NL2025444B1 - District heating system for controlling heat demand in district heating - Google Patents

Abstract

The present invention relates to a district heating system, comprising a piping network for transporting a heating medium comprising a supplying and returning section and one or more heat sources, for heating the heating medium to a predetermined supply temperature and providing it to the supplying section, and receiving the heating medium from the returning section, and at least one heat extractor, wherein at least one heat extractor is connected to the piping network through an interface, comprises a supply connection, for receiving the heating medium from the supplying section of the piping network, a return connection, for delivering the heating medium at a return temperature to the returning section of the piping network, at least one heat extracting element, placed between the supply connection and the return connection, for extracting heat from the heating medium, a controllable flow regulator, such as a valve, for determining a flow resistance to regulate a flow rate of the heating medium, a local controller, the local controller is configured to control the controllable flow regulator based on a return temperature setpoint and/or flow rate setpoint.

Description

District heating system for controlling heat demand in district heating The present invention relates to a heating system, in particular to a district heating system.

In a conventional district heating system heat is generated in a heat production plant. The generated heat is used to heat up a specific heating medium, conventionally water is used, to a predetermined temperature. The heating medium, after reaching the predetermined temperature, is distributed into a piping network. Buildings are connected to the piping network, and the heating medium runs through the buildings. In the buildings the heating medium is used to heat up radiators or the like, which are installed in the buildings to heat up the building to a preferred temperature. The colder heating medium is then returned to the heat production plant.

District heating systems are usually designed to reduce the carbon footprint of buildings. Conventional district heating systems have some drawbacks making them less preferable with respect to central heating which can be installed at the building locally. The system's efficiency is for example highly related to the ratio between a peak heat demand and the average heat demand. A low ratio between the two yields a better economic efficiency. It is known that district heating systems have to cope with a volatile heat demand. The heat demand has shown to be strongly related to the living patterns of the buildings’ inhabitants, may it be daily, weekly, monthly, or even yearly living patterns. These living patterns introduce high peaks in the heat demand and therewith lower the district heating systems efficiency.

The efficiency of district heating systems can be improved in three different ways, which are all referred to in this document under the name efficiency. The first form of efficiency is an energetic perspective, where optimization leads to consumption of less fuel, a second efficiency is an economic perspective where the production is optimized for example with respect to electricity pricing. And finally, a capacity perspective, where with the same amount of heat sources more users can be supplied by lowering the peak demand.

The buildings are conventionally outfitted with equipment to regulate a preference temperature of the building. The district heating system makes sure this temperature is maintained until a new temperature setpoint is given. The outgoing medium is fed back to the production plant, where it is heated again and optionally used as a coolant. This introduces difficulties: in order to be effectively heated, the returning heating medium should not exceed a maximum temperature. In case a building uses high flow, typically the outgoing heating medium temperature will be high, potentially exceeding the given maximum. As a consequence of this, valuable heat is lost to the surroundings during transportation., thereby decreasing the district heating system's efficiency.

It is a goal of the present invention to eliminate, or at least provide an alternative, for the drawbacks of the district heating system as mentioned before. The invention thereto proposes a district heating system, comprising a piping network for transporting a heating medium comprising a supplying and returning section and one or more heat sources, for heating the heating medium to a predetermined supply temperature and providing it to the supplying section, and receiving the heating medium from the returning section, and at least one heat extractor, wherein at least one heat extractor is connected to the piping network through an interface, comprises a supply connection, for receiving the heating medium from the supplying section of the piping network, a return connection, for delivering the heating medium at a return temperature to the returning section of the piping network, at least one heat extracting element, placed between the supply connection and the return connection, for extracting heat from the heating medium, a controllable flow regulator, such as a valve, pump or controllable differential pressure controller, to regulate a flow rate of the heating medium, a local controller, the local controller is configured to control the controllable flow regulator based on a return temperature setpoint and/or flow rate setpoint, which in a further embodiment possibly further comprises measurements of the actual flow rate and actual return temperature.

