Determining head pressure by GPM?

Discussion in 'Pumps and Tanks Well Forum & Blog' started by TinHead, Oct 12, 2007.

  1. TinHead

    TinHead HVAC

    Messages:
    9
    Location:
    CT
    Hola
    I'm looking to install a barely used Geo Heat Pump in my home and I'm trying to decide on a new pump h.p.
    The existing well has served it's intended purpose flawlessly for 18 years with a 5GS07 (I had to figure that out -- goulds box drawing 7.5 amps on two legs at around 5 GPM).

    I've read several threads here about this type of application, but could find no answer to the following question...
    If I know my pump model, and measure my exact GPM, could I determine (with manufacturers performance graph) the working head pressure of the system accurately?

    I understand my results would only be for that moment and would vary with static level.
    I will be taping directly into pump line (removing pvc from flexible line) to eliminate any interior piping resistance.

    Thanx in Advance
    TinHead
  2. Bob NH

    Bob NH In the Trades

    Messages:
    3,317
    Location:
    New Hampshire
    You would have to know that the performance of the pump matched the pump curve. Since manufacturers may have different practices about margin of performance on pump curves, and wear on an 18 year old pump is unknown, I would not rely on the curve and flow measurements to determine pressure at some point in the system.

    I would find a way to get into the system and measure pressures directly with a gauge.

    A 5GS07 is a very high pressure pump for a geothermal heat pump. My curves show that it delivers 5 GPM at about 370 ft of head (160 psi). I would expect that pressure drop across the water side of an evaporator would be on the order of 10 to 15 psi. I wouldn't rely on the accuracy of trying to infer the pressure drop in a heat exchanger for those conditions.
  3. speedbump

    speedbump Previous member

    Messages:
    4,540
    Location:
    Riverview, Fl.
    I'm a little foggy about what you did. You measured the amps with the pump producing 5 gpm. Where did you measure this 5 gpm from? If that is the total output of the pump it won't run a GWHP larger than two tons. And at that rate you will have zero water for the house.

    bob...
  4. TinHead

    TinHead HVAC

    Messages:
    9
    Location:
    CT
    Bob NH
    OK, I see the GPM isn't really gonna help me here, with all those variables involved... Thanx.

    I went out and got a pressure gauge, only to find while cleaning the years of soot-web-and dust, there was already a pressure gauge hiding underneath the pressure switch and wires.

    This is what my existing system registered while watching the guage...
    System called for pump at 30PSI (Pressure switch setting)
    System went up 1PSI every 2 seconds
    System shut pump off at 59 PSI

    I was not expecting the incremental nature of the results, so I'm at a loss if this data is helpfull.

    Note - I wasn't planning on using the existing pump for the geo-heatpump, I was trying to determine the optimum replacement HP of a new pump, using the performance of the exiting system.
    New pump will be around 13gpm @ .75 hp.

    Heatpump is looking for a 7.2 GPM @ a 9psi coil loss, but I'm setting it up for the future install of a 9 GPM unit with a similar coil loss.
    My existing 6" 450' well, with a normal static of 1', will be used as the supply with a return pipe added to below water level (I'm thinking 80' should suffice).
    I ran a draw down test this summer (2hrs@5gpm) and found the static at 107'
    Normal static is about 6' higher than the Heatpump coil

    The enigma of the Heatpump needing gpm's, but the domestic water needing PSI is kicking this simple tinknockers brain :confused:
    I think I'd rather cater to the Heatpump, and add a booster for the domestic water pressure if needed.
    I don't like the idea of another pump in the well, I think 3 pipes is a wee bit overcrowded.

    Any input you might have is well appreciated... pun intended :D
  5. TinHead

    TinHead HVAC

    Messages:
    9
    Location:
    CT
    speedbump
    I was thinking about taking an exact gpm from where the well line enters my basement, in order to get a grip on how hard my existing pump is working, as to assist me in sizing a replacement pump to accomodate the Geoheatpump I've aquired.
    Sorry if I gave you the wrong impression!

    You can get the details from my previous post to Bob NH.

