Farm Hack: Coolbot Walk-in Cooler

The Coolbot is an invention that makes a walk-in cooler a viable option for a farm with low cash flow.  By using a Coolbot instead of a conventional walk-in cooler, farmers lower expenses while still helping enhance produce quality at the point of sale.

Since 2006, Ron and Kate Khosla have sold thousands of Coolbots, a technology they developed to convert off the shelf air conditioners into a compressor unit for a walk-in cooler.  Instead of purchasing a conventional cooler for $2500 or more, with about 30 seconds of modification, one can turn an A/C unit into a cooler for about $600. Further, electricity costs will be lower and the modification does not void the warranty on the A/C unit, protecting the investment for typically five years.

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How it works

installdiagram

A standard air conditioner is designed to cool a room down to as low as 60 °F, but no lower. It does this by cooling its coils down to nearly freezing temperature and blowing air through them, cycling the compressor on and off according to the temperature in the room– adding more cold air to the room only when necessary. Since the air that comes right out of the A/C unit is close to freezing temperature, a big enough air conditioner can theoretically cool a small, well-insulated room down to nearly 32 °F.

So that’s where the Coolbot comes in. It uses a small heater element to “fool” the A/C’s thermostat into thinking that the room is warmer than it is, so that the compressor will keep running the the room will cool down to below the A/C’s minimum temperature of 60 °F.

The problem with this system alone is that if the A/C compressor were to run constantly, and the coils were constantly at freezing temperature, any moisture in the air would freeze onto the coils and begin to build up a sheet of ice. Pretty soon the coils would be completely iced over, the air wouldn’t be able to blow through them, and the room would stop being cooled at all. That’s why commercial walk-in coolers have much bigger sets of coils and many more fans; to prevent the icing-up (and to cool the air down faster).

The Coolbot solves this problem by adding a second temperature sensor, on the fins of the A/C unit. When this sensor detects icing on the coils, the Coolbot tells the A/C unit to stop cooling, preventing the ice from building up.

coolbot

Advantages

 

The Coolbot is a killer Farm Hack. Of the thousands of units sold, only about a dozen A/C units have failed since 2006. Malfunctions were caused by a lack of routine equipment maintenance; there was water dripping on a circuit board, or a critical component got dirty.  These repairs are easy to deal with, and make the total cost of ownership lower than a conventional cooler. A typical A/C unit will cost about $300 plus, the Coolbot itself costs $299.  Electricity costs are lower for an A/C unit versus a normal cooler compressor.  It is essentially a win-win-win to utilize the Coolbot if your business requires a walk-in cooler system: lower start-up cost, lower electric bills, and greater reliability.

 

Vegetable Quality

 

After the balance sheet savings, vegetable growers/CSA operators can take advantage of a cooler’s ability to significantly affect the quality of preserved fruits and vegetables.  The quality of produce begins to decline immediately after it leaves the soil/plant stem and is stored around room temperature or a shaded area. Strawberries, for example, picked and kept in the shade for a few hours and then placed in a cooler will maintain themselves at an acceptable quality for two to three days.  On the other hand, if strawberries are picked and immediately placed in a cooler around 36 °F, they will maintain an exceptional quality for around a week.

 

Who Uses this Technology

 

In developing the Coolbot, Khosla scratched an itch that wasn’t on the radar of large companies. While he admits that his technology is used by convenience stores and even mortuaries, the Coolbot created out of the inability of a small vegetable to raise $2500+ for a walk-in cooler.  For a farmer who is only going to walk in and out of a cooler at most a few times an hour, the Coolbot is the perfect alternative to a conventional cooling system.

 

Who shouldn’t use this Technology

 

The Coolbot system has a lot of advantages over a conventional cooler, but with them come some compromises. Because conventional coolers have bigger cooling coils and more numerous, more powerful fans, they can cool air and produce down faster than an A/C unit with its small surface area and single fan. If you are going to bring a pallet of broccoli into your cooler that has 80 degrees of field heat in it, and you need it cold quick, the Coolbot might not do the trick. However, coupled with a hyrdo-cooling system to get the field out of your produce before entering the cooler, the Coolbot might be the perfect tool to then keep your produce at temperature.

The Coolbot also isn’t a good choice if you have an oversized space, or a poorly insulated space. The Coolbot does a great job at squeezing out a lot of cooling power from a small A/C unit, but there is a limit. Make sure to use the chart linked below to ensure that the room you’re trying to cool is the right size and insulated sufficiently.

What you Need

1. Off the shelf A/C unit

2. Coolbot

3. Insulated cooler space

4. This chart from the Coolbot web site, to help you plan what size room you can cool with what size A/C unit. It’s important to get it right, or you will end up struggling to get your cooler down to the desired temperature.

 

History of DIY coolers

Before the Coolbot, farmers were making DIY (Do It Yourself) walk-in coolers using the same principle of trying to trick a store-bought A/C unit into making a room cooler than 60 degrees. To do that, farmers would fool the A/C unit’s thermostat by taping it to an incandescent light bulb (a heat source) hooked up to a standard thermostat. When the temperature in the room rose above, say, 40 degrees F, the thermostat would turn the light bulb on, making the A/C unit think it was hot in the room, and cycling on the cooling compressor.

This system would often have problems, due to the icing-up issue mentioned above. Some farmers tried to improve the system by adding a timer into the loop, which would automatically cycle off the light bulb (and therefore the compressor) every so often, to allow any ice build-up to stop. But the conditions under which ice-up would happen depended a lot on outside air temperature and humidity, and it was hard to predict whether you would walk into your cooler in the morning and find a sheet of ice on your A/C, an inside temperatures of 65 degrees, and a room full of warm broccoli. The Coolbot’s coil frost sensor and it’s circuit board that is specially programmed to cycle off at certain times solves these problems and makes a DIY cooler relatively foolproof.

4 Replies to “Farm Hack: Coolbot Walk-in Cooler”

  1. MY COOLER IS 4W, 8H AND 8L, WITH 4INCH INSULATION ALL AROUND. ITS BEEN RUNNING FOR THREE WEEKS, ALL WAS FINE UNTIL TODAY, 10/21/12.ITS THE AC THAT WAS RECOMMENDED,A 10,000 BTU. I NOTICED TODAY 2-3 INCHES HIGH OF ICE ON THE BOTTOM FINS. THE UNIT IS PITCHED OUT SO ITS DRAINING WELL. OTHER THAN THAT IT THE BEST THING SINCE SLICED BREAD.CAN YOU TELL ME WHAT THE PROBLEM IS, PLEASE.

  2. We have 1750ft on the bottom floor of our home. It is totally spray foam insulated. Due to our AC duct installer, our bedroom (15X16) does not get cool like it should. We have decided to get a mini split unit. We cannot find one that gets below 64 degrees. We have a new home and really do not want a window unit hanging out the front window, but when I found this site, we might just do that. We need the room to stay between 55 and 60 degrees. Can we get some direction on what we should do?

    Thank you, Charlie

  3. I’m helping out a CSA that recently installed a coolbot. They have a heavy demand for cold storage three days a week, and a virtually empty cooler the other four days a week. They’re planning to turn the unit off Saturday night and back on Wednesday night, thinking this will save electricity. I’m thinking that the power requirements of cooling the space down would make this a wash at best. All I can find on the web is stuff about turning a residential refrigerator off when the house is going to be empty for weeks or months.

    Any advice?

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