The present invention improves the efficiency of the district heating system. By controlling the return temperature of the heating medium the invention enables a better consumption of the heat. That is, less heat will be shed to the surroundings. Since less heat is lost the system's efficiency increases. However, not only the efficiency is increased by regulating the returning temperature. Also the amount of heat needed in total is decreased, and because of that the carbon footprint is reduced. A heat source can for example be a factory, which requires cooling for equipment. And by cooling the equipment with the heating medium, the heating medium heats up. However, any source of heat can be used for heating the heating medium. The flow regulator allows for continuous adjustments to the flow of the heating medium. The flow regulator can operate anywhere between fully restricting the flow or fully allowing the flow. By implementing the continuous operation and control of the flow the invention is distinct over the prior art, which uses valves which are either fully opened or fully closed. The control of the flow allows to align the heat flow to the heat extractor with the heat demand of the heat extractor. In particular whenever the demand of the heat extractor is constant, the flow can be controlled such that it exactly meets the heat demand, and hence all necessary heat is extracted. This results in a lower return temperature of the heating medium compared to the prior art solutions. The controllable flow regulator can in particular determine a flow, wherein said flow can be set by regulating a flow resistance. The improvement according to the present invention can be used in both direct and indirect district heating applications. A direct district heating system is formed when the heat extractor is directly connected to the piping network, and hence the heat extractor’s interface is directly connected to the piping network. An indirect district heating system is formed when the heat extractor is connected to the piping network through a heat exchanger. That is, the interface can be formed by the heat exchanger, connecting a separate closed piping system at the heat extractor to the district’s piping network. The heat extractor’s system can be heated through the heat exchanger in the interface of the heat extractor.

In a further embodiment of the invention the system further comprises a global controller, for amending settings of the local controller of at least one heat extractor. The global controller enables a more optimized control of the system’s efficiency.

However, the global controller can be overruled by the local controller by a “opt-out” signal. Such a signal might be used in the case that the building inhabitant is leaving his building temporarily, and the signal informs the global controller. It might also be used to overrule an artificial heat demand signal created by either the global or local controller if the building inhabitant does not want that. In case no heat demand is required, for example due to holiday or absence, this “opt-out” signal can be used to avoid unnecessary demand of heat. The global controller allows for predictive maintenance and using live data for better diagnosis and helpdesk support. The global controller is configured for simultaneously interacting with multiple heat extractors.

In an even further embodiment of the invention, the global controller is configured to minimize a peak demand, the global controller thereto determines and controls the value and/or moment of a heat demand setpoint of the heat extractor, in particular the value and/or moment of the heat demand setpoint related to the peak demand. Minimizing the peak demand is important for an increase of the system’s efficiency.

The minimized peak demand lowers the ratio between peak demand and average demand, which yields an increase of the system’s efficiency. By controlling both the value and/or moment of the heat demand setpoint and the flow of the heating medium the overall efficiency of the system is increased. Preferably when the heat demand of the heat extractor is constant the global and/or local controller compute the lowest possible heating medium flow rate which both satisfies the heat extractor’s heat demand as well as returning the heating medium at a lower temperature compared to district heating systems according to the prior art. In addition, the system can reduce the flow further to achieve heat curtailment, temporarily delivering less or no heating medium to specific heat extractors allowing other heat extractors to use the available flow and / or to overcome local and /or global system limitations.

In yet a further embodiment of the invention, the peak demand is determined by historic heat demand setpoint data of the heat extractor, and/or wherein the moment determined by the global controller. This method of reducing the peak demand is reliable since it is computer controlled. In general, the model of the global controller related to predicting the peak demands is improved over time by means of optimization using data analysis and/or artificial intelligence. The model of the global controller related to the peak demands automatically includes heat demand setpoint data of users to update the models. The goal of improving the model is to continuously optimize the returning temperature. It has turned out that this specific range of time to counteract a peak demand is the best ratio between system efficiency and the comfort of the heat extractor. Building inhabitants use a smart thermostat to set their heating preferences, usually by providing a program describing the desired building temperatures throughout the week. From this temperature program, the smart thermostat derives a heating program by estimating the building's thermal properties and calculating the required heating times. The estimated thermal properties are updated by continuously comparing the expected temperature with the realized temperature, resulting in a locally optimized heat controller. Smart thermostats typically communicate with a client's heating system through the OpenTherm protocol. Communication can be wired, or using wireless local radio protocols like Z-Wave, Zigbee, Bluetooth, DECT, Wi-Fi, other ISM band RF protocols or comparable. Through this channel the thermostat communicates, among other information, its heat demand to the heating system, represented by a continuous numeric variable. Finally, most smart thermostats’ data regarding the heat extractor’s near real-time temperature information and temperature program can be accessed remotely. The global controller accesses this data through server interaction with the smart thermostat’s manufacturer’s servers. It is also thinkable that the global controller directly accesses the smart thermostat data without going through the smart thermostat’s manufacturer's servers. In yet another embodiment the local controller accesses the smart thermostat’s data by communication with the thermostat either wired or wireless. The local controller can further send the data of the smart thermostat to the global controller. Also, the local controller features a digital temperature sensor measuring the outside temperature of the outgoing hot tap water pipe. Using this temperature sensor, 5 the local controller can detect hot tap water consumption.

