Methods and systems for low temperature thermal grids

Abstract

A method for a thermal grid (100) is provided. The thermal grid (100) comprises a warm pipe (10) and a cold pipe (20), and the method comprises: determining a grid demand balance indicator value (5), associating a current temperature region for the warm pipe (10) and / or the cold pipe (20) of the thermal grid (100) as a balanced temperature region (115) or as an unbalanced temperature region (110, 120) based on the grid demand balance indicator value (5), selecting a balanced control algorithm or an unbalanced control algorithm for the thermal grid based on the current temperature region, and controlling the thermal grid by the selected control algorithm.

Description

Technical Field

[0001] The present invention relates to methods and systems for low temperature thermal grids. In particular, the present invention relates to improved control of such low temperature thermal grids.Background

[0002] Low temperature thermal grids have gained increased interest during the last decades. For intelligent use of energy especially in urban areas, E.ON ectogrid ™< has been developed. The E.ON ectogrid ™< combines features of small-scale modern heat pump technology with fundamentals of large-scale hydraulic distribution grids, allowing optimized balancing by allowing temperature control in both the warm and the cold pipe of the grid and utilizing thermal inertia of the grid and of the associated buildings.

[0003] The E.ON ectrogrid ™< is designed as a 5 th< generation district heating and cooling (5GDHC) system. The first generation was developed to support the increasing size of cities and their need for comfort heat. Saturated steam at temperatures of 140-220°C was produced in steam boilers, and circulated to connected facilities in one-way systems through dedicated pipeline. One key improvement as the next generations have developed is the decrease in temperature.

[0004] By the emerge of 5GDHC systems, decentralized production is performed by heat pumps for heating and cooling demands. Any surplus of each production system is shared on a common low-temperature grid consisting of only two pipes - a warm pipe and a cold pipe. The low temperatures, generally not exceeding 40°C, provides the possibility to insert low-temperature waste heat when there is an imbalance between heating and cooling demand.

[0005] A typical 5GHDC system comprises a plurality of substations, such as buildings, each of which is equipped with at least one heat pump and / or chiller. The heat pump and / or chiller is connected to a thermal grid comprising a warm pipe and a cold pipe. When a substation is in need for heating, water is taken from the warm pipe and just a small amount of electrical energy is required to power the heat pump of the substation to raise the temperature to the desired level. The cooling is sent back to the cold pipe to be reused by a building in need of cooling.

[0006] Variations in supply and demand are handled efficiently by utilizing a passive balancing unit in the form of an accumulator tank being configured to store thermal energy. The passive balancing unit effectively increases the inertia of the system, facilitating control and especially balancing variations in demands between day and night. The passive balancing unit may further function as the pressure zero-point in the system. When the passive balancing unit is insufficient for balancing the difference between the heating and cooling needs of the system, one or more energy sources are provided to supply or dispose thermal energy. Such energy sources may be active, e.g. one or more large scale heat pumps, or passive, e.g. a lake.

[0007] The temperatures in the cold and warm pipes vary based on the balance between heating and cooling demands within the 5GHDC system. The temperatures are controlled to provide suitable temperatures in relation to many factors such as i) type of energy sources, and ii) obtaining the highest coefficient of performance of the decentralised heat pumps / chillers. Furthermore, it is important to always maintain a temperature difference (ΔT) between the cold and warm pipe.

[0008] During wintertime, when the heating demand is high, the temperature of the grid is typically kept low (e.g. 7°C in the cold pipe, 15°C in the warm pipe). This enables efficient energy harvesting of heat from low temperature energy sources, like waste energy from industry or geothermal energy.

[0009] During summertime, when the cooling demand is high, the temperature is typically kept higher (e.g. 25°C in the cold pipe, 40°C in the warm pipe). This enables efficient energy harvesting of cooling energy from cooling energy sources, like cooling towers or geothermal energy.

[0010] When there is energy balance between heating and cooling demand there is a transition time, as the passive balancing unit and the inertia of the system is supplying the required energy, to maintain balance in the temperatures changes between the two positions. A predefined set point curve may be used to stay at stable temperatures in heating or cooling mode.

[0011] Control of the grid temperatures, i.e. the temperatures of the warm pipe and the cold pipe, is a key parameter for ensuring efficient operation of the 5GHDC system. Hence, there is a need for improvements in order to increase energy performance of the system.Summary

[0012] According to a first aspect, a method for a thermal grid comprising a warm pipe and a cold pipe is provided. The method comprises determining a grid demand balance indicator value, associating a current temperature region for the warm pipe and / or the cold pipe of the thermal grid as a balanced temperature region or as an unbalanced temperature region based on the grid demand balance indicator value, selecting a balanced control algorithm or an unbalanced control algorithm for the thermal grid based on the current temperature region, and controlling the thermal grid by the selected control algorithm. The first aspect may seek to allow for improved efficiency of the thermal grid. A technical benefit includes the dynamic selection of control algorithm for controlling the thermal grid, thereby adapting the control of the thermal grid to the actual current temperature region for the warm and / or cold pipe.

[0013] The thermal grid may further comprise a balancing unit and the grid demand balance indicator value may represent a minimum temperature and / or a maximum temperature of the balancing unit. This allows for well-defined temperature boundaries for the thermal grid, which enables simple control based on the well-defined boundaries.

[0014] The grid demand balance indicator value may also represent a mean temperature of the balancing unit. This allows for well-defined temperature boundaries for the thermal grid, which enables simple control based on the well-defined boundaries.

[0015] The grid demand balance indicator value may also represent a maximum temperature difference of the balancing unit. This allows for well-defined temperature boundaries for the thermal grid, which enables simple control based on the well-defined boundaries.

[0016] The grid demand balance indicator value may also represent a current temperature difference between the warm pipe and the cold pipe. As this generally corresponds to the maximum temperature difference of the balancing unit, this allows the temperature boundaries to be set according to real time conditions of the system, thereby improving control and accuracy of the temperatures of the thermal grid.

[0017] The method may further comprise, possibly when the unbalanced control algorithm is selected, determining a requirement to either add heat to the warm pipe or to add cooling to the cold pipe, determining a merit order of one or more energy sources connected to the thermal grid, said merit order being based on the temperature of each energy source and / or the temperature difference between the outflow from each energy source and the warm pipe or the cold pipe, selecting an energy source having the highest merit order, and regulating the temperature of the warm pipe and / or the cold pipe of the thermal grid by i) activating the selected energy source (35) to heat or cool the thermal grid, and / or ii) changing the mass flow through the warm pipe and / or the cold pipe, wherein the temperature regulation is based on the temperature of the selected energy source. This improves thermal control of the thermal grid and provides for a more efficient use of the one or more energy sources.

[0018] The idea of applying merit order control is to adapt the temperatures in the grid (i.e. in the conduits) based on the properties of the energy sources. Preferably, the heat pumps in all of the buildings connected to the grid can be centrally controlled such that a certain temperature in the hot and / or the cold conduit is reached.

[0019] This is one of the benefits with having heat pumps between the grid and the buildings. When this control cannot be maintained (i.e. the temperatures in the grid) by what can be balanced between the buildings, the passive balancing will be affected by a reduction or increase in temperature thereof. When the balancing unit is sufficiently affected as determined by a decreasing or increasing mean temperature thereof (i.e. the grid demand balance indicator), the unbalanced region will be entered either on the cooling or heating side where merit order control is implemented to rank the passive (mainly) and active energy sources.

[0020] In order to make use of the passive energy sources (which cannot be controlled other than to selectively pump / connect via valve(s) to the grid), the temperatures of the grid must be adapted to be able to extract heat / cold from each passive energy source. By applying merit order control, the curves may be defined according to each energy source and interpolation therebetween.

[0021] Merit order may be determined in the simplest case based on the temperature for each energy source but within the context of this disclosure, this can also be based on other data as well. Each energy source may be tracked and assigned data according to below in addition to the temperature thereof, all of which can hypothetically be included in determining the merit order: i) energy type (heating or cooling), ii) minimum ΔT, iii) maximum ΔT, iv) maximum capacity (nominal) [kW], v) nominal source temperature (optional, if there is no measurement) [°C], vi) rank - number indicating the energy source preference (only for active energy sources).

