A method for controlling input of a heated fluid received from a heat pump to a buffer tank of a heat pump arrangement

Abstract

The disclosure relates to a method for controlling input of a heated fluid received from a heat pump (10) to a buffer tank (110) of a heat pump arrangement (1), the buffer tank (110) comprises a housing (111) defining an interior housing volume (114) having a first volume portion (114a), a second volume portion (114b), and a third volume portion (114c), said buffer tank (110) further comprising: a first heat pump inlet structure (151), a second heat pump inlet structure (152), a heat pump outlet structure (200), and a fluid control circuit (605) configured to control a fluid passage to the first heat pump inlet structure (151) and a fluid passage to the second heat pump inlet structure (152), said method comprising: determining a temperature of the heated fluid to be input to the buffer tank (110); determining, based on said measured temperature, a control setting for the fluid control circuit (605); and configure the fluid control circuit (605) to input the heated fluid to the buffer tank (110) based on said determined control setting.

Description

[0001] A METHOD FOR CONTROLLING INPUT OF A HEATED FLUID RECEIVED FROM A HEAT PUMP TO A BUFFER TANK OF A HEAT PUMP ARRANGEMENT

[0002] Technical field

[0003] The present disclosure relates to a method for controlling input of a heated fluid received from a heat pump to a buffer tank of a heat pump arrangement.

[0004] Background art

[0005] 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. In order to reduce the carbon dioxide emissions there are plans to replace such gas grid with more “green” energy efficient energy systems.

[0006] One such energy efficient energy system is cold thermal grids. Cold thermal grids are an evolution of district heating and district cooling systems, where combined district heating and district cooling system with aid of using heat pumps for heating and cooling can provide both cooling, heating and tap water preparation to buildings.

[0007] In order to succeed with the replacement of gas grids, wherein the respective gas boiler is replaced by a heat pump, the heat pump arrangements used need to be smaller, less costly, easier to manufacture and control, and with lower technical complexity, e.g. with fewer and / or less complex sensors for measuring the space and tap water energy consumption than presently used heat pump arrangements.

[0008] The conventional energy systems are associated with several drawbacks and there is thus a need in the art of making energy systems more flexible and optimized for the occasion.

[0009] It is an object to mitigate, alleviate or eliminate one or more of the above-identified deficiencies in the art and disadvantages singly or in any combination. These and other objects are at least partly met by the disclosure as defined in the independent claims. Preferred embodiments are set out in the dependent claims.

[0010] According to a first aspect there is provided a method for controlling input of a heated fluid received from a heat pump to a buffer tank of a heat pump arrangement, wherein the buffer tank comprises a housing defining an interior housing volume for accommodating a buffer fluid, said interior housing volume having a first volume portion which connects with a top bottom end of the buffer tank, a second volume portion which connects with a bottom top end of the buffer tank, and a third volume portion which is located between the first and second volume portions, said buffer tank further comprising: a first heat pump inlet structure which is fluidly connected to the first second volume portion, a second heat pump inlet structure which is fluidly connected to the second third volume portion, a heat pump outlet structure which is fluidly connected to the first volume portion, and a fluid control circuit which is fluidly connected to said first heat pump inlet structure and said second heat pump inlet structure and configured to control a fluid passage to the first heat pump inlet structure and a fluid passage to the second heat pump inlet structure, said method comprising: determining a temperature of the heated fluid to be input to the buffer tank; determining, based on said measured temperature, a control setting for the fluid control circuit; and configure the fluid control circuit to input the heated fluid to the buffer tank based on said determined control setting.

[0011] The heat pump arrangement may be introduced in a housing or a zone, e.g., in a controlled space of a building. The heat pump arrangement may be configured to cover, i.e. , being able to heat and / or provide hot tap water to, an area. The area may be the whole, or a part of, the building. The heat pump may comprise a refrigerant circulation path which includes a first heat exchanger unit, a compressor, a second heat exchanger unit and an expander which may be connected to one another in a sequence. The buffer tank may be fluidly connected to a tap water heat exchange circuit. The tap water heat exchange circuit is preferably a hot tap water heat exchange circuit. The buffer tank may be used for hot tap water storage acting as a thermal battery for the heat pump arrangement, and especially for the tap water heat exchange circuit and optionally also for the radiator system.

[0012] The buffer tank may also be referred to as a hot water storage tank, hot water tank, thermal storage tank, hot water thermal storage unit, heat storage tank and hot water cylinder.

[0013] As readily appreciated by the person skilled in the art, the housing of the buffer tank is a closed housing in order to be able to accommodate the buffer fluid.

[0014] With this design, in which the input of the heated fluid from the heat pump to the buffer tank may be controlled, based on the determined temperature of the heated fluid, may be advantageous as it allows for that a thermal stratification in the buffer tank is maintained also in transient heat pump operation modes, i.e. such as start of operation of the heat pump. Thus, it increases the thermal efficiency of the buffer tank. Thermal stratification is the process where a fluid will naturally strive to be vertically distributed such that the density decreases as function of vertical position. Since a buffer fluid, such as e.g., water, has a density which monotonically decreases with increasing buffer fluid temperature in the operating temperature region of the buffer tank (it is noted that no buffer tank storing water is run close to the inflection point at 4 degrees Celsius), the thermal stratification will ensure that the buffer fluid having the highest temperatures are located at the top end of the buffer tank, and that the buffer liquid having the lowest temperatures are located at the bottom end of the buffer tank.

[0015] The heat pump supplies heated liquid to the buffer tank via the first heat pump inlet structure. To make sure the thermal stratification inside the buffer tank is maintained, the first heat pump inlet structure is fluidly connected to an exterior of the housing with the second (top) volume portion thus ensuring the heated fluid will be introduced at the top end of the buffer tank. The fluid retrieved from the tank to be heated by the heat pump is retrieved from the heat pump outlet structure. To make sure that the fluid retrieved from the buffer tank is from the lowest temperatures, the heat pump outlet structure fluidly connects the exterior of the housing with the first (bottom) volume portion. By the provision of the second heat pump inlet structure fluidly connecting to the third volume portion being located between the first and second volume portions, and the fluid control circuit, the administration of heated fluid into the buffer tank may be tailored to improve maintaining the thermal stratification. The method takes the temperature of the buffer fluid received from the heat pump into account to determine how to administer the buffer fluid to the buffer tank. The method may take further data into account, such as a temperature of the buffer fluid within the tank, a temperature distribution of the buffer fluid within the tank, a temperature of the buffer fluid measured within the tap water heat exchange circuit, etc.

[0016] The method may be further advantageous as it allows for a costefficient solution compared to conventional solutions in which typically a diffusor is used to passively distribute heated buffer fluid to the buffer tank.

[0017] In this context, the first, second and third volume portions of the buffer tank may be referred to as a first, second and third sub-volumes of the buffer tank. It should be noted that the different volume portions are portions of the same interior housing volume of the buffer tank, but the buffer fluid comprised in the different volume portions may have different properties, e.g., different temperature, different density, or the like. The different volume portions are upheld by natural layering as will be detailed further below. It should be noted that the smaller the property differences may be, the less distinct may the layering be. With this design, a temperature of the buffer fluid provided in the first volume portion may be lower than the temperature of the buffer fluid provided in the second and third volume portion. The buffer fluid of the third volume portion may have a temperature between the temperature of the first volume portion and the second volume portion, i.e. the temperature may be higher than temperature of the first volume portion but lower than the temperature of the second volume portion. By way of example, the buffer fluid of the second volume portion may have a temperature between 55-90 degrees Celsius and the buffer fluid of the first volume portion may have a between 10-50 degrees Celsius.

[0018] Since the fluid density varies with temperature, a natural layering will occur in the vertical direction of the buffer tank. This is often referred to as thermal stratification. By providing the high temperature fluid to the upper part (i.e. providing the second volume portion at the uppermost part of the tank) and providing the low-temperature fluid to the lower part (i.e. providing the first volume portion at the lowermost part of the tank) the natural layering will strive to maintain the separation between the first and second volume portions also over time.

[0019] As indicated, heated buffer fluid being received from the heat pump to the buffer tank may be provided to the second volume portion via the first heat pump inlet structure, and / or to the third inlet portion via the second heat pump inlet structure. Heated fluid retrieved from the buffer tank may be retrieved from the first volume portion via the heat pump outlet structure.

[0020] By the terms “first heat pump inlet structure, “second heat pump inlet structure” and “heat pump outlet structure” are herein meant structures which are configured to fluidly connect different volume portions of the buffer tank to the heat pump. By way of example, the heat pump inlet and outlet structures may be a respective conduit arrangement. The heat pump inlet and outlet structures may be any structures suitable for fluidly connecting the buffer tank and the heat pump. It should be noted that the buffer tank and the heat pump may be fluidly connected at all times, via the heat pump inlet and outlet structures, but may not be in fluid communication with each other at all times, i.e. may not be able to supply fluid between the buffer tank and the heat pump at all times. The heat pump inlet and outlet structures may be referred to as fluid connecting structures.

[0021] By the term “fluid control circuit” is herein meant a conduit circuit through which the heated fluid may be supplied to the buffer tank. The fluid control circuit may be configured to control a fluid flow direction of the heated fluid to the buffer tank based on the determined control setting. This may be advantageous as it allows for a flexible input of the heated fluid to the buffer tank, wherein the heated fluid may be inputted to the buffer tank in different ways depending on the determined control setting. Typically, a fluid control circuit comprises conduits and controllable valves, as will be detailed later.

[0022] By the term “fluid passage” is herein meant that a fluid is able to move through a structure. As previously noted, as used herein: fluid passage between two positions may, at least temporarily, be prevented e.g. by means of a valve, even if the two points are fluidly connected to each other.

[0023] According to some embodiments, the step of determining the control setting comprises: comparing the measured temperature with a predefined threshold temperature; wherein, upon the measured temperature being higher than the predefined threshold temperature, the control setting comprises instructions to maintain fluid passage through the first heat pump inlet structure and to prevent fluid passage through the second heat pump inlet structure; and wherein, upon the measured temperature being lower than the predefined threshold temperature, the control setting comprises instructions to prevent fluid passage through the first heat pump inlet structure and to maintain fluid passage through the second heat pump inlet structure.

[0024] Thus, the heated fluid may be supplied to the buffer tank via the first heat pump inlet structure or the second heat pump inlet structure depending on the temperature of the heated fluid. This may be advantageous as it allows for adapting a temperature distribution of the heated fluid supplied to the buffer tank to a temperature distribution of the buffer fluid which is already residing in the buffer tank. In other words, the buffer tank may provide a means to distribute the heated fluid of a specific temperature predominately in regions of the buffer tank having that same temperature. As readily appreciated by the person skilled in the art, this reduces the risk that the heating process via the heat pump arrangement influences the temperature distribution of the buffer fluid within the buffer tank. This effect occurs due to the way the heated fluid is introduced into the buffer tank via the respective buffer tank connections. This example embodiment of the method may be advantageous as it allows for a simplified control, also allowing selecting cheaper components. Specifically, no modulating controllable valves are required. Instead, simple on-off type valves may be used.

[0025] By way of example, the first threshold may be 45-70 degrees Celsius, preferably 50-65 degrees Celsius, more preferably 55-60 degrees Celsius.

[0026] According to some embodiments, the step of determining the control setting comprises: determining, based on the measured temperature, a fluid passage distribution between the first heat pump inlet structure and the second heat pump inlet structure; and wherein the control setting comprises instructions for the fluid control circuit to control the input of the heated fluid to the buffer tank via the first heat pump inlet structure and the second heat pump inlet structure according to said determined fluid passage distribution.

