Cooling small area for thermal testing ... suggestions?

[jqm]

Hello,

I am performing testing on load cells over a thermal range (40-135F).
Currently I have a NON-insulated area made of Bent Sheet metal, this
area is relatively closed up with an opening on one side for the
application of hot/cold via a portable ceramic heater / air
conditioner respectively.

Currently I have no problems with heat, I can hold it relatively
stable to +/- 0.2 degrees over (80-130F).

On the cold side I would like to get down to 40 deg F, . the problem
is stability. The unit gets down to 45 deg f, then begins to frost
up, then the output slowly increases to about 55 deg F where it
stabilizes off.

I understand one method would be to get a frostless, however I think
that it may introduce thermal output fluctuations.

Any Suggestions... I would like to hold +/- 0.2 deg F from 45 deg F-
Room Temp


Thank you for your time
jqm

 

[pipedown]

You are probably cooling in an open loop. That is you are cooling humid
room air, pushing it into the test chamber then letting that exhaust
anywhere it pleases.

You should use a closed loop. Recirculate the exhaust from the box back to
the A/C inlet air duct. This way the air will be somewhat cooler (improving
efficiency) but more importantly, already dehumidified by the first pass
through the cold coil.

This will also improve energy efficiency for hot as well. An alternative is
to use an LN2 cooled test chamber but that's more overhead and cost (get a
tank, plumbing, etc)



"jqm" <jqmobile@gmail.com> wrote in message
news:de676f74-13b9-42e7-a755-678317cc5604@x41g2000hsb.googlegroups.com...

Hello,

I am performing testing on load cells over a thermal range (40-135F).
Currently I have a NON-insulated area made of Bent Sheet metal, this
area is relatively closed up with an opening on one side for the
application of hot/cold via a portable ceramic heater / air
conditioner respectively.

Currently I have no problems with heat, I can hold it relatively
stable to +/- 0.2 degrees over (80-130F).

On the cold side I would like to get down to 40 deg F, . the problem
is stability. The unit gets down to 45 deg f, then begins to frost
up, then the output slowly increases to about 55 deg F where it
stabilizes off.

I understand one method would be to get a frostless, however I think
that it may introduce thermal output fluctuations.

Any Suggestions... I would like to hold +/- 0.2 deg F from 45 deg F-
Room Temp


Thank you for your time
jqm