Graduating to Better IAQ

HVAC solutions for educational facilities range from remedial tutoring to advanced degrees

By Scott Wilson, P.E., Einhorn Yaffee Prescott, Albany, N.Y. June 1, 2001

The most fundamental goal in the design of educational facilities is to provide an environment conducive to learning, one that is safe and healthy for students and teachers alike. Mandatory compliance with codes, standards and publicized research reduces the likelihood that the health of students will be jeopardized. A proactive design process and regular inspections also help insure the well-being of students.

Indoor-air quality (IAQ) can affect learning. If not explored early, poor IAQ can negatively impact student health and ultimately result in unacceptable learning environments. One way to avoid the problem is to proactively address IAQ during the school design process; engineers and architects must begin the design phase by working with the owner to set goals for IAQ. Different schools—elementary, middle and high schools, colleges and universities—often require different approaches.

Elementary schools. Elementary schools are generally the simplest educational facility type (see “The Perils of ‘Progress,'” page 18). Because of cost issues, the most basic heating, ventilation and air-conditioning (HVAC) systems have historically been the norm. Typical solutions consist of: unit ventilators in classrooms; simple heating and ventilation systems serving gymnasiums, cafeterias and multipurpose spaces; and unitary equipment serving media centers and other areas requiring heating and cooling. IAQ initiatives beyond code requirements are challenging because of tight budgets (see “Elementary Solution,” page 26).

Middle schools and high schools. Beyond the elementary level, schools begin to benefit from larger design and construction budgets. They rely more on technology, have more extracurricular activities and attempt to prepare students for college and beyond (see “Secondary Strategies,” page 26).

Colleges and universities. Generally the most advanced with regard to IAQ issues, institutions of higher education often have a full-time staff devoted to construction projects and even their own design and construction standards. Furthermore, sophisticated building types at universities may have special environmental needs, such as science laboratories and art studios (see “The Art and Science of College IAQ,” page 28). The owner and design team may spend a significant amount of time reviewing and critiquing HVAC system plans prior to construction, allowing many opportunities to explore and implement IAQ initiatives.

Top school IAQ issues

Overall, leading IAQ concerns for educational facilities include humidity control, air filtration, outside-air control and special hazards.

High humidity is a concern during warm months, which in occupied spaces can lead to discomfort and, worse, conditions conducive to fungal growth, including mold and mildew. To combat these problems, relative humidity (RH) should be kept below 65 percent, combined with good air filtration and proper housekeeping practices. To keep room RH below 65 percent, HVAC-unit supply air must be cooled to a point where moisture is condensed out. With an occupancy of 30 students, a classroom would need discharge-air temperatures no warmer than 58°F to properly dehumidify supply air.

Unfortunately, constant-volume systems tend to suffer from supply-air temperatures that overcool spaces during periods when solar- and wall-transmission loads are low. Constant-volume equipment like unit ventilators and small unitary rooftop packages tend to cycle or otherwise adjust discharge temperatures higher as room loads shrink, causing room RH to rise. Available solutions include specifying a zone-heating coil on the discharge of an air-handling unit, which allows discharge temperatures to be lower than needed in the space. The heating coil compensates for the low-temperature supply air and prevents overcooling.

The use of variable-volume air supply can reduce the energy consumed at fans and zone-heating coils. Whether constant-volume or variable-air-volume (VAV) supply, the energy consequences of reheating supply air dictate that reclaimed energy should be the first choice for the zone-heating device.

To use this type of system—which is common in many noneducational building types—the design of the building needs to accommodate both the air-handling units (AHUs) and associated ductwork. The impact is usually to increase the floor-to-floor height of the building and possibly to add fan rooms to the floor plans. The obvious outcome is an increased construction cost.

In contrast, during the coldest months of the year, the main concern is low humidity. The American Society of Heating, Refrigerating and Air-conditioning Engineers (ASHRAE) recommends a minimum space RH of approximately 30 percent, a level that is known to improve comfort and reduce susceptibility to airborne infection. However, 30-percent room RH is difficult to maintain when outside air is cold and dry. The author’s preferred option is to use a “clean-steam” generator in conjunction with steam dispersion tubes. The clean-steam generators use electricity, gas or steam as the heating energy source, and they vary in size. After water is converted to steam, it is sent to dispersion tubes, which are installed in the supply air of an air-handling system. The tubes uniformly distribute the steam into the air stream, permitting quick absorption into supply air. Care must be taken to insure that there are no obstructions or changes in direction in the air stream.

