Heat exchange substation of a district heating system

Abstract

The present invention relates to a heat exchange substation (50) of an energy distribution system comprising: a heat exchanger (51) with thermal inertia comprising a primary side (37a) connected to a primary supply line (36) and to a primary return line (37) and a secondary side (37b), opposite the first primary side (37a), the secondary side (37b) being connected to a secondary supply line (56) and to a secondary return line (57) of a secondary heating circuit (68), the secondary supply and return lines (56, 57) being in communication with one or more heating units (18), wherein the heat exchanger (51) comprises a tank (67) within which a first shell- and-tube circuit (81) is arranged connected at the inlet to the primary supply line (36) and at the outlet to the primary return line (37) and a second shell-and-tube circuit (82) connected at the inlet to the secondary return line (57) and at the outlet to the secondary supply line (56), and the tank (67) contains a phase change material (71), the first shell-and-tube circuit (81) and the second shell-and- tube circuit (82) being in contact with the phase change material (71).

Description

[0001] Heat exchange substation of a district heating system

[0002] DESCRIPTION

[0003] The present invention concerns a heat exchange substation of an energy distribution system, in particular of a district heating system. A district heating system is a centralised energy distribution system that uses a heat transfer fluid, such as hot water or steam, typically superheated, to distribute heat to a community of consumers. The district heating system comprises a heat production plant, i.e. a heat source generally arranged at a distance from the consumers. The heat source can be a thermal power plant or a renewable energy source such as, for example, solar thermal or low-temperature geothermal energy, or the use of heat pumps, or even a multi-fuel cogeneration plant.

[0004] The heat, which comes from the heat generation plant, is conveyed to consumers, such as buildings or industries, through a distribution network. For example, hot water or steam is pumped at high pressure to a network of thermally insulated pipes, typically buried underground. The distribution network reaches one or more heat exchange substations that are responsible for transferring heat to the consumers. The distribution network from the heat generation plant to one or more heat exchange substations is referred to hereafter as primary distribution network or primary circuit. The distribution network from the heat exchange substation to the interior of the building(s) served is referred to hereafter as secondary distribution network or secondary circuit.

[0005] The heat exchange substation comprises at least one heat exchanger to transfer heat from the fluid received from the primary distribution network to the secondary distribution network.

[0006] Figure 1 schematically illustrates a heat exchange substation 10 of a district heating network, of a known type, which is configured to supply energy for both heating and domestic hot water to the consumers of a building 12.

[0007] The heat exchange substation 10 comprises a first heat exchanger 11, e.g. a plate heat exchanger, in which the carrier fluid is water. The first heat exchanger 11 is arranged between the primary circuit and a first secondary circuit or secondary heating circuit 28. The heat exchanger is connected on one side, referred to below as the primary side 37a, to a primary supply line 36 in communication with the district heating system (not shown). On a side opposite the primary side 37a, referred to below as secondary side 37b, the first heat exchanger 11 is connected to a first secondary supply line 13 in communication with a plurality of heating units 18 in the building such as heaters or radiators.

[0008] The first secondary circuit 28 is a closed circuit comprising a first secondary return line 15 connecting the heating units 18 with the first heat exchanger 11, e.g. radiators, radiant floor or other heat distribution devices.

[0009] A second primary return line 37, primary side 37a of the first heat exchanger 11, transports the lower-temperature fluid back to the primary distribution network, specifically to the heat production plant, where it is reheated to be sent back to the primary distribution network. The direction of the primary and secondary supply lines 36, 13 is indicated by an arrow 38a and the direction of the primary and secondary return lines 37, 15 is indicated by an arrow 38b.

[0010] In ways known per se, a circulation pump 14 configured to circulate water from the first heat exchanger 11 is arranged along the first secondary supply line 13.

[0011] The heat exchange substation 10 comprises a second heat exchanger 12 for domestic hot water supply. The second heat exchanger 12 is arranged between the primary circuit and a second secondary circuit 29 or hot water secondary circuit. The heat exchanger 12 is connected on the primary side 37a to a second primary supply line 21 in communication with the district heating system (not shown). On the secondary side 37b, the second heat exchanger 12 is connected to a second secondary supply line 26 in communication with a plurality of hot water distribution devices in the building 30. The second secondary circuit 29 comprises a second secondary return line 27 that connects the hot water distribution devices with the second heat exchanger 12. A second primary return line 25, primary side 37a of the second heat exchanger 12, transports the cooled fluid back to the primary distribution network, in particular to the heat production plant, where it is reheated to be sent back to the second secondary distribution network 29.

[0012] On the primary side 37a, a first and second valve 17, 20 is installed to regulate the mass flow rate and thus the temperature of the heat transfer fluid in each of the first and second secondary circuit 28, 29. The flow rate of each valve is regulated according to the temperature detected by a respective temperature probe 41, 42 positioned on the respective secondary circuit 28, 29.

[0013] The second domestic hot water circuit 29 may provide for the presence of a thermal storage for storing domestic hot water in order to guarantee continuity of service to the consumer, implemented by means of a storage tank 24 which is positioned downstream of the second heat exchanger 12 with respect to the second primary supply line 21. The storage tank 24, which is typically equipped with water heating elements, is configured to receive hot water from the second primary supply line 21 and cold water from the waterworks shown in the figure with reference number 43. The storage tank 24 heats water from the waterworks. In this way, the heat transfer fluid and the water from the waterworks do not come into direct contact.

[0014] Downstream of the storage tank 24, with respect to the secondary supply line 21, the hot water is cooled slightly with water from the waterworks by means of a mixing valve 34, e.g. a motorised three- way mixing valve, which is configured to regulate the temperature according to the temperature detected by a temperature probe 44, downstream of the mixing valve 34.

