Science Questions

Would a solar powered air conditioner be a good idea? I used to go camping we used a gas powered fridge could you use the same principle? Steven, Cambridge

A gas powered fridge is an immensely cunning device invented by Einstein that works by seperating ammonia from water by boiling the mixture then cooling the ammonia to liquify it which gives out lots of heat. This heat can then be absorbed again when the ammonia evaporates in a hydrogen atmosphere a bit like when your sweat evaporates, cooling down the fridge. The hydrogen is then seperated from the ammonia by dissolving it in water which makes an ammonia water mixture to go back to the start.

If you could get the boiler hot enough there is no reason that you shouldn't use this principle to cool buildings, although it would probably involve concentrating the sun with lots of mirrors.

Perhaps a better solution would be to use a stirling cycle engine, this is a form of engine that generates heat by moving heat from a hot place to a cold one, by allowing gas to expand at the hot end and then contract at the cold one.  This drives a piston back and forth.  So if you concentrated sunlight on the hot end and cooled the other end with air or water you cound generate power which could be used to drive an air conditioner.

All of these processes move a lot of heat from somewhere hot to somewhere warm in order to pump a little heat from somewhere cold to somwhere warm, by far the most efficient solution is to not heat up the building in the first place by painting the roof white and insulating it, or to cool the building by natural convection.

July 2007