Homemade water to water heat pump help

scottorious · 04-09-24, 06:31 AM

I built a heat pump for educational purposes and I want to determine how efficient it was operating. Very roughly I think I figured it out but my method was ugly. Feel free to rip apart my build because I'd love to improve it. Currently using plain propane from a small torch cylinder. I intentionally used a needle valve just to play around and watch what happens when I increase or decrease refrigerant flow on it and thats also why I permanently installed gauges into it. They were also cheaper than buying a manifold gauge set.

I had the evaporator side of the heat pump connected to the Garden hose with a constant temperature water flowing through it. I did not measure the temperature of that water because I thought it didn't matter.

on the condenser side the inlet water was 65.1 degrees Fahrenheit and the outlet water temp was 81.5 degrees Fahrenheit. so a change in temperature of 16.4 degrees Fahrenheit. I assumed that time and volume of water would be important so I timed the water flow into a jug with a 2 quart measurement and it took 73 seconds to fill it. I measured the power draw from the compressor and it was 258 watts. I did not consider the power draw from the pump in this but I guess for complete accuracy it should be included.

So here's my ugly math

2 quarts = 4 pounds of water

raising 1 pound of water 16.4 degrees would be 16.4 Btu so 4 pounds would be 65.6 Btu.

3600(seconds in an hour)/73 seconds=49.32

65.6Btu x 49.32=3,235 Btu/hour?..... This is where it got ugly.

I found an online calculator to convert my 3,235 Btu/hour into watts and got 948 watts.

If I divide the 948 watts by the 258 watts of the compressor draw I get 3.67.

Does that math out right? would my rough COP be equal to 3.67? I didn't do anything to insulate the condenser or capture heat from the compressor so with some work I could possibly push that up past 4 which seems pretty good for a DIY garage build.

jeff5may · 05-26-24, 08:09 PM

Not bad for a first experiment! That's about 15 eer in USA standard, so about the same efficiency as a non inverter split air source unit. Much better than a $300+ window unit. You can do better, though. Most water source factory units have a COP around 5.

04-09-24, 06:31 AM	#1
scottorious Helper EcoRenovator Join Date: Nov 2011 Location: bloomington IL Posts: 46 Thanks: 0 Thanked 1 Time in 1 Post	Homemade water to water heat pump help I built a heat pump for educational purposes and I want to determine how efficient it was operating. Very roughly I think I figured it out but my method was ugly. Feel free to rip apart my build because I'd love to improve it. Currently using plain propane from a small torch cylinder. I intentionally used a needle valve just to play around and watch what happens when I increase or decrease refrigerant flow on it and thats also why I permanently installed gauges into it. They were also cheaper than buying a manifold gauge set. I had the evaporator side of the heat pump connected to the Garden hose with a constant temperature water flowing through it. I did not measure the temperature of that water because I thought it didn't matter. on the condenser side the inlet water was 65.1 degrees Fahrenheit and the outlet water temp was 81.5 degrees Fahrenheit. so a change in temperature of 16.4 degrees Fahrenheit. I assumed that time and volume of water would be important so I timed the water flow into a jug with a 2 quart measurement and it took 73 seconds to fill it. I measured the power draw from the compressor and it was 258 watts. I did not consider the power draw from the pump in this but I guess for complete accuracy it should be included. So here's my ugly math 2 quarts = 4 pounds of water raising 1 pound of water 16.4 degrees would be 16.4 Btu so 4 pounds would be 65.6 Btu. 3600(seconds in an hour)/73 seconds=49.32 65.6Btu x 49.32=3,235 Btu/hour?..... This is where it got ugly. I found an online calculator to convert my 3,235 Btu/hour into watts and got 948 watts. If I divide the 948 watts by the 258 watts of the compressor draw I get 3.67. Does that math out right? would my rough COP be equal to 3.67? I didn't do anything to insulate the condenser or capture heat from the compressor so with some work I could possibly push that up past 4 which seems pretty good for a DIY garage build. Attached Thumbnails

05-26-24, 08:09 PM	#2
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,431 Thanks: 431 Thanked 619 Times in 517 Posts	Not bad for a first experiment! That's about 15 eer in USA standard, so about the same efficiency as a non inverter split air source unit. Much better than a $300+ window unit. You can do better, though. Most water source factory units have a COP around 5.