In the spring of 2005, I'm planning to build a house in the country near Sandpoint, ID. If you're not familiar with Sandpoint, it's in the panhandle, about 60 miles from Canada. The interesting thing about Northern Idaho is that even though it is about 6-7 degrees North of where I grew up, Southern MN, the winters are
much more mild. I want to make the house as efficient as possible, not only to save money and the environment, but for the bragging rights as well. It's just cool to tell people you have no utility bills.
From most standpoints, it will be self-sufficient. It will have a well, a septic system, a solar hot water system, and a solar electric system. Due to the nature of solar insolation at such a high latitude, which I'll get into below, I haven't finalized the design yet. I need to decide if my backup heat will be gas or electric. If I go with gas backup heat, I would also probably use a gas stove and dryer.
The first rule of making an efficient system is to reduce losses, so the house will be insulated very well. I'm thinking of going with 8" walls with higher density fiberglass insulation. The roof will probably be a gambrel (barn) design, 12", again with HD fiberglass. There will be a basement, probably ICF, surrounded with 3" or so of blueboard.
The heating system will be in-floor radiant heat. Here is where it get's fun! I'm thinking of tying the solar hot water system, radiant, and domestic hot water systems together, thermally at least. I should have plenty of room to put 114 ft2 of hot water collectors on the lower part of the roof, at 30 degrees from vertical. I may either build my own using low-iron glass and selective coatings, or just buy them. The solar hot water loop would be closed, using a water and non-poisonous antifreeze mixture. It would have a copper tubing heat exchanger inside an insulated stainless steel box filled with water. The box would be 2'x3'x4', or 180 gallons. (BTW, do you think feeding the collectors serially will work okay?) The heating loop would also be closed, but separate (using plain water.) The return from the heating loop would be fed into another heat exchanger in the box, to pick up heat. It would then go through the primary of a radiant gas boiler as backup. (I could also use a tankless heater here.) The domestic hot water system would also use heat from the storage tank. Well water would be fed through another heat exchanger in the tank, then through the/a heater as backup, and distributed.
I'm shooting for a decently large array of solar panels with a tracking controller. I'm going to go for grid-tie, and attempt to reduce my yearly electric bill as much as possible. BTW, I won't be needing A/C. The house should only get up to about 80 degrees for about 6 hours each day in the summer time. As soon as the sun sets, it cools down rapidly to about 50-60.
The problem with being at such a high latitude is that the amount of solar energy available in the winter is less than half of what's available in the summer. The azimuth of the sun at solar noon on 12/21 is like 17 degrees! That doesn't present a problem for the solar electric system if I have net metering. It does present a problem for my solar hot water system, however. I'm hoping that the size I've designed will supply nearly all of my heating and domestic hot water needs in the winter. If it does, I'm going to have a huge abundance of hot water in the summer. I think I have two options here: 1. Cover up some of the panels in the summer. 2. Use the excess heat to do something useful. If I could get an appropriately sized Stirling engine w/ a generator, I believe I could use the excess heat to generate electricity, which means I could reduce the size of my solar electric array. However, I don't think that's going to happen in the next couple years.
If you have any thoughts on whether I should use gas or electric for my backup/appliances, please do share. I'd also welcome any thoughts on the issue of excess heat in the summer.
cheers,
brian
