Water Source Heat Pump Deep Pump Sizing

[Greg-VA]

After reading (lurking) forums on well sizing and geo thermal heat pumps, I have not found a central source of expertise for proper sizing a deep well to a GSHP. Standard single speed pump coupled to a good size pressure tank is old tech, but dependable. The newer variable speed pump solutions sound expensive and maybe too short of a track record. I am willing to spend a little more on electricity use if less on more costly fancy electronics and repairs for the long term cost of ownership.
So I found this forum to be the most helpful, on many topics, and thought that I would start with the expertise here.
I have a 405ft well with static level about 15ft from cap (cap sits 14in above ground and about 70ft form house). It is 6in diam. well. I will be using a Addison (www.addison-havc.com) water source heat pump - 3tons. Specs list 8.6GPM at 4.7PSI/10.9Ft.HD.(?). It is an open loop system - well to GSHP to lake.
Well supplies domestic water use to house - 3.5 baths, 1 kitchen, 2 outside faucets. Well was hydro-fracted at 405ft due to only 3GPM. Drillers siad I had a good 12-15GPM.
I have not found anyone locally who will/can size this system. Most guys just say throw a 1HP of their choice and it will be fine.
Any suggestions a system solution or the right methods I can use to size this greatly appreciated.
P.S. I am the builder of this house and the owner, have a hand in everything!!! and still fightig the county to NOT hook up to their water 1000ft away! What a water bill a GSHP that would be!!
Thanks to all for suggestions!:)

[sammyhydro11]

Greg,
it sound like this well supplies both the geothermal system and your home. The pump that i reccomend would be a 7 gallon per minute 1 horse power pump. It will start off giving you a good 15 gallons per minute at 40 psi but wont take out any more than what the well produces because the gpm will eventualy level out to the production of the well as the water level drops. That would be the correct pump for that well and what it produces for water. My question for you is how long does the heating sytem call for that 8.6GPM??

As far as the flow for the geothermal unit,i'm not too sure what type of valve you could put in to regulate the water to that 4 psi. Maybe valveman could help you out there.

SAM

[Bob NH]

Water requirements for a ground source heat pump are so different from the requirements for a household supply that you should find a way to make them both work efficiently.

You don't want a household water supply pump working at 150 ft of head to be wasting energy pumping water through the GSHP system.

Because the GSHP will be discharging to the lake, the most efficient way to do it is to run the discharge pipe to below the surface of the lake, and use a large pipe. I would use at least a 1 1/4" pipe for suction and discharge to keep the head loss at a minimum.

A 1 HP pump for the GSHP is WAAYYY to big. The problem is that most water supply pumps have far too much head.

You need to determine how much drawdown (final water elevation) you will have when drawing water for your GSHP. Then, you need to determine the elevation diference between the lake surface and the drawdown level in the well.

You also need to determine the elevation difference between the highest point in your GSHP and the surface of the lake to be sure you don't get cavitation in the heat exchanger.

With that information, an engineer or a knowledgable pump supplier can select an efficient pump.

For example, at 10 GPM and 20 ft of head, you need only about 0.05 horsepower in the water to serve your GSHP system. At a terrible efficiency of 20%, that would be a 1/4 HP pump.

If the drawdown is too great for a centrifugal pump located on the surface, the best solution might be a submersible with an 1800 RPM motor to get the head down to a reasonable level.

You could serve your household water supply needs with a simple jet pump or a mustistage centrifugal pump with suction connected to the discharge of the GSHP system. That pump should be selected based on the head and flow that the GSHP pump will deliver, and your requirements for household use.

It might be possible to put two submersibles in the 6" well. That would let the two pumps operate independently, perhaps with interlocked controls if the well won't support both flows at the same time.

Neither pump should be 1 HP. A 3/4 HP submersible such as the Goulds 10GS07 will deliver 12 GPM at about 70 to 80 psi, depending on drawdown, for your water supply.

[sammyhydro11]

That 10GS07 will only continue putting out that 12GPM @ 60 to 70 psi as long as the wells drawdown stabilizes at roughly 60'. Most rock wells get more than 50 percent drawdown before the pumping water level stabilizes. So the pump need to be sized according to that. I guess what he realy needs is a pump test. I did a pump test on a well this past summer that was 380' deep and produced 55GPM. The drawdown didn't stabilize until 230'.

SAM

[Bob NH]

That 10GS07 will only continue putting out that 12GPM @ 60 to 70 psi as long as the wells drawdown stabilizes at roughly 60'. Most rock wells get more than 50 percent drawdown before the pumping water level stabilizes. So the pump need to be sized according to that. I guess what he realy needs is a pump test. I did a pump test on a well this past summer that was 380' deep and produced 55GPM. The drawdown didn't stabilize until 230'.

SAM
He needs to do the drawdown test at the expected pumping rate and daily demand. There is no point in testing for drawdown at 55 GPM if the requirement is 5000 gallons per day for the GSHP with a peak hour demand of maybe 900 gallons, which is about what he says he needs.

[sammyhydro11]

Bob,
i was simply using that pump test that i did last summer as an example to show people how much drawdown you can get from rock wells before they stabilize.I know his well dosen't produce 55 gallons per minute.

SAM

[speedbump]

I like the two pump idea. My friend down in Punta Gorda has that same system in a five inch well. One is a 4" and the other pump is a 3". One for the house the other for sprinklers. His water is so nasty, he has a whole house RO, that's the reason.

I don't like to see one pump do it all on a system that is so varied. House use would be around 5gpm at the peak times for the most part and the GWHP is using a steady 9gpm most of the time in winter and summer if it cools also. This is at or near the wells expected max flow.

A cistern might also be considered, for the home only, then let the pump keep it full and keep the GWHP satisfied too. This would guarantee enough water for the home while that GWHP is cranking away. Then the little 1/2hp 10 gpm submersible would be the perfect pump for the job.

bob...

[Greg-VA]

Bob & Sam,

Thanks for the replies! Much to contemplate and learn from all the info. I am trying to find my well report that had to filed w/the county. It has specs on drawdown, GPM, etc.
There is a spring "Home Show" in Richmond, VA on the Jan 19th. I will attend this, as there will be a number of trades that I need to contact for info and estimates. Trades also offer show/spring discounts at these. I am sure that I can find several local HVAC and/or plumbing trades experts to do estimates after an onsite survey.
When I get this info, should be about 4 weeks from now, I will post back their "solutions" for review and comments here.
I love problem solving and learning from everyone in the different trades. Makes me more knowledgeable and better understand how to relate and coordinate the various trades - hence, a better builder!
A GSHP certainly does cross-over and combine several different and/or related trades. I expect several different solutions.
Thanks again, and I will post back on this in several weeks. :D

[bravo454]

It appears that the flow requirements listed are for a closed loop system in which there is a small circulating pump to move the fluid in out of the ground loop. I have an open loop 5 ton GWHP similar to the one you indicated and it is connected directly to the the house well water supply set 40/60. The water is then dumped into the river that flow in front of my house. This system requires 8 gal/min and has been in operation for 18 years. The rule of thumb for GWHP operation for an open loop system is 1.5 gal/min per ton. The flow rate is nearly double for a closed loop system.

[speedbump]

The rule of thumb for GWHP operation for an open loop system is 1.5 gal/min per ton. The flow rate is nearly double for a closed loop system.

I was always told 2.5 gpm. for well systems. Why less for closed loop systems? That doesn't make sense to me. It would seem like the closed loop system's water would be warmer than the well water due to friction. Of course if your heating that would be a good thing.

bob...

[sammyhydro11]

Speedbump,
i just got done working on a geothermal unit where the pump wasn't installed right. The guy has a well that is 600' deep with a twin pipe pitless adapter. The heating system discharges water back down the well through the 1 1/4" on the pitless. I guess originaly the well was only 125' but the guy decided to go with the geothermal system and the design called for the well to be drilled to 600'. They did this so the water would stay cool in the summer and the cool water below wouldn't be influenced by the warm water being discharged. It ran off a Sub Drive 75 that converts the 230 volt single phase to a 230 volt 3 phase and brings the motor up to the speed of a 3H.P. motor.The pump was a 18GS10. It works good but the guys that installed it hung it on 1 1/4" polly pipe and didn't use any wire guides. Also they installed the polly pipe to the pump on a slight angle so when the pump hung in the hole it was resting on the inside wall of the well rubbing every time the pump kicked on. The motor had 2 holes in it and the wire was bad. I couldn't believe it! I thought the unit was interesting but was amazed by the lack of good craftsmanship on the installation.

