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. This document covers meters for closed systems only, where the differential pressure over the thermal load is limited. This document is not applicable to: - electrical safety requirements; - pressure safety requirements; and - surface mounted temperature sensors.