Defrost Suggestions for Gravity Coolers

[Brian_UK]

Recently been given a site with a Frigadon (FWC 2000) 4 compressor water chiller running R1270 and Hycool brine solution. Brine temperature is -7°C.

The gravity coolers are in a large cool room, fish market, and also a cold store. The main areas are open to ambient conditions due to roller shutter loading doors and the cold store is inside this area. Not sure about the required cold room temperature but probably around +10°C (?); the cold room runs at +4°C I believe. (Got more reading to do to catch up with this site.)

The present defrost has been set for a one off period of 1.5 hours which is allowing the room temperature to rise too much.

I haven't worked with gravity coolers before and as yet haven't seen these ones running under load so don't know what the coils look like after a cooling period.

Would a single defrost period normally be sufficient or would several periods be better for the the system.

Any advice welcomed.