    I do have another question that I failed to ask in my other post...
    While examining my pressure switch I noticed I have L1 and L2 wired to A1 & B1 on the pressure switch, and the pump motor is wired to A2 & B1 (A being first contactor and B being the second).
    So one of my two hot legs is always in contact with one leg of the pump, is this OK?
    (I did check the wiring diagram at SquareD, and they show it the way you would expect A1 & B1, A2 & B2)

    Thanx in Advance for any input you might have 8)
  6. speedbump

    speedbump Previous member

    Messages:
    4,540
    Location:
    Riverview, Fl.
    The switch, L1 and L2 are the hot legs, these are the two outer screws. The two inner screws are the load or the motor lugs. You can reverse the wires from outer to inner and it won't have any ill effects.

    If you did a pump test on that well at only 5 gpm and drew it down over 100 feet, I don't think this thing is going to run a GWHP. Your well does not have the capacity you will need. If it were my well, I would be happy to have enough water for the home and forget all about the GWHP.

    bob...
  7. valveman

    valveman Moderator Staff Member

    Messages:
    4,549
    Location:
    Lubbock, Texas
    I have a 3 ton Heat Pump that is working at 4.5 GPM. My well only makes 4 GPM and has about 100 gallons of storage. This well also feeds two houses but, everything is run through the Heat Pump first. This causes the cold water in the houses to come out a little warm in the summer and a little colder in the winter. Doesn't seem to be a problem anywhere unless you are in the shower when the heating or AC comes on or off. Then you have to readjust the temperature of the shower a little.

    If your well is 450' deep and you have only pulled the level down to 107' while pumping 5 GPM for two hours, you should have plenty of stored water in the well to make it work. You need your return pipe 80' deeper than the lowest pumping level will ever be. You may not know this pumping level until you can pump more GPM with a larger pump.

    If you take the line directly off the well head, you should be able to get a little over 7 GPM with the pump you have until the water level gets below 200'. You will still be getting about 5 GPM when the water level drops to 380'. This should be a good enough test to see how your well holds up, and at what level you will be pumping from. Then you can size a pump to produce the GPM you need from the actual pumping level in the well.

    When you run the water through the Heat Pump first, the more water you use in the house, the more is going through the Heat Pump. That way when you use 7 or 9 GPM for the Heat Pump, that same water goes to the house if needed before it is dumped back down the well. Otherwise you need 9 GPM for the Heat Pump and another 5 GPM for the house for a total of 14 GPM from the pump.

    Other then not being able to get a cold glass of water from the faucet in the summer, this seems to be working great. It uses a smaller pump, which is good for energy consumption, and doesn't pump the well dry.

    You may have to add in a little for friction loss but, the GPM output of the pump will give you a pretty good indication of the pumping level. You can also get a pumping level by testing the shut off head of the pump. This pump will build 233 PSI if you close off a valve. For every pound less than 233 PSI you see, the pump is lifting from 2.31' deeper. In other words, if you only see 200 PSI after closing a valve, the pump is lifting from 76'. Don't leave this valve completely closed for more than 30 seconds or you will melt your pump but, it is a good way to test for pumping level.

    BTW, my Heat Pump cycles on and off. When it is off the well has time to recover. So you could use twice as much water as the well produces, as long as it only runs half the time.
  8. Bob NH

    Bob NH In the Trades

    Messages:
    3,317
    Location:
    New Hampshire
    Running the heat pump flow (the total gallons, not the GPM) to the higher pressure needed for domestic use is an enormous waste of energy.

    Putting two pumps in the well might be possible but would be a nuisance.

    My approach to developing engineered systems is to develop a concept that will work, and then try to improve on it in ways that make it simpler, more effective, or more efficient. Other solutions are compared by analysis and the real improvements become the new baseline against which further improvements are analyzed or tested.

    I don't know enough of the details of your well and heat pump to design a system, but the following is a concept that could be the basis for a design, and a basis for improvements.

    CONCEPT:
    One pump in the well will supply the flow and pressure required for the heat pump. That pump will supply a greater flow at lower pressure. For example, a Goulds 10GS07 will supply 10 GPM at 250 ft of head and 13 GPM at 195 ft of head.

