WO2016010634A1

WO2016010634A1 - Use of 1,1,2,2-tetrafluoroethane in high temperature heat pumps

Info

Publication number: WO2016010634A1
Application number: PCT/US2015/033094
Authority: WO
Inventors: Konstantinos Kontomaris; Eric Paul YOUNGDALE
Original assignee: The Chemours Company Fc, Llc
Priority date: 2014-07-18
Filing date: 2015-05-29
Publication date: 2016-01-21
Also published as: CN106662369A8; CN106662369A

Abstract

Disclosed is a method for producing heating in a high temperature heat pump. The method comprises extracting heat from a working fluid in a heat exchanger, thereby producing a cooled working fluid, wherein said working fluid comprises a refrigerant consisting of 1,1,2,2-tetrafluoroethane; said high temperature heat pump comprising a centrifugal compressor. Also disclosed are a method for producing heating wherein heat is exchanged between at least two stages, a method for raising the condenser operating temperature in a high temperature heat pump apparatus, a high temperature heat pump apparatus, a method for replacing HFC-134a in a high temperature heat pump and a method for improving the energy efficiency of a centrifugal high temperature heat pump. Also disclosed are a method of producing heating and a high temperature heat pump apparatus wherein the high temperature heat pump comprises a screw compressor.

Description

TITLE

USE OF 1 , 1 ,2,2-TETRAFLUOROETHAN E I N H IG H

TEM PERATU RE H EAT PUMPS

FIELD OF THE INVENTION This invention relates to methods and systems having utility in numerous applications, and in particular, in high temperature heat pumps.

BACKGROUND OF THE INVENTION

Current trends shaping the global energy landscape suggest an expanding utilization of low temperature heat in the near future. Such heat may be recovered from various commercial or industrial operations, can be extracted from geothermal or hydrothermal reservoirs or can be generated through solar collectors. Motivation for low temperature heat utilization is provided by increasing energy prices and a growing

awareness of the environmental impacts, in general, and the threat to the earth's climate, in particular, from the use of fossil fuels.

Elevation of the temperature of available low temperature heat through high temperature mechanical compression heat pumps (HTHPs) to meet heating requirements is one promising approach for the use of low temperature heat. Heat pumps require the use of working fluids. New heat pump and high temperature heat pump working fluids are needed.

SUMMARY OF THE INVENTION

In accordance with the present invention a method for producing heating in a high temperature heat pump is provided. The method comprises extracting heat from a working fluid in a heat exchanger, thereby producing a cooled working fluid, wherein said working fluid comprises a refrigerant consisting of 1 ,1 ,2,2-tetrafluoroethane and said high temperature heat pump comprises a centrifugal compressor.

Also, a method for producing heating in a high temperature heat pump wherein heat is exchanged between at least two stages arranged in a cascade configuration is provided. The method comprises absorbing heat at a selected lower temperature in a first working fluid in a first cascade stage and transferring this heat to a second working fluid of a second cascade stage that supplies heat at a higher temperature; wherein the first or second working fluid comprises a refrigerant consisting of 1 ,1 ,2,2- tetrafluoroethane.

Also a method for raising the condenser operating temperature in a high temperature heat pump apparatus is provided. The method comprises charging the high temperature heat pump with a working fluid comprising a refrigerant consisting of 1 ,1 ,2,2-tetrafluoroethane; wherein said high temperature heat pump apparatus comprises a centrifugal compressor.

Also, a high temperature heat pump apparatus is provided. The apparatus contains a working fluid comprising a refrigerant consisting of 1 ,1 ,2,2-tetrafluoroethane; wherein said apparatus comprises a centrifugal compressor.

Also, a method for replacing HFC-134a in a high temperature heat pump is provided. The method comprises charging said high temperature heat pump with a working fluid comprising a refrigerant consisting of HFC- 134; wherein said high temperature heat pump comprises a centrifugal compressor.

Also, a method for improving the energy efficiency of a centrifugal high temperature heat pump operating with HFC-134a is provided. The method comprises charging said centrifugal high temperature heat pump with a working fluid comprising a refrigerant consisting of HFC-134. Also, a method for producing heating in a high temperature heat pump is provided. The method comprises extracting heat from a working fluid in a heat exchanger, thereby producing a cooled working fluid, wherein said working fluid comprises a refrigerant consisting of 1 ,1 ,2,2- tetrafluoroethane and said high temperature heat pump comprises a screw compressor. Also, a high temperature heat pump apparatus is provided, which contains a working fluid comprising a refrigerant consisting of 1 ,1 ,2,2- tetrafluoroethane; wherein said apparatus comprises a screw compressor.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of one embodiment of a flooded evaporator heat pump apparatus according to the present invention.

FIG. 2 is a schematic diagram of one embodiment of a direct expansion heat pump apparatus according to the present invention.

Figure 3 is a schematic diagram of a cascade heating pump system according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Before addressing details of embodiments described below, some terms are defined or clarified.

Global warming potential (GWP) is an index for estimating relative global warming contribution due to atmospheric emission of a kilogram of a particular greenhouse gas compared to emission of a kilogram of carbon dioxide. GWP can be calculated for different time horizons showing the effect of atmospheric lifetime for a given gas. The GWP for the 100 year time horizon is commonly the value referenced. Ozone depletion potential (ODP) is defined in "The Scientific

Assessment of Ozone Depletion, 2002, A report of the World

Meteorological Association's Global Ozone Research and Monitoring Project," section 1 .4.4, pages 1 .28 to 1 .31 (see first paragraph of this section). ODP represents the extent of ozone depletion in the

stratosphere expected from a compound on a mass-for-mass basis relative to fluorotrichloromethane (CFC-1 1 ).

Refrigeration capacity (sometimes referred to as cooling capacity) is a term to define the change in enthalpy of a refrigerant or working fluid in an evaporator per unit mass of refrigerant or working fluid circulated. Volumetric cooling capacity refers to the amount of heat removed by the refrigerant or working fluid in the evaporator per unit volume of refrigerant vapor exiting the evaporator. The refrigeration capacity is a measure of the ability of a refrigerant, working fluid or heat transfer composition to produce cooling. Therefore, the higher the volumetric cooling capacity of the working fluid, the greater the cooling rate that can be produced at the evaporator with the maximum volumetric flow rate achievable with a given compressor. Cooling rate refers to the heat removed by the refrigerant in the evaporator per unit time. Similarly, volumetric heating capacity is a term to define the amount of heat supplied by the refrigerant or working fluid in the condenser per unit volume of refrigerant or working fluid vapor entering the compressor. The higher the volumetric heating capacity of the refrigerant or working fluid, the greater the heating rate that is produced at the condenser with the maximum volumetric flow rate achievable with a given compressor.

Coefficient of performance (COP) is the amount of heat removed in the evaporator divided by the energy required to operate the compressor. The higher the COP, the higher the energy efficiency. COP is directly related to the energy efficiency ratio (EER), that is, the efficiency rating for refrigeration or air conditioning equipment at a specific set of internal and external temperatures.

As used herein, a heat transfer medium (also referred to herein as a heating medium) comprises a composition used to carry heat from a body to be cooled to the chiller evaporator or from the chiller condenser to a cooling tower or other configuration where heat can be rejected to the ambient. For a heat pump, the heat transfer medium carries heat from the heat source to the heat pump evaporator (heat exchanger) or from the heat pump condenser to a body to be heated.

As used herein, a working fluid comprises a compound or mixture of compounds that function to transfer heat in a vapor compression cycle. In some embodiments, the working fluid undergoes a phase change from a liquid to a gas and back to a liquid in a repeating cycle. Subcooling is the reduction of the temperature of a liquid below that liquid's saturation point for a given pressure. The saturation point is the temperature at which a vapor composition is completely condensed to a liquid (also referred to as the bubble point). But subcooling continues to cool the liquid to a lower temperature liquid at the given pressure. By cooling a liquid below the saturation temperature, the net refrigeration capacity can be increased. Subcooling thereby improves refrigeration capacity and energy efficiency of a system. Subcool amount is the amount of cooling below the saturation temperature (in degrees) or how far below its saturation temperature a liquid composition is cooled.

Superheat is a term that defines how far above its saturation vapor temperature (the temperature at which, if the composition is cooled, the first drop of liquid is formed, also referred to as the "dew point") a vapor composition is heated. As used herein, the terms "comprises," "comprising," "includes,"

"including," "has," "having" or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus. Further, unless expressly stated to the contrary, "or" refers to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present) and A is false (or not present) and B is true (or present. The transitional phrase "consisting of excludes any element, step, or ingredient not specified. If in the claim such would close the claim to the inclusion of materials other than those recited except for impurities ordinarily associated therewith. When the phrase "consists of appears in a clause of the body of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause; other elements are not excluded from the claim as a whole. The transitional phrase "consisting essentially of is used to define a composition, method or apparatus that includes materials, steps, features, components, or elements, in addition to those literally disclosed provided that these additional included materials, steps, features, components, or elements do not materially affect the basic and novel characteristic(s) of the claimed invention. The term 'consisting essentially of occupies a middle ground between "comprising" and 'consisting of.

Where applicants have defined an invention or a portion thereof with an open-ended term such as "comprising," it should be readily understood that (unless otherwise stated) the description should be interpreted to also describe such an invention using the terms "consisting essentially of or "consisting of."

Also, use of "a" or "an" are employed to describe elements and components described herein. This is done merely for convenience and to give a general sense of the scope of the invention. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety, unless a particular passage is cited. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.

1 ,1 ,2,2-Tetrafluoroethane (HFC-134, CHF2CHF2) is available commercially or may be made by the hydrodehydrochlorination of 1 ,2- dichloro-1 ,1 ,2,2-tetrafluoroethane (i.e., CCIF2CCIF2 or CFC-1 14).