[0027] Thus, the heated fluid may be supplied to the buffer tank via the first heat pump inlet structure and the second heat pump inlet structure. This may advantageous as it allows reducing transients which may occur in an on-off control scheme as outlined above, thus improving maintaining the temperature distribution in the tank. The fluid control circuit may for this example embodiment include means to continuously, and steplessly, control the amount of buffer fluid that enters through each of the first and second heat pump inlet structures. Such means could be e.g. a modulating controllable valve, such as a shunt valve.

[0028] According to some embodiments, the method comprises: determining an internal temperature of the buffer fluid within the buffer tank; and wherein the step of determining a control setting for the fluid control circuit comprises determining said control setting based on both the measured temperature of the heated fluid to be input to the buffer tank and on said internal temperature of the buffer fluid within the buffer tank.

[0029] This may be beneficial as it allows tailoring the administration of buffer fluid to the tank differently dependent on the conditions of the buffer tank during administration. As an example, if excessive tap water heating has occurred during a time period, the temperature of the second volume portion may be temporarily lowered, sometimes becoming even lower than the temperature in the third volume portion. In such situations, it may be beneficial to supply all the heated buffer fluid to the second volume portion and nothing to the third volume portion.

[0030] According to some embodiments, the control circuit comprises a controllable valve which is structured and arranged within the fluid control circuit to allow heated fluid received from the heat pump to be selectively branched to the first heat pump inlet structure and / or to the second heat pump inlet structure.

[0031] This may be advantageous as it allows for an easy, efficient, and flexible branching conduit module which is configured to selectively supply the heated fluid to the buffer tank via different heat pump inlet structures. Thus, it allows for administrating the heated fluid to the buffer tank via more than one inlet structure. As said, the first and second heat pump inlet structures are fluidly connected to different volume portions of the interior housing volume. This allows for that the heated fluid may be distributed to different parts of the buffer tank depending on which heat pump inlet structure the heated fluid is supplied through.

[0032] The controllable valve may be advantageous as it allows for directing the heated fluid to the first heat pump inlet structure and / or to the second heat pump inlet structure. Thus, this may be advantageous as it allows for controlling the fluid flow to the buffer tank in an easy, efficient, and flexible way. The controllable valve may be a three-way valve. The controllable valve may be a modulating valve, but may for other embodiments be an on-off valve. The controllable valve may be a ball valve, a rotary valve, or the like.

[0033] According to some embodiments, the controllable valve is a thermostat comprising temperature sensing means for allowing adjusting said selective branching of the heated fluid to the first heat pump inlet structure and / or to the second heat pump inlet structure based on a temperature of the heated fluid.

[0034] As said, the first heat pump inlet structure and the second heat pump inlet structure may be fluidly connected to different volume portions of the buffer tank. With this design, the heated fluid may be supplied to different volume portions depending on a temperature of the heated fluid. By providing a thermostat, no external sensor data are needed in order to carry out the method.

[0035] According to some embodiments, the housing comprises a main housing portion and at least one further housing portion which together define the interior housing volume for accommodating the buffer fluid; and a plurality of buffer tank interaction structures which includes at least said first heat pump inlet structure and said second heat pump inlet structure; and wherein the main housing portion and the at least one further housing portion are releasably attached to each other, and wherein the plurality of buffer tank interaction structures is provided in the at least one further housing portion.

[0036] The plurality of buffer tank interaction structures may together form a buffer tank interaction system. The buffer tank interaction system may be structured and arranged for fluidly connecting the buffer tank with the heat pump and / or the tap water heat exchange circuit as well as monitoring and controlling properties of the buffer fluid. The plurality of buffer tank interaction structures may include further interaction structures which will be discussed further below.

[0037] With the disclosed design, in which the plurality of buffer tank interaction structures is provided in the at least one further housing portion, it allows for that the plurality of buffer tank interaction structures is introduced to the buffer tank via the at least one housing only, thereby allowing the main housing portion to be free from buffer tank interaction structures. That said, the buffer tank of the disclosure should not be construed as limited to embodiments where the main housing portion does not include any connections. There may be reason to arrange connections also on the main housing portion. However, the person skilled in the art realizes that reducing the number of connections on the main housing portion to, preferably, zero, thereby providing majority, or even all, connections via the at least one further housing portion, achieves the strongest technical effect, as detailed further below. This may be advantageous in that the buffer tank may be less complex to build, especially in high volumes. Thus, a simplified construction of the buffer tank which enables a reduced production time for manufacturing the buffer tank is achieved. This may be further advantageous as it allows for a reduced size needed for the buffer tank in the heat pump arrangement. This may be yet further advantageous as it allows for making possibilities for using robots in the manufacturing which may further reduce the production time.

[0038] Thus, with the disclosed design, a less complex buffer tank which may be easier and more efficient to produce is achieved, wherein the possibilities of using robots in the manufacturing process may facilitates this even further. The buffer tank may be advantageous as it allows for automate the manufacturing process of the buffer tank. Hence, an improved manufacturing process is achieved.

[0039] As readily appreciated by the person skilled in the art, the housing is a closed housing in order to be able to accommodate the buffer fluid. Thus, the main housing portion and the at least one further housing portions together forms the closed housing which defines the interior housing volume. The main housing portion may comprise at least one opening. The at least one further housing portion may be arranged to cover the at least one opening of the main housing portion. The at least one further housing portion may comprise at least one through-hole. The plurality of buffer tank interaction structures may be arranged to cover the at least one through-hole of the at least one further housing portion. In this way, the closed housing is formed, and the interior housing volume is defined and is able to accommodate the buffer fluid. If more than one buffer tank interaction structure is provided in one through-hole, or are covering one through-hole, there may be seals between the structures in the through-hole. Preferably, each of the plurality of buffer tank interaction structures is arranged in its own through-hole. The at least one further housing portion may thus typically comprise the same number of through-holes as the number of buffer tank interaction structures, i.e. if there is four buffer tank interaction structures provided in the at least one further housing portion, the at least one further housing portion preferably comprises four through-holes. This may be advantageous as it allows for a reduce risk of leakages through the through-holes. Each of the plurality of buffer tank interaction structures may be arranged in the at least one further housing portion such that it extends from an exterior of the buffer tank to an interior of the buffer tank. Each of the plurality of buffer tank interaction structures may extends from the exterior to the interior of the buffer tank via a through-hole of the at least one further housing portion.

[0040] The main housing portion may have larger surface area than the at least one further housing portion. Thus, the surface area of the main housing portion may be more than 50% of a total surface area of the housing. By way of example, the surface area of the main housing portion may be 55-95% of the total surface area, preferably 65-85% of the total surface area, more preferably 75% of the total surface area.

[0041] The main housing portion and the at least one further housing portion may be releasably attached to each other by means of bolts, nuts or the like. Thus, the main housing portion and the at least one further housing portion may be releasably attached to each other by any means which is suitable for such attachment. This may be advantageous as it allows for providing the plurality of buffer tank interaction structures in the at least one further housing portion prior to attaching the at least one further housing portion to the main housing portion. In this way, a simpler and less complex manufacturing process may be achieved making possibilities for using robots in the manufacturing.

[0042] This may be further advantageous as it allows for an easy and efficient maintenance of the plurality of buffer tank interaction structures provided in the at least one further housing portion. Thus, if one of more of the plurality of buffer tank interaction structures need to be replaced or repaired, it is possible to detach the at least one further housing portion from the main housing portion and thereafter replace or repair the interaction structure(s). Thus, replacement and update of functionalities of the buffer tank and / or the plurality of buffer tank interaction structures may be provided in an easy and less complex way.

[0043] This may be yet further advantageous as it allows for being able to provide different types of buffer tank interaction structures to the buffer tank in an easy and efficient way. Thus, it is possible to replace one further housing portion with another, wherein the different further housing portions may be provided with different types of buffer tank interaction structures.

[0044] The main housing portion and the at least one further housing portion may be sealingly attached to each other by means a sealing means, such as e.g. sealing rings, or gaskets. This may prevent any leakage of buffer fluid from the buffer tank.

[0045] The main housing portion may comprise a respective flange portion arranged at an interface between the main housing portion and each one of the at least one further housing portion, wherein each flange portion protrudes out from an outer surface of the main housing portion so as to define a guide for the associated further housing portion.

[0046] This may be advantageous as it allows for a simplified attachment of each of the at least one further housing portion to the main housing portion. The flange portion may be a protruded lip or rim and in addition to being defined as a guide for the associated further housing portion, the flange portion may also serve to increase strength and providing for an easier attachment between the main housing portion and the associated further housing portion.

[0047] According to some embodiments, the housing extends from said top end to said bottom end and is defined by a top wall at the top end, a bottom wall at the bottom end, and a lateral wall which extends between, and interconnects, the top wall and the bottom wall, wherein the at least one further housing portion defines at least a part of the top wall or the bottom wall.

[0048] With the term “the at least one further housing portion defines at least a part of the first wall” is herein meant that the at least one further housing portion defines a part of the wall or the complete wall.

[0049] The buffer tank typically has a cylindrical geometry. This implies that a cross-section of the buffer tank along a vertical direction is circular. It is however also conceivable that the buffer tank has another shape, such as an elliptical cross section, or a square cross section. By way of example, the at least one further housing portion may be planar. The at least one further housing portion may be circular. The at least one further housing portion may be a circular plate. The at least one further housing portion may be formed as a lid with sidewalls arranged to engage with sidewalls of the opening in the main housing portion.

[0050] It should be noted that the at least one further housing portion may, alternatively, define at least a part of the second wall. It should be further noted that the at least one further housing portion may, alternatively, define at least a part of the lateral wall. If the at least one further housing portion is more than one housing portion, each of the at least one further housing portion may define at least a respective part of the same wall. If the at least one further housing portion is more than one housing portion, each of the at least one further housing portions may define at least a respective part of different walls. Thus, as a non-limiting example, it is conceivable that the at least one further housing portion comprises a first further housing portion which defines at least a part of the first wall, and a second portion which defines at least a part of the second wall or the lateral wall.

[0051] According to some embodiments, the at least one further housing portion defines at least a part of the bottom wall.

[0052] This may be advantageous as it allows for an efficiently insulated buffer tank. The housing of the buffer tank is typically insulated in order to reduce heat losses to the surroundings. By providing the at least one further housing portion at the bottom end of the main housing portion, the lateral and top walls of the housing may be provided free from connectors and other structures, which thereby allows easy access for insulation material, such as insulating foam, to be applied during manufacture for covering the entire outer surface of the main housing portion. In short, this may facilitate an insulation procedure during the manufacturing process. Thus, a time-efficient insulation procedure may be achieved. In addition, the insulation procedure may be automated which also improves the manufacturing efficiency. This may be further advantageous as it allows for an easy access to the at least one further housing portion when attaching or detaching the at least one further housing portion to the main housing portion. For embodiments where the first end is a bottom end of the housing, the second end will be the top end of the housing. The lateral wall extends between and interconnects the bottom end and the top end.

[0053] According to some embodiments, the plurality of buffer tank interaction structures further comprises one or more of: one or more further fluid connecting structures, a direct electric heater, a flexible bladder, one or more temperature sensors, one or more pressure sensors, and a venting pipe.

[0054] This may be advantageous as it allows for providing the at least one further housing portion with the buffer tank interaction structures which may be needed for the buffer tank and / or the heat pump arrangement. Thus, it may be possible to design the at least one further housing portion with the desired buffer tank interaction structures. The plurality of buffer tank interaction structures may be further advantageous as they allow for operating the buffer tank in a suitable way. The plurality of buffer tank interaction structures is further advantageous as they allow for monitoring the buffer tank in an easy and efficient way.

