Interview with Dr. Joe Lstiburek — The Ventilation Debate Continues
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.
ab3 Why is distribution such a big deal? Do you have experience from the work you’ve done or research papers?
JL 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.
ab3 Another question that came in the comments of my article was: Are we exchanging one set of guesses for another?
JL 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.
ab3 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?
JL 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.
ab3 Where did the 0.35 come from?
JL 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.
ab3 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?
JL 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.
ab3 As I understand it, the problems that have happened in humid climates with positive pressure systems is mostly they’re getting overventilated…
JL 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.
ab3 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%.
JL That’s correct.
ab3 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.
JL 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.
ab3 How do you see the new standard getting out there and getting adopted?
JL Well, it’ll be adopted by individual state building codes and programs.
ab3 Are you finding a lot of interest in BSC-01 vs. 62.2?
JL 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.
ab3 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.
JL 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.
ab3 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?
JL I’m assuming they’re going to have some kind of forced air as well, right?
JL 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.
ab3 I wasn’t thinking that would count for distributed because it’s just a point-source ERV.
JL 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.
ab3 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.
JL 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.
ab3 BSC-01 is just for new homes. Do you have any plans to introduce one for existing homes?
JL The answer is yes.
ab3 Do you want to say anything about how that might look?
JL It’ll be very similar.
ab3 What about the issue of deciding when the house has crossed a threshold and needs ventilation and when it won’t do any good.
JL My feeling is that the magic number is 5 air changes at 50 Pascals.
ab3 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?
JL 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.
ab3 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?
JL That’s right but the big thing is going to be the emphasis on combustion safety.
ab3 And no infiltration credit?
JL 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.
ab3 So BSC-01 is formally going to be introduced at Summer Camp?
JL The Westford Symposium on Building Science.
ab3 All right.
JL There might be some interesting news with respect to the standard as to who’s adopting it.
ab3 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.
ab3 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?
JL “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.
See this followup interview, too:
ASHRAE 62.2 Committee Chair Predicts Confusion & Frustration from BSC-01
Lstiburek Has New Ventilation Standard—Resistance May Not Be Futile
A Blower Door Can’t Tell You How Much Mechanical Ventilation You Need
Why Do Airtight Homes Need Mechanical Ventilation?
How Much Fresh Air Does Your Home Need? by Martin Holladay, Green Building Advisor
First Deal with the Manure and Then Don’t Suck by Joseph Lstiburek, Building Science Corporation
This Post Has 28 Comments
I have yet to see an HRV or
I have yet to see an HRV or other formal ventilation device in a residence.The most I’ve seen is an intake vent from the outside to the return of the furnace/air handler.
Commercial is different, it really is needed there.
This will certainly be an
This will certainly be an interesting Summer Camp. I agree with Joe’s findings and recommendations.
Thanks Allison for the great work.
I have seen ERV’s installed
I have seen ERV’s installed in homes. Seems like the unit was installed related to good HVAC sales effort by someone, really interested in IAQ, to the customer.
When installed most units should be dampered and are not.
My big question is getting a balanced system installed. What does it take?
Bob: I can
Bob: I can assure you that they’re out there. I did a QA HERS rating on a house Friday that had an ERV. That’s it in the second photo above. Habitat for Humanity is going more and more with the Panasonic Whisper Comfort ERV I asked Joe about.
Anthony G.: Yes, it sure will be interesting!
John N.: I
John N.: I’m not sure exactly how you mean that question, “What does it take?” The basic answer is that it takes someone (builder, homeowner…) wanting to do it and then making it happen. Or do you mean, how do we get home builders to see the need for balanced ventilation systems?
John P.: Yeah, I think that may be the first time in my life I’ve been called Bubba. I guess those Canucks see any man from south of the Mason-Dixon line as Bubba.
We have been putting them
We have been putting them (ERV’s) in houses for years.
This all points the the real answer which is that we should be basing ventilation on air quality. Technically a challenge, I know. When stack effect is ventilating the house, the system would be off, but would be operating when it’s stagnant. And not ventilating for the plants and the dogs, when nobody is home.
Joseph: Well, I guess that includes everyone from Toronto, since their latitude is less than 44°. Right?
Thank you Allison and Joe!
Thank you Allison and Joe!
Our customers have never heard about HRV’s, let alone had someone explain to them why they should have one. The majority of our customers are now saying “yes to the dress” since we no longer sugar coating exhaust only ventilation strategies (as programs and paybacks encourage) as being adequate for promoting good IAQ, once the (assumed) bad places were drastically reduced. Fully ducted HRV’s now go in with the majority of our home performance projects (dry climate) because as Dr. J says, “exhaust only sucks”.
