I'm looking for clarification on required ventilation levels in residential settings.  For instance if I have a home that indicates an ach rate of considerably less than .35 that would suggest the addition of mechanical ventilation. I'm unclear, however on how much is enough, how much is too much?  It would seem that the additional air exchange rate should be based around the actual natural rate difference between the measured amount and .35.

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Thank you very much for such a detailed answer. I appreciate the help.

As an Android user, I have not found an equivalent app, yet, though I'm hopeful.

I am not aware of an Android app.   Rick sat on the 62.2 committee, so did Paul Raymer. Paul wrote a spreadsheet to do the calculations.  It is free.  http://bit.ly/PEqvoq

Thanks again!

Since you have your ventilation question solved, might as well take the next step. Install a 4 inch HEPA filter from one of the top two companies, or save your client some money by using at least a no name four inch w/o a special cabinet. This should knock down the smoke, dust, dander, and pollen. Add a 1/4 inch carbon filter to the front of the filter for odor control. Now you're properly ventilating and filtering! 

Awesome idea for the filtering, it's what I've done in my own home !! No HEPA, but a regular 4" Merv 7 that can be purchased for under $10.

EPA says, "The process of solving indoor air quality problems that result in health and comfort complaints can be a slow one, involving several trial solutions before successful remedial actions are identified."

I’d like to share my own personnel experience with ventilation and air quality.  Last winter LBNL tested air quality in my home (and a couple of dozen other homes).  The testing and results were, to say at the least, illuminating and after a few adjustments ended up very well.

 As a bit of background, I live in a 3100 square ft home 50 miles north of San Francisco.  In 2003 we preformed an energy upgrade to the home and since then our utility bills average $10.50 a month.  The home is generally kept between 69 and 73 degrees, a level that we (and ASHRAE) believe is comfortable.  The home is fairly leaky, I don’t recall the exact amount. We have a Panasonic Whisper fan (the name is a bit of a misnomer) exhausting at 125 CFM. This now operates constantly.  We also have a Honeywell F300E electronic air filter, approximately MERV 14 equivalent, which as it turns out actually works as advertized, when it is maintained and operated.

The process of testing our air quality started when I received an email looking for high performance homes for LBNL to perform air quality tests on.  I responded and Brennan Less and an assistant arrived mid January to install the testing equipment.  The testing gear was left for a week of sampling and then retrieved.  The testing equipment consisted of a Dylos particulate meter, another meter that tested CO and CO2 along with recording temperature and humidity, and a bunch of test tubes than absorbed VOCs and formaldehyde.

My favorite device was the Dylos meter.  The meter reports particulate counts for PM2.5 and PM10.  The meter displays real-time data and is battery operated so you can take it from room to room or outside. Unfortunately the meter doesn’t report in a scale that can easily be adjusted to other common scales so the readings are a bit difficult to interpret.  Our initial PM2.5 readings were in the 600 range.  Brennan assured me that a reading of 600 was pretty good, the best that he had seen was 500 and not to start worrying unless it gets over 1200 or so.  PM2.5 particulates are known to cause health problems and there is no minimum safe level, i.e. the safe level is zero.

Testers hate to have their environment modified during a test and I have to admit I made a few ‘minor’ changes during the first few days.  Perhaps more accurately stated, ‘simple’ changes.  The first was I was in the habit of, on cold nights, turning off the Panasonic fan.  In the morning I was in the habit of forgetting to turn it back on.  I left the Panasonic fan on and it has been left continuously on ever since.  The electronic filter hadn’t been cleaned for a period I won’t admit to and can’t remember. I cleaned it which consists of just hosing it off.  The last change to system operation was to turn on the HVAC fan in “fan on” mode. I did this mostly just to test if cleaning the filter made any difference.  Within a couple of hours the PM2.5 readings were at 150.  The PM2.5 levels generally stabilized at about 50 and overnight would drop to 20 when there was no household activity.  The PM10 readings would drop to zero.  Some activities, such as cooking or washing dishes, would increase the PM2.5 level to 200.  Cooking bacon on the stove top would raise the level to over 4000.  Cooking bacon in the microwave would raise the PM2.5 readings to about 4000.  Lesson learned here is cook bacon outside.

One of the nice features of the Dylos meter was that it was battery operated.  At one point I took it from room to room and all of the room readings were consistent at around 50.  I believe that this indicates even air distribution.  On a day that was very nice for January, I opened a number of windows, just to let fresh air in.  The meter reading crept up and, at about when the PM2.5 count was at 300, I was wondering what was going on.  Taking the meter outside showed the outside air to be at 600, the outside air was worse than the inside air.  After closing the windows the PM2.5 count began dropping.  Lesson learned here is that there is no guarantee that opening a window is good for your air quality.

