Energy Recovery Ventilators, The Basics...Energy recovery ventilators, heat recovery ventilators, and total recovery ventilators can play a large role in creating a safe and healthy home. These units improve the overall indoor air quality by bringing fresh air into the home. A heat recovery ventilator uses the air being exhausted from the home to preheat or cool the incoming air. These units are normally used in colder climates. The system is usually activated by a timer control. In the typical system, the control starts and stops an intake and exhaust fan on a scheduled basis. The two different air streams pass through opposite sides of a heat exchanger where heat is transferred from the warmer air to the colder air. This fresh air is then distributed through a duct system to the home. Typically, the system uses the existing hvac system ducts. An energy recovery ventilator is usually used in warm and humid areas with heavy air conditioner usage. These units work in much the same way except the heat exchanger is replaced with a special membrane called a core. This core allows moisture to pass from one air stream to the other as well as the heat. This is necessary to minimize the increase in humidity during operation. The excess humidity would otherwise have to be removed by the homes' air conditioner. Total recovery ventilators combine both types into one unit. They are normally used in areas with cold winters and hot/humid summers. The right type of unit for your home will depend on your location. They can be an independently ducted system, integrated into an existing ducted hvac system, or window/wall mounted units. The units have a TOTAL RECOVERY EFFICIENCY (TRE) rating. This is a measure of the units' ability to save energy. The typical unit can recover 70-80% of the energy required to condition the incoming air. Some high efficiency units can recover over 90%. When shopping for a unit it is important to get the proper size. They are typically sized to provide .35 air changes per hour. That means that for about every three hours of operation, the unit will completely replace the volume of air in the home. To find the proper size you can multiply the square footage of the home by the ceiling height. Then divide your answer by 60. Finally, multiply that answer by .35 and you will have the unit size in cfm.
There are some disadvantages to these units. They require monthly maintenance which includes filter cleaning. Also, each year, the core, condensate drain and pan should be cleaned. Without proper cleaning, mold can grow in energy recovery ventilators. This can occur on the core as well as in the drain pain. These units are expensive usually over $1000. It can take a long time to pay for them with energy savings. But, the added benefit of healthier indoor air makes them worth while.
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