Homemade Heat Pump Water Heater (R290)

[Hv23t]

Originally Posted by 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!

Xringer ,

What is the temp in the area surrounding your a7?
The HX is 25 feet of 1/4 copper tubing coiled in the tank. I like the a7's fittings, but I'm not sure I could have made the bend at the end of the loop without kinking it going thru a 3/4" pipe. The 1" plug was a pretty sharp bend but I managed.
1kw a day is amazing, my GE Geospring water heater is rated at just under 1900kwh a year so about 5kwh a day. I wish I could hook the kill a watt up to it. (240 volts)

Hv23t

[Xringer]

Hi Hv23t,
It's about 57F down at the A7 right now. I don't think it's going to get much cooler during the winter.
(It's 35F outdoors right now).

That general area around the A7 can drop down to 55F while it's running,
but the area warms back up a few degrees pretty fast.

I guess it's the slightly warm floor of the basement warming up the air.
So, my A7 ASHP is really a ground-source Geothermal unit..

Maybe I should drill some holes in the floor and implant some long heat-pipes?
Of course they would be dripping wet during the summer months..

Haha, I just shot my IR pistola down into the sump pump holes,
and the temperature two feet under the basement floor is 57F.

The year-round average temp here is 54.3°F and that does have
a large effect on the upper few feet of soil..
So, maybe we'll see the floor drop down to around 54F,
but I'm pretty sure the A7 won't notice it much..

[Hv23t]

Let the testing begin. I ran water thru the tank for a few minutes until the out put was stable at 56 deg. I moved the WH inside the garage where the air temp is stable and wind won't cool anything off quicker. The air temp in the garage is 60.3 deg f.
I will update with results when its done.
Hv23t

[Hv23t]

Well I finished the 2nd test of the system on Friday. I havnt had time to do the calcs on efficientcy till this morning. Here are the results:

Time (hr:min) H2o (f) Watts used

0:00. 56. 0
0:20. 65. 210
0:40. 73. 360
1:00. 78. 510
1:20. 86. 670
1:40. 88. 810
2:00. 89. 910
2:20. 95. 1090
2:40. 100. 1270
3:00. 105. 1450
3:20. 109. 1630
3:40. 115. 1810
4:00. 119. 1990
4:20. 122. 2170
4:40. 125. 2360
5:00. 129. 2550

I used the formula that AChacker gave me to figure out COP.
The COP Changes over time with temp so I just did it for total at each hour.

1 HR. COP=3.16
2 HR. COP=2.65
3 HR. COP=2.69
4 HR. COP=2.32
5 HR. COP=2.10

For my first attempt at something like this I'm very happy with the results. And I know there is room for improvement. #1 is going to do something about a defrost cycle. After about an hour the HX was just a block of ice. What air was able to work its way around it was coming out at 41-45 deg. The dehumidifier only went into its own defrost cycle once at the 1:40 mark. So I think I'm going to install a recycling relay that will turn the compressor off every hr for 4 to 5 minutes. #2 is going to be insulate the feed and return line to the tank HX seperately. Now one line is about 30-40 deg hotter and some of the heat is escaping to the return line befor reaching the tank. After reaching 130 the system shut down at the preset thermostat setting. I was playing with my ir temp gun and found that while the temp was 130 toward the bottom of the tank where the thermostat is located. The top of the tank was at 148 deg. So ac- was probably right about installing a circulation pump to get more accurate numbers. My plan this next week is to install this system inline ahead of the main water heater at my parents house. Essentially being a preheater for the existing one and making sure they don't run out of water if this one breaks down.

Hv23t

[Xringer]

If you want a simple way to turn it off and back on every hour, maybe one of these will work? (at least for 20 hours)..
Timex Electronic 7 Day Timer for Use Inside or Outside The House | eBay

You can set up to 20 off-on cycles for each day.

I'm using one of these to keep my A7 AirTap off during the late night hours.
So far, it's working just fine.
You might want to use one setting to keep the ASHP off between midnight and 4AMish..
Since it's not likely to be needed during those hours..

I like these timers so much (and the price), I just ordered # 4..

[AC_Hacker]

Originally Posted by Hv23t

I used the formula that AChacker gave me to figure out COP.
The COP Changes over time with temp so I just did it for total at each hour.

1 HR. COP=3.16
2 HR. COP=2.65
3 HR. COP=2.69
4 HR. COP=2.32
5 HR. COP=2.10

The reason your COP declines is because the temperature difference between your HX in the water tank and the water gets smaller as the water gets hotter... quite normal.

You are totally successful! For making a heat pump water heater out of junk that you dragged back from the jaws of hell, COP=2.1 is nothing to be ashamed of... and when you average them up, you certainly have genuine bragging rights!

It's possible that you could improve on the performance by using a larger evaporator HX... That just might mean another trip to the dump... maybe a re-design of the basic layout.

But if you built that car that's in your garage, you are no stranger to changing things around.

On the timer thing, you might watch and time the frost build up and melt down. I would suspect that night time would be the worst frost conditions. Then plan your on & off cycles accordingly.

BTW, if you're gonna run your unit with R-290, be sure that the area where it is located has the possibility of ventilation... I'm just thinking about the safety thing. The volume of propane in your unit is pretty small, but best to be safe.

Congratulations on a great job.

Best,

-AC

[AC_Hacker]

Originally Posted by Xringer

Hi Hv23t,
It's about 57F down at the A7 right now. I don't think it's going to get much cooler during the winter.

Tell me what the basement temperature is about Mid February...

-AC

[Hv23t]

I was looking last night for a recycling timer, preferably an adjustable one so I could fine tune my defrost cycle. I was just getting ready to order a cool DIY kit for $18, when I found a couple omron timers on eBay nobody had bid on yet. Well I just finished out bidding the others on both. I got one omron H3CA-8

And the other is a omron H5CR-B, which is a real sweet heart with all the bells and whistles.

And all for less than $30 with shipping.
I love eBay.
Hv23t

[Hv23t]

But if you built that car that's in your garage, you are no stranger to changing things

Yeah I'm used to making things work. Unlike the car I'm hoping this thing will end up saving some money.....

Hv23 t

[Hv23t]

Today I went to my parents house and uninstalled their 50 gallon propane water heater. I've installed two 30 gallon electric units. One is hooked up in the normal fashion. The second which is my homemade heat pump water heater is hooked up in series as a preheat tank. If everything works out fine the heat pump will heat all the water and the other one won't have to do any work. But if it's to cold or they use to much water it will turn on and take over. I havnt got all the electrical worked out with the defrost cycle. In working on that at my house where I have all my tools. Then I will go over and install it after I think I have everything worked out. I'll get the kill a watt on it after its all buttoned up and see how effiecent it turns out to be.

Hv23t