Tweaking my GSHP

[mejunkhound]

Main return duct that is 30 feet long (12x24 inch).

Added a secondary blower, 12" dia wheel, run slow at abut 700 rpm so no floor noise. It pulls about 300 watts running.

Ran the BTU measurements.

09.8 GPM water flow 54 to 56F inlet
Room temp set at 69F;
Extra blower at 3.2A, 120V, 0.78 PF = 300W
Main blower is 430W, water pump is 620W

No extra blower, about 1210 CFM flow, 106F air outlet
leaving water temp around 42F; about 63, 400 BTU/hr
Compressor amps = 16.8, at 0.85PF, about 4480W; overall COP = 4.4 overall

After extra blower, about 1560 CFM, 102F outlet
leaving water temp 40F - getting about an extra 3/4 ton of heat from the blower. (73,200 BTU)
Compressor amps = 16.4; about 3350W + 300W+1050 = 5190W; COP = 4.34 overall

Next step is to use a more efficient water pump which is a big hit on overall COP, but was able to add over 3/4 ton heat output for almost no reduction in overall COP (includes water pump and fans)

DIY setup using nominal 4T scroll R22 compressor for GSHP using well water, homemade tube in tube evaporator, old 7.5 T carrier finned tube condenser.

Was surprised at the large increase in heat output, but thought the COP would increase slightly due to the horizontal lines of the Mollier diagram being closer together - the extra 300 W blower drives down overall COP even though the compressor power does drop as expected.

[Fordguy64]

Taco has some really nice brushless dc pumps out. I think one of them is the bumblebee?

[superlen]

+1 on getting a variable speed pump.

If you currently have +40f leaving, you should be able to slow your gpm down from the 9.8gpm and gain the efficiency of less pipe friction. You exit water temp should then go down further, I would target 35F to give some headroom against freezeup. I know some of the pumps have a Delta T function that control their speed to maintain a certain temp. I haven't looked at a datasheet, but something of that nature might work well here.

I *think* this shouldn't affect your compressor draw. Edit.. (As long as)It's still the same amount of BTUs being pulled from the evaporator. If that is indeed the case, the lower pump amps will boost your COP a bit.

Edit - after re-reading and thinking a bit...I added this:

This is where I get a little puzzled. In your first test, you added more fan energy to pull more heat out of the condenser which lowered the compressor power. The summary actually lowered cop just a bit. This makes sense. You did a great capacity increase for effectively NO more power added. That's awesome. I think that means you tweaked in the right direction.

With my example of less water pump power, my first thought was that it will just result in a greater delta T on your water in/out & still the same btus pulled from evap, therefore same compressor draw, definitely resulting in better COP as the water pump is pulling less amps. It sounds wrong however. We would be moving less water, so unless the evaporator got more efficient at the same time (bigger or better design), the amount of btus absorbed has to be less, so the compressor amps are going to change. As to the effect on COP, I suppose it's a horse race on how much energy saved on the water pump vs how much energy increased on the compressor.


Len