Bitzer refrigerant report: Part 2

Bitzer refrigerant report: Part 2

Published with permission of Bitzer

Stratospheric ozone depletion as well as atmospheric greenhouse effect due to refrigerant emissions have led to drastic changes in refrigeration and air conditioning technologies since the beginning of the 1990s. For reference to earlier information, please see Part 1 published in the previous issue of Cold Link Africa

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).

Also read: Bitzer refrigerant report: Part 1

Environmental impact: Global Warming and TEWI Factor

Bitzer Refrigerant Report A 501 20 6 fig1

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 1kg 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 0.45kg per kWh of electrical energy. This results in a significant greenhouse effect over the lifetime of the plant.

Bitzer Refrigerant Report A 501 20 6 fig2

Due to a deciding proportion of the total balance, there is not only a need for alternative refrigerants with a favourable (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 Figure 1. The TEWI factor can be calculated and the various areas of influence are correspondingly separated.

An additional example is shown in Figure 2 (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 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.

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.

Bitzer Refrigerant Report A 501 20 7 page7

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 minimising 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; and
  • 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 optimised plant equipment (minimised operating costs).

Hereby, the choice of refrigerant and the associated system technology play an important role. Eco-Efficiency can be illustrated in graphic representation (see Figure 3). 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 EcoEfficiency. This means that systems or processes with different life cycle costs and environmental impacts can quite possibly result in the same Eco-Efficiency.

Bitzer Refrigerant Report A 501 20 17 page 17 2

Substitutes for R22/R502 in refrigeration systems: R404A and R507A

These blends are chlorine free substitutes (ODP = 0) for R22 as well as for R502 in medium and low temperature ranges. A composition which was already launched at the beginning of 1992 is known under the trade name Suva® HP62 (DuPont). Long term use has shown good results. Further blends were traded as Forane® FX70 (Arkema) and Genetron® AZ50 (Allied Signal/ Honeywell) or Solkane® 507 (Solvay). HP62 and FX70 have been listed in the ASHRAE nomenclature as R404A and AZ50 as R507A. The basic components belong to the HFC group, where R143a belongs to the flammable category.

Due to the combination with a relatively high proportion of R125 the flammability is effectively counteracted, even in the case of leakage. A feature of all three ingredients is the very low isenropic compression exponent which results in a similar, with even a tendency to be lower, discharge gas temperature to R502 (Figure 5).

The efficient application of single stage compressors with low evaporating temperatures is therefore guaranteed. Due to the similar boiling points for R143a and R125, with a relatively low proportion of R134a, the temperature glide with the ternary blend R404A within the relevant application range is less than one Kelvin. The characteristics within the heat exchangers are therefore not very different than with azeotropes. The results obtained from heat transfer measurements show favourable conditions.

Bitzer Refrigerant Report A 501 20 18 page18

R507A is a binary substance combination which even gives an azeotropic characteristic over a relatively wide range. The conditions therefore tend to be even better. The performance (Figure 6) gives hardly any difference between the various substances and is very similar to R502. This also explains the high market penetration of these refrigerants.

With regard to the thermodynamic properties, they are particularly suitable for commercial medium and low temperature systems. Typical metallic materials are compatible with HFC refrigerants. Elastomers, however, must be adapted to the changed characteristics. Suitable lubricants are polyol esters. The relatively high global warming potential (GWP = 3922 .. 3985), which is mainly determined by the R143a and R125, is something of a hitch.

However, it is better than R502 and with regard to the favourable energy demand also leads to a reduction of the TEWI value. Other improvements are possible in this respect due to further developed system control. Nevertheless, due to their high global warming potential (GWP), the use of R404A and R507A will no longer be allowed in the EU in new installations from 2020.

This has been settled in the F-Gas Regulation No. 517/2014 to be applied since 2015. However, the current requirement of phase-down in connection with a strict quota system will lead to an earlier phase-out in many applications. In the USA, Canada and Australia there are also requirements to phase-out R404A and R507A. For an international phase-down (starting in 2019) of HCFC and HFC refrigerants, the so-called Kigali Amendment was agreed upon in 2016 as part of the Montreal Protocol.

The system technology can be based on the experience with R22 and R502 over a wide area. On the thermodynamic side, a heat exchanger between the suction and liquid line is recommended as this will improve the refrigerating capacity and COP.

To be continued in the next issue of Cold Link Africa

Click here to read the issue of Cold Link Africa 


 

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