RESPONSIVE POWER STEERING AND REDUNDANCY

Abstract

The disclosure relates to a method for controlling a thermal distribution system. The method comprises producing heat at a production plant, and determining a capacity limit of the production plant. At a central server, the current and/or forecasted production of heat in the production plant in relation to the capacity limit of the production plant is evaluated. The method further comprises to in response to the current or forecasted production at the production plant approaching the capacity limit, output from the central server a respective control signal to one or more of a plurality of local control units, and receiving the control signal at the respective local control unit. The method further comprises to in response to receiving the control signal at the respective local control unit, reduce an associated local distribution system's outtake of heat or cold from a distribution grid connected to the production plant.

Claims

1. A method for controlling a thermal distribution system, the system comprising: a distribution grid for a fluid based distribution of heat and/or cold, a production plant for producing heat or cold and for delivering the heat or cold to the distribution grid, and a plurality of local control units, each local control unit being associated with a local distribution system in a building, the local distribution system being configured to distribute heating or cooling in the building, each local control unit further being configured to control the associated local distribution system's outtake of heat or cold from the distribution grid, wherein the method comprises: determining a capacity limit of the production plant, evaluating, at a central server, a current and/or forecasted production of heat or cold in the production plant in relation to the capacity limit of the production plant, in response to the current and/or forecasted production at the production plant approaching the capacity limit, outputting, from the central server, a respective control signal to one or more of the plurality of local control units, wherein the respective control signal comprises information pertaining to a temperature offset, receiving the respective control signal at the respective one or more of the plurality of local control units, and in response to receiving the respective control signal at the respective one or more of the plurality of local control units, determining a respective steering temperature based on a temperature outside and/or inside the respective building and on the respective temperature offset, and controlling, at the respective one or more of the plurality of local control units, the associated local distribution system's outtake of heat or cold from the distribution grid based on the steering temperature, and thereby reducing the associated local distributions system's outtake of heat or cold from the distribution grid.

2. The method according to claim 1, wherein the act of evaluating is performed periodically.

3. The method according to claim 1, wherein the method further comprises: setting a production threshold value lower than and related to the capacity limit of the production plant, wherein the act of evaluating comprises comparing the current production with the production threshold value, and wherein, upon the current production reaching the production threshold value, determining that the current production at the production plant approaches the capacity limit.

4. The method according to claim 1, wherein the steering temperature is a set-point temperature for a regulator regulating the temperature of a feed of heat transfer fluid in the local distribution system.

5. The method according to claim 1, further comprising producing heat or cold at the production plant.

6. The method according to claim 1, further comprising: determining, at at least one of the one or more of the plurality of local control units, a base steering temperature for the associated local distribution system based on the temperature outside and/or inside the associated building, determining a return temperature of a return of heat transfer fluid in the associated local distribution system, upon the determined respective steering temperature being lower than the return temperature, determining a temporary steering temperature being higher than the return temperature and lower than the base steering temperature, and controlling the associated local distribution system's outtake of heat from the distribution grid based on the temporary steering temperature.

7. The method according to claim 6, further comprising: over time, determining the return temperature of the return of heat transfer fluid in the associated local distribution system, gradually decreasing the temporary steering temperature while securing that the temporary steering temperature is greater than the return temperature, until the temporary steering temperature reaches the steering temperature.

8. The method according to claim 6, further comprising: until the temporary steering temperature reaches the steering temperature: over time determining a temperature of the feed of heat transfer fluid in the associated local distribution system, and in response to the determined feed temperature reaching the temporary steering temperature: determining the return temperature of the return of heat transfer fluid in the associated local distribution system, and determining a new temporary steering temperature being higher than the determined return temperature and lower than the previous temporary steering temperature.

9. The method according to claim 1, further comprising: determining, at at least one of the one or more of the plurality of local control units, a base steering temperature for the associated local distribution system based on the temperature outside and/or inside the associated building, determining a return temperature of a return of heat transfer fluid in the associated local distribution system, upon the determined respective steering temperature being higher than the return temperature, determining a temporary steering temperature being lower than the return temperature and higher than the base steering temperature, and controlling the associated local distribution system's outtake of cold from the distribution grid based on the temporary steering temperature.

