Does Shading Your AC Unit From The Sun Save Energy?

There are trending social media articles that claim shading your outdoor ac unit will reduce the energy used. The claim is that shading your outdoor unit will stop the sun from heating the unit up, so the unit does not have to work as hard, hence saving energy. The articles have an image like the one shown (Picture 1). The way the outdoor unit functions when in cooling operation, is by drawing air in through the sides of the condenser (outdoor unit) and is blowing it out the top of the unit. The air is moved by the condenser fan which pulls ambient air in, passing through a lattice of tubes which contain freon. The air picks up heat from the freon and blows it out the top of the unit. Air coming out of the condenser unit is warmer than the air ambient, due to the transfer of heat from freon, before it is pumped back into the indoor unit.

The process is similar to a car radiator which removes heat from the coolant circulating around an engine. Covering the top of the unit will cause the hot air to be directed back into the condenser, increasing the air temperature running over the condenser tubes. The higher air temperature reduces the condensers’ ability to pull heat from the freon, reducing the efficiency of the heat transfer process. The effect is making the unit work harder to remove heat, increasing the energy usage. The increased load on the condenser will increase the working pressures within the compressor leading to early failure.

Using a thermal camera on a 100 degree plus afternoon. The unit is running at full speed to cool the indoor space. The thermal image of the unit in operation, shows the different temperatures around the unit. Blue is coolest area and white being the hottest. The thermal image shows the air coming out the condenser is around 110 degrees. The wall behind the unit is hotter than the surrounding area due to the hot air from the condenser heating the surface, in this example the wall is around 109 degrees roughly 3 degrees warmer that areas with sun only. The sides of the condenser pulling in the ambient air are around 104 degrees. Shading the unit, without restricting the air flow to allow the ambient air to flow in and the hot air to be removed will not help due to the volume of air being moved when the unit is running. A 3-ton condenser, mid-sized unit, will have around 4000 cubic feet per minute of air being pulled through the sides of the unit and out the top. The volume through the outdoor is approx. 4 times the volume that is moving through the indoor unit. The aim is to allow unrestricted air to flow in and hot air to be pushed upward not to return. All manufacturers are similar with a minimum of 5 feet above and 3 feet around the unit. Restricting the sides of the condenser will restrict the air volume that can be pulled in, for example from plants or a fence, which will reduce the ability to cool effectively.