Here is the text version of the Zero Energy Ready Home webinar, "Best Practices for Ventilation in Zero Energy Ready Homes," presented in August 2018. Watch the webinar.
Alex Krowka:
Presentation cover slide:
Hi, everyone, and welcome to DOE Zero Energy Ready Home's training webinar series. We're excited that you can join us today for "Best Practices for Ventilation in Zero Energy Ready Homes." Today's session is one in a continuing series of training webinars to support our partners in designing, building and selling DOE Zero Energy Ready Homes. My name is Alex Krowka, and I provide account management support for the program. I'm just going to take a moment here to cover some general notes on webinar housekeeping. All attendees will be in listen-only mode, however, we do invite you to ask questions throughout the session in the questions section of the GoToWebinar. We'll monitor these throughout the webinar, and after the presentation, we'll have some time to go over your submitted questions that weren't answered earlier. This session is being recorded and will be placed on the resources page of the Zero Energy Ready Home website. Please allow some time for this, since it does take a bit to go through the process to be added online. However, we will notify everyone once everything is uploaded. Our presenter today is Paul H. Raymer, senior technical specialist with ICF. Paul has been working with building science for more than 40 years. He's taught numerous building science courses and holds a number of BPI certifications. He's a certified rater, an IREC assessor, IREC certified master trainer, a full member of ASHRAE and a voting member of the 62.2 SSP. He is the author of the "Residential Ventilation Handbook," version 2, and "Recalculating Truth," a novel, which may or may not have spent time on the New York Times bestseller list. Before we get to Paul, I'm going to hand it over to Jamie Lyons, technical director of the Zero Energy Ready Home program, to give a quick intro to our program and the importance of ventilation to the program. So, go ahead, Jamie.
Jamie Lyons:
Great; thanks, Alex, and thanks to all of our attendees and to Paul for presenting today. That's a tough bio to follow, but I'll do my best here with a quick overview just to set the stage a little bit. So for those of you familiar with the DOE Zero Energy Ready Home program, we like to keep our partners informed as much as possible by doing deeper technical dives on specific topics. That might be building envelope design, or indoor air quality, or in this case, mechanical ventilation. So we've been doing these for several years and created a series of online recorded webinars, which are available on our website. And I believe there's probably approaching two and a half dozen now, 28, 30 or so such webinars at this point with industry experts like Paul. We're really excited about today's webinar, because as most of you are probably well-aware, mechanical ventilation is really a critical topic, not just for high-performance homes, I would say, but really for modern homes just built to the current standards for air-sealing of the building envelope. Good, effective ventilation that works over the long haul is real important to builders. And from the Zero Energy Ready Home perspective, we take a real special focus on this because our program focuses both on energy efficiency as well as performance. We don't just want one or the other; we really need to have both. So effective mechanical ventilation is a big part of that performance aspect of the home. This is also a very often-discussed topic with our builder partners when we have roundtable meetings. And they're looking for guidance from experts on not just what system types to use in a certain climate but also options for controls, what they can do to increase the likelihood that the system continues to perform well over time, and then even what are some of the installation pitfalls that they should watch out for in the field and try to avoid. So I think Paul is going to walk you through a lot of those really juicy topics, and I think it could be great session. So with that context and review, Paul, I'll hand it over to you to get us started.
Paul Raymer:
Well, thanks, Jamie. Appreciate it. Welcome, welcome, welcome to the wonderful world of mechanical ventilation. I want to thank you all for sharing this time with me. Time is precious. I'm going to start this off by asking a question I'm often asked. Do we really need mechanical ventilation? The equipment is expensive. It doesn't save energy. And isn't it just there to get rid of smoke and smells?
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Well, yes, we do need mechanical ventilation. Expensive? Compared to what? Not breathing? I guess it doesn't save energy the way insulation does, but good ventilation allows the house to be better insulated. It's part of the system, right? It is there to get rid of smells and smoke and a lot of other pollutants that get trapped inside the pressure boundary of the house. Ben Franklin felt ventilation was important. In a conversation between John Adams and Ben Franklin, who while traveling in 1776 were forced one night to share a room in a crowded inn, a window was open. "And I, who was an invalid, was afraid of the air in the night blowing upon me, shut it closed," Adams wrote in his autobiography. And ole Ben Franklin demurred, demanding that he reopen the window, lie down and listen to why he was being a jackass. So Adams endured the lecture until he fell asleep. Adams was a highly educated man who would later become president, who nevertheless believed that when the sun went down, air suddenly turned into poison. This was not, therefore, simple superstition. Indeed, over the next century and a half, even doctors and other educated folk propagated the myth.
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Alright, I agree that there are some houses that don't need fans. This house doesn't need mechanical ventilation. And it's obviously not very energy efficient. Energy efficiency and mechanical ventilation go hand in hand.
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In his book, "Ventilation: A Textbook to the Practice of the Art of Ventilating Buildings," written in 1891 -- I like that he added "Art" to his title -- William Buchan cited a number of studies that were done and incidents that occurred proving that people need fresh air. So even before we started tightening buildings, smart people recognized that fresh air was important. He called mechanical ventilation artificial ventilation.
