Introduction

Unfortunately for indoor mushroom farmers, the very environmental conditions that produce bumper mushroom crops – subdued light, high humidity and cool temperatures – also promote mould growth in farm air conditioning systems, resulting in their premature failure, lower heat transfer efficiencies and exorbitant maintenance costs.

The background

For J-M Farms, in Miami city, Oklahoma, producer of 27 million pounds of produce annually, HVAC maintenance and energy costs for dozens of mushroom growing quarters were escalating exponentially and cutting into profits. J-M Farms is a wooden tray operation, in which final growing and harvesting phases occur inside unique satellite Quonset huts.

Case-in point

The problem:

Mushrooms thrive in 85% (±2-percent) relative humidity (RH) and 59 degrees F (15 degrees C) to 64 degrees F (17.78 degrees C) temperatures. Unfortunately, so do a myriad of undesirable mould varieties when harboured in an AC’s dark spaces and nourished by a perpetual supply of condensed humidity during 24/7 operation.

“All mushroom farmers experience similar HVAC coil mould challenges,” says Scott Engelbrecht, J-M Farms’ Growing Operations Manager.

As if coil maintenance costs weren’t enough, costs to replace units prematurely corroded from frequent exposure to cleaning chemicals were approximately USD 5,000 each.

The solution:

Hospitals, schools and other commercial buildings have installed ultraviolet germicidal irradiation (UVGI) in HVAC systems for years to keep coils clean of microbial growths for both maintenance and indoor air quality (IAQ) reasons, but the technology is new to mushroom farms, reveals Engelbrecht. Like many newcomers to UVGI, Engelbrecht was somewhat sceptical. He, therefore, took advantage of the “Free UV Trial Demonstration Programme” offered by Florida-based air purification manufacturer, Fresh-Aire UV. The programme offers building owners a free UV installation and 90-day performance analysis conducted by a certified HVAC service technician. The facility owner can choose to purchase the equipment or have it uninstalled at no cost.

The free installation included Fresh-Aire UV’s Tubular Rack UV System mounted to a recently cleaned air conditioning coil. It featured a 60-inch-long, 254-nanometer UV lamp with a Teflon-coating that minimises breakage and contains shattered glass and lamp gases if accidentally broken. The power supply and ballast carries a lifetime guarantee. The only maintenance required is a quick lamp replacement every two years to guarantee optimum performance.

Positive outcomes and sustainable initiatives

The trial coil showed no signs of the black, brown and slimy mould that typically coats coils after three months of 24/7 operation. Now Engelbrecht is rolling out the UV light retrofit of 42 remaining Quonset hut air handlers expedited by Service Solutions and assisted by in-house technicians trained by Fresh-Aire UV to install systems and replace lamps. He expects a payback of less than one year on each UV light system when considering the reduced maintenance costs and the HVAC units’ extended lifecycles due to less cleaning chemical exposure.

UV light systems offer additional benefits beyond coil cleaning, such as killing airborne mould spores related to diseases that affect mushrooms and reduce harvest outputs. “What mushroom farmers grow is technically a type of mould,” Engelbrecht explains. “So our environments can potentially create undesirable competing mould or mould-generated diseases that affect the mushroom crop.”

Conventional particulate media filters can entrap mould spores. However, they continue to live and reproduce within the system. UV light systems, on the other hand, provide chemical-free disinfection that scrambles the microbe’s DNA, so it can’t reproduce. Not all UV light is the same. UV-A (used for black lights), UV-B (used in tanning salons and causes sunburns) and UV-C wavelengths are all present in sunlight. However, higher frequency UV-C wavelengths are filtered by the Earth’s upper atmosphere. Therefore, microorganisms, such as mould have no experience or defense against it. UV-C light is strong enough to sterilise microbes, but not enough to degrade an HVAC system’s coil or interior surfaces.

Before installing UV light systems, J-M Farms satellite operations was hiring local HVAC contractor, Service Solutions Inc, for quarterly in-unit cleanings on more than 40 Quonset hut air handlers, costing nearly $20,000 annually. That figure did not include maintenance for more than 50 other coils ranging from 24×36-inch to 48×96-inches providing cooling to phase II brick/mortar spawn and setback rooms. While expensive, the coil cleaning was critical to improving static pressure by 15% to 20%, which was proven with post-cleaning airflow tests using an anemometer manufactured by Utah-based Weather Hawk.

Additionally, Service Solutions and J-M Farms’ in-house maintenance staff has had to recondition all the operation’s HVAC coils. This process requires removing a dirty coil, replacing it with a spare coil and then deep-clean submerging it in a chemical solution for two days. The clean coil is then reinstalled to replace another dirty coil, which starts the process again. The staff also streamlined the reconditioning process by customising the air handlers with coil isolation valves and flange fittings.

The air handlers run 24/7, and typically bring in large amounts of outdoor air to maintain CO2 levels at 1,000-2,000-ppm. CO2, temperature, humidity and even compost temperatures are all monitored and controlled by a building automation system (BAS) manufactured by Netherlands-based Fancom. The BAS controls all the set points via the 8,000-cfm air handlers, manufactured by Carrier.

J-M Farms’ staff has also constructed some of its own air handlers to handle the heavy cooling and humidity load demands of mushroom farming. The Quonset hut air handlers are each supplied typically by two 80-tonne Carrier chillers. Air is distributed through clear plastic 24-inch-diameter duct runs in the middle of each Quonset hut. The Quonset huts themselves are steel-framed structures with concrete pad foundations and R-20 insulated, nylon-reinforced plastic walls and ceilings.

Conclusion

For Engelbrecht, his UVGI discovery represents a chemical-free, maintenance-free cleaning process that does not degrade coils and provides an optimal energy-saving efficiency. “I don’t know why the mushroom industry hasn’t discovered this previously,” Engelbrecht says, “but they should certainly know about it.”

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