Where do I get an ACCURATE humidity meter?

[Tough Guy no. 1265]

Well mine will be sat in one position, so it will be at equilibrium.

[Tough Guy no. 1265]

ALL? Is that even possible with simple refrigeration?

[Martin Brown]

Something that is humidity sensitive. Three competing methods:

Of course not. Harry is every bit as unreliable as you.

[Chris Hogg]

Only if the humidity in the room is uniform everywhere, not changing and has been static for some time.

[Chris B]

When I studied it (oK many years ago so things might have changed) they didn't add any moisture afterwards, but heat.

Chill the air down to below its dew point and get all the surplus water dropped out (so you are left with 100% humidity at a known low temp (say

5C)) then re warm it back up to the required temperature, and if you have cooled it correctly you will have the required RH at the higher temperature.

(A classic tutorial problem for undergraduate engineering students)

[Tough Guy no. 1265]

That's how a dehumidifier works, as the output and input radiators of the compressor are both in the same place. But an air conditioner is supposed to cool the air, I don't expect it to warm it back up.

[tabbypurr]

I wonder who knows better, dehumidifier manufacturers or someone that has to ask basic questions about them.

NT

[Tough Guy no. 1265]

How stupid can you be? The dehumidifier is required to run until the ROOM has a humidity of (value on dial)%, set by the user. The user doesn't give a shit about what is coming out of the unit, they care what the ROOM is at. The only thing the dryness of the air coming out of the unit tells you is how QUICKLY it is DRYING the room, it does not tell you how dry the room is. The air coming out of the dehumidifier will ALWAYS be dry, so a sensor located at the out vent of the unit will gather no information apart from "the unit is switched on".

Same with a heater, you don't stick the thermostat above the heater, the thermostat is always located at the bottom, with the INTAKE of air.

Jesus Christ I understood this simple principle when I was in primary school.

P.S. I just checked my dehumidifier to make sure they weren't as stupid as you, and just as I thought, the sensor is right at the front behind the air intake filter, BEFORE the cooling pipes. Funny that.

[gremlin_95]

In air-conditioning applications, it is known as 'reheat'. A central unit can cool the air down the a temperature low enough to suit the zone with the highest heat load but then some zones (or indeed all) require the air reheating to prevent overcooling but still benefit from the dehumidification. These systems are generally out of favour as more energy efficient systems are available.

[tabbypurr]

se it's a pointless reading. The dehumidifier needs to know how damp the r oom is, so it knows whether to turn off yet. How dry the air is coming out of it is completely irrelevant.

side. The dehumidifier function thus gets it to move much further, so it m oves far enough to switch the thing off.

and eventually switches back on.

bove the heating element.

as to ask basic questions about them.

M has a humidity of (value on dial)%, set by the user. The user doesn't gi ve a shit about what is coming out of the unit, they care what the ROOM is at. The only thing the dryness of the air coming out of the unit tells you is how QUICKLY it is DRYING the room, it does not tell you how dry the roo m is. The air coming out of the dehumidifier will ALWAYS be dry, so a sens or located at the out vent of the unit will gather no information apart fro m "the unit is switched on".

thermostat is always located at the bottom, with the INTAKE of air.

s you, and just as I thought, the sensor is right at the front behind the a ir intake filter, BEFORE the cooling pipes. Funny that.

Thank you for answering my question. Clearly the manufacturers have a bit m ore clue than you.

NT

[Chris B]

Not necessarily, both radiators might be on a portable domestic dehumidifier unit (in which case the total effect on the air would be to dry it out and heat it up) but this is not necessarily true on what I would call "proper" air conditioning schemes. these need to control at least temperature and humidity (and possibly other pollutants).

But an air conditioner is

A wall mounted "air conditioning unit" with the one radiator outside and the other inside would cool the air and reduce the total water content, but probably increase the RH, but there would be little control of the final humidity. To properly control the humidity you need to overcool and then re-warm. Or possibly these days use some form of desiccant dryer.

>

[Tough Guy no. 1265]

Did you even read the P.S.? So you're illiterate aswell as stupid? "the sensor is right at the front behind the air intake filter, BEFORE the cooling pipes"

[tabbypurr]

rwise it's a pointless reading. The dehumidifier needs to know how damp th e room is, so it knows whether to turn off yet. How dry the air is coming out of it is completely irrelevant.

put side. The dehumidifier function thus gets it to move much further, so i t moves far enough to switch the thing off.

in, and eventually switches back on.

r above the heating element.

t has to ask basic questions about them.

