Indoor Environmental Quality Design Considerations
Have you ever had to deal with occupant complaints in new buildings? Perhaps excessive room noise from the ventilation systems, or transient smells or nuisance odors being repeatedly drawn into the building? Well, we have, and so this Safety Guys feature will address some of the most common issues relating to air and environmental quality indoors, and provide some recommendations to eliminate or prevent problems from occurring.
Laboratories, with their plethora of chemicals and diversity of activities and specialized equipment, have the potential to drastically impact indoor air quality. More widely grouped today into indoor environmental quality (IEQ), these issues can affect employee comfort, productivity, and, possibly, health. But fear not, most of these conditions are preventable and/or correctable with minimal effort. Often the fix is very simple and costs almost nothing. However, too many times the problem can be traced back to poor design, which may lead to expensive renovations and the associated disruption to normal operations.
The following recommendations have been culled from years of dealing with IEQ complaints. They are grouped into major building system headings. If you can find and eliminate any of these during laboratory or building design, it can save lots of time and money. Therefore, we strongly recommend that you develop an IEQ policy. Ensure all building managers and maintenance personnel are trained on it, and make sure all architects and engineers are given a briefing prior to the start of any new construction project.
It is paramount that the ventilation systems are generally consistent with all appropriate recommendations of the latest version of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard 62, Ventilation for Acceptable Indoor Air Quality.1 Isolate all odoror contaminant-generating activities from the return air system, and make sure adequate exhaust is provided. Examples of these types of spaces include laboratories; lavatories; autoclave rooms; animal housing areas; kitchens; and document printing, copying, and reproduction areas. Ensure all laboratories and other similar areas are under slightly negative pressure with respect to surrounding office and reception areas. This means slightly more air is exhausted from these spaces than is being supplied. This negative pressurization ensures contaminants or odors do not migrate into surrounding areas. In addition, the overall building pressure differential should remain slightly positive in relation to the outside atmosphere to discourage infiltration of outdoor air.
Ensure all local exhaust ventilation (LEV) systems, such as specialized hoods or snorkel systems, meet criteria in the most recent version of the American Conference of Governmental Industrial Hygienists (ACGIH) Industrial Ventilation, a Manual of Recommended Practice. 2 When evaluating the LEV systems, include the exhaust stack discharge design and proper height.
In consideration of the maintenance personnel, we suggest you require proper roof access, provided by adequate openings with stairs and not ladders or fixed ladder systems, as it is difficult to climb vertically wearing a heavy tool belt and carrying handfuls of spare parts.
If you have ever had to explain black particles falling from supply vents, you know this is usually due to internally insulated ducts eroding over time. Therefore, pay attention to the types of ducts that move the conditioned supply air around the facility. We recommend all ductwork associated with the HVAC systems supply and return air distribution, as well as outside air intakes, not have internal lining or insulation. Only metal ducts should be used in industrial settings, and all ducts should be effectively sealed.
We recommend that flexible duct, if it must be used, only connect diffusers to the main trunk duct, and lengths should not exceed six feet. Avoid long, convoluted runs of flexible duct—a common trick used for sound attenuation.
All supply and return air runs should be conveyed using sealed ducts. Do not allow ceiling plenums (the space above ceilings and below the roof deck or floor above) or hallways to be used for moving supply or return air.
Verify and test all diffusers (the terminal ends, where supply air is delivered into the workspace) to show that mixing is adequate and drafts on occupants are minimized. Ensure enough space—at least six feet—between supply and return grills to prevent short-circuiting.
Controls are becoming very sophisticated and complex, with sensors and feedback loops that monitor air temperature and adjust the amount of outside air. With these advanced systems, it is critical that thermostats are located away from drafts, direct sunlight, or heat from nearby equipment. In addition, review overall system operation with your mechanical contractor so that temperature control zones do not combine areas with greatly differing heating or cooling loads. Manual damper controls are still used frequently for cost savings. It is a good idea to have the full open and closed positions clearly and permanently marked. Also, after final system balancing, mark damper positions, and lock or fix them in place.
Mechanical systems provide dehumidification during full occupancy as well as during partial cooling load conditions. Specify air handlers and filter configurations at the outset to minimize potential problems down the road. Consider your maintenance workers and provide sufficient clearance on all sides of the equipment. If equipment is elevated, install walkways with railings for safe access.
Recommendations for air handlers to prevent indoor air quality issues:
- Double-wall air handler housings with no internal insulation.
- Well-sealed filter banks or cells to prevent infiltration of bypass air.
- Filters located upstream of the cooling coils.
- Condensate pans located under the coils and made of stainless steel, and double-walled. Design should be pitched, tapered, and bottom-drained to prevent water stagnation.
- Drain lines should include a standard plumbing trap and discharge to the sanitary sewer. Also provide an air gap to prevent back-drafting of sewer gases during times of low condensate flow.
Filters and air cleaning devices
As we all know from maintaining our personal homes, filters are critical to system performance. Higher grade filters remove more dust, pollen, spores, etc. It is harder to force air through more efficient filters; therefore, they must match the system. We recommend pleated, extended- surface area filters with a minimum dust spot efficiency of 60% (MERV 11). Routine checking and replacing is also vital.
New technologies continue to emerge for IEQ and HVAC systems. Ultraviolet (UV) lighting arrays for controlling microbial growth in drain pans and on coil surfaces appear to work well in our experience, but they must be specifically designed for use in air handling units. Other devices include negative and/or positive ion generators, electrostatic precipitators, and ozone generators. We strongly recommend a thorough review of all available independent data prior to choosing one of these designs.
Outside air intakes
ASHRAE standard 62 recommends the minimum amount of outside air for mixing with conditioned air to maintain good indoor air quality based on types of use and occupancy.1 Therefore, fresh air intakes must be located during design to prevent introduction of pollutants into the building’s air supply. Adequate distance between outside air intakes and all potential pollution sources is necessary. Driveways, exhaust outlets, plumbing vents, hood exhausts, cooling towers, traffic, and garbage storage areas should get careful consideration. Additionally, protect intakes from rain intrusion by installing louvers or rain hoods, and exclude birds and other unwanted animals by installing quarter-inch mesh screening. Modulated damper systems should account for occupancy or contain mechanical stops to ensure a minimum supply of fresh air.
One last thing—when planning construction, consider outside air intakes of any adjacent existing buildings so construction activities do not impact occupants in those neighboring buildings.
1. Ventilation for Acceptable Indoor Air Quality. American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard 62-2009. Atlanta, GA.
2. Industrial Ventilation, a Manual of Recommended Practice. American Conference of Governmental Industrial Hygienists (ACGIH). 26th Edition, 2007. Cincinnati, OH.