[0015] In order to reduce the combustion of fossil materials, the supply of primary fluid to buildings is typically managed in such a way as to interrupt or significantly reduce the supply of primary fluid during the times of day when consumption is lowest, i.e. typically at night. The Applicant has considered that the plant configuration for the supply of energy for heating described with reference to Figure 1 does not always allow for adequate flexibility on the management of the daily variability of consumption by consumers, with particular reference to the management of consumption peaks during peak hours.

[0016] The Applicant noted that the provision of a thermal storage in a substation connected to the district heating network would allow heat to be stored during periods of low demand.

[0017] In particular, the Applicant realised that the provision of an integrated thermal storage in the heat exchanger between the primary circuit and the secondary circuit of a district heating network capable of both transferring thermal energy and of storing and releasing a significant amount of heat at different times of the day would allow for greater flexibility in the use of the heat exchange substation, which would be reflected in a better management of the district heating network.

[0018] For example, the heat transferred from the primary distribution network to the secondary heating network can be stored and released to the user at a later time in the form of thermal energy at a relatively high temperature, at least for a certain period of time, without drawing from or sparingly drawing energy from the primary district heating network.

[0019] In particular, the Applicant realised that the provision of a thermal inertia material inside the heat exchanger would allow for greater adaptability in managing the daily variability of consumption by consumers.

[0020] The present invention relates to a heat exchange substation of an energy distribution system, in particular of a district heating system, comprising a thermal inertia heat exchanger comprising: a primary side connected to a primary supply line and to a primary return line, wherein the primary supply line and primary return line are in communication with a district heating system configured to deliver a primary fluid, and a secondary side, opposite the first primary side, the secondary side being connected to a secondary supply line and to a secondary return line of a secondary heating circuit, the secondary supply and return lines being in communication with one or more heating units, the secondary supply line being configured to deliver a secondary fluid to the one or more heating units.

[0021] Preferably, the heat exchanger with thermal inertia comprises a tank within which a first shell-and-tube circuit is arranged, connected at the inlet to the primary supply line and at the outlet to the primary return line and a second shell-and-tube circuit connected at the inlet to the secondary return line and at the outlet to the secondary supply line.

[0022] Preferably, the tank contains a phase change material. The first shell-and-tube circuit and the second shell-and-tube circuit are in contact with the phase change material. Specifically, the first and second shell-and-tube circuits are immersed in the phase change material.

[0023] Preferably, the phase change material has a melting temperature between 45°C and 80°C.

[0024] In an embodiment, the phase change material has a heat of fusion comprised between 240 and 300 J / g.

[0025] In embodiments, the phase change material is selected from the group consisting of a non-paraffinic organic compound, a paraffinic compound and an inorganic hydrated salt.

[0026] Preferably, the tank is a thermally insulated and hydraulically sealed container. In particular, the thermal inertia heat exchanger (also referred to in the following as "heat exchanger") communicates with the outside world via the inlets and outlets on the primary and secondary side.

[0027] Preferably, the primary side of the heat exchanger is connected to the primary supply line at a primary side inlet and to the primary return line at a primary side outlet.

[0028] Preferably, the secondary side of the heat exchanger is connected to the secondary supply line at a secondary side outlet and to the secondary return line at a secondary side inlet.

[0029] Preferably, the substation comprises a first variable mass rate valve positioned on the primary supply line.

[0030] In an embodiment, the first variable mass rate valve has a fluid passage section of variable area. Preferably, the first variable mass rate valve is operatively connected to a first temperature probe arranged on the secondary supply line through a control line. The first variable mass rate valve is configured to regulate the flow based on a secondary fluid temperature value set by the first temperature probe.

[0031] Preferably, a first circulation pump is arranged on the secondary supply line. The first circulation pump is configured to deliver the secondary fluid from the heat exchanger with thermal inertia to the one or more heating units.

[0032] Preferably, a second circulation pump is arranged on a first connection line which joins the secondary supply line to the secondary return line, the first connection line being arranged upstream of the first circulation pump with reference to the flow direction in the secondary supply line. The second circulation pump is configured to circulate the secondary fluid from the secondary supply line to the secondary return line.

[0033] In preferred embodiments, the heat exchange substation is configured to operate in a first operational state and a second operational state.

[0034] Preferably, when the substation is in a first operational state, the heat exchanger with thermal inertia is configured to receive primary fluid from the primary supply line, the first circulation pump is operational and is configured to deliver secondary fluid to one or more heating units and the second circulation pump is non- operational.

[0035] Preferably, when the substation is in a second operational state, the heat exchanger with thermal inertia is configured to receive the primary fluid from the primary supply line, the first circulation pump is non-operational and the second circulation pump is operational, so as to define a loop sub-circuit of the secondary heating circuit. The loop sub-circuit comprises or is defined by a portion of the secondary supply line extending from the secondary side outlet to the first connection line, the first connection line and by a portion of the first secondary return line extending from the secondary side inlet to the first connection line. Preferably, the first variable mass rate valve has a fluid passage section with area from 0% to 100%. In the first operational state, the first variable mass rate valve has a passage section area from 70% to 100% and in the second operational state the first variable mass rate valve has a passage section area from 1% to 35%.

[0036] Preferably, the substation is configured to operate in a third operational state subsequent to the second operational state, wherein the first variable mass rate valve has substantially zero mass rate, the first circulation pump is operational and the second circulation pump is non-operational.

