Homemade Heat Pump Water Heater (R290)

[jeff5may]

Sweet! That unit looks like a million bucks to me. My wife would tell me to put the covers back on....
Your dehumidifier is just like mine. I'm anxious to hear how it's going to perform. My guess is that it depends on where this beast will live. Hopefully indoors where it won't get chilly.

[Hv23t]

Here you go... More wife friendly..

[Hv23t]

I fired her up for the first time today..
I haven't really thought of how I'm going to conduct tests yet.
So this is probably meaningless, but for a first run I'm happy.
I'm not sure I trust me thermometer but here is what It was saying.
Time. Temp (water) f
0:00. 67
0:20. 81
0:40. 86
1:00. 90
1:20. 94
1:40. 98
1:51. 101 tripped thermostat
On water heater set
At 100 deg + or -

Hv23t

[Hv23t]

I left the water heater turned on overnight. It got down to 34 deg last night, which I know is way to cold for this thing to work. I just went out and the dehumidifier was off and the water was still at 115 deg. I went and checked the kill a watt and it read out .70kwh. So it ran for an hour and 20 minutes to keep it warm. I'm very happy it turns on and off using the thermostat that was on the WH.

Hv23t

[ecomodded]

Great mod
Congratulations ! on its success.

[Fordguy64]

Wanna make me one?

[AC_Hacker]

Originally Posted by Hv23t

I fired her up for the first time today..
I haven't really thought of how I'm going to conduct tests yet...

Awesome project you have going on here! And your photos will be useful for everyone.

As far as figuring efficiency... if you could let the unit cool down for a while, like maybe a day or two, and measure the water temperature. It may be a bit tricky since the water temperature will be stratified somewhat, hotter at the top, cooler at the bottom. If you had a tiny circulation pump laying about, this would help. But leaving all this aside, just measure the water temperature before you start. Then run your unit with the Kill-a-Watt attached, until it shuts off, then measure the water temp again.

one BTU is the amount of energy required to raise the temperature of one pound of water one degree Fahrenheit

Look up on the Internet how much a gallon of water weighs, and multiply that by the capacity of your water heater... this will give you the number of pounds of water you are heating.

Then, look at the temperature rise from beginning to the end of the run... Let's say it was 67 F in the beginning, and 101 F at the end.

So, in such a case, your temperature rise would be 101 F - 67 F or 34 degrees F.

If your tank capacity is 50 gallons, and if the Internet tell you that the weight of a gallon of water is something like 8.3454 pounds per gallon, then the weight of your water is:

weight = gallons x 8.3454

weight = 50 x 8.3454 = 417.27 pounds.

Then the BTUs would be:

BTU = (weight of water) x (temperature rise)

BTU = 417.27 x 34 = 14187.18 BTUs

To calculate efficiency, you will have to have all the units the same, and since your Kill-a-Watt measures watts (where is a Kill-A-BTU?) and you will want to convert your calculated BTUs to watts, so:

watts = BTU / 3.412 = 14187.18 / 3.412 = 4158 watts

Next, you will need to know how many watts were consumed to heat the water.

if your Kill-a-Watt reads something like 2.34 KW, you multiply that by 1000 to get to watts:

watts = Kw x 1000 = 2.34 x 1000 = 2340 watts.

So, to find your efficiency, you would divide your power out by the power in:

Efficiency = power out / power in

Efficiency = 4158 / 2340 = 1.77

In engineering terms, the above number, 1.77 is called the coefficient of performance or COP for short.

So, you could say:

COP = 1.77

If you multiply that by 100, you get your efficiency as a percent:

% efficiency = COP x 100 = 1.77 x 100 = 177% efficient

Not a bad deal really, you are using one Kw of electricity, but you are getting 1.7 KW worth of hot water, just by preventing junk from going to waste!

But between you and me, I think your actual efficiency will be much greater than that!

Hope this helps...

Great work!!!

(* BTW, that is a nice looking car there in your garage, too! *)

Best,

-AC

[Xringer]

NICE!! Very professional looking hack!

I got confused about how long the HX loop is.?. I don't know how long my A7 HX is,
but I think it's 18 to 20 feet long (36' to 40' total length), it's a smaller diameter too.

I think that it would be easier to seal the HX, if you didn't have to pre-twist the 3/4" 'plug' CCW.
The method used on the A7 is pretty good. See pic.
I'm pretty sure that I could make a plug in my shop, that would fit into standard 3/4" plumbing fittings. Maybe use a flare type nut fitting.?.

~~~
We don't use a lot of hot water (2 retirees) and the A7 uses less than 1 kWh per day.
Which I think is pretty dang good when compared to other heating methods..


Keep up the good work!

[Daox]

Looks great, nice project!

[Hv23t]

Thanks -AC
That helps alot. I'll move the unit into the garage so its in a more stable environment. I might be able to do a circulation pump, seems like I have a sur-flo around here somewhere. I'll see what I can get done this weekend.

Hv23t