The great ventilation debate of 2013 roars on. Last month, I wrote about Building Science Corporation’s residential ventilation standard for new homes, to be released officially at Building Science Summer Camp this week, and then followed that up with an interview with Dr. Joseph Lstiburek. To provide some balance to the debate, I spoke with Paul Francisco, the new chair of the ASHRAE 62.2 committee, last week. (I asked Max Sherman for an interview, but he didn’t reply.)
Paul and I spoke for 37 minutes, so he did a lot more than just predict confusion and frustration as a result of the new BSC standard. We talked about a number of topics related to ventilation standards, research, and whether homeowners should have control of their ventilation system. If you’re trying to keep up with what’s going on in the world of residential ventilation, you probably ought to read the whole thing, but I should warn you that this article, as was the case with the others in this series, is pretty technical and not really for contractors who just want to know what they should do. I’ll write an article to address contractor concerns soon, though.
Paul’s a smart guy who’s been in this field for a while, so let’s get to that interview now.
Interview with Paul Francisco
Allison Bailes: Max Sherman says 62.2 is based on the intention to have 0.35 air changes per hour. That number isn’t anywhere in the standard, and it seems to be at the heart of the debate since Joe says 0.25 ACH is a better number. So, if the 62.2 rates are based on 0.35 ACH, why does the committee think that’s the best number?
Paul Francisco: So the 0.35 air changes per hour is what we used to have before 62.2 back when we were using 62 and Max was the first chair of 62.2 and I wasn’t there on the committee at the time. My understanding is that part of the grand bargain was to make the most common combinations of house size and occupancy end up at somewhere around 0.35 air changes so that the overall ventilation rates wouldn’t change that much for most houses.
It doesn’t mean the number is right, and for many combinations of house size and occupancy, 62.2 does not lead to that result. One of the problems is, though, that if you’re going to change the number, you have to have a good and compelling argument to something else. It’s always harder to change a number that people are already using than to pick a number in the first place. The bar is higher to change the number.
Obviously there are people who do believe the number should go down, often for humidity control reasons. There are also a number of people who believe that the ventilation rates should go up based on studies of health outcomes and nonhumidity issues so when you have competing viewpoints, you often end up with the status quo.
A.B.: Armin Rudd and Daniel Bergey of BSC recently published a report on ventilation effectiveness. One of their findings is that exhaust-only systems “showed lower uniformity of outdoor air exchange rate between living space zones, and higher concentrations of particulates, formaldehyde and other Top 20 VOCs than did the supply and balanced ventilation systems.” Why does 62.2 treat exhaust-only ventilation the same as supply or balanced ventilation?
P.F.: There are a number of issues here. First, I have looked at the report somewhat and I think a really important thing to understand about that report in this context is it was in unoccupied houses so it did not include the types of contaminants generated by people which may have a very different pattern in terms of where they’re generated and how much is generated than when you’re just testing what’s going on without the people but a major point of this is related to distribution and mixing.
One of the things people figured out over time is that there are a number of ways to get mixing. One way is to use a mechanical system to provide mixing. Another way is to have significant infiltration. Infiltration does act as a mixing agent. And another method is to have open doors. Any of those do promote mixing.
Now in the study from Armin Rudd and Daniel Bergey, they had tight, unoccupied houses and they ran it with all the bedroom doors closed, so if we have three mechanisms for mixing — infiltration, open doors, and mechanical — and they have tight houses with the doors closed, then they’ve essentially shut off two of those options, leaving only the mechanical mixing option.
That’s not necessarily something that should be applied to all houses, not even all new houses. I think that it needs to be looked at in that context. They set up the experiment in a way that will maximize the opportunity for mechanical mixing and therefore supply and balanced systems will show better and exhaust systems to show worse. So there’s that as a major issue.
We have looked at a lot of modeling results, some from BSC, some from LBL. We had several years where Max and his folks at LBL and Joe and BSC people showed modeling results and occasionally sampling results from a very small number of unoccupied homes. One of the things we learned from that was that whether or not a supply or exhaust system was better depends a huge amount on how leaky the house is, where the contaminants are generated, what your assumptions are about where the contaminants are.
There’s some work done at the University of Texas that showed that the majority of contaminants in a house are generated by people but that does not mean that they generate them consistently. They generate them more in certain areas.
