The need for cooling never ceases, even in winter. We stressed this point in our introductory post about preparing for cooling system challenges, and we believe it bears repeating. Your HVAC equipment is vital to the smooth operation of your facility – and your tenants’ comfort and satisfaction. It is imperative, then, that you prepare your HVAC system for cooling system challenges, no matter what time of year it is.
As a starting point, we recommend three fundamental steps as part of any preventive maintenance (PM) cooling season program: 1) performing an electrical inspection of the system and 2) cleaning the condensing and evaporating coil.
Through our years of experience in the field, we have found that heating systems generally are more reliable over time than cooling systems. A big reason why is that electrical supplies usually are less taxed in the winter, so units draws less current.
During hot summer months, many communities face “brown outs” which translated, means low voltage. Quoting from an electrical trade school textbook: “Low voltage and single phasing are the two greatest enemies of three phase motors.” Overheating due to low voltage or voltage imbalance will reduce the life of all motors and compressors. “In fact,” says Jean Revelt, Motor Product Manager from Lincoln Electric Company, “…if two motors are operating at a 100 C differential, the one at the higher temperature will have only half the life of the cooler motor.”
Every city, town and state in the country faces the possibility of a brown out. For this reason, we at CLS Facility Services recommend that electrical power wiring be tightened inside the disconnect switch, terminal blocks and contactor as part of regular cooling PM service. Tightening all of connections reduces the resistance of each connection, allowing maximum voltage available to an HVAC unit. A qualified technician will also look for evidence of overheating in the electrical system and correct the problem.
Cleaning the Condensing and Evaporating Coils
Clean coils maximize heat transfer at the coil surface, so it’s essential to keep them free of the buildup of all forms of debris that harm efficiency of your equipment. There are three basic ways to clean a coil:
- The easiest and least expensive way is to brush clean the coil with a soft brush. For comparison’s sake, this would be similar to cleaning the lint in a household clothes dryer’s metal filter.
- Second, you can spray the coil with a detergent from a hand sprayer. All coils that are sprayed should be rinsed after spraying, allowing them to stay wet with detergent for 15 minutes or more. This procedure is relatively simple and does not use much cleaning solution. If done regularly in conjunction with a good filter program, you will dramatically reduce the need for pressure washing the coils.
- Finally, you still can pressure wash coils. Pressure washing equipment is similar to coin operated pressure wand car washing equipment – albeit with significantly greater water pressure. Pressure washing can be expensive, since it is necessary to bring the equipment onto the roof, locate a water supply on that roof, and then secure 110 volts to operate the pump. Pressure washing does the most effective job of cleaning coils, but setting up the equipment is labor intensive and uses more cleaning solution.
Coil Cleaning: Effects on Heat Transfer and Energy Consumption
Both the condensing coil and the evaporator coil in an HVAC unit should be clean at the start of each cooling season. The condensing coil must be clean because it rejects or transfers the heat from the building it is cooling, as well as the heat of compression from the compressor into the air that passes over its surface. This is comparable to the radiator of a car that rejects heat from the engine. The water acts like the refrigerant – again, the heat is transferred to the air that passes over its surface.
The cleaner the coil, the less electric power you must purchase, and the lower compression ratio your compressor will experience. From both an electrical and mechanical standpoint, a lower compression ratio reduces compressor failure. Usually, it is sufficient to wash the coil with a hand sprayer loaded with a properly inhibited alkaline detergent. The detergent also should have a neutral or pleasant smell. We do not recommend “brightening” a coil by removing a layer of aluminum oxide.
To efficiently condition the air inside a commercial space, heat transfer surfaces must be free of dirt and other residue such as biological contaminates. The evaporator coil must be clean, because it absorbs heat from the return air passing over its surface. The cleaner the coil, the more heat it can absorb, thus increasing the overall efficiency of the air conditioning unit.
A clean evaporator coil will reduce electrical consumption and also reduce the compressor compression ratio, leading to longer compressor life. When cleaning the evaporator coil, the first step is to use the same detergent described above for use on the condensing coil. The cleaning solution with a pleasant or neutral odor is now more important than on the condensing coil, because the cleaning solution odor will migrate into tenant spaces. After cleaning the coil with a detergent, rinse and then spray the coil with a sanitizing algaecide.
Next, clean the drain pan and drain line. It may be necessary to run a “snake” through the drain piping or disconnect the piping in order to clean it. Clean the drain pan with a brush, and then flush with an algaecide. Put time-release chemical treatment tablets or a bar in the condensate pan to keep the water flowing.
In our next installment, we will provide a list of cooling season maintenance checks. In the meantime, if you want to learn more about CLS’s national HVAC services call us at 800-548-3542.