Substitutes for R22 in air conditioning systems and heat pumps

As the HCFC refrigerant R22 (ODP = 0.05) is accepted only as a transitional solution, a number of chlorine-free (ODP = 0) alternatives have been developed and tested extensively. They are being used for a large range of applications.

Experience shows, however, that none of these substitutes can replace the refrigerant R22 in all respects. Amongst others there are differences in the volumetric refrigerating capacity, restrictions in possible applications, special requirements in system design and considerably differing pressure levels. According to the specific operating conditions, various alternatives may be considered.

Apart from the single-component HFC refrigerant R134a, these are mainly blends (different compositions) of the components R32, R125, R134a, R143a, and R600(a). The following description mainly concerns the development and potential applications of these. The halogen-free substitutes NH3, propane and propylene as well as CO2 should also be considered, however, specific criteria must be applied for their use (Halogen free (natural) refrigerants).

In addition, R32 and HFO/HFC blends can also be used as alternatives (R32 as substitute for R22 and "Low GWP" HFOs and HFO/HFC blends as alternatives to HFCs).

R407C as substitute for R22

Mixtures of HFC refrigerants R32, R125 and R134a were considered to be the preferred candidates for short-term substitutes for R22 in the EU in view of the early ban of R22. Performance values and efficiency are highly comparable (R407C/R22 – comparison of performance data of a semi-hermetic compressor). At first two blends of the same composition have been introduced under the trade names AC9000* (DuPont) and KLEA® 66* (ICI). They are listed in the ASHRAE nomenclature as R407C. In the meantime there are also further blend varieties (e.g. R407A/R407F/R407H) with somewhat differing compositions, whose properties have been optimized for particular applications (R407A/407B/407F/407H as substitutes for R22 and R502).

Unlike the substitutes for R22 in refrigeration systems with identical blend components (R407A/407B/407F/407H as substitutes for R22 and R50 and R422A as substitute for R22 and R502), the substitutes for R22 in air conditioning systems and heat pumps under consideration contain higher proportions of R32 and R134a. A good correspondence with the properties of R22 in terms of pressure levels, mass flow, vapour density and volumetric refrigerating capacity is thus achieved. In addition, the global warming potential is relatively low (GWP = 1774), which is a good presupposition for favourable TEWI values.

Thus, R407C also complies with the requirement of the new EU F-Gas Regulation which from 2020 onwards will only allow refrigerants with GWP < 2500. However, the quantity limitation through the "phase-down" will also lead to significantly restricted availability.

The high temperature glide is a disadvantage for usual applications which requires appropriate system design and can have a negative influence on the efficiency of the heat exchangers (General characteristics of zeotropic blends).

Due to the properties mentioned, R407C is preferably an R22 substitute for air conditioning and heat pump systems and (within certain limitations) also for medium temperature refrigeration. In low temperature refrigeration, because of the high proportion of R134a, a significant drop in refrigerating capacity and COP is to be expected. There is also the danger of an increased R134a concentration in the blend in evaporators, with reduced performance and malfunctioning of the expansion valve (e.g. insufficient suction gas superheat).

Material compatibility is similar to that of the blends discussed previously; the same applies to lubricants.

* Previous trade names are not used any more.

Resulting design criteria

With regard to system technology, previous experience with R22 can only be utilized to a limited extent.

The distinctive temperature glide requires a particular design of the main system components, e.g. evaporator, condenser, expansion valve. In this context it must be considered that heat exchangers should preferably be laid out for counterflow operation and with optimized refrigerant distribution. There are also special requirements with regard to the adjustment of control devices and service handling.

Furthermore, the use in systems with flooded evaporators is not recommended as this would result in a severe concentration shift and layer formation in the evaporator.

BITZER products for R407C

BITZER can supply a widespread range of semi-hermetic reciprocating, screw and scroll compressors for R407C.

Converting existing R22 plants to R407C

Because of the above mentioned criteria, no general guidelines can be defined. Each case must be examined individually.

R410A as substitute for R22

In addition to R407C, the near-azeotropic mixture listed by ASHRAE as R410A is available and widely used for medium-sized capacities in air conditioning and heat pump applications.

