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I have a general question concerning air condition systems. Basically to me the air coming out of the AC unit doesn't feel natural.

I've experienced different types of AC units, from small to quite large, with compressor/gas or simply water cooling. And on all of them, it feels to me that the air has changed in some way and is no longer fresh and natural.

As far as I've researched online, any AC unit is supposed to only change temperature without changing anything else with the air that is fed into the desired location... so why do I have this feeling then?

I've asked a number of friends and pals, and one person shares my observation. The others haven't experienced the same.

So... is there something wrong with me and my perception? Or do AC units really make the processed air more... "artificial"? And if yes, can anything be done about it?

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    it is not the air that is unnatural, it is cold wind blowing at you indoors that is unnatural – jsotola Oct 8 '19 at 6:33
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    An AC unit conditions the air. It lowers the temperature AND the humidity. Moisture in the air is removed in the AC unit. Drier air feels different (light and crisp like late autumn air vs heavy humid warm air). What does "feels unnatural" mean? – Gunner Oct 8 '19 at 10:32
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    Your concern sounds very "sciencey". It's not science. It's a gut feeling, which are known to be deceptive and artificially distressing. The comments above are right. – isherwood Oct 8 '19 at 13:32
  • It's either working as they've always have, or you have a stir setting on your thermostat. – Mazura Oct 8 '19 at 19:41
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A typical (I am sure there are exceptions for various extreme situations - perhaps clean rooms, hospital operating rooms, extreme environmental situations, space station (ISS), etc. - though it may turn out that nearly all (except ISS) are really just "regular air conditioning with higher power and/or more filtering") does the following:

  • Use some method of cooling to indirectly cool the air in a building. In a traditional home air conditioner that is via freon which goes through a compression/expansion cycle so that it gets very cold to go inside and cool your air and then releases the heat outside. The mechanism is a little different with a chiller, but the basic result is the same: some method gets something really cold and the building air transfers heat to that thing (e.g., freon or water) and the air ends up colder. But the air does not "touch" the actual freon or other cooling fluid.
  • Filter the air to remove dirt/dust/pollen/etc. That can range from a simple replaceable filter to a HEPA "super" filter that can get the really small stuff out. Some systems use an electrostatic filter to get the dust out electrically - but the goal (and result, hopefully) is always the same - make the air cleaner. Air circulated through a house repeatedly (and especially with modern buildings that are well sealed) collects a lot of dirt from people, pets, etc. so filtering is important.
  • Blow the air through the building. This is required for air conditioning because, unlike heating where the heat can radiate through the house naturally, cold air will not do much unless it gets pushed to where you need it.

There is a lot more variety on heating systems, but for HVAC that's all there is to it. So why does it feel unnatural?

  • Dry air. A natural consequence of air conditioning is that it will lower the humidity of the air. In many areas, hot summer air is also humid air ("It's not the heat, it's the humidity!") and that is because hot air can hold more water vapor than cold air. When the air is cooled, it goes below the dew point and water vapor condenses and needs to be removed (preferably by gravity, but if that is not sufficient then there will be a condensate pump). As the air warms up again, it will end up much less humid and feel different. This is good for a number of reasons, provided it doesn't get too dry. But it will definitely feel different. As an example, if you have a hot, humid day but at night if the temperature outside drops to 72 F, the inside air at 72 F will feel different because it has been dried over the course of the day when it was cooled.
  • Blowing air. A breeze feels different than stagnant air. While the average air speed inside a house is very low, next to each air vent it will be fairly high.
  • Cold air. You can't easily cool a house to 72 F by blowing 70 F air. So you blow air at 60 F (or colder). That is much colder than you are normally comfortable with, but it mixes with the rest of the air quickly and averages out to the set temperature. Similarly, in the winter (if you have forced air heating), the air coming out of the vents will be a lot warmer than 72 F but it will all average out. Some people like that feeling "I'm hot - ahh, nice cold air" and "I'm cold, ahh, nice hot air" but some people are uncomfortable with that differential.
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Generally, (newer) buildings are well sealed - this is very good because it limits air leaks and means your heating and cooling bills are lower. However, it also means that you have to have a method for intentionally exchanging inside air with outside air.

The air inside will get stale as it is breathed by anyone who is inside. It will pick up odors from cooking, pets, bodies, etc. It may be that you're somewhat more sensitive to the "staleness" of the air in buildings that aren't exchanging the air fast enough. This would apply to both heating and cooling - it may just be that you notice it more during cooling season than you do heating season.

I wouldn't consider this something that's "wrong" with you, just that you notice it more than most people do, like the lady in Ed Beal's answer who seemed to be sensitive to electric fields and how I notice flicker in old tube-type monitors that have a 60 Hz refresh rate while others have no idea what I'm talking about.

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Or do AC units really make the processed air more... "artificial"?

They make the air more dry.

Air contains water vapor. Warm air is able to hold more water vapor than cold air. The air conditioning equipment chills the air quite cold, as low as 5 degrees C, and air that cold can hold very little water. So the water falls right out of the air. Seriously, look under any car on a hot day, you'll see a puddle of water dripping down. That is that.

Thus, the water coming out of the vent is very dry.

And if yes, can anything be done about it?

Stay hydrated. Which is good advice anyway.

Run a humidifier, but not one that makes heat (or else the A/C will run extra to remove the heat, and remove the humidity too.

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AC air or air that is recycled from the living space run over a set of coils that are cold, just like a glass of ice water in the room collects the moisture in the air collects on the cooling coil , this makes less humid and may be why you feel the difference. I had a customer a few years back that was so irritated by this I did some research and found that adding ozone into the air close to the air handler was supposed to help and keep the system mold free. I gave her the white paper and she thought it was worth the cost to try, ozone has a very short life and is not good to breathe so the air speed or flow had to be reduced. She was happy with the results, that was the only air based system I ever installed most ozone systems are for water. To tell the truth I could not tell any difference with the system powered on or off, but she also had me install a faraday grid on the wall where her service panel was some people may just be sensitive different fields who knows.

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