**2. Strategies for carbon emissions reduction in the refurbishment of wide-open industrial buildings**

As it was mentioned in the previous section, in the rehabilitation of wide-open industrial buildings, at least three problems, related one to another, must be faced. Namely:


humidity has to be maintained between 30% and 70%.

consumption associated with conditioning.

• A reduction of energy consumption.

**wide-open industrial buildings** 

the proposed system will be:

climate, as it happens in most of European countries, is very low.

Article 7 and Annex III of R.D. 486/1997 (1997) set out the environmental requirements that are mandatory in work places for health and safety reasons: temperature must be kept between 17°C and 27°C if sedentary work is performed, and within a range of 14°C up to 25°C in the case of light work. Air velocities must be less than 0.25 m/s when working in cool environments, below 0.5 m/s in warm environments for sedentary jobs and lower than 0.75 m/s if the work done is light with a warm environment. In all cases the relative

Even if the extreme values of the range are considered (temperatures in the range of 14ºC and 27°C with air velocities below 0.75 m/s) the possibility of achieving these higrothermal indoor conditions without mechanical equipment in an open building exposed to a severe

Nevertheless, in this type of buildings, HVAC systems that control temperature and humidity inside the premises are not feasible, for the high rate of infiltration would lead to extreme cooling and heating loads, as it will later be demonstrated by some examples.

If, despite what has been exposed, it is found necessary to project a technical system that improves thermal conditions for labourers while increasing the working hours, the first problem to be solved is to establish an effective climate separation of indoor climate that allows to obtain thermal comfort at a reasonable cost. In this sense, the provision of air curtains in fixed openings is an essential strategy prior to air conditioning the premises.

It should be noted that the climate separation, though reducing building demand of energy by nearly 90 %, causes yet another problem: the indoor air quality worsens, as natural ventilation due to air infiltration through the openings tends to be neglected. At this point, when the need for mechanical ventilation becomes clear, the inevitably decision of air conditioning is derived, and so is the necessity to establish the basis for choosing the best technical system that ensure the higrothermal comfort of the occupants and the air quality of the premises as well as minimize both the installed thermal power and the energy

Therefore, this chapter seeks to propose a methodology for facing the refurbishment of wide-open industrial buildings. Firstly, by establishing a climatic separation via air curtains and, finally, by choosing a high efficiency air conditioning system. The expected benefits of

• An increase in hours of work, taking into account the existing labour legislation;

**2. Strategies for carbon emissions reduction in the refurbishment of** 

buildings, at least three problems, related one to another, must be faced. Namely:

As it was mentioned in the previous section, in the rehabilitation of wide-open industrial

• An improvement of comfort, compared with a conventional system; and

A holistic approach to building design suggests a long list of possible strategies to improve its energy efficiency. However, to guide the development of a more efficient HVAC system, the concept of adaptive comfort criteria was used (Clark & Edholm, 1985; Nicol, 1993).

What this means in practice is that less fossil fuel is used to maintain comfortable temperatures if the building can be kept to a relatively constant level through an interactive control system that adapts the internal environment conditions in response to carbon dioxide levels and air velocities. In order to reduce the carbon emissions of the heating and ventilation system the following steps need to be taken:

#### **2.1. Thermally isolate the building**

This includes solar shading as well as an improvement of the insulation materials, as it derives from the following reasons.

With respect to buildings heating and cooling energy demand, Spanish legislation (R.D. 314/2006, 2006a) states:

*" Buildings shall have an enclosure that adequately limit the energy demand required to achieve thermal comfort, depending on the local climate, the use of the building during summer and winter, as well as on the characteristics of isolation and inertia of the materials, the air permeability and the exposure to solar radiation, and adequately considering thermal bridges, in order to properly limit heat gains or losses and to avoid the higrothermal problems related to them"* 

Thermal characterization of the opaque elements of the building enclosure (walls, roofs and floors) is made by the thermal transmittance *U* (W/m2· K), which is defined:

$$\frac{1}{nL} = R\_T = \frac{1}{h\_i} + \sum\_{i=1}^{n} \frac{e\_i}{\lambda\_i} + \frac{1}{h\_e} \,. \tag{1}$$

with *hi*, surface heat transfer coefficient for the inside air layer (W/m2· K); *he*, surface heat transfer coefficient for the outside air layer (W/m2· K); *e*, thickness of the layers that forms the enclosure (m); and *λ*, thermal conductivity of the material of each layer (W/m· K).

