SE540972C2

SE540972C2 - Methods, devices and system for controlling a heating network

Info

Publication number: SE540972C2
Application number: SE1750623A
Authority: SE
Inventors: Martin Ek
Original assignee: Tekniska Verken I Linkoeping Ab
Priority date: 2017-05-18
Filing date: 2017-05-18
Publication date: 2019-02-12
Also published as: SE1750623A1

Abstract

The present disclosure provides a method of operating a heating network. The method comprises circulating a heat-carrying liquid in the network (3), controlling a temperature of the liquid at a central unit (1), and picking up heat with the network (3) at a plurality of local units (2). Moreover, the method comprises adjusting the temperature of the liquid at the central unit (1) by a predetermined amount (dT), during a predetermined time (dt), and measuring incoming liquid temperature at one of the local units (2). The method also comprises detecting, at the local unit (2), said adjustment of the temperature of the liquid by said predetermined amount (dT) during said predetermined time (dt), and adjusting the heat exchange at the local unit (2) in response to said detection.The disclosure also provides a system for controlling a heating network, a method for controlling the local unit and a device for controlling the local unit.

Description

METHODS. DEVICES AND SYSTEM FOR CONTROLLING A HEATING NETWORK Technical field The present disclosure relates to a method for controlling heating systems, and to devices which are used to achieve such control.

The disclosure finds particular application in district heating networks.

Background District heating systems are used in many places. Typically, a district heating system comprises a central unit, such as a power plant, or other type of heat source, and a number of local units, typically buildings. Heat is distributed from the central unit via a network in which a fluid medium, typically water, is circulated. At each local unit, heat is picked up from the network via a heat exchanger. To determine energy consumption at the local unit, incoming and outgoing medium temperatures, and volume used, may be measured.

It is known, that in district heating networks, the load, or energy demand, may vary during the day. For example, the load may be lower than average during late evening and night (“low load hours”), and higher than average during morning hours (“high load hours”), when large parts of the population are preparing to go to work, and thus using showers, etc.

One strategy to reduce the effect of peaks is to “charge” the local units with heat, typically one or a few degrees centigrade, during “low load hours”, and to recover this heat during “high load hours”. This may be achieved by increasing the temperature of the liquid leaving the central unit by about 5-10 degrees centigrade compared to a nominal temperature during low load hours, and by decreasing the temperature of the liquid leaving the central unit by about 5-10 degrees centigrade during high load hours.

The district heating system includes a central controller, which controls the flow and temperature of medium going out from the central unit, and a local controller at the respective local unit, which controls the energy pick-up from the network.

WO07136344A1 discloses a method of optimizing the power usage in a district heating system by using a communication system for signaling to the local units to reduce energy pick-up by reducing flow into the local unit.

A disadvantage of the system disclosed in WO07136344A1 is that a communication link needs to be established, which may require additional hardware to be installed both in the local units and in the central unit.

Summary It is an object of the present disclosure to provide a method and device which allow such “charging” of the network, and which can be realized at a lower cost.

The invention is defined by the appended independent claims, with embodiments being set forth in the dependent claims, in the following description and in the drawings.

According to a first aspect, there is provided method of operating a heating network. The method comprises circulating a heat-carrying medium in the network, controlling a temperature of the medium at a central unit, and picking up heat from the network at a plurality of local units. The method further comprises adjusting the temperature of the medium at the central unit by a predetermined amount, during a predetermined time, and measuring incoming liquid temperature at one of the local units. Moreover, the method comprises detecting, at the local unit, said adjustment of the temperature of the liquid by said predetermined amount during said predetermined time, and adjusting the heat pick-up at the local unit in response to said detection.

The above described method may be implemented in most district heating systems today. As the sensors and controllers are already in place, a comparatively simple reprogramming is sufficient to modify the local controller to detect rapid changes in network temperature and to adjust heat pick-up in dependence thereof.

The method may also be implemented in other heating networks, such as local or private heating networks supplying a number of units with heat from a central heat source.

