Reduce energy usage – I think the point is finally sinking in that freezer room doors are not your friends but an unfortunate necessity that need to be designed in such a way as to eliminate the ingress of moisture.
Of course, doors aren’t the only route for moisture to gain access.
Inferior insulated panel sealing will have the same effect as will access holes for light fittings and electrical cables which are not properly sealed. Pallets left for extended periods on warm loading docks will bring a surprising amount of moisture into the freezer. The moisture that gets through our defences makes its way to the coldest surface which is normally the evaporator fins. Any build-up of ice here reduces the heat that can be removed as part of the refrigeration cycle.
Your compressors can be going flat out, but with ice on the evaporators, their efficiency is significantly reduced. In those instances where the evaporators get turned off and the freezer door is left open, a fairly common occurrence when stock takes are in progress, the incoming moisture heads for the coldness of the floor. Even the smallest build-up of ice on mobile rails can cause the bases to slip, or worse still prevent them from moving at all.
When I joined the industry, freezer doors, protected if at all by half eaten plastic strip curtains, were left open all day. Indeed I suspect that refrigeration plants were designed on this basis. Slowly we were persuaded to close them by various means, none of which worked beyond the short term. Door keepers lost interest.
Motorised doors had a short life expectancy when faced with forklifts, those ever present weapons of mass destruction. Air curtains sounded good, but on a 5 metre high door the air volume, velocity and angle were rarely correct and they could end up encouraging moisture in rather than keeping it out.
Out of this confusion certain truths emerged.
The number of freezer doors must be kept to a minimum and their size likewise. This led to additional doors designed to allow reach trucks in and out but which were otherwise kept closed. The main access door could then be significantly lower at say 2.5 metres to reduce moisture ingress. These worked even better when high speed doors were fitted. Unfortunately not enough design was sometimes put into the reach truck doors, where faulty seals could cause them to stick and allow for troublesome ice formation.
Another European development is the use of man on riders to move pallets from the freezer into the waiting trucks. This is now almost standard and allows access door heights to be further reduced. There are challenges, including how to position pallets on the forks so as not to break the bottom bearers when the front wheels are extended, and the angles between the airlock floor, dock leveler and truck floor. These can be resolved and have been at a local fruit packing operation.
Roll up doors are an Australian speciality. But they don’t like ice. If it builds up on the the roll up mat it becomes heavier and thicker which impedes operation. Hence they are always used with fans to keep them dry.
The use of pallet conveyors to move product in and out of freezer stores was a popular option in South Africa 20 years ago, faded from view and is now staging something of a comeback.
Conveyors reduce door sizes to the minimum, just slightly bigger than the pallet, overcome any height differences between loading dock and freezer and provide a magazine effect which can balance the work rates in both areas. Pallets are stored at operating temperatures which reduces moisture build up. The interface between the conveyors and the doors needs to be properly designed and ice formation inside the hatches avoided. Capital costs can be a negative, but are normally justified if the savings from improved efficiencies are properly accounted for.
Then dehumidifiers came along.
While they can be energy intensive to run, if designed into airlocks or for loading platforms where the loading docks are properly sealed, and truck doors can be opened once the vehicle had docked, they work extremely well. I have been in one European freezer store where the success of the de-humidifiers and dock sealing caused an unexpected challenge, that of dust. This is a problem I have yet to encounter in a South African freezer store.
The latest development is a combination of dehumidifier and high speed door. I saw an example working in a UK cold store some years ago but at that stage the pricing was prohibitive. Now there are some models on the local market which are proving very popular.
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