How does filling a vinyl window frame with foam affect condensation resistance?
ranson
| Posted in Energy Efficiency and Durability on
I was looking at a Paradigm’s double hung window offerings. It seems like foam injection has little effect on CR of windows coated on surface 2 and 4, but severely decreases the CR of windows coated on just surface 2 or surface 3. Is this an oddity of the CR calculation, or a real world effect?
For example:
CLR / ARG / LoE 270 (DS-DS) 3/4″
Foam: U 0.26, CR 51
No Foam: U 0.27, CR 60
No Foam: U 0.27, CR 60
LoE 270 / ARG / LoE i89 (DS-DS) 3/4″
Foam: U 0.23, CR 45
No Foam: U 0.25, CR 47
No Foam: U 0.25, CR 47
LoE 180 / ARG / LoE i89 (DS-DS) 3/4″
Foam: U 0.24, CR 48
No Foam: U 0.25, CR 46
No Foam: U 0.25, CR 46
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
I took a quick look at some OKNA windows, and foam fill had negligible effect on the condensation resistance. I find the Paradigm data somewhat suspect now.
If the voids are small, foam fill doesn't offer much. In larger hollow spaces within the frame, foam fill adds insulating value. The reason the size of the void matters is that with small voids, there isn't much air movement so the air itself takes care of the insulation. In larger voids, the air can circulate with convection currents and move heat around -- the foam fill in that case prevents that air movement and adds to the insulating value of the frame as a result.
Condensation will occur whenever a surface drops below the dew point of the surrounding air. Insulation works to help keep interior surfaces at warmer temperatures in the case of a window frame like this. I wouldn't expect glazing alone to make a difference, but a different seal between different IGU types (the seal at the edge of a double or triple pane window that seperates the panes) might. You'd have to call the manufacturer to find out if that's the case.
I always like that window manufacturer's name. "Окна" (cyrillic), which transliterates to "Okna" is the Russian word for "Window" :-)
Bill
The effect that I see in the Paradigm's NFRC data is that adding foam reduces the condensation resistance substantially in windows with only surface 2 or surface 3 coatings. That seems highly counterintuitive.
I agree, that sounds very odd to me. I don't see how the coatings on the glass would have any effect on the ability of the insulation in the frame to do it's job.
Bill
Well, I reached out to Paradigm. They reached out to their testing lab. Between them, they found a simulation error that was significantly reducing the condensation rating. On the particular triple pane window they used as an example, fixing the error increased the CR from 50 to 64, matching its hollow frame counterpart.
I have two takeaways.
One: NFRC data comes from simulations that rely on skilled and careful data entry. It's easy for manufacturers to compute and publish bad data.
Two: Foam fill does not reduce the condensation resistance of Paradigm's windows.