In the method, the liquid may be supplied by the central unit at a nominal temperature which varies by less than 2 degrees centigrade during at least 99 % of a day.

The system is particularly suitable for use in district heating systems which are relatively stable in terms of supply temperature.

Alternatively, the 3 liquid may be supplied by the central unit at a nominal temperature which varies at a rate of less than 6 degrees centigrade per hour during at least 99 % of the day.

Such varying nominal temperature will be sufficiently stable not to trigger the local units to adjust heat pick-up.

During normal operation, the liquid may be supplied at a nominal temperature of 55-90 degrees centigrade, preferably of 60-80 degrees centigrade.

Systems operating at 55-90 degrees centigrade are normally known as “low temperature heating systems”. Such systems are normally more stable with respect to supply temperature than systems operating at higher temperatures.

The predetermined amount may be 3-10 degrees centigrade, preferably 4-8 or 5-7 degrees centigrade.

The predetermined time may be 1-20 minutes, preferably 2-15 minutes or 3-10 minutes.

The heat pick-up may be adjusted by adjusting of a flow rate of incoming liquid at the local unit, and/or by adjusting a flow rate of a local liquid at the local unit.

The incoming liquid is the liquid from the network and the local liquid is a liquid circulated within the local unit.

In the method, said adjusting the temperature of the liquid at the central unit by a predetermined amount, during a predetermined time may comprise increasing the temperature of the liquid at the central unit, and maintaining a thus increased temperature for about 3-10 hours, preferably about 3-6 hours.

During such period of increased temperature, the network and, due to the signaling effect, also the local units, will accumulate some heat.

For example, the increased temperature may be maintained during low load hours, preferably between 00:00 and 06:00.

The increased temperature may be increased by a certain amount compared to a nominal temperature. Such nominal temperature may be fixed or slowly variable, e.g. during a predetermined temperature curve.

In the method, said adjusting the temperature of the liquid at the central unit by a predetermined amount, during a predetermined time may comprise decreasing the temperature of the liquid at the central unit, and maintaining a thus decreased temperature for about 3-10 hours, preferably about 3-6 hours.

During such period of decreased temperature, accumulated heat in the network will be returned.

The decreased temperature may be maintained during high load hours, preferably between 06:00 and 10:00.

The decreased temperature may be decreased by a certain amount compared to the nominal temperature, or compared to the increased temperature. As one example, the temperature during the high load hours may equal the nominal temperature.

According to a second aspect, there is provided a control system for a heating network, comprising a central unit having a central controller and a central actuator, controlled by the central controller to control a temperature of a heat-carrying liquid that is to be circulated in the system; and a local unit having a local controller, a local actuator, arranged to control heat pick-up from the network, and a local temperature sensor, arranged for measuring temperature of the liquid. The central controller is arranged to adjust the temperature of the liquid by a predetermined amount during a predetermined time; and the local controller is arranged to receive temperature data from the local temperature sensor, to detect the adjustment of the liquid by the predetermined amount during the predetermined time, and to cause the local actuator to adjust heat pick-up from the network in response to said detection.

According to a third aspect, there is provided a method of operating a central controller in a heating network, comprising circulating a heat-carrying liquid in the network, controlling a temperature of the liquid at the central unit, and signaling to local units of the heating network to adjust their heat pick-up from the network by adjusting a temperature of the liquid at the central unit by a predetermined amount, during a predetermined time.

According to a fourth aspect, there is provided a control device for use in a central unit of a heating network, comprising a central controller, and a central actuator, controlled by the central controller to control a temperature of a heat-carrying liquid that is to be circulated in the system. The central controller is arranged to signal to local units of the heating network to adjust their heat pick-up from the network by adjusting a temperature of the liquid at the central unit by a predetermined amount during a predetermined time.

According to a fifth aspect, there is provided a method of controlling a local unit that is connected to a heating network. The method comprises measuring a temperature of a liquid supplied by the system, detecting an adjustment of a temperature of the liquid by a predetermined amount during a predetermined time, and adjusting heat pick-up from the liquid in response to said detection.

