By this time a fair amount of the newer buildings were mechanically ventilated. In Sweden, mechanical ventilation was primarily used in industrial buildings before 1947, but the invention of the less noisy radial fans opened the market for ventilating other buildings [30]. When the energy crisis hit in 1973, the energy used for ventilating buildings suddenly became a liability. The lowered ventilation requirements in the standard of 1981 can therefore be understood in terms of the corresponding decrease in the energy use for the fans in mechanical ventilation and for heating (or cooling) the air supplied. The air supplied into dwellings was further reduced by efforts to reduce air leakages through the building envelope, particularly in the Nordic countries. After a while, reports of occupant discomfort started pouring in. It appeared that up to 30% of the newly built office buildings had an unusually high amount of complaints. In some cases, causal relations to ill-health could be found: e.g. in the use of new materials, moisture damage, or improperly performed building techniques [39, 45]. A large group of diffuse symptoms such as headache, fatigue, lack of concentration and irritation of the skin and mucous membranes remained unexplained. In 1984 the WHO Regional Office for Europe collectively referred to these symptoms as a new medical diagnosis: Sick Building Syndrome (SBS) [46]. The onset of constructing tighter building envelopes seemed to be a likely cause. This sparked a renewed research interest in finding the optimal ventilation requirements.

Fanger and coworkers repeated the Yaglou experiments, but with a much larger sample size in the 1980s [47]. In addition, Fanger attempted to quantify the perceived emissions from the human body and suggested a new subjective, relative unit: *olf*, the emission rate of air pollutants (bio-effluents) from a standard person (from Latin *olfactus* "smelling"). The idea of relative units related to standard people came from previous studies of thermal comfort. Fanger's standard person was characterized as a sedentary white-collar worker (or student) aged 18–30 with a hygienic standard corresponding to 0.7 baths/day and changing underwear daily. Deodorants were used by 80% and some were smokers, but the proportion is not specified. By varying the test chamber ventilation rate (*q*) in a cohort study of 1000 people judged by 168 "judges" (probably from the same cohort), Fanger found the following correlation (*r* <sup>2</sup> = 0.79 and valid for *q* ≥ 0.32 L s�<sup>1</sup> per person, or *olf*):

$$PD = \text{395} \cdot \exp\left(-1.83 \cdot q^{0.25}\right) \tag{1}$$

where PD is the percent dissatisfied "judges", *q* is the ventilation rate (L s�<sup>1</sup> ) per person, L is liters [dm*<sup>3</sup>* ] and s is seconds. **Figure 2** shows the correlation curve given by Eq. (1). These results corresponded well with contemporary measurements [48]. In field studies in 15 office buildings, using a similar experimental method, Fanger et al. found that the sources of disagreeable indoor air pollutants were definitely not limited to human bio-effluents. The olf-equivalents attributed to other indoor sources were: indoor materials, 1–2 *olf*;: the mechanical ventilation system itself, 3 *olf*;: tobacco smoking, 2 *olf* [49]. These and other studies highlighted the necessity to control all indoor air pollution sources in order to reach an acceptable indoor environment in terms of perceived air quality. In a large study of school workers by Smedje et al. [27], it was also shown that their perceptions of the air quality at work were confounded by personal, psychosocial and domestic factors. In short, studying human perception is complicated by many factors and pose some challenges on experimental design.

No single factor causing SBS has yet found any consensus. Sometime after its last official document on SBS in 1995, WHO discontinued the use of SBS as a medical diagnose. A contemporary search on the homepage of WHO yields zero hits. However, that a correlation seem to exist between SBS-related issues and some ventilation parameters receives some consensus in the multidisciplinary field concerned with healthy buildings. In 2001 [50], Jan Sundell managed to convene several European principal researchers in the field to search for consensus on the connection between

#### **Figure 2.**

*Fanger's correlation between the required ventilation rate per person (or* olf*) and the percent dissatisfied judges upon entering the test chamber. The numbers in the figure correspond to the required ventilation rates for the 10%, 20%, and 30% levels of the percent dissatisfied judges.*

ventilation and health. There are few well-designed studies that adequately account for all the multiple factors that are encountered when assessing indoor environments. Out of the selected 105 scientific papers in peer-reviewed journals only 30 were deemed conclusive for the question at hand. The consensus statement include the conclusions that there is:

"*a strong association between ventilation and comfort (as indicated by perceived air quality) and health (as indicated by SBS symptoms, inflammation, infections, asthma, allergy, short- term sick leave). … also indicates that there is an association between ventilation rate and productivity (as indicated by performance of office work).*" [50].

A similar exercise, with a larger geographical spread of the researchers, was initiated by Jan Sundell and Hal Levin in 2010. Many conclusions were similar, but it should be noted that the panel members were divided as to whether the association between ventilation and health outcomes (excluding SBS) was strong or simply suggestive [51]. Both studies conclude that air change rates (see Section 2.2) below 0.5 h<sup>1</sup> leads to increased infestations of house dust mites in the Nordic countries. The latter was deemed important, since there is a plausible link between exposures to the feces of house dust mites and the prevalence of asthma and allergic rhinitis [52].

This concludes the selective short history of ventilation. The idea that ventilation promotes health by removing harmful substances has been a lingering and recurring theme. The effects of indoor exposure to harmful substances are typically studied as dose–response assessments [39]. The relevant exposure dose is the *concentration* of the harmful substance in the indoor air and the responses are the measureable effects on humans. When adverse health effects are established, the exposures of those harmful substances are usually regulated or their use simply forbidden [39]. This also means that, in principle, there should be no *known* harmful substances to be removed by ventilation in the indoor environment. As will be evident in Section 2.3, most guidelines for ventilation requirements are based on perceived indoor air quality, and not health, criteria.

Nevertheless, there is a case for using ventilation as a precautionary measure to prevent adverse health effects caused by the indoor environment. There has been a significant increase in the number of chemicals never before encountered in the indoor environment, particularly in the last fifty years [43]. Today, literally thousands of chemicals are present in the indoor air (see for example [53]). Since most studies of dose–response assessments focus on one single substance at the time, the effects of mixtures of substances are largely unknown [54]. In addition, a majority of these new indoor chemicals have not been studied for health effects. When a harmful substance is forbidden, it is often substituted for new substances with (as yet) unknown health effects. In light of these *known unknowns*, it may be prudent to specify some minimum ventilation requirements as a precautionary health measure.

#### **2.2 Some insights from the theory of ventilation**

Before critically examining the existing guidelines for ventilation requirements a few theoretical explanations of the salient points are needed. Consider first the Onezone model as shown in **Figure 3a**. The flows of air supply to, and air exhaust from, the zone are equal. An air pollutant is emitted at a constant rate into the zone. The assumption for now is that the zone is fully mixed, i.e. the concentration of air pollutant is exactly the same everywhere in the zone. The validity of this assumption, and other assumptions, will be discussed below.

**Figure 3.** *Simple zone models. (a) One-zone model. (b) Two-zone model.*

Assuming that the initial concentration of air pollutant is zero and no air pollutant enters via the air supply (*c*<sup>0</sup> ¼ *cext* ¼ 0), the mass balance equation for the air pollutant in the zone is

$$V\frac{dc\_t}{dt} = \dot{m} - c\_t Q \tag{2}$$

where *V* [m<sup>3</sup> ] is the volume of the zone, *m*\_ [kg h�<sup>1</sup> ] is the constant emission rate of air pollutant, *ct* [kg m�<sup>3</sup> ] is the concentration *c* of air pollutant in the zone at time *t* [h], and *Q* [m3 h�<sup>1</sup> ] is the rate of air flow into and out of the zone. (The conversion factor between *Q* [m3 h�<sup>1</sup> ] and *q* [L s�<sup>1</sup> ] is *Q* ¼ 3*:*6*q*). The steady state solution of Eq. (2) is obtained when a constant equilibrium concentration is established in the fully mixed zone. Setting the left hand side to zero gives

$$
\omega\_{\infty} = \frac{\dot{m}}{Q} \tag{3}
$$

where *c*<sup>∞</sup> is the constant equilibrium concentration at *t* ¼ ∞. This is an important result. It appears that, given a constant emission rate of an air pollutant, it is the ventilation rate that determines the final concentration of air pollutant in the zone (i.e. the exposure to the air pollutant). However, this conclusion is only valid *provided that* the zone is completely mixed at all times.

For the case of a hermetically closed zone, i.e. when *Q* ¼ 0 in Eq. (2), it can be solved by integration to yield

$$
\omega\_t = \frac{\dot{m}}{V} t.\tag{4}
$$

Eq. (4) shows that the air pollutant concentration will increase linearly with time in a hermetically closed zone. Note that the volume of the zone (*V*) buffers the rate of concentration increase in the zone. The larger the volume, the slower the rate of increase of the air pollutant concentration in the zone.

Another illustrative one-zone case is obtained by allowing an initial concentration *c*<sup>0</sup> of the pollutant in the zone at *t* ¼ 0 and assuming that *m*\_ ¼ *cext* ¼ 0. Solving for the concentration gives

$$\mathfrak{c}\_t = \mathfrak{c}\_0 \mathfrak{e}^{-(Q/V)t} = \mathfrak{c}\_0 \mathfrak{e}^{-\mathcal{N}t} \tag{5}$$

where the hourly air change rate (ACH) for a completely mixed zone is defined as *N* ¼ *Q=V*. Eq. (5) means that for any temporary emission of air pollutant in the zone, *Building for Sustainable Ventilation and Air Quality DOI: http://dx.doi.org/10.5772/intechopen.97719*

its concentration will decay exponentially with time. The rate of decay is gauged by the air change rate *N*. A higher air change rate means a faster decay.

