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Old 01-07-13, 02:33 PM   #1
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Default Utilizing stream water for heat pump

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.

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Old 05-11-13, 12:54 AM   #2
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I saw your original post on this subject in the manifesto thread and thought your initial questions had been answered, and that you had been pursuing a stategy.

So what have you come up with in the meantime? Have you decided which way to go with the idea?

I see you posted that you may want to reconfigure your 3 ton heat pump into an air-to-water unit that transfers heat to and from your stream. This approach will not get you as much heat transfer as a true underground loop, since the stream temperature tends to follow the outdoor temperature. You also have a long distance to travel between your heat pump and the stream source, so the pressure drop in your loop would dictate a larger size pipe and a larger pump than if it were closer to you. However, this distance underground could work in your advantage by transferring more heat into the ground. Some temperature logging would be needed to figure out the details, especially during the high demand times of the year.

A modified system would perform better on those extremely hot and cold days than what you have now, but during the other 80-90% of the year, you might not save much energy over a 15 SEER unit. A proper energy audit or heat load analysis is always a good first step to take before you start modifying your existing HVAC system. A large portion of homeowners discover that sealing and insulating their existing envelope is all they need to do to reduce their energy consumption to a much lower level.

Last edited by jeff5may; 05-11-13 at 01:00 AM..
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Old 05-11-13, 06:13 AM   #3
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Upon intitial investigation of the system without actually crunching numbers I determined that, at my current favorable power rate, that the pay back would be too long. During the winter months, since I have fossil fuel backup, I get the power used on the heat pump at half the normal cost per KWH.

In the summer when I am paying full rate is when I need more help. I have also considered buying and old ac or heat pump unit and removing the condenser coils and wrapping them around the outside of my current unit. Using these coils with water circulating from the stream to pre cool the air entering my existing condenser coils. I thought this would be an inexpensive way to lower the incoming air temp during hot weather at a minimal cost.

Just a thought rumbling around in my head. As usual though I will think on it longer than it would take to implement. The water is free and the pex tubing would be cheap, I all ready have a small pump and for the trial I would not bury the pipe. Not sure what the cost of an old unit large enough for the job.

But then we digress from the original posters question. We can save this for a new post when I undertake the implementation.

Thanks for the input and I hope the info on the thermostat and use of a propane unit with a heat pump has helped the poster with his decision.

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