In another embodiment the data gathered from the heat extractors, said data retrieved from the thermostat and/or sensors, is used to create a thermal model of every heat extractor. The thermal model relates current and historic data and setpoints to the heat extractors actual temperature. The thermal model is updated and improved continuously with every newly available data point. The thermal model can be used as part of the control strategy of the local and/or global controller for the setting of the flow regulator. In another embodiment according to the present invention, the return temperature is reduced as much as possible, whilst providing the heat extractor with the desired amount of heat. Control of the flow rate increases the system’s efficiency. By consuming the heat in the heating medium, no heat has to be shed to the surroundings. By regulating the flow of the water, the return temperature is regulated by adjusting the flow according to the heat demand.

Heat extractors can be connected in series or in parallel to the piping network. To eliminate mutual influence of the heat extractors parallel connections to the piping system are preferred. Therefore at least some of the heat extractors, and preferably all of the heat extractors are connected in parallel to the piping network.

In another embodiment of the invention, the district heating system further comprises at least one substation located between one or more heat sources and the first heat extractor, wherein each substation is connected in parallel to the heat source, and comprises a connection for the supplying and returning section. The substations are part of the piping network, in the substations water is distributed to a number of heat extractors. It is also possible to connect two substations in series under the requirement that the second substation further comprises an additional connection to the one or more heat sources. Data form the substations is combined with data from the heat extractors connected to the substation in order to simultaneously optimize both the substation and the heat extractor for maximum effect. The substation may comprise a heat exchanger with a pump. The heating medium pumped towards the substation will be heated by the heat exchanger, by regulating the pump speed the temperature can be regulated.

In yet a different embodiment of the present invention, the heat extractor comprises a 3-way switch, for at least partially redirecting the heating medium from the supply connection to a heat exchanger to heat up tap water. The 3-way switch allows to connect the tap water system to the district heating system. The 3-way switch may for example be a 3-way solenoid valve, which can be controlled. Alternatively the 3-way switch may be replaced by two controllable switches, dedicated to heating and hot tap water respectively, for example two 2-way solenoid switches, which can both be controlled individually.

In another embodiment of the present invention, the heat extractor further comprises a thermostat, wherein the thermostat can communicate with the local controller through at least one communication means consisting of the group of: wire, or using wireless local radio protocols like Z-Wave, Zigbee, Bluetooth, DECT, Wi-Fi, other ISM band RF protocols or comparable. Communication of the thermostat with the local controller is important for the control of the system. The thermostat itself can be used to change the heat demand temporarily, or provide a heat demand pattern, usually by providing a program describing the desired building temperatures throughout the week.

In yet another embodiment of the invention, the district heating system is a closed loop district heating system, wherein the returning heating medium functions as coolant for one or more of the heat sources. This allows for efficient use of the heating medium, said heating medium can be used as coolant for one or more of the heat sources. Since the heating medium flow is controlled and preferably maintained constant, the cooling can be effectively regulated since the unwanted return temperature fluctuations are limited by the control system.

In yet another embodiment of the invention, the heat extractor further comprises sensors, in particular at least one temperature sensor and a flow rate sensor, more in particular two temperature sensors and a flow rate sensor. The temperature and flow measurements are important for updating the models of the heat extractor, for making a better prediction of future heat demand. Typically the supply temperature, return temperature and the flow are measured. The heat demand is determined through these parameters.