SAM

[speedbump]

I'm trying to imagine how many times that motor stopped and started to wear holes in a stainless motor. The wire I could see, but the motor? Wow. It's probably a miracle it didn't cycle it'self to death before the holes showed up.

bob...

[sammyhydro11]

Speedbump,
the whole pump and motor was right up against the inside of the well. The top portion of the wet end had just as much wear as the bottom portiion of the motor. I think every time the pump kicked on the bottom portion of the motor would smack the inside of the well and kickout causing the wet end to hit up top. These guys just pulled this up 9 months ago and replace the braided wire with UF cable. I just can't believe that they didn't pick up on the fact that this pump was sitting in the well like it was because of the way the polly was fastened to the pump. Needless to say i installed the pipe so its was perfectly vertical and also put in 2 TA's above the pump.

SAM

[speedbump]

Sounds like these guys should stick to drilling and leave the pump installs to the pros. It's these types that give the rest of us a bad name.

Sounds like you got them fixed up though Sam. Keep it up, your customers will definately appreciate your efforts.

bob...

[bravo454]

The reason for 1.5 gal/min versus the 2.5 gal/min open versus closed system is that the open systeem is using the water only once and will stay at a constant temp throughout the year. The closed system due to the thermodymnamic properties of the earth and the tubing used to bury in the ground, the fluid temp will drop in the summer and rise in the winter as the demand for cool/heat continues for long periods of time. The flow rates need to comensate for these temp changes in the closed system.

[valveman]

Sammy, those Sub Drives and Mono Drives use a little go/no go switch instead of a pressure transducer. So they can never lock in on any one speed. They just continually ramp up and down to produce the varied amount of water being used. Put your amp meter on an incoming power leg and you will see it bounce up and down about 45 times per minute. You are right that it probably would not have caused a hole in the pump or motor housing if the pump had been hung straight. However, the motor torqing 45 times a minute witch is a million times every 21 days, will still probably wear out the wire down hole in short order. I hear of lots of people pulling these out after 6 months or a year and saying that the wire looked 20 years old.

[sammyhydro11]

yeah the guy was happy with the work. I was told that double jacket wire was the way to go but once i told him the price and how long it would take to get it the guy said no way. So i used the braided wire,wire guides every 30',and taped the wire every 7'. I hope it holds up.

SAM

[Raucina]

Just a few foolish observations - if the well is 500' deep why not put the water back into the well? Seems like enough earth to absorb the temperature change.

I tape every 5 feet and use standoffs every 25 feet on all wells. Must be why they last so long.....

[Bob NH]

The reason for 1.5 gal/min versus the 2.5 gal/min open versus closed system is that the open systeem is using the water only once and will stay at a constant temp throughout the year. The closed system due to the thermodymnamic properties of the earth and the tubing used to bury in the ground, the fluid temp will drop in the summer and rise in the winter as the demand for cool/heat continues for long periods of time. The flow rates need to comensate for these temp changes in the closed system.

In the summer, the AC is taking heat from the house and putting it into the water, raising the temperature of the water. If the water is pumped back into the well, then the temperature will slowly RISE in the summer.

In the winter, the heat pump is taking energy from the water, causing the water to be cooled, and discharging it to the house. If the water is put back into the well, then it will cause the temperature of the well supply to drop.

The most effective way to circulate the water to the ground is to inject it into the aquifer at some distance from where it was withdrawn from the aquifer. It then tends to flow through the aquifer from the injection point to the withdrawal point at the well.

If the water level in the well is much below the surface the systems use a lot of electricity you usually don't recover all of the available head when the water is reinjected.

[speedbump]

The problems with injecting back into the well is the oxidation of iron and other minerals that tend to plug the well up in short order. Especially screened wells.

I have been around GWHP's since I was a kid, owned one that came with the house. I still don't see why anyone would want one.

bob...

[Bob NH]

If I had a good gravel aquifer with water at 25 ft below the surface, with enough space to reinject the water about 100 ft away, I would use it. If you have that kind of water source, you can extract or add heat with minimum pumping power. The water would not be exposed to air so it would should not increase precipitation of iron.

[speedbump]

I suppose if it's done right, the water wouldn't have to see any air. I've seen the pipe going into a well seal then running the rest of the way down the casing through a column of air. With iron in the water you can imagine what the inside of that casing looked like.

bob...

[speedbump]

The problem arises when the return line is just stuck through the top of a well seal with no droppipe into the water below. This allows for a lot of oxidation and a real nasty looking casing in a short time.

bob...

[Bob NH]

I suppose if it's done right, the water wouldn't have to see any air. I've seen the pipe going into a well seal then running the rest of the way down the casing through a column of air. With iron in the water you can imagine what the inside of that casing looked like.

The problem arises when the return line is just stuck through the top of a well seal with no droppipe into the water below. This allows for a lot of oxidation and a real nasty looking casing in a short time.
bob...
Someone can always find a way screw it up, but with the vast amount of information available on the internet, the knowledge is available to do it right.

http://www.energystar.gov/index.cfm?c=geo_heat.pr_crit_geo_heat_pumps
http://www.geoexchange.org/
http://www.geoexchange.org/publications/maryland.htm

[speedbump]

In your opinion Bob, do you think the GWHP's (ground water heat pumps is how I remember them) are actually worth the extra money and maintenance required? I had one not too many years ago and didn't see any savings whatsoever. The only reason I didn't change it out to air/air was the fact I was in the pump business and could keep it working cheaper than the average homeowner.

Do you think they save that much in electricity in heating and cooling?

bob...

[Bob NH]

In your opinion Bob, do you think the GWHP's (ground water heat pumps is how I remember them) are actually worth the extra money and maintenance required? I had one not too many years ago and didn't see any savings whatsoever. The only reason I didn't change it out to air/air was the fact I was in the pump business and could keep it working cheaper than the average homeowner.

Do you think they save that much in electricity in heating and cooling?

bob...
Air-to-air heat pumps don't work well when the air gets down near freezing. Water to air heat pumps work well for heating if the incoming water is above about 45 F (warmer is better), and they work well for cooling if the water is a few degrees less than ambient air.

Ground water heat pumps have a coefficient of performance greater than 3 (see first link in my previous post). That means that you get more than 3 kiloWatts of heat effect from one kiloWatt of power. That is a big saving if you are using electric heat. With fuel prices going up, it approaches the cost of gas or fuel oil in some areas.

It will become even more important when we implement a coordinated energy and environmental policy that includes building more nuclear power plants to reduce both oil imports and production of greenhouse gasses. Also, the can't export many nuclear power plant construction jobs to China.

In cooling applications the ground water systems have energy efficiency ratios (EER) in the range of 14 to 16 BTUs per watt-hour, which corresponds to a coefficient of performance of about 4.1 to 4.7.

[speedbump]

Here; everything is electric and gas and very little gas. This keeps the electric costs less than they would be in the north.

I am just curious with all the maintenance required with the well, pump, solonoid valve, return water (depending on where it is discharged) etc. Is it really that much of a savings. And the added initial expense for the installation.

bob...

[Bob NH]

Here; everything is electric and gas and very little gas. This keeps the electric costs less than they would be in the north.

I am just curious with all the maintenance required with the well, pump, solonoid valve, return water (depending on where it is discharged) etc. Is it really that much of a savings. And the added initial expense for the installation.

bob...
If I had a good source of ground water as I described earlier, my design for the ground water source would be as follows:

The source pump would be a low-head submersible in a well in a shallow aquifer where the static water level is not more than about 30 ft down. The return pipe would be into the same aquifer around 100 ft away (that is just a guess without calculation), and the pipe would be submerged in the aquifer. That would keep the pressure at the top of the return pipe above zero psi absolute and would allow recovery of the elevation head. The energy cost would be the inefficiency of the pump, the losses in the pipe and heat exchanger, and the inlet and discharge losses in the source and injection wells. The pipes would be large enough to keep the pipe losses small.

The pump would be matched to the heat exchanger requirements and there would be no flow control. The pump is on or off depending on demand.