[0055] The term “one or more fluid connecting structures” is herein meant structures which are configured to fluidly connect the buffer tank to the heat pump and / or to the radiator system and / or the tap water heat exchange circuit and thereby being able to supply fluid between the buffer tank and the heat pump and / or the radiator system and / or the tap water heat exchange circuit. By way of example, the one or more fluid connecting structures may be a respective conduit arrangement. The one or more fluid connecting structures may be any structures suitable for fluidly connecting the buffer tank and the heat pump.

[0056] The direct electric heater may be provided to heat the buffer fluid accommodated in the housing. The direct electric heater may be provided to contribute to the heating provided by the heat pump. The provision of the direct electric heater may be advantageous as it allows for providing a faster heating which thus improves comfort for a user. In particular, the provision of the direct electric heater allows to better tailor the operation of the heat pump of particular conditions. As an example, when the outside temperature is low, the heat transfer provided by the heat pump may have to be directed to the radiator system only. The direct electric heater may then be used to selectively provide heat to the tap water heat exchange circuit.

[0057] The flexible bladder may be used to replace the expansion tank which in prior art arrangement is fluidly connected to the conduit system and thereby with both the radiator system and with the buffer tank. The purpose of the expansion tank is to compensate for the volume variations occurring in the buffer fluid as a result from variations in its temperature. By the provision of a flexible bladder inside the buffer tank, the same function can be mover to the buffer tank itself, thereby removing the need for the expansion tank. Thus, the flexible bladder may be arranged for protecting the heat pump arrangement from excessive pressure. By way of example, the flexible bladder may be a balloon-like bladder arranged to adjust the pressure and temperature variations and absorb thermal expansion within the heat pump arrangement. With the disclosed design, in which the flexible bladder is arranged inside the housing, the size needed for the buffer tank may be reduced compared to conventional solutions in which the flexible bladder typically is comprised in an external expansion tank. Thus, the need of the external expansion tank is removed. This may be further advantageous as it allows for a simplified construction of the buffer tank which enables a reduced production time for manufacturing the buffer tank.

[0058] The flexible bladder may define an interior bladder volume which is filled with a gas. It should be noted that the flexible bladder is arranged such that the buffer fluid in the housing and a gas in the flexible bladder does not come in contact with each other. Thus, as said, it is only the outside of the flexible bladder which is in contact with the buffer fluid while the gas is filled in the interior bladder volume of the flexible bladder.

[0059] The one or more temperature sensors may be provided for measuring a temperature of the buffer fluid. The one or more temperature sensors may be provided for measuring a temperature in the buffer tank. The one or more pressure sensors may be provided for measuring a pressure in the buffer tank.

[0060] The venting pipe may be provided for venting air from the buffer tank. According to some embodiments, the first heat pump inlet structure and the second heat pump inlet structure each extend through the at least one further housing portion from an exterior of the housing to an interior of the housing.

[0061] This may be advantageous as it allows for fluidly connecting the buffer tank and the heat pump in an easy and efficient way. The first and second heat pump inlet structures may be a respective conduit arrangement which extends through the at least one further housing portion from the exterior of the housing to the interior of the housing and thereby fluidly connecting the exterior of the housing with the interior of the housing.

[0062] Preferably, all of the plurality of buffer tank interaction structures extends through the at least one further housing portion from the exterior of the housing to an interior of the housing.

[0063] As indicated above, the one or more fluid connecting structures may be arranged to fluidly connect the buffer tank with the heat pump and / or the tap water heat exchange circuit and / or the radiator system. The one or more fluid connecting structures may be respective conduit arrangements which extends through the at least one further housing portion from the exterior of the housing to the interior of the housing and thereby fluidly connecting the exterior of the housing with the interior of the housing. Preferably, the one or more fluid connecting structures extends between the interior of the buffer tank and the heat pump and / or the tap water heat exchange circuit and / or the radiator system (i.e. the exterior of the buffer tank).

[0064] Other buffer tank interaction structures (i.e. the direct electric heater, the flexible bladder, the temperature sensor(s), the pressure sensor(s) and the venting pipe) may extend through the at least one further housing portion from the exterior of the housing to the interior of the housing in order to being able to i.e. monitoring the buffer fluid or the like. With this design, said buffer tank interaction structures may be attached to the housing from its exterior. This may be advantageous as it facilitates the accessibility to the buffer tank interaction structure such that maintenance of the interaction structures may be simplified. According to some embodiments, the first heat pump inlet structure and the second heat pump inlet structure are each releasably attached to the at least one further housing portion.

[0065] The first and second heat pump inlet structures may be releasably attached to the at least one further housing portion e.g. by means of bolts, nuts or the like. Thus, the first and second heat pump inlet structures may be releasably attached to the at least one further housing portion by any means which is suitable for such attachment. This may be further advantageous as it allows for an easy and efficient maintenance of the first and second heat pump inlet structures provided in the at least one further housing portion. Thus, if one or both of the first and second heat pump inlet structures need to be replaced or repaired, it is possible to detach said heat pump inlet structure from the at least one further housing portion and thereafter replace of repair the inlet structure, without requiring dismantling the at least one further housing portion from the main housing portion. Thus, replacement and update of functionalities of the buffer tank and / or the heat pump inlet structures may be provided in an easy and less complex way. With this design, the replacement or maintenance of the first and / or second heat pump inlet structure may be performed with a reduce risk of impact other buffer tank interaction structures comprised in the buffer tank.

[0066] It should be noted that one or more further buffer tank interaction structures of the plurality of buffer tank interaction structures may be releasably attached to the housing. By way of example, all buffer tank interaction structures comprised in the buffer tank may be releasably attached to the housing. The plurality of buffer tank interaction structures may be releasably attached to the housing by means of bolts, nuts, sealing rings or the like.

[0067] One or more of the at least one buffer tank interaction structure may, alternatively, be fixedly attached to the at least one further housing portion. The one or more of the at least one buffer tank interaction structure may be fixedly attached to the at least one further housing portion by welding, soldering or the like. According to some embodiments, the at least one further housing portion is one further housing portion. In particular, the at least one further housing portion may be only one further housing portion.

[0068] This may be advantageous as it allows for an easy, efficient, and simplified manufacturing of the buffer tank in which all buffer tank interaction structures may be provided to the buffer tank from one single side of the buffer tank. This may be further advantageous as it allows for introducing all buffer tank interaction structures in one single move. This may be further advantageous as it allows for a limited number of housing portions (i.e. two housing portions, the main housing portion and the further housing portion) to be attached to each other.

[0069] According to some embodiments, the fluid control circuit is comprised within a branching conduit module configured to be connected to a radiator system in a building and to a heat pump, the branching conduit module comprising: a housing; an inlet configured to fluidly connect the branching conduit module to the heat pump for receiving heated fluid therefrom; a first buffer tank connection configured to fluidly connect the branching conduit module to the buffer tank via the first heat pump inlet structure; a second buffer tank connection configured to fluidly connect the branching conduit module to the buffer tank via the second heat pump inlet structure; wherein the housing comprises a buffer tank interface portion configured to abut the buffer tank, wherein the buffer tank interface portion comprises a fastening system for releasably fastening the branching conduit module to the buffer tank, and wherein the first buffer tank connection and the second buffer tank connection is arranged in the buffer tank interface portion.

[0070] The branching conduit module may be arranged for fluidly connecting the heat pump to the buffer tank and the radiator system. The branching conduit module may be arranged for fluidly connecting an output from a warm side of the heat pump, via the inlet, to the buffer tank, via the first buffer tank connection, and the radiator system, via the outlet. As said, the branching conduit module is configured to be releasably attached to the buffer tank via the fastening system. This may be advantageous as it allows for easily attaching the branching conduit module to the buffer tank. This may be further advantageous as it allows for easily detaching the branching conduit module from the buffer tank. This may e.g. facilitate simple maintenance of the branching conduit module. By way of example, this may be advantageous as it allows for simple replacement of a branching conduit module if needed instead of demounting of several discrete components as in conventional solutions.

[0071] The branching conduit module may comprise necessary components, i.e. the inlet, the first buffer tank connection and the outlet, needed for fluidly connecting the heat pump to the buffer tank and radiator system. This may be advantageous as it allows for a simplified construction of the heat pump arrangement and especially the buffer tank. This may be further advantageous as it allows for enabling robot production and thereby reducing manufacturing time. Thus, the buffer tank may be manufactured at one place and the branching conduit module may be manufactured at another place, wherein the buffer tank and the branching conduit module may be fastened to each other via the fastening system at a third place. The attachment may be provided by using robots. With this design, in which the inlet, the first buffer tank connection, the outlet and the internal conduit circuit may be integrated in the branching conduit module, a size needed for the heat pump arrangement may be reduced.

[0072] The branching conduit module may be releasably fastened to the buffer tank by means of bolts, nuts, sealing rings or the like. Thus, the branching conduit module may be releasably fastened to the buffer tank by any means which is suitable for such attachment. This may be advantageous as it allows for attaching and detaching the branching conduit module to / from the buffer tank in an easy way. In this way, a simpler and less complex manufacturing process may be achieved making possibilities for using robots in the manufacturing. This may be further advantageous as it allows for an easy and efficient maintenance of the branching conduit module. Thus, it may be possible to detach the branching conduit module from the buffer tank and thereafter replace or repair the branching conduit module. Thus, replacement and update of functionalities of the branching conduit module may be provided in an easy and less complex way.

[0073] The branching conduit module may be formed from an integral one- piece element, e.g. having a box form factor, in which element one or more cavities have been provided. For such example embodiments, the integral one-piece element will define the housing and the one or more cavities will define at least a part of the internal conduit circuit.

[0074] Alternatively, the branching conduit module may be formed by a plurality of elements which are attached to each other. The housing may for such example embodiments be a separate element, such as a box within which the internal conduit system is defined by piping.

[0075] The first buffer tank connection may be configured to fluidly connect the branching conduit module to the buffer tank for supplying heated fluid thereto. With this design, the first buffer tank connection may be defined as a first buffer tank inlet connection. The first buffer tank connection may be configured to fluidly connect the branching conduit module to the buffer tank for receiving heated fluid therefrom. With this design, the first buffer tank connection may be defined as a first buffer tank outlet connection. Thus, the first buffer tank connection may be structured and arranged such that it may be an inlet or an outlet of the branching conduit module. This may be advantageous as it allows for a flexible design of the branching conduit module.

[0076] As readily appreciated by the person skilled in the art, if the first buffer tank connection is defined as the first buffer tank inlet structure, configured to supply fluid to the buffer tank, the buffer tank may comprise an outlet through which fluid may be retrieved. If the first buffer tank connection is defined as the first buffer tank outlet structure, configured to supply fluid from the buffer tank, the buffer tank may comprise an outlet through which fluid may be received.

[0077] By the term “fluidly connected” is herein meant that the branching conduit module is configured to be connected to the heat pump and / or the buffer tank and / or the radiator system such that a fluid communication between the branching conduit module and the heat pump and / or the buffer tank and / or the radiator system is formed. It should be noted that the branching conduit module may at all-time be physically connected to the heat pump, the buffer tank and the radiator system but may be fluidly connected, i.e. having fluid communication with, one or more of the heat pump, the buffer tank and the radiator system.

[0078] By the term “inlet” is herein meant an inlet of the branching conduit module, i.e. an inlet from the heat pump to the branching conduit circuit. The inlet may be configured to connect the branching conduit module to the heat pump via one or more conduits such that the heated fluid may be supplied therebetween.

