ASHRAE Journal - January 2013 - 69

thresholds, and the building operates in as dry an environment as practically possible, the problem of mold can be minimized. Energy-efficient humidity control in hot, humid climates has a strong bearing on thermal comfort, IAQ and eventually on the health and productivity of occupants in air-conditioned buildings. The following discusses some key considerations for energy-efficient humidity control. Air-conditioned buildings in hot, humid climates are invariably cold. Is this due to occupant preference or an inevitable outcome of current design practices? A study of five office buildings in Singapore showed air temperatures in the range of 21.7°C and 23.8°C (71°F and 75°F).1 In another study,2 it was found that the air temperatures in the two buildings studied were in the range of 20.8°C to 23°C (69°F to 73°F). It is important to consider humidity issues at design and part loads. This is to prevent buildings from being operated at cold conditions. This is due to the oversized design of AHUs, particularly cooling coils. An oversized coil will tend to provide less dehumidification unless overcooling is used. Since active reheating is not typically permitted for comfort air-conditioning in hot and humid climates due to energy considerations, the buildings stay cold. The situation worsens during part loads when considerably more dehumidification is demanded. It is possible to explore a

means of optimizing cooling coil operation even though it was over-designed, which can be done with a coil that has the capability of dynamically varying its effective surface area.3 Another possible solution is to decouple the requirements of ventilation from that of cooling and handle their conditioning separately. Thermal comfort acceptability of tropically acclimatized subjects may well be different from their temperate climate counterparts. Can a warmer and drier thermal environment be more acceptable? Can a cooler micro-environment (immediate breathing zone) coupled with warmer ambient conditions be more acceptable? Personalized ventilation (PV) systems that can deliver the conditioned outdoor air directly to the occupant breathing zone can significantly enhance thermal comfort and IAQ, while saving energy.4 These studies, which have involved the effect of cooler (around 23°C [73°F]) air in the breathing zone, using a PV system working in conjunction with a warmer (around 26°C [79°F]) background air using conventional mixing ventilation (MV) system, found significant enhancements to thermal comfort, IAQ and energy efficiency. The issue of cold feet with underfloor air-distribution (UFAD) systems has been overcome with the integration of such systems operating at a warmer supply air temperature with a cooler PV system so that the whole body thermal comfort is achieved without stratification.5

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January 2013

ASHRAE Journal

ASHRAE Journal - January 2013

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