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: 341

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

Glass Block Windows

Started by Ken Kalke in Best Practices. Last reply by Sean Lintow Sr on Saturday. 1 Reply

What's the Most Profitable HVAC Job for Your Company?

Started by Wayne Melancon in HVAC. Last reply by Ken Kalke on Friday. 1 Reply

Lighting replacement - 300 watt LED flood light

Started by Mary Sinkler in General Forum. Last reply by Eric Kjelshus on Friday. 1 Reply

EZ Green Home is Hiring!

Started by Chloe Chapman in General Forum Jan 5. 0 Replies

Videos

  • Add Videos
  • View All

Latest Activity

Bruce Fillmore joined Diane Chojnowski's group
Thumbnail

Home Energy Pros on Twitter

We've created a twitter list of members of Home Energy Pros who tweet about home performance and…See More
59 minutes ago
Bruce Fillmore posted photos
1 hour ago
Profile IconMark Freeman and Bruce Fillmore joined Home Energy Pros
18 hours ago
Sean Lintow Sr replied to Ken Kalke's discussion Glass Block Windows
"Well as most I know (if not all) wont meet the energy code - none and for those that do opt…"
Saturday
Steve Gadsby posted a photo
Friday
Steve Gadsby commented on Perry Ning's blog post Warnings About Portable Air Conditioners
"We couldn't agree more about the problems caused by portable air conditioners. Here at Canada…"
Friday
Diane Chojnowski commented on Home Energy Magazine's blog post New Case Study: Arizona Leverages Industry Standards to Improve Home Performance Program
"Ted. I followed the link and found a place to download the Case Study on PDF:…"
Friday
Dale@EnergyWright commented on Joseph Burley's blog post Asbestos Shingle Nailpoint Debris
"I don't buy it. Shingles are typically pre-drilled and nails are pointy and wiped clean in the…"
Friday

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