If your school buildings are old, you've probably seen and smelled the telltale signs of poor indoor air quality: stuffy buildings, warped ceiling tiles, health complaints. Maybe you've returned to your school in the fall to find mold on carpets, library books or ventilators. If you can see or smell it, mold and fungi are probably lurking in your walls or thriving in your HVAC system.
By themselves, these symptoms are worrisome in light of a growing focus on indoor air quality (IAQ). However, when you consider the added burden it places on your staff to maintain aging HVAC, plumbing and electrical systems, it becomes a problem that must be addressed.
What does bringing your facilities up-to-date involve? Can you afford it? More important, can you afford not to do it? Where do you start?
The first step in addressing this challenge is selecting an engineering firm to survey your buildings and develop a master plan. The firm should have substantial infrastructure renovation experience and extensive knowledge of IAQ design standards.
The master plan should include an assessment of your facilities, including an analysis of the age, condition and life expectancy of equipment and an evaluation of the IAQ at each facility.
As with any renovation project, close coordination of mechanical and electrical designs with existing conditions is crucial. Detailed and accurate building surveys are imperative and should include complete documentation of field conditions. Old architectural and engineering drawings typically are inaccurate and do not reflect actual conditions.
Because an HVAC system affects IAQ most directly, choosing the right system is critical. An HVAC system must fit into the space available; be energy-efficient and easily maintained; work for all schools undergoing renovation; have a low initial cost; and above all, provide good indoor air quality.
THE RIGHT SYSTEM
A four-pipe primary air system with heat recovery meets these criteria. Physically compact and easy to install, this system provides excellent IAQ and precise control of ventilation air quantity, temperature and humidity.
The initial cost of the system ranges from $15 to $17 per square foot, approximately $2 to $3 per square foot less than a comparable fan-powered VAV system. Energy savings, compared with a VAV system, are estimated at $0.20 per square foot annually.
A four-pipe primary air system consists of a central chilled-water plant, a central heating water plant, a primary (ventilation) air system and a space heating and cooling air system.
The chilled water plant consists of a chiller, a cooling tower or an air-cooled condensing unit, constant-volume primary chilled-water pumps and variable-volume secondary chilled-water pumps with variable-frequency drives for energy savings. On buildings with a cooling tower, a heat-recovery system should be installed on the condenser water loop. This system uses heat rejected from the chiller to provide building reheat during summer months. This provides dehumidification without operating boilers in the cooling season.
The heating water plant consists of two boilers each sized at two-thirds of the building's heating load. This sizing procedure allows for redundancy in the event of boiler failure and flexibility for future capacity requirements. The plant also consists of constant-volume primary heating water pumps and variable-volume secondary heating water pumps with variable frequency drives for energy savings.
The primary air system includes primary air handling units (PAUs) with heat recovery and ductwork from the PAUs to the individual spaces served. The constant-volume PAU draws 100 percent outside air into the unit. In summer months, it cools and dehumidifies the ventilation air to 72 degrees and 45 percent relative humidity. In winter months, it heats outside air to 72 degrees. A combination of heat recovery wheels is used to transfer sensible and latent energy from the building exhaust/relief air to ventilation air.
The first energy-recovery wheel is capable of cooling humid, 95°F outside air to 72°F without mechanical cooling. The air is then subcooled at the cooling coil to 48°F and reheated by the second energy-recovery wheel to 72°F. The heat source for the reheat process is the heat contained in the building exhaust/relief air stream. The air is then filtered by 65 percent final filters before being distributed to classrooms. At this point, ventilation air delivered to classrooms by the PAU is adequately dehumidified to keep the classroom below 55 percent relative humidity. This will ensure that fungi and mold will not have a suitable environment in which to thrive.