At an energyefficiency ratio of 14 for cooling, a 5 ton (60,000 BTU/hr) unit would require about 4.3 kW, or about 15,000 BTU of electrical power, so the heat exchanger would have to remove 75,000 BTUs per hour.

At a temperature difference of 10 degrees F, it would require 7500 # per hour of water, or about 15 GPM. If you take 40 ft of head loss through the water system, that is 300,000 ft-# per hour or 0.1515 HP or 0.113 kW. With a pump at a wire-to-water efficiency of 40 percent, the pumping power is 0.283 kW.

Add another .283 kW for each additional 40 ft to water. For that condition, skip the injection well unless it is necessary to recover the water.

That number tells you how much is saved by the return well. If there is enough supply so the water can be wasted without reinjecting it, then maybe 20 ft of head is recoverable with the injection well. The additional pumping power to discharge it at ground level would be about 0.14 kW. If the water can be wasted and the cost of the return well (probably just a 2" pipe driven into the aquifer) is more than about $1000, it is probably not worth it.

The advantage of groundwater cooling for A/C is that you are operating at far lower temperatures in the condenser, and therefore, with much less power for the compressor.

The economics of the system would have to be calculated. I suspect that for the large multi-million dollar places that I see reported in Florida, a ground water source would be economical. I don't think it will be economical for a 1200 square foot place that uses one condensing unit.

[speedbump]

That was the answer I suspected.

In the million dollar + homes that are being built here, the other problem would be the water itself. We have requirements that are constantly changing. 25 years ago if you had a GWHP, you could discharge the water through sprinklers anytime of day or night any day of the week. Everyone else had water restrictions. Now, (last I checked) you have to reinject it into the aquifer. And you will do everything their way and that means more permits etc. etc.

Of course if these folks in the million dollar + homes are worried about their heating and cooling, they should be far more concerned about their taxes and rising insurance costs. That's what's killing everyone.

bob...

[mbartosik]

I have just had fitted a 5 ton (two stage) heat pump with open loop.
The spec sheet for the heat pump says 7 gpm on stage 1, and 14 gpm on stage 2. Stage 1 is about 3 tons, stage 2 is another 2 tons.
The water supply will be two stage (tomorrow) by fitting a second valve for stage 2 demand from the heat pump.

The well driller said that the well is capable of much more, so I presume that there is minimal draw down.
The source well is 56 ft deep and the motor is sat in plenty of water (about 20ft I think).
The discharge well is 70 feet away from the source, with about 50 ft of pipe between each well and the heat pump.
I have a large rubber bladder tank in the water circuit.

I have a few questions about optimal operation (my aim is to conserve energy).

The well motor is 3/4 HP variable speed with a Franklin Monodrive. The pump and motor appear capable of more than the 14 gpm required for heat pump. Most of the time I only use stage 1 of heat. At 14 gpm a current clamp on the input of the mono drive shows a steady 5.2A (1.25KW power factor is 1.0). If I reduce the flow to 7 gpm the current flow drops to about 2.8A (varies between 2.6 and 3.2A or 0.67KW). If I reduce the flow to 6 gpm or lower the pump cycles off for a second or two each minute (bad).

1) I am a little bothered that the pump motor has been over sized an I could have used a 1/2 HP or even 1/3 HP motor. Any comment?

2) Are the heat pump manufactures (Flordia Heat Pump) asking for too much gpm? (Higher gpm makes their COP value look better, but wastes KWh on the well pump)

3) Would a 1/2 HP or even 1/3 HP variable speed motor use much less KW? A smaller motor would work closer to its upper limit more of the time which is typically more efficient, or is the difference marginal?

4) I saw a post that the Franklin Mono Drives ramp the speed of the motor up and down. What's the alternative? I'm already unhappy with the Franklin Mono Drive because it consumes 40W constantly on standby (energy efficiency is my aim). It is probably too late to do much now, but I'd like to hear the alternatives.

5) I would like to conditionally switch the Franklin Mono Drive on when the heat pump or irrigation system call for water. The aim is to avoid the 40W standby loss of the Mono Drive. I could do this via a relay powered from the fan control of the heat pump and the pump control of the irrigation system. Any comments?

6) I'm planning on connecting the irrigation system to the well. My plan is to use only the one pump. Local permits are not a problem. The question is should I connect on the supply side or the discharge side of the heat pump?

If I connect the irrigation on the supply side, then the well pump will likely be able to provide for the heat pump on stage 1 and irrigation together, and then the irrigation can work independantly of the heat pump. For stage 2 (which is rare) the heat pump may be short changed, but demand from stage 2 would be hyper rare at the same time as irrigation.

If I connect on the discharge side of the heat pump, then the heat pump will always have enough flow for both stages but then I either need to have the heat pump on to operate the irrigation or have the irrigation system open the heat pump's supply valve. Also unless I shut off the pipe to the discharge well with another valve the pressure seen by the irrigation system would be lessened.

thanks
Mark

[Bob NH]

Are the heat pumps really staged (discharge of one to suction of the other) or are they in parallel (both operate off the same evaporator)?

Monodrives allow vendors to avoid matching the pumps to the system and cover any errors in head loss or flow calculations. You pay the bill for the monodrive and they avoid the engineering effort and risk of screwups.

If you look at my posts on this thread you will find that my recommendation is that pumps used for heat pump systems should not be selected or operated to produce enough head for irrigation. That is a waste of energy.

I discussed how a combined system should be set up with a second pump to take water from the heat pump source for irrigation, and manage the irrigation and heat pump operation with controls. You can set heat pump or irrigation priority and the system will water the lawn and heat the house without your intervention.

A 3/4 HP pump is probably more than you need unless the heat exchanger is sized to produce a lot of pressure drop. A 3/4 HP Goulds 10GS07 delivers 14 GPM at 175 ft of head (75 psi). A 10GS05R (really a 1/3 HP pump) delivers 14 GPM at 80 ft of head (35 psi). I don't have the service factors on those motors so they may be operating at more than the nameplate horsepower.

The only reason I can see for selecting a 3/4 HP pump would be to be able to irrigate with the same pump, which is an inefficient way to operate a heat pump system. That is also the only reason that I can see why you would have a bladder tank. If a variable head pump can't be matched to a heat pump system without a bladder tank, then the designer should get some engineering help with his design.

Your MonoDrive pump may not be operating at its most efficient point. I made a calculation for a 5 ton heat pump source in my post of January 10. You can substitute your own numbers.

The pipe to your injection well should go all the way down into the static water level so that you recover the available head from the heat exchanger down to the water level in the aquifer. The pipes should be large enough to keep velocity, and therefore pressure loss, low.

I can't tell you exactly what pump you need because I don't know the pressure drop in the heat exchanger. If it is all one heat exchanger, then the pressure drop will go up dramatically when you double the flow.

[mbartosik]

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 -->
.........PSI
.........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 -->
.........PSI
.........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?


thanks
Mark

[speedbump]

I'm not a fan of variable speed pumps and am not sure if you intend on using this water for your home as well as your irrigation and heating/cooling. But like Bob said, using one pump to do all three is never going to be economical. If you had a large enough well, you might be able to put two or maybe even three pumps in it.

If the pipes were large enough going through this heat pump, you might be able to discharge all or some of the discharge water to the sprinklers killing two birds with one stone. I'm sure this could be done with a little engineering. This way you would only have two different flow rates for the same pump.

Three wells and three pumps is the economical solution. But the up front costs could be a bit staggering.

bob...

[mbartosik]

The point about having the variable speed was to be able to match the heat pump at between 7 and 14 gpm without wasting energy.

My problem now appears to be that the minimum power on the pump is slightly greater than the maximum that I need.

Also the minimum power for a MonoDrive that is required to do the variable speed is 1/2 HP, but I only need about 1/3 HP max, since the variable speed can regulate 60 Hz pumps down to 30 Hz a 1/2 HP can run at between 1/4 HP and 1/2 HP so the energy saving with the variable speed is the difference between 1/4 and 1/3 HP (not a lot), which is probably burnt up in the overhead of the controller.

The other advantage of the variable speed pump is that the wear and tear is on the pump and the well is meant to be less (but for a complication of having the controller).


For drinking water, washing, plus toilet etc, I use street supply.

