Technical field

The present invention relates to a method for controlling heat transfer between a local cooling system and a local heating system. Background

Nearly all large developed cities in the world have at least two types of energy distribution grids incorporated in their infrastructures: one grid for providing heating and one grid for providing cooling. The grid for providing heating may e.g. be used for providing comfort and/or process heating, and/or hot tap water preparation. The grid for providing cooling may e.g. be used for providing comfort and/or process cooling.

A common grid for providing heating is a gas grid providing a burnable gas, typically a fossil fuel gas. The gas provided by the gas grid is locally burned at a building for providing comfort and/or process heating, and/or hot tap water preparation. An alternative grid for providing heating is a district heating grid. The district heating grid is used for providing heated heat transfer liquid, typically in the form of water, to buildings of the city. A centrally placed heating and pumping plant is used for heating and distributing the heat transfer liquid. The heat transfer liquid is delivered to buildings of the city via one or more feed conduits and is returned to the heating and pumping plant via one or more return conduits. Locally at a building heat from the heat transfer liquid is extracted via a heat exchanger. Further alternative, electrical energy of an electrical energy grid may be used for heating. The electrical energy may e.g. be used for heating tap water or for heating local heat transfer liquid used for comfort and/or process heating.

A common grid for providing cooling is the electrical energy grid. The electrical energy may e.g. be used for running refrigerators or freezers. The electrical energy may e.g. be used for running air conditioners for providing comfort cooling. An alternative grid for providing cooling is a district cooling grid. The district cooling grid is used for providing chilled heat transfer liquid, typically in the form of water, to buildings of the city. A centrally placed cooling and pumping plant is used for cooling and distributing the heat transfer liquid. The heat transfer liquid is delivered to buildings of the city via one or more feed conduits and is returned to the cooling and pumping plant via one or more return conduits. Locally at a building cold from the heat transfer liquid is extracted via a heat exchanger.

The use of energy for heating and/or cooling is steadily increasing influencing the environment negatively. By improving utilization of the energy distributed in the energy distribution grids, negative influences on the environment may be reduced. Hence, there is a need for improving utilization of the energy distributed in energy distribution grids.

Summary of the invention

It is an object of the present invention to solve at least some of the problems mentioned above.

According to a first aspect a method for controlling heat transfer between a local cooling system and a local heating system is provided. The method comprises:

determining a local energy consumption need of the local cooling system;

determining a local energy consumption need of the local heating system;

controlling, based on the local energy consumption need of the local cooling system and the local energy consumption need of the local heating system, a heat pump connected between the local cooling system and the local heating system and configured to transfer heat from the local cooling system to the local heating system.

First of all, by connecting a heat pump between a local cooling system and a local heating system and configuring the heat pump to transfer heat from the local cooling system to the local heating system it is made possible to reduce the overall energy consumption. The coefficient of performance (COP) of a heat pump is typically in the range of 4-5, i.e. for a given energy input, typically electrical power, the heat pump is able to move 4-5 times this energy input in form of moving heat from the cooling system to the heating system. Thus, during periods when there is a simultaneous need for cooling and heating a certain amount of the energy may be transferred by the heat pump from the cooling system to the heating system at a low energy input compared to the overall gain. By removing heat from the cooling system, the cooling system may meet the local cooling need at a lower local energy consumption need of the local cooling system. If the local cooling system e.g. is connected to a cooling grid, the local cooling system does not need to draw all of the local cooling need from the local cooling grid since some of the heat is removed by the heat pump. Furthermore, by transferring heat to the heating system, the heating system may meet the local heating need at a lower local energy consumption need of the local heating system. If the local heating system e.g. is connected to a heating grid, the local heating system does not need to draw all of the local heating need from the local heating grid since some of the heat is provided by the heat pump.

Since the heat pump requires energy input it should be properly controlled in order to achieve the desired energy saving. This is in short performed by determining a local energy consumption need of the local cooling system; determining a local energy consumption need of the local heating system; and controlling the heat pump based on the local energy consumption need of the local cooling system and the local energy

consumption need of the local heating system. By determining the local energy consumption need of the local cooling system, the maximum available heat that may be drawn from the local cooling system is established. By determining the local energy consumption need of the local heating system, the maximum available heat that may usefully be transferred to the local heating system is established. By controlling the heat pump such that the energy drawn and energy transferred is within these limits, an efficient and useful energy transfer is achieved.

It may be noted that the local energy consumption needs do not necessarily need to be strictly simultaneous if one or more of the systems is capable of storing heat or cold. Heat from the cooling system may e.g. be transferred to a hot tap water storage tank or to a swimming pool. As long as the entity being able to store heat or cold is still capable of receiving heat or having heat drawn from it, there may still be considered that a local energy consumption need is present.

