Glaring mistakes

conventional v/s curtain wall

In hot climates, the overall energy usage rises as you increase the glazed area. Curtain walls, therefore, are highly inappropriate.

I have ranted about glass façades for a long time and this editorial by Sunita Narain of DTE has inspired me to add a couple of paragraphs to the original one.  Among other things, she has written about a recent study by IIT-Delhi which found that, in our hot climate, the manufacturers’ claims of special coated glass or double/triple glazing being able to reduce heat gain are rather hollow.

One of the other specious arguments put forth in an attempt to portray glass curtain walls as green systems is to say that it reduces the electricity consumed for lighting. This is a half-truth. Leave aside the uncomfortable glare that people working inside such buildings have to put up with, let us make a simple comparison.

Consider a 10m² conventionally designed space. Assuming that we don’t take passive cooling techniques into account, the air-conditioning load will be in the region of 3,500W (1 ton).  Lighting the same space, on the other hand, will need just 50W with fluorescents or 40W if we’re using LED fittings.

Now, imagine a similar sized curtain-walled space. The maximum saving that can be achieved by reducing lighting is a puny 50W. However–and this is the big problem–air-conditioning requirements will probably have risen to a whopping 5,000W.  Even with all the specially coated and multi-layered of glass in the world, the total requirement is unlikely to be anything less than 4,500W.

So yes, we may not use as much electricity for lighting but, I’m afraid, the energy usage for cooling will go right through the roof and no amount of marketing spin can get around this simple fact.

Glass Curtain Walls


Glass curtain walls and façades, seen as signs of modernity & progress, are inappropriate for our tropical climate.

Unfortunately, there is a strong trend in India these days towards designing building with glass curtain walls. These are seen as making a break from the bad old days when we were perennially short of power and couldn’t afford to run air-conditioning to keep ourselves cool. Well, I have some news for people with this view — we’re still perennially short of power and cannot afford to run so much air-conditioning.

Our country has a huge shortfall of electric power and that’s not going to change any time soon — at least not unless we suddenly manage to generate power from cold-fusion. In the meanwhile, huge quantities of fossil fuel will continue to be burned thereby exacerbating climate change and making things even worse for everybody and their pet dog.

Glass curtain-wall buildings are inappropriate for our climate for two reasons:

  1. Having a glass skin means that the inside is subjected to an enhanced greenhouse effect. Glass easily allows short wavelength light to pass through. Once this light has reflected off objects in the room, is of a longer wavelength which glass blocks. As a result, the internal temperature of the building builds up because the heat has now been trapped.
  2. This trapped heat has, somehow, to be expelled and – since there is never any significant natural ventilation in a glass building – this calls for massive (and environmentally expensive) air-conditioning. Let us not also forget that living and working in permanently enclosed spaces leads what is known as “sick building syndrome”.

Heat-reducing glass is like a pick-pocket returning your empty wallet.

Glass manufacturers will claim that their specialised products reduce heat build-up by 30%-40%. What they don’t tell you that not having a glass wall in the first place will reduce your heat-gain by twice that amount!

Another specious argument put forth is that using glass walls reduces the usage of electricity for lighting. Again, this is half-truth. Let us, for a moment, leave aside the amount of glare that people working inside such buildings have to put up with.

Consider a 10m² space.  Under normal circumstances, the air-conditioning load would be about 3,500W (or 2,500kW if you’re using a highly efficient HVAC system).  Lighting the space needs less than 100W if you’re using fluorescent lights and even less if you’re using LED fittings.

Now, the maximum saving you can achieve in lighting is 100W. On the other hand, your HVAC energy requirements will increase exponentially.  Even if expensive special glass is used, I’m afraid no amount of mathematical spin can bury this simple fact.

There are other aspects too, although unrelated to energy consumption. Migratory birds get confused by the glass and often die or sustain critical injuries when they slam against the huge transparent panes.

Further, if you happen to be in a glass building during a fire, there is no scope for ventilation so you asphyxiate–unless the glass curtain wall shatters, thereby endangering both, you and your rescuers from the fire department.