La ciencia como bien público

2.3.2.1 Orientation

Building orientation is one of the main factors in reducing building energy demand and keeping the interior conditions in comfort range. Decisions made in adjusting the building orientation will have impacts on the energy performance of the building over its entire life cycle mainly with regard to solar radiation and wind. Proper building orientation can diminish the unwanted effects of severe weather a great deal.

Therefore, it is very important to orient a building to optimize the effects of the nature (Nasrollahi, 2013).

Orientation of building determines the amount of radiation the building receives. A good orientation should allow maximum access to the sun when needed; or, likewise, eliminate it when unwanted. Moreover building orientation should provide maximum natural light in all climatic conditions.

The best orientations for a building can literally vary from location to location and should be evaluated accordingly. The past studies by Yohanis and Norton (2002), Jaber and Ajib (2011); Al-Tamimi et al., (2011) showed approaches for optimal orientation selection in different climate zones.

2.3.2.2 Building form

Building form is one of the basic determinants of the building energy performance and the comfort of residents. Form refers to the shape or configuration of a building and it is mainly determined by the building’s height, width, and depth (Harvey, 2012).

The building form also defines the building footprint, building volume, floor-to-floor height and more importantly, the size and the orientation of the exterior envelope exposed to the outdoor environment.

The surface area to volume ratio (S/V) is a significant factor determining the magnitude of the heat transfer in and out of the building. The larger the S/V ratio, the greater the heat gain or loss for a given volume of space is.

There is a trade-off between a compact form that minimizes conductive heat transfer through the envelope and a form that facilitates daylighting, solar gain, and natural ventilation therefore it should be developed considering the trade-offs.

The role of building form in energy consumption has been investigated by several researchers including Depecker et al.(2001); AlAnzi et al. (2009), Danielski et al.

(2012); Ling at al., (2007) where their work showed that the building morphology is an important design parameter in the process of energy-efficient building design.

2.3.2.3 Building envelope

Building envelope thermally and physically separates the interior and the exterior building environments. It includes the outer elements of a building such as foundations, walls, roof, windows, doors and floors.

Building envelope is an integral part of a building and functions as a thermal shell. It regulates how well the building can benefit from solar radiation, daylight, wind and natural ventilation and provides the ability to control of solar radiation, heat flow, airflow and moisture. Therefore, appropriate selection and arrangement of building envelope elements can enhance the comfort and energy performance a great deal (Harvey, 2012).

Building envelope consists of the following elements:

Opaque building elements

As summarized by Harvey (2012), opaque elements of the building include walls, roof, floor etc. Thermo-physical properties of the layers comprising the building elements determine the energy-flow behaviour and the energy storage capacity of the building.

Heat transfer through the opaque building elements is a combination of convective, radiative and conductive processes.

Building elements such as walls, roofs consist of multi layers and total heat transfer coefficient (U-value, W/m2.K) is used to estimate how much heat can be transferred through a building element.

In addition to heat transfer, thermal mass enables building materials to absorb, store, and later release thermal energy. Due to thermal mass buildings can absorb and store excess thermal energy when the building’s thermal load is high and release the energy when the load is low. This way, thermal mass moderates temperature swings inside a building. Appropriately sized thermal mass can help buildings manage their thermal energy resources

Radiation is a significant component of heat transfer in buildings in both heating and cooling. Solar radiation incident on building envelope can be absorbed, reflected and transmitted depending on the surface characteristics and consequently it influences interior and exterior surface temperatures, heat flow entering the building, light distribution and the occupant’s comfort. For opaque components, reflectivity, absorptivity, emissivity and long wave radiation behaviour characterize the surface behaviour.

Abundant literature is available on impact of the thermal resistance of building envelope against heat flow (e.g. Kim and Moon, 2009) and many studies shows how to determine the appropriate values for the overall heat transfer coefficients for building opaque elements. (e.g. Farhanieh and Sattar, 2006; Sanea and Zedan, 2011;

Al-Homoud, 2005; and Bojic et al., 2002). These studies reveal that appropriate arrangement of thermal resistance of building envelope significantly reduces building loads.

Similarly, there is significant research carried out about the relationship between the building thermal mass and the thermal performance. Gregory et al (2008), Balaras

(1996), Al Sanea et al (2012), Cheng et al (2005), and Zhou et al (2008) investigated the different aspects and applications of building thermal mass. The results conclude that thermal mass has the ability to significantly reduce the building energy requirements and improve internal temperatures. Optimum amount of thermal mass should be estimated for true energy efficiency.

