GB2524079A

GB2524079A - District heating system

Info

Publication number: GB2524079A
Application number: GB1404545.4A
Authority: GB
Inventors: Benny Martin Mathiesen; Alexander James Philbrook
Original assignee: Ista International GmbH
Current assignee: Ista International GmbH
Priority date: 2014-03-14
Filing date: 2014-03-14
Publication date: 2015-09-16
Also published as: EP3117375A1; WO2015136082A1; GB201404545D0

Abstract

A district heating system DHS comprises decentralised prepayment units PPU associated with respective decentralised heat consumption arrangements DHCA, the prepayment units PPU being communicatively coupled with a district heating backend system DHBS. The decentralised prepayment units PPU are arranged to transmit a top-up order TUO related to the respective decentral heat consumption arrangement DHCA, and the district heating backend system DHBS is arranged to enable and authorise a payment transaction request PTR in response to receiving the top-up order TUO from one of said decentralised prepayment units PPU. The payment transaction request PTR is based on a unique ID received from the decentralised prepayment unit PPU and payment authorisation data PAD. A payment transaction confirmation PTC is received in response to the payment transaction request PTR, and a client record CR associated with said unique ID is updated according to the received payment transaction confirmation PTC. The updated account data AD is transmitted to the decentralised the prepayment unit PPU identified by said unique ID.

Description

DIST1UCT HEATING SYSTEM

Field of the invention

The invention relates to district heating systems.

Background of the invention

District heating is an advantageous method of distributing energy for heating purposes in buildings. A challenge related to district heating is, however, that the technology involves physical movement of a heating medium in closed circuits, and it is difficult to measure and control individually, because it is difficult to regulate flow and/or temperature of the centrally provided heating medium.

Summary of the invention

The present invention is defined in the independent claims to which reference is now IS made, and some preferred features of embodiments of the invention are set out in the dependent claims.

The present invention relates to a district heating system DHS comprising decentral prepayment units PPIJ associated with respective decentral heat consumption arrangements DHCA, the prepayment units PPU being communicatively coupled with a district heating backend system DUBS, a plurality of the decentral prepayment units PHi being arranged to transmit a top-up order TUO related the respective said decentral heat consumption arrangement DHCA, and the district heating backend system DHBS being arranged to -enable and authorize a payment transaction request PTR in response to receiving said top-up order from one of said decentral prepayment units PPIJ, the payment transaction request PTR being based on a unique ID UJD received from said decentral prepayment unit PPU and payment authorization data PAD; -receive a payment transaction confirmation PTC in response to said payment transaction request PTR; -update a client record CR associated with said unique ID TJID according to the received payment transaction confirmation PTC; and -transmit updated account data AD to decentral the prepayment unit PPU identified by said unique ID UID, District heating systems, or similar heating systems such as community heating, heat networks or teleheating, all of these considered within the scope of the present invention, are systems for distributing heat generated in a centralized location for residential and commercial heating requirements such as space heating and water heating. Different scales of such heating systems are within the scope of the present invention, comprising e.g. large-scale district heating systems covering an entire municipality or part of a town, as well as small-scale community heating where a single central boiler distributes heat and hot water within one or a small number of 1 0 apartment blocks to each tenant.

By a two stage application of authorizations an advantageous system may be applied by which payment authorization data need only be stored in a central database, thereby reducing the risk of users compromising the security related to personal data, in particular credit cards details or other sensitive data and at the same time offering users of a decentral pre-payment unit an easy and secure way of topping up the credit available for heat consumption by the prepayment unit-controlled decentral heat consumption arrangement DEICA, The system facilitates that sensitive data are both not required and not stored decentrally at the prepayment units, thereby making the system robust to the decentral users.

By applying payment authorization data PAD constrained to a specified unique ID, misuse of the system may be counteracted due to the fact, that payment authorization data PAD unintentionally obtained by a third party cannot by applied for the benefit of the third-party, The district heating backend system DHBS may comprise a single sewer, a number of sewers, be cloud-based, or combinations thereof The sewers and/or the different services provided by the district heating backend system may be managed or operated by a single provider, or be distributed among different providers. An advantageous embodiment of a distributed backend system within the scope of the present invention comprises having a heat billing service provider operating most of the district heating backend system, but e.g. using a hosted credit card processing service provider for storing and processing e.g. the payment authorization data PAD.