The simple One-zone model of ventilation presented above has two main problems: (i) Emission sources are not evenly distributed in the zone volume. They are local and confined to surfaces, objects or humans. (ii) Complete mixing of a zone is difficult to achieve. Both points can be illustrated with a simple Two-zone model, originally proposed by Etheridge and Sandberg [55], as shown in **Figure 3b**. In the Two-zone model, emission sources are allowed to be slightly more local and the required mixing air flows are made slightly more explicit in terms of the inter-zonal air flows. Inter-zonal air flows are given as *βQ*, so when *β* ¼ 1 the inter zonal air flows have the same magnitudes as the supply and extract air flows. For simplicity, complete mixing of both zones are assumed. The mass balance equations in each zone for the case *cext* ¼ *c*<sup>10</sup> ¼ *c*<sup>20</sup> ¼ *m*\_ <sup>1</sup> ¼ 0 becomes

$$\begin{aligned} V\frac{dc\_1}{dt} &= \beta Qc\_{2t} - (1+\beta)Qc\_{1t} \\ V\frac{dc\_2}{dt} &= \dot{m}\_2 + \beta Qc\_{1t} - \beta Qc\_{2t} \end{aligned} \tag{6}$$

The steady state solutions for the concentrations in each zone are then

$$\begin{aligned} c\_{1\infty} &= \frac{\dot{m}\_2}{Q} \\ c\_{2\infty} &= \frac{(1+\beta)\dot{m}\_2}{\beta Q} \end{aligned} \tag{7}$$

Note that the steady state result for *c1* in Eq. (7) is the same as for the completely mixed One-zone model in Eq. (3). If nothing is known about the distribution of concentrations within the zone, the proper interpretation of steady state in Eqs. (2) and (3) is that the emitted amount equals the exhausted amount and that the accumulation of air pollutant in the zone has stopped. The interpretation that the concentration is constant in the zone is not correct. Unless, of course, complete mixing is established by other measurements. In general the concentrations are not equal, as is evident in **Figure 4** where the dimensionless quotient *c*2*=c*<sup>1</sup> of the steady state

#### **Figure 4.**

*Increase in the relative concentration in the lower zone (2) as a function of the interzonal flows. When* β *= 1 the interzonal flows are equal to the air supply.*

concentrations from Eq. (7) are plotted against *β*. Note that *c2* approaches *c1* very slowly as *β* increases in **Figure 4**. In order to reach complete mixing the inter-zonal air flows must be much larger than the supply and extract flows. In experiments where complete mixing of the whole zone is important, e.g. using the decay in Eq. (5) to measure the air change rate using tracer gases, several extra fans are employed to come as close as possible to the ideal case of complete mixing. It is also clear from **Figure 4** that the concentration of air pollutant in the lower zone rises very quickly as *β* decreases below unity. From an exposure point of view, it is problematic that concentrations of air pollutants may differ considerably within a room when mixing is incomplete.

The special case when the fresh air from the supply flow never enters the lower zone and directly exits by the extract is called ventilation short-circuiting. In this case, *β* is zero and the lower zone essentially behaves as a hermetically closed zone (Eq. (4)) and the concentrations of all air pollutants emitted in the lower zone rise without bounds. To be fair, ventilation systems are designed to deliver fresh air to occupants and complete short-circuiting is rare. However, poorly designed systems do exist. One example is shown in **Figure 5**. Typical situations when short-circuiting may occur are: if inlet and exhaust devices are close to each other; if there are obstacles in the flow path of a mechanical ventilation air inlet; if the air supplied is warmer than the air in the room and the extract is near the roof.

In a more general theoretical approach, allowing for non-homogeneous concentration distributions in the zone, all possible paths of a very small package of air from the inlet to the outlet are considered (see Etheridge and Sandberg [55] for a complete treatment). A long and tortuous path for the package or air will result in a long residence time for the package within the zone, whereas a short path corresponding to a ventilation short-circuit would lead to a very short residence time. At the outlet, packages of air escaping the zone in every instance of time will represent many different residence times. At steady state, in a similar manner as in Eqs. (3) and (7),

#### **Figure 5.**

*Retrofit of cooling beam (with attached light fixture) leading to a high degree of ventilation short-circuiting. Air supply device to the left and air exhaust to the right.*

the distribution of residence times will converge to a constant average residence time ⟨*τr*⟩ for the air packages. The average residence time can also be interpreted as an average age of the air packages exiting the zone, if the age of an air package is set to zero as it enters into the zone through the inlet. This concept of ages of air packages is useful when examining the interior of the zone.

The simple process of plug (or piston) flow illustrates the age concept well. It is the most efficient method to ventilate and is used in so called "clean rooms". The idea is to achieve a laminar flow by supplying slightly colder air from the roof and letting it fall vertically to the floor where it is extracted. Ideally, all air packages entering from the whole area of the roof fall at the same speed and reach the floor simultaneously. This means that all air packages have exactly the same residence time in the zone. It is easy to show that the residence time only depends on Q and V, regardless of the shape of the zone, and is given by

$$\langle \tau\_r \rangle\_{plugflow} = \frac{V}{Q} \equiv \tau\_n \tag{8}$$

where the nominal time constant of the ventilation system *τ<sup>n</sup>* is defined. For plug flow the average residence time is equal to the nominal time constant. Since the air packages follow the shortest route from the roof to the floor in plug flow, the nominal time constant can be interpreted as the shortest possible residence time. It is also easy to determine the local age of the air packages in the interior of the zone. It must increase linearly from age zero at the roof to an age equal to the residence time at the floor. Consider an arbitrarily small volume element within the zone. It will contain many air packages with ages that vary linearly with height. The local mean age of air *τ* is defined as the average age of the air packages within the small volume element. The local mean age of air can be interpreted in terms of how well the ventilation system delivers fresh air to the volume element. As the packages of air enters the zone, they start to equilibrate by diffusion with the concentrations of contaminants in the local environment and start to become less fresh. The older the air, the less fresh it is. Now let the volume element be as small as one package of air. The average local mean age of air with respect to the entire zone must then be equal to the local mean age at half the height. Think of a process where all volume elements with a low age above the middle height can be paired with volume elements with a high age below the middle height so that their average is exactly the local mean age of air at half height giving

$$
\langle \bar{\pi} \rangle\_{plugflow} = \frac{\tau\_n}{2} \tag{9}
$$

This result can be generalized since the residence time and the local mean age of air of an arbitrary path of the air packages are related by

$$
\tau\_i + \tau\_{rl} = \tau\_r \tag{10}
$$

where *τ<sup>r</sup>* is the residence time of the path, *τ<sup>i</sup>* is the time already spent in the interior of the zone (i.e. the local mean age of air of the air package) and *τrl* is the residual life time until the air package exit the zone. This is obviously valid for all paths and all air packages will eventually complete their paths to the exit. It will therefore always be possible to pair air packages (with the same residence time), so that their average local mean age is exactly half the residence time. Taking the average of all possible paths, a generally valid relation is given by

$$
\langle \overline{\pi} \rangle = \frac{\langle \pi\_r \rangle}{2}. \tag{11}
$$

Note that the averages of the local mean age of air over all paths or over the zone space give the same results.

Since no other ventilation process can be more efficient than plug flow, the average local mean age of air for other ventilation processes cannot be lower than that for plug flow. It therefore seems natural to assign a 100% air change efficiency to plug flow and consequently define the general air change efficiency in a zone as

$$
\langle \varepsilon\_a \rangle = \frac{\tau\_n}{2 \langle \bar{\tau} \rangle} \cdot \mathbf{100\%}. \tag{12}
$$

For the case of complete mixing, the paths of all air packages should reach any volume element within the zone with the same probability. Complete mixing may also be viewed as a process where all volume elements in the zone are instantaneously considered identical at all times. All volume elements have identical characteristics, such as the same concentrations of molecules and the same local mean age of air. Air entering through the inlet will therefore, in theory, simultaneously enter all volume elements. Within each volume element, air packages with increasing ages will continue to accumulate until the steady state is reached and the local mean age of air stays constant. In analogy, the mass balance given in Eq. (2), describes how a contaminant is accumulated in each volume element until a steady state concentration is reached. Since the mixing conditions are the same, the accumulation of ages and of concentration, respectively, follow the same time evolution. Solving for *ct* in Eq. (2) gives

$$\mathcal{L}\_t = \mathcal{c}\_\infty \left( \mathbf{1} - \boldsymbol{\mathcal{e}}^{\frac{-Q}{V}} \right) = \mathcal{c}\_\infty \left( \mathbf{1} - \boldsymbol{\mathcal{e}}^{\frac{-\epsilon}{v\_0}} \right) \tag{13}$$

where Eqs.(3) and (8) were used. In the field of statistics, *ct=c*<sup>∞</sup> is an example of a cumulative distribution function. By analogy, it is also the cumulative distribution function for the ages of the air packages. A probability distribution function is obtained by taking the time derivative of the cumulative distribution function. Thus, it is evident that, for a completely mixed zone, the ages of the individual air packages accumulated within a volume element at steady state are exponentially distributed according to

$$f\_{\tau\_i}(t) = \frac{1}{\tau\_n} e^{\frac{-t}{\tau\_n}} \tag{14}$$

Now the average local mean age of air for a volume element (and for the whole zone) can be evaluated to *τn*. This gives the following relations for a completely mixed system

$$
\langle \bar{\tau} \rangle\_{\text{mixed}} = \tau\_n,
$$

$$
\langle \tau\_r \rangle\_{\text{mixed}} = 2\tau\_n,
$$

$$
\langle \varepsilon\_d \rangle\_{\text{mixed}} = \mathbf{50} \boldsymbol{\%}.\tag{15}
$$