With respect to the openings (windows, doors and skylights), thermal transmittance is also used. In this case it is obtained from the respective transmittances of glass, *Uv*, and window frame, *Um*, according to the expression.

$$\mathbf{U}\_{\rm H} = \begin{pmatrix} 1 \text{-FM} \end{pmatrix} \mathbf{U}\_{\rm V} + \mathbf{F} \mathbf{M} \mathbf{U}\_{\rm m} \tag{2}$$

being FM (%) the fraction of the opening taken up by the frame.

Due to the high contribution of the openings to the heat gains, an additional coefficient is used in order to characterize its response to the solar radiation. It is the modified solar factor, F (-), defined as:

$$\mathbf{F} = \mathbf{F}\_{\circ} \ . \ \{ \{ 1 \text{ - FM} \} \ . \ \mathbf{g} + \text{FM} \ . \ 0 \text{,} 0 \text{4 } . \ \mathbf{U}\_{\mathrm{m}} \ . \ \ \text{ or} \} \tag{3}$$

High Efficiency Mix Energy System Design with Low Carbon Footprint for Wide-Open Workshops 109

Boiler losses depend on the type of heat generator and on the range of power output. According to the European legislation (BS EN 15603:2008, 2008), boilers must comply with the heat conversion efficiency requirements, always referred to the fuel net calorific value,

Type of boiler Range of power output (kW)

Type of boiler Range of power output (kW)

**Table 1.** Normative heat conversion efficiency requirements for different types of boilers

 50 100 200 300 400 Standard 87.4 88.0 88.6 89.0 89.2 Low temperature 90.0 90.5 91.0 91.2 91.4 Gas condensing boilers 92.7 93.0 93.3 93.5 93.6

 50 100 200 300 400 Standard 85.1 86.0 86.9 87.4 87.8 Low temperature 90.0 90.5 91.0 91.2 91.4 Gas condensing boilers 98.7 99.0 99.3 99.5 99.6

On the other part, seasonal efficiency is difficult to determine, as it is related to the size of the boiler, the burner type and the method of operation all over the heating session. A simple way to approach the problem can be consulted in (R.D. 275/1995, 1995). To obtain more accurate results, the use of energy simulation programs is strongly recommended.

**2.3. Reduce the amount of carbon from the energy source used by the system** 

Primary energy is an energy that has not been subjected to any conversion or transformation process. Thus, to determine the primary energy required to provide the final energy demanded by a technical system, it is taken into account the energy content associated with the extraction, processing, storage, transport, generation, transformation, transmission, distribution and any other operation necessary to supply energy to the area where it is used. Primary energy is the essential energy indicator to determine the net heat balance of a building (when heat production involves different energy vectors), or to compare the energy performance of different technical systems. As such is considered by European official methodology of calculation (Moss, 1997), and has been accordingly incorporated into rating procedures for energy building performance of different member countries, including Spain

It is calculated by multiplying the energy supplied to the system by a factor greater than unity. If, however, the carbon emission is preferred as indicator, a second conversion factor

According to it, the method used to evaluate the carbon emission due to the energy source

that are set out in the following Table 1:

**Efficiency at rated output** 

**Efficiency at partload (30%)**

(R.D. 47/2007 (2007).

has to be applied.

for the heat production is:

where *Fs* (-) is called shadow factor, which is defined as the percentage of the solar radiation incident on a vertical plane that eventually reaches the opening. Its value is affected by remote obstacles, the self-shadowing of the building, facade obstacles like setbacks, overhangs or projections, and the sun control devices, fixed or movable exterior shades included.

