August 26, 2015
Building America - Ventilation Strategies for High Performance Homes, Part I: Application-Specific Ventilation Guidelines
Iain Walker, Scientist, Lawrence Berkeley National Laboratory
Hello everyone! I am Linh Truong with the National Renewable Energy Laboratory, and I’d like to welcome you to today’s webinar hosted by the Building America program. We are excited to have Dr. Iain Walker here today to discuss what makes high-performance homes different from a ventilation perspective and how they might need...how they might need to be treated differently than traditional construction.
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We have an exciting program prepared for you today that will cover several topics including: combustion safety, identifying indoor and outdoor key pollutants, filtration, and installation/durability/maintenance issues. Specific guidance will be given for recommended systems based on climate, single vs. multifamily, envelope tightness and the presence of central forced air heating and cooling. The webinar will conclude with a look to the future of high-performance ventilation systems.
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The U.S. Department of Energy’s Building America program has been a source of innovations in residential building energy performance, durability, quality, affordability, and comfort for more than 20 years. This world-class research program partners with industry to bring climate specific guidance and resources to market. Visit our website at buildingamerica.gov to find more information about the program and the Building America Solution Center, which provides expert information on hundreds of high-performance construction topics, including air sealing and insulation, HVAC components, windows, indoor air quality, and much more.
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And now, on to today’s presentation! Our webinar today is Ventilation Strategies for High Performance Homes, Part I: Application-specific Ventilation Guidance. If you would like detailed information about this effort, please feel free to contact our speaker.
Our speaker today is Dr. Iain Walker, a scientist at Lawrence Berkeley National Laboratory who leads the Residential Building Systems group. With more than 20 years of experience as a building scientist, his current work focuses on Indoor Air Quality, retrofits, Zero/Low Energy Homes, and HVAC systems in residential buildings. He is an ASHRAE fellow and serves on standards and technical committees for ASHRAE, American Society of Testing and Materials (ASTM), Residential Energy Services Network (RESNET), and Air Conditioning Contractors of America (ACCA). With that, I’d like to welcome Iain to start the presentation. Thanks, Iain.
Iain: Thank you very much for that lovely introduction. I am going to start out today with a little bit of background. Basically think about, before we get into specifics about individual house types and climates and so on, think about why would we be ventilating anyway? Basically we want to remove or dilute pollutants in a home. Pollutants can either be health-rated or not. For example, moisture is the traditional thing that has been ventilated for many many centuries if not thousands of years where we have moisture generated by all sorts of activities and we try to control that through ventilation. Then there are odors generated by people, the things we do - from cooking, from stinky sneakers. We'd also like to live in places that are not offensive to us from the perspective of odor. And then we think a little bit more about health related pollutants. Some recent work has been done to figure out about these chemical soups that we live in and there are a lot of chemicals in our environment. We find that the vast majority of them though are at very low concentrations. They're not at concentrations that are a health issue and a few pollutants that have come to top are ones that are prevalent in many many homes and are prevalent at levels that we worry about from the perspective of health. They are particles that mostly come from combustion, formaldehyde that we find in building materials and sometimes the contents of homes in furnishing and things like that, and also NO2 - oxide of nitrogen, which again is primarily from combustion. Those are primarily the three major health related concerns and the reason I wanted to highlight those three is that when we're thinking about how we ventilate and how we are going to address indoor air quality in high performance homes it's good to think about what exactly are our targets and what are the things that we want to put our efforts into. One last note here is that for a long, long time, perspective has been that we'll use the outdoor air to remove or dilute these indoor pollutants. However, we also know that there are sources of pollutants that are outdoors. Particles in the ozone are probably most prevalent that most of you will have heard of. The Environmental Protection Agency regulates, or I should say tries to regulate, these pollutants in the outdoor environment but they are often at levels that are high and are high enough to be of concern from a health perspective and so we can't simply think of bringing lots of outdoor air into a home. We have to think sometimes about what's in that outdoor air also.
That's a little bit about the sort of things that we think we are going to control with ventilation and now I am going to talk a little bit about what are our current best practices; how do we think we are going to do this. I should tell you that I have put a little graphic there of the ASHRAE 62.2 standard and I am the current vice chair of that standards committee. We have a committee of just over 20 people with a wide range of expertise who are working on this national standard for indoor air quality and I'll refer to that throughout this talk her today because that provides a touchstone for what we're talking about and it's used in many voluntary programs, some states required and so on. It becomes sort of the defacto standard but I want to emphasize that this is the minimum performance standard. This is not talking about the best systems you can install in a house. The 62.2 standard is about what is the absolute minimum. What is the worst we will let you do? And say you are doing something acceptable for indoor air quality. That's important perspective that we want to keep in mind in this discussion here today.
I talked about pollutants that often come from cooking and if you have a kitchen, probably most of you have a range hood, and we like this idea about local exhausting these pollutants right where they are generated. So for kitchens you have cooking moisture, odors, and combustion. Combustion comes from both if you have natural gas and you are burning it but also from the act of heating up food. If you're frying a steak or frying onions or something there's lots of particles and combustion products coming from that. And also, we put exhaust systems in bathrooms, mostly for moisture and odor control although one could consider you could have cleaning products in the bathroom that might have chemicals in them that you don't want to be breathing. You could be ventilating for that also but local exhaust is a pretty widely accepted way of dealing with some of these pollutants for particular rooms, in this case kitchens and bathrooms. For all the other pollutants that are sort of spread out throughout the house we have to think about what we call whole house ventilation, which is for everything else. Once we've dealt with these significant point sources, whether it's moisture from showering in a bathroom that you want vent right away or you're burning your favorite food while you're cooking in the kitchen, you use local exhaust for that.
The question we also have to answer is, so, how much ventilation is the right amount? And as I said earlier, we can look at this ASHRAE standard as minimum requirements and for the local exhaust it's 100 cfm for your kitchen if you are using a range hood and 50 cfm in a bathroom. Those are not on all the time. That's why I use the word intermittent here. Those are exhaust systems that you control with a switch. So when you're cooking you turn on the range hood. When you go in the bathroom you turn on the exhaust fan. They don't run continuously. You then turn them off when you left the room or you finished cooking or you finish showering. Those are intermittent exhausts that are just those point sources. The whole house approach is to ventilate continuously for all the other stuff because it's emitting all the time. If you're thinking about formaldehyde, for example, is a pollutant that people think about a lot. That's emitted from building materials all the time there unlike, say, particles from cooking, which are only there intermittently. So for all these other pollutants we can ventilate all the time and the ASHRAE approach uses...it calculates and therefore is roughly based on the floor area of the home, which for that you can think about accounting for all the sort of materials that are in the home like carpeting or wood products with formaldehyde in them or what have you. Then another add on is for the number of occupants. There the idea is that people's activities also generate pollutants and we need to ventilate for them too.
