Question Air-Conditioning, Use and care.

[dbeachy1]

Wrong, sorry. Assuming you are talking about relative humidity. And relative humidity is (along with wind speed) the most important factor when it comes to comfort.

When you chill air down below its dew-point, you will remove water. But air that's at its dew point has by definition a relative humidity of 100%. To lower the relative humidity you have to increase the temperature of the air.

A "real" AC lowers the temp to where dew point has the correct water mass/air mass (specific humidity), and then heats it up again to lower relative humidity.

Maybe we're talking semantics, but we'll just have to agree to disagree on dew point being a more accurate measure of comfort. Dew point is the absolute measure how much actual moisture is in the air, independent of temperature, whereas relative humidity is just that: relative to how warm the air is. Warm air can hold more water than cooler air. Take air with a dew point of 75 F (100% relative humidity), which is rather uncomfortable (it's sticky and your clothes don't dry out once you sweat). Now heat that same air up to 90 F: Now the relative humidity is "only" 61.5% (calculator here), but it still contains the same amount of water (dew point 75 F) only now it feels a lot more miserable even than it did at 75 F, despite the relative humidity being "only" 61.5% (at 90 F) instead of 100% (at 75 F): the amount of water in the air did not change, only the air's capacity for holding even more water increased along with the temperature (because warm air can hold more water than cooler air).

The dew point article I linked before explains the difference in detail: Dew Point - The Best Indicator of Comfort. Quoting:

Ever wonder why television meteorologist and weather broadcasters rarely show the current humidity numbers? During the summer, especially when it is as hot and sticky like it has been we will get a few emails maybe even a phone call or two asking why aren't you showing the humidity? Even though we use the term "Humid" to describe the air outside, humidity is actually a bad indication of just how comfortable or uncomfortable the air really is.

Relative humidity is just that... relative. It is relative to the temperature and moisture content of the air. Here is an example of what I mean.
On a hot, sticky, rather uncomfortable summer day you could have an outside temperature of 92 with a dew point temperature of 68 (which is listed in the uncomfortable zone in the chart above) this would give you a relative humidity of about 46%

On a pleasant, warm yet comfortable spring day you could have an outside temperature of 72 with a dew point temperature of 55 (which is listed as pleasant in the above chart) you would have a relative humidity of about 55%
Although the summer day feels more humid than the spring day its relative humidity is actually lower.

The Wikipedia article on dew point also explains it:

When the air temperature is high, the human body uses the evaporation of sweat to cool down, with the cooling effect directly related to how fast the perspiration evaporates. The rate at which perspiration can evaporate depends on how much moisture is in the air and how much moisture the air can hold. If the air is already saturated with moisture, perspiration will not evaporate. The body's thermoregulation will produce perspiration in an effort to keep the body at its normal temperature even when the rate it is producing sweat exceeds the evaporation rate, so one can become coated with sweat on humid days even without generating additional body heat (such as by exercising).
As the air surrounding one's body is warmed by body heat, it will rise and be replaced with other air. If air is moved away from one's body with a natural breeze or a fan, sweat will evaporate faster, making perspiration more effective at cooling the body. The more unevaporated perspiration, the greater the discomfort.

Here's an article from the National Weather Service clarifying the difference between relative humidity and dew point:

The dew point is the temperature the air needs to be cooled to (at constant pressure) in order to achieve a relative humidity (RH) of 100%. At this point the air cannot hold anymore water in the gas form. If the air were to be cooled even more, water vapor would have to come out of the atmosphere in the liquid form, usually as fog or precipitation.

The higher the dew point rises, the greater the amount of moisture in the air. This directly effects how "comfortable" it will feel outside. Many times, relative humidity can be misleading. For example, a temperature of 30 and a dew point of 30 will give you a relative humidity of 100%, but a temperature of 80 and a dew point of 60 produces a relative humidity of 50%. It would feel much more "humid" on the 80 degree day with 50% relative humidity than on the 30 degree day with a 100% relative humidity. This is because of the higher dew point.

