Air conditioning raising controversy

[SFBruin]

dChan, are you saying that you should use a dehumidifier and an A/C simultaneously?

Not that this is relevant for me right now, but if I ever live on the East Coast...

[JManc]

Originally Posted by SFBruin

dChan, are you saying that you should use a dehumidifier and an A/C simultaneously?

Not that this is relevant for me right now, but if I ever live on the East Coast...

We do. One in our master bathroom and another in our bedroom.

[SFBruin]

Ah, good to know!

[dchan]

Originally Posted by SFBruin

dChan, are you saying that you should use both a dehumidifier and A/C simultaneously?

Yes. It sounds like a crazy concept - "Why the heck am I heating my home while also cooling it?"

But it works, and is absolutely recommended for warm humid climates. Most of the summer discomfort comes from moist air. By removing this moisture from the air first, you're doing the vast majority of the work in improving indoor occupant comfort. Even running the dehumidifier itself without A/C can drastically improve occupant comfort.

BUT, as I noted in my second post, I would absolutely recommend air-sealing your home as much as possible first. For existing occupied homes, it's almost impossible to air-seal your walls, windows, doors, and roofs perfectly. But if you air-seal as much as possible (start with big holes, work your way down to small holes), then you reduce how long your dehumidifier will need to run to remove moisture from the air.

Either way, once you dry the air out, you won't need to run the A/C for a long time to cool your home either.

[dave8721]

Originally Posted by SFBruin

Have summers been getting noticeably warmer on the East Coast due to climate change?

I feel like last summer in Seattle was warmer than I was expecting, but it was also my first summer here, so I didn't really have a baseline.

Definitely so in South Florida. I looked up old temp records a few months back and back in the 1980's it would typically reach the 90's maybe 5 to 10 days total in July/August. These days we typically see 30-40 straight days in the 90's that time of year. Days above 93-94 used to be unheard of in South Florida now they are the norm during summer time. Also Winter simply ceased to exist as well.

[SFBruin]

^ That's not good.

[Pedestrian]

Originally Posted by SFBruin

Have summers been getting noticeably warmer on the East Coast due to climate change?

I feel like last summer in Seattle was warmer than I was expecting, but it was also my first summer here, so I didn't really have a baseline.

Not just summers. As far as I'm concerned, we didn't have winter this year in southern AZ. Normally I have to cover up my sensitive plants at least half the nights in January and February but hardly at all this year.

Generally we have the opposite weather of what happens in the East and I'm aware that it seemed like a cold winter in the northeast and upper midwest. But in 20 years I can't remember one as warm as we had this year.

[Steely Dan]

Originally Posted by Pedestrian

Generally we have the opposite weather of what happens in the East and I'm aware that it seemed like a cold winter in the northeast and upper midwest.

Not in chicago.

We had a ridiculously mild winter overall, outside of february.

It was like an entire winter's worth of cold and snow all got distilled down and then crammed into february. That was it; 4 weeks of actual winter. December, January and March were all above normal and very mild (relatively speaking) for the most part.

If the new pattern in chicago is going to be more intense, but RADICALLY shorter winter seasons, I'll gladly take it. As I've said before, I like chicago winters, just not always their length. Short and angry is right up my alley.

[Pedestrian]

Originally Posted by dchan

Yes. It sounds like a crazy concept - "Why the heck am I heating my home while also cooling it?"

But it works, and is absolutely recommended for warm humid climates. Most of the summer discomfort comes from moist air. By removing this moisture from the air first, you're doing the vast majority of the work in improving indoor occupant comfort. Even running the dehumidifier itself without A/C can drastically improve occupant comfort.

BUT, as I noted in my second post, I would absolutely recommend air-sealing your home as much as possible first. For existing occupied homes, it's almost impossible to air-seal your walls, windows, doors, and roofs perfectly. But if you air-seal as much as possible (start with big holes, work your way down to small holes), then you reduce how long your dehumidifier will need to run to remove moisture from the air.

Either way, once you dry the air out, you won't need to run the A/C for a long time to cool your home either.

I certainly agree with your second point--just running a dehumidifier can make elevated temps more tolerable. But refrigeration air-conditioning doesn't just cool. It also removes moisture. Warm air can hold more moisture than cold air and running the air across the cold evaporator coil wrings the moisture out of it which, in window units, you can see dripping away.

Now simultaneously running a dehumidifier probably reduces the humidity even further but I wonder how much. You ought to do an experiment and check it and tell us. And your A/C has to be properly sized. If it's bigger than needed for the space it won't run enough to keep the humidity properly low (that's what all the experts say and it seems to contradict your idea that the humidity will stay low without running the A/C much and it makes sense to me--there are many sources of evaporative moisture in most homes).