[0037] In preferred embodiments, the first shell-and-tube circuit of the heat exchanger comprises a plurality of first tubes aligned with each other with respect to a tube extension direction. The plurality of first tubes is in fluid communication (i.e. in hydraulic communication) with the primary supply line and with the primary return line of the primary circuit. Preferably, the second shell-and-tube circuit comprises a plurality of second tubes, the second tubes being aligned one to another in a second tube extension direction, the plurality of second tubes being in fluid communication, at the inlet, with the secondary return line and, at the outlet, with the secondary supply line.

[0038] Preferably, the first tubes of the plurality of first tubes are arranged in a first plurality of rows of first tubes, the rows being spaced apart and parallel to each other.

[0039] Preferably, the second tubes of the plurality of second tubes are arranged in a second plurality of rows of second tubes spaced apart and parallel to each other.

[0040] Preferably, each row of first tubes of the plurality of rows of first tubes and each row of second tubes of the plurality of rows of second tubes are parallel to a longitudinal axis and transverse, for example substantially perpendicular, to the first extension direction of the first tubes.

[0041] Preferably, the rows of second tubes are arranged alternately with the rows of first tubes both along a transverse direction with respect to the longitudinal axis and to the first and second extension directions of the first and second tubes. Preferably, the plurality of first tubes is in fluid communication with a first primary manifold connected to the primary supply line, and with a second primary manifold connected to the primary return line. Preferably, the first tube extension direction is perpendicular to the longitudinal axis.

[0042] Preferably, the second tube extension direction is perpendicular to the longitudinal axis.

[0043] Preferably, the first tube extension direction and the second tube extension direction are substantially parallel to each other.

[0044] In particular and preferably, the first tubes of each row of first tubes of the plurality of rows of first tubes are fluidly connected to each other. Each row has a respective inlet in communication with the first primary manifold and a respective outlet in communication with the second primary manifold.

[0045] In an embodiment, the first inlet manifold comprises a plurality of inlet nozzles equal in number to the rows of first tubes and the first outlet manifold comprises a plurality of outlet nozzles equal in number to the rows of first tubes.

[0046] Preferably, the plurality of second tubes is in fluid communication with a first secondary manifold connected to the secondary return line and with a second secondary manifold connected to the secondary supply line.

[0047] In an embodiment, the second inlet manifold and the second outlet manifold are configured so as to divide the second plurality of parallel rows of second tubes into a plurality of sections. The sections are defined in a transverse direction, e.g. perpendicular with respect to the longitudinal axis.

[0048] Preferably, the second inlet manifold comprises a plurality of inlet distributors, each inlet distributor duct comprising a plurality of inlet nozzles in a number corresponding to the second plurality of parallel rows of second tubes.

[0049] The second outlet manifold comprises a plurality of outlet distributor ducts corresponding to the number of inlet conductor ducts. Each outlet distributor duct comprises a plurality of outlet nozzles in a number corresponding to the plurality of parallel rows of second tubes.

[0050] Further characteristics of the present invention will become clearer from the following detailed description of some preferred embodiments thereof, made with reference to the appended drawings. In these drawings:

[0051] - Figure 1 schematically illustrates a heat exchange substation of a known district heating network.

[0052] - Figure 2 schematically illustrates a heat exchange substation of a district heating network, in accordance with an embodiment of the present invention.

[0053] - Figure 2A shows a portion of the substation in Figure 2 in more detail.

[0054] - Figure 3 is a partially cross-sectional view schematically illustrating an embodiment of the thermal inertia heat exchanger in accordance with the present invention.

[0055] The representations in the accompanying figures do not necessarily have to be understood in scale and do not necessarily respect the proportions between the various parts. In the figures, the same or similar elements of different embodiments will be indicated by the same reference numerals.

[0056] The same elements have been indicated with the same reference numbers in the different drawings. For the sake of clarity, only those elements and steps that are useful for understanding the present invention have been shown in the drawings and will be described.

[0057] Figure 2 schematically illustrates a heat exchange substation 50 of a district heating network, according to an embodiment of the present invention.

[0058] Reference numbers equal to those used for the description in Figure 1 refer to the same elements or elements with similar functionality. In particular, the elements of the second secondary circuit 29 for domestic hot water correspond to the elements described with reference to Figure 1.

[0059] It remains understood that, in the present invention, the provision of a second secondary circuit 29 for domestic hot water is optional, i.e. it may not be part of the heat exchange substation 50. For example, domestic hot water can be delivered to individual consumers at the level of individual homes by means of a boiler, or consumers can receive hot water from a storage tank that includes a heat exchanger of a known type.

[0060] The heat exchange substation 50 of Figure 2 comprises a heat exchanger 51 with thermal inertia comprising a primary side 37a connected to a first primary supply line 36 and to a first primary return line 37 and a secondary side 37b connected to a first secondary supply line 56 and to a secondary return line 57 of a secondary heating circuit 68.

[0061] As illustrated in more detail in Figure 2A, the heat exchanger 51 comprises a primary side inlet 61 connected to the first primary supply line 36 and a primary side outlet 62 connected to the first primary return line 37.

[0062] The heat exchanger 51 further comprises a secondary side outlet 63 connected to the first secondary supply line 56 and a secondary side inlet 64 connected to the secondary return line 57.

[0063] The heat exchanger 51 comprises a tank 67 that communicates with the outside via the primary and secondary side inlets and outlets.

[0064] Preferably, the tank 67 is a thermally insulated container and is hydraulically sealed so that it only communicates with the outside via the supply and return lines of the primary and secondary circuits. Two shell-and-tube circuits are arranged within the tank 67: a first shell-and-tube circuit 81 which is connected at the inlet with the primary side inlet 61 and at the outlet with the primary side outlet 62, and a second shell-and-tube circuit 82 connected at the inlet with the secondary side inlet 64 and at the outlet with the secondary side outlet 63 (shown in Figure 3).