[0022] For example when determining the temperature of the hot and cold conduits, for a passive heating energy source, the measured temperature of a certain energy source may define the temperature of the hot conduit while the temperature of the cold conduit is actively controlled for allowing the energy source to be able to reach the hot conduit temperature. Vice versa for a cooling energy source. This is also where the aforementioned data comes in, as for each passive energy source there is a maximum capacity of energy that can be extracted. Hence, the temperatures of the hot and cold conduits may be interpolated so that more than one passive energy source can be used simultaneously if needed.

[0023] The method may further comprise determining a minimum temperature difference between the outflow from each energy source and the warm pipe or the cold pipe, and determining the requirement to either add heat to the warm pipe or to add cooling to the cold pipe when the determined minimum temperature difference is zero. This improves thermal control of the thermal grid and provides for a more efficient use of the one or more energy sources.

[0024] The method may further comprise determining a warm temperature curve of the warm pipe of the thermal grid and a cool temperature curve of the cold pipe of the thermal grid; determining a required heating region extending up to a first threshold temperature of the warm temperature curve, a required cooling region extending from a second threshold of the cool temperature curve, and a balanced region extending between the heating region and the cooling region, and determining at least one of the first and second threshold temperatures based on the outflow temperature of the energy source having the highest heating merit order or the highest cooling merit order. This allows the temperature boundaries to be set dynamically according to real time conditions of the system, thereby improving control and accuracy of the temperatures of the thermal grid.

[0025] The method may further comprise determining the warm temperature curve of the warm pipe of the thermal grid by determining a minimum temperature and a maximum temperature of the warm pipe, and / or determining the cool temperature curve of the cold pipe of the thermal grid by determining a minimum temperature and a maximum temperature of the cold pipe. This allows for well-defined temperature boundaries for the thermal grid, which enables simple control based on the well-defined boundaries.

[0026] The method may further comprise updating the merit order of the one or more energy source connected to the thermal grid. This is beneficial as it allows the merit order to be adapted and adjusted continuously, or at regular or specific intervals, based on actual parameters of the system.

[0027] The method may further comprise determining the first threshold temperature as being equal to the maximum outflow temperature of the at least one energy source, and determining the second threshold temperature as being equal to the minimum outflow temperature of the at least one energy source. This is beneficial as it allows the thresholds to be adapted and adjusted continuously, or at regular or specific intervals, based on actual parameters of the system.

[0028] The method may further comprise, possibly when the balanced control algorithm is selected, determining a continuous temperature difference between the warm pipe and the cold pipe by assigning a plurality of temperature difference set points, and by interpolating the warm temperature curve and the cool temperature curve based on the temperature difference set points. This is advantageous as the temperatures can be adapted dynamically in order to improve pump usage and to optimize flow in the thermal grid.

[0029] The method may further comprise interpolating the warm temperature curve and the cool temperature curve based on the outflow temperature of at least one energy source. This is advantageous as the temperatures can be adapted in order to improve pump usage and to optimize flow in the thermal grid.

[0030] The method may further comprise maintaining the assigned temperature difference between the warm pipe and the cold pipe by controlling the mass flow through the thermal grid. This is advantageous as the temperature difference of system can be kept balanced and be more energy efficient.

[0031] The temperature difference between the warm temperature curve and the cool temperature curve of the balanced region may increase from a central portion of the balanced region towards the heating region and the cooling region.

[0032] According to a second aspect, a method for a thermal grid comprising a warm pipe and a cold pipe is provided. The method comprises determining a requirement to either add heat to the warm pipe or to add cooling to the cold pipe, determining a merit order of one or more energy sources connected to the thermal grid, said merit order being based on the temperature of each energy source and / or the temperature difference between the outflow from each energy source and the warm pipe or the cold pipe, selecting an energy source having the highest merit order, and regulating the temperature of the warm pipe and / or the cold pipe of the thermal grid by i) activating the selected energy source to heat or cool the thermal grid, and / or ii) changing the mass flow through the warm pipe and / or the cold pipe, wherein the temperature regulation is based on the temperature of the selected energy source. This improves thermal control of the thermal grid and provides for a more efficient use of the one or more energy sources.

[0033] The method may further comprise determining a minimum temperature difference between the outflow from each energy source and the warm pipe or the cold pipe, and determining the requirement to either add heat to the warm pipe or to add cooling to the cold pipe when the determined minimum temperature difference is zero. This improves thermal control of the thermal grid and provides for a more efficient use of the one or more energy sources.

[0034] The method may further comprise determining a warm temperature curve of the warm pipe of the thermal grid and a cool temperature curve of the cold pipe of the thermal grid; determining a required heating region extending up to a first threshold temperature of the warm temperature curve, a required cooling region extending from a second threshold of the cool temperature curve, and a balanced region extending between the heating region and the cooling region, and determining at least one of the first and second threshold temperatures based on the outflow temperature of the energy source having the highest heating merit order or the highest cooling merit order. This allows the temperature boundaries to be set according to real time conditions of the system, thereby improving control and accuracy of the temperatures of the thermal grid.

[0035] The method may further comprise determining the warm temperature curve of the warm pipe of the thermal grid by determining a minimum temperature and a maximum temperature of the warm pipe, and / or determining the cool temperature curve of the cold pipe of the thermal grid by determining a minimum temperature and a maximum temperature of the cold pipe. This allows for well-defined temperature boundaries for the thermal grid, which enables simple control based on the well-defined boundaries.

[0036] The method may further comprise updating the merit order of the one or more energy source connected to the thermal grid. This is beneficial as it allows the merit order to be dynamically adapted and adjusted continuously, or at regular or specific intervals, based on actual parameters of the system.

[0037] The method may further comprise determining the first threshold temperature as being equal to the maximum outflow temperature of the at least one energy source, and determining the second threshold temperature as being equal to the minimum outflow temperature of the at least one energy source. This is beneficial as it allows the thresholds to be adapted and adjusted continuously, or at regular or specific intervals, based on actual parameters of the system.

[0038] The method may further comprise determining a grid demand balance indicator value, associating a current temperature region for the warm pipe and / or the cold pipe of the thermal grid as a balanced temperature region or as an unbalanced temperature region based on the grid demand balance indicator value, selecting a balanced control algorithm or an unbalanced control algorithm for the thermal grid based on the current temperature region, and controlling the thermal grid by the selected control algorithm. The first aspect may seek to allow for improved efficiency of the thermal grid. A technical benefit includes the dynamic selection of control algorithm for controlling the thermal grid, thereby adapting the control of the thermal grid to the actual current temperature region for the warm and / or cold pipe.

[0039] The thermal grid may further comprise a balancing unit and the grid demand balance indicator value can represent a minimum temperature and / or a maximum temperature of the balancing unit. This allows for well-defined temperature boundaries for the thermal grid, which enables simple control based on the well-defined boundaries.

[0040] The grid demand balance indicator value may also represent a mean temperature of the balancing unit. This allows for well-defined temperature boundaries for the thermal grid, which enables simple control based on the well-defined boundaries.

[0041] The grid demand balance indicator value may also represent a maximum temperature difference of the balancing unit. This allows for well-defined temperature boundaries for the thermal grid, which enables simple control based on the well-defined boundaries.

[0042] The grid demand balance indicator value may also represent a current temperature difference between the warm pipe and the cold pipe. This allows the temperature boundaries to be set according to real time conditions of the system, thereby improving control and accuracy of the temperatures of the thermal grid.

[0043] The method may further comprise determining a continuous temperature difference between the warm pipe and the cold pipe by assigning a plurality of temperature difference set points, and by interpolating the warm temperature curve and the cool temperature curve based on the temperature difference set points. This is advantageous as the temperatures can be adapted in order to improve pump usage and to optimize flow in the thermal grid.

