REFRIGERANT COMPOSITION

This invention relates to refrigerant compositions which have no adverse effect on stratospheric ozone and have Global Warming Potentials of less than 2500. The invention also relates to compositions which are for use both in refrigeration and air conditioning systems designed to use Ozone Depleting Substances (ODS) such as HCFC22 (chlorodifluoromethane). These refrigerant compositions are compatible with mineral oil and other hydrocarbon lubricants commonly found in refrigeration and air conditioning systems, and also the synthetic, oxygen-containing lubricants (e.g. polyol ester oils).

Various terms have been used in patent literature to describe refrigerant mixtures. The following definitions are taken from Standard 34 of the American Society of Heating, Refrigerating & Air Conditioning Engineers (ASHRAE);

Azeotrope: an azeotropic blend is one containing two or more refrigerants whose equilibrium vapour and liquid phase compositions are the same at a given pressure. Azeotropic blends exhibit some segregation of components at other conditions. The extent of the segregation depends on the particular azeotrope and the application.

Azeotropic temperature: the temperature at which the liquid and vapour phases of a blend have the same mole fractionation of each component at equilibrium for a specified pressure.

Near azeotrope: a zeotropic blend with a temperature glide sufficiently small that it may be disregarded without consequential error in analysis for a specific application.

Zeotrope: blends comprising multiple components of different volatilities that, when used in refrigeration cycles, change volumetric composition and saturation temperatures as they evaporate (boil) or condense at constant pressure.

Temperature glide: the absolute value of the difference between the starting and ending temperatures of a phase-change process by a refrigerant within a component of a refrigerating system, exclusive of any subcooling or superheating. This term usually describes condensation or evaporation of a zeotrope . Percentages and other proportions referred to in this specification are by mass unless indicated otherwise and are selected to total 100% from within the ranges disclosed.

Chlorofluorocarbon (CFC) refrigerants, such as R12 and R502, and hydrochlorofluorocarbon refrigerants, such as R22, are ozone depleting substances (ODS). While being energy efficient, non-flammable and of low toxicity, they are broken down by UV radiation in the stratosphere generating chlorine atoms that destroy the ozone layer. Hydrofluorocarbons (HFCs) are non-ozone depleting alternatives, which are also non-flammable, efficient and of low toxicity. However, HFCs do not have adequate solubility in hydrocarbon lubricants, such as mineral and alkylbenzene oils used for CFCs and HCFCs, so synthetic oxygen-containing polyol- ester (POE) and polyalkylene-glycol (PAG) lubricants have been introduced specifically for new equipment. These lubricants are expensive and, being hygroscopic, are liable to absorb atmospheric moisture, especially during maintenance, which can contribute to excessive corrosion and wear in equipment which can reduce the reliability of the equipment. In designing new units to operate specifically with HFC blends and the synthetic oxygen containing lubricants, equipment manufacturers have been able to minimise this problem.

However, a considerable number of legacy units using HCFC-22 remain with many years of effective operating life, which it would be economically nonsensical to scrap. In principle, some at least might be retrofitted with commercially- available R404A or R507A, but in many cases this is not possible because the maximum operating pressures of R404A and R507A are too high for units designed to operate with R22.

Furthermore, R404A and R507A contain only HFC components, so cannot be used with hydrocarbon lubricants. If these blends are used to replace CFCs and HCFCs in existing equipment, the manufacturers recommend that no more than 5% of the hydrocarbon lubricant in the system be retained, requiring an essentially complete change of lubricant to a synthetic oxygen containing lubricant. This is often costly and technically unsatisfactory.

It is an object of this invention to provide non-ozone depleting blends that enable the continued use of hydrocarbon oils in both existing and new equipment. While HFC blends such as R404A and R507A have desirable thermodynamic properties as ozone depleting R22 and R502 substitutes, they have comparatively high direct Global Warming Potentials (GWP), compared to carbon dioxide. The European Union has therefore restricted their availability according to their GWPs; for example, HFCs with GWPs greater than 2500 will not be permitted for the maintenance of existing equipment after 2020.

It is, therefore, an object of this invention to provide HFC blends that have direct GWPs of less than 2500.

R434A is a unique, near-azeotropic refrigerant that can replace R22 in existing equipment. It combines a maximum operating pressure acceptable in equipment designed for R22 with non-flammability, low toxicity, zero ozone depletion and a small temperature glide, enabling it to be used in flooded shell and tube evaporators. However, its GWP is >2500 so in Europe it cannot be used after 2020 to top-up after part leakage of the original charge. This invention therefore further relates to a method for progressively extending the use of refrigerant R434A remaining in a refrigeration, air conditioner or heat pump device after part leakage by adding a blend with a GWP <2500.

