Building science consultant Steve Easley walks through fresh air ventilation strategies at the Scottsdale ReVISION House, explaining why a balanced energy recovery ventilator (ERV) beats positive- or negative-pressure systems for indoor air quality and durability.
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Steve Easley: Welcome to Scottsdale Revision House project. I'm Steve Easley. I'm a building science consultant. And today we're going to talk about fresh air ventilation systems. Now balanced controlled fresh air ventilation is really a key component to every healthy home. We want to have good indoor air quality and that's dependent upon fresh air for one second. There are basically three ventilation strategies that we have developed homes.
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Steve Easley: We have positive pressure system, which is simply a fan that forces air into the home. And the problem with that is, is that it puts the home under a positive pressure. And that means that if we have warm, humid air in the winter months, that's going to force that warm, humid air into the colder wall cavities where it can condense and lead to mold and decay.
00:00:48:20 - 00:01:11:13
Steve Easley: The second type of system that we have is what we call negative pressure system. And that's where we simply have a fan, like a bathroom fan that's designed to run continuously. But the problem with that is it puts the home under a negative pressure. And that's problematic in the summer months in hot, humid climates because it sucks that hot, humid air into the wall systems where it can dampen building materials and lead to mold and decay.
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Steve Easley: So that's not good. Another thing is, with negative pressure systems, we never really know where that is coming from. So it might be coming from places that they are not quite so fresh, like a crawl space or a basement, an attic, or even a garage. So what we want to have is a balanced system. We want to have a system like this.
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Steve Easley: ERV and balanced systems basically mean that the same amount of air that's being brought into the home is being exhausted out of the home, so the homes never under a positive or negative pressure. So when they talk about EVs or HVS, which are heat recovery ventilators, eaves or energy recovery ventilators, we're talking about, you know, devices that have the ability to provide balance, ventilation as well as heat or energy recovery.
00:01:53:01 - 00:02:10:23
Steve Easley: Now, you might be asking, how do we size these systems? Well, there is a national ventilation standard and that's Ashrae 62.2. Now that's been around for almost 20 years. So this ventilation standard gives us guidance about how to size the system for our home. In other words, how many cubic feet of air of intermittent or continuous ventilation do we need.
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Steve Easley: And so we can size these systems based on the formulas from Ashrae. Or we could use an algorithm or a computer program based on those formulas. Or we could simply go to the Ashrae 62.2 ventilation chart. And so for example, if we have a 2500 square foot house that has three bedrooms, that would require a 120 cfm of continuous ventilation from the outdoors.
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Steve Easley: Now that air is not conditioned, remember we have to eat and cool that. So over the course of an hour, if we multiply that 120 cubic feet of air per minute times 60 minutes in an hour, that is 7200 cubic feet of air every hour of unconditioned air that's coming into my house. I got to pay to reheat and cool that.
00:02:53:04 - 00:03:13:10
Steve Easley: So over the course of three hours for that 2500 square foot house, guess what? I'm going to have to reheat and cool that air all the time. So that's why we liked EVs, because even have the capability to recover that energy. Now, I selected this unit, and part of the reason I did is because it's 75% efficient. In other words, it's going to recover 75% of that energy.
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Steve Easley: It has the central core. And so what happens is when the outdoor air comes into the unit, it passes over the stale air going out and the exchange their energy. So we recover 75% of the energy we use to pay to heat and cooler home. So that means we have good ventilation. At the same time, it's also affordable.
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Steve Easley: Now there are other reason I selected this prone AI unit was because it has some really smart technology built into it. In other words, when you set these systems up, you typically have to spend a lot of time fiddling and balancing them. But this is self-balancing. It's got a brain that automatically regulates the dampers and so forth. So it can self balance.
00:03:49:25 - 00:04:09:12
Steve Easley: And so it's much easier to set up. Another cool feature of it is, is that in the course of its life, during its operation itself balances in every mode. So what that basically means is, is that if I have, say like a dirty filter or some pressure changes in the system, this will automatically rebalance itself. So our homes never under a positive or negative pressure.
00:04:09:14 - 00:04:32:00
Steve Easley: Another thing I really like about this prone unit is its ability to control a variety of different circumstances. It's a really smart machine. I mean, it has the ability to monitor indoor humidity, outdoor temperatures, and automatically regulate itself. It's got a whole variety of different control scenarios. So for example, if I'm cooking, I can turn on turbo mode and it will exhaust maybe humidity and other things out of the air quicker.
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Steve Easley: It has a recirculation mode, so if I just want to filter the air and not bring air in from the outside has the capability of that, it can run intermittently. It's just got a lot of different control options that I can have. So I can really have this fresh air ventilation system suited to my specific needs of my own home.
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Steve Easley: Another feature that I love about this is that it's really easy to install. They've got a lot of different mounting scenarios and brackets and assemblies that make this super fast and easy to mount. And then also, it's really cool that we have up to a Merv 13 filter. So a 13 filter basically can filter up to 90% efficiency particles between 1 and 3 microns.
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Steve Easley: Now micron is a millionth of a meter. There are 25,000 microns to an inch. And what we're really concerned about today is PPM 2.5. Those are particles that are less than two and a half microns. And the reason we're concerned about this is that these particles basically come from vehicle exhaust. And so they have the ability to go deep into your lung tissue and cause significant respiratory issues, as well as even cardiovascular disease.
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Steve Easley: So there's real concerns about being able to filter air down to those levels. So that's another thing I like about it. So key here is a V is a must to building a high performance, energy efficient home that has good indoor air quality.