Blast Freezer Wall Problem

[Brad on Island]

I just installed a big freezer/blast freezer 28' x 85' x 20' high with a 8'x10' sliding door. It has two heated vents in it. one is the dual flap kind and the other one is a kason 1845 vent. both seem to be working. no ice build up on kason but little ice on dual flap style. But problem is the two long walls have blown out on the 85' sides. approx 2". It is butyled,foamed,blue skinned,has thermo breaks. Have installed lots of freezers (only install panels not refrigeration) and never had a problem but the walls have pushed out twice on this freezer. Any ideas why ???

[COOLJIM]

could be due to internal pressure after a defrost , i would check the spec of the pressure relief valves as to the room volume , with a view to adding more of them , i have seen hinged doors burts open after defrost with out a correctly sized PRV , also have the service tech check the defrost system is not overheating , that size of room probably has several evaps with a large defrost KW.

[Brad on Island]

Thanks COOLJIM,

The ref tech came and said it was due to the defrost on the units set at 4 min and had temps up to 156 degrees and then when came on it had a huge blast of warm air that caused the walls to be pushed out. the heated vents were fine he said. so he set the defrost for 2 min bringing the temp way down. If this makes sense to you. But all is good now. thanks for your reply.

[icemeister]

Kason has a selector chart for pressure reliefs. (See p.B-62):

http://www.kasonind.com/Walk-In_Cat_sept2010.pdf

For a blast freezer with 50,000 cu ft volume you would need two of their model 1845 vents.