The whole expression represents an average solar factor of the opening, taking into account the aforementioned effect of shadowing, and the weighted contribution of glass and frame in the response to solar radiation. The contribution of the glass is expressed by its total solar thermal transmittance, *g* (-), determined, for a quasi-parallel radiation and for a quasi normal inclination, with the definition formula (BS EN 410:1998, 1998).

$$\log = \frac{\alpha \, h\_i}{h\_e + h\_i} + \pi \tag{4}$$

where *α* is the absortivity and *τ* the transmissivity, both dimensionless. This factor is obviously much higher than the frame one, which is representative only when having small openings or thick window frames.

Finally, with respect to the thermal inertia of the envelope, in buildings such as those discussed in this chapter, with light walls, its influence can be neglected.

### **2.2. Produce hot water more efficiently**

In addition to the energy demand, which has been analyzed in the previous section, the average performance of the HVAC systems is the determining factor in the final energy consumption of buildings. From all the subsystems that takes part in the air conditioning (heat emission, distribution and production), the latter has the higher incidence in the energy efficiency of the building.

When producing heat by means of combustion, two aspects of boiler design have to be considered: the heat losses and its efficiency. What is desired is a highly efficient boiler system which minimizes the heat losses, especially those associated to combustion gases, so that less fuel is needed to heat the water. On the other hand, the boiler needs to be as effective as possible at transferring heat from the energy source to water.

The method used to evaluate the final energy consumption of the heat production system is:


Boiler losses depend on the type of heat generator and on the range of power output. According to the European legislation (BS EN 15603:2008, 2008), boilers must comply with the heat conversion efficiency requirements, always referred to the fuel net calorific value, that are set out in the following Table 1:

108 Energy Efficiency – The Innovative Ways for Smart Energy, the Future Towards Modern Utilities

factor, F (-), defined as:

openings or thick window frames.

energy efficiency of the building.

(1+Boiler losses)

**2.2. Produce hot water more efficiently** 

Due to the high contribution of the openings to the heat gains, an additional coefficient is used in order to characterize its response to the solar radiation. It is the modified solar

where *Fs* (-) is called shadow factor, which is defined as the percentage of the solar radiation incident on a vertical plane that eventually reaches the opening. Its value is affected by remote obstacles, the self-shadowing of the building, facade obstacles like setbacks, overhangs or

The whole expression represents an average solar factor of the opening, taking into account the aforementioned effect of shadowing, and the weighted contribution of glass and frame in the response to solar radiation. The contribution of the glass is expressed by its total solar thermal transmittance, *g* (-), determined, for a quasi-parallel radiation and for a quasi

> *i e i h <sup>g</sup> h h* α

τ

= +

+

where *α* is the absortivity and *τ* the transmissivity, both dimensionless. This factor is obviously much higher than the frame one, which is representative only when having small

Finally, with respect to the thermal inertia of the envelope, in buildings such as those

In addition to the energy demand, which has been analyzed in the previous section, the average performance of the HVAC systems is the determining factor in the final energy consumption of buildings. From all the subsystems that takes part in the air conditioning (heat emission, distribution and production), the latter has the higher incidence in the

When producing heat by means of combustion, two aspects of boiler design have to be considered: the heat losses and its efficiency. What is desired is a highly efficient boiler system which minimizes the heat losses, especially those associated to combustion gases, so that less fuel is needed to heat the water. On the other hand, the boiler needs to be as

The method used to evaluate the final energy consumption of the heat production system is: • Annual energy needed by the boiler to meet the demand = Annual energy demand x

• Total annual energy consumption for the boiler and its fuel = Annual energy needed by

the boiler to meet the demand / (Calorific potential x Seasonal efficiency)

projections, and the sun control devices, fixed or movable exterior shades included.

normal inclination, with the definition formula (BS EN 410:1998, 1998).

discussed in this chapter, with light walls, its influence can be neglected.

effective as possible at transferring heat from the energy source to water.