This method provides both benefits for the local energy consumption and for the overall energy consumption. Local is primarily intended to be interpreted as being a building or a building complex in which there is installed a cooling system and a heating system within reasonable distance from each other such that it is reasonable to install a heat pump between the two systems.

The local heating system may comprise a heating circuit having:

a feed conduit for an incoming flow of heat transfer fluid having a first temperature, and

a return conduit for a return flow of heat transfer fluid having a second temperature, the second temperature being lower than the first temperature.

The local cooling system may comprise a cooling circuit having:

a feed conduit for an incoming flow of heat transfer fluid having a third temperature, and

a return conduit for a return flow of heat transfer fluid having a fourth temperature, the fourth temperature being higher than the third temperature.

The fourth temperature may be lower than the second temperature.

The heat pump may be connected to the local cooling system and to the local heating system.

The method of controlling heat transfer between a local cooling system and a local heating system may also be used as an aid to balance need and capacity of heating, cooling and/or electric power grids. This may be performed in the control method by introducing a heating control parameter, a cooling control parameter, and/or an electric power control parameter.

The method may further comprise introducing a heating control parameter and determining a value indicating an overall heating consumption need of a plurality of local heating systems in relation to overall available heating capacity of a heating grid to which the local heating systems are connected, wherein the controlling of the heat pump is also based on the value of the heating control parameter.

The method may further comprise introducing a cooling control parameter and determining a value indicating an overall cooling consumption need of a plurality of local cooling systems in relation to overall available cooling capacity of a cooling grid to which the local cooling systems are connected, wherein the controlling of the heat pump is also based on the value of the cooling control parameter.

The method may further comprise introducing an electric power control parameter and determining a value indicating an overall electrical power need in relation to overall available electrical power of an electric grid to which the heat pump is connected, wherein the controlling of the heat pump is also based on the value of the electric power control parameter.

By introducing one or more of these control parameters and

determining values thereof and then control the heat pump based on these values, it is possible to use the local cooling system, the local heating system and/or the heat pump of one or more buildings to compensate for imbalances between overall need(s) compared to overall available capacity/power. If there e.g. is a comparably high overall demand on cooling capacity it is beneficial if the heat pump is run to such an extent that the local system does not draw any cooling capacity from the cooling grid and instead transfers all of the required cooling energy from the local cooling system to the local heating system even though there is no actual need for all this energy at the local heating system. The heat may then be stored locally in the tap water tank or in a pool. It may even on a short-term basis be beneficial to allow some of the heat to escape from the local heating system as long as there is provided a local relief on the cooling grid. By providing this in a plurality of buildings connected to the same cooling grid and/or heating grid and electrical grid, respectively, it is possible to connect a greater number of buildings to a grid of a certain capacity, to allow for greater changes in cooling and heating need for the different users, to allow for more intermittent production of the cooling capacity, heating energy and/or electrical energy. The control parameters may also be used to take into account other factors than purely the relation between the overall need and the available capacity. The parameters may also take into account the environmental impact of the production of cooling capacity, heating energy and electrical energy. The parameters may also take into account predictions. If the total heating need reaches a critical point where it is almost necessary to start-up another heating plant, the heating control parameter may be determined and then set to indicate an even greater overall heating consumption need than is actually the case and thereby steer the heat pumps such that they draws maximum amount of energy from the cooling systems together reducing the need for heating capacity from the heating grid thereby hopefully avoiding start-up of another heating plant. The control parameters may be expressed as price per energy amount. The control parameters may be expressed as a numerical index value having no direct relation to an energy amount.

It may also be noted that when the local system is run to aid in balancing the overall grids, the determination of the local consumption need is not the actual need for the system to perform it's cooling/heating task but may rather be considered as the acceptable limit, i.e. an artificial value of the local consumption need.

The heat pump may have:

a first heat exchanger having a first circuit for circulating heat transfer fluid and a second circuit for circulating heat transfer fluid, wherein the first circuit has an inlet and an outlet connected to the cooling circuit,

a second heat exchanger having a third circuit for circulating heat transfer fluid and a fourth circuit for circulating heat transfer fluid, wherein the fourth circuit has an inlet and an outlet connected to the heating circuit,

wherein the second circuit and the third circuit is a common circuit of the first and second heat exchangers.

In the context of the present disclosure the wording "heat transfer fluid" shall be construed as a fluid having the ability to transfer thermal energy. The heat transfer fluid may carry thermal energy from one place to another. The heat transfer fluid may comprise water. However, according to other embodiments other heat transfer fluids may be used. Some non-limiting examples are ammonia, anti-freezing liquids (such as glycol), oils and alcohols. The heat transfer fluid may also comprise a mixture of two or more of the heat transfer fluids mentioned above.

