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Old 03-10-13, 12:59 AM   #4
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Originally Posted by michael View Post
I'm pretty sure we'll need something bigger than this 1-ton because on the coldest days our house requires about 200k Btu for heat, and that would require running it nearly all day. I'm working on reading your posts...that may be the best textbook I could find. mm
Well, I was all prepared to tell you you wouldn't be able to do it with GSHP, but your floor layout sounds really great.

I'm going to be away for about a week, and I'll be glad to help you all I can when I get back, but there are some really competent folks here, too.

So, here is the general idea, your house will exhibit some number of BTU's of heat loss on the very coldest day. But then there are what they call the 3% days, where it's not quite so cold. You are better off designing for the 3% day and using supplemental heat for the really cold day (or two). Reason being your heat pump will achieve it's greatest efficiency when it is run full out.

And you will need some amount of loop field that is at least big enough to supply your heat for the 3% days. If your loop field is too big, it's not a bad thing at all, because the seasonal temperature drop will be smaller. But a bigger loop field will be more expensive. Trade-offs.

And then you'd want to choose a heat pump that could move the heat for the 3% days from the field into the house.

But you already have your heat pump, a 1 Ton job.

So what you need to do is a heat load analysis. HERE'S A PRETTY GOOD ONE over at Build it Solar. Be honest when you do this measure carefully. It should give you a pretty good idea how much heat you're gonna need.

The look and see how that matches up with the heat pump you already have.

If your heat load is smaller than what your heat pump can provide, you are 'in high cotton' (a Southern expression meaning thing s are looking good). If you come up short, your choices are:
  • Go after all the infiltration leaks you can find
  • Inuslate, Insulate, Insulate
  • Use the unsufficient heat pump anyway and fill in the rest with your usual heating methods
  • Get a bigger heat pump

Personally, I would recommend doing everything you possibly can to prevent your house from losing heat before you start thinking about cheaper ways to get heat.

After a rigorous attack on heat loss, you may find that previously insufficient heating methods have become sufficient.

Another thing you may want to consider is that due to your mild winter, an ASHP might be a good choice for you. Unless you are really handy with heavy equipment, doing a loop field is not a trivial affair.

Also, ask around locally what it takes to do a 1 Ton loop field.

That's it for now, I'll be out of touch for a week...

Enjoy the Manifesto. There's also an excellent thread on DIY radiant flooring that addresses many of the related issues. The two really go together.


I'm not an HVAC technician. In fact, I'm barely even a hacker...
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