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.
In 2012 the Energy Efficiency Directive (EED) has set mandatory installation of individual metering and submetering systems for accounting thermal energy consumption in buildings where centralized heating/cooling sources are present, when technically feasible and cost efficient. As a consequence, direct thermal energy meters or indirect heat accounting systems have spread widely in residential buildings, for metering and submetering in space heating applications. On the other hand, individual metering of thermal energy in space cooling is a difficult task, due to the very different types of cooling systems and to the lack of technical and legal metrology regulation. In this paper possible solutions available for direct metering and submetering of different types of centralized cooling systems are discussed. Indeed, for direct metering application, the cooling fluid flow metering is a particularly crucial issue due to small pipe diameters and different fluid properties. Thus, the authors carried out an experimental comparison between a Coriolis flow-meter and an ultrasonic clamp-on flowmeter in the cooling fluid circuit of a direct expansion system. Tests have been performed at different operative temperature differences between flow and return, showing relative errors within ± 10%.
One of the main issues in natural gas transmission networks is represented by the so-called Unaccounted-for-Gas (UAG), that is the amount of gas related to the unavoidable measurement and estimation errors in the balancing equation of the network. In particular, accuracy of flow-rate measurement in transmission network pipelines is a very crucial issue due to the numerous related metrological criticalities. This paper is aimed at evaluating the influence of the flow-meter accuracy on UAG. To this aim, the rangeability limits of the flow-rate measuring device in delivery points characterized by large fluctuation of gas flows have been investigated, together with the effect of the drift of the instrument due to the absence of punctual periodic calibrations. From the analysis carried out, it was found that about 12% of the average daily flow rates measured at DSO measuring plants is below the minimum flow rate of the meter and that a significant correlation between monthly UAG and registered rangeability faults of flow-meters has been found.
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