Need advice:

Am creating a small geothermal heating/cooling system and need to know where I can get a circulating water pump, and which to get.

I have a 900 ft2 freestanding office that has an old 25' deep well in it. At the bottom is 8 feet of 54 degree water, 3' diameter.
I plan to devise a closed loop tubing sytem with 1/2" copper spiral coiled tube (refridgerator coil) down in the well, then garden hose up 25' to a car radiator in the office with a fan on it. I do not plan to use the well water as such; only to get its temperature. The water in the closed loop will circulate. Need to know what small quiet pump I should use and where to get it. How many GPH? don't know, but not a lot I would think. Can it run continuous? If I put antifreeze in the closed loop will that hurt the pump? This is an audio production room, so need it to be quiet.

Any ideas?