    A second pump at the surface (maybe a shallow well jet or a booster) will be fed by the well pump and will pressurize water for the other uses. The second pump should have a flow characteristic that is not greater than the well pump will supply at near zero pressure at the takeoff point.

    Domestic uses (total gallons per day) are usually small compared to heat pump demand, but they tend to have high short-term demand. To avoid having the well pump sized for both demands at the same time, I would have the household pump operate with priority over the heat pump compressor system and would cut off the water flow through the heat pump. That could be accomplished by a check valve on the discharge side of the heat pump water circuit so that the domestic pump would automatically take any flow it needs from the well pump circuit.

    If the well pump needs to be a little larger to provide the domestic flow that is not a problem because the increased flow through the heat exchanger will increase heat transfer rates and reduce temperature differences, which will result in some saving in compressor power.

    The well pump should be operating into a fairly large pressure tank so that the interruptions to the heat pump system are infrequent.

    If you are operating an irrigation system, the timing of that system should be set to operate when there is minimal usage of the heat pump system.

    Features of the described system:
    1. Minimizes pumping energy for all uses.
    2. Automatic control of the cycle with priority to household water supply.

    You will need to avoid exposing the water to oxygen so you don't precipitate iron in the well. If the depth to the surface of the water in the well is so great that it reduces the pressure in the heat exchanger to the point where the second pump will cavitate, then it will be necessary to provide a little back-pressure regulation in that return pipe.

    Improvements:
    Possible improvements to the system should be compared on the basis of life cycle costs (investment, energy, maintenance, ??).
  9. speedbump

    speedbump Previous member

    Messages:
    4,540
    Location:
    Riverview, Fl.
    Has anyone looked at the actual savings afforded by owning a GWHP. In my opinion they aren't worth the investment. I owned one with it's own dedicated pump and didn't see any savings at all. Just a lot more maintenance. I also know a lot of people after owning one; traded it in for a good old air to air system.

    I also don't agree with discharging the heated or cooled water down the same well. As you tend to over cool or heat that water the efficiency goes down even more.

    I am surprised at all the GWHP questions lately. Are they trying to make a comeback and is someone doing a lot of advertising? These things came out in the late 60's or early 70's and didn't make much of an impression on energy saving individuals then, so I don't understand the interest in them today.

    bob...
  10. valveman

    valveman Moderator Staff Member

    Messages:
    4,549
    Location:
    Lubbock, Texas
    I work with a lot of heat pump owners. I also helped with some big heat pumps systems on some resorts in Mexico.

    Just installed a 3 ton unit for myself about a month ago. It will be some time before I know how long it will last. So far though, I really like it. It draws about 12 amps of current (240 volt) when the compressor is on, compared to a regular type AC unit that would be using about 21 amps. Availability of water is the key to saving energy and money. If your water well is deep, it cost more to pump it. If the well is shallow or you have surface water, it cost much less to pump it.

    I have a 1/3 HP submersible pumping from about 80' deep. It runs all the time anyway to fill a stock pond. So, I basically just piped it to the house, through the heat pump, teed into the house for supply, and then back to the stock tank. I have a ½" modulating pressure relief valve at the pond. This valve is set to hold back 57 PSI, and dumps anything over 57 PSI to the pond. 57 PSI makes this pump supply 3 GPM all the time. I have a small 1/25th HP pump that comes on when the heat pump comes on, this increases the flow rate to about 4.5 GPM. I can run 4.5 GPM for about 200 minutes before the well runs dry. Then it needs to be off for about 200 minutes for the well to recover. What I have seen so far is that the AC unit runs about 5 or 10 minutes, and then is off for about 5 or 10 minutes. This gives the well plenty of time to recharge and keep up.

    The ½" modulating pressure relief valve, will shut off and stop the water to the pond anytime water is being used at the house. When no water is being used at the house, the pressure relief valve starts dumping 3 GPM to the pond.