The well pump is only for the heat pump, and if I could have used it for irrigation it would be a bonus.
The current size of pump is enough for irrigation, but of course that's only about 35 hours a year, and there is no point running at 45 or 55 PSI for 1500 hours a year just for the sake of having enough pressure for irrigation and wasting at least 20 PSI all year long (at least 1500 hours) for the sake of the 35 hours.

So now I'm feeling pretty let down, but will speak with the well driller, and if he will resize it for minimal cost I'll be happy.

[speedbump]

One of the problems with variable speeds it the horse power of the motor doesn't match the pump. It's always bigger than the pump. That in itself is a waste of electricity.

Doing two or three different things with one pump always has and probably always will be a problem. Not only for the sake of electricity used, but in maintenance and longevity of the pump and motor.

bob...

[mbartosik]

Why does the horse power of the motor have to be greater than of the pump with a variable speed drive?
I think that you are thinking of the SubDrive series, not MonoDrive.

I appear to have a 3/4 HP pump and 3/4 HP motor with variable speed controller MonoDrive.

From the manual from my MonoDrive:
"The MonDrive is designed to convert a conventional 0.5 0.75 1.0 HP pump system to a variable speed constant pressure system by simply replacing the 3 wire control box. Maximum pump output using the MonoDrive is similar to the performance achieved using a conventional control box. Therefore, the pump selection criteria are the same as if a control box were used. Please refer to the pump manufacture's literature for details of pump selection procedure."

However for the SubDrive the manual says use a 3/4 pump with 1.5HP motor (SubDrive 75).

From my system with a 3/4 HP pump and motor, assuming 40% combined efficiency of pump and motor, my input is a little over 1.25KW max, and at 40% that is not far off the 0.55KW that corresponds to 3/4 HP.

[speedbump]

When you ramp a pump up past it's normal RPM's it will require more horsepower. So if the pump is a 3/4hp, the motor could easily be a 1.5hp or so. I don't see any other way to spin these pumps faster without having more horsepower to do so.

Unless they don't allow the motor to go over 3450 RPM's and just ramp down to keep the motor running. I'm not the expert on variable speeds, so you might want to get an answer from someone who knows.

bob...

[mbartosik]

The MonoDrive ramps down (30 to 60Hz) i.e. about 1800 to about 3600 rpm.
The SubDrive ramps between 30 and 80 Hz i.e. about 1800 to about 4800 rpm (using more HP).

So for me the MonoDrive is the more suitable, but of course that's if it is worth having variable speed at all. I think that my problem is that I'd like a variable speed on a lower HP size than is accomodated. I'd like variable speed on 1/3 HP not 1/2 HP, but I actually have 3/4 HP installed.

[speedbump]

And then there is the Cycle Stop Valve.

I don't think we want to get that discussion started again. So all I'll say is you might want to research some of the CSV discussions that have been hashed over in the past. You might want to look into them further.

For my money, that's what I would have on my well. As a matter of fact I do, on two different wells.

bob...

[valveman]

"At 14 gpm a current clamp on the input of the mono drive shows a steady 5.2A (1.25KW power factor is 1.0). If I reduce the flow to 7 gpm the current flow drops to about 2.8A (varies between 2.6 and 3.2A or 0.67KW). If I reduce the flow to 6 gpm or lower the pump cycles off for a second or two each minute (bad)."

I have been following this post with great interest as I am in the process of designing a heat pump system for my own home. I really appreciate the explanations given by BobNH as they are very helpful. I was told by Franklin Electric that their Mono and Sub drive units are made to vary the flow rate of a pump for intermittent use only. Intermittent being taking a shower or filling a washing machine. Any long term water uses such as heat pumps and irrigation needs to be matched to the max output of the pump. When you are using 7 GPM or low flow rates the amps are varying between 2.6 and 3.2 amps. This is showing you that the (go/no go) switch used with the Mono Drive instead of a pressure transducer is causing the pump to ramp up and down about 45 times per minute. Then as you have seen, once per minute the unit does a "bump" as Franklin calls it, which increases the pressure about 4 PSI and completely shuts off the pump/motor. Then because water is still being used the pressure quickly drops and the pump restarts after only a couple of seconds. With a Mono or Sub Drive this process is repeated over and over as long as the flow required is less than the max output of the pump. When you are running 14 GPM the amps stay steady. That is because this is the only amount of water that the pump is "designed" to pump for any long term water use. What I am hearing and seeing in the field is that the continuous ramping up and down of the Mono Drive controlled pumps is causing the wire down hole to wear out quickly and even wearing holes in the side of the pump or motor from touching the casing. This motor torque is happening 45 times per minute which is a million times every 21 days of use. I am also hearing that the fan in the Mono Drive needed to cool the electronics is drawing in lint and other debris which reduces the air flow and causes overheating of the Drive itself. Not to mention the ones I have heard about that where destroyed from this air flow area being taken over by fire ants and other critters. Then there is the "stray voltage" caused by the Mono Drive or any VFD. Do a search for "VFD stray voltage" and it will give you other problems to worry about. I agree with BobNH that to save energy the pump needs to be sized for the minimum head to make things work without any kind of regulation. You certainly do not need 55 PSI or a bladder tank to make this work. However it looks like to me that when using 14 GPM, your pump is not oversized by very much. I think you should change out the Mono Drive controller for a standard control box, remove the pressure tank, and wire a relay to run the pump anytime the heat pump is on. There won't be any change of power consumption or pressure at 14 GPM. At lower flow rates the pump pressure will be much higher than needed but, the high pump pressure and low flow rate will cause the amps to drop almost the same as when using the Mono Drive. This is best for the pump/motor and will make it last considerably longer. If you have to purchase a new pump/motor and or Mono Drive every 2 or 3 years, which is all I expect, energy consumption is the least of your worries. If your pump system last 15 or 20 years as it should, you can afford to use considerably more energy and still be better off. Save a little energy and spend $1,000.00 on a new pump every 2 years, or use a little more energy and have that $1,000.00 pump system last 20 years, do the math. If the total head needed when pumping 14 GPM can be done with a smaller pump, then that is the best and maybe only way to reduce the energy consumption. Also when restricted to low flow, some pumps will reduce in amperage more than others. The Goulds pump like many others, uses a floating stack impeller design. When the flow is restricted, all these floating impellers drag on each diffuser causing the amps from lowering any further. A pump with a fixed impeller design (locked to the shaft), such as a Grundfos pump, will not allow the impellers to drag and the power consumption at low flow will be much less than floating stack impeller pumps. I have a 2 HP Grundfos pump at my home now and when the flow is restricted, the amps drop from 12 to 5.5 (using a CSV not a VFD). A floating stack pump would only drop from 12 to about 8 or 9 amps. This makes a big difference in power consumption at low flow.

[mbartosik]

Valveman, thanks for this post, it is enlightening although saddening to learn that about the only thing right with my system is likely the two holes in the ground.

You said:
"Intermittent being taking a shower or filling a washing machine. Any long term water uses such as heat pumps and irrigation needs to be matched to the max output of the pump."

The MonoDrive will only reduce the flow to be less than the max flow of the pump. The SubDrive can over drive the motor from up to 80Hz (rather than standard 60Hz).

The fact that the MonoDrive will only reduce the flow appears to be in direct opposition to your/Franklin's statement that I quoted above.

So I think that I need to find a 1st stage flow rate and pressure (if I use a MonoDrive) that will give a steady current and a 2nd stage flow rate at the same pressure that will also give a steady current. I think that there are settings that are less than the maximum that will give that. Also I was not able to reduce the pressure in the bladder along with the sensor, and they are meant to be reduced together within +/-2 PSI so that could have been a cause of stutter/bump/hammer that I observed at 7GPM and 45 PSI.

[valveman]

The Mono Drive runs at a maximum of 3450 RPM with is standard speed anyway. The 80 Hz of a Sub Drive spins the pump at a maximum of like 4700 RPM. At this 4700 RPM a 3/4 HP pump end will deliver 1.5 HP flow, pressure, and load, so it has to have a 1.5 HP motor on a 3/4 HP pump. The Sub Drive is still just reducing the speed of the pump to reduce the flow rate, it just starts at 4700 RPM instead of 3450 RPM. Otherwise there is no difference in how the two drives actually work. You have to be using enough water to keep the pressure below the setting of the pressure switch or it still bounces up and down 45 times per minute. With the Mono Drive I have in my test pit, I am only able to reduce the flow rate a small amount from max flow before the switch starts bouncing the pump up and down. I know this sounds funny but, if you will turn the pressure switch up as high as you can, you will have greater variation in low flow rates without the pump continually bouncing up and down. Actually you could wire the two little wires on the pressure switch to a dry contact relay that makes when the heat pump comes on. In this way the pump will be locked in at 3450 RPM, and the flow rate will vary according to how much water you are using. The pressure will be high when using low flow but, the pump will not be bouncing a million times every 21 days. However, if you are going to run the pump at full RPM anyway, it would still be better to replace the Mono Drive box with a standard capacitor type control box.