The average air change efficiency of a mixing ventilation system is at best 50% as compared to plug flow. In analogy with the nominal air change rate *N* (or ACH) being given as the inverse of the nominal time constant *τ<sup>n</sup>* as

*Building for Sustainable Ventilation and Air Quality DOI: http://dx.doi.org/10.5772/intechopen.97719*

$$N = \frac{Q}{V} = \frac{1}{\tau\_n},\tag{16}$$

An effective local air exchange rate of the zone can be defined as

$$N\_{\it eff} = \frac{1}{\langle \overline{\mathbf{r}} \rangle} \tag{17}$$

where *Neff* is the effective air exchange rate and note that the local mean age of air average is spatial and taken over the zone. It can be interpreted as the local ability of the ventilation system to dilute contaminants with fresh outdoor air in the point *p*. This an important property from an exposure viewpoint.

The aim of the above theoretical exercises for two mixing models is mainly to introduce the concept of local mean age of air and its properties. The fact that it is a local property that can be determined experimentally by tracer gas techniques [55] means that interior points of any ventilated zone can be characterized by it. In particular, in means that the distribution of fresh air to the occupied volumes of a zone can be tested.

The insights from this subsection can now be summarized. It has been shown that requiring a specific ventilation rate is not a guarantee for good performance of a ventilation system. The supplied air must also be distributed efficiently and this capacity should be evaluated. Possibilities for ventilation short-circuiting should be eliminated. Finally, a large zone volume can be a strategy to prevent build-up of concentrations from transient sources of air pollutants.

#### **2.3 A critical examination of guidelines for ventilation requirements**

Most of the contemporary legislative guidelines for ventilation requirements are based on criteria for perceived air quality, as concluded in Section 2.1. For more than 20 years, the basic guidelines in the U.S.A. (and also in Europe) have been based on the recommendation that no more than 20% of the occupants should be dissatisfied with the perceived indoor air quality [56]. Nevertheless, the adaptation of the human nose adds a dimension and there is a difference between the philosophy in Europe and the U.S.A on how perceived air quality should be measured. The guidelines in Europe (following Fanger et al. [49]) are based on the perceived air quality as judged by an un-adapted visitor to the room, whereas the guidelines in the U.S.A. (ASHRAE) are based on the perceived air quality by a judge that has been allowed to adapt to the room air for 15 minutes [5]. The American guidelines therefore recommend lower ventilation rates than the European guidelines at the same level of dissatisfied judges. [5]

Comparison of the work place ventilation rates required per sedentary person in **Table 1** (i.e. 7 L�s �1 /person) with the ventilation rates given in **Figure 2**, show that The Swedish Work Environment Authority appears to follow the European philosophy in the old [57], as well as in the new, guidelines [58]. In line with the findings of Fanger et al. [49], many guidelines assume that all other indoor emissions of pollutants (e.g. from building materials and human activities, such as smoking, cleaning, and cooking) should be added to the emissions of bio-effluents from the occupants. All these emissions are lumped into a floor-area-based emission rate. The total required ventilation rate is then the sum of two contributions as shown in Eq. (18).

$$q\_{\rm tot} = n\_p \cdot q\_p + A \cdot q\_A \tag{18}$$

where *qtot* is the total required room ventilation rate [L�s �1 ], *np* is the number of occupants, *qp* is the required ventilation rate per person [L�s �1 /person], *A* is the room area [m<sup>2</sup> ], and *qA* is the required ventilation rate per square meter [L�s �1 �m2 ]. The required *qA* in **Table 1** are based on a room with very low emitting materials and no smoking. The Pettenkofer number (1000 ppm CO2) can also be recognized in the guidelines in **Table 1**. However, the lowest required *qp* (4 L�s �1 /person) from The Public Health Agency of Sweden [59] can only keep the CO2 concentrations below 1500 ppm in most realistic scenarios [60]. The Public Health Agency of Sweden is the only government agency recommending a specified air change rate of 0.5 h�<sup>1</sup> [59]. Note that the floor area based ventilation rate 0.35 L�s �1 �m<sup>2</sup> corresponds to an air change rate (*N*) equal to 0.5 h�<sup>1</sup> if the room height is 2.5 m (a common room height in the Swedish building stock). While there are common elements between the required ventilation rates in **Table 1**, it is clear that the more generally valid recommendations from The Public Health Agency of Sweden prescribe lower ventilations rates than the recommendations from The Swedish Work Environment Authority that are valid only in nonresidential buildings.

There are mutual dependencies between the ventilation rates presently required by government agencies and the properties of the existing building stock [8]. If the building stock can be shown to cause health problems that can be traced to inadequate ventilation, then the government agencies will try to improve the situation by requiring higher ventilation rates. On the other hand, if air leakages through the building envelopes provide ample contributions to the ventilation of the building stock, in addition to the controllable ventilation rates, then the required ventilation rates need not be as stringent because the total ventilation rate will be sufficient anyway. The point here is to highlight plausible dependencies on average, even though there may be a wide spectrum of properties in the building stock. Thus, changes in the properties of the building stock will lead to changes in the ventilation requirements recommended by government agencies.

The EPBD objective to transform the building stock to NZE- buildings with tighter building envelopes should, with the above logic, lead to a more stringent requirements for ventilation rates [8]. However, as mentioned in the Introduction, the "energy efficiency first" principle in EPBD [12] pushes other incentives towards their


#### **Table 1.**

*Values are extracted from the official Swedish guidelines for ventilation requirements and air quality. FoHMFS are the ventilation guidelines issued by The Public Health Agency of Sweden. [59] AFS are the old [57] and the new guidelines (valid from 1 January, 2021) [58] issued by The Swedish Work Environment Authority. The + sign signifies that the required air supply per m2 must be added to the air supply per person.*

*Building for Sustainable Ventilation and Air Quality DOI: http://dx.doi.org/10.5772/intechopen.97719*


#### **Table 2.**

*Values are extracted from the official European guidelines for ventilation requirements and air quality. CEN EN 15251:2006 are the old guidelines from 2006 [61] and CEN EN 16278.1:2019 are the new guidelines (valid from 8 May, 2019) [62] issued by European Committee for Standardization. The bold figures are the recommended values.*

minimum legal limits when they are in conflict with the efforts to improve the energy performance of buildings. Maintaining a good indoor air quality by ventilation is such an incentive, and therefore ventilation rates will be pushed towards their minimum legal limits. As a consequence, in the coming EPBD transformation of the building stock, the minimum legally required ventilation rates play a critical role as counterbalances to prevent a decline in indoor air quality. The required ventilation rates will probably need to be increased to maintain the present levels of indoor air quality in the building stock.

It is therefore doubly worrying that the ventilation requirements in the standards on the European level recently have been lowered as shown in **Table 2**. For example, in a standard 10 m<sup>2</sup> office for one person, the required ventilation rate (*qtot*) is lowered by 43% from 10.5 Ls <sup>1</sup> in the old guideline CEN-EN15251:2006 [61] to 6 L<sup>s</sup> <sup>1</sup> in the new guideline CEN-EN16798:2019 [62]. The change corresponds to recommending 30% dissatisfied un-adapted judges in the new guidelines as compared to 20% in the old guidelines. The guidelines in the European Standards provide the "floor" upon which the legal requirements of the member countries rests. Lowering the required ventilation rates in the European Standard opens for a corresponding lowering in the legislation of the member states. While it is slightly encouraging that the Swedish legislation is unchanged at the moment, as seen in **Table 1**, it is obvious that the risk of EPBD creating unhealthy indoor environments will be augmented. The present levels of indoor air quality in the building stock risk being lowered by the combined effect of tighter building envelopes and the prospect of lower required ventilation rates.

As concluded in the previous section, simply specifying required ventilation rates cannot guarantee an adequately low exposure to indoor pollutants [63]. Legislation also need to address the air distribution. In the European Standard [62] and in the ASHRAE Standard [56], the given ventilation rates assume complete mixing in the room. Thus, they presuppose a mixing mechanical ventilation system. Other ventilation systems are accommodated by dividing with a correction factor. ASHRAE [26] proposes a

correction factor called the air change effectiveness defined as *ε<sup>I</sup>* ¼ *τn=*⟨*τ*⟩ evaluated in the breathing zone [56]. For mixing ventilation this gives *εI*,*mixed* ¼ 1 and for plug flow *εI*,*plugflow* ¼ 2. The correction factor in the European Standard is similarly defined, but evaluated as a room average, and is called ventilation effectiveness *εv*. (The nomenclature for the correction factors is a bit confusing and may be easily mixed-up with the air change efficiency defined in Eq. (12).) If the system is not fully mixed, the correction factor is less than unity and the required ventilation rate should be correspondingly increased. If displacement or plug flow ventilation systems are used, that are more efficient than mixing ventilation, the correction factor is larger than unity and the required ventilation rates may be correspondingly decreased.