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We have been conditioned to thinking that enough air will move through a home without mechanical assistance. But we're getting better at building tight homes that need less energy to heat and cool. We have reached the point that we recognize that mechanical ventilation can dilute the pollutants and is critical to the health of the occupants and the building. Building components used to be subjected to continuous wetting and drying and lasted hundreds of years. Now we seal everything with foam and caulk and plastic, and our margin for error has become narrower and narrower.
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While we are building tight homes to keep the conditioned air in and the exterior conditions out, we are trapping the interior pollutants in. If you close all the windows in your car with a hornet buzzing around inside it, it might encourage you to open the windows and let it out, right? People have been known to drive off the road and die rather than stay in a car with a hornet.
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We could live in spacesuits and control the conditions around us, but talk about expensive. We would be addressing the pollutants at the source -- the volume of air that needed to be heated or cooled or refreshed would be small -- but it would be somewhat confining. Not very intimate or social. We need to control the environment in our homes. We need to stay dry and be sheltered from the wind. So we build walls and roofs. We need to have light, so we add windows. We need to have ways to get in and get out, and so we add doors. We need to stay thermally comfortable, so we add heating and cooling systems. We need to control the temperature swings, so we add insulation. We need to control the quality of the air we breathe, so we have to add controlled mechanical ventilation.
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And if mechanical ventilation is unnecessary, why is the market for air fresheners so good? Next time you're in a supermarket, check out the air freshener aisle. The toxic chemicals released by air fresheners, particularly those with pine, orange and lemon scents, are known as volatile organic compounds, VOCs. These are well-proven toxins, many of which have been linked to a range of diseases and conditions when being inhaled, even in low concentrations, over a long period of time. Some of these chemicals include benzene, xylene, phenol, naphthalene and formaldehyde, a colorless, odor, unstable gas. Inhaling formaldehyde fumes, in even small amounts, can cause coughing, a sore throat and respiratory and eye problems. Formaldehyde has been linked to cancer, particularly in the nasal cavity.
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So what is this magic thing that people grumble about called mechanical ventilation? A house is a system; ventilation is part of the system, just like windows and doors. Ventilation must be a controlled flow of air. So it moves in the right direction at the right times at the right volume. How much flow is determined by how much work ventilation has to do to control odors and other contaminants, including moisture. Like the experience Goldilocks had with the three bears, it can't be too little, it can't be too great -- it has to be just right. Unfortunately, unlike the Goldilocks bears, just right is a variable. The purpose of the ventilation system is to control the level of pollutants in the house. It must not adversely affect the building envelope or suck the air the wrong way down the chimney. Both the building and occupants need fresh air.
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And if you put a bunch of independent ventilation systems in a house and turn them all on at once, they compete for the air that is available. These are the mechanical ventilations. And then there are the passive ventilation systems, like the air moving up chimneys, stack effect, pulling air in and pushing air out. And wind loads that can generate high pressure, pushing against the house on one side, and low pressure, pulling from the house on the other side. The same amount of air moves out of the house as comes into the house. One cubic foot of air leaving the house draws one cubic foot of air into the house. Now you probably can't see this fan sitting on my desk that has louvres that blow open on one side, and just a grill on the other side. If I slide this piece of cardboard across the grill, you can see the louvres closing. The fan doesn't stop spinning, but the air flow stops. I guess you'll just have to imagine it.
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So there are some fundamental ventilation rules. The first one may be a bit tough to believe. Seems like there's so much air in the house. You can clearly see this effect if you have a fan like mine, or a box or a window fan that is running and you block the input side. You can feel the air flow stop. So any air that you want to leave the house has to be replaced by air coming in. If you want the kitchen fan to extract 1,000 CFM, for example, 1,000 CFM has to come in from any cracks, holes, pipes, etc. So in a tight house, you might have to open a window to get the range hood to work. So ventilation rule No. 1 is one CFM in equals one CFM out.
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This all works with pressure. Like a balance scale, pressure is always seeking to equalize the system. Sometimes the pressure is there naturally. Sometimes it has to be induced mechanically. You need air, you need a hole, and you need a force. Take away any one of these three things, the flow will stop.
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A natural pressure difference can be the force. Ventilation rule No. 2 explains why a chimney draws exhaust gases out of the house when the pressures are right. It's how an air handler works, drawing air into the return vents and pushing air out of the supply vents. The second law is one of the most important fundamentals in understanding how a house works. So ventilation rule No. 2 is air flows from areas of higher pressure to areas of lower pressure.
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And air is lazy. That's ventilation rule No. 3. It's always going to move toward the closest, biggest hole. It's always going to obey the second law of thermodynamics, moving from high pressure to low pressure. It's always going to take the easy way out.
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Alright, I'm going to give a shameless plug for my book, which is bound to come out as a movie soon, although I haven't seen the contract yet. There are 64 pages of ventilation codes in here, including a handful of specific state codes. Some of them I'm sure are rarely mentioned, like the equivalent duct lengths for dryer ducting. And 0.75 CFM per square foot for garage ventilation. But they're in there.