[0044] The method may further comprise interpolating the warm temperature curve and the cool temperature curve based on the outflow temperature of at least one energy source. This is advantageous as the temperatures can be adapted in order to improve pump usage and to optimize flow in the thermal grid.

[0045] The method may further comprise maintaining the assigned temperature difference between the warm pipe and the cold pipe by controlling the mass flow through the thermal grid. This is advantageous as the temperature difference of system can be kept balanced and be more energy efficient.

[0046] The temperature difference between warm temperature curve and the cool temperature curve of the balanced region may increase from a central portion of the balanced region towards the heating region and the cooling region.

[0047] According to a third aspect, a method for a thermal grid comprising a warm pipe and a cold pipe is provided. The method comprises determining a continuous temperature difference between the warm pipe and the cold pipe by assigning a plurality of temperature difference set points, and by interpolating the warm temperature curve and the cool temperature curve based on the temperature difference set points. This is advantageous as the temperatures can be adapted in order to improve pump usage and to optimize flow in the thermal grid.

[0048] The method may further comprise interpolating the warm temperature curve and the cool temperature curve based on the outflow temperature of at least one energy source. This is advantageous as the temperatures can be adapted in order to improve pump usage and to optimize flow in the thermal grid.

[0049] The method may further comprise maintaining the assigned temperature difference between the warm pipe and the cold pipe by controlling the mass flow through the thermal grid. This is advantageous as the temperature difference of system can be kept balanced and be more energy efficient.

[0050] The temperature difference between warm temperature curve and the cool temperature curve of the balanced region may increase from a central portion of the balanced region towards the heating region and the cooling region.

[0051] The method may further comprise determining a grid demand balance indicator value, associating a current temperature region for the warm pipe and / or the cold pipe of the thermal grid as a balanced temperature region or as an unbalanced temperature region based on the grid demand balance indicator value, selecting a balanced control algorithm or an unbalanced control algorithm for the thermal grid based on the current temperature region, and controlling the thermal grid by the selected control algorithm. The first aspect may seek to allow for improved efficiency of the thermal grid. A technical benefit includes the dynamic selection of control algorithm for controlling the thermal grid, thereby adapting the control of the thermal grid to the actual current temperature region for the warm and / or cold pipe.

[0052] The thermal grid may further comprise a balancing unit and the grid demand balance indicator value can represent a minimum temperature and / or a maximum temperature of the balancing unit. This allows for well-defined temperature boundaries for the thermal grid, which enables simple control based on the well-defined boundaries.

[0053] The grid demand balance indicator value may also represent a mean temperature of the balancing unit. This allows for well-defined temperature boundaries for the thermal grid, which enables simple control based on the well-defined boundaries.

[0054] The grid demand balance indicator value may also represent a maximum temperature difference of the balancing unit. This allows for well-defined temperature boundaries for the thermal grid, which enables simple control based on the well-defined boundaries.

[0055] The grid demand balance indicator value may also represent a current temperature difference between the warm pipe and the cold pipe. This allows the temperature boundaries to be set according to real time conditions of the system, thereby improving control and accuracy of the temperatures of the thermal grid.

[0056] The method may further comprise determining a requirement to either add heat to the warm pipe or to add cooling to the cold pipe, determining a merit order of one or more energy sources connected to the thermal grid, said merit order being based on the temperature of each energy source and / or the temperature difference between the outflow from each energy source and the warm pipe or the cold pipe, selecting an energy source having the highest merit order, and regulating the temperature of the warm pipe and / or the cold pipe of the thermal grid by i) activating the selected energy source to heat or cool the thermal grid, and / or ii) changing the mass flow through the warm pipe and / or the cold pipe, wherein the temperature regulation is based on the temperature of the selected energy source.. This improves thermal control of the thermal grid and provides for a more efficient use of the one or more energy sources.

[0057] The method may further comprise determining a minimum temperature difference between the outflow from each energy source and the warm pipe or the cold pipe, and determining the requirement to either add heat to the warm pipe or to add cooling to the cold pipe when the determined minimum temperature difference is zero. This improves thermal control of the thermal grid and provides for a more efficient use of the one or more energy sources.

[0058] The method may further comprise determining a warm temperature curve of the warm pipe of the thermal grid and a cool temperature curve of the cold pipe of the thermal grid; determining a required heating region extending up to a first threshold temperature of the warm temperature curve, a required cooling region extending from a second threshold of the cool temperature curve, and a balanced region extending between the heating region and the cooling region, and determining at least one of the first and second threshold temperatures based on the outflow temperature of the energy source having the highest heating merit order or the highest cooling merit order. This allows the temperature boundaries to be set according to real time conditions of the system, thereby improving control and accuracy of the temperatures of the thermal grid.

[0059] The method may further comprise determining the warm temperature curve of the warm pipe of the thermal grid by determining a minimum temperature and a maximum temperature of the warm pipe, and / or determining the cool temperature curve of the cold pipe of the thermal grid by determining a minimum temperature and a maximum temperature of the cold pipe. This allows for well-defined temperature boundaries for the thermal grid, which enables simple control based on the well-defined boundaries.

[0060] The method may further comprise updating the merit order of the one or more energy source connected to the thermal grid. This is beneficial as it allows the merit order to be adapted and adjusted continuously, or at regular or specific intervals, based on actual parameters of the system.

[0061] The method may further comprise determining the first threshold temperature as being equal to the maximum outflow temperature of the at least one energy source, and determining the second threshold temperature as being equal to the minimum outflow temperature of the at least one energy source. This is beneficial as it allows the thresholds to be adapted and adjusted continuously, or at regular or specific intervals, based on actual parameters of the system.

[0062] According to a fourth aspect, a method for controlling the temperature of a thermal grid is provided. The method comprises performing the method according to any of the previous aspects, and regulating the temperature of the warm pipe and / or the cold pipe of the thermal grid by i) activating one or more energy sources to heat or cool the thermal grid, and / or ii) changing the mass flow through the warm pipe and / or the cold pipe. This is advantageous as the temperature can be effectively controlled.

[0063] Activating the one or more energy sources may further comprise controlling the heat flow between the one or more energy sources and the warm and cold pipes.

[0064] According to a fifth aspect, a thermal grid is provided. The thermal grid comprises a warm pipe and a cold pipe, a plurality of substations connected to the warm and cold pipes, one or more energy sources connected to the warm and cold pipes, and a control unit configured to determine a grid demand balance indicator value, associate a current temperature region for the warm pipe and / or the cold pipe of the thermal grid as a balanced temperature region or as an unbalanced temperature region based on the grid demand balance indicator value, select a balanced control algorithm or an unbalanced control algorithm for the thermal grid based on the current temperature region, and control the thermal grid by the selected control algorithm.

[0065] Some further aspects of the disclosure will be given in the following paragraphs.

[0066] According to a sixth aspect, a method for a thermal grid is provided. The method comprises determining a warm temperature curve of a warm pipe of the thermal grid and a cool temperature curve of a cold pipe of the thermal grid; determining a required heating region extending up to a first threshold temperature of the warm temperature curve, a required cooling region extending from a second threshold of the cool temperature curve, and a balanced region extending between the heating region and the cooling region, and determining at least one of the first and second threshold temperatures based on the temperature of at least one balancing unit connected to the thermal grid. The first aspect may seek to allow for improved efficiency of the thermal grid. A technical benefit includes a dynamic setting of at least one threshold temperature, thereby adapting the warm and / or cold temperature curve to the actual conditions of the at least one balancing unit.

[0067] The method may further comprise determining the warm temperature curve of the warm pipe of the thermal grid by determining a minimum temperature and a maximum temperature of the warm pipe, and / or determining the cool temperature curve of the cold pipe of the thermal grid by determining a minimum temperature and a maximum temperature of the cold pipe. This allows for well-defined temperature boundaries for the thermal grid, which enables simple control based on the well-defined boundaries.

[0068] The method may further comprise updating at least one of the first and second threshold temperatures based on the temperature of at least one balancing unit connected to the thermal grid. This is beneficial as it allows the temperature set points to be adapted and adjusted continuously, or at regular or specific intervals, based on actual parameters of the system.