Legal ventilation requirements also address air distribution, but rephrased into requirements that newly installed ventilation should be shown to function as designed, that the ventilation rate should be sufficient, or by requiring a specified air change efficiency as in **Table 1**. I have the impression that air change efficiency is seldom tested in the field. The control of newly installed ventilation systems mostly consist of ensuring that the design ventilation flows are obtained, otherwise the ventilation system components are assumed to function with the same efficiency as in laboratory tests. However, there are a number of factors that may lower the ventilation system efficiency in a real building. Some of these factors were mentioned in connection with ventilation short-circuiting in previous section (see also **Figure 5**); ventilation systems may be very complex and design choices may have unforeseeable consequences; a ventilation designer may enter late in the planning process and may be forced to make suboptimal choices, e.g. inlets vents may end up too close to outlet vents; or occupants may tamper with the intended function of the ventilation components to minimize perceived draft. It may be prudent to verify that air is distributed with the intended efficiency in new and old ventilation installations.

The above standards clearly favor mechanical ventilation systems where ventilation rate is an easy parameter to measure. It is not that easy to measure ventilation rate for natural ventilation systems. It is more difficult to demonstrate that natural ventilation systems are in compliance with the legal requirements than it is for mechanical ventilation systems. In addition, rooms with natural ventilation systems typically have higher room heights, than rooms with mechanical ventilation systems. Naturally ventilated rooms require larger room volumes to prevent concentration build-up of transient pollution sources to offset the natural fluctuations in the ventilation rate. Historically, the introduction of mechanical ventilation systems allowed building entrepreneurs to squeeze in three floors in the same volume where previously there would be two floors in older naturally ventilated buildings [30]. Using this observation, rooms with natural ventilation are roughly estimated to be 50% larger than rooms with mechanical ventilation. If there is a legally required air change rate or a required ventilation rate per floor area (as exemplified in **Table 1**), the prescribed ventilation rates will also be 50% larger for naturally ventilated rooms, as compared to a mechanically ventilated room. This increase is probably unnecessary and it arises because the legal requirements does not consider the different ventilation strategies used in natural ventilation systems. It would be desirable that all ventilation strategies should be treated equally in the eyes of the law, with the same objective requirements for adequate indoor air quality.

If the objective of the legal regulations is to ensure that 80% of the occupants find the perceived air quality to be acceptable, as it appears to be, then it would be more fitting to simply require that less than 20% of the occupants are feeling uncomfortable. This could be tested in a questionnaire. Note that this approach is suggested in some environmental certification systems for buildings, e.g. the level GULD in Miljöbyggnad *Building for Sustainable Ventilation and Air Quality DOI: http://dx.doi.org/10.5772/intechopen.97719*

3.1 [64]. The problem with such an approach is that other factors, than the actual air quality, may affect the outcome [27]. Alternatively, the regulations should apply specifically to the occupied zone of a room. This would lead to more balanced demands on natural ventilation systems as compared to the demands on mechanical ventilation systems. To specify concentration limits in the occupied zone would be preferable because of the direct link to exposure, but the challenge is that the human nose is very sensitive so some substances and there may be difficulties to measure such low concentrations at the present time. An indirect approach would be to specify some local ventilation parameter, such as the local mean age of air, in the occupied zone.

The fact that ventilation requirements primarily targets occupant comfort, does not mean that ventilation is irrelevant for the health of the occupants. Adverse health effects caused by exposure to indoor air pollution have been estimated to cause that approximately two million disability-adjusted lifetime years (DALYs) are lost annually, based on the population in 26 European countries. In economic terms this corresponds to a societal cost exceeding €200 billion [60]. It is very likely that the combined effect of the lower ventilation requirements and tighter building envelopes due to EPBD will increase this societal cost considerably. The prospect of turning buildings into unhealthy containers for the occupants certainly tempers my enthusiasm for the projected EPBD energy savings.

#### **3. Conclusions**

Most legislations concerning ventilation are based on perceived air quality, but ventilation is also important for the health of the occupants. Perceived air quality can be viewed as a pragmatic tool to achieve an adequate ventilation for precautionary health measures. From a perceived air quality and health perspective, the ventilation rate and an efficient air distribution are both important for achieving a healthy and comfortable indoor environment. Yet, most legislative requirements focus on the ventilation rate. This is not enough, and it is recommended that legislation also address the air distribution with equal zeal. In particular, verifying the efficient distribution of fresh air to the occupied zones or the concentrations of pollutants in the occupied zones.

Because there are clear links between ventilation and health, [3, 4, 50, 51, 60], it is extremely worrying that the "energy efficiency first" principle advocated in EPBD has led to decreasing ventilation requirements in the EU legislations, at the same time as the objective is to aggressively tighten the envelopes of the building stock. A second consequence of EPBD is probably that many naturally ventilated buildings will be retrofitted with mechanical ventilation systems. It is not clear that this would be the more sustainable solution in the long run.

Every citizen's right to a healthy indoor environment has been suggested to be a basic Human Right by WHO [65]. Adequate ventilation is at the heart of the solutions to reach this commendable goal. The mantra "build tight – ventilate right" [66] is a good one, but do not forget the second part!

#### **Acknowledgements**

The author wishes to acknowledge helpful discussions with Jan Sundell. He will be missed.

### **Conflict of interest**

The author also works as a ventilation consultant.

### **Author details**

Mikael Björling Department of Electrical Engineering, Mathematics and Science, Faculty of Engineering and Sustainable Development, University of Gävle, Gävle, Sweden

\*Address all correspondence to: mikael.bjorling@hig.se

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Building for Sustainable Ventilation and Air Quality DOI: http://dx.doi.org/10.5772/intechopen.97719*

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[53] Farmer DK, Vance ME, Abbatt JPD, Abeleira A, Alves MR, Arata C, Boedicker E, Bourne S, Cardoso-Saldana F, Corsi R, DeCarlo PF, Goldstein AH, Grassian VH, Hildebrandt Ruiz L, Jimenez JL, Kahan TF, Katz EF, Mattila JM, Nazaroff WW, Novoselac A, O'Brien RE, Or VW, Patel S, Sankhyan S, Stevens PS, Tian Y,Wade M,Wang C, Zhou S, Zhou Y. Overview of HOMEChem: House Observations of Microbial and Environmental Chemistry. Environ. Sci.: Processes Impacts, 2019;21:1280–1300. DOI: 10.1039/C9EM00228F

[54] EC (European Commission). Toxicity and assessment of chemical mixtures. Brussels: European Commission. Directorate-General for Health & Consumers – Scientific Committee on Health and Environmental Risks (SCHER), Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR), Scientific Committee on Consumer Safety (SCCS), final approved opinion; 2011. Available from: http://ec.e uropa.eu/health/scientific\_committees/e nvironmental\_risks/docs/scher\_o\_155. pdf [Accessed: 2021-02-05]

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[57] Workplace design: Provisions of the Swedish Work Environment Authority on workplace design and general recommendations on the implementation of the provisions (AFS 2009:2) [Internet]. Stockholm: The Swedish Work Environment Authority. Available from: https://www.av.se/globalassets/filer/ publikationer/foreskrifter/engelska/work place-design-provisions-afs2009-2.pdf [Accessed: 2021-02-05]

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#### **Chapter 11**

## Some Aspects of HVAC Design in Energy Renovation of Buildings

*Taghi Karimipanah*

#### **Abstract**

It is well-known fact that air conditioning systems are responsible for a significant part of all energy systems in building energy usage. In EU buildings, the building HVAC systems account for ca 50% of the energy consumed. In the U.S., air-conditioning accounts on average about 12% of residential energy expenditures. The proper choice of air distribution systems and sustainable energy sources to drive the electrical components have a vital impact to achieve the best requirements for indoor climate including, hygienical, thermal, and reasonable energy-saving goals. The building energy system components that have a considerable impact on the demand for final energy in the building are design, outdoor environment conditions, HVAC systems, water consumption, electrical appliances, indoor thermal comfort, and indoor human activities. For calculation of the energy balance in a building, we need to consider the total energy flows in and out from the building including ventilation heat losses, the perimeters transmission heat loses, solar radiation, internal heat from occupants and appliances, space and domestic water heating, air leakage, and sewage heat losses. However, it is a difficult task to handle the above time-dependent parameters therefore an energy simulation program will always be used. This chapter aims to assess the role of ventilation and air-conditioning of buildings through the sustainability approaches and some of the existing renewable energy-based methods of HVAC systems are presented. This comprehensive review has been shown that using the new air distribution systems in combination with renewable energy sources are key factors to improve the HVAC performance and move toward Nearly Zero Carbon Buildings (NZCB).

