Refrigerant

Refrigerant enthalpy transport (ie, thermal energy) of the material to be cooled to ambient. The difference from the refrigerant is that a refrigerant in a refrigeration cycle can do so against a temperature gradient, so that the ambient temperature may be even higher than the temperature of the cooled object, while a coolant is only capable, in a refrigeration cycle, the enthalpy along transport of the temperature gradient to a location of lower temperature.

According to DIN EN 378-1 paragraph 3.7.1, the refrigerant is defined as " fluid, which is used to transfer heat in a refrigeration system, and that at low temperature and low pressure absorbs heat and emits at a higher temperature and higher pressure, heat, usually changes of state of the fluid take place. "or 8960, Section 3.1 according to as" releases heat working medium, which takes in a refrigeration process at low temperature and low pressure heat and higher temperature and higher pressure. " definitions DIN refer to compression chillers. As a change of state in terms of the standard is a change of state is meant ( see refrigeration machine).

Refrigerants are used in closed or open refrigeration systems as working medium. While for refrigerants in the strict sense of heat is absorbed by evaporation at low pressure and low temperature, this takes place in a cryogen chemically by mixing or solution reaction. Therefore, the regeneration takes place in refrigerants by liquefaction ( in a conventional compressor with subsequent condenser), or in cold mixtures by separation ( " thermal compressor " in an absorption chiller ).

Ammonia, carbon dioxide and water, but also hydrocarbons and air are, in contrast referred to halogenated hydrocarbons as natural refrigerants, as these substances occur in nature. It ignores that in a natural way both microorganisms and plants as well as a result of volcanic activity not inconsiderable amounts are released to halogenated hydrocarbons. Natural refrigerants do not contribute to ozone depletion and have either no or very little direct influence on the greenhouse effect.

• 4.2.1 HCFC
• 4.2.2 HFC
• 4.2.3 CFC
• 4.2.4 HFC
• 4.2.5 PFCs

• 5.1 Designation of organic refrigerant
• 5.2 Designation of inorganic refrigerant

• 6.1 Designation of organic refrigerant 6.1.1 R -xx hydrocarbons with one carbon atom
• 6.1.2 R -1xx hydrocarbons with two carbon atoms
• 6.1.3 R 11xx hydrocarbons having 2 carbon atoms, and C double bond
• 6.1.4 R 2xx hydrocarbons with 3 carbon atoms
• 6.1.5 R 12xx hydrocarbons having 3 carbon atoms, and C double bond
• 6.1.6 R -3xx Fluorinated hydrocarbons having 4 or more carbon atoms
• 6.1.7 R -6xx chlorine and fluorine-free hydrocarbons having 4 or more carbon atoms

• 6.2.1 R- 7xx Inorganic Compounds

• 6.3.1 R -4xx Zeotropic mixtures of hydrocarbons
• 6.3.2 R- 5xx Azeotropic mixtures of hydrocarbons

Historical development

As the first "professional" refrigerant initially diethyl ether was used, then ammonia (R- 717). Ammonia is used for over 130 years in industrial refrigeration systems and is considered environmentally friendly, economical and energy efficient. Also a long tradition in refrigeration technology has the refrigerant carbon dioxide ( R -744 ).

However, a disadvantage of this refrigerant is the physiological hazard ( lung injury, in diethyl ether and anesthetic effect). However, ammonia has a characteristic odor and is already at a concentration of 3 mg / m³ in the air perceptible. The warning effect therefore occurs long before a harmful concentration a ( > 1,750 mg / m³). Diethyl ether is highly flammable and forms an explosive mixture with air.

In contrast, have brought in the 1930s to market synthetic refrigerants, which are also referred to as safety refrigerants, based on halocarbons the advantage that they have no direct toxicity or flammability. By varying the chemical composition of a wide range of properties could be developed. Common commercial names for these halocarbons are the terms Freon (DuPont ) or Freon (Hoechst ), followed by the abbreviations for the respective chemical compositions. For example, are the names of Freon 502 and Freon 502 for the same refrigerant is used for which today impartially the abbreviation R -502 (R for Refrigerant ).