    In my case the water is running to the pond all the time anyway. This cost me about $60 to $70 per month in electricity. This makes drawing the heat or cool from the water a freebie. If the well was dedicated to the house and heat pump and not filling a pond, it would probably cost me $30 to $40 per month just for the well. Then the compressor on the heat pump would cost another $50 per month. And then yes, I could probably heat or cool the house with a gas or electric unit for about $100 per month. This would keep the Heat Pump from really saving any money or energy. But, since the water is running anyway, it just makes since to get all the good out of it that I can.

    If the water is deep, maybe 2 or 300' to water, the siphon effect of dumping back into a deep well might not reduce the horse power required by very much. In this case it may be less expensive to use gas or electric instead of a Heat Pump. Many Heat Pump systems use a closed loop to re-circulate the same water in a buried pipe system. This allows the use of a very small pump, maybe 1/25th of a horse power. However, the drilled wells or excavating for the closed loops needed can add considerable expense on installation.

    With ground water Heat Pumps, the depth of the water determines the power cost. However, with shallow or deep wells, many people tell me it is the life of the submersible pump that makes the difference. If the pump is not set up to exactly match the heat pumps needs, the pump is quickly destroyed from cycling. If you must replace the pump every year or two instead of every twenty years, the energy consumed is the least of the problem. With a Cycle Stop Valve on the well pump, the cycling is eliminated and the pump will last a long time. If the pump last long enough, there could possibly still be energy savings even from a deep well application.

    The efficiency of the coils and compressors of the new style heat pumps has made them much more efficient than they were in the 60' and 70's. However, increasing the efficiency has probably made them less durable. Only time will tell if these new style Heat Pumps will last long enough for you to actually see any savings.

    Using the same pump for the domestic use adds very little to the energy equation. It is still the depth to water that has the greatest impact on energy cost.
    Last edited: Oct 15, 2007
  11. TinHead

    TinHead HVAC

    Messages:
    9
    Location:
    CT
    Speedbump
    Sorry for the delayed response.

    As for the wires... Line1 is opposite Load1 as it should be (open circuit),
    but Line2 & Load2 are on the same terminal screw, they are ALWAYS in contact (bypassing the contactor entirely).
    I didn't know if this was intentional, or a screwup.

    As for my 5 GPM yield...
    The heat sink application I'm intending is a standing column well, all the water used for the heat pump, goes back to the well.
    Only domestic water usage leaves the circuit, and thats been fine for 20 years.
    You know more than me, so if I missed something in my reasoning, be sure to point it out, I'm trying to learn.

    Yes, I have done an energy usage calculation using my last years oil consumption, and comparing it to an increase in electricity using the COP of a new GWHP unit and a load calculation of my home.
    At last years prices... my $2,100 oil bill for the winter would translate into a $700 increased electric bill (this does not include the extra electric for the pump).
    In retrospect I should probably have turned my gallons (of oil) used into BTUH and then used the COP of the GWHP to find a more accurate comparison.

    I'll check my supply water temp in Jan and post the numbers for you, but I'm feeling confident my heat sink has more capacity than I will require.
    Standing column wells are supposed to be more efficient than vertical loops at transferring heat (and not as efficient as open loops).

    Thanks for your time.
  12. speedbump

    speedbump Previous member

    Messages:
    4,540
    Location:
    Riverview, Fl.
    I would put the two wires on each terminal instead of both on one. That way you are disconnecting all the potential current from going anywhere when the switch is in the open position.

    I have never heard of taking and putting the water in the same well before. It's a new one to me. I have seen two wells, one for intake and one for exhaust and also the ground loop system. I really don't see how yours could work efficiently with the temperatures being so different from intake to exhaust.

    Well good luck with it, I hope you save some money. With todays fuel costs, thats high on the wish list for most of us.

    bob...
  13. TinHead

    TinHead HVAC

    Messages:
    9
    Location:
    CT
    valveman
    Thanks so much!

    You gave me the info I was originally looking for, which was how to measure the head pressure in my system, in order to size a replacement pump.
    Then you gave me a possible solution that didn't require a pump change at all!