PS; When the pressure gets low the hammering is caused by having more air in the little tank than what the system pressure is at that time.

[valveman]

I have a ½ HP 10 GPM Grundfos pump that is throttled back with a valve to 4 GPM (64 degree water) since that is all the well produces. This pump runs 24/7 filling a pond for livestock and fish and uses about $60.00 per month. This well will make 10 or 12 GPM for a few hours but, has a recovery rate of 4 GPM. I now plan on running this well to a small house and a heat pump system. I used as small of a well pump as I could and restricting the flow to 4 GPM only holds back about 20 PSI. This is plenty of pressure for the heat pump and the water will be continually flowing through the heat exchanger before being dumped into the pond. I will put a back pressure valve on the discharge and hold back 20 PSI before the water enters the pond. After the heat exchanger I plan on a tee to a ½ or 3/4 HP jet pump with a CSV and a small bladder tank to feed 40/60 PSI pressure to the house. When the house needs water and the jet pump starts, the back pressure valve at the pond will close if needed trying to hold back 20 PSI. When the house is using more than 4 GPM, the pressure in the line will drop from 20 PSI to 0 PSI with no water going to the pond. At 0 PSI the well pump will produce about 9 gpm. The jet pump will pick up at 0 PSI and deliver up to 9 GPM at the 40/60 needed for the house. When the house is no longer using water, the jet pump will shut off at 60 PSI. Then the pressure in the well line will increase to 20 PSI and the back pressure valve will again open to allow 4 GPM to the pond. Other than my water for the house being 10 degrees warmer when the heat pump is working, does anyone see a problem with this set up?

I think Mbartosik could use this same type set up. He can use as small a pump in the well as needed for the heat pump, then boost that pressure with a jet pump for the irrigation. He would just need the pressure switch for the jet pump tied in conjunction with the relay for the well pump/heat pump. In this way if the heat pump was not being used and the irrigation system was needed, the pressure switch for the booster jet pump would also start the well pump at the same time.

[mbartosik]

Valveman, as I was reading your post I was thinking that sounds like a system that I could use. I'll think about it more too (not like I'm an expert by a long way).

[mbartosik]

A possible alternative (maybe better for my system which already has a MonoDrive). To have two pressure sensors, one at a lower pressure that is okay for the heat pump (not wasteful) and one at a higher pressure for irrigration. The demand from the irrigation would use a relay to swap the sensor to the monodrive to the higher pressure.

I wouldn't go for this as an initial design, but given the equipment that I already have...

Whether this would work depends on being able to set lower pressure and flow rates without the MonoDrive bouncing around, and to do that I likely need to reduce the size of motor and pump. However, it may work as a way to do limited irrigation and heat pump with a single motor.

[valveman]

The lower you set the switch on the Mono Drive, the more flow the pump can deliver and the worse the bouncing is going to be. You could use a CSV set lower than the switch and that will keep it from bouncing but, then you don't need the variable speed at all.

The way I am talking about you can install as small a pump as possible for the heat pump. Don't really need much pressure, just volume. Then if you want to irrigate you use another pump to boost the pressure. Also could come out of the heat exchanger and tee off into an electric solenoid valve that feeds a ground storage tank. Level controls in the storage tank open and close the solenoid valve as needed. When the storage tank is full, water from heat pump goes right past the tee off and back down the dump well. Now you have a storage tank full of water and can hook it up a booster pump for irrigation needs. Don't need much pressure to fill a storage tank either so you can still use as small a pump in the well as the heat pump can live with.

[mbartosik]

The bouncing at low pressure really makes the MonoDrive a pain for GSHP.

I think that I am going to have the well guy come back and reduce the pressure, while measuring the pressure at the entrance to the return well. At the entrance to the return well the pressure only needs to be minimal (correct me if I'm wrong here). All pressure at the return well is litterally energy/money down the drain (correct me if I'm wrong).

My guess is that the pressure will have to be dropped to the minimum of 25 PSI that the MonoDrive will handle. Then it is likely to bounce all over the place. Then I need him to show me the variable speed working at the 25 PSI between 7 and 15 GPM (my heat pump requirements).

If it is unable to handle that I'll have to discuss with him what he can do.

[valveman]

It will do the 25 PSI all right, just going to keep bouncing unless you use enough water to get the pressure lower than 25 PSI. Bouncing a million times every 21 days, probably not going to last long.

[mbartosik]

I just spoke to the well driller.

He thought that the electrical energy required was proportional to the volume of water moved (i.e. gpm) and unrelated to the pressure. I explained that I believed otherwise (and so does physics).

He said that I should try reducing the pressure to about 30 PSI, and that having a little pressure at the return well is good, not for now but for the future if deposits build up in the return well, but only a little pressure. He also explained how to reduce the bladder pressure and the sensor pressure.

I didn't get a price from him for swapping out the pump and motor for 1/2 HP, but the implication was in the order of $1000 and I'd then have a pump and motor to place on web auction. So his mistake, my money.

With two pumps in a well, can they both use the same supply pipe or do separate supply lines need to be used? My idea here is to fit a smaller pump in the same well for the GSHP but sharing the same supply line from the supply well head to the basement. Fitting a new supply line from the well head to the basement below the frost line would be expensive. Then I could have the irrigation turn on the existing pump 3/4 HP, and the GSHP control the smaller pump 1/3HP or 1/2 HP. This way less gets sold via web auction. I would probably need a check valve to stop the higher pressure pump from backfeeding the lower pressure pump, and to only run one of them at a time. All getting more complex.

If the pump is forced to cycle until it breaks, then that might be a good thing just as long as it breaks within warrentee and in summer :D Then I'd maybe not have to fork out another $1000 to get something smaller.

[Bob NH]

I just spoke to the well driller.

He thought that the electrical energy required was proportional to the volume of water moved (i.e. gpm) and unrelated to the pressure. I explained that I believed otherwise (and so does physics).

With two pumps in a well, can they both use the same supply pipe or do separate supply lines need to be used? My idea here is to fit a smaller pump in the same well for the GSHP but sharing the same supply line from the supply well head to the basement. Fitting a new supply line from the well head to the basement below the frost line would be expensive. Then I could have the irrigation turn on the existing pump 3/4 HP, and the GSHP control the smaller pump 1/3HP or 1/2 HP. This way less gets sold via web auction. I would probably need a check valve to stop the higher pressure pump from backfeeding the lower pressure pump, and to only run one of them at a time. All getting more complex.

If the pump is forced to cycle until it breaks, then that might be a good thing just as long as it breaks within warrentee and in summer :D Then I'd maybe not have to fork out another $1000 to get something smaller.

The well driller is wrong. Power to a pump is proportional to the product of the flow and the head (pressure). Since a centrifugal pump delivers head proportional to the square of the speed, and flow proportional to speed, the power varies as the cube of the speed.

The characteristic curve of the pump scales as follows with speed.
1. Adjust the GPM by the ratio of the actual speed to rated speed.
2. Adjust the head at the new flow point by the square of the speed.

For example, if a pump delivers 10 GPM at 100 ft of head at the speed on the pump curve, then at 80% speed it will deliver 8 GPM and the head at 80 GPM will be 64 ft.

There will be some difference because low flow will reduce the losses in the pump.

You can reduce power a bit by throttling the pump, but you do this at a serious loss of wire-to-water efficiency because you waste energy in the throttling and you drive the operating point away from the most efficient operating point.

It is pretty clear that your well driller is out of his league when it comes to non-standard systems.

I would do some engineering to see if I could match the pump to the system. You can get 3-phase motors that are made to run with variable frequency drives, and small 3-phase converters that run on single phase are not very expensive. It is also be possible to get single-phase converters.