[0065] The first shell-and-tube circuit 81 and the second shell-and-tube circuit 82 are circuits independent from one another.

[0066] The first shell-and-tube circuit 81 is configured to receive a primary fluid from the primary supply line 36, e.g. superheated water at 130°C or hot water at 80-90°.

[0067] The second shell-and-tube circuit 82 uses technical water as the secondary fluid for heat transfer. The tank 67 contains a phase change material 71 inside it. The first shell-and-tube circuit 81 and the second shell-and-tube circuit 82 are in contact with and immersed in the phase change material 71. As is generally known, a phase change material (PCM) is capable of absorbing a significant amount of heat by using the thermal energy associated with the transition from one physical state to a different physical state. This thermal energy is then released in the reverse state transition.

[0068] In particular, the phase change material 71 uses the latent heat of fusion to absorb energy, storing thermal energy associated with the physical change of state from the solid to the liquid phase. The stored thermal energy is then released in the transition from the liquid phase to the solid phase.

[0069] The amount of heat stored at constant temperature is typically within a range of + / -2°C relative to the melting point of the material. Preferably, the phase change material 71 has a melting temperature between 45°C and 80°C.

[0070] In embodiments, the phase change material has a heat of fusion comprised between 240 and 300 J / g.

[0071] In an example, the phase change material 71 has a peak melting temperature of about 71°C and a heat of fusion of about 290 J / g.

[0072] The energy stored within the heat exchanger 51 depends not only on the heat of fusion of the phase change material, but also on the amount of phase change material contained within the tank 67. The quantity of material can be selected according to the number of consumers, and thus to the thermal power to be delivered. In an example, the material and its quantity can be selected so as to achieve a nominal heat storage within the heat exchanger of 20 to 60 kWh.

[0073] In an example, the thermal discharge power released, which typically depends also on the design of the exchanger as well as the characteristics of the phase change material, can be comprised from 100 to 200 kW .

[0074] In some examples, the phase change material 71 may be a non- paraffinic organic compound, a paraffinic compound or an inorganic hydrated salt.

[0075] According to a preferred embodiment, the phase change material 71 is an organic compound, preferably one of an ecological nature. In particular, the organic material 71 is a non-paraffinic organic material.

[0076] In other examples, the phase change material is a paraffinic compound and an inorganic hydrated salt.

[0077] The heat exchanger 51 with thermal inertia, whose shell-and-tube circuits 81, 82 are immersed in the phase change material 71, is configured to function both as a heat exchanger, since it directly transfers thermal power from the primary grid to the consumers, and as a thermal storage device, since it stores or transfers heat to the consumers.

[0078] As described in more detail below, in some embodiments, heat transfer can also be implemented with reduced or no inflow of the primary fluid from the district heating network at least for a certain period of time.

[0079] With reference to the embodiment in Figure 3, the first shell-and- tube circuit 81 comprises a plurality of first tubes 83, shown in a cross-section. The first tubes 83 are aligned longitudinally to each other, i.e. they extend parallel to each other along a first tube extension direction (not shown), in a direction perpendicular to the plane of the sheet in Figure 3 (YZ).

[0080] The first tubes 83 are arranged in a first plurality of parallel rows 81a arranged along a longitudinal axis Z. The parallel rows 81a of tubes 83 are in a relationship spaced apart from each other along a transverse direction Y relative to the longitudinal axis Z.

[0081] The first tubes 83 of each row 81a are fluidly connected to each other, e.g. by respective U-shaped metal connecting tubes not shown and known per se. These connection tubes may be external or internal to the tank 67. In an embodiment, each connecting tube connects two proximal neighbouring tubes 83 of a respective first row of tubes 81a.

[0082] The second shell-and-tube circuit 82 comprises a plurality of second tubes 84. The second tubes 84, which are shown in a cross-section, are aligned longitudinally to each other, i.e. they extend parallel to each other along a second tube extension direction (not shown), in a direction perpendicular X to the plane of the sheet YZ in Figure 3. The second tubes 84 are arranged in a second plurality of parallel rows 82a arranged along the longitudinal axis Z. The parallel rows of tubes 82a are in a relationship spaced apart from each other along a transverse direction Y relative to the longitudinal axis Z.

[0083] The second tubes 84 of each row are fluidly connected to each other, e.g. by means of U-shaped metal connecting tubes (not shown). These connection tubes may be external or internal to the tank 67. In an embodiment, each connecting tube connects two proximal neighbouring tubes 84 of a respective row of second tubes 82a. In an embodiment, the first tubes 83 and second tubes 84 are straight and extend parallel in a respective first and second extension direction perpendicular to the plane YZ. The first and second extension directions are parallel to an axis X perpendicular to the plane YZ.

[0084] The rows 81a of first tubes 83 and rows 82a of second tubes 84 are arranged in mutually parallel directions.

[0085] The first plurality of parallel rows 81a of first tubes 83 and the second plurality of parallel rows 82a of first tubes 83 are arranged alternately along the transverse direction Y. In particular, between two parallel rows 81a of the first proximal neighbouring shell-and- tube circuit 81 with respect to the direction Y, a row of second tubes 84 is arranged.

[0086] The first shell-and-tube circuit 81 is connected to a first inlet manifold 85, which is fluidly connected to the primary supply line 36 (via the primary side inlet 61). The first shell-and-tube circuit 81 is also connected to a first outlet manifold 86, which is fluidly connected to the primary return line 37 (via the primary side outlet 62).

