The proof of the pudding is, as they say, is in the eating. But eating a house is ill-advised, so we’re monitoring it instead. Specifically, we want to know:
- How much energy is the house using? Is it living up to its energy goals?
- What’s using the energy? How does this compare to our assumptions?
- Is the home staying comfortable? Recall that this house is designed with no conventional air conditioning (but with plans to add it if needed). Can it maintain comfort in hot, humid Iowa summers?
- How does the home operate passively? — i.e. without active heating or cooling?
To that end, we are continuously monitoring temperature, relative humidity, and energy use.
We've been monitoring temperature and relative humidity in the house since January 2017, just prior to window installation. Three sensors capture data in 15-minute increments and send the data wirelessly to a server. The system (including the webpage that displays the data) is a custom creation of one of the homeowners.
You can explore the data for yourself here.
We've been monitoring energy use since July 2019, just after occupancy. We use an eGauge system, with individual monitoring of all major appliances and on each zone of the electric radiant heating system. This system will also monitor the production of the solar panels once installed.
You can explore the data here.
Summary
As of December 2019, here are preliminary answers to the four questions outlined above:
- How much energy is the house using? The base load is a mere 27W (~$2/mo), from the refrigerator and ERV. Add lighting, cooking, and hot water, and we’re at about 460kWh/mo (~$16) . As of this writing, the active heating system has only been on for about a week; we will update with heating energy use as we get deeper into the winter.
- What’s using the energy? I’ve not done a formal analysis, but judging from the eGauge data, hot water looks like the single largest end use. As heating comes on-line, that may overtake it.
- Is the home staying comfortable? Yes. It appears that little heating is needed to maintain winter-time comfort. In the summer the home got into the 80’s (degF), but the shading and natural ventilation strategies were not fully utilized. Even so, with air movement, lower surface temperatures (thanks to earth berming) and a small amount of dehumidification from the ERV, the home was surprisingly comfortable.
- How does the home operate passively? During the polar vortex in January 2019, the home was complete but not yet occupied. With outdoor temperatures dipping to -26 degF, the home’s interior temperatures averaged 50-60 degF — with NO heating. That’s a delta of ~80 degF through passive design alone.
Further Analysis
You can find posts I’ve written analyzing the results of our data collection here.