I would look at the system to find the pump that would provide the maximum required flow and head at the standard speed. Then I would operate the pump at a constant lower speed (no variation or feedback control) to provide the lower flow and head.

A simple pump in the size you need is not that expensive and you may be able to use some of your existing equipment. You can bolt a new motor onto most submersible pumps.

[mbartosik]

Thanks Bob.

Your post requires careful reading but is a lot of help. Care is required for accurate understanding (this is meant to be praise not a critism). Your comments are most useful.

I am sad to say that I spoke with 3 well drillers and they all proposed about the same system just at different prices, although one was 1HP! Today I spoke to the HVAC company owner that installed the heat pump, and my observation is similar, he said that he liked to see about 45 PSI at the pump to get enough flow. I told him that flow and pressure are different, and the heat pump required flow not pressure and his answer was "um, yes". "Um, yes" is not good to hear when you are paying over $30K plus the well costs, especially from someone who should know better since he does air duct pressure and flow calculations (most likely table lookups rather than calculations).

The local utility (which is state owned) is giving me a $4000 rebate ($800 per ton). They do this to encourage GSHP because of the efficiency. I know who are the right people to talk to at the utility, and I want to encourage them to require the pump sizing and flow and pressure settings to be reviewed by a qualified professional to qualify for the rebate, otherwise they are litterally paying to have energy pumped down a hole. They already do this for the solar rebates. My whole motivation is energy conservation (not the money).

Over the weekend I will try to lower the pressure. You point out that power is proportional to the cube of the speed, I had forgotten that (I last had to do such physics a long long time ago). The Franklin MonoDrive (what I have) has a range of 30Hz to 60Hz (or about < 1800 rpm to about < 3600 rpm) that I think means that the power range should be 1/2^3 or 1/8 (12.5%) to 1 (100%). Since input power is 240v * current * power factor, then I should be able to get in the order of a factor of 8 variation in input current (assuming a wishful linear efficiency curve for the inverter). So far (without adjusting pressure much, mostly adjusting flow) I have been able to vary the input current by about a factor of 2, so there should be a lot more variation available by adjusting pressure.

Also tonight while monitoring current I noticed the current sit at a steady 1A for several seconds, which is encouraging. If I can get to a point where it draws only 1A without cycling then I think that will be sufficient.

As I make adjustments I'll record pressure, flow, and current (and input power) and post my results here.

[Bob NH]

)
As I make adjustments I'll record pressure, flow, and current (and input power) and post my results here.
You should also try to measure pressure drop across the water side of the evaporator along with flow. That requires a pressure gauge on both ends.

You need to know the pressure drop across the evaporator, and across other elements of the water system, to correctly select the pump if you ever want to change it.

To get maximum efficiency on the water side, the pressure in the return pipe (which should go into the water in the return well) at the elevation of the water in the return well should be close to atmospheric pressure (0 psi gauge). That may cause the water pressure at the discharge from the evaporator (if there are no unreasonable restrictions) to be less than atmospheric pressure. You shouldn't have cavitation in the evaporator as long as the pressure at the discharge end is above about 5 psi absolute (Vacuum of 20" Hg).

If there are any valves in the water circuit, try running the system with all of them wide open and see what the flow is. If the flow substantially exceeds what you need for the evaporator, that is a sign that the pump is too big or is running too fast. Slowing it down to the point where you get required flow with no restrictions in the water circuit should give minimum power consumption.

Higher velocity on the water side will increase the heat transfer rate so the extra pumping power may be balanced by lower power for the compressor. There is a limit to that because the the evaporation side is often the limiting factor.

[mbartosik]

My original plan (until I found some of your posts on this forum) was to do some fine tuning of the power required by the well pump vs the improvement in heat transfer due to higher fluid velocity (making compressor work less hard). That is to say adjusting flow without concern for pressure, but when I saw your posts.....

My plan for this was to get two precise (but not necessarily accurate) logging thermostats, i.e. 0.1 F resolution with RS232 or RS485 data logging to measure the fluid temperature difference across the compressor. First ensuring that I know their relative offsets at the same temperature. Then I could use fluid flow, fluid temperature delta, and thermal mass to calculate the energy extracted from the fluid. Using a current clamp and RS232 logging I could measure the current draw on the combined well pump and compressor (need to know power factor or use a KW meter). Then I could tune the flow to find the "sweet spot" where most energy is extracted for least current draw (energy in).

The idea with RS232 was have my computer dynamically calculate the efficiency coefficient (COP) based on time averaged data because thermocouples don't have an instantaneous response. Effectively the computer would use the data logging to do a little integration in realtime.

If I manage to drop the well pump current draw enough (by dropping the pressure). Then I'll do this fine tuning. But it is clear that my main inefficiency is too much pressure.

Also if I manage to drop the pressure a sensible amount (down to 20 to 30 PSI) I might dig up the return well and fit a 'T' so that I can fit a pressure gauge there. The ideal would be to fit a pressure transducer so that I can rebury it (below the frost line) but leave the wires on the surface where I can measure with a multimeter. That's a load more work so it will have to wait.

If I do end up installing a smaller pump and motor, what do you think my chances are of getting a reasonable price at internet auction for the pair that I have now which are only a few weeks old?

[valveman]

I know Bob meant 8 GPM at 64 ‘ not 80 GPM and he is exactly right. The problem is that you lose head by the square of the speed so, you can’t slow it down enough that saving energy by the cube of the speed makes any difference. In other words you will save more energy by having exactly the right size pump compared to slowing a pump down with a drive or restricting the flow with a valve. Personally I like your two pump in the same well idea except, it may be hard to get them to fit. Done it lots of times in 8" and larger casing but, 6" and smaller is tough unless it is shallow enough for a jet pump instead of a sub. I think BobNH wrote about this earlier. Anyway the Mono Drive that he has is a single phase drive and the Sub Drive is a three phase drive. Only difference is that they now use a go/no go switch instead of a pressure transducer but, the effect on the power consumption is the same. Systems with pressure transducers can be slow reacting and not very reliable, usually sticking in the full speed position. So the go/no go switch solved some of the slow reaction problems and caused a few others. The bouncing and weaving is just how it maintains the speed required. What I hear from Heat Pump customers a few years into it, is that the energy consumption is less important than the life of the pump system.

I think my idea with a ½ HP sub in the well and a ½ HP booster on top is as good as the two pumps in the well idea but, will fit in 4"casing and work from over 50' deep . Instead of a 1 HP in the well that can be slowed down or restricted to maybe 3/4 HP, I will have a ½ HP restricted a little so pulling maybe 4/10 HP. Then the ½ HP booster will only come on if I need pressure for the house or irrigation. The ½ HP sub has already been running 24/7 for 10 years feeding the pond. Since I am already running the water, the heat exchange and the water supply to the house should be a bonus. This sub has already been running for ten years without shutting off, so I know that running steady and not cycling or ramping in anyway is what makes it long lasting. If the pump system will last a long time and only use 4/10 HP on average for the heat pump, it should be worth it.

[Bob NH]

In most heat exchanger applications with variable speed drives you can usually just set the speed with a potentiometer or manual control and let it run. The water side pressure drop is proportional to the square of the flow, and characteristics of the water circuit shouldn't change much.

The problem arises when you have variable demands on the pump supplying the evaporator. That is why it is hard to use that pump to irrigate or supply other needs while running the evaporator.

[valveman]

Yes you can set the speed with a potentiometer or manual control but, anytime you vary the speed you are burning energy compared to having the right size pump.
See http://cyclestopvalves.com/comparisons_13.html

There are also many negative side effects to VFD control that you will never hear about from the people who make or sell drives.
See http://cyclestopvalves.com/comparisons_5.html

Stray voltage has also become a major problem with VFD controls. The following link is just one of many you can find doing a search for VFD stray voltage.
See http://www.electricalpollution.com/

[mbartosik]

Here are some results of the input power saved by adjusting flow and pressure:

At 55 PSI and 15 GPM the current draw was 5.2A i.e. 1.25KW
At 55 PSI and 7 GPM current draw is about 2.8A i.e. 672W
At 45 PSI and 7 GPM current draw is about 2.4A i.e. 576W
At 40 PSI and 7 GPM current draw is about 2.3A i.e. 552W
At 35 PSI and 7 GPM current draw is about 2.2A i.e. 528W can only get 14 GPM max
At 30 PSI and 7 GPM current draw is about 2.1A i.e. 502W can only get 12 GPM max
At 25 PSI and 7 GPM current draw is about 1.9A i.e. 456W can only get 10 GPM max

35 PSI is the minimum required pressure to get the 14 GPM required for stage 2 of the compressor.
I could probably drop to about 18 PSI if I only wanted stage 1 of the compressor, and that might get me to 400W.
Since I only run stage 2 rarely, I might drop to 30 PSI. Running on stage 1 mostly at 35 PSI and 528w means that I'm wasting about 100w in excess pumping capacity.

