One of the biggest factors in how hot your home feels during the summer and how efficiently your air conditioning works is the humidity level inside your home. High humidity leads to a decrease in both your comfort level and your AC system’s energy efficiency. In this article, we’ll explain exactly why that is to show you why humidity control is so important. We’ll also look at the options for overcoming your home’s humidity issues during the summer.
Why High Humidity Makes You Feel Hotter
The first thing you should understand about humidity is that it directly impacts how hot any environment feels. The terms heat index, apparent temperature and feels-like temperature are all used interchangeably and express how people sense temperature based on a combination of the relative humidity level in the air and the actual air temperature. Even if the air temperature remains constant, you’ll feel like the air is hotter the higher the relative humidity level is.
Sweating allows your body to regulate its temperature so that you shouldn’t ever get too hot and become at risk of developing heat stroke. The reason that it works is your skin cools down as the sweat evaporates, which helps you feel less hot. However, the process only works if the sweat can evaporate fairly quickly so that your skin cools down, which in turn keeps your body temperature from increasing.
Relative humidity is a measurement of air saturation, i.e. the percentage of water vapor in the air compared to how much total moisture the air could potentially hold. When the relative humidity level is fairly high, it means the air is already quite saturated and can’t hold as much additional moisture. The reason that this matters in terms of your comfort is that high relative humidity prevents your sweat from evaporating nearly as quickly as it would if the air was dry and could hold much more additional moisture. That means your body can’t cool itself as well in humid conditions, resulting in you feeling hotter. In extremely hot, humid conditions, sweat evaporates so slowly that your body temperature can start increasing to the point where you can develop heat stroke.
The Link Between Indoor Humidity and AC Efficiency
Part of the issue when the air inside a home is quite humid is that it often leads to people turning their thermostat to a lower temperature in an effort to stay cool. The result of this is obviously that the air conditioning system runs more, leading to it using more energy. Nonetheless, the much bigger issue is that air conditioning works less effectively and doesn’t cool as well when the relative indoor humidity level is higher.
The reason for this has to do with sensible heat and latent heat. Sensible heat is just how much heat energy you need to add or remove to raise or lower the air temperature. Latent heat has nothing to do with actual temperature and instead is the amount of energy needed for any substance to change its state of matter, i.e. from a liquid to a solid or a gas to a liquid. In terms of air conditioning, latent heat is how much energy it takes to transform moisture in the air into liquid water.
Humid air contains a large amount of latent heat, and an AC system has to first remove much of the latent heat through condensation before it can finally start removing sensible heat and lowering the air temperature. Under normal circumstances where the humidity level inside a house isn’t too high, the temperature drop in an AC system should be around 18 to 22 degrees. Temperature drop refers to the difference in the air coming into the system through the return ductwork and the conditioned air flowing back out into the home through the supply ductwork.
If the house is overly humid, you’ll sometimes only have a temperature drop of around 10 degrees or possibly even less. This happens because the AC system has to remove so much latent heat to dehumidify the air that it can’t remove nearly as much sensible heat, which prevents it from cooling the air as much as it should. The result is that the system doesn’t work as energy efficiently since it takes a longer time for it to cool the house to the desired temperature.
Another issue is that you end up with much more moisture condensing on the AC evaporator coil when the relative humidity level is higher. Although the water that forms on the coil’s copper tubes continually drips off into the drain pan, the tubes still end up being much wetter when the indoor humidity level is higher. The reason that this matters is that the layer of water on the tubes somewhat insulates them, which reduces how much heat the cold refrigerant moving through them can capture from the air flowing over the coil. This also leads to decreased efficiency since it results in the refrigerant not removing as much heat before it exits the coil on its way back outside to the AC condenser.
Options for Controlling Indoor Humidity and Improving AC Efficiency
Despite being a desert climate, Arizona can get extremely humid during the monsoon season. Even if you always keep your windows shut and your AC running, the relative humidity level inside your home still tends to be higher the more humid it is outside. This is one reason why it’s essential that your home is properly insulated and the exterior structure is sealed up tight. If not, you’ll end up with quite a bit of hot, humid air flowing in from outside and your AC not working as efficiently or cooling as effectively. If your home is poorly insulated, having any air leaks sealed up and additional insulation added to your exterior walls and attic can potentially improve the energy efficiency of your air conditioning by up to 20%.
There are also many things in a home that contribute to increased indoor humidity. One thing is simply the moisture that evaporates into the air as you sweat. Cooking, bathing and running the dishwasher and clothes dryer also add quite a bit of moisture to the air. That’s why it’s important to run the exhaust fan in your kitchen when cooking and your bathroom when bathing to draw the moist air outside. Drying your clothes outside whenever possible also helps to eliminate a major source of moisture. Another thing to consider is trying to only do laundry and dishes in the early morning or late evening when the temperature and relative humidity are lower.
All that said, the most effective option for eliminating issues with high humidity in your house and improving the efficiency of your air conditioning is with a whole-home dehumidifier. This type of unit is installed within the return air duct so that it removes a large percentage of the moisture in the air coming into the AC system. The result is that there is much less latent heat in the home that the AC has to deal with, which allows it to remove much more sensible heat and thus provide more efficient cooling.
Most whole-home dehumidifiers are controlled by a humidistat, which measures the current relative humidity level inside the house. During periods of more humid weather, the dehumidifier will usually run each time your AC system does. If the conditions are drier, the dehumidifier may only run every other cooling cycle or sometimes only a few times a day. That means your home also won’t ever get overly dry since you can program the humidistat to your desired humidity level so that the dehumidifier only runs when needed. Also, it means you won’t need to worry about the dehumidifier running unnecessarily and wasting energy.
Since 1976, Christian Brothers Air Conditioning Plumbing Electrical has been one of the most trusted home service companies in the Glendale area. Our certified HVAC technicians can help if you’re having any issues with your AC or heating or want to install a dehumidifier or any other type of indoor air quality equipment. For more information or to schedule any HVAC, plumbing or electrical service, contact us today.
