[GSBN] Fwd: The Mechanical Ventilation Debate

[Danny Buck]

Let's all remember that the vast majority of Passive and other well designed houses have that wonderful (and traditional) feature of operable windows and cross ventilation.

There is your back up system or your seasonal option.

Wonderful discussion this one.

Danny Buck
Santa Fe, NM


Sent from my iPhone

Begin forwarded message:

> From: Derek Stearns Roff <derek at unm.edu>
> Date: March 22, 2013, 9:06:07 PM GMT
> To: Global Straw Building Network <GSBN at sustainablesources.com>
> Subject: Re: [GSBN] The Mechanical Ventilation Debate
> Reply-To: Global Straw Building Network <GSBN at sustainablesources.com>
> 
> I think it is great that this conversation has stimulated the posting of many ideas and viewpoints.  I'm glad that GSBN draws contributions from people with diverse goals and approaches to building and living questions.  I appreciate the focus and dedication of all those working on social change, technical excellence, and other aspects of our shared issues.  
> 
> However, I am concerned that a few basic facts have not always been presented accurately, and that this is distorting the debate.  The statement has been made more than once, that a house with mechanical ventilation will have dangerous indoor air quality problems when the power fails.  John has already stated that this isn't true, and I would like to reiterate related aspects of the comparison between average, fairly leaky houses, and good, tight houses.  In comparing the indoor air quality, in the absence of wind, the amount of passive ventilation occurring in a leaky house is on par with that of a house whose mechanical ventilation is off during a power failure.  Whatever risks one imagines in the latter case also apply equally to the former.  However, the number of hours without wind is probably a thousand times greater than the number of hours without electricity, in my location.  And I live in a fairly windy rural spot, with fairly frequent power failures.  Furthermore, it is reasonably common to have no wind for twelve or more hours in a row, while it is rare to be without power for more than two hours at a time.  Hence indoor pollutants build up more often and more severely in the homes where ventilation is left to chance.  
> 
> The same is true if we make the comparison on a room by room basis.  While the whole-house ventilation rate for a chance-ventilated house may be completely adequate in an average breeze, the studies that I have read indicate that even on a breezy day, bedrooms are frequently seriously under-ventilated.  Therefore, these bedrooms will always have poorer indoor air quality than similar mechanically ventilated bedrooms, except during very prolonged power failures, when bedroom ventilation in both houses will be nearly equal.  In summary, it is backwards to suppose that a leaky house generally protects the residents from bad indoor air quality, and that a mechanically ventilated home puts them at risk.  
> 
> I'm also in disagreement that mechanical ventilation adds a significant burden to be "managed" by the occupant.  On the one hand, much less management and maintenance is needed for the ventilation system than for the refrigerator or dishwasher that is accepted, even demanded, in most homes that are a candidate for mechanical ventilation.  But a more telling comparison, in my opinion, is to compare maintenance of a mechanically ventilated house with the kind of back-to-the-land house that I aspired to thirty years ago.  Managing a wood stove takes vastly more time and attention than managing an HRV or ERV, at higher costs, and even a well-managed wood stove is likely to contribute significant pollutants to the home environment.  
> 
> I've just started documenting this with my new super-sensitive carbon monoxide meter.  I've tested the houses of two friends, who have fairly new, good-quality wood stoves.  When I visited, my CO meter initially read 0 parts per million.  This reading  continued during the first fifteen minutes, with a fire burning happily in the stove.  Then, the owner opened the stove door, added more wood, and closed the door.  Almost immediately, the meter showed an increase in the CO level in the room, measured at a distance of about 12 feet from the stove.  In one case, the meter hit over 40 ppm, in the other, around 30 ppm.  In both cases, the readings were still over 15 ppm an hour later, in both the room with the stove and the adjoining room.  I don't know how long it takes for these homes to return to a reading of zero ppm, but it probably depends in part on the current wind speed.  I will let you know whether my additional testing maintains this pattern.  I've also measured two other homes with wood stoves, where I never saw a reading below 15 ppm.  
> 
> I share a disappointment with many aspects of life identified with "progress".  I feel sad about over-population, over-consumption, environmental degradation, and the enhanced efficiency of our killing machines.  I think it may be true that we will soon face a cataclysmic decrease in every aspect of our access to imported resources and energy.  I am slightly more optimistic than Robert, in believing that human societies have sometimes made intelligent choices without extreme coercion.  Either way, I think that the wiser choice for the developing world in the interim is to explore and implement various measured and measurable approaches to home ventilation, rather than hoping that chance will solve the problems.  
> 
> Derek
> 
> 
> On Mar 22, 2013, at 11:48 AM, Oasis Design wrote:
> 
>> I've realized that all of ecological systems design can be boiled down to one sentence:
>> 
>> 
>> "Do what makes sense in the context"
> 
> Derek Roff
> derek at unm.edu
> 
> 
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