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Openstudio/energyplus precision cooling

asked 2016-09-28 08:34:19 -0600

HJOJOA gravatar image

updated 2017-09-09 13:24:34 -0600

Hi,

I´m trying to simulate a one thermal zone datacenter with a precision cooling air conditioning system, formed by a water condenser dx coil (water to air heat pump zone equipment) and a water coil, located in Bogota Colombia. Some hours at the day, its very common to use dry coolers fore full dx operation, several hours at the day we can use the dry cooler with water-cooled dx system and water coil at the same time (partial indirect free cooling), ant other hours total indirect freecooling to cool the datacenter.

The thing is the coil an the zone equipment are in the same water loop, the question is. How can i set the coil operation to be available only when the water loop temperature leaving the dry cooler is below the air supply temperature, and turn off the dx coil when the water loop leaving the dry cooler is below 60°F.

In the water loop, which set point manager is better for dry coolers? If there are two different system in the water loop (cooling water coil and water to air heat pump) which loop type do i need to set? cooling, condenser ? C:\fakepath\DATACENTER.jpg

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answered 2016-09-29 11:25:57 -0600

updated 2016-09-29 15:37:33 -0600

Here's what I'd do: (link to the test model)

Create an AirLoopHVAC to serve the Data Center Zone with:

  1. Coil:Cooling:Water
  2. AirLoopHVACUnitarySystem (with WaterToAir HeatPump)
  3. SetpointManager:SingleZoneReheat
  4. AirTerminal:SingleDuct:Uncontrolled

image description

Create a PlantLoop to act as the heat rejection loop with:

  1. Sizing:Plant (click dotted line in middle of loop and scroll down)
    • Loop Type = Condenser
  2. Pump:VariableSpeed or Pump:ConstantSpeed
    • Control Type = Intermittent
  3. FluidCooler:SingleSpeed or FluidCooler:TwoSpeed
  4. SetpointManager:FollowOutdoorAirTemperature
    • Reference Temperature Type = OutdoorAirDryBulb
  5. HeatExchanger:FluidToFluid
    • Control Type = CoolingSetpointOnOff
    • Heat Transfer Metering End Use Type = FreeCooling
  6. Connect the Heat Pump Heating and Cooling Coils from the AirLoopHVACUnitarySystem to this loop

image description

Create a PlantLoop to act as the free cooling loop with:

  1. Sizing:Plant (click dotted line in middle of loop and scroll down)
    • Loop Type = Cooling
    • Design Loop Exit Temperature = 60F
  2. Pump:VariableSpeed or Pump:ConstantSpeed
    • Control Type = Intermittent
  3. Connect the HeatExchanger:FluidToFluid (from My Model)
  4. SetpointManager:Scheduled
    • Make a 60F schedule and assign it here
  5. Connect the Coil:Cooling:Water (from My Model)

image description

Here is the cooling rate before adding the chilled water coil and free cooling loop:

image description

Here is the cooling rate after. Notice that the chilled water coil (blue) is picking up part of the load, and the heat pump coil (orange) is picking up the rest of the load.

image description

EDIT Yes, the water-to-air HP is actually doing less cooling in the second picture, it's just hard to see since the scales and screenshots aren't identical. Here's a before (green) and after (pink) of the HP coils plotted on the same plot.

image description

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Comments

1

Nice summary, Andrew! Interesting that, in your second chart the cooling rate of the HP coil is not actually reduced compared to the no-CHW case.

Eric Ringold gravatar image Eric Ringold  ( 2016-09-29 12:01:56 -0600 )edit

@Eric Ringold check out this new plot, which makes it easier to see.

aparker gravatar image aparker  ( 2016-09-29 15:38:55 -0600 )edit

@aparker: nice.

Eric Ringold gravatar image Eric Ringold  ( 2016-09-29 15:46:41 -0600 )edit

Cool, great stuff!

Lyle K gravatar image Lyle K  ( 2016-09-30 16:27:31 -0600 )edit
1

answered 2018-04-25 14:18:09 -0600

NasimMirian gravatar image

updated 2018-04-25 14:18:33 -0600

Thank you for the great explanation. I used the same method to create a free cooling coil coupled with water cooled DX system for an office building in Phoenix AZ. the problem is the Free cooling coil does not show any cooling effect on the passing air while the water temperature after the coil is increase and there is some cooling rate. should there be any set point temperature after the FCC? any suggestion?

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1

answered 2016-10-01 13:17:56 -0600

HJOJOA gravatar image

Thank you, with problems comes the answers necessity, i appreciate the time everybody took to help me.

I create the model, similar and is evident the reduction in cooling compressors energy consumption, but the only item i don´t understand is How the freecooling loop work when the outdoor condition is not sufficient to use indirect freecooling and the effect is reverse, to heat the air in place of to cool the air.

In other words, how do i tell the program to deactivate the freecooling loop when the water is above 60°F?

with this "Heat Transfer Metering End Use Type = FreeCooling"

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Comments

That's what the "CoolingSetpointOnOff" control type in the heat exchanger does; whenever the heat exchanger can meet the cooling setpoint of the loop (in this case, created by the 60F SetpointMananger:Scheduled), the heat exchanger opens up all the way for maximum heat transfer, potentially undershooting the 60F setpoint. Check out this documentation to see the description of the heat exchanger control types.

aparker gravatar image aparker  ( 2016-10-01 14:45:44 -0600 )edit

Thank you, understood.

HJOJOA gravatar image HJOJOA  ( 2016-10-01 23:18:06 -0600 )edit

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Asked: 2016-09-28 08:34:19 -0600

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Last updated: Apr 25 '18