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Unitary system (Water- Air) CC control issues

asked 2023-01-04 12:56:51 -0500

Nithya's avatar

updated 2023-01-04 15:50:27 -0500

Hello fellow modelers! Happy new year!

Background- In an attempt to model an air loop (variable volume, VAVs) with water-to-air heat pump coils (heating and cooling) a Unitary system(s) has been used in Open studio v3.4. The desired control type is Setpoint - air loop is to provide a range of tempered air temperatures based on season (~55F to 65F)

Heating coil is functioning as expected, however cooling coil is not. Upon reviewing these threads on unmet hours, a few alternates have been tried with no resolution.

Solution 1- Eplus migration & change load to SP with setpoint set to after the heating coil.

Result- The load is not seen by the coils and temperature is delivered at 74-75F (zone temp)

Solution 2- More eloborate- creating one Unitary system/ component. It is understood that when using Setpoint control, only 1 coil/component can be used. Change in eplus include:

  • Remove all other components in Unitary system (fan, supplemental coil, heating coil), except for heating or cooling coil
  • Include Fan on Air loop
  • Modify node connections so that Unitary system represents only the coil
  • SPMs on each Unitary system/coil outlet node

Result- Cooling coil still does not activate.

Solution 3- Leave the system on load control.

Result- temperatures coming out of the coil are all over the place with temperatures dipping as low as 44F. Note that CW is being supplied at 85F with district cooling source so CW loop capacity is clearly not the reason.


  • Why doesn't the setpoint control with specified SPM on AHU supply out node act as intended?
  • How is it that control type load which is referncing one zone control act better than setpoint?
  • Why is the cooling coil over cooling when load control is selected?

Here is a snip to the component features in energy plus- image description

Looking forward to your insights here!

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Solutions 1 and 2 should both work. Please share the full idf files with a link here or send to the helpdesk at

MJWitte's avatar MJWitte  ( 2023-01-09 09:41:36 -0500 )edit

@MJWitte - Files submitted to energy plus support-

Nithya's avatar Nithya  ( 2023-01-09 10:08:11 -0500 )edit

1 Answer

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answered 2023-01-30 09:14:51 -0500

Both of these approaches should work, and they did for this coil type until EnergyPlus v9.5. AirloopHVAC:UnitarySystem with setpoint control and water-to-air heat pump coils will be fixed in v23.1 along with some other related issues.

Other coil types are working correctly in AirloopHVAC:UnitarySystem with Setpoint control, but there is some inconsistency about the need for specifying the setpoint control node in coils such as Coil:Heating:Electric. This will also be cleaned up in v23.1 (March 2023 release).

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Asked: 2023-01-04 12:56:51 -0500

Seen: 154 times

Last updated: Jan 30 '23