    Cudos to whomever came up with using the return water for domestic use.
    I was completely fixated on adding the volume for dual call situations, I would have never come up with that 8)

    If my pump can do 7gpm's (until 200' to water), then I'm golden, my max GWHP flow is 7.2 (33MBTUH heating@40 degree water).

    OK, so the return pipe should be 80' deeper than the lowest point (to water) expected.
    I'm a little worried about bypassing 40% of my heat sink if I pipe down to 180'.

    In a existing well situation, where GSHP is added later, how is the return line normally installed into the well...
    Is the pitless swaped with a dual pitless, or is it possible just to add another?

    Sounds like you've got quite the system installed at your place.
    It's always good to hear from people who are running a similar system, when you're trying to design one.
    Resorts in Mexico!?!? WOW... that's impressive!

    Thanks again for your time!
  14. Rancher

    Rancher Guest

    Bob, the exchanged heat or cold is going to be transferred to the surrounding earth and aquifer, my Ground Exchange Heat Pump is exactly that, no water involved, lots of copper refrigeration 1/4" tubing buried in a 50' x 50' pit 8' down. It works OK, not sure I would do it again... I wouldn't have done it if I had to pay for the pit to be dug, but I had the time and the backhoe to do it. Yes two wells would have been more efficient.

    Rancher
  15. speedbump

    speedbump Previous member

    Messages:
    4,540
    Location:
    Riverview, Fl.
    Yes a lot more efficient. If your constantly running an air conditioner in a home for instance. Your circulating 7 gpm into a 6" well while drawing water from above it, your going to heat that water in a big hurry. So where is the savings? A GWHP when working properly should send the exhaust water at a temperature of between 90° and 110°. So you can see just how quick 120 gallons of water in that casing is going to heat up. Here in Florida your starting at 72°, so you don't have too far to go before the water is the same temp as the exhaust water.

    bob...
  16. valveman

    valveman Moderator Staff Member

    Messages:
    4,549
    Location:
    Lubbock, Texas
    I would think you should have plenty of heat sink. I would try to keep the discharge pipe as far below the pump as possible. And yes, I don't see why you couldn't use another pitless off to one side and higher or lower than the first one. The domestic use is the only thing that will pull down the water level in the well. The water going to the Heat Pump is returned to the well and should not lower the pumping level. Running 5 GPM for 2 hours before the water level dropped to 107', means that house use would probably not lower the water level much. You would need to check this more closely if you have any irrigation. Otherwise you can probably use a 7GS05 pump which would cut your energy cost by 1/3rd.

    Put a ½" modulating pressure relief valve on the discharge pipe before it enters the well. Set this regulator to hold back about 40 PSI. When the water level is high, this will give you about 8 GPM going through the Heat Pump. If the water level pulls down to 107', this will still give you about 7.2 GPM for the Heat Pump.

    When the Heat Pump is running and someone uses water in the house, the regulator will choke back the amount going down the well to make sure you still have 40 PSI in the house. When water is being used in the house, the flow rate will increase, and the cold water to the house will not have much of a temperature change.

    I also have an 85 gallon bladder tank that give me about 30 gallons of stored water. This keeps the domestic use from taxing the well. However, when you stop using water in the house, the temperature differential across the Heat Pump increases until the pressure tank refills. I think I would have been better off with a much smaller pressure tank. Then the Heat Pump would not be starved for water while the pressure tank is refilling. When this happens my output temp increases from 98 degrees to 126 degrees for about 2 minutes. With a 20 gallon tank that stores 5 gallons of water, I don't think I would be seeing the temp rise for very long. The production from my well is so low that I really need this extra 30 gallons of water for the domestic use. Your well has plenty of water and should not need a very large tank.

    Here is a picture of my set up. Incoming water is 74 degrees. When cooling the outgoing temp is 98 degrees, when heating outgoing is 58 degrees. This unit also has the HWG, which give me free hot water in the 50 gallon tank when the unit is cooling. The blue circulating pump comes on when the AC unit comes on to increase the flow from 3 to 4.5 GPM.

    The brown circulating pump is for another line that feeds a coil in the back of my wood burning stove. This gives me free hot water in the winter when the wood stove is hot. The electric water heater has been turned down. It only comes on if everything else fails to give me free hot water.