[0087] In the example in Figure 3, the first plurality of parallel rows 81a of the first tubes 83 extend from the first inlet manifold 85 to the first outlet manifold 86. The first inlet manifold 85 comprises a plurality of inlet nozzles 85a equal in number to the rows 81a of first tubes, and the first outlet manifold 86 comprises a plurality of outlet nozzles 86a, again equal in number to the rows 81a of first tubes.

[0088] In particular, each nozzle 85a of the first primary manifold 85 is in communication with the inlet of each row 81a of the plurality of rows of first tubes 84 and each corresponding nozzle 86a of the second primary manifold 86 is in communication with the outlet of each row 81a of the plurality of rows of first tubes 84.

[0089] Each nozzle 85a of the first primary manifold 85 is in communication with the inlet of each row 81a of the plurality of rows of first tubes, and each corresponding nozzle 86a of the second primary manifold is in communication with the outlet of each row of the plurality of rows of first tubes.

[0090] In an embodiment, the plurality of parallel rows 81a of the first tubes extend approximately from a first end of the tank 95a to an opposite second end 95b with respect to the longitudinal axis Z.

[0091] In an embodiment, the plurality of parallel rows 81a of second tubes extend approximately from the first end of the tank 95a to the opposite second end 95b.

[0092] In an embodiment, the first plurality of tubes 83 are made of steel or copper.

[0093] The second shell-and-tube circuit 82 is connected to a second inlet manifold 87, which is fluidly connected to the secondary return line 57 (via the secondary side inlet 64) and to a second outlet manifold 88 fluidly connected to the secondary supply line 56 (via the secondary side outlet 63).

[0094] In the embodiment of figure 3, the second inlet manifold 87 and the second outlet manifold 88 are configured to divide the second plurality of parallel rows 82a of the second tubes 84 into a plurality of sections. The sections are defined in a transverse direction, e.g. perpendicular (Y), with respect to a direction parallel to the longitudinal axis Z.

[0095] In an embodiment, the second tubes 84 are made of copper.

[0096] The second inlet manifold 87 comprises a plurality of inlet distributor ducts 91a-91c, each comprising a plurality of inlet nozzles (not visible in the figure) in a number corresponding to the second plurality of parallel rows 82a of second tubes 84.

[0097] The second outlet manifold 88 comprises a plurality of outlet distributor conduits 92a-92c, each outlet distributor conduit comprising a plurality of outlet nozzles in a number corresponding to the plurality of parallel rows 82a of second tubes 84.

[0098] In the non-limiting example, the plurality of inlet distributor ducts comprises a first, second and third inlet duct 91a, 91b, 91c and the plurality of outlet distributor ducts comprises a first, second and third inlet duct 92a, 92b, 92c.

[0099] The first and second distributor ducts define sections 93, 94, 95 of the second plurality of parallel rows 82a of the second tubes 84. Specifically, a first section 93 extends from the first inlet distributor duct 91a to the first outlet distributor duct 92a; a second section 94 extends from the second inlet distributor duct 91b to the second outlet distributor duct 92b, and a third section 95 extends from the third inlet distributor duct 91c to the third outlet distributor duct 92c. Naturally, the number of sections of the second shell-and-tube circuit 82 can be different from that shown in Figure 3, e.g. the number of sections of the second shell-and-tube circuit is 2 to 4.

[0100] In embodiments, the sectioning of the second shell-and-tube circuit 82 distributes the flow rate of the secondary circuit 68 making the temperature inside the tank 67 of the heat exchanger 51 more uniform.

[0101] In a further embodiment not shown in the figures, there is no division of the second tube bundle into sections.

[0102] In this description and claims, "parallel" when referring to shell-and- tube circuits means that the tubes or rows of tubes are substantially parallel to each other within an angular range of 0° to 20°.

[0103] In embodiments, the first shell-and-tube circuit 81 and the second shell-and-tube circuit 82 are in contact with each other so as to increase the heat transfer by conduction between the two circuits.

[0104] In an example, the heat exchanger 51 is of the finned pack type. In particular, the tubes 83, 84 of the two shell-and-tube circuits are equipped with a plurality of fins of metal material (not shown in the figures) extending outwards from the surface of the tubes. In a further embodiment, the rows of tubes 83, 84 alternating with each other are joined by aluminium sheets in order to increase the heat exchange surface.

[0105] The number of tubes of the first and second shell-and-tube circuit 81, 82 illustrated in Figure 3 is purely illustrative and depends on several factors, such as, for example, the size of the heat exchanger 51 or the configuration of the tube bundles.

[0106] Referring again to Figures 2 and 2A, a first variable mass rate valve 59 is installed on the primary side 37a to regulate the mass flow rate and thus, by virtue of the heat exchange within the heat exchanger 51, to regulate the temperature of the heat transfer fluid of the secondary heating circuit 68.

[0107] The flow rate of the first valve 59 can be adjusted by setting a temperature in a first temperature probe 74, e.g. an immersion probe, which is located on the secondary circuit 68, on the first secondary supply line 56. In a known way, the first variable mass rate valve 59 receives signals detected by the first temperature probe 74 via a control line 58. In the example in the figures, the first variable mass rate valve 59 is a two-way valve.

[0108] The secondary circuit 68 comprises a first consumer circulation pump 54 configured to push water from the heat exchanger 51 to the heating units 18 (e.g. heaters or radiators). The first consumer circulation pump 54 is located on the first secondary supply line 56. The secondary circuit 68 comprises a second circulation pump 52 arranged on a first connection line 69 which places the first secondary supply line 56 in fluid communication with the secondary return line 57. The second circulation pump 52 is arranged upstream of the first circulation pump 54 with reference to the flow direction in the first secondary supply line 56, indicated by Fl in Figure 2.

