WO2025228821A1

WO2025228821A1 - A buffer tank and a heat pump arrangement

Info

Publication number: WO2025228821A1
Application number: PCT/EP2025/061365
Authority: WO
Inventors: Michael Lindahl; Peter JOCIC; Per Rosén; Bengt Lindoff
Original assignee: Qvantum Industries AB
Current assignee: Qvantum Industries AB
Priority date: 2024-04-30
Filing date: 2025-04-25
Publication date: 2025-11-06
Anticipated expiration: 2026-10-30

Abstract

The disclosure relates to a buffer tank (110) for a heat pump arrangement (1) comprising: a housing (111) which defines an interior housing volume (114) for accommodating a buffer fluid; and a plurality of buffer tank interaction structures (102) which includes at least: 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); 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); and a flexible bladder (170) defining an interior bladder volume (171) which is filled with a gas, the flexible bladder (170) being arranged inside the housing (111) such that an outer surface (172) of the flexible bladder (170) is in contact with the buffer fluid accommodated in the housing (111) for allowing the flexible bladder (170) to adapt its interior bladder volume (171) for pressure variations in the buffer fluid.

Description

A BUFFER TANK AND A HEAT PUMP ARRANGEMENT

Technical field

The present disclosure relates to a buffer tank for a heat pump arrangement. The present disclosure further relates to a heat pump arrangement for domestic heating.

Background art

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.

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.

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.

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. Summary

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.

According to a first aspect there is provided a buffer tank for a heat pump arrangement comprising: a housing which defines an interior housing volume for accommodating a buffer fluid; and a plurality of buffer tank interaction structures which includes at least: a heat pump inlet structure and a heat pump outlet structure configured to fluidly connect the buffer tank to a heat pump; a tap water inlet structure and a tap water outlet structure configured to fluidly connect the buffer tank to a tap water heat exchange circuit; and a flexible bladder defining an interior bladder volume which is filled with a gas, the flexible bladder being arranged inside the housing such that an outer surface of the flexible bladder is in contact with the buffer fluid accommodated in the housing for allowing the flexible bladder to adapt its interior bladder volume for pressure variations in the buffer fluid.

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 the 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. The buffer tank may also act as a thermal battery for a radiator system which may be arranged in the housing or the zone, wherein the heat pump arrangement may be fluidly connected to the radiator system.

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.

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.

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. Further, the size needed for the heat pump arrangement which comprises the buffer tank may be reduced as well. 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. Further, this may also be advantageous as it allows for a simplified construction of the heat pump arrangement in which the buffer tank is comprised. 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. It should be noted that the flexible bladder is arranged such that the buffer fluid in the housing and the 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.

By the term “for allowing the flexible bladder to adapt its interior bladder volume for pressure variations in the buffer fluid” is herein meant that the interior bladder volume is adaptable for pressure variations, but also temperature variations, in the buffer fluid. The buffer fluid is, as said, accommodated in the housing. In this way, the interior bladder volume is adaptable for temperature and pressure variations in the buffer tank but also in the heat pump arrangement. 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.

By the terms “heat pump inlet structure” and “heat pump outlet structure” are herein meant structures which are configured to fluidly connect the buffer tank to the heat pump and thereby being able to supply fluid between the buffer tank and 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.

By the terms “tap water inlet structure” and “tap water outlet structure” are herein meant structures which are configured to fluidly connect the buffer tank to the tap water heat exchange circuit and thereby being able to supply fluid between the buffer tank and the tap water heat exchange circuit. By way of example, the tap water inlet and outlet structures may be a respective conduit arrangement. The tap water inlet and outlet structures may be any structures suitable for fluidly connecting the buffer tank and the tap water heat exchange circuit. It should be noted that the buffer tank and the tap water heat exchange circuit may be fluidly connected at all times, via the tap water 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 tap water heat exchange circuit at all times. The tap water inlet and outlet structures are preferably hot tap water inlet and outlet structures.

Thus, the buffer tank may be arranged to receive fluid from the heat pump and/or the tap water heat exchange circuit and a temperature of the received fluid may depend on from which part of the heat pump arrangement (i.e. the heat pump and/or tap water heat exchange circuit) the fluid is received.

The heat pump inlet and outlet structures and the tap water inlet and outlet structures may be referred to as fluid connecting structures.

According to some embodiments, the gas is air, nitrogen, hydrogen or helium.

This may be advantageous as it allows for a flexible bladder which may be adaptable for pressure variations and temperature variations in the buffer fluid in an efficient way.

According to some embodiments, the flexible bladder is made of a resilient material.

