Patent Description:
Nearly all large developed cities in the world have at least two types of energy grids incorporated in their infrastructures: one grid for providing electrical energy and one grid for providing space heating and hot tap water preparation. Today a common grid used for providing space heating and hot tap water preparation is a gas grid providing a burnable gas, typically a fossil fuel gas. The gas provided by the gas grid is locally burned for providing space heating and hot tap water. An alternative for the gas grid for providing space heating and hot tap water preparation is a district heating grid. Also, the electrical energy of the electrical energy grid may be used for space heating and hot tap water preparation. Also, the electrical energy of the electrical energy grid may be used for space cooling. The electrical energy of the electrical energy grid is further used for driving refrigerators and freezers.

Accordingly, traditional building heating and cooling systems use primary high-grade energy sources such as electricity and fossil fuels or an energy source in the form of industrial waste heat to provide space heating and/or cooling, and to heat or cool water used in the building. Furthermore, it has been increasingly common to also install a district cooling grid in cities for space cooling. The process of heating or cooling the building spaces and water converts this high-grade energy into low grade waste heat with high entropy which leaves the building and is returned to the environment.

In this kind of existing systems, it is well known to use cooling towers to exhale heat from the system and let it diminish into the air, to thereby get rid of waste heat. This is especially used in regions having a hot climate during most of the twelve months. However, also these regions have, at least during a part of the year, a lower temperature where there may be a need for an active supply of heat into the system. Examples of such regions are those where the winter temperature rarely go below <NUM> degrees Celsius. There is however no real economical and climate smart solutions of how to make this without involving high grade energy sources.

Hence, there is a need for improvements in how to provide flexible heating and cooling to a city and especially a versatile system that may be based on existing systems of the type described above.

<CIT> discloses a district energy sharing system (DESS) comprising a thermal energy circuit which circulates and stores thermal energy in water, at least one client building thermally coupled to the circuit and which removes some thermal energy from the circuit ("thermal sink") and/or deposits some thermal energy into the circuit ("thermal source"), and at least one thermal server plant that can be thermally coupled to external thermal sources and/or sinks (e.g. a geothermal ground source) and whose function is to maintain thermal balance within the DESS.

<CIT> (by the same applicant as the present application) relates to a method for controlling setting of reversible heat pump assemblies of a district thermal energy distribution system in either a heating mode or a cooling mode.

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

According to a first aspect, a thermal energy balancing device is provided. The thermal energy balancing device is connected to a thermal energy circuit comprising a hot conduit configured to allow a district heat transfer liquid of a first temperature to flow therethrough, and a cold conduit configured to allow district heat transfer liquid of a second temperature to flow therethrough, the second temperature being lower than the first temperature, the thermal energy balancing device comprising:.

Accordingly, by the invention, a thermal energy balancing device is provided which is configured to balance the temperature difference between the hot and cold conduits in a district heating or district cooling grid by taking advantage of heat transfer geothermal liquid provided by subterranean warm and cold wells. By a secondary valve arrangement, the flow of heat transfer geothermal liquid may be set in either direction between the two wells. The setting is depending on if the client using the district grid is requesting the district grid to act as a district cooling grid or a district heating grid, which may vary across the year and the local climate.

The thermal energy balancing device uses, as one part thereof, a hot conduit and a cold conduit forming part of a thermal energy circuit. The thermal energy circuit may be part of a district grid. The two conduits do both have a flow of a district heat transfer liquid therethrough, but with an inherent temperature difference. The thermal energy circuit may by way of example be a bidirectional grid, such as a grid known as ectogrid™ which connects buildings with different needs and which balances residual thermal energy flows between the buildings. The two conduits are each, via a primary valve arrangement, connected to the primary side of a heat exchanger. The secondary side of the heat exchanger is connected to a warm well and a cold well via secondary valve arrangement.

The warm well and the cold well are subterranean liquid fluid supplies. The subterranean liquid may in its easiest form be groundwater. It is however to be understood that also other liquids may be used within the scope of the invention.

The wells may be drilled bore holes, conduits submerged in the bedrock, or natural subterranean flows of groundwater in the bedrock or in the ground. No matter type, there is a temperature difference between the warm well and the cold well. The liquid in the warm well is warmer than the liquid in the cold well. The warm well and the cold well may be hydraulically connected. Alternatively, the warm well and the cold well may be without any hydraulic connection, in which case the two wells may be seen as discrete wells. Further, the warm well and the cold well may be geographically separated in the horizontal and/or vertical direction. Thus, they may be arranged on different depths and on different locations.

The thermal energy balancing device may be set, either into a heat exhale mode or into a heat inhale mode, depending on if there is a need to exhale or inhale heat from or to the primary side of the thermal energy circuit. An exhale mode is applicable when clients in the district grid, which as such is part of the primary side of the thermal energy circuit, are seeking for a supply of cold to their system, such as indoor cooling during the warmer months of the year. Correspondingly, an inhale mode is applicable when clients in the district grid are seeking for a supply of heat to their system, such as indoor heating during the warmer months of the year. By the present invention this may now be made by exchanging heat or cold between a district grid, which as such is a well-known and often an existing infrastructure, with a geothermal liquid supply of heat transfer geothermal liquid in the form of a warm well and a cold well. Within the scope of the invention, the geothermal liquid supply with its warm and cold wells is part of the secondary side of the thermal energy circuit. The temperature difference of the heat transfer geothermal liquid in the warm and cold wells is used to either inhale or exhale heat to the district grid depending on the client's needs.

At least one of the two liquid circuits circulating district heat transfer liquid and heat transfer geothermal liquid respectively, may be provided as a closed loop. Especially the supply of heat transfer geothermal liquid to the secondary side valve arrangement may be provided as an open loop without any hydraulic connection between the warm well and the cold well. Both liquid circuits may be provided as closed loops.

In the event of the thermal energy balancing device being set to a heat exhale mode, the district heat transfer liquid from the hot conduit is allowed to be transferred via the primary side of the heat changer to the cold conduit, during which transfer the temperature of the hotter district heat transfer liquid will be lowered before being fed to and intermixed with the district heat transfer liquid in the cold conduit. Heat will be exhaled from the district heat transfer liquid while passing across the interface between the primary side and the secondary side of the heat exchanger. During this passage, heat exhaled from the primary side of the heat exchanger will be inhaled by the flow of heat transfer geothermal liquid which is passing across the interface between the secondary side and the primary side of the heat exchanger. More precisely, in the heat exhale mode of the thermal energy balancing device, the secondary side valve arrangement is set to direct a flow of heat transfer geothermal liquid from the cold well across the secondary side of the heat exchanger to the warm well. The cold heat transfer geothermal liquid will inhale the heat exhaled from the primary side of the heat exchanger and the thus heated heat transfer geothermal liquid will be directed by the secondary side valve arrangement to the warm well.