[0109] As described in more detail below, the second circulation pump 52 is configured to convey the secondary fluid from the first secondary supply line to the first secondary return line 57.

[0110] A second connection line 73 places the first secondary supply line 56 in fluid communication with the secondary return line 57. The second connection line 73 is arranged downstream of the first connection line 69 (and thus downstream of the second circulation pump 52), with reference to the flow direction Fl of the first secondary supply line 56.

[0111] A second variable mass rate valve 53 is arranged on the secondary return line 57 at the second connection line 73. The second valve 53 is in particular a mixing valve configured to keep the temperature of the secondary supply fluid at a temperature consistent with a set target value.

[0112] In an example, the second variable mass rate valve 53 is a three- way valve connected to the secondary return line 57 and the second connection line 73. In the embodiment of the figure, the second valve 53 has a first outlet on the left side, a second outlet on the right side on the return line 57 and a third outlet connected to the second connection line 73.

[0113] In a known way, the second variable mass rate valve 53 receives signals detected by a second temperature probe 55 located on the first secondary supply line 56. The second temperature probe 55 is arranged downstream of the second connection line 73 with reference to the flow direction Fl of the secondary supply line 56.

[0114] The flow rate of the second variable mass rate valve 53 is regulated according to the temperature detected by the second temperature probe 55, e.g. an immersion probe. The second variable mass rate valve 53 is typically motorised and power-operated remotely, e.g. via a remote control system. In one example, when the second temperature probe 55 detects a deviation of a certain magnitude from a target temperature value of the inlet flow, the second variable mass rate valve 53 acts on the mixing of the secondary inlet fluid with the secondary return fluid to regulate the temperature.

[0115] The remote control system can be configured to set a plurality of target values for heat delivery temperature to the consumers 18, e.g. according to time slots and / or the operational status of the heat exchange substation 50, as described in more detail below.

[0116] Along the first secondary supply line 56, in particular between the heat exchanger 51 and the second circulation pump 52, a plurality of probes and / or meters (not shown in the figure) are typically installed to control parameters such as pressure and temperature of the secondary fluid. Also typically installed on the secondary side 37b are one or more safety devices configured to signal a malfunction and, if necessary, to block the system.

[0117] As indicated above, the first variable mass rate valve 59 is configured to change the mass flow rate of the primary fluid entering the heat exchanger 51. In an embodiment, the first valve 59 has a variable cross-sectional area for the passage of fluid. Adjustment of the mass flow rate is carried out by changing the cross-section. For example, the first variable mass rate valve 59 is configured to change the flow section from fully open (maximum area), i.e. a maximum flow rate of 100%, to fully closed, i.e. a zero flow rate of 0% (no flow into the heat exchanger).

[0118] In known ways, the first variable mass rate valve 59 is typically motorised and, in some embodiments, remotely power controlled, e.g. by means of a remote control system.

[0119] In preferred embodiments, the substation 50 is configured to operate in a first operational state and a second operational state.

[0120] In the first operational state, the heat exchanger 51 with thermal inertia is configured to transfer thermal power from the primary network to the heating units 18. In particular, the heat exchanger 51 is configured to receive the primary fluid from the district heating system. This operational state typically corresponds to a time slot with high energy demand from consumers, e.g. during a morning or evening time slot.

[0121] The primary flow rate at the outlet of the first variable mass rate valve 59 and thus at the inlet of the first shell-and-tube circuit 81 in the heat exchanger 51 is relatively high. In a non-limiting example, the first valve 59 has an opening section in the range of 70% to 100%.

[0122] In the first operational state, the secondary heating circuit 68 is configured to supply secondary fluid to the heating units 18. The first circulation pump 54 is operational and is configured to push the secondary fluid in the secondary supply line 56 to the heating units 18. The secondary return line 57 feeds the secondary fluid, at a lower temperature, back into the heat exchanger 51.

[0123] The second circulation pump 52 is non-operational (e.g. is switched off). With reference to the above, the flow supply temperature to the heating units 18 can be set and / or regulated by means of the first variable mass rate valve 59.

[0124] In the first operational state, the secondary circuit 68 is defined by the first secondary supply line and the secondary return line 57 to / from the heat exchanger 51 to / from the heating units 18.

[0125] With a relatively high primary fluid flow rate, the heat exchanger 51 works mainly on the heat exchange between the first shell-and-tube circuit 81 and the second shell-and-tube circuit 82, while the amount of energy absorbed by the phase change material 71 is relatively limited. For example, in the first operational state, the material 71 may not evenly reach the melting temperature that allows heat to be released.

[0126] The secondary flow rate on the supply line 56 is primarily defined by the flow rate of the first circulation pump 54 (supply pump). The first circulation pump 54 can either be a constant flow rate pump or a variable speed pump and thus a variable flow rate pump.

[0127] In the second operational state, the supply of heat to the consumers is significantly reduced. This operational state typically corresponds to a time slot with minimum energy demand from the heating units 18, e.g. in a night time slot.

[0128] In the second operational state, the first circulation pump 54 can be configured to deliver the secondary fluid at a reduced flow rate or be switched off (or non-operational).

[0129] During the second operational state, the primary fluid continues to flow within the heat exchanger 51, however, at a lower flow rate than the flow rate in the first operational state. The primary fluid flow rate is regulated by adjusting the flow of the first variable mass rate valve 59. In a non-limiting example, the opening cross-section of the first variable flow valve 59 is in the range of 1% to 35%.

