How do HVAC compressors work?
In: Engineering
It depends on the type of compressor but the most basic design is a 1 or more pistons on a crankshaft which is connected to a pulley or an electric motor. The piston is moved up an down. Gas flows in when the piston is up and gets compressed when the piston is pushed down.
It is similar to an engine, except instead of the engine turning wheels, the wheels are turning the engine
Compressors in HVAC are more-or-less the same and any other refrigerant compressors, like what’s in your refrigerator. There are special compressors that that are equipped with speed controllers and solenoid valves so that they can compress different amounts of refrigerant to match the need, but most compressors are just on/off.
As another commenter explained, they work kind of similar to a combustion engine, where a piston moves back, which draws in gaseous refrigerant, then pushes forward, suddenly compressing and superheating it. The variable speed compressor, a common type is called a digital scroll compressor, uses a metal scroll which rotates to draw in refrigerant, and a special mechanism to lift the scroll, causing the compression and pushing the refrigerant further into the system.
If you’re asking about how refrigerant systems cool in HVAC, that’s a slightly more involved question. Compressors are only 1 piece of a slightly more complex system then.
When the pressure of a gas drops its thermal energy is spread out, thus making the temperature lower. So you pressurize the gas first and then use a heat exchanger to make it the same temperature as the outside air. When that gas is pumped inside to a second heat exchanger the pressure is allowed to drop back to normal making is several degrees colder than whatever the temperature outside is.
This is why an air conditioning system may not seem to work so well on a really hot day, as the temperature the system gives you is always related to the temperature outside. Typically you can see an AC system aceive a temperature of 20-30°F below the outside temp but not much more. And overworking a system can cause humidity to condense on the heat echanger on the unit and freeze over and block airflow even further reducing its ability to cool.
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