Correspondingly, in the event of thermal energy balancing device being set to a heat inhale mode, the colder district heat transfer fluid from the cold conduit is allowed to be transferred via the primary side of the heat changer to the hot conduit during which transfer the temperature of the colder district heat transfer fluid will be increased before being fed to and intermixed with the district heat transfer fluid in the hot conduit. Heat will be inhaled to the district heat transfer liquid while passing across the interface between the primary side and the secondary side of the heat exchanger. During this passage, heat will be inhaled from the flow of heat transfer geothermal liquid which is passing across the interface between the secondary side and the primary side of the heat exchanger. More precisely, in the heat inhale mode of the thermal energy balancing device, the secondary side valve arrangement is set to direct a flow of heat transfer geothermal liquid from the warm well across the secondary side of the heat exchanger to the cold well. The hot heat transfer geothermal liquid will exhale the heat and the thus cooled heat transfer geothermal liquid will be directed by the secondary side valve arrangement to the cold well.

The heat exchanger is preferably of a liquid-to-liquid type heat exchanger.

The fluid flow between the hot and cold conduits on the primary system side is controlled by a primary side valve arrangement. The primary side valve arrangement may have a design with a plurality of valves which, depending on their mutual setting, allow the flow of district heat transfer liquid to and from the two conduits to be controlled. The valves may be of the on/off type. Correspondingly, flow of heat transfer geothermal liquid between the hot and cold wells on the secondary system side is controlled by a secondary valve arrangement. The secondary primary side valve arrangement may have a design with a plurality of valves which, depending on their mutual setting, allow control of the flow of heat transfer geothermal liquid to and from the warm and cold wells. The valves may be of the on/off type.

The primary and secondary valve arrangements may have the same overall design.

The hot and cold wells may be closed loop wells and may be hydraulically connected via a conduit. The term "closed loop well" is in the context of the application to be understood as a flow of liquid that is circulated in a closed circuit between the two wells having different temperatures. The connections between the warm and cold wells and the secondary side valve arrangement are geographically separated from each other and also, the warm and cold wells are hydraulically connected to each other via a physical conduit. Upon the thermal balancing device is set into the heat exhale mode the physical conduit is configured to conduct heat transfer geothermal liquid from the cold well to the warm well. Upon the thermal balancing device is set into the heat inhale mode the physical conduit is configured to conduct heat transfer geothermal liquid from the warm well to the cold well.

The warm and cold wells may be open loop wells and the warm and cold wells may be hydraulically connected. The term "open loop well" is in the context of the application to be understood as that the connections between the warm and cold wells and the secondary side valve arrangement are geographically separated from each other and also that the warm and cold wells are hydraulically connected to each other by means of a naturally occurring subterranean fluid flow provided by the bedrock or by the ground. By taking advantage of the natural subterranean fluid flows, a cheaper installation may be provided for since there is no need for any excavation/drilling to allow installation of a ducting providing such hydraulic communication.

The warm and cold wells may be open loop wells, and the wrm and cold wells may be without any hydraulic connection. In such embodiment, the connections between the warm and cold wells and the secondary side valve arrangement are geographically separated from each other. Also, the warm and cold wells are geographically separated by the bedrock with no hydraulic communication therebetween. Thus, the warm and cold wells may be seen as discrete wells where fluid is pumped from one of the two wells and released in the other of the two wells without any return flow. A cheaper installation may thereby be provided for since there is no need for any excavation/drilling to allow installation of a ducting providing such hydraulic communication.

The warm and cold wells may be horizontally and/or vertically separated. This is applicable, no matter if the two wells are arranged to be in a hydraulic communication with each other or if they form discrete wells.

The thermal energy balancing device may further comprise a pump. The pump may be arranged in a position between the secondary side valve arrangement and the heat exchanger. Thereby there is no need for any submerged pumps. This facilitates installation and maintenance.

The primary side of the heat exchanger may comprise an inlet and an outlet, and the primary side valve arrangement may be configured to direct a flow of district heat transfer liquid from the inlet to the outlet when the primary side valve arrangement is set into the heat exhale mode and when the primary side valve arrangement is set into the heat inhale mode.

Accordingly, one and the same inlet on the primary side of the heat exchanger is used, no matter if the thermal energy balancing device is set to operate in an exhale mode or an inhale mode. Only the conduits in the thermal energy circuit from which the liquid is fed from and returned to are altered, and this is made by controlling the valves of the primary side valve arrangement.

The secondary side of the heat exchanger may comprise an inlet and an outlet, and the secondary side valve arrangement may be configured to direct a flow of heat transfer geothermal liquid from the inlet to the outlet when the secondary side valve arrangement is set into the heat exhale mode and when the secondary side valve arrangement is set into the heat inhale mode.

Accordingly, one and the same inlet on the secondary side of the heat exchanger is used, no matter if the thermal energy balancing device is set to operate in an exhale mode or an inhale mode. Only the wells from which the heat transfer geothermal liquid is fed from and returned to are altered, and this is made by controlling the valves of the secondary side valve arrangement.

The thermal energy balancing device may further comprise a regulator and a pressure difference determining device adapted to determine a local pressure difference, Δplocal, between a local hot conduit pressure, ph, of district heat transfer liquid of the hot conduit and a local cold conduit pressure, pc, of district heat transfer liquid of the cold conduit (<NUM>), Δplocal=ph-pc; and wherein the regulator is configured to, based on the determined local pressure difference, regulate the flow of district heat transfer liquid between the hot and cold conduits.

The pressure difference determining device is configured to sense local pressure in the hot conduit and in the cold conduit respectively and determine a difference between the two pressures. The pressure difference determining device may also be configured to determine if the determined local pressure difference is acceptable in view of a predetermined set value.

The local pressure in the two conduits will vary depending on where in the thermal energy circuit the pressure is measured. The local pressure differences are the result of different client's activity and needs. Examples of different clients are different households, different offices or different stores, which all have different needs which also vary over time and across a day.

The regulator may be provided as a pump which is arranged in a position between the hot conduit and the cold conduit. The regulator may be arranged either in a position before the inlet to the primary side of the heat exchanger, or after the outlet from the primary side of the heat exchanger. The purpose of the regulator is to promote the flow of liquid to the heat exchanger in the event the determined local pressure difference between the hot conduit and the cold conduit should be determined to be below a set value. In the event the determined local pressure difference instead should be determined to be above the set value, the regulator may instead be set into a passive mode and instead act as an open valve allowing a flow of district heat transfer liquid to pass therethrough.