Yet in another embodiment of the present invention, the controllable flow regulator is a valve, wherein the smart valve is continuously controllable between a fully open and a fully closed setting. A valve has the benefit of being easily controllable. The valve can preferably be electronically controlled by the local and/or the global controller. The valve can in a further embodiment also be controlled by means of Pulse Width Modulation with a frequency between 0.001 Hz and 0.025 Hz, preferably between

0.0015 Hz and 0.015 Hz, and more preferably between 0.002 Hz and 0.01 Hz. It has turned out that this frequency range is optimal for the control of the return temperature. In general, with a district heating system according to the present invention the duty cycle of delivering heat and not delivering heat changes with respect to a regular district heating duty cycle. In fact, according to the present invention the period of delivering heat increases, with a lower flow rate. The periods wherein no heat is delivered to the heat extractor remains roughly the same. It is to be noted that the smart valve might in a different embodiment be replaced by a controllable pump.

The invention will now be elucidated into more detail with reference to the following figures. Herein: - Figure 1 shows schematic view of the district heating system; - Figure 2a shows the physical network of a heat extractor connectect to the piping network directly; - Figure 2b shows the physical network of a heat extractor connected to the piping network indirectly; - Figure 3 shows the communication scheme between the district heating system and heat extractor.

Figure 1 shows a schematic view of the district heating system according to the present invention. The district heating system 1 comprises a piping network 2 for transporting a heating medium comprising a supplying 3 and returning 4 section and one or more heat sources 5, for heating the heating medium to a predetermined supply temperature and providing it to the supplying section 3, and receiving the heating medium from the returning section 4, and at least one heat extractor 6, wherein at least one heat extractor is connected to the piping network 2 through an interface 10, which comprises a supply connection 7 (shown in figures 2a and 2b in more detail), for receiving the heating medium from the supplying section 3 of the piping network 2, a return connection 8, for delivering the heating medium at a return temperature to the returning section 4 of the piping network 2, at least one heat extracting element 9, placed between the supply connection 7 and the return connection 8, for extracting heat from the heating medium, a controllable flow regulator 11, such as a valve, for determining a flow resistance to regulate a flow rate of the heating medium, a local controller 12, the local controller 12 is configured to control the controllable flow regulator 11 based on a flow rate setpoint and a measurement of the actual return temperature. The district heating system further comprises at least one substation 14 located between one or more heat sources 5 and the first heat extractor 6, wherein at least one substation 14 is connected in parallel to the heat sources 5, and comprises a connection for the supplying 3 and returning section 4. Preferably all of the heat extractors 6 are connected in parallel to the piping network 2. The district heating system 1 is a closed loop district heating system, wherein the returning heating medium could function as coolant for the heat source 5.

Figure 2a shows the physical network at one of the heat extractors 6. wherein at least one heat extractor 6 is connected to the piping network through an interface 10, comprises a supply connection 7, for receiving the heating medium from the supplying section 3 of the piping network 2, a return connection 8, for delivering the heating medium at a return temperature to the returning section 4 of the piping network, at least one heat extracting element 9, placed between the supply connection 7 and the return connection 8, for extracting heat from the heating medium, a controllable flow regulator 11, such as a valve, for determining a flow resistance to regulate a flow rate of the heating medium, a local controller 12 the local controller 12 is configured to control the controllable flow regulator 11 based on a return temperature setpoint and/or flow rate setpoint in combination with measurements of the actual flow rate and/or actual return temperature. The heat extractor 6 comprises a 3-way switch 15, for at least partially redirecting the heating medium from the supply connection 7 to a heat exchanger 16 to heat up tap water. The heat extractor 6 further comprises sensors, in particular at least one temperature sensor and a flow rate sensor, more in particular two temperature sensors and a flow rate sensor. The controllable flow regulator 11, 3-way switch 15 and at least one sensor are located in a heat interface unit 10, forming the interface 10 between the heat extractor 6 and the piping network 2.

Figure 2b shows a second possible connection between the heat extractor 6 and the district heating system. This connection is called an indirect connection, which is shown by the inclusion of the Heat Exchanger 19. That is, the heat extractor 6 has its own piping network, and the heating medium of the heat extractor 6 is heated by means of the Heat Exchanger 19 installed in the heat interface 10. In such an embodiment a pump 18 is required to circulate the heating medium in the heat extractor’s 6 piping network.

Figure 3 shows the communication scheme between the district heating system and the heat extractor.

