Adding flexibility to specify location of the radiant barrier

[prsh5175]

Pull Request Description

Allowing Radiant Barrier for Attic Floor

Addresses: #1435

Checklist

PR Author: Check these when they're done. Not all may apply. strikethrough and check any that do not apply.

PR Reviewer: Verify each has been completed.

• Schematron validator (EPvalidator.xml) has been updated
• Sample files have been added/updated (via tasks.rb)
• Tests have been added/updated (e.g., HPXMLtoOpenStudio/tests and/or workflow/tests/hpxml_translator_test.rb)
• Documentation has been updated
• Changelog has been updated
• openstudio tasks.rb update_measures has been run
• No unexpected changes to simulation results of sample files

[afontani]

Here is the ASTM Standard Specification for Radiant Barriers: ASTM C1313

I would like to see a default value of 0.1 emissivity with an input available for soiling that increases the emissivity as over time dust will accumulate and increase the amount of radiative heat transfer.

[shorowit]

It looks like we are currently assuming a radiant barrier emittance of 0.05:

OpenStudio-HPXML/HPXMLtoOpenStudio/resources/materials.rb

Lines 302 to 311 in 4fd2701

	if grade == 1
	gap_frac = 0.0
	elsif grade == 2
	gap_frac = 0.02
	elsif grade == 3
	gap_frac = 0.05
	end
	rb_emittance = 0.05
	non_rb_emittance = 0.90
	emittance = rb_emittance * (1.0 - gap_frac) + non_rb_emittance * gap_frac

As far as I can tell, we have been using this number since at least 2010 (in BEopt).

[afontani]

It looks like we are currently assuming a radiant barrier emittance of 0.05:

OpenStudio-HPXML/HPXMLtoOpenStudio/resources/materials.rb

Lines 302 to 311 in 4fd2701

	if grade == 1
	gap_frac = 0.0
	elsif grade == 2
	gap_frac = 0.02
	elsif grade == 3
	gap_frac = 0.05
	end
	rb_emittance = 0.05
	non_rb_emittance = 0.90
	emittance = rb_emittance * (1.0 - gap_frac) + non_rb_emittance * gap_frac

As far as I can tell, we have been using this number since at least 2010 (in BEopt).

ASTM C1313 3.2.1 defines a radiant barrier as <= 0.1.

[afontani]

For soiling of radiant barriers on the attic floor, ORNL published an article that gives an anecdotal estimate of reduced performance RADIANT BARRIER:
Effect of Radiant Barriers on Heating and Cooling Bills.

There is probably a technical report somewhere with actual reductions in performance. But if an emittance required by ASTM C1313 is 0.1 and wood emittance is 0.9, then half the difference would be 0.5.

[shorowit]

I ran the HPXML test files and inspected the IDFs; the attic floor case is definitely not correct. I pointed out a couple places where the code looks wrong. Please diff the IDF for the attic floor case against another similar file and verify that you see the expected changes.

[shorowit]

Attic temperatures in Dallas (blue=no RB, red=RB on attic floor, orange=RB on attic roof/walls):

Cooling energy for same cases:

[shorowit]

Looks good to me. Will double-check final results from the CI but this should be good to merge. Nice work, @prsh5175!

[shorowit]

Energy use went down slightly in this test file because we added radiant barriers to the attic gable walls. All other files are unchanged. Results look good.