The Air Conditioner is my Heater?!

Air Conditioners don’t necessarily just cool your building. An air conditioner essentially moves heat from one place to another. In the case of your typical AC set up, we absorb the heat in your office and we put it outside with a gigantic condenser coil. What if we did the opposite?   Air Conditioning the Outside Speaking in terms of pure-physics, there’s pretty much always heat outside. To us living, breathing creatures, 0 degrees may seem like there is no-heat, but to a physicist, that’s orders of magnitude above the coldest cold possible “absolute zero.” That means we can put that ‘heat’ to use. In a configuration like this, the outdoor coil will become incredibly cold. This will allow it to absorb heat from the outside air and bring it indoors. Inside, the refrigerant is condensed and we basically get heat. We’re literally switching the roles of a traditional air conditioner. Systems such as this are often called Heat Pumps. Technically speaking, anything that moves warmth is a heat-pump, even an air conditioner or a fridge, but the term in particular is related to using air conditioning hardware for heating purposes.   The Extra Hardware Achieving this requires some special tweaks. If we’re going to have an air-conditioning-heater, we need some extra valves, control logic, and tweaking the design of your coils. Your coils will now both be able to function as evaporator and condenser coils. There’ll be two expansion […]

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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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Evolution of Air Conditioners

When Air Conditioners first came out, they were a commercial-only piece of equipment. They were almost always custom designed and installed equipment. The first major system was built by Willis Carrier to regulate humidity for a printing company. There was no going out to the store or your contractor to buy this technology. It was made from scratch.   Public AC The first air conditioners were installed in factories. These started out with textile mills and pharmaceutical companies in the 1910s. In the 1920s, department stores and movie theaters would start investing in air conditioners. In these days, a large department store could get hot enough for customers and workers alike to faint. Cool stores attracted customers looking to escape the heat. The Milam Building, in San Antonio, Texas would later be built specifically to be air conditioned from top to bottom. The entire building had special accommodations built-in to ensure consistent airflow to every floor, room, and store. This custom system was first put to use in 1928 and would not be retired until 1989 after a full 60 years of service. These innovations all lead to better technology, but it still was not accessible. These 1920s systems were hand-designed, in many cases by Willis Carrier himself. His sales team could pitch an air conditioner to any client for any purpose and he would design whatever it took to make it work. This isn’t entirely unique today, but at […]

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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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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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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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Why Are There So Many Fins in a Coil?

If you look really close at your air conditioner’s evaporator or condenser coil, you’ll see a ton of tiny fins sandwiched between two tubes. You might ask yourself, why are we making this so fragile. A screwdriver could puncture these fins with just the smallest bit of force, let alone what some ice could do. Why are we using such tiny parts instead of just a few, massive fins or something more robust?   Old Radiators Let’s start with a trip to the past: the classic heating radiator. A radiator like this is just another type of heat exchanger, almost the same thing as your air conditioner’s coils, but designed to heat the home or office. These were massive, robust pieces of equipment. They weighed hundreds of pounds of cast iron and could break your foot, leg, and back all at once during a botched installation. These work on the same principle as other heat exchangers: we change the temperature of the heat exchanger, and it in turn changes the temperature of the air. With such beefy components though, it requires a lot of water or steam to make any significant changes. Sure, the radiator will get hot enough to fry an egg or reduce just about anything to a piece of charcoal, but it doesn’t have a lot of contact with the air. It ends up being slower as a result.   Surface Area When we radiate or absorb […]

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How to Tame Your Cooling Costs

Air conditioning is expensive, but essential for most of the world except perhaps the arctic circle. It improves employee productivity and attracts customers on the hottest of days. Unfortunately,  it also makes an electric meter look more like a helicopter, buzzing along as we suck down ever more watts in search of comfort.   The Little Things Use light-colored windows blinds and curtains. Every place that light gets into your building is some place it’s going to raise the temperature. Light ultimately creates heat, the sun is giant, nuclear, laser ball. If we can make sure its light falls on reflective things, like lighter colors, curtains and blinds, we can reduce the amount of heat generated inside the room. It would be impractical to close off grand entry ways with curtains, but everywhere else is probably fair game. Even some window blinds in the office can reduce the heat coming in by half, while still keeping the room fairly bright for your staff. Dial back the temperature The greater the temperature difference, the harder the air conditioner has to work to maintain that difference. Remember that you need to only create apparent comfort. If it’s 100 degrees out, your employees and customers will probably be grateful for anything less than 85 degrees. You don’t need to make the office 60 degrees. Close the doors Ensure you’re not venting cool air wastefully. Keep the doors closed or install a closing mechanism […]

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Outdoor Air Conditioning?

It’s summer. It’s hot and humid and we’ll do anything to ease the heat off, even a little bit. Or in some cases, we’ll do anything to ensure our guests, customers, and clients don’t melt just for coming to a major public event. The problem is, how do we cool people down outside? It can’t be that hard, right?   Mother Nature’s Onslaught We first need to understand what we can’t do. On a hot sunny day, there’s effectively hundreds of thousands of BTUs of heat in the air. If we attempt to use a standard air conditioner outside, it’d be every bit as effective as blowing in the wind or using a match to solder 6″ piping. We’re fighting an uphill battle. Modern air conditioning works because we can keep it inside. Air naturally wants to mix and achieve a temperature equilibrium. By putting cool air into buildings, we contain it and prevent any significant dispersal from occurring. Our 40,000 or 400,000 BTU of cooling is able to actually get something done in this way. We could put these massive machines outside and try, but chances are they would have to remain constantly on. Even if a target temperature could be reached, the movement of the air would soon blow our nice, coolness away. It quickly becomes a matter of impracticality. The size, cost, and logistics of the cooling equipment to cool your company picnic or cool an entire […]

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