[EnergyPlus_Support] Re: "strange" autosize of Coil:Cooling:DX:SingleSpeed

The problem is that the reviewers wrote that the cooling capacity of the baseline model seems to be oversized (17 times). They have compared the sum of the capacities of the Coil:Cooling:DX:SingleSpeed objects with â??COOLING:ELECTRICITY {Maximum}[W]â?? (report PeakEnergyEndUseElectricityPart2Monthly) and the ratio is about 17. The fact is that a lot of spaces are not cooled in the real building and for them I imposed a cooling setpoint temperature equal to 40Â°C (both for the design day and for the annual simulation).

Iâ??m trying to understand how the cooling coils are autosized when in the table â??Zone Coolingâ?? the â??Calculated Design Loadâ??, â??User Design Loadâ??, â??Calculated Design Air Flowâ??, and â??User Design Air Flowâ?? are equal to 0. In EngineeringReference.pdf Iâ??m reading the paragraph â??DX Coil Sizingâ?? . It seems that to autosize the DX cooling coil EnergyPlus considers the â??rated air flow rateâ??, which is â??the maximum of the heating and cooling design flow rates from the design arrayâ??. If I have understood the reference guide correctly, the DX cooling coil is autosized in order to cool the "rated air flow rate" to the supply temperature, which is evaluated by the setpointmanager (in this case SetpointManager:SingleZone:Cooling).

I could explain to the reviewers that since those coils never work they donâ??t affect the energy requirements.

---In EnergyPlus_Support@xxxxxxxxxxxxxxx, <jim@...> wrote :

Francesco,

I think E+ sizes a coil whenever it does autosizing, but its size or capacity has nothing to do with whether it actually is used.

I often include a coil in my objects because its part of a template, but just schedule it to be OFF. E+ sizes it, but never actually uses the coil., so energy = 0. It's normal and OK.

On Thu, Dec 4, 2014 at 12:34 PM, fpasserini.tn@... [EnergyPlus_Support] <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:

I'm autosizing HVAC systems according to appendix G of ASHRAE 90.1 (baseline model). They are Systems 3 (PSZ-AC Packaged rooftop air conditioner).
In a zone where in the real building there is no cooling I have imposed 40Â°C as cooling setpoint. I can see in the .eso output that during the design day the zone temperature is always less than 40Â°C and the â??Cooling Coil Total Cooling Rateâ?? (Coil:Cooling:DX:SingleSpeed) is always equal to 0 W. Moreover, in the .html report â??HVAC Sizing Summaryâ?? in the table â??Zone Coolingâ?? the â??Calculated Design Loadâ?? and the â??User Design Loadâ?? are equal to 0. Nevertheless, in the table â??DX cooling coilâ?? of the html report â??Equipment Summaryâ?? the â??Standard Rated Net Cooling Capacity [W]â?? is not 0 (it is quite high? 35603 WW). Why? If the design load is 0 and the coil is autosized, then its capacity should be equal to 0, shouldn't it?
The coil is controlled by SetpointManager:SingleZone:Cooling
The system doesn't provide outdoor air.
In Sizing:System the "Cooling Design Air Flow Method" is DesignDay.
With Regards
Francesco

--

James V Dirkes II, PE, BEMP, LEED AP
The Building Performance Team
1631 Acacia Drive, Grand Rapids, MI 49504
(M) 616 450 8653
If I decide to act with strength and honor in some instances, but not always, I have made my integrity optional. It's all or nothing.