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District heating leakage measurement: Development of methods
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16th International Symposium on District Heating and Cooling, DHC2018, 16th International Symposium District HeatingGermany and Cooling, DHC2018, 9–12 Septemberon2018, Hamburg, 9–12 September 2018, Hamburg, Germany
District heating leakage measurement: Development of methods The 15th leakage International Symposium on District Heating and Cooling District heating measurement: Development of methods E. Filippiniaa, I. Mariniaa*, M. Ongariaa, E. Pedrettiaa Filippini , I. Marini M. Ongari , E. Pedretti AssessingE.the feasibility of *,using the heat demand-outdoor A2A Calore e Servizi S.r.l., via Lamarmora 230, Brescia, 25124, Italy
A2A Calore for e Servizi via Lamarmora 230, Brescia, 25124, Italy demand forecast temperature function aS.r.l., long-term district heat
Abstract a,b,c *, A. Pinaa, P. Ferrãoa, J. Fournierb., B. Lacarrièrec, O. Le Correc Abstract I. Andrić A2A aCalore e Servizi carries out maintenance programs; one of the main activities is leak detection performed according to different IN+ Center for Technology andpressure Policy Research - Instituto Superior Av.detection Rovisco Pais 1,measurement 1049-001 Lisbon, Portugal A2A Calore e Servizi carries bout maintenance programs; one of the main activities leak performed according different procedures. The firstInnovation, method was based on measurements and then itTécnico, hasis evolved in a direct of to water loss. Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France procedures. The first method was based on pressure measurements and then it has evolved in a direct measurement of water loss. A new methodc has been tested; fixed metering devices have been installed. According to the law of mass conservation, the mass Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France A new method has been tested; devices haveprocedure been installed. to the law leak of mass conservation, the mass difference is a calculation of thefixed watermetering lost in the area. This allowsAccording reliable continuous measurements, simplifying difference a calculation of the immediate water lost in the area. This procedure allows reliable continuous leak measurements, simplifying operationalisactivities and giving results on field. operational activities and giving immediate results on field. ©Abstract 2018 The Authors. Published by Elsevier Ltd. © 2018 2018 The The Authors. Authors. Published Published by by Elsevier Elsevier Ltd. Ltd. © This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) This is an and open access article under the CC BY-NC-ND (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection under responsibility of committee ofone the of 16th Symposium onfor District Heating District heating networks are commonly addressed inlicense the literature asof theInternational most effective solutionson decreasing the Selection and peer-review peer-review under responsibility of the the scientific scientific committee the 16th International Symposium District Heating Selection and peer-review under responsibility of the scientific committee of the 16th International Symposium on District Heating and Cooling, DHC2018. greenhouse emissions from the building sector. These systems require high investments which are returned through the heat and Cooling, gas DHC2018. and Cooling, DHC2018. sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease,
Keywords: district heating network; leakage measurement; flow meters; maintenance strategy. prolonging the investment return period. Keywords: district heating network; leakage measurement; flow of meters; strategy. The main scope of this paper is to assess the feasibility usingmaintenance the heat demand – outdoor temperature function for heat demand
forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665
1.buildings Introduction that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district 1.renovation Introduction scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were A2A Calore e Servizi is the main district heating (DH)developed companyand in Northern Italy it manages the DH compared with results from(ACS) a dynamic heat demand model, previously validated by the and authors. A2A Calore e Servizi (ACS) isweather theMilan. main district heating (DH) company intoNorthern and itfor manages the DH The results thatBergamo when onlyand change is considered, the margin error could be Italy acceptable some applications networks ofshowed Brescia, These three systems differ ofone the other because of the individual networks of Brescia, Bergamo and Milan. These three systems differ one to the other because of the individual (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation characteristics, such as construction technologies, materials, lengths and heat production. scenarios, error increased uptechnologies, to 59.5% (depending on the weather renovation combination considered). characteristics, suchvalue asoperate construction materials, lengths andand heat production. The firstthe system to is the one in Brescia; it started functioning in 1972 andscenarios it is widely developed in the The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds tothe the The first system to operate is the one in Brescia; it started functioning in 1972 and it is widely developed city; in fact, it is around 670 km long (trench length) and supplies heat to more than 21.000 connections (moreinthan decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and city; in fact, it is around 670 km long (trench length) and supplies heat to more than 21.000 connections (more than 70% of the municipal area connections). renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the 70% of the municipal area connections). coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.