Alternatively, HFC-134 may be made by catalytic hydrogenation of tetrafluoroethylene (TFE), wherein catalyst may be any that are effective at producing the desired product, including but not limited to palladium and platinum among others.

High temperature heat pump methods In accordance with this invention, a method is provided for producing heating in a high temperature heat pump. The method comprises extracting heat from a working fluid in a heat exchanger, thereby producing a cooled working fluid wherein said working fluid comprises a refrigerant consisting of 1 ,1 ,2,2-tetrafluoroethane (HFC-134) and said high temperature heat pump comprises a centrifugal compressor. The working fluid for use in the method for producing heating may optionally further comprise a lubricant.

In one embodiment of the method for producing heating, the heat exchanger is selected from the group consisting of a supercritical working fluid cooler and a condenser.

In one embodiment of the method for producing heating, the heat exchanger operates at a temperature of greater than 55°C. In another embodiment, the heat exchanger operates at a temperature of greater than 71 °C. In another embodiment, the heat exchanger operates at a temperature from about 71 °C to about 80°C; from about 71 °C to about 1 15°C; from about 71 °C to about 135°C; from about 80°C to about 135°C; from about 90°C to about 135°C.

In one embodiment of the method for producing heating, the method further comprises passing a first heat transfer medium through the heat exchanger, whereby said heat extraction heats the first heat transfer medium, and passing the heated first heat transfer medium from the heat exchanger to a body to be heated.

A body to be heated may be any space, object or fluid that may be heated. In one embodiment, a body to be heated may be a room, building, or the passenger compartment of an automobile. Alternatively, in another embodiment, a body to be heated may be a heat transfer medium or heat transfer fluid, in which case the heat transfer medium or heat transfer fluid may be transferred to a space or object needing heating.

In one embodiment of the method for producing heating, the first heat transfer medium is water and the body to be heated is water. In another embodiment, the first heat transfer medium is water and the body to be heated is air for space heating. In another embodiment, the first heat transfer medium is an industrial heat transfer liquid and the body to be heated is a chemical process stream.

In another embodiment of the method for producing heating, the method to produce heating further comprises compressing the working fluid in a centrifugal compressor.

In one embodiment of the method for producing heating, the heating is produced in a heat pump having a heat exchanger comprising passing a heat transfer medium to be heated through said heat exchanger, thus heating the heat transfer medium. In one embodiment, the heat transfer medium is air, and the heated air from the heat exchanger is passed to a space to be heated. In another embodiment, the heat transfer medium is a portion of a process stream, and the heated portion is returned to the process. In some embodiments of the method for producing heating, the heat transfer medium (or heating medium) may be selected from water or glycol (such as ethylene glycol or propylene glycol). Of particular note is an embodiment wherein the first heat transfer medium is water and the body to be cooled is air for space cooling. In another embodiment of the method for producing heating, the heat transfer medium may be an industrial heat transfer liquid, wherein the body to be heated is a chemical process stream, which includes process lines and process equipment such as distillation columns. Of note are industrial heat transfer liquids including ionic liquids, various brines such as aqueous calcium chloride or sodium chloride, glycols such as

propylene glycol or ethylene glycol, methanol, and other heat transfer media such as those listed in Chapter 4 of the 2006 ASHRAE Handbook on Refrigeration.

In one embodiment, the method for producing heating comprises extracting heat in a flooded evaporator high temperature heat pump as described above with respect to FIG. 1 . In this method, the liquid working fluid is evaporated to form a working fluid vapor in the vicinity of a first heat transfer medium. The first heat transfer medium is a warm liquid, such as water, which is transported into the evaporator via a pipe from a low temperature heat source. The warm liquid is cooled and is returned to the low temperature heat source or is passed to a body to be cooled, such as a building. The working fluid vapor is compressed and then cooled in the vicinity of a second heat transfer medium, which is a chilled liquid which is brought in from the vicinity of a body to be heated (heat sink). The second heat transfer medium cools the working fluid such that, in some cases, it is condensed to form a liquid working fluid. In this method a flooded evaporator heat pump may also be used to heat domestic or service water or a process stream.

In another embodiment, the method for producing heating comprises producing heating in a direct expansion high temperature heat pump as described above with respect to FIG. 2. In this method, the liquid working fluid is passed through an evaporator and evaporates to produce a working fluid vapor. A first liquid heat transfer medium is cooled by the evaporating working fluid. The first liquid heat transfer medium is passed out of the evaporator to a low temperature heat source or a body to be cooled. The working fluid vapor is compressed and then condensed in the vicinity of a second heat transfer medium, which is a chilled liquid which is brought in from the vicinity of a body to be heated (heat sink). The second heat transfer medium cools the working fluid such that, in some

embodiments, it is condensed to form a liquid working fluid. In this method, a direct expansion heat pump may also be used to heat domestic or service water or a process stream. In one embodiment of the method for producing heating, the high temperature heat pump includes a compressor which is a centrifugal compressor.

In one embodiment of the method for producing heat, heat is

exchanged between at least two heating stages, the method comprises absorbing heat in a working fluid in a heating stage operated at a selected condensing temperature and transferring this heat to the working fluid of another heating stage operated at a higher condensing temperature;

wherein at least one of the working fluids comprises a refrigerant consisting of HFC-134.

In one embodiment, a method for producing heating in a high temperature heat pump is provided, wherein heat is exchanged between at least two stages arranged in a cascade configuration, comprising absorbing heat at a selected lower temperature in a first working fluid in a first cascade stage and transferring this heat to a second working fluid of a second cascade stage that supplies heat at a higher temperature; wherein the first working fluid or the second working fluid comprises a refrigerant consisting of HFC-134. In embodiments where HFC-134 is the first working fluid, the second working fluid may comprise at least one refrigerant selected from the group consisting of HFC-245fa (1 ,1 ,1 ,3,3,- pentafluoropropane), HFC-245eb (1 ,1 ,1 ,2,3,-pentafluoropropane), HFC- 365mfc (1 ,1 ,1 ,3,3-pentafluorobutane), HFC-431 Omee (1 ,1 ,1 ,2,3,4,4,5,5,5- decafluoropentane) HFO-1336mzz-E (E-1 ,1 ,1 ,4,4,4-hexafluoro-2-butene), HFO-1336mzz-Z (Z-1 ,1 ,1 ,4,4,4-hexafluoro-2-butene), HFO-1438mzz-E (E- 1 ,1 ,1 ,4,4,5,5,5-octafluoro-2-pentene), HFO-1438mzz-Z (Z-1 , 1 ,1 , 4,4,5,5,5- octafluoro-2-pentene), HFO-1438ezy-E (E-1 ,3,4,4,4-pentalfuoro-3- trifluoromethyl-1 -butene), HFO-1438ezy-Z (Z-1 ,3,4,4,4-pentalfuoro-3- trifluoromethyl-1 -butene), HFO-1336yf (3,4,4, 5,5, 5-hexafluoro1 -butene), HFO-1336ze-E (E-1 ,3,3,4,4,4-hexafluoro-1 -butene), HFO-1336ze-Z (Z- 1 ,3,3,4,4,4-hexafluoro-1 -butene), E-HFO-1234ye (E-1 ,2,3,3- tetrafluoropropene), Z- HFO-1234ye (Z-1 ,2,3,3-tetrafluoropropene), HCFO-1233zd-E (E-1 -chloro-3,3,3-trifluoropropene), HCFO-1233zd-Z (Z- 1 -chloro-3,3,3-trifluoropropene), HCFO-1233xf (2-chloro-3,3,3- trifluoropropene), HFO-1234ze-Z (Z-1 ,3,3,3-tetrafluoropropene), HFC- 236ea (1 ,1 ,1 ,2,3,3-hexafluoropropane), HFC-236fa (1 ,1 ,1 ,3,3,3- hexafluoropropane) and mixtures thereof. In embodiments where HFC- 134 is the second working fluid, the first working fluid may comprise at least one refrigerant selected from the group consisting of HFO-1234yf (2,3,3,3-tetrafluoropropene), E-HFO-1234ze (E-1 ,3,3,3- tetrafluoropropene), HFO-1243zf (3,3,3-trifluoropropene), HFC-161 (fluoroethane), HFC-32 (difluoromethane), HFC-125 (pentafluoroethane), HFC-245cb (1 ,1 ,1 ,2,2-pentafluoropropane), HFC-134a (1 ,1 ,1 ,2- tetrafluoroethane), HFC-143a (1 ,1 ,1 -trifluoroethane), HFC-152a (1 ,1 - difluoroethane), HFC-227ea (1 ,1 ,1 ,2,3,3, 3-heptafluoropropane), and mixtures thereof.

In one embodiment, the first working fluid comprises a refrigerant consisting of HFC-134 and the heat transferred to the second cascade stage is at a temperature of at least 10°C; at least 20°C; at least 30°C; at least 40°C; at least 50°C; at least 60°C; 65°C; at least 70°C; at least 72°C; at least 75°C; at least 80°C, at least 90°C, at least 100°C, at least 1 10°C, at least 1 15°C, or at least 1 17°C.

In another embodiment, the second working fluid comprises a refrigerant consisting of HFC-134 and the second cascade stage supplies heat at a temperature of at least 65°C; at least 70°C; at least 72°C; at least 75°C; at least 80°C, at least 90°C, at least 100°C, at least 1 10°C, at least 1 15°C, or at least 1 17°C.

In another embodiment of the invention is disclosed a method for raising the condenser operating temperature in a high temperature heat pump apparatus comprising charging the high temperature heat pump with a working fluid comprising a refrigerant consisting of HFC-134.

