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Cooling tower outlet temperature error

asked 2018-01-26 09:36:00 -0600

updated 2018-01-27 04:52:09 -0600

I'm modelling a water cooled chiller loop in EnergyPlus. I set the cooling tower to cool down water from 35 to 30°C:

  • I set 30°C as Design Loop Exit Temperature in the Sizing:Plant object;
  • All mass flow rates are autosized;
  • Reference Entering Condenser Fluid Temperature is set to 30 in the Chiller object;
  • The outlet temperature of the cooling tower is set to 30 in the SetpointManager:Scheduled object.

I would expect the inlet and outlet temperatures of the cooling tower to range between 35 and 30°C, but in fact they are as plotted below. I've modelled this kind of system other times, that's why I don't get what I'm missing out. What other input should I check to see where the error is? Thanks

image description

Edit: the outdoor wb temperature is below.

image description

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Could you add the outdoor wet-bulb temperature to this plot?

rraustad gravatar image rraustad  ( 2018-01-26 13:00:33 -0600 )edit

I added the temperature plot. Shouldn't I expect the inlet and outlet temperature of the cooling tower to be independent of the oudoor temperature? Thanks

jack_l gravatar image jack_l  ( 2018-01-27 04:54:13 -0600 )edit

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answered 2018-01-27 12:26:53 -0600

updated 2018-01-27 13:16:21 -0600

The performance of a cooling tower is very dependent on outdoor wet-bulb temperature. See equation 17.3 on pg 977 in V8.8 Engineering Reference. However, if there is a set point temperature on the condenser loop, the tower should control to that temperature. Also read section 17.1.1.4 Calculating the Actual Exiting Water Temperature and Fan Power on pg 980.

CondenserLoop,
  Chilled Water Condenser Loop,  !- Name
  Water,                         !- Fluid Type
  ,                              !- User Defined Fluid Type
  Tower Loop Operation,          !- Condenser Equipment Operation Scheme Name
  Condenser Supply Outlet Node,  !- Condenser Loop Temperature Setpoint Node Name
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Thank you, I will check that out.

jack_l gravatar image jack_l  ( 2018-01-29 02:48:47 -0600 )edit

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Asked: 2018-01-26 09:36:00 -0600

Seen: 275 times

Last updated: Jan 27 '18