Another in Our Spring Air Conditioning Series...

Cleaning Coils Doesn't Cost - It Pays!

Air conditioning and refrigeration coils must be clean in order to transfer heat as designed; dirty coils result in running a system longer and harder to accomplish the same amount of cooling.

Longer system running times obviously result in higher operating costs. In addition, as the system works harder the energy consumption increases, as does the wear on the compressor. This additional work appears as an increase in compressor discharge (head) pressure, which is detrimental to the unit’s operating efficiency. Keeping coils clean will result in overall energy savings, better performance, and longer equipment life.

The function of the coil, either evaporator or condenser, is to transfer heat. As the air moves across the coil, heat from the air inside the conditioned space is given up to the evaporator coil; and heat from the condenser coil is given up to the outside air around the condenser. Any material that insulates the coil surface, such as dirt, dust, lint, grease, leaves, and cottonwood seeds or other pollen reduces the rate of heat transfer and increases the operating cost of the unit.

Manufacturer’s studies suggest that dirty coils can increase energy consumption by as much as 35 – 40%.

Considering the cost of electricity at a nationwide average of approximately $0.08/kWh, and air conditioner operation based on average annual use, the increased energy cost for a 10 ton rooftop unit with dirty coils could exceed $ 350.00 per year.

System cooling capacity also decreases as coils become dirty. The coil is designed to allow a relatively high amount of heat transfer, which decreases as insulating dirt adheres itself to the coil. As this fouling occurs, system capacity may fall below what is required to cool the space.

For example, a dirty condenser coil on a rooftop unit may lower the system’s cooling capacity by as much as 30%, thus a 10 ton unit would have only 7 tons of cooling capacity. This capacity loss affects building occupants when they need the cooling most, that is, on the hottest days.

A cooling system’s life expectancy is shortened by increased pressure and temperature in the compressor, which is a direct result of a lack of coil maintenance. If the unit’s compressor has to work harder, as it does when pressures and temperatures get higher, the potential for chemical breakdown of the lubricating oil increases. As the oil degrades, loss of lubrication causes increased equipment wear, leading to premature compressor failure.

By comparison, cleaning of the unit’s condenser coil, a process taking no more than 1 - 2 hours and requiring very little cleaning material, may cost the building owner up to $50.00 per unit for labor and materials. The net savings thus amount to approximately $300.00, or $30.00 per ton of capacity. This savings will vary, of course, based on factors such as the unit size and type, coil condition, energy cost per kWh, and hours of operation per cooling season.