An advantage of the invention is that the central district heating backend system may be used for adding security in relation to validation of the top-order. This added check may include a great variety of parameters including comparison with usual consumption level, comparison with a subscriber-defined threshold with respect to consumption or prepayment to ensure that the top-up order overall complies with the wishes of the client as defined in the client record. The added check may also include a comparison with an expected consumption over a thture period to ensure that the subscriber does not unintentionally prepay more than intended or more than necessary.

Furthermore, the centrally held confidential data may be kept confidential in an efficient way to ensure that subscribers' confidential data may not be retrieved in any way by tampering of the prepayment units or by hacking any runtime communication between the prepayment units and the district heating backend system.

It is also noted that in the prepayment system and the prepayment method according to the invention, a user may operate the system with no daily requirement of having smartphones or the like and web access, due to the fact the prepayment unit serves as a complete and fully functioning payment platform to the subscriber.

A further and very important feature of the invention is that an automatic payment transaction may be invoked with no or little technical skills. The subscriber may in the simple instance of the invention simply look at a display of the prepayment unit or receive a warning that the account is close to the lower threshold and then push a button TOl to communicate a top-up order to the district heating backend system.

An advantageous embodiment is obtained when the district heating system DHS comprises a central heat source Cl-IS supplying the plurality of decentral heat consumer arrangements DHCA with heated liquid, e.g. water, through pipes P. An advantageous embodiment is obtained when said unique ID UID received from said decentral prepayment unit PPU is derived from said top-up order TUO.

An advantageous embodiment is obtained when the payment authorization data PAD are stored in the district heating backend system DHBS associated to said unique ID JO hID in a client record CR.

According to a preferred embodiment of the invention, the payment authorization data may be stored centrally in the district heating backend system, thereby to provide a secure communication and control of the decentral heat consumption 1 5 arrangement.

An advantageous embodiment is obtained when the payment authorization data PAD comprises credit cards details.

An advantageous embodiment is obtained when the payment authorization data PAD are stored in the decentral prepayment unit.

An advantageous embodiment is obtained when said payment transaction request PTR is transmitted to a payment processor PP. A payment processor is a technical platform upon which a request through the payment gateway may invoke a payment transaction between the acquiring banking institution of the district heating backend system and the banking institution of the subscriber defined in the client record by means of the payment authorization data PAD.

An advantageous embodiment is obtained when said payment transaction confirmation PTC is received from the payment processor PP. An advantageous embodiment is obtained when the payment authorization data PAD are initially uploaded to the district heating backend system DFIBS via the pre-payment unit PPU or a secure web-accessible portal.

The upload of the payment authorization data PAD, such as credit card details, to the district heating backend system may be performed in any a secure way, by means of a manual contract, secure upload. The basic concept however, is that the data used for payment transactions need not be stored decentrally at the pre-payment units.

An advantageous embodiment is obtained when the payment authorization data PAD are comprised in a central server in a secure environment.

An advantageous embodiment is obtained when the decentral prepayment units PPU are connected communicatively with the district heating backend system DUBS via an encrypted connections.

An advantageous embodiment is obtained when the client record CR is mapped to said decentral heat consumption arrangement DHCA, thereby facilitating that information derived from a received top-up order is looked up in said client record and applied for a subsequent payment transaction request.

An advantageous embodiment is obtained when the client record is updated at the district heating backend system DHBS in response to heat measurements performed at the decentral heat consumption arrangement and payment confirmation received in response to a top-up order invoked payment transaction request PTR.

An advantageous embodiment is obtained when said payment transaction request invokes a transaction between at least four parties, seller, purchaser, issuing bank and acquiring bank.

An advantageous embodiment is obtained when the prepayment unit PPU and the district heating backend system DHIBS form a two stage authorization, wherein the first stage is an activation step performed by the prepayment unit PPU by means of a top-up order and the second stage is an authorization step performed by the district heating backend system DT-JES in response to the top-up order, thereby enabling that the authorization step for all prepayment units are performed by the district heating backend system DHBS, but the activation step for the individual prepayment units PPU are performed by the individual users of the pre-payment units.