F = Fs . [(1 - FM) . g + FM . 0,04 . Um . α] (3)

(4)


**Table 1.** Normative heat conversion efficiency requirements for different types of boilers

On the other part, seasonal efficiency is difficult to determine, as it is related to the size of the boiler, the burner type and the method of operation all over the heating session. A simple way to approach the problem can be consulted in (R.D. 275/1995, 1995). To obtain more accurate results, the use of energy simulation programs is strongly recommended.

#### **2.3. Reduce the amount of carbon from the energy source used by the system**

Primary energy is an energy that has not been subjected to any conversion or transformation process. Thus, to determine the primary energy required to provide the final energy demanded by a technical system, it is taken into account the energy content associated with the extraction, processing, storage, transport, generation, transformation, transmission, distribution and any other operation necessary to supply energy to the area where it is used. Primary energy is the essential energy indicator to determine the net heat balance of a building (when heat production involves different energy vectors), or to compare the energy performance of different technical systems. As such is considered by European official methodology of calculation (Moss, 1997), and has been accordingly incorporated into rating procedures for energy building performance of different member countries, including Spain (R.D. 47/2007 (2007).

It is calculated by multiplying the energy supplied to the system by a factor greater than unity. If, however, the carbon emission is preferred as indicator, a second conversion factor has to be applied.

According to it, the method used to evaluate the carbon emission due to the energy source for the heat production is:

	- Annual energy consumption of the primary fuel used in the boiler = Annual energy needed by the boiler x Coefficient for the primary energy used.

High Efficiency Mix Energy System Design with Low Carbon Footprint for Wide-Open Workshops 111

фS = Q . (Te - Ti) . ρa . ca (6)

фLv = Q . (we - wi) . ρa . L (7)

where *z* = *h*/2 (considering that the neutral pressure level passes through the centerline of the side opening), and *n* is the flow exponent that indicates the degree of turbulence. An *n*

From the volume flow rate obtained, the sensible and latent losses (or gains) are calculated

Heating (or cooling) loads laws distribute at both sides of the neutral pressure level

According to the technical services prevailing code (R.D. 1027/2007, 2007), the design of a partially open building, with 8 side openings of 4x4 m2 each, which keeps the indoor environment between 19°C and 28°C throughout the year, would require a heating power close to 2.5 MW if the outdoor temperature were 5°C. In summer, sensible cooling power

At this point it should be emphasized the importance of the latent loads in warm and humid climates. In these cases, the use of direct expansion cooling machines leads to high electrical consumption for hardly maintaining the desired internal temperature conditions. This fact alone would justify the use of climate separators in these climates, for all type of buildings,

It should also be noted that the infiltration air flow rate, and consequently the thermal load, is usually increased due to wind pressures acting on opposite faces of the building. In this case, even more so air curtains reveal as the essential strategy to reduce the thermal load of this type of buildings, for they create a barrier between the two environments, the inside working area of the workshop and the outside air. The air curtains also are highly energy efficient terminal units, and their coils permit a choice of the type of energy they run on, hot

provided that a high frequency of doors opening and closing is expected.

value of 0.5 represents fully turbulent flow and 1.0 represents fully laminar flow.

**Figure 1.** Heating loads due to thermal buoyancy through openings

reaches 1.5 MW for an outside temperature of 35°C.

using the well known expressions:

according to the Figure 1:

water included.

• Amount of carbon emitted = Annual energy consumption of primary fuel x Carbon conversion factor.

The following Table 2 shows the conversion coefficients used by the official program for energy rating process in Spain, CALENER (IDAE, 2009). Each different energy source has two energy conversion factors, for carbon emissions and primary energy.


**Table 2.** Carbon emission and primary energy conversion factors used by CALENER

Therefore, a significant reduction of carbon emissions can be carried out in two ways. The first is to choose a primary source of energy with the lowest carbon footprint, eg. natural gas. The second is to use a source of renewable energy.
