Now that the house is weathertight we have started MEP (mechanical, electrical, plumbing) work. Our HVAC contractor has been out routing ducting and has started installing and connecting up the system components. There are two separate systems: the heating and air conditioning system to control air temperature and humidity, and the ventilation system to provide fresh air and remove stale air.
The heating and air conditioning system is a Mitsubishi air source heat pump system with a combination of air handlers and ductless units distributed throughout the house. Because ASHPs don’t actually create heat, but instead merely transfer it from one point to another (like a refrigerator), they can be much more efficient than a traditional heating system. They don’t produce combustion products like a boiler or furnace. And their variable-speed components can operate at just the level necessary to maintain temperature, further inproving efficiency. You can learn more about ASHPs here and here. The three external components (compressors) will be behind the garage, with the internal units (air handlers or ductless heads) located throughout the house in the basement and attic.
The ventilation system is a Zehnder ERV (Energy Recovery Ventilator) system, which operates continuously to pull fresh air into the house, pre-heat (or cool) it, and then distribute it throughout the home to ensure there is a steady supply of fresh filtered air. The system is balanced, which means that an exhaust system removes stale and moist air from bathrooms and other spaces and dumps it outside. The system helps prevent the buildup of allergens like dust mites, mold, pollen, and chemicals. It can also help control the buildup of carbon dioxide in bedrooms, and reduce moisture in bathrooms. Their website has more info on the benefits of mechanical ventilation. To ensure high air quality, we’re installing three separate systems located in the basement (for basement and first floor), attic (second and third floor), and yoga room (living spaces over the garage).