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Let’s take a closer look at the equipment involved.
BREAKING DOWN THE EQUIPMENT, CONTROLSHere are the pluses and minuses regarding the various systems and controls:
• Single-stage air conditioners - Starting with the basics, air conditioners do dehumidify. And, some do it better than others. However, they all have one thing in common: each must be running, fill up the coil with condensate, and overflow. An air conditioner really only dehumidifies when the water has left the building.
This system works great on hot days when the air conditioner runs for long periods of time. However, humidity removal suffers when the outside temperature is below the design temperature, especially if it is cloudy or raining. This can result in the air conditioner quickly cooling a home. This leads to short run times, which proves to be the enemy of dehumidification.
It is more of an issue for contractors who oversize, believing that bigger must be better. If this is done, even on very hot days the air conditioner will cycle.
Where two-stage air conditioners can fall short is when they are oversized. If a two-stage system cycles a lot on its first stage, very poor dehumidification results.
• Specialty controls - Sometimes it takes special controls to solve humidity problems. For instance, the AC-Enhancer® - a solid-state device that installs in the control wiring between the thermostat and the air handler or gas furnace - is designed to solve many issues by taking control of the system to reduce the inefficiencies every time the system starts. This specialty control is also designed to help defeat many of the devices that the manufacturers use to force the blower to run at the end of the cooling cycle. This control has built-in logic, enabling it to know if the system is in the heating or cooling mode. It is then supposed to adjust its sequence of operation accordingly.
This device is designed to hold the fan off completely at the end of the cooling cycle for 10 minutes. This is to allow the majority of the moisture to run off the coil before the fan is allowed to come back on. It is also designed to hold the indoor fan off for a short period of time when the cooling cycle starts. This is designed to allow the system to start easier and get to its peak efficiency and dehumidification capacity sooner.
It’s nice to know that many of the new thermostats coming out on the market today can and do help control humidity. For example, there’s the Honeywell Vision Pro IAQ. Most advanced humidity-sensing thermostats lower fan speed to enhance dehumidification; some also override the thermostat setting.
The bottom line is this: Some specialty controls and some new thermostats can help in the humidity department, but these devices are still relying on the HVAC equipment to do the work. Therefore, if the equipment is oversized, a contractor will still run into problems.
VALUE OF DEHUMIDIFIERS, SUMMARYThe best approach to wipe out summertime humidity, for many homes, is to simply install a dehumidifier, which come in various sizes. Like most systems, dehumidifiers must be sized properly in order to do the job properly.
These units can be set up to work in various ways. In a home with a basement, for instance, a unit can be used to dehumidify just the basement in winter and then the upstairs in summer. This is accomplished by adding some controls and motorized dampers. This system can also work in a home with a crawlspace. Because most dehumidifiers give off heat, a contractor should factor this into the equation before installing a dehumidifier.
While a dehumidifier is a solution, it should not be used as a band-aid. An improper diagnosis can lead to a dehumidifier not working due to improper sizing. It can also cost the homeowner a lot of money to run a dehumidifier. (I recently talked with a contractor who told me in order to get a client’s leaky house down to the proper humidity level, his firm installed six dehumidifiers and energy use was over $2,500 per month.)
Summing this all up, summertime humidity control in a home can be achieved. However, one needs to tighten up the ducts and the home so that the installed equipment will work properly and as designed. Without home and duct performing testing and repair, the system in place may not work properly, could cost the homeowner a lot of money to run it, and it could eventually get a contractor into hot water.
Publication Date: 08/18/2008