What's really important here, why, and this is really important in high performance homes, is that after you've calculated how much whole house ventilation you need there's a credit for infiltration. That credit scales with envelope leakage so a very leaky house will get a lot of credit and you won't have to install a very big fan and eventually if your home is leaky you could have no fan at all. What we're talking about here today is probably the other end of that spectrum, which is for very tight homes. They get a lot less credit for infiltration than say a current standard home. That will be one of the key things that we talk about here today, this idea of how much infiltration you have in a tight home through the envelope. One last thing on this is that multi-family homes are treated slightly differently in the ASHRAE standard. You can't get that credit for infiltration. If you build a very leaky multi-family building you don't get any credit from an infiltration perspective and the main reason for that is that for many multi-family buildings only say one of the six sides of the building is actually exchanging air with outside. The other surfaces are exchanging air with apartments and that way you're getting say the odors and moisture and possibly cooking pollutants from other apartments, not from outside, and that really shouldn't count as diluting those pollutants. So there's no credit in multi-family. Typically the ASHRAE standard, just the minimum rate, is something like 1/3 of an air change per hour. This varies a little bit depending on the floor area and number of occupants but 1/3 is a typical number. And lastly, there are some special allowances for existing homes. If it's going to be very very difficult, for example, to install the point source kitchen and bathroom ventilation, say you're in an organization program, then there are some allowances that allow you to not do that and increase a little bit the whole house ventilation.
So, that's sort of background for sort of the minimum things that we do in homes to try and deal with those pollutants. The question is, today, what's different about high performance homes because we want to have good indoor air quality in all the homes, obviously, but there are some interesting things in particular about high performance homes that bring some interesting perspectives. The first one, as I mentioned earlier, is that new high performance homes are tighter. The existing housing stock in the country is at about 15 ACH 50 Pascals. In the 90s we found this was reduced in the range of 7-10 ACH50 and the natural infiltration you get from that level of leakage is roughly 1/3 of an air change an hour, so roughly like what the ASHRAE minimum standard is. New home code, new code homes, sorry, are going down to this range of 3-5 ACH50, so half as leaky again as they were in the 90s. High performance homes are tighter yet. A typical number is around 2 ACH50, although there are some programs like if you are familiar with passive house design standards, they're much, much lower. They're getting down to .6 ACH50, which is really a very, very tight home and it does get a lot of effort to get from that to ACH50 down to the .6. It's sort of incrementally harder each step as we go down these bullets to get homes tighter, but if we're here today talking about high performance homes I think the sort of numbers when I think about more how tight these homes are is probably less than the code, similar to 2 ACH50. You're probably looking at much, much lower than that 1/3 of an air change per hour we got in our existing homes and that's not enough. That's why we need mechanical ventilation as specified in the ASHRAE standard. A tight home will definitely be under-ventilated if you rely on natural ventilation. There's no way you'll get enough air flow through the home to dilute pollutants to an acceptable level, whether you're trying to take care of odor, you're concerned about moisture, or the pollutants that are health concerns. This makes tight homes, and therefore high performance homes, much more dependent on their mechanical ventilation system. If you're in a very, very tight house it's essential that the mechanical ventilation system is commissioned, so you're actually getting the air flow that you want, and that it's robust. By that I mean 2 years after you've commissioned it then the air flows are still good. It's possible that there's an argument for not going tighter than say 1.5 ACH50. Is it essential to get that last ACH50 out of the home? I'm not going to debate that today. It's just a topic to think about when we think about leakage of high performance homes is that as you get tighter you're even more dependent on mechanical systems. A passive house, for example, is going to be absolutely chronically under-ventilated with no mechanical system, whereas a new code home, you know, it's not going to be such a problem. That's important when we talk about what sort of systems you want to install in a house because having a system that is incredibly robust and is unlikely to fail then has a lot of value or rather it's more important in a very, very tight house than it is in a typical house.
One last thing on tighter envelopes, which is really the key issue here I think in high performance homes, is that people...I talked to you earlier about the pollutants outdoors that we probably don't want to have indoors. A tight envelope has very, very small cracks and it turns out that if you measure how many particles from outside come inside we can lose quite a lot in the envelope and the tighter the envelope is the more those particles we lose and so an added benefit from your tight envelope - you're getting benefits from an energy perspective but there's also a filtration effect that's getting rid of some of those outdoor particles. There is a caveat in that I think there is still some research that needs to be done in that area looking at different sized particles and so on but it's important to realize that tight homes are not just giving energy benefits. There are other benefits too and we think they're protecting us somewhat from outdoor sources of pollutants.
Another positive thing about high performance homes that makes ventilation and indoor air quality that gives benefits too is that we have a lot less of what we call natural draft combustion. Certainly furnace and water heater backdrafting is a safety issue and most programs that are involved in house tightening or energy ratings have a consideration for doing safety testing for combustion appliances, but if you are using say a high efficiency sealed combustion furnace or water heater or you're using a heat pump or electric heat, basically goes away. This problem that we have about backdrafting water heaters and furnaces goes away if the devices don't have that capability and are using electricity. So that sort of reduces the likelihood that we're going to have a problem. Another way of dealing with it is to have that combustion happen outside your super tight envelope. For example, there are attached spaces like attics and garages where so long as that wall or ceiling between the attic or garage is tight and has very little air flow across it, then we've sort of effectively put that combustion outside and again we don't have to worry so much about backdrafting because those pollutants are not going to end up in the home. However, there is one source of combustion that we do allow in our home and many people actually preferentially put in their home, which is to use gas for cooking. This is opening up all the combustion products into the house unless, of course, you have a range hood and you use it. The last point is important. In our surveys that we've done we find that many people have a range hood and it would be really helpful if they used it but it doesn't get used. The usual explanation is that it's too noisy and we're going to be working on that. I'll talk more about that later in terms of trying to get better range hood design and quieter to make them more likely to be used and/or make them automatic. It's important to notice that these high performance homes often have a lot less combustion safety hazards because of combustion being outside and when we don't have it the exception is cooking and that is why we want to have a range hood to vent outside.
I want to make a few notes on combustion safety. This is based on questions that are commonly asked. A lot of this revolves around high performance homes that put in what I would call a commercial kitchen exhaust. These are large high flows. By high flows I mean 3-400 cfm and up that are popular in high end homes. They are exhausting a lot of air and if you exhaust a lot of air in a tight house, you're likely to have product problems with natural draft combustion appliances and really you just can't have these large commercial kitchen exhausts and then a water heater in the kitchen that's using combustion air from the house. You're going to have chronic problems all the time. It's best to simply not do that. Another thing that people like to have in a high performance home is open fireplaces. By an open fireplace I mean a fireplace that takes its combustion air directly from the house. You can get sealed combustion fireplaces with nice sealed doors on them that take their combustion air from outside and they're fine because then you're isolating that combustion from the living space, but this comes up time and time again with the large commercial kitchen exhaust and open fireplace. That fireplace will not vent properly and really the only answer is don't do this. It's best not to have that. Again, for these large commercial kitchen exhausts when you're at those high air flow rates most of the time a building code and/or the manufacturer’s instructions will actually require tempered supplier. I would say you absolutely must have it even if you're not worried about natural draft combustion appliances or open fireplaces. It's still a really, really good idea to supply a tempered supplier. This is often quite expensive and so there is a lot of resistance to it but I really think we have to see these large exhaust systems as part of a system that includes tempered supply air. You can't treat them separately. It will only lead to problems.
Now for what I call regular exhaust. We have much lower exhaust air flow rates, which are more typical - say a whole house exhaust fan or smaller kitchen or bathroom fan. We don't have these absolute chronic problems where you're basically designed in failure but we still need some combustion safety testing. We're in the process of trying to simplify what it means to do combustion safety testing. It's probably still critical, for example, to measure your appliance to see if it's producing any carbon monoxide both in the living space and in the flue itself because carbon monoxide is the thing that we're really worried about because it's an instant life safety issue. It's still not a great idea even if there's no carbon monoxide to vent into the house because you're filling the house with a lot of moisture, a lot of other combustion products - oxides and nitrogen particles that we have health concerns about, but CO is the one that gets all the headlines. It's the important one because if it gets high enough it will actually kill you right there and then, whereas these other pollutants have long term health effects. CO is a very important immediate health effect. You should always test for CO. The other test you can do is test for draft to make sure that air is actually flowing up the flue when the device is firing. There's a lot more details to combustion safety testing that I don't have time to get into today but we still recommend that you do that if you have any combustion appliances in the space with you.
