Dxgshpwh (ground source heat pump water heater)

[MEMPHIS91]

I think this data will show more about whats going on.
Minutes - Temp F - Watts - Borehole Temp F
00 - 93 - 00 - 63.3
30 - 96.5 - .17 - 60.8
70 - 102 - .43 - 60.8
90 - 104.2 - .57 - 60.8
120 - 107.6 - .77 - 60.8
150 - 11.7 - .97 - 60.6
180 - 114.2 - 1.18 - 60.4
200 - 117.3 - 1.34 - 60.6
230 - 121.4 -1.66 - 60.8

As you can see my borehole temp hit about 60.8 and stayed there even in the hardest part of the cycle. My COP was around 2.08 - 2.37.

Here is the charge info, what I found was that my cap tube size is stopping me from going past 42 psi suction pressure therefore limiting mass flow and forcing my discharge temp and pressure to increase. With more flow I can heat more water faster at a lower amp draw due to lower discharge pressure.

Borehole temp: 60.6F
Water temp in tank: 96.5F
Discharge line temp at entrance of tank:184.1F
Line temp at exit of tank: 101.7F
Discharge temp at compressor: 186F @ 260psi
Suction line temp at compressor: 64F @ 42psi
Amps:3.55

Borehole temp: 60.8F
Water temp in tank: 107.7F
Discharge line temp at entrance of tank:195F
Line temp at exit of tank: 112F
Discharge temp at compressor: 196.7F @ 300psi
Suction line temp at compressor: 65F @ 41psi
Amps:3.55

Borehole temp: 60.6F
Water temp in tank: 1116.5F
Discharge line temp at entrance of tank:200F
Line temp at exit of tank: 120F
Discharge temp at compressor: 203F @ 310psi
Suction line temp at compressor: 65F @ 40psi
Amps:3.63

My plan is to use the nice hot water I have and either find a larger cap tube or trim this one back some more.
The compressor never seems to be working to hard and casing never got over 205F.

[jeff5may]

Awesome data and conclusions! You are moving quickly in the right direction.

An important part of the heat transfer you seem to be overlooking is the latent heat transfer. From your summary of the hot side, I can tell. Yes, the gas is coming out very hot from the compressor, then quickly drops to the condensing temperature. This sensible heat transfer is tiny compared to the heat released when the gas condenses to a liquid. Just as water temperature rises quickly to boiling temperature and takes a long time to boil off completely when set on a hot plate, the reverse is also true. Your uberheated discharge gas will quickly be quenched to its boiling point. This sensible heat transfer amounts to less than 10 percent of the total transfer, even with your massive superheat.

The refrigerant will then remain at boiling temperature until all the gas distills. Since a temperature change cannot be measured while the refrigerant is changing phases , this is known as latent heat transfer. The latent heat transfer is where all the magic and "free energy" is. It cannot be measured directly. In a lab, you could catch all the liquid leaving the condensing hx and weigh it to calculate the latent heat of condensation. With this rig, it is much easier to measure the temperature rise of your water tank and calculate the heat that way.

Once all the gas has condensed, the liquid goes back into sensible heat transfer range. It quickly cools to a temperature between the condensing temperature and the tank temperature. This heat transfer is teensy in your system. It can be calculated directly.

The latent heat transfer amounts to greater than 90 percent of the heat transferred into your water on a bad day. On a good day, this value is around 98 or 99 percent. Maximizing this fraction is the main goal. Some superheating and subcooling is necessary to keep the system stable, but too much of either eats at efficiency and COP. Propane has not been researched as throughly as the conventional refrigerants, but it has been found that superheat and subcooling are not as undesirable with propane.

[MEMPHIS91]

Wow tons of info there, I did a lot of research on what you were saying.
Thank you.
So the plan is to cut off 2 inches of cap tube and start her back up. I should have a measurable change that I can calculate to make a final cap tube adjustment.

[NiHaoMike]

I'd recommend changing to a TXV if you can find one of the right size. About 1/2-1/3 ton R22 would be about right for your application and preferably get one that is adjustable with external equalizer.

[MEMPHIS91]

Ok here is the data for the test with cap tube trimmed 2 inches. Ignore the first number,
I think I had left over heat still in the system that helped that temp a lot.

