Modeling PTAC system with economizer (E+)

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Hi, all,

I'm trying to model a PTAC system with economizer within E+ environment.

The specification of the system is:

The OA economizer here is to provide "free" cooling during times of cool
ambient conditions. The amount of outside air taken into the building will
vary between the design percentage and the maximum percentage. And
the design percentage of OA of the system is not defined as related to
occupancy or floor area but 25% of total supply air.

I read the I/O reference about Controller:OutdoorAir, but it seems:

"If all the limits are satisfied, the outdoor air controller does the
following for cycling fan systems: the outdoor air flow rate is set to the
maximum when the fan cycles on. If the limits are not satisfied, the
outdoor air flow rate is at the minimum when the fan cycles on."

The problem is it's either minimum or maximum instead of modulating
according to outdoor and return air condition?

Does anyone have suggestions on this? Help greatly appreciated.

Do I have to go to EMS for this control scheme?


Qinpeng Wang

Qinpeng Wang's picture
Joined: 2012-03-05
Reputation: 0


You might get responses to your question on the EnergyPlus_Support bulletin board than on

Joe Huang

Joe Huang's picture
Joined: 2011-09-30
Reputation: 406

Normal PTAC equipment does not ever have an economizer, so the E+ object does not allow it.
If you really need to model a DX cooling system with economizer, construct an E+ air loop with equivalent components for the fan, DX coil, supplemental heat, etc.

James V Dirkes II, PE, BEMP, LEED AP

James V Dirkes II, PE's picture
Joined: 2011-10-02
Reputation: 203