Courtesy of Jame K., Virtually Green, San Francisco, CA
Here’s a few quick thoughts about walkin cooler design, largely based on what my appropriate technology group used to recommend for village small-scale DIY walkin cooler systems. We didn’t have the Coolbot at the time though: it’s a great alternative to commercial refrigeration units.
Here’s a link to a Canada Plan Service document that lays out some of the basics for designing and building a walkin cooler.
The Coolbot retrofit of window air conditioners is a reliable solution, but do follow the Coolbot suggestions for the best air conditioner unit. I know someone who went cheap and regretted it immediately. I also recommend that you get two air conditioners rather than one, so you have redundancy in this critical component of the walkin cooler. You really don’t want to find yourself with a failed air conditioner and a cooler full of spoiled produce. If one of the units goes down the other can pick up the extra load until you can replace the failed unit.
Another thing. Use a strip door to keep cool air in when you’re entering and exiting the cooler. These are thick wide plastic strips that hang vertically from the top of the door to the floor and that overlap each other horizontally. You push through them to enter and exit. These can radically reduce the loss of cool air when moving quantities of produce in and out.
The size of a walkin cooler is based upon peak use, in other words the moments in the harvest cycle when you have the most produce needing cool storage. Use the dimensions of your standard sizes of storage containers: bins, boxes, tubs, etc. If you’re doing the routine crop planning for SPIN beds then you should be able to estimate the maximum volume of your various harvested crops needing container storage in your walkin cooler during your harvest weeks. Leaving 50% of the interior volume for aisles and air circulation is a good rule of thumb, which can also in emergencies temporarily handle extra produce volume if needed.
You’ll likely be using pallets or shelves for your containers, so remember to leave room for maneuvering dollies and lift-trucks in and out of the walkin cooler. Shelves that can be adapted to different dimension containers allow you to flexibly respond to changes in the quantities of your harvests. Also with shelves remember the work safety, ergonomics and back strain issues of lifting containers on and off high shelves.
You need to have the air inside the cooler circulating freely to avoid hot or cold spots or major differences in humidity in the horizontal and vertical volume of the cooler. Set the Coolbot air conditioners to optimize their effects on air circulation.
One thing you don’t want inside a walkin cooler is condensation problems, which can lead to mold and mildew that can affect produce quality. You want high humidity to avoid dessication and wilting of produce, but not so high that water condenses on surfaces. Mount a couple digital dual humidity/temperature meters inside your walkin cooler to monitor humidity and temperature at different horizontal and vertical locations. You can use these to monitor and better calibrate the performance of your air conditioners as well. I recommend buying ones with NIST certification to ensure that they will perform as advertised and also to satisfy any food safety regs or or insurance concerning produce storage. Here’s an example of what I have in mind: http://www.calright.com/products/prod_id/1794/