[Equest-users] Window replacement and infiltration rate changing
Alex Krickx
akrickx at seriousmaterials.com
Thu Sep 16 09:28:52 PDT 2010
I think Carol's approach is spot-on in terms of calculating infiltration. I always figure out the wall infiltration first (usually an estimate, but it stays constant) and then figure out my "before" and "after" window infiltration values, area weight them with the wall values.
My only caveat is that I'm not sure 3x is always the right number. I threw that out as an example. 1 CFM/SF is pretty high infiltration, so the actual reduction may be less. But 0.3 CFM/SF is the maximum allowable - if you substitute a low-leakage window that has an infiltration of 0.1 CFM/SF then you could get a 10x improvement. Again, that 3x or 10x is just for windows, not the whole façade - you need to know Window-Wall Ratios to figure out the total infiltration reduction.
Unless I've been told that the windows are "the leakiest things ever" I'll typically assume 0.3 CFM/SF for existing windows. Even though this corresponds to a pretty tight new window, I don't like to overstate savings - especially as I work for a manufacturer, I don't want to unfairly manipulate variables to make a product look better than it is. And without more public information available, it's hard to assign a performance to existing windows.
Alex
From: Carol Gardner [mailto:cmg750 at gmail.com]
Sent: Thursday, September 16, 2010 3:18 AM
To: Chris Jones
Cc: Alex Krickx; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Window replacement and infiltration rate changing
So maybe we can use what Alex said: new windows must be 3x less leaky than old ones. Since that is just the window, not the whole exposure leakage, I'd go ahead and pull a number from the table Alex sent that matched my window, reduce it by 3 and then do an area weighted average for the entire wall. As a guide you could use .038 cfm/sf or 0.05 cfm/sf for a wall of the same exposure as yours and with the same glass area as yours to figure out what the wall cfm/sf is, unless you happen to know it. As an example xx sf wall x wall cfm/sf + yy sf window x yy cfm/sf for your window = xx+yy sf x .038 cfm/sf, you know your xx and yy sf, you can pick a reasonable cfm/sf for your window, or ask Alex for one, and then solve for your wall cfm/sf. Assuming you aren't doing anything to improve your walls you then have your xx cfm/sf. Then reduce your yy cfm/sf by a factor of 3, plug all the numbers in and solve for your new xx+yy, or overall wall cfm/sf. Put that number in eQUEST, document your calcs for the LEED, or whoever, reviewer and you are good to go.
Carol
On Wed, Sep 15, 2010 at 4:07 PM, Chris Jones <cj at enersave.ca<mailto:cj at enersave.ca>> wrote:
ASHRAE 90.1-1989 prescribed the amount of infiltration to use in the design and budget cases as 0.038 cfm/sq. ft. of gross exterior wall area. I believe that subsequent versions of 90.1 dropped any reference to modelling infiltration rates. The infiltration is "on" when the fans are off.
The MNECB/CBIP in Canada uses 0.05 cfm/sq. ft of gross exterior wall area - with a schedule on all of the time.
Who knows where those numbers came from and it doesn't really answer the question of how much infiltration will be saved with new windows but it gives a starting point.
At 06:16 PM 15/09/2010, Alex Krickx wrote:
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Yeah, it does sound high, doesn't it? But when compared to the maximum level for new windows of 0.3, then it doesn't sound as high... new windows must be 3x less leaky than old ones - that sounds like the right reduction to me.
The only link I could find on performance of old windows was this one: http://www.bfrl.nist.gov/IAQanalysis/CONTAM/table00_arld.htm
It gives leakage areas in "area per linear meter of seam". A colleague converted this to leakage area in CFM/SF at 75 pa. His number was 1.4 CFM/SF based on the table (not sure which value he used).
As a thought: perhaps 1 CFM/SF seems too high because we imagine it as the infiltration for a whole wall, when in actuality it only applies to the window? Assuming the wall has little infiltration, a 25% WWR would bring 1 CFM/SF (window) to around 0.25 CFM/SF (whole façade) - probably a little higher if accounting for the wall leakage, but not significantly so. Does that number still raise alarm bells? Not to me, but I don't have as good a feel for this as Carol does.
I've definitely seen some leaky windows - unfortunately I've never tested how leaky they are so I'm stuck with looking for industry papers and best practice. I definitely would like to learn more about this though. Typical infiltration values of old windows seems to be a big question mark with people I've asked....
Regards,
Alex
From: Carol Gardner [ mailto:cmg750 at gmail.com]
Sent: Wednesday, September 15, 2010 2:57 PM
To: Alex Krickx
Cc: YingQi Chen; equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: Re: [Equest-users] Window replacement and infiltration rate changing
Wow! It seems like 1 cfm/sf for infiltration would be a lot. The people's hair next to the windows would be blowing all around! That's the average number I use for HVAC ventilation.
Carol
On Wed, Sep 15, 2010 at 2:36 PM, Alex Krickx < akrickx at seriousmaterials.com<mailto:akrickx at seriousmaterials.com>> wrote:
Hi Yingqi,
I'm pretty sure eQUEST does not automatically adjust infiltration rates.
If you search through the archives and look up "infiltration windows" you can find some relevant posts. I've attached one email that was sent around earlier this year describing one way to change the infiltration between current and proposed cases.