Initially the installers configured the water side to 55 PSI and 15 GPM constantly using 1.25KW, wasting about 850W down the return well.
I asked for a second valve to be fitted to reduce flow when only 1 stage is used, this reduced power required most of the time to 672W.
Then I started reading this forum, and now I've got the input power down to 528W.
Total power saved so far is about 60% of pumping power, or about 20% of total system power (including heat pump load).

The Franklin MonoDrive manual has a table of limit switch and tank pressures. The lowest pressure in the table is 25 PSI, but it does not say that a lower pressure cannot be used. The lowest that I could likely go is 18 PSI for stage 1 compressor on, not sure how I'd run stage 2 then.
What do you think to running that MonoDrive at 18 PSI?

If I was to compare this against the energy used by using a fixed speed pump, if I was to use 1/3 HP (the smallest that I think that I can buy)...
1/3 HP == 0.25KW
assuming 40% efficiency between motor and pump losses, that would require 0.6KW of input power.
It looks like I'm already using less power than the minimal simple system, but I know that it is not that simple.
My other way to reduce power usage is to use a smaller (1/2 HP motor and pump), but still using the MonoDrive, the 1/2HP would be in a sweeter point of the performance curve.

[valveman]

It should not hurt anything to run at 18 PSI, if the switch will turn down that low. I also don’t see why you can’t use two switches. Just put in a relay that lets the higher pressure switch override the lower switch when using stage two. Also like BobNH said you can put a ½ HP pump on that 3/4 HP motor and lower the power a little more also. My question is, how are you getting these steady amp readings? Isn’t the amp meter still bouncing while the pump is maintaining the pressure you have adjusted the switch to hold? Also how much in dollars is saving 850W in your area. If I am thinking right this morning, in my area that would only be less than 10 cents per day, $3.00 per month, $36.00 per year. Sounds minimal to me, am I adding wrong?

[mbartosik]

I might use two switches, however, then the problem becomes the bladder.
The MonoDrive manual says to set the bladder pressure at 70% of the switch pressure. That means
18 PSI on switch set bladder at 13 PSI
35 PSI on switch set bladder at 25 PSI
I don't have a way to change the bladder pressure dynamically. If I used 35 PSI on the switch but 13 PSI on the bladder then I would risk damage to the bladder (a burst), and the other way round would be ineffective.

The bladder appears to be oversized also, I have an Amtrol WX203 tank volume of 32 gallons max accept factor 0.35 thus 11 gallons variation. The MonoDrive manual says that I only need 4 gallon tank total capacity (so x8 larger than needed).

As for the steady amp readings I should have said in the post. I averaged them, there was a clear seeking up and down, and I choice the mid point. For example (these are actual measurements):

At 40 PSI and 7 GPM input current varied between 2.2 and 2.5, the average appeared to be 2.3A.
At 40 PSI and 8 GPM input current varied between 2.4 and 2.9A, the average appeared to be 2.6A.
At 30 PSI and 7 GPM input current varied between 2.0 and 2.2A, the average appeared to be 2.1A.
At 25 PSI and 7 GPM input current varied between 1.8A and 2.1, the averaged appeared to be 1.9A.

There was a clear seeking up and down. I am unsure of the frequency, probably about 20 cycles per minute. The seeking didn't get any worse as the pressure dropped, I guess that's because this time I lowered the bladder pressure with the limit switch. I understand that this seeking is one of the one of the potential problems (e.g. worn wires). I think that they could use smarter software in the MonoDrive in conjunction with a lower limit pressure switch set just a couple of PSI below the other to almost reduce the seeking to zero with a good sized bladder.

Your $36 per year calculation - it may be right for you, but here is mine:

In my area electricity costs about 18c per KWh. I consider that to be under priced considering the uncharged costs (foreign energy dependance, wrecking the planet etc.).

So for a 100W saving in pump efficiency, assuming 30% duty cycle for 8 months a year (heating and cooling), that's roughly 2000 hours, or 200KWh.
Or $36 per year for just 100W or $288 for 850W.

Now since my motivation is energy conservation. My whole house will be powered by solar, so far with net metering (no batteries) I had 100% net solar power before the heat pump was installed. I have to look at the long term. Assuming a 10 year payback on solar, that $288 in one year is equivalent to about $3000 over 10 years, which is about the cost of installing 2 x 200W DC solar panels after install costs (before rebates).

As for changing the pump or motor or both to get to the "sweet point", then I have to work out what my likely power saving will be. I have to save at least 100W to make it a consideration even given the 10 year cost. So I'll try to find out the speed that the motor is running at my preferred load point maybe 30 PSI and 7 GPM, and then look at a pump and motor efficiency graph. To find the motor speed I will try to borrow a good frequency meter or an osciloscope (and look at the MonoDrive output wave form).

So if I was to change only the pump or the motor, is it the pump that should be downsized, or is it better to do both?
If only the pump is down sized will the motor then naturally demand less power, because of less brake power by the pump?
?

[Bob NH]

As for the steady amp readings I should have said in the post. I averaged them, there was a clear seeking up and down, and I choice the mid point. For example (these are actual measurements):

At 40 PSI and 7 GPM input current varied between 2.2 and 2.5, the average appeared to be 2.3A.
At 40 PSI and 8 GPM input current varied between 2.4 and 2.9A, the average appeared to be 2.6A.
At 30 PSI and 7 GPM input current varied between 2.0 and 2.2A, the average appeared to be 2.1A.
At 25 PSI and 7 GPM input current varied between 1.8A and 2.1, the averaged appeared to be 1.9A.

There was a clear seeking up and down. I am unsure of the frequency, probably about 20 cycles per minute. The seeking didn't get any worse as the pressure dropped, I guess that's because this time I lowered the bladder pressure with the limit switch. I understand that this seeking is one of the one of the potential problems (e.g. worn wires). I think that they could use smarter software in the MonoDrive in conjunction with a lower limit pressure switch set just a couple of PSI below the other to almost reduce the seeking to zero with a good sized bladder.

Your $36 per year calculation - it may be right for you, but here is mine:

In my area electricity costs about 18c per KWh. I consider that to be under priced considering the uncharged costs (foreign energy dependance, wrecking the planet etc.).

So for a 100W saving in pump efficiency, assuming 30% duty cycle for 8 months a year (heating and cooling), that's roughly 2000 hours, or 200KWh.
Or $36 per year for just 100W or $288 for 850W.

Now since my motivation is energy conservation. My whole house will be powered by solar, so far with net metering (no batteries) I had 100% net solar power before the heat pump was installed. I have to look at the long term. Assuming a 10 year payback on solar, that $288 in one year is equivalent to about $3000 over 10 years, which is about the cost of installing 2 x 200W DC solar panels after install costs (before rebates).

As for changing the pump or motor or both to get to the "sweet point", then I have to work out what my likely power saving will be. I have to save at least 100W to make it a consideration even given the 10 year cost. So I'll try to find out the speed that the motor is running at my preferred load point maybe 30 PSI and 7 GPM, and then look at a pump and motor efficiency graph. To find the motor speed I will try to borrow a good frequency meter or an osciloscope (and look at the MonoDrive output wave form).

So if I was to change only the pump or the motor, is it the pump that should be downsized, or is it better to do both?
If only the pump is down sized will the motor then naturally demand less power, because of less brake power by the pump?
?

Your economic/power analysis should be broadened to consider the cost of the solar panels and evaporator.

Two solar panels with 200 Watts capacity will collect how many kWH per year? At what cost per kWH?

Part of the problem comes from the pressure drop in the evaporator. You might be able to double the size of the evaporator (put another one in parallel) and cut the pressure drop by 2/3. That would also reduce the temperature difference between the water temperature and the suction temperature, increasing the Coefficient of Performance.

