Fast running refrigeration has its benefits, and it has a downside, too.
There’s quite a variety of passers-by to be seen from my front porch of an evening, and most seem to be walking a dog or two, or three. The majority of walkers fit in a velocity band somewhere between comfortable stroll and brisk jog, but there are also those on the fringes of the extremes, and these are the most interesting to observe.
At the hyper-speed end is Speedy Meanie, and he’s a runner on a mission. He’s lean and long-legged, and usually shirtless (in Summer anyway). He and his hound bound along in perfect synchronicity and appear out of nowhere in a flash, so you need a keen eye to catch him. He’s well known in the neighborhood for having a bit of a mean temper, and woe betide anyone that dares to get in his way. If Speedy Meanie arrives just as one happens to be putting the bins out, one can get an earful of colorful curses if he has to maneuver around them.
At the opposite end of the scale is dear old Ambling Archie. Archie is a truly loveable little dog, and as well as being small, he is very, very slow. Unlike Speedy Meanie, it is Archie that controls the pace, which is excruciatingly slow and difficult to watch, while his companion digs around in his smart-phone for something interesting to help pass the time. Ambling Archie doesn’t go very far, just to the end of the block and back, but it’s all the exercise he needs, and it’s quality time for him and his master.
Observing these two got me to thinking how this speed disparity relates to the variable speed compressors we have now in both refrigeration and air conditioning systems. If there’s not much work to do, then why not slow the compressor down and run it at reduced capacity. This will result in a longer run time, but will result in better efficiency than running a fixed-speed compressor for short blasts with long rest times. The measure of compressor efficiency we use is the Coefficient Of Performance (COP), which is the ratio of watts of power consumed compared to watts of cooling produced, i.e. Watts In : Watts Out. The slower the compressor is run, the higher the COP, and the lower the amount of power consumed. Frigoboat developed the Merlin II Smart Speed Control to utilize the variable speed capabilities of the Danfoss/Secop BD 35 and 50 compressors used in marine refrigeration. This plug-and-play device regulates the speed of the compressor dependent on the demand, resulting in big gains in efficiency, with super-cold freezer bins as a side benefit.
Think of it this way. Speedy Meanie can be likened to a compressor running at full speed. He needs to run far and run fast in order to satisfy his need to push himself to the limit, as well as being able to bark insults at as many people as he can along the way. Slowing down would not achieve his objectives, although his canine companion might appreciate it.
Ambling Archie on the other hand moves only as fast as he needs to, and uses the least amount of energy doing so, just like a slow-running compressor. I’m not sure if Archie is on his maximum speed setting, but I like to imagine that instead of ambling steadily along, he is actually capable of spurting between sniffing spots and leg-lifting posts, spending long rest periods investigating whatever intriguing odors catch his attention. But that would use up too much of his precious energy, and time is of no consequence to him, although it may be to the oh-so patient individual on the other end of the leash.
So, whether you’re a compressor or a dog walker/runner, the message is clear. Go only as fast as you need to go to get the job done, and save energy doing so. And if you’re ever in the Eastport area of Annapolis around sundowner time and hear the patter of a speeding feet and paws behind you, look out, because you just might be about to get an earful from the Speedy Meanie.