It is important to vent kitchens to outside. There's an awful lot of kitchens that have a range hood but it's just a recirculating range hood. Frankly, they're not worth dealing with. They're not really getting you the benefit because they don't get rid of the moisture or the particles of the pollutants or the odors. You must vent outside to call it effective kitchen ventilation.
Lastly, I might have been a little harsh in my "don't do it" comment here but in more higher end kitchens we do see separate cooktops and ovens where the oven is mounted in the wall with some cabinetry, separate from the cooktop. There's often a very nice range over the cooktop so that it vents all the combustion products and the odors and the moisture from cooking but ovens are not vented and we very rarely see a separate range hood over an oven. In fact, never, right? That never happens. We should not discount ovens. Ovens produce a lot more CO than the burners on a cooktop, if you're concerned about CO will levels, particularly at startup. They're also producing all of the same combustible products we worry about, like water vapor, moisture, and particles and so on all the time. We want to ventilate that too. I see this really as a problem. If you're looking to have good indoor air quality in a high performance home, don't separate the cooktop and the oven. You're creating a very tricky venting system. It's true that you can vent the whole kitchen and try and get rid of these pollutants but you must ventilate a kitchen at a much higher airflow rate than is required for your range hood, which has energy penalties. It can have issues again with combustion safety if you have appliances again using the air in the home for combustion. You're going to pressurize the house a lot more if you have 500 cfm of general kitchen exhaust then 100 cfm through a range hood. You could ventilate the kitchen that way but it's not recommended. It's particularly difficult in modern open plan designs where you don't have a kitchen, which is a room with four walls that defines the kitchen volume. Most modern homes, the kitchen is completely open to the living space whether it's a family room or a dining room, what have you. Then you've got a really big volume that you've got to ventilate and it becomes even more problematic.
Lastly in combustion safety, as I said, the one thing that doesn't get its own vent in the house is usually the cooktop or the oven. If you use an induction cooktop, if we're looking at the ultrafine particles that we worry about for health, we get a lot less particles in the emitted from an induction cooktop, sometimes 50 times less. The reason for that is it just doesn't get very hot like say the flame from a gas oven or the glowing red hot element that you have for a regular electric cooktop. Induction cooktops just operate at a lower temperature. They don't create these ultrafine particles. I should say that particles get emitted from the cooking are still there of course, but the induction cooktop is a good way to reduce the particles that you emit and admittedly the most expensive. Again, if you are looking for...if part of your high performance home includes high performance indoor air quality, this is something else to consider.
Another good thing about high performance homes is by and large they are emitting less pollutants. This is sort of a general home issue more than just high performance but it’s well worth considering. We are putting less formaldehyde in building materials and home contents and we have seen, in comparing older homes and newer homes here in the state of California, something like a 50% reduction in formaldehyde levels because we're regulating that and we no longer exceed the California acute standards in new homes. Some harmful chemicals are basically disappearing. We don't see mothballs much in homes anymore, so we don't see paradichlorobenzine, and just benzene in general is going...this is a long list of chemicals that's slowly disappearing. Some people would say, "Yes!" but there are new ones that we're adding that we don't know the health effects of. That is certainly true but the ones that we know have solid background information that this is a health hazard, like benzene. Those concentrations are certainly going down in homes because those chemicals are just simply not in the products we're putting in our homes and just in general there are lower VOCs we find in homes.
Lastly here about formaldehyde, we almost have federal regulation. Hopefully later this year we'll have this regulation go into force. Nothing is definite in the world of politics, because it has to be a political rather than a technical decision at this point, but these reductions that we're seeing in California may go broader nationally if we have some federal regulation of formaldehyde in building products and I think from the indoor air quality standpoint that can only be a good thing. So I guess what I'm saying is this high performance aspect is not just moving air to dilute it. Selecting low-emitting materials is a really really important part of what you do in your high performance home to make it high performance, high IQ.
You can, as a builder or a contractor or designer or architect you can, of course, specify low-emitting materials for the construction, which is great. We can't always restrict the materials that people bring into homes so that is still a bit of a challenge but I think as we are the buildings community our job is the control what we can control. I think specifying low-emitting materials are a fantastic idea. There are many many lists out there of products that have low emissions. I listed one here just as an example of Living Building Challenge "Red List." You can find your own favorite one and go with it. Again, highly, highly recommended for high performance homes is to use low-emitting materials.
As I said, there is a third-party assessment. This is not a complete list by any means but it sort of gives you some places to start looking. If you want to prioritize, you want to look at materials with lots of surface area - carpets, for example, have a lot of surface area and have direct path of exposure where people are going to be near these things. And also, it's a little trickier but often these lists of approved materials will talk a little bit about exactly what the chemicals are and how they contribute to IAQ issues.
That's on the emission side of things and a bit of source control, which I would say is essential. We should do it in all high performance homes or in all home but in particular high performance homes we can go there. I want to talk a little bit now about the three balanced system designs for providing whole house ventilation. Probably the first one and the one that we see most often in high performance homes is a balanced system, mostly because of that first bullet. You can do heat recovery through heat exchanger if you do a balanced system with fans to blow air in and out of the house. That can be an important part of getting high performance, particularly in harsher climates. However, there is a cost associated with that. You need ducting. There is higher cost equipment. There are less combustion safety issues because we don't have to worry too much about depressurization and just a little bullet there is that, of course, you have less combustion safety issues if you don't put natural draft combustion in the house with you, which is always the best thing to do. If you do a balanced system it's not going to impact that too much. You do get the opportunity to filter outdoor air to particles, which is a good thing to do. The flip side of that is we have a really big concern about balanced systems and plugged air inlets. We don't have any large scale definitive survey studies across the nation. We just have lots and lots of anecdotal evidence that it's beyond not unusual to have the air in the plug on your balanced system. Then basically you've converted it into and exhaust only system. It gives you the opportunity to do heat recovery. You can introduce combustion safety issues that you didn't think you would have. We're thinking about things that we need to start putting an alarm on these systems on the outdoor air. It's just so important to keep that outdoor air coming in for a balanced system and we so chronically don't do it that we may have to think about this. A parallel system might be if we think about your smoke alarm or carbon monoxide alarm. It starts beeping at you when it's about to stop protecting you. Maybe your ventilation system could do that too. If you think about indoor particles, unfortunately, with a balanced system you can filter the outdoor particles but not the indoor ones. So some sort of way of filtering indoor particles is a good idea. Often HRVs are just connected to a central forced air system. If you've put a good filter in that central forced air system, then run its fan at the same time as the HRV, you can do a really really good job of filter for indoor air particles. I like that idea. That's a really really good system or you can put some standalone filtration in to filter indoor particles. If you don't have a central forced air system, and some high performance homes don't. If you are, for example, running several mini splits in the home and there's no central system you don't really have this opportunity to filter indoor particles with a filter on the central forced air so you need some sort of standalone filtration.
Another thing, is more of a control that we've seen in some high performance homes where, particularly passive homes, which are very very tight, where they have concerns about, well, can we actually get enough air flow to our kitchen range when we turn it on because our house is so tight. A good idea is that you can interlock the operation of the kitchen exhaust with your HRV with some dampers that go to the HRV when it goes into supply only mode for when you're cooking to balance that out. Mostly that's going to apply only to the very very tight homes.
