This document specifies commissioning, operational monitoring and maintenance and applies to thermal energy meters. Thermal energy meters are instruments intended for measuring the energy which in a heat-exchange circuit is absorbed (cooling) or given up (heating) by a liquid called the heat-conveying liquid. The thermal energy meter indicates the quantity of thermal energy in legal units. Electrical safety requirements are not covered by this document. Pressure safety requirements are not covered by this document. Surface mounted temperature sensors are not covered by this document. This document covers meters for closed systems only, where the differential pressure over the thermal load is limited.