1.3 Working fluid 1.3.1General The term "working fluid"means the process medium in heat pump system (for refrigeration process termed medium refrigerant).The discussion here is mostly limited to the processes of absorption and emission of heat at approximately constant temperature,in other words to the usual evaporator- /compressor process("cold-vapor process")with a single component medium. Since the first cold steam plant saw the light (Jacob Perkins'refrigeration from 1834),a series of working fluids have been applied,Perkins even used ether,but in turn was working fluids such as carbon dioxide (CO2),ammonia(NH3),sulfur dioxide(SO2)and methyl(CH3C1).Today,only the ammonia back of these "pioneer fluid",and then primarily used in large refrigeration systems and heat pumps.The rest are replaced with synthetic derived fluid,where the base material is hydrocarbons methane(CH4)and ethane (C2H6).Intentional properties are achieved by a varying number of hydrogen atoms are replaced with mainly chlorine(Cl)or fluorine(F).Other halogens may also occur,such as bromine(Br).The fluid's official designation is "R xyz",where R stands for"Refrigerants"and xyz is the digits of a number that reflects the chemical composition.This symbol covers the rest of the family of the working fluid(see below). Working fluid who have a basis in ethane or methane(hydrocarbon derivatives)and where all Hydrogen atoms are replaced with chlorine and fluorine,termed full-halogenated chlorine-fluorine carbohydrates or just CFC's.Not full-halogenated chlorofluorocarbons containing one or more hydrogen atoms and is designated as HCFCs,If the fluid also are chlorine free and contains only hydrogen,fluorine and carbon, called the llFK,one often uses halocarbons (short for halogenated hydrocarbons)as a generic term for CFCs,HCFCs and HFCs. The pure hydrocarbon derivatives are numbered according to the following key: 1.digit:Number of C atoms-1 2.digit:Number of H atoms +1 3.digit:Number of F atoms If the first digit is zero HP,it will be not printed.This means that all the fluid that have been withdrawn from methane only get two digits.About a bromine atom is substituted,provided the addition B1 to R- number, Example: R-134a C=1+1=2 R-22 H=4-1=3 C=0+1=1 F=3 H=2-1=1 Letter code says that this is an Isomer F=2 That means the refrigerant consist of the same number of atoms,but the CI=1 molecule have a different composition Therefore:CHCIF2 Therefore:C H F 233 In addition to the clean fluid,are also called azeotroper.An azeotrop is a(mixed fluid)mixture of two fluid,which at a given mixture has the same properties as a pure medium,that is evaporation and condensation temperature is constant at a given pressure.Normally,mixtures of fluid that dissolve in each other
1.3 Working fluid 1.3.1General The term "working fluid" means the process medium in heat pump system (for refrigeration process termed medium refrigerant). The discussion here is mostly limited to the processes of absorption and emission of heat at approximately constant temperature, in other words to the usual evaporator- /compressor process ("cold-vapor process") with a single component medium. Since the first cold steam plant saw the light (Jacob Perkins' refrigeration from 1834), a series of working fluids have been applied, Perkins even used ether, but in turn was working fluids such as carbon dioxide (CO2), ammonia (NH3), sulfur dioxide (SO2) and methyl (CH3C1). Today, only the ammonia back of these "pioneer fluid", and then primarily used in large refrigeration systems and heat pumps. The rest are replaced with synthetic derived fluid, where the base material is hydrocarbons methane (CH4) and ethane (C2H6). Intentional properties are achieved by a varying number of hydrogen atoms are replaced with mainly chlorine (Cl) or fluorine (F). Other halogens may also occur, such as bromine (Br). The fluid's official designation is "R xyz", where R stands for "Refrigerants" and xyz is the digits of a number that reflects the chemical composition. This symbol covers the rest of the family of the working fluid (see below). Working fluid who have a basis in ethane or methane (hydrocarbon derivatives) and where all Hydrogen atoms are replaced with chlorine and fluorine, termed full-halogenated chlorine-fluorine carbohydrates or just CFC’s. Not full-halogenated chlorofluorocarbons containing one or more hydrogen atoms and is designated as HCFCs, If the fluid also are chlorine free and contains only hydrogen, fluorine and carbon, called the IIFK, one often uses halocarbons (short for halogenated hydrocarbons) as a generic term for CFCs, HCFCs and HFCs. The pure hydrocarbon derivatives are numbered according to the following key: 1. digit: Number of C atoms - 1 2. digit: Number of H atoms + 1 3. digit: Number of F atoms If the first digit is zero HP, it will be not printed. This means that all the fluid that have been withdrawn from methane only get two digits. About a bromine atom is substituted, provided the addition B1 to R - number, Example: R-134a C = 1 + 1 = 2 H = 4 – 1 = 3 F = 3 Letter code says that this is an Isomer. That means the refrigerant consist of the same number of atoms, but the molecule have a different composition Therefore: C 2 H 3 F 3 R -22 C=0+1=1 H=2-1=1 F=2 Cl=1 Therefore: CHClF2 In addition to the clean fluid, are also called azeotroper. An azeotrop is a (mixed fluid) mixture of two fluid, which at a given mixture has the same properties as a pure medium, that is evaporation and condensation temperature is constant at a given pressure. Normally, mixtures of fluid that dissolve in each other