By a two stage application of authorizations an advantageous system may be applied by which payment authorization data need only be stored in a central database, thereby reducing the risk of users compromising the security related to personal data, in particular credit cards details or other sensitive data and at the same time offering users of a decentral pre-payment unit and easy and secure way of topping of the credit available for heat consumption by the prepayment unit-controlled decentral heat consumption arrangement DHCA.

The security of the individual prepayment units may therefore be easy to establish in the sense, that the prepayments units are only authorized to invoke tnmsactions, where the decentral heat consumption arrangement DE-ICA will benefit. The individual consumers will therefore benefit from an easy-to-use interface without risking third-party tampering and fraud in relation to payment transactions due to the fact that the central system may be maintained for secure payment transactions.

An advantageous embodiment is obtained when the individual prepayment unit is communicatively coupled with one or more heat meters 1-JlvI located at the decentral heat consumption arrangement DEltA for measuring of the heat consumption at the decentral heat consumption arrangement DHCA covered by the prepayment unit PPU.

An advantageous embodiment is obtained when the measured heat consumption is gathered by the prepayment unit PPU and wherein a decentral consumption account DCA, e.g. a counter, is updated in the prepayment unit PPU in response to the gathered measure for heat consumption.

An advantageous embodiment is obtained when a measure of the measured heat consumption is transferred to the district heating backend system together with the unique ID UID of the prepayment unit PPU for updating of a central consumption account (CCA) of a client account associated with said unique ID, An advantageous embodiment is obtained when the one or more heat meters comprises calorie meters, flow measurement meters and/or temperature sensors and wherein the applied meters or sensors are applied for automatically deducing a heat consumption.

An advantageous embodiment is obtained when the prepayment unit is communicatively coupled with an ambient temperature sensor arrangement of one of more temperature sensor.

An advantageous embodiment is obtained when the prepayment unit comprises an ambient temperature sensor arrangement of one of more temperature sensor.

An advantageous embodiment is obtained when the prepayment unit PPU controls a supply valve system SVS associated to the individual decentral heat consumption arrangement DHCA in a shut-down mode on the basis of measurement of the ambient temperature sensor arrangement to keep the measured temperature TE1VIP above a predefined minimum temperature TMIN.

An advantageous embodiment is obtained when the prepayment unit PPU comprises a displaying of the updated account balance to the prepayment unit PPU.

An advantageous embodiment is obtained when the prepayment unit PPTJ displays the updated account balance as a monetary value.

An advantageous embodiment is obtained when the prepayment unit PPTJ displays the updated account balance in energy units.

An advantageous embodiment is obtained when the prepayment unit PPTJ has a dedicated interface TOT for a top-up order TUO.

An advantageous embodiment is obtained when a top-up order TUO is restricted to a number of available frmnctions including a unique identifier identifying the prepayment unit.

By restricting the number of available functions, the system provides a certainty that the prepayment units are not used for anything other than the intended ifinction. The restricted number of available frmnctions of the top-up order at the prepayment unit may efficiently be kept to its intended function as this functionality may be maintained in the system even if the unit is tampered with due to the fact that the district heating backend system may be designed to only accept this restricted number of available functions.

An advantageous embodiment is obtained when the updated account balance is transmitted from the district heating backend system DUES to the prepayment unit PPU in update intervals, The update intervals may e.g. be days or weeks. It may of course be shorter intervals or even performed in real-time depending on the preferred data-load to and from the prepayment units and the data-load to and from the financial institution, Tt may also be preferred that an update of the account balance is transmitted to the individual prepayment unit as soon as a confirmation of valid payment has been received from the financial institution, An advantageous embodiment is obtained when the prepayment units PPU are communicatively coupled to respective supply valve systems SVS associated with the individual decentral heat consumption arrangement DHCA, and wherein the prepayment unit controls the respective supply valve systems SVS.

An advantageous embodiment is obtained when the prepayment units PPU are communicatively coup'ed to respective supply valve systems SVS associated to the individual decentral heat consumption arangement DHCA, and wherein the prepayment unit controls the respective supply valve systems SVS on the basis of accountdataAD.

