How an Energy Recovery Ventilator Works
The best time of the year for me is when I can open my windows and allow fresh air to come into my home. Nothing beats the smell of fresh spring air and the health benefits associated with open windows. When fresh air is brought into a home, indoor pollutants such as radon gas, carbon monoxide and chemicals from building materials, cleaners, furniture, and carpets are removed. Fresh air also helps to control moisture levels, which is vital for good home indoor air quality.
What you are probably not even aware of is that without any windows open, the air is constantly changing in your home. Even when you have all the doors and windows in your home closed tight, outside air is entering your home. In fact, when you turn on a bathroom exhaust fan, or the vent over your stove, you are bringing air into your home. Where does this air come from? Older less energy efficient homes “leak” air, so when you turn on an exhaust fan you are pulling air in through the walls, windows, and doors of the home. In striving for better energy efficiency, builders have started to build homes much “tighter”, and, as a result, they do not leak as much air. Because replacement air has to come from somewhere, in newer homes it tends to leak in through undesirable places such as basements, cracks in the walls and crawl spaces.
The problem of properly ventilating living spaces is hardly new. In fact, most modern office buildings and shopping centers do not have windows that open. This might make you wonder how fresh air is brought into these spaces. The answer is a ventilation system that works together with the system that heats and cools the air in the building. A modern HVAC (heating, ventilation, and air conditioning) system brings fresh outdoor air into the building while at the same time controlling temperature and humidity.
You can install a ventilation system in your home that will bring fresh air into it and remove stale air from your home. Although much like the ones that are used in buildings, they are obviously much smaller. The most common types of home ventilation systems are exhaust-only and balanced systems. In an exhaust-only system, a fan is used to remove air (there is no fan to draw in fresh air). These types of ventilation systems are not that different from the bathroom fans you have in your house. A balanced energy recovery ventilator, on the other hand, has two fans, one that brings air into your home and another balanced fan that removes the same amount of stale air from your home. The fans in a balanced energy recovery ventilator maintain an inflow of fresh outdoor air, while at the same time exhausting an equal amount of stale air.
The most common home energy recovery ventilator is designed for the entire home and uses ducts to draw air into and out of the home. Whole home units tend to be more efficient because they are able to distribute the air more effectively. Whole home ventilation systems are commonly installed near your furnace and need to be readily accessible for cleaning and filter replacement. Ventilation systems can be installed in attics, crawlspaces, or storage areas. They require two vents, one to bring fresh air in and one to exhaust stale air from your home. These vents should not be close to another so that the stale air is just pulled back into your home. It is best to install the vents on different sides of your house to ensure that the fresh air is actually fresh! It is possible to purchase wall or window ventilation systems designed to ventilate a single room. Wall systems are usually used in multifamily homes where a whole home system would not be practical.
While bringing fresh air into your home is a good thing, it is can also waste precious energy. On a cold day, you are exhausting warm air from your home and replacing it with fresh cold air that needs to be heated. In the summer, the cool dry air in your home is replaced with fresh but hot humid air from outside. This does not seem to be very energy efficient – you might as well just open your doors and windows to bring in fresh air! This is where an energy recovery ventilator (ERV) or a heat recovery ventilator (HRV) can help. An ERV/HRV transfers the heat and moisture passing through it so that the energy spent conditioning the inside air is not wasted. In the summer, an ERV/HRV will transfer the heat coming into your home to the air stream leaving your home. In the winter, it will transfer the heat in the air leaving your house to the cold air entering the house. This allows you to recover some of the energy used to condition the air inside your home.
The main difference between an ERV/HRV and a home ventilation system is the addition of a heat exchanger that is used to transfer the heat between the air streams. There are several different types of cores that are available including cross flow plate cores, counter flow flat-plate cores, heat pipe cores, and rotary wheel cores. ERVs commonly offer the ability to control the humidity in your home and can help to remove moisture from hot summer air and add moisture to incoming dry winter air.
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