It is not obvious to a skilled person that this objective is achievable because several conflicting requirements must be satisfied simultaneously. It is generally considered by the refrigeration industry to be an unacceptable and potentially dangerous practice to mix refrigerants containing different fluid components within a unit. For example, if inappropriate refrigerants are mixed, the maximum operating pressure may exceed the design rating. Furthermore, recovery and recycling is compromised because a more complex combination of fluids is generated. To avoid these problems, the compositions of this invention contain only the same components as R434A, namely HFC- 125, HFC- 143a, HFC- 134a and 2-methyl propane. The latter fluid ensures the continued use of hydrocarbon lubricants by facilitating oil return. However, the quantities of the flammable components, R143a and 2-methyl propane, must not induce flammability in the blends as determined by the ASHRAE 34 standard. The performance, especially efficiency and capacity, of an R434A unit that has been topped-up with a blend claimed in this invention should remain acceptable for at least 8 years based on a mass leakage rate of 10% to 20% per year with an annual maintenance top-up. Surprisingly we have found blends that meet all the above constraints.

Furthermore, detailed simulations of an R434A-containing unit topped-up with Blend 2 revealed unanticipated advantages. The results in Table 4 summarise the performance of the R434A/Blend 2 mixture over 8 years. During Year 0 the unit is operating on pure R434A. During the Years 1 to 7 the unit is progressively operating with an increasing Blend 2 content mixed with the remaining R434A. Advantageously, over this period the energy efficiency (COP) progressively increases while the GWP of the refrigerant in the unit decreases, which respectively reduce the indirect and direct contributions of the unit to global warming. The lower flow rate compared to R434A is also advantageous, helping to reduce pressure drops in pipes and thus contributing to higher energy efficiencies. The lower discharge pressures reduce the loadings on the compressor bearings reducing wear and improving reliability. Friction will also be reduced helping to improve the isentropic efficiency of the compressor. Although the refrigerant capacity has dropped slightly relative to R434A, it is still adequate since equipment is typically over-designed for its rated duty. In any case, the lower discharge pressure also reduces refrigerant backflow increasing volumetric capacity and thus helps to compensate for the reduced suction specific capacity. The improvements in isentropic and volumetric capacities have not been included in the calculations so the efficiency and capacity values given in Table 4 and Table 5 can be regarded as worse case. Their contributions will depend upon the specific type and design of compressor used.

According to the present invention a refrigerant with a Global Warming Potential of not greater than 2500 consists essentially of:

R134a 77 to 40%

R125 15 to 45%

R143a 6 to 25%

where the amounts are by mass and selected to total 100%, together with an optional hydrocarbon additive.

In this specification, percentages or other amounts are by mass unless indicated otherwise. Amounts are selected from any ranges given to total 100%.

The present invention provides a refrigerant composition which consists essentially of an hydrofluorocarbon component consisting of a mixture of R134a, R125 and R143a and optionally a hydrocarbon additive so that the composition does not have a GWP greater than 2500 and is compatible with both hydrocarbon and synthetic oxygen containing lubricants.

The GWP of the components are:

GWP

R125 (pentafluoroethane) 3600

R134a (1,1,1,2-tetrafluoroethane) 1430

R143a (1,1,1-trifluoroethane) 4470

Hydrocarbon additives may comprise a single component or a mixture of components boiling between -25°C and +37°C.

Preferred hydrocarbon additives may be selected from the group comprising: propane, propene, 2-methylpropane, n-butane, but-l-ene, but-2-ene, 2-methylpropene, iso pentane, n-pentane and mixtures thereof.

Especially preferred hydrocarbon additives may be selected from the group consisting of 2-methylpropane, n-butane, iso-pentane, and mixtures thereof.

In a further embodiment, a refrigerant composition which may find application to replace R22 comprises;

A refrigerant composition consisting essentially of:

R134a 77 to 40% R125 15 to 45%

R143a 6 to 25%

the amounts being by mass and selected to total 100%; together with an optional hydrocarbon additive with a percentage mass in the range 0.6 to 3.5% of the mass of the HFC composition. A preferred embodiment consists essentially of:

R134a 74 to 38%

R125 18 to 43%

R143a 7 to 22%

the amounts being by mass and selected to total 100%, together with an optional hydrocarbon additive with a percentage mass in the range 0.6 to 3.5% of the total mass of the HFC composition selected from the group consisting of: 2- methylpropane, n-butane, iso-pentane and mixtures thereof.