zeotrope,that is,they evaporate and condense over a temperature interval(sliding temperature).In R- sisters are the azeotrope fluid numbered 500 and upwards,for example.R-500(73.8%R12,R152a 26.2%) andR502(48.8%R-22,51.2%R-115). Hydrocarbons are referred to in the same way as halocarbons.Examples of this are propane(C3H8)and propylene which respectively have the designation R-290 and R-1270. Inorganic fluid are collected in a separate group with 7 as the first digit and Molecular weight as sequential digits.Examples include ammonia,which,with Molecular weight equal to 17 have the designation R-717,water is designated as R-718 and R-744 carbon dioxide(CO2). 1.3.2 What determines the medium's versatility as a working medium? There are many factors that come in,partly due to deviations from the idealism of the basic process,and partly of more practical nature.To simplify the overview,the elements are grouped according to the following pattern: 1)Features that determine the theoretical process in terms of goodness energy and volume needs.That is to say: power factor [- volumetric thermal performance [kj/m3] 2)Properties of importance for the practical implementation of the process, such as: resulting system pressure [bar] possible operating range of one-step compression -Volume and energy in the compressor heat exchanger effectiveness Dimensions of pipes,valves,etc. compared to oil relation to water conditions for construction materials 3)Properties of the significance of the leak to the environment toxicity flammability -panic creative ability -warning properties(odor,color,etc.) -dilution properties ozone-depleting ability("ozone depletion potential,ODP) -contribution to global warming("global warming potential,GWP) -contribution to environmental damage at the soil surface(smog,acid rain,etc.) -Other possible environmental disturbances 4)Pricing and Availability
zeotrope, that is, they evaporate and condense over a temperature interval (sliding temperature). In Rsisters are the azeotrope fluid numbered 500 and upwards, for example. R-500 (73.8% R12, R152a 26.2%) and R502 (48.8% R-22, 51.2% R-115). Hydrocarbons are referred to in the same way as halocarbons. Examples of this are propane (C3H8) and propylene which respectively have the designation R-290 and R-1270. Inorganic fluid are collected in a separate group with 7 as the first digit and Molecular weight as sequential digits. Examples include ammonia, which, with Molecular weight equal to 17 have the designation R-717, water is designated as R-718 and R-744 carbon dioxide (CO2). 1.3.2 What determines the medium's versatility as a working medium? There are many factors that come in, partly due to deviations from the idealism of the basic process, and partly of more practical nature. To simplify the overview, the elements are grouped according to the following pattern: 1) Features that determine the theoretical process in terms of goodness energy and volume needs. That is to say: - power factor [-] - volumetric thermal performance [kj/m3] 2) Properties of importance for the practical implementation of the process, such as: - resulting system pressure [bar] - possible operating range of one-step compression - Volume and energy in the compressor - heat exchanger effectiveness - Dimensions of pipes, valves, etc. - compared to oil - relation to water - conditions for construction materials 3) Properties of the significance of the leak to the environment - toxicity - flammability - panic creative ability - warning properties (odor, color, etc.) - dilution properties - ozone-depleting ability ("ozone depletion potential, ODP) - contribution to global warming ("global warming potential, GWP) - contribution to environmental damage at the soil surface (smog, acid rain, etc.) - Other possible environmental disturbances 4) Pricing and Availability
1.3.3 Actual working fluid 1.3.3.1 General Until 1990,heat pumps,mainly used R-12(CFC-12;CF2Cl2)and R-22(HCFC-22;CHF2Cl)as a medium, with maximum temperature of heat supply,respectively,ca.83C and 61C with standard construction equipment(25 bar pressure rating).Azeotropic R-500(CFC-500)and R-502(CFC-502)has also been used to a certain extent.In high-temperature heat(80-120C)for industrial purposes,R-114(CFC-114; CF2CICF2Cl)has been the dominant medium of work.A common feature of the mentioned fluids is that they are neither flammable/explosive or toxic and moreover,not aggressive towards copper or copper alloys. 1st of January 1989 came the so-called Montreal Protocol in force,with demands for substantial reduction of the consumption of certain ozone-depleting substances including CFC substances R-12 R-114,R-115. Reduction Plans also included azeotropic fluids containing the regulated CFCs fluid,including R-500 and R- 502.In Norway,from July 1,1991 is prohibited to manufacture,import,make,install and sell refrigeration and heat pumps with CFCs as heat transfer medium.From 1995 it was fully implemented import bans,but it will still be a time permitted to use CFCs used for replenishment of existing facilities.From 1992,HCFC- fluid including R-22 incorporated into the Montreal Protocol's reduction plans.Although full phase-out is set to approx.2020,many European countries prohibit new installations of R-22 from approx.2000. It's over the years carried out extensive research to identify alter-native working fluids to CFCs and HCFCs fluid.Table 1.2 provides an overview of today's most current synthetic and natural working fluids. Working fluid for high temperature industrial applications are described in(5,11). Table 1.2 Recent alternatives to CFC-12(R-12)and HCFC-22(R-22) Fluid Formula Boiling Critical Critical Saturation Flammable Toxic Ozone Greenhouse point C temperature, pressure, temperature, depletion warming (1 bar) C bar C,25 bar potential potential CFC-12 CCL2F2 -298 118,8 41,1 84,2 No No 1,0 7300 HCFC- CHCIF2 -40,8 96,2 49,9 61,4 No No 0,055 1500 22 HFC- HFC-mix -26,1 101,1 40,6 77,6 No No 0 1300 134a R-404a HFC-mix -46,5 72,1 373 55 No No 0 3750 R-407c HFC-mix -43,6 86,1 46,2 60 No No 0 1610 R-410a HFC-mix -505 72,5 49,6 43 No No 0 1890 R-717 NH3 -33,3 133,0 114,2 58,2 No Yes 0 0 Propane CaHio -42,1 96,8 425 68,1 Yes No 0 0 C02 C02 -78,4 31,1 73,7 No No 0 1
