Passive and active cooling designs in India

Passive and active cooling designs in India

Interview with Sanjay Prakash, Principal Consultant at SHiFt: Studio for Habitat Futures

What has been the evolution of cooling techniques in the recent past in Northern India?

In north India, evaporative cooling was very common until recently. The so-called desert coolers are low energy devices which were able to cover cooling requirements for the first half of the summer, the dry summer. Then the monsoon would come, the cooler would decrease its efficiency, but many people could still manage fairly high temperatures thanks to ceiling fans or desert coolers running without water in them. 

Workers in front of desert coolers in Delhi, November 2019 – (c) Gaia Squarci – All rights reserved

But, lately two things are happening.

On the climate change side, the month of May which used to be dry is now becoming increasingly rainy, so humid, that I had to retire my evaporative cooler 2 years ago. 

On the socio-economic side people with affluence are increasingly getting used to air-conditioning. Even though AC is getting more efficient, there is a limit to the efficiency you can achieve because of its functioning: it is basically a process where the device brings humidity out of the system, and to do that it has to bring the air to a fairly low temperature, and allow it to rise again. 

AC is becoming cheaper and cheaper, but the unfortunate part of the story is that in my experience AC is somehow addictive: families who install it tend to use it more and more over the years. 

A residential building in Delhi, November 2019 – (c) Gaia Squarci – All rights reserved

Why passive solutions are not widely adopted in modern India?

We must adopt new mechanical systems, as the two stage evaporative cooling systems available in Australia and in the US, which use only twice the energy needed by ceiling fans and not 6-times as a normal AC. These devices can be more effective than a desert cooler in the wet season, as they do not reduce humidity but they don’t increase it either. They work by evaporating the water and by cooling the air in a separate set of chambers, to then subsequently mix them.

We still need to invent some passive systems which gives people the impression they are sufficiently comfortable without leaving them with the impression they are missing something.

Sanjay Prakash, Architect

The problem with these solutions is that they do not have the capacity to cool below 1°C the average outside temperature. For instance, if temperature vary say from 20 to 35°c in dry summers, the average is 27.5, them we can accept that a passive system can go to 26-27 °C inside the building. This is in theory acceptable, as it has been found, for instance in Pakistan, that people acclimate to their local environment and find more conformable 26°C than 22.

Also you don’t want to have the same temperature in rooms during the 24 hours but rather slightly cooler temperature by night and slightly warmers during the day. If you vary the room temperature during the different hours of the day, this will improve dramatically the efficiency of your cooling systems.

As an architect what is your experience in terms of building design and cooling solutions?

There is another important problem. A really optimized building design without air conditioning typically has many open windows to let air circulate. On the opposite if you design a highly efficient building which uses AC, it needs to be highly ceiled. Take insulation for instance: insulation is beneficial if the temperature inside the building is always cooler than outside.  On the opposite, insulation can be harmful if it is a naturally designed building, because the insulation stops the heat from going out at night time. 

The Sehgal foundation in Gurugram, November 2019 – (c) Gaia Squarci – All rights reserved

In any architectural project, you have to define very early with the client what he wants: a passive building, an hybrid one, an active building, or even an hyper-active building. You then want to have the most efficient building in the category you choose. In the early stage of each project, I interact a lot with the clients to understand if they necessarily want AC. Almost all of them want something to cool mechanically, while they usually don’t want completely passive systems. 

A passive system would need that you accept typically the constraints which come with this choice: a little bit of selective ventilation, opened at night, closed during the day.  An active system would typically have 2 stage ACs, coolers, fans, forced ventilation to take out the heat.

An hyper active one: these clients want cooling everywhere, with no compromises possible. These are getting quite common, and there you can make them invest in good ACs, good insulation, good materials and so on. Very often you can make good economy with good choices on these issues, showing the clients how much saving they may achieve thanks to certain solutions.

What should be the way forward in your view?

I don’t think we can rely on technological advances which most likely will not be available soon, nor on enabling policies which won’t change peoples’ mind. 

What we require is  lifestyle change which convinces people that dealing with high temperatures and open windows is not a bad thing, we actually need opinion leaders which can show the example.

Sanjay Prakash, Architect