An experimental evaluation of Nocturnal Cooling System- Case Study

Nocturnal Cooling is based on the principle of heat loss by long-wave radiation from one surface to another body at a lower temperature In many Indian locations, the available night cooling exceeds the residential nighttime cooling loads and in moderate climates such as Bangalore may be considerably in excess of total daily cooling requirements. Careful examination of air conditioner operation in Bangalore shows that night sky radiation could substantially reduce cooling needs. Over a 10 hour night, theoretically night sky radiation amounts to about 250 - 2 450 Wh/m if all could be effectively utilized. However, that is not easily achieved. Various physical limitations (e.g. air flow pattern under the radiator, fan power, convection and roof conductance) limit what can be utilized, so that perhaps half of the potential rate of cooling can be practically obtained. However, passive systems with additional systems such as ETS (Earth Tunnel Cooling Systems), Air washers (ECS), Stack effect with turbo-ventilation system- 2 2 combined will achieve net cooling rates of 4 - 5 W/m . With a four floor 200 m up to a nearly free cooling rate of 500 - 1000 Watts (1700 - 3,400 Btu/hr). of roof in a typical home that adds In addition, the system offers enticing potential for low energy humidification. Materials placed in the attic, may absorb humidity from the interior during night cooling while exhausting moisture during daytime solar heating. An experimental evaluation has been conducted on a night sky cooling system designed to substantially reduce space cooling needs in homes in Bangalore climates. The system uses a sealed attic covered by a highly conductive metal roof (a roof integrated radiator) which is selectively linked by air flow to the main zone with the attic zone to provide cooling − largely during nighttime hours. Available house mass is used to store sensible cooling. Currently, the system’s capability for solar dehumidification with minimal electricity input was demonstrated.