According to a sixth aspect, there is provided a control device for use in a local unit of a heating network, comprising a temperature sensor, arranged for sensing temperature of an incoming heat-carrying liquid, an actuator, arranged to control an amount of heat that is picked up from the liquid, and a local controller, connected to the sensor to receive temperature data and to the actuator to control the actuator. The controller is arranged to detect an adjustment of the temperature of the liquid by a predetermined amount during a predetermined time, and to cause the actuator to adjust heat pick-up from the network in response to said detection.

Brief description of the drawings Fig. 1 is a schematic view of a simplified district heating network.

Fig. 2 is a schematic view of a building which is connected to the district heating network.

Detailed description Referring to Fig. 1, there is illustrated a simplified version of a district heating network, comprising a central unit 1, a plurality of local units 2a, 2b, 2c, 2d and a distribution network, comprising a feed line and a return line.

The central unit is 1 arranged to supply a heat-carrying liquid via the feed line. At the local units 2a, 2b, 2c, 2d, which may be connected in parallel, as illustrated, a portion of the liquid is deviated, and heat taken off by means of one or more heat exchangers, after which the liquid is returned, at a slightly different temperature, to the return line of the network 3.

It is understood that the network 3 may be used to transport heat, for heating the local units, or remove heat, i.e. to cool, the local units.

At the central unit 1, there is provided a heat source 10, which may be a power plant or some other source of heat, such as excess heat from a process, a heat pump, a geothermal station, a boiler, etc. As another option, the heat source may be a first district heating network, e.g. a hightemperature district heating network, i.e. a network operating at approximately 90-120 degrees centigrade.

The heat source 10 is connected to one side of a heat exchanger 13. To the other side of the heat exchanger 13, there may be a distribution network 3 connected. This network may be a high temperature network, or a low temperature network, i.e. a district heating network which operates at a temperature of 55-90 degrees centigrade.

At the central unit 1, there may also be provided a central controller 14, an outdoor temperature sensor 11 and a network temperature sensor 12, for sensing a temperature of the liquid in the network 3, typically for sensing the temperature of the outgoing liquid.

The controller 14 is connected to an actuator 15, such as a valve ora pump, which is configured to regulate the temperature of the liquid supplied in the network 3.

Such actuator 15 may operate on one or both sides of the heat exchanger 13 to regulate flow on that side.

The controller 14 may be configured to provide a constant nominal temperature throughout the day. Alternatively, the controller may be configured to provide a slowly varying temperature, i.e. a temperature which varies by less than 2 degrees centigrade per 20 minutes.

The controller 14 is configured to make rapid adjustments of the temperature of the outgoing liquid. The timing of such adjustment may be based on statistical data on use of the system, i.e. knowledge about when the network usage is higher or lower.

The rapid adjustment may be performed at a rate of 3-10 degrees during 3-20 minutes. Typically, an adjustment is made by a temperature difference dT of about 4-6 degrees during a time period dt of 3-7 minutes.

Referring to Fig. 2, there is illustrated a local unit 2, which may be a building or other type of facility, which may consume heating or cooling from the central unit.

The local unit 2 has a connection 31 to the network 3, comprising a feed line and a return line. At the local unit, there is provided one or more heat exchangers 24a, 24b, which may be used for e.g. hot water and heating purposes, respectively.

The local unit 2 may comprise an outdoor sensor 21, for sensing outdoor temperature, an incoming liquid temperature sensor 22, for sensing a temperature of incoming liquid and local network sensors 23a, 23b for sensing temperature of the local circuits, such as hot water circuit and/or heating circuit. Moreover, one or more pumps 28, expansion vessels 26 and actuators (pumps, valves 20a, 20b) may be provided. The heating circuit may comprise a plurality of radiators 29a, 29b, 29c, or other means for supplying or picking up heat to/from the local unit.

The local unit also comprises a controller 25, which is connected to the respective valves, pumps 28 and local sensor 23a, 23b, as is conventional.