This allow for heat absorbed by the heat transfer fluid in the cooling circuit, which absorbed heat normally is carried away from the building via e.g. a district cooling grid or normally is emitted to the environment using e.g. cooling columns, to be re-used for heating the heat transfer fluid of the heating circuit. Hence, the need for extracting heat from the building at the cooling circuit is lowered at the same time as the need for providing the building with a heat through the district heating grid or the gas grid is lowered. Hence, an improved utilization of the energy distributed in energy distribution grids is provided.

The inlet of the first circuit may be connected to the return conduit of the cooling circuit.

The inlet of the fourth circuit may be connected to the return conduit of the heating circuit.

The outlet of the first circuit may be connected to the return conduit of the cooling circuit. By connecting the outlet of the first circuit to the return conduit of the cooling circuit the installation of the heat pump causes a minimum of interference on and adaptation of a control system of the heat pump.

The inlet of the first circuit may be connected to the return conduit of the cooling circuit upstream relative to the outlet of the first circuit.

The outlet of the fourth circuit may be connected to the return conduit of the heating circuit. By connecting the outlet of the fourth circuit to the return conduit of the heating circuit the installation of the heat pump causes a minimum of interference on and adaptation of the control system of the heat pump.

The inlet of the fourth circuit may be connected to the return conduit of the heating circuit upstream relative to the outlet of the fourth circuit.

The outlet of the first circuit may be connected to the feed conduit of the cooling circuit. By connecting the outlet of the first circuit to the feed conduit of the cooling circuit the installation of the heat pump causes a minimum of interference on and adaptation of a control system of the local cooling system.

The outlet of the fourth circuit may be connected to the feed conduit of the heating circuit. By connecting the outlet of the fourth circuit to the feed conduit of the heating circuit the installation of the heat pump causes a minimum of interference on and adaptation of a control system of the local heating system.

The common circuit may comprise a compressor.

The common circuit may comprise an expansion valve.

The first heat exchanger may be an evaporator heat exchanger.

The second heat exchanger may be a condenser heat exchanger.

A further scope of applicability of the present invention will become apparent from the detailed description given below. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the scope of the invention will become apparent to those skilled in the art from this detailed description.

Hence, it is to be understood that this invention is not limited to the particular component parts of the device described or steps of the methods described as such device and method may vary. It is also to be understood that the terminology used herein is for purpose of describing particular embodiments only, and is not intended to be limiting. It must be noted that, as used in the specification and the appended claim, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the elements unless the context clearly dictates otherwise. Thus, for example, reference to "a unit" or "the unit" may include several devices, and the like. Furthermore, the words "comprising", "including", "containing" and similar wordings does not exclude other elements or steps.

Brief Description of the Drawings

The above and other aspects of the present invention will now be described in more detail, with reference to appended drawings showing embodiments of the invention. The figures should not be considered limiting the invention to the specific embodiment; instead they are used for explaining and understanding the invention.

As illustrated in the figures, the sizes of layers and regions are exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures of embodiments of the present invention. Like reference numerals refer to like elements throughout.

Fig. 1 is a schematic diagram of a heat transfer system according to one embodiment.

Fig. 2 is a schematic diagram of a heat transfer system according to an alternative embodiment.

Fig. 3 is a schematic diagram of a heat transfer system according to yet an alternative embodiment.

Fig. 4 is a schematic diagram of a heat transfer system according to an alternative embodiment.

Fig. 5 is a schematic diagram of a plurality of local heat transfer systems.

Fig. 6 is a schematic diagram indicating the method. Detailed description

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This 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 for thoroughness and completeness, and to fully convey the scope of the invention to the skilled person.

Fig. 1 illustrates a heat transfer system 1 . The heat transfer system 1 comprises a heating circuit 30, a cooling circuit 40 and heat pump 50. The heat transfer system is typically installed in a building (not shown). In Figs 2 and 3 alternative embodiments of the heat transfer system 1 are illustrated.

The difference between the different embodiments is directed towards how heat is transported to and from the heat transfer systems 1 . This will be discussed in more detail below.

The heating circuit 30 comprises a feed conduit 34 and a return conduit 36. The feed conduit 34 is configured to carry heat transfer fluid from a heat source 32 to a heat emitter 38. The heat source 32 is configured to heat the heat transfer fluid. Hence, the feed conduit 34 is configured to carry heated heat transfer fluid from the heat source 32 to the heat emitter 38. The return conduit 36 is configured to carry heat transfer fluid from the heat emitter 38 to the heat source 32. The heat emitter 38 consumes heat from the heat transfer fluid for heating its surroundings. Hence, the heat transfer fluid is cooled at the heat emitter 38. Thus, the return conduit 36 is configured to carry cooled heat transfer fluid from the heat emitter 38 to the heat source 32. In other words, the feed conduit 34 is configured to carry a, to the heat emitter 38, incoming flow of heat transfer fluid having a first temperature and the return conduit 36 is configured to carry a, from the heat emitter 38, return flow of heat transfer fluid having a second temperature, wherein the second temperature is lower than the first temperature.

