The research activity described in this thesis is concerned with the development and characterization of a standard for thermal energy and with the study of innovative applications and measuring solutions for smart heat metering. After an initial overview on the current state of the art and regulations for direct thermal energy measurement devices and heat accounting systems, the activities related to the development and the metrological characterization of the Italian standard of thermal energy, carried out at the Istituto Nazionale di Ricerca Metrologica (INRIM), are presented and discussed. INRIM, according to its responsibilities as National Metrological Institute (NMI), realizes the primary standards for the basic and derived units of the International System of Units (SI) and ensures the operation and maintenance of such standards, providing the national metrological traceability to the SI. Along this line, the development and the characterization of the national standard for thermal energy is fundamental in order to ensure the metrological traceability of thermal energy measurements, which is achieved through an unbroken sequence of calibration steps, each characterized by its corresponding uncertainty. Such a metrological activity is essential for the provision of accurate measurements of the thermal energy exchanged by heat conveying fluids in a number of applications, contributing significantly to the improvement of the efficiency of energy systems and processes. The INRIM national standard for thermal energy has gone through deep changes since 2011, when extensive renovation works have been planned and carried out to improve its features and performances. Thus, a metrological analysis of the system was required to assess the quality of measurements, through the investigation of all the uncertainty contributions affecting the main measurement outputs of the system: water mass and volume flow rate and thermal energy. In particular, the activities related to the development and characterization of the national standard for thermal energy were focused on the set up of a new measurement system for testing and calibrating direct heat meters in experimental conditions close to the actual operating ones, the automatization of the whole measuring process and the evaluation of the uncertainty associated to the INRIM thermal energy standard. According to the Supplement 1 of the Guide to the expression of Uncertainty in Measurement (GUM), the evaluation of the uncertainty has been carried out by means of the Monte Carlo method, which allows evaluating the probability distribution of the measurands from the probability density functions associated to the input quantities of the measurement model. In order to evaluate and confirm the metrological capabilities of the INRIM measurement system and method with respect to other NMIs’ laboratories worldwide, a pilot study on the comparison between national standards for thermal energy has been organized with the PTB Heat and Vacuum department in Berlin (Working Group 7.52, New Methods for Thermal Energy Measurement). Such an activity has been detailed from the design of the test plan for the comparison, to the discussion of the results of the first round of tests carried out at INRIM. The experimental plan has allowed observing and analyzing the effect of fluid temperature on the volume flow measurement provided by the electromagnetic flow meter used as transfer standard for the comparison. Since flow meters are typically calibrated at ambient flow conditions, understanding and quantifying the temperature effect on volume flow measurement is important, in particular, for heat metering applications. Furthermore, the analyses of two innovative measuring solutions for the non-invasive flow rate and temperature measurement in pipe flows, which can be effectively applied to thermal energy measurement, are presented and discussed. The first is related to the combined measurement of flow rate and temperature in liquid pipe flows by the clamp-on transit-time ultrasonic technique. In particular, the feasibility and the accuracy of such a non-intrusive measuring solution for the simultaneous measurement of flow rate and temperature has been analyzed by modelling the ultrasound propagation in a typical clamp-on sensor for a wide set of simulated measuring conditions. From the results of the numerical simulation, it has been possible to observe how the temperature dependent acoustic refraction of ultrasound beams can affect the accuracy of these sensors, in particular, in terms of non-intrusive temperature measurement. The second measuring solution is related to the proposal of a direct heat metering technique, based on the non-invasive measurement of the fluid flow rate circulating through a generic heat exchanger, exploiting the correlation between fluid velocity and internal heat transfer coefficient in forced pipe flows. A preliminary thermal fluid dynamic analysis has been carried out for different simulated operating conditions, in order to get a first evaluation of the feasibility and the accuracy of this non-invasive measuring technique. One of the most important application fields for heat metering devices is the measurement of thermal energy consumptions in buildings. In such a context, the fair heat cost allocation among the residents of multi-apartments and multi-purpose buildings with central heating systems, based on the accurate measurement of the actual individual thermal energy consumptions, represents an effective tool to promote energy saving and improve energy efficiency, as declared by the European Directive 2012/27/EU, recently implemented in Italy by the Decree 102/2014. Anyway, in many cases, i.e. in outdated central heating systems with vertical hot water distribution networks (rising main central heating plant configuration), the accurate measurement of individual thermal energy consumptions by means of the measures of flow rate and temperature difference of the heat conveying fluid (direct heat metering) may be neither feasible nor affordable because of installation and economic constraints. In these situations, indirect methods for the estimation of individual heat consumptions or innovative heat accounting solutions should be applied, providing their compliancy to at least one of the current technical standards for heat metering or heat cost allocation. Along this line, a novel heat cost allocation method for apartment buildings has been proposed and validated. Such a heat accounting method is particularly suitable for central heating systems characterized by room heating radiators connected to vertical hot water distribution networks and provides the indirect estimation of individual thermal energy consumptions without the need of temperature measurements at radiator heating surfaces. The proposed heat cost allocation method is based on the hydraulic modelling of hot water distribution networks, which allows estimating the water flow rates circulating through each radiator from the measurement of the overall water flow rate in the circuit and the corresponding head loss. The novel indirect heat accounting method has been validated at the INRIM central heating system test facility, a unique laboratory, consisting of 40 fully-instrumented water radiators equipped with a SI-traceable direct heat meter each and connected to an automatically reconfigurable hydraulic circuit, which allows testing indirect heat cost allocation methods in experimental conditions very close to those in the field.

Development of a standard for thermal energy and smart heat metering applications / Saba, Fabio. - (2017).

