Mechanical ventilation systems have evolved from passive gravity vents (circa 1900) by adding modifications to improve comfort, occupant health, and energy efficiency. Early on, the maintenance of the system basically related to making sure the furnace was on and the windows would open. If you were lucky the school might have draft deflectors on the windows so the wind would not blow directly on your head. However, today and in the future, more complex components are added into the HVAC 'system' making it a magnificently complex one, requiring educated, sophisticated technicians to operate and maintain it. Such complexities these systems include, computerized temperature and air flow controls, energy optimizing controls, maintaining minimum outside air requirements, humidification control, multiple pressurization requirements, specialized air cleaners and air quality monitors. The more complicated the systems, the more complex and frequent the problems.
These complexities and specializations in maintenance and operations vary in the types of buildings being served. Institutional facilities, such as schools and hospitals, require some of the most complex HVAC system design, installation and maintenance. Add to that complexity of detail the onset of renovations while the building is occupied, and the problems are more complicated and the pollutant loads magnified. In our litigious society, whether a student has an asthma attack or a patient acquires a noscomial infection, the designers, facility engineers, maintenance technicians and installation contractors all play an important part in protecting building occupants.
As a consultant investigating indoor air quality and microbial contamination concerns, one is exposed to many of the problems that occur, how they come to pass and how they get addressed. Sometimes they are addressed in the design of the building and sometimes they are addressed in the court room years later. This article is an attempt to share some of the observations made during many years of investigating air quality concerns in schools and healthcare facilities. In the last few years, a number of organizations have been attempting to address these issues. These include ASHRAE Standards 170, 180, JCAHCO, AHA and USGBC's LEED programs. Several government agencies (EPA in schools and CDC in healthcare) have issued guidelines as well. These guidelines are seldom in the form of regulations but many times do result in changes to building codes.
Engineers and architects have difficult tasks in the HVAC system design process of balancing the building requirements, occupant needs, code requirements and costs. Compromises that are made can make proper building maintenance difficult or costly. Unit ventilators in each room or large central roof top units, which are the better design? If you ask the maintenance staff, they know there are fewer filters to change and coils to clean with large central air handler units. It is less likely that access to the coils and filters will be compromised by plumbing or room contents. However individual thermal control and less ductwork are associated with unit ventilators, providing individual controls. Automating these individual controls with timers or motion sensors, and it can result in cost controls. Unit ventilators have outside air intakes and many various levels and locations. Ground level air intakes have to consider grounds keeping issues, vehicle emission and vandalism. Roof top air handler unit air intakes should be located with respect to sanitary vents, exhaust fans, exhaust stacks/flues and cooling towers. Architects like to keep the roof line uncluttered. They hide equipment behind facades and parapets. Of course these facades and parapets have been known to restrict air flow and allow reentrainment of building exhausts if equipment is too close together or not designed perfectly. Maintenance crews are not always fond of climbing on roofs (particularly in bad weather). Roof top unit locations must also be protected from bird/bat intrusions into improperly installed or maintained bird screens. The condensate drain traps need to be maintained and if the roof is not pitched properly then ponding of condensate or rain water in front of the air intakes can lead to problems.
Healthcare facilities have a wide range of HVAC requirements not seen in education facilities. Humidification systems are seldom seen in educational buildings. Humidification is a sensitive mechanical system where a source of fresh water steam is critical. Steam generated by power plants usually contain anti-corrosive additives which are not desirable in breathing air. Of course there is a cost for separate clean steam systems and additional maintenance. Hospitals require isolation areas where positive air pressure is required such as operating rooms, organ transplant areas and any area where immune compromised patients are located. In these areas the supplied air is filtered through HEPA filters and is designed to leak out. Alternatively, infectious disease containment requires negatively pressurized air. Recirculating a percentage of the ventilation air is a common practice in most buildings. Recirculating air is not feasible when the air being exhausted may contain waste anesthetic gases or otherwise contaminated air. Maintenance of these specialized systems takes a sophisticated, adequately sized and dedicated maintenance staff. Design mistakes can make proper maintenance impossible. Duct work that is insulated internally rather than externally wrapped can trap dust from the air stream. Duct work that passes through cold plenums can condense moisture on the inside of the duct. The air handler insulation can be abraded by maintenance staff unless protected. The dust components include pollen, human skin flakes, paper dust and clothing fibers can support microbial growth when and if they are exposed to moisture.