The thermal energy balancing device may further comprise a controller connected to one or more of the pressure difference determining device, the regulator, the primary side valve arrangement and the secondary side valve arrangement.

Hence, it is to be understood that this invention is not limited to the particular component parts of the device described as the realization of the device may vary.

These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiments of the invention. The figures are provided to illustrate the general structures of embodiments of the present invention.

To facilitate the understanding of the invention, reference is made to <FIG> which discloses one example of a district thermal energy distribution system <NUM> according to prior art in which the invention may be applicable.

The district thermal energy distribution system <NUM> comprises a thermal energy circuit <NUM> and a plurality of buildings <NUM>. The plurality of buildings <NUM> are thermally coupled to the thermal energy circuit <NUM>. The thermal energy circuit <NUM> is arranged to circulate and store thermal energy in heat transfer liquid flowing through the thermal energy circuit <NUM>.

According to one embodiment the heat transfer liquid comprises water. However, according to other embodiments other heat transfer liquid may be used. Some non-limiting examples are ammonia, oils, alcohols and anti-freezing liquids such as glycol. The heat transfer liquid may also comprise a mixture of two or more of the heat transfer liquids mentioned above.

The thermal energy circuit <NUM> comprises two conduits <NUM>, <NUM> for allowing flow of heat transfer liquid therethrough. The temperature of the heat transfer liquid of the two conduits <NUM>, <NUM> is set to be different. A hot conduit <NUM> in the thermal energy circuit <NUM> is configured to allow heat transfer liquid of a first temperature to flow therethrough. A cold conduit <NUM> in the thermal energy circuit <NUM> is configured to allow heat transfer liquid of a second temperature to flow therethrough. The second temperature is lower than the first temperature.

In case heat transfer liquid is water, a suitable normal operation hot temperature range for heat transfer liquid in the hot conduit <NUM> is between <NUM> and <NUM> and a suitable normal operation cold temperature range for heat transfer liquid in the cold conduit <NUM> is between <NUM> and <NUM>° C. A suitable temperature difference between the first and second temperatures is in the range of <NUM>-<NUM>°C, preferably in the range of <NUM>-<NUM>, more preferably <NUM>-<NUM>.

Preferably, the system is set to operate with a sliding temperature difference which varies depending on the climate. Preferably, the sliding temperature difference is fixed. Hence, the temperature difference is always set to momentarily slide with a fixed temperature difference.

The hot conduit <NUM> and the cool conduit <NUM> are separate. The hot conduit <NUM> and the cool conduit <NUM> may be arranged in parallel. The hot conduit <NUM> and the cool conduit <NUM> may be arranged as closed loops of piping. The hot conduit <NUM> and the cool conduit <NUM> are fluidly interconnected at the buildings <NUM> for allowing of thermal energy transfer to and from the buildings <NUM>.

According to one embodiment the two conduits <NUM>, <NUM> of the thermal energy circuit <NUM> are dimensioned for pressures up to <NUM> MPa (<NUM> bar). According to other embodiments the two conduits <NUM>, <NUM> of the thermal energy circuit <NUM> may be dimensioned for pressures up to <NUM> MPa (<NUM> bar) or for pressures up to <NUM> MPa (<NUM> bar).

Each building <NUM> comprise at least one of one or more local thermal energy consumer assemblies <NUM> and one or more local thermal energy generator assemblies <NUM>. Hence, each building comprises at least one local thermal energy consumer assembly <NUM> or at least one local thermal energy generator assembly <NUM>. One specific building <NUM> may comprise more than one local thermal energy consumer assembly <NUM>. One specific building <NUM> may comprise more than one local thermal energy generator assembly <NUM>. One specific building <NUM> may comprise both a local thermal energy consumer assembly <NUM> and a local thermal energy generator assembly <NUM>.

The local thermal energy consumer assembly <NUM> is acting as a thermal sink. Hence, the local thermal energy consumer assembly <NUM> is arranged to remove thermal energy from the thermal energy circuit <NUM>. Or in other words, the local thermal energy consumer assembly <NUM> is arranged to transfer thermal energy from heat transfer liquid of the thermal energy circuit <NUM> to surroundings of the local thermal energy consumer assembly <NUM>. This is achieved by transferring thermal energy from heat transfer liquid taken from the hot conduit <NUM> to surroundings of the local thermal energy consumer assembly <NUM>, such that heat transfer liquid that is returned to the cold conduit <NUM> has a temperature lower than the first temperature and preferably a temperature equal to the second temperature.

The local thermal energy generator assembly <NUM> is acting as a thermal source. Hence, the local thermal energy generator assembly <NUM> is arranged to deposit thermal energy to the thermal energy circuit <NUM>. Or in other words, the local thermal energy generator assembly <NUM> is arranged to transfer thermal energy from its surroundings to heat transfer liquid of the thermal energy circuit <NUM>. This is achieved by transferring thermal energy from surroundings of the local thermal energy generator assembly <NUM> to heat transfer liquid taken from the cold conduit <NUM>, such that the heat transfer liquid that is returned to the hot conduit <NUM> has a temperature higher than the second temperature and preferably a temperature equal to the first temperature.

The one or more local thermal energy consumer assemblies <NUM> may be installed in the buildings <NUM> as local heaters for different heating needs. As a non-limiting example, a local heater may be arranged to deliver space heating or hot tap hot water preparation. Alternatively, or in combination, the local heater may deliver pool heating or ice- and snow purging. Hence, the local thermal energy consumer assembly <NUM> is arranged for deriving heat from heat transfer liquid of the hot conduit <NUM> and creates a cooled heat transfer liquid flow into the cold conduit <NUM>. Hence, the local thermal energy consumer assembly <NUM> fluidly interconnects the hot and cool conduits <NUM>, <NUM> such that hot heat transfer liquid can flow from the hot conduit <NUM> through the local thermal energy consumer assembly <NUM> and then into the cool conduit <NUM> after thermal energy in the heat transfer liquid has been consumed by the local thermal energy consumer assembly <NUM>. The local thermal energy consumer assembly <NUM> operates to draw thermal energy from the hot conduit <NUM> to heat the building <NUM> and then deposits the cooled heat transfer liquid into the cool conduit <NUM>.

