pumps &wells

I recently installed a heat pump to heat my home. It will run about 3000
hrs. a year and require 8 gallons of water per minute at 20 psig.
When my well was drilled they installed a 1.5 hp. pump. I`v been told it`s
way oversized. Electricity here costs 16 cents a kw.
Will a VFD pump such as a "franklin mono drive" supply the heat pump at 20 psig, satisfy domestic pressure at 50 psig, and lower kws. used?

Sounds like a perfect application for a CSV, Speedbump/Valveman, where are you when I need you?

Rancher

You have conflicting requirements.

Your heat pump is probably using water that should be pumped back into the aquifer to be heated or cooled again. It is unusual to dump that water. Also, the head available to go back down the hole will reduce the required power.

You DO NOT want a 50 psi pump for your heat pump circulation. If you must use the same water source for consumption, you should use a booster (probably a jet pump) to get the water to your pressure tank.

Your heat pump systems should be supplied by a very efficient centrifugal pump. Even the smallest submersible in my catalog (Goulds 7GS05R, 9 stages) puts out 130 ft of head (56 psi) at 8 GPM. That is a great waste of energy.

You could use a submersible if you could get that pump with only 3 or 4 stages. I don't know if it is practical to remove impeller stages from a submersible pump.

Someone must make efficient pumps for your application. Your system is not unique.

Your flow and pressure (8 GPM at 20 psi) constitute less than 0.1 HP of work in the water. Even with efficiency losses it should require less than 0.25 HP or about 200 watts. That is about $96 per year at your rate. With a 1.5 HP pump at typical efficiencies you are probably going to pay more than $1000 per year for electricity.

Rather than using an expensive and only marginally efficient variable speed drive, you should find a pump that will be very efficient to match your system.

What is the depth to water to supply your heat pump? Is it susceptible to a lifting pump (less than 20 ft) or deep enough to require a submersible pump. You don't want to use an inefficient jet pump for that system.

Are you putting the water back into the aquifer? That will save energy but requires another bore-hole to the aquifer.

Send some more details so I can suggest things that are appropriate.

"Sounds like a perfect application for a CSV, Speedbump/Valveman, where are you when I need you?"

I would like to see the economic analysis of that setup. I wouldn't want to pay the electric bill!

I agree with Bob about the Constant pressure pump and the needing of more info to make recommendations.

I don't think the ground water heat pump cares what pressure the water goes through the coil at just so the flow is adequate to heat/cool the Freon.

If you wanted to use two separate pumps for the two applications, your well would have to be big enough in diameter to accept another pipe for the jet pump to draw water through. This would mean a minimum of 4" and that would be a stretch. If you have a Pitless adapter, that idea is out the window.

You could pump into a cistern then use two pumps to do the two jobs, but that's rather costly.

It would be so much better if people in this business didn't set things up this way. They should know better.

I would like to see the economic analysis of that setup. I wouldn't want to pay the electric bill!

Click to expand...

I believe with the right size pump and the CSV it might be the least costly in the long run, considering the cost of setting up a cistern, adding two more pumps and all the controls to make it work. The extra two motors would probably cost more to operate than the submersible with the CSV. Think about it. One motor instead of three. The sub fills the cistern while the other two are running to empty it.

bob...

The heat pump water source running 3000 hours per year should not be permitted to have any extraneous head loss; therefore no CSV in that circuit.

If it were mine, I would install a booster pump (probably a small multistage horizontal pump) with suction off the heat pump water circuit. Then I would run both pumps when I needed water supply. The booster pump would only be required to provide the additional head for the domestic supply, and the flow capacity of the pumps should be reasonably matched.

It might be necessary to regulate the return flow of the heat pump circuit (such as with a solenoid valve) to ensure that the booster gets enough water.

Therefore, no intermediate tank required and only two pumps.

The instantaneous power of the heating pump is small and running it for the little extra time when domestic water is required would be better than running a storage tank system. If necessary, the heat pump compressor could be locked out when the water supply pump is supplying domestic water.

How is the booster pump going to get water? What is going to turn it on? With the probably 3/4" line feeding the heat pump, are you suggesting installing a multistage 40 gpm + on a 3/4" suction line?

It all sounds too undoable and complicated.

bob...

Bob NH said:

You have conflicting requirements.

