The surface area to volume (S/V) ratio (the three dimensional extrapolation of the perimeter to area ratio) is an important factor determining heat loss and gain. The greater the surface area the more the heat gain/ loss through it. So small S/V ratios imply minimum heat gain and minimum heat loss.
To minimize the losses and gains through the fabric of a building a compact shape is desirable. The most compact orthogonal building would then be a cube. This configuration, however, may place a large portion of the floor area far from perimeter daylighting. Contrary to this, a building massing that optimizes daylighting and ventilation would be elongated so that more of the building area is closer to the perimeter. While this may appear to compromise the thermal performance of the building, the electrical load and cooling load savings achieved by a well-designed daylighting system will more than compensate for the increased fabric losses.
In hot dry climates S/V ratio should be as low as possible as this would minimize heat gain. In cold-dry climates also S/V ratios should be as low as possible to minimize heat losses. In warm-humid climates the prime concern is creating airy spaces. This might not necessarily minimize the S/V ratio. Further, the materials of construction should be such that they do not store heat.
The factors of the external environment that influence heat transfer through the building envelope are:
- Temperature of ground, air or snow with which the building envelope is in contact
- the direction and speed of winds blowing at the building
- Solar radiation incident on the building
In principle, to minimise heat transfer through the building envelope the building shape should be as compact as possible,tending toward a cube. However, to optimize the building shape while considering the three factors above is a more complex matter.
A cube may not be optimum if, for instance, you need to minimize the exposure of walls to hot winds from the West as well as solar radiation from the western side. Here the orientation of the building as well as the relative dimensions of surfaces facing different directions would have to be considered.
Basam Behsh, who researched this problem, found that the S/V ratio is not a correct indicator of thermal behaviour of buildings with complex plans.
In order to compare different options of building shape, especially for buildings with complex plans, one would have to resort to simulation by an advanced computer software.
References:
- Basam Behsh, Building Form as an Option for Enhancing the Indoor Thermal Conditions
- Heating, Cooling, and Lighting as Form-Givers in Architecture
Level Eleven: Surface Area to Volume Ratio
Prime Parameters: Radiation
Minimizing the surface area to volume ratio minimizes heat transfer.
Other Parameters:
Climatic Implications
The surface area to volume (S/V) ratio (the three dimensional extrapolation of the P/A ratio) is an important factor determining heat loss and gain.
Theoretical Understanding
The greater the surface area the more the heat gain/ loss through it. So small S/V ratios imply minimum heat gain and minimum heat loss.
Building Design
In hot dry climates S/V ratio should be as low as possible as this would minimize heat gain. In cold-dry climates also S/V ratios should be as low as possible to minimize heat losses. In warm-humid climates the prime concern is creating airy spaces. This might not necessarily minimize the S/V ratio. Further, the materials of construction should be such that they do not store heat.
How does surface area to volume ratio affect the retention of heat in animals in cooler climates?
Abstract
Animals exposed to cold temperatures in their natural environment are able to survive and flourish due to their better insulation and ability to retain heat. Animals in cooler climates tend to be larger because their small surface-area to volume (SA/V) ratio cause them to lose heat at a lower rate. We tested this by placing cubes of clay in a bucket of ice and measuring their internal temperature to determine which retained heat better. Both large and small models were measured at room temperature and placed side-by-side in a bucket of ice. The large cubes lost heat at a lower rate than the smaller models. The large cubes were therefore able to retain their initial heat loner because of their smaller SA/V ratio. In this study, we conducted four trials to help explain why animals with a smaller SA/V ratio are able to withstand colder environments than smaller animals with larger SA/V ratios.
References
French, D. 2014. Investigating Biology: A Laboratory Resource Manual. 2014 Edition. Fountainhead Press: Fort Worth, TX. Print.
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