Summer 2009

The CoolBot “fools” an air conditioner into thinking that the temperature in a room is 65 F, even when it is much colder. The small device enables growers to turn a storage room with an ordinary air conditioner into a cold storage facility. Photo by Phil Norris.

By Phil Norris

Now and then an invention comes along that is so good that it changes forever the landscape of its own branch of technology – the telephone, the light bulb, the computer, etc. While the CoolBot’s influence may not be so earthshaking to the average person as those three examples, it is a breakthrough for the small farmer.

The CoolBot is an electronic device about the size of a paperback book that, in conjunction with an ordinary consumer-type air conditioner, becomes the heart and brain of a walk-in cooler.

The Need

One of the issues of small farming is cold storage. The zucchini needs to be picked today, but the farmers’ market isn’t until Saturday. The refrigerators in the house and barn are full. So what do you do with all that beautiful produce until then? You need a walk-in cooler.

Walk-in coolers have been around for decades, but their cost and complexity put them out of reach of many do-it-yourselfers. Compressors and evaporators must be installed and lines charged with liquid refrigerant. The know-how to put together a walk-in cooler is not part of the vernacular of the average farmer but is a specialized field. When a tractor needs to be repaired, a farmer reaches for the toolbox; but when the refrigeration goes out, the farmer reaches for the telephone.

The CoolBot is changing that. If you can throw up some studs in a corner of the barn, cover them with 4 inches of foam insulation and plywood, and cut an air conditioner-sized hole in the wall, you can build your own cooler.

Organic Inventor
Ron Khosla, an organic farmer and the inventor of the CoolBot, developed it for use on his own farm.

“It was totally out of necessity,” he said. “I couldn’t afford a cooler.”

Ron and his wife, Kathryn, run Huguenot Street Farm, a 200-member CSA in New Paltz, New York. Khosla spent many hours trying to make various kinds of air conditioners go down to 32 F. He admits that several air conditioners “gave their lives” in the pursuit of his goal.     

Khosla eventually was able to make an air conditioner cool a room to 32 – but only if he monitored it constantly. Then he enlisted the help of a college friend to develop the electronics to do the monitoring.

The CoolBot has a microcontroller that becomes the “brain” of the air conditioner. It fools the air conditioner into thinking that the temperature in the room is 65 even when it is much colder. Ron figured out an ingenious method to accomplish this without changing the air conditioner circuitry: A small square of aluminum foil holds a tiny heating element against the temperature sensor of the air conditioner. The CoolBot also employs a temperature sensor that detects when the air conditioner is getting too cold and starting to ice up. At this point, the air conditioner is allowed to idle until the ice melts.

Reached by phone about the CoolBot, Khosla was effusive about his invention. He has been surprised at how quickly sales have ramped up with virtually no advertising; his best PR has been word-of-mouth.

The first CoolBots went on sale in 2006. Khosla said that he gave a lot of them away that year so that people could test them for him. In 2007, word started spreading, and his product was in demand.

When asked whether the CoolBot is mass-produced, Khosla laughed. He, his wife and a helper assemble all the CoolBots on the N.Y. farm. He estimated that by the end of January 2009, they will have sold 1800 units. The CoolBots sell for $300.

Successes in Maine

At Morning Dew Farm in Newcastle, Maine, Brendan McQuillen and Brady Hatch think the CoolBot works pretty well. They have a 6-by-10-foot CoolBot cooler that they built to store their greens, lettuce, summer squash and other produce.

“We’ve worked it pretty hard, jam packed full on hot summer days, and it has performed well,” said McQuillen. “It’s a really good solution for the scale we’re at.”

Ginger Dermott and Dan Price, who run the 55-acre Freedom Farm in Freedom, Maine, have two CoolBot coolers, both 8-by-8 feet. They grow about 10 acres of vegetables and sell them at farmers’ markets and to restaurants. Price said that the CoolBots are “effective at cooling the vegetables even when the rooms are fully loaded.” In the winter they run an electric space heater on a thermostat to keep the coolers from getting too cold. “It seems to do the trick and use minimal electricity,” said Price.

Andrew Marshall, MOFGA’s educational programs director, built a walk-in cooler at MOFGA’s Common Ground Education Center last July with help from the two farmers-in-residence, Christa Sanders-Fleming and Molly Crouse. Together they built an 8-by-8-foot, freestanding cooler with 6 inches of rigid foam insulation in the walls, floor and ceiling. Marshall said the $1750 cost covered all materials, including plywood, studs, insulation, roofing, air conditioner and the CoolBot. The foam insulation was by far the most expensive item, about $900.

Sanders-Fleming said that the CoolBot was able to keep their greens, lettuce and carrots in the mid-30s last summer.

Marshall built another CoolBot walk-in at his own farm in Montville, reducing the cost of insulation 40 percent by using recycled rigid foam.
First-Hand Experience with Apples
I first heard about the CoolBot at the 2008 Common Ground Country Fair. For me, the information was extremely timely: My 40 apple trees were loaded with soon-to-be ripe fruit, and I was on the verge of hiring a refrigeration professional to install equipment in a 7-by-8-foot insulated box I had built. Instead, I bought the CoolBot and a $325, 11,000-BTU A/C unit and suddenly had a walk-in cooler.

We put 25 bushels of apples in right away. I set the air conditioner on 65 and the CoolBot on 32. The room temperature seemed to fall to 40 quickly but took longer to get to 38 and even longer to get to 36.

At that point, in early November, the outside temperature was going below freezing at night, so I decided to let the temperature in the walk-in go down gradually in tandem with mother nature. I set the air conditioner on Energy Saver mode, which meant that the fan would cycle on and off instead of running continuously, and I monitored the temperature of the apples carefully. My goal was to gradually bring the temperature of the apples down to 32, which is ideal for apple storage.

By December the outside temperature was low enough that I was able to disconnect the CoolBot, pull the air conditioner onto a shelf in the room and plug the hole with foam. The walk-in cooler remained at 32, day after day, with no energy input.

During the January cold snap, the temperature in the cooler dropped below 30, so I interjected my own addition to the CoolBot cooling system: I plugged in a Dampp-Chaser – a 25-watt heating rod used in piano humidity control systems. I suspended the 4-foot rod in the middle of the cooler. Although the temperature outside went to minus 18, the temperature in the cooler climbed to 34 over the next couple of days, at which point I unplugged the rod. A Winter Watchman or other inline thermostat set to 32 would be an excellent addition to the Dampp-Chaser for someone who was unable to monitor the cooler temperature every day or two.

At the beginning of March, our apples had kept beautifully. At some point, as the mercury rises this spring, I will remove the foam plug, reinstall the air conditioner and attempt to keep the fruit as near to their optimum storage temperature as possible.

For more information about the CoolBot, see

About the author: Phil Norris, now in his 50s, manages Clayfield Farm, a 13-acre organic farm in East Blue Hill, Maine, along with his wife, Deborah Wiggs, and a young apprentice.

Scroll to Top
Sign up to receive our weekly newsletter of happenings at MOFGA.