Defrosting all HT Cabinets fed from Central HT Pack together at once

Hi All,

I have a retail client who is trying to reduce energy consumption on site with minimum investment. They recently ask me to remove heated defost for all high temperature cabinets (13 in total) on site and just run off-cycle defrost 6 times a day for 35mins at a time for each cabinet. All high temperature cabinets are fed from a central plant located on the roof of the building. To push this out further they have asked me if it would be possible to run the defrost of all cabinets at the same time; i.e. set up all cabinets being fed from the central plant to run defrost cycles at the same time. Their idea is that, with all cabinets defrosting and no cabinet calling for coolant from the plant, it will cause the central plant to power down during these defrost cycles, giving up to 3.5 hours of plant down time during the day.

Is there any detrimental impact to the system that anyone could see to doing this? Any advice is appreciated.

Thanks,

cpad

If you defrost all the cabinets at the same time the duty on the pack when it restarts will negate any energy savings made during the down time, due to the high current draw of the compressors under high load.
A properly done defrost schedule will be the most efficient.
If you have suction optimisation/floating suction capability this is the way to go, if not then the best you can do is to commission the pack and cabinets up to the top of their control band for temperatures.

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Originally Posted by Silhouette

If you defrost all the cabinets at the same time the duty on the pack when it restarts will negate any energy savings made during the down time, due to the high current draw of the compressors under high load.
A properly done defrost schedule will be the most efficient.
If you have suction optimisation/floating suction capability this is the way to go, if not then the best you can do is to commission the pack and cabinets up to the top of their control band for temperatures.

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it wopould possibly cost you alot more to pull all cabs down and put excesssive wear on all your compressors hussmann protocol ht packs would only run down to -6 (the refrigerant in use ) and all the HT cabs had no defrost heaters installed it worked well and the compressors chugged away nicely you may get away with 4 40min defrosts on units make your diffs wider say 3 deg C units should be good just make sure all cabs clear of ice first or it wont work so good you can also try increasing yr compressor start delays from 6 to 10 min it wont make a massive difference but as the saying goes "Every little helps" :) :) :) :) :) :) :) :)

You'll have no defrost issues, any HT cabinet i've done has had electric heaters disabled, 4 defrosts of 45 mins max would nearly do you, as said above by wiser souls stagger the defrost, look at pushing your suction pressure as high as you can, have you EEV's fitted?

al

Only individual cabinet controllers (no central gateway) and TEV's in place. I'll revisit the compressor setpoints.

Thanks for all the replies.

cpad