[0130] If the flow of the secondary fluid inside the heat exchanger 51 is significantly reduced or is absent (the first circulation pump 54 is switched off or inoperative), the circulation of the primary fluid in the heat exchanger allows the phase change material 71 to absorb a relatively large amount of heat and reach the melting temperature of the phase change material and thus a thermal energy storage. The second operational state is also referred to as the "charging" state of the heat exchanger with thermal inertia.

[0131] In an embodiment, the charging phase has a time duration, referred to in the following as charge time, such that the desired thermal energy storage within the heat exchanger 51 is achieved. The charge time depends on the temperature and the mass flow rate of primary fluid leaving the first variable mass rate valve 59. In particular, it depends on the value of the opening cross-section of the valve 59. In an example, the charge time is comprised between 0.5 and 2 hours.

[0132] In an embodiment, the regulation of the flow rate of the primary fluid is achieved by adjusting the flow of the first valve 59 via the remote control system by varying the valve opening and thus determining the time required to store a sufficient amount of heat in the phase change material 71.

[0133] In the second operational state, the second circulation pump 52 is operational. The activation of the second circulation pump 52 defines a sub-circuit of the secondary heating circuit 68, which is indicated in Figure 2A with a circular arrow 65. In particular, the sub-circuit is defined by the portion 56a of the secondary supply line 56 extending from the secondary side outlet 63 to the first connection line 69, the first connection line 69 and the portion 57a of the secondary return line 57, the portion 57a extending from the secondary side inlet 64 to the first connection line 69. The secondary side inlet and outlet 64, 63 are in communication with the sub-circuit 65.

[0134] Activation of the second circulation pump 52 allows a certain flow rate to be maintained in the secondary circuit 68, in particular in a part of it. In this way, the temperature of the phase change material 71 inside the heat exchanger 51 can be equalised during the heat absorption process, in particular by preventing high temperatures or excessive thermal gradients from being reached inside the tank 67 of the heat exchanger 51. The presence of the second circulation pump 52 can also avoid an internal imbalance between the temperatures inside the heat exchanger 51.

[0135] By ensuring a continuous circulation of the secondary fluid on the secondary side within the heat exchanger 51 and in the sub-circuit 65, as well as equalising the temperature of the phase change material 71, it is possible to guarantee correct operation of the safety devices installed on the secondary circuit 68, also preventing the part of the phase change material in contact with the shell-and-tube circuits from reaching excessively high temperatures.

[0136] In an embodiment, the substation 50 is configured to operate in a third operational state. In the third operational state, the supply of the primary fluid in the primary supply line 36 to the heat exchanger 51 is absent, i.e. the mass flow rate out of the first variable mass rate valve 59 is essentially zero.

[0137] The first circulation pump 54 is operational, i.e. it is configured to supply heat to the heating units 18. The first variable mass rate valve 59 is in the closed position so as not to draw thermal power from the district heating network.

[0138] Also in the third operational state, the second circulation pump 52 is switched off or inoperative.

[0139] In an embodiment, the third operational state may be subsequent to the second operational state. In the second operational state, the phase change material 71 has accumulated a certain amount of heat that can be maintained inside the thermally insulated tank 67 for a limited period of time, which represents the third operational state of the station 50. This heat is transferred to the second shell-and- tube circuit 82 and then to the secondary circuit 68.

[0140] In particular, the thermal energy stored by the phase change material 71 during the second operational state continues to be released to the secondary circuit 68 for a certain period of time. In this way, energy can be saved in the substation 50, for example if the third operational state is programmed in a time slot immediately preceding the time slot of maximum energy demand.

[0141] In a further example, the configuration of the substation 50 in accordance with the third operational state, with the primary fluid at a standstill, may allow a temporary disconnection of the secondary circuit 68 from the primary circuit to be managed by ensuring that a secondary flow continues to be distributed to consumers.

[0142] In an example, after the second or third operational state, the substation can be configured to operate in the first operational state. More generally, the heat exchanger substation 50 is configured to operate in the first, second or third operational state in any order.

[0143] It is also noted that the substation 50 makes it possible to manage, at least to a certain extent, the primary distribution network independently of the management of the secondary distribution network since the consumer can manage the substation's operational states independently.

[0144] A further possible advantage is that, even in the event of an interruption of service to the consumer, the thermal inertia heat exchanger can continue to supply heat to the consumer, reducing the risk of service disruption and improving the consumer experience.

[0145] A person skilled in the art will recognize that it is possible to combine the various characteristics of the embodiments described above to obtain further embodiments, all falling within the scope of the present invention as defined by the subsequent claims.

Claims

CLAIMS1. Heat exchange substation (50) of an energy distribution system, in particular of a district heating system, comprising: a heat exchanger (51) with thermal inertia comprising a primary side (37a) connected to a primary supply line (36) and to a primary return line (37), wherein the primary supply line and primary return line are in communication with a district heating system configured to deliver a primary fluid, and a secondary side (37b), opposite the first primary side (37a), the secondary side (37b) being connected to a secondary supply line (56) and to a secondary return line (57) of a secondary heating circuit (68), the secondary supply and return lines (56, 57) being in communication with one or more heating units (18), the secondary supply line (56) being configured to deliver a secondary fluid to the one or more heating units (18), wherein the heat exchanger (51) with thermal inertia comprises a tank (67) within which is arranged a first shell-and-tube circuit (81) connected at the inlet to the primary supply line (36) and at the outlet to the primary return line (37) and a second shell-and-tube circuit (82) connected at the inlet to the secondary return line (57) and at the outlet to the secondary supply line (56), and the tank (67) contains a phase change material (71), the first shell- and-tube circuit (81) and the second shell-and-tube circuit (82) being in contact with the phase change material (71).

