Global Warming and TEWI Factor

As already mentioned (Refrigerant developments and legal situation), a method of calculation has been developed to judge the influence upon the global warming effect for the operation of individual refrigeration plants (TEWI = Total Equivalent Warming Impact).

All halocarbon refrigerants (including the non-chlorinated HFCs) belong to the category of greenhouse gases. An emission of these substances contributes to the global warming effect. The influence is much greater than for CO₂, which is the main greenhouse gas in the atmosphere (in addition to water vapour). Based on a time horizon of 100 years, the emission of 1 kg R134a is roughly equivalent to 1430 kg of CO₂ (GWP = 1430).
Thus, the reduction of refrigerant losses must be one of the main tasks for the future.

On the other hand, the major contributor to the global warming effect of a refrigeration plant is the (indirect) CO₂ emission caused by energy generation. Based on the high percentage of fossil fuels used in power stations, the average European CO₂ release is around 0.365 kg per kWh of electrical energy (average for EU 2019, source: www.carbonfootprint.com). This results in a significant greenhouse effect over the lifetime of the plant.

Due to the large proportion of the total balance, there is not only a need for alternative refrigerants with a favorable (thermodynamic) energy balance, but an increased demand for highly efficient compressors and associated equipment as well as optimised system components and system control.

When various compressor designs are compared, the difference of indirect CO₂ emission (due to the energy requirement) can have a larger influence upon the total effect than the refrigerant losses.

A usual formula is shown in the following figure (Method for the calculation of TEWI figures). The TEWI factor can be calculated and the various areas of influence are correspondingly separated.

Additionally, the following figure (Comparison of TEWI figures (example)) shows TEWI values with various refrigerant charges, leakage losses and energy consumptions (example: medium temperature with R134a).

This example is simplified based on an overall leak rate as a percentage of the refrigerant charge. The actual values vary very strongly, so the potential risk of individually constructed systems and extensively branched plants is especially high.

Great effort is made worldwide to reduce greenhouse gas emissions, and legal regulations have partly been developed already. Since 2007, the "Regulation on certain fluorinated greenhouse gases" – which also defines stringent requirements for refrigeration and air conditioning systems – has become valid for the EU. Meanwhile, the revised Regulation No. 517/2014 entered into force and has to be applied since January 2015.