Use of HFC-134 in high temperature heat pumps increases the capability of these heat pumps because it allows operation at condenser temperatures higher than achievable with HFC-134a used in similar systems today. Thus is provided a method for raising the condenser operating temperature in a high temperature heat pump apparatus. The method comprises charging the high temperature heat pump apparatus with a working fluid comprising 1 ,1 ,2,2-tetrafluoroethane; wherein said high temperature heat pump apparatus comprises a centrifugal compressor.

In one embodiment, the method for raising the condenser operating temperature in a high temperature heat pump apparatus uses a working fluid comprising a refrigerant consisting of HFC-134.

When HFC-134a is used as the working fluid in commonly available high temperature centrifugal heat pumps, the maximum practical condenser operating temperature is about 71 °C. In certain embodiments of the method to raise the condenser operating temperature, when a composition comprising a refrigerant consisting of HFC-134 is used as the heat pump working fluid, the condenser operating temperature is raised to a temperature greater than about 71 °C; greater than about 72°C; greater than about 73°C, greater than about 75°C; greater than about 76°C;

greater than about 77°C; greater than about 78°C; greater than about 79°C; greater than about 80°C. In other embodiments, the condenser operating temperature is raised to a temperature from about 71 °C to about 80°C.

In accordance with this invention it is also possible to use a working fluid comprising a refrigerant consisting of HFC-134 in a system originally designed as a chiller using a conventional chiller working fluid (for example a chiller using HFC-134a or HCFC-123 or HFC-245fa) for the purpose of converting the system to a high temperature heat pump system provided that the chiller equipment can withstand the intended operating pressures with HFC-134. For example, a conventional chiller working fluid can be replaced in an existing chiller system with a working fluid

comprising a refrigerant consisting of HFC-134 to achieve this purpose. In accordance with this invention it is also possible to use a working fluid comprising a refrigerant consisting of HFC-134 in a system originally designed as a comfort (i.e., low temperature) heat pump system using a conventional comfort heat pump working fluid (for example a heat pump using HFC-134a or HCFC-123 or HFC-245fa) for the purpose of converting the system to a high temperature heat pump system provided that the comfort heat pump equipment can withstand the intended operating pressures with HFC-134. For example, a conventional comfort heat pump working fluid can be replaced in an existing comfort heat pump system with a working fluid comprising a refrigerant consisting of HFC-134 to achieve this purpose.

In another embodiment HFC-134 has been found to be useful as a working fluid in a high temperature heat pump comprising a centrifugal compressor. In this embodiment, said high temperature heat pump further comprises a condenser and said condenser operating temperature is greater than about 71 °C.

In another embodiment, a method for replacing HFC-134a in a high temperature heat pump is provided. The method comprises charging said high temperature heat pump with a working fluid comprising a refrigerant consisting of HFC-134; wherein said high temperature heat pump comprises a centrifugal compressor. In replacing HFC-134a, said high temperature heat pump may further comprise a condenser and the condenser operating temperature is raised to a temperature greater than about 71 °C. Additionally, the condenser operating temperature may be raised to a temperature from about 71 °C to about 1 17°C; from about 71 °C to about 1 15°C; from about 71 °C to about 1 10°C; from about 71 °C to about 100°C; from about 71 °C to about 90°C; from about 71 °C to about 80°C; from about 71 °C to about 79°C; from about 71 °C to about 78°C; from about 71 °C to about 77°C; from about 71 °C to about 76°C; o from about 71 °C to about 75°C.

In one embodiment, the high temperature heat pump may be suitable for use with HFC-134a. In another embodiment, the high temperature heat pump may have been designed for use with HFC-134a. In another embodiment, the high temperature heat pump may have been previously operated with HFC-134a. In another embodiment, a method for improving the energy efficiency of a centrifugal high temperature heat pump operating with HFC-134a comprising charging said centrifugal high temperature heat pump with a working fluid comprising a refrigerant consisting of HFC-134. It has been found that the coefficient of performance (COP) can be increased by at least 5% by replacing HFC-134a with HFC-134.

High Temperature Heat Pump Apparatus

In one embodiment of the present invention is provided a high temperature heat pump apparatus containing a working fluid comprising a refrigerant consisting of HFC-134; wherein said apparatus comprises a centrifugal compressor.

A heat pump is a type of apparatus for producing heating and/or cooling. A heat pump includes an evaporator, a compressor, a condenser or supercritical working fluid cooler, and an expansion device. A working fluid circulates through these components in a repeating cycle. Heating is produced at the condenser or supercritical working fluid cooler where energy (in the form of heat) is extracted from the working fluid to form cooled working fluid. Cooling is produced at the evaporator where energy is absorbed by the working fluid. In one embodiment, the high temperature heat pump apparatus of the present invention comprises (a) an evaporator through which a working fluid flows and is evaporated; (b) a compressor in fluid communication with the evaporator that compresses the evaporated working fluid to a higher pressure; (c) a condenser in fluid communication with the compressor through which the high pressure working fluid vapor flows and is condensed; and (d) a pressure reduction device in fluid communication with the condenser wherein the pressure of the condensed working fluid is reduced and said pressure reduction device further being in fluid communication with the evaporator such that the working fluid then repeats flow through components (a), (b), (c) and (d) in a repeating cycle. In one embodiment, the high temperature heat pump apparatus uses a working fluid comprising a refrigerant consisting of HFC-134.

Heat pumps may include flooded evaporators, one embodiment of which is shown in FIG. 1 , or direct expansion evaporators one

embodiment of which is shown in FIG. 2.

Heat pumps may utilize positive displacement compressors or centrifugal compressors. Positive displacement compressors include reciprocating, screw, or scroll compressors. Of note are heat pumps that use centrifugal compressors. Residential heat pumps are used to produce heated air to warm a residence or home (including single family or multi-unit attached homes) and produce maximum condenser operating temperatures from about 30°C to about 50°C.

Of note are high temperature heat pumps containing a working fluid comprising a refrigerant consisting of HFC-134 that may be used to heat air, water, another heat transfer medium or some portion of an industrial process, such as a piece of equipment, storage area or process stream. In one embodiment, high temperature heat pumps operate at condenser temperatures greater than about 55°C. In another embodiment, high temperature heat pumps operate at condenser temperatures greater than about 70°C. In another embodiment, high temperature heat pumps operate at condenser temperatures greater than about 72°C. In another embodiment, high temperature heat pumps operate at condenser temperatures greater than about 75°C. The maximum condenser operating temperature that can be achieved in a high temperature heat pump will depend upon the working fluid used. This maximum condenser operating temperature is limited by the normal boiling characteristics of the working fluid and also by the pressure to which the heat pump's compressor can raise the vapor working fluid pressure. In certain embodiments, the maximum condenser operating temperature for the high temperature heat pump is from about 71 °C to about 1 15°C; from about 71 °C to about 1 10°C; from about 71 °C to about 100°C; or from about 71 °C to about 80°C.

HFC-134 enables the design and operation of centrifugal heat pumps, operated at condenser temperatures higher than those feasible with HFC- 134a. In one embodiment, the high temperature heat pump also comprises a condenser operating at a temperature greater than about 71 °C. In another embodiment, the heat exchanger operates at a temperature from about 71 °C to about 80°C; from about 71 °C to about 1 15°C; from about 71 °C to about 135°C; from about 80°C to about 135°C; from about 90°C to about 135°C.

Also of note are heat pumps that are used to produce heating and cooling simultaneously. For instance, a single heat pump unit may produce heating to be used to generate high temperature steam for industrial use and may also produce cooling to be used to cool an industrial process stream.

Heat pumps, including both flooded evaporator and direct expansion, may be coupled with an air handling and distribution system to provide drying and dehumidification. In another embodiment, heat pumps may be used to heat water or generate steam. To illustrate how heat pumps operate, reference is made to the Figures. A flooded evaporator heat pump is shown in FIG. 1 .

In this heat pump a second heat transfer medium, which in some embodiments is a warm liquid, which may comprise water, and, in some embodiments, additives, or other heat transfer medium such as a glycol (e.g., ethylene glycol or propylene glycol), enters the heat pump carrying heat from a low temperature source (not shown), such as for instance, an industrial vessel or process stream, shown entering the heat pump at arrow 3, through a tube bundle or coil 9, in an evaporator 6, which has an inlet and an outlet. The warm second heat transfer medium is delivered to evaporator 6, where it is cooled by liquid working fluid, which is shown in the lower portion of evaporator 6. The liquid working fluid evaporates at a lower temperature than the warm first heat transfer medium which flows through tube bundle or coil 9. The cooled second heat transfer medium re-circulates back to the low temperature heat source as shown by arrow 4, via a return portion of tube bundle or coil 9. The liquid working fluid, shown in the lower portion of evaporator 6 in FIG. 1 , vaporizes and is drawn into compressor 7, which increases the pressure and temperature of the working fluid vapor. Compressor 7 compresses this vapor so that it may be condensed in condenser 5 at a higher pressure and temperature than the pressure and temperature of the working fluid vapor when it exits evaporator 6. A first heat transfer medium enters the condenser via a tube bundle or coil 10 in condenser 5 from a location where high temperature heat is provided ("heat sink") such as a service water heater or a steam generation system at arrow 1 in FIG. 1 . The first heat transfer medium is warmed in the process and returned via a return loop of tube bundle or coil 10 and arrow 2 to the heat sink. This first heat transfer medium cools the working fluid vapor in condenser 5 and causes the vapor to condense to liquid working fluid, so that there is liquid working fluid in the lower portion of condenser 5 as shown in FIG. 1. Condensed liquid working fluid in condenser 5 flows back to evaporator 6 through expansion device 8, which may be an orifice, capillary tube or expansion valve. Expansion device 8 reduces the pressure of the liquid working fluid, and converts the liquid working fluid at least partially to vapor, that is to say that the liquid working fluid flashes as pressure drops between condenser 5 and evaporator 6. Flashing cools the working fluid, i.e., both the liquid working fluid and the working fluid vapor to the saturated temperature at

evaporator pressure, so that both liquid working fluid and working fluid vapor are present in evaporator 6.

