1、BRITISH STANDARD Thermal performance of building products and components - Specific criteria for the assessment of laboratories measuring heat transfer properties - Part 2: Measurements by guarded hot plate method The European Standard EN 19462: 1999 has the status of a British Standard ICS91.100.01
2、; 91.120.10 BS EN 1946-2:1999 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW STD-BSI BS EN LSqb-Z-ENGL 1999 6 Lb211bb9 0779524 935 m AmdNo. BS EN 1946-2:1999 Date Text affected National foreword This British Standard is the English language version of EN 194621999. The UK par
3、ticipation in its preparation was entrusted by Technical Committee RIEB, Thermal insulating materials, to Subcommittee RHE/9/2, Thermal properties of insdating makriak, which has the responsibility to: - aid enquirers to understand the text; - present to the responsible internationalEuropean committ
4、ee any enquiries on the inteqxetaton, or proposals for change, and keep the UK interests - monitor related international and European developments and promulgate iIlfOITlled; them in the UK. A list of organizations represented on this subcommittee can be obtained on request to its secretary. Cross-r
5、eferences The British Standards which implement international or European publications referred to in this document may be found in the BSI Standards Catalogue under the section entitled “Intemationai Standards Correspondence Index”, or by using the “Find” facility of the BSI Standards Electronic Ca
6、talogue. A British Standard does not purport to include ail the necessasy provisions of a contract. Users of British Stan- are responsible for their correct apphcation. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document compri
7、ses a front cover, an inside front cover, the EN title page, pages 2 ta 16, an inside back cover and a back cover. This British Standard, having been prepared under the direction of the Engineering Sector Committee, was published under the authority of the Standards Committee and comes into effect o
8、n 15 May 1999 O BSI 051-1999 ISBN O 580 32162 2 EUROPE24N STANDARD NOFmE EUROPENNE E;uROPm NORM EN 1W2 Januaty 1999 ICs 91.100.01; 91.120.10 Descriptors: building products, heat transfer, thermal resistance, testing, laboratory assessment, hot plate, error analysis, performance check English version
9、 Thermal performance of buildmg products and componen. - specific criteria for the assessment of laborabries measUrin$ heat transfer pmperties - Part 2: Measmrnents by guarded hot piate method Peromce thermique des produits et composants pour le btiment - Crit2res pmculim pour lvaluation des labomoi
10、res measlucuit les proprits de trammis ion thermique- Partie 2: Mesurages selon la mthode de la plaque chaude garde Wilrmetechnkzhes Verhalten von Bauprodukten und Bauteilen lchnische Kriterien zur Begutachtung von Laborcitoien bei der Durchfuhnuig der Messungen von Weiiberhgmgseigenschafkn - %il 2:
11、 Messung nach Verfahren mit dem Plaengert This European Standard was approved by CEN on 13 December 1998. CEN members are bound to comply with the CENKENELEC Internai Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration
12、. Upto-date iists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CEN member. This European Standard exists in three official versions (English, French, German). A version in any other language made by each subsequ
13、ent past covers the specific technical criteria applicable to each heat transfer property measurement method described in appropriate standards. “he following parts have been developed Part 1: Cmmn criteria Part 2: Measurements by guarded hot plate method Part 3 Meusurmts by kwatjow meter method Par
14、t 4: Measurements by hot box methods Part 5 Measurements by pipe test methods According t the CEN/CENELEC Internal Regulations, the national standards organizations of the foilowing countries are bound to implement this European standard: Austria, Belgium, Czech Republic, Denmark, Finland, France, G
15、emX Greece, Iceland, Ireland, It - thermai resistance; - temperature diference across the specimen; - heating and cooling unit temperature; - surrounding environment (temperature, relative humidity) at the edge of the specimen during the test. 4.3 Equipment description The following information shal
16、l be documented and shall be available for examination during the assessment - principle of opedon (see 1.6.1 of Is0 83021991); - type of apparatus (see 1.6.2.1, 1.6.2.2 and 1.6.4 - principal dhnensions of apparatus, in particular heating unit width, guard width and gap width; - simple diagrams illu
17、strating the design of the equipment with special attention to the gap design (see 2.1.1.6 of IS0 8302:1!3!31), the coolmg unit piping (see 2.1.2 of IS0 8302:1991) and edge insulation (see 2.1.3 of IS0 83021991); - position, connections and numbering of temperahre sensom (see 2.1.4.1 of Is0 83021991
