Researching GSHP (ground source heat pump
A friend asked me how he can lower his utility bills. Most of the ideas he had are non starters. The best Idea that I can thing of is to replace his propane furnace & AC with a GSHP. His house is 22 years old and the furnace is 90-95% efficient & is original to the house. The house is about 2200 sqft, well insulated and in central MN. I am thinking that the existing furnace and AC are probably on their last legs, so it is not like he would be replacing a HVAC system with a lot of life left. Couple of questions Would we be saving that much money if we installed the slinky coil system ourselves? We have the equipment & the operators. Does anyone know where I can find a chart with the historical price of both propane and electricity for the past 20-25 years? As a mechanical engineer I like charts. I know that prices have gone up but I am guessing that propane is outpacing electricity in % of increase. The math looks good now, but I want to do my homework. Other than the local electrical rebated that are $400 / ton & the 30% tax credit what other financial credits am I missing? Are there some cheap loans out there for this type of projects? He also has a heat recovery air exchanger that runs 24 – 7 Is it a good idea to put it on a controller. so it only runs, say 1/3 of the time. Seems like a no brainier as long as the air quality is still good.
Replies
Your local electric utility is your friend here -- they'll have all the info on rebates, etc.
and as I have posted before, some utilities dual meter heat pumps at a much lower rate. My normal rate is $.11 but my interuptable rate is $.04. In exchange for the lower rate you give the utility the ability to shut your system down in a peak emergency. The end story is they could cut your AC off for a couple of hours during some of the hottest days in the summer but you pay half as much the whole year.
If you can dig the trench, I would think you would save a ton of money but the only way to know is to have them bid it both ways.
Remember too that a lot of the savings with GSHP comes not in the winter but in the summer by using the waste heat to make hot water. My brothers electric bill actually goes down in the summer when he uses the AC which too a little getting used to. Make sure you ask your installer about installing a water heat option on the system at the same time.
You can literally save many thousands DIY GSHP, esp if you have the equipment and engineering skills. Like in save $10K.
Drilled my own wells, and did a total GSHP for under $500 and $350 of that was for a new 4T rated Copeland scroll compressor on a Grainger closeout and the refrigerant cost. I used a scrap 7-1/2 T carrier condensor and built my own tube in tube evaporator using scrap/surplus pipe. Only drawback is nobody is gonna give you any rebates, needs to be ARI listed.
e-mail me if you want to know how to clean old copper so it is perfectly clean and oxide free inside and good enough for refrigeration use with TXV, etc.
You do not need any license for 410A. .
My GSHP in Seattle area runs at a COP of 5.6 with 55F inlet water at 9.5 GPM, no problem heating 5300 sq ft. as the 4T rated compressor in the GSHP configuration puts out 58,000 BTUs.
If you dont already have a vacuum pump, brazing outfit, etc. you will after a diy GSHP, not included in the $500 total, nor was the time spent drilling well, etc..
Do your cost trade study and include a few mollier diagrams to scope a self-designed system. The only commercial GSHP I've seen spec on even close to diy design is the tranquility 27, mucho big $$. .
You'd save a bundle doing your own excavation work and slinky install. That's often the big ticket cost item, I think in GSHP systems. Just make sure you backfill right (i.e. the right materials) ... don't know much about that, but understand that proper backfill can be important.