According to a non-limiting example, in case of the heat transfer fluid comprises mainly water the first temperature is in the range of 25-70°C and the second temperature is in the range of 0-50°C. As mentioned the heat transfer fluid may be water 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.

As mentioned above the heat source 32 is configured to heat the heat transfer fluid of the heating circuit 30. The heat source 32 may be embodied in different ways. According to the heat transfer systems 1 of Figs 1 and 3 the heat source 32 may be a heat exchanger 31 configured to transfer heat from a district heating grid 10 to the heating circuit 30. This may be done by letting heat transfer fluid of the district heating grid 10 to flow from a district heating grid feed conduit 12 to the heat exchanger 31 where the heat transfer fluid of the heating circuit 30 is heated and as a result the heat transfer fluid of the district heating grid 10 is cooled. The cooled heat transfer liquid of the district heating grid 10 may thereafter be returned to a district heating grid return conduit 14. Typically, the heat transfer fluid of the district heating grid 10 is water. However, other fluids or mixtures of fluids may as well 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. In the case of the heat transfer fluid of the district heating grid 10 mainly comprising water, the heat transfer fluid flowing to the heat exchanger 31 has a temperature in the range of 60- 95°C. In this case, the heat exchanger 31 is typically set such that the heat transfer fluid returned to the district heating return conduit 14 has a

temperature in the range of 20-50°C.

Alternatively or in combination, the heat source 32 may be embodied as a burner 33 burning a burnable gas, typically a fossil fuel gas. This is illustrated in connection with Fig. 2. By burning the burnable gas the heat transfer fluid of the heating system 30 is heated at the heat source 32. The burnable gas is typically feed to the burner 33 via a gas grid 16.

As mentioned above the heat emitter 38 is configured to consume heat from the heat transfer fluid for heating its surroundings. Non-limiting examples of processes where heat is consumed are at hot tap water preparation, comfort heating and/or process heating.

The cooling circuit 40 comprises a feed conduit 44 and a return conduit 46. The return conduit 46 is configured to carry heat transfer fluid from a cooler 48 to a heat extractor 42. The cooler 48 is configured to absorb heat from its surroundings in order to cool the surroundings. At the cooler 48 the absorbed heat is transferred to the heat transfer fluid of the cooling circuit 40. Hence, the return conduit 46 is configured to carry heated heat transfer fluid from the cooler 48 to the heat extractor 42. The heat extractor 42 extracts heat from the heat transfer fluid for cooling the heat transfer fluid. Hence, the heat transfer fluid is cooled by the heat extractor 42. The feed conduit 44 is configured to carry heat transfer fluid from the heat extractor 42 to the cooler 48. Thus, the feed conduit 44 is configured to carry cooled heat transfer fluid from the heat extractor 42 to the cooler 48. In other words, the feed conduit 44 is configured to carry a, to the cooler 48, incoming flow of heat transfer fluid having a third temperature and the return conduit 46 is configured to carry a, from the cooler 48, return flow of heat transfer fluid having a fourth temperature, wherein the fourth temperature is higher than the third temperature. According to a non-limiting example, in case of the heat transfer fluid comprises mainly water the third temperature is in the range of 5-10°C and the fourth temperature is in the range of 10-15°C. As mentioned the heat transfer fluid may be water 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.

As mentioned above the heat extractor 42 is configured to extract heat from the heat transfer fluid of the cooling circuit 30. The heat extractor 42 may be embodied in different ways. According to the heat transfer systems 1 of Figs 1 and 2 the heat extractor 42 may be a heat exchanger 41 configured to transfer heat from the cooling circuit 30 to a district cooling grid 20. This may be done by letting heat transfer fluid of a district cooling grid 20 to flow from a district cooling grid feed conduit 22 to the heat exchanger 41 where the heat transfer fluid of the cooling circuit 40 is cooled and as a result the heat transfer fluid of the district cooling grid 20 is heated. The heated heat transfer fluid of the district cooling grid 20 may thereafter be returned to a district cooling grid return conduit 24. Typically, the heat transfer fluid of the district cooling grid 20 is water. However, other fluids or mixtures of fluids may as well 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. In the case of the heat transfer fluid of the district cooling grid 20 mainly comprising water, the heat transfer fluid flowing to the heat exchanger 41 has a temperature in the range of 4-10°C. In this case, the heat exchanger 41 is typically set such that the heat transfer fluid returned to the district cooling return conduit 24 has a temperature in the range of 8-12°C. Alternatively or in combination, the heat extractor 42 may be embodied as a heat pump 43. The heat pump 42 may be part of a local cooling machine, such as an air conditioner, a freezer, a refrigerator or the like. This is illustrated in connection with Fig. 3.