Eliminating contaminants through air filtration is another important IAQ tool. While building codes often reference ASHRAE Standard 62, ASHRAE standards and design manuals should be consulted for filter selection. For equipment commonly used in educational facilities, such as unit ventilators and unitary air conditioners, filtration options are limited. Early attention to IAQ issues is necessary to be sure that finances are available to support the appropriate systems needed to meet the IAQ goals of the project.

While school control systems traditionally are as simple as possible, outside-air control can be helpful, and the cost of digital control systems—which provide more precise and reliable control—has dropped to the point that they can be considered for educational facilities. Digital control, in conjunction with airflow measuring devices, can also offer verification.

Of course, outside-air intakes should be located well away from contaminant sources, including horizontal surfaces where contaminants can collect. Taking outside air from areaways should be a last resort because of the work required by owners to keep areaways clean.

Special conditions should also be considered. Care must be taken not only to document the contaminants present in specific buildings, but also to determine ways that students and staff become exposed to the sources.

Informed decisions need to be made about whether to use local-exhaust or general-dilution ventilation, or both. The assistance of technical consultants specializing in specific hazards should be considered.

Some IAQ challenges require attention to several of these issues. A good example is the presence of mold and mildew , both symptoms of the problem of fungal growth. Fungi are almost always naturally present in ambient air. They become a problem in buildings when they can collect near nutrient sources and in areas of high humidity—above 65 percent RH—and at moderate or warm temperatures. The solution is to provide HVAC systems that provide good filtration of the outside air, control of the room RH, excellent air circulation within high-risk spaces and good housekeeping practices. Case in point

A mid-Atlantic university client, for example, recently needed to solve a mold problem in its library and also to expand its chiller plant to serve adjacent buildings. Testing revealed active fungi growth both inside and outside the air-handling systems. Also discovered were poor air filtration—by today’s standards—as well as water carry-over at cooling coils and controls that were precooling the building at night with 100-percent outside air to partially compensate for inadequate cooling.

In other words, low-efficiency filters were allowing dirt and nutrients to accumulate on ductwork liner and elsewhere throughout the building. Water carryover at the cooling coils brought moisture to fungi on dirty duct liner at the unit discharge. Purging the building at night with cool air would bring in air at very high RH and at moderate temperatures. All conditions encouraged fungi growth.

The author’s firm recommended discontinuing the night purge as well as removing contaminated lined ductwork and replacing AHUs. New units would have cooling coils sized to avoid water carryover and to deliver colder supply air. The retrofit plan also suggested adding reheat coils to the AHUs to permit constant low-temperature air leaving the cooling coil, and an upgrade of the chiller plant to ensure adequate cooling capacity at cooling coils. Further, steam-to-steam type humidifiers were specified for winter humidification. Filters in the air handling units were upgraded to a minimum-efficiency reporting value (MERV) of MERV 13—80-percent to 90-percent efficiency—to remove dirt and fungi from supply air. As a final measure, the cooling tower was moved to a new location and intake locations were consolidated to reduce the potential of contamination at the intakes. IAQ Roles and responsibilities

This university project not only demonstrated the importance of technical solutions but also the roles and responsibilities of IAQ project participants. First, design professionals must educate owners about IAQ issues in the earliest phases of any project. Second, owners and designers should maintain a constant dialogue to make IAQ decisions in a collaborative fashion. Last, the entire project team—owner, design team and construction firm, if present—must fully explore issues and options to agree on a path forward.

At minimum, the following should be discussed for all occupied spaces:

How outside air is delivered.

Control schemes to maintain the appropriate flow of outside air over time.

ASHRAE standard compliance.

Types of air filtration.

Control of humidity variation.

Special IAQ hazards, associated use-related issues and design solutions.

Building-control systems and monitoring features needed by the owner.

The need for commissioning and other testing beyond typical testing and balancing procedures.