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For Zero Energy Ready Homes, once you've complied with all the state and local codes, there are the additional ENERGY STAR® requirements, which in all fairness overlap many of the national codes. Not much that's radical here in this list of terms of mechanical ventilation.
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For most of the basic Indoor airPLUS specifications, it considers materials. The ventilation requirements flow right along with the ENERGY STAR requirements. So if the house complies with the codes in the ENERGY STAR requirements, it will be all set with ventilation for the Indoor airPLUS program.
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And again, there's not much beyond the basic requirements that is added to the Zero Energy Ready Homes, for ventilation. This is what is required in terms of energy efficiency in table R 403.6.1 in the International Energy Conservation Code. Now just between you and me, I'm not sure how a building inspector is going to enforce this.
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So when you go through all this, you can see what's required in terms of mechanical ventilation for Zero Energy Ready Homes. And a home built to code is not really much different in terms of mechanical ventilation. It is, however, clear that as we move up this stair of requirements, homes get better and better, safer, healthier, more energy-efficient, and a pleasure to live in.
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Alright, so what is this damned ASHRAE thing, anyway? These are the fundamentals of the standard. It is a national minimum ventilation standard. It applies to single-family, multifamily, manufactured and modular buildings. Although it considers chemical, physical and biological contaminants, it does not consider thermal comfort. The idea is to provide adequate ventilation without limiting it by thermal issues. It's going to cost something to ventilate because the air will need to be conditioned. But it costs something to have windows in the house, as well. And as a standard state's applying all the conditions of the standard, does not necessarily mean that acceptable indoor air quality will be met. The homeowner may do things in the house that go way beyond an average minimum ventilation application. Remember this is a minimum national ventilation standard.
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So typically, how many decisions do adults make in a day? The ASHRAE 62.2 committee consists of 24 voting members including me, seven of whom have PhDs, whatever that means. To most outsiders, they are very boring people. All they seem to think about is mechanical ventilation. They talk about it. They think about it. They write about it. They educate people about it. They dream about it. And their families won't take them to dinner parties because mechanical ventilation is not that interesting to most normal people. So these volunteer, highly educated geeks on the committee put all that brain time into working on things like ASHRAE 62.2 so you don't have to. You have 34,999 other decisions to make today. The point is, that the 62.2 standard is a thoughtful guideline for minimum ventilation on a national basis. Does it satisfy the conditions in every house and every locality, every day of the year, no matter how many occupants there are? No. And if you think it can be improved, great. We would welcome your wisdom.
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If outside air is worse than inside air, where can you get better air? You can't go to the store and buy organic air or free-range air. And you certainly don't want "green" air. You can't get it from your basement, attic or crawl space, unless you have a very special kind of basement, attic or crawl space. That's a question I don't have an answer to, sort of like the meaning of life. But luckily most of the time in most places the outside air is better than the inside air. Let's see if we can get close to some answers.
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If we follow Ben Franklin's wisdom and agree that we need to be breathing fresh air, how much air is necessary? The ASHRAE 62 standard provides answers to the "how much" question on a national basis. And we have an app for that. We just need to fill in answers to a few basic questions like where the house is and how big it is, etc.
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So once we know how much air we need to move, we need to figure out the best way to accomplish it. There are two fundamental parts of the standard: whole-building ventilation and local exhaust ventilation. We'll go through these in some more details. For both fundamentals, the standard offers sizing procedures, outlines equipment parameters, and requires install system testing.
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There are four basic system type choices. They all have advantages and disadvantages. You can suck the air in or blow the air out.
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Or you can suck and blow the air both ways at the same time. Remember, the one-CFM-in-equals-one-CFM-out rule is demonstrated by that fan on my desk that you couldn't see. They are all balance systems, some by nature and some mechanically.
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So since we're imagining systems today, let's imagine a perfect ventilation system. I wish I could play John Lennon's "Imagine" while we go through this, but I couldn't afford the royalties. It would always be balanced -- except when the house needs a little extra one way or the other. The amount of air flow would be automatically based on the level of pollutants in the house, including the number of occupants. The amount of air flow would be automatically based on the differential in air quality between the inside and the outside. It would have distribution throughout the house. It would be completely silent. Air flow measurement would be simple for performance verification. It wouldn't look like a ventilation system. Installation would be brainless. It would be maintenance-free. And it would be inexpensive. Everything else is a compromise.
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So unfortunately we haven't gotten to the perfect ventilation system yet, so we have to compromise a bit here and there. And we have to decide what to sacrifice. If cost is no object, of course, you have to make fewer sacrifices. Exhaust ventilation has a lot of good things going for it. It's familiar, there's low or no maintenance. In fact, it covers five of the 10 criteria pretty well. Supply ventilation gets about four out of the 10 because it requires maintenance to clean the filter. But it's not familiar, except when it's connected to the air handler. And balance ventilation like an HRV or ERV only get three out of the 10. Functionally they do distribute the air throughout the house, but they do require maintenance and they ain't inexpensive. So here's my main thought. Ventilation only works when it's working. I know that sounds silly, but if the homeowner shuts the system off, it doesn't matter how carefully the thought, design or installation is done. Period. Full stop.