Your heat pump is probably using water that should be pumped back into the aquifer to be heated or cooled again. It is unusual to dump that water. Also, the head available to go back down the hole will reduce the required power.

You DO NOT want a 50 psi pump for your heat pump circulation. If you must use the same water source for consumption, you should use a booster (probably a jet pump) to get the water to your pressure tank.

Your heat pump systems should be supplied by a very efficient centrifugal pump. Even the smallest submersible in my catalog (Goulds 7GS05R, 9 stages) puts out 130 ft of head (56 psi) at 8 GPM. That is a great waste of energy.

You could use a submersible if you could get that pump with only 3 or 4 stages. I don't know if it is practical to remove impeller stages from a submersible pump.

Someone must make efficient pumps for your application. Your system is not unique.

Your flow and pressure (8 GPM at 20 psi) constitute less than 0.1 HP of work in the water. Even with efficiency losses it should require less than 0.25 HP or about 200 watts. That is about $96 per year at your rate. With a 1.5 HP pump at typical efficiencies you are probably going to pay more than $1000 per year for electricity.

Rather than using an expensive and only marginally efficient variable speed drive, you should find a pump that will be very efficient to match your system.

What is the depth to water to supply your heat pump? Is it susceptible to a lifting pump (less than 20 ft) or deep enough to require a submersible pump. You don't want to use an inefficient jet pump for that system.

Are you putting the water back into the aquifer? That will save energy but requires another bore-hole to the aquifer.

Send some more details so I can suggest things that are appropriate.

Click to expand...

The heat pump is two stage. The first stage uses 5gpm, the second stage uses 2 gpm. The second stage would only be used about 10 % of the time.
Some water is returned to aquifer, most is bleed off to water cattle.
The return line from the heat pump is eguiped with dole flow control valves
and taco zone valves. The present water supply includes a pressure tank.
It was suggested that a vsd pump would be most effecent because it would supply the heat pump at 20 psig and would ramp up to full speed when domestic supply is needed. This is a dairy farm, and we have a vsd on a ten hp vacumn pump. It has really cut the cost of supplying vacumn. It`s my only experance with VSD.

This must be a fairly small unit. All the heat pumps I am familiar with use 2.5 gpm per ton.

Can you tell us anything about the well? Water depth, production capability etc. Water level would be helpful. Model # of pump would help also.

bob...

It's only complicated and undoable if you want to find a reason not to do it.

If you want to do it, here is how.
1. Find a pump that provides the required 8 GPM at 20 psi for the heat pump system. This in not the easiest to do but it is essential for efficient operation of the heat pump system. The circulating pipe will probably be at least 1" because you want to keep the pressure loss as low as possible.

2. At the branch of a tee on the inlet side of the heat pump heat exchanger, connect something like the 1/3 HP Grainger 2P373 which delivers 7.3 GPM at 40 psi and 5.8 GPM at 60 psi. This is the water supply pump. This pump will discharge through a check valve into the pressure tank. The pump has 3/4" inlet and outlet ports.

3. Connect the water supply pump to the electric supply through relays that operate as follows:
a. When the pressure switch demands water, it disconnects the heat pump compressor and turns on both the heat pump water supply pump AND the domestic water supply pump.

b. If there is insufficient back pressure in the heat exchanger and return pipe for the heat pump system, then close a solenoid valve in that return so that there is enough water and pressure for the suction of the multistage booster.

Notice that the booster pump capacity (GPM) is a little less than the capacity of the pump that supplies the heat pump.

If the domestic supply requirement is large, such as for watering the lawn, then it will be necessary to have a larger heat pump water supply. This can usually be accommodated by proper selection of the heat exchanger and piping system.

The small interruption of the heat pump while you are pumping water for the domestic supply will have negligible effect on heating or cooling the house.

The process of understanding the requirements and coming up with a system that meets the needs of the customer is called ENGINEERING.

speedbump said:

This must be a fairly small unit. All the heat pumps I am familiar with use 2.5 gpm per ton.

Can you tell us anything about the well? Water depth, production capability etc. Water level would be helpful. Model # of pump would help also.

bob...

Click to expand...

The heat pump is a 4 ton unit requiring 1.5 gpm.. Water temp. drops from 50
degrees to 38.
The well is 480 ft to pump, produces 11 gpm. water level is 30 to 40 ft. from serface. Gould pump model ''7GS15".