© 2017 The Authors. Published by Elsevier Ltd. * Corresponding author. Tel.: +390303554228; fax: +390303554084. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and E-mail address:author. [email protected] * Corresponding Tel.: +390303554228; fax: +390303554084. Cooling. E-mail address: [email protected] 1876-6102 © 2018 The Authors. Published by Elsevier Ltd. Keywords: Heat demand; Forecast; Climate change This is an open access under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) 1876-6102 © 2018 Thearticle Authors. Published by Elsevier Ltd. Selection under responsibility of the scientific of the 16th International Symposium on District Heating and Cooling, This is an and openpeer-review access article under the CC BY-NC-ND licensecommittee (https://creativecommons.org/licenses/by-nc-nd/4.0/) DHC2018. Selection and peer-review under responsibility of the scientific committee of the 16th International Symposium on District Heating and Cooling, DHC2018. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. 1876-6102 © 2018 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of the scientific committee of the 16th International Symposium on District Heating and Cooling, DHC2018. 10.1016/j.egypro.2018.08.193
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ACS performs several activities, such as designing, coordinating interventions and maintenance. The latter has a vital importance, especially for wide and old networks, as the one in Brescia. The leak detection process consists of different steps: leak identification, its localisation and estimation of water loss. Although leak detection can be achieved using different methods, the correct localisation and the estimation of water loss are more complex, but these elements are extremely useful for efficient maintenance. Actually, it is essential to identify, locate leakages and estimate the magnitude of water loss to organize a careful maintenance strategy in order to ensure the correct operation of the system and a longer lifespan [1]. In the last years, ACS has developed and tested several methods to detect leaks, each of whom is briefly described in the following paragraphs. 2. The DH system in Brescia The DH network in Brescia has an important development and a yearly average of about 1.000 GWh of supplied heat; it is a single system, meaning that it cannot be hydraulically divided in smaller systems. The supply pipeline temperature can reach at maximum 130°C in winter and 90°C in summer, while for the return, temperature is almost constant all year long, and is around 60°C; the maximum operative pressure of the network is 16 bar. Since the network was partially constructed in the early ‘70s, pipes’ characteristics have been evolving since that moment; nowadays the network is composed of three different types of pipe. From 1972 to 1979, steel pipes were installed in concrete ducts and sustained by rollers or metallic saddles; this type of pipe represents around 20% of the entire network length. From 1979 to 1985, the “wanit” technology was employed, now it constitutes less than 2% of the network length. According to this method, pipes were laid in preinsulated sheathes, composed by two concentric fibrocement pipes with a layer of polyurethane in the middle. The remaining 78% of network length consists of preinsulated pipe and is made of steel covered by external casings: an inner layer of polyurethane foam and a layer of polyethylene. The production plant consists of a waste to energy plant and a CHP plant, both located in the southern part of the network, boilers are located in other part of the city and they are switched on during peaks. 3. Leak detection method Planning effective maintenance is fundamental; thus, measuring the amount of water lost by each leakage provides information regarding the priority of the interventions to perform. Normally, the first monitored parameter is the amount of daily make-up water, but that describes the entire network scenario, thus, it can only be used as trend indicator. To understand where to perform fixing and maintenance activities it is necessary to have more information regarding the location and the magnitude of each leakage; hence, a system able to provide this information has been experimented in Brescia DH network implementing pressure tests, a tool already in use. Pressure tests are routine maintenance activities, performed during warm seasons (mid-April – mid-October) on the 80% – 90% of the entire network. They consist in choosing an area to test, dividing the examined area from the rest of the network and in evaluating its pressure drop trend for less than half an hour; the pressure drop speed could give information about the leak size. To perform these tests it is necessary to operate on site on valves; in order to do so, at least a temporary working site has to be created and managed. Operators in charge of these activities have gained experience and sensitiveness, however this procedure does not provide necessary information to complete a list of interventions, but it can be used as preliminary test. Therefore, it was decided to develop procedures, which would allow a more accurate measurement of leakages; thus, a method had been designed to define replicable approaches. This was based on measurements of pressure drop while the test area was separated from the rest of the network and on weighting the discharged volume of water; these parameters were used to estimate the bulk modulus of the area [2]. The registration of data allowed subsequent calculations of the amount of water loss in the examined area; in fact, to obtain an indirect estimation of water loss magnitude the orifice flow equation was applied, whose results could be estimated again only by calculations. The orifice flow equation was applied assuming that the DH network is compressible and it has its own bulk modulus; this parameter is calculated based on pressure and volume variation, as stated previously, hence, the higher the water loss,
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the higher the overestimation of this coefficient. Moreover, regarding the estimation of the leak, it is supposed that water loss can be compared to the flow that passes through an orifice, so it is possible to apply the orifice flow equation to have an approximate calculation of the amount of water loss and the size of the leak [3]. This approach required particular care during operational activities and, in addition, data could be obtained only after calculations and not immediately. A further improvement was the employment of portable flow metering devices, which allowed an instantaneous and direct measurement of water loss. Even though, it was possible to have instantaneous measurements, that was feasible only for a short period of time, less than half an hour, and it was still mandatory operating on site with the creation of temporary working sites. At this point, it appeared important to improve and optimize detection procedures; not all the methods described above allowed making immediate estimations of leaks size and magnitude, as mentioned; that was possible only after calculations and it was allowed only to estimate the total area of the leaks in the examined zone. Furthermore, data could be recorded only for short periods, hence, during warm seasons it was possible to monitor each area only once per year. In addition, it must be noted that operational activities have to be taken into account: most of the times, these tests were performed on streets, requiring the creation of temporary working sites, traffic management, high safety measures and temporary interruption of service for clients. 4. Fixed metering devices In 2016, two fixed metering devices were operating in two areas of the Brescia DH network, one device monitors around 100 km of pipes, while the other around 105 km of pipes. These fixed devices consist of roadside cabinets containing a supply and a return pipe where valves, flow-metering devices and air vents are installed (as shown in Figure 1). The operating tools inside the cabinet are thermal energy meters and related static flow sensors; they calculate energy and measure flow, power and temperature; these results can be read both directly on the display tool and remotely. Flow measurements are based on bidirectional ultrasonic technique and on transit time method: two sound signals are sent, against and with flow direction; the sound signal sent with the flow direction reaches the opposite transducer first, hence the time difference between the two elements can be used to calculate the flow velocity and then translated as volume. At this point, heat meters compute energy and mass based on measurements of temperature and volume. It was chosen to install the same type of heat meters that are normally employed in consumers’ substations, in order to have solid, easy to find and reliable instrumentations.
Figure 1: a: roadside cabinet under construction, b: roadside cabinet in operation.
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Figure 2: Scheme of the mass conservation theory applied to the employment of fixed metering device.
