On Mon, Jul 26, 2010 at 4:16 AM, RussellMc <apptechnz@gmail.com> wrote:
> VG said
>> I have algorithms that can manage that pretty well. Also, tolerance is
>> wide enough.
>
> What Vasile is saying is "Y' canna break the laws of Physics" (as
> Scotty noted from time to time).
>
> In a =A0completely closed system you CANNOT control both temperature and
> RH at once.
> Read on for what you can do, and how.
>
> For practical purposes, in a closed system =A0there is a completely
> constrained relationship in a closed system between temperature,
> pressure, volume and Relative Humidity for a given chamber size,
> amount of air, and amount of water.
>
> Assuming that your other contents do not alter (and what eg plants do
> MAY or may not violate that constraint) then messuring eg just mean
> temperature will give you mean RH and controlling just temperature
> will control RH - not necessarioly in a manner that is desired.
>
> IF the system under consideration is not closed then you CAN control
> both temperature and RH.
> If it IS closed then you cannot.
>
> eg you may have a growing space in a semi sealed container inside a
> larger lab. The space can be ventilated with a fan from the lab and
> can be heated. Air circulation is provided by an internal fan. If the
> test box is too be held warmer than the outside lab then it can be
> heated and controlled. Heating the air will reduce the RH. If the RH
> in the box is to be lower than the lab then you can probably juggle in
> blown air and heating to achieve a desired RH and temperature mix
> (don't take that as Gospel.)
>
> You can reduce RH in the box with eg a Peltier cooler that reduces air
> below its dew point so that it loses water content. If you reintroduce
> the coiled dier air directly into the box then net temperature and RH
> will fall. If you reheat the air before reintroduction you can reduce
> box RH and lower or raise temperature depending on degree of reheat.
>
> If there IS no box and the lab is your whole environment then the
> above method works if you drain the condensed water to outside the
> lab. If instead you want to increase RH you can use steam or eg an
> ultrasonic fogger and water supply. Overall the heater, cooler, water
> drain and fogger will give you complete control. The system is not
> closed as you allow water to enter and leave and energy for heating
> and cooling. For a true otherwise sealed system you will need to vent
> your Peltier hot side to outside the system in some cases or at all
> times + more heating.
>
> BUT if you do not have these cross boundary linkages OR a system
> within a system (eg box inside lab) you cannot control both
> temperature and RH at once. But you can have years of harmless fun
> trying.

Haha, thanks. But I've already thought of all that!

> Have you found a source of 1-2577 in small quantity yet ? :-)
> (I have a 1 litre bottle thereof but am 'a bit far away').

I have not found the exact product, but there seems to be some sort of
lacquer coating at my university electronics store. I'll go take a
closer look.

--=20
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