Duct insulation air film #2
Conversation
…tion R-value variables for both supply and return ducts.
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@nathancoliver, can you make this DRYer? Since the air film is calculated, it probably shouldn't be an input parameter in the template. |
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@nealkruis do you think I could change the .pxv files so that the duct air film is equal to 6, and change the base.pxt file to include an if-else statement, where the if statement uses the default air film, and the else statement uses the equation to calculate the air film? |
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@nealkruis I updated the branch per our conversation. The changes should be self-explanatory, but for our records, here is an overview of the changes.
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base.pxt
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| def calculate_duct_air_film_r_value(duct_insulation_r_value,duct_type) | ||
| if duct_type == "SUPPLY" | ||
| return 2.2438 - 0.4381 * duct_insulation_r_value | ||
| elsif duct_type == "RETURN" | ||
| return 2.0388 - 0.2947 * duct_insulation_r_value | ||
| end | ||
| end |
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Did you test what happens if the air film is less than 1?
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I performed some tests, and it appears that negative air films close to zero produce unusual and unexpected heating and cooling energy use results. Other air film values, including positive numbers between 0 and 1 and negative numbers less than 1, do not produce strange results.
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@nealkruis I moved the air film calculation when the duct is uninsulated into the 'calculate air film r-value' function. |
I would like to start a conversation about updating uninsulated and insulated duct supply and return R-values, per Std 301 changes. Below is a summary of the changes.
base.pxt
<case name>.pxv
Let me know if there is anything that should be updated.