An advantageous embodiment is obtained when the prepayment units PPTJ control the respective supply valve systems SVS directly or via the district heating backend system DHBS An advantageous embodiment is obtained when the prepayment units PPIJ are controlling the associated supply valve system SVS between at least two modes; a prepayment mode and a shutdown-mode, An advantageous embodiment is obtained when the prepayment mode of a prepayment unit PPU implies keeping the supply valve system SVS open as long as an account balance stored at the prepayment unit PPU and/or at the district heating backend system DUBS is above a predefined account balance threshold ABMIIN.

An advantageous embodiment is obtained when the shutdown-mode of a prepayment unit PPU implies closing the supply valve system SVS completely or at least partly as long as an account balance stored at the prepayment unit PPU andior at the district heating backend system DHBS is below a predefined account balance threshold ABMIN.

An advantageous embodiment is obtained when the supply valve system SI/S is arranged to regulate one or more of hot water supply and space heating supply individually; wherein the prepayment units PPU are controlling the associated supply valve system SYS between at least two modes comprising a prepayment mode and a shutdown-mode; and wherein the shutdown-mode implies fully or partly closing a predetermined number of said one or more of hot water supply and space heating supply.

The present invention according to various embodiments comprises the technical setup for allowing implementation of several different ways of warning, encouraging or motivating a user to top-up the credits when relevant. A supply valve system controllable by the pie-payment unit or from the district heating baclcend system which may be utilized in several advantageous ways as described herein is one way to accomplish this. In various embodiments the system may close or reduce the supply to a decentral heat consumption arrangement DHCA entirely, or only close or reduce the supply e.g. hot water or space heating. In various embodiments such regulation may be triggered by different criteria, notably the current balance of credits according to the prepayment unit getting below a predetermined threshold.

An implementation of a multi-stage warning/motivation approach may comprise closing or reducing the hot water supply at one predetermined threshold, e.g. zero or slightly above zero, and at a lower, predetermined threshold, e.g. zero or slightly below zero, further reducing or closing the hot water supply, or reducing or closing the space heating, too.

An advantageous embodiment is obtained when a representation of the account balance threshold ABM1IN of the prepayment units is stored centrally in the district heating backend system associated to the respective relevant client records CR.

An advantageous embodiment is obtained when a representation of the account balance threshold ABMIN of the prepayment units is stored in the individual prepayment unit.

An advantageous embodiment is obtained when the threshold value may be centrally pushed from the district heating backend system to the prepayment units.

An advantageous embodiment is obtained when a data value may be sent uniquely to a prepayment unit PPU from the district heating backend system for switching the prepayment unit between at least two different modes; a prepayment mode and a credit mode.

The individual prepayment units may be addressed individually by the district heating backend system for override of the prepayment unit. If this happens, the addressed prepayment unit will simply shift from the normal purpose of the unit, namely to be operated as a prepayment unit to a simple communication device for measuring and transmitting the heat consumption associated to the unit while e.g. displaying current account balance. When the unit is in credit mode, there will be no direct correlation between the controlling of the supply valve system and the current account balance.

An advantageous embodiment is obtained when readings from a group of prepayment units are applied for deducing an accumulated consumption AC and wherein the accumulated consumption is applied for detection of fraud or leakage.

An advantageous embodiment is obtained when the account balance of the individual prepayment unit PPU is updated regularly with application of a subscription fee.

An advantageous embodiment is obtained when metering of the heat consumption related to the individual prepayment units are performed by meters located between the heat supply and heat exchangers located at the decentral heat consumption arrangement DHCA.

Heat exchangers may advantageously be applied for transferring of heat energy from one closed heat transmission circuit to another. In this way it may be possible to measure and control the complete decentral heat consumption arrangement DHCA.

The present invention ifirther relates to a method of operating a district heating system DI-IS comprising a central heat source CHS supplying a plurality of decentral heat consumer arrangements DHCA with heated liquid, e.g. water, through pipes P. the system fbrther comprising a plurality of pre-payment units PPU associated with and controlling respective decentral heat consumer arrangements DHCA and a central district heating backend system DHBS communicatively coupled to the plurality of decentral heat consumption arrangements DHCA through said prepayment unit PPU, each of the prepayment units PPTJ being communicatively coupled to or comprising at least one heat meter MM, the at least one heat meter MM measuring the heat consumption of the respective decentral heat consumption arrangement DHCA, the prepayment units PPU being communicatively coupled to the central district heating backend system DHBS, and the prepayment units PPU being uniquely identified to the central district heating backend system DHBS, the central district heating backend system DHBS being communicatively coupled with a payment processor PP, the prepayment unit PPU comprising a user interface, the central district heating backend system DHBS comprising a plurality of client records CR related to the pre-payment units PPU communicatively coupled to said central district heating backend system DUBS, wherein the user interface is user operable for communication of a user triggered top-up order TUO to said central district heating backend system DHBS, wherein the central district heating backend system DUBS in response to said top-up order executes an authorized secure transaction by communication with said payment processor PP in compliance with said client records CR.