There is something wrong with your numbers.

First post was 8 GPM; now 1.5 GPM.

One ton is 12,000 BTU per hour.

1.5 GPM x 8.34 #/gal x 60 min/hr x (50F - 38F) x 1.0 BTU/#degF = 9007 BTU/Hr = 0.75 Ton.

Was the 8 GPM correct? That would produce 4 tons at 12 F temperature difference.

If the water comes to within 40 ft of the surface, why did they install a pump that produces 510 ft of head (220 psi) at the design flow rate?

Are you dumping 8 GPM to waste?

Excuse me but it seems the answers are over complicated and the question misinterpeted.. If the 1.5 hp pump is for the entire water system then it is not too big at all. It is irrelevant to the operation of the heat pump. The well is not for the heater only, it services the house and cattle. It seems the thread starter wants to save money on water pumping cost in general. He is not looking for a pump to feed the heat pump!

The heat pump needs water, thats all. Take water from any tap after the tank and give it to the heatpump. The heat pump appears to have valving and sensors that control the water flow. [all do that I ever saw] If not, add a regulator and some sort of flow control.

Now you have a column of water 400 odd feet tall. Dump the damn water back in the hole and its sure to be warm again before it hits pump zone - after all this is a hole with water being pulled from it regularly, most of it not being returned. Give some to the cattle or the corn - but that was not the queston.

A high head grundfos radiant circulator for 139$ would do it easily but methinks you need take no action at all. Much ado about nothing.

probably the question was posed wrong and the 20psi - 8 gpm is simply a minimum feed spec from the mfg.

SO..... to really answer the question. NO NO NO after pulling the working pump and buying a vaiable speed unit you would NEVER recover your costs. Wait till the pump dies, maybe get a larger or more storage tanks in the meantime, and then call us back for low KW use pump setups.

ENGINEERING is essential but sometimes we fall into our navel and OVER ENGINEER. Don't think so hard guys, you might hurt yourselves!

VFD won't save energy

Sorry I missed this post, I ‘ve been working. The CSV is used a lot for heat pump systems. It probably will not save any energy, but neither will a VFD system. What the CSV will do is keep the pump from cycling as flow rates for the heat pump and house vary. Saving energy is not really an important issue if you keep burning out pumps prematurely from cycling. You can afford to waste a little energy if you can make the pump last 20 years instead of cycling itself to death every 5 years. The CSV also simplifies the system because you only have one pump and no storage tank. The CSV will keep the pump from cycling while using a 2.5 GPM shower, 5 GPM first stage heat pump, 7 GPM second stage heat pump, etc.. I agree with Speedbump and BobNH that if you want to save energy on pumping cost, you need a smaller pump. If the well makes 11 GPM and has a static level of 30-40 feet, a well test might show that the pumping level would only be 100' while using 8 GPM. If the pumping level is only 100', you could use a 7GS07 which is a 3/4 HP instead of the 1.5 HP pump you have now. Many times pump guys will install a 7GS15 because the well is 480' deep and they don't know what the pumping level will be. So they install a pump that will pump from 480' just in case. If the pumping level is only 100', then even though your pump is set at 480', it is only lifting water from 100'. If you know the pumping level, you can install a smaller pump that will lift from that depth. If you don't know the pumping level, then you install a large pump that will lift from 480' just because that is how deep the well is. I suggest installing a smaller pump if possible, then use the CSV to reduce the cycling and make that pump last longer.

stray voltage

I forgot to mention. If you are running a dairy, a VFD on the vacuum pump will save energy. However, on pumps with centrifugal impellers, VFD reduces head by the square of the speed which limits the minimum speed and any possible energy savings. Also you should do a web search for "VFD stray voltage". VFD can cause stray voltage that can be detrimental to the health of the cows and causes reductions in milk production

You DO NOT want a 50 psi pump for your heat pump circulation. If you must use the same water source for consumption, you should use a booster (probably a jet pump) to get the water to your pressure tank.

Click to expand...

BobNH, why would 50 psi be a problem with his heat pump? I forgot to ask that last post.

bob...

The reason that 50 psi would not be appropriate for the heat pump is that it runs 3000 hours per year (see first post) and he needs 20 psi, so it would be a big waste of energy.