[0069] The method may further comprise determining the first threshold temperature as being equal to the maximum temperature of at least one balancing unit, and determining the second threshold temperature as being equal to the minimum temperature of at least one balancing unit. This allows the temperature boundaries to be set according to real time conditions of the system, thereby improving control and accuracy of the temperatures of the thermal grid.

[0070] The method may further comprise determining the temperature difference between the warm temperature curve and the cool temperature curve of the balanced region by assigning a plurality of temperature difference set points, and by interpolating the warm temperature curve and the cool temperature curve based on the temperature difference set points as well as on the first and second threshold temperatures. This is advantageous as the temperatures can be adapted in order to improve pump usage and to optimize flow in the thermal grid.

[0071] The temperature difference between the warm temperature curve and the cool temperature curve of the balanced region may increase from a central portion of the balancing region towards the heating region and the cooling region. This further improves flow optimization and provides for a more efficient pump usage of the thermal grid.

[0072] The method may further comprise determining the maximum temperature of one or more balancing units and / or each one of a plurality of active or passive energy sources connected to the thermal grid, and assigning a heating merit order for the plurality of active or passive energy sources based on the determined maximum temperatures. This improves thermal control of the thermal grid and provides for a more efficient use of the plurality of balancing units and / or energy sources.

[0073] The method may further comprise determining the minimum temperature of one or more balancing units and / or each one of a plurality of active or passive energy sources connected to the thermal grid, and assigning a cooling merit order for the plurality of active or passive energy sources based on the determined minimum temperatures. As for heating, this improves thermal control of the thermal grid and provides for a more efficient use of the plurality of balancing units and / or energy sources.

[0074] According to a seventh aspect, a method for controlling the temperature of a thermal grid is provided. The method comprises performing the method according to any of the previous aspects, determining that the actual temperature of the warm and / or cold pipe is outside the balanced region, and regulatingthe temperature of the thermal grid by activating one or more active or passive energy sources to heat or cool the thermal grid.

[0075] Activating one or more active or passive energy sources may comprise controlling the heat flow between the one or more active or passive energy sources and the warm and cold pipes.

[0076] The method may further comprise reassigning a heating merit order and / or a cooling merit order upon a change or temperature of one or more active or passive energy sources after activation.

[0077] According to an eight aspect, a thermal grid is provided. The thermal grid comprises a warm pipe and a cold pipe, a plurality of substations connected to the warm and cold pipes, and one or more balancing units connected to the warm and cold pipes. The thermal grid further comprises a control unit configured to determine a warm temperature curve of a warm pipe of the thermal grid and a cool temperature curve of a cold pipe of the thermal grid; to determine a required heating region extending up to a first threshold temperature of the warm temperature curve, a required cooling region extending from a second threshold of the cool temperature curve, and a balanced region extending between the heating region and the cooling region, and to determine at least one of the first and second threshold temperatures based on the temperature of at least one balancing unit connected to the thermal grid.

[0078] According to a ninth aspect, a method for a thermal grid is provided. The method comprises determining a warm temperature curve of a warm pipe of the thermal grid and a cool temperature curve of a cold pipe of the thermal grid by: assigning a plurality of temperature difference set points; and determining a temperature difference between the warm temperature curve and the cool temperature curve of the balanced region based on the plurality of temperature difference set points.

[0079] The method may further comprise interpolating the warm temperature curve and the cool temperature curve based on the temperature difference set points. This is advantageous as the temperatures can be adapted in order to improve pump usage and to optimize flow in the thermal grid.

[0080] The method may further comprise determining a required heating region extending up to a first threshold temperature of the warm temperature curve, a required cooling region extending from a second threshold of the cool temperature curve, and a balanced region extending between the heating region and the cooling region, and determining at least one of the first and second threshold temperatures based on the temperature of at least one balancing unit connected to the thermal grid.

[0081] The temperature difference between the warm temperature curve and the cool temperature curve of the balanced region may increase from a central portion of the balancing region towards the heating region and the cooling region. This further improves flow optimization and provides for a more efficient pump usage of the thermal grid.

[0082] The method may further comprise determining the warm temperature curve of the warm pipe of the thermal grid by determining a minimum temperature and a maximum temperature of the warm pipe, and / or determining the cool temperature curve of the cold pipe of the thermal grid by determining a minimum temperature and a maximum temperature of the cold pipe. This allows for well-defined temperature boundaries for the thermal grid, which enables simple control based on the well-defined boundaries.

[0083] The method may further comprise updating at least one of the first and second threshold temperatures based on the temperature of at least one balancing unit connected to the thermal grid. This is beneficial as it allows the temperature set points to be adapted and adjusted continuously, or at regular or specific intervals, based on actual parameters of the system.

[0084] The method may further comprise determining the first threshold temperature as being equal to the maximum temperature of at least one balancing unit, and determining the second threshold temperature as being equal to the minimum temperature of at least one balancing unit. This allows the temperature boundaries to be set according to real time conditions of the system, thereby improving control and accuracy of the temperatures of the thermal grid.

[0085] The method may further comprise determining the maximum temperature of each one of a plurality of active or passive energy sources connected to the thermal grid, and assigning a heating merit order for the plurality of active or passive energy sources based on the determined maximum temperatures. This improves thermal control of the thermal grid and provides for a more efficient use of the plurality of the active or passive energy sources.

[0086] The method may further comprise determining the minimum temperature of each one of a plurality of active or passive energy sources connected to the thermal grid, and assigning a cooling merit order for the plurality of active or passive energy sources based on the determined minimum temperatures. As for heating, this improves thermal control of the thermal grid and provides for a more efficient use of the plurality of active or passive energy sources.

[0087] According to a tenth aspect, a method for a thermal grid is provided. The method comprises determining the maximum temperature of each one of a plurality of active or passive energy sources connected to the thermal grid, and assigning a heating merit order for the plurality of active or passive energy sources based on the determined maximum temperatures.

[0088] The method may further comprise determining the minimum temperature of each one of a plurality of active or passive energy sources connected to the thermal grid, and assigning a cooling merit order for the plurality of active or passive energy sources based on the determined minimum temperatures. As for heating, this improves thermal control of the thermal grid and provides for a more efficient use of the plurality of active or passive energy sources.

[0089] The method may further comprise determining a warm temperature curve of a warm pipe of the thermal grid and a cool temperature curve of a cold pipe of the thermal grid; determining a required heating region extending up to a first threshold temperature of the warm temperature curve, a required cooling region extending from a second threshold of the cool temperature curve, and a balanced region extending between the heating region and the cooling region, and determining at least one of the first and second threshold temperatures based on the temperature of at least one active or passive energy source connected to the thermal grid. A technical benefit includes a dynamic setting of at least one threshold temperature, thereby adapting the warm and / or cold temperature curve to the actual conditions of the at least one active or passive energy source.

[0090] The method may further comprise determining the warm temperature curve of the warm pipe of the thermal grid by determining a minimum temperature and a maximum temperature of the warm pipe, and / or determining the cool temperature curve of the cold pipe of the thermal grid by determining a minimum temperature and a maximum temperature of the cold pipe. This allows for well-defined temperature boundaries for the thermal grid, which enables simple control based on the well-defined boundaries.

[0091] The method may further comprise updating at least one of the first and second threshold temperatures based on the temperature of at least one active or passive energy source connected to the thermal grid. This is beneficial as it allows the temperature set points to be adapted and adjusted continuously, or at regular or specific intervals, based on actual parameters of the system.

[0092] The method may further comprise determining the first threshold temperature as being equal to the maximum temperature of at least one active or passive energy source, and determining the second threshold temperature as being equal to the minimum temperature of at least one active or passive energy source. This allows the temperature boundaries to be set according to real time conditions of the system, thereby improving control and accuracy of the temperatures of the thermal grid.

[0093] The method may further comprise determining the temperature difference between the warm temperature curve and the cool temperature curve of the balanced region by assigning a plurality of temperature difference set points, and by interpolating the warm temperature curve and the cool temperature curve based on the temperature difference set points as well as on the first and second threshold temperatures. This is advantageous as the temperatures can be adapted in order to improve pump usage and to optimize flow in the thermal grid.

