Hi,
From my experience with conventional airconditioners in our NMR lab, I am
of the opinion that these units cannot control air temperature to better
than +/- 2 degrees. There are many reasons for this. First is the
control system that is used to decide when to turn the compressor on or
off. It is either a bimetallic element or a bourdon-tube that has
significant hysteresis (this is generally for the sake of the compressor
as this should not be cycled on and off too rapidly). Then, the fan speed
that is used to blow air is not generally dependent on room temperature,
but is set by the user. Finally, the temperature sensor is positioned at
the output of the air duct and not in the center of the room where it
would be best positioned to sense the actual room temperature.
Also, unless air circulation is very good, there will be hot and cold
spots inside the room. People entering the room would cause a fluctuation
in temperature that takes time to restore.
The ideal would be an A/C unit with an electronic control, utilizing a
sensor in the middle of the room (or multiple sensors throughout the
room), coupled to fan speed and an elaborate control of the compressor (or
better yet, two compressors for faster cycling) would be what you are
looking for, but I'm afraid this doesn't exist (yet). But good luck
anyway. If you find such a system, I would be glad to hear of it.
-Edward
On Thu, 10 May 2001, Charles G. Fry wrote:
> Dear AMMRL's:
>
> Having a problem that I hope this group can help with:
>
> We are undergoing remodeling, and I have requested new
> air-conditioning with specified plus-or-minus 1 degree
> Celsius temperature control. I keep getting back from
> our physical plant designers something like:
>
> Client would like +/- 1 degree C. This is not
> feasible.
>
> I would appreciate hearing from those of you that have
> managed to make this temp control--clearly a critical
> aspect of any high-field facility--feasible, to send
> back as a response to my physical plant.
>
> Thanks,
> Charlie
>
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Edward T. Chainani Nuclear Magnetic Resonance Laboratory Manager
National Chemistry Instrumentation Center (NCIC)
Ateneo de Manila University phone: (632) 426-6001 loc. 5629
Loyola Heights, Quezon City e-mail: etch_at_ginto.chem.admu.edu.ph
Philippines FAX: (632) 426-1323
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Received on Fri May 11 2001 - 12:42:03 MST