This may be advantageous as it allows for the flexible bladder to absorb energy when it is deformed elastically, i.e. when the gas expands, and release that energy upon unloading. By way of example, the flexible bladder may be made of rubber which is a material that has a very high modulus of resilience, i.e. a high maximum energy that may be absorb per unit volume without creating a permanent distortion. The flexible bladder may be made of other resilient materials suitable to being adaptable due to pressure and temperature variations in the buffer fluid.

By way of examples, the flexible bladder may be similar to a bladder comprised in a conventional external expansion tank known in the art.

According to some embodiments, the flexible bladder is releasably attached to the housing.

The flexible bladder may be releasably attached to the housing e.g. by means of bolts, nuts or the like. Thus, the flexible bladder may be releasably attached to the housing by any means which is suitable for such attachment. This may be advantageous as it allows for an easy and efficient maintenance of the flexible bladder. Thus, if the flexible bladder needs to be replaced or repaired, it is possible to detach the flexible bladder from the housing and thereafter replace it with another bladder or repair the bladder, without requiring dismantling the housing. Thus, replacement and update of functionalities of the buffer tank and/or the flexible bladder may be provided in an easy and less complex way.

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.

According to some embodiments, the housing extends from a first end to a second end and is defined by a first wall at the first end, a second wall at the second end, and a lateral wall which extends between, and interconnects, the first wall and the second wall, wherein the flexible bladder is attached at the first end of the housing.

The first end may be a bottom end of the buffer tank. This may be advantageous as it allows for an easy access to the flexible bladder when attaching or detaching the flexible bladder to/from the housing. It may be further 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.

The further plurality of buffer tank interaction structures may be attached at the first end of the housing. Thus, all buffer tank interaction structures may be arranged at the same end of the housing. This may be advantageous as it allows for an easy access to the further plurality of buffer tank interaction structures when attaching or detaching the further plurality of buffer tank interaction structures to/from the housing.

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 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.

According to some embodiments, the interior housing volume of the housing has a first volume portion and a second volume portion which are spaced from each other within the housing, wherein the flexible bladder is arranged in the first volume portion.

In this context, the first and second volume portions of the buffer tank may be referred to first and second sub-volume of the buffer tank which are spaced from each other. The first and second volume portions may be spaced from each other by a third volume portion. It should be noted that the first and second volume portions are volume 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. It is conceivable that the spaced apart first and second volume portions are upheld by their mere distance from each other. For example, a buffer tank having a relatively long elongated extension in the horizontal dimension could have a first volume portion in the first end of the elongated extension and a second volume portion at the second end of the elongated extension. However, preferably the first and second volume portions are upheld by natural layering as will be detailed later. It should be noted that the smaller the property differences may be, the less distinct may the layering be.

Preferably, the first volume portion of the interior housing volume may be defined, as seen along a longitudinal direction, in a lowermost part of the interior housing volume and the second volume portion of the interior housing volume is defined, as seen along the longitudinal direction, in an uppermost part of the interior housing volume. With this arrangement, the temperature of the buffer fluid provided in the second volume portion may be higher than the temperature of the buffer fluid provided in the first volume portion. 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. 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 the temperature of the first volume portion but lower than the temperature of the second volume portion.

Since the water 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. This is advantageous as it may ensure that the warmer buffer fluid, provided in the second volume portion, will be supplied to the tap water heat exchange circuit (which is connected to the second volume portion via the tap water outlet structure) and that the cooler buffer fluid, provided in the first volume portion, will be supplied to the heat pump (which may be connected to the first portion).

As said, the temperature of the buffer fluid in the first volume portion may be lower than a temperature of the buffer fluid in the second volume portion. With this design, in which the flexible bladder is arranged in the first volume portion, in which the buffer fluid typically has a lower temperature compared to the buffer fluid of the second volume portion, an increased lifetime of the flexible bladder is achieved. Temperature variations of the buffer fluid in the first volume portion may be smaller compared to temperature variations of the buffer fluid comprised in the second volume portion and hence, great temperature variations may decrease the lifetime of the flexible bladder. As said, the flexible bladder is arranged to adapt due to temperature or pressure variations in the buffer fluid and hence, if there is great temperature or pressure variations in the buffer fluid, the flexible bladder has to be adapted to a greater extent compared to if there is smaller temperature or pressure variations.

According to some embodiments, the interior housing volume of the housing has a first volume portion and a second volume portion which are spaced from each other within the housing, wherein the heat pump inlet structure fluidly connects an exterior of the housing with the second volume portion; wherein the heat pump outlet structure fluidly connects the exterior of the housing with the first volume portion; wherein the tap water inlet structure fluidly connects the exterior of the housing with the first volume portion; and wherein the tap water outlet structure fluidly connects the exterior of the housing with the second volume portion.

