Panasia Corporation, Mumbai – headed by Surendra Shah - has come out with a cooling system that does not need electricity or power to produce a basic cooling effect. It is a simple roof cooling system. One needs to cover the roof during the day with a low emissivity cover, and withdraw it at night exposing the roof for cooling by radiation to the sky. The system does not use any electricity or water. The only energy required is for opening and closing the cover once each in a day – which may even be done manually. During the trials, the slab bottom temperature remained below 34°C. Since this is below the human skin temperature, there is no heat transmitted by the roof to the occupants. Cooling the roof also prevents its heat from spreading into the rest of the building. During the night, the cover is retracted and the slab remains open to the sky. This allows radiant heat transfer from the slab surface that is 30°C to the sky that can be -40° to -60°C depending on haze and clouds. The rate of heat transfer depends on the difference in the fourth powers of their absolute temperatures and the emissivity of the slab (0.85). So the slab bottom cools down to 27°C.
From sunrise to sunset this flexible cover, with a very shiny bottom, is drawn over the slab. It shades the slab, while its low emissivity (0.01) due to the shiny surface prevents any radiant heating of the slab. So even though the slab gains some heat from the ambient air, its bottom still remains below 30°C – at least five degrees below the body temperature – so it feels cool enough to be free of heat stress.