Evaporative Cooling: Load Minimisation

Introduction | Status Quo | Alternatives | Requirements | Load Minimisation | Conclusions | Bibliography

In order to reduce the amount of both water and energy necessary to provide any form of evaporative cooling, it is essential to minimise the cooling load. Daytime heat gain minimisation is essentially a matter of good architectural design, involving considerations of shading, thermal mass and insulation which are beyond the scope of this report. However, two design features are of particular relevance here: zoning and infiltration.

Zoning refers to the isolation of particular sections of a building in order to lessen the cooling load by lessening the volume to be cooled. Van Meter (1994) claims water consumption reductions of 50 to 75% as a result of zoning. For example, in summer residents of hot arid regions may opt to sleep outdoors on rooves or verandahs rather than in interior bedrooms, meaning that daytime cooling can be confined to one or two rooms only. Sleeping outdoors, or in lightweight, naturally ventilated structures such as verandahs is a common summertime practice in most hot arid areas of the world including Australia.

Traditional architecture from hot arid areas typically combines structural extremes (substantial thermal mass for day-time use and very lightweight, well-ventilated construction for night-time use) which reflect the extremes of very large daily temperature ranges. Sometimes, thermal mass becomes almost total in the case of underground and earth-covered buildings. Sometimes, the lightweight construction gives way altogether to shaded outdoor living spaces such as pergolas, patios and courtyards.

Infiltration refers to the unwanted entry of (hot exterior) air via doors, windows, vents and other cracks and gaps. Good insulation practice normally includes measures to prevent unwanted infiltration. In passive cooling systems, infiltration management is essential as the effectiveness of positive and negative air pressures created by ventilation devices may be undermined by a "leaky" building envelope.

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