With a higher performance home, the details made during the construction phases of the home are designed to absolutely minimize natural ventilation through the home. With air leakage comes lost energy from infiltration and exfiltration. A tight structure will consume much less energy but does require a method of ventilation. This can be done passively but normally a heat recovery ventilator or energy recovery ventilator is installed as an active ventilation system. Moisture will be contained within the structure if ventilation is not provided to remove it. This usually first shows up as sweating windows and sill plates. Higher levels of interior relitivly humidity will cause condensation on interior walls, door jams, and any other location where warm humid air can come in contact with cool outside temps.
Removing moisture from a home is best done by use of a HRV, providing the outdoor conditions are suitable. Doing ventilation to remove humidity in Seattle would be a poor choice due to the never ending rain and 101% relative humidity. In much of Montana it is relitivly dry and ventilation works well. A ventilation system can be a rather large affair and requires ducting. A dehumidifier uses refrigeration to do the job and they can work very well. They do consume quite a bit of energy and typically warm up an area where they are located. Lennox has a system that installs in your existing ducting. It works very well but again, energy consumption is higher than with a HRV system.
Ventilation is something we assume is happening in our homes and business. We all need fresh air and it becomes quite apparent when you walk in a building and it has the aroma of sweaty socks that maybe somebody should open a window. We are building homes tighter and tighter to increase efficiency, this just seals in more contaminates that otherwise would be whisked away outside. Specifying a ventilation system in a new or existing home is often times just thought of as a frill that can be cut from the budget. Many times I have visited very nice, well built homes that bottle up every volatile organic compound that it took to build the home. It smells better than sweaty feet but, it is absolutely not a cocktail that you want to breathe.
Some of the applications of HRV’s are described above but what they are needs some description. Generally they are around four feet wide, two and half feet tall, and two and half feet deep. They hang in a basement or mechanical room by small chains or straps. Two ducts go outside (fresh air in and exhaust air out), and two ducts go inside (exhaust from home, and fresh air into home. All this air goes through a heat exchanger that uses panels of plastic or aluminum and looks much like corrugated cardboard. In one direction the warm air flows through the tiny slots of the corrugation, in the other direction, the air flows around the smooth side, just outside of the corrugations. The proximity between the two passing airstreams, exchanges energy and transfers 65-95% of the energy back into the home. Very good for removing humidity and all kinds of noxious odors.
These units are the younger brothers of the HRV’s and are very similar in design and function. The main difference is ERV’s remove minimal amounts of moisture from the home and HRV’s are designed to remove as much as possible. This is done by the design of the heat exchanger and uses different materials to prevent absorption and rejection of moisture. The typical home installation would be a fairly tight home that needs ventilation but does not have many people living in it. Running an HRV could dry out the building, where an ERV will provide the ventilation and maintain normal levels of humidity.