Why are our homes cooler than our neighbours ?

Friends from Kochi, Chennai, Mumbai and Bhiwadi asked me how to cope with the heat when home. I have shared some ideas before. Am reiterating some of them again.

My claim is that our homes have been way cooler than our neighbours’ facing the same orientation with same flat design. Everyone who visits remarks how cool our homes are in summer.

Our homes are not only cool, but continuously provide some interaction with nature (most homes remain largely shut off from it), and more fresh air than available in a normal home.

The principle components to address heat loads at your home are : 1 Roof. 2. Windows 3. Ventilation 4. Shading open areas around your home. We will let the discussion on roofs be for now, but can have it if one of you wants to.

WINDOWS

Windows are typically only 18% of the overall house but account for 50% of a home’s energy loss. Single paned glass windows are about 15 times less insulated than the typical walls and roof of a well-built house.

Indian homes normally have casement windows of 3 mm glass, pictured below.

Picture by Karl Gruber

I was surprised to discover today that the casement windows we are used to in india have much lower performance on many parameters than do louvre windows, including on cross ventilation. A louvre window is pictured below but I have not seen it used in the Indian context in living areas.

If ever some window glasses break and have to be replaced, you may consider thicker glass as replacement, say 10mm. It is better at noise control and passes 10 % less solar radiation into your home. It also conducts heat 5 % less than the normally used 3 mm glass.

But double glazing – having two parallel fixed glass window panes rather than one, can lessen transfer of heat through glass (conductivity) by more than half compared to a single window glass. And it can lessen solar radiation (how much sunlight passes through the glass) by 25 %.

We did our double glazing cheaply without breaking the window frames - by installing a second fixed glass of 6 mm inside for windows we did not wish to open. It was fixed where the jali windows wld have come had we wanted them. The openable glass windows on the outside were replaced by 8 mm fixed glass. Having varying thickness of glass creates better sound insulation as well.

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SUNBLOCK roller blinds OUTSIDE glass windows and doors will reduce conduction of heat by one-third over SINGLE glass windows alone, and reduce solar radiation by over 40 %.

But sunblock roller blinds outside DOUBLE glass windows will reduce heat conduction and solar radiation by two-thirds.

Thick CURTAINS INSIDE will perfom only half as much to block heat as sunblock roller blinds outside. The same roller blinds inside, will perform much better than curtains.

VENETIAN blinds, a picture of which is given below, apparently perform inside better than curtains, but I have not yet begun using them.

My experience with using FILMS on glass says, the films cut out only light and still let in nearly all of the heat.

For any window covering, curtain or roller blind, lighter colours or WHITE are much better to reflect heat than darker colours, and make a substantial difference to heat gain inside the building.

VENTILATION

I know of just ONE household that uses ventilation like we do – and they too, say their home is much cooler than their neighbours.

So what is it that we are doing ? When outside air feels cooler than inside (anywhere from 6-11 pm these days), we open ALL possible windows and doors fully, and let them be open till about 8-9 am the next morning.

In our present 850 sq feet utsav flat for example, there are EIGHT openings to the outside – all are opened and closed as per schedule.

When the outside air feels warmer than inside in the morning, we shut doors and windows, only to open them again in evening.

SHADING OPEN AREAS AROUND YOUR HOME

If the areas around your home are hot, they will RADIATE heat inside. So balconies, aangans and soil areas around your home should be protected from getting hot.

We do this by hanging thick plastic or canvas curtains outside our balconies (once these are gone we will graduate to sunblock roller blinds).

We have trees and vines shade large areas around the house, also installing green nursery cloth at roof level over open areas as needed.

We have had garden areas with ground soil surrounding our house / flat for only 10 years.

For twenty years before that, we only had balconies / paved areas outside/around the house.

We planted TALL TREES IN POTS (even 10-12 inch diameter pots will support 6-8 feet tall trees and bushes) and placed them outside windows and in paved areas around the house so they brought coolness and gave us the feeling of gardens.