More than 18,000 CoolBots use standard window air conditioners to turn super-insulated rooms into walk-in coolers. These cooler systems cost significantly less up front than conventional compressor-cooled walk-in refrigerators or coolers. Conventional coolers also use more electricity, cost more to repair and tend to dry out greens.
CoolBot systems are ideal for users who access their cooler less than five times per hour and want to maintain a cooler temperature of 37° F or higher. These users will save the most electricity compared to using conventional coolers. Users who seek 36° F will need to open the door less often and be patient while the temperature drops to 36°. These users will save some electricity compared to using a conventional cooler.
Users who need coolers to maintain temperatures below 34° F should use conventional coolers with compressors.
Anyone can build a super-insulated room. Used refrigerator trucks or refrigerated shipping containers work well. Used equipment like this often saves people money over building a new super-insulated room. The industry standard for walk-in cooler insulation is 4” of rigid foam insulation in walls, ceiling and floor (minimum R-24).
Whether using a truck body or shipping container, remove the 3-phase refrigerator unit. Install a tight-sealing insulated door. A typical 8’ x 10’ x 7’ high super-insulated room can be chilled by a standard window air conditioner.
For his farm’s second and third walk-in coolers, Skip Paul of Wishing Stone Farm in Little Compton, RI purchased a 40’ refrigerator container. Paul installed PVC strip doors and built an insulated wall across the middle. A separate CoolBot and air conditioner will cool each room. The two spaces will have different temperatures and humidity levels for storing various crops. Paul recommended buying big box stores’ extended warrantees on air conditioners.
“When we built our super-insulated room we used 2 x 6 rather than 2 x 4 lumber,” said Paul. Changes in thermal properties and air leaks are challenges, Paul said. He installed a narrow strip of rigid foam insulation to the inside of the 2 x 6 studs and attached 2” rigid foam panels to the outside of the plywood before adding siding. He had a local contractor blow in expansion foam between the studs creating nearly 8” of insulation in the walls. His cooler walls have washable fiberglass panels inside. The cooler ceiling has 10” of insulation. The floor has 4” of rigid foam insulation below and 2” of insulation around the sides of the foundation.
Cooler door openings should include PVC strip doors or strip curtains as well as insulated doors. Paul purchased a salvaged oversized door from a restaurant supply company, cut it to size and used barn door hardware to hang it. An auto salvage yard supplied the windshield gasket Paul installed as a door gasket. Paul recommended installing a latch that pulls the door tight against its gasket.
Paul advised keeping a small fan running to the side of the air conditioner to maintain air movement, which prevents condensation and mold growth and also minimizes pooling of produce outgases and early spoilage.
CoolBot controllers, which were invented by Ron Kholsa of Huguenot Street Farm in New Paltz, NY, cost about $300. Khosla’s website says most good air conditioners running with CoolBots should last up to 20 years. Installation is quick and simple.
Standard window air conditioners do not cool below 60° F. CoolBot use a micro-controller that overrides the air conditioner settings to keep a walk-in cooler or super-insulated rooms between 34 and 40° F. CoolBot sensors install quickly and easily. CoolBots utilize most, but not all, air conditioners’ BTUs. Khosla recommended buying one size larger than the standard recommendations for the cubic feet of the cooler. Further upsizing will offer faster cooling and recovery after door opening. Paul recommended buying the largest window unit sold at your nearby big box store.
CoolBot systems cool down slowly. They recover temperatures more slowly after their doors are opened compared with conventional coolers with compressors. CoolBots systems are ideal for keeping kegs cold at breweries, pubs and restaurants. Few people access those coolers each day.
CoolBot coolers and conventional coolers can remove field heat. Paul recommended putting greens and produce into coolers after washing. The cold wash water removes field heat five times faster than air-cooling. Fast chilling of greens, produce and fruit improve post harvest quality and shelf life.
Khosla recommended purchasing GE, LG, Haier or Samsung air conditioners. Paul said he planned to add a thermostat and fan to pump in cool air when outside temperatures matched his produce needs.
Ben Wolbach of Skinny Dip Farm in Westport, MA said he had a thermostat and portable space heater in his cooler. When winter temperatures made his cooler too cold (below 35° F), the CoolBot and air conditioner turned off and his heater turned on. When temperatures were marginal, he sometimes left the light on to add just a little heat.
Khosla recommended matching the air conditioner size to the walk-in cooler area*:
• 6’ x 8’ —10,000 BTU
• 8’ x 8’ —12,000 BTU
• 8’ x 10’ —15,000 BTU
• 8’ x 12’ —18,000 BTU
• 10’ x 14’ —24,000 BTU
* For CoolBot system at 38° F with 8’ ceiling, opened up to 4 times/hour.
Restaurant coolers must maintain temperatures below 40° F. Most users want a buffer and set their coolers to 38° F. Users who want a more consistent temperature near 36 degrees F should upsize the air conditioner at least one size. If the cooler will be opened six or more times/hour, Khosla recommended upsizing two sizes.
Florists and convenience stores with glass doors on their display coolers need to upsize their air conditioner at least two sizes. Customers will be opening these coolers frequently. Glass is not a good insulator. Florists should upsize one level to accommodate a lower fan speed to reduce drying.
Users who need 50° F for wine coolers, cheese caves or meat curing rooms can downsize air conditioners from the table above.
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