Does high humidity affect the cooling or A/C systems?

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With miserable humidity and dew points in the upper 70's I was wondering if that affects the cooling and A/C systems in any way. Is it harder for the radiator to give off heat when the humidity is high? What about the condenser?
 
It takes energy to condense water. High humidity significantly increases the demand on an A/C refrigeration system. Think of what it would take to boil the water as it comes out of the drain pipe.
 
Originally Posted by mk378
It takes energy to condense water. High humidity significantly increases the demand on an A/C refrigeration system. Think of what it would take to boil the water as it comes out of the drain pipe.


I'm confused. The refrigerant converts from a liquid into a gas as it pulls heat (i.e. energy) out of the air passing through the evap coil. That heat is rejected by the outdoor condenser as the gaseous refrigerant returns to the outdoors. The only energy I can see in the system is that which runs the compressor converting gaseous refrigerant back into a liquid.

How does humidity increase the demands on the system?
 
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YES.

Cabin air can't get cooler without moisture first being removed from the air. Especially when it's humid out, recirc is your friend. Also, lower fan speed allows deeper dehumdification, as the coils can stay colder and/or the air spends more time against the cold surface before moving on.

So, if you're running fresh air and it's humid out, the A/C will be limited in how cold it can blow, because it may not be able to pull enough moisture out in a single pass to cool the air enough. What blows will be sort of cool, and sort of wet. Moving to recirc gives the A/C multiple passes to dry the air and achieve colder temps.

2018 F150 must be run in recirc down here to get it cold, especially when it's our normal 95F and 85% humidity. Then it's quite comfortable, and the system does pull in a small mix of fresh air even in recirc to keep good air in the cab.
 
The coil is cold and below the dew point, so when humid air hits it, the water condenses. It requires no extra energy from the AC system. It is also false that the AC will not start cooling until air is dehumidified. The air moves across the cold evaporator and exchanges heat with it regardless of the level of moisture in it.

Now, moist, cold air may feel less comfortable than dry, cold air, but it has no relation to air vent remperature.
 
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Not directly. Pulling moisture from the air is just an intended side effect. It does make it more comfortable to animals because their perspiration evaporates easier, but this is not an extra load on the system unless you set the A/C to a lower temperature in order to have comfort by pulling more moisture out of the air, instead of set to a specific temperature... so, yes and no, depends on how you look at it.
 
Originally Posted by Dave9
Not directly. Pulling moisture from the air is just an intended side effect. It does make it more comfortable to animals because their perspiration evaporates easier, but this is not an extra load on the system unless you set the A/C to a lower temperature in order to have comfort by pulling more moisture out of the air, instead of set to a specific temperature... so, yes and no, depends on how you look at it.


Animals? Dogs and cats don't sweat,
 
Originally Posted by atikovi
Originally Posted by Dave9
Not directly. Pulling moisture from the air is just an intended side effect. It does make it more comfortable to animals because their perspiration evaporates easier, but this is not an extra load on the system unless you set the A/C to a lower temperature in order to have comfort by pulling more moisture out of the air, instead of set to a specific temperature... so, yes and no, depends on how you look at it.


Animals? Dogs and cats don't sweat,


Through the bottoms of their paws.
wink.gif
 
Of course modern home systems let you set both desired humidity and temperature …
 
Humidity removal produces latent heat at the evaporator as the dew point is crossed. It is the same as real heat in how the compressor and condenser must strain to deal with it. There is no change in temperature with latent heat but there is a release of energy. Another example (the reverse) is that you can put a lot of heat into a pot of boiling water without changing its temperature-- it will take a lot of gas for the stove to get rid of the water which wouldn't be necessary if the pot were dry in the first place. You doubters now know what to search for.
 
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Originally Posted by mk378
Humidity removal produces latent heat at the evaporator as the dew point is crossed. It is the same as real heat in how the compressor and condenser must strain to deal with it. There is no change in temperature with latent heat but there is a release of energy. Another example (the reverse) is that you can put a lot of heat into a pot of boiling water without changing its temperature-- it will take a lot of gas for the stove to get rid of the water which wouldn't be necessary if the pot were dry in the first place. You doubters now know what to search for.



Ah ok. Now that makes sense. Gas -> liquid = higher to lower energy state, so that phase change releases energy.

Q: So does the refrigerant absorb the latent heat as if converts from a liquid into a gas?
 
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A pot of boiling water is an open system, an AC is a closed system.
The phase change of the refrigerant is what does the work. It will only do as much work as the capacity of the system. As the heat is exchanged in the condenser it evaporates the refrigerant. It doesn't matter if the heat comes from the air or water being condensed, because only a set amount of heat can be exchanged and accomplish the phase change. The final amount of work done by the system remains the same.
 
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That is the biggest reason why automotive a/c is run in recirculation mode. Otherwise there would be little use for this feature.
 
Originally Posted by BMWTurboDzl
Q: So does the refrigerant absorb the latent heat as if converts from a liquid into a gas?

It absorbs heat which is rejected at the condenser.
 
Read some recommendations that after a car is super heated in the sun … don't start out on recirculating AC

Maybe that's from the days of window cranks … ?
pretty easy to vent the hot air and I'm gonna use my windshield screen.
 
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