Climbing temperatures and soaring summer heat means greater expenditure to cool homes, provided there are no issues with electricity supply. However, here is an easy way to cool your house even in the peak of summer, at minimal cost.
I stay in the rural town of Phaltan in western Maharashtra. Phaltan weather is mild, but in the months of April and May, the air temperatures reach 45°C.
For the last 33 years, I have been living in a house which is passively air-conditioned. I designed and built the house and its cooling system in 1984. The house has 16-inch thick stonewalls, and on the roof we have put a green shade net on a simple angle frame to stop the sun heating up the roof surface. The roof surface is covered with jute gunny sacks which are sprinkled with water either once or twice a day.
This simple system cools the house very nicely. The evaporating water from the soaked gunny sacks cools the roof, and the ceiling fan inside the room drives the cool air down.
The green shade net does not allow the direct sunlight to heat the gunny sacks, so together with the evaporating water, they remain cool throughout the day and night.
This coolness is conducted through the roof to make the room cool.
We also close the windows and draw the curtains in the morning so that radiative heat and glare do not come inside the room. The 16″ thick walls have a thermal lag of about 10-12 hours, and thus allow the heat to come inside the house through the walls only late at night.
Thus, when the outside temperatures have been 40-45 Centigrades, our house has remained cool with temperatures around 28-30 Centigrades inside, and under the ceiling fan, it can sometimes become chilly.
This simple rooftop cooling system is a very effective air-conditioning system, with very little energy and cost involved. The gunny sacks last for about two years, after which they need to be replaced, and the water requirement is only 1.5 liters per square metre.
Costing done by us has shown that this system is one-tenth the cost of a regular electric A.C. system, and when the electricity supply is irregular—especially during summer—the rooftop system provides a very cost-effective method of cooling the house.
In addition, the capital cost of this system, including the shade net and gunny sacks, is only ₹250 per square metre.
This system can also work nicely in existing houses which have thin brick walls, since 80 % of the total heat input comes from the roof.
It should, however, be pointed out that this system works best in areas which have dry summers. With high humidity conditions, the roof evaporation will be less, and hence cooling will drop.
We also use this system in our offices, and lots of people have copied this simple technique for their house and offices.
For more content and innovations like this, check out NARI’s website.