refrigeration evaporator performance

[buster]

My work involves an environmental test chamber (hot, cold & humidity, the issue I have is during cold tests (-20°F or so) the evaporators frost up from traffic into and out of the chamber (reducing performance of the refrigeration system). Looking for information on evaporator de-rating as ice is accumulated and sucessful stratigies to combat or reduce ice formation on evaporators. [sig][/sig]

 

I have listed some concepts that hopefully you can apply.
Never have the evap fan running when the door is open. It draws in more moisture.
Employ air curtains and install plastic curtains and educate all who have access to your freezer to the price of introducing additional moisture.
Have your refrigeration people explain to you what deicing controls have been installed. If it is a timed initiation, have them drecrease the interval. It it has a pressure sensing control have them decrease the pressure setting for quicker initiations. I would suggest that a manual defrost switch be added as a defrost will be required every time the door is opened long enough to allow moisture to block airflow. A human can better predict when to defrost before ice accumalates enough to effect performance. There will be a price to pay for each defrost as it is adding heat to your freezer, so education and prudent initiations are much preferred to wasting energy.
Hope this helps.