If I have something that needs a modest flow at 20 psi for 3000 hour per year, then I don't want to throttle a big pump to deliver that flow. That is also the reason that I don't want to use a CSV, because it throttles the pump.

This is a good case for a Variable Frequency Drive, where one pump can provide the reduced flow and pressure for the heat pump, and can respond to the higher pressure and flow demand when it is needed for the water supply.

Since he has a flow control valve on the heat pump, the VFD pump at full speed will probably provide enough flow for both the heat pump and the water supply. When there is no high pressure demand, the pump will probably provide enough flow for the heat pump at 1/2 speed.

The existing 1.5 HP pump will require less than 1/4 HP at half speed.

He could get a 1.5 HP Franklin variable speed drive for his existing pump. Franklin says their 3 Phase motors can be operated down to 30 Hz.
http://www.franklin-electric.com/manual/AIM_36.htm

You can get a 3 Phase VFD that operates off single phase input power. The easiest solution for the system described would be to put a 3 Phase 1.5 HP motor on the pump and run it with a Single Phase to 3 Phase VFD.

I disagree with the VFD being the answer, but then that's the norm.

I just wondered why you didn't want the 50 psi. Now I know why you said that. Although at 50 psi, the 1.5hp sub is using less power than it would be at 20 psi. all things being equal. Which of course they are not. At 50 the pump would be producing less water pulling the amps down. But since the heat pump already has a flow restricter, that would not apply.

I say just keep it simple.

bob...

The VFD could save some energy if you can reduce the pressure to 20 PSI for the heat pump. The problem is that this pump is used for both the heat pump and domestic use. That means that anytime the heater or AC is being used, there is only 20 PSI for domestic use. You can get a PLC to control a VFD, then you can have it change the pressure delivered from 50 down to 20 when only the heat pump was being used. A demand switch on the domestic system could then cause the PLC to ramp up the VFD to 50 PSI when domestic water is needed. The domestic system would only see 20 PSI when any tap is first opened. Then the pressure will gradually increase to 50 PSI as needed. When there is no flow to the domestic system, the flow switch would cause the PLC to ramp down the VFD to 20 PSI. This will take a bit more sophisticated VFD / PLC / flow switch than the Mono Drive or the Sub Drive made by Franklin Electric. Which BTW the Mono drive uses a single phase motor, the Sub Drive uses a three phase motor. Both the Mono and Sub Drive now use a go/no go switch instead of a pressure transducer. The only adjustment is in the switch itself. A small screw in the switch is the only way to adjust the pressure. One might could use two switches, one set at 20 the other at 50 PSI, and use the PLC to switch from one switch to the other when needed. Now with 2 pressure switches, a PLC, a VFD, and a flow switch to coordinate, the system becomes complicated and therefore less dependable.

Also, according to Franklin Electric, the variable flow part of it's Mono and Sub Drive is made for intermittent use only. They recommend that any long term uses like irrigation and heat pumps, still be exactly matched to the design of the pump. One reason being that their new go/no go switch instead of a transducer causes the pump to ramp up and down as much as 45 times per minute instead of holding at a steady flow and pressure as a transducer would do. So any flow rate lower than the maximum will cause the pump to ramp up and down and the little switch to make and break about a million times every 21 days. Franklin says the little switch has been tested to well over a million cycles. Even if the switch is good for 3 million cycles, that is only 63 days worth of variable flow rates as the switch makes and breaks 45 times per minute. This ramping up and down 45 times per minute is also causing the down hole wire to wear out quickly as the motor torques 45 times per minute. I also know of a few dairy's that have had to remove these particular VFD's from service because of the stray voltage, to get their milk production back to normal. These VFD's are not lasting very long in the field and are very hard on the motor and wire. So you would have to save a LOT of energy to be able to afford replacing the VFD and motor on a regular basis compared to using a standard pump with a CSV that will use a little more power, but should last at least four times as long.

The pump you are using has a very steep curve and would actually be a good one for VFD control because it is way oversized for a 40' water level and 50 or 20 PSI. I still think you would be better off resizing the pump for the correct pumping level, using the CSV to vary the flow rate and eliminate the cycling, and stay with a simple, dependable, and long lasting system.

Cary,

I would like to think the installers used the 1.5hp pump in this deep well because of it's limited supply and the fact that some of it's pumping will be done from a much deeper water level at times of peak use. If not, they sure did oversize it.

bob...