Unreasonable setting of Approach in HVAC:Template:Plant:Tower

asked 2021-08-16 23:41:34 -0500

Keigo gravatar image

updated 2021-08-17 11:55:22 -0500

When we use HVAC:Template:Plant:Tower or HVAC:Template:Plant:Tower:ObjectReference, the expidf file automatically sets condenser water temperature reset control by SetpointManager:FollowOutdoorAirTemperature as follows:

  CHWloop CndW Temp Manager,                               !- Name
  Temperature,                                             !- Control Variable
  OutdoorAirWetBulb,                                       !- Reference Temperature Type
  0,                                                       !- Offset Temperature Difference
  80,                                                      !- Maximum Setpoint Temperature {C}
  5,                                                       !- Minimum Setpoint Temperature {C}
  CHWloop CndW Supply Setpoint Nodes;                      !- Setpoint Node or NodeList Name

I think Offset Temperature Difference can be regarded as "Approach" of cooling tower. It's set to 0°C, which is unachievable in principle. A quite large range of Minimum Setpoint Temperature and Maximum Setpoint Temperature is also unnatural.

As mentioned in this post, cooling tower is controlled to deliver an unachievable approach of 0°C, and therefore we get high fan energy consumption. When I use HVACTemplate, I always edit expidf file to change this SetpointManager:FollowOutdoorAirTemperature setting.

Is there any reasonable reason why Offset Temperature Difference is set to 0°C by default? I may have overlooked something.

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You haven't overlooked anything. It definitely shouldn't be 0°C for real world applications. It's done on this line https://github.com/NREL/EnergyPlus/bl... The Energy+.idd could use a default for the numeric field too. I suggest making it an enhancement request on https://github.com/NREL/EnergyPlus/is...

Julien Marrec gravatar image Julien Marrec  ( 2021-08-18 05:12:30 -0500 )edit

Thank you for your comment. I'm a little relieved to hear that. I'd like to post a request later. It would be great if HVACTemplate:Plant:ChilledWaterLoop had Condenser Water Temperature Reset fields, as well as Chilled Water Setpoint Reset fields.

Keigo gravatar image Keigo  ( 2021-08-18 21:52:48 -0500 )edit