Another preferred embodiment consists essentially of: R134a 70 to 38%

R125 20 to 42%

R143a 8 to 22% the amounts being by mass and selected to total 100% together with an optional hydrocarbon additive with a percentage mass in the range 0.6 to 3.5% of the total mass of the HFC composition selected from the group consisting of: 2-methylpropane, n-butane, iso-pentane and mixtures thereof.

Yet another preferred embodiment consists essentially of:

134a 70 to 41%

R125 20 to 40% R143a 9 to 21% together with an optional hydrocarbon additive consisting of 0.6 to 3.5% by mass of a hydrocarbon selected from the group consisting of: 2-methylpropane, n-butane, iso pentane and mixtures thereof.

Preferred specific compositions consist of the following mixtures:

(1) R134a 54.2%

R125 23% R143a 20%

Isobutane 2.8%

(2) R134a 49.2%

R125 38% R143a 10%

Isobutane 2.8%

(3) R134a 52.2%

R125 30%

R143a 15% Isobutane 2.8%

(4) R134a 60.2%

R125 27%

R143a 10%

Isobutane 2.8% (5) R134a 54.5%

R125 23%

R143a 20%

Isobutane 2.5%

(6) R134a 55% R125 23%

R143a 20%

Isobutane 2%

(7) R134a 56% R125 23%

R143a 20%

Isopentane 1 %

(8) R134a 55.5%

R125 23%

R143a 20%

Isopentane 1.5%

EXAMPLES

The invention is further described by means of example but not in any limitative sense.

Example 1

The performance of Composition 1 (Table 1) in a chiller was modelled using NIST Cycle D under the following conditions.

System cooling capacity (kW) =100.00

Compressor isentropic efficiency = 0.800

Compressor volumetric efficiency = 0.900

Electric motor efficiency = 0.900

Pressure drop (in sat. temp.) (C): in the suction line = 1.5; in the discharge line = 1.5 Evaporator: average sat. temp. (C) = 0.0 Superheat (K) = 5.0

Condenser: average sat. temp. (C) = 45.0 Subcooling (K) = 5.0

Parasitic powers (kW): evaporator pump = 3.000; condenser fan = 4.000;

controls = 1.000

Example 2 The performance of Composition 2 (Table 1) in an a /c chiller was modelled using NIST’s Cycle D under the following conditions.

System cooling capacity (kW) = 1.00

Compressor isentropic efficiency = 0.800 Compressor volumetric efficiency = 0.900

Electric motor efficiency = 0.900

Pressure drop (in sat. temp.) (C): in the suction line = 0.0; in the discharge line = 0.0 Evaporator: average sat. temp. (C) = 7.0 Superheat (K) = 5.0

Condenser: average sat. temp. (C) = 35.0 Subcooling (K) = 5.0 Example 3

The performance of Composition 3 (Table 1) in a low temperature refrigeration unit was modelled using NIST’s Cycle D under the following conditions.

System cooling capacity (kW) = 50.00

Compressor isentropic efficiency = 0.800

Compressor volumetric efficiency = 0.900

Electric motor efficiency = 0.900

Pressure drop (in sat. temp.) (C): in the suction line = 1.5; in the discharge line = 1.5 Evaporator: average sat. temp. (C) = -30.0 Superheat (K) = 5.0

Condenser: average sat. temp. (C) = 35.0 Subcooling (K) = 5.0

Parasitic powers (kW):evaporator fan = 1.500 ; condenser fan = 2.000;

controls = 0.500

Example 4

The performance of Composition 4 (Table 1) in a medium temperature refrigeration unit was modelled using NIST’s Cycle D under the following conditions.

System cooling capacity (kW) = 10.00

Compressor isentropic efficiency = 0.800

Compressor volumetric efficiency = 0.900

Electric motor efficiency = 0.900

Pressure drop (in sat. temp.) (C): in the suction line = 1.5; in the discharge line = 1.5 Evaporator: average sat. temp. (C) = -10.0; Superheat (K) = 5.0

Condenser: average sat. temp. (C) = 40.0; Subcooling (K) = 5.0

Parasitic powers (kW): indoor fan = 0.300; outdoor fan = 0.400;

controls = 0.100 Example 5

Composition 4 Table 1 was mixed with R434A (composition 7, Table 1) in a mass ratio of 1:2 and the performance of the resulting composition 5 (Table 1) was modelled in a medium temperature refrigeration system under the operating conditions given in Example 4. The performances of R434A (composition 7, Table 1) and composition 6 (Table 1), a 1:2 mixture of composition 1 and R434A were also modelled under the same conditions.