So if you want a real judge of just how "dry" or "humid" it will feel outside, look at the dew point instead of the RH. The higher the dew point, the muggier it will feel.

General comfort levels that can be expected during the summer months:

less than or equal to 55: dry and comfortable
between 55 and 65: becoming "sticky" with muggy evenings
greater than or equal to 65: lots of moisture in the air, becoming oppressive

 

[Loru]

... gigantic block of frozen rusty hydrogen ...

:blink: Must be powerfull heat exchanger then.

 

[C3PO]

The rate at which perspiration can evaporate depends on how much moisture is in the air and how much moisture the air can hold.

Isn't that exactly describing relative humidity?

And I can tell you from experience that 15°C/59°F @100%RH is a lot more uncomfortable than 32°C/90°F @36%RH, even if the dew points are identical.

When we talk about temperatures around freezing (0°C) high humidity can be deadly. Around here temps range between -5°/+15°C (23°/59°F) 95% of the time and the RH rarely dips below 85%. "Warm" days feel way too hot if there's no wind. But a windy "cold" day can have you in serious trouble if you're not careful. I've worked in Norway at -28°C/-18°F and it didn't feel nearly as cold as a typical winter day in the Faroe islands.

Perhaps dew point works better for some temp and/or RH ranges, but I'm sure there's a reason dew point is never mentioned in our weather reports.

---------- Post added at 02:09 AM ---------- Previous post was at 02:07 AM ----------

:blink: Must be powerfull heat exchanger then.

Oxidized hydrogen isn't that hard to freeze. :speakcool:

 

[Loru]

Oxidized hydrogen isn't that hard to freeze. :speakcool:

Missed the meaning of rusty.

*note to self: don't post after 2 am. Nothing good happens after 2 am.

 

[MaverickSawyer]

Just remember this, Notebook (And anyone else with a "portable" AC):
NEVER, EVER TIP THEM.
They won't explode or anything. They're even safe to run after a day. But until that 24 hours has passed after yo tipped the unit and then set it back upright, you stand a fairly high chance of either hydraulic locking the compressor cylinder, getting metal-on-metal contact in the compressor, or letting oil mingle with the freon coolant. Any of those three will cause your unit to fail if it gets plugged in and run within 24 hours.

This applies to refrigerators, too, btw.

Source: 4 years at Home Depot as a loader, warning people not to do this, and having them come back the next day with busted units.

 

[Urwumpe]

I am a notorious AC denier... My car has one now, its quite nice for longer distance travel, but I can't imagine needing one for my house. Even during a "heatwave" like today (32°C announced... yes, thats what those hipsters call heat wave), I just make sure I get enough cool air during the early morning and keep everything closed until the late evening or when the next thunderstorm arrives.

But yes, drinking enough and enough of the good stuff is mandatory now.

 

[Notebook]

Just remember this, Notebook (And anyone else with a "portable" AC):
NEVER, EVER TIP THEM.
They won't explode or anything. They're even safe to run after a day. But until that 24 hours has passed after yo tipped the unit and then set it back upright, you stand a fairly high chance of either hydraulic locking the compressor cylinder, getting metal-on-metal contact in the compressor, or letting oil mingle with the freon coolant. Any of those three will cause your unit to fail if it gets plugged in and run within 24 hours.

This applies to refrigerators, too, btw.

Source: 4 years at Home Depot as a loader, warning people not to do this, and having them come back the next day with busted units.

Too late, already have.
Couldn't get it out the packaging without putting it on its side, and pulling it out. Too heavy.

Hopefully, will get away with it. Its worked about 6 hours non-stop, then intermittently yesterday and evening.
Much cooler today, not needed yet.

Nothing on the packaging about not tipping, just the usual signage.

Just had another look, yes there is a "No Tip" graphic. Hoh Hum...

Thanks, N.