10. The method according to claim 9, further comprising: over time determining the return temperature of the return of heat transfer fluid in the associated local distribution system, gradually increasing the temporary steering temperature while securing that the temporary steering temperature is lower than the return temperature, until the temporary steering temperature reaches the steering temperature.

11. The method according to claim 9, further comprising: until the temporary steering temperature reaches the steering temperature: over time, determining a temperature of the feed of heat transfer fluid in the associated local distribution system, and in response to the determined feed temperature reaching the temporary steering temperature: determining the return temperature of the return of heat transfer fluid in the associated local distribution system, and determining a new temporary steering temperature being lower than the determined return temperature and higher than the previous temporary steering temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The invention will by way of example be described in more detail with reference to the appended schematic drawings, which shows a presently preferred embodiment of the invention.

[0051] FIG. 1 is a schematic diagram of a thermal distribution system;

[0052] FIG. 2 is a schematic diagram of two different local distribution systems.

[0053] FIG. 3 is a flow diagram of the method, according to some embodiments.

[0054] All figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the embodiments, wherein other parts may be omitted.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0055] Detailed embodiments of the present inventive concept will now be described with reference to the drawings. The present inventive concept, may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will convey the scope of the inventive concept to those skilled in the art.

[0056] An example of a thermal distribution system 100 is schematically illustrated in connection with FIG. 1. The thermal distribution system comprises a distribution grid 110 for fluid based distribution of heat and/or cold and a production plant 120 for producing heat or cold and for delivering the heat or cold to the distribution grid 110. The thermal distribution system also comprises a plurality of local control units 140a, 140b, each associated with a local distribution system 150a, 150b. In the in FIG. 1 shown example two local control units 140a, 140b, each associated with a local distribution system 150a, 150b are shown. It is however contemplated that any number of local control units may be used. Further, each local control unit may be configured to service one or more local distribution system 150a, 150b.

[0057] Each local distribution system 150a, 150b is configured to provide heat and/or cold to one or more buildings 160a, 160b. The buildings 160a, 160b, may be office buildings, business premises, residential homes, factories or other buildings in need for heat and/or cold. In the in FIG. 1 shown example each local distribution system 150a, 150b is configured to provide heat and/or cold to one respective building 160a, 160b. However, each local distribution system 150a, 150b may be configured to provide heat and/or cold to a plurality of buildings.

[0058] The local distribution systems 150a, 150b are connected with the distribution grid 110 such that heat and/or cold may be exchanged between the distribution grid 110 and the respective local distribution system 150a, 150b. The exchange of heat and/or cold between the distribution grid 110 and the respective local distribution system 150a, 150b may be made using a heat exchanger. Alternatively, the exchange of heat and/or cold between the distribution grid 110 and the respective local distribution system 150a, 150b may be made using heat pump.

[0059] The distribution grid 110 may be formed by a hydraulic network that deliver a heat transfer fluid. The heat transfer fluid is typically water, although it is to be understood that other fluids or mixture of fluids may be used. Some non-limiting examples are ammonia, anti-freezing liquids (such as glycol), oils and alcohols. A non-limiting example of a mixture is water with an anti-freezing agent, such as glycol, added thereto.

[0060] The production plant 120 is configured to heat or cool the heat transfer fluid of the distribution grid 110. The heated or cooled heat transfer fluid may be transported via a feed conduit 111. Return heat transfer fluid may be transported via a return conduit 112 to the production plant 120. In the case of the heated heat transfer fluid is transported via the feed conduit 111 and cooled heat transfer fluid is returned via the return conduit 112 the distribution grid 110 may be considered as a district heating grid. In the case of the cooled heat transfer fluid is transported via the feed conduit 111 and heated heat transfer fluid is returned via the return conduit 112, the distribution grid 110 may be considered as a district cooling grid. According to another embodiment the distribution grid 110 may be a district thermal energy distribution system as disclosed in WO 2017/076868. In such case the feed conduit 111 may be considered to be the hot conduit disclosed in WO 2017/076868 and the return conduit 112 may be considered to be the cold conduit disclosed in WO 2017/076868.

