Clean those filthy coils

March 29, 2000
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Gary McCorquodale’s customers have “got the dirt” on coils in his humble town. He goes in and gets the dirt off.

McCorquodale is the manager of the Coil Cleaning Division of Service Refrigeration Co., a contractor in Humble, TX, just outside Houston. He doesn’t claim to be stronger than dirt, but no dirt has gotten the best of him yet.

His division does 100% coil cleaning and concentrates on commercial jobs.

Pointing out the problems that customers will see with dirty coils, he noted that on condenser coils, dirt “makes you run with a higher head pressure.” For evaporator coils, it causes “low airflow and low suction pressure, which has a tendency to flood the compressor back.”

Presenting the example of a 10-ton unit using a Copeland 9RJ compressor, McCorquodale said that with a clean condenser coil at 168-lb pressure, “You’re getting the equivalent of 10 tons of cooling at 27 amps.” If that condenser is dirty, it can raise the head pressure to 298 lb, “which reduces the capacity to about 7.5 tons and increases the amperage to 32.75 amps.”

All dirty systems are affected like this, he said.

Besides reducing system capacity and increasing costs, a dirt buildup will also increase heat — a major problem.

“Heat on the compressor is what knocks them out,” stated McCorquodale. “A dirty condenser coil will also shorten the life of your fan motors because it’s running too hot.”

Dirty coils can also lead to Sick Building Syndrome problems, due to the microbiological growth that can be generated.

Coils that haven’t been cleaned can have quite a buildup of dirt and may be clogged with debris.

“It’s unbelievable how dirty some are,” McCorquodale said. He’s cleaned systems that had “as much as an inch of dirt in them.” When he shows people pictures of their system before cleaning, they can’t believe it could be that dirty.

Wash and vacuum

Service Refrigeration’s coil-cleaning crews remove the dirt from coils by washing and vacuuming them. For each two-person crew, one sprays the coil while the other continuously vacuums out the water.

Their truck gives them up to 600 ft of hose to access the job. The specially designed nozzle allows them to spray up to 35 gpm running at 1,500-lb pressure. McCorquodale remarked that the crew can do this high-pressure spraying without damaging the coils.

This equipment allows the crew to clean faster, he said. “But the main thing is, it’s more efficient.” They’re able to get virtually all the dirt out of the coil.

Surprisingly, the truck sprays only water; no coil cleaners are used. “We clean the coils until the water is clear,” he explained.

Despite the fact that he has encountered some incredibly filthy coils, McCorquodale said he hasn’t yet come across a coil he couldn’t clean with his equipment. He related that he was cleaning a unit in Houston where the dirty coil was 17-in. thick and he had to hit it with a full 35 gpm to penetrate it. After finishing the cleaning, the building’s maintenance man was able to shine a light through the coil.

Besides coils, other components need to be inspected and cleaned as well.

“On air handlers, it’s very important to clean out the drain pan,” McCorquodale emphasized. “We get buckets and buckets of stuff out of these units — mold, algae, slime.”

Usually every two years, he said, is sufficient for cleaning the pan.

He also noted that a lot of people won’t bother cleaning the dirt out of the transition when cleaning coils. “Of course, when they don’t do that, it’s just going to be sucked back in.” Another important cleaning chore is to flush the drains.

Keep it clean

The advantages of keeping coils clean include:
  • Equipment operates cooler because it’s removing more heat.
  • You have lower operating amperage, resulting in lower operating costs.
  • Compressor capacities are maximized resulting in less run time.
  • Equipment lasts longer.

To demonstrate the savings achievable, McCorquodale cited an example of 10-ton unit, based on 2,000 cooling hrs, with a design temperature of 95°F, using Houston electricity rates. With a clean condenser, the operating cost is $2,214. With a dirty condenser, the cost is $3,024.

So in this example, it costs $810 more to cool the building when the coils are dirty.

Regarding how often to clean coils, it depends on the application. In supermarkets, if the fresh air damper is closed, he said, it may be every two years. For some customers, his crew goes back once year.

“For some applications around cottonwood trees, you may have to go twice in the summer.”

But no matter how caked in dirt coils may be, the Service Refrigeration crew doesn’t leave until they’re fully clean.

“I can honestly say the units are like brand new, as far as airflow going through, when we’re finished with them,” said McCorquodale.

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coil cleaning

david jacques
February 13, 2009
i have resently starte working in a hotel in the maintenance department. please explain how to clean the coils of a wall unit that uses water to heat and cool. a fan circulates the air. my e-mail is walt1160@yahoo.com

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