The one or more local thermal energy generator assemblies <NUM> may be installed in different buildings <NUM> as local coolers for different cooling needs. As a non-limiting example, a local cooler may be arranged to deliver space cooling or cooling for freezers and refrigerators. Alternatively, or in combination, the local cooler may deliver cooling for ice rinks and ski centers or ice- and snow making. Hence, the local thermal energy generator assembly <NUM> is deriving cooling from heat transfer liquid of the cold conduit <NUM> and creates a heated heat transfer liquid flow into the hot conduit <NUM>. Hence, the local thermal energy generator assembly <NUM> fluidly interconnects the cold and hot conduits <NUM>, <NUM> such that cold heat transfer liquid can flow from the cold conduit <NUM> through the local thermal energy generator assembly <NUM> and then into the hot conduit <NUM> after thermal energy has been generated into the heat transfer liquid by the local thermal energy generator assembly <NUM>. The local thermal energy generator assembly <NUM> operates to extract heat from the building <NUM> to cool the building <NUM> and deposits that extracted heat into the hot conduit <NUM>.

The local thermal energy consumer assembly <NUM> is selectively connected to the hot conduit <NUM> via a non-disclosed valve and a non-disclosed pump. Upon selecting the connection of the local thermal energy consumer assembly <NUM> to the hot conduit <NUM> to be via the valve, heat transfer liquid from the hot conduit <NUM> is allowed to flow into the local thermal energy consumer assembly <NUM>. Upon selecting the connection of the local thermal energy consumer assembly <NUM> to the hot conduit <NUM> to be via the pump, heat transfer liquid from the hot conduit <NUM> is pumped into the local thermal energy consumer assembly <NUM>.

The local thermal energy generator assembly <NUM> is selectively connected to the cold conduit <NUM> via a non-disclosed valve and a non-disclosed pump. Upon selecting the connection of the local thermal energy generator assembly <NUM> to the cold conduit <NUM> to be via the valve, heat transfer liquid from the cold conduit <NUM> is allowed to flow into the local thermal energy generator assembly <NUM>. Upon selecting the connection of the local thermal energy generator assembly <NUM> to the cold conduit <NUM> to be via the pump, heat transfer liquid from the cold conduit <NUM> is pumped into the local thermal energy generator assembly <NUM>.

Preferably, the demand to inhale or exhale thermal energy using the local thermal energy consumer assemblies <NUM> and the local thermal energy generator assemblies <NUM> is made at a defined temperature difference. A temperature difference in the range of <NUM>-<NUM>, preferably in the range of <NUM>-<NUM>, more preferably <NUM>-<NUM> corresponds to optimal flows through the system.

The local pressure difference between the hot and cold conduits <NUM>, <NUM> may vary along the thermal energy circuit <NUM>. Especially, the local pressure difference between the hot and cold conduits <NUM>, <NUM> may vary from positive to negative pressure difference seen from one of the hot and cold conduits <NUM>, <NUM>. Hence, sometimes a specific local thermal energy consumer/generator assembly <NUM>, <NUM> may need to pump heat transfer liquid there through and sometimes the specific local thermal energy consumer/generator assembly <NUM>, <NUM> may need to let heat transfer liquid flow through there through. Accordingly, it will be possible to let all the pumping within the system <NUM> to take place in the local thermal energy consumer/generator assemblies <NUM>, <NUM>. Due to the limited flows and pressures needed small frequency-controlled circulation pumps may be used.

The basic idea of the district thermal energy distribution system <NUM> as described above and which is illustrated in <FIG> is based on the insight by the applicant that modern day cities by them self provide thermal energy that may be reused within the city. The reused thermal energy may be picked up by the district thermal energy distribution system <NUM> and be used for e.g. space heating or hot tap water preparation. Moreover, increasing demand for space cooling will also be handled within the district thermal energy distribution system <NUM>. Within the district thermal energy distribution system <NUM> buildings <NUM> within the city are interconnected and may in an easy and simple way redistribute low temperature waste energy for different local demands.

In order to balance the thermal energy within the district thermal energy distribution system <NUM>, the system <NUM> may further comprise a thermal server plant <NUM>. The thermal server plant <NUM> functions as an external thermal source and/or thermal sink. The function of the thermal server plant <NUM> is to maintain the temperature difference between the hot and cold conduits <NUM>, <NUM> of the thermal energy circuit <NUM>. The function of the thermal server plant <NUM> is further to regulate the pressure difference between the hot and cold conduits <NUM>, <NUM> of the thermal energy circuit <NUM>.

Now turning to <FIG>, a first embodiment of a thermal energy balancing device <NUM> according to the invention is disclosed. The thermal energy balancing device may be integrated in the prior art system described above with reference to <FIG>.

The thermal energy balancing device <NUM> comprises a primary side valve arrangement <NUM>, a heat exchanger <NUM>, and a secondary side valve arrangement <NUM>. The thermal energy balancing device <NUM> is connected to a thermal energy circuit <NUM> via the primary side valve arrangement <NUM> and to a well arrangement <NUM> via the secondary side valve arrangement <NUM>.

The thermal energy balancing device <NUM> is configured to be connected to the thermal energy circuit <NUM> which comprises a hot conduit <NUM> and a cold conduit <NUM>. The overall design and function of the thermal energy circuit <NUM> is the same as that described above with reference to <FIG>. Thus, the features of the prior art circuit described above are equally applicable and to avoid undue repetition, reference is made to the above.

The hot conduit <NUM> is like in the prior art system configured to allow district heat transfer liquid of a first temperature to flow therethrough. Correspondingly, the cold conduit <NUM> is configured to allow district heat transfer liquid of a second temperature to flow therethrough. The second temperature is lower than the first temperature. The flow in the hot conduit <NUM> and the cold conduit <NUM> may be bidirectional.

In case the district heat transfer liquid is water, a suitable normal operation hot temperature range for district heat transfer liquid in the hot conduit <NUM> is between <NUM> and <NUM> and a suitable normal operation cold temperature range for district heat transfer liquid in the cold conduit <NUM> is between <NUM> and <NUM>° C. A suitable temperature difference between the first and second temperatures is in the range of <NUM>-<NUM>, preferably in the range of <NUM>-<NUM>, more preferably <NUM>-<NUM>.

The heat exchanger <NUM> is a liquid-to-liquid heat exchanger. The heat exchanger <NUM> may be a water-to-water heat exchanger. It is however to be understood that other liquids than water may be used. The heat exchanger <NUM> may be part of an existing infrastructure, such as an existing cooling or heating machine in a building.

The heat exchanger <NUM> comprises a liquid phase primary side <NUM> and a liquid phase secondary side <NUM>. The liquid phase primary side <NUM> comprises one primary inlet <NUM> and one primary outlet <NUM> allowing a flow of district heat transfer liquid to pass across the liquid phase primary side <NUM>. The primary inlet <NUM> and the primary outlet <NUM> are connected to the primary side valve arrangement <NUM>. The primary side valve arrangement <NUM> is arranged in fluid communication with the hot conduit <NUM> and with the cold conduit <NUM>.

