CoolBots(TM): Inexpensive Cold Storage

Demand for on-farm cold storage of produce and other Vermont agricultural products is increasing as local markets for these goods expand. I receive many inquiries regarding CoolBotsTM, an adaptation of a window air-conditioner to make a cooler out of an insulated space. This article is intended to collect related resources in one place and to also highlight some considerations adopters of CoolBots should be aware of.

In a nutshell:

A farmer-built cooler (photo from storeitcold.com).

These systems utilize a commercially available controller ($299) to allow the AC unit to run with a lower temperature than normal. Store-It-Cold, The manufacturer’s website has excellent resources and FAQ’s. They include a list of AC units that they have had positive experiences using. They are also very clear about who should consider NOT using a CoolBot. Applications for which the CoolBot is not well suited, according to the manufacture, include;

  • rapid “pull down” of temperature (e.g. high levels of field heat or frequent exchanges of product)
  • freezers – CoolBots perform best above 36 °F.
  • sites with many door openings per day (e.g. > 6 times per hour)
  • running through the winter – not a show stopper, but you need to be more careful about which AC unit you choose

Other things to be very aware of, according to the CoolBot controller manufacturer, include

A CoolBot installation (photo from storeitcold.com)

A report commissioned by NYSERDA summarizes the cost, energy efficiency, and greenhouse gas emission benefits of a CoolBot installation when compared to a conventional walk-in cooler system at certain conditions. The cost estimate of the CoolBot system (15,000 BTU/hr) is $750 installed compared to $4,400 for a conventional system (8’x10′ cooler box cost not included).

The authors conclude that a CoolBot system can result in approximately 230 kWhr/year of energy savings ($30/year at $0.13/kWhr VT average) when cooling 100 ft2 of cooler floor area to 35 °F (assumes Albany, NY conditions). It is important to note that this analysis highlights the main energy efficiency benefit of the CoolBot system comes from the reduced operating time of evaporator fans. High efficiency fans and improved controls exist for conventional walk-in systems and they are even supported by rebates from Efficiency Vermont. When the CoolBot system was compared with a conventional cooler that also had evaporator fan controls, the savings went the other way; i.e. the conventional walk-in system resulted in 74 kWhr/year savings.

Energy and Waste in the Food System

Although estimates vary, we invest about 14 calories of fossil fuel-based energy and 15-20 calories of energy in general into every 1 calorie of food produced.  And (here’s the kicker) 30-50% of the food produced never makes it to a digestive track.  So those energy input numbers are actually low by any true measure of efficiency and productivity.

Calorie for Calorie

A recent report from the USDA ERS sums it up this way, “use of energy along the food chain for food purchases by or for U.S. households increased between 1997 and 2002 at more than six times the rate of increase in total domestic energy use. … The use of more energy-intensive technologies throughout the U.S. food system accounted for half of this increase, with the remainder attributed to population growth and higher real (inflation-adjusted) per capita food expenditures.”

Here is a similar idea, displayed in a slightly different way by the University of Michigan Center for Sustainable Systems (this uses units of millions of pounds, not energy).

US Food System - flows in million pounds

And it isn’t all about energy efficiency and renewable energy and boring engineering BTU, calorie and bean counting (although I do like counting beans).  The food wasted post-harvest is a real loss that we can do something about. (NOTE: The report linked above where I take the 30-50% waste figure from was done by a UK engineering trade organization, IMECHE).

Some of the loss occurs in storage, and I think we all can agree that we can do better with our storage practices. Regardless of whether you are root cellaring, using a CoolBot(TM) or a commercial walk-in cooler, the principles remain the same. Some loss occurs in transport and distribution which speaks to the benefit of the broader food system considerations espoused by UVM’s Food Systems Spire and the Vermont Farm to Plate Initiative. Some, of course, occurs in the kitchen or in consumer storage and suggests we have some work to do with consumers as well.

As one grower recently said to me, “By the time we put food in our farm cooler, 99% of our cost is sunk into that product. We gotta pay attention to what goes on in there and make sure we get paid for it.

FIDO – A Do-it-yourself Temperature Monitor with Text Message Alerts

As I’ve mentioned in several other posts, I think the continual monitoring of conditions in greenhouses and food storage spaces is incredibly important for quality and safety and insightful for any operation. There is a really clever design for a do-it-yourself temperature monitoring system called Fido, on the FarmHack site.  It uses an Arduino control and electronics platform, a cheap cell phone, and a few other pretty inexpensive pieces to do the job.

“A farmer-built electronic tool that can monitor greenhouse temperature, record greenhouse data, and alert the farmer to problems in the greenhouse via cell phone text message. This tool will be much more affordable and useful than commercially available greenhouse alarms (which rely on landline connections or internet connections, which usually aren’t available in the greenhouse).

I’ll be trying to add RH monitoring to this soon, and will update the post when that is complete.