ASHRAE Journal:
ASHRAE Journal presents.
David Schurk:
Welcome to this episode of ASHRAE Journal Podcast. My name is Dave Schurk. I'm national sales manager and director of applied engineering for Innovative Air Technologies. We are manufacturers of desiccant dehumidification equipment. Joining me today is Allison Bailes. Allison,
why don't you introduce yourself?
Allison Bailes:
Good morning, David. How are you? My name's Allison, and I am the founder and co-owner of Energy Vanguard. We are a small firm in the Atlanta, Georgia area. We do residential HVAC design. We do training, consulting. I have a book out on introduction of building science called A House Needs to Breathe... Or Does It?
David Schurk:
So we are going to be talking about dehumidification today. We're going to tag team the topic. Allison's going to take it from the perspective of residential, perhaps light commercial, applications and construction. I'm going to be looking at commercial industrial environments as we move forward.
So Allison, as this is a podcast on dehumidification, why don't we tee up the topic and talk a little bit about what is dehumidification? I'll say that from the standpoint of the 2020 ASHRAE Handbook: HVAC Systems and Equipment, they define dehumidification as the removal of water vapor from air, gases, or other fluids. Now that's technically accurate, but there's a lot more to it as we will get into as our discussion moves further. But why don't you give your take on that particular tee up?
Allison Bailes:
Sure, and I'm going to back up a little bit because I'm going to start with a precursor question, and that is, what is air? You may think that air is full of all kinds of stuff: nitrogen, oxygen, carbon dioxide, water vapor. But really air is two things from the standpoint of psychrometrics. Air has two components only: dry air, which is lots of different things; and water vapor. Dry air and water vapor. So what we're talking about today, dehumidification, is reducing the amount of water vapor in the air. So taking actual water vapor molecules and turning them into liquid usually. They can turn into solids sometimes, but we don't want to do that in a dehumidifier most of the time.
David Schurk:
What's interesting to most people is, you may go outside on a very hot and humid day and you may think that air is full of water vapor. It certainly may have a high dew point temperature, but the air itself only contains about 3% to 4% water vapor as a whole. So it's a relatively small total quantity of its constituent makeup. But boy, can it be a big deal in making sure that buildings are maintained comfortably and from a standpoint of compliance and productivity. Right? So let's expand on that topic a little bit. We've talked about what dehumidification is. Let's talk a little bit about why dehumidification. Allison, from a perspective of residential applications and buildings, why don't you give us your perspective on that?
Allison Bailes:
So the building codes have a lot to do with this because the building codes are requiring more efficient houses, more air tightness, more insulation, and the primary dehumidifier in homes has been the air conditioner. Also, we should talk about climate zones. We haven't mentioned climate zones yet. The eastern part of North America is where generally you're going to have to do dehumidification, maybe in the Phoenix area on monsoon season, and that's a whole other topic right there. So building codes have resulted in houses being more efficient, more airtight, and that changes the balance of loads and it changes the ability of air conditioners to handle the dehumidification needs of a house. So we end up with houses where the air conditioner doesn't run enough. More efficient equipment, also often doesn't dehumidify as well as the older, less efficient equipment. I have heard people joke that, "Hey, if we want better dehumidification, let's just go back to 10 SEER air conditioners," which is not what we want to do. We want the more efficient equipment.
But what's happening is, now the air conditioners aren't often able to handle all the dehumidification loads so sometimes we need supplemental dehumidification. In a lot of climates, that happens in the nighttime when the air conditioner's not running as much because in the daytime, properly sized air conditioner is running enough to pull enough water out of the air. At nighttime, the air conditioner doesn't run as much because it's cooler outdoors. And that's more often when you might need supplemental dehumidification, or on the cool, cloudy days when you're not hitting those design temperatures.
David Schurk:
So from the perspective of commercial industrial dehumidification, there's several reasons we dehumidify. Comfort, most certainly, is one of them, but many times, productivity or compliance play a big part as well. An example might be a hospital operating room where you have surgeons that are heavily garbed and performing underneath stressful conditions, to say the least, highlighting loads, a lot of activity occurring in the space from their perspective, and they begin to perspire underneath all that garbing. So in that environment, comfort is important. They believe that they are too warm, and they are, so they ask for the temperature of the operating room to be lowered. And when the temperature goes down based on the chilled water being fed to the coils, the relative humidity goes up.