1.3.3 Actual working fluid 1.3.3.1 General Until 1990, heat pumps, mainly used R-12 (CFC - 12; CF2Cl2 ) and R-22 (HCFC-22; CHF2Cl) as a medium, with maximum temperature of heat supply, respectively, ca. 83 ° C and 61 ° C with standard construction equipment (25 bar pressure rating). Azeotropic R-500 (CFC-500) and R-502 (CFC-502) has also been used to a certain extent. In high-temperature heat (80-120 ° C) for industrial purposes, R-114 (CFC-114; CF2ClCF2Cl) has been the dominant medium of work. A common feature of the mentioned fluids is that they are neither flammable / explosive or toxic and moreover, not aggressive towards copper or copper alloys. 1 st of January 1989 came the so-called Montreal Protocol in force, with demands for substantial reduction of the consumption of certain ozone-depleting substances including CFC substances R-12 R-114, R-115. Reduction Plans also included azeotropic fluids containing the regulated CFCs fluid, including R-500 and R- 502. In Norway, from July 1, 1991 is prohibited to manufacture, import, make, install and sell refrigeration and heat pumps with CFCs as heat transfer medium. From 1995 it was fully implemented import bans, but it will still be a time permitted to use CFCs used for replenishment of existing facilities. From 1992, HCFCfluid including R-22 incorporated into the Montreal Protocol's reduction plans. Although full phase-out is set to approx. 2020, many European countries prohibit new installations of R-22 from approx. 2000. It's over the years carried out extensive research to identify alter-native working fluids to CFCs and HCFCs fluid. Table 1.2 provides an overview of today's most current synthetic and natural working fluids. Working fluid for high temperature industrial applications are described in (5, 11). Table 1.2 Recent alternatives to CFC-12 (R-12) and HCFC-22 (R-22) Fluid Formula Boiling point C (1 bar) Critical temperature, C Critical pressure, bar Saturation temperature, C, 25 bar Flammable Toxic Ozone depletion potential Greenhouse warming potential CFC-12 CCL2F2 -29,8 118,8 41,1 84,2 No No 1,0 7300 HCFC- 22 CHCIF2 -40,8 96,2 49,9 61,4 No No 0,055 1500 HFC- 134a HFC-mix -26,1 101,1 40,6 77,6 No No 0 1300 R-404a HFC-mix -46,5 72,1 37,3 55 No No 0 3750 R-407c HFC-mix -43,6 86,1 46,2 60 No No 0 1610 R-410a HFC-mix -50,5 72,5 49,6 43 No No 0 1890 R-717 NH3 -33,3 133,0 114,2 58,2 No Yes 0 0 Propane C4H10 -42,1 96,8 42,5 68,1 Yes No 0 0 CO2 C02 -78,4 31,1 73,7 - No No 0 1
1.3.3.2 Presentation of the most appropriate working fluid a)R-22(HCFC 22) R-22 has been almost supreme as working fluid in heat pumps with moderate temperature requirements (<61C).This is partly because the fluid has a high volumetric heat output,so that the necessary compressor volume is in the range of 35-40%less than the use of R-12 and R-500.A significant drawback of R-22 is that the gas temperature from the compressor is relatively high compared with other halocarbons.In some systems that have worked with a relatively high temperature lift,this has led to the decomposition of the oil with subsequent acid formation,flat copper ring and compressor failure.This has to some extent,given the heat a bad reputation. Although R-22 is regulated by the Montreal Protocol,the medium is still in use in a variety of applications, including small reversible air conditioning units for combined cooling and heating(so-called comfort heat pumps)and larger number of climate coolers. b)R 134a(HFC 134a HFC-134a is a chlorine-free medium without ozone-depleting effect.The medium was early identified as a promising substitute medium for R-12 in refrigeration and heat pumps,since the medium is non-toxic, non flammable and also closest to the R-12 with respect to important thermodynamic properties.A drawback of R-134a is the medium's relatively high GWP(Global worming potential)value.Increased focus on the harmful effects of the greenhouse effect has led to R-134a and other HFCs now been incorporated into the international environmental agreements(Kyoto Protocol). R-134a is currently available in desired quantities,but the price is relatively high because of the complicated manufacturing process.It is designed compressors,heat exchangers,valves,etc.especially for R-134a,and the medium is well suited for turbo compressors(high performance)because of high molecular weight(102.03).R-134a has approx.2-3%lower volumetric heat performance than R-12 at 0 C evaporation temperature so compressor volume must be increased accordingly to achieve the same performance.Impact factor for a heat pump system with R-134a is approximately the same as using R-12. Because of the medium sized throttling recommended however to use the remote during cooling,such as water-cooled in subcooling heat exchangers. R-134a has minimal solubility in mineral oil,and it must be used only ester based lubricating agents(fully synthetic).It should be noticed that moisture in the plant in combination with high temperatures will quickly lead to acid formation and subsequent operational problems.It is therefore very important to keep the humidity level in the plant at a minimum through proper handling of ester oil(hygroscopic),and best practices for installation and vacuum ring of the plant. Heat pump system with R-12 and R-500 can be converted to R-134a if the system is in good technical condition.To avoid future operational problems as a result of mineral residue,high moisture levels, residual chlorine,etc.The facilities must be cleaned very thoroughly before adding R-134a(the default flush method has been developed)
1.3.3.2 Presentation of the most appropriate working fluid a) R-22 (HCFC 22) R-22 has been almost supreme as working fluid in heat pumps with moderate temperature requirements (<61 ° C). This is partly because the fluid has a high volumetric heat output, so that the necessary compressor volume is in the range of 35-40% less than the use of R-12 and R-500. A significant drawback of R-22 is that the gas temperature from the compressor is relatively high compared with other halocarbons. In some systems that have worked with a relatively high temperature lift, this has led to the decomposition of the oil with subsequent acid formation, flat copper ring and compressor failure. This has to some extent, given the heat a bad reputation. Although R-22 is regulated by the Montreal Protocol, the medium is still in use in a variety of applications, including small reversible air conditioning units for combined cooling and heating (so-called comfort heat pumps) and larger number of climate coolers. b) R 134a (HFC 