I believe the more we prioritize the discussion on ventilation with customers, the easier it is to get them driving the Porsche system (balanced designed and ducted with energy/heat recovery) (credit to Dr. Joe, a Porsche owner). The AC system will always happen, and so spending time on that discussion is silly to me. Simply explaining that of course you will be comfortable 24/7, but the best part is having control of the quality and condition of the air like never before.
Tight homes with Porsches and giving the occupants the keys- what a great concept. “There is no substitute.”
I am very interested in
I am very interested in ventilation strategies for older housing stock as I feel this is where the greatest impact of comfort improvement and energy efficiency can be made (whole lot more existing housing stock than new construction). To that end – and especially in the mid-Atlantic-to-New-England (where population is most dense, housing stock is most aged and climate is so broad) – how best to cost-effectively implement appropriate ventilation? Like when air infiltration is greatly decreased yet there are atmospheric combustion devices? Or where there is no existing duct work? And use of mixing technology (i.e., ERV or HRV) when the single-stage (very expensive) models’ efficiency is about 70% energy recovery and the dual-stage (ultra-expensive) is about 90%? I’d like to see more evaluations of distributed systems (one per living space) or a dual supply-exhaust system included with the central “mixed” systems. And include economic data – purchase/installation/maintenance/replacement costs.
Thanks for doing this Allison
Thanks for doing this Allison – this is very important stuff.
However, I’m still confused. Are we saying that ventilation rates are based on people’s perceptions? Can we state what the problem is? Can we show the science that proves that problem is solved? I see the words “reduce risk” without a statement about what that risk is.
If the only true measure of air leakage is tracer gas, why is a blower door OK for the point at which a house needs to be ventilated (5 ACH50)?
And the houses from the 70’s,80’s and 90’s at .2 to .3 ACHnat with tracer gas? In the Middle Atlantic we see plenty of them at 12 ACH50 – can this translate to these lower natural numbers? Is this a Canadian thing because they have had to deal with discomfort? Are houses in Minnesota from that era are pretty tight too?
Also in the Middle Atlantic, we see 200 exhaust only systems in new houses for every ERV/HRV that we see.
And if a point-source ERV coupled with a duct system is OK, why isn’t an exhaust only fan coupled with a duct system OK too – they both theoretically deliver the same amount of outside air into the house?
If we should not be using infiltration credits, why is the 5 ACH50 a magic number? And why would an existing house be different than a new house except for these infiltration credits?
This is a very unsatisfying discussion – I believe we are trading one set of guesses for a slightly more educated set of guesses, and we are not talking about what the problem might be.
If I read this right, Joe is
If I read this right, Joe is suggesting that the proper ACH is .25 because that’s what the average was for homes with healthy people and little associated comfort problems. But we are actually replacing a variable ACH that averages out at .25 with a consistent .25.
Are the people healthy because they live in a house with that average, or because they have higher rates for part of the year, or would they be healthy at the low fall/spring rates?
The point is that you can’t equate a .25 averaged variable ACH with a .25 continuous ACH because they are not the same. It’s still a guess, isn’t it?
Ed, I would call the "
Ed, I would call the “slightly more educated set of guesses” judgement based on experience. The existing numbers are causing problems and these problems need to be addressed.
The 5ACH50 is just a convenient way to separate new houses from existing houses. Nothing more. No real “science” behind it beyond the IRC code definition which is where the number comes from. Do I think houses with higher ACH50 values than 5 have no problems? No. I think they do and they need to be addressed but I am saving that for a separate document.
My question to you Ed is “what is the problem” we should be addressing. I am curious because I see no health science behind any of this.
Skye, to your point, yes it is still a guess. I think a better guess than other guesses, but still a guess. And that is a key point for people to understand. There is almost no real data or measurements to back up the existing number from a health science perspective. But lots of data or measured numbers to show problems with the high rates from the perspective of part load humidity and comfort and operating costs.
Thanks for the response. I feel much better about the state of the “science” of ventilation.
But if an exhaust only fan does not produce any complaints, no humidity issues, and excessive bills, why is that not OK? If the customer throws the breaker to make that fan stop running and there are still no “symptoms”, why is that not OK?
Thanks for your work on this.
I have recently started a
I have recently started a blog that discusses DIY zero energy home construction. I am interested in cheap, low tech solutions to conventional problems such as this. That being said what do people think of this idea?