An essential feature indicates nearly 50% higher volumetric refrigerating capacity (R410A/R22 – comparison of performance data of a semi-hermetic compressor) compared to R22, but with the consequence of a proportional rise in system pressures (R410A/R22 – comparison of pressure levels).

At high condensing temperatures, energy consumption/COP initially seems to be less favourable than with R22.

This is mainly due to the thermodynamic properties. On the other hand, very high isentropic efficiencies are achievable (with reciprocating and scroll compressors), so that the real differences are lower.

Another aspect are the high heat transfer coefficients in evaporators and condensers determined in numerous test series, resulting in especially favourable operating conditions. With an optimized design, it is quite possible for the system to achieve a better overall efficiency than with other refrigerants.

Because of the negligible temperature glide (< 0.2 K), the general usability is similar to that of a pure refrigerant.

The material compatibility is comparable to the previously discussed blends, the same applies to the lubricants. However, the pressure levels and the higher specific loads on the system components need to be taken into account.

Resulting design criteria

The fundamental criteria for HFC blends also apply to the system technology with R410A. However, the high pressure levels have to be considered (43°C condensing temperature already corresponds to 26 bar abs.).

Compressors and other system components designed for R22 are not suitable for this refrigerant (or only to a limited extent).

Though, suitable compressors and system components are available.

When considering to cover usual R22 application ranges, the significant differences in the thermodynamic properties (e.g. pressure levels, mass and volume flow, vapour density) must be taken into account. This also requires considerable constructional changes to compressors, heat exchangers, and controls, as well as measures of tuning vibrations. There are stricter safety requirements, e.g. affecting the quality and dimensions of piping and flexible tube elements (for condensing temperatures of approx. 60°C/40 bar).

Another criterion is the relatively low critical temperature of 73°C. Irrespective of the design of components on the high pressure side, the condensing temperature is thus limited.

R410A complies with the requirements of the EU F-Gas Regulation, which will only allow refrigerants with GWP < 2500 from 2020 onwards. However, the quantity limitation through the "phase-down" will also lead to significantly restricted availability. Due to the extremely high demand for R410A, a timely switch to alternatives is needed in the EU.

BITZER products for R410A

For R410A, BITZER offers a series of semi-hermetic reciprocating compressors and scroll compressors.

R417A/417B/422D/438A as substitutes for R22

Similar to the development of R422A (R422A as substitute for R22 and R502), one aim of developing these blends was to provide chlorine-free refrigerants (ODP = 0) for the simple conversion of existing R22 plants.

R417A was introduced to the market years ago, and is also offered under the trade name ISCEON® MO59 (Chemours). This substitute for R22 contains the blend components R125/R134a/R600 and therefore differs considerably from e.g. R407C with a correspondingly high proportion of R32.

Meanwhile, a further refrigerant based on identical components, but with a higher R125 content, has been offered under the ASHRAE designation R417B. Due to its lower R134a content, its volumetric refrigerating capacity and pressure levels are higher than for R417A. This results in different performance parameters and a different focus within the application range.

The same applies to a further blend with the same main components, but R600a as hydrocarbon additive. It is offered under trade name ISCEON® MO29 (Chemours) and listed as R422D in the ASHRAE nomenclature.

Another refrigerant belonging to the category of HFC/HC blends was introduced in 2009 under the trade name ISCEON® MO99 (Chemours) – ASHRAE classification R438A. This formulation was designed especially for a higher critical temperature for applications in hot climate areas. The base components are R32, R125, R134a, R600 and R601a.

Like R407C, all four substitute refrigerants are zeotropic blends with a more or less significant temperature glide. In this respect, the criteria described for R407C also apply here.

Apart from a similar refrigeration capacity, there are fundamental differences in thermodynamic properties and in oil transport behaviour. The high proportion of R125 causes a higher mass flow with R417A/B and R422D than with R407C, a lower discharge gas temperature and a relatively high superheating enthalpy. These properties indicate that there are differences in the optimization of system components, and a heat exchanger between liquid and suction lines is of advantage.

Despite the predominant proportion of HFC refrigerants, conventional lubricants can be used to some extent because of the good solubility of the hydrocarbon constituent. However, in systems with a high oil circulation rate and/or a large volume of liquid in the receiver, oil migration may result.