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So by definition, a Zero Energy Ready house is energy-efficient, but you know that. It's ready to use no extra energy, or it may already generate as much energy as it uses. Everything has to be efficient, from the doorbell to the thermal envelope conditioning system. Ventilation systems use energy, from their motors to their dampers to their controls. When I was designing an attic control box for a fan, I thought about putting a light on it to verify that it was getting power. And then I thought, wait a sec, how often do I need to know that? And all the rest of the time it's just going to sit there in the dark in the attic, trickling power like a slow drip out of a faucet. Is that really necessary? So I left it off. Now I mean, why does my toaster need to have a clock on it? Really? There is going to be conditioned air to pay for, because one CFM in equals one CFM out. So we can't dilute the pollution without paying for it.
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So when we sum up all the electrical energy used, it's pretty small. These electric-powered air fresheners that are supposed to take care of the smells use two Watts. If that's running 24/7, 365, that's 17,520 Watts. Or 17.5 kilowatt hours. Where I live at 21 cents per kilowatt hour, that's $3.68 a year. Well, I guess that's not so bad. Alright then, how about the doorbell transformer? Do you unplug that when you're not using it? That's about $7.35 a year. Well, I guess that's not so bad, either. So how about an efficient bath fan? Oh, wait -- that's $5.89 a year. I guess we better get rid of the doorbell. But here's a question for you: Why bother to turn this off with some sort of sophisticated timer or control? Why not let it just run 24/7, 365? It will save a bunch of up-front money, greatly simplify the installation, and greatly reduce the risk that someone will shut it off and never turn it back on again.
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Alright, so electric cost is not so bad, even at 21 cents a kilowatt hour. Of course, not all fans are as efficient as that one. Conditioned air cost is more complex to figure out because there are so many variables. But depending on how you do the math, it works out to be between $1 and $1.75 per CFM per year. You're going to have to trust me on that or do the math yourself. So for a 60 CFM ventilation system, that's between $60 and $105 per year in conditioned air cost. I designed, installed, balanced and commissioned a very nice ERV in a very, very tight house, of a mere 4,000 square feet. The owner called me up about six months after I left the house and asked me how he could turn it off. I said, you don't. Don't do it. He said, but Paul, it's been running since you left. And I said, Mr. Smith -- I'm protecting his name here -- Mr. Smith, that system is costing you about the same for the year as the bottle of wine you had for dinner last night. Let 'er be. Move on to your other 34,999 decisions. My clients love me.
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So now that we know how much air we want to move and had some thoughts about system configuration, how do you select the equipment? The system has to be certified by either AMCA or the Home Ventilating Institute, HVI, for it to comply with ASHRAE 62.2. HVI has an exceptional program for testing, verifying and maintaining certifications. Sometimes it may seem as though a fan rated at 50 CFM, for example, is really not moving 50 CFM. And it probably isn't. The fans are tested at (audible) resistance or static pressure, a static pressure that is rarely seen in an actual installation. When an installer kinks and twists and steps on the ducting, the static pressure is going to change from how it was tested in the lab. But in the lab it was really truly 50 CFM. And what about bent sound? If a fan isn't quiet, it is definitely going to be turned off. Tight houses are quiet houses. A sone is a linear measurement of sound. Two sones are twice as loud as one sone. Think about the sounds around you right now. What do you hear? The fan in your computer is commonly more than one sone. For the whole-dwelling ventilation requirements in the 62.2 standard, the sound has to be one sone or less. So going back to an intermittent control strategy, if the fan is just running all the time, the sound blends into the background just like the hum of your doorbell transformer.
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The house may be tight enough. The purposeful inlets may need to be provided. They need to be selected and located carefully. Located in the wrong place, they may serve as outlets instead of inlets. Products are available to work as smart holes, letting in only a prescribed amount of air when it is required.
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And one of the good things about exhaust systems is that they don't require filter maintenance, since they are drawing air out of the building. Quiet and don't require operational sound (inaudible) ... can be used to vent for more than one place with one fan and one (inaudible).
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Manufacturers really want to work with builders; it's just smart business. They have bent over backwards to make ventilation systems quieter, easier to install and more energy-efficient. Using the range hood as the whole-dwelling exhaust system makes incredible sense. How many kitchens do you know that have doors to the rest of the house to block circulation? Kitchens are centrally located. Air can be drawn from all over the house. But wait, you say -- range hoods are noisy, rattling behemoths. Ah, but new technology throttle down the fan speed, use a larger blower wheel, make it easier for the air to move. And then install separate control just for the whole-dwelling ventilation, and hide it under the filter so that homeowners can't mess with it and turn it off. Leave the controls for the big air flow like burning the bacon, obvious. Make the fan housing pretty. The only problem I have with these things is that HERS raters don't always know that that background ventilation is there, and so it doesn't get shut off during a blower door test. But isn't that sort of cool? This is getting closer and closer to my perfect fan. So quiet that you don't even know it's there.
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An alternative to exhaust systems are supply systems. These systems push air into the house and allow it to leak out through leaks and cracks in the pressure boundary and shell. This approach works best in places where the outside air is relatively warm, avoiding the problem of uncomfortable drafts. If it's used in a hot and humid climate, keeping the house pressurized keeps that humid air from leaking in and striking a cool, condensing surface somewhere in the building system and growing mold. These systems do require a filter and the accompanying maintenance.