**Keywords:** sustainable HVAC systems, building energy systems, thermal comfort, indoor human activities, energy balance, energy saving potential, Nearly Zero Carbon Buildings (NZCB)

#### **1. Introduction**

The generation and use of energy is the largest contributor to anthropogenic CO2 emissions and therefore the most important factor to tackle greenhouse gases and climate change issues. According to the International Energy Agency (IEA), World Energy Outlook 2010, the worldwide contribution of the building sector to the final energy demand has steadily increased to about a third of the world's final energy demand. Therefore it makes the building the most energy-intensive sector which contributes almost 30% of the anthropogenic greenhouse gas emissions. More

unfortunate is that the energy use in buildings will increase to 67% by 2030. A major cause for high energy use in buildings is the demand for better thermal comfort and air quality in indoor environments. It is estimated that heating, ventilation, and air conditioning systems are responsible for almost 50% of the total energy use in buildings which is about 10-20% of the national energy use in most developed countries. To reduce global CO2 emissions, the economic use of energy resources is of outstanding significance. The buildings sector is a significant contributor to energy-related sustainability challenges. That is why buildings should be considered as a key element to a sustainable future because of their processes of design, and construction including their operation, and all human indoor activities. Therefore, reducing energy demand in buildings can play one of the most important roles in solving these challenges. A sustainable and efficient energy supply in buildings needs the use of more energyefficient manufacturing materials which are a part of the futures critical is to tackle the sustainability-related challenges.

It is indicated that the air conditioning systems as a considerable part of building energy systems and account for about 12% of residential energy expenditures in the U.S., and the building HVAC systems are responsible for ca 50% of the energy usage in EU buildings [1].

The air distribution systems in buildings are of vital importance to achieving the best requirements for indoor climate including, hygienical, thermal, and reasonable energy-saving goals. Yang et al. [2] in a comprehensive review article tried to describe all existed air distribution methods in which the benefits and shortcomings are treated. The air distribution systems are the main element for good ventilation systems which play a key role in creating an acceptable microclimate in the indoor environment. Thus, the development and adoption of sustainable ventilation and air conditioning systems are a viable solution to mitigate climate change and curtail carbon emissions [3].

It is worth mentioning that globalization, economic development, and population growth will be among the factors that will increase energy use worldwide in the future.

According to Gustafsson [4], solar systems, including both thermal and solar cells, can be applied to reduce the environmental impact of buildings. He also pointed out that without an input tariff for surplus electricity and government subsidies for the Central and Northern European buildings, it is still not economically feasible.

However, in the renovation of multi-family houses, the solar energy systems can reduce the total lifecycle costs (LCC) both in Southern as well in Northern European climates.

In cold climates, air heat recovery and low-temperature heating were both found to have a larger impact in colder climates. To improve the performance factor of heat pumps, low-temperature heating systems can be used, particularly when the space heating demand is relatively high concerning the hot water demand. It is worth mentioning that this chapter is based on a comprehensive review of existing literature in the research area. We tried to show that using the new air distribution systems in combination with renewable energy sources are key factors to improve the HVAC performance and move toward the EU's directives for Nearly Zero Carbon Buildings (NZCB).

#### **2. Energy flow in buildings**

Maintaining the indoor climate has a direct impact on energy usage, that is to say, the energy is used to clarify and control the indoor air quality. Danielski [5] described the main energy balance in buildings as all the energy flows to and from the building which includes:


The building's components which their interaction have an impact on the demand for final energy in the building and henceforth on the whole energy system are [5]:

1.Design process


However, each of the energy flows includes many variables that can vary with time, therefore an energy simulation program will always be used (see, later on about energy simulation).

#### **2.1 Energy renovation of buildings**

Gustafsson [4] stated that the building sector accounts for around 40% of the total final energy use in the EU. Therefore, the energy renovation of buildings, or increased energy efficiency through renovation, can be considered vital in the work toward the EU climate and energy goals for the year 2030. It is noted that comparing the building renovation without energy efficiency measures, the energy renovation can often reduce life-cycle costs as well as the environmental impact.

When making renovation of old apartment buildings, the improvement of ventilation is unavoidable. By using a modern and energy-saving ventilation strategy one can provide a healthy indoor environment for the occupants [6].

Randazzo et al. [7] stated that: using data for 8 industrial countries shows that when households adapt to the increasing temperature of global warming and climate change, then the electricity demand increases yearly between 35–42%. They pointed

out that this is because of adapting new air condition systems and consequently the rate of poverty for the lowest-income increases as well. They also show that CDDs (the colling degree days) affect electricity expenditures and forced households to purchase and then use air conditioners. They also pointed out that households on average spend 35–42% more on electricity when they adopt air conditioning. Therefore, by recognizing the role of space cooling in energy consumption to drive up emissions, the national policy agendas should thus prioritize increasing the supply of electricity from renewable sources [7].

#### **2.2 Energy saving potential in the building sector**

The building sector is an important candidate for energy usage and presents a lot of potentials for energy saving. The population growth and desire for a better living standard are responsible for increasing energy demand. But researchers predict that there are a lot of potentials for energy saving in old and new buildings. Thus, the implementation of energy efficiency measures is calculated to result in up to 30% savings in the building sector by 2020 [8].

Many measures and methods are implemented to reduce energy use in the construction sector:


In the European Union, policies for demands on energy efficiency in buildings have been stricter according to the EU2030 goals to meet the EU's long-term 2050 greenhouse gas reduction target [9].

The above report pointed out that, the European Parliament approved the "*Directive on the Energy Performance of Buildings in 2010*" as a measure to realize this longterm potential. Thereby, all newly constructed buildings in the EU should be *nearly zero-energy buildings* (NZEB) as the directive demanded by the end of 2020. This means that all EU member states could convert existing buildings under renovation into almost energy-efficient buildings.

We may explore many energy-saving measures for this sector such as improving the building energy management, incorporating energy-efficient technology, and the awareness of energy efficiency for building occupants [10].

Residential energy consumption can be determined in two different ways, namely [11]:

1.Top-down approach: which is concerning with the building industry as an energy reduction and which does not differentiate energy consumption due to individual end uses. Top-down models determine the effect on energy consumption due to ongoing long-term changes or transitions in the housing sector, primarily to determine the need for delivery. Variables commonly used by top-down models include macroeconomic indicators (gross domestic product (GDP), employment rate, and price index), climatic conditions, housing construction/demolition levels, and estimates of appliance ownership and number of units in the housing sector.

2.Bottom-up approach: The bottom-up method covers all models that use input data from a hierarchical level that is smaller than that for the sector as a whole. Models can account for the energy consumption of individual end uses, individual houses, or groups of houses and then extrapolate to represent the region or nation based on the representative weight of the modeled sample.

The ventilation and air conditioning systems in operation are a potential energysaving area in the building sector. This can be done by achieving thermal comfort and good health of the building occupants with minimized use of energy is the essence of HVAC systems [12].

#### **2.3 Sustainable and well-designed air distribution systems and energy saving**

Ventilation is a major player in air-conditioning and HVAC systems; therefore, it should effectively and properly be designed to save a reasonable amount of energy. The main goal of a ventilation system is to remove excess heat from the space, contaminant removal, and provide and distribute fresh air to the space.

There are two ways to ventilate occupied spaces, namely: natural ventilation and mechanical ventilation.

	- Constant air volume system (CAV): Concerning the CAV systems, supply or exhaust fans generate steady airflow to room space, the fan keeps the same power all the time. But temperature for the heating unit changes with the heating demand. For these systems, the operation cost is high because when the space is empty it is still on and uses its full capacity.
	- Variable air volume systems (VAV): The VAV systems mainly installed in school and office and the system has a relatively high initial cost and consist of more mechanical components. But its operation cost is lower than the CAV system. In a VAV system, the temperature will maintain at a certain level. Airflow is controlled by a damper and changes with heating or cooling demand. To the last, the indoor air temperature will be kept at the desired level. Therefore, the VAV system has the potential to save energy by reducing the airflow rate. Related to the variable air volume method (VAV), *Demand control ventilation* (*DCV*) is used and has the function to adjust the airflow rate with demand. Supply or exhaust airflow can vary with factors such as temperature, occupants, indoor polluting concentration, time, and relative humidity (RH). The research shows that ca 5-60% of energy can be saved with demand control [14].

The traditional air distribution and supply devices in ventilated rooms are not always able to effectively remove excess heat from the space. Therefore, chilled beams, especially the active systems, are used to achieve the desired cooling demand [15].

Yang et al. [2] explained that there are many different types of air distribution and ventilation systems which can briefly be defined as:


(jet) ventilation (ACV). The air jet with high momentum is directed downward and then reaches the floor level, impinges to corner, and then separates from the vertical wall surface and re-attaches to the floor to generate a clean air layer ("air reservoir").


It is well known that traditional HVAC systems are predesigned and operated using a fixed airflow pattern. The research conducted by Wang et al. [19] - using Adjustable Fan Network (AFN) for improving airflow pattern maneuverability indicates that great progress has been achieved in the fundamental theory of

nonuniform environment, based on which the multi-mode ventilation (MMV) system and the online identification method were proposed and shows energy-saving potential. The MMV system is generally based on the solid foundation of DOV. It is believed that with further development of this system, the DOV system can come up soon and play an important role in high-efficiency ventilation and energy saving in the future [19].

However, in real life operations of the conventional design and operation of the ventilation systems are based on the non-uniform indoor environment assumption but many calculation methods are based on a uniform airflow pattern. Thus, based on the design method, theoretical model, and control strategy of DOV an integrated theory for non-uniform indoor thermal environments should be established and developed.