Nomenclature Qs Qr Ql
𝑄𝑄𝑄𝑄 = 𝑄𝑄𝑄𝑄 + 𝑄𝑄𝑄𝑄
(1)
supply mass flow return mass flow mass flow of the leak
4.1. Background theory The idea behind the construction of these tools is based on the theory of mass conservation; the same amount of water should enter and go out of the examined area, as shown in Figure 2 and Equation (1). In order to apply this theory, the chosen area has to be connected to the rest of the network by a single branch (both supply and return), by opening and closing selected valves, this way it can behave as a branch and can be monitored easily. The difference between supply and return flow is the amount of leak (Ql). It must be noted that analyses have to be based on mass flow; hence, it is possible to compare supply and return data, while volumetric flow rate depends on temperature and then it cannot be examined together. 4.2. Laboratory tests By design, any size of flow metering device has a nominal flow and a related measurement error. To verify these data, flow meters undergone laboratory tests to monitor and evaluate the range of error and their behavior; these tests were performed in an ACS laboratory. A test bed was built and it consisted in a series of three meters, as shown in Figure 3: a device to test, a tap (behaving as a loss in the system), another device to test and a calibrated device. This test bed has run for few days monitoring two scenarios: in the first scenario, the tap was closed (no water loss), while in the second scenario the tap was open (system with water loss). Tests have confirmed the error ranges reported in the instruction manuals and, in all the cases, measured values were lower than the design ones; errors obtained after laboratory analyses were lower than 0,5% in both scenarios, thus they were classified as negligible.
Figure 3: Scheme representing the test bed.
/ Energy 149 (2018) Filippini E., MariniE.I.,Filippini Ongari et M.,al.Pedretti E./Procedia Energy Procedia 00297–306 (2018) 000–000
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Nomenclature Flow metering device to test Calibrated flow metering device Pipe Tap simulating water loss
4.3. Cabinet features Flow metering devices can operate continuously only during warm seasons (mid-April – mid-October) when flow is lower and supply temperature is more constant, in winter they can be used for instantaneous measurements. They operate as bypasses and, since most of them are above - ground installations, it was preferred to create size-limited tools, and hence, all the designed instrumentation was dimensioned according to summer flows to limit measurement error of metering devices and costs. The investment is in the range between 15.000 and 25.000 €. A supply pipe connects instruments inside the cabinet to the main network, allowing water to pass through the metering device before running again in the pipe that goes to clients; for the return, a pipe allows water flow to be measured inside the cabinet and then it flows back to the main pipeline, as shown in Figure 4.
Figure 4: Hydraulic scheme of a typical roadside cabinet Nomenclature Return line Supply line Valve (open) Valve (closed) Flow metering device Cabinet area Direction of flow, red supply flow, blue return flow
Flow sensors measure volumetric flow rate in m3/h and temperature in Celsius degree, this way the calculator in the heat meter can compute mass flow and energy, as stated in paragraph 4. Water flow measurements are recorded continually during warm seasons (i.e. around for 5 months), readings are saved automatically and they can be downloaded easily; normally operators download data once per month. Records can be
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Figure 5: Hourly recorded data
Figure 6: Daily recorded data
saved both on hourly (instantaneous) and daily (sum of the 24 hours) basis. It can be observed, in Figure 5, that instantaneous readings are strongly influenced by the sensitivity of measurement devices, temperature and ordinary hourly flow fluctuations. As visible, hourly measurements are characterized by important variations, although it is possible to easily identify the daily trend (plotted in orange); Figure 6 represents data on a daily basis and, differently from the previous figure, this approach provides more constant data, able to describe the trend effectively; thus, daily basis was chosen. It must be noted that, most of the times, to activate these devices it is necessary to create a temporary working site, but differently from the previous methods, here it is necessary only to activate and deactivate the metering systems, thus, twice a year and for a shorter period, without service interruptions for customers. Furthermore, for previous
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methods, the work of three operators, at least, was necessary for each test, while fixed metering devices require at least three operators twice a year, during activation and deactivation phases, and another operator once per month to download data. 5. Monitoring results After the installation of the first flow metering devices, it was possible to monitor the trend of water flowing in the areas under test; the following paragraphs show the results obtained for the “Oltremella Sud” area since 2014 and for the “Sereno” area since 2016. Data registered by roadside cabinets were validated by measurements recorded by portable meter device and it was observed that fixed metering devices were able to identify water losses lower than 5 t/d. 5.1. Sereno This flow-metering device was activated for the first time in June 2014; it monitors 105 km of pipe (around 8% of the entire network). The following graph (Figure 7) represents the trend from June 2014 to October 2017; it is visible that the trend is recorded only during warm seasons (mid-April – mid-October), the analysis should focus on daily difference of mass flow, which is related to the other represented parameters: supply and return temperatures and supply average flow. The daily difference of mass flow is calculated as the difference between supply mass in tons and return mass in tons that are measured by flow meters and divided by the maximum value of water loss recorded in the examined period. During measurements recorded in 2014, it is possible to observe a peak around mid-August, as reported in Figure 7, which represents a leak that was fixed quite quickly, approximately in one week, because of its magnitude. Similarly, as represented in Figure 8, the trend of the following year defines a leak, from April to mid-June; in this case, the peak is not as high as it was in the previous year but the repair of the leak is clearly visible, the mass difference goes from 67% the 15th of June to 20% the 19th of June. Moreover, it can be observed that, in the first period, the daily difference of mass flow is above 60% of the maximum value of the year, while after mid-June it is halved, around 30%.
Figure 7: Graph representing measurements of daily difference mass flow, average supply flow, supply and return temperature in the “Sereno” area, June 2014 – October 2017.
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Figure 8: Graph representing measurements of daily difference mass flow, average supply flow, supply and return temperature in the “Sereno” area, April – October 2015.
Figure 9: Graph representing measurements of daily difference mass flow, average supply flow, supply and return temperature in the “Oltremella Sud” area, June – October 2017.