[0094] The temperature difference between the warm temperature curve and the cool temperature curve of the balanced region may increase from a central portion of the balancing region towards the heating region and the cooling region. This further improves flow optimization and provides for a more efficient pump usage of the thermal grid.

[0095] According to an eleventh aspect, a method for a thermal grid is provided. The method comprises determining the minimum temperature of each one of a plurality of active or passive energy sources connected to the thermal grid, and assigning a cooling merit order for the plurality of active or passive energy sources based on the determined minimum temperatures.

[0096] The method may further comprise determining the maximum temperature of each one of a plurality of active or passive energy sources connected to the thermal grid, and assigning a heating merit order for the plurality of active or passive energy sources based on the determined maximum temperatures. As for cooling, this improves thermal control of the thermal grid and provides for a more efficient use of the plurality of active or passive energy sources.

[0097] The method may further comprise determining a warm temperature curve of a warm pipe of the thermal grid and a cool temperature curve of a cold pipe of the thermal grid; determining a required heating region extending up to a first threshold temperature of the warm temperature curve, a required cooling region extending from a second threshold of the cool temperature curve, and a balanced region extending between the heating region and the cooling region, and determining at least one of the first and second threshold temperatures based on the temperature of at least one active or passive energy source connected to the thermal grid. A technical benefit includes a dynamic setting of at least one threshold temperature, thereby adapting the warm and / or cold temperature curve to the actual conditions of the at least one active or passive energy source.

[0098] The method may further comprise determining the warm temperature curve of the warm pipe of the thermal grid by determining a minimum temperature and a maximum temperature of the warm pipe, and / or determining the cool temperature curve of the cold pipe of the thermal grid by determining a minimum temperature and a maximum temperature of the cold pipe. This allows for well-defined temperature boundaries for the thermal grid, which enables simple control based on the well-defined boundaries.

[0099] The method may further comprise updating at least one of the first and second threshold temperatures based on the temperature of at least one active or passive energy source connected to the thermal grid. This is beneficial as it allows the temperature set points to be adapted and adjusted continuously, or at regular or specific intervals, based on actual parameters of the system.

[0100] The method may further comprise determining the first threshold temperature as being equal to the maximum temperature of at least one active or passive energy source, and determining the second threshold temperature as being equal to the minimum temperature of at least one active or passive energy source This allows the temperature boundaries to be set according to real time conditions of the system, thereby improving control and accuracy of the temperatures of the thermal grid.

[0101] The method may further comprise determining the temperature difference between the warm temperature curve and the cool temperature curve of the balanced region by assigning a plurality of temperature difference set points, and by interpolating the warm temperature curve and the cool temperature curve based on the temperature difference set points as well as on the first and second threshold temperatures. This is advantageous as the temperatures can be adapted in order to improve pump usage and to optimize flow in the thermal grid.

[0102] The temperature difference between the warm temperature curve and the cool temperature curve of the balanced region may increase from a central portion of the balancing region towards the heating region and the cooling region. This further improves flow optimization and provides for a more efficient pump usage of the thermal grid.Brief Description of the Drawings

[0103] Embodiments of the invention will be described in the following; references being made to the appended diagrammatical drawings which illustrate non-limiting examples of how the inventive concept can be reduced into practice. Fig. 1 shows a schematic setup of a thermal grid according to one embodiment. Fig. 2 shows an example of a balancing unit connected to a thermal grid. Fig. 3 is a diagram showing examples of a temperature curve of a warm pipe and a temperature curve of a cold pipe. Fig. 4 is a diagram showing set points for the temperature difference between the warm pipe and the cold pipe in the balanced temperature region. Figs. 5-8 are schematic diagrams of methods for a thermal grid according to different embodiments. Detailed Description

[0104] Hereinafter, certain embodiments will be described more fully with reference to the accompanying drawings. The invention 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 be thorough and complete, and will fully convey the scope of the invention, such as it is defined in the appended claims, to those skilled in the art.

[0105] Fig. 1 shows a thermal grid 100 according to one embodiment. The thermal grid 100 comprises a warm pipe 10, a cold pipe 20, a plurality of substations 40 connected to the warm and cold pipes 10, 20, a number of energy sources 35 connected to the warm and cold pipes 10, 20, one balancing unit 30 connected to the warm and cold pipes 10, 20, and a control unit 50. Any suitable number of pipes, substations, energy sources and balancing units are possible.

[0106] The energy sources 35 can apply different types of energy, for example they may be in the form of air / water reversible heat pumps, geothermal sources or boreholes, excess heat supplies from industries, data centres, shopping malls, public baths and / or district heating services / district cooling services. The energy sources 35 can be heating sources or cooling sources and this classification can be redefined as the temperature of the grid shifts. The energy sources 35 can be both passive energy sources and active energy sources, where a passive energy source is assumed not be able to adjust its output temperature.

[0107] Preferably, each substation 40 and active energy source 35 is provided with a flow controller used to control flow in order to return a desired temperature to the warm pipe 10 and / or the cold pipe 20. Activating one or more energy sources 35 can therefore also comprise controlling the heat flow between the one or more energy sources 35 and the warm pipe 10 and / or the cold pipe 20.

[0108] The substations 40 connected to the thermal grid 100 may for instance be buildings with one or more associated heat pumps and / or chiller that provides the required thermal energy according to the need of the substation. For instance, when a substation needs heating, heat can be taken from the warm pipe 10 and just a small amount of electric energy is necessary to raise the temperature to the desired level of the building. The thermal energy of the cool side can then be returned to the cold pipe 20 to be reused by a substation 40 in need of cooling.

[0109] One advantage of this system is that the temperatures in the pipes 10, 20 do not need to be as warm or cold as the actual demand of heating or cooling of the substations 40, which is both safe and provides a reduced amount of heat losses. It can also enable heat pumps and / or chillers to perform better since they can run within more favourable temperature ranges which boosts the efficiency.

[0110] The control unit 50 of the thermal grid 100 can be configured to perform one or more steps according to any embodiment of the methods described herein. A current temperature difference ΔT 10,20 between the warm pipe 10 and the cold pipe 20 of the thermal grid 100 can be used as a grid demand balance indicator value 52. The grid demand balance indicator may thus represent a current temperature region of the warm and / or cold pipe 10,20 of the thermal grid 100. The current temperature region is a balanced temperature region 115 or an unbalanced temperature region 110, 120. This will be described in more detail below.

[0111] Fig. 2 shows an enlarged view of the balancing unit 30 connected to the thermal grid 100. The balancing unit can for instance be an accumulator vessel with temperature stratification / mixing and it can have a gradient temperature profile rather than a sharp boundary between warmer and colder temperatures. The balancing unit 30 can be used for handling variations in supply and demand by storing thermal energy that can be used when there is a demand.

[0112] The balancing unit has a minimum temperature T min , a maximum temperature T max and a temperature difference ΔT 30 that represents the difference between the maximum temperature and the minimum temperature, i.e. ΔT 30 = T max - T min . The balancing unit also has a mean temperature T mean which is the mean temperature of the balancing unit. Any of these temperatures can represent a grid demand balance indicator value 5 based on which a current temperature region of the warm and / or cold pipe 10,20 of the thermal grid 100 can be associated as a balanced temperature region 115 or as an unbalanced temperature region 110, 120. The cold temperature pipe 20 of the thermal grid can connect to a part 32 of the balancing unit 30 having a colder temperature and the warm pipe 20 to a part 34 of the balancing unit 30 having a warmer temperature.