Development of a standard for thermal energy and smart heat metering applications

SABA, FABIO
2017

Abstract

The research activity described in this thesis is concerned with the development and characterization of a standard for thermal energy and with the study of innovative applications and measuring solutions for smart heat metering. After an initial overview on the current state of the art and regulations for direct thermal energy measurement devices and heat accounting systems, the activities related to the development and the metrological characterization of the Italian standard of thermal energy, carried out at the Istituto Nazionale di Ricerca Metrologica (INRIM), are presented and discussed. INRIM, according to its responsibilities as National Metrological Institute (NMI), realizes the primary standards for the basic and derived units of the International System of Units (SI) and ensures the operation and maintenance of such standards, providing the national metrological traceability to the SI. Along this line, the development and the characterization of the national standard for thermal energy is fundamental in order to ensure the metrological traceability of thermal energy measurements, which is achieved through an unbroken sequence of calibration steps, each characterized by its corresponding uncertainty. Such a metrological activity is essential for the provision of accurate measurements of the thermal energy exchanged by heat conveying fluids in a number of applications, contributing significantly to the improvement of the efficiency of energy systems and processes. The INRIM national standard for thermal energy has gone through deep changes since 2011, when extensive renovation works have been planned and carried out to improve its features and performances. Thus, a metrological analysis of the system was required to assess the quality of measurements, through the investigation of all the uncertainty contributions affecting the main measurement outputs of the system: water mass and volume flow rate and thermal energy. In particular, the activities related to the development and characterization of the national standard for thermal energy were focused on the set up of a new measurement system for testing and calibrating direct heat meters in experimental conditions close to the actual operating ones, the automatization of the whole measuring process and the evaluation of the uncertainty associated to the INRIM thermal energy standard. According to the Supplement 1 of the Guide to the expression of Uncertainty in Measurement (GUM), the evaluation of the uncertainty has been carried out by means of the Monte Carlo method, which allows evaluating the probability distribution of the measurands from the probability density functions associated to the input quantities of the measurement model. In order to evaluate and confirm the metrological capabilities of the INRIM measurement system and method with respect to other NMIs’ laboratories worldwide, a pilot study on the comparison between national standards for thermal energy has been organized with the PTB Heat and Vacuum department in Berlin (Working Group 7.52, New Methods for Thermal Energy Measurement). Such an activity has been detailed from the design of the test plan for the comparison, to the discussion of the results of the first round of tests carried out at INRIM. The experimental plan has allowed observing and analyzing the effect of fluid temperature on the volume flow measurement provided by the electromagnetic flow meter used as transfer standard for the comparison. Since flow meters are typically calibrated at ambient flow conditions, understanding and quantifying the temperature effect on volume flow measurement is important, in particular, for heat metering applications. Furthermore, the analyses of two innovative measuring solutions for the non-invasive flow rate and temperature measurement in pipe flows, which can be effectively applied to thermal energy measurement, are presented and discussed. The first is related to the combined measurement of flow rate and temperature in liquid pipe flows by the clamp-on transit-time ultrasonic technique. In particular, the feasibility and the accuracy of such a non-intrusive measuring solution for the simultaneous measurement of flow rate and temperature has been analyzed by modelling the ultrasound propagation in a typical clamp-on sensor for a wide set of simulated measuring conditions. From the results of the numerical simulation, it has been possible to observe how the temperature dependent acoustic refraction of ultrasound beams can affect the accuracy of these sensors, in particular, in terms of non-intrusive temperature measurement. The second measuring solution is related to the proposal of a direct heat metering technique, based on the non-invasive measurement of the fluid flow rate circulating through a generic heat exchanger, exploiting the correlation between fluid velocity and internal heat transfer coefficient in forced pipe flows. A preliminary thermal fluid dynamic analysis has been carried out for different simulated operating conditions, in order to get a first evaluation of the feasibility and the accuracy of this non-invasive measuring technique. One of the most important application fields for heat metering devices is the measurement of thermal energy consumptions in buildings. In such a context, the fair heat cost allocation among the residents of multi-apartments and multi-purpose buildings with central heating systems, based on the accurate measurement of the actual individual thermal energy consumptions, represents an effective tool to promote energy saving and improve energy efficiency, as declared by the European Directive 2012/27/EU, recently implemented in Italy by the Decree 102/2014. Anyway, in many cases, i.e. in outdated central heating systems with vertical hot water distribution networks (rising main central heating plant configuration), the accurate measurement of individual thermal energy consumptions by means of the measures of flow rate and temperature difference of the heat conveying fluid (direct heat metering) may be neither feasible nor affordable because of installation and economic constraints. In these situations, indirect methods for the estimation of individual heat consumptions or innovative heat accounting solutions should be applied, providing their compliancy to at least one of the current technical standards for heat metering or heat cost allocation. Along this line, a novel heat cost allocation method for apartment buildings has been proposed and validated. Such a heat accounting method is particularly suitable for central heating systems characterized by room heating radiators connected to vertical hot water distribution networks and provides the indirect estimation of individual thermal energy consumptions without the need of temperature measurements at radiator heating surfaces. The proposed heat cost allocation method is based on the hydraulic modelling of hot water distribution networks, which allows estimating the water flow rates circulating through each radiator from the measurement of the overall water flow rate in the circuit and the corresponding head loss. The novel indirect heat accounting method has been validated at the INRIM central heating system test facility, a unique laboratory, consisting of 40 fully-instrumented water radiators equipped with a SI-traceable direct heat meter each and connected to an automatically reconfigurable hydraulic circuit, which allows testing indirect heat cost allocation methods in experimental conditions very close to those in the field.
2017
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11583/2683495
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