Such attention to all facets of IAQ issues do not end in the design phase. During construction, ventilation systems must be protected to prevent contamination, especially when a project is phased. The design team should make regular site visits to insure compliance with project specifications; however, it is equally necessary for both owner and design team to be prepared for unforeseen obstacles. The builder should keep owners and designers informed about unexpected changes.

Above all, IAQ projects demand attention to building operation. Owners must be trained in operation and maintenance of newly installed HVAC systems to make them as effective as possible.

Careful consideration of the project process and a collaborative working relationship is a formula for success in addressing IAQ. Through better education, the owner, design team and builder can be effectively proactive in creating healthy educational environments.

Elementary IAQ Solution: Benton Hall Academy

Benton Hall Academy, part of the Little Falls (N.Y.) School District, is a historic, 110,000-square-foot elementary school that was recently gutted. The scope of work included removing interior floors in a large portion of the building for more efficient use of the interior volume, while preserving the character of the building’s historic exterior.

As part of the renovation, ceiling space, shafts and mechanical rooms were provided to permit central air-handling systems in many areas of the building. Unit ventilators were added to the remainder of the conditioned building areas. The IAQ features of this project include:

A central chilled-water plant and two-pipe unit ventilators to cool most occupied zones of the building.

Central air-handling units for supply air with 45-percent-efficiency air filters to many areas.

Outside-air intakes integrated in the cupolas above the roof.

Secondary Strategies: Cobleskill-Richmondville High School

A 170,000-square-foot new high school, Cobleskill-Richmondville High School in Warnerville, N.Y, is located in a rural setting. For this secondary school, IAQ features were included in the HVAC system design. The key IAQ features of the project include:

Cooling provided for computer rooms, media center, district offices and the auditorium.

Central air-handling units for supply air with 45-percent-efficiency air filters to many areas.

Careful placement of all outside-air intakes. Locations were carefully selected to avoid contamination from vehicle and building exhaust.

The Art and Science of College IAQ

The Bulmer Telecommunications and Computations Center at Hudson Valley Community College, Troy, N.Y., is a 90,000-square-foot classroom and faculty office building designed to integrate computers and distance learning in a very flexible format. Most of the classroom spaces have raised floors for cable distribution. The building includes a large atrium, a 250-seat distance-learning auditorium and two video studios for broadcast and coursework preparation. Central variable-air-volume (VAV) systems carry capacity to suit a phased fit-up of conventional classrooms into computer classrooms. IAQ features of the project include:

Central variable-volume air-handling units for supply air with 45-percent-efficiency air filters.

Outside-air intakes carefully placed to avoid contamination from vehicle and building exhaust.

Series fan-powered VAV air-terminal units with hot-water heating coils for good air circulation. This has been identified by the American Society of Heating, Refrigerating and Air-conditioning Engineers (ASHRAE) as improving IAQ.

Another recent project is the Sage Arts Building, a 43,000-square-foot classroom/studio and faculty office building at the Sage Colleges, Albany, N.Y. The project was designed to integrate local and general exhaust systems into classroom and studios in a flexible format. The facility includes photography, painting, printmaking, sculpture and ceramics studios. Snorkel type exhaust arms were incorporated into the design. IAQ features include:

Air conditioning throughout.

Central VAV air-handling units for supply air with 85-percent-efficiency filters.

Snorkel exhaust arms in printmaking, ceramics and welding areas, and a dust-collection system in clay-mixing areas.

Outside-air intakes placed to avoid contamination from vehicle exhaust.

Science and laboratory buildings also often need special steps for IAQ issues. For example, the Williams Unified Sciences Building, Williamstown, Mass.—a 115,000-square-foot complex of laboratory and library additions with 180,000 square feet of renovated science facilities—was designed by Portland, Ore.-based Zimmer Gunsul Frasca Partnership to interconnect biology, chemistry and physics departments and a common science library. For those needs, and for biology and chemistry laboratories, IAQ features were selected that include:

VAV terminals fitted with heating coils.

Central VAV air-handling units for supply air with 85-percent-efficiency air filters.

Restricted, bypass-type VAV laboratory fume hoods.

Snorkel exhaust arms throughout for special needs.

Outside-air intakes carefully placed to avoid contamination from vehicle and building exhaust.

A centralized laboratory exhaust that terminates with a constant-volume/constant-high-velocity discharge-fan system that sends an exhaust plume high above the building.