Re: [EnergyPlus_Support] Is it possible to use alternative HVAC system instead of those defined in 90.1 Standard?

Hi,

It's perfectly doable to model this using a ZoneHVAC:PackagedTerminalAirConditioner.

Two ways:

- Use the ZoneHVAC:PTAC Availability Schedule to be always one during occupied hours and zero otherwise: this completely turns off the PTAC at night, so no heating/cooling if there's a need for it...

- Or, my preferred way: keep the ZoneHVAC:PTAC Availability Schedule to Always one, but use the Supply Air Fan Operating Schedule Name to be always 1 during your occupied hours and always zero otherwise. Make sure you do introduce a setback for unoccipied hours for the zone thermostat.

What this second way will achieve:

- During occupied hours, the value of 1 for this Supply Air Fan Operation Schedule means that the fan runs continuously.

- During unoccupied hours, the value of 0 means the fan is off unless there's a call for heating/cooling. If you do have a big setback, it shouldn't happen much if at all, but if it does you won't get unmet hours since the PTAC will kick in. If it happens, you'll be introducing some fresh air which doesn't seem like a big deal to me (I'm not sure you shouldn't, and it'll have a minimal effect).

Cheers,

Julien

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Julien Marrec, EBCP, BPI MFBA
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2016-08-19 18:44 GMT+02:00 Jim Dirkes jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx [EnergyPlus_Support] <EnergyPlus_Support@xxxxxxxxxxxxxxx>:

Â
Sean,
Clarifying....
I think you are correct that a PTAC in EnergyPlus cannot vary outdoor air amount between occupied and unoccupied periods; it's a fixed amount, although it can differ between heating and cooling modes.
Baseline systems are required to match the flow rate (cfm or m3/s) of the Proposed systems, and outdoor airflow during unoccupied periods must be zero for the Baseline system. (This is not very explicit in Standard 90.1, but the LEED Minimum Energy Performance Calculator clearly requires it.)
If you create an AHU which is equivalent to PTAC, that should be perfectly valid. Details which should match typical PTAC are:
fan power per ASHRAE 90.1
EER / COP per ASHRAE 90.1
The LEED reviewer won't know which part load performance curves that you choose for the DX coil, but I recommend using a curve set which is appropriate for PTAC
On Fri, Aug 19, 2016 at 10:39 AM, seanking.1970@xxxxxxxxxxx [EnergyPlus_Support] <EnergyPlus_Support@yahoogroups.com> wrote:

Â

Hi all,

I meet difficulty to modelÂ ASHRAE 90.1 baseline system #1 (packaged terminal air conditioner) in EnergyPlus to match minimum outdoor ventilation rate with proposed design, which is required by 2007 version G3.1.2.5. My proposed design requires theÂ ventilation of outdoor air flow during occupied hours, but needs to set OA flow rate to 0 during unoccupied hours.

It looks like this cannot be controlled in terms of using schedules in EnergyPlus. My question is, if it is possible for me toÂ use an AHU (CAV, DX cooling coil, hot water coil) in baseline model instead of a PTAC system so that LEED could take it as a valid approach?

I would like very much to receive advice/comments from your experience gained from LEED projects. Thank you very much indeed.

Sean

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James V Dirkes II, PE, BEMP, LEED AP
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Website l Â LinkedInÂ | May 2016 ASHRAE Journal article on energy modeling
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