I'm curious to hear from anyone with experience in Multi Family Auditing what your thoughts on the muti-point blower door test are, and if there are ideas for performing a valid audit without the need of 5+ blower doors/auditors.

Thanks!

Thom

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Just a quick thought, but you might get better results posting in the group for that - http://homeenergypros.lbl.gov/group/multifamilybuildings

As I recall emails get sent out when a new topic is posted in the group wheras they may get missed in the general section

You might also want to describe what type of multi-family units you are considering as opinions &procedures vary based on the type of structure and what you are looking for 

 

Hi Thomas,

I ran your question by Colin Genge, CEO or Retrotec.  Here's what he had to say:

"Multi point tests are only useful if you are testing to a standard that requires a specified level of tightness and the acceptance of the building relies on a super accurate and compliant number. This is expensive and time consuming.
Alternatively, if you are performing diagnostics, you may not be that interested in overall building enclosure leakage. Leakage between floors and between units tend to be much more important. My Home Energy article shows how to test compartment by compartment using two blower doors and two auditors. Our training schools cover this in detail but perhaps what is needed is a straightforward article that shows how to get the most information possible for the least effort."
The article he is referring to is attached. I've also attached others that may interest you. Let me know what you think.
Silvie

Attachments:

 

I have done several multi family blower door tests and I think Colin Genge has done an excellent job of describing the technical aspects of doing multifamily properly (in the articles provided by Silvie). There are also many human factors, as you can imagine, and they play a big part in the proper set up of the test. Most multifamily BD tests require a pre test site visit and careful planning so there are no surprises on the day of the test.   

There aren't many situations where you can get an accurate number on multifamily with just one blower door, maybe if the whole building is just the size of a typical house and the apartments are interconnected.  If you have 2 doors you can start to isolate units that share just one common wall (or floor, or ceiling, etc.) by pressure balancing across the common surface.  Generally, If you want accurate airtightness data you need multiple doors/ auditors, there are no shortcuts.  A test with just one door in one unit is meaningless. 

Alternatively, and if the efficiency program you are working for allows, you may opt not to do a blower door test at all.  An experienced auditor can learn a lot about air leakage with a smoke pencil, visual inspection, and a micromanometer at natural pressures.  When I get a call for a multi family the first thing I try to do is feel out how open the owner and tenants are going to be to the level of disruption our blower door test is going to be.  If I get lots of push back I start to propose alternate methods for getting most of the critical data without doing the full blower door test.   

Thanks Silvie and Jon!  This is all very helpful information.  I'm working with mostly garden style and town house, low-rise complexes, but the high-rise articles were very informative.  It is clear that more blower doors and auditors give a more accurate picture than a minimal test.  I'm just wondering how important that accuracy really is in the end.  If we have to use a big chunk of the available funds for making energy improvements on auditing, we might not be as effective as if we were a little less accurate about our measurements and spent more on the actual improvements.  The ultimate goal should be to save energy.  After all, it's just one number and we are only able to speculate on how it may change through airsealing.

Thom,

I suppose you don't need to test -- that's what everyone weatherizing townhomes and low-rise buildings has been doing for years. And maybe it works better than single-family weatherization worked before we started doing blower door testing on houses, given all we've learned from testing and air sealing hundreds of thousands of houses. But no one knows, because no one actually measures their results.

Yes, the sarcasm is intentional -- just as in my my article in Home Energy magazine. (See http://www.homeenergy.org/show/article/nav/auditing/id/1711 ) Every once in a while I get this real attitude about an entire professional community that understand the benefits of measured results -- except when doing rented housing. And then "what everybody knows" is good enough.

Off soapbox! Contact me offline if I can be of assistance.

 

Don

Another message from Colin regarding the latest comments:

 

"There is a big leap from testing an entire Multi-Family building with 8 blower doors and using a smoke pencil and a gauge. Surely there must be middle ground if we could develop a series of test methods that we could add to our tool kit and use them as possible and as needed. The problem is that with detached houses, we can generally run all the same tests without too much analysis with respect to effectiveness.  Even though we can perform numerous tests with 1 or 2 blower doors on a MF, the answer could be "what does it really mean?". 

