For many cash-strapped school districts, shutting down HVAC units in unused buildings for part of summer vacation to help cut cooling costs is an annual routine. However, this can lead to issues with humidity, mold, odors, and more inside the school, not to mention the potential mechanical problems that can arise from letting equipment sit idle for long periods when it’s not designed to do so.

But, there are things contractors can do to get this equipment back online and ensure it’s operating as efficiently as possible in time for the first school bell this fall.


While some schools’ HVAC systems run all summer to accommodate teacher workshops, renovations, summer camp, and more, others sit unused — and often forgotten about — for part or all of the summer season.

“Most schools sit idle with limited HVAC use for two to three months each summer,” said Alan Wozniak, president and CEO of Pure Air Control Services Inc., Clearwater, Florida. “While some schools will turn off their systems completely, others simply increase the building temperature when students and faculty are not present. This ‘duty cycling,’ as we call it in the industry, is primarily used to save energy and money, but it can have its consequences, such as higher humidity levels; musty rooms due to higher interior relative humidity; and microbial growth on building surfaces, furnishings, and HVAC systems.”

Wozniak said humidity is the most common problem he encounters. “[This] can cause ‘dirty sock syndrome,’ where the facility begins to retain a smell — a mustiness — from microbial growth on the building surfaces, furnishings, and HVAC systems. As a result of the elevated humidity, as well as microbial burden, occupants with sensitivities will often experience allergy-like symptoms — coughing, sneezing, wheezing, etc.”

In some cases, the problem may transcend simple mustiness, said Douglas Lindstrom, owner, Lindstrom Air Conditioning & Plumbing, Pompano Beach, Florida. “If the unit is not cycled and run enough, the building can experience sick building syndrome.”

Dan Jones, president of UV Resources, agreed. “When school buildings are shuttered during summer months, the dark, warm, and wet environment generates the perfect breeding ground for biological proliferation. Even after the moisture is gone, the dormant biologicals begin to grow again when moisture is reintroduced — for example, when school begins and children are present.”

The equipment itself can also be negatively affected by sitting unused for so long, said Greg Crumpton, founder, technology and business development, AirTight FaciliTech, Charlotte, North Carolina. “Motors are made to run. When a system has been idle for a while, bearings and shafts — and, really, any lubricated part — may have to run for a while before they get up to temp and are back to peak efficiencies, but they will come back. Coils dry out and can leave behind a weird smell, [and] P-traps dry out from no condensate flowing; really, though, these things are short-term, and, typically, within a week of normal operation, you are good to go.”


Before starting up idle equipment, reputable contractors recommend performing routine maintenance on all equipment and thoroughly cleaning the units — especially the coils.

“I suggest normal operational and functional preventive maintenance per the OEM’s recommendations,” Crumpton said. “These will include air filter replacement, cleaning of the indoor and outdoor coils, drive package adjustment, possibly a fan belt change, and a full complement on the electrical and refrigerant systems for functionality.”

Wozniak said facilities managers should “have the evaporator coils, blower assembly, and interior components of the rooftop unit or air handler environmentally cleaned to minimize the microbial burden within the HVAC system and surrounding areas.” To improve IAQ and system performance, he added, contractors should “add some type of dehumidification to the building to keep up with the latent moisture removal needs” and “use a bound, topical antimicrobial application to all surfaces — this will make it difficult for microbial propagules to spread.”

Keith Springstead, field service supervisor, Pleune Service Co., Grand Rapids, Michigan, said the first thing he likes to do is to “clean out the condensate trap and pan.” Then, it’s on to “filters, belts, bearings, checking the charge, and conducting an amp draw of the compressor and condenser fan motors.”

In addition to ensuring improved IAQ, cleaning indoor and outdoor coils helps improve equipment efficiency and should be a part of preventive maintenance, said Mike Hardy, managing director of SpeedClean.

“There have been studies done by utility companies that show fouling of coils can increase the electrical load by up to 40 percent,” Hardy said. “You’re reducing your cooling capacity by 40 percent and increasing your energy load by 35-40 percent. Clean coils maximize the heat transfer, and it’s not something that should be shortchanged in any budget — it should be an active part of any maintenance or any indoor air quality program.”


When it comes to cleaning and servicing idle rooftop units and air handlers, different contractors prefer different methods and products. Additionally, the age of the equipment plays a role in how and with what it is cleaned.

“As easy as it sounds, compressed air, or nitrogen, go a long way in keeping equipment operating, along with some fresh water,” Crumpton said. “We have to remember that, in today’s world of high-efficiency equipment, the tried-and-true chemicals of yesteryear could come back and haunt us today. Know what the product requires, spend some time on your smartphone, and actually read the OEM’s recommendations. They built the equipment; our customers hire us as professionals. That has to extend all the way to the smart end of the water hose.”

“I like to use Nu-Brite condenser coil cleaner,” Springstead said. “The other is Nu-Calgon Pan-Treat.”

Wozniak suggests limiting chemical cleaning of the evaporator coils because of the environmental impact the chemicals themselves may have. “Pure Air Control Services recommends a chemical-free Green Clean Institute (GCI)-certified green process called PURE-Steam Coil Cleaning. The process uses proprietary 350-degree steam at approximately 350 psi with a high-volume combination to provide a deep cleansing and sanitization of the evaporator coils.”

Maintenance visits are also a good time to consider implementing products that can help improve IAQ and system efficiency, even when the units have been shut down for the summer. UV-C lights, which help prevent microbial growth on the condenser and evaporator coils while the unit is not in use, are one such option, Jones said.

“While the HVAC systems are shut down over the summer, it is recommended that the UV fixtures remain on, continuously cleansing the coil and inside of the system — this can use as few as 25 watts,” Jones said. “In the fall, when classes resume, the ultraviolet energy will have cleaned and maintained the coil and many other components. Therefore, there will not be the typical biological growth to create additional pressure drop, lower airflow levels, or impede the coil’s ability to remove heat. In other words, the tech will have no issues typically caused by a dirty coil.”

Scott Hetchler, construction manager, John C. Cassidy Air Conditioning Inc., Riviera Beach, Florida, prefers the Magnetic Mount Package Air Purification System from RGF Environmental Group Inc. “The RGF product limits the need for cleaning up the systems on startup,” he said. “Because the light will help keep them clean during the summer when they are not being used, this could save time and labor.”

“RGF’s product helps prevent sick building syndrome, which can lead to a variety of problems that would need to be addressed,” Lindstrom added.

Regardless which methods a particular contractor or technician uses to clean and service HVAC equipment in schools, the most important thing they can do is be thorough.

“It’s tough,” Hardy said. “It’s a school, and you’re running against the budget. Don’t take shortcuts — do it right the first time. That way, you don’t have a callback, and the equipment is functioning properly. You should maintain the unit as if your kid was going to school there.”

Publication date: 8/3/2015

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