Results 1 to 23 of 23
  1. #1
    Join Date
    Mar 2010
    Location
    Bangladesh
    Age
    34
    Posts
    151
    Rep Power
    8

    Chilled water Pump



    We have a closed loop chilled water system with three circulation pump installed in parallel. Capacity of the three pump is not equal, two of them is 55 m3/hr and another one is 45 m3/hr. Did it cause any problem with the smaller one if we run the three pump at a time?



  2. #2
    Join Date
    Oct 2007
    Location
    manchester
    Age
    44
    Posts
    5,707
    Rep Power
    39

    Re: Chilled water Pump

    Depends if each pump outlet has non return valves

  3. #3
    Join Date
    Oct 2001
    Location
    Nottingham UK
    Posts
    5,078
    Rep Power
    42

    Re: Chilled water Pump

    I would ask if the connected pipework can handle 155m3/hr?
    I'm back on the Pale

  4. #4
    Join Date
    Mar 2010
    Location
    Bangladesh
    Age
    34
    Posts
    151
    Rep Power
    8

    Re: Chilled water Pump

    yes we have non return valves for each pump. NRV is good enough?

  5. #5
    Join Date
    Mar 2010
    Location
    Bangladesh
    Age
    34
    Posts
    151
    Rep Power
    8

    Re: Chilled water Pump

    Connected pipe can handle more then 500 m3/hr. So may be it's not a problem.
    But as we know "All parallel installed pumps must have the same head this usually means they must be running at the same speed, with the same diameter impeller". It make me confused.

  6. #6
    Join Date
    Dec 2008
    Location
    Portugal
    Age
    41
    Posts
    1,039
    Rep Power
    13

    Re: Chilled water Pump

    Quote Originally Posted by Bashir01219 View Post
    Connected pipe can handle more then 500 m3/hr. So may be it's not a problem.
    But as we know "All parallel installed pumps must have the same head this usually means they must be running at the same speed, with the same diameter impeller". It make me confused.
    Each pump has a certain flow at a certain head. When all pumps works at the same time it will obligate all the pumps working at the same head. So an equilibrium of each pump will be reached in manner that a specific flow will be obtained at that head. But that it's not a problem if the head is inside the permissible range of the all pumps, so you will not have problems of minimum flow, as example.

    It's not mandatory the diameter impeller and the speed be the same.
    To make progress is never good enough, I want to do better and better and better

  7. #7
    Join Date
    Mar 2010
    Location
    Bangladesh
    Age
    34
    Posts
    151
    Rep Power
    8

    Re: Chilled water Pump

    Thanks.
    Is it make any adverse effect on the smaller pump, as smaller pump will take similar load like bigger one?
    Quote Originally Posted by Sandro Baptista View Post
    Each pump has a certain flow at a certain head. When all pumps works at the same time it will obligate all the pumps working at the same head. So an equilibrium of each pump will be reached in manner that a specific flow will be obtained at that head. But that it's not a problem if the head is inside the permissible range of the all pumps, so you will not have problems of minimum flow, as example.

    It's not mandatory the diameter impeller and the speed be the same.

  8. #8
    Join Date
    Dec 2008
    Location
    Portugal
    Age
    41
    Posts
    1,039
    Rep Power
    13

    Re: Chilled water Pump

    Bashir,

    You find on the market "smaller" pumps with large Head and small flows and "big" pumps with small Head and large flows. That it doesn't matter if the operating point is inside of the operating envelope of the pump.

    If you want you can send me the curves of each pump and I will check. Also need to know what's the differential pressure between the inlet and outlet of the pumps. Also what's the density of the fluid (is it water)?
    To make progress is never good enough, I want to do better and better and better

  9. #9
    Join Date
    Mar 2010
    Location
    Bangladesh
    Age
    34
    Posts
    151
    Rep Power
    8

    Re: Chilled water Pump

    Quote Originally Posted by Sandro Baptista View Post
    Bashir,

    You find on the market "smaller" pumps with large Head and small flows and "big" pumps with small Head and large flows. That it doesn't matter if the operating point is inside of the operating envelope of the pump.

    If you want you can send me the curves of each pump and I will check. Also need to know what's the differential pressure between the inlet and outlet of the pumps. Also what's the density of the fluid (is it water)?
    I am attaching a simple diagram of our chilled water system. Give me some idea how the system will work? Our total pump flow rate is lesser than chiller required flow rate, so if we add a bigger size pump by replacing on of the three pump, is it will work or we need to do any modification?
    In the isometric diagram all AHU are controlled by 3 way valve and FCU are controlled by electrical solenoid valve and sensors. We run Pump and chiller manually when required at morning. Pump model DMT-65-320 & DMT-50-320 brand: MONOFLO.
    If you required any further data I can supply.
    Attached Files Attached Files

  10. #10
    Join Date
    May 2007
    Location
    Auckland
    Age
    67
    Posts
    3,362
    Rep Power
    31

    Re: Chilled water Pump

    an increase in NPSH ( net positive suction head ) will increase pump flow and motor current draw of motor, so allow for power increase on any pump if any other pump stops, comes down to selection of pump and motor Kws. Mono pumps are good selection so long as installed in horizontal arrangement so are self ventilating for any air in system.
    Last edited by Magoo; 26-09-2012 at 05:02 AM.

