I read an article today that said that modern AC units require a dryer built into them as HFC refrigerants like R-134a absorb water, whereas old Freon AC units did not require a dryer. Does this mean that AC units from the 50s did not dry out the air like modern ones do?
In: Physics
The refrigerant doesn’t contact air. It’s in a fully sealed closed system. But like the helium balloon you bought 3 days ago, even a sealed container can leak.
The reason air conditioning dehumidifies the air is not because the refrigerant absorbs water. A/C is a sealed system. If the refrigerant comes in contact with the air, it will escape the system. A/C removes moisture from the air through condensation. When warm air passes the evaporator, its temperature is reduced below the vapor point, and excess moisture condenses out.
Yes, older A/C systems had a filter-drier in them.
You’re confusing 2 things here. AC units capability to dehumidify and a refrigeration component known as a filter drier.
AC units, by design, are dehumidifiers. An older AC unit would’ve dehumidified just the same as an AC unit today. Possibly less efficiently but more or less the same. The fan passes air over a cold coil and heat is removed from the air, which causes any moisture in the conditioned air to condense.
Now a filter drier is a refrigeration component. Not to be confused with an air filter, the filter drier has nothing to do with drying the conditioned air, instead it deals with the refrigerant within the pipes.
For an AC unit to work, within the closed loop, you need to have pure refrigerant that follows a predictable and definite pressure and temperature relationship. When the pipes are sealed all air and moisture must be removed through the process of evacuation, pulling a vacuum. Previous refrigerants, CFCs and HCFCs, were somewhat forgiving and the oils they used were less hydroscopic. Filter driers were used but less frequently. With the shift to HFCs and polyester oil, which is significantly more hydroscopic, filter driers and more stringent evacuation procedures are necessary when adding refrigerant to systems. Really though, any time a closed system is opened for repair, the filter drier should be replaced regardless of the refrigerant type.
The filter drier is a refrigerant loop component that has a desiccant core and its purpose is to remove any additional moisture from a closed loop after refrigerant has been added during installation. It has nothing to do with the AC units dehumidification of the conditioned space.
It is not possible to make AC that doesn’t dry out air. Cold air is inherently drier than hot air.
> I read an article today that said that modern AC units require a dryer built into them as HFC refrigerants like R-134a absorb water
So that’s not quite what they are talking about.
ACs dry the air because as the air passes over the cold radiator it forms condensation. That condensation was the mosture in the air, so the air comes out colder and dryer. This is true of an R-134a based AC unit, a freon based unit, even thermoelectric coolers that don’t contain any refrigerants.
Why R-134a needs a dryer system is in case there is any leak and water does get into the refrigerant lines (even just temporarily while doing maintanence), as you don’t want that water messing the compressor up.
(Edit a missing word)
As others have said, these are two different things. I’ll try an ELI5.
Imagine a glass of iced tea sitting outside on a hot day. It’ll get drops of water on the outside of the glass. That water is called condensation.
Now imagine a glass of ice water sitting outside on a hot day. It’ll get drops of water (condensation) too.
Now imagine a glass of iced soda sitting … you get the idea. Same thing. All three glasses get water on the outside. Not because of exactly what is inside them, but because they are cold. And when moist air gets cold, it gives up some of it moisture. That’s just how air works.
So older AC units dried out the air, just like modern ones do, because they made the air cold, just like modern ones do. They used a different thing inside the AC unit (different type of refrigerant, see below), but they still made the air cold, so they still made the air dryer.
Now, what are dryers for? They’re not for the air. They’re for something else.
Inside your AC are special pipes through which a substance called a “refrigerant” flows. This refrigerant is the special sauce that actually makes the AC work. Describing that is a little beyond ELI5 (although I’m sure someone could do a decent job of it if OP is interested). Setting aside HOW it works, one important thing is the the refrigerant gets pumped into these special pipes, and then the pipes get closed forever (or at least until there’s a leak or something and the system needs more refrigerant).
Problem is, the world is a messy place and it is really hard to not let any water at all into these special pipes while you’re working on the AC unit (or that maybe rode in with the new refrigerant, or whatever). And water in these special pipes is bad for a variety of reasons. So the dryer sucks up any water that snuck in, so that everything keeps working happily.
Depending on what kind of refrigerant your AC uses, this may be more or less of a problem, so that’s why the type of refrigerant may matter. But it is still a thing, regardless.
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