The second system that we're going to talk about here is about supply systems and, although the illustration here shows it connected to a central forced air system, there are standalone ways to do this. In humid and cooling dominated climates this is often a good idea because you pressurize the homes slightly. This stops humid outdoor air coming in through the envelope contacting cold surfaces and then you have condensation and moisture problems in the actual building structure itself. If you have a supply system, and pressurize it a little bit, I'm not going to say you are going to remove those problems but you certainly are going to minimize them and that's why we see supply systems in those climates. It's a really good idea. Again, if you're going to have combustion things in the house with you, you are going to have less combustion safety issues with a supply system that's slightly pressurized rather than depressurized. Like with the balanced system you have this opportunity to filter the particles in the outdoor air however you do need some sort of temperate tempering. Either you connect to some sort of central HRV mixed with some indoor air, and this is something which has two sides to it. This means you are going to need more ducting, more fan power, but this idea of tempering this indoor air with a fan and some ducts means that again you have the opportunity to also filter in the indoor air as well as the outdoor particles. I really like this idea of filtering. Just like the HRV system, a big big concern is plugged air inlets because once the air is plugged here there is no ventilation going on. Unlike the balanced system, at least there is still an exhaust if the air inlet is plugged. For a dedicated supply you better make sure that air inlet stays open all the time.
The last of the three mechanical systems is one that you probably see the most and this is an exhaust system. I think it's popular because it's simple and it's cheap. For example, you could put a bath pan in there. It's a double duty bath pan that operates at a low speed for whole house ventilation that you can put into boost mode quite a lot. There's no tempering of the air required. The temping happens as the air comes into the building envelope. The big downside that we touched on earlier is that if you have combustion appliances in the space it can be a combustion safety concern and so there is extra testing you probably have to do to your home if you use this system and that testing becomes more important as the house gets tighter as high performance homes tend to be. Unlike the other systems we have much less opportunity to filter outdoor particles, although we have some data that says that tight envelopes can be a pretty good filter for particles. It is more robust mostly because we don't have to worry about an air inlet plugging up and like the supply system, you need another filter system for the indoor air particles. If you have a central forced air system you can put it on a timer and have a really good filter to operate totally separately from the exhaust in order to clean the indoor air and that's probably a good idea for an exhaust only system.
I talked in those three systems about filtration and why did I talk about it so much. Really this is a health issue. Particles are the most important pollutant in homes for health. They're in almost all homes. They're ubiquitous and levels are a concern and it's a really really good idea to remove them. The ASHRAE minimum standard 62.2 it requires a filter in a central forced air system. It's only a MERV 6 filters. That's not going to move the particles concerned with health but you should know that it is, in fact, being considered whether it's an actual requirement that you filter air. I don't think we're ready to go there yet for a host of reasons but it's going to appear likely as a credit, in other words, if you have a central system recirculating air through a good filter, probably in the MERV 13 range. You won't need so much whole house ventilation because you believe you are having such a positive health impact by moving all those particles.
A kitchen range hood, by the way, is a great way of reducing the indoor particles from cooking. Again I'm going to hammer on this install a range that vents to the outside and use it. It must turn on because cooking is by far the most indoor source. There are other sources, like if you have incense or candles burning obviously, you get particles in the air.
Just to fill out a little bit more about this ASHRAE credit, I did a quick back of the envelope calculation for this credit. This is currently not part of the standard but it's likely to be coming up soon. You only need to move 150 to 200 cfm of recirculating filtered air to get the credit. So that is going to the bullet at the bottom of the page here. Because you don't need the much higher air flow that you'd normally have for heating and cooling systems. This means you can maybe take your forced heating and cooling systems, only operate it periodically, or if you install a very good variable speed blower you can operate it at the lowest slowest speed and that gives you very big benefits in terms of reducing the fan power requirements in order to this filtration. I've seen systems that if you are running them down in that 150-200 cfm range, with a well-designed blow pressure air duct system, you're looking at something like 25 watts continuously to provide this filtered air. People might say yes but I have a high performance home. I need to reduce the power as much as possible but so I guess that this is an option because that's a requirement but it's something to think about. You definitely are going to see air quality improve by moving the particles. The question is do you think 25 watts is too much or too little. It is something that I won't answer here but something, you know, one can debate.
What about installation and durability issues? The reason why I say this is that it's no good to simply install a system that absolutely has to work. As I mentioned earlier, in homes with super tight envelopes you can't rely on natural infiltration. It really really absolutely has to work. We need to verify air flows. We need to get flow measuring devices and go measure them. That sounds like that should be pretty trivial right now. You buy the right piece of equipment and you spend a few minutes in each house verifying that you have air flow. It turns out it's not so easy. Kitchen range hoods could be quite tricky to measure the airflow on. It's kind of hard to get underneath the range hood and have something that captures the flow there, particularly some range hoods suck air not just directly from the cooking surface but also in from the kitchen and the top and the sides, particularly, I'm thinking, microwave ranges. They have several air inlets and it's hard to measure them all at once. You could say, well then, find where the outlet is and then go measure that. That could be inaccessible or hard to access if it's on a roof and so on. So I think we need some better ways of measuring kitchen range hood air flow. It can also be tricky for supply systems. Again, a lot of it has to do with how do you get access to the actual duct that has the air flow in it. The inlet might be on a roof or high on a wall, making it hard to get to. On the inlet side, if it's connected to a central forced air system coming into a return plenum, some places can be hard to access. And for both kitchen and supply, and I think for the next one, the HRVs, there are some manufacturers that are thinking about building in a little flow meter, or at least access to install a calibrated flow station, which I think is great. We're not there. It's kind of rare but I highly highly encourage that. Another tricky thing for HRVs is that it's in a very very low air flow per inlet and outlet and a lot of devices on the market for measuring airflows are very poor at these low airflows and that makes it tricky to measure and verify.
And the last thing on HRVs is we're not actually installing connection. Usually there are four connections on an HRV. You've got fresh air from outside that then gets supplied to the house with inlets and outlets. Then you've got the return from the house that gets exhausted to outside, so another inlet to an outlet and sadly it's relatively common to see those connections switched. It's not just enough to verify that you've got the right airflows to the HRV. You better go to that HRV unit and make sure that the ducts are actually going where you think that they are going.
Again, there are issues with clogged inlets and filters. This is a relatively graphic image here but this is what we see on intake hoods. These are critical for supply and balance systems. This is a durability issue. How if you can trust people to clean them that would be great but that's not possible and I think in the future we're going to look to having some sort of alarm system or some automated system that tries to take care of that.
Typical surveys that have also been done in the US and Canada and a few other places looking at several hundred supply and HRV systems shows that roughly half of them are not working properly - a combination of the incorrect connections, they never verified airflow to make sure that they were plugged into inlets and filters, and half not working properly is far too many. It's really an issue our industry is going to have to try and deal with. We're not there yet. I think there are some positive things coming along. I think that as more of these devices get installed and installers get used to it they will definitely get better at it. I think this idea of verifying air flows is just getting more traction and we'll do that more and more simply because we're getting more and more interested in fine home performance in general. This is just another aspect of that.
