Freezer Containers Vs. Freezer Stores
Pictured: Freezer Container (Source)
In Luanda and Lagos there are companies that stack old freezer or reefer containers (6 and 12 meter) up to 4 high and use them mainly for the storage of frozen chicken. Companies with limited cold storage requirements in South Africa also use reefer containers for the same purpose but on ground level only. Reefer containers can be used to store frozen foods on shore but they are problematic when used as a long term solution. Reefer containers are designed to keep product at the same temperature as when the container was loaded so long as the doors are kept closed and sealed. They are not designed to decrease product temperatures. When used as cold stores in Lagos and Luanda, frequent door openings quickly allow the cold air to escape and raise product temperatures which can cause product to go “off”. The containers stacked off the ground are normally accessed by means of ladders which cause additional delays in loading and offloading.
Reefer containers, when properly sealed and with good insulation can use around 5 KW of electricity per hour. If left sealed, the refrigeration unit will come on only as required to maintain the set temperature.
The use of old reefer containers for cold storage is not recommended. The insulation and door seals degrade over time. It is difficult to keep the T section floor clean and hygienic. Power usage is high. Stock inside the container is difficult to access. While it is possible to upgrade containers with smaller doors and refurbished refrigeration units, purpose built cold stores are a better long term solution.
An energy usage comparison between a freon cold store and reefer containers from refrigeration consultant Christo van der Merwe is attached as is a cold store design for 208 pallets using Storax mobiles.
Christo says, I have looked at 10 x containers at 20 pallets/container vs 1 x 200 pallet freezer store operating at -20°C.
Containers have the following limitations:
- They can hold product that is on temperature but they are not designed to cope with warm product being loaded above the holding temperature.
- You have access to the 2 x front pallets and if you want to access a pallet that is stored in the back of the container you have to remove all the containers loaded in front of it.
- The loss of temperature can be dramatic is every pallet is unloaded to access a pallet at the back and then the remaining pallets are loaded in again-it will take time to regain room temperature.
- If there is any refrigeration equipment failure then the container has to be emptied until the component is repaired.
The container refrigeration system for a 40 ft (12m) container = 20 pallets at -20°C has a cooling capacity of ± 4.5 kWR.
The refrigeration system has a power consumption of ± 5 kW depending on manufacturers specs but at best we can expect a COP of 0.9 in summer conditions.
For 10 x containers the total power consumption will be ± 50 kW.
200 Pallet Freezer Store (mobile racking)
The 200 pallet freezer store is fitted with mobile racking so we have the smallest possible foot print.
- With mobile racking you have access to every pallet position.
- Double handling of product can be avoided
- The refrigeration system generally has some redundancy so if there are any equipment failures then the store will still operate but it will lose a bit of temperature.
- The system generally has pull down capacity so some warm product can be loaded into the store without affecting the room temperature too much.
Refrigeration system – Freon
The freezer store refrigeration system is based on ± 28 to 30 kWR which is required to maintain temperature with no product being loaded.
The refrigeration system has a power consumption of ± 27 kW which includes evaporator and condenser fans so a COP of ± 1.04
Refrigeration system-Ammonia (for interest)
The freezer store refrigeration system is based on ± 30 kWR which is required to maintain temperature with no product being loaded.
The refrigeration system has a power consumption of ± 18 kW which includes evaporator and condenser fans so a COP of ± 1.66 (so 40% lower power consumption).
- Power consumption for 10 x containers = 200 pallets
± 50 kW = 277%
- Power consumption for 200 pallets freon freezer store
± 27 kW = 150%
- Power consumption for 200 pallets ammonia freezer store
± 18 kW = 100%
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