As mentioned, the local unit 2 comprises an incoming liquid temperature sensor 22, which is connected to the local controller 25. Hence, the local controller 25 may sense the temperature of the incoming liquid.

The system may be operated as follows.

As mentioned, the central controller 14 is capable of controlling the temperature of the liquid supplied to the network 3.

Based on knowledge of system usage, the central controller may, at a first point in time, rapidly adjust, e.g. increase, the temperature ofthe outgoing liquid. Such adjustment may be on the order of 3-10 degrees during a period of 1-20 minutes.

As the thus temperature-adjusted liquid reaches a local unit 2, 2a, 2b, 2c, 2d, the local controller 25 may detect this rapid adjustment of temperature.

In response, the local controller may increase heat pick-up from the network 3 by the local unit. For example, the heat pick-up may be increased, and maintained for a certain time, typically during low load hours.

In the case of a temperature increase, the increased pick-up at the local unit will result in additional heating of the local unit. Depending to the inertia of the local unit, such heating will typically be relatively slow, and if the additional heating takes place for a limited number of hours, such as 3-10 hours, hardly noticeable for inhabitants of a building. However, the increased heating will accumulate heat in the building, including in the heating network.

At a second point in time, the central controller 14 may again rapidly adjust, e.g. decrease, the temperature of the outgoing liquid. Such adjustment may be on the order of 3-10 degrees during a period of 1-20 minutes.

Again, as the temperature-adjusted liquid reaches the local unit 2, 2a, 2b, 2c, 2d, the local controller 25 may detect this rapid adjustment of temperature.

In response, the local controller 25 may decrease heat pick-up from the network 3 by the local unit 2. For example, the heat pick-up may be decreased, and maintained for a certain time.

It is possible to provide a protocol of temperature adjustments.

For example, the system may vary between two levels of energy exchange, one higher, triggered by a rapid increase in liquid temperature in the network 3, and one lower, triggered by a rapid decrease in liquid temperature in the network 3.

As another alternative, the system may vary between three or more energy exchange levels, transitions between which may be triggered by rapid adjustments up or down.

It is noted that the above disclosed communication protocol may be used in systems which supply heated liquid at a stable temperature, or which supply heat at a slowly varying, e.g. cyclic temperature.

Claims

1. A method of operating a heating network, comprising: circulating a heat-carrying liquid in the network (3), controlling a temperature of the heat-carrying liquid at a central unit (1), picking up heat from the network (3) at a plurality of local units (2), characterized by adjusting the temperature of the heat-carrying liquid at the central unit (1) by a predetermined amount (dT), during a predetermined time (dt), and measuring incoming heat-carrying liquid temperature at one of the local units (2, 2a, 2b, 2c, 2d), detecting, based on the measurement at the local unit (2, 2a, 2b, 2c, 2d), said adjustment of the temperature of the heat-carrying liquid by said predetermined amount (dT) during said predetermined time (dt), and adjusting the heat pick-up at the local unit (2, 2a, 2b, 2c, 2d) in response to said detection.

2. The method as claimed in claim 1, wherein the heat-carrying liquid is supplied by the central unit (1) at a nominal temperature which varies by less than 2 degrees centigrade during at least 99 % of a day.

3. The method as claimed in claim 1, wherein the heat-carrying liquid is supplied by the central unit (1) at a nominal temperature which varies at a rate of less than 6 degrees centigrade per hour during at least 99 % of the day.

4. The method as claimed in any one of claims 1-3, wherein, during normal operation, the heat-carrying liquid is supplied at a nominal temperature of 55-90 degrees centigrade, preferably of 60-80 degrees centigrade.

5. The method as claimed in any one of the preceding claims, wherein the predetermined amount (dT) is 3-10 degrees centigrade, preferably 4-8 or 5-7 degrees centigrade.

6. The method as claimed in any one of the preceding claims, wherein the predetermined time (dt) is 1-20 minutes, preferably 2-15 minutes or 3-10 minutes.