An advantageous embodiment is obtained when the method of operating a district heating system DHS comprises a district heating system as described above. In Ii

The drawings The invention will is described with reference to the drawings, where fig. 1 illustrates an exemplary embodiment of the invention, fig. 2 illustrates an example of a layout design of a decentral heating consumption arrangement according to an embodiment of the invention, fig. 3 illustrates a prepayment unit according to the an embodiment of the invention, and fig, 4 illustrates a functionality of entering a shut-down mode according to an embodiment of the invention.

Detailed description

District beating, less commonly called community heating, heat networks or teleheating, is a system for distributing heat generated in a centralized location for residential and commercial heating requirements such as space heating and water heating. The heat is often obtained from a cogeneration plant burning fossil friels but increasingly biomass, although heat-only boiler stations, geothermal heating, and central solar heating are also used, as well as nuclear power. District heating plants can provide higher efficiencies and better pollution control than localized boilers.

Also heating systems sometimes referred to as community heating where a single central boiler for one or more apartment blocks distributing heat and hot water thin the building or a small number of collected buildings to each tenant, is considered within the scope of district heating according to the invention.

Fig. I shows an exemplary embodiment of the invention illustrating a district heating system D1-TS comprising a plurality of decentral prepayment units PPIJ associated with respective decentral heat consumption arrangements DHCA. The prepayment units PPIJ are communicatively coupled with a district heating backend system DHBS, The illustrated district heating system DHS comprises a central heat source CHS supplying the plurality of decentral heat consumer arrangements DHCA with heated liquid, e.g. water, through pipes P. The plurality of decentral prepayment units PPTJ enables transmittal of a top-up order TIJO related to the respective decentral heat consumption arrangements DHCA. The district heating backend system DHBS enables a payment transaction request PTR in response to a top-up order RIO received from the prepayment unit PPU based on a unique ID lID, received from said decentral prepayment unit PPIJ and payment authorization data PAD. The payment authorization data PAD are preferably held in a client record of the district heating backend system.

In response to said payment transaction request PTR, the district heating backend system DHBS receives a payment transaction confirmation PTC and updates the client record CR associated to the unique ID UID according to the received payment transaction confirmation PTC and transmits updated account data AD to the prepayment unit PPU identified by said unique ID.

The updated account data AD will enable the individual prepayment units to control the inflow of heated liquid or steam to the relevant controlled decentral heat consumption arrangements DHCA by means of respective supply valve systems SVS, The payment transaction request will preferable be sent through a payment gateway PG to a payment processor PP known in the art for automatic execution of the payment transaction and the payment process will return the payment transaction confirmation PTC to the district heating backend system DHBS.

The present payment gateway protect credit card details by encrypting sensitive information, such as credit card numbers, to ensure that information is passed securely between the district heating backend system the payment processor.

A payment gateway facilitates the transfer of information between the district heating baclcend system and the payment processor.

In the present context a payment gateway includes online services for accepting electronic payments by a variety of payment methods including credit card, bank-based payments such as direct debit, bank transfer, and real-time bank transfer based on online banking. The payment processor may thus process a transaction based on automatic data flow between the acquiring bank of the district heating backend system and the bank of the subscriber/client designated by the individual client record.

A payment processor is a technical platform upon which a request through the payment gateway may invoke a payment transaction between the acquiring banking institution of the district heating backend system and the banking institution of the subscriber defined in the client record by means of the payment authorization data PAD.

A payment transaction PTR request may be an automatically generated request for a payment transaction to a payment processer PP. The payment transaction request is automatically generated by the district heating backend system upon receipt of a top-up order received from a prepayment unit.

