Infiltration of Outdoor Pollutants: Field Notes
Parallel to the research undertaken by Brent Stephens and others (see “Infiltration of Outdoor Pollutants” in the upcoming May/June 2015 issue), there has been a recent Pittsburgh-based initiative called Reducing Outdoor Contaminants in Indoor Spaces, or ROCIS, led by Linda Wigington and Norm Anderson. The main goal of the ROCIS project is to reduce the impact of exterior environmental pollution in southwestern Pennsylvania to ensure healthy and energy-efficient indoor environments, both residential and commercial. There have been two papers prepared, one by Don Fugler, dealing with houses, and one by Tom Phillips, dealing with larger buildings (see “learn more” for links to the ROCIS web site and these papers).
The papers discuss the many ways to reduce or block the entry of outdoor pollutants, either periodically or permanently. These mitigation measures include good building airtightness, high-efficiency air filters, pressure boundaries, walk-off mats, and others, including combined approaches. However, preventing the entry of outdoor air is a relatively new concept. Most codes and standards have been concentrating on increasing house ventilation rates with outdoor air. Because outdoor air pollution has not yet become a major focus in green and healthy building practices, there are not many good case studies where practitioners have solved individual problems with high concentrations of outdoor pollutants.
I asked several building scientists who had not been part of the ROCIS group to comment on the following “case studies” that I created. I did not know whether the answers would be congruent or divergent. Here are the responses I received (plus a couple of my own opinions):
- House in a temperate coastal climate (high precipitation), narrow valley, lots of wood burning in winter in the vicinity. House is older, relatively leaky, and of low resale value (from a real estate perspective).
Iain Walker: Tighten envelope. Alternatively or in conjunction, install stand-alone filter (if house is small) or forced-air furnace filter (if ducting system exists).
Greg Labbé: Tighten envelope. Install balanced system and filter intake air. Another solution is a stand-alone filter in the bedroom of affected persons.
- New raised ranch, moderately airtight, in rural Pennsylvania. Fracking operation set up less than 1 mile west of house. Rural road is now seeing 300+ diesel trucks per day. Problems with road pollution, noise, and odors from extraction site.
IW: Tighten envelope further. If there is a forced-air system, have ECM (electrically commutated motor) fan on low with good filtration. May require ductwork improvements or sealing.
GL: Tighten envelope further. Identify pollutants causing irritation. Use forced-air filtration (if possible). Remove shoes at door.
- New urban house with forced-air furnace, mechanical heat recovery ventilation (HRV), tighter envelope. One occupant has respiratory problems, including high sensitivity to pollen-induced hay fever.
IW: Put MERV 10 or better filter on HRV intake. Ensure maintenance.
GL: Do house inspection to look for pollutant sources. Put a good filter on the HRV intake.
Don Fugler: Bias HRV in summer operation to pressurize house. Use a good filter on HRV intake.
- Sixty-year-old bungalow facing four-lane road that has evolved into a major commuting route. House is not worth much; family income is low. Two older occupants concerned with poor air quality (traffic-induced particles and ozone).
Brent Stephens: Tighten house to at least 5–7 ACH50 to avoid particle infiltration. If tighter than 5 ACH, install HRV/ERV (energy recovery ventilation) with particle and activated-carbon filters.
IW: Tighten house, if financially possible. Improve indoor filtration, again dependent upon funding.
GL: Air seal, if possible. Have windows closed during peak traffic periods. Install whole-house forced-air filtration, if possible; room filtration if whole-house system unaffordable.
- Local dry-cleaning shop had been disposing of cleaning fluid through a hole in the basement floor for years, and now neighborhood groundwater is contaminated. Strong chemical smells in the basements of houses, although ambient air seems relatively unaffected. Two-story house, several decades old, is half a block from the pollution source.
IW: Subslab depressurization system (radon mitigation system)
GL: Depends: air seal cold-climate house (to reduce stack) or use pressurization in house with milder climate. A radon mitigation system works, too.
DF: Consider a ventilation system that preferentially exhausts from basement and sets up a negative pressure there, if the basement is rarely occupied.
The papers by Don Fugler and Tom Phillips mentioned at the beginning of the article are available from the Reducing Outdoor Contaminants in Indoor Spaces (ROCIS) website.
The responses have more similarities than I expected and usually show a comprehensive approach with air sealing and filtration. Weatherization activity can play a part in the exclusion of outdoor pollutants, according to these experts. The effectiveness of the proposed solutions would require verification in field work.
Don Fugler is an independent building science researcher in Ottawa, Ontario. He spent 25 years doing housing research with the Canada Mortgage and Housing Corporation, or CMHC, with projects on energy consumption, indoor air quality, moisture, ventilation, attics, basements, combustion safety, and straw bale housing, among others.
Iain Walker is a scientist at Lawrence Berkeley National Laboratory.
Greg Labbé is a weatherization specialist and trainer with the BlueGreen Consulting Group in Toronto, Ontario.
Brent Stephens is an assistant professor in architectural engineering at the Illinois Institute of Technology.
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