Summer ventilation is accomplished by sucking (warm) air from the ceilings of the second story of the house and venting it outside. This is easy because the second story air return ducts are in the ceilings (see heating and cooling system design).
During winter air inside the house is warmer and more humid than outside air. Straight ventilation would introduce uncomfortable cold drafts, and extra demands on the heating system. A heat recovery ventilator from FanTech is used to heat and humidify incoming air using the outgoing air stream. This air exchange is balanced, so that air pressure in the house is roughly the same as air pressure outside the house. Warm humid air is less likely to seek a path out through walls, windows and doors.
Finally, exhaust vents such as the kitchen hood, bathroom fans and fireplace should not have to fight a tightly sealed house. In our house the EarthTube (summer) and/or HRV inlet (winter) can be activated when the exhaust fans turn on, guaranteeing that air drawn into the house is coming in through desirable intakes.
Ventilation is an Art
- Green builders and homeowners are desparate to find residential HVACcontractors. Today's residential heating/air-conditioning contractors are not familiar with ventilation. Our HVAC contractor is a crossover contractor - they do part commercial and part residential. Several people asked me for our HVAC contractor's contact information.
- The larger Fantech ventilation fans are quite noisy but can also move a lot of air, while the smaller Panasonic fans are whisper quiet by comparison. I intend to do a test run with the house ventilation fans to see how they fare.
- Piping inlet air directly to desired rooms is important, because air flow rates for ventilation are a lot lower than those typical of forced air systems. Very important for bedrooms, since so much time is spent there. Check this in your house!
- Heat recovery ventilators are less efficient with lower delta-T. It is important to duct exhaust air though conditioned space as much as possible prior to connection to the Heat Recovery Ventilator.
- The amount of ventilation (air exchange) required for a building is a function of many things. ASHRAE has a minimum value based on square footage. The baseline air exchange rate we had chosen barely met this number.