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
VII. Detail design A. General
The detail design for passive solar heating and natural cooling involves the careful checking and selection of the various elements of the building. Some design issues are important to both passive solar heating and natural cooling principles such as the control of conductive heat flow (control of heat out in winter and in during summer) whilst the design or selection of shading is important for its summer control and important in its absence in winter to let the sun in.
It has been found in recent studies undertaken for the 5-star design rating system that thermal-storage materials inside a house influence comfort levels in both summer and winter. The mass has little effect however on the heating loads of an intermittently heated house (the more common pattern of heating in most of Australia except in the very cold areas).
1. Passive solar heating
In both the cool-temperate and the hot-arid zones, passive solar heating is necessary in winter. The detailed design procedure should be as follows:
(a) Locate as many habitable rooms as possible with a northerly outlook to receive winter sun and buffer spaces to the south as natural insulation to habitable rooms. Provide adequate air-lock protection to main entrances for draft control;
(b) Determine the desirable glass-mass relationship for specific location and building use;
(c) Select or adapt the desired construction system to achieve the appropriate glass-mass relationship;
(d) Develop construction details to facilitate the economic installation of appropriate insulation levels in all external fabric;
(e) Select and specify glazing and window treatments for optimum daytime solar gains and minimum conductive losses:
(f) Develop construction details to minimize heat loss due to infiltration.
2. Natural cooling and summer comfort
In much of the year overheating inside buildings is the result of excess solar heating and internally generated heat reaching the interior spaces. This is certainly the case where the ambient air temperatures are no greater than about 27C. In such cases it is usually practicable to maintain comfort conditions with appropriate control of those heat gains (such as shading of windows and exhausting internal heat) and good ventilation and air movement patterns.
Where air temperatures are above reasonable comfort levels it is necessary to apply other strategies that will collect or soak up the excess heat for disposal into the cooler earth or to the cooler night air. In these cases the design approach should be as follows:
(a) Reduce solar gains to the interior by correctly designed shading;
(b) Minimize conductive gains by shading wall and other surfaces as appropriate and insulating the external fabric of the building;
(c) Minimize the effects of internal gains (lights and other appliances) by exhausting the heat:
(d) Design night ventilation openings to optimize the cooling of thermal sinks (thermal mass):
(e) Allow for appropriate air movement (ceiling fans and the like) to raise the occupants' comfort threshold;
(f) Design for minimum air infiltration during the day when external air is 3 deg.C greater than the upper comfort limit.
The overall goal is to be warm in winter and cool in summer. The sections that follow will assist the designer to achieve these goals by design, not by accident.