**4. Retrofitting toward a nearly zero energy future**

In retrofitting a building, one of the critical aspects to consider is the material properties of the existing building and the carbon content typically residing therein.

#### *Energy-Efficient Retrofit Measures to Achieve Nearly Zero Energy Buildings DOI: http://dx.doi.org/10.5772/intechopen.101845*

The London Energy Transformation Initiative (LETI) proposed an embodied carbon budget of 600kgCO2e/m2 for us to attain our carbon reduction goals [22]. To understand the feasibility of achieving this low figure, one must comprehend the total embodied energy typically present in an old building. Aecom, in a web article titled "The carbon and business case for choosing refurbishment over new build," breaks down the embodied carbon within various components of typical residential buildings: Frame 24%; substructure 19.6%; upper floors (14.9%); building services (13.4%); internal finishes (12.4%); external walls; windows and doors (8.8%); roof (5%); fitting and furnishings (1.2%); internal walls and doors (0.6%). The elements typically associated with the highest embodied carbon (substructure, frame, upper floor, and roof) are candidates that qualify for retrofitting to save on emissions produced during the breaking down of an old building and re-constructing these buildings elements while building anew.

To holistically retrofit existing buildings for enabling the transition toward a nearly zero energy building, three main scopes encompassing passive and active strategies should thus be considered:


To explain these three strategies, the chapter, apart from providing theoretical advice, also elaborates upon the results of a simulated case study—an educational building in Iran. An initial comfort analysis in terms of visual and thermal condition and energy use of this existing building provides insights on the required improvements and thus informs retrofitting strategies. The elaborated project deploys the three-stage retrofit process on an educational building in Tehran (35.6892° N, 51.3890° E), Iran, in a cold semiarid climatic condition (Köppen climate classification: BSk). The process adopted by the authors incorporated radiance and energy plus simulation engines. According to the weather data for a typical year in this area, January is the coldest month, and August represents the hottest time of the year, each with an average monthly temperature of 3.89°C and 30.07°C. The site also enjoys a high level of solar exposure and experiences cloudy sky conditions only 15% of the time.

Situating a to-be retrofitted building within its environmental context is an ideal strategy for understanding the reasons behind its current energy performance. To strive toward an energy-efficient status for an existing building, both interior and exterior aspects are equally crucial to be considered. Visual and thermal comfort components can be primarily linked with the urban positioning of the building itself and imply conducting on-site solar radiation analysis for extracting the degree of solar exposure received by the building's external facades. In addition to this, mapping the demand for lighting and thermal energy of the interior programs of the building is vital. This step aids in making informed decisions to re-position or augment a building's program to take the best advantage of the building's solar exposure while naturally reducing the amount of energy required to heat or cool the building's interiors.

For instance, in our educational Building case study, solar radiation analysis (**Figure 2**) revealed that the Southern zones witnessing the highest solar radiation

**Figure 2.** *Solar radiation analysis on building envelope.*

constituted of primary programs and were induced to a high level of daylight and solar heat gain. On the contrary, northern zones were the coldest spaces with a pleasant daylight quality without experiencing visual discomfort caused by glare. The Eastern and Western zones were typically dedicated to circulation and service areas. Daylighting and thermal requirement-based zoning and categorization of the building's program are also conducted to determine the ideal spatial distribution of the program within the building (**Figure 3**).

The other important aspect of understanding visual comfort is calculating daylight quality to evaluate illuminance levels and glare probability and subsequently calculate thermal conditions to evaluate the total amount of discomfort hours within the primary programs of a building. It is vital to educate and to understand the importance of using the sun for solar tempering. Working with rather than against natural solar movement and exposure also aids in achieving energy savings otherwise required for heating purposes, and appropriately shading also aids in reducing cooling requirements. A strategic manner of avoiding added costs and energy expenditure for added thermal mass required for maximizing passive solar heating can thus be achieved. Such concerns are primarily best addressed during the design phase of the proposed retrofit.

In the case of the studied institution building, the south-facing spaces tend to receive excessive sunlight and suffer excessive visual discomfort (ASE > 10%, LEED 0 point). Therefore, the use of optimum shadings is suggested in the retrofit process. Despite this, the northern zone achieves all 3 points of the LEED rating system, which indicates that both sufficient daylight level (sDA > 75%) and visual comfort

**Figure 3.** *Spatial zoning based on the solar geometry.*

*Energy-Efficient Retrofit Measures to Achieve Nearly Zero Energy Buildings DOI: http://dx.doi.org/10.5772/intechopen.101845*

**Figure 4.** *Visual comfort (daylight distribution and glare) assessment.*

(ASE < 10%) is achieved in these zones. Therefore, it is highly suggested to consider solar geometry in the renovation process to establish the feasibility of removing or adding the interior partitions. An overall analysis of daylight distribution on each floor (**Figure 4**) can elaborate on the optimal positioning of the interior program of a building in relation to solar radiation. Such strategic thinking and informed decision-making pertaining to program positioning before beginning the retrofitting process can thus ensure reducing the total energy consumption of a building considerably.