As we know the ventilation is a major player in air-conditioning and HVAC systems as a whole, therefore it should effectively and properly be designed to save a reasonable amount of energy. The main goal of a ventilation system is to remove excess heat from the space, contaminant removal, and provide and distribute fresh air into space. Liang et al. [20] postulate that: ventilation which is a significant part of the HVAC system needs to be designed properly to save energy. The proper treatment of the space cooling load in the indoor environment relies on the effective use of different ventilation systems.

The ventilation energy can be reduced by the following parameters:


It has been demonstrated by Fong et al. [21] that the use of advanced and sustainable ventilation methods like stratum ventilation (SV) and displacement ventilation (DV) systems in specific configurations can reduce the carbon emissions up to 31.7% and 23.3%, respectively. It has been concluded that with a properly designed supply air velocity and volume, location of diffusers and exhausts, the SV system has the potential to maintain better thermal comfort with a smaller vertical temperature difference, lower energy use, and better IAQ in the breathing zone [22].

Comparison of the mean air temperatures in the occupied zone confirmed that Stratum (SV) systems offered the highest cooling efficiency, followed by displacement ventilation (DV) and then mixing ventilation (MV) systems [23].

Studies involving Impinging Jet ventilation (IJ) and Confluent Jets ventilation (CJ) systems have shown that these methods of room air distribution methods are capable of providing considerably better air quality performance and at the same time require less energy than the MV system and a higher cooling capacity than DV systems, see [24–26]. In this part, the performance of systems based on the hybrid (Impinging Jet and Confluent Jets ventilation systems) method is compared with the mixing and displacement methods of air distribution, which are the most commonly used for

*Some Aspects of HVAC Design in Energy Renovation of Buildings DOI: http://dx.doi.org/10.5772/intechopen.98824*

**Figure 1.** *Hybrid air distribution systems (HAD); (a) impinging jet; (b) confluent jets. Based on Awbi [27].*

room air distribution presently. **Figure 1** shows an impinging jet supply device and confluent jets system that is called a hybrid air distribution system (HAD) [27].

Comparing with the mixing ventilation system, it is known that a displacement system is a more efficient method of air supply, but it suffers from two main problems, namely:


Therefore, hybrid air distribution systems (HAD) have been developed. HAD systems combine the benefits of both MV and DV systems to use the stratification effect of the DV, the entrainment effect of MV, and to overcome the shortcomings of the DV system. Two HAD systems have recently been developed by the author of this chapter and colleagues in Sweden and the UK, that is the impinging jet ventilation (IJ) system and the confluent jets ventilation (CJ) system, see **Figure 1**. The contaminant distribution is very similar to that in a (DV) system because of the fresh air supply to the breathing zone in both the (IJ) and (CJ) methods of air distribution.

There is a need for assessing current methods of building ventilation and developing ventilation systems that are capable of providing good IAQ and energy performance to satisfy building occupants and, at the same time, meet new building energy regulations [28].

As we consider late on, the performance comparisons between the HAD air distribution systems, i.e. the imping jet and the confluent jets system, with the common mixing system show much better indoor air quality with lower ventilation energy requirement can be achieved by using the (HAD) systems of (IJ) and (CJ). One can see that the (DV) system generally performed well in cooling cases too. As we mentioned before, the (DV) system has limitations on the delivered cooling load, has less penetration depth of the DV jet in the occupied zone, and cannot be used for heating. Anyway, because of the higher supply air jet momentum, the other two systems of (IJ) and (CJ) were also shown to be used for both cooling and heating purposes, maintain good performance, providing higher cooling loads, and penetrating deeper into the room [28].

Cho et al. [29] and Karimipanah et al. [24], conducted some studies on the energy consumption of air supply processes for a ventilated rooms involving one MV (highlevel) and three a wall displacement ventilation (DV), impinging jet ventilation (IJ), and confluent jets ventilation (C) which all later three were low-level supplies.

To achieve the same environmental performance for each case, the measures of energy usage were distinguished in terms of the fan power consumption and at the same time to the related airflow rate. The performance of the above-mentioned air distribution systems was compared using data from measurements in an environmental test chamber and computational fluid dynamics (CFD) simulations, see **Figure 2**.

The Air Distribution Index (ADI) concept was developed by Awbi [30], to obtain, simultaneously, the evaluation of the thermal comfort and air quality:

$$\text{ADI} = \sqrt{\mathbf{N\_{TC}} \times \mathbf{N\_{AQ}}} \tag{1}$$

where NTC is the Thermal Comfort Number, and NAQ is the Air Quality Number.

Applying the Air Distribution Index (ADI) in a CFD study, compared the airflow rates for four different types of air distribution systems that are required to achieve an equal indoor environment.

The fan power (E) equation *E*∝*q*<sup>3</sup> was used to compare the four systems. When the required air supply rate was changed to obtain an *ADI* � 16, as shown in **Table 1**. It was distinguished that the lowest required airflow rate (i.e. 0.025 m<sup>3</sup> /s) was found to belong to the (CJ) system. Instead of the (IJ) system, the flow rate was slightly higher (1.4 times higher than that of CJ) which required 2.74 times more fan power compared to that of the (CJ) system. But the research showed that impinging jet (IJ) system used the fan power of ca half of that consumed by the mixing (MV) system. It was demonstrated that in comparison with the confluent jets (CJ) systems, the displacement system (DV) required a 1.1 times greater flow rate and 1.33 times higher power consumption. The results obtained for IJ and DV systems were almost similar.

#### **Figure 2.**

*The air distribution index from tests on four air distribution systems. (DV = wall displacement ventilation; DF = floor displacement ventilation; MX = mixing ventilation; IJV = impinging jet ventilation. Cases I and II refer to cooling loads of 36 and 60 W/m<sup>2</sup> respectively).*

*Some Aspects of HVAC Design in Energy Renovation of Buildings DOI: http://dx.doi.org/10.5772/intechopen.98824*


#### **Table 1.**

*Comparison between the fan power consumption of the ventilation systems for the same ADI (air distribution index) [24].*

The results reveal that mixing ventilation requires the highest fan power and the confluent jets ventilation needs the lowest fan power to achieve nearly the same value of ADI. The following results were obtained:


**Figure 2** shows that the total ventilation performance of a system in terms of combined heat removal effectiveness and ventilation efficiency can be interpreted by the value of the air distribution index (ADI) it achieves. It is also shown that with the higher value of ADI (e.g. ADI > 10) the compared systems archive better performance. At the same time demonstrating that the adverse comfort conditions (no cause of draughts) were presented.

As shown on the right-hand side of **Figure 2**, the mixing ventilation (MV) can perform quite well at higher cooling loads and it is surpassed by the DV and IJ systems for both cooling loads (36 and 60 W/m2 ).

The results show that although mixing ventilation can perform reasonably well at the higher cooling load, it is outperformed by the DV and IJ systems for the higher cooling loads (60 W/m2 ).

In a displacement ventilation system (DV) the thermal forces are more dominant than the flow forces but in impinging ventilation systems (IJ) the flow forces are more dominant therefore the IJ system performs better (higher ADI) than the DV system [24].

As one can see from studies of Karimipanah et al. [24], see **Table 1**, the energy performance of a ventilation system is directly related to the choice of room air supply system. When choosing a proper air distribution method as a major part of the total HVAC systems, will cause large differences in the thermal and air quality effectiveness and finally the requirements of energy usage. The research also shows that the overall performance of the confluent jets air supply system is somewhat better than the displacement and impinging jets systems (both low-level supply) but superior to the mixing system (high-level supply). The confluent jets behave like the displacement and the impinging jet ventilation systems combined. The energy consumption was presented in **Table 1**.

The above-mentioned air distribution index (*ADI*) is suitable for a *uniform* thermal environment in the occupied zone, but may not be suited for cases, as in the displacement ventilation, in which a major part of thermal stratification in ventilated spaces is present. Therefore, a modified Air Distribution Index (ADINew) Has been developed for a *non-uniform* environment by Awbi [27] that will be described in the following section.

The new index (ADI)New for non-uniform (and some unform cases as can be described late on), combines the thermal comfort and air quality numbers as follows: The proposed air distribution index ( ADI ð ÞNew) combines the thermal comfort and air quality numbers as follows [31, 32]:

$$(ADI)\_{New} = \underbrace{\left[\left(1 - \frac{|S|}{3}\right) \* \varepsilon\_l\right]}\_{N\_{TC.}} + \underbrace{\left[\left(\frac{\varepsilon\_n}{\overline{\varepsilon}\_p}\right) \* \varepsilon\_\varepsilon\right]}\_{N\_{A\_\odot}}\tag{2}$$

where *NT:C:* is the thermal comfort number, *NA:Q:* is the air quality number, j j *S* is the absolute value of the average overall thermal sensation over the exposure time, *ε<sup>t</sup>* is the ventilation effectiveness for heat removal, *τ<sup>n</sup>* is the room time constant, *τ<sup>p</sup>* is the local mean age of air and ε<sup>c</sup> is the ventilation effectiveness for contaminant removal. These parameters are calculated as follows:

$$
\varepsilon\_t = \frac{T\_o - T\_i}{T\_m - T\_i}, \varepsilon\_\varepsilon = \frac{\mathbf{C}\_o - \mathbf{C}\_i}{\mathbf{C}\_m - \mathbf{C}\_i}, \tau\_n = \frac{\mathbf{1}}{\mathbf{A}\mathbf{C}\mathbf{H}} \tag{3}
$$

the used parameters in Eq. (3) are: *To*, *Ti* and *Tm* representing the outlet temperature, the inlet temperature, and the mean temperature value in the occupied zone respectively. *Co*, *Ci* and *Cm* are the concentrations of contaminants (here CO2) at the same locations as above and *ACH* is the air change rate per hour for the ventilated enclosure.

