Moore (1993) state three forms of building type in response to climate, from climate responsive through combination to climate rejecting (Figure 4.4). Moore believes that in the past architects had to utilize the building envelope as the principle mediator between exterior and interior environmental conditions. Building envelope was the principle means of controlling the thermal environment and the
Ch 4: Thermal Comfort and Buildings’ Thermal Performance
Fatima M Elaiab 68 building was completely an adapted to its environment. An example on climate adapted building is the old Arabic house, which is inward looking with rooms arranged around a central court, and the external walls often are windowless and so houses can be built up against one another, except for the facade which faces the street. The street is also designed to create a comfortable micro-climate. Unfortunately, industrial revolution changed all of that type of buildings and the development of the structural frame where the role of external walls was reduced to that of a skin to exclude wind and rain and large area of glazing where fitted within these new buildings without considering the environment around these buildings. Therefore, thermal qualities of the massive construction were lost, and this functions replaced by mechanical heating and cooling systems. Buildings were motivated slowly from completely climate friendly to combination buildings and then complete rejected buildings with no concern extended to energy consumption. Figure 4.4 illustrate the stage of change through architecture development.
Figure 4.4: Continuum of building climate response_ plotted after Moore, 1993
And so, building form and envelope parameters have a significant effect on thermal comfort and energy saving indoor which have to deal with it carefully, that is because achieving a correct form for its climate could enhance the free running condition in some periods during the year. This research is concerned with a form of buildings that described by Hawkes (1981) as a selective mode which work with the environment even so it is not easy to achieve all the points listed in his mode. Table 4.2 illustrates this mode and compared it with other mode (exclusive mode).
Table 4.2: comparison between selective and exclusive modes_ source: Hawkes, 1981
Selective mode Exclusive mode Environment is controlled by a
combination of automatic and manual means and is a variable mixture of
natural and artificial
Environment is automatically controlled and is predominantly artificial
Shape is dispersed, seeks to maximise the use of ambient energy
Shape is compact, seeks to minimize the interaction between exterior and interior of
environments
Orientation is a crucial factor Orientation is relatively unimportant
Windows are restricted certain directions. Solar control is required
sometimes
Windows are generally restricted in size
Energy is a combination of ambient and generated. Its use is variable
throughout the year
Energy is primarily from generated sources and is used throughout the year in a relatively
Ch 4: Thermal Comfort and Buildings’ Thermal Performance
Fatima M Elaiab 69 Subsequently, Thomas (1984), mentioned that buildings with interior open space such as courtyards and open atria showed the possibility of a significantly reduce energy demand, if passive solar heat gain is accounted for. If not, it is advised to avoid using the court or any complex forms which tend to increase the surface area and may cause self-shadowing. This advice brings another effort towards numeric characterisation of building shapes, the relation between volume and area is explored as related to building’s fabric heat loss as argued by Markus and Morris (1980). Utilizing the standard formula for steady state building heat loss calculations, their research established the following relationship between heat loss and building geometry. For instance, in rectangular buildings the ratio of surface area to volume is established by using the height (H), length (L) and width (W) variables of the building. The ratio of surface area to volume is given by:
... (eq. 4.1) Where,
To compare the surface area to volume ratios of buildings with different shapes, the volumes must be equal; Table 4.3 explains the relation using three forms with same volume and four cubes having different volumes. It has been stated that cube has the least surface area to volume ratio as compared to other shapes with the same volume. (Markus &Morris 1980).
Table 4.3: surface area, volume and ratio_ source: Markus & Morris 1980. Dimension Surface area
(A) Volume (V) Ratio (A/V) 4× 4×4 3× 3×7.1 2× 2×16 1× 1×1 5× 5×5 10×10×10 20× 20×20 96 103.2 136 6 150 600 2400 64 64 64 1 125 1000 8000 1.5 1.61 2.13 6 1.2 0.6 0.33
Table 4.3 shows that the ratio decreases as the dimensions of the cube increase. The relation between the height of the building, its volume and plan shape is also investigated by the same authors to obtain minimum envelope heat loss per unit volume; these results are shown in Table 4.4. It is observed that the ideal height increases rapidly with changes in volume when the building is small, but when it is
Ch 4: Thermal Comfort and Buildings’ Thermal Performance
Fatima M Elaiab 70 large the rate of increase is much less. It is also obvious that the less compact the building the smaller the ideal height becomes.
Table 4.4: Relation between surface area and volume _ source: Markus &Morris 1980.
In conclusion, this study showed that the cube produced the minimum ratio of surface area / volume, and the tall block produced the maximum one, also the study showed that there are unlimited numbers of possible building configuration, beside the interrelated effects of the radiant heat gains, are of openings, orientation,. etc, which all make the optimization impractical. Another conclusion can be drawing from the above discussion, is that one factor in relation to the energy conservation and human factor in the hot and worm climates would be to minimize exposed walls to high solar radiation especially east, west or south walls depends on solar latitude, minimize surface area particularly the roof, maximise shade and integrate opening area and location within the form analysis to provide adequate ventilation and natural light with no glare.