The significance of total solar reflectance and optical properties of the exterior facade has been well studied by Joudi et al (2011), Filho et al. (2010), Berdahl et al (2008), Synnefa et al (2007), and Stathopoulou at al. (2009).

Shading

Nasrollahi (2009) explains that solar shading is a part of building envelope and it controls the amount of sunlight that strikes and enters into a building. Accordingly, it blocks the solar radiation incident on the exposed surfaces of a building and reduces heat gain, modifies thermal gains and influences daylighting levels. Shading of surfaces can be achieved by the self-shading profiles of buildings such as in H-type or L-type buildings or by integrated building shading elements. The use of well-designed sun controls save energy, reduce heat and glare, improve occupant’s comfort.

Solar and visual transmittance, thermal resistance, location and dimensions of shading element together with any control strategy associated with it determines the performance of the shading device in term of energy and visual performance.

The performance of building solar shading in terms of energy and daylighting and optimal shading design for better Indoor thermal environmental conditions was explored deeply by many researcher such as Ho et al (2008), Alzoubi and Al-Zoubi (2010), Palmero-Marrero and Oliveira (2010), Kim et al (2012), Bessoudo et al (2010), and Datta (2001).

Finally, there is extensive research about control strategies for shading devices.

Moeseke and de Herde (2007) investigated the impact of control rules on the efficiency of shading devices and free cooling for office buildings. Guillemin and Molteni (2002) explored energy-efficient controller for shading devices self-adapting to the user wishes. Tzempelikos and Athienitis (2007) discussed the impact of shading design and control on building cooling and lighting demand.

Transparent building elements

Transparent elements such as windows and skylights allow the direct admittance of solar gains into the building. Major portion of the solar radiation is transmitted directly to the interiors, while the remaining small fraction is absorbed and/or reflected back. Furthermore, an element may also be openable (e.g. skylight, window, door, etc.), thereby allowing for air exchanges between the building and its surroundings. Thus, the transparent buildings components affect the building energy balance a great deal

Nasrollahi (2009) mentions that according to the diurnal changes in sun’s position, the intensity of solar radiation differs considerably among the exterior surfaces of the building. Therefore location and orientation of transparent elements changes the amount of solar radiation enter the building.

Nasrollahi (2009) also explains that the area of the transparent elements also influences the building energy performance. The dimension of transparent elements (with and length) and the ratio between the total glazed area of the building and the total wall area which is called as window-to-wall ratio (w-t-w) are the influential parameters.

Heat is transferred through the transparent components by conduction, convection and radiation.

Solar heat gain coefficient (SHGC) refers to the fraction of incident solar heat admitted through a window glazing both directly transmitted, and absorbed and subsequently released inward.

Visible transmittance (Tvis) refers to the fraction of visible light transmitted through a window glazing. It is an optical property that indicates the amount of visible light transmitted.

U-Value is a rate of non-solar heat transfer through transparent components and it measures the ability of the component to reduce heat gain.

Air leakage defines heat loss and gain occurs by infiltration through cracks in the assembly of transparent components. It is indicated by an air leakage rating expressed as the equivalent m3 of air passing through a square meter of window area.

In addition to the air leakage there is also natural ventilation can be provided to the building through operable transparent building elements such as windows.

Ventilation lets in the fresh air and exhausts room air. This way heat is transported by the convective means and: the thermal energy is associated with the air replaced.

The studies about the impact of glazing area on building energy performance appear frequently in the literature. For example, Kontoleon and Bikas (2002) discussed the influence of glazed openings percentage and type of glazing on the thermal zone behaviour. Su and Zhang (2010) highlight the environmental performance optimization of window-to-wall ratio for different window type in hot summer and cold winter zone in China based on life cycle assessment. Hassouneh et al (2010) explore influence of windows on the energy balance of apartment buildings in Amman highlighting the selection of the optimum window size for each direction.

Furthermore, visual and energy performance of windows regarding solar and optical properties were deeply investigated in a wide scope as well. Nilsson and Roos (2009) review the evaluation of optical and thermal properties of coatings for energy efficient windows Karlsson and Roos (2001) inspect the heating and cooling energy impact of low thermal emittance values for architectural glazings. Johnson et al.

(2004) systematically explores the influence of glazing systems on component loads and annual energy use in prototypical office buildings.

Nabinger and Persily (2011) describe the retrofits and the results of the pre- and post-retrofit assessment of building airtightness, ventilation, and energy use. Hassan et al, (2007) investigate the effects of window combinations on ventilation characteristics for thermal comfort in buildings.