By Charles Cochrane
As air-handlers age, they become less efficient and can diminish IAQ. Capital improvements can help the equipment operate at optimum efficiency, but basic operations and maintenance are often overlooked.
One of the most neglected HVAC-maintenance tasks is removing soil/dirt build-up and corrosion from blower blades. Simple cleaning can improve air-movement efficiency by 50 percent, but be careful not to unbalance the blades; in addition, remove stagnant water (if left standing, it could promote rapid bacteria and mold growth, and lead to overflow spills that could possibly impact the entire HVAC system).
Replacing filters on a regular basis is an inexpensive job that pays for itself quickly. Use filters recommended for your system or look into newer filter technologies that provide improved filtration with less static pressure. Higher-efficiency filters provide a cost-effective means of improving IAQ performance while minimizing energy consumption; low-efficiency filters can become deformed and even “blow out.” Turn off fans when changing the filter to prevent air contamination, and be sure the filters fit tightly in the filter housing.
The ability of cooling coils (evaporator coils) to cool air to the correct temperature is directly tied to cleanliness. First, use an alkaline detergent (it breaks down the dirt and biofilm that tends to accumulate on coils without causing oxidation or damage to aluminum coil fins). If heavy scaling is present, use an acid-based coil cleaner after the initial cleaning to break down scale deposits. Determine the clean pressure drop across the coil, and use this data to determine when cleaning is needed in the future. The Virginia Beach, VA-based National Air Filtration Association provides a way to calculate the cost of increased static pressure based on kilowatt-per-hour cost.
Cleaning condensate pans is important - dust and debris accumulate and clog drain lines. If drain lines clog, moisture carryover could occur and dampen nearby ductwork. If ducts are made from uncoated fiber glass ductboard, mold and other microbial growth can occur when ductboard gets wet.
Due to heavy corrosion, cleaning condensate pans isn’t usually an option. While replacement is possible, removing and replacing condensate pans can be costly. Special equipment is often needed to lift heavy system components so that the pan can slide out and a new one can be put in place. Relining pans, however, is a cost-effective solution.
How the system was built (and the materials used) will determine what needs to be done to extend ductwork life. Galvanized sheet metal ductwork that is externally insulated does not typically present issues beyond routine inspection and occasional cleaning. Flexible ductwork that is improperly secured can loosen, causing conditioned air to flow into the ceiling plenum rather than occupied spaces. Duct liner can also affect system performance by coming loose and impacting air flow, and by getting wet and fostering mold growth. Inspect duct liners regularly for water damage, erosion, and delamination.
Duct components (mixing boxes, reheat coils, VAV boxes, and volume dampers) should be inspected on a regular basis. Typically, it’s not necessary to inspect each component annually; different areas of the facility can be inspected each year, resulting in a full inspection over a number of years.
Charles Cochrane is president at Cochrane Ventilation Inc. (www.cochraneventilation.com), based in Wilmington, MA.