Operational ways to reduce energy costs in freezer stores

By James Cunningham Managing Director Barpro Storage SA

THE latest challenge facing cold store managers is controlling  the monthly electricity cost, which in most cases has overtaken labor as the single largest freezer store operating expense. While the  absence of  load shedding has almost eliminated  diesel usage, every year electricity prices still increase  faster than storage fees. Assuming no changes to the refrigeration plant and the basic cold store structure, how can  cold store managers achieve Significant Electricity Savings?

1. Study the  monthly  electricity bills. Understand how they are made up. Track maximum demand charges. Investigate if lower off-peak KW hour rates are available. Make simple graphs and share them with your staff so that the reasons for sudden peaks  or high unit usage can be discussed and identified.  Compare the current month’s KW and Max demand with the same month last year. 
2. Find out how much electricity is required to run each item of equipment, which may  include fork lift battery chargers, mobile racks, pallet conveyors, air curtains, dehumidifiers, high speed doors  and even under floor heater mats. Can  the heavy users be operated via timers at night if off peak rates apply? 
3. Test product core temperature on arrival. If it’s less than -18 degrees or any other minimum agreed with the customer ,reject the load or blast freeze the pallets before putting them in the freezer store. Some freezers can now blast freeze inside the main store  which is cheaper in terms of electricity cost. Make sure the real costs are known and  charged to the customer.
4. Find out what the costs are per 24 hours if you have plug in points for containers, or part thereof and make sure to pass them on. 
5. The earliest cold stores were accessed through the ceiling for a reason. Expensive cold air could not easily escape.  Access doors are expensive and can cost up to R400/500 000 per annum in electricity costs, per door, if left open. Doors are the single biggest reason for high electricity bills. 
6. Don’t allow freezer doors to stand open if it has two access doors, as drafts will increase electricity bills exponentially.
7. Plastic strip curtains with no broken strips are the absolute minimum protection for an open freezer door way. They may stop the ingress of warm moist air at the top of the door, but the heavy cold air will still push  out at up to 6m³ per second. An air curtain can reduce the loss of cold air by up to 80%. 
8. The ingress of moist warm air is also a problem, initially  becoming ice or snow above the door, as it eventually sublimates to the evaporators and insulates them with ice reducing their cooling capacity. This ice is periodically removed via defrosts. If the number of defrosts can be reduced, electricity consumption will go down. Some freezer stores defrost  three times per day.Evaporator pods were introduced in South Africa largely because  freezer doors were left open and evaporator drip trays couldn’t cope with the constant ice build- up and removal. Some local freezer refrigeration plants have been designed  on the basis that the doors will be left open which in itself  increases electricity usage.

9. Decreasing the volume of warm air and moisture entering the freezer room is critical in reducing electricity costs. Powered conveyors, while expensive ,reduce the door size to just more than the highest pallet. This is a big improvement on the standard reach truck door which is 2400 mms wide and up to 5500 mms high. Alternatively fast opening doors, insulated or not, together with air curtains  work where conveyors are not an option. Removing moisture before it enters the freezer can be achieved with an air drier vestibule arrangement which reduces the air volume to be dried.Powered conveyors, while expensive, reduce the door size to just more than the highest pallet. This is a big improvement on  the standard reach truck door which is 2400 mms wide and up to 5500 mms high. Alternatively fast opening doors, insulated or not,  together with air curtains  work where conveyors are not an option. Removing moisture before it enters the freezer can be achieved with an air drier vestibule arrangement which reduces the air volume to be dried.

10. Some older freezers still have 1000-watt tungsten halogen lights. Swapping them for LEDs isn’t easy but will save electricity. 
11. Consider installing eutectic tubes in the depth of the  top rack beam. While eutectic plates won’t remove  air moisture, by  attracting  heat they  allow the refrigeration system to be idled/turned off during peak cost periods. Potential savings here are up to 30%.
12. Don’t bring pallets out of the freezer for case picking as the product loses temperature and the unpicked boxes  introduce heat and moisture into the freezer when eventually put away.

From my experience in South African cold stores,  if you follow these 12 points, significant electricity savings are almost guaranteed.