Q: What should I know about central air conditioning in order to make it a healthy and efficient option?

A: As the summer heats up, you may be considering an investment in a central air conditioning (A/C) system. Or, maybe you already have a central A/C system that just doesn’t seem to be keeping you comfortable. Either way, before you start flipping through the yellow pages in search of the best, the cheapest, the most efficient, the most professional, the quickest, etc., take a moment to learn about what you’re looking for. There are a few core concepts that are extremely important when it comes to the proper performance of A/C systems. Hopefully after reading this article, you’ll know more about what to look for in an HVAC contractor and what components are most critical for a system in the delivery of efficiency, air quality and proper moisture management.

If you already have a system in place that you think isn’t working properly, the first step is to have a professional evaluate how well it is working. Don’t make the mistake of assuming the unit needs to be replaced. Often the unit isn’t the problem. If it turns out that it is time to replace the A/C unit, or if you’re already installing a new system, there are some key ingredients that should be part of the process if optimum performance is the goal.

The first key aspect to having an A/C system that performs well is that it is sized according to the house in which it’s installed. If it’s too big or too small, there are sure to be problems. To determine the proper size of an A/C system, a load-calculation must be performed. Do not assume that this step was done before the last unit was installed. The sizing process is commonly known as a “Manual-J,” which determines how much heat will need to be removed from the house to maintain comfort. The less heat that needs to be removed, the smaller the unit needs to be (and smaller the operating cost will be). Think scooter versus SUV. You obviously wouldn’t want to use a scooter if you had to haul a trailer full of bricks all day long. In order to achieve comfort in your house with a small unit, the house must be well insulated against the heat from outside. If the heat can’t get in to begin with, then there’s not a lot of heat that needs to be removed (less bricks to haul with your scooter). The insulation levels, types of windows, air infiltration rate and orientation of the home are all important in determining the proper size of your A/C system.
Assuming the system is sized correctly for the load on the whole house, the next step is to make sure that the right amount of cold air gets to the right room. Air distribution is the job of the ductwork. In a home with an existing duct system, it’s critical that the system be analyzed for performance issues, as the ducts are frequently the culprit of poor air quality, efficiency and comfort. Lack of insulation, air leakage and improper duct sizing/installation can all lead to poor performance. Poor insulation leads to condensation issues, improper sizing leads to a starving air handler, and duct leakage can actually vacuum the air from the crawlspace or attic into the house! A quality contractor will diagnose the health of the ductwork as part of a thorough diagnostic assessment and emphasize the importance of fixing these issues to deliver optimum performance.

Another core A/C concept that most people typically overlook is the importance of moisture control. Not only are A/C units there to keep you cool, but they play a vital role in removing moisture from the air as well. Not only does the amount of moisture in the air (relative humidity) affect your comfort, but it can also affect your air quality. Dust mites and mold growth both require high levels of moisture. If your A/C system is oversized or not properly designed/installed, its ability to remove moisture decreases. There are a number of things that affect the moisture removal capacity of the A/C unit. A quality contractor will measure the “enthalpy change” achieved by your A/C system for you, showing you the system’s actual moisture removal capacity.

If you’re installing a new system, consider a “variable speed” unit that has the ability to monitor and control humidity independent of temperature. This means that the thermostat will also measure the relative humidity. When the humidity is high, the unit will turn on to dehumidify, even if the temperature is under the thermostat set point.

The last item is air quality. Two elements of an A/C system that can improve air quality are properly designed/installed filtration and a fresh-air introduction system. Filtration removes particulates from the air while fresh-air systems actually create a true exchange of air with the outside, bringing in fresh air while exhausting stale air. It’s important to note that 99 percent of A/C systems are “closed-loop” systems, meaning there is no fresh air being introduced. It’s also important to note that “better” filters are also more resistant to airflow. This means that ductwork should be sized based on the type of filter to be used. If you add a better filter without increasing the size of your return ducts, you may do more harm than good.

As the saying goes, the house is a system. And it’s important to make sure that the A/C system is working in harmony with the rest of the house. If you’re unsure about how well your A/C system may be performing, take the A/C Health Quiz below. If you answer “yes” to any of the questions, you should consider a closer look at your system’s performance.

A/C Health Quiz
Are there rooms in your home that are uncomfortable?
Do some registers seem to blow too much or too little air?
Do doors seem to slam by themselves?
Can you smell the garage or the crawlspace when the air handler is running?
Is your home constantly dusty, even though you have the windows closed?
Does your A/C seem to run a lot but never get the house cooled off?
Does it feel sticky or humid in the house?
Does the A/C system turn off and on a lot?
Is any part of your ductwork made of compressed fiberglass board?
Is your air filter thin enough to see through?
Does your A/C system only control temperature (no humidistat built into the system)?
Does your energy usage seem excessively high?

Isaac Savage is founder and president of Home Energy Partners, a full-service home performance contracting firm located in Asheville. He can be reached at 828-350-1155 or on the Web at www.HomeEnergyPartners.com.
Send your home questions to healthyhome@newlifejournal.com.

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