In recent years, a few new buildings have come back to haunt us after occupants have moved in. Even though Environmental Health and Safety was plugged into the design review and dutifully examined and signed off on construction specifications, important considerations were being overlooked and we forgot about what conditions would be like for the actual occupants.
Sometimes it would be something immediately after occupancy, such as noise from the ventilation system. Often it would be delayed until transient smells or nuisance odors were repeatedly drawn into the building. And a few took much longer, maybe years, until the black particles began pouring from the supply vents. But all these affect indoor environmental quality (IEQ) and thus employee comfort, productivity and possibly health. Further, most of these conditions are preventable.
The following recommendations have been culled from years of dealing with IEQ complaints. Often the fix is very simple and costs almost nothing. However, more often than not the problem is traced back to poor design and ends up costing lots of money for renovations, not to mention the disruption to normal operations. If you can catch any of these during design, it can save immense sums down the road. We would strongly recommend that you develop an IEQ design policy and make sure all architects and engineers receive a copy when beginning a project.
First and foremost, you want to ensure 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 areas utilized for containment and any odor- or contaminantgenerating activities from the return air system, and ensure that adequate exhaust air is provided. Examples include laboratories; lavatories; autoclave rooms; animal housing areas; kitchens; and document printing, copying and reproduction areas. Maintain laboratories and other such areas at a slightly negative pressure with respect to surrounding office and reception areas. In other words, slightly more air is exhausted from these spaces than is supplied to ensure that 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.
If local exhaust ventilation (LEV) systems are used, such as specialized hoods or snorkel systems, their design should follow the most recent version of the American Conference of Governmental Industrial Hygienists’ (ACGIH) Industrial Ventilation: A Manual of Recommended Practice for Design.2 Be sure to include the exhaust stack discharge design and proper height when evaluating the LEV system.
Finally, consider the maintenance personnel and require proper roof access provided by adequate openings with stairs, not ladders, not even fixed-ladder systems. It is not easy to climb vertically with a heavy tool belt and your hands full of spare parts.
One of the most important (and potentially troublesome) components is the system of ducts that moves the ventilation around the facility. The black particles pouring from supply vents mentioned above—nine times out of ten are due to internally insulated ducts eroding over time. Therefore, all ductwork associated with the HVAC systems supply and return air distribution as well as outside air intakes (more on these later) must not have internal lining or insulation. We highly recommend only metal ducts in industrial settings; duct board is just not acceptable. Construct all ducts so that they are effectively sealed.
We recommend that flexible duct, if used at all, only connect diffusers to the main trunk duct and lengths should not exceed six feet. By all means, avoid long, convoluted runs of flexible duct, a common trick used for sound attenuation.
All supply and return air runs should go through 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.
At the terminal ends, where supply air is pushed into the workspace, verify and test all diffusers to show that throw and mixing is adequate and drafts on occupants are minimized. Ensure enough space between supply and return grills to prevent short-circuiting.
Controls are becoming very sophisticated and complex, with sensors and feedback loops that can call for air of a certain temperature and even the amount of outside air. However, the simpler things can still get overlooked. Make sure that thermostats are located away from drafts, direct sunlight or heat from nearby equipment. Question your mechanical contractor to guarantee that temperature control zones do not combine areas with very different heating or cooling loads.
Manual damper controls, still used frequently for cost savings, must have their full open and closed positions clearly and permanently marked. After final system balancing, mark their positions and lock or fix in place.
Air handlers and filters come in many configurations and price ranges. However, providing a few specifications at the beginning can go a long way toward narrowing the field of choice and minimizing potential problems down the road. In general, system design must provide dehumidification during full occupancy as well as during partial cooling load conditions. Also, be kind to your maintenance workers and provide sufficient clearance on all sides of the equipment. If equipment is elevated, install walkways with railings for safe access. Here are our must-haves:
• Double-walled 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, also double walled (Design should be pitched, tapered and bottom drained to prevent water stagnation.)
• Drain lines that 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 home units, filters are critical to system performance. Better filters remove more dust, pollen, spores, etc., but they must match the system. It is harder to push air through more efficient filters. We recommend pleated, extended-surfacearea filters with a minimum dust spot efficiency of 60 percent (MERV 11). Routine checking and replacing is also paramount.
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 minimum amounts of outside air to mix with conditioned air in order to maintain good indoor air quality.2 These are based on types of use and occupancy. Locating fresh-air intakes during design must prevent introduction of pollutants into the building’s air supply. You must ensure adequate distance between outside air intakes and all potential pollution sources. Give careful consideration to driveways, exhaust outlets, plumbing vents, hood exhausts, cooling towers, streets and highways, and garbage storage and treatment areas. In addition to keeping clear of pollution sources, protect intakes from rain intrusion by installing louvers or rain hoods. Preclude birds and other unwanted animals by installing ¼-inch mesh screening. Modulated damper systems should account for occupancy or contain mechanical stops to ensure a minimum supply of fresh air. Finally, when planning your new building design, consider outside air intakes of all adjacent existing buildings so construction activities do not impact occupants in those neighboring buildings.
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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 for Design.” American Conference of Governmental Industrial Hygienists (ACGIH). 26th edition, 2007. Cincinnati, OH.