The connection of the valve arrangement <NUM> to the hot and cold conduits <NUM>, <NUM> may be made via non-disclosed service valves. The service valves may be used for connecting and disconnecting the valve arrangement <NUM> and thereby the heat exchanger <NUM> to/from the thermal energy circuit <NUM>.

The liquid phase secondary side <NUM> comprises one secondary inlet <NUM> and one secondary outlet <NUM> allowing a flow of heat transfer geothermal liquid to pass across the liquid phase secondary side <NUM>. The secondary inlet <NUM> and the secondary outlet <NUM> are connected to the secondary side valve arrangement <NUM>. The secondary side valve arrangement <NUM> is arranged in fluid communication with the well arrangement <NUM> comprising a warm well <NUM> and a cold well <NUM>.

The primary side valve arrangement <NUM> comprises four valves <NUM> that are interconnected in series to form a closed loop. Each valve <NUM> is configured as a valve of the on/off-type. It is however to be understood that other valve types are equally applicable. The closed loop comprises four connections points A, B, C, D, with one connection point between two adjacent valves <NUM>. The hot conduit <NUM> is arranged in fluid communication with the primary side valve arrangement <NUM> via a conduit connecting to the first connection point A. The primary side inlet <NUM> of the heat exchanger <NUM> is arranged in fluid communication with the primary side valve arrangement <NUM> via a conduit connecting to the second connection point B. The cold conduit <NUM> is arranged in fluid communication with the primary side valve arrangement <NUM> via a conduit connecting to the third connection point C. The primary outlet <NUM> of the heat exchanger <NUM> is arranged in fluid communication with the primary side valve arrangement <NUM> via a conduit connecting to the fourth connection point D. Thereby, depending on how the four valves <NUM> are set, the flow between the heat exchanger <NUM> and the hot and cold conduits <NUM>, <NUM> respectively may be controlled.

The primary side valve arrangement <NUM> is thus configured to direct a flow of district heat transfer liquid from the inlet <NUM> to the outlet <NUM> when the primary side valve arrangement <NUM> is set into the heat exhale mode and when the primary side valve arrangement is set into the heat inhale mode. Accordingly, one and the same inlet on the primary side <NUM> of the heat exchanger <NUM> is used, no matter if the thermal energy balancing device <NUM> is set to operate in an exhale mode or an inhale mode. Only the conduits from which the liquid is fed from and returned to are altered, and this is made by controlling the valves <NUM> of the primary side valve arrangement <NUM>.

The secondary side valve arrangement <NUM> comprises four valves <NUM> that are interconnected in series to form a closed loop. Each valve <NUM> is configured as a valve of the on/off-type. It is however to be understood that other valve types are equally applicable. The closed loop comprises four connections points E, F, G, H, with one connection point between two adjacent valves <NUM>.

The warm well <NUM> is arranged in fluid communication with the secondary side valve arrangement <NUM> via a conduit connecting to the first connection point E. The secondary inlet <NUM> of the heat exchanger <NUM> is arranged in fluid communication with the secondary side valve arrangement <NUM> via a conduit connecting to the second connection point F. The cold well <NUM> is arranged in fluid communication with the secondary side valve arrangement <NUM> via a conduit connecting to the third connection point G. The secondary outlet <NUM> of the heat exchanger <NUM> is arranged in fluid communication with the secondary side valve arrangement <NUM> via a conduit connecting to the fourth connection point H. Thereby, depending on how the four valves <NUM> are set, the flow between the heat exchanger <NUM> and the hot and cold wells <NUM>, <NUM> respectively may be controlled.

The secondary side valve arrangement <NUM> is thus configured to direct a flow of heat transfer geothermal liquid from the inlet <NUM> to the outlet <NUM> when the secondary side valve arrangement <NUM> is set into the heat exhale mode and when the secondary side valve arrangement is set into the heat inhale mode. Accordingly, one and the same inlet on the secondary side <NUM> of the heat exchanger <NUM> is used, no matter if the thermal energy balancing device <NUM> is set to operate in an exhale mode or an inhale mode. Only the conduits from which the liquid is fed from and returned to are altered, and this is made by controlling the valves <NUM> of the secondary side valve arrangement <NUM>.

The primary side valve arrangement <NUM> and the secondary side valve arrangement <NUM> may be controlled by a controller <NUM>. The controller <NUM> is connected to the primary and secondary valve arrangements <NUM>, <NUM> to selectively allow a setting of the valves <NUM>, <NUM> to thereby control the flow through the valve arrangements <NUM>, <NUM> depending on which operation mode of the thermal energy balancing device <NUM> is desired, i.e. if a heat exhale mode is desired or if a heat inhale mode is desired.

The thermal energy balancing device <NUM> may further comprises an optional pump <NUM>. The pump <NUM> may by way of example be arranged in a position between the secondary side valve arrangement <NUM> and the heat exchanger <NUM>. Thereby there is no need for any submerged pumps. This facilitates installation and maintenance.

The pump <NUM> may be connected to the controller <NUM> to thereby be controlled thereby. In the event it is determined by the controller <NUM> that there is no need for any promotion of the flow, the pump 910may be set to allow a through-flow.

The warm and cold wells <NUM>, <NUM> are in the embodiment of <FIG> disclosed as two discrete wells that are arranged in the bedrock on two different geographical locations. The bedrock may by way of example be clay or the like. The temperature in the warm well is higher than the temperature in the cold well. In the disclosed embodiment, each well comprises a closed loop conduit.

The two closed loop conduits are hydraulically interconnected via connection conduit <NUM>. Depending on how the valves <NUM> in the secondary side valve arrangement <NUM> are set, liquid may be transferred either from the warm well <NUM> to the cold well <NUM> while passing from the inlet <NUM> to the outlet <NUM> of the secondary side of the heat exchanger <NUM>, or from the cold well <NUM> to the warm well <NUM> while passing from the inlet <NUM> to the outlet <NUM> of the secondary side of the heat exchanger <NUM>.

In the following, the two modes of the thermal energy balancing device <NUM> will be exemplified with reference to <FIG> and <FIG>. The two modes differ in how the individual valves <NUM>, <NUM> in the primary and secondary valve arrangements <NUM>, <NUM> are set and hence how the flows of district heat transfer liquid and heat transfer geothermal liquid respectively are allowed to flow.

To facilitate understanding, a closed valve is illustrated by a solid black valve icon, whereas an open valve is illustrated by a solid white valve icon. Also, to facilitate understanding, <FIG> and <FIG> have been simplified by removing some components.