5.2. Oltremella Sud This flow-metering device monitors around 100 km of pipe (around 7% of the Brescia DH network) and it has been operating since 2016. The graphs represented in Figure 9 show the trend of the daily difference of mass flow, the supply average flow, the supply and return temperature during the warm season 2017. This device has been operating only for two warm seasons, furthermore, it must be noted that data describing daily difference of mass flow in 2016 are not reliable, in fact, that year there were problems during some fixing operations performed on the network. Data describing 2017 identifies a water loss in the second part of the season, from end of
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August to October when values are higher than 80%. It can be observed that the second part of the period is characterized also by two minimums; regarding these two values, it is important to specify that they correspond to devices switching off during maintenance operations. 6. Discussion and following steps The employment of fixed flow-metering devices have improved leak detection process; in fact, these tools allow measurements (about 5 months, continuously) of the quantities of the supply and return water in selected areas; the “Sereno” and “Oltremella Sud” flow meters monitor about 15% of the Brescia DH network. As stated previously, these tools can work continuously only during warm seasons (mid-April – mid-October) when supply temperature is more constant and the amount of supply and return flow are lower than in winter periods. At the moment, these measurements are not readable remotely, they need to be downloaded on site and they can provide the sum of total amount of water lost in an examined area; in fact, the value of mass difference is related to the entire analyzed area. It must be added that flow-metering tools can restrict the area to inspect providing data almost immediately, if necessary and moreover by creating subsections, it is possible to identify the area with higher water loss. Before their installation, it was not possible to individuate the area without operating on site on valves and this approach did not even allow having an immediate feedback regarding the presence of a leak. The measured data do not require processing nor particular calculations, thus, their analyses can be done quite quickly and readings can be downloaded every time it is necessary. As shown in the previous graphs (Figure 7, 8 and 9) the trend of the daily difference of mass flow is an important parameter that can give information regarding both water losses and operations on the network, as stated in the description of the “Sereno” and “Oltremella Sud” areas. The available data could give also information regarding the quantity of energy supplied and lost (estimated by calculations from water loss) in the examined area, as plotted in Figure 10. At the beginning of May 2018, ACS activated another flow-metering cabinet “P.le Cremona”; the area monitored by this new device is Brescia downtown, about 25 km of pipes. This zone represents only about 1% of Brescia DH network, but this is one of the eldest area, characterized by a very high rate of water loss thus, having the possibility to monitor it continuously would improve maintenance efforts. In the last months, some experiments on data radio transmissions employing LoRaWAN protocol have being tested. ACS is finalizing the design of another device in “Chiesanuova” area, which should be tested by the end of summer 2018; this new device should monitor about 54 km of the network. At that point, the total inspected area would be slightly higher than 20% of the pipeline of the city network, as summarized in Table 1, giving an important improvement in the yearly maintenance strategy. 7. Conclusions ACS performs several activities, one of the main is leak detection; this process is fundamental to ensure the correct operation of the system and a longer lifespan of the network. Leak detection requires an effective analysis on the amount of water lost, thus ACS has been developing several procedures to provide this information. These experimentations aimed at the identification of a method able to provide, continuously, the amount of water lost in an area, minimizing the operations on the network and avoiding the interruption of the service to customers. Table 1. Area description. Data in brackets refer to the entire network length and the total number of customers Daily supply Number of Nominal flow Length (pipes) average flow Name of the area customers [n] meter [m³/h] [km] (summer) [m³/h]
Year of activation
Sereno
101,72
35
1.506
40
2014
Oltremella Sud
105,07
47
1.459
60
2016
P.le Cremona
24,32
23
534
25
2018
Chiesanuova
54,54
45
548
60
Expected: end of summer 2018
Total
285,65 (21,3%)
4.047 (19,2%)
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Figure 10: Graph representing the energy loss calculated from water loss in the “Oltremella Sud” area, June – October 2017
Pressure tests were initially employed, they can identify the presence of water loss in the examined area, but they cannot provide the necessary information to classify a leak, such as number of losses, location and magnitude; thus, they are used as preliminary tests. Later, a method based on the application of the orifice flow equation was tested successfully; it was observed that these practices could be performed only for short periods, about half an hour, requiring several operations on site and data processing. Then, portable flow metering devices were applied, this method allowed having instantaneous and direct measurements of water loss, but it was possible only for short periods. All the methods described above could be performed only for less than one hour, requiring the creation of a working site, often, the interruption of service for customers and processing of the measured data; thus, a new method requiring less operational activities and continuous measurement was implemented. Fixed metering devices are able to monitor continuously, during warm season (from mid-April to mid-October), the amount of water loss (allowing then the calculations of energy loss) in the area where the roadside cabinet is installed. The theory behind this application is based on mass conservation: the same amount of water entering the area has to flow out, if these quantities differ, there is a leakage. Fixed metering devices consist of roadside cabinets equipped with valves, air vents and flow meters that calculate energy and measure flow, power and temperature; readings are saved automatically and they can be downloaded easily, normally operators do it once per month. In 2016, two flow-metering devices were in operation, monitoring two areas of the Brescia DH network, in May 2018 a new device was activated and another one is under construction. At the moment, about 17% of the city DH network is monitored continuously during warm season, providing necessary information for maintenance programs. In fact, the installation of these devices have improved leak detection processes, allowing continuous monitoring of the quantities of supply and return water flow during warm season; they can provide information immediately, when necessary, regarding the presence of one or more leaks, without requiring processing nor particular calculations. The next step is testing and implementing radio data transmission to allow remote readings. ACS aims at further implementing the employment of fixed metering devices to ensure effective operation of the DH systems it manages, both the old one, as in Brescia, and the more recent, as in Milan. References [1] Frederiksen Svend, Werner Sven, “District heating and cooling”, Studentlitteratur, (2013), AB, Lund. [2] Astori P., “Dispense del corso di Impianti aerospaziali”, Politecnico di Milano, Milano, (2005), pp. 3.6 – 3.9. [3] Filippini Ettore, and Ongari Marco. “Method for the quantification of a leakage in a district heating network”, (2014), The 14th International Symposium on District Heating and Cooling.