Unlike a typical variable-air-volume system, PAUs are constant volume. This ensures that 15 cfm of outside air per student is constantly delivered to classrooms and meets the recommendations of ASHRAE 62-1989, the standard for ventilation and indoor air quality. If ASHRAE 62-1989 guidelines are not followed, your institution could be liable for breach of standard of care.
Classrooms are heated and cooled by individual blower coil units (BCUs) or classroom unit ventilators (CRUVs), depending on the ceiling plenum space available. Both types of units are 100 percent recirculating and contain a heating coil, cooling coil, fan and filter. BCUs are concealed above the ceiling, while CRUVs are floor-mounted in classrooms. BCUs should be used where possible to prevent acoustic and aesthetic intrusion in the classroom.
Because ductwork between PAUs and classrooms delivers only the ventilation air required, ductwork is considerably smaller than that of a standard system. It does not require insulation, because the air in the duct is 72°F and does not cause condensation or energy loss to the ambient air. These are important considerations when examining space available for ductwork and the system's first cost. Where ceiling space is not available, a bulkhead may be constructed between classrooms and the corridor to house the primary air ductwork. This has little effect on classroom space.
With its energy-recovery wheels and chiller heat recovery, the system provides greater energy efficiency than a VAV system with comparable maintenance requirements and simplicity.
For new or renovated facilities, the four-pipe PAS with heat recovery can provide healthy learning environments for students. It ensures humidity, temperature and noise control, along with proper filtration, energy efficiency and ease of maintenance at a moderate cost.
Odle, AIA, is president and CEO of The Odle McGuire & Shook Corporation, Indianapolis, a full-service architectural/engineering firm providing planning and design services for K-12 and higher education facilities. The firm worked on the CPCSC project (see sidebars). Bieghler is a senior mechanical engineer specializing in indoor air quality and mechanical design for educational facilities.
Case in (Crown) Point
Crown Point Community School Corporation (CPCSC), Ind., did not have a lot of money, but it could not ignore the needs at six of its eight schools. Poor indoor air quality and lack of technology were the greatest concerns, and aging HVAC, plumbing and electrical systems were requiring additional maintenance.
As part of a facilities master plan, the architect surveyed existing buildings to evaluate the condition of the infrastructure and systems.
What they found was typical of old buildings. Poor indoor air quality was the result of poor ventilation, lack of dehumidification, poor temperature control and buried supply air ductwork that housed standing water — a breeding ground for fungi and mold. The existing HVAC systems were a mixed bag of system types and manufacturers. They provided no humidity control and were difficult to maintain.
The physical attributes of the buildings posed challenges: basement mechanical rooms made equipment replacement difficult. Limited ceiling space or no ceiling plenum at all meant that a typical variable-air-volume HVAC system would be nearly impossible to install. Plumbing systems were failing, and there was not enough power to accommodate new technology.
The architect compiled recommendations and cost estimates. Based on this information, Crown Point's administration selected the four-pipe primary air system with heat recovery, in addition to technology and plumbing upgrades. The design team provided a modern mechanical system and flexible technology infrastructure in limited space.
Getting it built
Crown Point Community School Corporation, Ind., bid its infrastructure renovation projects separately, but the school district wanted to have the same equipment manufacturers for all six buildings needing upgrades. Therefore, each piece of major equipment was bid as an alternate by manufacturer. This allowed the district to choose similar manufacturers for all projects.
Crown Point wanted the project to be constructed with as little disruption to the students as possible. This required major corridor work to be completed during summer months. By the time school started in the fall, most visible work had been completed, and the buildings were ready for occupancy. Classroom work that remained was done on a rotating basis. Schools rotated students in and out of modular units as classrooms were being renovated. The central plant and mechanical room work continued while school was in session, with little disruption to students.
The Crown Point schools now have a new infrastructure, good indoor air quality, technology in the classrooms, and energy-efficient systems. Superintendent Steve Sprunger says the renovations will help the school system “experience greater energy savings and vastly improved indoor air quality, both of which will have a substantially positive effect on our students.”