In some embodiments the working fluid vapor is compressed to a supercritical state and condenser 5 is replaced by a gas cooler where the working fluid vapor is cooled to a liquid state without condensation. In some embodiments the second heat transfer medium used in the apparatus depicted in FIG. 1 is a medium returning from a location where cooling is provided to a stream or a body to be cooled. Heat is extracted from the returning second heat transfer medium at the evaporator 6 and the cooled second heat transfer medium is supplied back to the location or body to be cooled. In this embodiment the apparatus depicted in FIG. 1 functions to simultaneously cool the second heat transfer medium that provides cooling to a body to be cooled (e.g. a process stream) and heat the first heat transfer medium that provides heating to a body to be heated (e.g. service water or steam or a process stream).

It is understood that the apparatus depicted in FIG. 1 can extract heat at the evaporator 6 from a wide variety of heat sources including solar, geothermal and waste heat and supply heat from the condenser 5 to a wide range of heat sinks.

It should be noted that for a single component working fluid

composition, the composition of the vapor working fluid in the evaporator and condenser is the same as the composition of the liquid working fluid in the evaporator and condenser. In this case, evaporation will occur at a constant temperature as in some embodiments of the present invention.

One embodiment of a direct expansion heat pump is illustrated in FIG. 2. In the heat pump as illustrated in FIG. 2, liquid first heat transfer medium, which in some embodiments is a warm liquid, such as warm water, enters evaporator 6' at inlet 14. Mostly liquid working fluid (with a small amount of working fluid vapor) enters coil 9' in the evaporator at arrow 3' and evaporates. As a result, first liquid heat transfer medium is cooled in evaporator 6', and a cooled first liquid heat transfer medium exits evaporator 6' at outlet 16, and is sent to a low temperature heat source (e.g. warm water flowing to a cooling tower). The working fluid vapor exits evaporator 6' at arrow 4' and is sent to compressor 7', where it is compressed and exits as high temperature, high pressure working fluid vapor. This working fluid vapor enters condenser 5' through condenser coil 10' at 1'. The working fluid vapor is cooled by a second liquid heat transfer medium, such as water, in condenser 5' and becomes a liquid. The second liquid heat transfer medium enters condenser 5' through condenser heat transfer medium inlet 20. The second liquid heat transfer medium extracts heat from the condensing working fluid vapor, which becomes liquid working fluid, and this warms the second liquid heat transfer medium in condenser 5'. The second liquidheat transfer medium exits from condenser 5' through condenser heat transfer medium outlet 18. The condensed working fluid exits condenser 5' through lower coil or tube bundle 10' as shown in FIG. 2 and flows through expansion device 12, which may be an orifice, capillary tube or expansion valve. Expansion device 12 reduces the pressure of the liquid working fluid. A small amount of vapor, produced as a result of the expansion, enters evaporator 6' with liquid working fluid through coil 9' and the cycle repeats. In some embodiments the working fluid vapor is compressed to a supercritical state and vessel 5' in FIG. 2 represents a gas cooler where the working fluid vapor is cooled to a liquid state without condensation.

In some embodiments the first liquid heating medium used in the apparatus depicted in FIG. 2 is a medium returning from a location where cooling is provided to a stream or a body to be cooled. Heat is extracted from the returning first heat transfer medium at the evaporator 6' and the cooled first heat transfer medium is supplied back to the location or body to be cooled. In this embodiment the apparatus depicted in FIG. 2 functions to simultaneously cool the first heat transfer medium (may be referred to as a working fluid heating medium since it provides heating to the working fluid or in some embodiments liquid heating medium) that provides cooling to a body to be cooled (e.g. a process stream) and heat the second heat transfer medium (or working fluid cooling medium or in some embodiments, liquid working heating medium) that provides heating to a body to be heated (e.g. service water or process stream).

It is understood that the apparatus depicted in FIG. 2 can extract heat at the evaporator 6' from a wide variety of heat sources including solar, geothermal and waste heat and supply heat from the condenser 5' to a wide range of heat sinks. Compressors useful in the present invention include dynamic compressors. Of note as examples of dynamic compressors are centrifugal compressors. A centrifugal compressor uses rotating elements to accelerate the working fluid radially, and typically includes an impeller and diffuser housed in a casing. Centrifugal compressors usually take working fluid in at an impeller eye, or central inlet of a rotating impeller, and accelerate it radially outward. Some static pressure rise occurs in the impeller, but most of the pressure rise occurs in the diffuser section of the casing, where velocity is converted to static pressure. Each impeller- diffuser set is a stage of the compressor. Centrifugal compressors are built with from 1 to 12 or more stages, depending on the final pressure desired and the volume of refrigerant to be handled. The pressure ratio, or compression ratio, of a compressor is the ratio of absolute discharge pressure to the absolute inlet pressure. The pressure a centrifugal compressor can develop depends on the tip speed of the impeller. Tip speed is the speed of the impeller measured at its tip and is related to the diameter of the impeller and its revolutions per minute. The tip speed required in a specific application depends on the compressor work that is required to elevate the thermodynamic state of the working fluid from evaporator to condenser conditions. The volumetric flow capacity of the centrifugal compressor is determined by the size of the passages through the impeller. Also of note as examples of dynamic compressors are axial

compressors.

Compressors for high temperature heat pumps also include positive displacement compressors. Positive displacement compressors draw vapor into a chamber, and the chamber decreases in volume to compress the vapor. After being compressed, the vapor is forced from the chamber by further decreasing the volume of the chamber to zero or nearly zero. Of note as examples of positive displacement compressors are reciprocating compressors, screw compressors, scroll compressors.

Of particular note are screw compressors for use in the high

temperature heat pumps of the present invention. In accordance with the present invention is provided a high temperature heat pump apparatus containing a working fluid comprising a refrigerant consisting of 1 ,1 ,2,2- tetrafluoroethane; wherein said apparatus comprises a screw compressor. It is expected that an apparatus comprising a screw compressor will provide improved energy efficiency.

In one embodiment, the high temperature heat pump apparatus has at least two heating stages. In one embodiment, the high temperature heat pump apparatus may comprise more than one heating circuit (or loop or stage) in a cascade arrangement. The performance (coefficient of performance for heating and volumetric heating capacity) of high temperature heat pumps operated with a refrigerant consisting of HFC-134 as the working fluid is drastically improved when the evaporator is operated at temperatures approaching the condenser temperature required by the application. When the heat supplied to the evaporator is only available at temperatures substantially lower than the temperature at which heating is required, thus requiring high temperature lifts leading to poor performance, a cascade cycle configuration with multiple circuits (or loops or stages) will be advantageous. The working fluid used in each cascade circuit (or loop or stage) is selected to have optimum

thermodynamic and chemical stability properties for the temperature range encountered in the cascade circuit or stage in which the fluid is used. In one embodiment of a cascade heat pump, the heat pump has two circuits or stages. In one embodiment, the low stage or low temperature circuit of the cascade cycle with two circuits or stages may be operated with a working fluid of lower boiling point than the boiling point of the working fluid used in the upper or high stage. In another embodiment, the high temperature heat pump apparatus comprises a first stage and a final stage, and optionally, at least one intermediate stage, arranged as a cascade heating system, each stage circulating a working fluid therethrough, wherein heat is transferred to the final stage from the first stage or an intermediate stage and wherein the working fluid in at least one stage comprises a refrigerant consisting of 1 ,1 ,2,2-tetrafluoroethane. In some embodiments, the high stage or high temperature circuit (also refered to as the final stage) of the cascade cycle may be operated with a working fluid comprising a refrigerant consisting of HFC-134. In these embodiments, the low stage or low temperature circuit of the cascade cycle may be operated with a working fluid (may be referred to as the first working fluid in this embodiment) comprising at least one refrigerant selected from HFC-161 , HFC-32, HFC-125, HFC-143a, HFC-152a, HFC- 134a, HFC-227ea, HFC-245cb, HFO-1234yf, HFO-1234ze-E, HFO- 1243zf, or mixtures thereof. In another embodiment, the first working fluid comprises at least one working fluid selected from CO2, NH3, or N2O.

