Replies

1. 
   DanH | May 28, 2012 06:32pm | #1

   A standard residential air conditioner condenser has an effective solar collector area of roughly 10 square feet.  Figure you get solar input of about 300 BTU/hour/sqft during peak sun, which means you're getting a heat input of about 3000 BTU/hour, of which maybe half is reflected/reradiated off without affecting the AC.  A ton of AC is 12,000 BTU/hour, and let's assume that you have a 2-ton unit.

   So, potentially, shading the AC could save you about 1/16th of your cooling cost on a sunny day, during peak daylight hours.

   But there are a bunch of other factors, such as to what extent the unit has been designed to "reject" solar heat, and much of your cooling is not done on bright sunny days during peak sun hours.  Plus, of course, any sort of shade risks reducing airflow to the unit.  So I would expect the overall savings to be significantly less.

1. 
   rdesigns | May 29, 2012 03:50pm | #2

   +1

2. 
   renosteinke | May 29, 2012 04:21pm | #3

   Your unit, with it's protective case and louvered grill, is already 'in the shade.'

   Far more important is that you have free air flow through the unit. Far too many units are placed in dead corners, then buried in bushes. Small wonder they work hard. Leaves and grit plug up the fins in no time at all.

   Likewise, if you build a protective steel cage for the unit, make sure there is plenty of airflow, and plenty of clearance between the unit and the cage.

3. 
   xxPaulCPxx | May 30, 2012 11:20am | #4

   They've actually done studies on this and found it made no difference.

4. 
   oops | May 30, 2012 06:59pm | #5

   A/c in the shade

   I know, I know this is not the question that was ask and it would not be practical or may even be unsafe, but what would be the effect of water sprayed on the cond. coil.

1. 
   DanH | May 30, 2012 07:53pm | #6

   A water spray is, in general, VERY effective at improving efficiency.  It can, of course (in fact almost certainly will), have serious deleterious effects on the unit, which is why (along with the water use/drainage issues) it's not commonly done.

   About 15 years ago we were trying to nurse a sickly, worn out AC through a particularly hot Minnesota summer.  The unit would run 24/7 and could not get the inside temp below 80.  So I rigged a water spray (using a spray nozzle intended for agricultural herbicide sprayers) to spray into the condenser unit, through the air intake grille.  Within two hours it was a pleasant 72 in the house, and the AC was only running for a few minutes at a time.  (I never got around to rigging a valve to the thermostat to turn the water on and off with the AC, though.)