I've thought about the heating system for the Mill Creek NetZero Home (MCNZH) for months now. The home will need a very tiny amount of heat because it's so superinsulated, super sealed, and passize solarized. The computer model that simulates the energy performance of the house (using HOT2000) has the MCNZH using 2500 kWh. That's roughly 6% of the heat that my renovated (with new insulation and windows) 1950s bungalow uses.
So we'll need the equivalent of 9 Gigajoules of natural gas per year for space heating. Given that being connected to the natural gas grid costs about $400/year, and 9 GJ are worth $50-$100/year, it makes no sense for us to connect to natural gas. Plus, Canadian natural gas production is waning, so I don't want to depend on having gas in the pipe in 20-50 years from now.
So we'll only be connected to the electricity grid. That leaves the following heating options:
1. A Seasonally-charged, Huge Solar Water Tank: This is what Peter Amerongen used for the Riverdal NetZero Project. I've eliminated this option. The system ends up being very complex, and I think that it loses too much heat from standby losses whilst waiting for the heating season to come around. Godo Stoyke told me that they modeled 1.5% heat loss per day, given a tank with R100 and heated to 90 degrees C. In the end, the benefit of whatever heat is left over from the summer in December, when you finally need it, doesn't justify the complexity.
2. Ground Source Heat Pump (GSHP): I was pretty set on this option until recently.There's a new one out that can heat your hot water too (at lower efficiency because domestic hot water needs to get quite a bit hotter than space heating hot water). It is expensive, though. Like $25,000 for a tiny system.
3. Baseboard Heaters On Each Floor And An Electric Instant Hot Water Heater. The big advantage is the heat delivery system is DEAD SIMPLE. The entire system is just so simple. Plus, although I'm not giving up on the concept of true net zero, we will have a wood stove in the home. If we burn fires during the winter (I know, I know, ground source pollutants - we'll consider the fact that we don't drive to be our offset for those), we will be using barely any electricity to heat with.
The question is, then, do we spend $20,000-30,000 on a GSHP that will almost never be used, or use the money to finance more solar electric, which will definitely be producing all summer long, regardless of how many fires we burn.
We've decided to go with the baseboard heaters.