134a ) HFC-134a is a chlorine-free medium without ozone-depleting effect. The medium was early identified as a promising substitute medium for R-12 in refrigeration and heat pumps, since the medium is non-toxic, non flammable and also closest to the R-12 with respect to important thermodynamic properties. A drawback of R-134a is the medium's relatively high GWP (Global worming potential) value. Increased focus on the harmful effects of the greenhouse effect has led to R-134a and other HFCs now been incorporated into the international environmental agreements (Kyoto Protocol). R-134a is currently available in desired quantities, but the price is relatively high because of the complicated manufacturing process. It is designed compressors, heat exchangers, valves, etc. especially for R-134a, and the medium is well suited for turbo compressors (high performance) because of high molecular weight (102.03). R-134a has approx. 2-3% lower volumetric heat performance than R-12 at 0 ° C evaporation temperature so compressor volume must be increased accordingly to achieve the same performance. Impact factor for a heat pump system with R-134a is approximately the same as using R-12. Because of the medium sized throttling recommended however to use the remote during cooling, such as water-cooled in subcooling heat exchangers. R-134a has minimal solubility in mineral oil, and it must be used only ester based lubricating agents (fully synthetic). It should be noticed that moisture in the plant in combination with high temperatures will quickly lead to acid formation and subsequent operational problems. It is therefore very important to keep the humidity level in the plant at a minimum through proper handling of ester oil (hygroscopic), and best practices for installation and vacuum ring of the plant. Heat pump system with R-12 and R-500 can be converted to R-134a if the system is in good technical condition. To avoid future operational problems as a result of mineral residue, high moisture levels, residual chlorine, etc. The facilities must be cleaned very thoroughly before adding R-134a (the default flush method has been developed)
c)HFC-mixtures It has in recent years been developing a series of synthetic mixtures of HFC R-22.The fluid has no ozone- depleting effect,and the basic components are HFC-32(flammable),HFC-143a(flammable),HFC-125 and HFC-134a.All blends contain a flammable component,but the composition is always the case that the mixture is not flammable.The most relevant fluid to R-404A,R-407C and R-410a. R-404a is a three-component mixture(HFK-125/143a/134a,44%/52%/4%)with low temperature drift (0.1C),which was originally designed to replace R-502 in the freezer-and cooling systems.The medium used also in small heat pump systems.Volumetric thermal performance is that of R-502,while energy consumption is slightly in excess.R-404a can be used in both new projects and by conversions. R-407c is a three-component mixture (HFK-125/32/134a,25%/23%/52%)developed for air conditioning,condensing temperature is approx.60C at 26 bar.The fluid provides almost the same volume compressor needs and energy efficiency through the use of R-22.R-407C has a very high temperature drift through evaporation and condensation (about 7C),and this means that the medium is primarily suited for new installations where one can design the heat exchangers for countercurrent heat exchange. R-410A is a blend two-component(HFK-125/32,50%/50%)with minimal temperature drift(100 kW)ice water coolers,etc. Ammonia has the disadvantage that when moisture is present attack copper and copper alloys,ammonia plant must be built without any hints of such materials.This has long ruled out the use of ammonia in the (semi)hermetic compressors windings when consumed.Some manufacturers have developed semi- hermetic compressors for ammonia,where the medium is separated from the motor windings,as well as hermetic compressors with aluminum windings. The main complaint against ammonia used as the working fluid in heat pump systems is that the medium is toxic,has a sharp pungent odor(panic-creating)and also is flammable/explosive in certain proportions with air. The danger of poisoning with ammonia plants are very small,as the medium by its distinctive odor is easily recognized even at a concentration of about 10 ppm(parts per million).Lethal concentration at 30- 60 min
c) HFC-mixtures It has in recent years been developing a series of synthetic mixtures of HFC R-22. The fluid has no ozonedepleting effect, and the basic components are HFC-32 (flammable), HFC-143a (flammable), HFC-125 and HFC-134a. All blends contain a flammable component, but the composition is always the case that the mixture is not flammable. The most relevant fluid to R-404A, R-407C and R-410a. R-404a is a three-component mixture (HFK-125/143a/134a, 44% / 52% / 4%) with low temperature drift (0.1 ° C), which was originally designed to replace R-502 in the freezer - and cooling systems. The medium used also in small heat pump systems. Volumetric thermal performance is that of R-502, while energy consumption is slightly in excess. R-404a can be used in both new projects and by conversions. R-407c is a three-component mixture (HFK-125/32/134a, 25% / 23% / 52%) developed for air conditioning, condensing temperature is approx. 60 ° C at 26 bar. The fluid provides almost the same volume compressor needs and energy efficiency through the use of R-22. R-407C has a very high temperature drift through evaporation and condensation (about 7 ° C), and this means that the medium is primarily suited for new installations where one can design the heat exchangers for countercurrent heat exchange. R-410A is a blend two-component (HFK-125/32, 50% / 50%) with minimal temperature drift ( 100 kW) ice water coolers, etc. Ammonia has the disadvantage that when moisture is present attack copper and copper alloys, ammonia plant must be built without any hints of such materials. This has long ruled out the use of ammonia in the (semi) hermetic compressors windings when consumed. Some manufacturers have developed semihermetic compressors for ammonia, where the medium is separated from the motor windings, as well as hermetic compressors with aluminum windings. The main complaint against ammonia used as the working fluid in heat pump systems is that the medium is toxic, has a sharp pungent odor (panic-creating) and also is flammable / explosive in certain proportions with air. The danger of poisoning with ammonia plants are very small, as the medium by its distinctive odor is easily recognized even at a concentration of about 10 ppm (parts per million). Lethal concentration at 30- 60 min