What to do about inlets and filters? I think we eventually will have to set up some sort of alarm system. A last point on this for installers and designers is it would be great if you could get to all the HRV or supply inlets and outlets. I showed a few examples of things here, which are incredibly difficult to get a measurement device over, meaning how do you verify that you've installed things properly. It's almost impossible for these things. That's sort of a design and installation issue where we need to get away from the idea of if you hide an air inlet high up in a corner and put it next to a light fixture that you'll ever be able to verify the airflow, because you won't. So when we were designing and installing these things we also need to think about where we place our inlets and outlets so we can actually make sure that these things are operating properly.
So I'd like to summarize now a little bit about...so given all this information about different systems and their performance and the caveats and what to look for, what might be some recommended ways to ventilate your high performance home? I think we can always agree that you should always exhaust from your kitchens and bathrooms. They are high sources of pollutants and we should exhaust them. That is by far the most efficient way to do it.
You need to install a range hood and use it. There are some automated ranges on the market, but very few and most of the operation is safety based and only operates at very very high temperatures. And so the range hood industry is not...you can't go out there and buy a whole bunch of automated ranges but we think this is coming and a few years from now we think there will be a lot more automated ranges around that as soon as you turn on the burner there is a switch happening there. That switch would be integrated to the range hood and will turn it on. If you must put in a really big range hood with more than 400 cfm exhaust, these commercial style range hoods, you've got to install the whole system and install the tempered makeup air that goes with that. You can't just simply install that thing and expect it to work and expect it not to have any impacts on the home. I would really, really like there to be no natural draft combustion inside the home. So either it's sealed or you put it outside your tight envelope.
From the whole house perspective, probably most high performance homes are going to be pretty tight, they're going to be close to this limit I put there, and particularly in cold climates you should almost always use an HRV. It's going to be great from a thermo efficient point of view. It's balanced so even if you do, say, put a water heater in a kitchen you're unlikely to backdraft it. If possible integrate that into the central air system so you can add some sort of filtration. These are just sort of standard HRV installation ideas. You would then supply to bedrooms and living rooms exhaust from kitchens and bathrooms and laundry rooms so you exhaust from places that you think are going to be more polluted than others and you supply to places that you think people are going to be in. I think that very tight homes, less than 1.5 ACH50, that don't have a central forced air system for heating and cooling, supplying to the bedrooms and living rooms I think becomes more critical. We do...and so a lot of high performance homes are going to fall into that category again - super tight forced air system. A plenum in the bedrooms is a good idea.
Things like I emphasize that that 62.2 air flow rates, which people often use as a reference, they're the worst you can do. That's the least air flow that you should have and so I think that it's nice to build in a bit of capacity to you system. So you can have a boost mode for higher occupancy if you are having a party or something or if your range hood isn't working or just if there is an event that creates some sort of odor in the house that you don't like or you've burnt the toast and there has been some cooking failure. It would be super nice to have, for any of these systems whether it's HRV, supply air exhaust, a button that you push that says double your air flow rate for 20 minutes. You put on a timer and it turns off again. That's a really good, really good idea, particularly when we're talking about super tight homes that don't have much natural infiltration. If you put 20 people in it, because you have parties of over 4 people that we set the minimum rate for, you're going to want some extra ventilation. And boy do we need to find a way to make these systems more durable and I think probably trying to figure out a way to have alarms is a really good idea. If your house is not that...if it's not down in the less than 1.5 ACH50 area, some things I think become a little less critical. I don't think you need to have a balanced system and maybe here there is some climate dependence. In a cold climate an exhaust system is probably a good idea, whereas you need a supply system. That difference has mostly got to do with moisture issues in walls and in the direction of the airflow where the moisture is. I think we do need to distinguish between the climates when we're trying to pick between exhaust and supply. Again, the supplier offers this opportunity for you getting a temperate system and you can attach it to a good filter. Independent of all the climates and envelope types, if you are talking about health impact, adding some sort of filtration, something like MERV 13 and up but MERV 13 is a good place to start, that's going to play the biggest health impact and it's highly recommended independent of these other systems.
I'd like to look at multifamily for a minute. As I said earlier, there's no credit for 62.2 for multifamily, which means that if you build a tight multifamily building and a loose multifamily building they are going to have the same requirements. Fair enough. That's because we don't want to be mixing pollutants between apartments and a key thing there is this thing I call compartmentalization. They are not talking about the air leakage to outside for a dwelling unit or apartment. This is the air leakage to other parts of the building, whether it's corridors, it's your neighbors above or below you or to each side of you and according to 62.2 we do have a specification and the idea is that you would do a pressurization or depressurization test, measure the airflow at 50 pascals, and for every square foot of the envelope area and that's the sides, not just the vented to outside, there's a limit of .3 cfm if you have a 500 square foot of envelope area or 1,000. Let's do it. It's easier for me if I do 1,000 square foot of envelope area then you move just a point over and 300 cfm of 50 Pascals is the limit. This used to be tighter. It was .2 but an issue came up that people thought we could not meet that. I think we need to discuss that a lot more. Is a .3 or even a .2; are those really good enough to say that we're not going to get pollutants mixing from adjacent apartments? Obviously we have to temper this with what can we reasonably achieve in construction and the tighter the better and the limit is I think currently I think something that the building community, we need to debate that. I think you probably need to get tighter. The examples I think of are ones that we've seen here complaints about are often odors from cooking and the number one thing is cigarette smoke from adjacent units and how we limit that. Sometimes people have gone to non-smoking buildings, which helps but many buildings are not going to be non-smoking. Eliminating transport odor from apartment to apartment is probably going to need better compartmentalization in this. That requires a lot more careful design and requires a lot of effort in multifamily buildings. If you're building a high performance multifamily building, I think good compartmentalization is definitely part of calling that a high performance unit.
In terms of whole house kitchen and bathroom exhaust, whole house installation kitchen and bathroom exhaust, it's basically the same as single family. Kitchen and bathrooms are the same. Normally the air flows will be smaller because each unit is smaller and it's done on a unit by unit basis. We talk about smaller fans and air flow but generally the whole house thing is the same. Kitchen and bath exhaust are the same airflow, unlike the whole house, as a single family. In other words, you still need 100 cfm in your range hood or 50 cfm in your bath.
Again, with very very tight units adding a balanced system is a good idea because of opportunities for heat recovery, opportunities for decent filtration and so on. Again, there is probably some climate related issues similar to single family because of moisture considerations, whether you want to exhaust in cold climates or supply in hot humid climates. Those issues of transporting moist air through the building envelope are going to be the same in a multifamily building as they are in a single family building.
One additional thing about multifamily is that there's probably a lot more options available. A single fan serving multiple units ducted with dampers in it and so on is something that obviously you would not do in a single family but in multifamily you have the opportunity of getting systems together and have designs that might, you know, optimize in terms of using less fan power, for example, because you're going to have one single very efficient fan that serves multiple units. We have to be a little bit careful about how we damper those and prevent air flows from apartment to apartment but that's all doable. Or we could have individual small systems just like in a single family. A lot of that is going to depend on how the multifamily is constructed, the construction methods that they use. Is it high rise? Is it low rise? That's going to determine those. Then you get into some, particularly if you are doing, you know, single family, you get into some fairly sophisticated designs that is a little bit more like commercial building ventilation design.
