03 Apr 2008 08:01:01

jqm

Cooling small area for thermal testing ... suggestions?

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

11 Apr 2008 22:09:31

pipedown

Re: Cooling small area for thermal testing ... suggestions?

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 >