[0079] By the term “outlet” is herein meant an outlet of the branching conduit module, i.e. an outlet from the branching conduit module to the radiator system. The outlet may be configured to connect the branching conduit module to the radiator system via one or more conduits such that the heated fluid may be supplied therebetween.

[0080] By the term “first junction” is herein meant a point in which two or more fluid lines of the internal conduit circuit are joined. Thus, in the first junction, the heated fluid received from the heat pump via the inlet is configured to be branched to the buffer tank via the first buffer tank connection and / or to the radiator system via the outlet.

[0081] It is noted that the inventive concepts relate to all possible combinations of features unless explicitly stated otherwise. A further scope of applicability of the present disclosure 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 disclosure, are given by way of illustration only, since various changes and modifications within the scope of the disclosure will become apparent to those skilled in the art from this detailed description.

[0082] Hence, it is to be understood that this disclosure 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.

[0083] The disclosure may also in short be said to relate to a method for controlling input of a heated fluid received from a heat pump to a buffer tank of a heat pump arrangement, the buffer tank comprises a housing defining an interior housing volume having a first volume portion, a second volume portion, and a third volume portion, said buffer tank further comprising: a first heat pump inlet structure, a second heat pump inlet structure, a heat pump outlet structure, and a fluid control circuit configured to control a fluid passage to the first heat pump inlet structure and a fluid passage to the second heat pump inlet structure, said method comprising: determining a temperature of the heated fluid to be input to the buffer tank; determining, based on said measured temperature, a control setting for the fluid control circuit; and configure the fluid control circuit to input the heated fluid to the buffer tank based on said determined control setting.

[0084] Brief descriptions of the drawings

[0085] The disclosure will by way of example be described in more detail with reference to the appended schematic drawings, which shows presently preferred embodiments of the disclosure.

[0086] Figure 1 is a schematic view of a heat pump arrangement according to the prior art.

[0087] Figure 2 is a schematic view of a heat pump arrangement comprising a buffer tank according to an example embodiment of the present disclosure.

[0088] Figure 3A is a cross-sectional view of an attachment between a buffer tank interaction structure and a further housing portion according to an example embodiment of the current disclosure. Figure 3B is a cross-sectional view of an attachment between a buffer tank interaction structure and a further housing portion according to another example embodiment of the current disclosure.

[0089] Figure 3C is a cross-sectional view of an attachment between a buffer tank interaction structure and a further housing portion according to yet another example embodiment of the current disclosure.

[0090] Figure 4A is a perspective view of a flexible bladder according to an example embodiment of the present disclosure.

[0091] Figure 4B is a cross-sectional view of parts of the flexible bladder of Fig. 4A.

[0092] Figure 5A is a perspective view of a branching conduit module according to an example embodiment of the present disclosure.

[0093] Figure 5B is a perspective view of the branching conduit module of Fig. 5A where its interior has been visualized in a transparent view.

[0094] Figure 5C is a cross-sectional side view of the branching conduit module of Fig. 5A.

[0095] Figure 6 is a schematic view of the branching conduit module of Figs 5A to 5C when connected to the buffer tank of Fig. 2.

[0096] Figure 7 is a schematic view of a branching conduit module according to another example embodiment of the present disclosure when connected to the buffer tank of Fig. 2.

[0097] Figure 8 is a schematic view of a branching conduit module according to yet another example embodiment of the present disclosure when connected to the buffer tank of Fig. 2.

[0098] Figure 9 is a schematic view of a branching conduit module according to yet another example embodiment of the present disclosure when connected to the buffer tank of Fig. 2.

[0099] Figure 10 is a schematic view of a branching conduit module according to yet another example embodiment of the present disclosure when connected to the buffer tank of Fig. 2.

[0100] Figure 11 is a schematic view of a branching conduit module according to yet another example embodiment of the present disclosure when connected to the buffer tank of Fig. 2. Figure 12 is a schematic view of a heat pump arrangement according to another example embodiment of the present disclosure.

[0101] Detailed description

[0102] 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. The present 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 addressee. Like reference characters refer to like elements throughout.

[0103] With reference to figure 1 , a heat pump arrangement 40 for domestic heating according to the prior art is illustrated by way of example to put the invention in context. The heat pump arrangement 40 comprises a heat pump 10, a buffer tank 51 , a switchable conduit system 3 and a tap water heat exchanger circuit 60. The heat pump arrangement 40 is configured to transfer heat to a radiator system 13 or to a tap water circuit 61. The heat pump arrangement 40 is using the same heat pump 10 for the radiator system 13 (i.e. , floor heating / radiator systems) and for generating hot tap water to the tap water circuit 61 . The tap water circuit 61 may therefore alternatively be called a hot tap water circuit. The tap water heat exchange circuit 60 may consequently alternatively be called a hot tap water heat exchange circuit.

[0104] The heat pump 10 is only schematically illustrated herein and could be any kind of heat pump known in the art which is able to deliver heated fluid to a grid. Such heat pumps 10 may be e.g. a liquid-to-liquid heat pump, or an air-to-liquid heat pump. The heat pump 10 is connected to a cold fluid side (not shown) which could be e.g. the earth or the outside air. The heat pump 10 is configured to transfer heat retrieved from the cold fluid side to the radiator system 13 and to the tap water circuit 61 .

[0105] The heat pump 10 is connected to the radiator system 13 and to the buffer tank 51 by means of the switchable conduit system 3. The switchable conduit system 3 is configured to fluidly connect the heat pump 10 to the radiator system 13 (as illustrated in figure 1 ) or to fluidly connect the heat pump 10 to the buffer tank 51 . Thus, it should be noted that the heat pump 10 is physically connected to the radiator system 13 and the buffer tank 51 at the same time. It should however be noted that the heat pump 10 is fluidly connected to either the radiator system 13 or the buffer tank 51 . When the heat pump 10 is fluidly connected to the radiator system 13, it is preventing fluid communication with the buffer tank 51. When the heat pump 10 is fluidly connected to the buffer tank 51 , it is preventing fluid communication with the radiator system 13. The fluid which is heated by the heat pump 10 and then circulated through the heat pump arrangement 40 via the switchable conduit system 3, the radiator system 13 and / or the buffer tank 51 by means of circulation pump 450. The switching is provided by controllable valve 550. The fluid is also termed herein as “buffer fluid”. This fluid is typically water.

[0106] Although not shown in detail herein, the heat pump 10 comprises a refrigerant circulation loop which comprises a first heat exchanger unit, a second heat exchanger unit, a compressor and an expander. The first heat exchanger unit is fluidly connected to the cold fluid side and is used to retrieve heat therefrom and transfer said heat to the refrigerant circulation loop. The second heat exchanger unit is fluidly connected to the switchable conduit system 3 and is used to transfer heat from the refrigerant circulation loop to the buffer fluid circulated in the switchable conduit system 3. To this end, a refrigerant is housed and circulated within the refrigerant circulation loop. The refrigerant undergoes phase change and completes a so called heat pump cycle as it retrieves heat from the first heat exchanger unit and supplies heat to the second heat exchanger unit. The person skilled in the art are well aware of how heat pumps operate and the heat pump 10 is therefore not further described herein.

[0107] The buffer tank 51 is configured to store buffer fluid heated by the heat pump 10. Buffer fluid is supplied to the buffer tank 51 through heat pump inlet structure 54 which is fluidly connected to an uppermost portion of the buffer tank 51 and is retrieved from the buffer tank 51 through heat pump outlet structure 52 which is fluidly connected to a lowermost portion of the buffer tank 51 . The buffer tank 51 further comprises tap water inlet structure 53 and tap water outlet structure 55, both being connected to the tap water heat exchange circuit 60. The tap water heat exchange circuit 60 comprises a heat exchanger 66 and a circulation pump 67. The tap water heat exchange circuit 60 is arranged to retrieve hot buffer fluid from the uppermost portion of the buffer tank 51 , via the tap water outlet structure 55, whereby allowing the retrieved hot buffer fluid to transfer heat to tap water which is also circulated through the heat exchanger 66. The retrieved hot buffer fluid is subsequently returned back to the lowermost portion of the buffer tank 51 via the tap water inlet structure 53. The tap water is supplied to the heat exchanger 66 via tap water circuit 61 . The tap water circuit 61 is connected to the heat exchanger 66 via a domestic hot water supply line DHW and a cold water supply line CW. The domestic hot water supply line DHW is arranged for supplying tap water heated by the tap water heat exchange circuit 60 to the tap water circuit 61 . The cold water supply line CW is arranged for returning tap water from the tap water circuit 61 to be heated by the tap water heat exchange circuit 60. A hot water circulation supply line HWC is connected to the cold water supply line CW. The hot water circulation supply line HWC is arranged for maintaining a constantly circulating base flow of hot tap water from the tap water circuit 61 such that hot tap water is always available once the tap water circuit 61 is activated. The tap water inlet structure 53 may alternatively be called a hot tap water inlet structure. The tap water outlet structure 55 may alternatively be called a hot tap water outlet structure.

[0108] The buffer tank 51 further comprises a direct electric heater 56. The direct electric heater 56 may be useful to boost the temperature of the buffer fluid within the buffer tank 51 .

[0109] The buffer tank 51 further comprises a venting pipe 57. The purpose of the venting pipe 57 is to allow ejecting air which tend to accumulate inside the buffer tank 110 during use.

[0110] The heat pump arrangement 40 further comprises an expansion tank 81 . The expansion tank 81 is in fluid communication with both the radiator system 13 and with the buffer tank 51 and acts to compensate for the volume variations occurring in the buffer fluid as a result from variations in its temperature. The expansion tank typically comprises a membrane or flexible bladder (not shown) and is well known by the person skilled in the art.

[0111] The arrangement may further comprise temperature sensors 70, 71 , 72, 73, 74 for providing data as input for a control system (not shown).

[0112] As indicated in Fig. 1 , the buffer tank 51 , the switchable conduit system 3, and the tap water heat exchange circuit 60 may be provided inside a dedicated unit 50 for domestic heating. Said unit may be installed e.g. in apartments or houses to heat, and supply hot tap water to, thereto.

[0113] There are many deficiencies in the prior art solution described above. The structural parts are relatively complicated to manufacture on a grand scale due to the several inlets and outlets, the many separate modules, and the sometimes intricate conduit system. Furthermore, the temperature stratification within the tank is not always optimally controlled. The aim has therefore been to improve of the existing solution and provide an overall improved arrangement. According to the inventive concept of the disclosure this is met by improvements to the buffer tank 51 , an improved way of compensating for the volume variations occurring in the buffer fluid, a modularization of at least a part of the switchable conduit system, and an improved way of inputting heated water to the buffer tank.

[0114] Specifically, it has been an aim to provide improvements to maintaining the temperature stratification of the buffer fluid stored within the buffer tank 110. To this end, a method is provided which utilizes dual inlet connections to a buffer tank such as the buffer tank 110 disclosed herein.

[0115] The method is described in detail with reference to Fig. 12. To facilitate understanding of the method, the buffer tank 110 and the heat pump arrangement 1 of which it forms a part will first be described with reference to Figs 2, 3A, 3B, 3C, 4A and 4B, and a branching conduit module 600-1 , 600-2, 600-3, 600-4, 600-5, 600-6 will be described with reference to Figs 5A, 5B, 5C, and Figs 6 to 11 .