To finish up here, I want to look a little bit to the future of how we're probably going to ventilate our lovely high performance homes. The first thing that I want to talk about is something that we call smart ventilation, which has at its core this concept of time shifting, so changing when you ventilate. A key thing here is if you are going to change the ventilation with time, we still need to make sure that if you have the same emissions in a home they are exposed the same as a continuous system. There are calculation methods to do that. What we want to do is things like if we move the time that they ventilate from times of high temperatures differences to times of low temperatures differences and still maintain that same exposure, we can definitely reduce building loads. We can reduce energy use. I suppose the classical application here would be if its winter and its cold outside you would ventilate less for say four hours just before dawn when it's coldest. Ventilate more in the afternoon when it's much less cold so your total for the day is the same exposure, but we've reduced our energy costs to do that.
Another one is if a home is unoccupied. You could reduce ventilation when a home is unoccupied because people are not there to breathe the pollutants. There are some caveats involved with that in that there's probably a minimum ventilation that we don't want to go below because you don't want to come home at the end of the day, open the door to a tight home that wasn't ventilated that now has very high levels of pollutants in it. You don't want to exceed acute levels of pollutants that will some sort of instantaneous health impact on you. So there are some caveats there. That's why I didn't say go to zero ventilation when unoccupied. We probably still have to ventilate a bit just so we don't have very very high peak concentrations you get exposed to when you reenter the space.
Another thing to do is to be more responsive to outdoor pollutants. You can get off the web information that's local for outdoor particle and ozone level and you could have a ventilation system that was able to use that information off the web. Ventilate less at times of high particle ozone levels. Ventilate more the rest of the time. High particle ozone levels tend to be periodic rather than high for extended periods of time, unless you're in the middle of a forest fire or something. And that means we can use this time shifting idea to, let's say, ventilate less during the morning commute if you live next to a freeway but ventilate more at night when there's a lot less traffic on the freeway and particle levels are lower. We can reduce our exposure to pollutants simply by time shifting.
From a utility perspective, we could use a ventilation system to respond to peak demand. We could turn off or reduce our ventilation during, say, the late afternoon in climates that have a lot of air conditioning like here in California, ventilate more the rest of the time. So again, the key is you need to maintain the same exposure by setting more of the times but we could reduce more of the ventilation contribution to peak loads in homes by time shifting to reduce peak demand.
For most implementations of this, the smart bit is, you need to track where your ventilation system is operated and what its air flow is when it's operated and do a calculation of what the exposure is to be able to control your whole house ventilation system but the algorithms are relatively simple. The key requirements are low and it's getting pretty low cost to put this sort of control strategy into ventilation systems and fan controllers.
Lastly, if you were to put this fantastic smart ventilation system, that maybe saved 40% of your ventilation related heating loads in the winter, you surely would like to get some sort of a credit for that whether you are doing a home energy rating or if you have a state energy code or local energy code you can comply with. So we do need some effort to get standards to recognize some of these advantages of smart systems. They're not there yet but I know from the ASHRAE 62.2 perspective we're certainly working on that so that you'll be able to get credit at least from the IAQ perspective. Hopefully if we can change energy codes from the energy perspective for doing some of these smarter things related to ventilation, particularly I think these are particularly effective in high performance homes when we think about how little building load there is from the envelope because we've got lots of insulation and really good windows. The fraction of the building load that is due to ventilation is going to be much higher in a high performance home than it is in a regular home. This ability to time shift and maybe save some of that I think is a really good tie in to having high performance homes work.
Some other things we want to do for range hoods; we want to get away from specifying an air flow rate to specifying their capture efficiency. What capture efficiency means is that if some pollutant is emitted on the cooktop, what fraction of that pollutant is going to go straight outside because it is going to get sucked up by the range hood? What fraction of it goes into the kitchen and mixes and is there for you to breathe? We've tested quite a lot of range hoods in recent years and this capture efficiency number has a huge range. Some range hoods are very good and capture a lot of the cooking pollutants right away. Some range hoods are not very good. It's all related to the actual size of the range. Does it fully cover the cooktop? It's related to the actual physical dimensions of the cooktop. Does it have a plenum that captures the plume, the hot plume that comes off the cooking? We are currently working on an ASTM test method for capture efficiency that will allow the manufacturers of range hoods to label their products with the capture efficiency and it will allow standards like mechanical codes like ASHRAE 62.2 or what have you to say we want to have minimum capture efficiency for the range hoods that you install. The reason we like capture efficiency better than air flow is that it's actually effecting something that we care about, which is how much pollutants enter the space, and also because it also allows us to do some clever designs. If you have a well-designed range hood maybe we can have good capture but lower airflow. The lower air flow will mean less noise and we know anecdotally that noise is the reason why people don't use their range hoods. So we're likely to get more vented operation. It may mean we need less fan power. The lower air flow means we'll have a lot less impact on combustion safety issues. So a high capture efficiency, low flow, low noise range hood I think is coming in the future and these range hoods, because they don't work if you don't turn them on, they probably need to be automatic. Current sensors are doing things like sensing the temperature above the stove. I think we probably want to move to things that are fully integrated with the controls of your cooktop or oven so that when you turn on the knobs, turn on the gas burner, or the electric burner the range hood is connected to that signal and it turns on even if it's at some low minimum speed. I think that would be a great step forward.
This idea that it's kind of tricky to measure the air flows for verification means that it would be nice to have some sort of more automatic systems and indeed there are some HRVs out there that have flow stations in them and might be able to do some sort of self-calibration. What we'd like to do if you want to simplify it is there could simply be a button that says push test and an HRV installer, after he's done, can push it and he either gets a red light or a green light or a series of red lights that say, you know, the problem is here or there. This sort of automatic verification I think would be a super duper idea and probably some sort of continuous monitoring, particularly for supplying systems or for filtration systems in general or some sort of alarm that tells you to change the filter. Particularly as we think more about particles and filtering then that's going to make them more important but simply to make anything that supplies air robust, that's probably a pretty good idea. I think we will do more filtration in homes for sure mostly because particles are the number one health issue. Possibly we will look at gas-phase removal levels. That means removing things like possibly formaldehyde, maybe some of the VOC - oxide of nitrogen and so on but I think the gas-phase is far into the future. In the near future I think we will be doing a lot more particle removal.
Another thing is I think most of you on the call are familiar with getting an energy score for your home. There are several energy scoring systems out there and I think what we need in order to reap the benefits of building this high performance home and putting in really good ventilation and filtration systems is some sort of a scoring system that reflects that so that you folks that are doing the right thing can be recognized for what you're doing and, you know, something that will account for smart systems, whether or not you verified the flow, what sort of filters you've installed, do you have, you know, an automatic range hood and so on. I think that we need some sort of scoring mechanism that will be analogous to these energy scores that we have where you require something from a simple observation - does a fan exist in this home - and then some diagnostics for air flow, which is kind of what we do right now for getting an energy score. We'll often use a blower to figure out the house leakage. Maybe we'll measure some air flows in the ventilation system. There will be a measurement component of the score and an observation component of the score. I really like that idea because a chronic problem with identifying indoor air quality and selling indoor air quality and so on is mostly what we're talking about here is invisible, particularly the health related aspect of it, are things that people do not detect. So it's a very intangible thing for most occupants. Getting some sort of a score might help us along there and we're currently at LBL starting up some of that work. We're working with Building America and some of the other national laboratories are contributing a bit, some of the teams, and we're trying to sort of put together people's ideas right now. We're just at the very very beginning of this trying to figure out what metrics look like and how do you compare the health and backup of a filter and more whole house ventilation. All those complications are still being worked out but I think from the perspective of high performance homes, high performance has got to include not just energy but indoor air quality and we need to recognize that in the same way that we do by scoring homes for high energy performance. We need to score them for high indoor air quality performance. That's I think I will wrap up with my basic presentation for now. We're going to have some Q&A. If you think of things afterward you can see here my contact number, my email, and phone number and if you want to know a little bit more about the group that I work in at LBNL you can go to homes.lbl.gov where there's quite a lot of resources and background information on a lot of the things that I've talked about here. A lot of our research is available online in various reports and so on.
