He is correct and latent heat IS the answer. Specifically the latent heat of vaporization of water. Let me explain:
When you put a pot with a gallon of 65 degrees tap water in it on the stove and turn on the heat, you will have to add 1 BTU of heat energy to raise the temperature of the water 1 degree Fahrenheit. So, from 65 to 66, 1 BTU. From 66 to 67, 1 BTU, and so on. Until you hit the boiling point, that's where something entirely different happens. In order to convert that 212 degree water into 212 degree steam, NO change in sensible temperature, you have to add 970 BTUs of heat energy. 147 BTUs to go from 65 degrees to 212 degrees. 970 BTUs to not even change the temperature one degree, just convert it to vapor, boil it away. That's the power of the latent heat of vaporization. (There's the latent heat of fusion too, ice, it's 244 BTUs per pound of water, that's how ice keeps your food cold in your cooler at the picnic.)
Your air conditioner also dehumidifies, since generally the evaporator coil above your furnace or in your fan coil is about 40 degrees and usually below the dew point. So the reverse is true, every gallon of water your air conditioner condenses out of the air HAS to also release 970 BTUs of heat energy into the coil to be carried away by the refrigerant inside. That energy does nothing to change the temperature of the air, only remove water from it.
Enter the dehumidifier. Every gallon of water it extracts from the air is 970 BTUs of heat energy your air conditioner does not. Now your air conditioner can go to work actually cooling your home rather than dehumidifying it also. Well, it will still dehumidify, but it'll have to work less moving that heat energy out of your home, to the outside via the condenser.
And, you'll have much better humidity control.
Science. Isn't it cool?

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He is correct and latent heat IS the answer. Specifically the latent heat of vaporization of water. Let me explain:
When you put a pot with a gallon of 65 degrees tap water in it on the stove and turn on the heat, you will have to add 1 BTU of heat energy to raise the temperature of the water 1 degree Fahrenheit. So, from 65 to 66, 1 BTU. From 66 to 67, 1 BTU, and so on. Until you hit the boiling point, that's where something entirely different happens. In order to convert that 212 degree water into 212 degree steam, NO change in sensible temperature, you have to add 970 BTUs of heat energy. 147 BTUs to go from 65 degrees to 212 degrees. 970 BTUs to not even change the temperature one degree, just convert it to vapor, boil it away. That's the power of the latent heat of vaporization.

There's the latent heat of fusion too, ice, it's 244 BTUs per pound of water,
that's how ice keeps your food cold in your cooler at the picnic.

Your air conditioner also dehumidifies, since generally the evaporator coil above your furnace
or in your fan coil is about 40 degrees and usually below the dew point.

So the reverse is true,
every gallon of water your air conditioner condenses out of the air HAS to also release 970 BTUs of heat energy into the coil to be carried away by the refrigerant inside.

That energy does nothing to change the temperature of the air, only remove water from it.
Enter the dehumidifier.

Well, it will still dehumidify, but it'll have to work less moving that heat energy out of your home, to the outside via the condenser.
And, you'll have much better humidity control.
Science. Isn't it cool?

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Latent Cooling is Condensation process.

Energy Evaluation

Q. TOTAL = 4.5 * CFM * DIFFERENCE IN ENTHALPY

Q. SENSIBLE = 1.08 * CFM * DT

Q. LATENT= Q. TOTAL - Q. SENSIBLE

S.H.R. is typically ~ 0.74 - 0.82 [ 0.90 ] in a moderately moist [ Dry / desert like ] region
Sensible Heat Ratio

https://www.goodmanmfg.com/pdfviewe...pdfurl=docs/librariesprovider6/default-document-library/ss-gsxc16.pdf?view=true

 

I wish I had you as my Physics teacher in High school. Very well explained. I now recollect quite a bit from my Physics knowledge and its all making sense. THANK YOU!! Wow - it should be a marketing material.

Thinking this thru a bit - vapor (in air) to water requires energy. So one would think whether it's the HVAC coil or the dehumidifier coil how does it matter? Its still the same amount of energy. But in the case of HVAC it's primary objective however is to cool the home, not dehumidify which is a side benefit. Which you correctly pointed out. Now it also makes sense why having correct air flow over the coil matters. To max extract the moisture or max cool.

 

You're welcome. My pleasure.

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Btus to melt a 1 lb. of ice is 144.

Concepts ok.

Adding a dehumidifier to an a/c to maintain 50%RH allows the a/c more dryout time which may slow corrosion and extend the like of the a/c. Adding fresh air to the home while maintaining 50%RH in most cases extends the life of occupants and the a/c. In many cases, Fresh air, reduces the chemicals and other pollutants that may corrode the metal parts of the a/c.

Over-cooling inside of a home in an attempt to lower indoor %RH in many cases causes condensation structural parts of the will rot and corrode.

Because dehumidifiers provide reheat which warms the air and decreases the %RH 2.5% per degree of warming.

There is a lot going on improves the home occcupancy.

Keep us posted.

Regards Teddy Bear

 

Yeah, sorry, I typoed the 144, and forgot it was pounds, not gallons. School was 29 years ago, after all...

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I was told there wasn't going to be any math.

I was in our local Johnstone and the head guy there said it is way more efficient, even in our market (northern NJ), to have a dehumidifier and AC compared to only an AC.

It seems counter intuitive. The dehumidifier will remove latent, but it's also adding heat (the heat from the motors). That will let you get the RH lower and hit your thermostat set point temp, but you've now got to get rid of the heat from the additional motors. It's not much but it is addition heat.

 

True… but sensible heat is negligible load compared to latent removal.
And we humans are sensitive to humidity levels… and lowering the humidity increases our comfort.
With low humidity the temp we are comfortable at is much higher, so the ac system need run far less.

I know customers that HAVE to have the temp at 62F… and when a dedicated dehumidifier is operational, they are suddenly comfortable at 74.