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Re: [EnergyPlus_Support] PTAC issues

My guess is infiltration or design airflow.  (this was the cause of a similar issue for me on previous models)

Jeremiah D. Crossett  | Senior Analyst  |  Phase Change Energy Solutions
120 E. Pritchard St.  | Asheboro, NC 27203  | Mobile 503-688-8951

On Thu, May 9, 2013 at 11:38 AM, Sankey, Maxim L <msankey3@xxxxxxxxxx> wrote:

Thanks for the response. But I'm still trying to figure out why there is effectively no heating being used. All my heating is coming from electric coils, and my loads/load schedules seem appropriate for the building (people,equip,light). However several of my interior zones have no heating load. I'm also not using fan or heating schedules, could this be the source of the problem?


From: "Richard Raustad" <RRaustad@xxxxxxxxxxxx>
To: "EnergyPlus Support" <EnergyPlus_Support@xxxxxxxxxxxxxxx>
Sent: Thursday, May 9, 2013 9:55:15 AM
Subject: Re: [EnergyPlus_Support] PTAC issues


The warning is telling you that the PTAC is operating in cooling mode when it is -3C outside. Creating a different performance curve will not eliminate the warning (although we should make this a recurring instead of printing thousands of them). What is means by special performance curves is that manufacturers do not provide cooling performance data at these cold temperatures, you need to assure yourself that the curves you are using are accurate at the cold outdoors temps.

DX equipment can have difficulty circulating oil at these temp's which can cause the compressor to fail. It won't fail in the simulation, but it might in a real building.

Although it is possible to need cooling during cold winters, it seems unlikely. For example, an economizer could be used instead. Or if cooling is required, a water-cooled condenser could be used.

You need to determine what in your simulation causes the zone(s) to request cooling. Equipment/lighting loads, ground temperature in contact with the slab, etc.

On 5/8/2013 11:06 PM, Sankey, Maxim L wrote:

I keep getting this error for each zone thousands of times per simulation. I'm using the HVAC PTAC Template. Is there a solution besides creating a performance curve? In the same building I'm getting unrealistic heating energy demand (almost zero). Could these warnings be the source of my low heating loads?

 ** Warning ** CalcDoe2DXCoil: Coil:Cooling:DX:SingleSpeed "FLOOR 5 CORRIDOR PTAC COOLING COIL" - Air-cooled condenser inlet dry-bulb temperature below 0 C. Outdoor dry-bulb temperature = -3.35
   **   ~~~   **  ... Occurrence info = RUN PERIOD 1, 01/01 00:00 - 00:10
   **   ~~~   ** ... Operation at low ambient temperatures may require special performance curves.

Richard A. Raustad
Senior Research Engineer
Florida Solar Energy Center
University of Central Florida
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Cocoa, FL  32922-5703
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Fax:     (321) 638-1439 or 1010
Visit our web site at: http://www.fsec.ucf.edu

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