Isolation & Specific Surface

The most important parameter for energy efficiency

The greater the outer surface and the greater the temperature differences between ambient and storage temperature, the higher is the heat input from the outside. Good insulation is therefore essential when storing at ultra-low temperatures. One possibility is to increase the wall thickness. But at a certain thickness this hardly brings any improvement and further limits the storage volume. This can be optimized by combining PU foam and integrated vacuum panels which result in high insulation values with moderate wall thicknesses.

The outer surface is significantly influenced by the geometry. Therefore it makes sense to keep the ratio of volume to surface as small as possible. The quotient of the external surface to the storage volume, which is referred to as the specific surface, is used as a reference value.

To illustrate this several individual refrigerators are compared to a large storage room. In general larger machines are more efficient than small ones. But even if many refrigerators are operated in the exact same way as one big storage room, they differ considerably in terms of energy consumption. This is due to the fact that the individual refrigerators have a significantly larger specific surface than the storage room. It can quickly add up to a factor of 10 in energy consumption.

Nature provides a fitting example for this. When looking at two different penguin species you can see from their natural habitats how drastic this influence is:

Refrigeration technology & regulations

Air as a refrigerant is the most suitable and safest solution

In the case of ultra-low temperature storage it is important to have a correspondingly high-performance and efficient refrigeration technology. The energy input from the environment (transmission), waste heat from electrical installations and loading and unloading procedures result in a corresponding power requirement. In addition, the moisture must be constantly removed from the cold room.

In terms of refrigeration technology it must also be ensured that it does not fall under the current regulations or is restricted by them. This currently affects the characteristic value "Global Warming Potential" (GWP) which is reduced to an average value of approx. 500 by 2030 due to the quota regulation of the European F-Gas Regulation and already prohibits refrigerants with GWP over 2500 for normal applications.

The refrigerants with high GWP, such as R23 (GWP = 14900 ) may still be used in ultra-low temperature applications as an exception. However, we strongly advise against this. For example R23 will most likely be banned in the next revision in 2021 and is currently massively affected by the shortage due to the quota regulation. New systems with this refrigerant are dubious and harmful to the environment. To make the impact on the environment tangible, let's compare the CO2 equivalent (GWP) of one kilo of R23 with the distance a car could travel until it emitted the same amount of CO2:

​

Loading and unloading processes

Locks reduce the heat input when access-ing the cold room

Opening the access to the storage room creates a brief, large flow of air which brings a lot of warm air into the cold room. This has a drastic effect especially in low-temperature applications as the difference in density of the air between the storage room and the ambient is high due to the temperature difference. This means that a lot of cold air leaves the cold room when the door is opened. Due to the integration of a sluice  which as a buffer zone is only tempered by transmission and convection from the cooling chamber the influence on the storage temperature in consequence of loading / unloading procedures remain low .