Thermal comfort analysis by assessing the average monthly temperature within an existing building's interior spaces can further help designers to understand overcooling or overheating scenarios throughout the year. Similarly, an annual analysis of discomfort hours also provides information on thermal conditions on a dynamic scale and can show critical thermal condition levels of interior space. Thermal imaging using an infrared camera can also be deployed for measuring on-site thermal conditions in individual rooms. Typically, such analysis can also be categorized under an energy audit of an existing building. For the case of the educational building understudy, the annual discomfort hours were calculated as 988.73 hours (**Figure 5**) and were associated with the average monthly temperature and the percentage of occupancy time that the hours corresponded with. The design phase of the retrofit being a calculated experimental phase also renders itself for making design decisions pertaining to elements such as atriums, window opening sizes, etc., while keeping in mind the window to wall ratio. Such additions, typically aimed at improving natural ventilation, can dramatically improve inside temperature conditions, thus impacting the total energy required for heating, cooling, and artificial ventilation. In the case of the educational building, the insertion of a central atrium combined with interior windows with a window to wall ratio of 20% was experimented with as a designed addition. A computational fluid dynamics (CFD) simulation analysis on a typical spring day (without an HVAC system operational) was able to provide a good overview of well-ventilated zones vs. zones which needed further improvement strategies such as supply vents etc., (**Figure 6**). Such initial analyses of the indoor environmental condition thus offer a basis for taking calculated decisions of the required retrofit strategies on a case-by-case basis.

#### **Figure 6.**

*Ventilation (velocity and temperature) assessment in the central atrium.*

Tangible aspects connected with thermal comfort can be further categorized into lighting, sealing, insulation, and window replacement components. Lighting inside a building is equally crucial. Older buildings typically make use of fluorescent lighting and light bulbs. These tend to consume much more energy than contemporary energy-efficient CFL or LED light bulbs that last longer and are mercury-free. Retrofitting should thus ideally involve replacing existing fluorescent lighting systems with LEDs equipped with linear controllers. This simple change can almost halve the energy used for lighting purposes. Using motion sensors in areas where lights are left on often also allows energy to be saved. For the case of the educational building, this small change in lighting coupled with a daylight sensor for controlling the intensity of lighting in real time can halve the total energy consumed (**Figure 7**).

Sealing the building envelope is another step that is a highly efficient and costeffective measure that can be deployed during the retrofitting phase for any building. Saving valuable energy required for heating and cooling and improving comfort,

*Energy-Efficient Retrofit Measures to Achieve Nearly Zero Energy Buildings DOI: http://dx.doi.org/10.5772/intechopen.101845*

**Figure 7.**

*The energy use of reference (fluorescent) VS. optimized lighting system (LED with linear control).*

reducing noise, and improving air quality are all direct impacts of sealing the building envelope, resulting in nearly zero energy targets. Often a blower door test can be conducted to evaluate the air leakage during air change per hour. Air change here implies the volume of air that equals the house volume exchanged with the outside air [23]. A blower door can establish a negative 50-pascal house pressure. Existing homes in need of retrofitting can often leak air at the rate of 15 air changes per hour (15 ACH50). Sealing the external and internal surfaces of a building can aid in bringing this level of leakage down between a range of 2ACH50 (airtightness standard for a cost-effective zero energy home)—0.7 ACH50 (airtightness standard for a passive house). Setting an airtightness goal for retrofitting projects can thus prove to be a wise decision for cutting down on energy consumption by optimizing the building envelope.

Building insulation should be considered as a fundamental component of any retrofit project. Different surfaces, such as walls, floors, and ceilings, require different types and thicknesses of insulating materials that are contextually derived based on climatic conditions and solar exposure. The R-value, or in other words, the ability of a material to resist the flow of heat, is important while choosing adequate insulation and is highly dependent on the kind of material used for insulation rather than the thickness of the material used. The climatic context of the region within which the retrofitting needs to be undertaken thus plays a significant role in determining the requisite R-value of the chosen insulation type and thickness. The Zero Energy Project report [24] outlines practical ways in which high-performance walls (exterior rigid insulation; single plate, double stud walls; double plate walls), highinsulated ceilings (blow insulation onto flat ceilings; insulating cathedral ceilings; exterior rigid insulation), and high insulated-floors (insulated slabs; insulated basements; crawl space), can aid in reducing energy loads by means of the application of appropriate insulation.

Similarly, window replacement and door replacements can play an essential role in transitioning to a nearly zero energy building. Organizations such as the National Fenestration Rating Council have contributed heavily toward establishing rating systems of window and door performance measurements in the form of labels affixed to off-the-shelf window and door units [25]. This process aids in the simplification of retrofitting wherein the everyday citizen can make informed decisions pertaining to the efficiency of these quintessential components of a building. Like the R-value of insulation, a U factor is of prime importance as it indicates the efficiency of a window

**Figure 8.** *Construction material optimization.*

as regards heat escaping from the interior of a building. For visual comfort purposes, the visible transmittance value is also associated with window ratings. It is responsible for measuring the effectiveness of a window to light the interiors of space with daylight. For doors, the solar heat gain coefficient value that demarcates the door's resistance toward unwanted heat gain and the air leakage value that indicates the entry of external air through the door are vital measures specified by such councils.

