Radiant Cooling and Earth Tunnel Ventilation for IITM – CCCR Building
The Indian Institute of Tropical Meteorology, Pune (IITM) wanted to set up a Research Centre for Climate Change, at the IITM campus in Pune. Given the objective of the research to be conducted in this facility, IITM expressed their desire to make it as energy efficient as possible by maintaining optimum indoor conditions consuming the least amount of power. The size of the facility is approximately 18,000 sq ft with three levels.
Always up for a good challenge, we brainstormed many ideas and suggested a system implementing ‘Radiant Cooling’ coupled with ‘Non-refrigerated Cooling’.
The system achieves optimal indoor temperatures by cooling the floors, ceilings and roof via embedding PEX piping in the RCC, and circulating water in the pipes. This will, in turn, cool the RCC mass and reduce radiant surface temperatures of the floor and ceiling. We recommended that no false ceilings be used in occupied areas to take advantage of radiant ceilings.
By operating the system even during the nights, we are able to take advantage of lower ambient temperatures and store the cooling effect in the concrete mass, using the flywheel effect of the large mass at lower than room temperature. Air for the shared load of air conditioning is drawn into an earth pipe heat exchanger that is pre-cooled with the constant temperature earth at 4M below the surface.
After this precooling, the air is further cooled in an air handling unit with water coils. This cooled water is supplied to the coils from a non-refrigerant cooling system with supply to the radiant slab. Air is distributed to each occupied Area at lower than ambient temperature and is directed on to occupants, to achieve adequate velocity. Masonry ducting from below ground connects to each flow. The air flows over into the central area and is exhausted from the topmost part of the building.
The cooling system for water comprises of a cooling tower with certified performance and cooling to within 20°C of ambient WBT. A cascaded indirect cooler using the same cooled water is used to precool the cooling tower air inlet to reduce WBT and cool the water to below ambient WBT, especially in summer. Two cooling towers of 75% capacity will ensure water temperatures.
With this system, in Pune, where WBT does not exceed 24°C in the monsoons and is around 20°C in summers, the operative temperature indoors will be maintained below 25°C except in the monsoons when the temperature can drift up to 27°C. To take maximum advantage of float available with ambient variations, no controls are used. A monitoring system has been installed to record temperatures so the system can be fine-tuned later as needed.
From the start, our target was to keep the maximum power required to below 25 kW/Hr. Since the system has been installed, we have conducted 18 months operation, indicating a power usage of 24 kW/Hr!
The expected power usage for the natural cooling system is 15 Watts/SqM. Power requirement for a conventional air-conditioning of similar capacity is approximately 95 to 110 kW/Hr. This plant consumes just 25% power as compared with conventional air-conditioning to achieve similar indoor conditions, with better indoor air quality as this system runs on 100% fresh air!
