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Heat Pumps with Variable Speed Fan

asked 2016-03-18 13:05:44 -0600

Pranav gravatar image

updated 2018-07-07 10:38:26 -0600


OS does not have an option of variable speed fan control for water to air heat pumps. Therefore, I tried modeling the variable speed control in E+ text based editor, but got the following error.

* Severe * MixedAir: Missing temperature setpoint for economizer controller OAC BAG DUMP * Severe * Node Referenced (by Controller)=NODE 189 * ~~~ * use a Setpoint Manager with Control Variable = "Temperature" to establish a setpoint at the mixed air node."

This error showed up after I specified the follwing schedule for "Supply Air Fan Operating Mode Schedule Name", which is needed for "Fan:VariableVolume". Production Schedule, !- Supply Air Fan Operating Mode Schedule Name

I don't understand what E+ is looking for. How could a setpoint be specified for mixed air? Also, why didn't this error show up when a setpoint controller was not specified in OS? Looks like this is an advanced level of HVAC requirement by E+ after variable speed control and fan operating schedule is specified.

Any feedback on this will be helpful!

Regards, Pranav

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answered 2016-03-18 13:27:11 -0600

Currently EnergyPlus only allows cycling fans (Fan:OnOff) for the ZoneHVAC:WaterToAirHeatPump object. Since this is the same in OpenStudio, I would recommend using it instead of the translated IDF for your model.

In the current version of OpenStudio, the Supply Air Fan Operating Mode Schedule Name field can be used for additional control of the fan. Here's the description:

Field: Supply Air Fan Operating Mode Schedule Name

This alpha field specifies the name of the supply air fan operating mode schedule. The supply air fan operating mode may vary during the simulation based on time-of-day or with a change of season. Schedule values of 0 denote that the supply air fan and the heating or cooling coil cycle on and off together to meet the heating or cooling load (a.k.a. AUTO fan). Schedule values other than 0 denote that the supply air fan runs continuously while the heating or cooling coil cycles to meet the load. If this field is left blank, the model assumes the supply air fan cycles with the heating or cooling coil throughout the simulation.

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@MatthewSteen, prima facie, it does not appear that specifying the "Supply Air Fan Operating Mode Schedule Name" will capture the "third power" fan savings of the variable speed control. It's still just an On/Off control. Is that correct?

Pranav gravatar image Pranav  ( 2016-03-19 06:03:17 -0600 )edit

Yes, but it will show savings compared to running continuously.

MatthewSteen gravatar image MatthewSteen  ( 2016-03-21 07:42:08 -0600 )edit

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Asked: 2016-03-18 13:05:44 -0600

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Last updated: Mar 18 '16