The fluid entering the buffer tank from the heat pump may be provided to the second volume portion of the buffer tank and the fluid exiting the buffer tank to the heat pump may be retrieved from the first volume portion of the buffer tank. The fluid exiting the buffer tank to the tap water heat exchange circuit may be retrieved from the second volume portion and the fluid entering the buffer tank from the tap water heat exchange circuit may be provided to the first volume portion. Preferably, the fluid exiting the heat pump into the second volume portion may have different properties than the fluid entering into the heat pump from the first volume portion because of the arrangement of the buffer tank which comprises the first and second volume portions as discussed above. This may be advantageous as it allows for retrieving buffer fluid with certain property to the heat pump and/or the tap water heat exchange circuit which is suitable for the heat pump or the tap water heat exchange circuit. This may be further advantageous as it allows for supplying fluid with certain properties to volume portions of the buffer tank in which buffer fluid with similar properties is provided.

According to some embodiments, the interior bladder volume of the flexible bladder amounts to 1-15%, preferably 2-10%, more preferably 3-6%, of the interior housing volume. As readily appreciated by the person skilled in the art, the appropriate size of the bladder volume will depend on the buffer tank in which it is mounted, the temperature variations of the heat pump arrangement including the heat pump and the radiator system.

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, one or more temperature sensors, one or more pressure sensors, and a venting pipe.

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.

By 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 and/or the radiator system and/or the tap water heat exchange circuit.

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.

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.

The venting pipe may be provided for venting air from the buffer tank.

According to some embodiments, the flexible bladder extends through the housing from an exterior of the housing to an interior of the housing.

This may be advantageous as it allows for ensuring that the gas in the flexible bladder and the buffer fluid in the housing do not come in contact with each other. With this design, the flexible bladder may be releasably attached at an outside of the housing. This may be further advantageous as it allows for attaching or detaching the flexible bladder to/from the housing in an easy way without the need of reaching an interior of the housing.

Preferably, all of the plurality of buffer tank interaction structures extends through the housing from the exterior of the housing to an interior of the housing.

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 housing 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).

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 housing 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 housing comprises a main housing portion and at least one further housing portion which together forms the housing for accommodating the buffer fluid, 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.

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 portion 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.

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.

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.

The main housing portion may have larger surface area than to 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.

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.

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.

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.

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.

According to some embodiments, the housing extends from a first end to a second end and is defined by a first wall at the first end, a second wall at the second end, and a lateral wall which extends between, and interconnects, the first wall and the second wall, wherein the at least one further housing portion defines at least a part of the first wall.

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.

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.

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.

According to some embodiments, the main housing portion comprises 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.

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 server to increase strength and providing for an easier attachment between the main housing portion and the associated further housing portion.

If the at least one further housing portion defines at least a part of the first wall defining the first end, wherein the first end is a bottom end of the housing (i.e. if the at least one further housing portion is releasably attached to the bottom end of the housing), the heat pump inlet structure may be a relatively long conduit, or pipe, configured to receive heated fluid from the heat pump and supply said heated fluid to the second volume portion of the buffer tank. This implies that the heat pump inlet structure may extend, internally within the housing of the buffer tank, from the first end of the buffer tank towards the second end of the buffer tank where the second volume portion is located. Further, with this design, the heat pump outlet structure may be a relatively short conduit, or pipe, configured to retrieve colder fluid form the first volume portion of the buffer tank and supply said heated fluid the heat pump. Further, the tap water outlet structure may be a relatively long conduit, or pipe, configured to retrieve heated water from the second volume portion of the buffer tank and supply said heated fluid to the tap water heat exchange circuit. The tap water inlet structure may be a relatively short conduit configured to receive colder fluid from the tap water heat exchange circuit and supply said heated fluid to the first volume portion of the buffer tank.

As readily appreciated by the person skilled in the art, if the at least one further housing portion defines at least a part of the first wall defining the first end, wherein the first end is a top end of the housing (i.e. if the at least one further housing portion is releasably attached to the top end of the housing), the heat pump inlet structure may be a relatively short conduit, or pipe, configured to receive heated fluid from the heat pump and supply said heated fluid to the second volume portion of the buffer tank and so forth. Thus, if the at least one further housing portion is attached to the top end of the housing, the relatively long conduits, or pipes, (as introduced above, wherein the first end is the bottom end) may be relatively short conduits, or pipes, in order to being able extend to the second volume portion of the buffer tank and the relatively short conduits, or pipes, (as introduced above, wherein the first end is the bottom end) may be relatively long conduits, or pipes, in order to being able to extend to the first volume portion of the buffer tank.