I don't have the answer to that question except when tools are provided, those of you in the field are generally quick to realize what tests are showing value and what tests are not.  I would like to create a series of test procedures, open the process to have others add theirs and then publicize them and wait for feedback from the field as to what was gained anecdotally in order to encourage others to try the same procedures." - Colin Genge

 

 

Thomas,

I think you are on the right track.  What can we do that still gives us reasonably accurate data yet not use up all the funds on the audit so there are none left for making improvements? I contend, and I can see that some disagree, that auditor experience with a few simple tests can fill in most of the blanks when we cannot conduct all the tests that we would like to.

Don,

I read your article and respectfully disagree.  We do not need to test all multifamily structures in order to be able to do a good job with air sealing.  The late Tony Woods and his colleagues at CANAM came up with an alternative method called ALCAP that was based on blower door tests and completed air sealing on several multifamily high rise buildings.  After a while they abandoned blower door testing in favor of ALCAP because it worked.  I believe that the Zerodraft folks (a spin off from CANAM) use ALCAP as part of their assessment procedures today.     

One final comment:  Not every auditor knows, but should know, that blower door results at 50 or 75 Pascals don't have an exact translation to air leakage at natural pressures.  In fact, a properly conducted blower door test can be off by as much as a factor of 2 from what a tracer gas test would say (not my words, page 34 in the Minneapolis blower door manual).  Also, the larger the building the harder it is to determine what the blower door number really means at natural pressures, and by extension, what are the potential energy savings.  This is a fact lost on most new auditors because many state and non-profit energy programs treat ACH natural as if it is a hard fact, not what is really is, a highly variable air leakage rate that literally changes with the weather. So, if we are going to get all "scientific" about making sure we test every single building then we have to ask ourselves the question that Colin Genge raised, "what does this all mean?"  If we show with pre and post blower door tests that our air sealing work decreased air leakage by 35% does that mean we can accurately predict what the building will save in heating fuel?  By my experience, the people I’ve talked to, and the research I’ve read probably not.

I don’t disparage the science or the proper test techniques.  I have several blower doors and use them to test buildings every week but the bottom line is auditor knowledge and experience is the most important tool out there.  All other tools we have come in second.   


Jon,

 

I'm so glad to hear someone else say these things. It does feel like we are putting a lot of faith in some numbers that pop up on a manometer and then we believe that we can make a truthful statement about the natural leakage of a building after we make a subjective judgment about the exposure for the LBL N Factor, and decide what zone we may be in on that tiny little map. I live right on the boarder of two zones and two different auditors could easily come up with vastly different results for ACH natural with the same blower door numbers.

It seems like a simpler test that uses 5 or so levels of leakiness could be just as effective as some "precise" number that we believe to tell the truth about a building. If we need to know the ACH, wouldn't there be a way we can use a fog machine or something to create a visual density to the air and measure how that changes over time, under certain weather conditions, to come up with a more truthful generalization? I don't know - I'm just spouting off - but isn't the whole point to know how contaminated but conditioned air inside reacts with fresh air from outside?

Don't get me wrong, I think that a blower door is a very good tool for locating leaks, especially when used with a thermal camera. I'm just not that convinced that the numbers are all that important, and at that point a window fan becomes just as effective.  I don't claim to know much about this and I appreciate anyone who wants to help me know more.  I'm also curious to know what they do on other continents, or if we are the only ones who worry about these numbers.

Thanks,

Thom

 

Don responds....

Don,

I read your article and respectfully disagree.  We do not need to test all multifamily structures in order to be able to do a good job with air sealing. 

In five years, after dozens of people have tested a few hundred buildings, we might know enough that I could agree with you. Right now, I think we are shooting blanks in the dark.

The late Tony Woods and his colleagues at CANAM came up with an alternative method called ALCAP that was based on blower door tests and completed air sealing on several multifamily high rise buildings.  After a while they abandoned blower door testing in favor of ALCAP because it worked.  I believe that the Zerodraft folks (a spin off from CANAM) use ALCAP as part of their assessment procedures today. 

I watched Tony run an ALCAP analysis--it was FAR more seat-of-the-pants than you know.

And, if you'd seen the blower door they had to work with in that time, you'd understand why even a seat-of-the-pants visual inventory would be far better -- half-way decent info at a small fraction of the cost and labor. With the hardware available now, I believe that argument no lnoger holds. 

