An insightful response to our previous article – “Freezer stores – implication of installing mobiles on the size of the refrigeration plant”

Last month James did an article on whether installing mobile racking in a cold store would increase the operation’s running cost (click here to read). Cape Town based Consulting Engineer at Marine & Refrigeration Engineering (MRE), Christo van der Merwe, had responded:


Freezer Store heat loads

The heat load in a freezer store comes chiefly from the following:

  • Heat gain through the walls and ceiling and infiltration through door openings.
  • Heat load from fan motors.
  • Heat load from warm product.
  • Heat load from lights is around 5 to 7% of the total heat load so is largely a minor factor
    • If the lights are switched off when the room is not in use then the effect of lighting is reduced.
    • With mobiles, if only the active aisle lighting is on then lighting heat load is very small.


If mobile racking is installed and the room is the same size but it can hold 80% more pallets then the effect on the heat load is:

  • Heat gain through the walls and the ceiling is the same for the same size of cold store but you can store 80% more product.
  • Heat gain for fans is the same for the same size of cold store but you store 80% more product.
  • Heat gain is the same for warm product if the warm product loading is the same for each scenario.
    • If you load warmer product in a mobile store because you can store more pallets then you will increase the heat load-this is because you have changed something-you have loaded more product.


Conversely, if you have to build a cold store say 60% larger to load the additional 80% of pallets then:

  • The heat load through the walls and ceilings will be higher.
  • The fan heat load will be higher.
  • The refrigeration plant has to have a larger capacity, have a higher first cost and cost more to operate.


So, except for the cost of the mobiles the cold store owner is better off in most other aspects when he installs mobiles.


Other efficiency aspects:

  1. Dehumidified airlocks reduce heat load in cold stores and hence the first cost and operating cost of the refrigeration system.
  2. Pallet conveyors and high speed doors will reduce heat load and hence first cost and operating cost.
  3. LED lighting.


These things are all good ideas and reduce the operating heat load but come at a capital cost.


I would suggest the reason that cold store owners do not go for the more expensive stuff are:

  • It costs more and SA people do not often appreciate the benefits of spending more on upfront costs to save on operational costs.
  • Cold store owners do not always understand the subtle benefits and are probably sceptical of technology.
  • More technology implies higher maintenance costs and employing better trained staff
  • No one company sells a package-we all sell our product for our own benefits.


You need a client who trusts you to be able to sell him more equipment with the intention of reducing his operating costs.


Further comment:

If a refrigeration plant is oversized then it should get to temperature quicker and reduce capacity when it gets to temperature and then you will be reducing the electrical costs.


If the plant does not reduce capacity on achieving room temps then the cold store will get colder (which does benefit the product or the cold store owner) but still operates at full electrical cost.


Good old common sense goes a long way to achieving a smarter and more efficient operation and only costs you effort.


For more information contact Christo at Marine & Refrigeration Engineering (MRE), on 27 (0) 21 551 0575 or via email