18、); - electrical components/instruments, apparatus enclosure and main ancillary equipment; - details of data acquisition system and related computer programs for data anaiysis. of IS0 83021991); To avoid duplication, reference can be made to manuals supplied by the insbxment manufacturers or to relev
19、ant clauses of IS0 8302: 1991. 4.4 Equipment design and error analysis 4.4.1 General Wih reference to the performance specificaton given in 4.2, details shail be given of the design guidelines followed, and the emr analysis based on 2.2 of IS0 83021991, as summeed in 4.4.2 to 4.4.11. Some guidelines
20、 on error analysis are given in this subclause; more specific information on some errors is supplied in annex B, while error caiculations are supplied in annex C for some typical cases. Examples of equipment confoming to annex C are supplied in D.2 of prEN 12664A996 and in D.2 of prEN 126671996. For
21、 equipment having characteristics exactly as inicated in this subclause or design details as indicated in annex C of this part and in D.2 of prEN 12664:1996 or in D.2 of prEN 126671996, no further calculations are needed In other circumstances similar caicWons can be perfonned by analogy O BSI 05-19
22、99 STD-BSI BS EN LSqb-Z-ENGL 1771 D 1bZLIbb7 0779528 580 D Overall size 200 300 300 Page 4 EN1946-2:lW . Metering Guard Maximum Flatness Minimum Max. gap Minimum section width thickness tolerance thickness thickness) (edge limit (0,02S%) (flat. toi.) (gap limit) for e = 0,25) 100 50 30 0,05 10,o 1,2
23、5 12,5 200 50 35 0108 15,O 2,50 25,O 150 75 45 0,08 15,O 1,88 188 4.4.2 Edge heat losses and maximum specimen thickness According to 3.2.1 of IS0 83021991, the sum of the imbalance error and edge heat loss error shaU be kept within 0,5 %I. In a good equipment design, the two errors wiil be of the sa
24、me order of magnitude, hence a 0,25 % limit can be suggested for both. ILible 1 shows for some apparatus dimensions the maximum allowed specimen thickness according to 2.2.1 of IS0 83021991, when there is no edge insulation and when the edge temperature ratio, e, is 0,25; e is defined as (Te - T2)/(
25、T, - T2), where Ti and T, are respectively the temperatures of the hot and cold surfaces of the specimen, and Te is the temperature at the edge of the specimen, assumed to be uniform. EXAMPLE: e = 0,25 corresponds to a temperature of the edge of the specimen 5 K below the mean test temperature, when
26、 the temperature difference between the hot and cold side of the specimen is 20 K NOTE The edge heat loss error is zero for homogeneous isotropic specimens when e is close to 0,5; the absolute value of the edge heat loss error increases almost symmetrically when e deviates on either side from 0,5. I
27、n the range 0,25 5 e I 0,75, this error is maximm for e = 0,25. Larger specimen thicknesses can be used for some specimens if edge indation or edge temperature control is used, if auxiliary or gradient guards are installed, or medium and high conductivity specimens are tested. See annex B for aditio
28、nal information. When the maximum specimen thickness to be specified according to 4.2 exceeds the appropriate value given in Wle 1, lateral losses shall be calculated If, according to these calculations, they exceed those permitted by IS0 83021991, the performance check data shall be examined and, i
29、f no experimental evidence exists to justify the claimed maximum specimen thickness, the maximum specimen thickness to be specified according to 4.2 sha be reduced. 4.4.3 Marimum gap width and minimum specimen thickness According to 2.1.1.3 of IS0 8302:1991 the gap width, g, shallbesuchthatthegapare
30、aislessthan5%ofthe metering area, i.e. the gap width, g, shall not be greater than 1,25 % of the metering area side, L. The maximum gap width resulting from this requirement is given in the seventh column of Wle 1. The minimum specimen thickness, d, is related to the gap width. d, SM be at least ten
31、 times the gap width, see 1.7.6 of IS0 8302:1991. Thus, when the gap width reaches its maximum allowed value according to the above criteria, the minimum specimen thickness shail not be less than 12,5 % of the side L of the metering section. The minimum specimen thickness resulting from these requir
32、ements is given in the eighth column of Wle 1. When the minimum specimen thickness to be specified according to 4.2 is less thCui those of the eighth column of Wle 1, the actual gap width, g, shall be used to compute dm = 10 9, see also 4.4.6. if this requirement is not met, then the minimum specifi
33、ed specimen thickness shall be increased to meet this requirement. Minimum specimen thickness shall also be checked against maximum allowed fiahes tolerances, see 4.4.9, 4.4.10 and 4.4.11. 4.4.4 Imbalance error According to 2.2.1 of IS0 83021991, an error heat flow rate Qg can be expressed as follow
