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Read this article from IEQ Connections, and the comment by Mark Lentz, Wisconsin Engineer specializing in healthy school HVAC systems.
IAQ in Schools – Maintaining Good IAQ During the Winter
William A. Turner, MS, P.E.
President/CEO
Steven M. Caulfield, P.E., CIH
Senior Vice President
Turner Building Science & Design LLC
Harrison, Maine
As you read this, it has been rather cold and snowy in many areas of the United States. In previous issues, we have focused on energy and IAQ. In this one, let’s look at possible health issues during winter operation.
To provide a healthy learning environment with good indoor air quality, a building should be reasonably clean and comfortable, not have mold growing inside it, not be over-ventilated, not be under-ventilated and have planned air flows in critical areas.
The goal is energy efficiency, good IAQ, good occupant comfort/productivity and reduced carbon dioxide emissions, or at least be carbon-neutral. Let’s discuss each of these.
Reasonably Clean
The visible dirt and dust that comes into a facility comes almost entirely from feet. A tiny fraction may come from open windows or from occupant activities. Schools are very high-traffic places without huge cleaning budgets, so there must be a system in place for daily removing the tracked-in dirt and not just making a dust cloud. This principle is very important with hard-surface flooring as well as soft. Whatever is used – treated dust mops, microfiber, autoscrubbers, wet mopping, near HEPA-filtered vacuums – must remove the dirt, not just redistribute it. Burnishing or buffing that creates dust clouds is also not desirable.
With textile flooring, the hidden dirt needs to be periodically removed with deep extraction of some sort, or you build up soil for a garden that germinates during high-humidity weather dampness at room temperature for more than 24–48 hours.
No one I know expects the HVAC system to clean the floor (you could do it, but the energy use would be very high and the cold-draft effect unacceptable – imagine a dust-collection system with huge, noisy fans and you get the picture). If the diffusers are dirty, they should be cleaned periodically; however the dirt on them originally came from the floor. This said, HVAC air filters should be a minimum of MERV 8 or better. If your air-filter supplier does not know what a MERV is, find a new supplier. There are lots of good ones around. The same principal applies to your homes, too.
Reasonably Comfortable
One of the best ways we know of to make people complain of poor IAQ is make it too cold in an all-air system in a cold climate area, then make it too hot each afternoon. Add in over-ventilation to contribute to the dryness, and poor cleaning practices, and you have a great recipe for IAQ complaints.
If one looks at the ASHRAE comfort chart, running an all-air building at 66–68 F with 10 percent relative humidity should be expected to keep nobody comfortable short of an exercise class gulping water. (By the way, an all-air system delivers both heating and cooling through the air and tends to be somewhat drafty with all of that air movement.)
If you are concerned about wasting energy operating the facility at 72 F during the occupied period, hire a good infrared camera contractor to find and plug the gross air leaks that heat the outdoors. This does the occupants and the planet a favor, saves lots of fuel and reduces the heating and cooling of the outdoors.
No Mold Growth Indoors
As many roofs and wall systems leak, this is an ongoing challenge. For the most part, porous materials that get wet need to be dried in 24 hours or you get mold growth. There are all kinds of water tarps now available with garden-hose barbs that capture leak water from roofs, expansion joints and other local areas, and direct it to a bucket or trash barrel to keep the wallboard paper, wood and fiberglass sponges from getting wet.
If you have textile flooring in places that routinely get wet, you likely need to stop this via a hard-surface fix or eliminate the wetting, or you get mold growth indoors.
Utility trenches and crawlspaces are the other typical sources, or cold walls in portable classrooms where someone left out the insulation or failed to seal the floor joint when they bolted the classrooms together on-site (see Planned Air Flow below). Lots of really cold surfaces in winter sometimes leads to lots of condensation.
Don’t Over-ventilate
In the absence of identifiable pollutant sources other than the occupants, ASHRAE and most others recommend about 15–20 cfm of outdoor air per person during the occupied period. In most settings, this gives one a carbon dioxide reading of about 800–1,000 ppm. In an occupied facility, readings much less than this at 11 a.m. likely mean you are just plain over-ventilating, which provides little if any benefit and, in the heating winter mode, likely means excess dryness (more dry eyes and noses), as well as wasted energy. Why do it if there is no benefit?
Don’t Under-ventilate
Ventilating to control bioeffluents to acceptable levels is the essence of the ASHRAE dilutions guidelines in Standard 62. Ten-to-fifteen cfm of outdoor air per person, depending on the setting, is recommended for dilution of non-point source pollutants (people). In most settings, this gives one a carbon dioxide reading of about 1,000–1,500 ppm. In an occupied facility, readings above 1,000 ppm at 11 a.m. likely mean you need to take a real close look at what the ventilation systems are doing and why.
Point source pollutants, such as those generated by reprographics equipment, bathrooms, art activities, etc. need local exhaust, not general dilution, unless you really like to waste energy (see below).
Planned Air Flow in Critical Areas
Planned air flow in critical areas is likely the key item for overall good building IAQ. Air should be exhausted from areas where irritating materials are likely to occur with negative-pressure exhausts. Typical areas include bathrooms, reprographics activity and boiler rooms.
All photocopying and most large printing activities involve heating, melting and drying a mixture of carbon black, styrene and iron particles onto paper. The fugitive byproducts, including ozone, are often irritating, so why would you purposely expose occupants to them? ASHRAE recommends exhaust at 25 air changes per hour.