So when we looked at all the results, we saw that sometimes supply looked better, sometimes exhaust looked better, and without a huge amount of data from occupied homes to really get at what’s going on, we did not find that there was sufficiently compelling evidence to grant one system generally better performance than another that would be applied to all houses. Now there was some consideration at the time that we could give some credit for distribution and mixing for tight new construction because that is a situation where you’ve definitely already shut off one of the mechanisms of mixing.
A.B.: A couple of things, based on your answer there. In their study, my understanding was that they didn’t have the doors closed all the time. They ran the houses like a normal house would be run with the bedroom doors closed at night. The other thing I’m thinking is, I know ultimately we want to come down to hard data, but just thinking about exhaust systems and how they work, that seems like it would be the least effective. Plus you have to consider where it’s bringing the air from, and exhaust systems can bring air from the attic or the crawl space, which isn’t so good.
P.F.: It’s certainly true that in a lot of houses, exhaust is not going to be your preferred solution. I’m not going to try to say that it is going to be a preferred solution in general. We’re not necessarily trying to always get the same amount of outdoor air into each room. We may really be trying to get contaminated air out and if there’s more contaminated air in one area of the home than in other areas of the home, then having distribution may not actually work.
Having mixing may not actually work. You end up taking some of those contaminants that are generated in a small area and spreading them throughout the house. This is where the problem really comes.
You can make assumptions that show that in terms of contaminant levels around the house, exhaust is better if most of the contaminants are all generated in one place. Then you can make other assumptions where you assume the contaminants are generated throughout the home. Then exhaust doesn’t work very well. We don’t really know the answer.
As far as the issue of having the makeup air coming from garages and attics and crawl spaces, places like that, each ventilation system has a way to try to make sure that the air comes in as clean as possible. When it comes to supply and balanced, it’s a filter, which may or may not get changed. When it comes to exhaust, it’s doing air sealing as much as you possibly can between the house and the garage, the house and the attic, the house and the crawl space. Then you may get some filtration through the insulation or you may not.
It’s certainly true that with exhaust you don’t know where it’s coming from but there are mechanisms to try to make sure as much as possible that it’s not coming from the so-called bad places. Given that filters get clogged and often don’t get changed, it’s not completely clear to me that you end up with a better system two years from now if you put in a supply or balanced system relative to a balanced system.
A.B.: That’s certainly true. Anyone who deals with houses knows that filter don’t get changed nearly often enough.
P.F.: Right. People ask me when I’m training, who’s going to change the filter, and I say, the same person who’s going to change the furnace filter. When you put in a better quality exhaust fan, they can get pretty dirty before you see a significant change in air flow. They tend to be fairly robust for a while, so my experience is they tend to be a little more robust to having the fan grille get dirty than air handler fans are for having the filter get dirty. Unless you have an ECM fan that’s adjusting its flow, but then you’re of course using a lot more energy to produce that flow.
The end result of all this is that it’s not really as simple as exhaust fans bringing air from bad places and don’t do a good job of providing acceptable indoor air quality. It depends a lot on the assumptions, and you really can make plausible assumptions that lead to both results. If we’re going to make an active decision to prefer one system over another in general, then we have to have more than contradictory assumptions.
That doesn’t mean that we can’t do better. We can potentially have something that says that in this situation, your tight house for example, maybe you do get some benefit from doing a supply or a balanced system.
A.B.: You’re talking about contradictory assumptions, but I think Armin’s study is more than just assumptions. They actually made measurements.
P.F.: They did make measurements. However my point with that is they made measurements in an unoccupied house, and if we go with what the University of Texas said, and most contaminants are generated by people, then using two homes that did not have any people, you may not want to base an entire standard that applies to the entire country on. It does provide data. It provides more data than we had before, and you’ve got to start somewhere. I don’t want to dismiss that, but I do want to make sure that we take into consideration the limitations.
A.B.: Rudd also wrote in his report on ventilation effectiveness, “the ASHRAE Standard 62.2 ventilation rates are themselves based only on the engineering judgment and experience of the committee members, not on any health or medical studies.” Do you agree?
P.F.: To a large extent, I think that is correct. You convene a committee that has a lot of people with a lot of experience, so there is engineering judgment. It is also a political document.
Now there are studies that have looked at health. For example, there is a really major paper that came out in 2011 by Sundell, Levin, and a number of others — Bill Nazaroff — a list of some really top people who determined that, and I’ll quote from the abstract, “Home ventilation rates above 5 air changes per hour have been associated with a reduced risk of allergic manifestations among children in a Nordic climate.”