As mentioned above, the cooler 48 is configured to cool down its surroundings by absorbing heat by the heat transfer liquid. Non-limiting examples of processes where heat is absorbed are at comfort cooling, process cooling, refrigerating and/or freezing.

The heat pump 50 is connected between the cooling circuit 40 and the heating circuit 30. The heat pump 50 is configured to transfer heat from the cooling circuit 40 to the heating circuit 30. This allow for heat absorbed by the heat transfer fluid in the cooling circuit 40, which absorbed heat normally is carried away from the building via the district cooling grid return conduit 24 or normally is emitted to the environment using e.g. cooling columns, to be re- used for heating the heat transfer fluid of the heating circuit 30. Hence, the need for extracting heat from the building at the cooling circuit is lowered at the same time as the need for providing the building with a heat through the district heating grid or the gas grid is lowered. The basic principle of the heat transfer system 1 is thus that heat absorbed at the cooling circuit 40 is re- used at the heating circuit. The heat pump 50 is used for updating the heat absorbed in the cooling circuit 40 to a useful temperature level that may be used in the heating circuit 30.

The heat pump 50 comprises a first heat exchanger 51 and a second heat exchanger 54. The first heat exchanger 51 may be an evaporator heat exchanger. The second heat exchanger 54 may be a condenser heat exchanger. The first heat exchanger 51 comprises a first circuit 52a for circulating heat transfer fluid. The first heat exchanger 51 comprises a second circuit 52b for circulating heat transfer fluid. The first and second circuits 52a, 52b are not in fluid contact with each other. The first circuit 52a has an inlet 53a and an outlet 53b. The inlet 53a of the first circuit 52a is connected to the return conduit 46 of the cooling circuit 40.

During operation of the heat pump 50 the first heat transfer

exchanger 51 is configured to absorb heat from the heat transfer fluid entering the same via the inlet 53a of the first circuit 52a. The heat transfer fluid returned to the cooling circuit 40 via the outlet 53b will thus be cooled. In the in Figs 1 -3 shown embodiments the outlet 53b of the first circuit 52a is connected to the return conduit 46 of the cooling circuit 40.

In the case of the inlet 53a and the outlet 53b of the first circuit 52a both being connected to the return conduit 46 of the cooling circuit 40, the inlet 53a of the first circuit 52a is preferably connected to the return conduit 46 of the cooling circuit 40 upstream relative to the outlet 53b of the first circuit 52a.

Moreover, in the case the heat pump 50 is in operation and the inlet 53a and the outlet 53b of the first circuit 52a both being connected to the return conduit 46 of the cooling circuit 40, the heat transfer fluid of the return conduit 46 will be cooled.

Alternatively or in combination to the above configuration of the outlet 53b of the first circuit 52a, the outlet 53b of the first circuit 52a may be connected to the feed conduit 44 of the cooling circuit 40. The connection of the outlet 53b of the first circuit 52a to the feed conduit 44 of the cooling circuit 40 will be discussed in more detail below in connection with Fig. 4.

According to the above, the first circuit 52a and the cooling circuit 40 are in fluid contact with each other.

The second heat exchanger 54 comprises a third circuit 52c for circulating heat transfer fluid. The second heat exchanger 54 comprises a fourth circuit 52d for circulating heat transfer fluid. The third and fourth circuits 52c, 52d are not in fluid contact with each other. The fourth circuit 52d has an inlet 55a and an outlet 55b. The inlet 55a of the fourth circuit 52d is connected to the return conduit 36 of the heating circuit 30.

During operation of the heat pump 50 the second heat transfer exchanger 54 is configured to heat heat transfer fluid entering the same via the inlet 55a of the fourth circuit 52d. The heat transfer fluid returned to the heating circuit 40 via the outlet 55b will thus be heated. In the in Figs 1 -3 shown embodiments the outlet 55b of the fourth circuit 52d is connected to the return conduit 36 of the heating circuit 30. In the case of the inlet 55a and the outlet 55b of the fourth circuit 52d both being connected to the return conduit 36 of the heating circuit 30, the inlet 55a of the fourth circuit 52d is preferably connected to the return conduit 36 of the heating circuit 30 upstream relative to the outlet 55b of the fourth circuit 52d.