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Supply systems can be as simple as a pipe from the outside to the return side of the air handler. Or there might be a controlling device in the pipe to limit the amount of air being drawn in. Or there can be a control with or without a motorized damper that monitors the operation of the air handler for heating or cooling, and subtracts that run time for the operating time needed for ventilation.
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If you put fans together in one box and use one fan motor with two blower wheels, it's a lot easier to create a balanced flow. A heat recovery ventilator or HRV has a heat recovery core. And it's like two layers of corrugated cardboard rotated 90 degrees for the outcoming and incoming air streams. The two streams never touch, but by the second law of thermodynamics the heat from the warmer air stream will transfer through the exchanger element to the cooler air stream. So in cold weather, the colder outside air coming in is partially warmed by the warmer inside air leaving the building. In hot weather, the warm outside air stream will be partially cooled by the interior cooler air leaving the building.
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Alright, so let's go back to ventilation rule No. 1, one CFM in equals one CFM out. The efficiency of HRVs and ERVs is certified when they are balanced. If they are not balanced in the installation, they are not operating at their specified efficiency. Too much supply air and the house will be pressurized. Too much exhaust air and the house will be depressurized. Now, there are times when you may want to do that, but if the system is supposed to be delivering factory-certified efficiency, that is only accomplished if the installed system is balanced. And they are not -- underlined "not" -- makeup air systems. Just because there's an HRV in the house does not mean that the range hood will draft properly. OK? Oh, and speaking of efficiency, HRV / ERVs have four or five different efficiency ratings, as outlined here. And REM/Rate just looks for the SRE and the TRE.
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For local exhaust ventilation, you have a variety of choices. The closer you can remove the pollutants to the source, the less mixing with other air in the house that will occur.
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Bath fans are the most common approach to local ventilation. There are a wide variety of ceiling-mounted fans, from basic fans to fans with lights to fans with lights and heating elements. Products are getting evermore sophisticated. Inexpensive fans generally have inexpensive motors. More-expensive fans can have very sophisticated motors that are more tolerant to poor installation details.
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Kitchen range hoods are a familiar way of removing pollutants at the source. These products have commonly been pretty noisy, but newer models have brought the sound level down. Alternatively, they can be remote-mounted, mounted on the exterior of the building, removing much of that sound. Inline fans can also be used with mufflers that bring the sound down further.
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For fans to work, they need to have some sort of switch or control to turn them on. If the system is connected to the HVAC system, the thermostat fan-on switch will satisfy the standard. It just needs to be labeled. You can't hide the switch or control, although a circuit breaker is acceptable, as long as it's labeled. And local exhaust switches will satisfy the local exhaust requirement.
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And it doesn't have to be anything complicated or sophisticated. It can be as simple as an on-off switch with a label.
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Controls like these can be used to operate the fan intermittently. They can be programmed to match the fan to the ASHRAE 62.2 requirements and serve as a nightlight and clock that homeowners are reluctant to defeat. Some switches will operate both the light and the fan. When the switch is turned off, the light will go off, but the fan may remain on depending on the setting.
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And some fans have their controls built right into them. You can set them up for low-flow background ventilation rate to meet 62.2, and then their flow can be boosted when the wall switch is activated. Or a motion detector can do that automatically. But I just want to remind you that two-speed operation is not a requirement of the 62.2 standard.
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It's interesting to note the relative humidity in a bathroom with a fan that turns on every 20 minutes and then turns off. In this particular application, note the relative humidity up to about 5 a.m., when the heat turned on in the bathroom and dropped the RH down to about 30 percent. Then the occupants came in to take a couple of showers. RH went up to over 95 percent. The following sawtooth pattern shows the fan turning on running for 20 minutes and quickly dropping the RH. It builds up again, and then the fan turns on. It takes most of the day for the RH to return to where it started.
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And this is interesting that the fan on an occupancy sensor like a motion detector or light switch is just about the same as having no fan at all. Two curves almost completely overlap. The RH drops again when the heat turns on at about 5 a.m., rises to 90-plus when the shower is used, and then gradually drops back over the course of the day.
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Even the circuit breaker will satisfy the ASHRAE 62.2 standard. And if it's labeled TV and ventilation, it will never be turned off.
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If you were to take a boat from New York to San Francisco, which would be the shortest route? And that seems kind of obvious. So why do installers make the air flow path the equivalent of traveling around the end of South America? The air is going to get tired and give up.
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Make the air travel the shortest, straightest path from the polluting spot to the outside. Twisting, bumpy, small-diameter ducting is like traveling around Cape Horn. And this is looking up at the ceiling of a house. The electrician used 3-inch diameter ducting to run about 30 feet across the ceiling. And then he transitioned to 4-inch ducting at the hood because he couldn't find a 3-inch diameter hood. I asked this electrician how he selected what fan he used. He said, well, it depends on what kind of car the owner drives. So much for all this scien-terrific analysis of air flow and stuff.
