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Building Science

An Interview with Dr. Joseph Lstiburek

Joe explains BSC’s new ventilation standard, why tracer gas is a better measure of infiltration than blower doors, and his plans for a ventilation standard for existing homes

Dr. Joseph Lstiburek, principal at Building Science Corporation.
Image Credit: Building Science Corporation

Dr. Joe Lstiburek of Building Science Corporation is on a mission. The issue is residential ventilation. He contends that the residential ventilation standard, ASHRAE 62.2, ventilates at too high a rate, causing problems with humidity in hot or mixed humid climates, comfort and dryness in cold climates, and too much energy use everywhere. The 2013 version makes it worse.

You can read the background in my last article, which covers the new ventilation standard he’s about to release. After I published that article, a number of questions came up that I thought would best be answered in an interview. I spoke with Joe last Thursday, and now present to you the transcript of our talk.

Interview with Lstiburek

Allison Bailes: Somebody said that it looks like BSC-01 is a dumbed-down version of 62.2, the rates aren’t that different, so why do you think BSC-01 is a better standard?

Joe Lstiburek: Well, the rates are a huge reduction. A balanced system with distribution & mixing is going to be about 40 cfm whereas an unbalanced sys. w/o distribution & mixing is going to be about 90 cfm, so there’s a huge difference in rates. The dumb system is one that doesn’t recognize the effects of distribution, doesn’t recognize the effects of supply vs. exhaust vs. balanced so the dumb sys. is 62.2 not the BSC system.

A.B.: Why is distribution such a big deal? Do you have experience from the work you’ve done or research papers?

J.L.: There’s all kinds of research papers and work that we’ve done that’s going to be posted on our website shortly that shows that if you don’t have mixing you’re going to have high concentrations in bedrooms that don’t get the same amount of air so what happens is mixing reduces the high contaminant locations. This is not new. This is recognized by the experience that I had in Canada with R-2000 in the 1980s so the fact that this is even a question or a controversy is bemusing to me and disappointing to me.

A.B.: Another question that came in the comments of my article was: Are we exchanging one set of guesses for another?

J.L.: The answer is that we’re not. We know the following that are not guesses. We know that houses ventilated at the 62.2 rate lead to comfort problems in cold climates by drying out the building and drying out furnishings. We know that ventilating at the 62.2 rates in houses built to the Model Energy Code lead to part-load humidity problems. We know for a fact that these rates lead to humidity problems in the South and dryness and comfort issues in the North, so that’s not a guess. We know this from experience.

We also know that millions of houses were constructed in the 1990s and 2000s that were between 3 and 5 air changes per hour at 50 Pascals with no ventilation systems and their air change rates are between 0.2 and 0.3 air changes per hour as tested by tracer gas work and that’s consistent with houses tested in the ‘70s and ‘80s as well. The myth of the old leaky house is just a myth. These houses had no ventilation systems in them at all and they’re not suffering from indoor air quality problems because nobody’s measured any contaminants. There’s no measurements.

What we’re doing is we’re actually adding controlled ventilation to houses that have not had any so we’re reducing risk but not adding an excessive amount that’s going to cause these systems to be turned off. We learned in cold-climate housing with R-2000 that the high rates caused the systems to be turned off so we had to moderate them. These are not guesses. This is based on actual experience.

A.B.: It sounded like you said that no matter if you have an old house with a really high blower door number or a newer house with a lower blower door number, the tracer gas results are about the same, 0.2 to 0.3 ACH. Is that correct?

J.L.: I’m simply saying that the typical house built in the ‘80s, ‘90s, and 2000s, the tracer gas work shows us that it’s between .2 and .3 air changes per hour. These houses are not…it’s a myth that we’re, oh my God, going to create all these problems by reducing the ventilation rate is just a myth because the ventilation rates have always been low. Max is going around and saying, my God, the ventilation rates are 0.5, 0.7, and 1. Well, that’s not true. He’s getting those numbers by taking his blower door numbers and applying his model to them. That’s bullshit. It’s just not true.

The only true measure of air changes is tracer gas. I quoted a reference that showed that an Ottawa house studied by Tamura and Wilson in 1963 had a tracer gas measurement of somewhere between 0.2 and 0.3. When I was director of research at the home builders association and in charge of R-2000, I went to NRCDBR [Ed.: Canada’s Natural Research Council, Division of Building Research] and said, look, what is the typical air change rate of the house built in the 1970s, and they said, our tracer gas work says between 0.2 and 0.3. So I said, well, the ventilation rate if we build an airtight house should be 0.25. That’s where that number came from.