So in those environments, we need to provide systems that can not only cool the air properly, but dehumidify the air to further levels. That air needs to be pretty darn dry. And the reason it needs to be dry is simply so that it can literally wick the moisture or the perspiration off the surgeon's skin through multiple layers of clothing into the environment that surrounds them. 25% of the way that we as human beings maintain our thermal comfort is through the evaporation of perspiration. Now, in most indoor environments, we have exposed skin, and we're not sweating profusely. In a surgery environment, for example, they are heavily garbed, there is no exposed skin, and they are sweating sometimes profusely. So that dry air that encapsulates them helps to wick that moisture off their skin, absorbing the latent heat of vaporization at 1,006 BTUs per pound, and helping to keep them comfortable. Allison, what's your perspective on this?
Allison Bailes:
Let's go all the way back to Willis Carrier because he's credited with inventing modern air conditioning, but he started by working on dehumidification. He was trying to keep the air in a paper plant in Brooklyn, I believe it was, dry enough that they didn't have problems with the paper quality. And that's where air conditioning started.
David Schurk:
All right. So from the standpoint of commercial industrial dehumidification, most certainly outside influences based on climatic conditions play a part. Right? The infiltration of moist air through cracks and openings and doors will carry moisture into the space as well, permeation based on vapor pressure differential. Higher vapor pressure outdoors, lower vapor pressure indoors will drive moisture literally through building components.
But quite honestly, when it comes to commercial industrial environments, probably the biggest source of moisture that we need to contend with is that that comes in with the ventilation air, bringing in outdoor air to ventilate the space for code compliance or for exhaust requirements or whatever the case might be. Certainly, it's important that when we are doing that, we analyze those climatic conditions or those weather conditions based on the ASHRAE weather data that's available for that specific state and location or area in the world. Use the dehumidification design day conditions if the dew point temperature or relative humidity control in the space is critical. We need to make sure that we can handle that ventilation load under the worst-case conditions since it is simply the largest contributor of moisture, again, to a commercial or industrial space.
Allison Bailes:
In the residential world, it's mostly the refrigerant-based systems where you make a cold coil. And it's not just making the air cold, it's putting the moist air in the presence of a cold surface. Because the air has a certain dew point based on the amount of water vapor in it, and when that air with that dew point temperature comes into contact with a surface that's at or below that dew point temperature, then you get condensation and you get moisture removal from the air. So it's not just cooling the air, it's also having surface nearby that's below the dew point. So you're cooling that coil, water vapor comes out.
David Schurk:
So let's talk briefly about the various types of dehumidification, and I typically put them into three different buckets, if you will. The first I consider traditional refrigerant based, what I'll call cold coil systems that use a cold cooling coil that's been chilled by some type of refrigerant or perhaps chilled water to a certain temperature. And as you run air through that coil, you both reduce its sensible temperature and condense moisture onto that cold coil, therefore dehumidifying the air.
As well, there are desiccant dehumidification systems, there are absorption systems, AB, they're typically liquid desiccants such as lithium chloride. There are also adsorption, AD, dehumidification systems. They're typically some type of a solid desiccant such as a silica gel. They're typically impregnated into a wheel through which air flows. Both these systems I consider to be molecular dehumidification. They remove moisture from the air at the molecular level by creating a vapor pressure differential. The desiccant itself is typically at a very low vapor pressure. The moisture in the air is at a higher vapor pressure, and through vapor pressure drive or vapor pressure differential, the desiccant is capable of removing or adsorbing or absorbing the moisture from the air and holding it in the desiccant until it's dehumidified. Allison, why don't you expand on that just a little bit?
Allison Bailes:
In the residential world, it's mostly the first of those three that we use, and that's the refrigerant-based systems. What's happening is, the air passes across a cold coil and then there's two things to understand here. One is, the dew point is a temperature and it tells you how much water vapor is in the air, and the other is that it's not making the air cold that causes the dehumidification, it's putting that air with a certain dew point in contact with a surface that's at or below that dew point temperature. So that's what's happening in a refrigerant-based system. The air is passing over a coil that's below the temperature of the dew point of the air that's passing over it. Also, let me ask you to expand on something, Dave, because you mentioned a word a while ago that you didn't define and maybe not everybody listening to this knows that word. It's hygroscopic. So what is hygroscopic? And does it have anything to do with any of the three types of dehumidification you mentioned?