[0113] Fig. 3 shows an illustration of how a current temperature region for the warm pipe 10 and / or the cold pipe 20 of the thermal grid 100 can be associated as a balanced temperature region 115 or as an unbalanced temperature region 110,120 based on a grid demand balance indicator value 5. This can be performed by any suitable method detailed herein. The grid demand balance indicator value 5 can represent any temperature or temperature difference of one or more components forming part of or being connected to the thermal grid 100, such as any of: the temperature or temperature difference associated with a balancing unit 35 as described above, a maximum and / or minimum temperature of the cold pipe 20 and / or the warm pipe 10, a temperature difference ΔT 10,20 between the warm pipe 10 and the cold pipe 20, a temperature difference between the outflow from any energy source 35 and the warm pipe 10 or the cold pipe 20 and / or a temperature of the warm pipe 10 and / or the cold pipe 20.

[0114] The unbalanced regions 110, 120 can constitute a required heating region 110 and / or a required cooling region 120. Associating a current temperature region can be done by comparing the grid demand balance indicator value 5 to one or more thresholds. For instance, a current temperature region of the thermal grid can be associated as an unbalanced region 110 where heating is required if the grid demand balance indicator value 5 is below a first threshold and as a balanced region 115 if the grid demand balance indicator value 5 is above the first threshold. A current temperature region of the thermal grid can be associated as an unbalanced region 120 where cooling is required if the grid demand balance indicator value 5 exceeds a second threshold and as a balanced region 115 if the grid demand balance indicator value 5 is below the second threshold.

[0115] A current temperature region of the thermal grid can be associated as a balanced region 115 if the grid demand balance indicator value 5 is between a first threshold and a second threshold and as an unbalanced region 110, 120 otherwise.

[0116] More specifically, the current temperature region can be associated as a required heating region 110 if the grid demand balance indicator value 5 is below the first threshold and as a required cooling region 120 if the grid demand balance indicator value 5 is above the second threshold. Alternatively, a current temperature region of the thermal grid can be associated as an unbalanced region 110, 120 if the grid demand balance indicator value 5 exceeds a specified threshold and as a balanced region 115 otherwise.

[0117] The first threshold, second threshold or any other threshold to which the grid demand balance indicator value 5 is compared to can be determined based on any temperature or temperature difference of one or more components forming part of or being connected to the thermal grid 100, such as one or more of: outflow temperature of any energy source 35, maximum outflow temperature of at least one energy source 35, minimum outflow temperature of at least one energy source 35, a minimum temperature difference between a passive heating source having the highest temperature and the cold pipe 20, a minimum temperature difference between a passive cooling source having the lowest temperature and the warm pipe 10, a minimum temperature difference between a passive heating source having the highest temperature and any temperature of the balancing unit including mean temperature, and / or a minimum temperature difference between a passive cooling source having the coldest temperature and any temperature of the balancing unit including mean temperature. The thresholds can be updated as the temperature and / or temperature difference determining the threshold changes.

[0118] Based on the associated current temperature region, a balanced control algorithm or an unbalanced control algorithm for controlling the thermal grid 100 can be selected. The unbalanced control algorithm may be based on merit order control and the balanced control algorithm may be based on gradient shaping. The concepts of merit order control and gradient shaping will be described in more detail below.

[0119] Fig. 3 shows a graphical illustration of an exemplary warm temperature curve 11 of a warm pipe 10 and a cool temperature curve 21 of a cool pipe 20 that can be determined by some embodiments of the methods described herein. The graph also illustrates a required heating region 110 extending up to a first threshold temperature 12 of the warm temperature curve 11, a required cooling region 120 extending from a second threshold 22 of the cool temperature curve 21, and a balanced region 115 extending between the heating region 110 and the cooling region 120. The temperature difference ΔT 11,21 between the warm temperature curve 11 and the cold temperature curve 21 of the balanced region 115 may increase from a central portion of the balanced region 115 towards the heating region 110 and the cooling region 120.

[0120] A current temperature region for the warm pipe 10 and / or the cold pipe 20 of the thermal grid 100 can be associated as a balanced temperature region 115 or as an unbalanced temperature region 110,120 based on the thresholds of the warm temperature curve 11 and / or the cool temperature curve 21. The unbalanced region 110,120 can be either a required heating region 110 or a required cooling region 120. When cooling is required, the balancing unit 30 can show an increasing mean temperature T mean and a decreasing temperature difference ΔT 30 . When heating is required, the balancing unit 30 can have a decreasing mean temperature T mean and a decreasing temperature difference ΔT 30 . Accordingly, the mean temperature T mean and / or the temperature difference ΔT 30 of the balancing unit can be used as the one or more grid demand balance indicator 5. When the current temperature region of the warm pipe 10 transitions from the balanced region 115 to the required heating region 110, i.e. at the first threshold temperature 12, the temperature of the thermal grid may be regulated such that the grid can efficiently use a first heating source 35 having the highest heating merit order. The temperature at which the first heating source can be efficiently used may be associated with the first threshold temperature 12. The regulation may be accomplished by changing the mass flow through the thermal grid by controlling the flow between substations 40 of the thermal grid and the warm pipe 10 and / or the cold pipe 20. If the grid demand balance indicator 5 continues to worsen, the temperature of the grid is regulated to move further into the required heating region in order to facilitate efficient use of energy sources 35 having a lower heating merit order than the first heating source. The energy source having the second highest heating merit order might be efficiently used when a third threshold 13 is reached. Any remaining heating sources may similarly be efficiently used at other temperature thresholds (not shown). Decreasing the temperature of the warm pipe 10 can allow energy sources 35 of lower heating merit order to be used. The heating sources may further be activated when a threshold 12, 13 is reached and / or deactivated when the thermal grid returns to the balanced region.

[0121] Similarly, when the current temperature region of the cold pipe 20 transitions from the balanced region 115 to the required cooling region 120, i.e. at the second threshold temperature 22, the temperature of the thermal grid may be regulated such that the grid can efficiently use a first cooling source 35 having the highest cooling merit order. The temperature at which the first cooling source can be efficiently used may be associated with the second threshold temperature 22. The regulation may be accomplished by changing the mass flow through the thermal grid by controlling the flow between substations 40 of the thermal grid and the warm pipe 10 and / or the cold pipe 20. If the grid demand balance indicator 5 continues to worsen, the temperature of the grid is regulated to move further into the required cooling region in order to facilitate efficient use of energy sources 35 having a lower cooling merit order than the first cooling source. The energy source having the second highest cooling merit order might be efficiently used when a fourth threshold 23 is reached. Any remaining cooling sources may similarly be efficiently used at other temperature thresholds (not shown). Increasing the temperature of the cold pipe 20 can allow energy sources 35 of lower cooling merit order to be used. The cooling sources may further be activated when a threshold 12, 13 is reached and / or deactivated when the thermal grid returns to the balanced region.

[0122] Further to this, the temperature of the grid may be regulated according to temperature curves defined from the temperature of the heating sources and / or cooling sources. The temperatures of more than one energy source can be interpolated and the resulting curve used, in combination with corresponding specified temperature differences between the grid and the more than one energy sources, to determine input temperatures for the regulation of the temperature of the grid.

[0123] . How the heating merit order and cooling merit order for the energy sources are assigned will be described in more detail below.

[0124] At least one of the first and second threshold temperatures 12, 22 may be determined based on the outflow temperature of the energy source 35 having the highest heating merit order or the highest cooling merit order. Similarly, at least one of the third and fourth threshold temperatures may be determined based on the outflow temperature of the energy source 35 having the second highest heating merit order or the second highest cooling merit order. The heating merit order can be assigned such that passive heating sources have a higher heating merit order than active heating sources and the cooling merit order can be assigned such that passive cooling sources have a higher merit order than active cooling sources.

[0125] The heating merit order for the passive heating sources can be assigned based on their respective temperatures, such that passive heating sources with a high temperature are assigned a higher heating merit order than passive heating sources with a lower temperature. Accordingly, the above mentioned first heating source 35 can be the passive heating source that has the highest temperature and the second heating source 35 can be the passive heating source with the second highest temperature. The active heating sources may also be assigned a merit order based on their respective temperatures in a similar way as the passive heating sources. Alternatively, the heating merit order may be assigned solely based on temperature without regards to if the heating sources are passive or active. The merit order may also be based on other factors such as efficiency, cost-of-operation, external energy requirements, etc. Hence if there is an increased effort to use a high temperature heating source a lower temperature heating source may be assigned a higher merit order, if the effort to supply thermal energy is less.