[0116] Figure 2 discloses a heat pump arrangement 1 which comprises a buffer tank 110 according to the inventive concept. The buffer tank 110 comprises a housing 111 which comprises a main housing portion 112 and at least one further housing portion 113a, 113b which together defines an interior housing volume 114 for accommodating a buffer fluid. The main housing portion 112 comprises at least one opening 103, and the at least one further housing portion 113a, 113b comprises at least one through-hole 104 (see Fig. 3A to 3C). To this end, the at least one further housing portion 113a, 113b is configured to mate with the at least one opening 103 of the main housing portion 112. As can be seen in Fig. 2, the main housing portion 112 constitutes the major part of the housing, whereas the at least one further housing portion 113a, 113b in the example embodiment constitutes a lid 113a, 113b. The housing 111 extends from a first end 115 to a second end 116. In the example embodiment, the first end 115 is a bottom end 115 and the second end 116 is a top end 116. The housing 111 is defined by a first wall 111a located at the first end 115, a second wall 111 b located at the second end 116, and a lateral wall 111c which extends between, and interconnects, the first wall 111a and the second wall 111 b. The at least one further housing portion 113a, 113b defines at least a part of the first wall 111a. In other words, the at least one further housing portion 113a, 113b is arranged as a bottom-mounted lid 113a, 113bto the main housing portion 112.

[0117] The main housing portion 112 comprises a flange portion 120 arranged at an interface between the main housing portion 112 and the at least one further housing portion 113a, 113b. In other now shown embodiments, the at least one further housing portion 113a, 113b may be two or more further housing portions 113a, 113b. For such embodiments, each further housing portion 113a, 113b may have an interface to the main housing portion 112 at which respective interface there may be provided with a respective flange portion 120. Thus, the buffer tank 110 may have more than one further housing portion 113a, 113b, and more than one flange portion 120. The flange portion 120 protrudes out from an outer surface 117 of the main housing portion 112 so as to define a guide for the associated further housing portion 113a, 113b.

[0118] The buffer tank 110 further comprises a plurality of buffer tank interaction structures 102. Each of the plurality of buffer tank interaction structures 102 are arranged in the at least one further housing portion 113a, 113b and protrudes therethrough via a respective one of the at least one through-hole 104. The plurality of buffer tank interaction structures 102 includes a heat pump inlet structure 151 and a heat pump outlet structure 200 configured to fluidly connect the buffer tank 110 to a heat pump 10 by connecting the heat pump inlet structure 151 and the heat pump outlet structure 200 to the switchable conduit system 3 by means of a heat pump inlet structure connection 151a and a heat pump outlet structure connection 200a, respectively. The plurality of buffer tank interaction structures 102 further includes include a tap water inlet structure 190 and a tap water outlet structure 160 configured to fluidly connect the buffer tank 110 to a tap water heat exchange circuit 11 by connecting the tap water inlet structure 190 and the tap water outlet structure 160 to the tap water circuit 61 by means of the tap water inlet structure connection 190a and the tap water outlet structure connection 160a.

[0119] The main housing portion 112 and the at least one further housing portion 113a, 113b are releasably attached to each other. As will be further discussed later, the provision of the plurality of buffer tank interaction structures 102 in the at least one further housing portion 113a, 113b allows simplifying manufacturing and assembling the buffer tank 110.

[0120] As readily appreciated by the person skilled in the art, these buffer tank interaction structures 102 have the same function as the features 52, 53, 54 and 55 in the prior art arrangement 40 for domestic heating described with reference to Fig. 1 .

[0121] To ensure that buffer fluid is supplied and retrieved at the appropriate level in the buffer tank 110, the plurality of buffer tank interaction structures 102 have different lengths. This allows maintaining the same fluid communication with the buffer tank 110 as for the prior art tank 51 even if all connections to the tank are situated in the at least one further housing portion 113a, 113b. As also illustrated in Fig. 2, the interior housing volume 114 of the housing 111 has a first volume portion 114a and a second volume portion 114b which are spaced from each other within the housing 111. The first volume portion 114a is also termed herein the bottom volume portion 114a, and the second volume portion 114b is also termed herein the top volume portion 114b. In other words, the first volume portion 114a of the interior housing volume 114 is defined, as seen along a longitudinal direction L (see Fig. 2), in a lowermost part of the interior housing volume 114 and the second volume portion 114b of the interior housing volume 114 is defined, as seen along the longitudinal direction L, in an uppermost part of the interior housing volume 114. As readily appreciated by the person skilled in the art, at equilibrium the temperature of the second (top) volume portion 114b will he higher than the temperature of the first (bottom) volume portion 114a.

[0122] Retrieving and supplying buffer fluid at an appropriate vertical position within the buffer tank 10 is beneficial to maintain a uniform thermal stratification within the buffer tank 110. Thermal stratification is the process where a liquid will naturally strive to be vertically distributed such that the density decreases as function of vertical position. Since a buffer fluid, such as e.g., water, has a density which monotonically decreases with increasing buffer fluid temperature in the operating temperature region of the buffer tank 110 (it is noted that no buffer tank storing water is run close to the inflection point at 4 degrees Celsius), the temperature stratification will ensure that the buffer fluid having the highest temperatures are located that the top end of the buffer tank 110, and that the buffer fluid having the lowest temperatures are located at the bottom end of the buffer tank 110.

[0123] The heat pump 10 supplies heated fluid to the buffer tank 110 via the heat pump inlet structure 151. To make sure the temperature stratification inside the buffer tank 110 is maintained, the heat pump inlet structure 151 is fluidly connected to an exterior 118 of the housing with the second volume portion 114b thus ensuring the heated fluid will be introduced at the top end 116 of the buffer tank 110. The fluid retrieved from the buffer tank 110 to be heated by the heat pump 10 is retrieved from the heat pump outlet structure 200. To make sure that the fluid retrieved from the buffer tank 110 is from the lowest temperatures, the heat pump outlet structure 200 fluidly connects the exterior 118 of the housing with the first (bottom) volume portion 114a. For the tap water heat exchange circuit 60, the tap water inlet structure 190 fluidly connects the exterior 118 of the housing with the first volume portion 114a and the tap water outlet structure 160 fluidly connects the exterior 118 of the housing with the second volume portion 114b. This allows retrieving buffer fluid from the second volume portion 114b having the highest temperatures to the heat exchanger 66 to efficiently transfer heat from said buffer fluid to the tap water circulated through the heat exchanger 66. The thereby cooled buffer fluid may then be returned to the buffer tank 110 to the first volume portion 114a at the bottom end 115 of the buffer tank 110 where the temperature of the buffer fluid is at its lowest.

[0124] As can be seen in Fig. 2, the plurality of buffer tank interaction structures 102 further comprises one or more further fluid connecting structures 150, 152. In Fig. 2, these are not connected to any conduits and are therefore not used. Disabling the one or more further fluid connecting structures 150, 152 may be achieved by plugging the connections 150a and 152a, respectively. Although comprised in the buffer tank 110, it should thus be understood that not all of the one or more further fluid connecting structures 150, 152 are required for the disclosed method, and that the buffer tank according to the disclosure may alternatively be provided with only one further fluid connecting structure. This will be evident later when the disclosed method is described. The one or more further fluid connecting structures 150, 152 will be further discussed later with reference to alternative embodiments. However, it may be noted already now that the heat pump inlet structure 151 mouths at the highest vertical position within the buffer tank 110, in the second volume portion 114b. The heat pump outlet structure 200 mouths at the lowest vertical position within the buffer tank 110, in the first volume portion 114a. The one or more further fluid connecting structures 150, 152 mouths at a central part of the buffer tank 110, in a third volume portion 114c which is located between the first 114a and second 114b volume portions. Moreover, fluid connecting structures 150 mouths at a higher vertical position within the third volume portion 114 than fluid connecting structures 152.

[0125] The plurality of buffer tank interaction structures 102 may optionally further comprise a direct electric heater 180. The direct electric heater 180 may be useful to boost the temperature of the buffer fluid within the buffer tank 110. The plurality of buffer tank interaction structures 102 may optionally further comprises a flexible bladder 170. By disposing a flexible bladder 170 within the buffer tank 110, the volume variations occurring in the buffer fluid as a result from variations in its temperature may be compensated without the need for an externally arranged expansion tank, such as the expansion tank 81 of the prior art solution (see Fig. 1 ). The flexible bladder 170 will be further discussed with reference to Figs 4A and 4B.

[0126] The plurality of buffer tank interaction structures 102 may optionally further comprise one or more temperature sensors 210a and / or one or more pressure sensors 210b. By disposing the active sensing element on an extended probe as illustrated in Fig. 2, the temperature may be selectively determined at any height inside the buffer tank 110.

[0127] The plurality of buffer tank interaction structures 102 may optionally further comprise a venting pipe 140. The venting pipe 140 comprises a tube which extends from the at least one further housing portion 113a, 113b along the longitudinal direction L all the way up to the second wall 111b, also called the top wall 111 b. A valve 141 is disposed at the bottom end 115 within the at least one further housing portion 113a, 113b. The purpose of the venting pipe 140 is to allow ejecting air which tend to accumulate inside the buffer tank 110 during use.

[0128] As evident from Fig. 2, the plurality of buffer tank interaction structures 102 extends through the at least one further housing portion 113a, 113b from an exterior 118 of the housing to an interior 119 of the housing. One or more of the plurality of buffer tank interaction structures 102 may be fixedly attached to the at least one further housing portion 113a, 113b, for example by welding, or soldering. Alternatively, one or more of the plurality of buffer tank interaction structures 102 may be releasably attached to the at least one further housing portion 113a, 113b. Various conceivable embodiments for a releasable attachment of the buffer tank interaction structures 102 will be discussed later with reference to Figs 3A to 3C.

[0129] As can be seen in Fig. 2, all buffer tank interaction structures 102 of a further housing portion 113a, 113b are aligned substantially in parallel with each other so as to allow mounting said all buffer tank interaction structures 102 to the further housing portion 113a, 113b in one single operation.

[0130] The example embodiment illustrated in Fig. 2 have two further housing portions 113a, 113b, termed herein as the first further housing portion 113a and the second further housing portion 113b, respectively. The first further housing portion 113a is releasably attached to the second further housing portion 113b and arranged within the same such that it is not directly attached to the main housing portion 112. At least one of the plurality of buffer tank interaction structures 102 is provided in the first further housing portion 113a. In the example embodiment, the flexible bladder 170 is provided in the first further housing portion 113a. This may be beneficial as it allows an easier replacement of the flexible bladder 170.

[0131] Fig 3A to 3C illustrates three example embodiments of the at least one further housing portion 113, 113’, 113” and a buffer tank interaction structure 102, 102’, 102”. In Fig. 3A, the further housing portion 113 comprises a plate 213 which is reinforced by a steel ring 214. The plate 213 and steel ring 214 may be welded or soldered together. Alternatively, they may be attached to each other releasably, e.g. by bolting. The buffer tank interaction structure 102, which may be any kind of buffer tank interaction structure 102 disclosed herein, is for this example embodiment releasably attached to the further housing portion 113 by a threaded engagement. The further housing portion 113 is provided with a through-hole 104 having an inner thread. The buffer tank interaction structure 102 is provided with an outer thread which mainly engages the inner thread of the through-hole 104. The sealing ring 215 provides a watertight seal to the buffer tank 110. Fig. 3B illustrates an alternative example embodiment. The further housing portion 113’ is provided with a through-hole 104’. Here the further housing portion 113’ is made from a thicker element than the plate 213, thus not requiring a reinforcing steel ring. The buffer tank interaction structure 102’ is releasably attached to the further housing portion 113’ by means of bolts 217. The sealing ring 215’ provides a watertight seal to the buffer tank 110. Fig. 3C illustrates an alternative example embodiment. The further housing portion 113” is similar to the further housing portion 113’ in that it is made from a thicker element than the plate 213, thus also not requiring a reinforcing steel ring. However, the further housing portion 113” is provided with a recess 216 which allows the buffer tank interaction structure 102” to protrude into the same to provide a more uniform interface. As for the example embodiment in Fig. 3C, the buffer tank interaction structure 102” is releasably attached to the further housing portion 113’ in through-hole 104” by means of a threaded engagement. The sealing ring 215” provides a watertight seal to the buffer tank 110.

