Utilizing stream water for heat pump

[jlaw]

I currently have a 15 seer heat pump on my home about 4 years old. I also have a small running stream about 125' from my heat pump.

I am kicking around the idea of adding a refrigerant to water heat exchanger to try to improve efficiency and save money. I need some opinions\advice on the feasibility of this project.

My intention is to bury just below the surface of the creek bottom some Pex pipe. the creek never freezes and is sand bottom.

Needed information:
I live in eastern NC and the nighttime temp rarely goes below 20f. I have a sand yard that extends 20' deep. The total rise from the stream to the heat pump is about 20'. The straight line distance to the stream is 120'. I have a bout 120' of stream bed to work with. I have a split system heat pump with 90+ propane backup. 1650 sq' house. Replacement window and doors. 12" insulation in attic, 3.5 in walls, 6" in crawl space. 30k btu unit. I currently have the heat pump to switch to backup at 25F.

Wanted information:
Would this project be feasible? I am currently on a 2 rate system for electricity. Oct to Mar is 1/2 rate for heat pump usage. Max fuel bill for all electric home has been $190.00. What size heat exchanger needed? How much pipe needed? what size pump needed?

Any input would be greatly appreciated.