34、s: Qg = (Qo + Ac)ATg (1) I I I I I I I 400 I200 I loo I60 I OJO I20,o I 2,50 125,O O BSI 051999 where ATg is the actuai gap temperahre imbalance through the apparatus and Go, representing the heat flow rate for a 1 K gap imbalance through the apparatus itseif, is the sum of: Ga through the air in th
35、e gap; Gr by radiaton through the gap; Gm through the mechanid connections through the Gc through copper wires; cPW through metal wires (excluding copper). gap; To calculate these tem, the elementary equations of heat transfer through a plane iayer can be used. Ac is the heat flow rak through both s
36、pecimens due to a 1 K gap imbalance with G expressed by the following equation: (2) In this equation U = L is the side of the metering area (centre gap to centre gap), g is the gap width and d is the maximum expected specimen thickness. If the edge heat loss error is 0,25 %, (see 4.4.2 of this stand
37、ard and 3.2.1 of IS0 8302:1991), ATg shal be such that Gg is smaller than 0,25 % of the heat flow rate through the metering section of both specimens. This calculation changes according to the gap design and is the most critical part of the evaluation of guarded hot plate accuracy Some calculations
38、are offered as an example in annex C of this standard. Because the balancing thermopile detects a temperature difference that does not correspond exactly with the actual temperahre imbalance through the surfaces of the metering section and guard ring metal plates facing the gap, the maximum acceptab
39、le value for ATg shall be iarger than the uncertainty in the imbalance detection. A discussion on the imbalance detection through the gap is given in 2.1.1.6 of IS0 8302:1991. When the balancing thermopile is placed directly within the central section and guard ring metal plates, see Figure 4b) of I
40、S0 83021991, the density of heat flow rate crossing them during the tests shall be evaluated and the corresponding temperature drop through the metal plates computed. if this temperature diference is smaller than ATg, the gap design is acceptable without further checks, otherwise the tolerances for
41、the pitions of thermopile junctions within the metai plates shall be checked. When the balancing thermopile is embedded in plastic sheets either placed between the metal plates and the heaters or between the metal plates and the specimen, the effect of the resistances between the metal phs and the t
42、hermopile junctions due to the plastic sheets and possible air pockets shali be evaluated as a temperature difference equal to the product of the relevant thermal resistance and the density of heat flow rate crossing it. c = (16 Un) ln4/(1 - exp(-ltg/d) Page 6 EN 1946-2:1999 The sum of imbalance and
43、 edge heat losses shai not be larger than 0,5 96 The electrical instrumentation used for the imbalance detection shall be capable of detecting voltages less than ATg multiplied by the number of elements of the balancing thermopile and by the thermoelectric power of each element. The electrical baian
44、ce maintained during the tests shal therefore be better than the voltage computed in this way If this requirement is not met, the measured data of the performance check shail be verified and if the sensitivity of the instrumentation for the imbalance detection is sti not satisfactory, this shall be
45、rectifed Particular care shall siso be taken to ascertain that the quality of the electrical connections and the switches (with reference, in particular, to thermal electromotive forces) is compatible with the level of imbalance to be detected. 4.4.5 Error in measured electrical power The uncertaint
46、y in the measwment of electrid power shail be within O, 1 % to comply with B. 1 of prEN 126671996 and B.l of prEN 12664:199. 4.4.6 Error in the see also 3.1 of IS0 8302:1991 for some speciai applications). This area is not equal in all testing conclitions to the actuai metering area of the specimen
47、crossed by the heat flow rate supplied by the metering section of the heating Unit; to this uncertainty shall be added the uncertainty in the measurement of the dimensions of the apparatus. An uncertainty due to mechanical tolerances in the measurement of the centregap to centregap distance up to 0,
48、1% can be accepted NOTE The distance between the line defining the actual metering area of the specimen and the line dehning the centre of the gap can be estimated to be within 5 % of the gap width. 4.4.7 Error in the temperature dmerence between the heating and cooling units of the apparatus Accord
49、ing to 2.1.4.1.2 of IS0 83021991, the total error in the temperature difference measured by the temperature sensors permanently mounted in the apparatus shall not exceed 1 %, made up as follows: - calibration of thermocouples (or other temperature sensors): less than 0,4 - accuracy of measuring instruments: less than 0,2 04 - uncertainty in the definition of the point where the temperature is measured by the sensor less than 0,4 %. NOTE 1 When special grade thermocouples (see annex B of IS0 83021991) mounted differentially are used, as in Figure 6 b) or