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16th International Symposium on District Heating and Cooling, DHC2018, 16th International Symposium District HeatingGermany and Cooling, DHC2018, 9–12 Septemberon2018, Hamburg, 9–12 September 2018, Hamburg, Germany
District heating leakage measurement: Development of methods The 15th leakage International Symposium on District Heating and Cooling District heating measurement: Development of methods E. Filippiniaa, I. Mariniaa*, M. Ongariaa, E. Pedrettiaa Filippini , I. Marini M. Ongari , E. Pedretti AssessingE.the feasibility of *,using the heat demand-outdoor A2A Calore e Servizi S.r.l., via Lamarmora 230, Brescia, 25124, Italy
A2A Calore for e Servizi via Lamarmora 230, Brescia, 25124, Italy demand forecast temperature function aS.r.l., long-term district heat
Abstract a,b,c *, A. Pinaa, P. Ferrãoa, J. Fournierb., B. Lacarrièrec, O. Le Correc Abstract I. Andrić A2A aCalore e Servizi carries out maintenance programs; one of the main activities is leak detection performed according to different IN+ Center for Technology andpressure Policy Research - Instituto Superior Av.detection Rovisco Pais 1,measurement 1049-001 Lisbon, Portugal A2A Calore e Servizi carries bout maintenance programs; one of the main activities leak performed according different procedures. The firstInnovation, method was based on measurements and then itTécnico, hasis evolved in a direct of to water loss. Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France procedures. The first method was based on pressure measurements and then it has evolved in a direct measurement of water loss. A new methodc has been tested; fixed metering devices have been installed. According to the law of mass conservation, the mass Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France A new method has been tested; devices haveprocedure been installed. to the law leak of mass conservation, the mass difference is a calculation of thefixed watermetering lost in the area. This allowsAccording reliable continuous measurements, simplifying difference a calculation of the immediate water lost in the area. This procedure allows reliable continuous leak measurements, simplifying operationalisactivities and giving results on field. operational activities and giving immediate results on field. ©Abstract 2018 The Authors. Published by Elsevier Ltd. © 2018 2018 The The Authors. Authors. Published Published by by Elsevier Elsevier Ltd. Ltd. © This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) This is an and open access article under the CC BY-NC-ND (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection under responsibility of committee ofone the of 16th Symposium onfor District Heating District heating networks are commonly addressed inlicense the literature asof theInternational most effective solutionson decreasing the Selection and peer-review peer-review under responsibility of the the scientific scientific committee the 16th International Symposium District Heating Selection and peer-review under responsibility of the scientific committee of the 16th International Symposium on District Heating and Cooling, DHC2018. greenhouse emissions from the building sector. These systems require high investments which are returned through the heat and Cooling, gas DHC2018. and Cooling, DHC2018. sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease,
Keywords: district heating network; leakage measurement; flow meters; maintenance strategy. prolonging the investment return period. Keywords: district heating network; leakage measurement; flow of meters; strategy. The main scope of this paper is to assess the feasibility usingmaintenance the heat demand – outdoor temperature function for heat demand
forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665
1.buildings Introduction that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district 1.renovation Introduction scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were A2A Calore e Servizi is the main district heating (DH)developed companyand in Northern Italy it manages the DH compared with results from(ACS) a dynamic heat demand model, previously validated by the and authors. A2A Calore e Servizi (ACS) isweather theMilan. main district heating (DH) company intoNorthern and itfor manages the DH The results thatBergamo when onlyand change is considered, the margin error could be Italy acceptable some applications networks ofshowed Brescia, These three systems differ ofone the other because of the individual networks of Brescia, Bergamo and Milan. These three systems differ one to the other because of the individual (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation characteristics, such as construction technologies, materials, lengths and heat production. scenarios, error increased uptechnologies, to 59.5% (depending on the weather renovation combination considered). characteristics, suchvalue asoperate construction materials, lengths andand heat production. The firstthe system to is the one in Brescia; it started functioning in 1972 andscenarios it is widely developed in the The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds tothe the The first system to operate is the one in Brescia; it started functioning in 1972 and it is widely developed city; in fact, it is around 670 km long (trench length) and supplies heat to more than 21.000 connections (moreinthan decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and city; in fact, it is around 670 km long (trench length) and supplies heat to more than 21.000 connections (more than 70% of the municipal area connections). renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the 70% of the municipal area connections). coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.
