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Plant overheating with continuous pumping

asked 2015-01-17 23:36:40 -0600

MattStewart's avatar

updated 2015-01-19 02:56:10 -0600

I have a boiler that supplies hot water to a number of coils. The circulation pump runs continuously however when I select this option my plant overheats. The errors message seems to indicate that additional setpoint managers are needed. As suggested by the error message, I have shortened the run period and results look good but I can only manage to run 7 months before overheating. If you could help me with a few questions maybe I can manage to figure out the problem.

  1. Does the Plant Loop Demand Side need setpoint managers?
  2. Do I need to add a bypass pipe (adiabatic) so that the pump is running a loop regardless of whether heat is being called for?

My thought is an adiabatic pipe parallel to the boiler in the plant loop and adding a setpoint managers before the boiler would be needed to allow the boiler to turn off and on depending on demand. When the boiler is off the pipe will allow the pump to run continuously bypassing the boiler.

My questions are about setpoint managers and where to place them.

Supply side in and out seems appropriate as a longer loop and more load will drop temperature and thus require the boiler to activate. You would want to control the boiler maximum supply temperature and also tell it when it needs to start.

Also, it seems a setpoint manager is needed after the pump to control bypassing the boiler and directing the continuous flow through a parallel pipe.

My pump and boiler are Autosized.

epilogue - after adding additional setpoint managers I am still crashing from excessive temperature. I will try adding additional pumps.

Diagram of the loop

First error occurs during sizing:

Warning ** Missing temperature setpoint for LeavingSetpointModulated mode Boiler named HW BOILER  **   A temperature setpoint is needed at the outlet node of a boiler in variable flow mode, use a SetpointManager * The overall loop setpoint will be assumed for Boiler. The simulation continues ...
   ** Warning ** GetDensityGlycol: Temperature is out of range (too high) for fluid [WATER] density **
   **   ~~~   ** ..Called From:PlantPumps:CalcPumps:,Temperature=[104.99], supplied data range=[0.00,100.00]

  ** Warning ** GetSpecificHeatGlycol: Temperature is out of range (too high) for fluid [WATER] specific heat **
   **   ~~~   ** ..Called From:PlantLoopSolver::EvaluateLoopSetPointLoad,Temperature=[125.02], supplied data range=[0.00,125.00]
   **   ~~~   **  Environment=RUN PERIOD 1, at Simulation time=06/02 23:50 - 24:00
   ** Severe  ** Plant temperatures are getting far too hot, check controls and relative loads and capacities
   **   ~~~   **  Environment=RUN PERIOD 1, at Simulation time=07/31 15:00 - 15:10
   **   ~~~   ** PlantLoop Name (SupplySide)= PLANT LOOP 2
   **   ~~~   ** PlantLoop Setpoint Temperature=67.0 {C}
   **   ~~~   ** PlantLoop Inlet Node (SupplySide) has a Setpoint.
   **   ~~~   ** PlantLoop Inlet Node (DemandSide) does not have a Setpoint.
   **   ~~~   ** PlantLoop Outlet Node (SupplySide) has a Setpoint.
   **   ~~~   ** PlantLoop Outlet Node (DemandSide) does not have a Setpoint.
   **   ~~~   ** PlantLoop Outlet Node (SupplySide) "NODE 19" has temperature=300.0 {C}
   **   ~~~   ** PlantLoop  Inlet Node (SupplySide) "NODE 18" has temperature=300.0 {C}
   **   ~~~   ** PlantLoop Minimum Temperature=0.0 {C}
   **   ~~~   ** PlantLoop Maximum Temperature=100.0 ...
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HI Matt - I retagged this with EnergyPlus, but if you are using an interface like OpenStudio or Design Builder can you please retag your question?

Benjamin's avatar Benjamin  ( 2015-01-18 00:21:39 -0600 )edit

Hi Benjamin, I am an Open Studio user and am excited by all the new features that are constantly added. However, I realize that I might need to learn more on the E+ side to get results.

MattStewart's avatar MattStewart  ( 2015-01-18 01:08:54 -0600 )edit

Hey Matt; did you ever come up with a solution for this issue? I'm experiencing the same (I think) and wanted to check before posting a new question.

NickC's avatar NickC  ( 2015-12-10 10:14:29 -0600 )edit

Hi Nick, no not really. I am interested in seeing your post. Best regards, Matt

MattStewart's avatar MattStewart  ( 2015-12-10 14:46:05 -0600 )edit

1 Answer

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answered 2015-01-18 05:28:29 -0600

updated 2015-01-18 17:54:02 -0600

I had a similar problem previously, and eventually traced the heat to the pump itself rather than the boiler firing when not needed (which could have been a setpoint problem). The solution in that case was to not have the pump run continuously, though you might also adjust the fraction of the pump losses which go to the fluid.

This problem of pump heat building up is mentioned in the suggested possibilities:

**   ~~~   ** Possible things to look for to correct this problem are:
**   ~~~   **   Capacity, Operation Scheme, Mass flow problems, Pump Heat building up over time.
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Jamie, Thank you. Everything runs fine with setting pump to intermittent. I had not thought about pump losses elevating the temperature. This opens up more questions - adiabatic pipe? My plumbing associated with delivery of HW to each air handler is not adiabatic. Thank you for your insights. I did try to add a second pump to represent Boiler Loop but this is not allowed in E+.

MattStewart's avatar MattStewart  ( 2015-01-18 09:06:05 -0600 )edit

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Asked: 2015-01-17 23:36:40 -0600

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Last updated: Jan 19 '15