The short answer is plenty! Dirty coils, or anything that blocks the free flow of air into or out of the evaporator and condensing units for your walk-in cooler’s refrigeration system can cost you in several big ways:
- It will cost you more in electrical energy to run all of the system’s components longer and harder, especially the compressor.
- Your refrigeration system may not be able to keep up and a too high temperature may prompt you to call for expensive emergency service.
- Perishable food in your cooler may, in fact, perish, and have to be thrown away to protect your customers’ health and your reputation.
- Your equipment may fail prematurely due to the increased strain dirty coils place on its operation. Refrigerant can return to the compressor as a liquid and cause it to fail due to “slugging”. Replacing a compressor is a capital expense that you would probably want to put off until another day.
Unfortunately, cleaning evaporator and condenser coils is one of the most overlooked commercial refrigeration maintenance jobs there is. Although your coils are always getting dirtier, even right now as you read this, it is much easier in the short run to just ignore the problem and hope it won’t catch up with you. However, given enough time, it always will. The longer you go between coil cleanings and the dirtier they get, the more it can cost you. It is much smarter and cheaper in the long run to have your refrigeration technician to institute a regular preventative maintenance program with coil cleaning being one of the top priorities. How often is regular? Cleanings should certainly happen at least yearly and perhaps as often as monthly, depending on how dirty the environment is in which the coils are operating.
Having clean coils makes your system more efficient. Evaporator coils pick up heat from the air circulating inside a walk-in cooler. Condenser coils transfer that heat to the air outside the cooled space. Just by having the evaporator and condenser fans operating and pulling air through the coils, dirt and dust is deposited on them. Dirt and dust are poorer conductors of heat than bare metal, so it takes air passing through dirty metal fins that are attached to the coils of the evaporator and condensing heat exchangers for a longer time to exchange the same amount of heat as clean fins. Dust, especially, can build up over time and reduce the spaces between the fins, so that less air is able to pass through the fins with the same amount of fan power. Let the crud build up as badly as the evaporator shown above, just like an evaporator coil covered with frost that chokes off the airflow, the efficiency of your refrigeration system will suffer due to increased compressor and evaporator runtime.
Without accurately testing the electrical energy going into and the heat coming out of your particular refrigeration system, before and after a coil cleaning, it is impossible to state for certain how much those dirty coils are costing you. Based on such testing of several randomly selected commercial refrigerators and freezers, the Food Service Technology Center estimates that dirty condenser coils alone are costing the owner of a typical commercial refrigeration unit between $220 and $625 a year in electric energy waste. Assuming an average of $400/unit/year that amounts to a total of $9.7 billion annual loss for the estimated 27 million commercial systems in the U.S. That’s a lot of wasted energy and money!
Many energy-related organizations warn of the danger of neglecting coil cleaning. The U.S. DOE advises that “a dirty condenser coil can increase compressor energy consumption by 30 percent.” and recommends inspecting coils a minimum of once per year. Pacific Gas & Electric (PG&E) also suggests an annual coil cleaning to its commercial customers as part of its ongoing efforts to promote energy-efficient HVAC-system operations.
The Federal Energy Management Program (FEMP) did a study that had some specific findings: “A dirty condenser coil that raises condensing temperature from 95°F to 105°F cuts cooling capacity by 7 percent and increases power consumption by 10 percent, with a net (compressor) efficiency reduction of 16 percent. In a 10-ton unit operating 2,000 hours a year, this wastes about $250 per year in operating costs. A technician can clean the condenser coil in about 1 hour, which typically costs about $50. In this example, the payback takes just over 2 months and delivers a net annual savings of $200.”
To make matters worse, dirty condenser coils are perhaps even less than half the story. That is because there are two types of heat exchangers in almost all refrigeration systems that collect dirt from the air passing through them: condenser coils, located outside the cooled space, and evaporator coils, located inside the cooler. Evaporator fans usually run all of the time, or about twice as much as a typical condensing fan, so they have twice the amount of time to collect dust and dirt from the air passing through the fins. And, unlike air conditioning systems, evaporators for refrigeration systems do not have filters that can be replaced, so the dirt builds up on, and in between, the coils and fins themselves.
While also delivering less air, all types of evaporator fan motors themselves consume more energy whenever the airflow is constricted. The Northeast Energy Efficiency Partnership (NEEP) performed tests in which the airflow through an evaporator unit’s coils was blocked in varying amount by sheets of styrofoam to simulate blockage by dirt and dust, frost, or boxes of product stored too close. They found that an old-fashioned shaded pole motor’s used 104 watts when air flowed freely through the unit, but that it increased 20% when they completely shut off the flow of the air, like what one might see with a totally frosted evaporator. An energy-efficient ECM evaporator motor of the same size fared even more poorly, relatively speaking, by burning 43 watts with clean coils and 60% more, or 69 watts, with the styrofoam covering all of the coils. Blocking the airflow in by 75% and an ECM used 23% more energy. Even blocking the flow of air out of an evaporator by only 50% increased the power consumption of either kind of motor about 16%. There are cardboard boxes on shelves in front of evaporators in many walk-in coolers in the real world that block more airflow than that.
The FSTC advises that you need to:
- Raise the evaporator temperature by efficiently moving as much air through the evaporator coils. This can be done by regularly (at least quarterly) cleaning the evaporator coils, straightening any bent fins, being sure that the coils are completely defrosted without ice remaining after a defrost cycle, and not blocking the flow of air into or out of the evaporator.
- Lower the condenser temperature by efficiently moving as much air through the condenser coils. This can be done by regularly (at least quarterly) cleaning the condenser coils, straightening any bent fins, and not blocking the flow of air into or out of the condenser.
So the question is: When was the last time you had your coils cleaned?