We've worked to make the enclosure of our lab home airtight and very well insulated, so that comfortable air stays inside where it belongs. But a highly efficient enclosure means we had to think about heating, cooling and ventilation in new ways.
In a nearly airtight home, heating and cooling systems don't need to work as hard, and proper ventilation and humidity levels become more important. Traditional systems aren't set up to deal efficiently with those changing needs. That's why we're evaluating several different approaches to heating, cooling and ventilation to understand what will work best under these conditions.
Since our lab home requires significantly less heating and cooling than most homes, the volume of air forced through those ducts is much less, too. That means that traditional large metal duct systems, with several main ducts branching out to the rooms above, won't deliver comfort.
The ducts need to be tighter to the core of the house and much smaller, to ensure that there's enough velocity to deliver the air and that the air is "thrown" into each room with enough force to spread throughout the space.
So, we're looking at three kinds of alternative ductwork-PVC (polyvinylchloride) pipe, a small-bore metal duct, and a combination of insulated duct board and flexible ducts-to see which distribution system is the most efficient. We'll monitor their performance and leave the most efficient system in place for the homeowner.
We're also experimenting with the equipment used to heat and cool the air. Usually heat pumps are used in addition to traditional systems, not as a replacement for them. In our zero energy lab home, though, our enclosure is so efficient at keeping conditioned air inside that the home can rely completely on a ground source heat pump for both heating and cooling.
The heat pump in our lab home is geothermal-it circulates a refrigerant liquid through pipes that run into wells deep underground. This liquid makes the most of small temperature differences between the ground and the house to produce hot and cold air. Our heat pump system will also be used to heat water within the home and dehumidify the air, so it stays dry during muggy summers and damp winters.
Digging a well deep into the ground can be expensive, though. It's not part of building a typical house, like excavating for a basement. So, we're also testing a second, different kind of well system where the pipes run horizontally, under the foundation. We'll check to see if the temperature of the earth underneath is affected by the temperature of the house itself, and if that makes a horizontal system less efficient. If it works, this new design approach will make ground source heat pumps a much more reasonably priced option and also make it possible to install them in the city, where small yards make it hard to use a deep well system.
If the house is airtight, how does the air stay fresh? How does humidity from everyday activities like cooking and showering escape? We're using a ventilation system called an ERV-for energy recovery ventilator-that constantly circulates fresh air into the house, while keeping it the right temperature and humidity.
Photo of three distribution systems in the Lab Home