Table 1

Example 6

An R434A, open-compressor chiller unit, which had suffered a 50% loss of the original refrigerant, was topped up with Blend 2. The performance of the unit running on the resulting 50/50 blend was simulated with CYCLE D under the following operating conditions. Table 2 gives the compositions of R434A and Blend 8. System cooling capacity (kW) = 100 Compressor isentropic efficiency = 0.800 Compressor volumetric efficiency = 0.900

Evaporator: average sat. temp. (C) = 7.0 Superheat (C) = 5.0

Condenser: average sat. temp. (C) = 45.0 Subcooling (C) = 5.0 Table 2

The results in Table 3 indicate that the performance of the R434A/Blend 2 mixture is better than the original R434A refrigerant as regards energy efficiency (COP) compressor discharge temperature and flow rate. The GWP of the 50/50 mixture is lower than that of the original R434A. The capacity has dropped slightly relative to R434A, but is still adequate since equipment is typically over-designed for its rated duty.

Table 3 Performance of 50/50 Mixture of R434A and Blend 2

Open compressor

Example 7

An R434A, open-compressor chiller unit, which was suffering a 10% refrigerant loss per year, was topped-up annually with Blend 2. The performance of the unit was simulated with CYCLE D under the following operating conditions after each top-up.

System cooling capacity (kW) = 100

Compressor isentropic efficiency = 0.800

Compressor volumetric efficiency = 0.900

Evaporator: average sat. temp. (C) = 7.0 Superheat (C) = 5.0 Condenser: average sat. temp. (C) = 45.0 Subcooling (C) = 5.0

Table 4 summarises that the performance of the R434A/Blend 2 mixture over 8 years. During Year 0 the unit is operating on pure R434A. During the Years 1 to 7 the unit is progressively operating with an increasing Blend 2 mixed with the remaining R434A. Over this period the energy efficiency (COP) progressively increases while the GWP of the refrigerant in the unit decreases. The lower flow rate decreases, which is also advantageous helping to reduce pressure drops in pipes and contributing to higher energy efficiencies. The lower discharge pressures reduce the loadings on the compressor bearings reducing wear and improving reliability. Friction will also be reduced helping to improve the isentropic efficiency of the compressor. The capacity has dropped slightly relative to R434A, but is still adequate since equipment is typically over-designed for its rated duty. The lower discharge pressure also reduces refrigerant backflow increasing volumetric capacity and thus helps to compensate for the reduced suction specific capacity. The improvements in isentropic and volumetric capacities have not been included in the calculations so the efficiency and capacity values given in Table 7 can be regarded as worse case. Their contributions will depend upon the specific type and design of compressor used. Ta ble 4 10% Refrigerant Loss per Year with Annual Service Top-up by Blend 2

Example 8

An R434A, open-compressor chiller unit, which was suffering a 20% refrigerant loss per year, was topped-up annually with Blend 2. The performance of the unit was simulated with CYCLE D under the following operating conditions after each top-up. System cooling capacity (kW) = 100

Compressor isentropic efficiency = 0.800

Compressor volumetric efficiency = 0.900

Evaporator: average sat. temp. (C) = 7.0 Superheat (C) = 5.0

Condenser: average sat. temp. (C) = 45.0 Subcooling (C) = 5.0 Table 5 summarises that the performance of the R434A/Blend 2 mixture over 8 years. During Year 0 the unit is operating on pure R434A. During the Years 1 to 7 the unit is progressively operating with an increasing Blend 2 mixed with the remaining R434A. Over this period the energy efficiency (COP) progressively increases while the GWP of the refrigerant in the unit decreases. The lower flow rate decreases, which is also advantageous, helping to reduce pressure drops in pipes and contributing to higher energy efficiencies. The lower discharge pressures reduce the loadings on the compressor bearings reducing wear and improving reliability. Friction will also be reduced helping to improve the isentropic efficiency of the compressor. The capacity has dropped slightly relative to R434A, but is still adequate since equipment is typically over-designed for its rated duty. The lower discharge pressure also reduces refrigerant backflow increasing volumetric capacity and thus helps to compensate for the reduced suction specific capacity. The improvements in isentropic and volumetric capacities have not been included in the calculations so the efficiency and capacity values given in table 7 can be regarded as worse case. Their contributions will depend upon the specific type and design of compressor used. Table 5 20% Refrigerant Loss per Year with Annual Service Top-up by Blend 2