On the metrological reliability of subsequent verification of thermal energy meters

Individual metering for heating and cooling has been recognized by EU as an effective tool to improve energy efficiency. Hence, thermal energy meters are widely spreading in district heating networks and in buildings. While type approval and initial verification of thermal energy meters are clearly regulated, no technical standards are available in EU for subsequent verification both in laboratory and in-field. Nevertheless, verification of thermal energy meters is a difficult task, due to the complex measuring chain and to the need to set appropriate verification points combined in flow-rate and temperature difference. In this paper, the authors present the results of an experimental campaign aimed at analysing the metrological issues and compatibility between subsequent verification of a thermal energy meter performed in the laboratory and in-field. The obtained results demonstrate that in-field verification outcomes in some cases are not consistent with the in-laboratory ones.