[time-nuts] Temp/Humidity control systems?
jimlux at earthlink.net
Thu Oct 27 09:12:24 EDT 2016
On 10/27/16 2:43 AM, Neville Michie wrote:
> The nature of air is that when you heat it by one degree Celcius the humidity falls by 10%.
> That does not change the moisture content of the air, just the activity of the same amount of
> water vapour with regards to any material with an equilibrium moisture content.
> So it is important to control temperature fluctuation if you are going to control relative humidity.
In this particular case, I did do the calculation of "mass fraction of
water" from the data - the AC really does pull the water out of the air.
The "test article" in this case has relatively small air volume, and a
large surface area of wood. Water goes out fast, comes in slow.
There might also be a surface condensation issue on the glass surfaces.
If you look at the wet bulb temperature, it runs a few degrees below the
air temperature, except when the AC is on, when it plunges several
degrees in seconds.
> Neville Michie
>> On 27 Oct 2016, at 8:17 PM, David J Taylor <david-taylor at blueyonder.co.uk> wrote:
>> From: jimlux
>> You can buy the smallest "window" airconditioner and "plumb" it to your
>> chamber (I used dryer vent hose, cardboard, and lots of duct tape)
>> Attached is a plot temperature and RH of an insulated box about 1.2
>> meter wide, 2 meters tall and 60 cm deep, filled with 100 or so 750 ml
>> bottles of liquid.
>> The temperature is fairly stable, but the RH varies wildly - basically,
>> when the AC unit kicks on, it sucks all the water out of the air in the
>> box, and then, when it turns off, the (damp) walls of the box rapidly
>> rehumidify the air.
>> Thanks for that, Jim, and for the graph.
>> Your graph suggests to me that using /any/ form of artificial control may give worse short-term results than simply leaving an underground, uninhabited room with outside walls just "as-is". The slow daily variations may be far more tolerable than excursions due to heaters etc. being switched on and off.
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