Size Your Cooling System Properly for Comfort and Energy Savings
In some areas of the country, whole house air conditioning is more than just a comfort decision. It’s hot enough in some areas that home cooling is necessary to live there. Whether it’s survival or comfort, you want to make cooling system sizing decisions based on proper load calculations and energy savings.
Heating and air conditioning professionals do a heat gain calculation to determine how much heat is entering the home through surfaces, leakage, and other sources. Once the amount of heat infiltration is calculated they can determine the size of the cooling system. When it comes to selection, upsizing the capacity isn’t a good decision.
Comfort Considerations of Oversizing Cooling Systems
A cooling system does two things. It cools the air, but just as important, it removes humidity. The human body comfort range in hot weather is affected by the humidity and temperature. The higher the humidity, the lower the temperature required for comfort.
There is a drain line on your cooling coil enclosure. Its purpose is to drain away the water that the cold coil removes from the air passing through it. This water removed from the air lowers the humidity, and the people in the home can be comfortable at a higher temperature. The size of the unit determines how well it functions in lowering humidity.
If the unit is too large, it cycles on and off a lot. While that may seem to be efficient because it’s not running a lot, you’re not comfortable at higher temperatures because the humidity remains high. The unit can’t remove humidity if it’s not running. So, you lower the temperature setting to compensate. You’re less comfortable overall due to the temperature swings resulting from too many on-and-off cycles.
You’re far more comfortable if the unit runs longer, removes more of the water from the air, and you can maintain your comfort at higher temperature settings.
Mechanical and Energy Considerations of Oversizing Cooling Systems
Motor windings are under higher stress the more amperage they draw while starting and running. The motor in an air conditioning compressor pulls multiple times as much amperage when it starts than once it settles into running. The heat generated during startup is what gradually wears out your compressor. Oversizing a system results in shorter run cycles and more startups. The wear on the compressor from these high-heat starts shortens its lifespan. The cost of compressor or unit replacement is high, so doing so earlier than necessary can cost you more than any perceived energy savings from running less.
Another consideration when determining energy consumption is the size of the compressor and fan motors (2 of them usually). When you oversize a unit, the compressor and both fan motors are larger, and they use more energy to operate. Running a shorter period of time is more than offset by the higher energy consumption of the larger components.
Use a professional to examine your home and do a heating load calculation to determine the size unit that should be installed. Doing so will keep you more comfortable at lower energy costs.