There were a lot of lessons learned.  Most of them are extremely obvious.  The first is that unless you test you air quality, you won’t know what it is.  You have to maintain your air filter or it won’t work.  You probably want a MERV 14 air filter or equivalent or the small particulates, mold, allergens and bacteria won’t be removed from the air.  You need to run the system so it has an opportunity to filter the air, this really means continuously.  The filtered air needs to be distributed to the entire house, particularly the bedrooms where most people spend most of their time.  You want to remove enough of the VOCs, formaldehydes, and other noxious stuff including moisture in the air and replace it with fresher air that you want to filter before it enters the house, which we don’t.  I have no idea where our ‘fresh’ air comes from. There are really two processes going on here, one is ventilation, the other is air filtration.  The ventilation standard, I guess is mostly designed to replace the oxygen that is consumed by the occupants and doesn’t really address removing the other pollutants.  Filtering the air, which isn’t really considered at all, needs to be done at much higher air flow rates.  I am guessing that the HVAC fan is operating at 500 cfm in fan only mode filtering approximately the volume of air in the home every hour.  Considering the filtered air blends with the unfiltered air in the house, 50 percent of the air is filtered every hour (50% of the particulates are removed) which both conceptually and in practice seems to be the case. Thus after 4 hours of operation about 95% of the particulates would be removed, hour 1 – 50% are removed, hour 2 – 50% of 50% or 75% of original total are removed etc. Ideally, we could improve our air quality further by running a duct from the return air side of the HVAC system to the outside, we could have also just not sealed our return air ducting.  Utilizing the return air would have the advantage of filtering the outside air before it enters the home and as a bonus positively pressurizing the house which would improve the function of various spot fans.  We could also add a carbon filter to the supply side of the air handler to remove some of the other pollutants that our air filter might not already catch.

I am really quite pleased with the air quality in our home, for that matter I am pleased with our entire house including the energy costs.  One should realize that good air quality doesn’t come cheap, either the initial installation costs or the operating costs.

I hope you find this of some use and interest.

Michael Kyes

Michael: wonderful anecdotal ! here's the general lbnl stuff: http://www.iaqscience.lbl.gov/vent-home.html . also recall seeing on google health quoted paper which said modern air recirculation systems in homes are responsible for declining health rates, can't locate it. You must be right that if you're going to do it, you must do a lot of it, measure, maintain, run it, & thank your lucky stars for how much air fenestration(where fresh air leakage comes from) you naturally have in your home! thank you for the stimulating data!

The ASHRAE ventilation Standard is NOT about replacing oxygen - it really is about diluting and removing pollutants that are generated indoors by bringing in outside air - wether that is through ducts using a supply fan or through the building envelope with an exhaust fan is irrelevant from the point of view of diluting and removing indoor pollutants.  The ASHRAE committee is currently thinking about what to do about filtration in the standard.  So maybe in few years the standard will have recommendations.

In full disclosure mode: I am the Indoor Air Quality subcommittee chair for 62.2.     

I'm glad to see that ASHRAE is looking at the filtration issue. Thanks, Ian!  I would ask the committee also address other common areas of indoor air quality issues.  Examples would be:  A) Duct Leakage. B) Moisture Control at windows, grade and sub-grade. C) Humidity Control with all intermittent or spot ventilation direct to the outside (not into a building space). D) Pest control issues E)  Pressure Balancing with HVAC System and return ducts.  Eliminate the possibility of manual dampers - AKA doors! F) Pollutant Source Control such as non-sealed combustion appliances and fire places. G) Attached Garage issues 

While addressing the filtration issues, address the static drop across any filter.  There should be maximum drops allowed. Encourage higher MERV value filters to be installed at the return registers.  If you seal the ducts and keep stuff out, no one has to worry about what is in the duct. So it saves on cleaning costs.

Iain, it’s good to know we have an ally on the ASHRAE committee.  Perhaps my comments on oxygen were a bit tongue and cheek.  One of the many issues that we are trying to address with ventilation is preventing the buildup of carbon dioxide, particularly in bedrooms.  This is a byproduct gas produced by humans when they consume oxygen.  One of the many challenges that we have as building performance experts is to supply an adequate amount of fresh air when humans are sleeping.

My point really had nothing to do with oxygen, my point was that without IAQ testing you really don’t know what you’re doing, you may be improving the indoor air quality, or you may be making it worse.

Michael Kyes

Michael,  What IAQ Testing do you do?  


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