[0061] The local distribution system 150a, 150b is configured to distribute heat and/or cold in the building 160a, 160b. The local distribution system may distribute heat or cold in the building via a heat transfer fluid. The heat transfer fluid is typically water, although it is to be understood that other fluids or mixture of fluids may be used. Some non-limiting examples are ammonia, anti-freezing liquids (such as glycol), oils and alcohols. A non-limiting example of a mixture is water with an anti-freezing agent, such as glycol, added thereto.

[0062] The local control unit 140a, 140b is configured to control the associated local distribution system's 150a, 150b outtake of heat and/or cold from the distribution grid 110. The heat transfer fluid of the local distribution system 150a, 150b is typically not in fluid connection with the heat transfer fluid of the distribution grid 110. As mentioned above, the distribution system 150a, 150b is thermally connected to the distribution grid 110 via a heat exchanger or a heat pump.

[0063] The thermal distribution system 100 further comprises a central server 130. The central server 130 is connected to the production plant 120 and to the local control units 140a, 140b. The central server 130 may be any type of server comprising a processing unit. The central server 130 may physically comprise one single server device. Alternatively, the central server 130 may be distributed over several server devices. The central server 130 may be comprised in a production plant 120, or at any other suitable location. The central server 130 is configured to communicate with the production plant 120. The central server may communicate with the production plant 120, for example, via a dedicated network, over the Internet, or a combination thereof. The central server 130 is further configured to communicate with the local control units 140a, 140b, for example, via a dedicated network, over the Internet or a combination thereof. The communication in the dedicated network or the Internet may be wireless and/or wired.

[0064] The central server 130 is configured to determine a capacity limit of the production plant 120. Further, the central server 130 is configured to determine and a current or forecasted capacity for the production plant 120. The central server 130 is further configured to send a control signal 131 to at least one of the plurality of local control units 140a, 140b.

[0065] The local control unit 140a, 140b may be configured to, in response to a control signal from the central server 130, decrease or increase the local distribution system's 150a, 150b outtake of heat or cold from the distribution grid 110.

[0066] The local control unit 140a, 140b may be configured to determine a temperature from outside and/or inside of the building 160a, 160b. The local control unit 140a, 140b may be configured to decrease or increase the local distribution system's 150a, 150b outtake of heat and/or cold from the distribution grid 110 based on the determined temperature.

[0067] Two examples of a local distribution systems 150a, 150b will now be described with reference to FIG. 2. The local distribution system 150a is configured to distribute heating in a building. The heating may be in form of comfort heating, hot tap water and/or any other heating need of a building. The local distribution system 150b is configured to distribute cooling in a building. The cooling may be comfort cooling, cooling for refrigeration or freezing purposes, and/or any other cooling need of a building. The local distribution systems 150a, 150b may be arranged in one and the same building. Alternatively, the local distribution systems 150a, 150b may be arranged in different buildings.

[0068] The local distribution system 150a comprises a local control unit 140a, a device 155a configured to exchange thermal energy between the local distribution system 150a and the distribution grid 110 and a heat emitter 156. In the in FIG. 2 shown example the device 155a configured to exchange thermal energy between the local distribution system 150a and the distribution grid 110 is a heat exchanger. However, device 155a configured to exchange thermal energy between the local distribution system 150a and the distribution grid 110 may instead be a heat pump. The use of a heat exchanger or heat pump is depending on the temperature of the heat transfer fluid in the distribution grid 110 and the wanted temperature of the heat transfer fluid of the local distribution system 150a. Via the device 155a configured to exchange thermal energy between the local distribution system 150a and the distribution grid 110, heat from the distribution grid 100 is distributed to the local distribution system 150a. Heat may thereafter be emitted to the building wherein the local distribution system 150a is located via the heat emitter 156. The local distribution system 150a may comprise one or more heat emitters 156. The local control unit 140a is configured to control the associated local distribution system's 150a outtake of heat from the distribution grid 110. The local control unit 140a is adapted to receive a control signal from the central server 120 and to control the associated local distribution system's 150a outtake of heat from the distribution grid 110 according to the received control signal.