Moreover, in the case the heat pump 50 is in operation and the inlet 55a and the outlet 55b of the fourth circuit 52d both being connected to the return conduit 36 of the heating circuit 30, the heat transfer fluid of the return conduit 36 will be heated.

Alternatively or in combination to the above configuration of the outlet

55b of the fourth circuit 52d, the outlet 55b of the fourth circuit 52d may be connected to the feed conduit 34 of the heating circuit 30. The connection of the outlet 55b of the fourth circuit 52d to the feed conduit 34 of the heating circuit 30 will be discussed in more detail below in connection with Fig. 4.

According to the above, the fourth circuit 52d and the heating circuit 30 are in fluid contact with each other.

The second circuit 52b and the third circuit 52c is a common circuit 56 of the first and second heat exchangers 51 , 54. The common circuit 56 may further comprise a compressor 57. The common circuit 56 may further comprise an expansion valve 58. The heat pump 50 is configured to update the heat absorbed in the cooling circuit 40 to a useful temperature level that may be used in the heating circuit 30.

As mentioned above, in connection with Fig. 4 the connection of the outlet 53b of the first circuit 52a to the feed conduit 44 of the cooling circuit 40 and the connection of the outlet 55b of the fourth circuit 52d to the feed conduit 34 of the heating circuit 30 will be discussed.

Starting at the cooling circuit 40. In the case the heat pump 50 is in operation and the outlet 53b of the first circuit 52a is connected to the feed conduit 44 of the cooling circuit 40, the heat transfer fluid of the feed conduit 44 will be affected. In this configuration it is favorable to control the heat pump 50 such that the temperature of the heat transfer fluid returned to the feed conduit 44 of the cooling circuit 40 is controlled. Preferably, the heat pump 50 is controlled such that the temperature of the heat transfer fluid returned to the feed conduit 44 of the cooling circuit 40 has the third temperature. This since, the third temperature is the temperature the cooler 48 is requesting as input temperature. In this case also the heat extractor 42 is preferably controlled such that it delivers heat transfer fluid of the third temperature. Alternatively, the heat pump 50 and the heat extractor 42 are jointly controlled such that the heat transfer fluids ejected by them individually when mixed exhibit the third temperature.

Turning towards the heating circuit 30. In the case the heat pump 50 is in operation and the outlet 55b of the fourth circuit 52d is connected to the feed conduit 34 of the heating circuit 30, the heat transfer fluid of the feed conduit 34 will be affected. In this configuration it is favorable to control the heat pump 50 such that the temperature of the heat transfer fluid returned to the feed conduit 34 of the heating circuit 30 is controlled. Preferably, the heat pump 50 is controlled such that the temperature of the heat transfer fluid returned to the feed conduit 34 of the heating circuit 30 has the first temperature. This since, the first temperature is the temperature the heater 38 is requesting as input temperature. In this case also the heat source 32 is preferably controlled such that it delivers heat transfer fluid of the first temperature. Alternatively, the heat pump 50 and the heat source 32 are jointly controlled such that the heat transfer fluids ejected by them individually when mixed exhibit the first temperature.

The heat transfer system 1 may comprise more than one heating circuit 30 or cooling circuit 40. In case of more than one heating circuit 30 or cooling circuit 40 the heat transfer system 1 may comprise a plurality of heat pumps 50, wherein a single heat pump 50 is connecting one cooling circuit 40 with one heating circuit 30. According to a non-limiting example the heat transfer system 1 comprises a first heating circuit 30 configured to provide comfort heating to a building, a second heating circuit 30 configured to provide hot tap water preparation to the building and a cooling circuit 40 configured to provide comfort cooling to the building. This heat transfer system 1 further comprises a first heat pump 50 connecting the cooling circuit 40 to the first heating circuit 30 and a second heat pump 50 connecting the cooling circuit 40 to the second heating circuit 30. Moreover, above two alternatives for the heat source 32 has been discussed. However, other heat sources 32 may as well be used by its own or in combination. One example of such other heat source 32 is an electrical heater (not shown).

Furthermore, in Figs 1 -3 and in the paragraph directly above some alternative embodiments of implementations on how thermal energy may be distributed to the heating circuit 30 and from the cooling circuit 40 are illustrated. It is realized that any combination of such distribution of thermal energy to and from the heat transfer system 1 may be used.

In the embodiments discussed in connection with Figs. 1 -3 the outlet 53b of the first circuit 52a is connected to the return conduit conduit 46 of the cooling circuit 40 and in the embodiments discussed in connection with Fig. 4 the outlet 53b of the first circuit 52a is connected to the feed conduit 44 of the cooling circuit 40. It is however realized that the outlet 53b of the first circuit 52a may be connected both to the return conduit conduit 46 and the feed conduit 44 of the cooling circuit 40. In this later case a valve of valves may be used to control the flow of heat transfer fluid into the return conduit conduit 46 and the feed conduit 44, respectively.