David Schurk:
Great question. I think the true definition of hygroscopic is water-loving, I believe, or moisture-loving. They are materials that have an affinity to either absorb or adsorb moisture. For example, a paper towel loves to absorb moisture. Drywall, for example, loves to adsorb moisture. It will hold moisture as a molecule, never truly condensing in the traditional form for the most part, but removing that moisture from the air in its molecular state. And Allison, I know you have a great differentiator between absorption and adsorption that I've seen in some of the materials you've written and you've got to tell us what that is. I love it.
Allison Bailes:
So in my undergraduate chemistry book, there was a great diagram which you can still find online. It's a perfect description of adsorption with a D versus absorption with a B. It shows a person with a pie. In the first case, the person eats the pie and that is absorption with a B, the pie is going inside the person. And adsorption is the pie being thrown in the guy's face. So he's got the pie all over his face, it's adsorbed, it's on the surface. So the pie comes in from the outside and sticks to the surface.
David Schurk:
And I use that all the time. It's such a simple way to explain a relatively complex dynamic. So that's a perfect segue into talking about how we determine dehumidification loads. Allison, I'll probably let you get into the specifics, but I'll say this much: People's eyes seem to kind of glass over when we think in terms of dehumidification only. We're used to air conditioning systems where we are both cooling and dehumidifying the air, and that seems like a safe, comfortable place to be. But when it comes to dehumidification, for some reason, people just can't quite get their heads wrapped around it.
And I like to give this example, if I may. If I'm sitting in my living room in the summertime and the hot sun is beating down on the roof in the windows and I want to maintain that space at 72 degrees Fahrenheit, if I turn my air conditioning unit on, I most certainly am not going to expect to get 72 degree Fahrenheit air out of the registers. I'm going to need air that is much cooler in order to maintain and absorb the cooling load of the space. So I may have 55 degree Fahrenheit supply air coming out of that register. I need a delta T, a difference in temperature, to be able to handle the cooling load required to maintain the space at the comfort set point that I've determined.
The same thing holds true with dehumidification. For example, if I want to maintain the space at a 45 degree Fahrenheit dew point temperature, I'm going to need air to the space that is at a lower dew point temperature, or drier. I need a delta in grains to be able to absorb the moisture load. Many times people just, for some reason, can't quite get their head wrapped around that. Many times I'll receive a request to dehumidify a space. It might be a 2,000 or a 20,000 or a 200,000 square foot space, it doesn't matter. And what they'll tell me is, "I want to maintain the space at 45% relative humidity. Can you size a dehumidification unit to handle the load?" Certainly I can't, there's no magic formula to be able to determine that load based on those types of input conditions. I have to be able to determine the load.
It's very important that we start with the basics of temperature and relative humidity. But from that, I normally will convert it over to dew point temperature, and that is where my load analysis will normally begin. I need to determine how much drier that air needs to be to be able to handle the conditions required in the space. Allison?
Allison Bailes:
Yeah. So determining the dehumidification load is an important part of the whole thing. In the residential world, there's a lot of rules of thumb going on, and unlike with air conditioning, it's not as bad with dehumidification to use rules of thumb. Now, there are more quantitative ways to do it, of course. But in the residential world, so unlike what you're talking about in the commercial and industrial world, there's a pretty narrow range of humidity that we're aiming for. The Air Conditioning Contractors of America, ACCA, has protocols for doing HVAC designs, starting with the Manual J load, calculating the heating and cooling loads. The cooling load comes in two parts. The sensible load, how much heat do we have to remove from the space to keep the temperature where we want it? And our design temperature recommended by ACCA is 75° Fahrenheit. The design humidity that we put in our load calculation, if we're going by the ACCA numbers, would be 50% relative humidity. 75 degrees and 50% relative humidity is a 55 degree dew point.
So we're trying to maintain a 55 degree dew point in the house when we do air conditioning and maybe supplemental dehumidification. The actual dehumidification loads, I referred to this earlier when I said that the loads that you get from the load calculation are in the design condition. So that's at your outdoor design, temperature, and humidity. Set your air conditioning capacity based on that. But your dehumidification load is going to usually occur at a different time of day because, as I said earlier, the air conditioning can handle most of the dehumidification load at the design conditions. At night it cools off, and that's when you have the dehumidifier going if you need one.