    Attached Files:

  17. speedbump

    speedbump Previous member

    Messages:
    4,540
    Location:
    Riverview, Fl.
    Valveman,

    I thought I was a gadget freak. WoW

    Check your PM's on my Forum.

    bob...
  18. TinHead

    TinHead HVAC

    Messages:
    9
    Location:
    CT
    valveman
    A picture!!! Hot Damn now we're talking my speed 8)

    I don't have any other water needs (irrigation) so I'm gonna give it a test 'go' with the pump I have, since I still have my oil baseboard system to back it up.

    I do have a few more questions, very newbie in nature.
    I also came up with a piping design that I thought was somewhat clever.
    I'm gonna try to attach a drawing (never done it before).

    Questions
    I have a 1" flexible line coming from my well (about 30' away), I'm told if I use a single insert fitting to change it to PVC I restrict the volume in the pipe to 6 gpm...
    is there any way around this, like an external fitting to adapt to pvc shed40/80?

    If domestic water use was not an issue with the GWHP water loop I am creating, would I have to install a device (backpressure valve?) to prevent my return line (back to well) from syphoning thru my Taco motorized shutoff?

    If I can't find the valves I need locally, is there a good online source to order from?

    Thanks so much valveman, your help, and everyone else as well, has been
    invaluable!!
    I learned more here than at the installers seminar in New Hampshire... way more!

    View attachment geo layout5.bmp

    My intention was to reduce the head pressure on the pump when the Heat Pump is the only thing calling.
    Last edited: Oct 18, 2007
  19. Bob NH

    Bob NH In the Trades

    Messages:
    3,317
    Location:
    New Hampshire
    When you put an insert fitting into the poly pipe to connect to the PVC you are removing an insert fitting somewhere else, and it shouldn't significantly affect flow. It will improve the flow through insert fittings if you chamfer the inner diameter of the incoming end. They are molded with a sharp corner but putting even a small chamfer at the inlet improves the dynamics of an orifice.

    There will be a tendency for the long drop to water level in the return pipe to cause the pressure in the heat exchanger to drop to the point where you might get cavitation. The pressure in the heat exchanger should not be allowed to drop below about 5 psi absolute.

    If the anti-siphon shown in the sketch is a vacuum breaker that admits air, then you are likely to get air in the water going back to the well, which can oxidize any iron in the water and cause problems. You should have a vacuum gauge on that pipe and throttle the return slightly to avoid cavitation in the heat exchanger.

    You will not get siphoning through the motorized shutoff because when the pump is off the pressure at the end of the return line will be the same as the pressure in the supply line.

    The source of heat for the heat pump is the heat coming through the casing of the well, since you are not drawing water from the aquifer during heat-pump-only operation. To maximize the available useful heat transfer area the water should be reinjected as far from the pump as possible, which means that the 80 ft submergance of the return pipe is losing heat transfer area. The water above that point is not contributing much to the flow and is therefore not a source of heat.

    You will probably want to turn off the compressor of the heat pump when the system calls for domestic water because it will not have an adequate supply of water and may pull the suction temperature below freezing.
  20. TinHead

    TinHead HVAC

    Messages:
    9
    Location:
    CT
    Bob NH
    Glad to hear that a single insert fitting won't inhibit flow much.
    (I really didn't want to have to dig up & replace that line & pitless too.)
    I will be sure to put a nice sanded bevel at that inlet side, as suggested.
    Should I install the new return line 1" as well?
    (as to not mess with pressures)

    As far as the low coil pressure causing cavitation...
    Are you saying to use a ball valve to throttle the pressure up?
    I'll include a pressure gauge upstream from a ball valve so I can watch how it reacts, as you suggest.

    Thanks for the answer on the Taco and syphoning, I can eliminate that from the design, or replace it with a back pressure valve to maintain the min 5psi.

    I'll be watching, and timing, how long it takes for the domestic to satisfy the tank in dual call situations. I might just have to give full priority to the pressure tank and hope it's not 10 below outside 8)

    Thanks for your time Bob, I really appreciate it!
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