Occasionally I get asked if it’s OK to put the condensing unit of an air conditioner or heat pump in a garage or other room that’s a buffer space. The thinking is that since the temperature may not be as hot in summer or as cold in winter, the system will operate more efficiently.
I saw recently that this same question came up in a column in Home Power magazine, so I thought this would be a good time to cover this issue (once and for all?) here.
The answer is no. In fact, the answer is an emphatic NO. Here’s why:
The way an air-source heat pump or air conditioner works is that it exchanges heat with the air surrounding the condenser. In summer, it dumps heat into that air. In winter, it absorbs heat from that air. When the condenser sits outdoors, it’s connected to a mass of air that’s practically infinite. In other words, no matter how much heat that unit dumps outside, it’s not going to change the outdoor temperature.
If you put the condenser in a garage, attic (as shown above), or other space, it’s now connected to a finite mass of air. As it dumps heat into that air in summer, the temperature in the room will rise. As it pulls heat from it in winter, the temperature will drop. The smaller that room, the more temperature change you’ll get.
What do you think happens to the efficiency and capacity of an air conditioner when it has to dump its heat into hotter air? It drops. What happens when the air gets too hot? The condenser may not be able to do its job — condensing the refrigerant so that it all becomes a liquid again. The refrigerant goes to the evaporator coil hotter and wetter and at higher pressure. That’s a recipe for failure.
Condensing unit in an attic?!
I have no idea why anyone would put an air conditioner in an attic, as shown above, but the second photo of that unit shows another problem. That system not only is working with a smaller, hotter volume of air, but it’s sucking blown insulation up against the coil, reducing the air flow. I guess they wanted to make sure that system failed as quickly as possible.
Even in a cold climate where you don’t use the system for cooling, you can’t do this. Not only is there not enough air, but if the temperature is higher, it’s at least partially due to heat loss from the house. A better building enclosure is a much more practical way to keep the heat in your home in winter.
Eleven condensers in one small room
The photo above is from a Facebook page called HVAC hacks and other screw ups. They show lots of good photos of HVAC gone wrong. If you think I post some ugly stuff here, take a look at their page.
They posted the photo above yesterday. The caption said that in addition to the six condensers you see here, another five were in the room, too. That’s eleven condensers in a room so small that the widest angle photo he could get shows only about a 10-foot section.
Wow! Not only is there a small volume of air, but you have eleven condensers fighting over the little that’s there. Yeah, they’ve got louvers connecting it to more air (a parking deck? outdoors?), but that’s not sufficient.
“Bright ideas” usually don’t work
Just because you shouldn’t put a condenser in a buffer space doesn’t mean that you can’t help it perform better with good placement. Put it outside and follow these two rules:
- First and foremost, make sure it has plenty of space around it for good air flow. Don’t put it in a corner or well, surround it with other condensers, or plant bushes all around it. Unlike a house, an air conditioner needs to breathe.
- Second, you can help it be more efficient by keeping it out of the afternoon sun. If it’s possible, consider placing it on the east or north side of a house.
The upshot of all this is that if the idea ever occurs to you to put a condenser in a place other than the outdoors, don’t do it.