As for sealing the home, my Arizona house is 45 years old but the construction is such that when temps were peaking at 105F last June, the house usually didn't climb to 76F until around 3 PM at which point I turned on the A/C. I usually run it at 76F during the day but around midnight I turn it down to 68F for sleeping and that's the starting point again next morning (I turn it off when I get up).

The fact the house is decently sealed is part of why it stays cool without the A/C but I think the most important thing is the roof which is foam covered with an elastomeric substance that the manufacturer claims reflects 98% of solar energy. I do know that if I'm on the roof I get a wicked sunburn in places exposed only to reflected sun.

[dchan]

Originally Posted by Steely Dan

Not in chicago.

We had a ridiculously mild winter overall, outside of february.

It was like an entire usual winter's worth of cold and snow all got distilled down and then crammed into february. That was it; 4 weeks of actual winter. December, January and March were all above normal and very mild (relatively speaking) for the most part.

If the new pattern in chicago is going to be more intense, but RADICALLY shorter winter seasons, I'll gladly take it. As I've said before, I like chicago winters, just not always their length. Short and angry is right up my alley.

Same here. We had a mild December, a somewhat cold January, then 4 weeks of snow in February. By the beginning of March, all the snow melted, and I was able to play basketball again.

I would love short angry winters, but I'm guessing that might be a sign that the climate is getting warmer. Not sure though.

Originally Posted by Pedestrian

I certainly agree with your second point--just running a dehumidifier can make elevated temps more tolerable. But refrigeration air-conditioning doesn't just cool. It also removes moisture. Warm air can hold more moisture than cold air and running the air across the cold evaporator coil wrings the moisture out of it which, in window units, you can see dripping away.

Now simultaneously running a dehumidifier probably reduces the humidity even further but I wonder how much. You ought to do an experiment and check it and tell us. And your A/C has to be properly sized. If it's bigger than needed for the space it won't run enough to keep the humidity properly low (that's what all the experts say and it seems to contradict your idea that the humidity will stay low without running the A/C much and it makes sense to me--there are many sources of evaporative moisture in most homes).

As for sealing the home, my Arizona house is 45 years old but the construction is such that when temps were peaking at 105F last June, the house usually didn't climb to 76F until around 3 PM at which point I turned on the A/C. I usually run it at 76F during the day but around midnight I turn it down to 68F for sleeping and that's the starting point again next morning (I turn it off when I get up).

The fact the house is decently sealed is part of why it stays cool without the A/C but I think the most important thing is the roof which is foam covered with an elastomeric substance that the manufacturer claims reflects 98% of solar energy. I do know that if I'm on the roof I get a wicked sunburn in places exposed only to reflected sun.

Yes, I mentioned all that about A/Cs also dehumidifying in my first post on the previous page. I was replying to others who also knew that A/Cs dehumidify the air.

You misunderstood what I wrote. What I wrote was that you don't need to run your A/C much if you use your dehumidifier as well. The dehumidifier does the bulk of the moisture removal (it's basically a reverse A/C - see post on previous page). Even using a correct-sized air conditioning won't help if there is too much moisture in the air, and if the moisture keeps seeping in because your home is not air-sealed well enough. That's why dehumidifiers are also recommended by HVAC experts for the Southeast climate zone.

Sounds like your house is built great! The roof is the best place to install tons of insulation (R50-60+ recommended). For the rest of the house, air-sealing with more modest amounts of insulation is fine (more wall insulation is better, of course, but not always practical).

I mentioned "Building Science" in my 2nd post on the previous page. Building science experts have come up with the four items that need to be controlled by your wall and roof, as ordered by priority:

1. Bulk water control
2. Air leakage control
3/4. Thermal control and water vapor control

The tricky part is controlling each item without compromising the other controls or creating other problems. One of the trickiest elements is water vapor control. "Vapor barrier" material and design needs to be carefully considered. Most people would think we should use an impermeable vapor barrier that blocks all vapor. That would be fine and dandy, except for when water gets behind a wall somehow. Where can the water evaporate to? If it's trapped behind impermeable vapor barriers, it goes nowhere and eventually encourages mold growth.

[badrunner]

Originally Posted by Pedestrian

Not just summers. As far as I'm concerned, we didn't have winter this year in southern AZ. Normally I have to cover up my sensitive plants at least half the nights in January and February but hardly at all this year.

Generally we have the opposite weather of what happens in the East and I'm aware that it seemed like a cold winter in the northeast and upper midwest. But in 20 years I can't remember one as warm as we had this year.

Monsoons have been MIA the last couple of years as well...

