The fan is variable speed and does run at a lower speed at times. I am running a short hot period to check SHR. If I put low SHR values I get RH calculation
failures. I have had to put in SHR greater than coil calculation to fix RH calculation for some reason.
kNed Lyon, P.E. (MA, WV)
Staff Consultant
SIMPSON GUMPERTZ & HEGER
781.907.9000 main
781.907.9350 direct
617.285.2162 mobile
781.907.9009 fax
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From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
Sent: Monday, July 10, 2017 10:42 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Coil:Cooling:DX:TwoSpeed and SHR
Ned,
This thread and, apparently, E+ assume that you have lower airflow at the lower DX capacity stage. Is that true for your model? (i.e., is fan speed constant?)
On Mon, Jul 10, 2017 at 10:34 AM, 'Edward G. Lyon'
eglyon@xxxxxxx [EnergyPlus_Support] <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:
Thanks for your full explanation�I agrree�my issue is that the inputs for a two speed D coiil are not following the game plan. Increasing SHR stops humidity calculation errors�
Ned Lyon, P.E. (MA, WV)
Staff ConsultantSIMPSON GUMPERTZ & HEGER
781.907.9000 main
781.907.9350 direct
617.285.2162 mobile
781.907.9009 fax
www.sgh.com
Send FilesFrom: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
Sent: Friday, June 30, 2017 4:05 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Coil:Cooling:DX:TwoSpeed and SHR
Edward,
DX cooling coils that are running at lower speed, which also implies lower supply air flow rate, is expected to have lower SHR compared to higher speed. The main reason is that the whole coil surface area is available for lower supply air flow, hence a better coil surface and air contact that enhances moisture removal. When the air has more contact with the cold coil surface, the fraction of supply air approaching the apparatus dew point increases, which enhances de-humidification potential.
Some humidity control features of DX system allow the supply fan to run at reduced supply air flow rate to enhance de-humidification potential.
Hope this helps,
Bereket
From: "'Edward G. Lyon' eglyon@xxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx>
To: "'EnergyPlus_Support@xxxxxxxxxxxxxxx'" <EnergyPlus_Support@xxxxxxxxxxxxxxx>
Sent: Friday, June 30, 2017 3:18 PM
Subject: [EnergyPlus_Support] Coil:Cooling:DX:TwoSpeed and SHR
I am modeling an existing building with several roof top VAV systems. I have system model numbers so I did not autosize any of the Coil:Cooling:DX:TwoSpeed system. The SHR inputs for the model and error messages running the model make no sense to me:
Manufacturer data says SHR at low speed is much lower than at high speed (makes perfect sense to me), but E+ complains if the high speed and low speed SHR differ too much.
Using manufacturer data to calculate SHR inputs results in psychrometric calculation errors about RH exceeding 100%. While the error message would suggest that more latent cooling is needed (lower SHR) the actual fix is to increase the SHR (less latent cooling).
So my model runs now runs without complaints with high speed SHR = low speed SHR = 0.77, not close to the manufacturer data. I would appreciate it if anyone could explain this E+ logic to me this.
Ned Lyon, P.E. (MA, WV)
Staff Consultant
SIMPSON GUMPERTZ & HEGER
| Engineering of Structures and Building Enclosures
41 Seyon Street, Building 1, Suite 500
Waltham, MA 02453781.907.9000 main
781.907.9350 direct
617.285.2162 mobile
781.907.9009 fax
www.sgh.com
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Posted by: "Edward G. Lyon" <EGLyon@xxxxxxx>
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