David Schurk:
I'll interject something here as well. So Allison, to your point with regards to temperature and relative humidity combinations, it's 75 degrees Fahrenheit and 50% relative humidity, you've determined that's a 55 degree dew point temperature. Now, depending on the moisture load in the space, you may need to provide air to the space that is at a dew point temperature below 55 degrees Fahrenheit, and the load will determine the delta in dew point temperature between that of which you want to maintain in the space and that of the supplier provided to the space to absorb the load. In commercial applications, for example, if I was trying to maintain a 45 degree dew point temperature in the space, I might need 35 or 40 degree dew point temperature air provided to the space to have enough difference in grains or delta grains to be able to absorb the moisture load.
Allison Bailes:
In residential and air conditioning systems, you generally get about a 20 degree delta T, so drop in temperature. So if the entering air is 75 degrees, you come out with 55 degree air close to a hundred percent relative humidity, which means you're at about a 55 degree dew point.
David Schurk:
So Allison, we touched briefly on how outdoor climate conditions impact dehumidification load calculations and operation, but do you want to go into a little bit more detail with regards to that? Because I think it's a very important topic for us to cover.
Allison Bailes:
Yeah. So there's two ways that the outdoor air will impact your dehumidification needs. One is infiltration and the other is ventilation. So when air leaks into the house from outdoors, and this summer has been horrible with outdoor humidity, in Atlanta, we often have dew points around 70 in the summer and it drops into the 60s regularly. We haven't seen dew points in the 60s for a few weeks now, I think, and we're getting up into the mid-70s, like 75 degree dew points, which is pretty nasty. Not as nasty as 80 degrees that they're having in some places like South Florida. But the amount of air that leaks in determines your dehumidification load. The amount of air that you bring in for ventilation air, you're bringing it in intentionally this time, but it's coming with that outdoor humidity. So you have to have a plan for that.
In coastal climates, Gulf Coast up the Atlantic Seaboard, all over the southeast, but especially closer to the water, supplemental dehumidification is almost a must, and one way you can do that is with a ventilating dehumidifier. So if you have a dehumidifier with controls, that can run the fan without the compressor or the fan with the compressor. So when it's nice outside, the air's just coming into the house through the dehumidifier, and when the humidity is high, the compressor will kick on and dehumidify the indoor air. So that's one good way to deal with the humidity coming in from outdoors, is with the ventilating dehumidifier.
In some places, it's more important than others. Some situations, it's more important than others, like hospital operating rooms, which I have nothing to do with, except that I've been in a few. It's really critical to get that right, as you mentioned earlier. Residential, it's more about keeping the place comfortable and allowing people to have the cool enough temperature in the summer and low humidity as well. What happens in a lot of homes is, the contractor puts in an oversized air conditioner, there's no supplemental dehumidification. That design conditions will still run enough generally to dehumidify, but if it's not dehumidifying enough, or on the cooler days or at night when it's feeling sticky inside, people will turn the thermostat down to get more runtime, to get more dehumidification. Well, when you turn the temperature down, you do get more runtime, you get cooler air, and you may end up with higher humidity, relative humidity. Now, you're removing moisture from the air, but you're also dropping the temperature, and relative humidity is relative. So you may end up with cool and clammy conditions, not cool and comfortable that they're after.
That makes me think of something else. Let's talk about condensation versus adsorption, but let's call it accumulation here. When you have porous materials like drywall or wood or brick or stone, you have water vapor coming out of the air and adsorbing on the walls of the pores and these materials. And it's not temperature so much that determines the water vapor coming out of the air into another phase. It's the relative humidity. Sorption isotherms and building science labs, they measure the ability of a sample, wood, brick, clay, some porous material, to absorb or accumulate water in the pores. So they start with very low humidity. They have this sample on a scale, and they increase the humidity gradually and keep the temperature constant, isotherm, and they measure the mass of this material, the weight. As the relative humidity increases, the mass of the sample increases so it's pulling in moisture from the air hygroscopically.
The sorption isotherm looks different for different materials based on pore size generally. They have a very characteristic shape. They increase quickly at first, and they kind of flatten out, then they increase quickly again as the pores start filling up. The big increase at the end is as the pores start filling up. That's another interesting distinction, porous materials versus non-porous materials. On non-porous materials, glass and metal, that's where you'll see condensation. You'll see those drops of water appearing on the cold days when you have a single pane window, or even a double or triple pane window in a really cold climate. And then the accumulation of moisture in porous materials is something that can cause mold to grow. Even if you don't have liquid accumulating, well, you don't think you have liquid accumulating, when those pores start filling with moisture, you can get enough water to grow mold, because mold needs spores, it needs the right temperature range, it needs water, and it needs a food source. So you put all those together in the pores of drywall, for example, and you can grow mold very quickly.
