The thermal output is an exponential function (characteristic equation) of the temperature difference between the ambient air and its external surfaces and of other relevant parameters. The combination of all the heat transfer phenomena, the varying heat flux and the different temperatures at each point of the external surface makes the computation of the characteristic equation of a radiator very difficult, too expensive and of insufficient accuracy. Physical testing of a sample product is therefore the only practical method to determine the characteristic equation with adequate accuracy. Testing requires a great number of measurements that have to be taken under steady state and in well defined boundary conditions. This is difficult to achieve and small variations influence significantly the reproducibility of test results. However, small differences in stated output have large consequences on the economic value of the products since the thermal output value is of great importance for the market. In Europe, the discrepancy between the results of the tests of the thermal output is approx. 10% which is unacceptably large. The greatest values acceptable for the customers and for the trade is +/- 1% ( total spread 2%).
The project has therefore two objectives:
- to establish the TRACEABILITY for the thermal output measurements of radiators and convectors in conformity with EN 45001; achieving the repeatability of 1% and the reproducibility of 2% fixed by the standard EN 442-2,
- to establish a draft accreditation procedure to be used by accrediting European Bodies in conformity with the standard EN 442.
The contract started on 1 July 1997 with work on a provisional draft for the accreditation of Laboratories and on the instrumentation to be installed by each laboratory. Development of special probes for temperature measurements is in progress and partly finished.
The equipment of each partner will be examined and the instrumentation identified which they need to install to meet the standard requirements. The procedures required to fulfil the objectives of the project will be defined. To meet the high tolerance requirements of EN 442-2, the group will develop appropriate devices and methods and the procedures for the calibration of the instrumentation. To avoid errors due to the operators involved in the test process, EN 442-2 states that measurements have to be performed by means of automatic systems. The automatic system will be developed including the required algorithms. Each laboratory will characterise its test installation using an existing set of secondary master radiators and ensure the conformity of the instruments to the requirements defined above. Using the Primary Master Radiators set as defined in EN442 (PMRs) the repeatability and the reproducibility of the five Reference Test Installations (RTIs) will be determined. As last output the final accreditation procedures will be developed.
Funding SchemeCSC - Cost-sharing contracts
RG12 7AH Bracknell
08290 Cerdanyola De Valles - Barcelona
10135 Torino (Turin)