exposure,however,150-200 times higher.The leakages will be also medium that is lighter than air rise up, quickly diluted in the air and effectively extracted by using the ventilation system.These conditions make the ammonia into a safe medium in use,when only basic safety requirements are met in relation to the engine and any other premises where the equipment is installed.Cold Norwegian norm would then also strict requirements for the design of the engine room ventilation and safety and protection of this type of plant /12,5/. The ammonia pungent smell and panic-creating effect of large uncontrolled emissions can pose a significant safety risk.However,an appropriate design of the plant,machinery,ventilation systems and safety equipment mean that the problem can be handled in a fully satisfactory manner. Ammonia is flammable and explosive mixed with air in the volume ratio of 15-28%.It should,however, very much to get built up such a concentration,and only under conditions where people do not want to stay in the premises.Ignition temperature is also high(630C)and rather low explosion pressure(3.7 bar).In many European countries refrigeration standards required when not explosion-proof electrical equipment in the engine room through the use of ammonia. Earlier it was only used mineral oil(PAO)with ammonia(no miscibility).In order to use the fluid in the construction of dry evaporators have been developed polyglycoloil (PAG),which is miscible with ammonia. e)Hydrocarbons Hydrocarbons has for years been used as working fluids in refrigeration in the petrochemical industry. Because of the favorable thermodynamic and environmental properties of hydrocarbons has gained new relevance in other applications,including heat pumps.Hydrocarbons are highly flammable and explosive, which means that they are primarily appropriate for use in small plants with little fluid filling. Of the hydrocarbons,it is primarily propane(R-290)and partly also propylene(R 1270),which are of interest in heat pump systems.It is also designed two-component mixtures with propane/iso-butane (replaces R-12)and propane/ethylene(replaces R-22)in terms of both conversions and new constructions,both propane and propylene has excellent thermodynamic properties,and is relatively Hp R-22 in terms of volumetric thermal performance and energy efficiency.However,they have the clear advantage that the discharge temperature is significantly lower than when using R-22,and compatibility with mineral oil and alkylbenzene is also very good. Propane and propylene has a lower explosive limit(LEL)and the ignition temperature of respectively 2.1/ 2.0%by volume and 470C/491C.The fluid is also heavier than air,and by a leak from the plant will explosive concentrations could easily built up.There are stringent requirements for the design of the facilities with respect to the joints(preferably vertically associate cost),electrical equipment,external safety and ventilation/5/propane and propylene can otherwise be considered non-toxic,as they do not give fatal or serious injury by concentrations below lower explosion limit
exposure, however, 150-200 times higher. The leakages will be also medium that is lighter than air rise up, quickly diluted in the air and effectively extracted by using the ventilation system. These conditions make the ammonia into a safe medium in use, when only basic safety requirements are met in relation to the engine and any other premises where the equipment is installed. Cold Norwegian norm would then also strict requirements for the design of the engine room ventilation and safety and protection of this type of plant / 12, 5 /. The ammonia pungent smell and panic-creating effect of large uncontrolled emissions can pose a significant safety risk. However, an appropriate design of the plant, machinery, ventilation systems and safety equipment mean that the problem can be handled in a fully satisfactory manner. Ammonia is flammable and explosive mixed with air in the volume ratio of 15-28%. It should, however, very much to get built up such a concentration, and only under conditions where people do not want to stay in the premises. Ignition temperature is also high (630 ° C) and rather low explosion pressure (3.7 bar). In many European countries refrigeration standards required when not explosion-proof electrical equipment in the engine room through the use of ammonia. Earlier it was only used mineral oil(PAO) with ammonia (no miscibility). In order to use the fluid in the construction of dry evaporators have been developed polyglycoloil (PAG), which is miscible with ammonia. e) Hydrocarbons Hydrocarbons has for years been used as working fluids in refrigeration in the petrochemical industry. Because of the favorable thermodynamic and environmental properties of hydrocarbons has gained new relevance in other applications, including heat pumps. Hydrocarbons are highly flammable and explosive, which means that they are primarily appropriate for use in small plants with little fluid filling. Of the hydrocarbons, it is primarily propane (R-290) and partly also propylene (R 1270), which are of interest in heat pump systems. It is also designed two-component mixtures with propane / iso-butane (replaces R-12) and propane / ethylene (replaces R-22) in terms of both conversions and new constructions, both propane and propylene has excellent thermodynamic properties, and is relatively Hp R-22 in terms of volumetric thermal performance and energy efficiency. However, they have the clear advantage that the discharge temperature is significantly lower than when using R-22, and compatibility with mineral oil and alkylbenzene is also very good. Propane and propylene has a lower explosive limit (LEL) and the ignition temperature of respectively 2.1 / 2.0% by volume and 470 ° C/491 ° C. The fluid is also heavier than air, and by a leak from the plant will explosive concentrations could easily built up. There are stringent requirements for the design of the facilities with respect to the joints (preferably vertically associate cost), electrical equipment, external safety and ventilation /5/ propane and propylene can otherwise be considered non-toxic, as they do not give fatal or serious injury by concentrations below lower explosion limit