Many people don't know this, but we usually get some some monsoon action here in SoCal as well, with the deserts and mountains getting thunderstorms in July and August, and sometimes even reaching the coast: One dead, 13 injured after lightning strikes at Southern California beach. It's been awhile since I've seen a good summer storm in the mountains. SoCal doesn't rely on monsoon moisture for our water but it's very concerning for AZ and NM.

[dchan]

Originally Posted by Doady

If humidity is an issue, people really should get a dehumidifier so the A/C runs more efficiently and the A/C temperature doesn't need to be set so low. Less wear on the A/C, less electricity consumption, increased comfort (lower humidex), and more water for the garden.

Originally Posted by Pedestrian

This is the second time you've posted this and you should study how modern refrigerated air condtioining works as well as basic meteorology. Warm air holds more moisture than cold air. As air conditioning forces the warm air through very cold coils, much of the moisture condenses out and drips out of the unit (look for a wet spot under your parked car when you've been running the A/C or for the watter dripping from a windown unit). Directly after passing through the coil, the air is very cold but when blown into the room it warms up and this means its ability to hold moisture, but not the moisture it actually holds, drops. Thus the relative (percentage) humidity drops too.

In this way, air conditioning is a very efficient dehumidifier and works as well as any other form of dehumidification. You don't need any additional equipment.

Pedestrian:

It's true that A/Cs dehumidify the air, but only up to a point. Doady was correct: dehumidifiers are needed when there is excessive moisture in the air. Even using correct-sized A/Cs won't work, especially (as I noted above) if the building exterior envelope has lots of air leaks in a humid climate.

Here's a picture to demystify how a dehumidifier works:



https://www.essentialhomeandgarden.c...midifier-work/

If a dehumidifier looks kind of like an A/C, that's because is also based on the efficient refrigeration cycle. Room air is drawn by a fan through cold evaporative coils first, then through hot condenser coils after. The cold coils dry the air through condensation, and the hot coils warm this air. The result is warm dry air.

Why warm dry air? Well, you clearly understand that warm air holds more moisture than cold air, but you underestimate how much more it can hold. A psychrometric chart can answer this question:



https://humiditycontrol.com/psychrometric-chart/

The air leaving an A/C is around 55-60F.
The air leaving a dehumidifier is around 90-100F.
If we draw a horizontal line from the wet bulb curve on the left to the absolute humidity vertical line on the right (weight of water in....), we see that 90-100F air can carry 2.5-3 times the moisture that 55-60F air can carry. That is why dehumidifiers are designed to output warm dry air instead of cool dry air.

For air-leaky buildings in extremely humid climates, dehumidifiers are absolutely necessary equipment to control latent heat issues. By removing as much moisture in the air, you can use your A/C for its intended purpose: cooling your room while providing supplemental dehumidification. A/Cs by themselves should not be used as dehumidifiers.

You are correct when you say that A/Cs should be sized correctly to properly dehumidify a room. Their rated BTUs/KWs will determine how quickly the A/C will cool a room. If it cools a room too fast, the coils won't be cold long enough to provide dehumidification. At the correct BTU/KW rating, the A/C won't cool the room as quickly, but its coils will stay cold long enough to dehumidify a room.

HOWEVER, even correct-sized A/Cs won't be able to handle swampy humid climates like the Southeast US, especially if humid air is constantly entering the house through various air-leaks in the building exterior envelope (walls, windows, doors, roofs, etc.). See my post from the previous page on exactly how much water vapor enters a building through a 1 square inch hole. This problem is going to get worse as we see the continued effects of climate change.

Even very airtight buildings benefit from dehumidification, especially if the buildings are also highly insulated. That's because the A/C doesn't need to run for long in such buildings. Therefore, you need a dehumidifier to dry the air, though the amount of moisture in the air would be considerably less than in a very air-leaky building.

[Pedestrian]

Originally Posted by dchan

Pedestrian:

The air leaving an A/C is around 55-60F.
The air leaving a dehumidifier is around 90-100F.
If we draw a horizontal line from the wet bulb curve on the left to the absolute humidity vertical line on the right (weight of water in....), we see that 90-100F air can carry 2.5-3 times the moisture that 55-60F air can carry. That is why dehumidifiers are designed to output warm dry air instead of cool dry air.

That's kind of irrelevant. The air leaving the A/C or the dehumidifier doesn't stay the temp it is very long. That 55 degree air warms (and the humidity in it drops) and the dehumidifier air cools (and its humidity rises).