  11. #11
    Join Date
    Mar 2010
    Location
    Bangladesh
    Age
    34
    Posts
    151
    Rep Power
    8

    Re: Chilled water Pump

    Quote Originally Posted by Magoo View Post
    an increase in NPSH ( net positive suction head ) will increase pump flow and motor current draw of motor, so allow for power increase on any pump if any other pump stops, comes down to selection of pump and motor Kws. Mono pumps are good selection so long as installed in horizontal arrangement so are self ventilating for any air in system.
    Its a closed loop, so may be NPSH is not an big issue only pipe friction is our concern.

  12. #12
    Join Date
    Dec 2008
    Location
    Portugal
    Age
    41
    Posts
    1,039
    Rep Power
    13

    Re: Chilled water Pump

    Quote Originally Posted by Bashir01219 View Post
    I am attaching a simple diagram of our chilled water system. Give me some idea how the system will work? Our total pump flow rate is lesser than chiller required flow rate, so if we add a bigger size pump by replacing on of the three pump, is it will work or we need to do any modification?
    In the isometric diagram all AHU are controlled by 3 way valve and FCU are controlled by electrical solenoid valve and sensors. We run Pump and chiller manually when required at morning. Pump model DMT-65-320 & DMT-50-320 brand: MONOFLO.
    If you required any further data I can supply.
    I don't know that mark of pumps. Can you give me the selected curves Q-H.

    If you replace one of a pump (for instead the smaller one) by bigger one the flow will increase and the head loss on the pipe, on the aircoolers and on the chiller will be higher due to the increase of the velocity on the pipe (dependence is the square flow, app.). See how much flow is need and what the total head loss you have on the piping. Also have in mind that increasing the head of the pumps each pump will delivery less flow than the present one.

    You also could increase the speed (N) of the two bigger pumps using a frequency converter for both the pumps. The H varies with N^2 and the flow with N. Be aware the electrical power will vary app. with the N^3.
    To make progress is never good enough, I want to do better and better and better

  13. #13
    Join Date
    Dec 2008
    Location
    Portugal
    Age
    41
    Posts
    1,039
    Rep Power
    13

    Re: Chilled water Pump

    ...Or why not increasing also the speed of the smaller one? All pumps running with the same frequency converter at the same speed.
    The system should be pressurized because with the increase of the speed the NPSH of the pump will be higher and they could cavitate mainly when the water is hot, at the cooling period.
    To make progress is never good enough, I want to do better and better and better

  14. #14
    Join Date
    Oct 2003
    Location
    Belgium
    Age
    56
    Posts
    5,519
    Rep Power
    28

    Re: Chilled water Pump

    Quote Originally Posted by Sandro Baptista View Post
    Each pump has a certain flow at a certain head. When all pumps works at the same time it will obligate all the pumps working at the same head. So an equilibrium of each pump will be reached in manner that a specific flow will be obtained at that head. But that it's not a problem if the head is inside the permissible range of the all pumps, so you will not have problems of minimum flow, as example.

    It's not mandatory the diameter impeller and the speed be the same.
    Sandro, good reply
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  15. #15
    Join Date
    Mar 2010
    Location
    Bangladesh
    Age
    34
    Posts
    151
    Rep Power
    8

    Re: Chilled water Pump

    Quote Originally Posted by Sandro Baptista View Post
    ...Or why not increasing also the speed of the smaller one? All pumps running with the same frequency converter at the same speed.
    The system should be pressurized because with the increase of the speed the NPSH of the pump will be higher and they could cavitate mainly when the water is hot, at the cooling period.
    I can measure the required flow rate but How can I measure total head loss on the Pipe (If I understand correctly, there is no head loss in a closed loop system, only friction loss. The chiller is installed in roof top and pipes vertical lift is 60' and horizontal lift is 500' supply+return)? Selected Q-H is not in the installation book, can we prepare it now? If yes then how?
    If we increase the pump rpm, will it not affect on pump motor?
    Last edited by Bashir01219; 29-09-2012 at 03:38 AM.

