CoolBot: Crazy Idea or Worth Considering?

First, welcome to the Spark Applied Efficiency blog!

If you’re into energy efficiency, this blog is for you. We’ll share the best thinking, the best products and the best practices we discover in the world of energy efficiency.

Can you really use an off-the-shelf AC unit to refrigerate a walk-in cooler?

We recently had a client ask us about CoolBot, an idea we had seen in operation in another facility. Here’s the hype:

Build Your Own Walk In Cooler

CoolBot turns an off-the-shelf air conditioner into a walk-in cooler compressor!

If you’ve received a quote for a $4 – $5,000 walk-in cooler installation, and someone tells you they can do the same thing for $800, you tend to pay attention. And we have to say, this is exactly the kind of outside-the-box thinking we love to do ourselves.

But is it too good to be true? The short answer: yes.

In some situations CoolBot does work. So it’s not a completely crazy idea. But you get better cooling performance and higher overall efficiency from a system that costs thousands of dollars than one that costs hundreds.

The CoolBot takes over the controls on a standard AC unit (either a split or through the wall) and allows it to be used to refrigerate a walk-in cooler by lowering the set point and maintaining a defrost cycle. If you insulate the heck out of the space you intend to use as a walk-in cooler, and don’t open the door very often, you’ll be in good shape.

If you read the web site, they claim, “CoolBot will not only save you on installation and repair costs, it will also help you save electricity, reducing your operating costs.” What’s the hitch?

Like most things in life, it’s a bit complicated.  It is true that the CoolBot idea works (but make sure you read the “Who Should NOT Buy a CoolBot” page). The basics are sound. You can turn an AC unit into a refrigeration system.

However, there are some pretty significant limitations to this system. First, your typical window shaker is actually not all that efficient. An Energy Star-rated through-the-window unit has a SEER of 11 or 12. A decent mini-split system, with Variable Frequency Drive Fans and more efficient compressors, has a SEER of twice that. While the rating system for conventional refrigeration systems is different from AC systems, we would expect the efficiency of a conventional system to be lower than the Mini-split, but higher than the window unit. So you will be using more energy than necessary by turning an inexpensive AC unit into a cooler. Any electricity you save with a CoolBot is probably due to operating your walk-in at a higher temperature or providing better insulation (less cooling requires less energy, no surprise there).

Another big disadvantage is that the window shaker is designed to lower the temperature to the 60’s inside while raising it to the 100’s outside.  If you only have cooling loads when it’s relatively warm outside, the CoolBot with a window unit will work fine.  However, if you need to keep the cooler cool inside when it’s cold outside (i.e. in the 40’s or below), that could be a problem. Some air conditioner brands just aren’t designed to be operated when it’s cold outside. You may run into reliability problems.

One solution is to shut off your CoolBot and bring in outside air when it gets really cold. (Check out Freeaire Refrigeration for one way to do this.)  This is a GREAT IDEA* as you can take some of the money you saved on installing a conventional system, and instead install a smart system that pulls in cold air when it’s cold outside. This would really lower your overall costs, since you’re using an inexpensive system for when it is appropriate, and switching over to free, cold outdoor air when it isn’t.

*Or is it really a GREAT IDEA? “Free” cold air isn’t really free because you have to factor in the cost to cut a hole in your walk-in, install a damper and a fan and controls. When it’s warm outside, that hole that’s designed to bring in cold air works against you by making it easier for warmth to get into your walk-in. Of course, during the warm season you could minimize heat flow by installing a plug and a hatch. Is all this worth the cost and hassle? Your actual costs and savings from “free” cold outdoor air get a little complicated to determine.

Our bottom line: we’re dubious that CoolBot alone can really reduce your operating costs if you compare apples to apples. We suspect that most of the savings come from simply not refrigerating your walk-in cooler to the same degree. But hats off to the clever thinking that can make an off-the-shelf AC unit do something it was never designed to do. If you are really keen on lowering your operating costs, combining the CoolBot and Freeaire ideas could minimize your energy use.

Our Thoughts

How about a more efficient “hybrid” system? Consider a CoolBot system that uses a mini-split heat pump instead of an off-the-shelf AC unit. Mini-split heat pumps are amazingly efficient; good ones work down to -5 degrees Fahrenheit. And they are still less than half the cost of a conventional refrigeration system. A hybrid mini-split refrigeration system should actually be more efficient than a conventional system AND provide cooling down to a reasonable temperature. You can depend upon it for serious cooling loads all year long without worry of failure in a climate like Maine’s. If you build a hybrid walk-in cooler with a mini-split, let us know!

Lower your operating costs for a conventional walk-in cooler or freezer. If you operate a walk-in cooler or freezer, here are several practical ways you can improve your energy efficiency.

  • Turn off lighting when not needed.
  • Replace incandescent or fluorescent lighting with LED lighting.
  • Upgrade evaporator fan motors.
  • Control anti-sweat door frame heaters.
  • Add insulation.

Be sure to take advantage of the Efficiency Maine rebate programs that can help pay for many of these efficiency upgrades!

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