ASHRAE 90.1 - 2007

[PostFrameSE]

I had a visit with some building officials in my State today regarding the vestibule requirements for walkdoors. I contend that it is foolish to vestibule a walkdoor when in the same building space you have large overhead doors that are slow-opening and slow-closing. The heat-loss with the large door would greatly exceed that which you would have with the opening of a small walkdoor multiple times!

It appears that ASHRAE completely ignored that fact, or only intended these vestibules in A, B, E, I, or M occupancies. I completely understand their purpose in an occupancy like that, but dispute it in an F or S occupancy where large doors are major sources of heat-loss when open.

I was told that you need to take the door opening and closing into the envelope design. I have no idea how to do that? Any thoughts or suggestions? I told the official that if the doors were open, it would be impossible to ever get a building to work. I was told "We're not designers.........that's your issue to deal with." That sounds snotty, but she was kind when she said it.

How do I deal with this? Does anybody have any insight to how ASHRAE thinks about this? Anybody have any contacts at ASHRAE that I could get in touch with?Thanks.

 

[tys90]

Is the space semi-heated or unconditioned? It sounds like it might be. If so, you don't need to comply with the vestibule requirements, it's pretty clear about that.

 

[PostFrameSE]

This is a general question. I am talking about conditioned buildings.

 

[tys90]

I should have added that I don't understand what envelope design has to do with the door opening or closing? The only thing I could think of is that you want positive pressure in the space to prevent infiltration through small doors. Infiltration through larger doors is going to happen, but 90.1 also has requirements for attempting to reducing it, depending on what climate zone you are in.

 

[tys90]

There's not enough information. In general, yes, you would need a vestibule. There are a number of exceptions though and they help determine if you need one or not.

 

[MintJulep]

Go to the source.

How to request an ASHRAE interpretation of a standard.

http://www.ashrae.org/technology/page/1833

 

[PostFrameSE]

OK. I recognize that there's not enough information. I'm not sure that I'm even filling out the ComCheck program correctly. For instance, if I have an overhead door (OHD) with an R-value of 10 or a U-value of .1, I would insert that as the value for the door. My walls are generally cavity insulation of R-19. Am I wrong to put in the full R-value or U-value for the OHD's or am I suppose to reduce it somehow for the fact that it will get opened now and then?

 

[GMcD]

Another question to you PostFrame - ASHRAE also requires you to use the "overall" U values for the assemblies, which means that a cavity wall with R-19 batt insulation might actually be an overall R-10 once you include and allow for all the thermal bridging of the framing, ditto for the overhead door. Same thing for windows - I've seen some nasty window details where triple glazed low-e windows were installed in a badly thermally bridged manner that yielded an overall window U value no better than double glazed windows.

This is one of the common big errors I see when reviewing energy models and heating/cooling load calculations - the failure to calculate the "overall" U values for the envelope assemblies. For some building science back-up visit buildingscience.com and Google the JBED magazine at the Whole Building Design website (

http://www.wbdg.org/references/jbed.php)

 

[PostFrameSE]

Thanks GMcD,

Pardon my ignorance, but it sounds like you folks who are responding know a whole lot more about this than I do. I will do some research on those sites you provided tomorrow. Maybe they will say, maybe not, but I'm curious..............is it basically a weighted average of different R-values in an entire wall to come up with the "overall" U-value? In other words, if my wall was 10% framing with an R-value of 5 and 90% insulation with an R-value of 20, do I have an overall U-value of .054, which is 1/18.5???? If so.............great.......and if not...........looks I have some studying to do!!

Windows have U-values located on them. I'm assuming that overhead doors do too...........but how would you calculate the effect of them being open?

Thanks.

Thanks.

 

[GMcD]

PostFrame- yes you are on the right track, but the R value of a thermally bridged stud wall plus header and footer plates is a lot less than R-5. Typically a wood framed exterior wall in standard "code minimum" construction assembly with R-20 batt insulation will yield more like an R-12 to R-14 at best, as the "overall" insulation value.

The U value on the window stickers is usually the "centre of glass" U value and does not normally include the degradation due to the window frame, or the wall opening detailing. To calculate the overall U value of a complete window installation, you have to account for the frame type (thermally broken and what type), as well as how the rough opening is detailed and sealed.

There is no calculation for how often or how much the doors and windows are open - the heating and cooling load calculations are based on the building normally closed up, and an engineering assumption can be made for the amount of expected infiltration through doors and windows, or use the ASHRAE default values.

You might need to do a bit more reading of the ASHRAE 90.1 manual before filling in the blanks on the prescriptive checklists.