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[EnergyPlus_Support] ASHRAE 90.1 building envelope compliance methods
- To: <EnergyPlus_Support@xxxxxxxxxxxxxxx>
- Subject: [EnergyPlus_Support] ASHRAE 90.1 building envelope compliance methods
- From: <seanking.1970@xxxxxxxxxxx>
- Date: 04 Oct 2013 03:58:39 -0700
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- Delivery-date: Fri, 04 Oct 2013 05:01:27 -0600
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Dearl all,
In ASHRAE Standard 90.1 2007 SI Edition, Page.18, it states:
5.5.3 Opaque Areas. For all opaque surfaces except doors, compliance shall be demonstrated by one of the following two methods:
1. Minimum rated R-values of insulation for the thermal resistance of the added insulation in framing cavities and continuous insulation only. Specifications listed in Normative Appendix A for each class of construction shall be used to determine compliance.
2. Maximum U-factor, C-factor, or F-factor for the entire assembly. The values for typical construction assemblies listed in Normative Appendix A shall be used to determine compliance.
My question is simple but very confused to me:
While modelling baseline buildings, there must be different U-factors between using these two options (using certain R-value from column next to U-factor column will certainly not generate the same U-factor shown in that column). Therefore EnergyPlus will generate different outputs on thermal performance (I am quite sure E+ works out heat transfer through building element using its U-factor).
So the question is: How do we know which method we should use in the model? I suppose everyone might prefer a bigger U-factor (when creating a baseline building) for whichever method being used.
Is my understanding right? I look forward to any advisable comments.
Sean
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