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Now if you're going to put a ventilation system in, it needs to work. Bad ducting will have a major impact on performance. Air is lazy. From ventilation rule No. 3, it will always take the easiest path. Point the outlet of the fan toward the outside of the building. Never use duct tape. It was never designed for ducts. It was tape made from canvas duct material. It will dry up and fall off quickly. Always choose the shortest, straightest, smoothest path to the outside. Remember the first point. Air is lazy. And the system must be serviceable. It's a mechanical system; it's going to break at some point. Don't bury it. You don't want to tear out the part of the house that will last 200 years to get to the equipment that may last 20 years. And never, ever vent into the attic. The ventilation system will deposit moisture into the attic and is destined to do damage. So don't be stupid.
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Different types of fans are designed for different purposes. Inline fan products are designed to pull air through ducts to work with high resistance. Propeller fans or axial fans don't deal with resistance well. They are better for window fans or room fans. And although often necessary, backdraft dampers are an impediment to the air flow. Moving air has to push the damper out of its way to move through the system. Spring-loaded dampers close nicely, but they can be difficult for the fan to open. Make sure the damper is suited for the purpose.
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And we went through this already. The efficiency certification of an HRV / ERV is based on its operating in a balanced mode. How are you going to balance it if it's connected to the HVAC system? I mean, think about it. Do you balance it when the HVAC blower is running, or off? The fan in the HRV / ERV is much less powerful than the fan in the HVAC system. When the HVAC system isn't running, the size of the ducting will dwarf the size of the HRV / ERV ducting. So which way is the air going to flow? How far is it going to get? Do you need to run the HVAC blower all the time? What does that do to the efficiency? So, throw stuff at me, but the only way to get solid, predictable performance from an HRV / ERV is to use its own ductwork that has been properly designed and properly installed. When they are installed with their own ducting, I think HRV / ERVs can be the best of the best. And install the HRV / ERV so that it can be maintained.
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All the fittings have some resistance to the air flow. Air is lazy. It wants to move forward in a straight line. Think of a crowd of people moving down a hallway. When they get to a corner, they slow down as they make the turn. If they have to go from three lanes to two, they have to merge together and slow down. These fittings also have little cracks and holes especially where they are joined in the field. The air in the duct is under pressure, so it leaks out. Good ducting design is an art, like William Buchan said. For a good HRV or ERV duct system, it needs to be carefully laid out so that its installed performance will match the design.
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And sometimes contractors meet the letter of the code by installing the fan, but they eliminate the duct resistance by eliminating the ducting.
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For some reason there is an urge to use two-speed operation for ventilation systems. To meet the standard and use an on-off ventilation strategy, the fan has to be more powerful. For a half-on-half-off strategy, the volume of air has to be double to get the equivalent air flow. Two-speed operation requires a control of some kind, which adds cost. It adds noise, both when the fan is running and when it turns on. And remember that tight houses are quiet houses. So it's going to be a disturbance, and the occupants may seek to defeat the fan, which would make the whole installation useless. Let's look at some difference between average air change and effective air change.
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These are two systems that achieve the same average air change in different ways. One system runs continuously at 0.35 air changes per hour. That's a bit high these days, but work with me. The other system runs at a lower ventilation rate of 0.22 air changes per hour, for 23 hours, and one hour of intense ventilation at 3.4 air change. Like a wind blowing through the house. I wouldn't recommend this installation to my worst enemy, but it proves a point.
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So into this lovely house we set some "Stinking Bishop" Limburger cheese on the counter in the kitchen. It emits let's say one Limburger or Lim per hour. If we do the math on the continuous ventilation system, the effective air change rate works out to be 0.35 ACH. Equal to the average air change rate. If the air change rate is continuous, the effective air change rate equals the average air change rate. No big surprise there.
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Now, for our intermittent system, we still have our Stinking Bishop on the counter, and we've just run our lower-flow background ventilation for 23 hours. And then we slam on our 860 CFM fan for an hour and see what happens. Although our average ACH still equals 0.35, the effective ACH drops to 0.23. So the lesson here is that we're going to have to remove the Stinking Bishop if we're ever going to get rid of the smell.
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Don't put termination fittings where human air can blow on, where people can walk. It can freeze. In fact, think about termination fittings in general, like friends and family; they can be surprisingly restrictive to air flow, sometimes equivalent to as much as 60 feet of straight duct.
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And I probably don't need to say this to this sophisticated audience, but a recirculating range hood is as effective as a recirculating toilet, as my friend Allison Bales pointed out. When they have a new charcoal filter in them, they absorb some of the smells, but they have zero impact on pollutant levels.
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Installation. When they painted this bathroom, they removed the grill on the fan, but painted right through the fan itself. Remarkably, the fan still worked. The 4-inch uninsulated ducting ran all the way across the attic to the gable wall, where it vented to the outside. The ducting was attached to the fan with a very tight metal clamp that compressed the plastic nozzle in the heat of the attic, so that the damper could only open halfway.
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Dips particularly occur when the uninsulated ducting is weighted down by water. Water forms little lakes and wave patterns that further resist the air flow. Flex ducting is 100 times rougher than PVC plastic pipe. Flex duct is 33 times rougher than galvanized steel pipe.
