Water-to-water heat pump rebuild? - Page 7

Bill Sanford · 01-11-13, 07:02 PM

Attached is a system diagram with temps and pressures after the repair. As I said in my prior post, these temps may not be very accurate. I'm posting this just so you can see a diagram of my WTW heat pump.

I will post accurate data when get my new thermometer.

Bill

Bill Sanford · 01-11-13, 07:04 PM

My drawing didn't get uploaded in my last post.

Here it is again I hope!

AC_Hacker · 01-12-13, 02:53 PM

Quote:

Originally Posted by Bill Sanford

...Here it is again I hope!

Thanks for the write-up, diagram, docs and photos, all very useful.

Best,

-AC

stevehull · 01-13-13, 08:02 AM

Quote:

Originally Posted by Bill Sanford

Attached is a system diagram with temps and pressures after the repair. As I said in my prior post, these temps may not be very accurate. I'm posting this just so you can see a diagram of my WTW heat pump.

I will post accurate data when get my new thermometer.

Bill

Bill, what water flows (on input and output) are you using. The delta T on water flow looks excellent (about 10 degrees F as well on output).

You may have just done it!!

Great job.

Bill Sanford · 01-13-13, 12:43 PM

Quote:

Originally Posted by stevehull

Bill, what water flows (on input and output) are you using. The delta T on water flow looks excellent (about 10 degrees F as well on output).

You may have just done it!!

Great job.

Yes, it was -5 F outside this morning and the system wasn't running too much to keep the house nice and warm, so I know it's working WAY better.

I guess we're sort of energy pigs!

We keep our great room at 72 F and the bedrooms at 67F all winter. Before the repair, when it got really cold, the system would run all night and not turn off until morning after sunrise. When it was cold enough with a low windchill, it wouldn't even keep up and the house on occasion would drop to 68 F unless I turned on the backup 10KW electric spa heaters to add more heat to the load side.

The reason I'm questioning the temps in my diagram is that they don't make sense. I have a commercial 10 GPM flow restrictor on the well side, and the flow rate meter I have on the load side shows about 9 GPM when both zones are flowing. This is the mode that the measurements were taking in on the diagram.

On the well side, the temp differential is 10.8 F, so:
10.8 F temp rise * 10 GPM * 8.325 lbs per gallon * 60 min/hr = 53,946 BTUs

On the load side, the temp differential is 8.9 F, so:
8.9 F temp rise * 9 GPM * 8.325 lbs per gallon * 60 min/hr = 40,010 BTUs

This makes no sense considering that in addition to the heat we have gained from the well, we should also see the addition of the compressor input power on the load side. The compressor draws about 13 amps at 240 VAC, or 3,120 watts. 3,120 watts * 3.412 BTUs per watt = 10,654 BTUs of added electric input.

Based on all this, the load side should be showing the well heat plus the added 10,600 BTU of AC power input unless I'm really missing something.

I'm guessing the issue is a restriction on the well side and that my well flow rate is actually quite a bit lower than the 10 GPM flow restrictor would lead me to believe. There is no easy way for me to measure the actual flow rate on the well side with a 5 gallon bucket right now, but my flow meter on the load side should be fairly accurate, so the load side heat output should also be fairly accurate.

I'm guessing the well flow rate is more like 6 GPM based on the well temp drop through the evaporator, the system heat output and the AC input power.

I know the well side heat exchanger is clean, but in the past I have had some fouling at the point where the well water exits my 3/4" copper and dumps into a 4" PVC pipe that heads over to my low area and dumps. I'll have to check this when it warms up a bit. It's still -2F out right now and the system is working so much better that I'm not overly concerned at this point, but it would be good to tweak it a bit so that it's running as efficiently as possible.

I'm guessing the actual COP is about 3.6. I'm putting in about 10,600 BTUs of AC power into the compressor and about another 650 BTUs of energy pumping water and getting about about 40,000 BTUs of heat out. Not too bad for an old heat pump. With some tweaking, I think it can get a bit better.

Also, I did get my new dual channel digital thermometer and did verify the temp differentials in my system diagram and came up with very similar numbers, so the temps shown on my system diagram are reasonably accurate.

I really did struggle quite a bit trying to get stable, accurate temp readings even with my new thermometer. The thermometer I bought was very cheap, but seems quite accurate. The issue is attaching the thermocouples to the copper water lines in such a way that it reads accurate temps.

What are you guys all using to measure temps and how do you actually connect the sensors to various points to get accurate readings? This is obviously a critical piece in determining system performance.

Again, thanks for following my thread!

Bill

01-11-13, 07:02 PM	#61
Bill Sanford Helper EcoRenovator Join Date: Jan 2013 Location: Northern Minnesota Posts: 32 Thanks: 1 Thanked 0 Times in 0 Posts	Attached is a system diagram with temps and pressures after the repair. As I said in my prior post, these temps may not be very accurate. I'm posting this just so you can see a diagram of my WTW heat pump. I will post accurate data when get my new thermometer. Bill Attached Thumbnails Last edited by Bill Sanford; 01-11-13 at 07:06 PM..