[0126] The cooling merit order for the passive cooling sources can be assigned based on their respective temperatures such that passive cooling sources with a low temperature are assigned a higher cooling merit order than passive cooling sources with a higher temperature. Accordingly, the above mentioned first cooling source 35 can be the passive cooling source that has the lowest temperature and the second heating source 35 can be the passive heating source with the second highest temperature. The active cooling sources may also be assigned a cooling merit order based on their respective temperatures in a similar way as the passive cooling sources. Alternatively, the cooling merit order may be assigned solely based on temperature without regards to if the cooling sources are passive or active. Also for cooling the merit order may be based on other factors such as efficiency, cost-of-operation, external energy requirements, etc. Hence if there is an increased effort to use a low temperature cooling source a higher temperature cooling source may be assigned a higher merit order, if the effort to supply cooling is less.

[0127] The heating merit order and / or cooling merit order may instead or further be determined based on one or more of an energy type (heating, cooling or both), a maximum temperature difference, a minimum temperature difference, a maximal (nominal) capacity, nominal source temperature (such as in cases where measurements are lacking), and a rank associated with the one or more energy sources. Rank refers to a number indicating the energy source preference and only applies to active energy sources.

[0128] Both the heating merit order and the cooling merit order can be dynamically reassigned based on measured or estimated temperatures of the energy sources 35. It is therefore possible that the merit order allocation changes on an hourly, daily or seasonal basis.

[0129] The warm temperature curve 11 of the warm pipe 10 can be determined by determining a minimum temperature and a maximum temperature of the warm pipe 10. The cool temperature curve 21 of the cold pipe 20 can be determined by determining a minimum temperature and a maximum temperature of the cold pipe 20. Alternatively or additionally, the warm temperature curve 11 and the cool temperature curves can be interpolated based the outflow temperature of at least one energy source 35 and / or based on assigned temperature difference set points.

[0130] While merit order control has been described in connection to the temperature curves 11, 21 and temperature thresholds 12, 13, 22, 23 shown in Fig. 3, it can also be based on the grid demand balance indicator value 5 as specified above. In such embodiment, the heating merit order and / or the cooling merit order of the energy sources 35 can be assigned in the same ways as described above. The grid demand balance indicator value 5 along with the first and second thresholds can be used to determine if the first heating source, i.e. the heating source with the highest merit order, and / or first cooling source, i.e. the cooling source having the highest cooling merit order, should be activated. For instance, if the grid demand balance indicator value 5 is below the first threshold, the first heating source may be activated and if the grid demand balance indicator value 5 is above the second threshold, the first cooling source may be activated. Similarly, more thresholds in the unbalanced regions 110,120 can be set and used to determine if heating sources 35 and / or cooling sources 35 of lower merit order should be activated.

[0131] Fig. 4 shows a graphical illustration of gradient shaping in the balanced region 115 according to one embodiment. Gradient shaping can be a way of defining the temperature profile for the balanced region 115 where no energy from an energy source is added to the thermal grid 100, but only the flow to and from the warm pipe and the cold pipe is controlled. This can be useful for varying the temperature difference ΔT as the demand balance of heating and cooling shifts and can be used to increase flow and therefore maintain capacity that would otherwise be lost in situations with very slow moving fluid in the system.

[0132] The temperature difference ΔT can represent a temperature difference of any one or more components forming or connected to the thermal grid. For instance, ΔT can represent a temperature difference ΔT 10,20 between the warm pipe 10 and the cold pipe 20, a temperature difference ΔT 30 of a balance unit 30, a temperature difference ΔT 11,21 between the warm temperature curve 11 and the cool temperature curve 21, a temperature difference between the outflow of an energy source 35 and the cold pipe 20 or the warm pipe 10, a temperature difference between a passive heating source 35 and a passive cooling source 35, a temperature difference between any two energy sources 35, or a temperature difference between any temperature of a balancing unit 30 and the cold pipe 20 or the warm pipe 10. Preferably, the temperature difference ΔT represents a temperature difference between the warm pipe 10 and the cold pipe 20. The balanced region (0-100%) can represent a relative "distance" between a heating requirement and a cooling requirement, such as the passive heating source having the highest heating merit order or the cooling source having the highest cooling merit order. The leftmost point in the graph may represent a set temperature difference between the first passive heating source and the cold pipe 10. The rightmost point in the graph may represent a set temperature difference between the first heating source and the cold pipe 20. Alternatively, these points may represent a minimum temperature difference between the first heating source and / or the first cooling source and any temperature of the balancing unit 30, respectively.

[0133] A continuous temperature difference ΔT, as shown in Fig. 4, can be determined by assigning a plurality of temperature difference set points ΔT sp and by interpolating between the set points or by interpolating the warm temperature curve 11 and the cool temperature curve 21 based on the temperature difference set points ΔT sp . The interpolation can also be based on the outflow temperature of at least one energy source 35.

[0134] Fig. 5 shows a method for a thermal grid according to one embodiment. The method comprises determining 52 a grid demand balance indicator value 5. The grid demand balance indicator value 5 can represent any of the temperatures or temperature differences mentioned above. The method further comprises associating 54 a current temperature region of the warm pipe 10 and / or the cold pipe 20 of the thermal grid 100 as a balanced temperature region 115 or as an unbalanced temperature region 110, 120 based on the grid demand balance indicator value. This can for instance be done by comparing the grid demand balance indicator value 5 to one or more thresholds as described above. The method further comprises selecting 56 a balanced control algorithm or an unbalanced control algorithm for the thermal grid 100 based on the current temperature region, and controlling 58 the thermal grid by the selected control algorithm. As previously mentioned, the balanced control algorithm may be based on gradient shaping and the unbalanced control algorithm on merit order control, which have been described above.

[0135] Fig. 6 shows a method for a thermal grid 100 comprising a warm pipe 10 and a cold pipe 20. The method comprises determining 62 a requirement to either add heat to the warm pipe 10 or to add cooling to the cold pipe 20, determining 64 a merit order of one or more energy sources 35 connected to the thermal grid, said merit order being based on the temperature of each energy source and / or the temperature difference between the outflow from each energy source 35 and the warm pipe 10 or the cold pipe 20. Determining 64 a merit order can also be performed in any other way described herein. The method further comprises selecting 66 an energy source 35 having the highest merit order, and regulating 68 the temperature of the warm pipe 10 and / or the cold pipe 20 of the thermal grid by i) activating the selected energy source 35 to heat or cool the thermal grid, and / or ii) changing the mass flow through the warm pipe 10 and / or the cold pipe 20. The temperature regulation can be based on the temperature of the selected energy source 35 and / or one or more of remaining energy sources 35. The temperature of the warm pipe 10 and / or the cold pipe 20 can be regulated such that a temperature difference between the selected energy source 35 and the pipe exceeds a predetermined threshold. The threshold may represent a temperature difference between the energy source and the pipe which facilitates efficient energy transfer between the energy source and the pipe. In embodiments where the thermal grid 100 comprises a plurality of substations 40 connected to the warm pipe 10 and / or the cold pipe 20, regulating the temperature of the warm pipe 10 and / or the cold pipe 20 may comprise regulating the flow between the substations 40 and the warm pipe 10 and / or the cold pipe 20.

[0136] Fig. 7 shows a method for a thermal grid 100 comprising a warm pipe 10 and a cold pipe 20. The method comprises determining 72 a continuous temperature difference ΔT between the warm pipe 10 and the cold pipe 20 by assigning 72a a plurality of temperature difference set points ΔT sp , and by interpolating 72b the warm temperature curve 11 and the cool temperature curve 21 based on the temperature difference set points ΔT sp . Determining 72 a continuous temperature difference ΔT between the warm pipe 10 and the cold pipe 20 can also be performed in any other way described herein.

