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 02453

781.907.9000 main

781.907.9350 direct  

617.285.2162 mobile  

781.907.9009 fax

www.sgh.com

Send Files

__._,_.___

Posted by: Bereket Nigusse <nigusse_ba@xxxxxxxxx>

EnergyPlus support is found at: http://energyplus.helpserve.com or send a message to energyplus-support@xxxxxxxx The EnergyPlus web site is found at: http://www.energyplus.net/ The group web site is: http://groups.yahoo.com/group/EnergyPlus_Support/ Attachments are currently allowed but be mindful that not everyone has a high speed connection. Limit attachments to small files. EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.

Visit Your Group

New Members 6

• Privacy • Unsubscribe • Terms of Use