Should Occupants Have Control of Their Home Ventilation System?
Some installers make mechanical ventilation difficult for occupants to override, but is that the right approach?
One of the points of contention in the great ventilation debate is whether a home's occupants should control their own ventilation systems. The issue came up again in my recent article, Will a Gas Furnace Dry Out a Home’s Air? I wrote that occupants should have control of their ventilation system and experiment with the rate to help prevent drying out the air by diluting it with too much cold, dry outdoor air. Paul Raymer, a friend and member of the ASHRAE 62.2A standard for residential mechanical ventilation systems established by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers. Among other requirements, the standard requires a home to have a mechanical ventilation system capable of ventilating at a rate of 1 cfm for every 100 square feet of occupiable space plus 7.5 cfm per occupant. committee, then questioned me on that:
"We can make ventilation system controls that do pretty much anything, like vary the rate automatically in response to other factors, but what would those factors be and would anyone be willing to pay for such controls? Do you know of any data that would tell us the percentage of impact from the mechanical ventilation on the RH in the house?"
Why not give control to the occupants?
The issue first came up in this blog about a year ago, though, when Michael Blasnik wrote in one of his comments on my article about blower doors and mechanical ventilation: "I'm also surprised how you (and Joe) are so adamant about mechanical ventilation but then think we can rely on occupants to set their own ventilation rates. That would be a good idea if radon, asbestos, CO, and other pollutants were all smelly — but they aren't."
The Joe he referenced is of course Joseph Lstiburek, PhD, PE. He and Michael went back and forth in what was probably the best comment debate ever hosted by this blog. In one of Joe's comments, he wrote:
"In our experience, the occupant is more intelligent on setting acceptable ventilation rates specific to them than the members of the ASHRAE 62 committees."
Then, last summer I interviewed Paul Francisco, chair of the ASHRAE 62.2 committee, and he told me:
"I don’t believe homeowners should have no control. I also think that homeowners can’t detect a lot of potential indoor air quality hazards and they’re not knowledgeable enough to know what levels of ventilation they need at any particular time."
One of the issues is the same one that has Joe riled up enough to create his own ventilation standard. What ventilation rates should we recommend for homes? Joe has been giving talks about the issue over the past year and says the rates we recommend are based on research about odor control. Dr. Max Sherman of LBNL sees things differently, and I'll come back to the question of optimal ventilation rates in another article.
Whose responsibility is it?
Over the past week, I’ve read a whole lot of comments posted about this question, and it seems there are about as many good arguments in favor as there are in opposition to giving control to the occupants. For example, David Eakin wrote that occupants absolutely should not have control:
"This is not new science. How long have submarines been in operation? How long have modern mining operations been in operation? What about the decades of study and application from NASA? The answer (and probably the solutions) are already old tech. Looks more like politics than science at work in residential air quality."
One pitfall mentioned by several people was the inability of many occupants to understand the ventilation system well enough to control it. This comment on LinkedIn by Ron Bolender is typical:
"My experience is most home owners/occupants don't understand the benefits of their whole house ventilation system, let alone how to control it so it is turned off. When installed in new houses very few builders are doing a good job of educating their purchasers on the purpose of the ventilation system and how to control it. Technical and IT people may be able to read a manual and figure out how to control them at the control panel however, many unfortunately don't know how to control them."
Here’s the thing, though. People will find ways to mess with the system despite the best efforts of the designer or installer. Also, why should professionals tell occupants they’re not smart enough to touch their ventilation system when we allow them to do much more dangerous things, like drive cars? “But, seriously, do any of us think ventilation issues are any more complicated than automobile safety? In fact it's way simpler, and the stakes are not as severe. We can do this -- but not if we try to do it all through the standard alone or through automated technology without user input,” wrote Eric Werling.
We can make this work
The real problems, it seems to me, are inadequate education and lack of good control options. Of course occupants need to have control. When they turn their HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. systems off and open the windows, the ventilation system needs to go off, too. When they’re having the extended family over for Thanksgiving, they should be able to crank it up. No, they can’t smell radon or carbon monoxide, but that’s a job for more than just the ventilation system.
No matter how sophisticated a ventilation system we put into a house, though, the occupants exert control in another way: They have a big impact on the source strengths of many of the pollutants, especially in older homes in which the building’s materials aren’t off-gassing much anymore. What are they keeping in the home or garage or crawlspace? What are they doing in the home?
There’s just no way a one-size-fits-all approach can work. Few occupants can afford to have their local ventilation pro make regular visits to make sure they’re getting the right amount of ventilation. The solution is to recognize that occupants will be in control no matter what we try to do to prevent that. We need better system designs and better controls to help them get the best possible results from their ventilation systems.
Will some of them do stupid things, like turn it off and never run it? Absolutely. Some people never change the filters in their air conditioner or the oil in their car. We need controls for the users on the lowest end that have feedback equivalent to the oil and temperature dummy lights on the dashboard of their car. For more interested and sophisticated occupants, devices like the Fantech controller shown above are one of the best solutions.
We can make this work! The question about who has control isn’t really the relevant question. The real question is, who will seize the opportunity to improve ventilation systems and controls so that residential indoor air quality starts to realize the gains that are possible?
N.B. If you're going to the ACI national conference in Detroit this year, I'll be a co-moderator of a panel on this topic: The Ventilation Standard Debate -- Real Housewives of 62.2. Duncan Prahl of IBACOS put it together and is the other moderator. The panelists will include Joe Lstiburek, Paul Francisco, Michael Lubliner, and Don Stevens. You really don't want to miss it!
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