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I've said this before -- installed results are different from lab results. The installed system has to be tested to verify the performance. There are a variety of test methods. Most of the equipment until recently was designed for commercial applications where the flow volumes are higher. But it's getting better. But you do have to set up the house consistently. Do you measure the flow from a bathroom fan with the bathroom door open or closed? Often, closing the door can cut the flow in half. It's a damper. Do you leave the air handler running? Won't the supply in the bathroom pressurize the bathroom? And do you leave the window open? The closest thing to a standardized ventilation protocol is the RESNET 380 standard, but at the moment it doesn't describe setting up the house very well, unless you follow the blower door setup. But just be consistent however you do the testing.
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If we didn't have people in houses, we wouldn't need mechanical ventilation. We probably wouldn't need houses. But we do have people in houses. That is what houses are for. In fact, people in houses and mechanical ventilations are a system, right? So ventilation systems are there to protect the people, so people need to understand how important mechanical ventilation systems are. So it's part of your job to teach the people how to use their ventilation and what it's for and why they shouldn't turn it off, ever. People still seem to think, as John Adams did, that outside air is scary. And sometimes it is. But generally, it's better than the air inside. Most of the time the solution to pollution in the house is ameliorated by dilution with outside air.
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If people don't understand the system, they will assume that it's wasting energy and do everything they can to defeat it, including stuffing the vent full of socks.
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Having gone through the effort to design-specify the ventilation system, documenting it shouldn't be all that hard. And it will provide anyone involved with a system understanding of what it is, what it's supposed to do, who designed and installed it. If this has been done, it should be reasonably simple to come back to the house and verify. The standard also requires that controls be labeled.
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The documentation should include all the necessary information -- all the design information. It should include the equipment information, what it's supposed to do, what it is, who to call if there's a problem.
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This is an example of the system for a 1,400-square-foot house with two bedrooms. The second line calculates the maximum CFM allowed from the two largest ventilating products running at full speed, to prevent backdrafting of atmospherically vented appliances. But in this house, outdoor air has been supplied for the combustion appliances.
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The HRV in this home is fabricated by the fictional Fanwho company, with the accompanying information. This page also includes the control information, as well as design notes and maintenance requirements. This provides information on how it's supposed to be working and how to maintain it.
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The information about the local exhaust system is here. And the information about the "Whambam" fictional exhaust hood.
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And finally, a page documenting the designer and installer contact information. If there are problems with the system, the homeowner or energy auditor knows who to get in touch with. And wouldn't it be great to have all this information about the systems in your house?
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But honestly, I have never ever seen this sort of documentation for the thousands of ventilation systems that I have experienced.
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So thank-you for listening. You've been a wonderful audience. Don't let mechanical ventilation haunt your dreams. And unlike John Adams, I hope you're still awake.
Alex Krowka:
Alright. Thank-you, Paul. That was a fantastic presentation. And you gave me my next great business idea. I think I'm going to start selling organic, free-range air. Kind of reminds me of the movie "Space Balls" a little bit. Now to some questions from the audience. We've had some great ones come in here, so let me just pull them up real quick. So the first one: I understand that using the electrical panel as an emergency shutoff switch meets ASHRAE 62.2, but does it meet the electrical requirements of the 2015 IRC?
Paul Raymer:
Uhm ... (laughs) ... It does meet ASHRAE 62.2; that I know for sure. And there is always a debate with local codes and electricians as to whether or not you have to be able to see the switch from what you're switching off. So I guess I would pass that one off to a local code official. I don't know why it wouldn't, except for that one reason, if they require it to be seen.
Alex Krowka:
Got it; thanks. And then another one is, we build in southwest Florida in a hot and humid climate. Your fresh-air strategy approach would work perfectly in the north. HRV and ERVs dehumidifiers just add an additional component, power consumption, lower HERS score, and more maintenance. When will ASHRAE recognize that 62.2 really won't work in our climate? Just using a mechanical damper set to open only when the compressor is engaged with exhaust ventilation using a smart switch. We do not need to bring humid air into a home that we are trying to protect from the very same air. The air cycler system simply allows too much air into the home without conditioning. How would you address that, Paul?
Paul Raymer:
Well, it sounded like the solution they were offering was the air cycler approach, bringing air from the outside into the return side of the air handler. Am I hearing that right?
Alex Krowka:
Um, I will let them follow up. And we'll move on to the next one. There was a question about a specific --
Paul Raymer:
By the way, just going back to the other one for a minute ... If that is just the pipe into the return side of the air handler, that is perfectly acceptable to meeting ASHRAE 62.
Alex Krowka:
Got it. So the next one, there was a question about a specific model of ERV / HRV small bath fan. We as a DOE program try to stay product-neutral, so if you do have any questions regarding specific products, feel free just to email Paul. I assume that's OK with you, Paul.
Paul Raymer:
Yea, that's fine.
Alex Krowka:
You'll see his email right there on the screen. Let's see here ... What is the best practice to exhaust from kitchens for Zero Energy Ready Homes?
Paul Raymer:
Um, a range hood? (Laughs) Yea, I mean, UL has very specific requirements about the area in which you can put a fan, or rather, a range or a stove. But the ASHRAE 62 standard recommends the range hood. Or if there is another fan from the kitchen, it has to be out of that comb around the stove.
