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:
- Understand your storage needs;
- Build a good cooler box
- Understand the limitations of the CoolBot
- Use an AC unit with a proven track record in these applications, and check the sizing
- Plan for maintenance (cleaning the coil, off-season storage, protection from elements, etc.)
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 well-constructed cooler box – Start with a well-insulated (>R24), well sealed (caulk and spray-foam everything, no gaps) cooler box. The University of Kentucky has an excellent set of documentation, plans, bill of materials and costs, and animation for a low cost cooler design. North Carolina State University also has a fact sheet with guidance on cooler sizing and construction.
- A well-suited AC unit – avoid portable AC units, see the Store-It-Cold website’s list of selected units. The AC unit will need to have a digital display.
- Cooling a space above 61 °F.
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.