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.
Conrad,
Thanks for another fascinating entry. I love this blog. Imagine if your annual space heating load is 100 GJ. This is probably a little less than the Edmonton average but a nice round number. That's 28000 kWh so if you heated your home with electric baseboard heaters that would cost you about $2800.00. A GSHP would save you 2/3 of that or about $1850. That might pay for the annual maintenance on your GSHP plus setting aside money every year to replace the compressor when it's totally obsolete in 25 years (the ground loops are maintenance free and should last for much longer than 25 years) plus the interest on the incremental capital cost of the GSHP over the baseboard heaters - say $10000 @ 7% or $700 dollars per year. 100 GJ of natural gas would cost you from $800 to $1200 plus the myriad of other fixed and variable charges. But in your example of 10 GJ per year, a GSHP would save you only about $185 per year over baseboard heaters. That's nowhere near enough to even cover the interest on your incremental capital cost. I think you've made a wise choice.
Thanks. In a way it's an example of Amory Lovins' "tunneling through the cost barrier". We are making the house so efficient that investments in efficient heating simply aren't needed.
And good point about the ground loops - in many ways they are an excellent investment for the super long term. In 200 years, I'm positive that they could be dug up and be in perfect condition.
Hello Conrad,
I know this may sound a little off base here but I think a masonery stove (possibly a light version) that uses wood as fuel. If there comes a time when we need to heat, cook, heat water, etc when we don't have gas then we can always heat our houses with wood. The problem with these stoves is that they are expensive and the house really needs to be built around them.
A good masonery stove would handle all the aspects that electricity can't.
I mentioned to another person about GSHPs that if you could make a local co-op with your neighbours then that spreads out the costs of installation, maintenance, etc. My problem with GSHPs is that the initial cost is so high and the electrical demand is quite high. If this cost could be spread out to more people then it becomes more ecological since the footprint is now shared.
Take care
Thanks Michael. It's not at all off base. I really wanted a masonry stove at the outset, but size/design considerations prevailed. My next MCNZH post will be about the wood stove that we will have in the home (78% efficient, surrounded by thermal mass). It's not as good as a masonry stove, but it will provide some of the resiliency (to other fuel shortages) that you alluded to.
How are you going to heat your water?
Without gas, is an on demand electric hot water going to meet your family's needs?
Or with electric is the best current option to just use a "regular" tank and insulate it well?
It's going to be a solar hot water tank (a relatively small system with only two collectors), that is boosted by an electric on-demand heater if it's not hot enough. So we'll be mostly using the on-demand heater (rather than solar) throughout the winter.
I have been wondering lately about using an on demand electric hot water heat to heat my home. The logistics of that are easy; but what I am looking for is information about using solar power to power the on demand heater, thus in effect getting "free heat". How expensive of a solar array would I have to emplace to run just my on demand electric h2o heater? My home is under 900ft2 of living space, well insulated, and currently is heated by an oil baseboard h2o heater. I want to eleminated the oil burner in order to free up my only chimeny (single flue) for my wood burner. Any ideas out there? olsenjamie@hotmail.com
I have been fascinated by the Riverdale project as well as this one. I have a couple of questions.
For the Mill Creek house you dismiss the Solar Water Tank used in the Riverdale project but seriously considered the GSHP. Even with the heat loss experienced by the tank, wouldn't the water temperature still be greater than the water temperature coming from the ground? If you did not draw DHW from the Solar Water Tank, and thereby not have to replenish it with cold water, would the hear loss be lessened a great deal?
I was suprised that you never mentioned radiant floor heat for either of the projects. Was this not an efficint manner of distibuting the heat, expecially since you do not need air conditioning?
What I like about the GSHP is that you install it, then forget about it. Once the boreholes are dug, the only active part of the system is the heat pump itself.
With a big hot water tank like the Riverdale one, you need multiple systems. You need a regular heat transfer coil to pull heat out when the water is more than 30 or so degrees (ballpark) because heat pump can't operate at very high temperatures. Then, you need the heat pump itself to pull the heat out of the water as it is going from 30 degrees to around 5 degrees. You don't want to keep operating the heat pump after that, because it might freeze the water. You also need a backup system - what if there isn't enough heat in the water to last through the winter? Finally, you have the complexity and risk that's involved with storing thousands of litres of water in a huge tank.
As for radiant in-floor, there is some robbing Peter to pay Paul with them, because we actually want our floors to be as cold as possible when the sun starts hitting them on a sunny day. Heating them up to 25 degrees with radiant heating before the sun starts warming them up would significantly reduce their capacity to absorb solar energy.
We ended up going with the absolute simplest, cheapest system available - the heat radiates, but it is transported through copper wires that will never break, and will never need maintenance unless someone kicks over a baseboard heater.
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