The district heating system comprises a global controller 13, for configuring the local controller 12 of at least one heat extractor 6. The global controller 13 is configured to minimize a peak demand, the global controller 13 thereto determines and controls the value, and/or moment of a heat demand setpoint of the heat extractor 6, in particular the value and/or moment of the heat demand setpoint related to the peak demand.

The peak demand is determined by historic heat demand setpoint data of the heat extractor 6. The global controller is further configured to achieve the overall highest efficiency of the system.

This overall highest efficiency is realized through the control strategy which is a result of minimizing peak demands and controlling the flow of the heating medium to reduce the returning temperature of the heating medium.

The heat extractor 6 further comprises a thermostat 17, wherein the thermostat 17 can communicate with the local controller 12 through at least one communication means consisting of the group of: wire, or using wireless local radio protocols like Z-Wave, Zigbee, Bluetooth, DECT, Wi-Fi, other ISM band RF protocols or comparable.

Claims (14)

Conclusions A heating system, in particular comprising a district heating system; - a pipe network for conveying a heating medium, comprising a supply section and a discharge section; - one or more heat sources, for heating the heating medium to a predetermined supply temperature, and supplying it to the supply section, and receiving the heating medium from the discharge section; - at least one heat consumer, - connected to the pipe network via an interface; also including; - a supply connection, for receiving the heating medium from the supply section of the pipe network; - a discharge connection, for supplying the heating medium, at a discharge temperature, to the discharge section of the pipe network; - at least one heat extraction element, placed between the supply connection and the discharge connection, for extracting heat from the heating medium; - an adjustable flow regulator, for example a valve, pump or adjustable differential pressure regulator, for controlling a flow rate of the heating medium; - a local flow controller controller, characterized in that the local controller is configured to control the adjustable flow controller based on a discharge temperature setpoint and/or flow rate setpoint. The district heating system of claim 1, wherein the local controller is further configured to control the adjustable flow controller based on measurements of the actual flow rate and/or the actual discharge temperature. A district heating system according to any one of the preceding claims, wherein the system also comprises a global controller for adjusting settings of the local controller of at least one heat consumer. District heating system according to claim 3, wherein the global controller is configured to minimize a peak demand, the global controller determines and therefore controls the value and/or timing of a heat demand setpoint of the heat consumer, in particular the value and/or the moment of the heat demand setpoint related to the peak demand. A district heating system according to claim 4, wherein the peak demand is determined by historical heat demand setpoint data from the heat consumer. A district heating system according to any one of the preceding claims, wherein at least a number of the heat consumers, and preferably all heat consumers, are connected in parallel to the pipe network. A district heating system according to any one of the preceding claims, wherein the district heating system also comprises at least one substation located between the one or more heat sources and the first heat sink, wherein at least one substation is connected in parallel to the heat sources, and a connection for comprises the supply section and the discharge section. A district heating system according to any one of the preceding claims, wherein the heat sink comprises a three-way switch for at least partially diverting the heating medium from the supply connection to a heat exchanger to heat tap water. A district heating system according to any preceding claim, wherein the heat sink also comprises a thermostat, the thermostat being configured for communication with the local controller via at least one communication means consisting of the group of: wire, or using wireless local radio protocols such as Z-Wave, Zigbee, Bluetooth, DECT, Wi-Fi, other ISM band RF protocols or similar. A district heating system according to any one of the preceding claims, wherein the district heating system is a closed district heating system, wherein the discharged heating medium acts as a coolant for the one or more heat sources. District heating system according to any one of the preceding claims, wherein the heat sink also comprises sensors, in particular at least one temperature sensor and a flow rate sensor, more in particular two temperature sensors and a flow rate sensor. A district heating system according to any one of the preceding claims, wherein the adjustable flow controller, three-way switch and at least one sensor are placed in a heat interface unit, which forms the interface between the heat sink and the pipe network. A district heating system according to any one of the preceding claims, wherein the controllable flow controller is a valve, the smart valve being continuously controllable between a fully open and fully closed position. A district heating system according to any one of the preceding claims, wherein the adjustable flow controller controls the flow rate by means of pulse width modulation at a frequency between 0.001 Hz and 0.025 Hz, preferably between 0.0015 Hz and 0.015 Hz, and more preferably between 0.002 Hz and 0.01 Hz.