[Bldg-sim] EnergyPlus Cooling Coils Question

[Michael J Witte]

Jim's comment is valid for the Standard Rated Net Cooling Capacity which 
is reported for DX coils.  I'm guessing you are referring to a chilled 
water coil.

EnergyPlus sizing factors are applied at the zone level, so the Design 
Coil Load already includes the extra 15%.  The difference is that the 
design coil load is based on the actual coil entering and leaving 
conditions at the coil peak load during the sizing calculations, but the 
nominal total capacity is reported at a standard set of inlet/outlet 
conditions (to provide a way to compare coil sizes on the same basis).  
In the Input Output Reference, the description of the Equipment Summary 
output report explains:

Cooling Coils includes the nominal total, sensible and latent 
capacities, the nominal
sensible heat ratio, the nominal efficiency, nominal UA value, and 
nominal surface
area for each cooling coil. These values are calculated by calling the 
cooling coil
simulation routine with the rated inlet conditions: inlet air dry bulb 
temperature =
26.67C, inlet air wet bulb temperature = 19.44C, inlet chilled water 
temperature =
6.67C.

Mike

On 9/9/2014 1:51 PM, King-Scott, Celia wrote:
>
> Hi,
>
> I am having difficulty formulating a response to USGBC about the 
> difference between the Design Coil Load (Btu/hr) and the Nominal Total 
> Capacity (Btu/hr). They are questioning why the difference between the 
> two isn't 15% as required by ASHRAE 90.1 Appendix G. I have over sized 
> all zones by the 1.15 at the zone level like EnergyPlus allows however 
> on this report the difference between the Design Coil Load (Btu/hr) 
> and the Nominal Total Capacity (Btu/hr) is 20%. I found online that 
> the design coil load is indeed the sensible load capacity so this 
> could be the reason that there is a greater percentage than 15% 
> between the two. However, there is not much information on this. I 
> would like to know a bit more about how each of these parameters are 
> calculated in the software. I cannot find much online about it.
>
> Does anyone have some insight on the difference between the Design 
> Coil Load (Btu/hr) and the Nominal Total Capacity (Btu/hr) reported in 
> the Cooling Coils table on the Equipment Summary report? Or direct me 
> to a reference where I can find such information?
>
> Thank you in advance for your help.
>
> Best regards
>
> for KEMA Services Inc., USA
>
>
> *Celia King-Scott PE, BEMP, LEED® AP BD+C *
>
> *Senior Engineer, Sustainable Buildings & Communities*
>
>
> E-mail celia.king-scott at dnvgl.com <mailto:celia.king-scott at dnvgl.com>
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