Dear all,
Our project recently received the comment below regarding window assembly U-value calculations. The project is located in Ireland and therefore the assembly values (which include frame and glass) have been calculated via a European software which complies with BS (British Standard), EN (European Standard) and ISO requirements. The following comment specifically refers to the LBNL software, however is it acceptable to demonstrate compliance with an European alternative?
Provide additional information to confirm that the framed assembly U-value was used for the Proposed Case windows (such as: showing that the whole window assembly has been tested by NFRC; verifying that LBNL Window5 calculations have been provided for the whole assembly; or verifying that the frame effects are captured within the energy modeling software).
Graham Langton
Building Services EngineerPM-Group
1 thumbs up
August 9, 2016 - 5:31 am
Hi Martin,
The reviewer seems to be giving you 3 options to comply here. As you correctly allude to - 1. NRFC tests are not likely to be carried out for EU Fenestration assemblies. 2. You could use WINDOW5 and calculate the entire U-value and show the reviewer these calculations and/or 3. Show the reviewer inputs to your simulation software that the entire U-value (including frame) has been used. Option 3 seems like the best bet as you seem to have calculated via this method.
Regards
Graham
Francesco Passerini
engineer90 thumbs up
August 9, 2016 - 6:51 am
I agree with Graham. Moreover, you could upload a datasheet relative to the windows and show to reviewers that the model is coherent with the real data.
Pay attention: the surface resistance coefficients of the European standards are different from the coefficients of the ASHRAE standard, which are considered for the U-values of the baseline case, if the building is a new construction.
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5867 thumbs up
August 9, 2016 - 9:28 am
I agree. Tell the reviewer what you based the assembly U-value on, how you have modeled it and provide the documentation you mention above. All too often modelers do not get this right when trying to model the frames separate from the glass. That will frequently produce results that are too low.