© 2017 The Authors. Published by Elsevier Ltd. * Corresponding author. Tel.: +390303554228; fax: +390303554084. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and E-mail address:author. [email protected] * Corresponding Tel.: +390303554228; fax: +390303554084. Cooling. E-mail address: [email protected] 1876-6102 © 2018 The Authors. Published by Elsevier Ltd. Keywords: Heat demand; Forecast; Climate change This is an open access under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) 1876-6102 © 2018 Thearticle Authors. Published by Elsevier Ltd. Selection under responsibility of the scientific of the 16th International Symposium on District Heating and Cooling, This is an and openpeer-review access article under the CC BY-NC-ND licensecommittee (https://creativecommons.org/licenses/by-nc-nd/4.0/) DHC2018. Selection and peer-review under responsibility of the scientific committee of the 16th International Symposium on District Heating and Cooling, DHC2018. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. 1876-6102 © 2018 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of the scientific committee of the 16th International Symposium on District Heating and Cooling, DHC2018. 10.1016/j.egypro.2018.08.193
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ACS performs several activities, such as designing, coordinating interventions and maintenance. The latter has a vital importance, especially for wide and old networks, as the one in Brescia. The leak detection process consists of different steps: leak identification, its localisation and estimation of water loss. Although leak detection can be achieved using different methods, the correct localisation and the estimation of water loss are more complex, but these elements are extremely useful for efficient maintenance. Actually, it is essential to identify, locate leakages and estimate the magnitude of water loss to organize a careful maintenance strategy in order to ensure the correct operation of the system and a longer lifespan [1]. In the last years, ACS has developed and tested several methods to detect leaks, each of whom is briefly described in the following paragraphs. 2. The DH system in Brescia The DH network in Brescia has an important development and a yearly average of about 1.000 GWh of supplied heat; it is a single system, meaning that it cannot be hydraulically divided in smaller systems. The supply pipeline temperature can reach at maximum 130°C in winter and 90°C in summer, while for the return, temperature is almost constant all year long, and is around 60°C; the maximum operative pressure of the network is 16 bar. Since the network was partially constructed in the early ‘70s, pipes’ characteristics have been evolving since that moment; nowadays the network is composed of three different types of pipe. From 1972 to 1979, steel pipes were installed in concrete ducts and sustained by rollers or metallic saddles; this type of pipe represents around 20% of the entire network length. From 1979 to 1985, the “wanit” technology was employed, now it constitutes less than 2% of the network length. According to this method, pipes were laid in preinsulated sheathes, composed by two concentric fibrocement pipes with a layer of polyurethane in the middle. The remaining 78% of network length consists of preinsulated pipe and is made of steel covered by external casings: an inner layer of polyurethane foam and a layer of polyethylene. The production plant consists of a waste to energy plant and a CHP plant, both located in the southern part of the network, boilers are located in other part of the city and they are switched on during peaks. 3. Leak detection method Planning effective maintenance is fundamental; thus, measuring the amount of water lost by each leakage provides information regarding the priority of the interventions to perform. Normally, the first monitored parameter is the amount of daily make-up water, but that describes the entire network scenario, thus, it can only be used as trend indicator. To understand where to perform fixing and maintenance activities it is necessary to have more information regarding the location and the magnitude of each leakage; hence, a system able to provide this information has been experimented in Brescia DH network implementing pressure tests, a tool already in use. Pressure tests are routine maintenance activities, performed during warm seasons (mid-April – mid-October) on the 80% – 90% of the entire network. They consist in choosing an area to test, dividing the examined area from the rest of the network and in evaluating its pressure drop trend for less than half an hour; the pressure drop speed could give information about the leak size. To perform these tests it is necessary to operate on site on valves; in order to do so, at least a temporary working site has to be created and managed. Operators in charge of these activities have gained experience and sensitiveness, however this procedure does not provide necessary information to complete a list of interventions, but it can be used as preliminary test. Therefore, it was decided to develop procedures, which would allow a more accurate measurement of leakages; thus, a method had been designed to define replicable approaches. This was based on measurements of pressure drop while the test area was separated from the rest of the network and on weighting the discharged volume of water; these parameters were used to estimate the bulk modulus of the area [2]. The registration of data allowed subsequent calculations of the amount of water loss in the examined area; in fact, to obtain an indirect estimation of water loss magnitude the orifice flow equation was applied, whose results could be estimated again only by calculations. The orifice flow equation was applied assuming that the DH network is compressible and it has its own bulk modulus; this parameter is calculated based on pressure and volume variation, as stated previously, hence, the higher the water loss,
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the higher the overestimation of this coefficient. Moreover, regarding the estimation of the leak, it is supposed that water loss can be compared to the flow that passes through an orifice, so it is possible to apply the orifice flow equation to have an approximate calculation of the amount of water loss and the size of the leak [3]. This approach required particular care during operational activities and, in addition, data could be obtained only after calculations and not immediately. A further improvement was the employment of portable flow metering devices, which allowed an instantaneous and direct measurement of water loss. Even though, it was possible to have instantaneous measurements, that was feasible only for a short period of time, less than half an hour, and it was still mandatory operating on site with the creation of temporary working sites. At this point, it appeared important to improve and optimize detection procedures; not all the methods described above allowed making immediate estimations of leaks size and magnitude, as mentioned; that was possible only after calculations and it was allowed only to estimate the total area of the leaks in the examined zone. Furthermore, data could be recorded only for short periods, hence, during warm seasons it was possible to monitor each area only once per year. In addition, it must be noted that operational activities have to be taken into account: most of the times, these tests were performed on streets, requiring the creation of temporary working sites, traffic management, high safety measures and temporary interruption of service for clients. 4. Fixed metering devices In 2016, two fixed metering devices were operating in two areas of the Brescia DH network, one device monitors around 100 km of pipes, while the other around 105 km of pipes. These fixed devices consist of roadside cabinets containing a supply and a return pipe where valves, flow-metering devices and air vents are installed (as shown in Figure 1). The operating tools inside the cabinet are thermal energy meters and related static flow sensors; they calculate energy and measure flow, power and temperature; these results can be read both directly on the display tool and remotely. Flow measurements are based on bidirectional ultrasonic technique and on transit time method: two sound signals are sent, against and with flow direction; the sound signal sent with the flow direction reaches the opposite transducer first, hence the time difference between the two elements can be used to calculate the flow velocity and then translated as volume. At this point, heat meters compute energy and mass based on measurements of temperature and volume. It was chosen to install the same type of heat meters that are normally employed in consumers’ substations, in order to have solid, easy to find and reliable instrumentations.
Figure 1: a: roadside cabinet under construction, b: roadside cabinet in operation.
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Figure 2: Scheme of the mass conservation theory applied to the employment of fixed metering device.