Starting with <FIG>, the inhale mode, is illustrated. In the inhale mode, the thermal energy balancing device <NUM> is set to supply heat to the hot conduit <NUM> to thereby allow clients to provide a heating effect.

By closing the valves <NUM> between connection points B-C and A-D, while opening the valves <NUM> between connection points A-B and C-D, a flow of district heat transfer fluid is allowed from the cold conduit <NUM>, through the open valve <NUM> between connection points A-B, into the liquid phase primary side <NUM> of the heat exchanger <NUM> via its inlet <NUM>, across the liquid phase primary side <NUM> of the heat exchanger <NUM>, out of the heat exchanger <NUM> via its outlet <NUM>, through the open valve <NUM> between the connection points D-C and into the hot conduit <NUM>. As the district heat transfer fluid flows across the liquid phase primary side <NUM> of the heat exchanger <NUM>, heat may be inhaled from a flow of heat transfer geothermal liquid on the secondary side <NUM> of the heat exchanger <NUM>. To allow this inhalation, the valves of the secondary side valve arrangement <NUM> are set so that the valves <NUM> between the connection points H-E and F-G are closed, while the valves <NUM> between the connection points H-G and E-F are opened.

Thereby a flow of heat transfer geothermal liquid is allowed from the warm well <NUM>, through the open valve <NUM> between the connection points E-F, into the secondary phase side <NUM> of the heat exchanger <NUM> via its inlet <NUM>, across the secondary phase side <NUM> of the heat exchanger <NUM>, out of the heat exchanger <NUM> via its outlet <NUM>, through the open valve <NUM> between the connection points H-G and into the cold well <NUM>. As the hot heat transfer geothermal liquid flows across the secondary phase side <NUM> of the heat exchanger <NUM>, heat will be transferred to the primary side <NUM> of the heat exchanger <NUM> from where it may be inhaled by the district heat transfer liquid.

As a result of the warm well <NUM> and the cold well <NUM> being hydraulically interconnected via the connection conduit <NUM>, the amount of heat transfer geothermal liquid removed from the warm well <NUM> will be returned to it from the cold well <NUM>.

This specific operation mode may by way of example be used during the colder period of a year in areas which have a hot climate during the major part of the year to provide heating of homes, offices, tap water etc. Thus, the inhale mode is typically run when clients connected to the thermal energy circuit <NUM> want a heating effect.

Now turning to <FIG>, system described above in view of <FIG> is now set to exhale mode. In all other aspects the system is the same. In the exhale mode, the thermal energy balancing device <NUM> is set to remove heat from the hot conduit <NUM> to thereby allow clients to provide a cooling effect.

By closing the valves <NUM> between connection points A-B and C-D, while opening the valves <NUM> between connection points A-D and C-D, a flow of district heat transfer fluid is allowed from the hot conduit <NUM>, through the open valve <NUM> between connection points C-B, into the liquid phase primary side <NUM> of the heat exchanger <NUM> via its inlet <NUM>, across the liquid phase primary side <NUM> of the heat exchanger <NUM>, out of the heat exchanger <NUM> via its outlet <NUM>, through the open valve <NUM> between the connection points D-A and into the cold conduit <NUM>. As the hot district heat transfer fluid flows across the liquid phase primary side <NUM> of the heat exchanger <NUM>, heat may be exhaled into the flow of heat transfer geothermal liquid on the secondary side <NUM> of the heat exchanger <NUM>. To allow this exhalation, the
valves of the secondary side valve arrangement <NUM> are set so that the valves <NUM> between the connection points E-F and G-H are closed, while the valves <NUM> between the connection points F-G and E-H are opened.

Thereby a flow of heat transfer geothermal liquid is allowed from the cold well <NUM>, through the open valve <NUM> between the connection points G-F, into the secondary phase side <NUM> of the heat exchanger <NUM> via its inlet <NUM>, across the secondary phase side <NUM> of the heat exchanger <NUM>, out of the heat exchanger <NUM> via its outlet <NUM>, through the open valve <NUM> between the connection points H-E and into the warm well <NUM>. As the cold heat transfer geothermal liquid flows across the secondary phase side <NUM> of the heat exchanger <NUM>, heat will be inhaled from the district heat transfer liquid on the primary side <NUM> of the heat exchanger <NUM>. Thereby the flow of district heat transfer liquid with a reduced temperature will be returned to the cold conduit <NUM>.

As a result of the warm well <NUM> and the cold well <NUM> being hydraulically interconnected via the connection conduit <NUM>, the amount of heat transfer geothermal liquid removed from the cold well <NUM> will be returned from the warm well <NUM>, and vice versa depending on if the system is set into a inhale mode or exhale mode.

Now turning to <FIG>, an alternative to the embodiments disclosed in <FIG> and <FIG> is disclosed. The embodiment in <FIG> differs from the embodiment of <FIG> and <FIG> in the design of the well arrangement <NUM>. In all other aspects, the design of the system is the same. The warm well <NUM> and the cold well <NUM> are vertically and horizontally separated. The warm well <NUM> is deeper than the cold well. The skilled person realizes that the same principle is equally applicable with the cold well being deeper than the warm well.

Like in the embodiment of <FIG> and <FIG>, there is a hydraulic communication between the two wells <NUM>, <NUM> by conduit <NUM>. Accordingly, the amount of heat transfer geothermal liquid removed from the cold well <NUM> will be returned from the warm well <NUM> and vice versa depending on if the system is set into a inhale mode or exhale mode.

In the disclosed embodiment, the thermal energy balancing device <NUM> is set to an inhale mode and operates in the very same manner as that previously discussed with reference to <FIG>. If the thermal energy balancing device <NUM> instead should be set to an exhale mode it operates in the very same manner as that previously discussed with reference to <FIG>. Thus, to avoid undue repetition regarding the operation, reference is made to the above.

Now turning to <FIG>, a third embodiment being an alternative to the embodiments disclosed in <FIG> and <FIG> is disclosed. The third embodiment differs from the previous disclosure in the design of the well arrangement <NUM> and also in an additional pump <NUM> being arranged in a position between the secondary valve arrangement <NUM> and the heat exchanger <NUM>. In all other aspects, the design of the system is the same.

In the third embodiment, the well arrangement <NUM> is of an open loop type, i.e. the warm well <NUM> and the cold well <NUM> are hydraulically interconnected without any physical conduit. In the disclosed embodiment, the hydraulic connection is instead provided by a naturally occurring flow <NUM> of heat transfer geothermal liquid in the bedrock. The flow may by way of example be groundwater. Thus, there is no need for any conduit connecting the warm well <NUM> and the cold well <NUM>. The warm well <NUM> and the cold well <NUM> are horizontally separated by arranging the inlet and outlets to the wells well separated.