[0132] The buffer tank 110 allows for simplified manufacturing and assembling. A method for manufacturing the buffer tank 110 may comprise arranging a plurality of buffer tank interaction structures 102 in the at least one further housing portion 113a, 113b such that the plurality of buffer tank interaction structures 102 covers the at least one through-hole 104 in the at least one further housing portion 113a, 113b; and attaching the at least one further housing portion 113a, 113b to the main housing portion 112 such that the at least one further housing portion 113a, 113b covers the at least one opening 103 in the main housing portion 112 thereby forming a closed housing for accommodating a buffer fluid. The method steps may be performed in different order. One embodiment of the method involves arranging the plurality of buffer tank interaction structures 102 in the at least one further housing portion 113a, 113b so as to provide an assembly as a first preparatory step. Then, as a second subsequent step, the method involves arranging said assembly into the at least one opening 103. The method may alternatively be carried out in the other order, i.e. to first attaching the at least one further housing portion 113a, 113b to the main housing portion 112 such that the at least one further housing portion 113a, 113b covers the at least one opening 103 in the main housing portion 112 thereby forming a closed housing for accommodating a buffer fluid, and then, as a second subsequent step, arranging the plurality of buffer tank interaction structures 102 in the at least one further housing portion 113a, 113b.

[0133] The flexible bladder 170 will now be described in detail with reference to Figs 4A and 4B. The flexible bladder 170 defines an interior bladder volume 171 which is filled with a gas, such as e.g. air, Hydrogen or Helium. As illustrated in Fig. 2, the flexible bladder 170 is configured to be arranged inside the housing 111 such that an outside outer surface 172 of the flexible bladder 170 is in contact with the buffer fluid accommodated in the housing 111. This allows the flexible bladder 170 to adapt its interior bladder volume 171 for pressure variations in the buffer fluid. The flexible bladder 170 is made of a resilient material, such as natural rubber, silicon rubber, polyurethane, thermoplastic elastomers (TPE), polyethene (PE), Polyvinylchloride (PVC), or the like. The flexible bladder 170 is releasably attached to the housing 111. This may be achieved for example by a threaded engagement as illustrated in Fig. 4B, where the flexible bladder 170 is sealingly arranged inside a mount 174 which in turn is configured to be threadedly attached to the at least one further housing portion 113a, 113b in the same manner as previously illustrated in Fig. 3A or 3C. Sealing ring 215 ensures fluid sealing of the buffer tank 110. Other attachments are conceivable. The flexible bladder 170 extends through the housing 111 from the exterior 118 of the housing 111 to the interior 119 of the housing 111. The flexible bladder 170 comprises a valve 173 for allowing exchanging the gas in its interior bladder volume 171. The flexible bladder 170 is arranged in the buffer tank 110 such that the valve 173 is accessible from an exterior outside of the housing 111 (see also Fig. 2). The interior bladder volume 171 of the flexible bladder 170 may amount to 1-15%, preferably 2-10%, more preferably 3-6%, of the interior housing volume 114. The flexible bladder 170 is preferably arranged in the first (lower) volume portion 114a. This may be beneficial, as the temperature of the buffer fluid within the buffer tank 110 is lower in the first volume portion 114a than higher up in the buffer tank 110, which may reduce material fatigue on the flexible membrane 170, thereby prolonging its expected lifetime. As described earlier, and illustrated in Fig. 2, the flexible bladder 170 is advantageously arranged in a first further housing portion 113a which, in turn, is arranged inside a second further housing portion 113b. The second further housing portion 113b may then be arranged in the opening 103 of the main housing portion 112. In other words, the first further housing portion 113a is releasably attached to the second further housing portion 113b and arranged within the same such that it is not directly attached to the main housing portion 112, and the flexible bladder 170 is provided in the first further housing portion 113a.

[0134] The switchable conduit system 3 as illustrated in Fig. 2 can tend to get quite complex, especially for example embodiments having one or more further fluid connecting structures 150, 152 in addition to heat pump inlet structure 151 and heat pump outlet structure 200. To this end, there is provided a branching conduit module 600-1 , 600-2, 600-3, 600-4, 600-5, 600- 6 which is configured to be attachable to a buffer tank, such as but not limited to the buffer tank 110 described earlier. Several alternative embodiments of the branching conduit module 600-1 , 600-2, 600-3, 600-4, 600-5, 600-6 will now be described with reference to Figs 5A, to 5C and Figs 6 to 11 . Although described in detail herein, it should be understood that the provision of the branching conduit module 600-1 , 600-2, 600-3, 600-4, 600-5, 600-6 is optional, and the disclosed method is equally possible to perform on heat pump arrangements which does not have the same. This will be further discussed with reference to Fig. 12.

[0135] Common features for the branching conduit module 600-1 , 600-2, 600- 3, 600-4, 600-5, 600-6 will now be described with reference to Figs 5A to 5C which illustrates the first embodiment 600-1 . The branching conduit module 600-1 comprises a housing 601 which may be made of one or more of brass, copper, and plastic.

[0136] The housing 601 comprises a buffer tank interface portion 602-1 configured to abut the buffer tank 110. The buffer tank interface portion 602-1 comprises a fastening system 603 for releasably fastening the branching conduit module 600-1 to the buffer tank 110. Several alternative fastening systems are conceivable. Fig 5C illustrates one of these, a bolt and screw arrangement.

[0137] The branching conduit module 600-1 further comprises and inlet 400 configured to fluidly connect the branching conduit module 600-1 to a heat pump 10 for receiving heated fluid therefrom, buffer tank connection 151 b configured to fluidly connect the branching conduit module 600-1 to the buffer tank 110, and outlet 430 configured to fluidly connect the branching conduit module 600-1 to a radiator system 13 for supplying heated fluid thereto. The buffer tank connection 151 b is arranged in the buffer tank interface portion 602. This allows the buffer tank connection 151 b to fluidly connect to the buffer tank 110 as will be described in detail below. As illustrated in Fig. 5C, the inlet 400, the outlet 430, and the buffer tank connection 151 b may each be structured and arranged to receive a connection, such as the heat pump inlet structure connection 151a of the buffer tank 110 (see Fig. 5C), and not shown connecting interfaces to the switchable conduit system 3. Once received, the branching conduit module 600-1 will sealingly engage with said connection. One way of providing such a sealing engagement is to provide sealing rings 105 on the connector. This is illustrated in Fig 5C for heat pump inlet structure connection 151a. Alternatively, sealing rings may be provided in the buffer tank connection 151 b of the branching conduit module 600-1 . The person skilled in the art realizes that there are many alternative ways to sealingly connect a conduit system for transferring a fluid to and from the branching conduit module 600-1 , and therefore this will not be described in detail herein. In Fig. 5C, the branching conduit module 600-1 is illustrated together with previously described at least one further housing portion 113b. The branching conduit module 600-1 , 600-2, 600-3, 600-4, 600-5, 600-6 should however not be construed as limited to buffer tanks having more than one housing portion. The branching conduit module 600-1 further comprises an internal conduit circuit 604-1 configured to fluidly connect the inlet 400, via junction J1 , to the buffer tank connection 151 b and to the outlet 430. This is best illustrated in Figs 5B and 5C.

[0138] Several alternative example embodiments of the branching conduit module will now be described. Each of these alternative example embodiments have the features just described for the branching conduit module 600-1 . In addition, each of these embodiments have further features. Like reference characters refer to like elements throughout Figs 5A to 5C and Figs 6 to 11 . To simplify understanding of how the branching conduit module 600-1 , 600-2, 600-3, 600-4, 600-5, 600-6 can be used in relation to the buffer tank 110, Figs 6 to 11 each illustrate the branching conduit module 600-1 , 600-2, 600-3, 600-4, 600-5, 600-6 schematically together with the buffer tank 110, the switchable conduit system 3, the heat pump 10 and the radiator system 13. The buffer tank 110 is the same as illustrated in Fig. 2, but has been compressed in the vertical dimension to more clearly illustrate the branching conduit module 600-1 , 600-2, 600-3, 600-4, 600-5, 600-6.

[0139] Figure 6 illustrates a buffer tank assembly 2 for the heat pump assembly 1 which has already been described with reference to Fig. 2. The buffer tank assembly 2 comprises the branching conduit module 600-1 and the housing 601 which have already been described with reference to Figs 5A to 5C. As indicated in the schematic figure, the branching conduit module 600-1 is fluidly connected to the buffer tank 110 via its buffer tank connection 151 b and heat pump inlet structure 151 of the buffer tank 110. The buffer tank 110 comprises further inlets and outlets which are not connected to the branching conduit module 600-1. Specifically, fluid connecting structure 152 and fluid connecting structure 150 are disabled in Fig. 6. The fluid connecting structure 152 may be referred to as a heat pump inlet structure. As described earlier, this can be achieved by plugging connections 150a and 152a of the same. Alternatively, a buffer tank which does not comprise heat pump inlet structure 152 and fluid connecting structure 150 can be used. The branching conduit module 600-1 is further fluidly connected, via its inlet 400 and outlet 430, to the switchable conduit system 3 which connects to the heat pump 10 and the radiator system 13. As readily appreciated by the person skilled in the art, by switching valve 550 to allow fluid flow from connection point 550a to connection point 550c but not from connection point 550b to connection point 550c, buffer fluid will be circulated by means of pump 450 between the heat pump 10 and the buffer tank 110 so as to heat the buffer fluid within the buffer tank 110.

[0140] Figure 7 illustrates the branching conduit module 600-2 according to an alternative example embodiment. The branching conduit module 600-2 is similar to the branching conduit module 600-1 , but differs from the same by the internal conduit circuit 604-2 further comprising circulation pump 450. By providing the circulation pump 450 inside the branching conduit module 600- 2, the assembly may be further simplified and modularized, since the switchable conduit system 3 does not have to include a circulation pump. Since the branching conduit module 600-2 has the same interface in relation to the buffer tank 110 as the branching conduit module 600-1 , the buffer tank interface portion 602-2 is the same as the buffer tank interface portion 602-1 . As readily appreciated by the person skilled in the art, the provision of the circulation pump 450 inside the branching conduit module 600-2 requires electrical connections for power and control. Such electrical connections are not explicitly illustrated herein. The person skilled in the art is well aware of how to provide such electrical connections.

