Cooling unplugged

There are alternatives to the ubiquitous air conditioner.

One of our consultants has just had his apartment upgraded by the landlord.  For cooling he had been using two window-mounted air conditioning units.  They were sufficiently powerful and reliable and he had no complaints, though they detracted a bit from the Old Town ambience.  This past week the landlord had a contractor install two modern heat-pump units.  A landlord who will spontaneously upgrade a property is to be cherished, though there is an incentive in that the new units are more efficient (especially since they can heat as well as cool) and the landlord pays the electric bill.  (We also suspect there are tax credits or something for installing more efficient devices.)  We will not complain, though so far the weather has been mild and the machines have not yet been thoroughly tested.

As air conditioners do, heat pumps work by shifting a fluid around, alternately compressing and expanding it.  There are a lot of moving parts.  It is possible to do heating and cooling by solid-state means, using for example the Peltier effect.  That significantly increases the reliability and flexibility of the device, though it’s a much less efficient process.  We’ve only seen it used in a few places, for instance among amateur astronomers trying to make their digital cameras less noisy (professionals tend to use liquid nitrogen, for colder temperatures).  Progress is being made, however, on making solid-state coolers more powerful and efficient.

What interests us, however, is how things can be cooled without plugging something in.  It was known long before our time that a black car would get hotter in sunlight than a white one.  Our navigator served on a Navy ship stationed in the Persian Gulf; its white paint job was said to be worth two industrial-sized air-conditioning units.  But paint is only the start.  We have a recent journal article describing a ceramic-based coating that reduced the electric demand of air-conditioning units in a Hong Kong building by 26.8%.  That’s a significant saving!  It was only a test example, but a number of practical issues were successfully dealt with, such as durability, and a continuing cooling effect even with dust and air pollution present.  We have another study showing how a species of ant in the Sahara has evolved its peculiar pattern of body hairs to provide a strong cooling effect.  That’s probably farther from any practical application by our species, though.  And things can get clever: here’s an article describing a textile, something you can wear, that changes its effects depending on temperature and humidity, so it would keep you warm in the cold and cool in the heat.

There are other avenues to pursue.  In Bahrain a traditional form of architecture was the wind tower, designed to produce a cooling breeze in the days before air conditioners.  There are similar approaches taking advantage of local conditions and materials in many tropical cultures.

The main problem, of course, is cost.  Rebuilding or just recoating a building is not cheap, even if the useful material can be made inexpensively.  To be useful in any general way, the unplugged cooling method must be cheaper or easier than adding an air conditioner.

And it helps if the landlord is the one paying the electricity bill.