Doing Your Homework on Indoor Air Quality Issues
Indoor air quality (IAQ) is not a top priority with college and university administrators. But, it should be.
A study conducted by the National Institute for Occupational Safety and Health (NIOSH) determined a number of reasons why we should pay attention to the crucial issue of indoor air quality, noted here.
• Synthetic building materials, furnishings, carpet adhesives, art supplies and lab spaces expel contaminants such as volatile organic compounds (VOCs) and formaldehyde.
- High or low humidity dramatically increases the incidence of airborne infections.
- High or low humidity conditions routinely exist in classrooms and dormitories. Schools in the northern area of the United States, where relative humidity is low, are seldom humidified. Schools in the south, where humidity is high, typically use low cost, air-conditioning systems that operate intermittently with limited dehumidifying capacity.
-• Many energy-saving practices have compromised indoor air quality.
In addition, a new standard for improved indoor air quality has been put in place by the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE). The“Ventilation for Acceptable Indoor Air Quality” recommends that the amount of outdoor air be increased from five cfm/person to a minimum of 15 cfm/person.
Project Considerations
Prior to the 1996 Summer Olympics in Atlanta, the Georgia Institute of Technology (GIT) built an Undergraduate Living Center (ULC). Initially, Olympic athletes occupied the space, though it now serves as a dormitory for GIT students. Facility managers and building designers from Nottingham, Brook and Pennington (NBP), in Macon, Ga., considered the following issues.
- A safe and comfortable indoor environment was the first priority.
- Each apartment needed separate heating and cooling controls.
- Humidity loads would fluctuate widely during each 24-hour cycle.
- The Southern Building Code was in the process of adopting ASHRAE’s air quality standard recommending a 24-hour supply of outdoor air for best indoor air quality.
- Low-cost installation and energy efficiency underlay all considerations.
When considering design options, both GIT Facilities Engineering Department and NBP benefited from previous IAQ research conducted by the Georgia Tech Research Institute (GTRI). A GTRI research group, headed by Dr. Charlene Bayer, has been conducting IAQ investigations for the past 15 years on all types of facilities, ranging from classrooms to office buildings.
Bayer notes that dormitories have humidity loads that can fluctuate widely. Allowing indoor relative humidities to exceed 70 percent for extended periods of time usually results in humidity problems ranging from occupant complaints (such as odor and allergic reactions), to damage to carpets and wall coverings from mold and mildew.
Further GTRI research, both in the laboratory and in the field as part of an elementary school IAQ investigation, confirmed that microbial growth can actually generate and emit VOCs.
If not dealt with, humidity problems would be particularly bad for dormitories during mild, humid days (early mornings or rainy days), when the building’s sensible load is low and when humid outdoor air is continually supplied to the space.
As a result, it was concluded that a mechanical design for the ULC would need to accommodate increased outdoor air to meet the IAQ requirements, while allowing for control of indoor relative humidity.
Design Solution
Both BNP and GIT, through the research conducted by GTRI, had experience with desiccant-based systems, which they decided to use. The chosen system allows the sensible and latent loads associated with the outdoor air to be“detached” from a building’s internal heating/cooling load. In other words, an outdoor air preconditioner buffers the building from outdoor air conditions, allowing the building’s mechanical system to be designed as if it were never exposed to winter or summer conditions.
Approximately 43,000 cfm of outdoor air is provided to the facility on a continuous basis by three dual-wheel, total-energy-recovery systems, located in the attic space above each of the three wings of the dormitory. This preconditioned air is ducted directly to the corridors, common study area and individual living spaces to provide effective dilution ventilation.
Approximately 28,800 cfm is exhausted from the bathroom areas and janitor’s closets located throughout the facility. These systems recover approximately 90 percent of the energy contained in the exhaust air and use it to precool and dehumidify outdoor air during the cooling season (conversely, to preheat and prehumidify outdoor air during the heating season).
Individual living spaces and all common areas are heated and cooled by four pipe fancoil units. These are fed by chilled water and hot water, and they allow for individual temperature control in each living space via wall-mounted thermostats. They are activated only when heating or cooling is called for in the space.
Project Economies
The system provides 265 tons of cooling with an input of only 112 tons. In other words, it provides 2,400,000 Btu of 'free' heating and humidification during the heating season.
The energy savings and first-cost savings in boiler and chiller capacity provided a one-year payback. When the savings associated with chilled-water distribution piping are considered, the payback was immediate.
Most importantly, GIT has recognized an estimated $67,240 in energy savings each year, when compared to the energy that would have been required by a conventional cooling-reheat preconditioning approach. Had the exhaust air volumes more closely approximated the supply air volumes, the economic justification would have been even more favorable.
Rick Caldwell is communications manager with Columbia, Mo.-based Semco Inc.