As homes become more tightly sealed against air infiltration, the number of air changes per hour (ACHs) becomes less. That's good and bad. It's good because it means you're using less energy and paying lower utility bills. It's bad because stale, humid air and indoor air pollutants begin to accumulate in the home, especially during the heating season when windows and doors are usually closed.
Poor indoor air quality can lead to ailments that range from rashes to respiratory diseases. If your house is relatively airtight (under 0.5 ACHs per hour) consider installing an energy ventilation system to remove bad air and replenish it with fresh air. Such systems are especially beneficial for smaller, air-tight homes, and for homes with three or more occupants.
The solution for many homes, especially in regions with very cold winters or very hot summers, is a heat recovery ventilator (HRV). A heat recovery ventilator is an efficient fan combined with an air-to-air heat exchanger. In winter, the fan expels warm, stale, humid air via a duct to the outside. A separate duct draws in an equal amount of fresh air inside, whereupon it is filtered and distributed throughout the house via supply air ducts. Meanwhile, the heat exchanger transfers heat from the outgoing warm stream of air to the incoming cold air—typically at a 75 to 90 percent efficiency. In summer, an HRV may be used in reverse. It transfers heat from incoming air to the stale air-conditioned air being expelled.
Energy recovery ventilators (ERVs), also known as enthalpy-recovery ventilators, are similar to HRVs. In addition to transferring heat from one air stream to the other, however, they transfer some moisture, too. This reduces the need for humidification during the heating season and helps keep the heat exchanger core warmer, minimizing problems with freezing. In some situations, ERVs may be operated in the summer while running air conditioning. In such cases, they transfer moisture from incoming air to the air being expelled, thereby maintaining comfort while reducing air-conditioning demands.
Energy ventilation recovery systems may use a home's existing forced hot-air or air-conditioning ducts--or separate dedicated air ducts. The HRV or ERV is typically located in the basement or crawlspace but may also be installed in attics or, in condos, in closets.
Energy ventilation systems should be installed only by experienced and certified HVAC contractors. Such systems are not common, so the chance for improper installation is greater. For example, intake vents have frequently been installed too close to the ground, becoming a source of pollution from dust, second-hand tobacco smoke, barbecue smoke, and pollen. In addition, intake vents positioned below the snow line may become blocked by snow—a potentially hazardous situation.
Finally, while energy ventilation recovery systems ensure an adequate supply of fresh air to air tight homes, expect your electricity and heating or cooling bills to increase slightly. The units use electricity and not all of the heat being expelled can be recovered.
A NO Dealers can help evaluate your ventilation systems and make the best suggestions as to whether an ERV or HRV would appropriately meet your needs and budget. As a specialist in energy efficiency and indoor air quality, we first identify the sources to your expressed concerns and provide the best solution. We can best diagnose your home using our home energy audit, which properly pinpoints problems and allows us to confidently make any repairs or upgrades.
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