SIST EN 13136:2002
(Main)Refrigerating systems and heat pumps - Pressure relief devices and their associated piping - Methods for calculation
Refrigerating systems and heat pumps - Pressure relief devices and their associated piping - Methods for calculation
1.1 This European Standard describes the calculation of mass flow for sizing pressure relief devices for components of refrigerating systems. Note: The term "refrigerating system" used in this standard includes heat pumps. 1.2 This European Standard describes the calculation of discharge capacities for pressure relief valves and other pressure relief devices in refrigerating systems including the necessary data for sizing these when relieving to atmosphere or to components within the system at lower pressure.
Kälteanlagen und Wärmepumpen - Druckentlastungseinrichtungen und zugehörige Leitungen - Berechnungsverfahren
Anwendungsbereich
1.1 Diese Europäische Norm beschreibt die Berechnung der Massenströme zur Größenbestimmung von Druckent-
lastungseinrichtungen für Teile von Kälteanlagen.
ANMERKUNG: Der in dieser Norm verwendete Begriff "Kälteanlage" schließt Wärmepumpen mit ein.
1.2 Diese Europäische Norm beschreibt die Berechnung der Abblaseleistungen von Druckentlastungsventilen und
anderen Druckentlastungseinrichtungen in Kälteanlagen einschließlich der hierzu erforderlichen Daten zur Größenbe-
stimmung dieser Einrichtungen, wenn sie ins Freie oder in Bauteile der Kälteanlage mit niedrigerem Druck
abblasen.
1.3 Diese Europäische Norm legt die Anforderungen an die Konstruktion und die Auswahl von Druckentlastungsein-
richtungen zur Vermeidung von unzulässigen Drücken, hervorgerufen durch innere und äußere Wärmequellen, den
Druckerzeuger und die Wärmeausdehnung eingesperrter Flüssigkeit, fest.
1.4 Diese Europäische Norm beschreibt die Berechnung des Druckabfalls in den zu- und abführenden Leitungen
von Druckentlastungsventilen und anderen Druckentlastungseinrichtungen einschließlich der erforderlichen Daten.
Systemes de réfrigération et pompes a chaleur - Dispositifs de surpression et tuyauteries associées - Méthodes de calcul
1 Domaine d'application
1.1 La présente norme européenne décrit le mode de calcul du débit massique pour le dimensionnement des dispositifs de surpression pour les composants des systemes de réfrigération.
NOTE Le terme "systeme de réfrigération", utilisé dans la présente norme, inclut les pompes a chaleur.
1.2 La présente norme européenne décrit le mode de calcul des capacités de décharge des soupapes de sureté et des autres dispositifs de surpression des systemes de réfrigération, y compris les données nécessaires a leur dimensionnement lors de leur décharge dans l'atmosphere ou dans les composants du systeme a basse pression.
1.3 La présente norme européenne spécifie les exigences de conception et de sélection des dispositifs de surpression pour éviter une pression excessive due aux sources de chaleur internes et externes, aux autres sources de génération de pression (par exemple compresseurs, rampes a gaz, etc.) et a la dilatation du fluide piégé.
1.4 La présente norme européenne décrit le mode de calcul de la chute de pression dans la tuyauterie, en amont et en aval des soupapes de sureté et autres dispositifs de surpression, et inclut les données nécessaires.