Time in Minutes - Water Temp F - Watts - Borehole F
00 - 85.5 - 00 - 63.1
30 - 96.2 - .20 - 60.8
70 - 104.6 - .45 - 60.4
90 - 106.9 - .58 - 60.8
120 - 109.8 - .78 - 60.8
150 - 112.2 - .97 - 60.8
180 - 115.5 - 1.17 - 60.8
210 - 118.2 - 1.37 - 60.8

Water temp in tank:85.6
Discharge line temp at entrance of tank:174.5
Line temp at exit of tank:92.3
Discharge temp at compressor: 178 @230 psi
Suction line temp at compressor: 46 @ 48 psi
Amps: 3.29 Borehole temp: 63

Water temp in tank:96.5
Discharge line temp at entrance of tank:184.3
Line temp at exit of tank:101.5
Discharge temp at compressor: 186 @ 250 psi
Suction line temp at compressor: 45 @ 46 psi
Amps: 3.57 Borehole temp:60.8

Water temp in tank:107.7
Discharge line temp at entrance of tank:192.9
Line temp at exit of tank:111.4
Discharge temp at compressor: 194 @ 265 psi
Suction line temp at compressor: 57 @ 43 psi
Amps:3.6 Borehole temp:60.8

Water temp in tank:116.5
Discharge line temp at entrance of tank:197.5
Line temp at exit of tank:119.8
Discharge temp at compressor:200 @ 275 psi
Suction line temp at compressor: 58 @ 40 psi
Amps:3.72 Borehole temp: 60.8

As you can see my pressure maxed out at 43psi, but dropped back down to 40psi by the end. The 2 inches drastically helped my discharge pressure.
I really think I needed more charge in the system but going over 3.7amps is a little more than I wanted to. I weighed the bottle of propane before
and after total of 5.4 oz.

NiHaoMike I'm really starting to think I like the txv idea best. BradC said it was a bad idea, and I would for sure like more info on it.
Maybe something like this, http://www.amazon.com/gp/product/B00...A22ZN1B182ACTT ??

[jeff5may]

In your setup, a txv is going to be trying to be a fixed orifice, running full bore, until something bad makes it close. This something bad is going to be excessively high liquid line pressure or a flooding evaporator. You might as well just install a CPEV (constant pressure expansion valve aka flowrator) or spring regulator. If you do get a valve, make sure it is adjustable and rated for high temperature operation, close to your borehole temperatures.

As I suspected, you are quickly moving in the right direction. Trimming your cap tube dropped your discharge temperatures across the range and dropped your suction superheat as well. You just got closer to your optimal cap tube length. The heat flowed into the tank faster, taking 3 hours instead of 4 for a 30 degree rise. My guess is your power usage decreased the same amount.

Sorry for the multiple long posts, not trying to hijack the thread. Not trying to tell you what to do, just trying to give you the info you need to make good choices. You are just steamrolling through this project, and I hate seeing fast doers getting bogged down in details and theoretical maybe-mess.

Are you sure you haven't done this before?

[MEMPHIS91]

Ah ok so no TXV. Looking at my numbers I still think I can go shorter on the cap tube. When first starting running test the cap tube would "squirt" and visibly shake at about 14 psi. That shaking doesn't start til 27psi now.
I am wondering if a larger diameter and longer cap tube might not work better for this.

[stevehull]

Memphis - why would you go to a LARGER cap tube and MORE length? Flow resistance is mostly by reductions in diameter (thinner cap tube) and a longer tube. Or do you mean a thinner cap tube and more cap length (more resistance, less gas flow)?

Am confused, but I highly enjoy your posts and your work.

Steve

[MEMPHIS91]

Steven, based on my understanding (which might be totally backwards at this point) I need more gas flow through my condenser, therefore I need a larger cap tube. I can loose some discharge temp and pressure to gain a more efficient mass flow through the condenser. But you might be seeing something I'm not.

[stevehull]

More gas flow will result from a larger diameter cap tube and shorter cap tube length. That said, tiny increases in cap tube diameter (10% increase) will double gas flow through it. Might be far easier to mess with length rather than change cap tube diameter.

I have just taken apart an old dehumidifier and am looking at the compressor with a lot of added interest. Sadly, here in central Oklahoma, we have a LOT of underground rock - some very hard.

But I do have a spare water well (4 inch pipe diameter) that has 65 F water in it up to within 25 feet of the surface (210 feet deep). The thought of contaminating the water well with compressor oil - if anything ever went wrong - has slowed me down.

Keep up the work, especially your documentation. Your work is being read round the world!

Steve



Steve