In this article, we discuss some of the key elements to the efficient and effective operation and maintenance of rooftop air conditioning units.
Performance can be improved through the establishment of systematic rooftop unit maintenance. The performance and maintenance opportunities for rooftop units can be classified in accordance with the two internal fluid loops: air and refrigerant.
- Filters. To maintain indoor air quality and protect air handling units from accumulating dirt, clean filters are essential. Compared to mat filters, pleated filters offer better filtration efficiency and lower total running costs. Although pleated filters made with cotton or synthetic fabrics cost more, they operate better than flat filters made of fibreglass or spun polyester mats.
- Coils. Dirt also causes problems to the evaporator coil as it degrades the coil’s heat transfer efficiency thus reducing cooling capacity and decreasing the system airflow. The coil’s cleanliness should be checked annually by measuring the supply fan’s amperage and filter/coil pressure drop.
- Bearings. It is important to keep track of the lubrication and condition of the bearings. Older rooftop units have sleeve bearings which need to be lightly oiled two to three times per year, whereas newer fans are typically equipped with self-lubricating bearings. Even though new equipment does not require re-greasing, it’s important to keep an eye out for warning signs of forthcoming bearing failure such as noise, heat emanation and vibration.
- Belts. Fan belts should be checked and adjusted regularly.
- Motors. Supply fan motors installed by the original equipment manufacturer are generally standard-efficiency induction motors. It pays to specify premium-efficiency motors for new rooftop units or as replacements for burnouts in existing equipment.
- Outside Air Damper. Another common rooftop unit issue is improper outside air damper operation and cabinet leaks. Damper servicing can increase energy efficiency and indoor air quality.
- Charge. The refrigerant charge needs to be verified and corrected to avoid both overcharges and undercharges.
- Compressor. To avoid replacing the rooftop unit compressor, it’s important to establish electrical tests during annual checkups. Electrical tests verify the compressor motor health by measuring ground resistance of motor windings. The unit’s voltage can also greatly affect the compressor motor. For this reason, it is wise to install a protective phase monitor which turns off the power reaching the unit when voltage is out of tolerance and restarts when conditions are safe again.
Reference: The following article information was originally sourced from the ASHRAE Journal.