Hladilni sistemi in toplotne črpalke - Tlačne varnostne naprave in njihove napeljave - Metode za izračun
General Information
Relations
Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Kälteanlagen und Wärmepumpen - Druckentlastungseinrichtungen und zugehörige Leitungen - BerechnungsverfahrenSystemes de réfrigération et pompes a chaleur - Dispositifs de surpression et tuyauteries associées - Méthodes de calculRefrigerating systems and heat pumps - Pressure relief devices and their associated piping - Methods for calculation27.200Hladilna tehnologijaRefrigerating technology27.080Heat pumpsICS:Ta slovenski standard je istoveten z:EN 13136:2001SIST EN 13136:2002en01-januar-2002SIST EN 13136:2002SLOVENSKI
STANDARD
SIST EN 13136:2002
EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 13136May 2001ICS 27.080; 27.200English versionRefrigerating systems and heat pumps - Pressure relief devicesand their associated piping - Methods for calculationSystèmes de réfrigération et pompes à chaleur - Dispositifsde surpression et tuyauteries associées - Méthodes decalculKälteanlagen und Wärmepumpen -Druckentlastungseinrichtungen und zugehörige Leitungen -BerechnungsverfahrenThis European Standard was approved by CEN on 7 March 2001.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the Management Centre or to any CEN member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and notified to the Management Centre has the same status as the officialversions.CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre: rue de Stassart, 36
B-1050 Brussels© 2001 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 13136:2001 ESIST EN 13136:2002
Page 2EN 13136:2001ContentsPageForeword .2Introduction .21 Scope .32 Normative references .33 Terms and definitions .34 Symbols .45 General .66 Pressure relief devices for protection of system components .67 Discharge capacities of pressure relief devices .7Annex A
(normative)
Values of functions, factors and properties ofrefrigerants .12Annex B
(informative)
Calculation of flow areas for non-evaporating andevaporating liquids .16Annex C
(informative)
Example of calculation for sizing pressure relief devices with the corresponding pipes .18Annex ZA (informative) Clauses of this European Standard addressing essential requirements or other provisions of EU Directives .22Bibliography . 23ForewordThis European Standard has been prepared by Technical Committee CEN/TC 182 "Refrigerating systems, safetyand environmental requirements", the secretariat of which is held by DIN.This European Standard shall be given the status of a national standard, either by publication of an identical text orby endorsement, at the latest by November 2001, and conflicting national standards shall be withdrawn at the latestby November 2001.This European Standard has been prepared under a mandate given to CEN by the European Commission and theEuropean Free Trade Association, and supports essential requirements of the EU Directive(s).For relationship with the EU Directive(s), see informative annex ZA which is an integral part of this standard.According to the CEN/CENELEC Internal Regulations, the national standards organizations of the followingcountries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark, Finland,France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden,Switzerland and the United Kingdom.IntroductionThis European Standard is based on ISO/DIS 4126-1:1995 modified to suit the specific requirements, and to includethe data, for refrigerating systems. It provides means of satisfying the pressure relief requirements of EN 378-1 andEN 378-2. SIST EN 13136:2002
Page 3EN 13136:20011
Scope1.1
This European Standard describes the calculation of mass flow for sizing pressure relief devices forcomponents of refrigerating systems.NOTE The term "refrigerating system" used in this standard includes heat pumps.1.2
This European Standard describes the calculation of discharge capacities for pressure relief valves and otherpressure relief devices in refrigerating systems including the necessary data for sizing these when relieving to atmos-phere or to components within the system at lower pressure.1.3
This European Standard specifies the requirements for design and selection of pressure relief devices toprevent excessive pressure due to internal and external heat sources, the sources of increasing pressure (e.g.compressor, heaters, etc.) and thermal expansion of trapped liquid.1.4
This European Standard describes the calculation of the pressure loss in the upstream and downstream lineof pressure relief valves and other pressure relief devices and includes the necessary data.2
Normative referencesThis European Standard incorporates, by dated or undated reference, provisions from other publications. Thesenormative references are cited at the appropriate places in the text and the publications are listed hereafter. Fordated references, subsequent amendments to or revisions of any of these publications apply to this EuropeanStandard only when incorporated in it by amendment or revision. For undated references, the latest edition of thepublication referred to applies (including amendments).EN 378-1Refrigerating systems and heat pumps – Safety and environmental requirements – Part 1: Basic requirements,definitions, classification and selection criteriaEN 378-2Refrigerating systems and heat pumps – Safety and environmental requirements – Part 2: Design, construction,testing, marking and documentationEN 764Pressure equipment – Terminology and symbols – Pressure, temperature, volumeprEN 12284:1996Refrigerating systems and heat pumps – Valves – Requirements, testing and markingISO/DIS 4126-1:1995Safety devices for protection against excessive pressure – Part 1: Safety valves prEN ISO 4126-2:1998Safety devices for protection against excessive pressure – Part 2: Bursting disc safety devices(ISO/DIS 4126-2:1998)3
