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Re: [EnergyPlus_Support] Re: Calculated load different from component sizing summery



Jeremiah,

So from a fairly inexperienced E+ user, I'd offer the point that there are two different questions and you should expect different results (although I'm surprised they are that different and figure there is an error in there somewhere).

The difference is the autosizing is being called differently for the design day and the system day. 

The way I understand the design day sizing (cooling) is it runs a sinusoidal case with the design conditions, sweeping the sun across the facade and sizes the system to meet this design day with a factor (typically 1.15 or 1.2 ish for cooling). The system sizing routine does this with a different weather file and can include the capacity changes due to heat recovery, latent loads, humidity control, and my favorite start up loads (snap loads). These other loads can SIGNIFICANTLY change the result and I've had to be really careful in examining the results to make sure I wasn't over/undersizing the equipment. 

I have notes from last months IBPSA USA advanced HVAC class where we talked about the autosizing routines in E+. They were not highly regarded (good start but be careful). Boiling it down the autosize for design day ignores heat recovery and latent loads. Need to check the boiler and/or A/C is loaded correctly on the design day. Recommendation was to size using HAP or Trane Trace and model in E+ not what I wanted to hear but at least honest.

Luck - wish I had more help to offer.
Jason

On Fri, Sep 14, 2012 at 12:41 PM, Jeremiah Crossett <jcrossett@xxxxxxxxxxxxxxx> wrote:
 

Update: I read much documentation and still can not understand why the HVAC sizing summery and the component sizing summery would be 54% different from one another. I did find the files ending in Zsz and this paragraph in the documentation that seems to indicate that the value from the "ZSZ.CSV" file would produce the actual sizing, but also I looked everywhere I could think of in the idf for anything that would change the size in component sizing and could not find anything. So my question remains- why would the component sizing be different from the HVAC sizing summery/"ZSZ.CSV"? and how could I make the results agree with each other? Any advise would be much appreciated as I need to understand how this works to explain it to others. 

Inline image 2

Here is a chart I piloted from the design cooling load "ZSZ.CSV" file- I would like to use this but can only do so if I can explain why this is correct and component sizing is not.
Inline image 1
The only description I could find on these objects below did not provide any insight..

Inline image 1


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

  






On Thu, Sep 13, 2012 at 7:19 PM, Jeremiah Crossett <jcrossett@xxxxxxxxxxxxxxx> wrote:
Dear E+ users, I provided results to an engineering firm today and they asked a question I am not sure how to search for the answer to in the documentation or archives, and I am hopeful that someone might get me up to speed so I can answer his question- 

First the math;
  • Calculated Design Load= [Btu/h]3244.06
  • Maximum Total Cooling Capacity=  [ton]0.416702 ( 0.416702*12,000=[Btu/h]5000.424 
  • So what is the cooling system size recommended by this E+ run , as there is a difference of  [Btu/h]1756.364/[ton]0.1463636
His questions on the attached HTML results are: 
  1. Design load is 3244btu/hr, system load is 5000 btu/hr (0.416 tons), why such a difference?  It seems too much of a difference to be the ventilation load only
  2.  Can you check the space sensible and latent load, the 4000 Btu/h cooling loads I have the system designed to is the total load (sensible + latent), therefore this may further explain the difference, I suspect energyplus is quoting only the sensible load under the calculated design load, this taps into the above question and the system load is likely both, but now this looks too high? 
From my understanding latent+sensible is total load, but if that is the case then why would the component sizing be different than the HVAC sizing summery? 

Many thanks for any thoughts--


Calculated Design Load [Btu/h]User Design Load [Btu/h]Calculated Design Air Flow [ft3/min]User Design Air Flow [ft3/min] Design Day NameDate/Time Of PeakTemperature at Peak [F]Humidity Ratio at Peak [lbWater/lbAir]
BLOCK1:ZONE1 3244.064055.08149.668187.086LOS ANGELES INTL ARPT ANN CLG 1% CONDNS DB=>MWB8/21 16:35:00 79.270.00955


Maximum Heating Air Flow Rate [ft3/min]Maximum Cooling Air Flow Rate [ft3/min]Maximum Total Cooling Capacity [ton]
ZONE1AIR32.12187.090.416702





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

  








--
Jason Quinn
Lead Engineer
Sustainable Engineering Ltd.
82 Liverpool Street
Wanganui 4500
New Zealand

+64 21 1846 911


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