• Cooling India
  • Aug 15, 2016

Sheetal Sutra

This article investigates the underlying causes of the high cost of providing thermal comfort in modern built environments in India...

Air conditioning energy costs are fast rising to unsustainable levels. Electricity demand for ACR averages 30% to 50% of the total energy budget of air-conditioned buildings. Skyrocketing energy cost has made air conditioning unaffordable for domestic users who cannot write it off as business expense. It has increased overhead costs of commercial users and production costs of industrial users to a level that makes them lose their competitive edge while facing global challenges. This article proposes a new formula that can reduce those energy bills substantially by reducing or eliminating air conditioning altogether.

Lowering The Energy Bills

  Much has been written about increasing the energy efficiency of the HVAC system that pumps out the solar and internal heat from the building. This article is about draining it out. Draining requires no energy, pumping uses that.

  The method described is rooted in our Indian heritage, but it does not involve khus screens or desert coolers. As a matter of fact the first known desert cooler in India was called the “Thermantidote.” A British engineer built it for the Jaipur royal family. It is still in the City Palace museum, albeit in the storeroom.
  Before talking about the solutions, let us understand the problem.

The Problem

  The problem is: thermal comfort in India is equated with air conditioning as its only stand alone solution. So far, every HVAC professional mechanically calculates the various heat gains into the building, either manually or by computers. A system is selected, tendered and installed, that will adequately meet the load.

  The main villain is that the designers, comprising the consultants, the sales engineers and the premises officers, fail to realise that we are applying, mindlessly, an energy hungry cooling technology born in a country where the buildings are insulated, the summers are mild and energy is cheap. Here the houses are bare, summers are sweltering and energy is not only very expensive, but also unreliable.

  So it is case of a right formula applied to a wrong problem. It is like walking down a Delhi street in a woolen suit, overcoat and a Bowler hat! It is proper in London but not here.

A Whole New Ball Game

  For example, a couple sleeping in a bedroom at night will generate only about 300 watts of metabolic heat. The heat load form will not show any other significant load. A one- ton air conditioner removes more than 3000 watts of energy from the room. Thus, in a 10- hour session, the compressor should work for a total of one hour only, and the monthly energy use should be less than 50 kWh. We know that it is much more. So, where is the extra load? Of course it is the stored solar gain.

  This example also establishes that all direct solar heat reaches the interior through, and only through, the structure. Even the sunlight coming through a window falls on the floor or the wall and is absorbed there.

  Also that all heat gains other than people, lights, fresh air and equipment are solar in origin and that solar loads are very heavy in India as compared to USA and Europe. Thus, providing thermal comfort in India is a whole new ball game.

  Herein lies one solution to our problem. If we could, somehow, keep the structure cool without using energy, then we would achieve a major reduction in our energy bill. The answer is in our heritage.

Our Heritage Has The Answer

  Our master builders of yore had learnt from nature to develop zero energy techniques that used mass to store heat, and flowing water or air to drain it out, thus keep masterpieces like the Gol Gumbaz and the Taj Mahal cool throughout the long hot Indian summers.

  The former, having 10- foot thick walls and measuring 100 feet square topped by a massive dome, depends on its enormous mass to absorb the solar load while maintaining its 18,000 odd square feet of its interior quite cool. Its exterior finish contains the mineral barite that is plentiful in that area, and has an emissivity of 0.95 in the infrared region. This allows re-radiation to the sky mostly during the night.

  The Taj Mahal is a massive building that sits on an equally massive podium measuring 325- feet square, 15 feet above ground and perhaps the same below.

  Their combined mass is tens of thousands of tons and can absorb an enormous amount of heat before its temperature rises by just one degree.

  The Yamuna River flowing next to it has near zero degree water all winter long. During that time, the whole massive podium cools down by a majestic heat transfer process and it turns into a heat sink for the superstructure, which gets additional cooling by rain water during the monsoon and by cold air during the winter.

  The heat absorbing capacity thus created is so large that by the time the building warms up, the summer has gone. This is the Sheetal Sutra or the Natural Cooling Principle.