David Schurk:
So most certainly, an issue that is universal to both residential, commercial, and even industrial settings is that of a potential for microbial contamination indoors. The proliferation of microbial contamination, mold, et cetera, on surfaces that are porous such as drywall and ceiling tiles, et cetera, can be a real problem. We've all seen mold spots or mold stains on these types of materials in the past.
Many times what contributes to that is an indoor environment that has been chilled too cold. Someone has come in and cranked the thermostat down to what would be considered a really low temperature, maybe 60 or 62 degrees Fahrenheit, and all the surfaces in the space have been chilled to approximately that same temperature as well. So when air in the space that is at a higher humidity comes in contact with those cold surfaces, those cold surfaces can then adsorb the water molecules out of the air and hold them in the material. At that point, there may be enough water vapor held in those surfaces molecularly that condensation can occur and mold can grow.
So Allison, probably one of the most confusing topics or subjects with regards to psychometrics is simply relative humidity. Let's talk a little bit more about what that is specifically.
Allison Bailes:
So there's different ways of measuring relative humidity. Relative humidity in a space, like I've got a device on my desk right here telling me right now it's 61% relative humidity in this room, but if you have a cold surface, so if you have an air conditioning vent blowing on a wall, that wall is colder than the space around it, and the air right next to that cold part of the wall is going to have a higher relative humidity. It might be a hundred percent right there, depending on how much water vapor you have in the room and how cold that surface is. As it gets closer to that cold surface, the air cools, the relative humidity increases. Oh, and there's a name for that too. There's water activity. Basically, the relative humidity at the surface is called water activity.
David Schurk:
Allison, let's talk a little bit about the pros and cons of the three dehumidification types that we discussed a little bit early, the traditional refrigerant-based system versus those that are adsorption, absorption type technologies that remove moisture molecularly.
Allison Bailes:
Sure. I mostly know about the refrigerant-based ones and putting air over a cold coil. So they're great at removing moisture. You run the air across the coil. Generally, these are package units. There have been split system dehumidifiers. The limitation is that because water can freeze on the coil, when that happens, then you're no longer dehumidifying, well, not very much because you're not getting the air flow anymore. So there's a lower limit to how much you can drop the dew point in the space by how cold that coil can get. So when you want to go to lower dew points, you need the kind of stuff that you're talking about, one of those other two methods.
David Schurk:
Sure, speaking to your points. So certainly, cold coil systems are limited to surface temperatures of 32 degrees Fahrenheit or higher. To your point, Allison, it's hard to move air through a block of ice. It just won't work. That's where perhaps desiccant systems come into play. Whether they're absorption or adsorption, liquids or solid systems, they're capable of dew point temperatures that are as low as perhaps -80 degrees Fahrenheit. These systems are capable of decoupling the latent load, so you're not limited to perhaps sensible heat ratios of 70% to 80%. You literally can do a dehumidification load that's 100%. In traditional cold coil systems, you're limited to surface temperatures of 32 degrees Fahrenheit, zero degrees Celsius. Since desiccant systems remove moisture molecularly versus condensation onto a cold coil surface, they're not limited to dew point temperatures of 32 degrees Fahrenheit or higher. They're capable of obtaining dew point temperatures, perhaps as low as negative 80 degrees Fahrenheit. And we see application for that in lithium battery manufacturing plants, for example.
Desiccant systems can decouple the latent load. Since they're not limited by surface temperatures that will freeze condensates, they're capable of sensible heat ratios well beyond the 70% to 80% that we see in the more traditional type air conditioning units. In fact, desiccants can handle 100% latent loads and are capable of garnering space dew point temperatures as low as perhaps negative 40 degrees Fahrenheit, delivering perhaps negative 80 degree Fahrenheit air.
Let's talk a little bit about ASHRAE's Damp Building, Human Health, and HVAC Design Guide. This was published in 2020. It's a free download, compliments of ASHRAE. It was chaired by Lew Harriman, who's a fellow in ASHRAE. Lew is, if Willis Carrier is the grandfather of air conditioning, I consider Lew Harriman to be kind of the godfather of dehumidification. Most everything I have read and learned over the last 40 years, Lew had his stamp of approval on. He's definitely an icon in the HVAC dehumidification world. The intent of the guide, which I have in front of me right now, is to be helpful to professionals who seek to avoid moisture, humidity issues.