[0141] Figure 8 illustrates the branching conduit module 600-3 according to an alternative example embodiment. The branching conduit module 600-3 is similar to the branching conduit module 600-2, but differs from the same by the internal conduit circuit 604-3 further comprising controllable valve 710. As can be seen in Fig. 8, the controllable valve 710 is arranged at junction J1 of the internal conduit circuit 604-3 such that connection point 710a is fluidly connected to the inlet 400 via the circulation pump 450, the connection point 710b is fluidly connected to first buffer tank connection 151 b and the connection point 710c is fluidly connected to the outlet 430. Although the controllable valve 710 may not be essential for controlling the fluid flow between the heat pump 10, the radiator system 13 and the buffer tank 110, controllable valve 710 may be beneficial since it, together with controllable valve 550, allows to completely disable fluid flow between the radiator system 13, the buffer tank 110, and the heat pump 10, which may be useful e.g. during system maintenance. Since the branching conduit module 600-3 has the same interface in relation to the buffer tank 110 as the branching conduit module 600-2, the buffer tank interface portion 602-3 is the same as the buffer tank interface portion 602-2. As readily appreciated by the person skilled in the art, the provision of the controllable valve 710 inside the branching conduit module 600-3 requires electrical connections for power and control. Such electrical connections are not explicitly illustrated herein. The person skilled in the art is well aware of how to provide such electrical connections.

[0142] Figure 9 illustrates the branching conduit module 600-4 according to an alternative example embodiment. The branching conduit module 600-4 is similar to the branching conduit module 600-2, but differs from the same by the internal conduit circuit 604-4 further comprising a further buffer tank connection 152b configured to fluidly connect the branching conduit module 600-4 to the buffer tank 110 via heat pump inlet structure 152 of the buffer tank 110. The branching conduit module 600-4 further differs from the branching conduit module 600-2 in that it further comprises controllable valve 500. As illustrated in Fig. 9, the controllable valve 500 is structured and arranged within the internal conduit circuit 604-4 of the branching conduit module 600-4 to allow heated fluid received via junction J1 to be selectively branched to buffer tank connection 151 b and / or to buffer tank connection 152b. To this end, the controllable valve 500 has a connection point 500a which is fluidly connected to buffer tank connection 152b, a connection point 500c which is fluidly connected to buffer tank connection 151 b, and a connection point 500b which is fluidly connected to both inlet 400 and outlet 430 of the branching conduit module 600-4 via junction J1 . The controllable valve 500 may, optionally, be a thermostat comprising temperature sensing means 490 for allowing adjusting the selective branching of the heated fluid to buffer tank connection 151 b and / or to buffer tank connection 152b based on a temperature of the heated fluid. The sensing means 490 may be any sensing means known in the art which is capable of temperature-controlling the controllable valve 500. The provision of dual connections to the buffer tank 110 and the controllable valve 500 being a thermostat may be beneficial as is allows improving the fluid flow configuration to and from the buffer tank 110. This will be apparent later where such configurations and methods related thereto will be further described. As for buffer tank connection 151 b, buffer tank connection 152b is arranged in the buffer tank interface portion 602-4, which thus differs from the buffer tank interface portion 602-1 , 602-2 and 602- 3 described earlier in that it provides dual fluid connections to the buffer tank 110.

[0143] Figure 10 illustrates the branching conduit module 600-5 according to an alternative example embodiment. The branching conduit module 600-5 is similar to the branching conduit module 600-4, but differs from the same by the internal conduit circuit 604-5 further comprising a further buffer tank connection 150b configured to fluidly connect the branching conduit module 600-5 to the buffer tank 110 via fluid connecting structure 150 of the buffer tank 110. The buffer tank connection 150b is arranged in the buffer tank interface portion 602-5. The buffer tank connection 150b is fluidly connected to the inlet 400 via junction J4 which is located between junction J1 and outlet 430. The branching conduit module 600-5 further differs from the branching conduit module 600-4 in that it further comprises valve 460. Valve 460 may be a controllable valve, but may alternatively be a passive valve, such as a check valve. As illustrated in Fig. 10, valve 460 is located between buffer tank connection 150 and junction J4, thereby allowing controlling the flow through buffer tank connection 150b. The branching conduit module 600-5 further differs from the branching conduit module 600-4 in that the branching conduit module 600-5 further comprises controllable valve 710 (see also Fig. 8). As can be seen in Fig. 10, the controllable valve 710 is arranged at junction J1 of the internal conduit circuit 604-5 such that connection point 710a is fluidly connected to the inlet 400 via the circulation pump 450, the connection point 710b is fluidly connected to connection point 500b and connection point 710c is fluidly connected to the outlet 430. The provision of a third connection (i.e. 150b) to the buffer tank 110 may be beneficial as is allows further improving the fluid flow configuration to and from the buffer tank 110. This will be apparent later where such configurations and methods related thereto will be further described.

[0144] Figure 11 illustrates the branching conduit module 600-6 according to an alternative example embodiment. The branching conduit module 600-6 is similar to the branching conduit module 600-4, but differs from the same by the buffer tank connection 152b, in the internal conduit circuit 604-6, being further fluidly connected to the inlet 400 via junction J2 which is located upstream of junction J1 , and in that the branching conduit module 600-6 further comprises controllable valve 410 located at junction J2 and in that the controllable valve 410 is structured and arranged to allow heated fluid received via the inlet 400 to be selectively branched to junction J1 (i.e. via inlet 410a to outlet 410b) and / or to buffer tank connection 152b (i.e. via inlet 410a to outlet 410c). The buffer tank connection 152b is arranged in the buffer tank interface portion 602-6. The branching conduit module 600-6 further differs from the branching conduit module 600-4 in that buffer tank connection 152b is fluidly connected to controllable valve 500 and to controllable valve 410 via junction J3, and in that the branching conduit module 600-6 further comprises a check valve 480 arranged between controllable valve 500 and junction J3. The provision of controllable valve 410 and its connection to the junction J3 may be beneficial as is allows further improving the fluid flow configuration to and from the buffer tank 110. This will be apparent later where such configurations and methods related thereto will be further described. Although not illustrated, it should be noted that all illustrated embodiments of Figs 6-11 may comprise the fastening system 603 as illustrated in connection with Figs 5A-5C.

[0145] A method for controlling input of a heated fluid received from a heat pump 10 to a buffer tank 110 of a heat pump arrangement 1 ’ will now be described with reference to Fig. 12, which schematically illustrates the buffer tank 110 connected to a switchable conduit system 3’ according to an example embodiment. The person skilled in the art realizes that the flow scheme illustrated in Fig. 12 is identical to the flow scheme illustrated in Fig. 9 when describing the branching conduit module 600-4. Thus, the disclosed method requires use of at least one further fluid connecting structure (more specifically: the fluid connection structure 152) for providing, altogether, two inlets to the buffer tank 110 for buffer fluid supplied by the heat pump 10. That said, it should be understood that the disclosed method is not limited to the specific buffer tank 110 described herein. The method may equally well be operated on a buffer tank of the prior art as long as it provides certain fluid connections to certain volumes within the buffer tank. This will be further described in what follows. Thus, the method may be carried out when equipping a buffer tank 110 with branching conduit module 600-4 (or alternatively either one of branching conduit modules 600-5 and 600-6). However, the method as such is not limited to embodiments having the branching conduit module 600-4, or any branching conduit module. This will be apparent in what follows.

[0146] The method requires a buffer tank 110 which comprises a housing 111 defining an interior housing volume 114 for accommodating a buffer fluid, said interior housing volume 114 having a first volume portion 114a which connects with a bottom end 115 of the buffer tank 110, a second volume portion 114b which connects with a top end 116 of the buffer tank 110, and a third volume portion 114c which is located between the first 114a and second 114b volume portions. The buffer tank 110 further comprises a first heat pump inlet structure 151 which is fluidly connected to the second volume portion 114b, a second heat pump inlet structure 152 which is fluidly connected to the third volume portion 114c, a heat pump outlet structure 200 which is fluidly connected to the first volume portion 114a, and a fluid control circuit 605 which is fluidly connected to the first heat pump inlet structure 151 and the second heat pump inlet structure 152 and configured to control a fluid passage to the first heat pump inlet structure 151 and a fluid passage to the second heat pump inlet structure 152.

[0147] The method comprises determining a temperature of the heated fluid to be input to the buffer tank 110; determining, based on said measured temperature, a control setting for the fluid control circuit 605; and configuring the fluid control circuit 605 to input the heated fluid to the buffer tank 110 based on said determined control setting.

[0148] The control circuit 605 comprises a controllable valve 500 which is structured and arranged within the control circuit 605 to allow heated fluid received from the heat pump 10 to be selectively branched to the first heat pump inlet structure 151 and / or to the second heat pump inlet structure 152. In the example embodiment illustrated in Fig. 12, the fluid control circuit 605 includes controllable valve 500, which is a shunt valve. As such, the controllable valve 500 allows for simultaneously branching the heated fluid entering the valve input 500b to both connection point 500a and 500c at any flow ratio. The controllable valve 500 may alternatively be operated to selectively open one branch (i.e. branch 500b-500a, or branch 500b-500c). The controllable valve 500 may be a thermostat comprising sensing means 490 for allowing adjusting said selective branching of the heated fluid to the first heat pump inlet structure 151 and / or to the second heat pump inlet structure 152 based on a temperature of the heated fluid. When operating the valve 500 selectively to open only one branch at a time, the step of determining the control setting comprises comparing the measured temperature with a predefined threshold temperature, wherein, upon the measured temperature being higher than the predefined threshold temperature, the control setting comprises instructions to maintain fluid passage through the first heat pump inlet structure 151 and to prevent fluid passage through the second heat pump inlet structure 152, and wherein, upon the measured temperature being lower than the predefined threshold temperature, the control setting comprises instructions to prevent fluid passage through the first heat pump inlet structure 151 and to maintain fluid passage through the second heat pump inlet structure 152.

[0149] When operating the valve 500 selectively to simultaneously branching the heated fluid entering the valve input 500b to both connection point 500a and 500c at any flow ratio, the step of determining the control setting may comprise determining, based on the measured temperature, a fluid passage distribution between the first heat pump inlet structure 151 and the second heat pump inlet structure 152; and wherein the control setting comprises instructions for the fluid control circuit 605 to control the input of the heated fluid to the buffer tank 110 via the first heat pump inlet structure 151 and the second heat pump inlet structure 152 according to said determined fluid passage distribution.

[0150] The method may be advantageous as it allows to input heated fluid at different positions in the buffer tank 110 dependent on its temperature. This allows to better maintain the temperature stratification present within the buffer tank 110 where the buffer fluid at the top end top end 116 (or more generally: in the second volume portion 114b) of the buffer tank 110 is several degrees hotter than the buffer fluid present at the bottom end 115 of the tank (or more generally: in the first volume portion 114a).

[0151] Since the overall temperature in the buffer tank 110 may differ dependent e.g. on the degree of use for tap water heating, the method may further include determining an internal temperature of the buffer fluid within the buffer tank 110, and determine said control setting for the fluid control circuit 605 based on both the measured temperature of the heated fluid to be input to the buffer tank 110 and on said internal temperature of the buffer fluid within the buffer tank 110. The internal temperature may e.g. be determined using the one or more temperature sensors 210a.

[0152] The branching conduit module 600-5 and 600-6 illustrated in Figs 10 and 11 has an advantage over the previously described embodiments 600-1 to 600-4, namely in that they allow using the buffer tank 110 as a heat reservoir to heat the buffer fluid within the heat pump arrangement 1 ,1’. The conventional heat source in the heat pump arrangement 1 ,1’ is the heat pump 10. However, there may be occasions where it is beneficial to, alternatively or additionally, use the buffer tank 110 as heat source. In other words, the buffer tank 110 may act as a thermal battery. Such occasions may be for example when electricity process peaks typically during mornings and afternoons. The heat pump arrangement 1,1’ may then be configured to operate with the heat pump 10 turned off, thus merely circulating the buffer fluid through its heat exchanger without the buffer fluid retrieving any energy therefrom. Instead, the internal conduit circuit 604-5, 604-6 may be configured to allow leading buffer fluid into the buffer tank 110 at a lowermost position therein, and retrieving hot buffer fluid from the buffer tank 110 from an uppermost position therein. The retrieved buffer fluid will then have a significantly higher temperature than the buffer fluid entering the buffer tank. The buffer fluid retrieved from the buffer tank may then be passed to the radiator system 13 for providing domestic heating.