In other embodiments, the low stage or low temperature circuit (or first stage) of the cascade cycle may be operated with a working fluid comprising a refrigerant consisting of HFC-134. In these embodiments, the high stage or high temperature circuit of the cascade cycle may be operated with a working fluid comprising at least one compound selected from HFC-245fa, HFC-245eb, HFC-236ea (1 ,1 ,1 ,2,3,3- hexafluoropropane), HFC-236fa (1 ,1 ,1 ,3,3,3-hexafluoropropane), HFC- 365mfc, HFC-4310mee, HFO-1336mzz-E, HFO-1336mzz-Z, HFO- 1234ze-Z (Z-1 ,3,3,3-tetrafluoropropene), HFO-1234ye-E or Z (1 ,2,3,3- tetrafluoropropene), HFO-1438mzz-E, HFO-1438mzz-Z, HFO-1438ezy-E, HFO-1438ezy-Z, HFO-1336yf, HFO-1336ze-E, HFO-1336ze-Z, HCFO- 1233zd-E, HCFO-1233zd-Z, HCFO-1233xf, HFE-7000 (also known as HFE-347mcc or n-CsF/OCHs), HFE-7100 (also known as HFE-449mccc or C4F9OCH3), HFE-7200 (also known as HFE-569mccc or C4F9OC2H5), HFE-7500 (also known as 3-ethoxy-1 ,1 ,1 ,2,3,4,4,5,5,6,6,6-dodecafluoro-2- trifluoromethyl-hexane or (CF3)2CFCF(OC2H₅)CF2CF2CF3),

1 ,1 ,1 ,2,2,4,5,5,5-nonafluoro-4-(trifluoromethyl)-3-pentanone (sold under the trademark Novec™ 1230 by 3M, St. Paul, Minnesota, USA), octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane,

octamethyltrisiloxane (OMTS), hexamethyldisiloxane (HMDS), n-pentane, isopentane, cyclopentane, hexanes, cyclohexane, heptanes, toluene or mixtures thereof. In another embodiment of a cascade heat pump, the heat pump has three circuits or stages. When the heat supplied to the evaporator is only available at even lower temperatures than in the previous example, thus requiring high temperature lifts leading to poor performance, a cascade cycle configuration with three stages or three circuits will be

advantageous. In one embodiment, the lowest stage or lowest

temperature circuit of the cascade cycle may be operated with a working fluid of lower boiling point than the boiling point of the working fluid used in the second or intermediate stage. In one embodiment, the high stage or high temperature circuit of the cascade cycle may be operated with a working fluid comprising a refrigerant consisting of HFC-134. In one embodiment, an intermediate stage or intermediate temperature circuit of the cascade cycle may be operated with a working fluid comprising a refrigerant consisting of HFC-134. In one embodiment, the low stage or low temperature circuit of the cascade cycle would be operated with a working fluid comprising a refrigerant consisting of HFC-134. In another embodiment, the low stage or low temperature circuit of the cascade cycle may be operated with a working fluid comprising at least one compound selected from HFC-161 , HFC-32, HFC-125, HFC-143a, HFC-152a, HFC- 134a, HFC-227ea, HFC-245cb, HFO-1234yf, HFO-1234ze-E, or mixtures thereof.

In one embodiment, the low stage or low temperature circuit (or first stage) of the three-stage cascade cycle may be operated with a working fluid comprising at least one compound selected from HFC-161 , HFC-32 HFC-125 HFC-143a HFC-152a, HFC-245cb, HFC-134a, HFC-227ea HFO-1234yf, HFO-1234ze-E, HFO-1243zf (3,3,3-trifluoropropene). Of note are working fluids for the low stage of a three-stage cascade heat pump such as HFO-1234yf/HFC-32, HFO-1234yf/HFC-32/HFC-125, HFO- 1234yf/HFC-134a, HFO-1234yf/HFC-134a/HFC-32, HFO-1234yf/HFC- 134, HFO-1234yf/HFC-134a/HFC-134, HFO-1234yf/HFC-32/HFC-

125/HFC-134a, E-HFO-1234ze/HFC-32, E-HFO-1234ze/HFC-32/HFC- 125, E-HFO-1234ze/HFC-134a, E-HFO-1234ze/HFC-134, E-HFO- 1234ze/HFC-134a/HFC-134, E-HFO-1234ze/HFC-227ea, E-HFO- 1234ze/HFC-134/HFC-227ea, E-HFO-1234ze/HFC-134/HFC-134a/HFC- 227ea, HFO-1234yf/E-HFO-1234ze/HFC-134/HFC-134a/HFC-227ea, etc.

The low temperature circuit (or low temperature loop) of the two-stage cascade cycle receives the available low temperature heat at the evaporator, lifts the heat to a temperature intermediate between the temperature of the available low temperature heat and the temperature of the required heating duty and transfers the heat to the high stage or high temperature circuit (or high temperature loop) of the cascade system at a cascade heat exchanger. Then the high temperature circuit, operated with a working fluid comprising a refrigerant consisting of HFC-134, further lifts the heat received at the cascade heat exchanger to the required condenser temperature to meet the intended heating duty. The cascade concept can be extended to configurations with three or more circuits lifting heat over wider temperature ranges and using different fluids over different temperature sub-ranges to optimize performance.

In one embodiment of the high temperature heat pump apparatus having more than one stage, the working fluid used in the lowest temperature stage comprises at least one refrigerant selected from the group consisting of HFO-1234yf, E-HFO-1234ze, HFO-1243zf, HFO- 1234ze-Z, HFC-161 , HFC-32, HFC-125, HFC-245cb, HFC-134a, HFC- 143a, HFC-152a, HFC-227ea, HFC-236ea, HFC-236fa and mixtures thereof.

In another embodiment of the high temperature heat pump apparatus having more than one stage, the working fluid of the final or highest- temperature stage comprises at least one refrigerant selected from the group consisting of HFC-245fa, HFC-245eb, HFC-236ea, HFC-236fa, HFC-365mfc, HFC-4310mee, HFO-1336mzz-E, Z-HFO-1234ze, HFO- 1234ye-E or Z (1 ,2,3,3-tetrafluoropropene, E- or Z- isomer), HFO- 1336mzz-Z, HFO-1438mzz-E, HFO-1438mzz-Z, HFO-1438ezy-E, HFO- 1438ezy-Z, HFO-1336yf, HFO-1336ze-E, HFO-1336ze-Z, , HCFO- 1233zd-E, HCFO-1233zd-Z, HCFO-1233xf and mixtures thereof. In accordance with the present invention, there is provided a cascade heat pump system having at least two heating loops for circulating a working fluid through each loop. In one embodiment, the high

temperature heat pump apparatus has at least two heating stages arranged as a cascade heating system, wherein each stage is in thermal communication with the next stage and wherein each stage circulates a working fluid therethrough, wherein heat is transferred to the final or upper or highest-temperature stage from the immediately preceding stage and wherein the heating fluid of the first stage or an intermediate stage comprises a refrigerant consisting of HFC-134.

In another embodiment the high temperature heat pump apparatus has at least two heating stages arranged as a cascade heating system, each stage circulating a working fluid therethrough comprising (a) a first expansion device for reducing the pressure and temperature of a first working fluid liquid; (b) an evaporator in fluid communication with the first expansion device having an inlet and an outlet; (c) a first compressor in fluid communication with the evaporator and having an inlet and an outlet;(d) a cascade heat exchanger system having: (i) a first inlet in fluid communication with the first compressor and a first outlet, through which passes the first working fluid and (ii) a second inlet and a second outlet through which passes a second working fluid in thermal communication with the first working fluid; (e) a second compressor in fluid communication with the second outlet of the cascade heat exchanger and having an inlet and an outlet; (f) a condenser in fluid communication with the second compressor and having an inlet and an outlet; and (g) a second expansion device in fluid communication with the condenser; wherein the first working fluid or the second working fluid comprises a refrigerant consisting of HFC-134. In one embodiment of the high temperature heat pump apparatus having at least two stages, the first working fluid comprises at least one refrigerant selected from the group consisting of HFO-1234yf, E- HFO-1234ze, HFO-1243zf, HFC-161 , HFC-32, HFC-125, HFC-245cb, HFC-134a, HFC-143a, HFC-152a, HFC-227ea, and mixtures thereof; and the second working fluid comprises a refrigerant consisting of HFC-134. In another embodiment of the high temperature heat pump apparatus having at least two stages, the second working fluid comprises at least one refrigerant selected from the group consisting of HFC-236ea, HFC- 236fa, HFC-245fa, HFC-245eb, E-HFO-1234ye, Z- HFO-1234ye, Z-HFO- 1234ze, HFC-365mfc, HFC-431 Omee, HFO-1336mzz-E, HFO-1336mzz-Z, HFO-1438mzz-E, HFO-1438mzz-Z, HFO-1438ezy-E, HFO-1438ezy-Z, HFO-1336yf, HFO-1336ze-E, HFO-1336ze-Z, HCFO-1233zd-E, HCFO- 1233zd-Z, HCFO-1233xf and mixtures thereof; and the first working fluid comprises a refrigerant consisting of HFC-134. In accordance with the present invention, there is provided a cascade heat pump system having at least two heating loops for circulating a working fluid through each loop. One embodiment of such a cascade system is shown generally at 110 in FIG. 3. Cascade heat pump system 110 of the present invention has at least two heating loops, including a first, or lower loop 112, which is a low temperature loop, and a second, or upper loop 114, which is a high temperature loop 114 as shown in FIG. 3. Each circulates a working fluid therethrough.

Cascade heat pump system 110 includes first expansion device 116. First expansion device 116 has an inlet 116a and an outlet 116b. First expansion device 116 reduces the pressure and temperature of a first working fluid liquid which circulates through the first or low temperature loop 112.

Cascade heat pump system 110 also includes evaporator 118.

Evaporator 118 has an inlet 118a and an outlet 118b. The first working fluid liquid from first expansion device 116 enters evaporator 118 through evaporator inlet 118a and is evaporated in evaporator 118 to form a first working fluid vapor. The first working fluid vapor then circulates to evaporator outlet 118b.

Cascade heat pump system 110 also includes first compressor 120. First compressor 120 has an inlet 120a and an outlet 120b. The first working fluid vapor from evaporator 118 circulates to inlet 120a of first compressor 120 and is compressed, thereby increasing the pressure and the temperature of the first working fluid vapor. The compressed first working fluid vapor then circulates to the outlet 120b of the first

compressor 120.