This seems to be a more direct solution to the problem that would be cheaper and save a lot of energy.
Ed, I do not have a problem
Ed, I do not have a problem with an exhaust only fan that does not produce any complaints, etc. I have a problem with the 62.2 committee that does not recognize that better more efficient systems do not have to ventilate at the same rate as the exhaust only fan to provide the same “quality” of air. I think balanced systems that provide distribution and mixing should be rewarded with “lower” rates because they do as good a job at the lower rate than a less effective exhaust only system with no distribution and mixing.
I also question where the rates come from in the first place. They certainly are not based on health science. They are “faith based” rates that have been repeated so many times by so many people that they must be true for that reason alone. I don’t buy that. The measurements and history do not support the rates currently being promulgated.
And for the record many systems I design are exhaust only but they are coupled with forced air systems that provide mixing and distribution. I of course set them up to run at a much lower rate due to the mixing and distribution. And even more sacrilegious I let the occupants have control of the rate and the entire system. They can then ramp the rate up or down based on their judgement. How totally unreasonable, eh?
Thanks for the clarification.
We work in MD, DE, NJ, PA and VA. MD is now a little over a year on the 2012 code, DE will get it shortly, and NJ and PA are in the middle of the discussion, so if you are going to try to change the standard, do something quickly as once the 62.2 is in place it will hard to change.
While I can’t argue with the
While I can’t argue with the improved overall performance of an ERV over a standard bath exhaust, I’ve seen very many of these fail due to lack of maintenance (changing the filters mostly).
In our state (Wi) program for existing homes we are being encouraged to install switches or fans that allow automatic background running. Somehow this satisfies 62.2 in the eyes of the managers.
My feeling is: install too much ventilation capacity and have the ability to dial it back to minimum automatic amounts. Every home is different, and every home is lived in differently. A “standard” no matter how well thought out just isn”t going to hit every situation so we should be prepared for the outliers.
David Eakin, I was wondering
David Eakin, I was wondering about older home retrofits as well. Up here in old stock it’s largely radiators, and no ductwork. How then to do a cost-effective & proper job of ventilating an old house w/ no ductwork that’s been tightened up?
Maybe higher-rate exhaust-only is the best we can do w/o an awful lot of retrofit?
Joe, are you saying that all
Joe, are you saying that all of these houses built in the 70’s 80’s 90’s 00’s which had no ventilation systems had no contaminants because contaminants were measured and there weren’t any, or are you saying that nobody’s measured contaminants in these types of houses?
So much good stuff! How to
So much good stuff! How to pick a favorite? This was the last favorite:
“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.”
Though I love their products, I’ll need convincing that using the Panasonic for whole house ventilation is an effective approach (Hope Don Steven’s isn’t watching!)
I’d like to know what Joe (and others) think of this: http://bit.ly/fanlessHRV
“A bunch of stuff BSC
“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”
great something else to look forward to.
in the meantime…where can I learn more about tracer gas???
glad to know that Joe will be addressing existing homes also. this is the bulk of my work now.
being in the south…and knee deep in houses with mold…something has to change!
thanks for the info Alison and Hey Joe…thanks for all you taught us after Katrina!
I was skeptical about BSC-01
I was skeptical about BSC-01 but after reading this through several times and relating it to real world experiences I think it’s going in the right direction.
The projects with distributed ventilation have seemed to have a more pleasing “nose quality”. Purely anecdotal, but several customers with HRV ventilation in their bedrooms have reported reduced sinus issues too.
Unusual spot loads will always cause problems for standardized formulas so I’m willing to set that aside as well. Even 62.2-2013 doesn’t ventilate enough for that small room with 30 aquarium tanks (That needed structural help also).
I like the lower rates for energy savings, but to me the most significant idea is having spare capacity and allowing the occupants to adjust the rate. Some engineers seem unwilling to concede control over systems they design, so this is a radical concept.
I hope this gets used in enough places that we can get real data and see where we go from here. Thanks Joe for having the, er, nerve to do this.
I doubt point source ERVs
I doubt point source ERVs will see adequate mixing if you’re doing them as bath fans. the bathrooms simply don’t need enough CFM from the HVAC circulation to really make that happen appropriately, right? If you want to tie your whispercomfort(s) into your HVAC duct, now you’re talking. I would go so far as to say that you should ONLY get mixing credit if the outside air is distributed to something like the ‘majority’ if not all of the HVAC cfm in circulation… i.e. duct tied (but not interlocked) supply air, or exhaust air with airlets around the home plus mixing timer on the HVAC duct.
beyond that, the “problems” with supply and exhaust situations are usually related to moisture intrusion into the building envelope structure, from what I get from builders… i.e. pushing moist air or pulling moist air through cracks in the walls and causing rot, etc. will the spec address this issue in any meaningful way?
