Has anybody successfully modeled window film installation using eQuest?
Specifically, I am trying to model the Vista EnerLogic low-e film (since
it is eligible for tax incentives). I've used Optics5/Window5 to
construct the glass type using the EnerLogic applied film (NFRC ID#
2545) and imported that into eQuest. When I test this retrofit in a
sample building, the savings are not what I expect (~65 yr. payback,
assuming $7 installed cost). I would expect to see a payback somewhere
around 10-15 years. What bothers me is that in the model, the heating
load increases, which would be expected for a typical window film, but
this film claims to have savings in all seasons due to the ability to
trap heat in the building. If anybody has had any success in modeling
these window films and could provide me with step-by-step instructions
or any guidance, it'd be greatly appreciated.
Thanks!
Dan Raphael
How does the film affect the U-value and the SHGC for the window? It sounds like the film is reducing the solar heat gain coefficient, and increasing the heating load. You should also keep in mind that outdoor air loads can dominate the heating load in winter and that envelope effects can be minimal depending on the climate and type of building. You may want to look into the loads reports in the SIM file to see what effects the film has on the building cooling and heating loads.
Cheers,
Dan
?
Daniel Knapp, PhD, LEED? AP O+M
On 2011-05-27, at 11:05 AM, McArdle, Mike wrote:
If the solar heat gain is reduced in winter, less heat from the sun will enter the windows and the heating load will be increased.
Low-e films reflect heat back into the space based on their emissivity
so you can expect heating savings even with a lower SHGC.
I'd expect Window5 to include the correct emissivity and for that to be
passed through the glass definition to eQuest. Is the film on the
correct surface in Window5? If you were entering your glass in eQuest
using the simplified method you would have to change the emissivity
manually.
Though this is from the manufacture, it's still an interesting read:
http://www.enerlogicfilm.com/pdf/EnerLogic-White-Paper.pdf
Matt Dubrovich
Does adding a Low-E film improve the U-factor, or just reduce the emissivity? Maybe posting some of the Window5 information up here will help us understand the performance increase/troubleshoot what?s happened.
Cheers,
Alex
Alex Krickx, LEED AP
I tried the window film again in eQuest, but this time I applied the film to the inside instead of the outside in order to trap the heat in the building. It looks like this has done the trick and both the electricity and natural gas consumptions have decreased. Thanks for the help, everybody!
Dan Raphael