Sheetal Sutra Runs Throughout Our History

  We find a continuum in the use of the same concept in lake palaces, temple/mosque complexes, royal residences etc. while searching our cultural history through ancient India. We could go past Mahabharata, where Duryodhan had fallen into a pool inside the Pandava palace, all the way back to the caves.

  Here we Homo Sapiens-Sapiens have lived for over forty thousand years. The caves are cooled by mountain streams, while the soil layer, with its trees, reduces solar heating. The mass of the mountain stabilises the inside temperature.

  Thus, conditions inside a cave are identified as a primary natural standard for human comfort. Radiant cooling of the human body by the cave walls is established as an important and necessary element for providing thermal comfort.

  Emulating the caves, our ancestors put massive buildings on massive bases, and provided a thermal path to a water body.

  Those of us who have visited a heritage building, or even the ancestral family home, know that this technique provides thermal comfort at zero energy cost.

  The reason why these buildings are comfortable is that the entire structure cools down to a temperature that is several degrees below that of the human skin.

  The reason why they consume little or no energy is because the heat is drained out to a low temperature sink in the form of an open water body.

  Anyone who has drunk water out of an earthenware jar knows how cool it is, particularly early in the morning.

  By contrast, air conditioning has to pump the heat out of the air to higher temperature ambient air. This requires oodles of energy.

  If used in an air-conditioned building, the heritage technique would reduce solar load by a good amount and would also shave the peak. It would mean a smaller plant and lower energy consumption. The question was how it could be implemented in modern times.

Modern Technology:

Modern Technology

  Things change. There are more people in Mumbai today than there were in the entire known world 2000 years ago. Space constraints and economics have forced us to live in crowded localities where massive buildings and water bodies are no longer practical. While this has spurred the growth of the AC&R industry, we no longer have cheap, abundant power to feed this energy hungry technology. An inescapable conclusion that emerges is that air conditioning is a right technology used in a wrong way and on a wrong day. It must be used like a cake- as dessert after a meal, not the meal itself. By using new technologies not known to our ancestors, the following idea adapts our heritage technique to modern times:

Modern Sheetal Sutra

  Use barriers to reduce solar gains; absorb and drain out heat from the structure; then use air conditioning to pump out the balance load, if any, by cooling the air.

the basic system


  EASIER SAID THAN DONE: Many innovative solutions were tried, The first trial was a coir mat laid on the roof and wetted by a sprinkler. But dust, mosquitoes and water leaks ended that. Then welded iron pipes with water under vacuum were tried, It needed skilled welders at site and the pipes were prone to rust.


The cooling system was a bit more complex than the basic model...


Predicted temperature profile using a simulation software...

  THE GAME CHANGER: The final solution was a game changer. A plastic tube was laid on a cured concrete slab and was covered by screed. Water flowing through it picked up the solar heat and was sent to a radiator, where most of the heat was dumped into the air. Lukewarm water returned to the tank, this was recycled through the radiator during the night and was cooled to the morning ambient temperature and the cycle began again. There was no loss of water, and the little energy needed for the pump and the fan was supplied by a PV panel. That is all there is to it!

  Our ancestors did not have the technologies of plastics, pumping or thermodynamics except perhaps in rudiments. Of course they did not have electricity. By infusing these into their technique of structure cooling, We were able to keep the occupants comfortable without air conditioning, air cooling or even a mechanical ventilation system.

  Therefore, providing thermal comfort in India is a Whole New Ball Game! We are not promoting rocket science. It is very simple and is easily replicable by anyone with minimal technical training, using Indian materials and non patented published data.

  The Game Changer building was a result of close cooperation between the Clients, the Architects and the Contractors.

  It is hoped that many more such teams, the green NGOs, Architecture and Engineering Colleges and the Government will take notice, wake up and start a mass movement that will strike a big blow for the environment.

  This is not an isolated example. There are many more installations around us at many parts of the country.


Surendra Himatlal Shah

Surendra Himatlal Shah
BE Mechanical Engg,
Clemson University, USA
Founder & Owner of
Panasia Engineers Pvt Ltd