The costs of poor design and maintenance are counted in human lives in addition to energy costs, and wasted man hours. There are diseases directly associated with microbial growth in the duct systems (Aspergilosis). Water temperature that is not high enough in water heaters can allow Legionella bacteria to become established.
A significant problem in schools with air conditioning is the moisture control during the summer. In areas near large bodies of water or in humid environments, schools that are not fully occupied during the summer will have an accumulation of moisture within the building. Air conditioning systems are designed around a defined population. The dehumidification capabilities are often not as flexible as the needs of a school system. The results are that the controls of the system cannot gradually remove moisture from a building. Millions of dollars have been lost when the excess moisture condenses on surfaces and is dripping on carpets, library books and mold prevents the building from being occupied. Healthcare facilities are not immune from the same problem if areas are not continuously occupied. Below grade areas of buildings are cooler in the summer months than floors not in contact with the earth. These areas are often not patient areas but are used for offices and laboratories in the hospitals. While they do not require as much cooling as the upper floors, they do require dehumidification. Porous surfaces such as carpeting which is utilized in the offices will tend to accumulate building dust. If not maintained perfectly they can become a reservoir of condensed moisture and related microbial contaminants. Newer buildings should have insulation below the concrete slabs and around the foundation to minimize this problem.
Can a maintenance staff adequately maintain an air handler that has inadequate access? If a construction project occurs next door what precautions can be taken to avoid making the dust, chemicals and fumes generated in that project from becoming your problem. What can be done when first floor renovations contaminants rise through the elevator shafts and stairwells and impact the third floor? The answers and the guidelines have been coming out rapidly in the last two years. ASHRAE Standard 170, Ventilation of Health Care Facilities addresses in detail what each area of the facility requires. It addresses cleanliness of ductwork, construction planning and should be required reading for all healthcare facility managers. Similarly the ASHRAE Standard 180, Standard Practice for Inspection and Maintenance of Commercial Buildings HVAC Systems provides a schedule of what should be inspected and when inspections should be conducted. It does not provide the how the work is to be performed but strict documentation is required in the 24 tables of checklists provided.
The National Air Filtration Standard has a Users Guide for ASHRAE Standard 52.2 which describes the MERV (Minimum Efficiency Reporting Value) which is used to better define the Dust Arrestance Standard 52.1 and particle sizing requirements. Knowing what MERV numbers are for your filters will be helpful in the future than the percentage of dust the filters capture. Testing filter installation by pressure drop across the filters is the most common method, but using a laser particle counter to determine if the installation is effectively removing particles in the air is much more sensitive.
Are individual staff members bringing in humidifiers, electric heaters, portable air cleaners and green plants a good idea, an additional hazard or even effective? In a classroom, plants on a unit ventilator are an obstruction to the air flow and a potential source of airborne mold. Cool mist humidifiers with standing water reservoirs are never a good idea. Electric heaters are almost always ineffective. Building occupants blocking supply diffusers because of draft complaints destroys any attempt at having a balanced air distribution system. Whereas a supply diffuser designed to not allow high velocity air flow will often avoid draft concerns.
Can ultraviolet lamps effectively sterilize a fast moving air stream? What filters and how long do they last can you use for removing non-particulate contaminants? Even with all the newest guidelines/standards there are questions without satisfactory answers. New guidelines will come in the future.
No doubt the challenges of facility management will be getting more complex. Of course, the downside of not managing HVAC systems to industry standards will not become easier either.
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