Heat Recovery Ventilation Systems
by Kim Kinrade
Humans can live for a long time without water and even longer without food. However, take away the air, or poison it, and the human body will shut down and eventually stop working. This is how important breathing is and so you would think that the quality of air would rank up there with the highest concerns for living. The sad fact it isn't. In fact there are many parts of the world where it is not safe to go outside of the home. But the outside air isn't necessarily the health problem.
Air Pollution in Older Homes
Another form of air pollution is the air quality in our own homes. Until recently the air in the home was refreshed through leaks in the home from windows and chimneys and when the doors were used. In the summer the windows would be left open but air pollutants from any outside source could get in. In cold areas the homes were tightened to prevent heat loss but this lead to the build up of carbon dioxide from breathing and heat sources as well as the transfer of germs and bacteria from one person to another. And this does not include the threat of formaldehyde from off-gassing from engineered wood and carpets or from moisture-laden air from cooking and leaking dryers.
New Home Problems
Stuffy House: During the past few years new home construction designs have witnessed the production of tightly-built houses which no longer have the energy leaks but have very little natural air exchanging possibilities. This why the building codes in most areas require ventilation systems. However, these systems are only as good as the people who install them because if they are poorly installed, or not being used to their potential by the homeowner, there can be high instances of high indoor humidity. This is where the house is stuffy and condensation forms on the windows.
Depressurization: A very low pressure area can occur in a tight home when the venting fans are used frequently. Air-tight fireplaces, the burners in heating systems, bathroom vents and kitchen exhaust fans drain the fresh air in the home. This creates depressurization and which can result in lack of oxygen for the home dwellers and the release of toxic gases from the heating system, diverted by the low pressure from their designated paths which are the chimneys.
Heat Recovery Ventilation Systems
The invention that came along to alleviate the problems of stuffy houses while maintaining the energy efficiency was the heat recovery ventilation system, or HRV. Using a small fan the HRV system maintains a continuous flow of filtered outdoor air in the home. To avoid pressurization the system removes an equal amount of stale, used air from the home, especially the kitchen and bathrooms where moisture and odors are heavy. Theses systems can change th entire air system in a home in under 3 hours.
The other operation that takes place inside an HRV is a heat recovery unit that uses the exhausting air to heat the incoming fresh air. This system recovers from 70 to 80 percent of the heat going out much less than the bathroom and kitchen fans which vent the air directly out.
The HRV unit is no bigger than a large suitcase and its location is critical to maintaining proper air quality. It has to be close an exterior wall for the installation of the intake air and exhaust venting and, as well, access to a drain is needed to accept condensed water from the unit and an AC outlet. In addition, the placement should minimize the amount of ductwork needed.
HRV Maintenance is Very Important
1. Air Filters: Dirty HRV air filters are not only unhealthy they can lower the ventilation efficiency. These should be cleaned at least every two months with a vacuum cleaner and then washed with a mild soap and water solution. Some older units have filters which can be replaced.
2. Inspect Intake Port and Exhaust Vents: Sometimes leaves and other small pieces of debris can get into the intake port. In the winter check for snow and frost which can also block the outside port.
3. Heat Exchange Core Cleaning: Your HRV should have an owner's manual. Check this to find the manufacturer's suggested cleaning method. Most of them, however, require vacuuming the dust and then washing with soap and water but it is important to get the right instructions.
4. Drain: The condensation drain can be cleaned by pouring ½ gallon of warm water in the drain inside the HRV.
5. Duct and Grill Cleaning: Cleaning the air flow parts should be done at least once a year. Again, using the manual follow the instructions for taking off the grills and then vacuum the ductwork. It also never hurts to get an authorized service technician to clean and inspect the unit.
6. Fan Servicing: All fans attract dirt so turn off the machine and clean off the blades. If the HRV is an older model there may be a place for a few drops of lubricating oil. If you don't have an HRV system it would be wise to have one installed for health reasons. There are also Hepa filters and anti-bacterial aids such as UV lights that can reduce sickness and allergy symptoms. This includes dust, insects and pollen.