In the embodiments discussed in connection with Figs. 1 -3 the outlet 55b of the fourth circuit 52d is connected to the return conduit conduit 36 of the heating circuit 30 and in the embodiments discussed in connection with Fig. 4 the outlet 55b of the fourth circuit 52d is connected to the feed conduit 34 of the heating circuit 30. It is however realized that the outlet 55b of the first circuit 52d may be connected both to the return conduit conduit 36 and the feed conduit 34 of the heating circuit 30. In this later case a valve of valves may be used to control the flow of heat transfer fluid into the return conduit conduit 36 and the feed conduit 34, respectively.

The connection of the outlet 53b of the first circuit 52a to the return conduit 46 of the cooling circuit 40 and/or to the feed conduit 44 of the cooling circuit 40 may of course be made independently of the connection of the outlet 55b of the fourth circuit 52d to the return conduit 36 of the heating circuit 30 and/or to the feed conduit 34 of the heating circuit 30. Hence, any permutation of the connections of the outlets 53b, 55b may be used. As will be discussed in connection with Figs 5 and 6, the heat transfer system 1 is controlled according to the following.

Unless otherwise provided for, the control method relates to the control of both the heat pump 50 and the heat pump 50'. The pumps 50, 50' are controlled according to the same basic method but due to the fact that the cooling and heating needs of the cooling systems 30 and 30' and heating systems 40, 40' of the different buildings may be different, the result concerning if the heat pump 50 or 50' is run or not be different. It may also be noted that the heat pumps 50 and 50' need not be of the same size and capacity which may also be varied due to the different needs of the

consumers of the different buildings. In the following, the method of

controlling a heat pump is disclosed and, unless otherwise provided for, the method is applicable for both heat pumps 50 and 50' (and for any heat pump connected in the above disclosed manner between a cooling system and a heating system).

A local energy consumption need of a local cooling system is determined. This may be performed e.g. by the cooling system measuring a ambient temperature or a temperature in the environment to be cooled. In response to this measurement, the cooling system may e.g. calculate a desired temperature and/or a desired flow of cooling fluid to be supplied to the cooler 48 via the feed conduit 44. In many typical systems, the flow is more or less fixed or changed in a few steps, whereas the cooling capacity is controlled by setting the desired temperature. In one embodiment, the determination of the local energy consumption need of the local cooling system is basically performed by receiving a signal concerning the desired temperature of the cooling medium in the feed conduit 44. By using this signal the control system 59, 59', 69 controlling respective heat pump 50, 50', the control system 59, 59', 69 may determine the maximum amount of energy that may be drawn from the local cooling system 40, 40'. When drawing maximum amount of energy from the local cooling system 40, the

temperature of the cooling fluid in the return conduit 46 is basically the temperature the cooling system 40 is set to deliver to the cooler 48. Similarly, a local energy consumption need of a local heating system is determined. This may be performed e.g. by the heating system measuring a ambient temperature or a temperature in the environment to be heated. In response to this measurement, the heating system may e.g. calculate a desired temperature and/or a desired flow of heating fluid to be supplied to the heat emitter 38 via the feed conduit 34. In many typical systems, the flow is more or less fixed or changed in a few steps, whereas the heating capacity is controlled by setting the desired temperature. In one embodiment, the determination of the local energy consumption need of the local heating system is basically performed by receiving a signal concerning the desired temperature of the heating medium in the feed conduit 34. By using this signal the control system 59, 59', 69 controlling respective heat pump 50, 50', the control system 59, 59', 69 may determine the maximum amount of energy that may be usefully transferred to the local heating system 30, 30'. When transferring maximum useful amount of energy to the local heating system 30, the temperature of the heating fluid in the return conduit 36 is basically the temperature the heating system 30 is set to deliver to the heat emitter 38.

In a straight-forward locally controlled system, the determined local needs concerning cooling and heating provides upper boundaries on respective side of the heat pump 50. If there is no need to take into account balancing of larger systems, the heat pump 50 and 50' may be controlled to run whenever there is a simultaneous cooling and heating need be set to run as hard as possible but such that it does not draw more energy from the cooling system 40 than the determined local energy consumption need of the cooling system and such that it does not transfer more energy to the local heating system 30 than the determined local energy consumption need of the local heating system 30. This part of the control method basically amounts to the steps inside the dashed-dotted box in Fig. 6.

The method of controlling heat transfer between a local cooling system and a local heating system may also be used as an aid to balance need and capacity of heating, cooling and/or electric power grids. This may be performed in the control method by introducing a heating control parameter, a cooling control parameter, and/or an electric power control parameter and determining values thereof.