  16. #16
    Join Date
    Dec 2008
    Location
    Portugal
    Age
    41
    Posts
    1,039
    Rep Power
    13

    Re: Chilled water Pump

    Quote Originally Posted by Bashir01219 View Post
    I can measure the required flow rate but How can I measure total head loss on the Pipe (If I understand correctly, there is no head loss in a closed loop system, only friction loss. The chiller is installed in roof top and pipes vertical lift is 60' and horizontal lift is 500' supply+return)? Selected Q-H is not in the installation book, can we prepare it now? If yes then how?
    If we increase the pump rpm, will it not affect on pump motor?
    Bashir the head loss is pressure loss, which includes friction loss either. Of course if you have a closed loop with all the pipe path fill with water the geodetic effect doesn't count.

    Measure the pressure loss by measuring on the gauges the pressure you have at the discharge of a operating pump (before check valve) minus the pressure loss at the suction inlet.

    Without the Q-H curve you can risk damaging the pumps internally. Try to get it from the internet or manufacturer.

    If we increase the pump rpm the motor can trip by overloading but also it can happen nothing if presently the shaft power absorbed is far way from the nominal power. You can check that on the the Q-H-P curves and check it with a current meter.
    To make progress is never good enough, I want to do better and better and better

  17. #17
    Join Date
    Mar 2010
    Location
    Bangladesh
    Age
    34
    Posts
    151
    Rep Power
    8

    Re: Chilled water Pump

    Quote Originally Posted by Sandro Baptista View Post
    Bashir the head loss is pressure loss, which includes friction loss either. Of course if you have a closed loop with all the pipe path fill with water the geodetic effect doesn't count.

    Measure the pressure loss by measuring on the gauges the pressure you have at the discharge of a operating pump (before check valve) minus the pressure loss at the suction inlet.

    Without the Q-H curve you can risk damaging the pumps internally. Try to get it from the internet or manufacturer.

    If we increase the pump rpm the motor can trip by overloading but also it can happen nothing if presently the shaft power absorbed is far way from the nominal power. You can check that on the the Q-H-P curves and check it with a current meter.
    Thanks a lot. It's working.
    Do you have any operation guideline for closed loop chilled water system with basic design criteria?

  18. #18
    moideen's Avatar
    moideen is offline Veteran Poster I am starting to push the Mods: of RE
    Join Date
    Apr 2008
    Location
    u.a.e
    Age
    42
    Posts
    417
    Rep Power
    16

    Re: Chilled water Pump

    find the link.it might be help you

    http://www.cedengineering.com/upload...cteristics.pdf

  19. #19
    Join Date
    Dec 2008
    Location
    Portugal
    Age
    41
    Posts
    1,039
    Rep Power
    13

    Re: Chilled water Pump

    Quote Originally Posted by moideen View Post
    That's a "hell" good information. Thanks a lot...it's very useful...as much info we can get better...
    To make progress is never good enough, I want to do better and better and better

  20. #20
    Join Date
    Dec 2008
    Location
    Portugal
    Age
    41
    Posts
    1,039
    Rep Power
    13

    Re: Chilled water Pump

    Quote Originally Posted by Bashir01219 View Post
    Thanks a lot. It's working.
    Do you have any operation guideline for closed loop chilled water system with basic design criteria?
    Bashir,

    Thanks your feedback.

    What you have done exactly?
    To make progress is never good enough, I want to do better and better and better

  21. #21
    Join Date
    Mar 2010
    Location
    Bangladesh
    Age
    34
    Posts
    151
    Rep Power
    8

    Re: Chilled water Pump

    Thanks.
    We have calculated the head loss and find H vs flow curve of the pump. Now we have a clear idea what our problem is. I hope so!
    We asked new quotation from the supplier according to our requirement, and also give them details data so that they can suggest us for betterment.

    Quote Originally Posted by Sandro Baptista View Post
    Bashir,

    Thanks your feedback.

    What you have done exactly?

  22. #22
    Join Date
    Mar 2010
    Location
    Bangladesh
    Age
    34
    Posts
    151
    Rep Power
    8

    Re: Chilled water Pump

    Thanks Sir.

    Already I have collect it. CED engineering have lots of effective reading materials.

    Quote Originally Posted by moideen View Post

  23. #23
    Join Date
    Dec 2008
    Location
    Portugal
    Age
    41
    Posts
    1,039
    Rep Power
    13

    Re: Chilled water Pump

    Quote Originally Posted by Bashir01219 View Post
    Thanks.
    We have calculated the head loss and find H vs flow curve of the pump. Now we have a clear idea what our problem is. I hope so!
    We asked new quotation from the supplier according to our requirement, and also give them details data so that they can suggest us for betterment.
    But said that is working...what changed? I presume you are waiting for the quotation so you didn't install yet the new pump.
    To make progress is never good enough, I want to do better and better and better

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •