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Thread: Defrost sequence
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23-02-2005, 05:01 PM #1
Defrost sequence
I look after a cold storage site, three stores each has its own plant room. each plant is pretty much the same set up, R22 pump curculated, flooded evaps, 2 stage compound compressors, hot gas defrosts (pressure regulators on evaps), PLC controlled. Grenco installs 130, 195 & 288kw
for some reason when installed the liquid & suction soleniods on each evap are controlled by one PLC output so they are either both on or both off, this means it's not posible to have a pump down before the evap is defrosted, in other words hot gas straight into a evap full of liquid.
Finally got the go ahead from the boss to spead some money and get this sorted, i'm going to fit output expansion blocks to the mitsi PLC's and add extra relays so the suction and liquid soleniods can be independantly controlled.
at the moment the sequence is as follows:
Stage 1, defrost initated fans stop perif heaters on, liq & suc closed, hot gas open (35 mins)
Stage 2, drain down, hot gas closes (4 mins)
Stage 3, snap freeze, liq & suc open (4 mins)
stage 4, fans on perif heaters off, back to normal running,
i'm looking to change it to:
Stage 1, pump down, liq closes (4 mins)
Stage 2, defrost, fans stop, perif heaters on, suc closes, hot gas opens (35 mins)
Stage 3, drain down, hot gas closes (4 mins)
Stage 4, snap freeze, liq & suc open (4 mins)
Stage 5, fans on, perif heaters off, back to normal running,
Im I on the right lines with the sequence above?
Does any one have any advice for the ideal sequence for this system?
The timers will all be ajustable via a HMI.
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