Controlling Humidity with the APR Control

Why does my space have high humidity despite the temperature being right where I want it?

Air Conditioning isn’t just about temperature control…dehumidification is arguably much more important in order to maintain a comfortable space! Without a properly sized air conditioning system, it’s going to be impossible to control the relative humidity in the space. The truth is, ALL DX air conditioners are oversized by design. The goal of air conditioning in it’s simplest form is:

  1. Remove heat from inside of the space (via the evaporator coil) and dump it outside (via the condenser coil)
  2. Remove moisture from the air inside the space and send this collected moisture in the form as condensation out to a drain

Since most standard thermostats only turn the unit on to control the temperature in the space, the relative humidity inside the space is often overlooked and assumed in the appropriate range. If the thermostat is satisfied for the temperature and the unit shuts off, the evaporator coil will not be able to remove any additional moisture from the space. If the evaporator coil is not active, the relative humidity in the space may continue to rise and create the “cold and clammy” environment that we all want to avoid.

Have you ever been outside in the summer with a cold drink and it starts to “sweat”? The reality is that the drink isn’t actually sweating; rather the moisture in the outside air is actually condensing on the surface of your cold drink. This occurs as the heat from the outside air is absorbed by your drink. The container will “sweat” because the temperature is BELOW the dew point of the outside air. If the temperature of the container’s surface is above the dew point, no condensation will occur.

The evaporator coil is very similar and that’s why we need the coil to be a lower temperature than the dewpoint of the entering air travelling across the coil! When the unit is off, the evaporator coil will not be cold enough to collect moisture from the air. This simple concept should help explain the role of the evaporator coil and why it’s critical we keep the coil active in order to lower the humidity inside the space.

APR Control

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The name of the game is Compressor Runtime!

In order for the air conditioning system to control the humidity in the space, we need the compressor ON and evaporator coil ACTIVE.

When you’re trying to figure out why your space has a high humidity problem, we highly recommend you look at compressor run-time. Runtime data is valuable in understanding the nature of your humidity problem! Check out this study by the department of energy in 2003:

The study examined the relationship between DX system humidity control and compressor run-time. The study demonstrated that the compressor needs to be running for at least 15 minutes before the system can START the dehumidification process. If you find that the compressor is off for much longer periods than the compressor is on, there’s no wonder why you have HVAC humidity problems! When the compressor is on and the evaporator coil is below dew point of the entering air, the moisture from the air will start to condensate on the coil. Until this condensation accumulates on the coil and drops down to the drain pan and down the drain, it’s not removed from the space. This is why extending the run-time of the compressor beyond the 15 minutes is recommended. If the thermostat satisfies and the compressor shuts off with the fan still on (as in most commercial buildings), the condensation on the coil will be blown back into the space. As a result, the relative humidity in the space will rise.

Rawal Devices’ APR Control: The Simple & Reliable Humidity Control Solution!

Are you thinking about replacing the unit you recently installed because it’s not dehumidifying properly? There is no need! We have the solution that will allow you to keep the existing system in place while improving the dehumidification capabilities.

The APR Control is an excellent humidity control solution by reducing the system capacity to match the lower load conditions in the space. The result is extending the run-time of the compressor and keeping the evaporator coil active. The goal is to avoid the thermostat satisfying in order to extend the latent removal process, also known as dehumidification. Since the APR Control varies the amount of refrigerant flow to the evaporator coil, it helps avoid the compressor shutting off due to over-cooling of the space. And, by preventing excessive compressor cycling, the APR Control helps stabilize the temperature in the space in addition to stabilizing the relative humidity.

Depending on the application, the APR Control can provide as much as 80%+ turndown percentage compared to the system’s nominal capacity. Reach out to our team today to discuss how much capacity control the APR Control can provide for your system to get you and your customer out of these “sticky” (pun-intended) situations!

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