The current code in Canada, if you read Gord Cooke’s comment [Ed.: He’s referring to a LinkedIn discussion in the Building Science Community group], is a very illuminating one. The Canadian code basically sizes the system at the rate of the 2010 62.2 but it’s operated at 40-50% of that which is exactly I had been saying for years. So we’re not guessing here. We have lots of experience.

By the way, under the Environments for Living program under MASCO and the Engineered for Life program with Green Fiber, we put in probably half a million ventilation systems in houses that are operating at these rates which don’t lead to humidity under part-load and don’t lead to dryness in cold climates. We significantly improved the air quality because we provided mixing and distribution. So I’d like to know where all these dead bodies are, where all of these problems are. There’s no health science basis to the 0.35.

A.B.: Where did the 0.35 come from?

J.L.: It was in the old ASHRAE 62-89 standard but remember, nobody was ever following that standard, right? The building code said you could have operable windows so nobody ever used that. It was a number that came from the ‘89 standard because they guessed that that’s what the actual air change rate was. It turns out that it wasn’t.

A.B.: You were talking about excessive humidity in the South, and I’ve seen some problems with positive pressure ventilation systems. What do you think about positive pressure systems? Do you think they’re better than exhaust-only systems, which you’ve talked about so much?

J.L.: Well they’re better because you know where the air is coming from and you provide distribution, but they’re not as good as balanced systems. Right? The best system is balanced that has exhaust and supply plus mixing and distribution. The supply systems that are connected to the air handler provide mixing, distribution, but they do not provide balance. But the most important thing is they provide a known location of air.

A.B.: As I understand it, the problems that have happened in humid climates with positive pressure systems is mostly they’re getting overventilated…

J.L.: But it’s not a problem with the positive pressure systems. It’s a problem with exhaust systems that run at too high a rate. It’s a problem with supply systems that run at too high a rate. And it’s a problem with balanced systems that run at too high a rate. I’m irritated that you’re saying the problem is with positive pressure systems. It’s a ventilation system that runs a too high of a rate. If you ran an exhaust only system at a lower rate, you wouldn’t have a part-load humidity problem. If you ran the positive pressure system—your outside air to the return—at a lower rate, you wouldn’t have a problem. Same with the balanced system. The problem is the rate.

A.B.: Speaking of rate, I want to clear something up that came up in our blog. You said that in the past, you were designing systems to 62.2, putting in 150% of the capacity, and commissioning at 50%.

J.L.: That’s correct.

A.B.: There was a discussion about whether you were talking about cutting the rate to 50% of 62.2 or running it half of the time.

J.L.: The rate. Your guys explained it correctly. At the end of those questions, they did a better job explaining it than I had done. They got it right.

A.B.: How do you see the new standard getting out there and getting adopted?

J.L.: Well, it’ll be adopted by individual state building codes and programs.

A.B.: Are you finding a lot of interest in BSC-01 vs. 62.2?

J.L.: The phone has not stopped ringing and the emails have not stopped coming. People are not happy with 62.2. You can say that…look, they’re [Ed.: the ASHRAE 62.2 committee] tone deaf and some of them are arrogant. Some of them are not listening to the problems and some of them are arrogant enough to believe they’re the only game in town. So guess what? Now they’re listening. And they realize they’re not the only game in town.

A.B.: What about combo systems where someone’s using a balanced system for part of the ventilation and an exhaust for the remainder to meet the requirements. I’ve seen this in some Habitat houses where they’re trying to do balanced with the Whisper Comfort, Panasonic’s ERV, and it doesn’t quite get them to the 62.2 level so they put controls on the bath fan.

J.L.: Well, under my approach, they’re going to be able to meet it simply because they get mixing and distribution. So the numbers will be low enough they will be able to meet it.

A.B.: So you see the Whisper Comfort, which is balanced but it doesn’t have distribution according to your definition, do you think that would count for distribution?

J.L.: I’m assuming they’re going to have some kind of forced air as well, right?

A.B.: Right.

J.L.: So the mixing also provides distribution, right? They’ve got it all so they’re going to get the lower rate. That’s a phenomenal approach. So you basically put in that system and you provide a timer on an AirCycler to mix the air, that mixing gives you mixing and distribution. You get it all, and you’re going to get it at the lowest rate. To me, that’s the least expensive way to get everything. I think that’s a phenomenal system.

A.B.: I wasn’t thinking that would count for distributed because it’s just a point-source ERV.

J.L.: Yeah, it’s a point-source ERV and the distribution and mixing’s provided by the mechanical system with a timer. You get it all.

A.B.: One thing that somebody brought up is about volume. So your standard and 62.2 are both based on square footage of conditioned floor area. Why not base it on the volume of the house if you’re circulating volumes of air.