OK, so it’s a Nordic climate. It was not done in the US so it’s got all the — their housing stock is different than ours, their climate is different than ours— it’s got all these things, but this was a review of a lot of scientific literature.
People could make the argument that if we were really going to be basing our ventilation rates on the available literature on health and medical studies, that it’s true, the 62.2 rates are not based on that. If they were, the rates would be even higher than they are now.
A.B.: Based on that one study you just mentioned?
P.F.: Well, this study was a review of the literature that looked at many different studies. The group judged 27 papers published in peer-reviewed scientific journals that were viewed as providing sufficient information on both ventilation rates and health effects to inform the relationship. It’s a review of 27 studies, not just one study.
A.B.: Joe and some others — Gord Cooke was one — say that ventilation systems that provide as much air as 62.2 specifies get turned off and left off because of comfort and humidity problems. Has the committee addressed this issue?
P.F.: This is an issue that we are working on. There’s a lot of interest on the committee in trying to level ventilation, providing a control that will reduce ventilation when outdoor conditions are more extreme and increase ventilation when outdoor conditions are more mild.
I was at a training session one time where I had somebody say, “Well I’m in Phoenix, and it gets really, really hot.” The next person said, “I’m in Fairbanks. It gets really, really cold.” You’ve got 200 degrees difference right there between two people and clearly they would like to reduce rates when it’s 80 degrees below zero or 120 degrees, so yes, we are working on this.
What we would like to do is develop some kind of control we can include this in the standard that says, if you have this type of control then it reduces the ventilation when conditions are more extreme, it increases the ventilation when conditions are more mild. It has benefit on the energy side since you would have less ventilation when it costs the most to heat or cool, more when it doesn’t cost very much. It would reduce comfort and humidity problems because you wouldn’t be having greater ventilation at those extremes.
There’s research being undertaken now to evaluate just how this would be done and incorporating it into the standard when it’s ready. There is also an issue with marketing. I don’t want to dismiss their concerns. They are valid concerns, and this is something that we are taking into consideration, but I have found people who focus on only one aspect of the ventilation, such as humidity, and who haven’t really convinced themselves of the value of ventilation pass that view on to homeowners, whether directly or indirectly.
Anecdotally, I’ve seen evidence in retrofit programs that homeowners that have ventilation installed by people who do value it are more likely to leave it on than those who have it installed by people who don’t value it. Some of that comes from the installers or the auditors or whoever, passing the view on to the homeowner. I think the most important thing is for us to continue working on a system that would meet the standard and would be explicit that would allow us to modulate the mechanical ventilation, adjusting it to outdoor conditions.
A.B.: What’s your view of 62.2 being a “one size fits all” standard?
P.F.: I really don’t agree with that view. I hear that a lot from people that here’s this rate and everybody has to have this rate and it’s causing all kinds of problems because of all the exhaust ventilation being put in.
This is a minimum standard. It is intended to make sure we don’t have problems, that we’ve addressed the most serious problems in most cases. That’s how I view a minimum standard. That’s how I view a lot of codes.
I feel that the 62.2 standard provides quite a bit of flexibility. If you do a blower door test, then you do get to adjust your rate somewhat based on that. If your house where you don’t think exhaust is a good idea, don’t put in exhaust. If you think you have a house where supply is not a good idea, don’t put in supply. You’ve got a range of options to meet the overall intent of providing good indoor air quality.
One of the things I’ve been comparing this to recently is venting of water heaters. An awful lot of [gas] water heaters don’t emit very much CO. I did a session recently where I asked how many people had measured CO in water heater [flue gas]. Almost everybody had. I asked how many people had measured really low numbers in water heater [flue gas], and everybody had measured really low CO numbers in water heaters.
So what is a water heater flue, but a hole that you have to cut and you have to put in materials that allows heated outdoor [I think he meant indoor] air to escape in the name of health and safety when a lot of times there’s not really a health and safety concern from this water heater. It is a one-size-fits-all approach.
I proceeded to ask how many people thought we should stop venting water heaters and nobody raised their hand. I asked why not. Well, I answered the question, that’s because we’re used to it. People have accepted that just in case something is bad, they’ll vent a water heater. We’re still working on having an acceptance of just in case there’s an indoor quality problem, we’re going to essentially vent the people.