7. The method as claimed in any one of the preceding claims, wherein the heat pick-up is adjusted by adjusting of a flow rate of incoming heat-carrying liquid at the local unit (2, 2a, 2b, 2c, 2d), and/or by adjusting a flow rate of a local heat-carrying liquid at the local unit (2, 2a, 2b, 2c, 2d).

8. The method as claimed in any one of the preceding claims, wherein said adjusting the temperature of the heat-carrying liquid at the central unit (1) by a predetermined amount (dT), during a predetermined time (dt) comprises increasing the temperature of the heat-carrying liquid at the central unit (1), and maintaining a thus increased temperature for about 3-10 hours, preferably about 3-6 hours.

9. The method as claimed in claim 8, wherein the increased temperature is maintained during low load hours, preferably between 00:00 and 06:00.

10. The method as claimed in any one of claims 1-7, wherein said adjusting the temperature of the heat-carrying liquid at the central unit (1) by a predetermined amount (dT), during a predetermined time (dt) comprises decreasing the temperature of the heat-carrying liquid at the central unit (1), and maintaining a thus decreased temperature for about 3-10 hours, preferably about 3-6 hours.

11. The method as claimed in claim 10, wherein the increased temperature is maintained during high load hours, preferably between 06:00 and 10:00.

12. A control system for a heating network, comprising: a central unit (1) having a central controller (14) and a central actuator (15), controlled by the central controller (14) to control a temperature of a heat-carrying liquid that is to be circulated in the network; and a local unit (2, 2a, 2b, 2c, 2d ) having a local controller (25), a local actuator (20a, 20b), arranged to control heat pick-up from the heat-carrying liquid, and a local temperature sensor (22), arranged for measuring temperature of the heat-carrying liquid; characterized by the central controller (14) is arranged to adjust the temperature of the heat-carrying liquid by a predetermined amount (dT) during a predetermined time (dt); and wherein the local controller (25) is arranged to receive temperature data from the local temperature sensor (22), to detect the adjustment of the heat-carrying liquid by the predetermined amount (dT) during the predetermined time (dt), and to cause the local actuator (20a, 20b) to adjust heat pick-up from the network in response to said detection.

13. A method of operating a central unit (1) in a heating network, comprising: circulating a heat-carrying liquid in the network (3), and controlling a temperature of the heat-carrying liquid at the central unit (1), and characterized by signaling to local units (2, 2a, 2b, 2c, 2d) of the heating network to adjust their heat pick-up from the heat-carrying liquid by adjusting a temperature of the heat-carrying liquid at the central unit (1) by a predetermined amount (dT), during a predetermined time (dt).

14. A control device for use in a central unit (1) of a heating network, comprising: a central controller (14), and a central actuator (15), controlled by the central controller (14) to control a temperature of a heat-carrying liquid that is to be circulated in the network; characterized by the central controller (14) is arranged to signal to local units (2, 2a, 2b, 2c, 2d) of the heating network to adjust their heat pick-up from the network by adjusting a temperature of the heat-carrying liquid at the central unit (1) by a predetermined amount (dT) during a predetermined time (dt).

15. A method of controlling a local unit (2, 2a, 2b, 2c, 2d) that is connected to a heating network, comprising: measuring a temperature of a heat-carrying liquid supplied by the network, characterized by detecting an adjustment of a temperature of the heat-carrying liquid by a predetermined amount (dT) during a predetermined time (dt), and adjusting heat pick-up from the heat-carrying liquid in response to said detection.

16. A control device for use in a local unit (2, 2a, 2b, 2c, 2d) of a heating network, comprising: a temperature sensor (22), arranged for sensing temperature of an incoming heat-carrying liquid, an actuator (20a, 20b), arranged to control an amount of heat that is picked up from the heat-carrying liquid, and a local controller (25), connected to the sensor (22) to receive temperature data and to the actuator to control the actuator, characterized in that the controller (25) is arranged to detect an adjustment of the temperature of the heat-carrying liquid by a predetermined amount (dT) during a predetermined time (dt), and to cause the actuator (20a, 20b) to adjust heat pick-up from the network in response to said detection.