Greenhouse effect and TEWI characteristic

As already explained, a calculation method was developed to address the consequences of the greenhouse effect in the operation of refrigeration systems can be assessed individually (TEWI = T otal E equivalent W arming I mpact).

All halogenated refrigerants, including chlorine-free HFCs, belong to the category of greenhouse gases. An emission of these substances contributes to the greenhouse effect. Compared to CO 2 - the predominant greenhouse gas in the atmosphere (in addition to water vapor) - the impact is considerably higher. For example, the emission of 1 kg R134a (time horizon 100 years) is roughly equivalent to 1430 kg CO 2 (GWP100 = 1430).

This fact alone makes it clear that reducing refrigerant losses must be one of the key tasks of the future.

In contrast, the highest share of the greenhouse effect of a refrigeration system is the indirect CO 2 emission from energy production. Due to the high proportion of fossil fuels in power plants, the released CO 2 mass - on a European average - is about 0.45 kg per kWh of electrical energy. Over the entire lifetime of a plant, this results in a significant greenhouse effect.

Because of the high proportion of the overall balance, there is therefore a demand for alternative refrigerants with a favorable (thermodynamic) energy balance and an increased compulsion to use highly efficient compressors and additional aggregates as well as optimized system components.

When comparing different types of compressors, the difference in indirect CO 2 emissions (due to energy requirements) may well be higher than the total impact of refrigerant losses.

The following Fig. 1 shows a common formula for calculating the TEWI characteristic, in which the respective areas of influence are subdivided accordingly.

Fig. 1   Calculation method for TEWI characteristics

In addition, Fig. 2 shows an example (normal cooling with R134a) of the ratios of TEWI characteristic values ​​for different refrigerant charge quantities (leakage losses) and energy demand values.

In this example, a flat rate leak rate as a percentage of the refrigerant charge is assumed as a simplification. As is generally known, effective values ​​disseminate very strongly in practice, with the potential risk for individually built and widely distributed systems being particularly high.

Fig. 2    Comparison of TEWI characteristics

Great efforts are being made worldwide to reduce greenhouse gas emissions and, in some cases, statutory ordinances have already been initiated. In the area of ​​the EU, a statutory "Regulation on certain fluorinated greenhouse gases" has been in effect since July 2007, which also sets strict requirements for refrigeration and air conditioning systems. The revised Regulation No. 517/2014 has meanwhile entered into force and has been in force since January 2015.

With kind permission of Bitzer Kühlmaschinenbau GmbH 

Source: Bitzer Refrigerant Report 19