Engine Driven Air Conditioners

The world of HVAC is a very strange place to live some days. We commonly think of air conditioners as being electrical devices. Perhaps the only real exception to that is the air conditioner in your car, which is essentially powered by your car’s engine. In the early days of air conditioning and refrigeration however, the opposite was true: cooling systems were mainly mechanically powered.   The World Before Electricity It’s the early 1900s. The telephone is still considered cutting-edge technology and you can go down to the local train station to send a telegram anywhere in the country. Electricity however, was not quite so common. In 1900, 3% of US homes had electricity. It wasn’t entirely feasible to just throw an air conditioner in your back room. Even businesses wouldn’t have had the easy option of just plugging in an air conditioning system, even if it occupied half their building. At this point, most working-power was mechanical. Factories would have massive boilers, which produced steam, that turned enormous turbines or ran crank systems, that ultimately ran everything in the facility. In order for any particular innovation to take off, it almost had to be mechanically driven. If you couldn’t throw some coal and water in a machine to power it, you probably couldn’t have it.   Steam Powered AC How exactly do we run an air conditioner on steam alone? Every motor in an air conditioner is doing just […]

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History of Refrigerants

The concept of mechanical refrigeration starts back in the 1750s. Researchers knew nothing about cooling except that pressure and gasses somehow played a key roll in absorbing and removing heat. In these early days, everything was tried as a refrigerant: ammonia, alcohol, air, carbon dioxide, and more. It was the days of trial and error to create the robust understanding of physics and chemistry we have today.   Low Temperature Boiling The first experiments in refrigeration used Ether and Alcohol, which are readily evaporated. At sea level, Ether boils at 94F and Alcohol can boil as low as 151F, depending on the exact chemical form. Sea level is important here, as pressure changes the boiling point. Lowering the pressure causes a decrease in the boiling point. These gasses with low boiling points were ideal for early experiments. The first experiments used vacuum chambers and potentially some custom hardware. There isn’t a lot needed to build a basic vacuum chamber. A jar with a good seal, a hose, and a pump can create a vacuum. An observable refrigeration can be done with almost no special equipment at all. At this scale, cooling was possible, but not feasible. Alcohol, Ether, and other chemicals were common and easy to acquire, but no one was going to put a chunk of meat in a vacuum chamber, cover it in alcohol, wait for it to freeze, and try to store it somewhere. There had to […]

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The Fridge Came First

Every now and then, we discover the weirdest facets of fate and history. We’re all familiar with Carrier’s major break through in creating air conditioning in the early 1900s, but it turns out, he wasn’t exactly the first. There were working, mechanical refrigerators before we had working air conditioners.   The Ground Work The first artificial refrigeration was done by a Scottish professor in the 1755. He used a vacuum chamber and ether to lower the temperature inside the chamber. When the ether boiled, it removed energy from the chamber, cooling it down. The effect was just powerful enough to produce some ice inside. In 1758, Ben Franklin and John Hadley at Cambridge University would conduct similar experiments with volatile liquids. They were able to cool a  chamber now to 7 degrees fahrenheit, from an ambient 65 degree starting point. Franklin wrote, “From this experiment, one may see the possibility of freezing a man to death on a warm summer’s day.” At that point in time, there wasn’t yet a practical way to actually freeze anyone. This refrigeration involved a vacuum chamber. Anyone cooled down would be all but freeze dried in the process. Further refinements would come over the next century. In 1820 there was a closed-cycle system that could continuously cool a chamber and condense it’s refrigerant, it would be able to keep cool indefinitely. In the 1860s, German researchers began work on refrigeration for breweries. During the […]

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Why is the AC Hissing?

Air conditioners produce liquid water by design and by the simple nature of physics. Sometimes this harmlessly leaks out around the air conditioner, such as with window units, and sometimes it leaks when a drain gets blocked. There is however, a second leak an air conditioner can develop: refrigerant leaks.   The Cooling Compound Air conditioners work by exploiting physics around state-changes. When liquid turns into a gas, it can absorb heat.The effectiveness of the state change varies from compound to compound. For air conditioning, we tend to use things like R134a (freon), R12 (phased out/illegal in much of the world now), and even propane. These are all chemicals which have particular properties ideal for cooling. For example, they won’t turn solid at 0 degrees C like water, so they won’t clog up the air conditioner’s tubing and fittings. These chemicals though have some downsides we can’t really escape. Propane is outright flammable and probably capable of turning your air conditioner into a flaming set piece in the next post-apocalypse movie. R12 destroys the ozone. And R134a is toxic. It causes a wide range of symptoms from headaches to hallucinations and death in the worst case exposures.   The Hissing Leak When the air conditioner is running or has recently been run, the refrigerant will be highly pressurized. In order for us to make it work, we compress it. We’re cramming a lot of material into a small space, which […]

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Is my AC Leaking?

Air conditioners aren’t necessarily restricted to just cooling the air. The cooling is actually a side effect of what the first air conditioners were meant to do: regulate humidity. This is in part why it’s an air conditioner, not an ‘air cooler’ or ‘air freezer’. We’re doing more than one thing to the air.   Water In The Air Humidity is essentially just gaseous water in the air. It weighs nothing, so it literally just floats around. This is good and bad. On the one hand, water in the air creates our weather. On the other, it makes the air feel hot and sticky, we just struggle to cool ourselves down. This poses an even bigger problem in industrial settings. Water in the air is readily absorbed by things like paper in printing presses. At one point in time, this could cause tens of thousands of dollars in lost productivity. Old color printings were done one color at a time. The paper was run through the equipment, printed with blue ink. Then yellow could be printed over that to create shades of green, and so on. Paper that absorbs water however, changes its size slightly. Over the course of a mile long roll, the small changes in length were enough to ruin prints. This is where we got the first air conditioner: a really big dehumidifier. Water condenses on a cool surface. By passing air over a freezing, or near-freezing […]