   

One final comment:  Not every auditor knows, but should know, that blower door results at 50 or 75 Pascals don't have an exact translation to air leakage at natural pressures. 

Anyone who's run the numbers on a power law multi-point test knows this intimately. But the only method we have to model that behavior at real working pressures is to run the multi-point test and model the curve.

 In fact, a properly conducted blower door test can be off by as much as a factor of 2 from what a tracer gas test would say (not my words, page 34 in the Minneapolis blower door manual).  

That assumes that a tracer gas test is better/more accurate/more useful. It is, if your only goal is to understand the behavior of a building in precisely the wind/sun/delta-t conditions on the day the test was run. As ASHRAE 977 makes clear, a multi-point blower door test is used to get info that CHARACTERIZES the building -- that allows the tester to predict the leakiness of the building shell under any conditions it is likely to experience.

Also, the larger the building the harder it is to determine what the blower door number really means at natural pressures, and by extension, what are the potential energy savings. 

I don't know why this should be true... Physics is physics, regardless of building size.

This is a fact lost on most new auditors because many state and non-profit energy programs treat ACH natural as if it is a hard fact, not what is really is, a highly variable air leakage rate that literally changes with the weather. 

This might be true for those programs that have never actually tested buildings. Good building scientists know better.

So, if we are going to get all "scientific" about making sure we test every single building then we have to ask ourselves the question that Colin Genge raised, "what does this all mean?"  If we show with pre and post blower door tests that our air sealing work decreased air leakage by 35% does that mean we can accurately predict what the building will save in heating fuel?  By my experience, the people I’ve talked to, and the research I’ve read probably not.

The only reason that belief exists is that few programs have tried. I know of one here in Wisconsin -- they are getting good results.

I don’t disparage the science or the proper test techniques.  I have several blower doors and use them to test buildings every week but the bottom line is auditor knowledge and experience is the most important tool out there.  All other tools we have come in second. 

Auditor knowledge and experience that comes from opinion rather than measured results? I'll pass, thanks...

All,

Are you aware of any efforts made at databasing a large collection of air leakage test results, either by blower door testing or tracer gas testing?

The collective results from years of testing and research might be sorted into bins of comp groups based on building characteristics and climate conditions.  A growing database would grow our understanding of the impact that air infiltration has on our building stock.  I suspect a serviceable sample of results is already "out there," but perhaps not centrally assembled.

I feel that testing is critical, but  I also feel that the financial hurdle of performing these tests is a formidable challenge.  I am working on a lot of high-rise multi-family in NYC....average of 250,000 sq ft and 30 stories with amenity spaces and multiple large AHU's.  A thorough air infiltration analysis with blower door testing would get REALLY expensive, as tracer gas testing already seems to be.

Hi Grant, your search for that mountain of information is something I have considered for many years in many fields.  Basically, it is hard to find a subject that hasn't been studied and researched to its smallest detail, yet where do they hide those results?  Energy efficiency at all levels has certainly been among the most studied topics and as you, I believe there is a vault somewhere with all of this info locked up.

Dr Mills from LBL who posts here may be able to give us some guidance and maybe even the key to accessing this info.  The next step in your search may be more daunting, the data-basing of all relevant information.  If you have ever worked with a data base you know they must be developed from the ground up so that everyone calls a house a house.  Different names and definitions can often make various collected information totally incompatibly.  Hopefully what you want has already been done, else it would be beyond any individuals capabilities and resources.

To add to your search, if they will share, Canada has a central office for handling all of Canada's energy work.  Then there is the UK and AU and many other countries that might have their information available.

Good luck and do let us know if you find that key.

Bud

Thanks for the thoughts, Bud.

We all likely have an opinion of the USGBC.  I sat a few weeks ago in on a discussion with David Gottfriend, one of the original founders of USGBC.  A (loose) quote of his I found to be interesting:

"The first generation of the LEED program was to develop a program and standards.  The second generation was to get buildings and owners to come "on-board" with green building standards and the LEED process.  The third generation, where we currently find ourselves, is to database and analyze all of the data that has to this point been collected so that we can understand where we actually stand, and how to improve."

Interesting, I thought, and certainly relevant to this conversation.

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