ROOM has a humidity of (value on dial)%, set by the user. The user doesn't give a shit about what is coming out of the unit, they care what the ROOM is at. The only thing the dryness of the air coming out of the unit tells you is how QUICKLY it is DRYING the room, it does not tell you how dry the room is. The air coming out of the dehumidifier will ALWAYS be dry, so a s ensor located at the out vent of the unit will gather no information apart from "the unit is switched on".

he thermostat is always located at the bottom, with the INTAKE of air.

d as you, and just as I thought, the sensor is right at the front behind th e air intake filter, BEFORE the cooling pipes. Funny that.

it more clue than you.

sensor is right at the front behind the air intake filter, BEFORE the cool ing pipes"

So not only have you never heard of hysteresis and lack of sensitivity, and are entirely unfamiliar with the methods used to work round them, but you also appear now to assume all dehumidifiers are like yours!

NT

[Chris Hogg]

Does a pedometer detect child molesters?

No, but as paedometer might.

[The Natural Philosopher]

No, that just measures children: You need a paedophilometer.

[Tough Guy no. 1265]

I WAS actually thinking of a portable dehumidifier, so the two radiators ARE in the same place, give or take a foot. The net heating effect is zero, plus the negligible heat from the motors.

I've never heard of humidity adjustments on them. If you have a humidity problem you get a dehumidifier, the air conditioner was because it was too hot, usually in the summer, when damp isn't a problem.

[Tough Guy no. 1265]

umidifier it is

otherwise it's a pointless reading. The dehumidifier needs to know how = damp the room is, so it knows whether to turn off yet. How dry the air = is coming out of it is completely irrelevant.

output side. The dehumidifier function thus gets it to move much furthe= r, so it moves far enough to switch the thing off.

again, and eventually switches back on.

eater above the heating element.

that has to ask basic questions about them.

the ROOM has a humidity of (value on dial)%, set by the user. The user = doesn't give a shit about what is coming out of the unit, they care what= the ROOM is at. The only thing the dryness of the air coming out of th= e unit tells you is how QUICKLY it is DRYING the room, it does not tell = you how dry the room is. The air coming out of the dehumidifier will AL= WAYS be dry, so a sensor located at the out vent of the unit will gather= no information apart from "the unit is switched on".

r, the thermostat is always located at the bottom, with the INTAKE of ai= r.

tupid as you, and just as I thought, the sensor is right at the front be= hind the air intake filter, BEFORE the cooling pipes. Funny that.

a bit more clue than you.

"the sensor is right at the front behind the air intake filter, BEFORE t= he cooling pipes"

, and are entirely unfamiliar with the methods used to work round them, = but you also appear now to assume all dehumidifiers are like yours!

You only need to work around it if you have a cheap shit sensor. The hy= steresis of my humidistat is 1-2%, when the machine is OFF. I've only e= ver seen the likes of what you describe on a really crap room thermostat= for =A35, which actually had a resistor under the bi-metallic strip bec= ause otherwise it clicked at about +/- 6C.

-- =

"I'll have the rump steak, rare, please." He said, "Aren't you worried about the mad cow?" "Nah, she can order for herself." And that's when the fight started....

[Tough Guy no. 1265]

It was a joke from America, where they can't distinguish someone who likes feet from someone who likes children.

[Tough Guy no. 1265]

That reminds me, a device in a factory which counts the number of odometers manufactured for European cars is a kilometreometerometer.

[tabbypurr]

midifier it is

ng it not the

therwise it's a pointless reading. The dehumidifier needs to know how damp the room is, so it knows whether to turn off yet. How dry the air is comi ng out of it is completely irrelevant.

output side. The dehumidifier function thus gets it to move much further, s o it moves far enough to switch the thing off.

again, and eventually switches back on.

ater above the heating element.

that has to ask basic questions about them.

he ROOM has a humidity of (value on dial)%, set by the user. The user does n't give a shit about what is coming out of the unit, they care what the RO OM is at. The only thing the dryness of the air coming out of the unit tel ls you is how QUICKLY it is DRYING the room, it does not tell you how dry t he room is. The air coming out of the dehumidifier will ALWAYS be dry, so a sensor located at the out vent of the unit will gather no information apa rt from "the unit is switched on".

, the thermostat is always located at the bottom, with the INTAKE of air.

upid as you, and just as I thought, the sensor is right at the front behind the air intake filter, BEFORE the cooling pipes. Funny that.

a bit more clue than you.

the sensor is right at the front behind the air intake filter, BEFORE the c ooling pipes"

and are entirely unfamiliar with the methods used to work round them, but you also appear now to assume all dehumidifiers are like yours!

teresis of my humidistat is 1-2%, when the machine is OFF. I've only ever seen the likes of what you describe on a really crap room thermostat for £5, which actually had a resistor under the bi-metallic strip because oth erwise it clicked at about +/- 6C.

Lots of dehumidifiers use cheap plastic strip sensors.

And there's nothing wrong with bimetal thermostats. They are designed to wo rk that way for a reason.

NT