[0153] For the branching conduit module 600-5 of Fig. 10, the above described method may operate as follows: The heat pump 10 is first turned off. The controllable valve 710 is configured to allow fluid to pass via connection point 710a and connection point 710b and then further via connection point 500b and connection point 500a to enter the buffer tank 110 via heat pump inlet structure 152 which mouths in the first (bottom) volume portion 114a of the interior housing volume 114. By controlling valve 460, buffer fluid may then be allowed to exit the buffer tank 110 through fluid connecting structure 150 which retrieves fluid from the first (upper) volume portion 114a of the interior housing volume 114. By controlling the outlet 710c of the shunt valve 710, the amount of buffer fluid that is retrieved from the buffer tank 110 may be regulated. Remaining buffer fluid is allowed to bypass the buffer tank 110 via passage 710a-710c of valve 710. During such operation, inlet 550a of valve 550 is typically closed and buffer fluid are only passing valve 550 via passage 550b-550c.

[0154] For the branching conduit module 600-6 of Fig. 11 , the above described method may operate as follows: The heat pump 10 is first turned off. The controllable valve 410 is configured to allow fluid to pass via connection point 410a and connection point 410c to enter the buffer tank 110 via heat pump inlet structure 152 which mouths in the first (bottom) volume portion 114a of the interior housing volume 114. By controlling valve 460, buffer fluid may be prevented to exit the buffer tank 110 through fluid connecting structure 150 which is thus disabled. Instead, buffer fluid is retrieved from the first (upper) volume portion 114a of the interior housing volume 114 via heat pump inlet structure 151 , which thus is used backwards (structure 151 is an inlet as default but is here used as an outlet). The retrieved buffer fluid is then allowed to pass valve 500 through via connection 500c-500b and passed to the radiator system 13 via outlet 430. By controlling the outlet 410b of the valve 410, the amount of buffer fluid that is retrieved from the buffer tank 110 may be regulated. Remaining buffer fluid is allowed to bypass the buffer tank 110 via passage 41 Oa-410b of valve 410. During such operation, connection point 550a of valve 550 is typically closed and buffer fluid are only passing valve 550 via passage 550b-550c.

[0155] As detailed above, this allows to retrieve buffer fluid from the second (upper) volume portion 114b and return buffer fluid to the first (lower) volume portion 114a. In order for such thermal battery operation to be efficient, it may be required to boost the temperature of the buffer fluid in the buffer tank 110 to temperatures higher than in conventional buffer tanks of the prior art. It may also be required to manufacture the buffer tank 110 to withstand such temperatures. When used as a thermal battery, the buffer tank 110, instead of storing fluid with up to 55-60 degrees Celsius, as is needed for tap water heating, the buffer tank 110 may have to be designed for storing fluid of temperature up to 70-90 degrees Celsius. The excess heat (above 60 degrees) may be stored in cases when there is a surplus of electric energy in the electric grid associated to the heat pump arrangement 1 , T (i.e. the electric grid the heat pump 10 is connected to), and therefore electricity may be relative cheap.

[0156] The example embodiment of Fig. 11 may alternatively be used for defrosting the heat pump 10, an operation which is required for embodiments where the heat pump 10 is an air-liquid heat pump. In such heat pumps, a 4- way switching valve will change the evaporator to becoming a condenser and vice versa which effectively turns the heat cycle backwards, transferring heat from, instead of to, the switchable conduit system 3. This heat can be used to defrost the air-liquid heat exchanger which is typically arranged in a unit outside the building. The defrosting also makes use of the buffer tank 110 as a thermal reservoir for providing energy to defrost the air-liquid heat exchanger. However, the energy required for defrosting is less, and therefore it may be beneficial to not retrieve the buffer fluid via heat pump inlet structure 151 which mouths at the second (upper) volume portion 114b of the interior housing volume 114. Instead, buffer fluid is retrieved via fluid connecting structure 150 which mouths at the third volume portion 114c which is located at a lower position within the interior housing volume 114. By deliberately retrieving buffer fluid a bit down in the buffer tank 110, the buffer fluid with highest temperatures is allowed to remain relatively unaffected in the second volume portion 114b at the very top of the interior housing volume 114, thus allowing an efficient heating of the tap water also during defrosting. Once buffer fluid has passed the heat pump 10 and transferred heat thereto for allowing defrosting, the buffer fluid will return to the branching conduit module 600-6 and valve 410 is configured to allow passage of buffer fluid via connections 410a-410c while preventing passage via connections 410a-410b, valve 480 is closed, thus allowing the buffer fluid to return to the buffer tank 110 through heat pump inlet structure 152. Thus, buffer fluid will be returned to the same volume portion from which it was retrieved, namely the third volume portion 114c, thus not significantly affecting the temperature of the second volume portion 114b.

[0157] The person skilled in the art realizes that the present disclosure 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. Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed from a study of the drawings, the disclosure, and the appended claims.

Claims

CLAIMS1 . A method for controlling input of a heated fluid received from a heat pump (10) to a buffer tank (110) of a heat pump arrangement (1 ), wherein the buffer tank (110) comprises a housing (111 ) defining an interior housing volume (114) for accommodating a buffer fluid, said interior housing volume (114) having a first volume portion (114a) which connects with a bottom end (115) of the buffer tank (110), a second volume portion (114b) which connects with a top end (116) of the buffer tank (110), and a third volume portion (114c) which is located between the first (114a) and second (114b) volume portions, said buffer tank (110) further comprising: a first heat pump inlet structure (151 ) which is fluidly connected to the second volume portion (114b), a second heat pump inlet structure (152) which is fluidly connected to the third volume portion (114c), a heat pump outlet structure (200) which is fluidly connected to the first volume portion (114a), and a fluid control circuit (605) which is fluidly connected to said first heat pump inlet structure (151 ) and said second heat pump inlet structure (152) and configured to control a fluid passage to the first heat pump inlet structure (151 ) and a fluid passage to the second heat pump inlet structure (152), said method comprising: determining a temperature of the heated fluid to be input to the buffer tank (110); determining, based on said measured temperature, a control setting for the fluid control circuit (605); and configure the fluid control circuit (605) to input the heated fluid to the buffer tank (110) based on said determined control setting.

2. The method according to claim 1 , wherein the step of determining the control setting comprises: comparing the measured temperature with a predefined threshold temperature;wherein, upon the measured temperature being higher than the predefined threshold temperature, the control setting comprises instructions to maintain fluid passage through the first heat pump inlet structure (151) and to prevent fluid passage through the second heat pump inlet structure (152); and wherein, upon the measured temperature being lower than the predefined threshold temperature, the control setting comprises instructions to prevent fluid passage through the first heat pump inlet structure (151) and to maintain fluid passage through the second heat pump inlet structure (152).

3. The method according to claim 1 , wherein the step of determining the control setting comprises: determining, based on the measured temperature, a fluid passage distribution between the first heat pump inlet structure (151 ) and the second heat pump inlet structure (152); and wherein the control setting comprises instructions for the fluid control circuit (605) to control the input of the heated fluid to the buffer tank (110) via the first heat pump inlet structure (151 ) and the second heat pump inlet structure (152) according to said determined fluid passage distribution.

4. The method according to any one of claim 1 to 3, further comprising: determining an internal temperature of the buffer fluid within the buffer tank (110); and wherein the step of determining a control setting for the fluid control circuit (605) comprises determining said control setting based on both the measured temperature of the heated fluid to be input to the buffer tank (110) and on said internal temperature of the buffer fluid within the buffer tank (110).

5. The method according to any one of claim 1 to 4, wherein the fluid control circuit (605) comprises a controllable valve (500) which is structured and arranged within the fluid control circuit (605) to allow heated fluid received from the heat pump (10) to be selectively branched to the first heatpump inlet structure (151 ) and / or to the second heat pump inlet structure (152).

6. The method according to claim 5, wherein the controllable valve (500) is a thermostat comprising sensing means (490) for allowing adjusting said selective branching of the heated fluid to the first heat pump inlet structure (151 ) and / or to the second heat pump inlet structure (152) based on a temperature of the heated fluid.

7. The method according to any one of claim 1 to 6, wherein the housing (111 ) comprises a main housing portion (112) and at least one further housing portion (113) which together define the interior housing volume (114) for accommodating the buffer fluid; and a plurality of buffer tank interaction structures (102) which includes at least said first heat pump inlet structure (151 ) and said second heat pump inlet structure (152); and wherein the main housing portion (112) and the at least one further housing portion (113) are releasably attached to each other, and wherein the plurality of buffer tank interaction structures (102) is provided in the at least one further housing portion (113).

8. The method according to claim 7, wherein the housing (111 ) extends from said top end (116) to said bottom end (115) and is defined by a top wall (111 b) at the top end (116), a bottom wall (111 a) at the bottom end (115), and a lateral wall (111 c) which extends between, and interconnects, the top wall (111 b) and the bottom wall (111 a), wherein the at least one further housing portion (113) defines at least a part of the top wall (111 b) or the bottom wall (111 a).

9. The method according to claim 8, wherein the at least one further housing portion (113) defines at least a part of the bottom wall (111 a).

10. The method according to any one of claims 1 to 9, wherein said first heat pump inlet structure (151 ) and said second heat pump inlet structure(152) each extend through the at least one further housing portion (113) from an exterior (118) of the housing (111 ) to an interior (119) of the housing (111 ).11 . The method according to any one of claims 1 to 10, wherein said first heat pump inlet structure (151 ) and said second heat pump inlet structure (152) are each releasably attached to the at least one further housing portion (113).

12. The method according to any one of claims 7 to 11 , wherein the at least one further housing portion (113) is one further housing portion.

13. The method according to any one of claims 7 to 12, wherein the fluid control circuit (605) is comprised within a branching conduit module (600-1 , 600-2, 600-3, 600-4, 600-5, 600-6) configured to be connected to a radiator system (13) in a building and to a heat pump (10), the branching conduit module (600-1 , 600-2, 600-3, 600-4, 600-5, 600-6) comprising: a housing (601 ); an inlet (400) configured to fluidly connect the branching conduit module (600-1 , 600-2, 600-3, 600-4, 600-5, 600-6) to the heat pump (10) for receiving heated fluid therefrom; a first buffer tank connection (151 b) configured to fluidly connect the branching conduit module (600-1 , 600-2, 600-3, 600-4, 600-5, 600-6) to the buffer tank (110) via the first heat pump inlet structure (151 ); a second buffer tank connection (152b) configured to fluidly connect the branching conduit module (600-1 , 600-2, 600-3, 600-4, 600-5, 600-6) to the buffer tank (110) via the second heat pump inlet structure (152b); wherein the housing (601 ) comprises a buffer tank interface portion (602-1 , 602-2, 602-3, 602-4, 602-5, 602-6) configured to abut the buffer tank (110), wherein the buffer tank interface portion (602-1 , 602-2, 602-3, 602-4, 602-5, 602-6) comprises a fastening system (603) for releasably fastening the branching conduit module (600-1 , 600-2, 600-3, 600-4, 600-5, 600-6) to the buffer tank (110), and wherein the first buffer tank connection (151 b) and thesecond buffer tank connection (152b) is arranged in the buffer tank interface portion (602-1 , 602-2, 602-3, 602-4, 602-5, 602-6).

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