Alex Krowka:
Got it; thanks. And then: Many homeowners complain about the noise from bath fans, from the backdraft from the outside air from the soffit. Any solutions?
Paul Raymer:
On the outside of the house -- the noise on the outside of the house -- is that what that's saying?
Alex Krowka:
Um, I believe so, yea.
Paul Raymer:
One of the things that I've found with these really, really quiet fans is that when they are noisy, it's because they have not been installed properly. The ducting is restricted or the damper is still taped closed, or some other thing. So you can almost determine if the thing has been installed right by the amount of noise it makes. So if you buy a fan that's like one sone or a third of sone, you shouldn't be able to hear it in the house at all. Now, outside the house, if you're hearing whistling in the ducting or the damper, again, it means that the air flow is being restricted somewhere in that path. So it's probably too tight a backdraft damper inside that hood that's causing it to whistle.
Alex Krowka:
Got it. And then: We've used our ERV as bathroom exhaust fans that run continuously and have booster buttons, which are locally installed in each bathroom. Additionally, we install a humidistat near the ERV, which will boost the ERV automatically if someone is taking a shower. Thoughts on that approach?
Paul Raymer:
OK. So, an ERV transfers some of the moisture as well as the thermal energy from one stream to the other. So if you are using an ERV when it is humid in the house and dry outside, like cold weather, for example, some of that humidity will come back in. If it's in hot, humid weather, then the ERV will extract some of the moisture from one stream and put it back in the other stream. So if you are in a hot, humid climate, some of the moisture from the outside will be removed if the house has air conditioning. So if you're using -- the dehumidistat is really probably not having a great effect. I mean, I think it's better to let these things run all the time, not turn them on and off, because of the fact that people have a tendency to leave them off once they turn them off.
Alex Krowka:
Alright. And then we had another question: Can you speak to ERV versus HRVs and which are the most appropriate in New England?
Paul Raymer:
I'm going to get into serious trouble. Usually I ask if there's a lawyer in the room before I get into these things. People get pretty emotional about HRVs and ERVs; it's amazing. But personally -- this is a personal opinion -- I believe that in a cold climate, an HRV is better because it gets rid of the moisture that you're trying to get out of a tight house, for example. In an air-conditioning climate, then I would probably want to use an ERV, because it would remove some of the moisture coming in. But personally, in New England, I would recommend an HRV to people. The other thing they need, of course, is a drain. The HRV does require that drain. And I think installers sometimes try to avoid putting extra fittings on things. But it really has to be in a location where it can be serviced. I've had people want to put them in attics, for either product, HRV or ERV. But that's a multi-beer conversation.
Alex Krowka:
(Laughs) Alright. And then, for exhaust-only ventilation systems, e.g. programmable bath fans, is there an ACH threshold where one should switch to a balanced system like an ERV / HRV? The house location is in zone 5.
Paul Raymer:
The thing I really like about using exhaust-only is because people are familiar with them, and they're less likely to try to defeat them. Switching from an exhaust-only system -- it really depends, like that electrician said, it depends on what kind of car the owner drives. If they have the ability to pay for a complete ducted HRV or ERV, that's a really good way to go, because it does provide intake air as well as exhaust air. And it can be balanced. But if you have to compromise, the exhaust-only running all the time is a great thing. I don't think that I have a threshold for air change rate that I would go the other way. Or go another way.
Alex Krowka:
OK. And following up on that: Are there any concerns using an exhaust-only system in a tight house?
Paul Raymer:
Well, I suppose if you get it tight enough, you know. I mean, we are getting these things down to the tiny rings on the blower doors. And so there may not be just enough holes. And so then you'd have to supply the fresh air inlets to accomplish the intake air So, you've got to balance it.
Alex Krowka:
Alright, and then, in two-story homes with one ERV and two heating and cooling systems, does ASHRAE 62.2 designate what percentages of fresh air need to be delivered to each floor?
Paul Raymer:
No. (Laughs)
Alex Krowka:
Alright, quick answer on that one. OK. So our time is just about up here. We did have a lot of questions come in, so I do apologize if we didn't get to yours. If we didn't get to your question, feel free to follow up with Paul, or follow up with myself, and I can pass a question along to Paul. Paul, thank-you so much for taking the time to do this for us. It's much appreciated.
Paul Raymer:
My pleasure. Thank-you for taking the time.
Alex Krowka:
The pleasure is all ours. So with that, I'm going to close out here in just a sec. A quick reminder for everyone on the line: On Thursday, September 13, we will have our next training webinar, "Solar PV Best Practices for Zero Energy Ready Homes." For the builders out there, that might be of interest to you. That webinar is from 1 to 2 p.m. Eastern. It should be posted on the Zero Energy Ready website, so feel free to register from there. Otherwise, keep an eye out for an email from DOE or Zero Energy Ready Home with the link to the registration page. So again, thank-you, everyone for joining. I hope you have a great rest of your week, and if you have any questions or concerns, please let me know. Thanks again, Paul.
Paul Raymer:
Thank-you.