The local mean age of air (*τp*) can be calculated as follows:

$$\overline{\tau\_p} = \frac{1}{C(0)} \int\_0^\infty \mathcal{C}\_p(t) dt \tag{4}$$

there *C*(0) is the input of tracer gas at the beginning of the measurements which is called for the initial concentration and *Cp* is the gas concentration at a certain point in the room (for this case in the breathing zone).

In Eq. (2), the ð Þ *ADI New* development follows a logic that when the thermal sensation of the occupant is neutral (i.e. j j *S* = 0). The is an ideal thermal condition, in which the thermal comfort number *NT:C:* reaches its maximum value. When j j *S* reaches its extreme values (i.e. -3 or +3), *NT:C:* reaches its minimum value (zero). In Eq. (2) the high value of the heat removal effectiveness (*εt*) gives rise to a higher


**Table 2.**

*Parameters for the index based on CFD simulations (airflow rate = 15 l/s and air supply temperature = 18 °C in each case), based on [26, 27].*

thermal comfort number (*NT:C:*) which implies that the ventilation system is efficient to remove excess heat from the occupied zone. In the same equation, both *ε<sup>c</sup>* and *ACH* are connected to the air quality number (*NA:Q:*) in ð Þ *ADI New* which involving the contaminant removal effectiveness and consequently assessing the air distribution performance in the ventilated enclosure. Obtaining a low value for both *τ<sup>p</sup>* and ACH and a high value for the *ε<sup>c</sup>* means that the ventilation system is performing well in removing contaminants and at the same time is capable of providing fresh air to the occupied zone. Consequently, the new air distribution index ADI ð ÞNew presented in Eq. (2) is a unique and useful tool for the evaluation of air quality in both *uniform* or *non-uniform* thermal environments. The index is also useful for thermal comfort (based on the local comfort concept), see [32, 33].

As one can observe in Eq. (2) the calculation of ð Þ *ADI New* the index needs both thermal comfort and air quality numbers. Almesri et al. [26], obtained the index for both mixing and displacement ventilation systems from tests in an environmental test chamber (2.78 m x 2.78 m x 2.3 m high). They used 4 males and 4 females for providing the thermal sensation data and for each test one subject was used [26]. All the tests were carried out with a supply temperature of 18°C and a total room cooling load of 21.2 W/m2 (ventilation load of 9 W/m<sup>2</sup> ) of the floor area. The supply airflow rate was also 15 l/s which is equivalent to 3.64 l/s/m<sup>2</sup> floor area.

By using Eq. (3), they measured air temperature distribution in the occupied zone of the chamber to calculate *εt*. But for the calculation of *ε<sup>c</sup>* and local the mean age of air (*τp*) at the breathing zone, the measured CO2 concentrations were used. They also used the CBE thermal comfort model [34], which was also checked for accuracy with the subjects' votes, the occupants' overall thermal sensation j j *S* was calculated. Finally, from Eq. (2) the ð Þ *ADI New* index was obtained.

**Table 2** summarized the results for the three ventilation systems. The results show that by using the above air supply conditions, the displacement ventilation system (DV) achieves higher, ð Þ *ADI New* index, thermal comfort, and air quality numbers (NTC and NAQ) than those for the IJ and MV. The IJ system was a close second and far behind was the MV system. These simulation results and others have been given in Almesri [33] which confirmed the findings from experimental measurements in an environmental chamber using human subjects as given in Karimipanah et al. [24] and the above **Table 1**.

#### **3. Parameters affecting the indoor environment and its energy**

There are at least seven main parameters that affect the indoor environment and its energy usage are:

#### 1.Building type

	- a. Urban, suburban, rural
	- b. Quality of local environment (air pollution, noise pollution, etc.)
	- c. External view (window sizes, glazing type, e.g. clear, tinted, number of panes, etc.).
	- a. Type of activity (office work, retail business, leisure, etc.)
	- b. Type of furnishing, floor covering, etc.
	- c. Equipment used in the building.
	- a. Mechanical/Natural ventilation
	- b. Type of air conditioning system
	- c. Type of heating system
	- d. Air distribution method
	- e. Natural/Electrical lighting.
	- a. Air temperature
	- b. Radiant temperature
	- c. Airspeed and turbulence
	- d. Relative humidity.

*Some Aspects of HVAC Design in Energy Renovation of Buildings DOI: http://dx.doi.org/10.5772/intechopen.98824*

	- a. Outdoor air pollution
	- b. Indoor air pollution
	- c. Ventilation rates
	- a. Building management system
	- b. Personal environmental control (lighting, temperature, humidity, etc.)

With the renovation of the old apartment and other types of buildings, the improvement of ventilation is unavoidable to provide a healthy indoor environment for the building occupants, see Noris et al. [6].

#### **3.1 The ways of assessing energy use in buildings**

When assessing the energy use in all types of buildings, the energy-saving policies are affected by the fear of extreme climate change and consequently, the occupant's health may sometimes set aside. Wargocki and Wyon [35]. stated that: poor ventilation in buildings has negative effects on occupants' health. Sufficient ventilation for indoor climate comfort has important, especially in school buildings. They also concluded that:

• To have a better connection to real-life situations like normally functioning offices and schools, the laboratory experimental results using paid subjects should be validated by the field intervention experiments and the performance of real work should be monitored over time [35]

As stated by Bluyssen et al. [36], for the energy-efficient and well-performed building it is of vital importance that:


The energy is used to control the indoor climate therefore large amounts of energy will be consumed to ensure a comfortable indoor climate in terms of heating or cooling demands.

Roulet [37] based on the recent European standard CEN 2006 [38] discussed two principal options for the energy rating of buildings. Firstly it is being calculated and secondly, it is measured. He called the above options as the *asset rating* and the *operational rating* which can be explained as follows:


#### **4. Applications of renewable energy for HVAC systems**

Historically, the severe entrance of renewable energy sources to the research area began during the oil crises in the 70:s which caused difficulties for the supply of oil products all over the world. The first UN conference about renewable energy and a sustainable global energy supply was held in Kenya's Nairobi in 1980 [39]. In the beginning, there were not any common definitions for all countries. To have a clear understanding of the above subject, in 2003, the International Energy Agency (IEA) defined renewable energy as follows: "*Renewable Energy is energy that is derived from natural processes that are replenished constantly. In its various forms, it derives directly or indirectly from the sun, or heat generated deep within the earth. Included in the definition is energy generated from solar, wind, biomass, geothermal, hydropower, and ocean energy and biofuels and hydrogen derived from renewable resources"* [40].

Nowadays, the high energy demand and at the same time struggle to mitigate the energy's environmental impact led to the following strategies [41]:


However, renewable energy considers the primary energy from recurring and nondepleting indigenous resources.

It is also noted by Gungah et al. [42] that for the development of renewable energy policy and to judge whether it is successful or not, the following common criteria will be identified:

a. The institutional feasibility and extent of political support for the policy.


They also concluded that when modeling the energy policies, there should be a systemwide analysis of the new technologies being incorporated into the system and their complexities.

#### **4.1 The environmental impact of renewable-powered HVAC**

In the last decays knowing more about the renewable energy sources benefits the house owners will change to the technology that reduces the greenhouse gases and carbon footprint. However, by spending the major part of our life in confined spaces of homes and offices, it is evident that using modern HVAC systems has a significant environmental impact.

That is why the HVAC manufacturers are tackling the environmental impact and struggling to create more sustainable products for end-users. That is why energy consumption reduction for air conditioning has become an extremely urgent task.

It is reported by IPCC (Intergovernmental Panel on Climate Change) that elevating indoor temperature in summer and decreasing indoor temperature in winter are necessary means in reducing the energy consumption of air conditioners. Hence, 195 countries agreed to enhance the indoor temperature by 1.5°C for the HVAC energy reduction in the Paris Agreement. Instead of the formerly estimated 2°C, this is done to minimize devastating climate change impacts on human health and their wellbeing [43].

By switching to renewable energy sources for HVAC systems will significantly lower or even eliminate greenhouse gas emissions.

*As the development of new techniques going on, the way HVAC systems operate and the impacts they have on our lives and environment are changing. For* instance, the use of R-22 or Freon is not allowed for newly manufactured HVAC equipment, and the industry has largely switched to R-410A or Puron which does not damage the ozone layer.

Some examples of the new renewable technologies which are becoming more prevalent in the HVAC industry are as follows:

1.Solar-powered HVAC system: With this system the electricity obtained from solar panels is used to power heating and air conditioning units. In other words, Photovoltaic cells capture the sun's rays and convert them into electricity through solar panels, and the energy is used directly or through the grid to supply power to a building's HVAC system. In case the solar power disappears at nighttime, the HVAC systems can use both powers from the grid. Customers may then be able to use excess energy to run other electrical components of their building or even sell extra energy back to the grid.