On systems with the fluid filling less than 1 kg placed in the new European cold norm(EN 378)no additional requirements for safety beyond the use of approved units(electrical connections,etc.)gas detector and the continuous extraction from the room where the unit is located. In larger facilities will safety measures be more comprehensive and include,for example,installation of generators at the gas-tight containers,or the breakdown of the engine room with a gas-tight wall. Electrical equipment can cause sparks together in that part of the engine room that will not be exposed to working fluid.It could alternatively be used explosion proof(Ex-proof)devices in the zone closest to the heat pump units.It must also be installed both active ventilation in the form of fans and passive ventilation in the form of drainage channels in the floor in case of power failure.Gas detectors placed along the floor and that is connected to a separate alarm system is also required.It may also be necessary to build one wall in the engine room as a relief wall to the outdoors,so as to avoid pressure build-up in case of explosion. f)Carbon dioxide(CO,) Carbon dioxide(CO2)is seen as a very promising working fluid for refrigeration and heat pumps because it is non-toxic,non flammable and does not contribute to the depletion of the ozone or global warming (GWP =0.01%of R-12).CO2 can also be used with conventional lubricants and does not attack common engineering materials. CO2 is a high-pressure medium with critical temperature and pressure,respectively,31.1C and 73.8 bar. The high pressure provides high energy density and high volumetric heat performance,and involve, among other things,that the necessary compressor volume is typically 5-6 times lower than for R-12.The dimensions of pipes,valves,etc.,are also very moderate.Because of the compactness of the plants and low internal volume,not the high pressure(100-150 bar)result in any extra security compared with conventional fluid. Because of the low critical point,using a cO,heat pump uses a so-called transcritical cycle,with evaporation at constant temperature below the critical point and heat dissipation by moving temperature (no condensation,but condensation of the gas)above the critical point.The condenser must be replaced with a gas cooler.The low critical temperature means that the theoretical power factor of a heat pump system with COz is 30-50%lower than with conventional working fluids.In particular the high expansion losses that contribute to this.In practical systems,however,a number of factors,including low pressure ratio(high compression efficiency),low pressure drop(C/bar)as well as good heat transfer properties, contribute at least as high power factor for CO2 systems as for conventional systems. CO2 is particularly suitable where the heat record with almost constant temperature and large temperature glide in the heat emission ago.Examples include hot water heat pumps,heat pumps in district heating systems,hydronic heating systems with large temperature drift and industrial systems for heating of process water.CO2 systems will not be commercially available until 2000
On systems with the fluid filling less than 1 kg placed in the new European cold norm (EN 378) no additional requirements for safety beyond the use of approved units (electrical connections, etc.) gas detector and the continuous extraction from the room where the unit is located. In larger facilities will safety measures be more comprehensive and include, for example, installation of generators at the gas-tight containers, or the breakdown of the engine room with a gas-tight wall. Electrical equipment can cause sparks together in that part of the engine room that will not be exposed to working fluid. It could alternatively be used explosion proof (Ex-proof) devices in the zone closest to the heat pump units. It must also be installed both active ventilation in the form of fans and passive ventilation in the form of drainage channels in the floor in case of power failure. Gas detectors placed along the floor and that is connected to a separate alarm system is also required. It may also be necessary to build one wall in the engine room as a relief wall to the outdoors, so as to avoid pressure build-up in case of explosion. f) Carbon dioxide (CO2 ) Carbon dioxide (CO2 ) is seen as a very promising working fluid for refrigeration and heat pumps because it is non-toxic, non flammable and does not contribute to the depletion of the ozone or global warming (GWP = 0.01% of R-12). CO2 can also be used with conventional lubricants and does not attack common engineering materials. CO2 is a high-pressure medium with critical temperature and pressure, respectively, 31.1 ° C and 73.8 bar. The high pressure provides high energy density and high volumetric heat performance, and involve, among other things, that the necessary compressor volume is typically 5-6 times lower than for R-12. The dimensions of pipes, valves, etc., are also very moderate. Because of the compactness of the plants and low internal volume, not the high pressure (100-150 bar) result in any extra security compared with conventional fluid. Because of the low critical point, using a CO2 heat pump uses a so-called transcritical cycle, with evaporation at constant temperature below the critical point and heat dissipation by moving temperature (no condensation, but condensation of the gas) above the critical point. The condenser must be replaced with a gas cooler. The low critical temperature means that the theoretical power factor of a heat pump system with CO2 is 30-50% lower than with conventional working fluids. In particular the high expansion losses that contribute to this. In practical systems, however, a number of factors, including low pressure ratio (high compression efficiency), low pressure drop (° C / bar) as well as good heat transfer properties, contribute at least as high power factor for CO2 systems as for conventional systems. CO2 is particularly suitable where the heat record with almost constant temperature and large temperature glide in the heat emission ago. Examples include hot water heat pumps, heat pumps in district heating systems, hydronic heating systems with large temperature drift and industrial systems for heating of process water. CO2 systems will not be commercially available until 2000