Cascade heat pump system 110 also includes cascade heat exchanger system 122. Cascade heat exchanger 122 has a first inlet 122a and a first outlet 122b. The first working fluid vapor from first compressor 120 enters first inlet 122a of heat exchanger 122 and is condensed in heat exchanger 122 to form a first working fluid liquid, thereby rejecting heat. The first working fluid liquid then circulates to first outlet 122b of heat exchanger 122. Heat exchanger 122 also includes a second inlet 122c and a second outlet 122d. A second working fluid liquid circulates from second inlet 122c to second outlet 122d of heat exchanger 122 and is evaporated to form a second working fluid vapor, thereby absorbing the heat rejected by the first working fluid (as it is condensed). The second working fluid vapor then circulates to second outlet 122d of heat exchanger 122. Thus, in the embodiment of FIG. 3, the heat rejected by the first working fluid is directly absorbed by the second working fluid.

Cascade heat pump system 110 also includes second compressor 124. Second compressor 124 has an inlet 124a and an outlet 124b. The second working fluid vapor from cascade heat exchanger 122 is drawn into compressor 124 through inlet 124a and is compressed, thereby increasing the pressure and temperature of the second working fluid vapor. The second working fluid vapor then circulates to outlet 124b of second compressor 124. Cascade heat pump system 110 also includes condenser 126 having an inlet 126a and an outlet 126b. The second working fluid from second compressor 124 circulates from inlet 126a and is condensed in condenser 126 to form a second working fluid liquid, thus producing heat. The second working fluid liquid exits condenser 126 through outlet 126b. Cascade heat pump system 110 also includes second expansion device 128 having an inlet 128a and an outlet 128b. The second working fluid liquid passes through second expansion device 128, which reduces the pressure and temperature of the second working fluid liquid exiting condenser 126. This liquid may be partially vaporized during this expansion. The reduced pressure and temperature second working fluid liquid circulates to second inlet 122c of cascade heat exchanger system 122 from expansion device 128.

Moreover, the stability of HFC-134 at temperatures higher than its critical temperature enables the design of heat pumps operated according to a supercritical or transcritical cycle in which heat is rejected by the working fluid in a supercritical state and made available for use over a range of temperatures (including temperatures higher than the critical temperature of HFC-134). The supercritical fluid is cooled to a liquid state without passing through an isothermal condensation transition.

For high temperature condenser operation (associated with high temperature lifts and high compressor discharge temperatures)

formulations of HFC-134 and lubricants with high thermal stability

(possibly in combination with oil cooling or other mitigation approaches such as fluid injection during the compression stage) will be

advantageous.

For high temperature condenser operation (associated with high temperature lifts and high compressor discharge temperatures) the use of magnetic centrifugal compressors (e.g., Danfoss-Turbocor type) that do not require the use of lubricants will be advantageous.

For high temperature condenser operation (associated with high temperature lifts and high compressor discharge temperatures) the use of compressor materials (e.g. shaft seals, etc) with high thermal stability may also be required.

The compositions comprising a refrigerant consisting of HFC-134 may be used in a high temperature heat pump apparatus in combination with molecular sieves to aid in removal of moisture. Desiccants may be composed of activated alumina, silica gel, or zeolite-based molecular sieves. In some embodiments, the molecular sieves are most useful with a pore size of approximately 3 Angstroms to 6 Angstroms. Representative molecular sieves include MOLSIV XH-7, XH-6, XH-9 and XH-1 1

(UOP LLC, Des Plaines, IL).

High Temperature Heat Pump Compositions

A composition is provided for use in high temperature heat pumps. The composition comprises (i) a refrigerant consisting of HFC-134; and

(ii) a stabilizer to prevent degradation at temperatures of 55°C or above; or

(iii) a lubricant suitable for use at 55°C or above, or both (ii) and (iii).

The compositions comprising a refrigerant consisting of HFC-134 may also comprise and/or be used in combination with at least one lubricant selected from the group consisting of polyalkylene glycols, polyol esters, polyvinylethers, mineral oils, alkylbenzenes, synthetic paraffins, synthetic naphthenes, perfluoropolyethers, poly(alpha)olefins and mixtures thereof.

Useful lubricants include those suitable for use with high temperature heat pump apparatus. Among these lubricants are those conventionally used in vapor compression refrigeration apparatus utilizing

chlorofluorocarbon refrigerants. In one embodiment, lubricants comprise those commonly known as "mineral oils" in the field of compression refrigeration lubrication. Mineral oils comprise paraffins (i.e., straight-chain and branched-carbon-chain, saturated hydrocarbons), naphthenes (i.e. cyclic paraffins) and aromatics (i.e. unsaturated, cyclic hydrocarbons containing one or more rings characterized by alternating double bonds). In one embodiment, lubricants comprise those commonly known as "synthetic oils" in the field of compression refrigeration lubrication.

Synthetic oils comprise alkylaryls (i.e. linear and branched alkyl

alkylbenzenes), synthetic paraffins and naphthenes, and

poly(alphaolefins). Representative conventional lubricants are the commercially available BVM 100 N (paraffinic mineral oil sold by BVA Oils), naphthenic mineral oil commercially available from Crompton Co. under the trademarks Suniso^® 3GS and Suniso^® 5GS, naphthenic mineral oil commercially available from Pennzoil under the trademark Sontex^® 372LT, naphthenic mineral oil commercially available from Calumet Lubricants under the trademark Calumet^® RO-30, linear alkylbenzenes commercially available from Shrieve Chemicals under the trademarks Zerol^® 75, Zerol^® 150 and Zerol^® 500, and HAB 22 (branched

alkylbenzene sold by Nippon Oil).

Useful lubricants may also include those which have been designed for use with hydrofluorocarbon refrigerants and are miscible with refrigerants of the present invention under compression refrigeration, air-conditioning and heat pump apparatus' operating conditions. Such lubricants include, but are not limited to, polyol esters (POEs) such as Castrol^® 100 (Castrol, United Kingdom), polyalkylene glycols (PAGs) such as RL-488A from Dow (Dow Chemical, Midland, Michigan), polyvinyl ethers (PVEs), and polycarbonates (PCs).

Lubricants are selected by considering a given compressor's

requirements and the environment to which the lubricant will be exposed.

Of note are high temperature lubricants with stability at high

temperatures. The highest temperature the heat pump will achieve will determine which lubricants are required. In one embodiment, the lubricant must be stable at temperatures of at least 55°C. In another embodiment the lubricant must be stable at temperatures of at least 71 °C. In another embodiment, the lubricant must be stable at temperatures of at least 75°C. In another embodiment the lubricant must be stable at temperatures of at least 79°C. In another embodiment the lubricant must be stable at temperatures of at least 1 15°C. In another embodiment the lubricant must be stable at temperatures of at least 135°C. Of particular note are poly alpha olefins (POA) lubricants with stability up to about 200-250°C and polyol ester (POE) lubricants with stability at temperatures up to about 200 to 250°C. Also of particular note are perfluoropolyether lubricants that have stability at temperatures up to from about 220 to about 350°C. PFPE lubricants include those available from DuPont (Wilmington, DE) under the trademark Krytox^®, such as the XHT series with thermal stability up to about 300 to 350°C. Other PFPE lubricants include those sold under the trademark Demnum™ from Daikin Industries (Japan) with thermal stability up to about 280 to 330°C, and available from Ausimont (Milan, Italy), under the trademarks Fomblin^® and Galden^® such as that available under the trademark Fomblin^®-Y or Fomblin^®-Z with thermal stability up to about 220 to 260°C.

formulations of working fluid comprising a refrigerant consisting of HFC- 134 and lubricants with high thermal stability (possibly in combination with oil cooling or other mitigation approaches) will be advantageous.

In one embodiment, the present invention includes a composition comprising: (a) a refrigerant consisting of HFC-134; and (b) at least one lubricant suitable for use at a temperature of at least about 55°C. Of note are embodiments wherein the lubricant is suitable for use at a temperature of at least about 71 °C. Also of note are embodiments wherein the lubricant is suitable for use at a temperature of at least about 75°C. Also of note are embodiments wherein the lubricant is suitable for use at a temperature of at least about 79°C. Also of note are embodiments wherein the lubricant is suitable for use at a temperature of at least about 1 15°C. Also of note are embodiments wherein the lubricant is suitable for use at a temperature of at least about 135°C. In one embodiment, any of the compositions of this invention may further comprise 0.01 weight percent to 5 weight percent of a stabilizer, free radical scavenger or antioxidant. Such stabilizers may include but are not limited to, nitromethane, hindered phenols, hydroxylamines, thiols, phosphites, or lactones. Single additives or combinations may be used. Optionally, in another embodiment, certain other refrigeration, air- conditioning, or heat pump system additives may be added, as desired, to the any of the working fluids as disclosed herein in order to enhance performance and system stability. These additives are known in the field of refrigeration, air-conditioning and heat pumps, and include, but are not limited to, anti-wear agents, extreme pressure lubricants, corrosion and oxidation inhibitors, metal surface deactivators, free radical scavengers, and foam control agents. In general, these additives may be present in the working fluids in small amounts relative to the overall composition. Typically concentrations of from less than 0.1 weight percent to as much as 3 weight percent of each additive are used. These additives are selected on the basis of the individual system requirements. These additives include members of the triaryl phosphate family of extreme pressure lubricity additives, such as butylated triphenyl phosphates (BTPP), or other alkylated triaryl phosphate esters, e.g. Syn-0-Ad 8478 from Akzo Chemicals, tricresyl phosphates and related compounds.