The demonstrated in the 1980s risk of halogenated especially with chlorine and bromine (CFCs and halons ), however, is that they are responsible for the ozone decomposition and essentially increase the greenhouse effect. Their use in new equipment was therefore prohibited on the basis of CFC- Halon Prohibition Ordinance.

The chlorinated hydrocarbons ( CFCs, HCFCs ) were in the 1990s, replaced by a plurality of hydrofluorocarbons ( HFCs, HFC ). These halogenated only with fluorine hydrocarbons have no ozone depletion potential, but a significant part of global warming potential. Thus, the HFC R -404A contributes frequently used 3,900 times more to the greenhouse effect than carbon dioxide.

Non-halogenated flammable hydrocarbons such as butane ( R-600/R-600a ) or propane (R -290 ) have so far been used mainly in niche applications due to the combustibility. In refrigerators and freezers with typical refrigerant charge of 50 to 150 g almost exclusively non-halogenated hydrocarbons are used in Germany. Larger refrigeration systems have so far been filled only rarely because of the required explosion protection measures with these refrigerants.

Therefore, also amplifies the non-flammable and hardly environmentally hazardous carbon dioxide ( R -744 ) is used recently. It does not contribute to ozone depletion and has a multiply - lower global warming potential as a conventional refrigerant, such as fluorocarbons. As a working fluid in vehicle air conditioning systems, hot water pumps, vending machines and in the supermarket and transport cooling the refrigerant CO2 is already being used. Due to the compared to the hydrocarbon compounds high system pressures and the low critical temperature, a new development of the cooling components is required in many application areas, however, is already underway or completed. Due to the system heat pumps with R744 are, however, only makes sense to use when the temperature difference between flow and return is at least 50 ° C.

In refrigeration carbon dioxide has a long tradition. Already more than a hundred years ago it was used before it has been largely replaced by synthetic refrigerants. Thanks to its environmental impact, it is now used again reinforced. As a refrigerant, carbon dioxide was first proposed by Alexander Twinning in his British patent of 1850. The first CO2 - compression refrigeration machine in Europe in 1881 built by Carl von Linde, manufactured by MAN and commissioned in 1882 at the Friedrich Krupp AG in Essen in operation.

Following the ban on CFCs and HCFCs also used as a replacement refrigerant substances such as CFCs and HFCs are now coming under fire. Due to their climate-damaging effect they are still facing a ban discussion. Thus, PFCs and HFCs in 1997 were recorded as greenhouse gases in the Kyoto Protocol. 2006 adopted the F-Gas Regulation, the EU, the requirements regarding the use of PFCs and HFCs makes and aimed at reducing their emissions. The climate-neutral refrigerant are not affected by the regulations.

Properties

Refrigerant should ideally have the following properties:

• High specific enthalpy of vaporization
• High volumetric cooling capacity
• High thermal conductivity
• High critical temperature
• No temperature glide
• Low viscosity
• Not flammable or explosive
• No ozone depletion potential
• No greenhouse effect
• Non-poisonous
• Noticeable at the outlet by scent
• Noncorrosive
• Should be compatible with the lubricant

Security groups, L- groups, stowage areas

The refrigerant flammability and toxicity are accordingly classified ( EN 378-1 Annex E) in the security groups A1, A2, A3, B1, B2, B3. The letters stand for

The figures for

For easier handling, the security groups A1, B1, A2 ( 378-1 5.4.2 EN ) ... etc. are in the so-called L- groups L1, L2, L3 summarized:

Furthermore, can be with refrigeration plants on the type of installation three stowage areas A, B, C are different ( EN 378-1 Annex C):

Depending on the L group and the installation area requirements apply to the allowable refrigerant charge ( EN 378-1 Annex C).

Commonly used refrigerants

In general, a distinction is made between natural and synthetic coolants. Under natural refrigerants are substances that occur in nature, such as Hydrocarbons, carbon dioxide, ammonia, water and air. Characteristic, the composition of the elements oxygen, carbon, nitrogen and hydrogen. Synthetic refrigerants are produced artificially. These substances include chlorofluorocarbons (CFCs ), partially halogenated hydrochlorofluorocarbons ( HCFCs ) and hydrofluorocarbons and hydrochlorofluorocarbons fluorocarbons ( PFCs and HFCs)

Among the natural refrigerants

Ammonia (R- 717)

Ammonia is a classic climate-neutral refrigerant that is used primarily in large-scale systems such as cold stores, slaughterhouses, breweries, central refrigeration in chemistry and ice rinks to use. There are also compact cold water chillers, which have a relatively small amount of refrigerant to reduce the potential danger. However, could compact ammonia refrigeration systems replace only limited areas of application of hydrocarbon refrigerants.