I don't think you can apply a percentage reduction without some more information. I believe that the requirement to meet the DOE's VPP for windows is a maximum infiltration of 0.3 CFM/SF - this leads me to believe that some new windows have more infiltration than this. My company manufacturers windows with infiltrations as low as 0.01 CFM/SF. I'm having a hard time finding a source, but I'm pretty sure I've heard of modeling existing windows with infiltration as high as 1 CFM/SF. A building with a large WWR and very leaky windows could substantially reduce whole-building infiltration values.
Good luck!
Alex Krickx
Alex Krickx
Building Energy Specialist
Error! Filename not specified.
1250 Elko Dr, Sunnyvale, CA 94089
(t) 408.541.8124
Warning: The information contained in this e-mail may be privileged attorney-client communications or attorney work product and/or proprietary and confidential. If the reader of this message is not the intended recipient then you have received it in error and any review, distribution or copying of this message is prohibited and you are to notify us immediately by reply e-mail and delete the original message immediately.
From: equest-users-bounces at lists.onebuilding.org<mailto:equest-users-bounces at lists.onebuilding.org> [ mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Carol Gardner
Sent: Wednesday, September 15, 2010 2:19 PM
To: YingQi Chen
Cc: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: Re: [Equest-users] Window replacement and infiltration rate changing
If eQUEST changed the infiltration between the two cases you would be able to see the change in your .inp deck. I'm not sure what the impact of doing the change using the EEM Wizard vs. simply copying and renaming your input deck and making the change in it's own .inp deck would be. You could experiment and see if there's a difference. If it doesn't change your infiltration I would lower the perimeter infiltration rate conservatively by a fixed percent. You might Google infiltration rates on line and find some information related to how much to expect for a single pane window to a double pane window. Also, be sure to account for your frames, too. Are they thermally broken? Does the frame material change, etc.
Carol
On Wed, Sep 15, 2010 at 2:05 PM, YingQi Chen <yingqi.chen at pertan.com<mailto:yingqi.chen at pertan.com> > wrote:
Dear eQuester:
I want to run a simulation by EEM wizard. I want to replace exiting single pane, clear windows with double pane clear windows for a school building.
I changed the class type form single pane clear to double pane clear windows. The energy saving doesn't look good. I have two following questions need someone's guidance.
Question 1:
My question is that this EEM will reduce perimeter infiltration rate of the building. I am not quit sure if I need to reduce the perimeter infiltration rate in the simulation. If, it does, how many percentage of infiltration rate do I need to reduce?
Question 2:
Does eQuest programmer has already considered this issue and changed the perimeter infiltration rate automatically with changing window glass type and insulation of the windows?
Yingqi Chen
The PERTAN Group
44 Main Street, Suite
Champaign, IL 61820
217-356-1348 ext 205
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Carol Gardner PE
---------- Forwarded message ----------
From: Nick Caton <ncaton at smithboucher.com<mailto:ncaton at smithboucher.com> >
To: Alex Krickx < akrickx at seriousmaterials.com<mailto:akrickx at seriousmaterials.com>>, " equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>" < equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>>
Date: Mon, 8 Mar 2010 16:47:48 -0800
Subject: RE: [Equest-users] Modeling Infiltration and Windows
I've done exactly that in the past for the exactly the same purpose!
The only difference is I believe I always punch in the differences in the metric of ACH. ASHRAE fundamentals provides some guidance regarding air change rates to expect for various classes of construction as a function of outdoor design temperature, and that was the best I could base my existing construction off of from what info I had available.
Come up with a "leakiness" for both you construction, old and new windows, and do the weighted average jig =).
Kudos on your fancy facade spelling also ;)!
~Nick
Error! Filename not specified.
NICK CATON, E.I.T.
PROJECT ENGINEER
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From: equest-users-bounces at lists.onebuilding.org<mailto:equest-users-bounces at lists.onebuilding.org> [ mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Alex Krickx
Sent: Monday, March 08, 2010 6:05 PM
To: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: [Equest-users] Modeling Infiltration and Windows
Hello all,
I am interested in modeling the energy savings that occurs when windows are replaced with lower-infiltration alternatives. In the wizard mode, the only place that I see infiltration is under the "Building Envelope Constructions" Screen.
I'm hoping someone can confirm my methodology:
Can I input a weighted average of window and wall air infiltration here? If I'm looking at a building with 20% Window to Wall Ratio, and the windows have 0.1 CFM/ft² while the walls have 0.04 CFM/ft²can I apply an area weighted average into this box? I would take (20%*0.1+80%*0.04) as the façade infiltration value.
That way I could use the same formula to determine the area weighted infiltration of the façade if better windows were installed.
How do other people model this?
Thanks in advance!
Alex Krickx
Alex Krickx
Building Energy Specialist
Error! Filename not specified.
1250 Elko Dr, Sunnyvale, CA 94089
(t) 408.541.8124
Warning: The information contained in this e-mail may be privileged attorney-client communications or attorney work product and/or proprietary and confidential. If the reader of this message is not the intended recipient then you have received it in error and any review, distribution or copying of this message is prohibited and you are to notify us immediately by reply e-mail and delete the original message immediately.
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Carol Gardner PE
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