Terms and definitionsFor the purposes of this standard the definitions given in EN 378-1, prEN 12284:1996, ISO/DIS 4126-1:1995,prEN ISO 4126-2:1998 and EN 764 apply.SIST EN 13136:2002
Page 4EN 13136:20014
SymbolsFor the purposes of this standard the following symbols are used:SymbolDesignationUnitAFlow area of the pressure relief valve
A
p×d24mm2AcCalculated flow areamm2ADNValve cross section related to DNmm2AinInside area of inlet tubemm2AliqCalculated flow area of liquid after expansionmm2AoutInside area of outlet tubemm2ARInside area of tubemm2AsurfExternal surface area of the vesselm2AvapCalculated flow area of vapour after expansionmm2CFunction of the isentropic exponents (table A.2) –DNNominal size (see EN ISO 6708 : 1995)–dActual flow diameter of the pressure relief valvemmdcCalculated flow diameter of the pressure relief valvemmdinInside diameter of inlet tubemmdoutInside diameter of outlet tubemmDROutside diameter of tube (table A.4)mmdRInside diameter of tubemmhvapHeat of vaporization calculated at 1,1 times the set pressure of the pressurerelief devicekJ/kgKbTheoretical capacity correction factor for sub-critical flow (table A.3)–KdCertified coefficient of discharge–KdrDerated coefficient of discharge (Kdr = Kd X 0,9)–KdrlDerated coefficient of discharge for liquid (Kdrl » Kdr X 0,8)–KvsValve constant (The rate of water flow for a differential pressure Dp of 1 barat the rated full opening)m3/hKvViscosity correction factor–kIsentropic exponent at the relieving inlet–LLength of tubemmLinLength of inlet tubemmLoutLength of outlet tubemmnRotational frequencymin
1(continued)SIST EN 13136:2002
Page 5EN 13136:2001SymbolDesignationUnitpatmAtmospheric pressure (1 bar)barpbBack pressure at outlet of pressure relief device, absolute barpcCritical absolute pressurebarpoActual relieving pressure po = 1,1 pset + patmbarpsMaximum allowable pressure of a component, gaugeabarpsetSet pressure, gauge (The predetermined pressure at which a pressure reliefvalve under operation starts to open)barp1Pressure at the inlet to downstream line absolute (in practice = pb)barp2Pressure at the outlet of downstream line absolutebarDpDifferential pressurebarDpinPressure loss in the upstream line of pressure relief valvebarDpoutPressure loss in the downstream line of pressure relief valvebarQhRate of heat production, internal heat sourcekWQliqFlow of liquid after expansionkg/hQmCalculated mass flow ratekg/hqmTheoretical discharge capacitykg/h × mm2q'mActual discharge capacity determined by testskg/h × mm2QmdMinimum required discharge capacity, of refrigerant, of the pressure reliefdevicekg/hQvapFlow of vapour after expansionkg/hRBending radius of tube (table A.4)mmReReynolds number–VTheoretical displacement m3voSpecific volume of vapour or liquidm3/kgw0Actual flow speed of liquid in the smallest section of pressure relief valvem/sw1Speed at the inlet into the downstream linem/sxVapour fraction of refrigerant at pC–aFlush connection angle (table A.4)°zPressure loss coefficient z
nn 1zn–zDNPressure loss coefficient related to DN–znPressure loss coefficient of a single component–hvVolumetric efficiency estimated at suction pressure and discharge pressureequivalent to the pressure relief device setting–(continued)SIST EN 13136:2002
Page 6EN 13136:2001SymbolDesignationUnitlFriction loss coefficient of tube (plain steel tube l » 0,02)–nKinematic viscositym2/s Density of vapour or liquid (
= 1/vo)kg/m3 10Vapour density at refrigerant saturation pressure/dew point at 10 °Ckg/m3jDensity of heat flow ratekW/m2a
The Pressure Equipment Directive 97/23/EC identifies the maximum allowable pressure by the symbol "PS".5
GeneralThe requirements for protection against excessive pressure in refrigerating systems and heat pumps are given inEN 378-2. Devices selected in accordance with this standard shall be designed and manufactured in accordancewith prEN 12284:1996, ISO/DIS 4126-1:1995 and prEN ISO 4126-2:1998.NOTE Calculations for flow areas for non-evaporating and evaporating liquids are given in annex B.Calculations for a pressure relief device with the corresponding pipes are given in annex C.6
Pressure relief devices for protection of system components6.1
GeneralCalculations shall be based on known or assumed processes which result in increases in pressure. All foreseeableprocesses shall be considered including those covered in 6.2, 6.3 and 6.4. For the purposes of this standard hvap iscalculated at 1,1 times the set pressure of the pressure relief device.6.2
Excessive pressure caused by heat sources6.2.1
External heat sourcesThe minimum required discharge capacity of the pressure relief device for each pressure vessel shall be determinedby the following: kg/h (1)Qmd
3600×j×AsurfhvapIn this standard j is assumed to be 10 kW/m2 but a higher figure shall be used if necessary.The sizing of the pressure relief device and calculating of pressure loss are carried out in accordance with clause 7.6.2.2