Additionally, the metal dialkyl dithiophosphates (e.g., zinc dialkyl dithiophosphate (or ZDDP), Lubrizol 1375 and other members of this family of chemicals may be used in compositions of the present invention. Other anti-wear additives include natural product oils and asymmetrical polyhydroxyl lubrication additives, such as Synergol TMS (International Lubricants). Similarly, stabilizers such as antioxidants, free radical scavengers, and water scavengers may be employed. Compounds in this category can include, but are not limited to, butylated hydroxy toluene (BHT), epoxides, and mixtures thereof. Corrosion inhibitors include dodecyl succinic acid (DDSA), amine phosphate (AP), oleoyl sarcosine, imidazone derivatives and substituted sulfphonates. Metal surface deactivators include areoxalyl bis (benzylidene) hydrazide, N,N'-bis(3,5- di-tert-butyl-4-hydroxyhydrocinnamoylhydrazine, 2,2,' - oxamidobis-ethyl- (3,5-di-tert-butyl-4-hydroxyhydrocinnamate, N,N'-(disalicyclidene)-1 ,2- diaminopropane and ethylenediaminetetra-acetic acid and its salts, and mixtures thereof. Any of the present compositions may include stabilizers comprising at least one compound selected from the group consisting of hindered phenols, thiophosphates, butylated tnphenylphosphorothionates, organo phosphates, or phosphites, aryl alkyl ethers, terpenes, terpenoids, epoxides, fluorinated epoxides, oxetanes, ascorbic acid, thiols, lactones, thioethers, amines, nitromethane, alkylsilanes, benzophenone derivatives, aryl sulfides, divinyl terephthalic acid, diphenyl terephthalic acid, ionic liquids, and mixtures thereof. Representative stabilizer compounds include but are not limited to tocopherol; hydroquinone; t-butyl hydroquinone; monothiophosphates; and dithiophosphates, commercially available from Ciba Specialty Chemicals, Basel, Switzerland, hereinafter "Ciba," under the trademark Irgalube^® 63; dialkylthiophosphate esters, commercially available from Ciba under the trademarks Irgalube^® 353 and Irgalube^® 350, respectively; butylated triphenylphosphorothionates, commercially available from Ciba under the trademark Irgalube^® 232;

amine phosphates, commercially available from Ciba under the trademark Irgalube^® 349 (Ciba); hindered phosphites, commercially available from Ciba as Irgafos^® 168; a phosphate such as (Tris-(di-tert-butylphenyl), commercially available from Ciba under the trademark Irgafos^® OPH;

(Di-n-octyl phosphite); and iso-decyl diphenyl phosphite, commercially available from Ciba under the trademark Irgafos^® DDPP; anisole;

1 ,4-dimethoxybenzene; 1 ,4-diethoxybenzene; 1 ,3,5-trimethoxybenzene; d-limonene; retinal; pinene; menthol; Vitamin A; terpinene; dipentene; lycopene; beta carotene; bornane; 1 ,2-propylene oxide; 1 ,2-butylene oxide; n-butyl glycidyl ether; trifluoromethyloxirane;

1 ,1 -bis(trifluoromethyl)oxirane; 3-ethyl-3-hydroxymethyl-oxetane, such as OXT-101 (Toagosei Co., Ltd); 3-ethyl-3-((phenoxy)methyl)-oxetane, such as OXT-21 1 (Toagosei Co., Ltd); 3-ethyl-3-((2-ethyl-hexyloxy)methyl)- oxetane, such as OXT-212 (Toagosei Co., Ltd); ascorbic acid;

methanethiol (methyl mercaptan); ethanethiol (ethyl mercaptan);

Coenzyme A; dimercaptosuccinic acid (DMSA); grapefruit mercaptan (( R)-2-(4-methylcyclohex-3-enyl)propane-2-thiol)); cysteine (( R)-2-amino- 3-sulfanyl-propanoic acid); lipoamide (1 ,2-dithiolane-3-pentanamide); 5,7- bis(1 ,1 -dimethylethyl)-3-[2,3(or 3,4)-dimethylphenyl]-2(3H)-benzofuranone, commercially available from Ciba under the trademark Irganox^® HP-136; benzyl phenyl sulfide; diphenyl sulfide; diisopropylamine; dioctadecyl 3,3'-thiodipropionate, commercially available from Ciba under the trademark Irganox^® PS 802 (Ciba); didodecyl 3,3'-thiopropionate, commercially available from Ciba under the trademark Irganox^® PS 800; di-(2,2,6,6-tetramethyl-4-piperidyl)sebacate, commercially available from Ciba under the trademark Tinuvin^® 770; poly-(N-hydroxyethyl-2,2,6,6- tetramethyl-4-hydroxy-piperidyl succinate, commercially available from Ciba under the trademark Tinuvin^® 622LD (Ciba); methyl bis tallow amine; bis tallow amine; phenol-alpha-naphthylamine;

bis(dimethylamino)methylsilane (DMAMS); tris(trimethylsilyl)silane

(TTMSS); vinylthethoxysilane; vinyltrimethoxysilane; 2,5- difluorobenzophenone; 2',5'-dihydroxyacetophenone; 2- aminobenzophenone; 2-chlorobenzophenone; benzyl phenyl sulfide;

diphenyl sulfide; dibenzyl sulfide; ionic liquids; and others.

In one embodiment, ionic liquid stabilizers comprise at least one ionic liquid. Ionic liquids are organic salts that are liquid or have melting points below 100°C. In another embodiment, ionic liquid stabilizers comprise salts containing cations selected from the group consisting of pyridinium, pyridazinium, pyrimidinium, pyrazinium, imidazolium, pyrazolium, thiazolium, oxazolium and triazolium; and anions selected from the group consisting of [BF ]-, [PFe]-, [SbFe]-, [CFsSOs]-, [HCF2CF2SO3]-,

[CF3HFCCF2SO3]-, [HCCIFCF2SO3]-, [(CF₃SO₂)2N]-, [(CF₃CF₂SO2)2N]-, [(CF3SO2)3C]-, [CF3CO2]-, and F-. Representative ionic liquid stabilizers include emim BF₄ (1 -ethyl-3-methylimidazolium tetrafluoroborate); bmim BF₄ (1 -butyl-3-methylimidazolium tetraborate); emim PF6 (1 -ethyl-3- methylimidazolium hexafluorophosphate); and bmim PF6 (1 -butyl-3- methylimidazolium hexafluorophosphate), all of which are available from Fluka (Sigma-Aldrich).

EXAMPLES

The concepts described herein will be further described in the following example, which does not limit the scope of the invention described in the claims. EXAMPLE 1

Improving the energy efficiency of an HFC-134a Centrifugal High Temperature Heat Pump by Replacing HFC-134a with HFC-134

Table 1 compares the calculated performance of a centrifugal high temperature heat pump operating at a representative set of conditions with HFC-134 as the working fluid to the performance operating with HFC-134a as the working fluid. Replacing HFC-134a with HFC-134 would increase the heat pump coefficient of performance for heating, COPheating, by 7.3%. The impeller tip speed required with HFC-134 would remain close to that required with HFC-134a thus enabling replacement of HFC-134a with HFC-134 without major heat pump modifications. The volumetric heating capacity with HFC-134 would be expected to decrease relative to that with HFC-134a by about 1 1 %. However, such a capacity decrease would be acceptable in many installations where, for example, the initial heat pump capacity was overdesigned relative to the current heating loads or where additional heat pumps could be added to meet the required total heating capacity. In view of the large typical annual electricity costs for operating a heat pump, an energy efficiency increase of 7.3% would outweigh the cost of adding heating capacity in many instances. Moreover, the increased heat pump energy efficiency with HFC-134 relative to HFC-134a and the reduced GWP of HFC-134 relative to HFC-134a would reduce the greenhouse gas emissions associated with the generation of the electricity required to operate the heat pump and with the refrigerant leakage, respectively.

Table 1

EXAMPLE 2

Method for increasing the heating temperature of a high temperature centrifugal heat pump operating with HFC-134a bv replacing HFC-134a with HFC-134 The maximum working pressure of commonly used large centrifugal heat pumps operating with HFC-134a as the working fluid is often limited to 2.18 MPa. Then the maximum condensing temperature feasible with HFC-134a is limited to about 71 .2 °C. The maximum condensing temperature of such an HFC-134a centrifugal heat pump can be increased up to 80.5 °C without exceeding the maximum permissible pressure of 2.18 MPa by replacing HFC-134a with HFC-134. Table 2 compares the heat pump operation after retrofitting to HFC-134 to the original operation with HFC-134a. A significant increase to the impeller tip speed by 16.93% would be required to realize operation at the higher condensing

temperature with HFC-134. In some instances it may be preferable to limit the condensing temperature with HFC-134 to values lower than 80.5 °C (but still higher than 71 .2 °C) so as to minimize the modifications to the heat pump to realize the higher required impeller tip speed relative to HFC-134a.

Table 2

If a heat source is available that allows the evaporating temperature to be suitably increased after conversion to HFC-134, the required impeller tip speed with HFC-134 could be adjusted to match the impeller tip speed with HFC-134a. Table 3 compares the performance of a centrifugal heat pump retrofitted from operation with HFC-134a at a condensing

temperature of 71 .2 °C and an evaporating temperature of 40 °C to operation with HFC-134 at a condensing temperature of 80.5 °C and an evaporating temperature of 50 °C. Elevating the evaporating temperature not only obviates the need to adjust the impeller tip speed after conversion to HFC-134 but also significantly improves the COP for heating and volumetric heating capacity relative to operation at a lower evaporating temperature (HFC-134 column in Table 3 versus HFC-134 column

Table 2).

Table 3

Claims

CLAIMS What is claimed is:

1 . A method for producing heating in a high temperature heat pump comprising extracting heat from a working fluid in a heat exchanger, thereby producing a cooled working fluid, wherein said working fluid comprises a refrigerant consisting of 1 ,1 ,2,2-tetrafluoroethane and said high temperature heat pump comprises a centrifugal

compressor.