[0137] Fig. 8 shows a method for controlling the temperature of a thermal grid 100. The method comprises performing 82 any method described herein, and regulatingthe temperature of the warm pipe 10 and / or the cold pipe 20 of the thermal grid by i) activating 84a one or more energy sources 35 to heat or cool the thermal grid, and / or ii) changing 84b the mass flow through the warm pipe 10 and / or the cold pipe 20.

[0138] Modifications and other variants of the described embodiments will come to mind to one skilled in the art having benefit of the teachings presented in the foregoing description and associated drawings. Therefore, it is to be understood that the embodiments are not limited to the specific example embodiments described in this disclosure and that modifications and other variants are intended to be included within the scope of this disclosure. For example, while embodiments of the invention have been described with reference to a thermal grid, persons skilled in the art will appreciate that the embodiments of the invention can equivalently be applied to other areas of thermal management. Furthermore, although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. Therefore, a person skilled in the art would recognize numerous variations to the described embodiments that would still fall within the scope of the appended claims. Furthermore, although individual features may be included in different claims (or embodiments), these may possibly advantageously be combined, and the inclusion of different claims (or embodiments) does not imply that a combination of features is not feasible and / or advantageous. In addition, singular references do not exclude a plurality. Finally, reference signs in the claims are provided merely as a clarifying example and should not be construed as limiting the scope of the claims in any way.

Claims

1. A method for a thermal grid (100) comprising a warm pipe (10), a cold pipe (20), one or more energy sources (35), and at least one balancing unit (30) configured to store thermal energy, the method comprising: determining a grid demand balance indicator value (5), associating a current temperature region for the warm pipe (10) and / or the cold pipe (20) of the thermal grid (100) as a balanced temperature region (115) or as an unbalanced temperature region (110, 120) based on the grid demand balance indicator value (5), selecting a balanced control algorithm if the current temperature region is associated as a balanced temperature region (115) or an unbalanced control algorithm if the current temperature region is associated as an unbalanced temperature region (110, 120), wherein the one or more energy sources (35) are deactivated when the balanced control algorithm is selected and at least one of the energy sources (35) are activated when the unbalanced control algorithm is selected, and controlling the thermal grid by the selected control algorithm.

2. The method according to claim 1, wherein the thermal grid (100) comprises a balancing unit (30), and wherein the grid demand balance indicator value (5) represents a mean temperature (Tmean) of the balancing unit (30).

3. The method according to claim 1, wherein the thermal grid (100) comprises a balancing unit (30), and wherein the grid demand balance indicator value (5) represents a maximum temperature difference (ΔT30) of the balancing unit (30).

4. The method according to claim 1, wherein the grid demand balance indicator value (5) represents a current temperature difference (ΔT10,20) between the warm pipe (10) and the cold pipe (20) of the thermal grid.

5. The method according to claim 1, wherein the thermal grid (100) comprises a balancing unit (30), and wherein the grid demand balance indicator value (5) represents a minimum temperature (Tmin) and / or a maximum temperature (Tmax) of the balancing unit (30).

6. The method according to any preceding claim, wherein when the unbalanced control algorithm is selected, the method further comprises: determining a requirement to either add heat to the warm pipe (10) or to add cooling to the cold pipe (20), determining a merit order of the one or more energy sources (35) connected to the thermal grid, said merit order being based on the temperature of each energy source (35) and / or temperature difference between the outflow from each energy source (35) and the warm pipe (10) or the cold pipe (20), selecting an energy source (35) having the highest merit order, and regulating the temperature of the warm pipe (10) and / or the cold pipe (20) of the thermal grid by i) activating the selected energy source (35) to heat or cool the thermal grid, and / or ii) changing the mass flow through the warm pipe (10) and / or the cold pipe (20), wherein the temperature regulation is based on the temperature of the selected energy source (35).

7. The method according to claim 6, wherein when the unbalanced control algorithm is selected, the method further comprises: determining a minimum temperature difference between the outflow from each energy source (35) and the warm pipe (10) or the cold pipe (20), and determining the requirement to either add heat to the warm pipe (10) or to add cooling to the cold pipe (20) when the determined minimum temperature difference is zero.

8. The method according to claim 6 or 7, wherein when the unbalanced control algorithm is selected, the method further comprises: determining a warm temperature curve (11) of the warm pipe (10) of the thermal grid (100) and a cool temperature curve (21) of the cold pipe (20) of the thermal grid (100); determining a required heating region (110) extending up to a first threshold temperature (12) of the warm temperature curve (11), a required cooling region (120) extending from a second threshold (22) of the cool temperature curve (21), and a balanced region (115) extending between the heating region (110) and the cooling region (120), determining at least one of the first and second threshold temperatures (12,22) based on the outflow temperature of the energy source (35) having the highest heating merit order or the highest cooling merit order.

9. The method according to claim 8, wherein when the unbalanced control algorithm is selected, the method further comprises: determining the warm temperature curve (11) of the warm pipe (10) of the thermal grid (100) by determining a minimum temperature and a maximum temperature of the warm pipe (10), and / or determining the cool temperature curve (21) of the cold pipe (20) of the thermal grid (100) by determining a minimum temperature and a maximum temperature of the cold pipe (20).

10. The method according to any of claims 6 to 9, wherein when the unbalanced control algorithm is selected, the method further comprises: updating the merit order of the one or more energy source (35) connected to the thermal grid.

11. The method according to any of claims 6 to 10, wherein when the unbalanced control algorithm is selected, the method further comprises: determining the first threshold temperature (12) as being equal to the maximum outflow temperature of the at least one energy source (35), and determining the second threshold temperature (22) as being equal to the minimum outflow temperature of the at least one energy source (35).

12. The method according to any preceding claim, wherein when the balanced control algorithm is selected, the method further comprises: determining a continuous temperature difference (ΔT) between the warm pipe (10) and the cold pipe (20) by assigning a plurality of temperature difference set points (ΔTsp), and by interpolating a warm temperature curve (11) and the cool temperature curve (21) based on the temperature difference set points (ΔTsp).

13. The method according to claim 12, wherein when the balanced control algorithm is selected, the method further comprises interpolating the warm temperature curve (11) and the cool temperature curve (21) based on the outflow temperature of at least one energy source (35).

14. The method according to claim 12 or 13, wherein when the balanced control algorithm is selected, the method further comprises maintaining an assigned temperature difference between the warm pipe (10) and the cold pipe (20) by controlling the mass flow through the thermal grid (100).

15. The method according to any of claims 12 to 14, wherein the temperature difference (ΔT11,21) between the warm temperature curve (11) and the cool temperature curve (21) of the balanced region (115) increases from a central portion of the balanced region (115) towards the heating region (110) and the cooling region (120).

16. A method for controlling the temperature of a thermal grid, comprising: performing the method according to any of the preceding claims, and regulating the temperature of the warm pipe (10) and / or the cold pipe (20) of the thermal grid by i) activating one or more energy sources (35) to heat or cool the thermal grid, and / or ii) changing the mass flow through the warm pipe (10) and / or the cold pipe (20).

17. The method according to claim 6 or 16, wherein activating (63) one or more energy sources (35) comprises controlling the heat flow between the one or more energy sources (35) and the warm and cold pipes (10, 20).

18. A thermal grid, comprising a warm pipe (10) and a cold pipe (20), a plurality of substations (40) connected to the warm and cold pipes (10, 20), one or more energy sources (35) connected to the warm and cold pipes (10, 20), a balancing unit (30) configured to store thermal energy, and a control unit (50) configured to determine a grid demand balance indicator value (5), associate a current temperature region for the warm pipe (10) and / or the cold pipe (20) of the thermal grid (100) as a balanced temperature region (115) or as an unbalanced temperature region (110, 120) based on the grid demand balance indicator value (5), select a balanced control algorithm if the current temperature region is associated as a balanced temperature region (115) or an unbalanced control algorithm if the current temperature region is associated as an unbalanced temperature region (110, 120), wherein the one or more energy sources (35) are deactivated when the balanced control algorithm is selected and at least one of the energy sources (35) are activated when the unbalanced control algorithm is selected, and control the thermal grid by the selected control algorithm.

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