In the disclosed embodiment, the thermal energy balancing device <NUM> is set to an exhale mode and operates in the very same manner as that previously discussed with reference to <FIG>. The flow of heat transfer geothermal liquid exiting the heat exchanger <NUM> is returned to the well arrangement <NUM> via its warm well <NUM> and the thus released heat transfer geothermal liquid is hydraulically transferred from the warm well <NUM> to the cold well <NUM> via the stream <NUM> in the well arrangement <NUM>. To better promote this flow, one or more pumps <NUM>, <NUM> may be used. Two pumps <NUM>, <NUM> are used in the disclosed embodiment.

This third embodiment has the advantage in that it as a reduced installation cost since there is no need of providing any hydraulic conduit between the hot and cold wells. Also, the one or more pumps <NUM>, <NUM> may be arranged in a position where they are easily accessible. Thus, there is no need of providing any submerged pump(s).

Now turning to <FIG>, the third embodiment discussed in view of <FIG> is disclosed when set to operate in an inhale mode. In all other aspects, the design of the system is the same as that disclosed in <FIG>. Thus, in the disclosed embodiment, the thermal energy balancing device <NUM> is set to an inhale mode. The flow of heat transfer geothermal liquid exiting the heat exchanger <NUM> is returned to the well arrangement <NUM> via its cold well <NUM> and the thus released heat transfer geothermal liquid is hydraulically transferred from the cold well <NUM> to the warm well <NUM> via the stream <NUM> in the well arrangement <NUM>. To better promote this flow, one or more pumps <NUM>, <NUM> may be used. Two pumps <NUM>, <NUM> are used in the disclosed embodiment.

Now turning to <FIG>, a fourth embodiment being an alternative to the embodiments disclosed in <FIG> and <FIG> is disclosed. The fourth embodiment differs from the previous disclosure in the design of the well arrangement <NUM> and also in an additional pump <NUM> being arranged in a position between the secondary valve arrangement <NUM> and the heat exchanger <NUM>. In all other aspects, the design of the system is the same.

In the fourth embodiment, the well arrangement <NUM> is of an open loop type without any hydraulic connection between the warm well <NUM> and the cold well <NUM>. Accordingly, there is no communication between the two wells other than that provided by the secondary valve arrangement <NUM>. The warm and cold wells <NUM>, <NUM> are provided as two discrete wells which are well separated and hence without any natural flow therebetween. The bedrock may by way of example be clay or the like. The temperature in the warm well <NUM> is higher than the temperature in the cold well <NUM>.

In the disclosed embodiment, the thermal energy balancing device <NUM> is set to an exhale mode and operates in the very same manner as that previously discussed with reference to <FIG> with the difference that the secondary valve arrangement <NUM> receives heat transfer geothermal liquid from the cold well <NUM> and passes it across the secondary phase side of the heat exchanger where it inhales heat. The thus heated heat transfer geothermal liquid is then fed through the secondary valve arrangement <NUM> to the warm well <NUM> where the liquid is released. To better promote this flow, one or more pumps <NUM>, <NUM> may be used. Two pumps <NUM>, <NUM> are used in the disclosed embodiment. This fourth embodiment has the advantage in that it has a reduced installation cost since there is no need of providing any hydraulic conduit between the warm and cold wells. Also, the one or more pumps may be arranged in a position where they are easily accessible. Thus, there is no need of providing any submerged pump(s).

Now turning to <FIG>, the fourth embodiment is disclosed where the thermal energy balancing device <NUM> is set to a heat inhale mode. The thermal energy balancing device <NUM> operates in the very same manner as that previously discussed with reference to <FIG> and <FIG> with the difference that the secondary valve arrangement <NUM> receives heat transfer geothermal liquid from the warm well <NUM> and passes it across the secondary phase side of the heat exchanger where it exhales heat. The thus cooled heat transfer geothermal liquid is then fed through the secondary valve arrangement <NUM> to the cold well <NUM> where the liquid is released.

Now turning to <FIG>, a fifth embodiment is disclosed. The fifth embodiment differs from the fourth embodiment disclosed in <FIG> by the warm and cold wells <NUM>, <NUM> being vertically separated from each other. In all other aspects the two embodiments are the same. Thus, the well arrangement <NUM> is of an open loop type without any hydraulic connection between the warm well <NUM> and the cold well <NUM>. Accordingly, there is no communication between the two wells other than that provided by the secondary valve arrangement <NUM>.

Like the fourth embodiment disclosed in <FIG>, the thermal energy balancing device <NUM> is set to an exhale mode and operates in the very same manner as that previously discussed with reference to <FIG>.

The two wells are arranged on different depths in the bedrock. The cold well <NUM> is arranged on a deeper level than the warm well <NUM>. The skilled person realizes that the same principle is equally applicable with the warm well being arranged on a deeper level than the cold well.

If the thermal energy balancing device <NUM> instead should be set to an inhale mode it operates in the very same manner as that previously discussed with reference to <FIG>. Thus, to avoid undue repetition regarding the operation, reference is made to the above.

Now turning to <FIG>, the thermal energy balancing device <NUM>, no matter which embodiment has been described above, may further comprise a regulator <NUM> and a pressure difference determining device <NUM>. The overall design of the thermal energy balancing device <NUM> in <FIG> is the same as previously discussed in view of <FIG>. To facilitate understanding, the connections between the secondary side valve arrangement <NUM> and the hot and cold wells have been omitted.

The thermal energy balancing device <NUM> is provided with a pressure difference determining device <NUM> which is configured to sense local pressure in the hot conduit <NUM> and the cold conduit <NUM> respectively and determine a difference between the two pressures. The pressure difference determining device <NUM> is adapted to determine a local pressure difference, Δplocal, between a local hot conduit pressure, ph, of district heat transfer liquid of the hot conduit <NUM> and a local cold conduit pressure, pc, of district heat transfer liquid of the cold conduit <NUM>, Δplocal=ph-pc. The regulator <NUM> is configured to, based on the determined local pressure difference, regulate the flow of district heat transfer liquid between the hot and cold conduits <NUM>, <NUM>.

The regulator <NUM> is disclosed in <FIG> as being arranged in a position between the hot and cold conduits <NUM>, <NUM>. The regulator <NUM> is disclosed as being arranged between the primary side valve arrangement <NUM> and the primary side <NUM> of the heat exchanger <NUM>. The regulator <NUM> may be a small frequency-controlled circulation pump. The regulator <NUM> may be arranged either in a position before the inlet <NUM> to the primary side of the heat exchanger <NUM>, or after (not disclosed) the outlet <NUM> from the primary side of the heat exchanger <NUM>.