Linh: Great, thank you so much Iain. I wanted to also thank the participants who've submitted questions and we have way too many for you to answer in the time that we have left so I'm going to start and we'll get through as many as we can. So I'm good?
Iain: Okay. Yes, go ahead.
Linh: Okay. The first question I have for you is - a tight home has a balanced ventilation system, shouldn't supply air dynamically balance exhaust depressurization?
Iain: I'm not exactly sure what the question is there. Yes, you could have separate supply and exhaust fans but not have an HRV installation, if that's the question. That's for sure. Or, if you think about a situation where you have a supply that's operating continuously when you turn on a bathroom exhaust fan or kitchen exhaust fan, if it's of a similar air flow and it will be for most homes, basically you are going from supply to balanced when you do that. That is certainly true.
Linh: Okay, the next question - is there an industry standard ASTM blower door test method for multifamily homes?
Iain: (laughter) That's a good loaded question. Well, probably most of you on the call are familiar with the ASTM E779 which is really applied for single family only and there are various protocols out there that various institutions have put together. There is no sort of ASTM or ISO standardized test method that deals with multifamily and it is a tricky issue because from an energy perspective you often want to simply isolate the air leakage to outside so pressurizing just one apartment isn't helpful. You need to pressurize all the other apartments around it and more than that because there is often a lot of interstitial spaces that are linked to other parts of the building, even that doesn't work. It's an incredibly difficult thing to isolate the air leakage to outside for an individual unit. It can...certainly we can do better by also pressurizing adjacent units and if you have say a row of townhomes it does get a little more straight forward in that now you don't have 5 extra faces. You only have two. There are definitely good protocols for testing row houses where you do broad tests on all three simultaneously. You do sort of what we call a guarded test. That's doable but in more multifamily or high rise it does get increasingly difficult. I will say however that the solution to that might be that we think these buildings should be tight to outside but also tight to their neighbors and probably very tight if we're thinking about air flow between units. So, some sort of leakage specification like the one I gave for compartmentalization, we're going to have super low target numbers. That's going to minimize...we're simply going to test the whole unit, get the leakage through all the faces of the unit. If that is super low the amount of leakage through the external part is even lower than that. Let's certainly put an upper bound on that might get through the face from an energy perspective. That's probably where we're going to end up and at which point maybe those air flows to the external envelope are going to be so small that we don't care about them, maybe not. It's going to depend on that compartmental criteria. Unfortunately we just don't have a super duper, always works, great method for air leakage testing in multifamily units to outside. There are some people who have done great work in this area and have done good testing but there isn't some sort of standardized test method that people can go and say, yeah, this is going to work.
Linh: Okay, the next question is - please explain why you wouldn't recommend make up air for kitchen exhaust less than 400 cfm in tight homes.
Iain: Well I think the main reason for that is that why would I care. If I don't have any combustion happening so I'm not worried about backdrafting, for example, a little bit of depressurization of a home doesn't really hurt anything so I'm not really concerned about turning on a range hood. It doesn't hurt the occupants. It doesn't hurt the structure. It's not on all the time, right? It's only on while you're cooking or while you're in the bathroom. I don't think for a typical, let's say, 100 cfm range hood that you need to provide makeup air in that situation unless you're living in a welded stainless steel box. Even in a passive house down at .6 ACH50 it probably does not need to have any make up air that supplies for the kitchen exhaust. I do like the idea, however, of having a control system in a very, very taught house that switches to supply mode only when you turn on the kitchen exhaust. It keeps the home balanced for starters if you care about that but also there may be issues in a very tight home. If you don't have a very good blower in the kitchen exhaust you might not get the air flow that you want and you might not get the exhaust of the kitchen pollutants, in which case balancing that out with a control system that makes the HRV go to supply only would be an assistance to make sure you do get the flow that you want through the kitchen range hood. Otherwise at the lower air flows, particularly once you've taken the kitchen appliances out, a little bit of depressurization is not an issue.
Linh: Okay great. The next question - in climate zone 3, mixed humid, what would you recommend for dehumidifying the whole house make up, short of having to add an ERV?
Iain: Yeah, I think that if your concern is about a humidity control an ERV can help in the sense that if you've put in a dehumidifier and are actively dehumidifying a home much below the outdoor humidity the ERV will certainly mean that that dehumidifier has to run less but the ERV on its own is not going to be enough to control humidity in your home. You're going to have to have some sort of deliberate dehumidification system, whether it's part of your air conditioner or a standalone unit. You're going to have to actively dehumidify and if you want to do that from an energy and efficiency point of view it's often better if it's much more humid outside than inside to dehumidify that incoming airstream simply because if you are using a vapor compression system and reheat, which is what most of these systems are going to be like, they are going to have a much higher latent to sensible ratio at higher air humidity content. So they become effectively more efficient dehumidifiers as the humidity content of the air goes up. You would like to dehumidify that incoming airstream when the outdoor air is more humid. If you want to get really advanced with your dehumidification you could install a damper and maybe have an indoor and an outdoor sensor and switch which airstream you would dehumidify depending on which has the most humidity in it. Again, then you're adding complexity to your controls and sensors that you have to make sure work and dampers. You know you could really eke out some more efficiency there but if you are going to dehumidify, and you've got a supply air system, then it's actually a good idea to actively dehumidify that air that you are supplying rather than the air in the house through some sort of internal mixing or what have you.
Linh: Okay, the next question is do you see air quality sensors being installed tied to ventilation systems in the future?
Iain: Well, the future is a long, long way away or its tomorrow. If it's tomorrow, no. In the near term we're a long, long way away from sensors that are either cheap enough or robust enough and I think the robust part is the key thing here. Certainly some sensors have come down in price to the point where you could reasonably consider adding it to your home HVAC system but whether or not they are doing the right thing 5 years from now is certainly problematic and almost certainly not the case. If we're talking, say, 10 years from now it's possible that there will be some breakthroughs. I know there is a huge, huge amount of activity in this area developing sensors for pollutants but they currently aren't there yet and won't be for a little while, at least at the commercial level. There are people trying to bring costs down doing, say, open source stuff so that if you are an equipment designer or specifier you could use some of those resources but again they are limited by the fact that these sensors do simply...they don't hold their calibration long enough or they don't work well enough for long enough for us to rely on that as controlling a ventilation system rather than what we do now, which is just outdoor air to dilute. The theory sounds great, right? The theory is that, well, if you have a bunch of really, really good detectors that tell you oh, there are almost no pollutants in the house today so you don't need very much ventilation you can see why that's attractive right? You can see some significant energy benefits there. The other side of that coin is if they see the pollutants are high they can go oh, we better turn up the ventilation a lot right now. Then you can see the alternative benefit. That's an ideal. We're just a long way from it and it's mostly due to cost and the sensors are simply not robust and reliable enough to be used in that way yet.
Linh: Another question for you Iain is - have you considered using dry volt temps in the depths calculating the effectiveness and using that to determine when filter needs change?
Iain: Oh, this is talking about some sort of knowing when you should change your filter?