Nomenclature Qs Qr Ql
𝑄𝑄𝑄𝑄 = 𝑄𝑄𝑄𝑄 + 𝑄𝑄𝑄𝑄
(1)
supply mass flow return mass flow mass flow of the leak
4.1. Background theory The idea behind the construction of these tools is based on the theory of mass conservation; the same amount of water should enter and go out of the examined area, as shown in Figure 2 and Equation (1). In order to apply this theory, the chosen area has to be connected to the rest of the network by a single branch (both supply and return), by opening and closing selected valves, this way it can behave as a branch and can be monitored easily. The difference between supply and return flow is the amount of leak (Ql). It must be noted that analyses have to be based on mass flow; hence, it is possible to compare supply and return data, while volumetric flow rate depends on temperature and then it cannot be examined together. 4.2. Laboratory tests By design, any size of flow metering device has a nominal flow and a related measurement error. To verify these data, flow meters undergone laboratory tests to monitor and evaluate the range of error and their behavior; these tests were performed in an ACS laboratory. A test bed was built and it consisted in a series of three meters, as shown in Figure 3: a device to test, a tap (behaving as a loss in the system), another device to test and a calibrated device. This test bed has run for few days monitoring two scenarios: in the first scenario, the tap was closed (no water loss), while in the second scenario the tap was open (system with water loss). Tests have confirmed the error ranges reported in the instruction manuals and, in all the cases, measured values were lower than the design ones; errors obtained after laboratory analyses were lower than 0,5% in both scenarios, thus they were classified as negligible.
Figure 3: Scheme representing the test bed.
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Nomenclature Flow metering device to test Calibrated flow metering device Pipe Tap simulating water loss
4.3. Cabinet features Flow metering devices can operate continuously only during warm seasons (mid-April – mid-October) when flow is lower and supply temperature is more constant, in winter they can be used for instantaneous measurements. They operate as bypasses and, since most of them are above - ground installations, it was preferred to create size-limited tools, and hence, all the designed instrumentation was dimensioned according to summer flows to limit measurement error of metering devices and costs. The investment is in the range between 15.000 and 25.000 €. A supply pipe connects instruments inside the cabinet to the main network, allowing water to pass through the metering device before running again in the pipe that goes to clients; for the return, a pipe allows water flow to be measured inside the cabinet and then it flows back to the main pipeline, as shown in Figure 4.
Figure 4: Hydraulic scheme of a typical roadside cabinet Nomenclature Return line Supply line Valve (open) Valve (closed) Flow metering device Cabinet area Direction of flow, red supply flow, blue return flow
Flow sensors measure volumetric flow rate in m3/h and temperature in Celsius degree, this way the calculator in the heat meter can compute mass flow and energy, as stated in paragraph 4. Water flow measurements are recorded continually during warm seasons (i.e. around for 5 months), readings are saved automatically and they can be downloaded easily; normally operators download data once per month. Records can be
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Figure 5: Hourly recorded data
Figure 6: Daily recorded data
saved both on hourly (instantaneous) and daily (sum of the 24 hours) basis. It can be observed, in Figure 5, that instantaneous readings are strongly influenced by the sensitivity of measurement devices, temperature and ordinary hourly flow fluctuations. As visible, hourly measurements are characterized by important variations, although it is possible to easily identify the daily trend (plotted in orange); Figure 6 represents data on a daily basis and, differently from the previous figure, this approach provides more constant data, able to describe the trend effectively; thus, daily basis was chosen. It must be noted that, most of the times, to activate these devices it is necessary to create a temporary working site, but differently from the previous methods, here it is necessary only to activate and deactivate the metering systems, thus, twice a year and for a shorter period, without service interruptions for customers. Furthermore, for previous
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methods, the work of three operators, at least, was necessary for each test, while fixed metering devices require at least three operators twice a year, during activation and deactivation phases, and another operator once per month to download data. 5. Monitoring results After the installation of the first flow metering devices, it was possible to monitor the trend of water flowing in the areas under test; the following paragraphs show the results obtained for the “Oltremella Sud” area since 2014 and for the “Sereno” area since 2016. Data registered by roadside cabinets were validated by measurements recorded by portable meter device and it was observed that fixed metering devices were able to identify water losses lower than 5 t/d. 5.1. Sereno This flow-metering device was activated for the first time in June 2014; it monitors 105 km of pipe (around 8% of the entire network). The following graph (Figure 7) represents the trend from June 2014 to October 2017; it is visible that the trend is recorded only during warm seasons (mid-April – mid-October), the analysis should focus on daily difference of mass flow, which is related to the other represented parameters: supply and return temperatures and supply average flow. The daily difference of mass flow is calculated as the difference between supply mass in tons and return mass in tons that are measured by flow meters and divided by the maximum value of water loss recorded in the examined period. During measurements recorded in 2014, it is possible to observe a peak around mid-August, as reported in Figure 7, which represents a leak that was fixed quite quickly, approximately in one week, because of its magnitude. Similarly, as represented in Figure 8, the trend of the following year defines a leak, from April to mid-June; in this case, the peak is not as high as it was in the previous year but the repair of the leak is clearly visible, the mass difference goes from 67% the 15th of June to 20% the 19th of June. Moreover, it can be observed that, in the first period, the daily difference of mass flow is above 60% of the maximum value of the year, while after mid-June it is halved, around 30%.
Figure 7: Graph representing measurements of daily difference mass flow, average supply flow, supply and return temperature in the “Sereno” area, June 2014 – October 2017.
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Figure 8: Graph representing measurements of daily difference mass flow, average supply flow, supply and return temperature in the “Sereno” area, April – October 2015.
Figure 9: Graph representing measurements of daily difference mass flow, average supply flow, supply and return temperature in the “Oltremella Sud” area, June – October 2017.