The purpose of the regulator <NUM> is to facilitate the flow of district heat transfer liquid to the heat exchanger <NUM> in the event the determined pressure difference between the hot conduit <NUM> and the cold conduit <NUM> should be below a predetermined set value. As long as the determined local pressure difference is determined to be above a set value, the regulator <NUM> may be set into a passive mode and act as an open valve allowing a flow of district heat transfer fluid to pass therethrough. Should the determined local pressure difference instead be determined to be below the set value, the regulator <NUM> may be set into an active mode and pump the district heat transfer liquid to thereby increase the pressure of the district heat transfer fluid as seen in a position downstream the regulator <NUM>.

The regulator <NUM> and the pressure determining device <NUM> may be connected to the controller <NUM>. The controller <NUM> may be the same as is used to control the primary side valve arrangement <NUM> and/or the secondary side valve arrangement <NUM>.

The pressure difference determining device <NUM> may be embodied in many different ways as will be given below. The pressure difference determining device <NUM> may, as is illustrated in <FIG>, be integrated in the regulator <NUM>. One example of such integrated regulator <NUM> and pressure difference determining device <NUM> is a differential pressure regulator.

If the detected pressure in a position adjacent an inlet end 940a of the regulator <NUM> should be determined to be lower than a predetermined set value, the regulator <NUM> is activated. Thereby, the pressure at the outlet end 940b of the regulator <NUM>, and hence the pressure of the district heat transfer liquid supplied from a first conduit to a second fluid in the thermal energy circuit <NUM> will be increased. Thereby a detected local pressure difference between the hot conduit <NUM> and the cold conduit <NUM> may be adjusted. In the event of a heat exhale mode, the first conduit will be the hot conduit <NUM> and the second conduit will be the cold conduit <NUM>. Correspondingly, in the event of a heat inhale mode, the first conduit will be the cold conduit <NUM> and the second conduit will be the hot conduit <NUM>.

Should the detected pressure difference be determined to be allowable, the regulator <NUM> will instead be set in a passive mode and allow a bypass of district heat transfer liquid.

In another embodiment, see <FIG> the pressure difference determining device <NUM> may be arranged as an independent device separate from the regulator <NUM>. In this embodiment, the pressure difference determining device <NUM> comprises a hot conduit pressure determining unit 950a which is connected to the hot conduit <NUM> for measuring the hot conduit local pressure, ph. Further, the pressure difference determining device <NUM> comprises a cold conduit pressure determining unit 950b which is connected to the cold conduit <NUM> for measuring the cold conduit local pressure, pc. The local pressure difference, Δplocal, is then determined as Δplocal=ph-pc. If the determined local pressure difference is determined to be below a predetermined set value, the regulator <NUM> is activated. Thereby, the pressure at the outlet end 940b of the regulator <NUM>, and hence the pressure of the district heat transfer liquid supplied from a first conduit to a second fluid will be increased. In the event of a heat exhale mode, the first conduit will be the hot conduit <NUM> and the second conduit will be the cold conduit <NUM>. Correspondingly, in the event of a heat inhale mode, the first conduit will be the cold conduit <NUM> and the second conduit will be the hot conduit <NUM>. Thereby a detected local pressure difference between the hot conduit <NUM> and the cold conduit <NUM> may be adjusted to be within a predetermined set pressure difference.

Should the detected pressure difference be determined to be allowable, the regulator <NUM> will instead be set in a passive mode and allow a bypass of heat transfer liquid.

No matter embodiment, the thermal energy balancing device may be provided with service valves. The service valves may be used for connecting and disconnecting the primary and secondary valve arrangements <NUM>, <NUM> and thereby the heat exchanger <NUM> to/from the thermal energy circuit <NUM> and the warm and cold wells. One such, highly schematic example is disclosed in <FIG> with four service valves <NUM>. The skilled person realizes that the number and positions of the service valves may be varied within the scope of the invention.

The primary and secondary valve arrangements <NUM>, <NUM> have been described as comprising four valves each which are interconnected in a closed loop with connection points to relevant conduits and ports of the heat exchanger. The skilled person realizes that the number of valves and their mutual interconnection and their connection with the heat exchanger and the conduits may be varied with remained function.

The regulator has been disclosed as being arranged between the valve arrangement and the liquid phase primary side of the heat exchanger. The skilled person understands that other positions are possible.

Claim 1:
A thermal energy balancing device (<NUM>) connected to a thermal energy circuit (<NUM>) comprising a hot conduit (<NUM>) configured to allow a district heat transfer liquid of a first temperature to flow therethrough, and a cold conduit (<NUM>) configured to allow district heat transfer liquid of a second temperature to flow therethrough, the second temperature being lower than the first temperature, the thermal energy balancing device (<NUM>) comprising:
a warm well (<NUM>);
a cold well (<NUM>);
a heat exchanger (<NUM>) comprising a primary side (<NUM>) and a secondary side (<NUM>);
a primary side valve arrangement (<NUM>) connecting the primary side of the heat exchanger (<NUM>) to the cold conduit (<NUM>) and to the hot conduit (<NUM>); and
a secondary side valve arrangement (<NUM>) connecting the secondary side of the heat exchanger (<NUM>) to the cold well (<NUM>) and to the warm well (<NUM>);
wherein the thermal energy balancing device (<NUM>) is configured to be selectively set in a heat exhale mode and in a heat inhale mode,
wherein when the thermal balancing device (<NUM>) is set into the heat exhale mode, the primary side valve arrangement (<NUM>) is configured to direct district heat transfer liquid to flow from the hot conduit (<NUM>) via the primary side (<NUM>) of the heat exchanger (<NUM>) to the cold conduit (<NUM>), and the secondary side valve arrangement (<NUM>) is configured to direct heat transfer geothermal liquid to flow from the cold well (<NUM>) via the secondary side (<NUM>) of the heat exchanger (<NUM>) to the warm well (<NUM>);
and wherein when the thermal balancing device (<NUM>) is set into the heat inhale mode, the primary side valve arrangement (<NUM>) is configured to direct district heat transfer liquid to flow from the cold conduit (<NUM>) via the primary side (<NUM>) of the heat exchanger (<NUM>) to the hot conduit (<NUM>), and the secondary side valve arrangement (<NUM>) is configured to direct heat transfer geothermal liquid to flow from the warm well (<NUM>) via the secondary side (<NUM>) of the heat exchanger (<NUM>) to the cold well (<NUM>).