Iain: Um, I think what's being talked about here is as a filter gets clogged, air flow resistance goes up and if you don't have a very good blower in your heating/cooling system as air flow goes up the air flow goes down. You expect then to be delivering hotter air from a heating system or cooler air through a cooling system. If you had a temperature sensor that carefully tracked that with time you could maybe detect, oh, I'm delivering air slightly colder now from my air conditioner and say that corresponds to a sudden change in air flow, which corresponds with a filter being clogged and say, you know, it's time to change the filter. I think that's possible but unfortunately more high performance heating and cooling systems tend to have blowers that don't change their speed with increase. They just work a little harder. That signal is not really available to us in high performance equipment. It's ironic I suppose that if you installed, you know, equipment that only meets minimum efficiency standards and is not particularly high performance you might actually have a signal you could respond to. It's theoretically possible. I think it's a little tricky but I'm sure it's doable. Again, I think it's a bit of a catch 22 here. We want to install really good high performance heating and cooling systems in high performance and unfortunately those are the systems that have the blowers that don't respond very much to air flow resistance. It's hard to find a way to make this temperature change be the sensor. I think that if we are got to sense something about filters I think it's going to have to have something to do with a really inexpensive way of sensing the pressure drop across the filter itself. It's the pennant of air flow rates and temperatures for these very reasons because a modern piece of equipment with a modern blower in it doesn't change its air flow.
I noticed some people have speculated about okay, so you have this fancy blower that maintains the air flow but we know the control is there for changing, right, as the air flow of the system changes. Maybe we could detect that and infer that the air flow resistance of the system has changed from blower motor power signatures and things like that. That's certainly possible but that's getting pretty esoteric but it's not beyond the realms of possibility. I genuinely think we'll find some way to measure across the filter itself. These things have been around before. There have been some basic simple what I would call your basic fluid mechanic system, which is simple whiffles that once a filter gets plugged up you get more filter bypass and if you put a whistle on there you reach a point where you've got airflow through a whistle to make a whistling noise. Those have existed for many many years. Or you could have a simple, maybe a simple monometer and a simple electric circuit to turn on a little red warning light that would be robust and last for 20 years without any maintenance and so on. I think a simpler approach is going to be better because it's more robust and I think we're going to probably actually sense the pressure drop because the filter itself because it's more of a direct indicator, if you will, of the actual filter performance. Some of these things have been around for 50 years. We just don't use them very much right now and maybe they're going to come back. We'll see.
Linh: We're going to see if we can get through a couple more questions before we do our quiz but the next question is - what is the origin of the .2 cfm square feet of envelope area tightness metric for multifamily homes?
Iain: The origin of that is that some very tight multifamily homes were built and got tested and that was roughly how tight they could get them. It's based on people going out and measuring this in the field. Now, the caveat is that by no means were thousands and thousands buildings tested and we didn't have a...there wasn't a program of how much would it cost to get any better or what have you. The basic number came from people. The best they could do and that was what they sort of felt was the best they could do because they wouldn't have measured it. It's not based on some optimum of how much the energy use will change or some optimum based on what we think the pressure differences are between apartments and the maximum flow we could get or we would allow that would allow for smoke transport. It's kind of based on what people could actually do in the field and so this is why I say I don't think this is a settled number. That's a debatable number. We might think that particularly tobacco smoke is going to be a number one because people are actually getting sued for transport of tobacco smoke between apartments and that gets people's attention. We might have to go to inspection of the question - what are the construction and techniques and can we do it. Then some people would have to go and do some more blow testing and see what we can get. The basic answer is it's based on some field testing of a few apartments that were tight and it's no more complex than that. Clearly I think some more thought and work is needed to finalize that number. I put it there as...I would call it more of a place marker than this is absolutely the right answer. I'd love to know what that number should be better than we do but it's sort of the best we know based on other experts that have gone out and measured air tightness of apartments and some of those people who did that work are on the 62.2 committee by the way. They're actively involved in writing the standard. As an industry I think boy would we like to know better what that number should be, both from the perspective of how low does it need to be to stop pollutant transport and how good can we reasonably expect construction to get.
Linh: Okay, let's go through. This will be the last question for Iain. Is there data showing the health issues with inadequate ventilation?
Iain: There are all sorts of stuff out there. There's a lot of...let me say that again. There's a lot of epidemiological studies but very few of them, unfortunately, answer some of our more specific questions like - you know, if I add 25 cfm ventilation to homes how much does health change? Those very specific answers we simply don't know. What we do know is what levels of pollutants are of concern from a health perspective and what ventilation rates are needed to control those to within reasonable levels. Again, this is a bit like the previous question in that there is a lot of work on the health side but in my mind we haven't really done enough measurements in homes. I'd love to do more but there are measurements we have done so that we need to have in order to keep, say, formaldehyde levels below a certain point based on standards or particle levels below a certain point or what have you. These are the ventilation rates. We need to control them. Of course, if you ventilated more you could make them lower and be further away from a health risk and health risk is never an absolute, right? They are population based. Sometimes they take the midpoint. Sometimes it's the 80th percentile. If you're trying to protect sensitive populations, the asthmatics, then you need much lower levels of pollutants and the air flow we're talking about is clearly going to be inadequate but from a minimum perspective or what you want to use in a typical home we probably don't want to go that far.
The answer for this is very squishy, right, because the range of health effects is large on people for the same amount of pollutant in the space. We're sort of doing the best we can. We looked at what the health community says about here are some standards, what level of pollutants are acceptable, and then we measured pollutants in homes and we think about emission rates and trying, you know, what air flow rate is about right to make sure these levels don't get too high in most homes most of the time, so it's not all homes all of the time. It's not sensitive populations. We have a fixed number but it's not the answer all of the time. It basically comes from large scale epidemiological studies that look at the health effects of various chemicals or particles or what have you and then what ventilation rates do we need to maintain those levels in the home. As I pointed out early on in our conversation here, if we emit a lot less in the home because we only bring in materials that don't emit then maybe there is a case there for saying well, I can ventilate less in the house, right? Conversely of course, if we emit a lot the opposite is true. The other bits of evidence we have tend to be...we just don't have the large scale changing of ventilation rate by x changes l, you know, this particular health thing. There have been many many small scale studies and intervention style that generally show that if you ventilate better you get better health outcomes but you can't quantify it to a great amount of detail and every study looked at of course a different aspect of health and every study had a subtly different way of thinking about ventilation. They are not exactly comparable but there is a considerable weight of evidence from many many studies for many years and many kinds of apartments that look at many health effects that ventilation does indeed have an impact. The impact is highly variable depending on the population that you're looking at and the health impact that you're looking at and what you mean by more and better ventilation. The results are all over the place but generally speaking there is enough data out there that we can reach some sort of reasonable guidance, if you will, on what is good practice. That's kind of where we're at right now in the indoor air quality business. A lot of it is what I call study indirect but there is plenty of evidence out there. It's just not - here is the right number - style evidence and frankly it never will be simply because people are highly variable. We're never going to control emissions that tightly. There is always going to be some squishiness with the numbers but we're doing the best we can with the information that we have and that's where we are.
Linh: Iain, thank you so much for presenting today. From the questions, you can tell that you generated a lot of discussion. We're sorry for the folks that we couldn't respond to in the time that we have today but we hope you take another minute and stay with us and complete our survey. Thank you Iain and do you have any closing remarks before we start our survey?
Iain: No, I'd just like to say thank you to Building America for hosting this and thanks to everybody who tuned in today. Hopefully this was constructive and people have a reasonable idea about why this matters for high performance homes and some of our alternative strategies for ventilating well.