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Re: [EnergyPlus_Support] Re: ASHRAE 90.1 Climate Zone Code


I've kept silent on this thread so far, but I'd like to add a point of view that's somewhat contrary to what has been posted.

While I agree with all the reasons given why the ASHRAE 90.1 Climate Zone may differ from the Climate Zone shown on EnergyPlus EPW weather files, I don't agree with the opinion that the former are more correct, except in the bureaucratic
sense that's what Standard 169 has stipulated and therefore must be used for that location.

ASHRAE 90.1 Climate Zones are based primarily on Heating and Cooling Degree Days (leaving aside the subregion classification
by humidity), and of course these will vary depending on the raw data used in their tabulation.  ASHRAE Standard 169 tabulates them for the same periods of record used to calculate the Climatic Design Conditions shown in the ASHRAE Handbook, so these  degree days can be regarded as long-term average values from at least 8 years to as much as 25 years (not 60!), ending a year or two before the Handbook Revision date.

The ASHRAE 90.1 Climate Zone on an EnergyPlus EPW (it's not part of the original weather file) are based on Heating and Cooling Degree Days calculated from that weather file.  If it's a "typical year" weather file, as are all those on the EnergyPlus Weather web site (and provided the creator did the job right :-)) , its degree days should be within a few percent of what would have been calculated from the original source data.  If the Climate Zone differs from what's listed in Standard 169, it's more likely the causes are: (1) different periods of record, e.g., the 229 IWEC weather files on the EnergyPlus Weather web site were developed in 2001, or (2) different source data, i.e., different weather stations were used.

Lastly, anytime Climate Zones are defined by climatic variables, there will always be locations near the boundaries that will shift when a different set of raw data are used. In the latest revision of ASHRAE Standard 169, hundreds of US locations got assigned to neighboring Climate Zones.

So what's my point?  My point is that while we should understand and appreciate why the ASHRAE Climate Zone may differ between ASHRAE 90.1/Standard 169 and a particular EPW weather file, and we should use the former when applying ASHRAE-90.1, we should not dismiss the latter as necessarily flawed or faulty.

Joe
Joe Huang
White Box Technologies, Inc.
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On 4/16/2014 7:07 AM, <mailto:seanking.1970@xxxxxxxxxxx>seanking.1970@xxxxxxxxxxx wrote:
>  
Dear Linda, Rahsan, Jean and Jason,

> 
> Thank you very much for all your replies.
> In order to do right baseline opaque/fenestration constructions (closely climate related), it now makes sense that the climate zone (number may or may not be followed by a letter) must be chosen from ASHRAE 90.1 Standard (E+ weather stat file does not often reflect the up-to-date weather conditions or differs from the conditions ASHRAE is using, or it has simply been converted by some mechanisms).
> For the weather file, we need to select/download one from E+ for an exact modeling location or as close as possible to where the model building is located, which is easy (not for a non popular location though) for us to implement.
> I would like to confirm this as a settled case, but still be happy to hear different voices.
> Thank you very much again for your valuable replies and help.
> Best regards,
> Sean


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