Payment authorization data PAD may be stored in the client record and enables the district heating backend system to automatically apply these data through a payment gateway to obtain prepayment for the service required by the user of the PPU. The payment authorization data may thus be combined with a top-up order received from a prepayment unit into a final payment transaction request automatically performed by the system when triggered by a top-up order.

In an embodiment where the district heating backend system DHBS is distributed, the payment authorization data PAD may e.g. be one of the parts that may advantageously be outsourced, e.g. to a hosted credit card processing system. In the current context, the payment authorization data PAD, may however still be considered part of a client record CR, in this case possibly a distributed client record, which is part of the district heating backend system DHBS, A payment transaction confirmation PTC may here be a response by a payment processer, confirming whether a payment has been approved or denied, The payment processor may base this payment transaction confirmation on automatic payment networks and methods between banking institutions. Such networks are well known inthe art.

A prepayment unit facilitates payment of a relevant amount related to heat consumption. The prepayment unit enables local activation of monitored heat consumption. PPU is located decentrally, making it possible for local users or subscribers to control and facilitate their own heat consumption In the present context, a subscriber is a user subscribing to a heat provider service, A subscription may in the present context involve a prepayment plan facilitated by the prepayment unit PPU. The subscriber is associated with a client record CR stored at the district heating backend system.

A client record associated with an individual subscriber is held centrally at the district heating backend system. The client record comprises service framework data and payment authorization data, each identified and associated to unique ID, The client records are kept at the district heating backend system in a client record database CRD.

A client record functions as a subscription plan and is associated to individual subscribers identified with a unique ID and comprises data determining how to technically deal with the individual subscriber in the system. The client record may typically comprise data defining the subscriber, one or more prepayment units associated with the subscriber, payment authorization data according to which the district heating baclcend system DHBS may complete a financial transaction by means of a payment transaction request to a payment processor PP. Preferably, a subscriber plan will determine one prepayment unit to be associated with one subscriber.

An advantage of the client record CR is that it is kept centrally in a district heating backend system and that it may be kept secure by means of centrally applied technical provisions, thereby offering individual subscribers a system which is safe and requires minimum technical skill or hardware by the subscriber, A client record may advantageously comprise a subscriber ID or be associated with it thereby connecting the subscriber ID, i.e. a subscriber with the specific unique ID of a prepayment unit.

A fbrther advantage of the present system is that the way of availing prepayment by means of the prepayment unit may facilitate easy change of subscriber. A typical problem of conventional district heating is that the management is heavy and expensive due to the fact that so-called sub-metering must be applied, thereby making it difficult to manage when tenants are moving in and out. In the present context and by means of the prepayment system of the invention it is possible to establish an almost instantaneous switch between tenants moving in and out, due to the fact that the district heating backend system may only need to register a date and establish a client record on the new tenant, The date and time determine a reading and a resetting of the prepayment unit and the reading is transmitted to the district heating backend system and the old tenant may automatically get a refund transfer by means of the payment processor. The new tenant may then simply operate the top-up interface invoking that district heating backend system initiates a payment transaction in relation to the client record of the moving-in tenant.

The decentral heat supply system enables controlling the availability of energy transfer from the district heating system to the decentral heat consumption arrangement DHCA by means of the supply valve system SVS, The decentral heat supply control system is decentral in the sense, that it is possible on an apartment level or building level to control the availability of heating by means of a locally arranged system.

The decentral heat supply control system may be operated in response to a control signal sent by the PPU, The control signal may either directly operate the supply valve system SVS or e.g. indirectly through the central district heating backend system DHBS or another centralized monitoring instance. In a preferred embodiment, the PPU controls the supply valve system SYS directly on the basis of the account data AD, The heat supply control system preferably comprises a supply valve system SVS.

The supply valve system may comprise a single controllable master valve for an entire apartment or building of a decentral heat consumption arrangement DHCA, or controllable individual valves ±1w e.g. a domestic hot water system and a heating system.

A decentral heat consumption arrangement DHCA is basically one of a plurality of points of energy consumption, i.e. a number of geographically distributed locations where the district heating system feed heated liquid or steam for local consumption at the individual heat consumption arrangements. The decentral heat consumption arrangements may be structured and/or built in many different ways. Each decentral heat consumption arrangement may thus be designed for space heating and also for heating of domestic water. The decentral heat consumption arrangement may be applied for heating different sizes of apartments and different types of locations, schools, small plants, offices, etc. Fig. 2 illustrate an example of a decentral heat supply system according to an embodiment of the invention. The illustrated system may e.g. be a district heating supplying a subscriber of district heating with heated medium. The subscriber may e.g. be a tenant of an apartment comprising a number of rooms rented or owned by the tenant.

