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close this bookDesign Handbook on Passive Solar Heating and Natural Cooling (HABITAT, 1990, 162 p.)
close this folderVI. Bio-climatic analysis and comfort strategies
View the documentA. Climatic factors
View the documentB. Bioclimatic design strategies

B. Bioclimatic design strategies

Bioclimatic analysis is a systematic procedure for the assessment of thermal comfort in relation to external climate. It has the purpose of identifying desirable adaptations of structure to meet human comfort needs under specific climatological conditions.

The various design strategy templates shown on the following pages, can be used in conjunction with local climatic data to determine appropriate thermal design strategies. Figure 61 defines the comfort zones considered appropriate for various Australian cities overlaid on a psychrometric chart, similar to those used by mechanical engineers. The comfort boundaries for specific cities is defined by the first letter of that city, i.e.. "H" for Hobart. The limits are defined by absolute humidity levels and dry bulb temperature (DBT) levels. Whilst the limits of absolute humidity are fixed at 12g/kg and 4g/kg, the upper limits of DBT vary for each city in accordance with the concept of thermal neutrality, proposed by Auliciems (see Szokolay for descriptive text). In addition, figure 61 also illustrates diagrammatically how the limits of thermal comfort inside can be extended by different design strategies such as cooling by ventilation and air movement.

The designer first chooses the bioclimatic chart for the project location from those in figures 61 to 70, or prepares a new chart with appropriate weather data for the specific location. The graph is prepared by plotting on a conventional psychrometric chart a straight line for each month of the year between the following points: monthly mean minimum DBT with 9 a.m. relative humidity (RH) joined to mean maximum DBT with minimum RH (the 9 a.m. data for maximum RH and 3 p.m. data for minimum RH are the most commonly available data).

The 12 lines so plotted are representative of the major proportion of the weather for the particular location. The appropriate design strategies which will be useful in achieving a thermally comfortable building are those in which the climate lines fall. Based on the data used to represent Adelaide it can be seen that passive solar heating design will be most effective for the winter months. while a number of strategies are useful for summer. Thermal mass would seem to be most important as the boundaries of its "comfort patch' are well away from the limits of January and February. In the case of Alice Springs in figure 63 it can be seen that again thermal mass is effective but evaporative cooling is also most effective. Considering the relative position of the climate lines for both Adelaide and Alice Springs it can be said that evaporative cooling is going to be useful more often in Alice Springs.

It is important to realise that the temperatures used in these bioclimatic charts are mean maximums and mean minimums and not the absolute minimums or maximums. With regard to ventilation cooling, on many of the very hot days the outside air will be too hot to let inside and so this strategy only applies to night ventilation to drain daytime heat from the thermal mass and lower the night-time temperatures. Additional data such as absolute maximum and minimum and 86 percentile temperatures can also be included if available. The monthly lines should be considered more as fuzzy zones rather than hard edged data. The usefulness of these charts is extended as more data are included.

The bioclimatic approach is especially useful for the designer who is not completely familiar with the climate of the project site. It assists in developing a holistic understanding of any climate and its influence on thermal comfort.

Figure 61. Bioclimatic chart - comfort zones and design strategies

Figure 62. Bioclimatic chart for Adelaide. South Australia

Figure 63. Bioclimatic chart for Alice Springs. Northern Territory

Figure 64. Bioclimatic chart for Brisbane. Queensland

Figure 65. Bioclimatic chart for Canberra. Australian Capital Territory

Figure 66. Bioclimatic chart for Darwin. Northern Territory

Figure 67. Bioclimatic chart for Hobart. Tasmania

Figure 68. Bioclimatic chart for Melbourne, Victoria

Figure 69. Bioclimatic chart for Perth. Western Australia

Figure 70. Bioclimatic chart for Sydney. New South Wales