#### *4.1.1 Renewable-powered HVAC with thermal storage*

Instead of using fossil fuels-powered, the available renewable-powered energy systems for heating and cooling of residential, office, and industrial buildings are an attractive alternative to overcome the considerable effects of global warming.

Hawxhurst et al. [44] integrated onsite renewable energy and thermal storage by coupling wind and solar power generation with a control strategy that matched load demand to power generation. They used renewable energy (alone) to charge building heating and cooling thermal storage systems using an isolated microgrid. As they pointed out, the control system will be designed to charge the thermal storage systems by matching their load to the available renewable supply and these thermal stores could then be used by the building control system at a later stage to offset energy consumption from either the grid or in the case of isolated systems, batteries or generators.

Thermal energy storage devices are more reliable compared with batteries because of their long life of spans, low cost, and robust nature. There are two types of thermal storage: Cold thermal storage and hot thermal storage. The cold thermal storage is achieved by using ice and the hot thermal storage is provided by ceramic bricks. It is worth mentioning that the significant part of the end-use energy is thermal thus these storage systems account for the majority of the energy storage capability.

The first advantage of the system proposed by Hawxhurst et al. [44] is a novel control strategy that matches load demand to power generation. The system stores excess energy in robust and low-cost thermal storage devices to ultimately reduce the demand for paired, grid-connected HVAC systems. The other advantage of their strategy is that the system does have batteries to store electrical energy for the control electronics.

#### **4.2 Strategies to eliminate the shortfalls of renewable energy sources**

Due to the intermittency of renewable energy resources which cause a shortfall of these technologies, various strategies to overcome this intermittency will be used. As Anthony et al. [45] pointed out, there is a lack of sufficient energy density to serve as a practical primary energy source for the industrial sector in its current clustered form. Unless factories were built adjoining custom renewable energy farms the current energy generation density is not sufficient.

They presented a methodology to investigate the generation, transport, and storage of energy based on a "*multi-physics approach*", tied to the end-use application [45].

#### *4.2.1 Multi-physics approach to energy generation, transport, and storage*

Instead of associating energy with electricity or hydrocarbons by default, the multi-physics approach simply requires consideration of different energy generation, storage, or transfer methods, based on all available physical phenomena, and considers the end-use of the energy form.

By employing such an approach the engineers will be free from the electricity and hydrocarbon-centric, default attitude toward energy to find efficiency gains in the margins. A particular application requires an approach modification for the design of an energy system to utilize multi-physics energy storage.

It is considered that different buildings have different energy needs. Therefore, different systems would be suited to each building application. The following structured approach to tackling this problem will be summarized as, see Anthony et al. [45]:


i. Lifecycle Costs: Finally, calculate the cycle life const (LCC) of the system.

Generally, there are two types of air conditioning (AC) systems namely [46]:


In their study Zhou et al. [46] show that in residential buildings, at the point where the centralized feature of the system meets the decentralized feature of users' load, the problems of high energy consumption and low energy efficiency could easily occur. They also pointed out that centralized AC systems are effective and should be promoted for the urban landscape. Also for the centralized AC in residential buildings, the adjustability in each segment (users' terminal, refrigeration equipment, and distribution system) would greatly influence the energy consumption and system efficiency.

In case the spaces do not have central HVAC systems or with inefficient heating and cooling options, ductless heat pumps provide efficient and easy-to-install HVAC systems. There are some advantages for the decentralized AC systems:


Zoned AC systems rely on thermostats installed in every room to provide climate control information to a central HVAC control panel and are ideal for multi-story houses with the following characteristics:


The Zoned AC systems minimize allergen transfer better than non-zoned HVAC systems, providing relief to those sensitive to airborne allergens.

#### *4.2.2 Liquid desiccant air conditioning system (LDAC)*

Liquid desiccant air conditioning systems (LDAC) belong to existing energyefficient and environmentally friendly air conditioning technologies [47]. LDAC systems can be driven by low-grade heat sources such as solar energy and industrial waste heat. As a potential universal scheme in practical Si solar cell applications, the

self-cleaning omnidirectional nano-based light-harvesting design with hierarchically structured packaging glass can be used. Since solar power has been considered as one of the most expensive sources of renewable energy, these renewable energy sources are still covering and assisting in merely a small portion of global energy demands. For instance, Photovoltaic (PV) power generates less than 1% of total electricity supplies.

#### *4.2.3 Solar-biomass hybrid for air conditioning system (SBAC)*

Another interesting system is a solar-biomass hybrid for air conditioning (SBAC) and cooling systems which is a completely renewable energy-based system as is illustrated in **Figure 3** [48]. It is demonstrated that the first part of **Figure 3**, the control volume on the left-hand side, is a solar water heating system.

The solar water system consists of a field of solar collectors, a hot water storage tank, and a circulating pump. The second part with a three-ways motor valve (in the middle of the Figure) is a biomass gasifier-boiler. The biomass gasifier-boiler consists of an automatic up-draft gasifier and gas-fired boiler. The control volume showed on the right-hand side of the figure is an absorption air-conditioner. The absorption airconditioner consists of an absorption chiller, fan coil unit (FCU), cooling tower, and three pumps (cooling, hot, and chilled water pumps) [48]. It will be noted that the model-based design of a renewable energy-based solar-biomass hybrid airconditioning system uses LiBr–H2O absorption chiller.

There are also other interesting renewable energy-based methods for HVAC systems. For instance, Wang et al. [49] presented a tri-generation system which is the combined process of heating, cooling, and power generation, see **Figure 4**. The system is using sewage treatment digestion biogas according to the principle of energy gradient utilization technology. The tri-generation system uses Lithium Bromide (LiBr) absorption cooling technology for office air conditioning, a biogas power generator and, a heating system for digestion tanks.

They developed an innovative and more efficient utilization way for using the digestion biogas from sewage treatment works. The main findings can be concluded as follows:

1.When replacing the boiler with Lithium Bromide absorption chillers, the cooling capacity produced by the chillers can be used for space air conditioning. The chiller will also be used for cooling the inlet air of the biogas generator to improve its power generation efficiency.

**Figure 3.** *Schematic diagram of the solar-biomass hybrid cooling system [48].*

#### **Figure 4.**

*Schematic diagram of the proposed tri-generation system [49]. The numbers in Figure 4 are: 1) biogas generator, 2) sludge digestion tank, 3) gasholder, 4) radiator, 5) Lithium bromide absorption chiller, 6) office building, 7) cooling tower, 8) combustor, 9) hot water generator, 10) flue gas generator, 11) inner air cooler, 12) compressor, 13) chimney damper, 14) controller, 15) temperature sensor, 16) thermometer, 17) pump, 18) three-port regulation valve, 19) valve and number 2, and 20) two-port regulation valve.*


A schematic diagram of the tri-generation system is shown in **Figure 4**, which provides multi services by using a single energy source, including electricity supply, space air conditioning, and heating of sludge digestion tank or hot water supply to other users [49].

Finally, about the future of cooling and air condition systems *Fatih Birol, IEA Executive Director* indicates that: *"Growing demand for air conditioners is one of the most critical blind spots in today's energy debate. Setting higher efficiency standards for cooling is one of the easiest steps governments can take to reduce the need for new power plants, cut emissions and reduce costs at the same time"* [50].

#### **5. Conclusions**

In comparison with the total energy use in a building, the proportion of ventilation and air conditioning energy is expected to increase as the building's fabric energy performance improves. These lead to ventilation standards that recommend higher ventilation rates for improving indoor air quality (IAQ). However, there is a great global emphasis on reducing the reliance of buildings on fossil fuel energy and a move toward Nearly Zero Carbon Buildings (NZCB), the researchers are determined to develop more sustainable ways of HVAC systems. At the same time, many promising energy-efficient solutions for air distribution systems are available.

Some existed methods of sustainable HVAC systems using renewable energy resources and at the same time, some methods for overcoming the renewable energy sources intermittency and fall-down are presented. The Solar-biomass hybrid for air conditioning (SBAC) and the Liquid desiccant air conditioning systems (LDAC) belong to existing energy-efficient and environmentally friendly air conditioning technologies.

Some other examples of the new renewable technologies which are becoming more prevalent in the HVAC industry are also described:


It was also described that a method, New Air Distribution Index (ADINew), for evaluating the performance of air distribution systems is to introduce ventilation efficiency and energy effectiveness.

It was pointed out that reducing energy demand for heating and cooling is essential for improving the energy efficiency of a building but not at the expense of deteriorating air quality and the health of the people. The energy flows in buildings can be assessed in two ways: by calculation or by measurements. Estimation of various energy flows brings the necessary knowledge for improving energy performance [37].

#### **Acknowledgements**

The author wishes to thank the financial support of the University of Gävle for publishing costs.

#### **Conflict of interest**

The author declares no conflict of interest.

#### **Nomenclature**



*Some Aspects of HVAC Design in Energy Renovation of Buildings DOI: http://dx.doi.org/10.5772/intechopen.98824*

### **Author details**

Taghi Karimipanah Faculty of Engineering and Sustainable Development, University of Gävle, Sweden

\*Address all correspondence to: tkh@hig.se

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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#### **Chapter 12**
