Thermostats live a simple life, uncomplicated by worldly concerns. Like some of our friends and spouses, they are always either happy or not happy. A hot AC thermostat is unhappy. Very unhappy. She wants to be cooled down, right now, and pushes out the voltage to prove it. Sort of a “I’m hot and I have a gun” attitude. In contrast a cool thermostat just sits there, calm, collected. As inwardly focused as any teenager, the cool thermostat does nothing, nothing, nothing. And because Engineers really do have a sense of humor, the difference between these two extremes of operation is called the dead zone, an exercise for the imaginative.

These controls are so basic, we call them bam-bam controls. After the Flintstones, I think. The advantage is reliability and simplicity. In years past, thermostats didn’t even need batteries, they were powered by the temperature change itself. And they only needed two wires and a voltage to start the compressor, the simplest connection ever. And what has changed since the 1940s? Very little, actually. The now famous NEST thermostat operates in exactly the same way (but with INTERNET!).

But oh, the disadvantages. Suppose your car only had the speeds of idle and full throttle? Disregarding the carnage, the efficiency would be terrible, with mileage worse than our old Expedition. And yet, that is how almost all air conditioners and refrigerators work. Bam-Bam. Bam-Bam.
And FYI, compressors don’t like bam-bam controls. Compressors suck 90% of the power for an AC, and for that matter probably 70% of the power of a whole house. If the compressor ain’t happy, nobody’s happy.

Get this . . . the ‘ol thermostat starts the compressor like a runaway train, all full of Freon and power with lots of capacity. After a few minutes, all the easy Freon is sucked out of the system and Mr. Compressor is stuck struggling to pull a few teaspoonfuls through the whole system. Too hard! That’s why ACs cool fast initially, then take 4 times as long to get that last degree of cool.

Hmmm, so thermostats doing the bam-bam makes for an unhappy and inefficient compressor. Surprise! Thermostats may not be the sharpest tools in the shed, but they do turn out to cost you the most. Think like a thermostat? Harrumph, only if you work inside the beltway. There must be a better way. And there is, really, really.

The latest innovation in air conditioning is inverter systems. This is Engineer talk for matching the revolutions (speed) of the compressor to the heat load. The compressor runs almost all the time, and speeds up when it gets hotter. This works really well! Mostly really well! Ok, pretty good. Inverter systems are genuinely efficient and reliable. But (always that but) inverters can’t be retrofitted to the 350,000,000 systems out there, and are costly, really costly for any significant capacity.

There is a middle ground, though. Suppose you could bolt on a control that could understand the system so well that it starts up in a timely way when cooling is productive, but cuts off before reaching the difficult part of the cycle. This method of cycle pattern control is called thermodynamic cycle optimization and can save 15-30% of the compressor’s energy cost. Not quite as effective as inverters, but just as reliable and a lot cheaper. These optimizers can be retrofitted in 1-2 hours to any size air conditioner. That’s any size, I’ve put them on 100 ton monster rooftops.

Smartcool Systems (from Vancouver) makes the only optimizer that works on both single and two stage (dual) systems, the ECO3. It not only figures out your system and runs it in the most efficient pattern, but it is a data logger (be still my Engineer heart!) and tells you exactly how the AC is running.
Now that’s cool.