Internal heat sourcesThe minimum required discharge capacity of the pressure relief device for conditions which arise due to an internalsource of excessive heat shall be determined by the following:
kg/h (2)Qmd 3600×
QhhvapThe sizing of the pressure relief device and calculating of pressure loss are carried out in accordance with clause 7.SIST EN 13136:2002
Page 7EN 13136:20016.3
Excessive pressure caused by compressorsThe minimum required discharge capacity of the pressure relief device for excessive pressure caused bycompressors shall be determined by the following:
kg/h
(3)Qmd 60×V×n× 10×hvNOTE 1 In cases where discharge shut-off valves are not fitted, a high pressure relief device will suffice,providing there are no intermediate shut-off valves.NOTE 2 Non-positive displacement compressors need not have a pressure relief device providing it is notpossible to exceed the maximum allowable pressure.NOTE 3 Relieving to the low pressure side may cause compressor overheating.NOTE 4 The setting of a compressor pressure limiter will be above the maximum allowable pressure of thesystem and does therefore not serve as protection of the entire system.NOTE 5 prEN 12693:1996 covers compressors which can run against a closed discharge valve.prEN 12693:1996 should, therefore, be considered, especially the requirement covering conditions underwhich the allowable evaporating temperature exceeds the value of 10 °C by more than 5 K.The sizing of the pressure relief device and the calculation of the pressure loss shall be carried out in accordancewith clause 7.6.4
Liquid expansionThe effective area [A × Kdr] of the pressure relief device to protect against excessive pressure caused by theexpansion of trapped liquid shall be at least 0,02 mm2 per litre of trapped volume, except that the minimum diametershall not be less than 1 mm.NOTE The possibility of contamination by dirt should be considered.Where practicable the pressure relief device shall relieve to the low pressure side of the system and the pressurerelief device shall with maximum back pressure meet the following requirements:po £ 1,1 X pset + patm
bar
(4)7
Discharge capacities of pressure relief devices7.1
GeneralWhen the operational characteristics have been satisfactorily established, it is acceptable to use steam, air or othergas of known characteristics as the fluid for flow characteristics tests except for valves designed for liquid service(see annex B). When discharged quantities are being assessed the valve disc shall be held at the minimum lift asdetermined by the operating characteristics test, see also ISO/DIS 4126-1:1995.7.2
Determination of pressure relief valve performance7.2.1
Determination of coefficient of dischargeThe coefficient of discharge is calculated from:
–
(5)Kd
q’mqmSIST EN 13136:2002
Page 8EN 13136:2001The derated coefficient of discharge is calculated from:
–
(6)Kdr 0,9×Kd7.2.2
Critical and sub-critical flowThe flow of a gas or vapour through an orifice, such as the flow areas of a pressure relief valve, increases as theoutlet pressure is decreased until critical flow is achieved. Further decrease in outlet pressure will not result in anyfurther increase in flow.Critical flow occurs when
–
(7)
pbpo£
2k 1k/(k 1)and sub-critical flow occurs when
–
(8)
pbpo>
2k 1k/(k 1)in accordance with ISO/DIS 4126-1:1995, where the validity of Rankine's law is assumed. If the flow is critical Kb =1, and if the flow is sub-critical, the correction factor shall be calculated according to formula (10) in 7.2.4 oder takenfrom table A.3.7.2.3
Function of the isentropic exponent (C) The function (C) of the isentropic exponent is calculated from:
–
(9)C 3,948×
k×
2k 1[k 1]/(k 1)For this calculation the value of k shall be as measured at 25 °C. Values of k and calculated values of C for somerefrigerants are given in table A.1, and values of C as a function of k are given in table A.2.7.2.4
Correction factor for sub-critical flow The correction factor for sub-critical flow is calculated from:
–
(10)Kb
2kk 1×
pbpo2/k
pbpo(k 1)/kk×
2k 1(k 1)/(k 1)For this calculation the value of k shall be as measured at 25 °C. Values of Kb as a function of pb/po are given intable A.3 for various values of k.7.2.5
Discharge capacity of pressure relief valves7.2.5.1
GeneralFor the most common use of pressure relief valves in refrigerating systems the back pressure is lower thanapproximately 0,5 × relieving pressure (pb £ 0,5 po) and Kb = 1, which indicates that the flow through the pressurerelief valve is "critical flow".SIST EN 13136:2002
Page 9EN 13136:2001For valves where the lift is a function of back pressure, the manufacturer shall, on request, supply specificinformation.7.2.5.2
Calculation of the mass flowThe mass flow for critical and sub-critical flow is calculated from:
kg/h
(11)Qm 0,2883×C×A×Kdr×Kb×
povoThe flow area Ac is calculated from the minimum required discharge capacity of refrigerant Qmd according toequations (1) to (3) as follows:Ac
Qmd0,2883×C×Kdr×Kb×
povo 3,469×
QmdC×Kdr×Kb×
vopo mm2
(12)where for critical flow Kb = 1.For the specific volume vo the value pertaining to pressure po is to be inserted.Values of C as a function of k are given in table A.2. Values of Kb as a function of pb/po are given in table A.3 forvarious values of k.It is not recommended to use an extremely overs
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