You should get rid of any device that causes pressure drop in the water circuit. Too often, system sellers cut costs on heat exchangers and pipes because the customer is not aware of how much that affects energy requirements.

If you put in a second evaporator, then you could consider switching them from parallel to series connection when you need less flow. Some hydraulic analysis would tell you if that would save energy in either the pump or compressor. Usually, more power for heat exchanger pumping will save some power in the compressor. You will want to be able to measure the suction pressure and/or the compressor current as you make changes on the water side of the evaporator.

With respect to the pump, I suspect that you will save more Watts per dollar by changing the pump head rather than the motor. However, that should be analyzed before making the purchase. The pump willl draw less power and require less electricity if you reduce the load on the pump.

A "correct size" single-speed pump with motor should no cost more than about $500. The rest is margin somewhere between the distributor and you.

If the discharge well pipe doesn't go all the way to the water level, then either it should be extended, or the casing should be sealed so that it will withstand a vacuum at the top. That will allow you to recover more of the elevation head when the water is discharged.

[mbartosik]

In my region (North East USA) 2 x 200W DC solar panels will generate about 440KWh per year. It is generally more economical to reduce demand than to add solar panels. Which is why I'm keen to get the demand down.

My point was that dropping the power demand by 850W was something significant, and I consider that the installers really messed up by wasting 850W down the return well. Fixing that waste has just paid for at least 2 panels when I install the next array.


Doubling the size of the evaporator is very interesting I will discuss with the HVAC people. I will also have to do some research there. Also switching from parallel to series with the evaporator is interesting.


There are no other devices that can cause a pressure drop in the water circuit. The pipes on the inside of the house are all 1" diameter copper, and on the outside 1" PVC (same as sprinkler pipe). In the well they are 1" poly pipe, and the return well goes down to the water line and is sealed. If all the pipes took straightest line rather than making 90 degree turns I doubt that I'd save more than 20' horizontal distance in total for supply and return together. But straight lines for the pipes would have been difficult.

I was a little surprised when they fitted the sprinkler type pipe in the trench (installed with a hydraulic missle/mole). Maybe a different type of pipe or larger diameter here would have been better? That really is too late now, other than to advise others.

[valveman]

If you can save $288.00 per year and your $1,000.00 pump will last more than 4 years then you are saving energy and money. If it does not last 4 years, you have got to decide how much extra you are willing to spend to save energy. Except for being able to change the operating pressure, I still think you could size a normal pump for the flow and head to get about the same energy savings. If you are really looking at energy savings alone, you may have to look back further. If saving a little energy means replacing a pump every 5 years instead of it lasting 20 years, then how much energy is used to manufacture, transport, install, and dispose of those extra pumps and motors. A big part of what you pay for the extra equipment, is used for energy. It is like the hybrid cars. If you have to replace the batteries every 35,000 miles, the money you save on gas is spent on energy mining, manufacturing, transporting, and disposing of batteries. It still seems to me that making equipment last, is the best way to save money and energy.

Putting a ½ HP pump end on that 3/4 HP motor will reduce the horse power. It would pull slightly less power with a ½ HP motor but, the 3/4 motor will run cooler and hopefully last longer, which I think is going to be your problem anyway. 13 PSI of air in a tank that runs at 35 PSI is not going to hurt anything. That larger tank is not doing you any better job than a 1 gallon size tank, it is just being used as a shock absorber. You have to have a pressure bandwidth like on at 20 and off at 40 to put any water in a tank or get any out. When a drive holds the pressure steady at 18 PSI all the time, no water comes in or out of the tank regardless of the size. Normally the water in the tank stays in the tank and gets stale and contaminated.

[mbartosik]

I've already saved the $288 per year (850W) by better tuning the pressure and flow, largely thanks to this forum.
The question is whether I can save more, I suspect that the most that I'd be able to save while the pump is running is another 250W (half the 500W currently).

Anyway I've learnt a lot from this forum.
I think that my remaining saving can come from....

1) Switching the MonoDrive on/off automatically will save 40W of standby power (240 KWh per year).

2) I'll look at fitting a second pressure switch, and use a relay to switch between 18 and 35 PSI. Saving about 100W for 2000 hours or 200KWh per year. This will also have a good effect of cycling the water in the bladder.

3) Using a 1/2 HP pump might save more, but this will require more analysis.
The difference between the Gould 3/4 HP and 1/2 HP pump is two rotors/stages (5 stages in 1/2 HP vs 7 in 3/4 HP), so I wonder if I could remove two stages, I doubt it?

The easy way to avoid the "emedded energy" loss of buying a replacement pump is to sell the existing one on internet auction, then the only wasted energy is transport for the pumps.

4) Using a second evaporator either in parallel or in series. -- Thanks Bob NH. Even better if it improves the COP of the heat pump.

5) For irrigation ground water is more efficient than street water, so I can lock the irrigation out when the heat pump is on (the two would rarely be on together anyway), I can use a valve to send the pump output directly to irrigation (without going via the bladder and locking the sensor switch on). This results in less pressure drop than on the return side of the heat pump.

Is the 1" PVC sprinkler type burried pipe between the wells and the house causing more pressure drop than another type of pipe?

6) I don't have a filter installed (thus no pressure loss from that), the water is pretty clear.

My total roof space for solar panels is 1300 ft^2, and I've already used 900 ft^2, that leaves 400 ft^2 with a max DC capacity of 4800W DC or about 5000KWh per year here. Beyond that I cannot install more solar power. So my aim is to get the heat pump and well pump to not use more than 5000KWh per year. More house insulation and replacing the drafty windows will go a long way too.

[valveman]

Yes you can take out two impellers if you grind off the outside of them and use the part thats left and fits just over the shaft as a spacer.

As for the irrigation, drip would use much less pressure than any kind of sprinkler and has less evaporation. I love my drip in the garden, uses 10 PSI and 3 GPM. A yard would take more volume than row crops. More expensive to install though. Like anything else, it has got to last long enough to pay back the difference.

[ncgeo]

In the summer, the AC is taking heat from the house and putting it into the water, raising the temperature of the water. If the water is pumped back into the well, then the temperature will slowly RISE in the summer.

In the winter, the heat pump is taking energy from the water, causing the water to be cooled, and discharging it to the house. If the water is put back into the well, then it will cause the temperature of the well supply to drop.

The most effective way to circulate the water to the ground is to inject it into the aquifer at some distance from where it was withdrawn from the aquifer. It then tends to flow through the aquifer from the injection point to the withdrawal point at the well.

If the water level in the well is much below the surface the systems use a lot of electricity you usually don't recover all of the available head when the water is reinjected.

I just found this thread and it involves the exact application I have, but not sure anyone is still reading it.

With regard to water re-injection to the well, I have a 3-way valve on the condenser water output so I redirect some of the water to a creek (rather than back down the well) on the most extreme days. That is usually only the coldest winter nights where the unit runs continuously. That redirection is done manually, would be nice if I could install some type of feedback circut (as well water temperature drops to/ rises above some level increase water redirection to creek).

The water reinjection concept is known as standing water column, where you are continually re-using your well water as heat transfer fluid. It relies on the water storage in the well and the heat transfer between the well water and bore wall to move heat.

I think of it as a less-than-optimal closed loop system. Reinjecting water may be less than optimal for heat pump efficiency but it beats pumping your well dry.

[Thumper]

I've been reading this thread with great interest as it touches on most of the things I am trying to do in this thread: [URL="http://www.terrylove.com/forums/showthread.php?t=27993"]

One of the things I can't figure out is just how far down into the recharge well can the return pipe really go? I thought anything longer than 34' weither it is placed below the standing water level or not causes water vaporization/off-gassing problems or vapor lock at the high point (geo exchanger)?

The other thing is if I put the normal domestic water pump in well #1 and the geo supply pump in well #2 then use well #1 as the recharge will that configuration work? What are potential problems with this setup? It would be a lot easier to put one pump in each well instead of two pumps in one. It would also be a way of "sharing" the total water useage load.

BTW, great thread.

Thump

[Thumper]

A bump from Thump :confused:

It's getting [too close] to time and pull the trigger and I'm seeking input on which way to go on the recharge well direction/reinjection pipe length questions posed in my last post in this thread.

Thanks,

T