J.L.: The reason for that is you’re penalizing a large-volume houses where what we’re worried about is the contaminants actually in the occupied space, and the large-volume houses allow you to distribute more contaminants because they’re able to…emission rates and concentration are different with large-volume houses. If you have the same source strength, and you have a smaller volume, obviously the concentration is higher. If you have  the same emission rate and you have a large volume, they’re actually better so the larger volume houses should have a lower value, not a higher value.

A.B.: BSC-01 is just for new homes. Do you have any plans to introduce one for existing homes?

J.L.: The answer is yes.

A.B.: Do you want to say anything about how that might look?

J.L.: It’ll be very similar.

A.B.: What about the issue of deciding when the house has crossed a threshold and needs ventilation and when it won’t do any good.

J.L.: My feeling is that the magic number is 5 air changes at 50 Pascals.

A.B.: So for existing homes, using a blower door to decide when you need ventilation can be a good thing and 5 ACH50 is your number?

J.L.: That’s correct because we’re talking about averages but the blower door’s no excuse for [ignoring] combustion safety. In other words, the source control is much more important. It’s much more important to deal with combustion safety and the source control issues than anything else. It’s preposterous that we’re missing the most important thing.

A.B.: So for existing homes, you think that if a house comes in at 5 ACH50 or lower, then you put in a ventilation system that’s going to have to meet, no matter where it is below 5, it’s going to have to meet the same number?

J.L.: That’s right but the big thing is going to be the emphasis on combustion safety.

A.B.: And no infiltration credit?

J.L.: That’s correct. And it gets even better. You ready? The control is in the hand of the occupant. It’s preposterous to say that you have to put in this system that has to be run at this rate and it’s not up to you because the committee decided it. That’s preposterous.

A.B.: So BSC-01 is formally going to be introduced at Summer Camp?

J.L.: The Westford Symposium on Building Science.

A.B.: All right.

J.L.: There might be some interesting news with respect to the standard as to who’s adopting it.

A.B.: Well, it’s going to be a very interesting Summer Camp.

JL Damn right it is, Bubba.

A clarification about air changes

When I was transcribing the recorded interview afterwards, it occurred to me that there seemed to be a contradiction. For someone with a PhD in physics, I’m not very quick to connect the dots sometimes, so I sent another question to Joe by email.

A.B.: You said that tracer gas shows that, “The myth of the old leaky house is just a myth.” If that’s true, is the emphasis on air-sealing a waste of time? If no matter how many holes there are, the ‘natural’ air change rate is 0.2 to 0.3, it would seem that’s the logical conclusion. But that doesn’t correlate with Blasnik’s contention [See the comments in my article about blower doors and ventilation.] that over the course of a year, the infiltration models are pretty good at predicting energy consumption from air leakage. What am I missing?

J.L.: “On average” is the key point. During colder weather with the stack effect driver air changes are higher. Worst is spring and fall – or summer houses without ac. No air change at all.

And it is not Blasnik’s contention, it is mine and was mine long before Blasnik, and I stole it from Handegord in 1982 who said that if you average things over a long enough time period you get the right answer. Just divide the ACH50 number by 10 or 15 or 20 and you get the right answer depending on the age of the house and the location. How is that for an infiltration model? Complicated eh? 

Why not use utility bill data to estimate infiltration? “The Blasnik Model”? Much better than the Sherman-Grimsrud model. You can quote me on that. Or use the Handegord model – “take the ach50 number and divide by a number….pick any number”.

There is lots of other tracer gas stuff in the literature. I am putting stuff together and will present it at summer camp. I did all of this in 1982 the first time. I did it periodically during the 1990’s. Apparently I have to do it again.

A bunch of stuff BSC has done is about to get released and posted that shows the effect of various ventilation system effectiveness on the same house using tracer gas analysis.

If you take away the “peaks” you save energy. That is a good idea. Filling in the valleys during non energy intensive periods is also a good idea. But then raising the average year round is a dumb idea. I want to keep the two good ideas and nix the dumb idea.

A note about Lstiburek’s air leakage credentials

Joe got his doctorate at the University of Toronto. His research was on the topic of air flow in buildings. You can download his dissertation from Building Science Corporation’s website: Toward an Understanding and Prediction of Air Flow in Buildings (pdf). He did a thorough review of the air leakage literature for his thesis. He also has a lot of experience with the Building America program, as he mentioned in the interview, and BSC’s many clients.

The debate continues next week

This week, I’ll be interviewing Paul Francisco, the new chair of the ASHRAE 62.2 committee. As far as I can tell, his views are more in line with Dr. Sherman’s, so if you’re looking for a more balanced look at the great ventilation debate, you’ll get your wish in my article next week.

Allison Bailes of Decatur, Georgia, is a speaker, writer, energy consultant, RESNET-certified trainer, and the author of the Energy Vanguard Blog. You can follow him on Twitter at @EnergyVanguard.


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