Bob, first thanks for the reply.
I couldn't find your post from 10 Jan, the closest I found was your post yesterday (17 Jan). I think that I understood most of that post. Key to that post is if you are injecting back to the same depth as pumping then the head pumping energy is only the friction losses (although power for priming is needed although not often).
In my case the two stages of heat pump are as I understand it in are parallel. I understand about the not sizing the pump for irrigation, it wasn't sized for that, the ability to use for irrigation is only a bonus, and will be relatively small percentage of the usage. The irrigation is only likely to be one or two hours a week for 3 months of peak summer use, compared with 25 to 40% duty cycle for the 3 or 4 months of heating season for the heat pump. So a second pump does not appear worth it. However as you see further down I think that lowering the pressure is practical for the GSHP (but that would make irrigation impractical).
The well pump is Goulds 13GS07, and the motor is 3/4 HP 3 wire Franklin 214 5079 004S.
As I understand the pump selection
13GS07 means optimal rate is 13 gpm (with a range of 4gpm to 20gpm), and 07 means 3/4 HP. This data is from the manual.
A 10GS may have been better with a range of 3 to 16gpm (given that 2nd stage heat rarely kicks in demanding the full 14 gpm).
Given that the well is 56ft deep and the pump is in 20 feet of water, I assume that means a static head of about 30 feet. I'll round up to 40 ft to allow for some draw down. Although since I have an injection well the friction loss is the key thing.
Flow rates for Goulds 13GS07 from Goulds manual
............20 ..40 ..60 ..80 ..100 ..120 ..140 depth to water -->
.........0................ 19.7 18.5 17.0 15.0 13.2 11.5 8.5
.........20..... 19.4 18.0 16.4 14.8 12.9 10.5 6.0
.........30 18.9 17.5 16.0 14.6 12.5 10.0 5.0
.........40 17.4 15.9 14.4 12.4 9.7 4.0
.........50 15.4 13.8 12.0 9.5
.........60 13.2 11.5 8.5
Shut-off PSI 86 78 69 61 52 43 35 26 17 8
Flow rates for Goulds 10GS05 from Goulds manual
............20 ..40 ..60 ..80 ..100 .120 .140 .160 .180 .200 .220 depth to water -->
.........0 ................16.0 15.3 14.3 12.8 11.3 9.0 6.4
.........20 .....15.9 14.9 13.8 12.5 10.8 8.3 4.8
.........30 15.7 14.6 13.5 12.3 10.5 7.8 4.0
.........40 14.5 13.4 12.0 10.3 7.5 3.0
.........50 13.0 11.5 9.8 7.2
.........60 11.3 9.0 6.4
Shut-off PSI 89 81 72 63 55 46 37 29 20 11
I don't know or understand what PSI value I need for the heat pump, but I know that the "Fluid Side Pressure Drop" across the heat pump is 7 psi with only one compressor (of two) running at 15gpm, so I would guess more drop with both running but maybe not, and there needs to be remaining pressure to discharge to the return well. The pressure at the bladder is set to about 50 PSI.
It looks to me like a 10GS05 (10 gallons ideal rate, at 0.5HP) could have done the job more optimally. But I don't know what PSI value is needed at the heat pump.
There is a table in the spec sheet for the heat pump:
Fluid flow Pressure drop
8 GPM 3.5 FOH 1.51 PSIG
12 GPM 7.2 FOH 3.13 PSIG
16 GPM 12.1 FOH 5.25 PSIG
18 GPM 15.0 FOH 6.49 PSIG
22 GPM 21.5 FOH 9.32 PSIG
If I understand this table right, then at about 14 GPM roughly interpolating that will be 4 PSIG or about equivalent to an extra 10 FOH (feet of head). (I think that FOH means feet of head). The measured drop was 7PSI at 15 GPM. Even allowing for 10PSI drop across the heat pump, I think that means the 0.5 HP pump is plenty sufficient.
So one of the key questions become:
What pressure is required at the heat pump. As I see it, the pressure required is the drop across the heat pump plus what ever pressure is required by the discharge well, and the discharge well is unlikely to require more than 10 PSI (it is only 40 feet deep with at most 20 feet of water in it). So the pressure at the bladder need not be more than 20 PSI (plus unknown for friction loss) 10 PSI for heat pump and 10 PSI for discharge well.
Very simply I have 30 feet of head, plus I need about 20 feet of equivalent head to push the water through the heat pump and into the return well. That's only an equivalent of 50 feet of head. The 10GS05 can pump 16 gpm at 80 feet of head and is thus still over kill but 0.5HP looks like the maximum that I need, and maybe the smallest that I can buy?
Should I adjust the pressure sensor down to 20 PSI?
If I was to ask the well guy to swap my 1 month old 3/4 HP motor and 13GS07 for a 10FS05 pump and 1/2 HP motor or even a 10FS05R with 1/3 HP motor then would that likely do the job? And would that use much less power, or does the Mono Drive mean that I've just paid for over spec motor and pump but the power consumed won't be much different?
I really don't care about paying over the odds for a larger pump and motor and Mono Drive, but I do care very much if it is using more power than it should. The entire system is net metered with a large photovoltaic solar array, and 1KW of DC power costs between $4000 and $6000.
If the pressure at the bladder is set at 55 PSI, and the drop on the heat pump is about 10 PSI plus say 5 PSI for other pipes, does that mean I'm just pooring 40 PSI worth of energy straight down the return well for no good reason?????
I've just done an experiment:
At 55 PSI and 15 GPM current draw is 5.2A so 1.25KW (at MonoDrive input, power factor is 1.0)
At 55 PSI and 7 GPM current draw is about 2.8A so 672W
At 45 PSI and 7 GPM current draw is about 2.4A so 576W
I cannot drop the pressure or gpm below this because the system cycles causing hammering.
If I interpolate to 20 PSI at 7 GPM thats about 225W, which sounds about right for 3 tons, since I read that about 75W pump power per ton is about right, and over 100W pump power per ton is bad. So the system appears to be set to use x5 the pump energy really required!
So I think that I should ask (or insist) that the well installer to swap the pump and motor for something a lot smaller. Then I just forget about using it for irrigation also since the pressure would not likely be enough.
Does a 10GS05R require a 1/3 HP motor or a 1/2 HP motor?
Would the MonoDrive work witha 1/3 HP motor, the manual say 1/2 3/4 or 1?
Should I be looking at 1/2 HP or 1/3 HP?