The method further comprises introducing a heating control parameter and determining a value indicating an overall heating consumption need of a plurality of local heating systems in relation to overall available heating capacity of a heating grid to which the local heating systems are connected. The overall heating consumption need may be determined by receiving information from the local heating systems. However, typically the company providing the distribution of a heating fluid in a heating grid measures the consumption of each local heating system relative to the heating grid and/or the overall heating consumption over the grid. This information concerning the overall need is compared with the overall available heating capacity. It may also be compared with other factors, such as production cost, environmental impact, etc. From this comparison a value of the heating control parameter is determined. This value may be a numerical index value. It may also be expressed as a value per energy amount, such as price per energy amount.

The method further comprises introducing a cooling control parameter and determining a value indicating an overall cooling consumption need of a plurality of local cooling systems in relation to overall available cooling capacity of a cooling grid to which the local cooling systems are connected. The overall cooling consumption need may be determined by receiving information from the local cooling systems. However, typically the company providing the distribution of a cooling fluid in a cooling grid measures the consumption of each local cooling system relative to the cooling grid and/or the overall cooling consumption over the grid. This information concerning the overall need is compared with the overall available cooling capacity. It may also be compared with other factors, such as production cost, environmental impact, etc. From this comparison a value of the cooling control parameter is determined. This value may be a numerical index value. It may also be expressed as a value per energy amount, such as price per energy amount.

The method further comprises introducing an electric power control parameter and determining a value indicating an overall electrical power need in relation to overall available electrical power of an electric grid to which the heat pump is connected. Typically the company providing the distribution of electrical power in an electric grid measures the consumption of electrical power at different granularity at various parts of the electrical grid. This information concerning the overall electrical consumption is the present electrical power need and is compared with the overall available electrical power capacity. This electrical power capacity may come from power plants controlled by the distributor or from buying electrical power from other companies or countries. The actual set-up varies greatly from country to country due to different regulations and legislative systems when it comes to control of the electrical grid. In any case, the electric power control parameter is introduced and the information concerning the present need is compared with the overall available electrical power capacity. It may also be compared with other factors, such as production cost, environmental impact, etc. From this comparison a value of the electrical power control parameter is

determined. This value may be a numerical index value. It may also be expressed as a value per energy amount, such as price per energy amount.

The control system 59, 69 may e.g. be set-up to, within the boundaries of the maximum amount of energy to draw from the cooling system and transfer to the heating system, minimize the overall value of the sum of; the local energy consumption need of the local cooling system times the value of the cooling control parameter plus the local energy consumption need of the local heating system times the value of the heating control parameter and the electrical energy consumption of the heating pump times the electrical power control parameter.

The control system 59, 69 may be fully localized to the heat pump 50; it may be fully localized at a central location 69 or it may be partly localized in the heat pump 50 and partly be centrally localized 69.

One set-up may e.g. be that the information concerning the control parameters (heating, cooling, electrical power) is sent from the companies providing the energy to the grids to a central control system 69 and that the local energy consumption needs (heating, cooling) are determined locally and that the control on the basis of these needs is performed locally. Alternatively, information concerning the local energy consumption needs is transmitted to the central control system 69 for use by the central control system 69 in controlling the heat pump 50. Yet, alternatively, all the information is sent to a local control system 59 controlling its associated heat pump 50.

It may be noted that there may be a single central control system 69 controlling all or several heat pumps 50, 50'. Alternatively, the central control system 69 may be controlling only a single or a few heat pumps 50, 50'. By introducing the control parameters, the method becomes robust and there is no real need to control many heat pumps by a central control system. The desired balancing may be performed by simply controlling respective heat pump each taking into account the desired balancing by taking into account the control parameters in the local controlling of respective heat pump.

The central control system 69 and/or the local control system 59 may be connected to a central database 70 storing information e.g. concerning typical variations over time when it comes to overall needs, overall capacities, and/or values of the control parameters. The database may also store information concerning acceptable amounts of energy to draw from a local cooling system or to maximum amount of energy to store in a local heating system even though an actual need is not present. By taking into account all or part of this information, the above mentioned minimization of the sum may be a minimization over a period of time further minimizing the overall energy consumption and maximizing the balancing capacity of the local heat transfer system.

The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

For example, it may e.g. be noted that the local energy consumption needs do not necessarily need to be strictly simultaneous if one or more of the systems is capable of storing heat or cold. Heat from the cooling system may e.g. be transferred to a hot tap water storage tank or to a swimming pool. As long as the entity being able to store heat or cold is still capable of receiving heat or having heat drawn from it, there may still be considered that a local energy consumption need is present.

Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.