Idea: DIY Ground Source add on to Air Source Heat Pumps
 

How about a ground source assist system that acts as an air preheater (or precooler in summer) for existing air source heat pumps?
You could lay the pipe, as much as you could handle, DIY... you could make the ground loops smaller than a traditional system if you only planned on using it in peak times and using the energy in the air for non-peak.
For the heat exchanger, purchase a big, used A/C unit from a local AC company that's scrapping it. Just needs to be bigger than your current condenser. Easily done for $50 or so - just can't have a big leak.
Wrap new unit's coils around the existing unit and seal gaps.
Add some pretty easy controls, a thermostat so you can use it in optimal times - like when the ground is significantly warmer(in winter) than the air, and a pump, and move the coolant through the lines that used to hold refrigerant in the recycled condenser. This wouldn't have any compression or anything and could be done easily by a DIYer, and wouldn't involve water inside the house or any new equipment. It would just improve the performance of your system in peak demand times by supplying it with ambient air that's closer do your desired temperature.
There appears to be nothing online that combines GSHP and existing ASHP but this would be a (relatively) easy add-on, half the cost of any GS system since you would have no special equipment except for the trench and pump to buy. And it could be done in a small fashion without committing 100% to it and ditching your ASHP and existing equipment.

I just purchased a home with two ASHPs and a big yard... the trench or well, ground loops... is obviously a big consideration for anyone doing GSHP but this might reduce cost enough for me to try it... just don't know if it would be worth it in terms of increased efficiency.

Since no one has replied to you yet, I'll relate what I did to my ASHP.
We only need heat here in PNW, have not used AC more than 10 hours in the last 10 years.

Got an old condenser and txv free off CL, banded out an enlargement in the ductwork, kinda like the old A-kcoil AC add on to furnaces.

Bought a scroll compressor off ebay, made an evaporator by putting 3/4 cu pipe inside 1-1/4" pvc pipe, run the GSHP water thru the annular space. Groud water here is 54-56F year around.

Set it up so only the ASHP runs when it is > 42F outside (outside thermostat) , GSHP only if <42F and > 15F, both if < 15F (never has happened yet since the setup completed 15 years ago)

You could try something like that?

Another ecorenovator has considered this approach also. He purchased a mini split unit to replace the electric resistance heaters he used to heat with and did a self install. He was planning on doing a borehole since he has a shallow water table. He was going to run the well water through a car radiator on the suction side of the outdoor unit. Never heard anything about it.

EDIT
His idea is here:
http://ecorenovator.org/forum/geothe...efficient.html
http://ecorenovator.org/forum/geothe...ini-split.html

I'm still working on that. We had a baby so. Things got put on hold. I do have e 250ft hole dug. Just got to go back and redig it and drop in the loop. I decided to go closed loop instead.

Congratulations on the baby!

-AC

Thanks he's growing and learning something new every day . I am going to be buying a 18kbtu multizone hopefully by summer for the rest of the house.

Evaporator length
 

mejunkhound, how did you size your length of the evaporator per ton?

Thanks, charlesfl

A few yrs ago (20) I had much the same idea while living in a town house with a heat pump with a roughly rectangular outside unit with somewhat rounded sides on the case - I concluded that the tube sizes in a larger wrap around condenser/evap coil wouldn't flow enough given the small drop/rise in geo water loop temp you had to work with - but I had a friend that had a bunch of large truck radiators (not the oddest of things he saved!) I borrowed 4 of them that would fit in a square outside the outside heat pump unit, connected them at the sides and blocked off the space between the top and bottoms of the radiators and the heat pump housing so no air leaks and, since I only wanted to try this and had no geo field, ran city water thru the radiators ,- I think I wound up with them hooked up with a pair in series and the incoming city water divided in two to feed those 2 series pairs. The heated water simply ran out in a restricted drain to make a mess in the yard. It was easy to hook up a solenoid valve so the water ran whenever the fan came on. It took a lot of water!
The effect in summer was dramatic - I didn't have a clamp meter but did have a run timer (read bedroom clock) - the run time on roughly the same hot 90 degree days was about roughly 1/2 to 2/3 of the unassisted unit and I think the current draw was down too. I was going to try it in winter but freezing temps would have been a big problem. I took it down when the friend had sale for the radiators.
I was going to make a neater try at the same idea when I had a house and geo bore by forming a circular annular fiberglass envelope around the existing air coil, killing the fan and pumping the geo loop water with antifreeze into the envelope directly over the enclosed air coil. Sealing the refrigerant in and out lines in the fiberglas case seemed the only problem. Kids happened to me as well though and I've enjoyed them more than fiberglass!

Nokiasixteth - I'm dying to know how you drilled to 250 feet - we are mostly clay and sand here but that would still be a homemade feat!