As readily appreciated by the person skilled in the art, if the at least one further housing portion is attached to the lateral wall of the housing, heat pump inlet structure, the heat pump outlet structure, the tap water inlet structure, and the tap water outlet structure may have a similar length. The required fluid connections with the respective one of the first and second volume portions within the buffer tank may instead be accomplished by choosing an appropriate location for the at least one further housing portion on the mail housing portion and/or choosing an appropriate location of the respective inlet and outlet structure in relation to the at least one further housing portion.

According to some embodiments, all buffer tank interaction structures of a further housing portion are aligned substantially in parallel with each other so as to allow mounting said all buffer tank interaction structures to the further housing portion in one single operation.

This may be advantageous as it allows for a simplified construction of the buffer tank making possibilities for using robots in the manufacturing in an easy and efficient way. This implies that said all buffer tank interaction structures of a further housing portion is structured and arranged in the further housing portion such that a common cross section of the all buffer tank interaction structures fits the opening of the main housing portion. It further implies that said all buffer tank interaction structures of one of the further housing portions is inserted into the opening along a mounting path. The mounting path may be substantially linear. The person skilled in the art realizes that for embodiments having more than one further housing portion arranged in the main housing within associated individual opening, the said all buffer tank interaction structures of one of the further housing portions may be inserted into its associated individual opening along one mounting path, whereas another one of the further housing portions may be inserted into its associated individual opening along another, different, mounting path.

According to some embodiments, the flexible bladder comprises a valve for allowing exchanging the gas in its interior bladder volume, wherein the flexible bladder is arranged in the buffer tank such that the valve is accessible from an exterior of the housing.

This may be advantageous as it allows for exchanging the gas in the flexible bladder in an easy and efficient way.

According to some embodiments, the buffer tank is configured to be in fluid communication with a radiator system.

This may be advantageous as it allows the interior bladder volume of the flexible bladder to adapt for pressure and temperature variations in the radiator system as well as in heat pump arrangement. Thus, the flexible bladder may act as an expansion tank for both the heat pump system as well as for the radiator system to which the heat pump arrangement is fluidly connected to.

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.

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.

According to some embodiments, the at least one further housing portion comprises a first further housing portion and a second further housing portion, wherein the first further housing portion is releasably attached to the second further housing portion and arranged within the same such that it is not directly attached to the main housing portion, and wherein the flexible bladder is provided in the first further housing portion.

This may be advantageous as it allows for an easy and efficient replacement of removement of the one or more of the buffer tank interaction structures which are provided in the first further housing portion without the need or detaching or removing the second further housing portion. Thus, a flexible maintenance of the buffer tank, and especially the buffer tank interaction structures, may be achieved.

According to a second aspect there is provided a heat pump arrangement for domestic heating comprising: a heating system for a building including at least one heat pump; a buffer tank according to the first aspect, and a conduit system for fluidly connecting the heat pump to the buffer tank via the heat pump inlet structure and the heat pump outlet structure.

The heat pump arrangement may further comprise a tap water heat exchange circuit for fluidly connecting the tap water heat exchange circuit to the buffer tank via the tap water inlet structure and the tap water outlet structure.

Effects and features of the second aspect are largely analogous to those described above in connection with the first aspect. Embodiments mentioned in relation to the first aspect are largely compatible with the second aspect. It is further 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.

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.

Brief descriptions of the drawings

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.

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

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

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.

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.

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

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

Figure 5A is a perspective view of a branching conduit module according to an example embodiment of the present disclosure. Figure 5B is a perspective view of the branching conduit module of Fig. 5A where its interior has been visualized in a transparent view.

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

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.

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.

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.

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.

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.

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.

Detailed description

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. 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. 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.

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 .

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.

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.

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.

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 .

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.

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.

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

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.

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.

Specifically, it has been an aim to provide an improved buffer tank 110 which simplifies the heat pump arrangement 1 , T by reducing the number of units that has to be assembled during manufacture. This may reduce the overall dimensions of the heat pump arrangement 1 , T. The improved buffer tank 110 further allows using robots in the manufacturing process. The buffer tank 110 may be advantageous as it allows for automating the manufacturing process. Hence, an improved manufacturing process is achieved.

The buffer tank 110 and the heat pump arrangement 1 of which it forms a part will be described with reference to Figs 2, 3A, 3B, 3C, 4A and 4B. Further features of the inventive concept will be described with reference to Figs 4A to 12.

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, 113b to the main housing portion 112.

