Boxed heat pump

[WisJim]

When we built a new house in the 1970s, we superinsulated it, and we used a couple of face cords of wood each winter to heat it. As I mentioned before, there is no substitute for good insulation and proper weathertiteness in a house. You don't need lots of expensive equipment to heat the place if you insulate, seal, and ventilate properly.

[Snax]

You also don't need expensive cooling with the same planning.

One of my favorite concepts is a foundation heat storage bank. Adequately sized and insulated from the surrounding ground, a large mass of sand can be used to store up heat in the late cooling season for later return in the heating season and vice-versa. Heating is provided by solar panels and a closed loop water/coolant circuit. And because the ground temperature surrounding the foundation is below normal household cooling temperature, there is no system required to cool the mass itself, as the extraction of heat through the winter is enough to provide cool mass through most of the summer.

[GasSavers_Ryland]

Originally Posted by Snax

You also don't need expensive cooling with the same planning.

One of my favorite concepts is a foundation heat storage bank. Adequately sized and insulated from the surrounding ground, a large mass of sand can be used to store up heat in the late cooling season for later return in the heating season and vice-versa. Heating is provided by solar panels and a closed loop water/coolant circuit. And because the ground temperature surrounding the foundation is below normal household cooling temperature, there is no system required to cool the mass itself, as the extraction of heat through the winter is enough to provide cool mass through most of the summer.

When I was building energy efficent houses that is the basic concept that we used, use solar hot water panals to heat a mass of sand under your concreat slab, insulate that slab, and the ground around the slab, and around augest or september you turn on the hot water panals to start heating the floor, and turn them off around april, that mass stays warm, and by the time it's cooled off in the spring, it's starting to keep your house cool, even if you leave home for a few weeks in the dead of winter a system like this will keep your house 65-70 degrees, like was said befor the heat from cooking, having lights on, and other parts of daily life help keep it warm, and if that is not enough you design the system with propane or natural gas back up for those that don't like to clean the twigs out of their yard, as that is about as much wood at some of the houses I've worked on use, a pickup truck load of small firewood and kindling.

I spoke a while back to an enegner about heat pumps, and he basicly said that a single family home is too small, that they will cycle on and off to much, and that they don't operate efficently when cycling on and off like that, that the best use for them would be a multi family appartment building, or office building, not a house.

[Telco]

Very interesting. So how large a sandbox do you need for this? Any links that describe it in more detail, like maybe with pics and efficiency reports?

[Snax]

I believe that a more industry standard term for it is High-mass Solar Heating. In 'Solar Water Heating: A Comprehensive Guide to Solar Water and Space Heating Systems', the author suggests 10.5 tons per 100 sq ft of space (or about 2' deep under the foundation).

I highly recommend that book.

[Telco]

Excellent, thanks! Mother Earth is an excellent resource.

Sweet! Did a search on "High-mass Solar Heating", and came up with this site. Methinks I need to start rethinking my overall design now. Better now than 3 years from now, eh?

[GasSavers_Ryland]

most of the houses that I worked on had a vapor barrier, 2" or more of foam, and 12" of sand, one house was built on an old foundation with part of the basment filled with 6 feet of sand and hot water tubes in the bottem, and in the middle, that was over kill and altho it never got cold, it never got really warm either, 1 to 2 feet of sand seens reasonable, and putting the hot water tubes in the sand not the concreat gets rid of hot spots, and reduces the chance of the tubes cracking if the slab shifts.

[Telco]

Hmm, looks like my boxed heat pump idea may not be a bad idea. This site describes a solar heater for a window that is kind of what I had in mind for a preheater for a heat pump. Essentially what I was looking at was a greenhouse for the heat pump, let the sun heat the air inside the enclosure, then let the heat pump extract that heat to warm the inside of the house. The main problem with a heat pump is it is always working against the outside, it is either trying to extract heat from cold air or push heat into hot air, this would at least help with the wintertime part of it.

[GasSavers_theCase]

I've got mixed feelings about a boxed-in heat-pump. I can understand the idea of preheating the air surrounding the heat pump making it work better, but remember a H/P would rapidly cool down any enclosed space it is in. If the space is too small isn't it possible that a H/P could drop the temp in the space below ambient causing the H/P to be less efficient than just being outside?

Obvious factors affecting this would be the climate, size and mass of the enclosed area, duty cycles, etc. How about a large cheap plastic open-ended lean-to covering the H/P on the south side of the house? maybe?

And here's a great link covering lots of DIY solar projects.

http://www.builditsolar.com/

Good luck!

[Telco]

Yeah, I was thinking about the heat pump depleting all the heat too. It would have to be a fair sized cover for it, yet not so large that the cover never gets warmed up. Guess it will need an engineer to come up with what size that cover would need to be to allow the heat pump to get a boost. If the cover could retain enough heat when the compressor were off that it was still warmer inside the cover when the compressor cycled off though, it would save energy having the cover vs not having it, even if it were only 1 degree warmer.

Thanks, I'll dig around on that solar website. I plan to start building a new house in about 2 years, and if at all possible I want it to be offgrid, with the backup generator doing nothing but gathering dust between monthly maintenance test runs.