1.3.4 Criteria for choosing a working fluid 1.3.4.1 Vapor pressure The choice of working fluid to the saturation temperature and corresponding saturation pressure at condensation and evaporation lie in the right area in relation to the application.It is important that the evaporation pressure is not lower than atmospheric pressure,so that there is a risk of intake of air(and therefore moisture)in the plant by,for example,packing boxes.This can cause interference in the process,which among other things can take that icing in the valves,with the risk of clogging and depletion of oil and working fluid (acid formation).Any sacked in air will also be collected in the condenser,resulting in higher total pressure for the process. Condensation pressure is limited by the fixed component pressure rating.Heat pumps use extensively the standard refrigeration equipment,which is largely designed for maximum pressure of around 25 bar(PN 25).Figure 1.27 shows vapor pressure curves for some working fluids,i.e.the curves for the saturation pressure [bar]as a function of condensing temperature [C]. 40 10 --R-744 35 NH =R40 R22 8- ==R-717 30 0-R-407C 7,38 Mpa -R-22-------=- 25 R-290 [edw] 6 --R-134电 —R-12 NHs 20 CO. 月12 /R22 日134a R410A 15 R290 2,5 Mpa R134a 10 2 R407 R12 0 0aata欧 40 50 60 70 80 40 -20 0 20 0 60 80 100 Condensing temperature [C] Saturation temperature,t[C][C] Figure 1.27 Saturation Pressure as a function of temperature for some working fluids A limit of 25 bar previously limited the use of ammonia in the heat with temperature requirements higher than approx.60C.40 bar piston compressor,however,was introduced on the market in 1992,and has increased the temperature limit to approx.77C.This has led to a renaissance for ammonia heat pumps in Norway,with many installations in commercial buildings and district heating systems. Operation pressure in CO-systems is typical 5 to 10 times higher than with use of HFC and ammonia and therefore normal refrigeration and heat pump systems are limited to approx 28C condensing temperature.Also it necessary with actions to handle high deadhead pressure during longer stops
1.3.4 Criteria for choosing a working fluid 1.3.4.1 Vapor pressure The choice of working fluid to the saturation temperature and corresponding saturation pressure at condensation and evaporation lie in the right area in relation to the application. It is important that the evaporation pressure is not lower than atmospheric pressure, so that there is a risk of intake of air (and therefore moisture) in the plant by, for example, packing boxes. This can cause interference in the process, which among other things can take that icing in the valves, with the risk of clogging and depletion of oil and working fluid (acid formation). Any sacked in air will also be collected in the condenser, resulting in higher total pressure for the process. Condensation pressure is limited by the fixed component pressure rating. Heat pumps use extensively the standard refrigeration equipment, which is largely designed for maximum pressure of around 25 bar (PN 25). Figure 1.27 shows vapor pressure curves for some working fluids, i.e. the curves for the saturation pressure [bar] as a function of condensing temperature [° C]. Figure 1.27 Saturation Pressure as a function of temperature for some working fluids A limit of 25 bar previously limited the use of ammonia in the heat with temperature requirements higher than approx. 60 ° C. 40 bar piston compressor, however, was introduced on the market in 1992, and has increased the temperature limit to approx. 77 ° C. This has led to a renaissance for ammonia heat pumps in Norway, with many installations in commercial buildings and district heating systems. Operation pressure in CO 2 -systems is typical 5 to 10 times higher than with use of HFC and ammonia and therefore normal refrigeration and heat pump systems are limited to approx 28°C condensing temperature. Also it necessary with actions to handle high deadhead pressure during longer stops
1.3.4.2 Pressure conditions Pressure relationship between the condenser and evaporator pressure is the next major fluid parameter. The reason is mainly that the compressor efficiency,with respect to energy and volume utilization (respectively,isentropic efficiency and delivery degree),is strongly connected to the pressure ratio.In Figure 1.28 the pressure ratio for the most appropriate working fluids plotted as a function of condensing temperature,evaporation temperature is assumed constant 0C. 10 9 NH 8 R134a 6 Propar R12/R22 3 2 1 0 40 50 60 70 80 Condensing temperature [CI Figure 1.28 Pressure ratio as a function of condensing temperature R 717 has higher pressure ratio then R 12 but propane will be more suitable.For ammonia it will compensate more or less due to higher efficiency of compression.For lager systems the result due to the high pressure ratio will be less due to three reasons.First,it throttle losses relatively smaller for a heat pump than for a refrigeration system,and efficiency characteristics will be significantly flatter and the difference in pressure conditions generally(slightly)less.Larger plants which have a relatively high temperature requirements of heat supply(such as heat pumps in district heating systems),which is normal for the two-stage compression/throttling and cooling of the gas pressure in the pressure level. 1.3.4.3 Volumetric heating performance Fluid properties are of great importance to determine 'sucked in'gas volume to the compressor,and thereby the compressor size and construction costs.This volume is determined by the medium's volumetric heat performance,qvol [kj/m3],which is given
1.3.4.2 Pressure conditions Pressure relationship between the condenser and evaporator pressure is the next major fluid parameter. The reason is mainly that the compressor efficiency, with respect to energy and volume utilization (respectively, isentropic efficiency and delivery degree), is strongly connected to the pressure ratio. In Figure 1.28 the pressure ratio for the most appropriate working fluids plotted as a function of condensing temperature, evaporation temperature is assumed constant 0 ° C. Figure 1.28 Pressure ratio as a function of condensing temperature R 717 has higher pressure ratio then R 12 but propane will be more suitable. For ammonia it will compensate more or less due to higher efficiency of compression. For lager systems the result due to the high pressure ratio will be less due to three reasons. First, it throttle losses relatively smaller for a heat pump than for a refrigeration system, and efficiency characteristics will be significantly flatter and the difference in pressure conditions generally (slightly) less. Larger plants which have a relatively high temperature requirements of heat supply (such as heat pumps in district heating systems), which is normal for the two-stage compression / throttling and cooling of the gas pressure in the pressure level. 1.3.4.3 Volumetric heating performance Fluid properties are of great importance to determine ‘sucked in’ gas volume to the compressor, and thereby the compressor size and construction costs. This volume is determined by the medium's volumetric heat performance, qvol [kj/m3 ], which is given
by the ratio between cast heat output qk and gas specific volume in the inlet of compressor,vi(see also Section 1.2.2.4,"pressure /enthalpy chart"). [kJ/m] Volumetric heat output expresses thus prepared heat output rates sucked in unit volume sucked in gas to compressor.The most important fluid attribute here is evaporating pressure when different fluid are compared,one will see that the volumetric heat performance is very close to inversely proportional to absolute pressure evaporates.Use of a low pressure medium,which is beneficial in that the condenser is located in a safe distance from the critical pressure will therefore result in a need for large and costly compressors.Figure 1.29(left)shows the volumetric heat output of some relevant working fluids varies with the condensation temperature at evaporating temperature at 0C.COz is not included in the figure, but because of its high pressure typically 5-6 higher volumetric heat performance than ammonia and propane.Right picture-the pressure ratio for most appropriate working fluids is plotted as function of evaporation temperature. 30000 8000 -t-R744 ·NHg R-410 7000 R22 25000 --R717 R-22 propar 407C 6000 12 R-290 20000 -R-134 134a 5000 R12 C02 15000 4000 R410A R4070 3000 10000 R290 2000 R134 5000 1000 30 40 50 60 70 80 0 20 20 0 60 80100 T[c] condensing temperature [C] Figure 1.29 Volumetric heat output as a function of condensing temperature at constant evaporation temperature 0C for a selection of working fluids(left),the same for different evaporation temperatures (right) 1.3.4.4 Power factor Basically,all process fluid as effective,provided that they work in a thermodynamically ideal process. When there are differences in theoretical power factor(in cold-steam process),tied up with differences in relative losses and overheating losses as previously described in Section 1.2.2.2,"Relative losses and overheating losses".Figure 1.11 page 1-12 shows the theoretical power factor of the heat pump ("lossless"cold steam process)as a function of condensing temperature at constant evaporation temperature at 0C for the most appropriate working fluids.The path for Carnot power factor plotted for comparison
by the ratio between cast heat output qk and gas specific volume in the inlet of compressor, v1 (see also Section 1.2.2.4, "pressure / enthalpy chart"). Volumetric heat output expresses thus prepared heat output rates sucked in unit volume sucked in gas to compressor. The most important fluid attribute here is evaporating pressure when different fluid are compared, one will see that the volumetric heat performance is very close to inversely proportional to absolute pressure evaporates. Use of a low pressure medium, which is beneficial in that the condenser is located in a safe distance from the critical pressure will therefore result in a need for large and costly compressors. Figure 1.29 (left) shows the volumetric heat output of some relevant working fluids varies with the condensation temperature at evaporating temperature at 0 ° C. CO2 is not included in the figure, but because of its high pressure typically 5-6 higher volumetric heat performance than ammonia and propane. Right picture – the pressure ratio for most appropriate working fluids is plotted as function of evaporation temperature. Figure 1.29 Volumetric heat output as a function of condensing temperature at constant evaporation temperature 0 ° C for a selection of working fluids (left), the same for different evaporation temperatures (right) 1.3.4.4 Power factor Basically, all process fluid as effective, provided that they work in a thermodynamically ideal process. When there are differences in theoretical power factor (in cold-steam process), tied up with differences in relative losses and overheating losses as previously described in Section 1.2.2.2, "Relative losses and overheating losses". Figure 1.11 page 1-12 shows the theoretical power factor of the heat pump ("lossless" cold steam process) as a function of condensing temperature at constant evaporation temperature at 0 ° C for the most appropriate working fluids. The path for Carnot power factor plotted for comparison
