How is “hot” indoor air hot enough to “boil” refrigerant and force a state change inside the evaporator from liquid to vapor?
Also, what are the dew points to the more common refrigerants for “standard” cooling systems found in homes n such?
Thanks well in advance!
Refrigerant/coolants low boiling point is the key.
When the ‘liquid’ refrigerant reaches the evaporator its pressure has been reduced, dissipating it’s heat content and making it much cooler than the fanned air flowing around it. This interaction causes the refrigerant to absorb heat from the warm air and reach its low boiling point rapidly. The refrigerant then vaporizes, absorbing the maximum amount of heat.
The hot air doesn’t do it. Very simply the refrigerant is pumped through an orifice at which time the suddenly reduced pressure allows the refrigerant to evaporate. the evaporated refrigerant ‘picks up’ the heat from house air passing over its coils. Evaporation is the key. On a hot day when sweat evaporates off your skin heat is removed from your skin. Same process. The temperature / pressure relationship of the refrigerant is key. Refrigerants evaporate readily at room temperature. when you then pressurize the refrigerant it gives off the heat as it changes state back to a liquid and the process starts over.
Thanks for the article!
Thanks for the diagram!
Great Diagram from Robert puts it all together.
Because the liquid refrigerant entering the evaporator has a really, really, low boiling point. For instance, R410 boils at -55 F.
The refrigerant enters the evaporator as a cold, low pressure liquid, the refrigerant begins to boil and evaporate, this evaporation causes a cooling effect in the room and the heat is carried away to be dumped in the condenser after the compressor. The refrigerant leaves the evaporator as a warm, saturated low pressure gas.
That article sucks (in many ways)!
The terminology is wrong or vaguely confusing. For instance,
It better not leave “WARM”!
There has to be ecnough refrigerating capacity to cool the compressor when it gets back there.
There is a specific “Superheat” temperature for each specific refrigerant and system design. R-22 for example required a 10 degree super heat (50F which is not warm).
No it does not “evaporate”.
A Swamp Cooler evaporates.
what is the correct term? vaporize?
edit: ah ha!
Vaporisation is defined as the phase transition of a compound or an element that occurs during the boiling or sublimation process. Evaporation is nothing but a type of vaporisation which mostly occurs at temperatures below the boiling point. Vaporisation can change the state of matter from a solid or liquid to a gas.
Interesting bit from the R-410A wikipedia, about the environmental effects of R-22 & R-410A… R-410 is less damaging to the Ozone layer than R-22 is, but the substance itself is actually worse for Global Warming concerns. But as long as it doesnt leak - it allows higher efficiency and is ultimately better for the environment.
Unlike alkyl halide refrigerants that contain bromine or chlorine, R-410A (which contains only fluorine) does not contribute to ozone depletion and is therefore becoming more widely used as ozone-depleting refrigerants like R-22 are phased out. However, like methane, its global warming potential (GWP) is appreciably worse than CO2 for the time it persists. Because R410A is a 50% combination of CH2F2 (HFC-32) and 50% CHF2CF3 (HFC-125), it is not easy to express their combined effects in a single global warming potential (GWP),[14][15] However, HFC-32 has a 4.9 year lifetime and a 100-year GWP of 675 and HFC-125 has a 29-year lifetime and a 100-year GWP of 3500.[14] The combination has a GWP of 2088, higher than that of R-22 (100-year GWP=1810), and an atmospheric lifetime of nearly 30 years compared with the 12-year lifetime of R-22.[16][17]
Since R-410A allows for higher SEER ratings than an R-22 system by reducing power consumption, the overall impact on global warming of R-410A systems can, in some cases, be lower than that of R-22 systems due to reduced greenhouse gas emissions from power plants.[15] This assumes that the atmospheric leakage will be sufficiently managed.[18] Under the assumption that preventing ozone depletion is more important in the short term than GWP reduction, R-410A is preferable to R-22.
Might be R-32 one of these days.
Nice graphic !!
Why call it an evaporator? Vaporize…
This was really great stuff! Thanks guys! It really gave my mind the missing pieces to put it all together!
Side question: do any of you ever feel like you still don’t understand something, even though you can explain well? It’s like the feeling of forgetting something, but you know you were careful to not. This HVAC class… oy vey!
You’ll retain about 20 percent and it will be helpful in the future. At some point, it will peak your interest again and back down the rabbit hole you will go. Each time coming out a bit wiser. One of the reasons why I love this job. (And this forum).
Imma need a lot of this!
Threads like this make me feel like I’m really not that smart 
To be honest I generally know most of what is being discussed but not to the detailed level. I remember taking physics in college and there is a section on thermodynamics. All I can say is that is some intense “stuff” (the s-word I wanted to use wouldn’t fly here).
On my inspections if anyone is interested I’ll talk about vapor and liquid paths through the compressor and evaporator and that’s as much as I’m comfortable talking about… and I’m quick to point out the limits of my knowledge. I’ve often told people I still can’t wrap my head around how I light the propane burner in my RV fridge and my beer gets cold. That gets a laugh and gets people away from me talking science. In reality my beer is in the cooler on ice when camping but a story about my cottage cheese just isn’t as exciting
Did you major in physics?
After reading my post I’d hope it’s obvious I didn’t
I took civil engineering but decided as a (not) wise 20-something year old it was more fun to drink beer and chase girls so I’m one of the many running around with 3.5 years of college credits.
Actually, my sister teaches physics at a community college and is a great go-to for things. I’m the “work harder not smarter” example in my family.
Yeah… Guilty here! I’m tryna change that with home inspection.
The reason I ask, I’ve also gone back to school to finish undergrad, (I have far fewer credits than 3.5 years), and am looking into physics as my major. Was curious about what progression of math classes should I consider implementing, relative to their physics counterpart, from start to finish.
Also, didn’t realize you’re on Maui!
I’m windward on Oahu!
Aloha