A.B.: Are you saying that you’re OK with having water heaters vent to the indoors?
P.F.: No, I’m absolutely not saying that. I absolutely think we should be venting water heaters. I also think we should be ventilating houses because there are times when things do get bad and we should not be allowing those, as I said a little bit ago.
A minimum standard is intended to make sure that the really bad things don’t happen, and a really bad thing from not venting water heaters is you do have a big CO problem, we absolutely should be continuing to vent water heaters.
But we have a similar sort of thing with ventilation. This particular house right now may not have a problem where this much ventilation is needed but there may be a time similar to there may be a time when a water heater has a problem that this isn’t a suitable amount of ventilation. So providing enough ventilation to make sure that the worst problems don’t happen. In my view, that’s the role of a minimum standard and sometimes you end up doing more than you needed to in a house. Don’t let people think that I’m endorsing not venting water heaters.
A.B.: That’s why I asked that question because what you said before could have been interpreted that way. Well, let me ask a related question: If you think that it’s important to vent water heaters, what about ventless gas fireplaces? That’s not covered by 62.2.
P.F.: Not yet.
A.B.: Is that coming?
P.F.: We have a change proposal in the works that passed through committee to include unvented space heaters in the scope, and I expect that that will be something that happens in the not too distant future and then we will be able to have our committee discuss that and figure out what kinds of dilutions would be appropriate for that.
A.B.: That’s good to hear. My next question, I think you touched on as well: Do you think occupants should have control of the ventilation system and be able to adjust it as they see fit?
P.F.: I don’t believe homeowners should have no control. I also think that homeowners can’t detect a lot of potential indoor air quality hazards and they’re not knowledgeable enough to know what levels of ventilation they need at any particular time.
This is really one of the big challenges. If you can’t smell stuff, you don’t know what effect it may be having at the sub-acute level. It’s hard to provide a proper response. I believe there should be some level of control. It shouldn’t necessarily be easy to override the system.
But as I mentioned earlier, I think one of the most important things is to use advances in technology to move towards systems that do a better job of adjusting to current conditions. I think that would result in more confidence across the board as well as fewer complaints.
A.B.: So you think it should be difficult for occupants to be able to turn off the system completely? Is that what you’re saying?
P.F.: Yeah, I do think it should be difficult to turn it off completely, especially when you get to tighter houses. I’m not going to say that we should have ventilation police going around and making sure that people have it at the full rate as specified by 62.2. People are in charge of their homes. We should not be taking that away but I also don’t think we should be making it easy for people who live in really tight homes to fully shut down their ventilation system.
If they’re really intent on it, they can always go and snip wires to fully disable it but I don’t think we should be, especially in tight houses, just be providing a switch that says, turn me off if you don’t want me right now.
A.B.: Michael Blasnik said something similar in a LinkedIn discussion recently in responding to a comment that Joe made. He said he also thinks occupants should have a control but he doesn’t want to see a zero on the dial.
P.F.: Well that’s good to hear. I’m not on LinkedIn so I hadn’t seen that discussion. It’s good to hear that I’m not the only one.
A.B.: Let me ask you what you think of 62.2 having some competition from BSC’s soon-to-be-released standard.
P.F.: I don’t think it’s going to help the market. There are a fair number of items in the BSC standard that really do have merit and it certainly speaks to people who don’t want to have to do as much ventilation as 62.2 specifies. In general, I think it’s just going to increase confusion and frustration further.
ASHRAE has to follow a pretty rigorous process where we convene a committee of knowledgeable people with a wide range of backgrounds, interests, and expertise. Issues get vetted by that process. It lends the standard credibility. It goes through a process that is considered fair and balanced. None of us gets to write a wish list into a standard.
I would rather see an engagement between BSC and the 62.2 committee. Some of the BSC ideas were put forth to the committee a few years ago and failed to garner enough support to pass, but I think it would be appropriate to work with us to try again.
For example, the distribution factors table that BSC is putting into their standard actually got a majority of votes but not the supermajority it needed to pass. One of the main concerns some people had was the combination of those factors in the default infiltration credit.
Now getting rid of that default infiltration credit, which is exactly what we did in the 2013 edition, seems to be the source of major consternation. It could be seen as the first step in getting some of BSC’s other concerns adopted so I believe that we could come together and make changes and come up with a package that everyone could live with, which I think would provide clarity and acceptance to the market. Hopefully that is where we will end up after all this process has been gone through.