2. The method of claim 1 wherein the heat exchanger is selected from the group consisting of a supercritical working fluid cooler and a condenser.

3. The method of claim 1 , wherein the heat exchanger operates at a temperature greater than about 71 °C.

4. The method of claim 1 further comprising passing a first heat transfer medium through the heat exchanger, whereby said extraction of heat heats the first heat transfer medium, and passing the heated first heat transfer medium from the heat exchanger to a body to be heated.

5. The method of claim 4, wherein the first heat transfer medium is an industrial heat transfer liquid and the body to be heated is a chemical process stream.

6. The method of claim 4, wherein the first heat transfer medium is

water and the body to be heated is air for space heating.

7. The method of claim 1 further comprising expanding the cooled

working fluid and then heating the working fluid in a second heat exchanger to produce a heated working fluid.

8. The method of claim 7 wherein said second heat exchanger is an evaporator and the heated working fluid is a vapor.

9. The method of claim 2 further comprising passing a fluid to be heated through said condenser, thus heating the fluid.

10. A method for producing heating in a high temperature heat pump wherein heat is exchanged between at least two stages arranged in a cascade configuration, comprising:

absorbing heat at a selected lower temperature in a first working fluid in a first cascade stage and transferring this heat to a second working fluid of a second cascade stage that supplies heat at a higher temperature; wherein the first or second working fluid comprises a refrigerant consisting of 1 ,1 ,2,2-tetrafluoroethane.

1 1 . A method for raising the condenser operating temperature in a high temperature heat pump apparatus comprising:

charging the high temperature heat pump with a working fluid comprising a refrigerant consisting of 1 ,1 ,2,2-tetrafluoroethane; wherein said high temperature heat pump apparatus comprises a centrifugal compressor.

12. The method of claim 1 1 wherein the condenser operating

temperature is raised to a temperature greater than about 71 °C.

13. A high temperature heat pump apparatus containing a working fluid comprising a refrigerant consisting of 1 ,1 ,2,2-tetrafluoroethane;

wherein said apparatus comprises a centrifugal compressor.

14. The high temperature heat pump apparatus of claim 13, having a condenser, wherein the condenser operates at a temperature greater than about 71 °C.

15. The high temperature heat pump apparatus of claim 13, said

apparatus comprising (a) a first heat exchanger through which a working fluid flows and is heated; (b) a centrifugal compressor in fluid communication with the first heat exchanger that compresses the heated working fluid to a higher pressure; (c) a second heat exchanger in fluid communication with the compressor through which the high pressure working fluid flows and is cooled; and (d) a pressure reduction device in fluid communication with the second heat exchanger wherein the pressure of the cooled working fluid is reduced and said pressure reduction device further being in fluid communication with the first heat exchanger such that the working fluid then repeats flow through components (a), (b), (c) and (d) in a repeating cycle.

16. The high temperature heat pump apparatus of claim 13 having at least two heating stages.

17. The high temperature heat pump apparatus of claim 16 comprising a first stage and a final stage, and optionally, at least one intermediate stage, arranged as a cascade heating system, each stage circulating a working fluid therethrough, wherein heat is transferred to the final stage from the first stage or an intermediate stage and wherein the working fluid in at least one stage comprises a refrigerant consisting of 1 ,1 ,2,2-tetrafluoroethane.

18. The high temperature heat pump apparatus of claim 16 having at least two heating stages, a first stage and a final stage, arranged as a cascade heating system, each stage circulating a working fluid therethrough comprising:

(a) a first expansion device for reducing the pressure and

temperature of a first working fluid liquid;

(b) an evaporator in fluid communication with the first expansion device having an inlet and an outlet;

(c) a first compressor in fluid communication with the evaporator and having an inlet and an outlet;

(d) a cascade heat exchanger system in fluid communication with the first compressor outlet having:

(i) a first inlet and a first outlet, through which flows the first working fluid and

(ii) a second inlet and a second outlet through which flows a second working fluid in thermal communication with the first working fluid; (e) a second compressor in fluid communication with the second outlet of the cascade heat exchanger system and having an inlet and an outlet;

(f) a condenser in fluid communication with the second

compressor and having an inlet and an outlet; and

(g) a second expansion device in fluid communication with the condenser; wherein the first or second working fluid comprises a refrigerant consisting of 1 ,1 ,2,2-tetrafluoroethane.

19. The high temperature heat pump apparatus of claim 18, wherein the first working fluid comprises at least one refrigerant selected from the group consisting of HFO-1234yf, E-HFO-1234ze, HFO-1243zf, HFC- 161 , HFC-32, HFC-125, HFC-245cb, HFC-134a, HFC-143a, HFC- 152a, HFC-227ea, and mixtures thereof; and wherein the second working fluid comprises a refrigerant consisting of HFC-134.

20. The high temperature heat pump apparatus of claim 18, wherein the second working fluid comprises at least one refrigerant selected from the group consisting of HFC-236ea, HFC-236fa, HFC-245fa, HFC- 245eb, E-HFO-1234ye, Z- HFO-1234ye, Z-HFO-1234ze, HFC- 365mfc, HFC-431 Omee, HFO-1336mzz-E, HFO-1336mzz-Z, HFO-

1438mzz-E, HFO-1438mzz-Z, HFO-1438ezy-E, HFO-1438ezy-Z, HFO-1336yf, HFO-1336ze-E, HFO-1336ze-Z, HCFO-1233zd-E, HCFO-1233zd-Z, HCFO-1233xf, HFE-347mcc, HFE-449mccc, HFE- 569mccc, 3-ethoxy-1 ,1 ,1 ,2,3,4,4,5,5,6,6,6-dodecafluoro-2- trifluoromethyl-hexane, 1 ,1 ,1 ,2,2,4,5,5,5-nonafluoro-4-

(trifluoromethyl)-3-pentanone, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, octamethyltrisiloxane,

hexamethyldisiloxane, n-pentane, isopentane, cyclopentane, hexanes, cyclohexane, heptanes, toluene and mixtures thereof; and wherein the first working fluid comprises a refrigerant consisting of

HFC-134.

21 . The high temperature heat pump apparatus of claim 17, wherein the working fluid in the final stage comprises at least one refrigerant selected from the group consisting of HFC-236ea, HFC-236fa, HFC- 245fa, E-HFO-1234ye, Z- HFO-1234ye, Z-HFO-1234ze, HFC-245eb, HFC-365mfc, HFC-4310mee, HFO-1336mzz-E, HFO-1336mzz-Z,

HFO-1438mzz-E, HFO-1438mzz-Z, HFO-1438ezy-E, HFO-1438ezy- Z, HFO-1336yf, HFO-1336ze-E, HFO-1336ze-Z, HCFO-1233zd-E, HCFO-1233zd-Z, HCFO-1233xf, HFE-347mcc, HFE-449mccc, HFE- 569mccc, 3-ethoxy-1 ,1 ,1 ,2,3,4,4,5,5,6,6,6-dodecafluoro-2- trifluoromethyl-hexane, 1 ,1 ,1 ,2,2,4,5,5,5-nonafluoro-4-

hexamethyldisiloxane, n-pentane, isopentane, cyclopentane, hexanes, cyclohexane, heptanes, toluene and mixtures thereof.

22. The heat pump apparatus of claim 18 wherein the first working fluid comprises at least one working fluid selected from CO2, NH3, or N2O.

23. Use of a refrigerant consisting of HFC-134 as working fluid in a high temperature heat pump comprising a centrifugal compressor.

24. The use of claim 23, wherein said high temperature heat pump

further comprises a condenser and said condenser operating temperature is greater than about 71 °C.

25. A method for replacing HFC-134a in a high temperature heat pump comprising charging said high temperature heat pump with a working fluid comprising a refrigerant consisting of HFC-134; wherein said high temperature heat pump comprises a centrifugal compressor.

26. The method of claim 25, wherein said high temperature heat pump further comprises a condenser and the condenser operating temperature is raised to a temperature greater than about 71 °C.

27. The method of claim 25, wherein the condenser operating

temperature is raised to a temperature from about 71 °C to about

80°C.

28. A method for improving the energy efficiency of a centrifugal high temperature heat pump operating with HFC-134a comprising charging said centrifugal high temperature heat pump with a working fluid comprising a refrigerant consisting of HFC-134.

29. he method of claim 28 wherein the coefficient of performance for the centrifugal high temperature heat pump is increased by at least 5% as compared to the coefficient of performance when HFC-134a is being used in the working fluid.

30. The method of claim 1 , wherein the heat exchanger operates at a temperature from about 71 °C to about 80°C.

31 . The method of claim 1 , wherein the heat exchanger operates at a temperature from about 71 °C to about 1 15°C.

32. The method of claim 1 , wherein the heat exchanger operates at a temperature from about 71 °C to about 135°C.

33. The method of claim 1 , wherein the heat exchanger operates at a temperature from about 80°C to about 135°C.

34. The method of claim 1 , wherein the heat exchanger operates at a temperature from about 90°C to about 135°C.

35. A method for producing heating in a high temperature heat pump comprising extracting heat from a working fluid in a heat exchanger, thereby producing a cooled working fluid, wherein said working fluid comprises a refrigerant consisting of 1 ,1 ,2,2-tetrafluoroethane and said high temperature heat pump comprises a screw compressor.

36. A high temperature heat pump apparatus containing a working fluid comprising a refrigerant consisting of 1 ,1 ,2,2-tetrafluoroethane; wherein said apparatus comprises a screw compressor.