Environmental aspects

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 however much greater in comparison to 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 from 1 kg R134a is for example 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 a refrigeration plant’s global warming effect 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 0.45 kg per kWh of electrical energy. This results in a significant greenhouse effect over the lifetime of the plant.

Due to a deciding proportion of the total balance, there is not only a need for alternative refrigerants with a favorable (thermodynamic) energy balance, but an increase in 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, Method for the calculation of TEWI figures. The TEWI factor can be calculated and the various areas of influence are correspondingly separated.

An additional example is shown in the following figure, Comparison of TEWI figures (example) (medium temperature with R134a) shows TEWI values with various refrigerant charges, leakage losses and energy consumptions.

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

Great effort is taken 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.

Example

Example
Medium temperature R134a
to-10°C
tc+40°C
m10 kg // 25 kg
L [10%]1 kg // 2,5 kg
Q013,5 kW
E5 kW x 5000 h/a
β0,45 kg CO2/kWh
α0,75
η15 years
GWP1430 (CO2 = 1)
time horizon 100 Jahre

Comparison of TEWI figures: example



Eco-Efficiency

An assessment based on the specific TEWI value takes into account the effects of global warming during the operating period of a refrigeration, air conditioning or heat pump installation. However, not the entire ecological and economical aspects are considered.

But apart from ecological aspects, economical aspects are highly significant when evaluating technologies and making investment decisions. With technical systems, the reduction of environmental impact frequently involves high costs, whereas low costs often have increased ecological consequences. For most companies, the investment costs are decisive, whereas they are often neglected during discussions about minimizing ecological problems.

For the purpose of a more objective assessment, studies* were presented in 2005 and 2010, using the example of supermarket refrigeration plants to describe a concept for evaluating Eco-Efficiency. It is based on the relationship between added value (a product's economic value) and the resulting environmental impact.

With this evaluation approach, the entire life cycle of a system is taken into account in terms of:

  • ecological performance in accordance with the concept of Life Cycle Assessment as per ISO 14040,
  • economic performance by means of a Life Cycle Cost Analysis.

This means that the overall environmental impact (including direct and indirect emissions), as well as the investment costs, operating and disposal costs, and capital costs are taken into account.

The studies also confirm that an increase of Eco-Efficiency can be achieved by investing in optimized plant equipment (minimized operating costs). Hereby, the choice of refrigerant and the associated system technology play an important role.

Eco-Efficiency can be illustrated in graphic representation (Example, Example of an Eco-Efficiency evaluation): The results of the Eco-Efficiency evaluation are shown on the x-axis in the system of coordinates, whilst the results of the life cycle cost analysis are shown on the y-axis. This shows clearly: A system that is situated higher in the top right quadrant exhibits an increasingly better Eco- Efficiency – and conversely, it becomes less efficient in the bottom left sector.

The diagonals plotted into the system of coordinates represent lines of equal Eco- Efficiency. This means that systems or processes with different life cycle costs and environmental impacts can quite possibly result in the same Eco-Efficiency.

*Study 2005: Compiled by Solvay Management Support GmbH and Solvay Fluor GmbH, Hannover, together with the Information Centre on Heat Pumps and Refrigeration (IZW), Hannover.
Study 2010: Compiled by SKM ENVIROS, UK, commissioned by and in cooperation with EPEE (European Partnership for Energy and Environment). Both projects were supported by an advisory group of experts from the refrigeration industry.