[0069] The local distribution system 150b comprises a local control unit 140b, a device 155b configured to exchange thermal energy between the local distribution system 150b and the distribution grid 110 and a heat absorber 157. In the in FIG. 2 shown example the device 155b configured to exchange thermal energy between the local distribution system 150b and the distribution grid 110 is a heat exchanger. However, device 155b configured to exchange thermal energy between the local distribution system 150b and the distribution grid 110 may instead be a heat pump. The use of a heat exchanger or heat pump is depending on the temperature of the heat transfer fluid in the distribution grid 110 and the wanted temperature of the heat transfer fluid of the local distribution system 150b. Via the device 155b configured to exchange thermal energy between the local distribution system 150b and the distribution grid 110, heat from the distribution grid 100 is distributed to the local distribution system 150b. Heat may thereafter be absorbed from the building wherein the local distribution system 150b is located via the heat absorber 157. The local distribution system 150b may comprise one or more heat absorbers 157. The local control unit 140b is configured to control the associated local distribution system's 150b outtake of cold from the distribution grid 110. The local control unit 140b is adapted to receive a control signal from the central server 120 and to control the associated local distribution system's 150b outtake of cold from the distribution grid 110 according to the received control signal.

[0070] The local control unit 140a, 140b may control the local distribution system's 150a, 150b outtake of heat or cold from the distribution grid 100 via a steering signal T.sub.steer. The local control unit 140a, 140b or the local distribution system 150a, 150b may comprise a PID-controller to control an outtake from the distribution grid 110 via the device 155a, 155b configured to exchange thermal energy between the local distribution system 150a, 150b and the distribution grid 110.

[0071] The local control unit 140a, 140b may be configured to determine a temperature T.sub.mes and decrease or increase the local distribution system's 150a, 150b outtake of heat or cold from the grid 110 based on the determined temperature. In the case of the local distribution system 150a being a system for emitting heat into the building T.sub.mes is typically determined just outside the building wherein the local distribution system 150a is located. In the case of the local distribution system 150b being a system for absorbing heat from the building T.sub.mes is typically determined inside the building.

[0072] A sensor may be arranged to sense a return temperature T.sub.ret of heat transfer fluid entering the device 155b configured to exchange thermal energy between the local distribution system 150a, 150b and the distribution grid 110. The sensor may be connected to the local control unit 140a, 140b associated with the local distribution system 150a, 150b.

[0073] A method for controlling the thermal distribution system 100 is described with reference to FIG. 3. It will be appreciated that in FIG. 3 the term TSP is an abbreviation for temporary steering temperature. The nodes A and B have been inserted to clarify the flow chart for the method between FIG. 3-1, FIG. 3-2 and FIG. 3-3 and are not part of the method. FIG. 3-1 shows a flow diagram for a method applicable to distribution systems for both heat and cold. FIG. 3-2 shows a flow diagram for a part of the method related to distribution of heat and FIG. 3-3 shows a flow diagram for a part of the method related to distribution of cold.

[0074] The method comprises producing S210 heat or cold at the production plant 120. The method 200 further comprises, at the central server 130, determining S220 a capacity limit of the production plant 110. The central server 130 may evaluate S230 the current or a forecasted production capacity in relation to the capacity limit. The central server 130 may determine S240 if the current or forecasted production at the production plant is approaching the capacity limit.

[0075] The central server 120 may further set S225 a production threshold, related to or based on the determined capacity limit, and lower than the determined capacity limit. If the server has set a production threshold, the act of evaluating S230 may comprise comparing the current production with the production threshold value. If so, the method further comprises determining S240, upon the current production reaching the production threshold value, that the current production at the production plant approaches the capacity limit.

[0076] In response to being determined S240 that a current or forecasted production at the production plant is approaching the capacity limit or the production threshold, the central server 130 may output S250 a control signal. If it is not determined S240 that the capacity limit is being approached, the central server may continue to monitor the capacity level of the production plant, in steps S220 or S230.