A.B.: Let’s get to infiltration. Is the Sherman-Grimsrud model for infiltration applicable to ventilation? It’s designed to model infiltration in a house.
P.F.: First off, in the 2013 edition, we’re not using the Sherman-Grimsrud model. We’re using the AME-2 model, and we’re assuming much greater sheltering from infiltration than we used to. This has the result of significantly reducing how much infiltration we estimate there is from a blower door result relative to older versions. We’re not really seeing as huge infiltration levels as we did before.
One thing to keep in mind here is that houses don’t stay at zero degrees temperature difference very much. Even in mild weather it tends to fluctuate, 10, 20 degrees, 30 degrees if it’s clear skies.
While I certainly don’t think that a blower door is good to really nail it precisely, I do think that a blower door can be useful in indicating whether a house is getting usually a noticeable amount of infiltration or not very much.
If it says it’s not very much, then you don’t get very much credit. If it says there’s quite a bit, you can still get a fair bit of credit. In existing where sometimes even after retrofit a house could be 12 to 15 air changes at 50, there are going to be very few hours where you’re underventilated with just infiltration. Even a 2 or 3 degree temperature difference could result in 50 cfm or so of infiltration so I think that a blower door is useful to indicate that sort of thing and we don’t really need to add mechanical ventilation for leaky houses. For tight construction, the right answer isn’t zero.
We know the house is getting some infiltration so as long as we use a conservative estimate, I think that it is a reasonable way to give some credit for the fact that houses are not totally airtight.
A.B.: Related to that, you did work with Larry Palmiter on tracer gas studies of infiltration. What do those data tell us, or not, about infiltration and ventilation?
P.F.: The results of those studies really were providing a competing model to the quadrature method that is in the Sherman-Grimsrud model, is in the ASHRAE Handbook of Fundamentals. It really was saying that until the ventilation rate is twice the infiltration rate, you’re only increasing the total amount of outdoor air by half of that unbalanced ventilation rate.
I think that in practice, the numbers are not going to be hugely different from what we have here using this model. There may be some cases where it would be different. What it does say for sure is when you have unbalanced ventilation, you don’t increase outdoor air by the total amount of the flow through the fan. That last thing I said is probably the real main takeaway.
A.B.: Can you repeat that?
P.F.: What it says is that when you have unbalanced ventilation, unless you have very low infiltration, the unbalanced ventilation does not increase the amount of outdoor air by as much as the flow going through the fan. It increases the amount of outdoor air by about half of the flow going through the fan. [This is the “Point Five Rule.”] For example, if you had a 50 cfm fan, you would be increasing the amount of outdoor going through the fan by about 25 cfm. So with the unbalanced ventilation, you’re not increasing the outdoor by as much if you were using balanced ventilation.
A.B.: Joe brought up tracer gas when I interviewed him and he said that the early work on tracer gas and I guess some of the work that you and Palmiter showed that the air changes in the houses were in the 0.2 to 0.3 range, less than the 0.35 that ASHRAE has sort of based on in 62.2. So he’s aiming for 0.25, which is in the middle of that range that he says tracer gas studies show. What’s your take on that?
P.F.: Well, Joe may be right. I think that’s something the committee should look at. Hopefully Joe will provide his documentation that he wants to use for that. One of the issues with tracer gas tests is it’s the same issues as with blower door tests. A blower door doesn’t tell you what the infiltration rate is at any specific time, and the tracer gas only tells you what the infiltration rate is at that time, under those conditions.
When the temperature difference is different, when the wind is different or coming from a different direction, if you’re doing a tracer gas test, you’d get a very different number. Simply taking the average of a bunch of tracer gas test results is not necessarily better than saying what the average infiltration rate is in a home than using a blower door test.
A.B.: Well, thanks for talking with me today, Paul. I appreciate your time.
About Paul Francisco
Paul Francisco is a research engineer at the University of Illinois at Urbana-Champaign. He is the director of the University of Illinois Weatherization Training Center and the Indoor Climate Research & Training group. He performs research on energy efficiency and indoor air quality in residential buildings, primarily in the retrofit sector, and provides training to residential energy auditors and contractors. He is currently the chair of the ASHRAE Standard 62.2 committee and vice-chair of ASHRAE’s Environmental Health Committee. He also serves on the BPI Board of Directors.