The preface, which I'm reading from right now, says that one of the results of this guide is to limit indoor dew point temperatures to 60 degrees Fahrenheit or 15 degrees Celsius by ANSI ASHRAE Standard 62.1. In mechanically cooled and ventilated buildings, the standard requires that the designs include equipment and controls that are capable of keeping the indoor air dry at all times, including periods when the building is not occupied. It goes on to deal with issues of persistent water activity at the surface of organic materials or coatings such as drywall and other hygroscopic materials, may be ceiling tiles and things of that nature. It strives to help facilitate productive, comfortable, and microbial-free indoor environments. Allison?
Allison Bailes:
Yeah, it's a great document. As you mentioned, Lew is one of the icons in the field of humidity and dehumidification. And also, we should mention Don Gatley, who recently died, who wrote the book Understanding Psychrometrics, has done a whole lot in this field when he was active as an engineer. This guide is a free download, everybody should have it who's interested in controlling moisture in buildings. It goes into all kinds of stuff, how to test for it, and what the epidemiological studies of damp building show. Really good resource.
David Schurk:
So I have all of Lew's books on my bookshelf at home. I have Don's psychrometric bible on my bookcase at home as well. I also have another book on my bookcase, and it happens to be yours, your newest one. Do you want to go into a little detail on what that book covers? I'm going to tell you right now. It is beautifully put together. Not only is the content phenomenal, but the book itself is a piece of art. It's hard bound. The paper is that shiny, thicker paper. The illustrations and photographs are crisp and clean, and of course the content is stellar. So tell us a little bit about that book, Allison.
Allison Bailes:
Sure. So this was my pandemic project. I started it in the spring of 2020, just as the pandemic was getting going. And it came out in the fall of 2022, so two and a half year project. It's an introduction to building science. The book is divided into three parts. The first section is called Start at the End. What is it that people need out of buildings that they occupy? And I'm focusing on residential. So what is it they need out of their homes? They want to be comfortable. They want to not spend the fortune on energy bills. They want to have a durable house that's going to last without needing repairs all the time and having time bombs built into them that are going to cost them later. And they want health. They want good indoor air quality and good indoor environmental quality. They want to be happy in these homes and raise their kids there. So that's the first part. You have to start with the end because if you don't know where you're going, who knows when you're ever going to get there?
And then the next two sections go into the heart of the subject. First is the building enclosure. So I talk about building science 101 and the properties of water. Very, very important. How to control liquid water, water vapor, heat, and air flowing across the building enclosure. The last section is on the mechanical systems that we use, and I talk about the fundamentals of heating and cooling. I talk about duct distribution systems, heating and cooling distribution systems. I talk about ventilation, dehumidification, hot water. Filtration, I got a chapter on filtration, one of my favorite topics as well. Yeah, that has sold well. Houses don't need to breathe, but the people inside them do. So we want an airtight house. We want controlled ventilation. We don't want uncontrolled air crossing the building enclosure because that leads to moisture problems. It leads to indoor air quality problems. It leads to energy efficiency problems. There's just a host of problems that come with uncontrolled air flow across the building enclosure. So we want to control that air flow and keep the people inside happy and comfortable and healthy.
David Schurk:
Well, Allison, I guess that just about wraps it up. I appreciate the time we spent together. As always, it was fun and enlightening. I hope that the ASHRAE members out there listening feel the same way and that they can garner something from our conversation today.
Allison Bailes:
Yes, and I hope the non-ASHRAE members listening can get something from this too. I think this is available to everybody, not just ASHRAE members. So it's been a great conversation. Dehumidification, humidity control, moisture control is really important for comfort, for health, for energy efficiency, for the durability of buildings. So it's important to pay attention to this and get it right. And there's a lot of good resources out there, like the damp buildings document from ASHRAE that you mentioned.
David Schurk:
We've always used the acronym HVAC when describing our industry. That being, of course, heating, ventilating, and air conditioning. But I'd love to see the letter D added to that because I think it has considerable importance, and the D of course stands for dehumidification. Maybe something like HVACD moving forward would be a little bit more inclusive.
Allison Bailes:
Well, that's it for today. Dave and I both thank you for listening and hope you got something out of this.
ASHRAE Journal:
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