5.2. Oltremella Sud This flow-metering device monitors around 100 km of pipe (around 7% of the Brescia DH network) and it has been operating since 2016. The graphs represented in Figure 9 show the trend of the daily difference of mass flow, the supply average flow, the supply and return temperature during the warm season 2017. This device has been operating only for two warm seasons, furthermore, it must be noted that data describing daily difference of mass flow in 2016 are not reliable, in fact, that year there were problems during some fixing operations performed on the network. Data describing 2017 identifies a water loss in the second part of the season, from end of
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August to October when values are higher than 80%. It can be observed that the second part of the period is characterized also by two minimums; regarding these two values, it is important to specify that they correspond to devices switching off during maintenance operations. 6. Discussion and following steps The employment of fixed flow-metering devices have improved leak detection process; in fact, these tools allow measurements (about 5 months, continuously) of the quantities of the supply and return water in selected areas; the “Sereno” and “Oltremella Sud” flow meters monitor about 15% of the Brescia DH network. As stated previously, these tools can work continuously only during warm seasons (mid-April – mid-October) when supply temperature is more constant and the amount of supply and return flow are lower than in winter periods. At the moment, these measurements are not readable remotely, they need to be downloaded on site and they can provide the sum of total amount of water lost in an examined area; in fact, the value of mass difference is related to the entire analyzed area. It must be added that flow-metering tools can restrict the area to inspect providing data almost immediately, if necessary and moreover by creating subsections, it is possible to identify the area with higher water loss. Before their installation, it was not possible to individuate the area without operating on site on valves and this approach did not even allow having an immediate feedback regarding the presence of a leak. The measured data do not require processing nor particular calculations, thus, their analyses can be done quite quickly and readings can be downloaded every time it is necessary. As shown in the previous graphs (Figure 7, 8 and 9) the trend of the daily difference of mass flow is an important parameter that can give information regarding both water losses and operations on the network, as stated in the description of the “Sereno” and “Oltremella Sud” areas. The available data could give also information regarding the quantity of energy supplied and lost (estimated by calculations from water loss) in the examined area, as plotted in Figure 10. At the beginning of May 2018, ACS activated another flow-metering cabinet “P.le Cremona”; the area monitored by this new device is Brescia downtown, about 25 km of pipes. This zone represents only about 1% of Brescia DH network, but this is one of the eldest area, characterized by a very high rate of water loss thus, having the possibility to monitor it continuously would improve maintenance efforts. In the last months, some experiments on data radio transmissions employing LoRaWAN protocol have being tested. ACS is finalizing the design of another device in “Chiesanuova” area, which should be tested by the end of summer 2018; this new device should monitor about 54 km of the network. At that point, the total inspected area would be slightly higher than 20% of the pipeline of the city network, as summarized in Table 1, giving an important improvement in the yearly maintenance strategy. 7. Conclusions ACS performs several activities, one of the main is leak detection; this process is fundamental to ensure the correct operation of the system and a longer lifespan of the network. Leak detection requires an effective analysis on the amount of water lost, thus ACS has been developing several procedures to provide this information. These experimentations aimed at the identification of a method able to provide, continuously, the amount of water lost in an area, minimizing the operations on the network and avoiding the interruption of the service to customers. Table 1. Area description. Data in brackets refer to the entire network length and the total number of customers Daily supply Number of Nominal flow Length (pipes) average flow Name of the area customers [n] meter [m³/h] [km] (summer) [m³/h]
Year of activation
Sereno
101,72
35
1.506
40
2014
Oltremella Sud
105,07
47
1.459
60
2016
P.le Cremona
24,32
23
534
25
2018
Chiesanuova
54,54
45
548
60
Expected: end of summer 2018
Total
285,65 (21,3%)
4.047 (19,2%)
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Figure 10: Graph representing the energy loss calculated from water loss in the “Oltremella Sud” area, June – October 2017
Pressure tests were initially employed, they can identify the presence of water loss in the examined area, but they cannot provide the necessary information to classify a leak, such as number of losses, location and magnitude; thus, they are used as preliminary tests. Later, a method based on the application of the orifice flow equation was tested successfully; it was observed that these practices could be performed only for short periods, about half an hour, requiring several operations on site and data processing. Then, portable flow metering devices were applied, this method allowed having instantaneous and direct measurements of water loss, but it was possible only for short periods. All the methods described above could be performed only for less than one hour, requiring the creation of a working site, often, the interruption of service for customers and processing of the measured data; thus, a new method requiring less operational activities and continuous measurement was implemented. Fixed metering devices are able to monitor continuously, during warm season (from mid-April to mid-October), the amount of water loss (allowing then the calculations of energy loss) in the area where the roadside cabinet is installed. The theory behind this application is based on mass conservation: the same amount of water entering the area has to flow out, if these quantities differ, there is a leakage. Fixed metering devices consist of roadside cabinets equipped with valves, air vents and flow meters that calculate energy and measure flow, power and temperature; readings are saved automatically and they can be downloaded easily, normally operators do it once per month. In 2016, two flow-metering devices were in operation, monitoring two areas of the Brescia DH network, in May 2018 a new device was activated and another one is under construction. At the moment, about 17% of the city DH network is monitored continuously during warm season, providing necessary information for maintenance programs. In fact, the installation of these devices have improved leak detection processes, allowing continuous monitoring of the quantities of supply and return water flow during warm season; they can provide information immediately, when necessary, regarding the presence of one or more leaks, without requiring processing nor particular calculations. The next step is testing and implementing radio data transmission to allow remote readings. ACS aims at further implementing the employment of fixed metering devices to ensure effective operation of the DH systems it manages, both the old one, as in Brescia, and the more recent, as in Milan. References [1] Frederiksen Svend, Werner Sven, “District heating and cooling”, Studentlitteratur, (2013), AB, Lund. [2] Astori P., “Dispense del corso di Impianti aerospaziali”, Politecnico di Milano, Milano, (2005), pp. 3.6 – 3.9. [3] Filippini Ettore, and Ongari Marco. “Method for the quantification of a leakage in a district heating network”, (2014), The 14th International Symposium on District Heating and Cooling.