[0077] The control signal may, for example, be a temperature offset. The offset may be an actual temperature value with which a local control unit should adjust the outtake from the distribution grid. The actual value may be a positive or negative value. The offset may be a percentage value to be applied to the current or calculated outtake. The offset may be determined according to the inertia of each building combined with the need to steer their aggregated need of effect connected to production units. Larger offset to handle larger steering needs and smaller offset to handle smaller steering needs.

[0078] Independently, a local control unit 140 may determine S260 a temperature T.sub.mes. T.sub.mes may be determined outside of the building with which it is associated. Alternatively, T.sub.mes may be determined inside the building. The local control unit 140 may be configured to control the associated local distribution system's 150 outtake of heat or cold from the distribution grid based on the determined temperature. The local control unit 140 may further determine S270 a base steering temperature for the associated local distribution system 150 based on the determined temperature. The base steering temperature is a temperature controlling the distribution system's 150 outtake of heat or cool from the distribution grid 110. The base steering temperature may be a set-point temperature for the heat transfer fluid.

[0079] The control signal is received S280 at the local control unit 140. The local control unit 140 may adjust the associated local distribution system's 150 outtake of heat or cold from the distribution grid 110 based on the control signal. For example, the local control unit 140 may adjust the base steering temperature based on an offset received via the control signal. If the control signal indicates a temperature value, the local control unit 140 may apply the value on the steering temperature, or if the control signal indicates a percentage value the local control unit 140 may apply the percentage on the steering temperature. For example, the offset may be added or subtracted from the base steering temperature. The local control unit 140 may thereby determine S290 a reduced or increased steering temperature. The reduced or increased steering temperature may be used until another control signal is received. The outtake of the local distribution system 150 may be adapted S295 accordingly.

[0080] It will be appreciated that the steps S210, S220-S250, S260-S270 and S280-S205 may be performed independently, and that all steps are optional. Some steps may be performed several times, other may be omitted or performed a small amount of times.

[0081] In some examples of the method, the local control unit 140 may further reduce or increase the steering temperature based on a return temperature, T.sub.ret, of the local distribution system. The local control unit 140 or a local distribution system 150 may determine S310 the return temperature of a return of heat transfer fluid in the local distribution system 150.

[0082] In case of heat is taken out from the distribution grid 110, the local control unit 140 may determine S320 that a determined reduced steering temperature is lower than the return temperature. If the reduced steering temperature is lower than the return temperature, the local control unit 140 may determine S330 a temporary steering temperature that is higher than the return temperature and lower than the base steering temperature. The local control unit 140 may thereby reduce the local distribution system's 150 outtake of heat in step S340. If the reduced steering temperature is not lower than the return temperature, the local control unit 140 may not adapt the reduced steering temperature.

[0083] The method may further comprise determining S325 the return temperature of the return of heat transfer fluid in the local distribution system over time, and gradually decreasing S327 the temporary steering temperature while securing that the temporary steering temperature is greater than the return temperature, until the temporary steering temperature reaches the reduced steering temperature. This may be achieved by performing steps S310, S320, S325, S327, S330 and S340 until the temporary steering temperature reaches the reduced steering temperature.

[0084] In case of cold is taken from the distribution grid 110, the local control unit 140 may determine S420 that a determined increased steering temperature is higher than the return temperature. If the increased steering temperature is higher than the return temperature, the local control unit 140 may determine S430 a temporary steering temperature that is lower than the return temperature and higher than the base steering temperature. The local control unit 140 may thereby increase the local distribution system's 150 outtake of cold in step S440. If the increased steering temperature is not higher than the return temperature, the local control unit 140 may not adapt the increased steering temperature.

[0085] The method may further comprise determining S425 the return temperature of the return of heat transfer fluid in the local distribution system 150 over time, and gradually increasing S427 the temporary steering temperature while securing that the temporary steering temperature is lower than the return temperature, until the temporary steering temperature reaches the increased steering temperature. This may be achieved by performing steps S410, S420, S425, S427, S430 and S440 until the temporary steering temperature reaches the increased steering temperature.

[0086] It is contemplated that there are numerous modifications of the embodiments described herein, which are still within the scope of the invention as defined by the appended claims. For instance, the steps performed by a local control unit may wholly or in parts be performed by the central server. The steps of the method may further be performed in a different order, where some steps are performed in parallel.