In such cases, additional measures are necessary. For further information on oil return and lubricants, (R422A as substitute for R22 and R502).

Due to the high global warming potential (GWP ≥ 2500), R417B and R422D will no longer be allowed for new installations in the EU from 2020. The requirements and restrictions are specified in the F-Gas Regulation 517/2014. However, the "phase-down" quantity limitation will also lead to significantly restricted availability of R417A and R438A.

BITZER products for R417A/417B/422D/438A

BITZER compressors are suitable for use with R417A/417B/422D/438A. An individual selection is possible upon request.

R427A as a substitute for R22

This refrigerant blend was introduced some years ago under the trade name Forane® FX100 (Arkema) and is now listed in the ASHRAE nomenclature as R427A.

The R22 substitute is offered for the conversion of existing R22 systems for which a "zero ODP" solution is requested. It is an HFC mixture with base components R32/R125/R143a/R134a.

In spite of the blend composition based on pure HFC refrigerants, the manufacturer states that a simplified conversion procedure is possible.

This is facilitated by the R143a proportion. Accordingly, when converting from R22 to R427A, all it takes is a replacement of the original oil charge with ester oil. Additional flushing sequences are not required, as proportions of up to 15% of mineral oil and/or alkyl benzene have no significant effect on oil circulation in the system.

However, it must be taken into account that the highly polarized mixture of ester oil and HFC will lead to increased dissolving of decomposition products and dirt in the pipework. Therefore, generously dimensioned suction clean-up filters must be provided.

Regarding refrigerating capacity, pressure levels, mass flow and vapor density, R427A is relatively close to R22. During retrofit, essential components such as expansion valves can remain in the system. Due to the high proportion of blend components with low adiabatic exponent, the discharge gas temperature is considerably lower than with R22, which has a positive effect at high compression ratios.

It must be taken into account that this is also a zeotropic blend with a distinct temperature glide. Therefore the criteria described for R407C apply here as well.

R427A meets the requirement of the EU F-Gas Regulation, which will only allow refrigerants with GWP < 2500 from 2020. However, the quantity limitation due to the "phase-down" will also lead to significantly restricted availability.

BITZER products for R427A

BITZER compressors are suitable for R427A. An individual selection is possible upon demand.

Supplementary information concerning the use of HFC blends

(see also https://www.bitzer.de)

  • Technical information KT-651 “Retrofitting R22 systems to alternative refrigerants”

R32 as substitute for R22

As described earlier, R32 belongs to the HFC refrigerants, but initially it was mainly used as a component of refrigerant blends only. An essential barrier for the application as a pure substance so far is the flammability. This requires adequate charge limitations and/or additional safety measures, especially with installations inside buildings. In addition there are very high pressure levels and discharge gas temperatures (compression index higher than with R22 and R410A).

On the other hand, R32 has favorable thermodynamic properties, e.g. very high evaporating enthalpy and volumetric refrigerating capacity, low vapor density (low pressure drop in pipelines), low mass flow, and favorable power input for compression. The global warming potential is relatively low (GWP = 675).

Looking at these favorable properties and taking into account the additional effort for emission reductions, R32 will increasingly be used as a refrigerant in factory produced systems (A/C units and heat pumps) with low refrigerant charges.

It was proven in flammability tests that the necessary ignition energy is very high and the flame speed is low. Therefore, R32 (like R1234yf and R1234ze) has been placed in the new safety group A2L according to ISO 817.

The resulting safety requirements are specified in the revised EN 378 (amended version 2016).

R32 is also considered an alternative for systems with larger refrigerant charge, e.g. liquid chillers for air conditioning and process applications and heat pumps previously operated with R410A. However, depending on the installation site of the system, appropriate refrigerant charge limits must be observed. On the other hand, there are no such restrictions when installed outdoors (without access to unauthorized persons) and in machine rooms (for example, according to EN 378-3: 2016). It should be noted, however, that R32 pre-charged chillers may be subject to special conditions during transport (according to the Pressure Equipment Directive, R32 is classified under Fluid Group 1).

BITZER products for R32

BITZER scroll compressors of the ORBIT GSD6 and GSD8 series have been approved and released for use with R32. Depending on the product group, a special compressor version may be required.