For the case of the studied educational building, to establish a lower heat transfer threshold, the application of interior insulation (0.10 m air gap +0.15 m wood wool), replacement of windows with highly sealed windows with a low U value and coated with efficiency-enhancing coatings (Dbl LOE Elec Abs Bleached 6 mm/13 mm Arg), provision of interior window shading (shade roll-medium opaque) and exterior localized shading elements (2 meters overhang), were explicitly deployed for enhancing the efficiency of south facing spaces (**Figure 8**).

The energy consumption component for a building retrofit process involves active strategies. HVAC systems are omnipresent in the majority of homes globally and how to reduce the energy required for heating or cooling purposes is of particular importance here. The strategies—visual and thermal comfort enhancements, already contribute to reducing conventional HVAC systems' load. However, apart from these passive measures, selecting appropriate HVAC systems conducive to the climatic context and the proportion of spaces to be conditioned are essential criteria to consider. For instance, for residential properties, air-source heat pumps are highly efficient and can take up the form of mini-split heat pumps for individual rooms or multi-zone installations. Variable speed operation by means of sensing temperature conditions inside a building and accordingly increasing or decreasing heating or cooling speeds results in air-source heat pumps in achieving energy savings.

Other strategies such as working with combinations of different heating and cooling systems per the degree of solar exposure and desired comfort levels could also be experimented with. For the case of the educational building, four different systems of radiator + evaporative cooling (the most common system used in the location), VAV, fan coil, and heat pump were simulated and optimized to establish the most efficient option. Accordingly, the optimum system of unitary heat pump can reduce heating, cooling, and the total energy use intensity (EUI) by 69.03%, 38.21%, and 28.81%, respectively. The final results indicated that the proposed method could reduce the annual energy consumption (EUI) by almost half while doubling the comfortable

*Energy-Efficient Retrofit Measures to Achieve Nearly Zero Energy Buildings DOI: http://dx.doi.org/10.5772/intechopen.101845*

**Figure 9.**

*Energy use and physical features (construction material, HVAC, and lighting systems) of the retrofitted case study.*

hours indoors. **Figure 9** represents the energy consumed by different energyconsuming components of the retrofitted case study and the suggested replacement of physical features of the building. Such informed and analytically validated suggestions can inform property owners and make them aware of the retrofitting process's impact in transitioning to a nearly zero energy future.

Another active mode of energy generation is the renewable energy sector. Harnessing the sun's power by means of solar photovoltaic (PV) panels is one of the most cost-effective modes of harvesting renewable energy. The efficiency of solar panels is typically dependent on the amount of unobstructed solar radiation captured by the panels over a period throughout the day. After calculating the amount of energy conserved by applying the aforementioned passive and active strategies, a well-thought-out plan for solar energy capture must be developed. This is also due to the limitations of existing homes regarding the amount of open and exposed roof surface square meters available for the installation of PVs. A well-developed plan can aid in calculating the exact number of panels needed to manage and balance out the amount of energy required to reach a near-zero energy target. The inclusion of microinverters rather than centralized inverters should become the norm to encourage capturing optimal performance per panel while future-proofing the ability to add more panels in the future. Governments globally are now encouraging the installation of panels by providing subsidies and encouraging schemes that make solar leasing affordable and easily accessible.

For instance, in the case of the educational building understudy, PVs were suggested to make the most from renewable energy sources, such as solar radiation, to transfuse an annual amount of 10.7 mWh of electricity to the grid supply a part of the projects' total energy consumption. Hence, 24 panels are suggested to be placed on the roof to bring it closer to an nZEB design. Accordingly, the final design incurs less than 55 kWh/m<sup>2</sup> energy consumption, from which 9.32% is supplied by harvesting solar energy. The associated carbon emission (operational) was also reduced by 17.96% (**Figure 10**).

As a proof of concept for the propositions made in this chapter, jointly—both passive and active strategies proposed for the retrofitting of the educational building exhibited the potential to reduce the energy consumed for heating, cooling, and lighting purposes up to 85.19%, 58.57%, and 23.68%, respectively, compared to the base case (**Figure 11**).

Furthermore, the annual EUI could effectively be reduced by 52.98%, while the associated carbon emissions (t CO2) and annual comfort hours also exhibit

#### **Figure 10.**

*Energy savings and CO2 emissions reduction by PV installation.*

#### **Figure 11.**

*The impact of the proposed retrofit strategies on the annual discomfort hours and CO2 emissions.*

#### **Figure 12.**

*The impact of retrofit strategies on annual energy use.*

improvement by 46.48% and 49.28%. Replacing existing windows with highly efficient windows proved to have the highest impact (22.58%) on the comfort experienced indoors, followed by using an optimum HVAC system and applying interior insulations, each with an effective percentage of 21.90% and 19.18%. The inclusion of an efficient HVAC system also aided in reducing operational carbon emission to a great extent (24.05%). Installing PV panels also exhibited a substantial reduction in carbon emissions (19.18%) (**Figure 12**).
