Now that the house is complete and I have had an opportunity spend several weekends enjoying it, I have begun to gain an appreciation for how to works.
The building envelope performs extremely well keeping the house warm, quiet, draft-free, and comfortable even in the coldest weather. The windows let in abundant sunlight and solar gain during the day and keep out the cold at night. The heat pumps are great at producing a nice, quiet, unobtrusive warmth. And of course, the HRV does a great job redistributing heat and providing fresh air throughout the house.
However, while all the systems work in-harmony well, they aren’t perfect. Fortunately, unlike a typical house-even a typical Energy Star or Passive House-mine is almost infinitely customizable. Nearly every device can be controlled from a tablet or computer-lights, heat, AC, water heater, locks, alarm, HRV, home theater, you name it!
I have been analyzing the data from my Smart Electric Meter in order to optimize the systems for energy efficiency and comfort.
The first graph shows a typical day when the house is occupied. The average temperature was 37 degrees. The majority of the homes energy usage is driven by the heat pumps. However, you will notice a couple of spikes where the water heater or oven were turned-on.
You may recall I chose to install a heat pump water heater. However, during the winter months I am operating the water heater in electric-only mode so as not to use the heat energy the mini splits put into the home.
The second graph shows the minimal energy usage of the house when it is unoccupied. You will notice on both graphs that from about noon through 9PM the heat pump idles. This is a result of the massive solar gain through the 200 square feet of glass windows on the front of the house. During sub-30 degree days I have found the solar gain is easily able to warm the house 10 degrees.
Of course the super tight well-insulated building envelope holds the heat long into the evening. The heat pumps usually resume operation around 9-10pm to maintain the temperature until the next day when the cycle repeats.