Metrological and operational issues during subsequent verification of thermal energy meters

Individual metering for heating and cooling application has been recognized as an effective tool to improve energy efficiency in buildings in EU. Hence, thermal energy meters are widely spreading in district heating networks and in buildings served by a central heating/cooling source. By a legal metrology point of view, while type approval and initial verification of thermal energy meters are regulated by MID and harmonized standards EN 1434, no technical common procedure is still available in EU for subsequent verifications both in laboratory and on the field and member states are tackling this issue with different approaches. Nevertheless, the 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 values. In this paper, the authors present the results of an experimental campaign aimed at analysing the key metrological issues and the compatibility between the results of subsequent verification of a thermal energy meter performed in the laboratory and on the field.