I am curious about the zone map developed by LBL that is used for calculating Building Tightness Limits (BTL)  The map is ubiquitous, but pretty crude.  It certainly doesn't correspond to avg wind speeds where I live.  Are there any other factors incorporated in that map? 

Using the wrong zone can result in a 15-20% error in the BTL

For reference, I'm attaching some maps from Montana

Thanks, Jim

Views: 344

Reply to This

Replies to This Discussion

Jim,
I'm chuckling as I remember reading an article years ago about the development of the LBL number. I have looked since and not been able to find that article so I cannot reference it. If anyone knows its whereabouts I would appreciate a link. Anyway, I'm a numbers person, so when the developer stated his accuracy estimates of -50% and +100% I quickly added this to my list of guesstimates that we base all of our very accurate results upon. After question the accuracy of almost every step we take, I finally decided that accuracy is not their target. It is consistency. I was looking at a rater certification at the time and what they wanted was for all auditors who might rate the same home, they should all get the same results. Thus, it mattered less that the number was wrong, and more that everyone arrived at the same answer.

If you want a correct number, use YOUR best guess. If you want to get an answer that others would also get, stick to where the pencil falls and use the LBL number you find. If it falls on a line, state which one you used and why.

Bud

I've forwarded to Max Sherman and Iain Walker.  They may get back to us.

 To the technical question asked, the map does include wind speed, but stack effect--i.e. indoor-outdoor temperature differences--is the bigger driver.  The zones follow a combinations of wind and temperature.

I am the father (or at least grandfather) of all of this.  I wrote a paper to show how the old rule-of-thumb (divide by 20) did not work and even if you did it right there would be big errors and generalizations.This was obviously the wrong thing to do, because those numbers got turned into the BTL.

Finally, finally, the BTL is dead.  ASHRAE, RESNET and BPI have moved on to do things in a much better way.  No one should use BTL anymore as these approaches are superior.

We are, however, coming out with a new (color!) map. It does not have BTL and it does not have zones, but it does have a single value for over 1000 weather stations in the country.  This paper has been accepted, by ASHRAE's HVAC&R Research Journal, but I don't know when it will come out.  It is possible to calcute a BTL from these numbers, but I am not going to say how. :)

RSS

Featured Forum Discussions

Too many BTU's. Too much horsepower?

Started by Steve in General Forum. Last reply by Eric Kjelshus 4 minutes ago. 4 Replies

Stack/wind pressure and flow networks.

Started by Daniel James Grundy in Training. Last reply by Daniel James Grundy yesterday. 5 Replies

BDT with vermiculite in hollow CMU walls?

Started by Brad Cook in General Forum. Last reply by John Nicholas yesterday. 2 Replies

Strange IR Image

Started by Larry Nissman in General Forum. Last reply by Brad Cook Mar 9. 7 Replies

Videos

  • Add Videos
  • View All

Latest Activity

Eric Kjelshus replied to Steve's discussion Too many BTU's. Too much horsepower?
"Its more about run time with high RH removing, than to large over sized AC unit, in houses.  …"
4 minutes ago
Sarah OConnell posted a blog post

Crowdsourcing for Innovation

Share Your Ideas!Novel Building Envelope Design for Increased Thermal PerformanceIn 2014, more than…See More
13 hours ago
Colin de Paor is now a member of Home Energy Pros
15 hours ago
Walter Ahlgrim replied to Steve's discussion Too many BTU's. Too much horsepower?
"The 5 ton system you have is not 500 hp racecar engines they are 500 hp truck engines. The duct…"
yesterday
Daniel James Grundy replied to Daniel James Grundy's discussion Stack/wind pressure and flow networks.
"So I wanted to start with a basic who can help then go into more detail later. But yes find…"
yesterday
Daniel James Grundy replied to Daniel James Grundy's discussion Stack/wind pressure and flow networks.
"My tutor got back to me and while areas don't quite feel right a little to much assumptions…"
yesterday
Brennan Less replied to Daniel James Grundy's discussion Stack/wind pressure and flow networks.
"Daniel, I'm assuming you're trying to predict the airflows through the different openings…"
yesterday
Martin Newmark joined allen p tanner's group
Thumbnail

Energy Auditing Equipment for Sale, Trade or to Purchase

Discuss the pros and cons of the equipment you are interested in prior to purchase. Post equipment…See More
yesterday

Home Energy Pros

Welcome to Home Energy Pros – the unique digital community by and for those who work in the home energy performance arena.

Home Energy Pros was founded by the developers of Home Energy Saver Pro (supported by the U.S. Department of Energy) and brought to you in partnership with Home Energy magazine.  Home Energy Pros is sponsored by the Better Buildings Residential Network. Please honor our Guidelines

© 2017   Created by Lawrence Berkeley National Laboratory.   Powered by

Badges  |  Report an Issue  |  Terms of Service