Bathrooms require exhaust by law to keep sewer gas and other odors out of normal building breathing air. In winter, dry traps in unused showers, sinks and floor drains also need to be addressed.
Boiler-room air should move out of the building not into it. Boiler exhaust must discharge well above the air intakes and out of the wake of the building if there are rooftop air intakes.
Welding, painting, cooking and other activities in kitchens and other vocational facilities require specialized systems to direct materials away from others. These large exhausts also require, often by code, planned make-up air systems that should be interlocked with the exhaust so they function at the same time.
Dirty crawlspaces and utility trenches likely need to be isolated with sealing and exhaust so the byproducts of the stuff growing inside move out of the building instead of into it due to normal stack effect or suction from unit ventilator returns. We should stipulate that “stuff” almost always grows in crawlspaces and utility trenches.
In most cold-climate designs, roofs are designed to stay cold. For this to occur, building air must stay out of the roof-venting area and cold outdoor air must flow in the vented space. Hot roofs are a different approach and can work well with enough super insulation to counter snow depths and suitable roofing materials where the lack of venting does not void the roofing warranty.
In many parts of the country, radon gas is a known, naturally occurring part of soil gases, and specialty suction systems are installed to keep the gas from passing through the school on the way to the atmosphere.
Conclusion
Winter is a challenging time for proper building operation to minimize the likelihood of an IAQ incident. With diligence to the above items and others the facility staff may have learned, some good planning for crisis intervention and a little luck, things can go well. If the building interior gets wet in the winter, the good news is that it can usually be rapidly dried out with some heat and dry outdoor air. In the cooling season, wet items are a lot harder to get dry fast enough to prevent mold growth.
William A. Turner, MS, P.E., is president and CEO of Turner Building Science & Design LLC. He has more than 25 years of experience in IAQ, HVAC and energy evaluation and development of solutions for building-system problems. Turner supervises a group of engineers, industrial hygienists, commissioning agents and building scientists who serve owners, architects, general contractors and construction managers. He can be reached by e-mail at
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or by phone at (207) 583-4571 ext. 11.
Steven M. Caulfield, P.E., CIH, is senior vice president of Turner Building Science & Design LLC. He can be reached by e-mail at
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or by phone at ext. 14.
The article by Mssrs. Wm. Turner, P.E., and S. Caulfield, P.E., CIH that you asked me to review contained a great deal of sound advice. I think the authors are absolutely dead-on as to the source of dirt and the consequences of poor housekeeping. Another area where they make particularly cogent comments are in their discussion of the formation of condensation in cold walls in winter.
There are a couple of areas where I disagree slightly, or have something to add.
I've been recommending an air filtration level equivalent to MERV 13 on all of our new designs and retrofits. I use that because it provides substantially better control of micro-organisms and you usually get better seals in the filter holding systems. With MERV 8, you don't get the seals and you get a lot of contaminants bypassing the filters.
When it comes to knowing what MERV stands for, I would add architects and engineers to the list of service providers school districts should replace. A very large part of the process is that the design system is broken. For the most part, most of them are simply clueless about these issues. Mssrs. Wm. Turner, P.E., and S. Caulfield, P.E., CIH are obvious exceptions to the rule.
Condensation can also occur within roof systems during cold weather. "Cold roofs" absolutely must have effective vapor retarder systems and air barriers. One of the chronic big mistakes I see in Wisconsin with "hot roofs" is the absence of vapor retarders.
Finally, at LEA, we have been going one step further in dealing with schools. We have gotten completely away from recirculation and have gone exclusively to 100% outdoor air systems for schools.
With 100% outdoor air, we do not recirculate and redistribute the contaminants coming from the inside. Mold spores, mico- and endo-toxins and other pathogenic materials accumulate in return air systems and because of that get continuously recycled. With 100% outdoor air systems, they get rejected from the building and never see the spaces served, again.
Ventilation is typically the most energy intensive function of an HVAC system. The problem is that most systems do not have the ability to either efficiently process it or effectively manage it. A proper thermodynamic analysis will show that mixing and recirculation does not save any energy at all. All it does is recycle contaminants. By using appropriate energy recovery techniques, ventilation can be efficiently processed. With appropriate air delivery techniques, 100% outdoor air systems can not only be used to effectively managed that ventilation down to the individual room level but also facilitate the use of displacement ventilation techniques.
These techniques permits dramatic reductions in HVAC energy use; from 60-90% over the traditional system types used in schools. Yes! There is that much waste in the traditional, "tried and truly awful" solutions usually provided by A/E's. Waste is designed right in to the systems.
LEA has been designing high performance HVAC systems since 1996 and has a significant amount of independently validated data to back those numbers up. That is why ASHRAE President Kent Peterson featured us as the response to his Presidential challenge to the HVAC industry on the ASHRAE home page.
When designed properly, the above advantages can be achieved without a first cost premium to a School District, in new construction, who then get the benefit of extremely powerful life-cycle economics. The economics are sufficiently powerful that full facility retrofits can now be justified on the basis of energy conservation, while upgrading the environment provided in the facility.
Mark S. Lentz, P.E., President
Lentz Engineering Associates, Inc.
511 Broadway, Suite 4
Sheboygan Falls, WI 53085
e-mail:
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Phone: (920) 467-1075 |