Ammonia has a very high specific enthalpy of vaporization, the circulating refrigerant mass is therefore relatively small. It also offers the advantages of a very low flammability and does not contribute to the greenhouse effect or ozone depletion at ( half-life in the atmosphere about 14 days). One drawback is its toxicity; Damage are primarily caused by burns in the lungs and eyes, because ammonia forms a basic reaction solution with water: NH3 H2O → NH4 OH - The pungent odor is, however, already at very low concentrations (5 ppm) perceptible, far below the maximum workplace concentration ( MAK value, 50 ppm - new name Technical Rule 900 WEL ( Technical Rules for Hazardous Substances workplace exposure limit ) new values ​​20 (40) ppm 20 ppm within 8 hours working time or within 8 hours working time 4 times 15 minutes 40 ppm). Due to this excellent warning properties ammonia ( greater toxicity, lower flammability according to EN 378-1:2008-06 Appendix Table E.1) and thus the L- group L 2 b is allocated in spite of its physiological danger to the security group B2. Ammonia plants are usually carried out in the nominal pressure PN 25 ( EN 378-2, Section 5.1). The installation costs for ammonia refrigeration systems is greater because, in contrast to systems with hydrocarbons no -ferrous metals ( such as copper pipes, brass fittings ) can be used.

Carbon dioxide (R -744 )

Carbon dioxide has a very high volumetric cooling capacity, the circulating refrigerant volume is relatively small. Also, carbon dioxide has the advantage of not being flammable, and does not contribute to ozone depletion in. Not Fossil carbon dioxide is considered climatically harmless since it is involved in the biological cycle; however, the release of carbon dioxide from fossil fuels increases the concentration of carbon dioxide in the atmosphere and thus promotes the greenhouse effect. However, the greenhouse effect per unit mass of only about 1 /1000 as compared with the hydrofluorocarbons (R-134a, R -404A ) is usually used. Compared to carbon dioxide, ammonia is less toxic; however, it is heavier than air and may already be fatal by obstruction of breathing in concentrations of about 8%. While it tingles in higher concentrations in the nose, as it forms carbonic acid with water; However, a significant warning effect is not because it is odorless.

Carbon dioxide is one of the safety group A1 (lower toxicity, no flame spread ) and thus to the L- group L1. A disadvantage are the relatively high operating pressures dar. Usually a distinction is made under critical or sub-critical CO2 refrigeration systems and supercritical or transcritical systems. Subcritical carbon dioxide systems are therefore usually in nominal pressure PN 40 or PN 64 is executed ( EN 378-2, Section 5.1). When switching off the heating system and on the ambient temperature, however, occur much higher pressures, so that the refrigerant must be either transferred to a high-pressure container, or a backup cooling system is to be installed.

Components for these systems are now available and carbon dioxide is used in commercial plants. It is partially in the two-stage refrigeration systems for the primary circuit (the lowest evaporation temperature ) is used, wherein the secondary circuit ( higher evaporation temperature) ammonia is used as the refrigerant. A major advantage of carbon dioxide is that unlike ammonia from leaking the direct evaporators which are not contaminated products to be cooled. This is a decisive advantage for example for the cooling of food and pharmaceutical products. Two-stage refrigeration systems in which both pressure stages are operated with the refrigerant carbon dioxide with supercritical liquefaction, are now used on a technical scale. The experiments on the use of carbon dioxide in automobile air conditioners are due to relatively high costs declined, but could be addressed again increased as a result of the failure of conversion of R -134a to R- 1234yf.

Water

Water (R- 718) is just above 0 ° C can be used as a refrigerant due to its freezing point and is used because of the low pressures and thus high-volume facilities only in special cases. However, it is well suited due to its high specific heat capacity as a coolant.

Hydrocarbons

Properties exemplified by 1,1,1,2- tetrafluoroethane ( R-134a); the properties of other hydrocarbons may also differ considerably according to the chemical composition.