Thanks for sharing this interview. I have been having clients trying to meet the ASHRAE 62.2-2007 because two programs I work with have adopted it as a required standard. What is interesting is that the projects in high humidity areas (Georgia–especially around and south of the I-16 corridor) are finding problems with mold and mildew because of humidity being pulled in by the fresh air intake systems even though the incoming air is being pulled directly into the HVAC through the filter and across the coils. Their only exhaust plan is (generally) bath fans at 80 cfm and a kitchen fan around 100 or 150 cfm that are run either when cooking or when taking a shower, etc.
After reading this, it seems to me that the problems are:
1. A high introduction of humid air into the conditioned space during the months-long high humidity periods.
2. Inadequate HVAC capabilities to remove the levels of humidity (as the only dehumidification) from the conditioned space.
3. Inadequate use of ventilation to assist in removing some of the humidity.
4. Convincing powers that be that ventilation is not a “one size fits all” solution but rather a solution that must take on many “faces” for the myriad of ventilation needs based on climates, locations, etc.
On behalf of my clients who are currently battling these problems and finding moving to ASHRAE 62.2-2007 to appear to have increased the problem… ARRRGGGHHHH!!!!!
Rob – Why does a point source
Rob – Why does a point source ERV have to be in a bathroom? If it is in the main body of the home, why would you need to tie it into the supply/returns? Why would you need airlets for a balanced system such as the Panasonic WhisperQuiet? It delivers the air to the house with an equal amount of stale air removed – then the air cycler turns on the HVAC fan – pulling the fresh air into the system and delivering it throughout the house. Sounds good to me.
they don’t “have”
they don’t “have” to be in the bathroom, but if you’re going to let people use a point source ERV and a mixing strategy, it is very important to note that the whispercomfort is primarily designed as a bath fan and that most people use them there, and that would NOT be adequate if whole house mixing is the goal. In fact the whispercomfort has a very low exchange rate so most homes would need 2 or 3 to hit even 62.2-2010 level air exchange… I doubt we’re going to 20 cfm exchange as adequate in the new standard.
so I’m not saying don’t use point source ERVs. Just that you can’t deploy them as designed if you want to use them with a HVAC timed mixing strategy. if you’re doing all your air exchange in two or three bathrooms that only take 20 or 30 cfm each from the HVAC system at best, then you’re not going to mix much of that freshened air into the rest of the home. In fact the volume of the bathroom, if totally fresh, may not be enough to make this mixing strategy succeed. So I think the standard would need to be clear that mixing strategies should only be used if HVAC supply duct is shared with the ERV, or fresh air is delivered to some significant volume of the home (great room etc).
you don’t need airlets in a balanced system. re-read my sentence, I specified an exhaust system relating to airlets.I am not advocated for exhaust systems but if you use airlets for incoming air and a mixing strategy that would be the “best” way to do exhaust only.
I think the original premise
I think the original premise was that the Whisper Comfort was deployed in the main part of the house and point exhaust fans(bath/laundry) were used to make up the difference to the standard. It was also for a habitat home which is on the low side of the square footage scale. I think with those parameters as presented, it can be used as part of a HVAC timed mixing strategy. If its a bigger house, then I would assume an actual ERV sized for the home would be in order instead of adding 3 more Whisper Comforts as bath fans. For a bigger house, I agree, not a good strategy.
From what I’ve read on this
From what I’ve read on this alledged contraversy, I must say that it appears to be a matter of opposing sides simply wanting to be declared right rather than accepting that depending on the circumstances, both sides are correct.
We need more fresh air ventilation than is currently being in most residences. We need to stop putting residences under negative pressure and we need to control humidity.
In high humidity areas where the outdoor temps are above freezing, bringing in outside air through any device that removes humidity (HRV, return air ducting etc.)and keeping the indoor air pressure slightly positive prevents humidity issues no matter how much outside air is brought in. In dry climates, there is no humidity issue, but keeping the house either equalized pressure or slightly pressurized gives better control for where infiltration air comes from.
I will be taking pointers from both sides of this issue and applying them to specific needs in my area. Being in the humidity soup bowl from the Chesapeake Bay to the Eastern U.S. mountains to the Atlantic Ocean, I have to deal with outside air and humidity conditions based on specific individual circumstances.
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