2. Heat exchange substation (50) according to claim 1, wherein the first shell-and-tube circuit (81) and the second shell- and-tube circuit (82) are immersed in the phase change material (71).

3. Heat exchange substation according to claim 1 or 2, in which the phase change material (71) has a melting temperature between 45°C and 80°C.

4. Heat exchange substation (50) according to any one of the preceding claims, wherein the phase change material (71) is selected from the group consisting of a non-paraffinic organic compound, a paraffinic compound and an inorganic hydrated salt.

5. Heat exchange substation (50) according to any one of the preceding claims, wherein the tank (67) is a thermally insulated and hydraulically sealed container.

6. Heat exchange substation (50) according to any one of the preceding claims, wherein the primary side (37a) of the heat exchanger (51) with thermal inertia is connected to the primary supply line (36) at a primary side inlet (61) and to the primary return line (37) at a primary side outlet (62), and wherein the secondary side (37b) of the heat exchanger (51) is connected to the secondary supply line (56) at a secondary side outlet (63) and to the secondary return line (57) at a secondary side inlet (64).

7. Heat exchange substation (50) according to any one of the preceding claims, further comprising a first variable mass rate valve (59) positioned on the primary supply line (36).

8. Heat exchange substation (50) according to claim 7, wherein the first variable mass rate valve (59) has a fluid passage section of variable area.

9. Substation according to claim 7 or 8, wherein the first variable mass rate valve (59) is operatively connected to a first temperature probe (74) arranged on the secondary supply line (56) through a control line (58), the first variable mass rate valve being configured to regulate the flow based on a secondary fluid temperature value set by the first temperature probe (74).

10. Heat exchange substation according to any one of the preceding claims, comprising a first circulation pump (54) arrangedin the secondary supply line (56), the first circulation pump (54) being configured to deliver the secondary fluid from the heat exchanger (51) with thermal inertia to the one or more heating units (18).

11. Heat exchange substation according to claim 10, comprising a second circulation pump (52) arranged on a first connection line (69) which joins the secondary supply line (56) to the secondary return line (57), the first connection line (69) being arranged upstream of the first circulation pump (54) with reference to the flow direction (Fl) in the secondary supply line (56), wherein the second circulation pump (52) is configured to circulate the secondary fluid from the secondary supply line (56) to the secondary return line (57).

12. Heat exchange substation (50) according to claim 11, wherein the substation is configured to operate in a first operational state and a second operational state, when the substation is in a first operational state, the heat exchanger (51) with thermal inertia is configured to receive primary fluid from the primary supply line (36), the first circulation pump (54) is operational and is configured to deliver secondary fluid to one or more heating units (18) and the second circulation pump (52) is non- operational, and when the substation is in a second operational state, the heat exchanger (51) with thermal inertia is configured to receive the primary fluid from the primary supply line (36), the first circulation pump (54) is non-operational and the second circulation pump (52) is operational, so as to define a loop sub-circuit (65) of the secondary heating circuit (68) comprising a portion (56a) of the secondary supply line (56) extending from the secondary side outlet (63) to the first connection line (69), the first connection line (69) and a portion (57a) of the first secondary return line (57) extending from the secondary side inlet (64) to the first connection line (69).

13. Heat exchange substation (50) according to claim 12, when dependent on claim 6, wherein the first variable mass rate valve (59) has a fluid passage section with area from 0% to 100%, and in the first operational state, the first variable mass rate valve (59) has a passage section area from 70% to 100% and in the second operational state the first variable mass rate valve (59) has a passage section area from 1% to 35%.

14. Heat exchange substation (50) according to claim 12 or 13, wherein the substation is configured to operate in a third operational state, wherein the first variable mass rate valve (59) has substantially zero mass rate, the first circulation pump (54) is operational and the second circulation pump (52) is non-operational.

15. Substation according to any one of the preceding claims, wherein the first shell-and-tube circuit (81) comprises a plurality of first tubes (83) aligned with each other with respect to a tube extension direction (X), wherein the plurality of first tubes (83) is in fluid communication with the primary supply line (36) and with the primary return line (37), and the second shell-and-tube circuit (82) comprises a plurality of second tubes (84), the second tubes (82) being aligned with each other in a second tube extension direction (X), the plurality of second tubes (84) being in fluid communication, at the inlet, with the secondary return line (56) and, at the outlet, with the secondary supply line (57).

16. Substation according to claim 15, wherein the first tubes (83) of the plurality of first tubes are arranged in a first plurality of rows (81a) of first tubes, the rows (81a) being spaced apart and parallel with each other, the second tubes (84) of the plurality of second tubes are arranged in a second plurality of rows (82a) of second tubes (84) spaced apart and parallel with each other, whereineach row of first tubes (81a) of the plurality of rows (81a) of first tubes (83) and each row of second tubes (82a) of the plurality of rows (82a) of second tubes (84) are parallel to a longitudinal axis (Z), the rows of second tubes (82a) being arranged alternately with the rows of first tubes (81a) along a transverse direction (Y) with respect to the longitudinal axis (Z) and the first and second extension directions of the first and second tubes.

17. Substation according to claim 15 or 16, wherein the plurality of first tubes (83) is in fluid communication with a first primary manifold (85) connected to the primary supply line (36), and with a second primary manifold (86) connected to the primary return line (37), and the plurality of second tubes (84) is in fluid communication with a first secondary manifold (87) connected to the primary return line (57), and with a second secondary manifold (88) connected to the secondary supply line (56).

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