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.

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.

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.

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 .

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.

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.

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.

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. 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Although the buffer tank 110 of the example embodiment is structured in this particular way, the person skilled in the art realizes that buffer tank of the disclosure is not limited to this embodiment. In particular, the buffer tank of the disclosure does not require comprising a main housing portion 112 and an at least one further housing portion 113a, 113b. Alternatively, the buffer tank of the disclosure may comprise a single housing, such as known from the prior art. Furthermore, the buffer tank of the disclosure does not require the plurality of buffer tank interaction structures 102 to be arranged at the same dedicated area of the buffer tank nor to have different lengths, which are also features described for the buffer tank 110.

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 operation of the buffer tank of the disclosure is equally possible without the same.

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.

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.

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.

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.

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.

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.

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.

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 151b 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.

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.

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.

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 600-5 600-6). 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.

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.

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.

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 comprises 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.

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.

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).

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.

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 ,T 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.

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.

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.

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.

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.

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

1 . A buffer tank (110) for a heat pump arrangement (1 ) comprising: a housing (111 ) which defines an interior housing volume (114) for accommodating a buffer fluid; and a plurality of buffer tank interaction structures (102) which includes at least: 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); 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 ); and a flexible bladder (170) defining an interior bladder volume (171 ) which is filled with a gas, the flexible bladder (170) being arranged inside the housing (111 ) such that an outer surface (172) of the flexible bladder (170) is in contact with the buffer fluid accommodated in the housing (111 ) for allowing the flexible bladder (170) to adapt its interior bladder volume (171 ) for pressure variations in the buffer fluid.

2. The buffer tank (110) according to claim 1 , wherein the gas is air, nitrogen, hydrogen, or helium.

3. The buffer tank (110) according to any one of the preceding claims, wherein the flexible bladder (170) is made of a resilient material.

4. The buffer tank (110) according to any one of the preceding claims, wherein the flexible bladder (170) is releasably attached to the housing (111 ).

5. The buffer tank (110) according to any one of the preceding claims, wherein the housing (111 ) extends from a first end (115) to a second end (116) and is defined by a first wall (111 a) at the first end (115), a second wall (111 b) at the second end (116), and a lateral wall (111 c) which extends between, and interconnects, the first wall (111 a) and the second wall (111 b), wherein the flexible bladder (170) is attached at the first end (115) of the housing.

6. The buffer tank (110) according to any one of the preceding claims, wherein 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 ), wherein the flexible bladder (170) is arranged in the first volume portion (114a).

7. The buffer tank (110) according to claim 6, wherein the interior bladder volume (171 ) of the flexible bladder (170) amounts to 1 -15%, preferably 2-10%, more preferably 3-6%, of the interior housing volume (114).

8. The buffer tank (110) according to any one of the preceding claims, wherein the plurality of buffer tank interaction structures (102) further comprises one or more of: one or more further fluid connecting structures (150, 152), a direct electric heater (180), one or more temperature sensors (210a), one or more pressure sensors (210b), and a venting pipe (140).

9. The buffer tank (110) according to any one of the preceding claims, wherein the flexible bladder (170) extends through the housing (111 ) from an exterior (118) of the housing (111 ) to an interior (119) of the housing (111 ).

10. The buffer tank (110) according to any one of the preceding claims, wherein the housing (111 ) comprises a main housing portion (112) and at least one further housing portion (113) which together forms the housing

(111 ) for accommodating the buffer fluid, 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). 11 . The buffer tank (110) according to claim 10, wherein all buffer tank interaction structures (102) of a further housing portion (114) 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 (114) in one single operation.

12. The buffer tank (110) according to any one of the preceding claims, wherein the flexible bladder (170) comprises a valve (173) for allowing exchanging the gas in its interior bladder volume (171 ), wherein the flexible bladder (170) is arranged in the buffer tank (110) such that the valve (173) is accessible from an exterior of the housing (111 ).

13. The buffer tank (110) according to any one of the preceding claims, wherein the buffer tank is configured to be in fluid communication with a radiator system (13).

14. The buffer tank (110) according to any one of claims 10 to 13, wherein the at least one further housing portion (113) comprises a first further housing portion (113a) and a second further housing portion (113b), wherein 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 wherein the flexible bladder is provided in the first further housing portion (113a).

15. A heat pump arrangement (1) for domestic heating comprising: a heating system for a building including at least one heat pump (10); a buffer tank (110) according to any one of claim 1 to 14, and a conduit system (12) for fluidly connecting the heat pump (10) to the buffer tank (110) via the heat pump inlet structure (151 ) and the heat pump outlet structure (200).