I've lived in swampy Florida and, like most people there, was perfectly comfortable with a properly sized A/C both cooling and dehumidifying. If you want to run a dehumifier also, it's your business and have at it but you will be running up your electrical bill unnecessarily (both to run the dehumidifier and to recool the air it puts out) in the opinion of most people. Makes sense if you are unusually sensitive to humidity but in that case I recommend a move to the desert Southwest.

In AZ where I am, none of this is an issue. The relative humidity commonly runs 5%. We talk in terms of dew points. Those can be 0F (zero degrees F). When the dew point rises to 55 degree F (air temp usually around 95-100F) we log the start of the summer monsoon and expect daily afternoon and evening thunderstorms.

[10023]

^ I could see the use of a dehumidifier as well in Florida. Otherwise make sure you buy individually packaged salty snacks. And drying hair after a shower takes forever.

[Pedestrian]

Originally Posted by 10023

^ I could see the use of a dehumidifier as well in Florida. Otherwise make sure you buy individually packaged salty snacks. And drying hair after a shower takes forever.

I lived there for 8 years. Once I went on a trip for 6 weeks and left the A/C off while gone. When I got back all my leather shoes were covered with green mold.

One of my mentors at the U. of FL said 3 things made the state inhabitable: Raid (insecticide), effective anti-skin fungus meds and A/C. I used to enjoy going out to the FL Turnpike toll booths and watch mosquitos commit suicide in the electric bug zappers.

• Video Link

^^In FL there was MUCH more action.

[dchan]

Originally Posted by Pedestrian

That's kind of irrelevant. The air leaving the A/C or the dehumidifier doesn't stay the temp it is very long. That 55 degree air warms (and the humidity in it drops) and the dehumidifier air cools (and its humidity rises).

I've lived in swampy Florida and, like most people there, was perfectly comfortable with a properly sized A/C both cooling and dehumidifying. If you want to run a dehumifier also, it's your business and have at it but you will be running up your electrical bill unnecessarily (both to run the dehumidifier and to recool the air it puts out) in the opinion of most people.

I don't agree that it's irrelevant. There's a reason why dehumidifiers are designed to output warm dry air. That warm air can hold more water vapor as it cools down than cool dry air from an A/C can hold as it warms up. That means it dries the air faster.

In addition, much of A/C's energy goes towards controlling latent heat rather than sensible heat. If we use a dehumidifier to control the latent heat and allow the A/C to control the sensible heat, the energy usage difference between dehumidifier + A/C combo vs. using A/C alone should be a wash.

[dchan]

Guide to A/Cs and controlling humidity, and why using dehumidifiers may be needed in certain climates:

https://www.greenbuildingadvisor.com...mid=1320557652

[jmecklenborg]

Originally Posted by jtown,man

Don't touch my AC, bro!

Really though, try living in Austin or pretty much anywhere in the South without it. If the government cares so much they should give us cleaner alternatives, which is happening quite quick in the US, as I believe we had the biggest decrease in emissions in 2017.

There would be no "sunbelt" without air conditioning. Florida had a population of 2 million in 1950. Now it's 20 million.

What's insane is that people used to take summer vacations to Michigan or Canada or Highlands, NC to avoid summer heat. Now people...GO FURTHER SOUTH AND SIT IN AIR CONDITIONING.

[Camelback]

Originally Posted by jmecklenborg

There would be no "sunbelt" without air conditioning. Florida had a population of 2 million in 1950. Now it's 20 million.

Think about what there wouldn't be without simple things like electricity and cheap fossil fuels used to generate that electricity and grow our food.

We would have a global population of about 500 million to 1 billion and extensively less knowledge as a species.

Humans have barely gotten to this point of comfort and excess in a fraction of a blink of an eye in geologic time. (Refer to the UFO thread).

[Pedestrian]

Originally Posted by jmecklenborg

What's insane is that people used to take summer vacations to Michigan or Canada or Highlands, NC to avoid summer heat. Now people...GO FURTHER SOUTH AND SIT IN AIR CONDITIONING.

A lot of them leave those southern spots. The population of my area in Arizona declines by about half in summer, most departing for places like Michigan or Canada. I'm a little unusual in heading for the CA coast (high temp forecast today = 70 degrees F).

I hate "sitting in air conditioning" although it's better than the alternative (not having air conditioning in places like Tucson). As it stands, I manage to live my life in places where you can have the windows open 365 days a year.

Still, for those who must have artificial temperature manipulation, it shouldn't be necessary to burn fossil fuels to do it. We now have the technology to avoid that with distributed solar (rooftop solar panels), industrial scale wind and solar to make up any deficiency in home generation, "green hydrogen" technology to store power for when the sun isn't shining or the wind isn't blowing and so on. And I'm for the more controversial nuclear power as well.