Climate-Specific Air Conditioners
John Proctor sells a $35 control that reduces cooling costs by 8% to 12% in dry climates — and he also has energy-saving advice for people in humid climates
If you live in a
Climate-Specific Air Conditioners
John Proctor sells a $35 control that reduces cooling costs by 8% to 12% in dry climates — and he also has energy-saving advice for people in humid climates
If you live in a humid climate (for example, in Florida), you need an air conditioner that does a good job of dehumidification. But if you live in a dry climate (for example, in Nevada), dehumidification is almost irrelevant, because the outdoor air is so dry. In Nevada, all you need is an air conditioner that lowers the temperature of the air in an energy-efficient way.
In theory, air conditioner manufacturers could tweak the design of their equipment to focus mainly on lowering the indoor air temperature (a process known as sensible heat removal), or they could produce equipment that devotes a lot of energy to dehumidification (a process known as latent heat removal). Unfortunately, though, air conditioner manufacturers don’t offer special equipment designed for dry climates. Instead, they sell the same equipment in Nevada that they do in Florida.
Most residential air conditioners sold in the U.S. are designed to operate at a sensible heat ratio between 0.75 or 0.80. (The sum of the sensible loadThis is the heat content of just the air; it does not include the heat content required to remove (condense) moisture from air. Sensible heat is measured by dry bulb temperature. Latent heat is measured by wet bulb temperature. and the latent loadCooling load that results when moisture in the air changes from a vapor to a liquid (condensation). Latent load puts additional demand on cooling systems in hot-humid climates. is the total load; the sensible heat ratio is the sensible load divided by the total load.) If you live in a very humid climate, this sensible heat ratio might be too high. If you live in a very dry climate, this sensible heat ratio is definitely too low.
John Proctor is the president of Proctor Engineering Group in San Rafael, California, and a nationally known expert on residential cooling. Proctor has always been irked by the failure of air conditioner manufacturers to address regional needs. “Air conditioners are designed and installed the same for Florida and Arizona,” says Proctor. “It makes no sense, since Florida and the Southwest have different climates and different cooling needs.”
A retrofit control to save energy
To improve the efficiency of air conditioners in dry Southwestern states, Proctor has developed a simple control device (the Western Cooling Control™) that can reduce cooling energy use by 8% to 12%. The cost of the control $35 — less if purchased in quantity — and it has a payback period of two years or less.
Here’s how it works: most air conditioner controls turn the air handler fan off when the compressor shuts down, or shortly thereafter. Even though the compressor is off, the indoor coil is still cold at that point. The coil is usually damp and dripping, and moisture has accumulated on the drip pan.
In a humid climate, you want the fan to be off at that point, so that all of the water droplets on the coil can drip down to the pan and find their way down the drain. If the fan continued to run after the compressor turned off, the water would re-evaporate and stay in the house — which would be bad, at least in a humid climate.
However, in a dry climate, you really don’t need any dehumidification, so you don’t really care if the moisture on the coil re-evaporates. “Since air conditioners were not designed for dry climates, they wring more water out of the air than they need to, wasting energy and costing you extra on your cooling bill,” Proctor says.
In a dry climate, there is an energy benefit to evaporating the water clinging to the coil and sitting in the pan: after all, the process of evaporation cools the air. (This phenomenon is known as evaporative cooling.) The Western Cooling Control (WCC) overrides the controls supplied by the air conditioner manufacturer and directs the air handler fan to run for a longer period of time after the compressor turns off. The WCC keeps track of compressor run time; the length of time that the fan runs after the compressor turns off is proportional to compressor run time.
It doesn’t take much energy to run the fan for a few extra minutes after the compressor turns off. By evaporating the moisture on the coil and the pan, the air handler temporarily acts like an evaporative cooler. “The energy cost is low, since the fan draws little power and only operates for a short time,” says Proctor.
Contractors can buy the WCC for about $35. For electric utility energy conservation programs, the price of the control is even lower. According to Proctor, “If you are a klutz, it takes 30 minutes to install. But it only takes 15 minutes if you’re good.”
New AC equipment has a fan time delay, but it isn’t long enough
Although newer models of air conditioners are more likely to have some length of fan time delay than older air conditioners, the programmed time delay has not been optimized for dry climates. “Air conditioner manufacturers provide a time delay setting on most new equipment as a means of incre