Central City Air

How equipment is linked to humidity control

There are four main factors to humidity control. These are related to equipment selection and the performance when installed. Of course every home is different, so we will concentrate on performance that affects the home environment no matter how the house is built.

In this era of high and super high efficiency, we get frequent questions about humidity concerns in the home environment. It is usually the fact that the previous air conditioning system did a better job than the new unit at removing humidity. Inspection reveals the problem as one of four delinquencies. Assuming that the right size tonnage is installed, the four factors that affect humidity removal are as follows: coil selection, airflow, refrigerant control device, and superheat setting of the refrigerant cycle. We will examine these factors individually and show how they affect a solution to your higher humidity problems.

Coil Selection:

This is the most critical component in the cooling cycle. The coil size determines the major balance between dry and wet heat removal. The coils remove dry heat (temperature) and the wet heat (humidity). The coil size determines this ratio. The larger the coil in size, the lower the humidity removal. In many cases, a smaller coil can increase the humidity removal by 30% to 40% resulting in greater dehumidification. At least a thousand times I have been asked by the manufacturers do not promote this concept. It is real simple to see that they are caught in a SEER game trying to outdo the competition. But the SEER rating of a system is based on USA average temperature and USA average humidity, neither of which we live in here in Houston. So the SEER rating of a system is bogus at best, but a guideline nonetheless. A smaller coil lowers the SEER rating of the system and makes it less attractive to consumers. Therefore, it is of little concern to equipment manufacturers. The bottom line is that the coil size is critical, especially in newer housing where the dry heat load has been reduced by improved methods of building barriers that keep the heat out of the home.

Air Flow:

When it comes to airflow, the laws of physics apply. Air follows the line of least resistance. So many of the duct systems are poorly designed that ductwork problems can seriously curtail proper system performance. These factors usually show up in uneven temperatures through the conditioned area. In addition, airflow across the cooling coil can greatly determine proper humidity removal. Too much air will result in poor dehumidification. Too little air can cause the ductwork to sweat in the unconditioned spaces and damage the home. The right amount of air is usually about 300 CFM to 400 CFM per ton. Lower airflows have increased humidity removal. Finding the right airflow balance can eliminate some if not all comfort and humidity problems.

Refrigerant Control Device:

The device used to make a cooling coil absorb heat and humidity is called an expansion control. The only effective control in this application is a balanced port expansion valve. The expansion valve allows exacting control of the refrigerant and provides consistent performance over a wide range of conditions that exist in any home. Without an expansion valve the entire sys- tem performance is compromised. Humidity control is usually poor at best, however adding an expansion valve to an existing system can often improve performance, reduce operating cost and extend the life of the overall system.

Superheat control of the refrigerant gas:

One factor that is often overlooked in trying to increase humidity removal is the superheat of the suction gas. This factor can often be out of design conditions and the system seems to work fine. What happens s that the cooling coil does not fill up completely and the coils runs a little warmer. Five degrees warmer coil temperature can reduce humidity removal by 20% or more. Correct superheat should be about 13 degrees at the coil and about 16 to 17 degrees at the compressor. This measurement should be taken at 90+ outdoor temperatures with indoor temperature no higher than 80 degrees. Since superheat is a measurement of heat these outdoor and indoor temperatures can affect the readings. The best time to set and adjust the superheat is in the summer season.

What to expect

If any of the above 4 factors is not correct you can expect that humidity problems may occur. There are other factors that can affect the humidity levels. These are the way the house was built, the number of people that live there and the live style of the occupants. That being said the correction of humidity problems is any residence can be accomplished simply be applying the factors stated above. This is why is essential that you find a company that you can trust or look elsewhere if they can't solve your humidity problems. Time is your enemy, as the problem only gets worse if neglected.

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