Proper maintenance of facility HVAC systems can result in many benefits. These include lower utility bills, increased service life of the equipment, and better comfort and health for the occupants of the building.

Correct filter specification and servicing is an important aspect of HVAC maintenance. ASHRAE assigns an efficiency rating to filters which relates to their ability to remove small particles. Using a filter with a higher efficiency can improve indoor air quality. Pleated filters utilizing cotton or synthetic fibers will cost more than conventional filters, but will result in an increase in filter efficiency and increased effective filtering area.

Filters capture dust that can serve to promote mold growth. Therefore, filters need to be replaced at frequent intervals. Depending on the type of HVAC system this may be as often as monthly or as infrequently as every six months. It is best to inspect filters on a monthly basis to determine when they should be changed. Once inspected, a replacement frequency can be determined and recorded in the unit’s maintenance log. Because filters are changed on a regular basis, filters should be easily accessible. It is a good maintenance practice to install easily removable panels (if not already in place) to allow fast filter inspection and change out.

The cleanliness of evaporation and condenser coils can directly affect HVAC capacity, efficiency and operating costs. In general, these coils should be cleaned once each year. Because of the damp environment under which evaporator coils operate, and because the coil is in contact with humid outside air and dirt not caught by the filter, mold is often growing on the coils.

The condenser coil, which is exposed to unfiltered outdoor air, suffers considerable degradation due to dirt buildup. While the condenser coil does not affect indoor air quality, cleaning this coil the same time the evaporator coil is cleaned will maintain the efficiency of the system.

Coils soiled with microbial growth are hard to clean. An appropriate cleaning solution is necessary to effectively remove all microorganisms. Often these solutions must be applied and left in place for a specific amount of time before being rinsed off. It is tempting to use an aggressive (high acid or caustic) cleaner. Such overly aggressive cleaners can damage metal surfaces. Damage can range from pitting of surfaces that interferes with rapid flow of condensate from fin surfaces to accelerated structural deterioration of components. Residues from such cleaners can also contaminate the indoor air if not fully rinsed. Keeping the coils clean through frequent maintenance and appropriate treatments will dramatically reduce the time required to complete this job.

As previously mentioned, energy savings is another reason to keep coils clean. A study completed by Pacific Gas & Electric indicates that the compressor efficiency of a 10 ton package unit can be improved 16 percent simply by cleaning the evaporator and condenser coils. These savings can pay for the time and materials to keep coils clean.

The area around the air intake should be inspected at least twice each year. Water can pool around air handlers, particularly those mounted on roofs. And, any place where water acuminates mold can grow. Mold near the air intake will increase the likelihood that spores are sucked into the ventilation system. Make sure that no standing water is allowed to gather around the air handler.

Cabinet and supply ducts should be checked annually for air leaks. Annual checkups should include a survey of air leaks and corrective action such as replacing screws or latches, and patching or replacing gaskets. Cabinet and duct integrity is particularly important on the supply-air side, because conditioned air is at high pressure and easily forced out through even small holes.

One of the most common problems with HVAC equipment is improper damper operation. This can negatively affect indoor air quality and also increase electric consumption. Unless they are kept clean and well-lubricated they can stick, causing improper unit operation. During servicing, moveable surfaces should be cleaned and lubricated.

After cleaning and lubrication, a damper should be run through its full range of movement to make certain it is working properly. After this is done, the damper set-point should be checked and adjusted if necessary.

While proper operation of fans, bearings, and belts has minimal impact on indoor air quality, to increase overall unit reliability and avoid unscheduled downtime, these components should be checked (at the beginning of the heating and cooling months) every six months. Impeller blades on a forward curved fan can fill up with dirt, lowering efficiency and air flow. Cleaning fan blades is time consuming but will restore fan efficiency to its original condition.

Often, fan motors are found to be running in the wrong direction. Because they still supply perhaps 50 percent of rated flow even running backward, this may not be readily apparent. The most common cause is switched wire leads on the motor. Clear labels on the fan housing, pulleys, motor and wires can help prevent this problem. Fans which are unusually noisy or vibrating excessively should be serviced. Sometimes a piece of insulation or trash caught in a fan will cause excessive vibration.

Improperly adjusted belts rob the drive-train of power, create noise and must be replaced sooner than well-adjusted belts. Belts should be aligned to prevent lateral wear. Proper tension should be maintained, loose belts slip on the pulley wheels causing torque loss and rapid wear. Belts that are too tight put an excessive load on the motor and fan shaft bearings, causing early failure of the bearings and/or belts.

There is no firm guideline regarding the frequency of cleaning supply and return air ducts. It will depend on the maintenance of the HVAC system (a well-maintained system will put a lower dirt load into the ducts) and the use of the building. The North American Duct Clearers Association (NADCA) recommends inspecting supply side and return air ducts every two years (annually in hospitals). If the inspection reveals contamination, the ducts should be cleaned.

HVAC is a necessary and important component of modern life. The proper maintenance of this equipment can reduce operating costs and provide a safer, healthier environment for humans. Hopefully, the above information has provided some useful tips concerning the proper maintenance of HVAC equipment.