# LBL map for determining "n" values

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: 343

### 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. :)

## Featured Forum Discussions

### Strange IR Image

Started by Larry Nissman in General Forum. Last reply by Bryan Gabriel yesterday.

### 7,200 Normal Homeowner Minds Blown by Proof Is Possible Tour, Private Market Demanding Proven Home Performance

Started by Corbett Lunsford in Marketing. Last reply by Robert DV Feb 16.

### BPI Supports Strong Consumer Protection in Residential PACE Financing Programs

Started by Quinn Korzeniecki in General Forum Feb 10.

### Hero Pace Program?

Started by Horace Douglas Hunt, Jr. in General Forum. Last reply by Ryan Miller Feb 9.

### BPI February Newsletter & New Logos

Started by Quinn Korzeniecki in General Forum Feb 9.

## Videos

• ### ZERH Webinar: Getting Enclosures Right in Zero Energy Ready Homes

Added by Tom White

• ### Weatherization: Attic Air Sealing

Added by Barbara Smith

• View All

## Latest Activity

Home Energy Magazine's blog post was featured

### Art Rosenfeld's Legacy

Art…See More
18 hours ago
Efficiency First California and Kevin Daly joined Home Energy Pros
yesterday
Kevin Daly joined allen p tanner's group

### 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
"Is this a close up or broad view?"
yesterday
Home Energy Magazine posted a blog post

### Art Rosenfeld's Legacy

Art…See More
yesterday
Ashique Ibrahim posted a status
"Hello everyone.Please suggest a software to carry out analysis of energy auditing."
yesterday
Ashique Ibrahim posted a status
"Hello guys. I am student im doing my project on emergy auditing and benchmarrking. Please suggest the best software to do the analysis."
yesterday
"Yes, one is still available ."
Monday

## Events

• ### Better Buildings Peer Exchange Call: Making an Impact: Low-Income Energy Efficiency Programs

February 23, 2017 from 1pm to 2:30pm – Eastern Time

## 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