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Variable Speed Compressors

Multi-speed compressors are a step in the right direction, but what about outright variable speed ones? Think about it, a two or three speed compressor has to pick the best speed for a given environment and it can only run at those two speeds. When it’s incredibly hot, full speed ahead. When it’s cooler, low speed. In between however, it becomes a game of the lesser evils.   Fixed-Speed Flaws This fixed-speed issue can be a bigger problem in the right scenarios. There’s only really a handful of conditions where the compressor can hit peak efficiency. You can crawl around the parking lot or go at highway blazing speeds, but you have no support for those middle roads between town. The same is true of the two speed compressor. The system can be forced to oscillate between stages or even be trapped in a single stage if the conditions are right. When it’s hot out, you’ll never get to use that second, lower speed. When it’s in between, the low speed might not be able to keep up and it’ll have to cycle between speeds, never really saving anything or improving comfort. It’ll almost always be this battle of the lesser evils: power hungry high speed and be too cool or have to work on wider margins of error, or fighting a losing battle with the low speed constantly running and only delaying the inevitable need for the high speed […]

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Multi-Stage Compressors

We often think of compressors as single-state devices. They’re on and they’re off. This holds true for most window units, portable indoor units, and even a number of central cooling systems. This simplifies things and lets us save power. Compressor on, hit target temperature, shut down. It’s better than running the compressor 24/7 and achieves the desired result.   Full Throttle The problem with this is that we have to constantly cycle. Imagine if your car had 1 speed. Instead of a gas pedal, you just had a button. Push the button, your engine revs itself through the roof, you do a burn out from your driveway, let off the button to avoid the kid running into the street, and you come to a dead stop in seconds. That’s how a single-stage compressor works and it’s a little wasteful. With this back and forth, on and off approach, you can never actually hit a precise temperature. You just hit a temperature range. When the thermostat is set to say 70 degrees, the air conditioner kicks on and runs until the room is approximately 65 degrees. Later, when the room has warmed to 75 degrees, it turns back on again. If we were to run the compressor at 71 degrees, it would be too soon, we’d be constantly starting and stopping. The air conditioner only spits out one temperature of air: really cold. If you run at 71 degrees, by the […]

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Why Isn’t There a Relay in This?

Relays are known for the bigger switching jobs, but they’re not the only game in town. There is a middle-ground where your five volt control board would fry and where a relay would be overkill or too slow to do the job. We turn to another special component for these “higher” but not necessarily “high” voltage jobs.   The Relay’s Weaknesses There are jobs where a relay just isn’t the answer. Relays come with two pretty big weaknesses: they’re mechanical and they’re slow. If we were to take apart pretty much any relay, we’d find perhaps some springs, an electro-magnetic coil, and some contacts. Whenever we actuate that relay, parts inside of it move. Moving parts are bad for speed and reliability. Eventually, the switching mechanism, contacts, or actuator inside that relay will degrade and fail. At the same time, we can only force that relay to move so fast. If the contacts inside are a half-inch apart, then we need to cover that half-inch before power will pass through. It’s a small distance, but consider that standard AC power in the US runs at 60hz. If we wanted to change the relay position based on the electrical frequency, it would need to move in 1/60th of a second. We need to accelerate to 2 mph and stop within 16 milliseconds, and that still costs us an entire 1hz cycle. Even then, chances are it will take longer to de-actuate. […]

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High Voltage in AC

Your air conditioner (and whole HVAC system) are a strange mix of parts. On the one side, we have low voltage, DC electronics that couldn’t tickle a fly. On the other, we have high voltage, AC equipment that could turn an ill-prepared reptile or rodent into a charred chunk of bones. How exactly do we mate these two, different systems together safely?   The Safety Issue In all electronics, we strive to separate high voltage and low voltage. We don’t want them to touch each other. In some systems, you have no choice but to put high and low voltage equipment on the same board, in other cases you try to keep them on separate boards altogether. If there’s any sort of electrical short between high voltage and low voltage, the low side is going to get destroyed. That’s your best case scenario. 240 volts or 440 volts blasting into some tiny microprocessors and capacitors, which then explode in a terrifying, but mostly harmless show of pyrotechnics. If the board is really well built, a diode will take the brunt of the failure before anything scary does. Sometimes though, these shorts don’t go like that. Some older equipment or equipment which never passed any reviews like Underwriters’ Laboratories can send high voltage straight to frame components, a button, or other areas where a user could come in contact with it. 220 Volts is not a pleasant experience, let me tell […]

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Rooftop vs. Roof Mounted Systems

When we say “roof top air conditioner,” your first thought is probably any old machine bolted to the roof and blasting air into your building. This is only partially correct. There are specialist systems designed to be roof mounted and regular systems which simply can be roof mounted. The difference is sort of like a big rig versus a regular pick up. They’re both trucks and both can haul a trailer, but only one of them was built to only haul trailers for it’s entire service life. Roof Top Units The easiest way to think of these is as a packaged system. A roof top unit is a fully self contained air conditioner and heating system, in one mass of hardware, that will blast air of an arbitrary temperature into your ductwork. In some ways this makes things easier. You don’t need to have separate systems, you have a single, bolt in system that does all the work in one place. Units like this take advantage of being pre-assembled at the factory. Everything about them is optimized from the start for the best possible performance. There can be tighter tolerances in assembly because it was all built at the factory. It’s also likely to never be seen by a customer, being tucked away on the roof, it won’t take up indoor space either, except for the duct work. It’s a really attractive idea for a business to consider. There are […]

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