Measures against dryness

November 18st
This morning, while listening to FM radio in the car on the way to the airport, the DJ said that just placing a cup next to the bed in a hotel is effective in preventing dryness. And that humidifying the air will make it warmer. I was intrigued by this, so I'd like to write about it.
First of all, hotel rooms are usually around 15 to 20 square meters for single rooms.
If the area is 20 m2.5 and the ceiling height is 50 m, the volume will be XNUMX mXNUMX.
I don't remember the legally required ventilation rate for hotels, but it seems to me that many hotels don't even ventilate half the amount required by law.
But for now, let's assume it's 0.5 times.
This means that 1 cubic meters of heated air that is slightly more humid than outside will leave the room per hour, and 25 cubic meters of cooler, dry air will enter the room in its place.
I'd say most rooms have an absolute humidity of around 4.5g/kg.
The density of air at 20°C is approximately 270 kg/mXNUMX, so there is about XNUMX kg of air in the room to begin with, which contains about XNUMX g of water.
Of this, 3g remains in the room, and the other half is replaced by dry air at XNUMXg/kg.
The amount of moisture is 3 x XNUMX = XNUMXg, which when added to the original XNUMXg gives XNUMXg/kg. We can see that the humidity, which was already low, decreases the more the air is ventilated.
The amount of water you need to drink while sleeping without feeling thirsty is about 7g/kg.
In this case, there would be 50g of water in a 350mXNUMX room.
If you ventilate 0.5 times per hour, 175g will remain, and after one hour the moisture content will be 1g, so by adding 250g per hour you can maintain the original humidity level.
In fact, just being around someone produces a little moisture.
Taking a shower also helps to remove moisture.
However, even taking this into account, even if you are staying for 22 hours, checking in at 8pm and checking out at 10am, you will still need to add enough humidification to subtract the amount of moisture generated from 750g.
This means that it is simply impossible to humidify an air conditioner using a cup of water where the water level does not drop even 1 mm overnight.
And one more thing.
About the fact that humidification makes the air warmer
This is half right and half wrong.
If you use a steam humidifier, which was common in the past, the air will definitely become warm.
This is because it is a method that uses thermal power to heat and evaporate water, so moisture and heat are generated at the same time.
On the other hand, with evaporative humidifiers, which are the most energy-efficient, the longer you operate them without heating, the more the room temperature will drop due to the latent heat of vaporization.
It may be easier to understand what evaporative cooling is like the refreshing feeling you get when you use alcohol to disinfect with water before an injection, or the slight drop in temperature on the road when water is sprinkled on the road in summer.
However, if you use it in conjunction with an air conditioner for heating, the air conditioner will have to run more as the room temperature drops.
If this happens, a humidified room at 20°C will definitely be warmer than 20°C without humidification.
As you may have figured out by now, the amount of moisture in the air is a type of heat.
The technical term for this is latent heat.