Hydrocarbons typically have specific heats of vaporization of the order of 200 kJ / kg. The flammability can be very different; such as R- 600 ( butane gas ) is very light, R- 13B1 ( bromotrifluoromethane ), however, non-flammable. Also, the ozone depletion potential and the greenhouse effect can be very different. Hydrocarbons are slightly to moderately toxic; they act anti grease and attack the lungs. Some Halogenated hydrocarbons are anesthetic and be partially used as an anesthetic (see CCl3H chloroform ). The smell is weak to strong and solvent-like.

The synthetic version of refrigerants

Halogenated hydrocarbons among the L groups L1 or L2, non-halogenated hydrocarbons the L groups L2 or L3. Hydrocarbon systems are usually carried out in PN 25 ( EN 378-2, Section 5.1).

Hydrocarbons are divided into halogenated hydrocarbons and non-halogenated hydrocarbons. The commonly used abbreviations ( EN 378-1, Section 3.7.9 ):

HCFCs

Partially halogenated chlorofluorocarbons hydrocarbons ( HCFCs ) used as refrigerants, propellants or solvents. HCFCs are synthetic substances that are chemically stable, non-flammable and odorless and tasteless. With them are hydrocarbons whose hydrogen atoms have been partially replaced by the halogens fluorine and chlorine. Compared to the CFC (eg R 12 with ODP = 1) have a lower ozone depletion potential (ODP = 0.02-0.06 ) and a lower direct global warming potential (GWP = 76-2270 ). In Europe, HCFCs are no longer allowed as a refrigerant in new plants. Representative: R 22, R 123, R 124, R 141 b, R 142b

HFC

Have Partially halogenated fluorocarbons ( HFCs) have ozone depletion potential (ODP = 0) and compared to the PFCs less direct global warming potential (GWP = 122-14310 ) and a shorter life span ( from 1.4 to 270 years). The use of HFCs is to be substantially reduced in accordance with the European F- Gas Regulation and the Kyoto Protocol. Representative: R 23, R 125, R 134 a, R 152 a, R 404 A, R 407 C, R 410 A, R 507 A

CFC

Chlorofluorocarbons (CFCs ) have been used in Europe since the 50s as refrigerants, aerosol propellants or detergent. CFCs are man-made substances that are stable, non-flammable and odorless and tasteless. With them are hydrocarbons whose hydrogen atoms have been completely replaced by the halogens fluorine and chlorine. They have a very high ozone depletion potential (ODP = 1 ) and a high direct global warming potential (GWP = 4680-10720 ). In Europe, CFCs are now banned. Representative: R 11, R 12, R 13, R 113

PFCs

Hydrofluorocarbons ( HFCs) have been used since 1995 in the wake of CFCs or HCFCs as refrigerants, propellant or solvent. PFCs are man-made substances that are stable, non-flammable and odorless and tasteless. For them there are hydrocarbons whose hydrogen atoms are partially ( HFC ) or completely ( PFCs ) have been replaced by fluorine. The PFCs are recorded as part of the Kyoto Protocol. Consist first restrictions for applications with high consumption such as car air conditioning in the European Union. Further restrictions on the use of HFCs are expected. It Per- fluorocarbons ( PFCs ) and partially halogenated hydrocarbons are used.

PFCs

Have per- fluorocarbons ( PFCs ) have ozone depletion potential (ODP = 0), but due to the complete substitution of hydrogen atoms by fluorine a very high direct global warming potential (GWP = 5820-12010 ) and an extremely long life ( 3200-50000 years). The use of PFCs to be greatly reduced in accordance with the European F- Gas Regulation and the Kyoto Protocol. Representative: R 14, R 116, R 218

Impact on the ozone layer and the greenhouse effect

While ammonia, carbon dioxide and non-halogenated hydrocarbons are largely compatible with the environment, the halogenated hydrocarbons have in this respect, two disadvantages:

Firstly destroy the released from the chlorinated and brominated hydrocarbons at higher altitudes under UV irradiation chlorine and bromine radicals, ozone layer:

Total so

Chlorine is not used up in this reaction, but can always anew ozone molecules (O3 ) into normal oxygen molecules ( O2) to convert. This effect is more pronounced the lower the stability and the higher the chlorine content of the compound. The stronger the ozone layer is damaged, the more the short-wavelength UV components are passed through to the earth's surface. Numerically detected, the contribution of a refrigerant deplete the ozone layer by ozone depleting potential (ODP ); this is, by definition, for trichlorofluoromethane (R -11) equal to 1.0. Very high ozone depletion potential of up to 10 have brominated hydrocarbons, such as Bromotrifluoromethane (R- 13B1 ); ODP values ​​still authorized refrigerant lie except for chlorodifluoromethane (R -22) is close to zero. Refrigerant from the groups of PFCs and HFCs do not contribute to the depletion of the stratospheric ozone layer (ODP = 0).

On the other hand, halogenated hydrocarbons like CO2 to the greenhouse effect. This short-wave radiation when impinging on the surface is converted into long-wavelength radiation, this is then reflected by the Kohlenstoffdioxidschicht (or CFC or Halon layer). While CO2 and hydrocarbons from non-fossil sources but harmless since are involved in the biological cycle, this applies not for artificially generated and biologically degradable hardly Halogenated hydrocarbons. This effect is more pronounced the higher the stability of the connection. Numerically detected, the contribution of a refrigerant to the greenhouse effect by the global warming potential (GWP ) (according to DIN 8960 Table 2); this is by definition equal to 1.0 for CO2. Similarly, especially for Halogenated hydrocarbons of HGWP value ( Halocarbon Global Warming Potential) was introduced; In contrast to the GWP is the HGWP value for trichlorofluoromethane ( R-11 ) is equal to 1.0. A particularly high global warming potential of about 12,000 reach chlorotrifluoromethane (R -13) and fluoroform (R- 23); the global warming potential of today refrigerant is 2000 to 4000.

Because of the ozone-depleting effect, it was decided in 1987 with the participation of about 70 Nations of the phase-out the production and use of CFCs ( " Montreal Protocol " ) and incorporated into national regulations, for Germany by a decision of the Federal Cabinet on 30 May 1990 ( " Regulation prohibiting the use of certain ozone -depleting halogenated hydrocarbons "," CFC- halon prohibition Ordinance "; halon = halogenated hydrocarbon which contains fluorine or chlorine and bromine). The CFCs were subsequently replaced by other Halogenated hydrocarbons in which the chlorine atoms are partially, as in the HCFC or completely, as are exchanged in the HFCs, PFCs and HCs by fluorine or hydrogen atoms. It applies to the chemical properties of the individual compositions generally that the connection combustible by a high hydrogen content, a high proportion of chlorine is toxic and stable by a high fluorine content.

In order to continue to operate the old CFC plants under the same conditions as possible, HCFCs used as a substitute refrigerant, HCFC, HFC and HC should have the same physical properties as possible, which can be in some cases only be achieved with mixtures. These mixtures are according to their boiling behavior in zeotropic and azeotropic mixtures divided (DIN 8960, Section 3.6): Zeotropic ( = non-azeotropic ) mixtures have a boiling range ( = temperature glide, the difference between boiling and dew point temperature at constant pressure ), and segregate during boiling; Liquid and vapor have this different compositions. Azeotropic mixtures have a boiling point and not segregate on boiling, liquid and vapor thus have the same composition

Designation

The general designation of the refrigerant (DIN 8960, Section 6 ) is carried out by the letter R and below three ( Special cases: two or four) digits z, ie in the form of R- zzz, under certain circumstances, with attached letter b in the form of a short character R- zzzbb.

The "R" stands for Refrigerant, English for refrigerant.

The sequence of digits " zzz " allows to draw conclusions on the empirical formula. The third digit from the left gives the group assignment.

The letters " bb " refers to variations in the structural formula.

Designation of organic refrigerants

The designation of organic refrigerants carried out according to the scheme (DIN 8960, Section 6.1)

Therefore, one molecule of the refrigerant R-123, for example, consists of

The remaining two bonds are filled by two chlorine atoms. The empirical formula is therefore C2HF3Cl2, so it is Dichlorotrifluoroethane.

