U and R values is the same. R=1/U. Its very weird if its not the same on ashrae. Maybe a mistake?
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