The district heating system comprises a district heating supply DS coupled to the primary side of a first heat exchanger HE via a district heating supply valve DHSV.

The district heating supply DS is further coupled to a second heat exchanger HEW and both heat exchangers being coupled via a heat meter HM to a district heating return DHR.

The first heat exchanger may on the secondary side be coupled to a local heat supply HES for circulation back in a closed circuit via the heat return HER of the first heat exchanger HE. Details, such as circulation pumps etc. are not illustrated in the present embodiment, but their applicability and implementation will be clear to a person skilled in the art of domestic heating. The first heat exchanger is applied for supply of space heating of the associated apartment.

The second heat exchanger HEW is on the secondary side couple to a domestic cold water inlet DCW for the purpose of generating heated domestic water to the domestic hot water outlet DHW.

The district heating supply valve DHSV is communicatively coupled to a prepayment unit PPU by means of wire or cordless.

The meter is also communicatively coupled to the prepayment unit PPU by means of wire or cordless.

The prepayment unit PPIJ is thrther communicatively coup'ed to a district heating backend system DUBS.

The prepayment unit PPIJ controls the district heating supply valve DI-ISV to open or close, and in a preferred embodiment also with the option of positions between open and closed. The control of the specific district heating supply valve may be performed according to a decentral control process run by the prepayment unit or the prepayment unit may act further directly or indirectly in response to control signals received from the district heating backend system DHBS.

In an embodiment separate supply vaNes are provided, e.g. for independently regulating space heating and hot water, and the prepayment unit may be arranged to control both or either one. For example, the pre-payment unit may in an embodiment be arranged to filly or partially dose the hot water supp'y valve when credits get below a predetermined threshold. In another embodiment, the space heating may be shut down or reduced, but the hot water supply remains. In an embodiment the district heating supply valve or all valves are closed fully or partially when all credits have been used. In a further embodiment, the hot water supply is closed fully or partially at one threshold as a warning to the user, and the space heating is ffilly or partially closed if an even lower threshold of credits is reached.

Fig. 3 illustrates a further advantageous embodiment of the invention, where a temperature sensor system is communicatively coupled for measuring of a temperature representation TEMP measured e.g. by an onboard temperature sensor or and external temperature sensor. The prepayment unit PPU controls a supply valve system SVS in response to communication from a district heating backend system DHBS. In the illustrated embodiment the control system of the prepayment unit switches to a minimum mode algorithm. The switching to the minimum mode algorithm may typically be performed automatically if the account held either locally at the prepayment unit PPU and/or centrally in the district heating backend system DHBS is below a predefined threshold, e.g. a remaining balance of zero, or in an embodiment the threshold may be slightly below zero to allow for being a bit late with top-ups. The minimum mode algorithm will control the supply valve system SVS so as to ensure that the temperature representation TEIVIP received by the prepayment unit does not drop below a certain minimum temperature TMIN even in spite of the fact that the tenant is without firnding or below a certain threshold level.

The minimum temperature TMIN may e.g. be selected in the range of 5 -15°C. The regulation of the supply valve system may involve setting a valve at a partially open position if possible, or by alternatingly open and close a valve that only supports resting in either end position. Fig. 4 is an example of an effect the minimum mode algorithm may have on the measured temperature.

A fUrther feature may be obtained if the prepayment unit is fitted with a manual switch TMA for switching to the minimum mode algorithm. The switch may be applied by a user of the prepayment unit for manually switching to a minimum mode algorithm if the user e.g. leaves the apartment and wishes to save energy. The manual switch may also be used for manually facilitating a return to normal operation. This embodiment of the prepayment unit PPU will nevertheless be under the control of the prepayment unit PPU to ensure that a manual switch for return to normal only will switch from the minimum temperature algorithm if the tenant is not without fUnding or below a certain threshold level. The prepayment unit PPU in fig. 3 also comprises a dedicated interface TOL, e.g. a button, for enabling a user to execute a top-up order 1110. fin Li