Special cases

If the number of carbon atoms C is 1, c - 1 = 0 The first number is not written in this case, and by the letter R followed by direct the second and the third digit. The refrigerant R-22 (actually R -022 ) for example, therefore, consists of

A remaining bond is filled by a chlorine atom. The empirical formula is therefore CHF2Cl, so it is chlorodifluoromethane.

If the compound contains bromine, naming the capital letter B is added, followed by the number of bromine atoms. The refrigerant R- 13B1, for example, consists of

A remaining bond is filled by a bromine atom (the number of available chlorine atoms may be the number of the bromine atoms is reduced ). The empirical formula is therefore CF3Br, so it is bromotrifluoromethane.

If it is an unsaturated organic compound which is in front of the first digit of another one inserted. Therefore, the refrigerant is R -1150, for example, consists of

The remaining one bond of the double bond. The empirical formula is therefore C2H4, so it is ethene.

If it is cyclic hydrocarbons, nor a C is inserted before the code. For example Cyclooctafluorbutan, molecular formula is C4F8, R- C318 respectively.

Since only the digits 0 to 9 are available, this scheme works only up to a maximum of 8 hydrocarbons with hydrogen atoms per molecule.

For butane, molecular formula C4H10, with its 10 hydrogen atoms, for example, so a different scheme is needed; it is therefore performed (DIN 8960, Section 6.3.1) under the group R -6xx.

Attached lowercase letters are used for the compounds with two or more carbon atoms to distinguish isomers (DIN 8960, Section 3.5 and 6.1). The higher the alphabet or the attached letter, the greater the asymmetry of the isomer. For compounds with two carbon atoms, the most symmetrical isomer gets thereby no appended letter; Thus, for example

For compounds with three carbon atoms ( propane derivatives) two lowercase letters are required to designate the isomer. The first letter then refers to the central carbon atom and is awarded in order of decreasing mass of the substituents (H, F and Cl):

The second letter also refers to the asymmetry of the isomer, that is awarded after increasing mass difference between the substituents on the terminal carbon atoms; the most symmetrical isomer receives the letter a ( in contrast to the notation in the ethane derivatives, in which the most symmetrical isomer receives no letters).

Zeotropic mixtures of hydrocarbons are R -4xx, azeotropic mixtures of hydrocarbons R- 5xx summarized (DIN 8960, Section 6.2). The last two digits indicate the qualitative composition; attached capitals are used here to characterize different mixing ratios.

Naming of inorganic refrigerant

The naming of inorganic compounds is carried out according to the scheme (DIN 8960, Section 6.3.2)

The first digit, 7, refers to the group of inorganic compounds; the following two digits indicate the molecular weight. The refrigerant R -717, NH3, for example, has a molecular weight of 17 g

Attached letters are used to distinguish similar molecular weight substances. For example, carbon dioxide R -744; for the new refrigerant nitrous oxide ( nitrous oxide ) is the designation R- 744A in the discussion.

Abbreviations

Designation of organic refrigerant

R xx hydrocarbons having 1 carbon atom

R -1xx hydrocarbons with two carbon atoms

R 11xx hydrocarbons having 2 carbon atoms, and C double bond

R 2xx hydrocarbons with 3 carbon atoms

In the last column the respective CAS number of the substance in question is also noted here.

R 12xx hydrocarbons having 3 carbon atoms, and C double bond

R -3xx Fluorinated hydrocarbons having 4 or more carbon atoms

R -6xx chlorine and fluorine-free hydrocarbons having 4 or more carbon atoms

Designation of inorganic refrigerant

R- 7xx Inorganic Compounds

Xx is the molecular weight

Designation of organic refrigerant mixtures

R -4xx Zeotropic mixtures of hydrocarbons

R- 5xx Azeotropic mixtures of hydrocarbons

Line marking

The identification of the lines in a refrigeration system is generally performed by one-sided sharpened, colored labels (DIN 2405 ). The tip here is the direction of flow, the base color the nature of the medium.

For flammable refrigerants, the tip is red.

For refrigerants are located behind the tip of one or more horizontal stripes.

The cross strip color indicates the state of the refrigerant.

The number of the transverse strips is the number of the respective stage of the refrigeration system. Starting point is the lowest temperature level: primary circuit = 1st stage, 2nd stage = secondary circuit, etc..

Allocation of the primary colors and horizontal stripes colors to the type and condition of the medium: