Hydronic system and method for transferring thermal energy from a heat pump to produce domestic hot water

Abstract

The present disclosure is directed to a method for providing domestic hot water, DHW, by a hydronic system (1) comprising a heat pump (3), a thermal energy storage tank (23) and a DHW system (49) with a thermal transfer element (61), wherein the method comprises: - identifying a DHW demand event, - controlling, in case of an identified DHW demand event, operation of a load circuit pump (17) for driving a load flow (qL) along a load feed circuit section (13) of the hydronic system (1) through a primary part of the thermal transfer element (61), - controlling operation of a heat pump circuit pump (11) for driving a heat pump flow (qH) through the heat pump (3) along a heat pump feed circuit section (7) of the hydronic system (1), - withdrawing a storage flow (qS) from the thermal energy storage tank (23) along a storage feed circuit section (19) of the hydronic system (1), and - mixing the heat pump flow (qH) with the storage flow (qS) at a feed connection point (27) where the heat pump feed circuit section (7), the load feed circuit section (13) and the storage feed circuit section (19) are connected upstream of the primary part of the thermal transfer element (61), wherein the storage flow (qS) results from the controlled operation of the heat pump circuit pump (11) and of the load circuit pump (17) so that the sum of the heat pump flow (qH) and the storage flow (qS) yields the load flow (qL) through the primary part of the thermal transfer element (61).

Description

[0001] Applicant: GRUNDFOS HOLDING A / STitle: Hydronic system and method for transferring thermalenergy from a heat pump to produce domestic hotwater 5Our Ref.: GP 3907 WODescription TECHNICAL FIELD10

[0001] The present disclosure is directed to a hydronic system and amethod for transferring thermal energy from a heat pump to produce domestic hot water. Preferably, the inventive hydronic system may be used in a domestic heating / cooling system with a heat pump as a heat source and radiators and / or underfloor heating as thermal energy loads. Preferably, the inventive hydronic system may also be used as at least part of a domestic hot water, DHW, system for providing hot water to a faucet, shower, bathtub or other domestic consumers of hot water. The inventive hydronic system is, however, not only applicable for do- mestic household systems, but also as part of larger heating / cooling 20 systems of larger private or commercial buildings. Most preferably, the inventive hydronic system may be implemented as an integrated water circuit, IWC, unit connecting a heat pump with at least one thermal en- ergy load. BACKGROUND

[02] Heating or cooling systems typically use a hydronic system fortransporting thermal energy from a thermal energy source to one or more thermal energy loads. The hydronic system typically comprises a30 piping system that contains a thermal energy transporting medium, e.g.water, that is circulated by one or more pumps through the hydronicPatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025 system. Thermal energy is added to the hydronic system at the thermal energy source, e.g. a boiler, a heat pump, a heat exchanger or an electric coil, and thermal energy leaves the hydronic system at the thermal energy load(s), e.g. radiator(s) or underfloor heating(s). 5

[03] In order to reduce consumption of fossil energy sources, e.g. gas,oil or coal, there is a trend to use electrically driven heat pumps as ther- mal energy source to add thermal energy to the hydronic system for heating or cooling purposes. Heat pumps use electric energy to extract 10 thermal energy from an outside thermal energy reservoir, e.g. outside air or geothermal energy. Heat pumps currently on the market come in two types: a split-type and a mono-block type. In case of a mono- block type heat pump, the full thermodynamic cycle is performed within one unit (mostly an outdoor unit), whereas in case of a split-type heat pump the thermodynamic cycle is split into an evaporator unit (mostly an outdoor unit) and a condenser unit (mostly an indoor unit). Both split-type heat pumps and mono-block type heat pumps typically have an outdoor unit and an indoor unit, wherein the indoor unit is used to distribute the thermal energy to the thermal energy loads and / or to20 integrate a domestic hot water, DHW, system.

[0004] The cost of operating a heat pump depends on the one handon the efficiency of the heat production, sometimes referred to as sea- sonal coefficient of performance (SCOP), and on the other hand on the electricity price. Nowadays, heat pump systems are mostly oper- ated to maximise the SCOP.

[05] However, the operating cost of today’s heat pump systems is stillfully dependent on electricity price fluctuations. If an electricity pro- 30 vider offers a flat electricity price, such a flat electricity price will have electricity price fluctuations factored in, so that a consumer does not benefit from low electricity prices as it would be possible.Patentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025

[0006] There is thus a need for a hydronic system for transferring thermalenergy from a heat pump to produce domestic hot water, which al-lows benefitting from low electricity prices and reduces cost when elec- tricity prices are high. There is also a demand for smaller and cheaper 5 hydronic systems that require a smaller buffer tank or no buffer tank at all. The present disclosure is further directed to providing an improvedindoor unit of a heat pump, wherein a pre-assembled hydronic system in form of an integrated water circuit (IWC) unit can be integrated into the indoor unit of the heat pump. 10 SUMMARY

[07] The hydronic system according to the present disclosure and themethod for operating such a hydronic system according to the presentdisclosure provides a solution to this problem.

[08] According to a first aspect of the present disclosure, a method isprovided for providing domestic hot water, DHW, by a hydronic system20 comprising a heat pump, a thermal energy storage tank and a DHW sys- tem with a thermal transfer element, wherein the method comprises: -identifying a DHW demand event,- controlling, in case of an identified DHW demand event, operationof a load circuit pump for driving a load flow along a load feed cir- cuit section of the hydronic system through a primary part of the ther- mal transfer element, -controlling operation of a heat pump circuit pump for driving a heatpump flow through the heat pump along a heat pump feed circuit section of the hydronic system,30 - withdrawing a storage flow from the thermal energy storage tankalong a storage feed circuit section of the hydronic system, and -mixing the heat pump flow with the storage flow at a feed connec-tion point where the heat pump feed circuit section, the load feedPatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025 circuit section and the storage feed circuit section are connected upstream of the primary part of the thermal transfer element, wherein the storage flow results from the controlled operation of the heat pump circuit pump and of the load circuit pump so that the sum of the 5heat pump flow and the storage flow yields the load flow through theprimary part of the thermal transfer element.

[09] It should be noted that the thermal energy storage tank is not afreshwater tank of a domestic hot water (DHW) system. The thermal en-10 ergy storage tank is not a hydraulic decoupling buffer tank either. Thethermal energy storage tank holds “technical water” for being circu-lated in a closed circuit. The thermal energy storage tank may be part of the hydronic system or connectable to the hydronic system. If the heat pump is a mono-block type heat pump, e.g. as an outdoor unit, it is connectable to the hydronic system which may serve as an indoor unit. In case of a split-type heat pump, the condenser unit, e.g. as anindoor unit, may be part of the hydronic system or connectable to the hydronic system. Further thermal energy load(s), e.g. radiators or under-floor heating, may be connectable to the hydronic system.20

[10] The method and hydronic system disclosed herein has the ad-vantage that domestic hot water, DHW, can be efficiently provided bya relatively small-sized thermal energy storage tank in combination with the heat pump flow. The controlled mixing of the heat pump flow with the storage flow to yield a required load flow allows for providing a rela-tively high volume of DHW compared to the volume of the thermal en-ergy storage tank, e.g. by a factor of two or more. Thereby, the designof the thermal energy storage tank, and thus of the overall indoor unit, can be smaller without compromising on the maximum providable vol-30 ume of DHW.Patentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025

[0011] Optionally, the method may further comprise determining a loadflow feed temperature of the load flow by a load flow feed tempera- ture sensor, wherein the load flow feed temperature sensor is arranged at the load feed circuit section, and wherein said controlling of the op- 5 eration of the heat pump circuit pump adjusts the mixing so that a devi- ation of the load flow feed temperature from a reference load flow feed temperature is minimised. During a ramp-up phase of the heat pump at the beginning of a DHW demand event, this results in a steep short rise of the storage flow followed by a gentle longer decline as the 10 heat pump flow is slowly ramped up. This is beneficial on the one hand to provide DHW quickly before the heat pump is fully ramped up and on the other hand to save as much storage flow as possible by substi-tuting as much as possible of the storage flow by the heat pump flow.Preferably, the heat pump circuit pump is ramped up significantly slower than the load circuit pump to account for the ramp-up phase of the heat pump. The heat pump flow is preferably increased during theramp-up phase of the heat pump to a maximum heat pump flow al- lowed without causing a drop of a heat pump flow feed temperature. If the heat pump flow were too high during the ramp-up phase of the 20 heat pump, the heat pump flow feed temperature would undesirably drop because the heat pump is not yet being able to provide the re- quested thermal power. If the heat pump flow were too low, the stor- age flow and thus the load flow feed temperature would be too high. The controlling of the heat pump circuit pump may include a closed- loop control to ramp up the heat pump circuit pump to a maximum without causing a drop in the heat pump flow feed temperature and / or load flow feed temperature. Ramping up the heat pump circuitpump while running the load circuit pump at a constant speed needed to provide the required load flow has the effect of reducing the storage 30 flow. Thereby, thermal energy in the thermal energy storage tank is saved as much as possible.Patentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025

[0012] A further advantage of the inventive method is that it automati-cally finds a required balance between the heat pump flow and the storage flow to meet the DHW demand even if any of the following var-iables changes: heat pump return temperature, the heat pump thermal5 power, the storage tank temperature, and / or added heating power byan electric heater.

[13] Optionally, the method may further comprise measuring or esti-mating the freshwater flow through the secondary part of the thermal10 transfer element, wherein the DHW demand event is identified if a fresh-water flow through the secondary part of the thermal transfer elementexceeds a pre-determined minimum flow. The DHW system may com-prise a flow sensor for measuring the freshwater flow. Alternatively, or inaddition, the DHW system may comprise a hot water temperature sen- sor and / or a DHW temperature sensor for identifying a DHW demand event by a certain temperature drop. In the simplest embodiments, it may be sufficient to identify if there is currently a DHW demand eventongoing or not, i.e. to set a Boolean flag. More sophisticated embodi- ments preferably quantify the DHW demand of a DHW demand event,20 e.g. based on a direct or indirect guess, estimation, and / or measure- ment of the freshwater flow through the secondary part of the thermaltransfer element, or of another variable that scales with said freshwater flow.

[14] Optionally, the method may further comprise adding, depend-ing on an electric heating mode, thermal power to the load flow by an electric heater being arranged in the load feed circuit section of the hydronic system downstream of the feed connection point and up- stream of the primary part of the thermal transfer element, wherein the30 thermal power is added to a sum of a heat pump thermal power pro- vided by the heat pump flow and a storage thermal power provided by the storage flow to meet a DHW demand of the identified DHW de-mand event. The DHW demand of the identified DHW demand eventPatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025 may be quantified by a direct or indirect guess, estimation, and / or measurement of the freshwater flow through the secondary part of thethermal transfer element, or of another variable that scales with said freshwater flow. Possible electric heating modes may be “off”, “eco”, 5 “comfort”, and / or “volume”. In the off-mode, use of the electric heater is vetoed and kept off to save electricity consumption. The eco-mode may keep the thermal power added by the electric heater to a mini- mum required to meet the DHW demand in case of an insufficient charging state of the thermal energy storage tank. The comfort-mode may be used to meet the DHW demand as quickly as possible during a ramp-up phase of the heat pump. In the volume-mode, the electric heater is operated at maximum power during a DHW demand event to reduce the storage flow as much as possible for providing a maximum volume of DHW during the DHW demand event, e.g. for filling a bath-15 tub.

[15] Optionally, said controlling, in case of an identified DHW de-mand event, operation of the load circuit pump may comprise drivingthe load flow qL to be a pre-determined factor RHEX of a freshwater flow20 qFW, i.e. ^^ = ^^^^ ∗ ^^^. This simplifies the controlling of the load circuitpump significantly. For example, the factor RHEX may be 1.15 or anothervalue in the range of 1.0 to 1.3.

[16] Optionally, the method may further comprise providing a DHWdemand signal to a signal-connectable or signal-connected heat pump control for ramping up the heat pump, wherein said controlling operation of the heat pump circuit pump ramps up the heat pump flow to make use of the currently available heat pump power already dur-ing the ramp-up phase of the heat pump. The DHW demand signal30 may communicate with a super-ordinate heat pump control to request a maximum heat pump power. For example, before the DHW demand event started, the heat pump may be switched off or running at a re-duced power for providing thermal power to a heating system. ThePatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025 DHW demand signal may trigger the heat pump to ramp up to its maxi- mum power, which may take three minutes or more until the heat pump has reached its maximum power. As the DHW demand is to be met within 10 seconds, the load circuit pump is quickly ramped up to 5 withdraw thermal energy quickly from the thermal energy storage tank.

[17] Optionally, the method may further comprise returning the loadflow along a load return circuit section of the hydronic system down- stream of the primary part of the thermal transfer element, wherein the 10 returned load flow is split up into the storage flow and the heat pump flow at a return connection point where the load return circuit section divides into a heat pump return circuit section of the hydronic system towards the heat pump and a storage return circuit section of the hy- dronic system towards the thermal energy storage tank. The thermalenergy storage tank thus holds “technical water” that is circulated through the hydronic system and not consumed. The thermal energy storage tank is not a buffer tank that reduces the number of start / stop cycles of the heat pump. The thermal energy storage tank is herein used as a thermal power source to complement with the thermal 20 power provided by the heat pump in the event of a DHW demand.

[18] According to a second aspect of the present disclosure, a hy-dronic system is provided for providing domestic hot water, DHW,wherein the hydronic system comprises: -a DHW system comprising a thermal transfer element, wherein thethermal transfer element comprises a primary part and secondary part being thermally coupled to each other, wherein the DHW sys- tem is configured to identify a DHW demand event, -a load feed circuit section for transporting a load flow through the30 primary part of the thermal transfer element, -a load circuit pump for driving the load flow along the load feedcircuit section,Patentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025- a heat pump feed circuit section for transporting a heat pump flowthrough a connectable or connected heat pump, -a heat pump circuit pump for driving the heat pump flow,- a storage feed circuit section for transporting a storage flow out of a5 connectable or connected thermal energy storage tank, and -control electronics,wherein the control electronics is configured to control operation of the heat pump circuit pump and of the load circuit pump for mixing the heat pump flow with the storage flow at a feed connection point where the 10 heat pump feed circuit section, the load feed circuit section and the storage feed circuit section are connected upstream of the primary part of the thermal transfer element, wherein the storage flow results from the controlled operation of the heat pump circuit pump and of the load cir- cuit pump so that the sum of the heat pump flow and the storage flow yields the load flow through the primary part of the thermal transfer ele- ment.

[19] Optionally, the hydronic system may further comprise a load flowfeed temperature sensor for determining a load flow feed temperature20 of the load flow, wherein the load flow feed temperature sensor is ar- ranged at the load feed circuit section, and wherein the control elec- tronics is configured to control the operation of the heat pump circuit pump so that the mixing is adjusted to minimise a deviation of the load flow feed temperature from a reference load flow feed temperature.

[20] Optionally, wherein the DHW system may be configured to meas-ured or estimate the freshwater flow through the secondary part of thethermal transfer element, wherein the control electronics may be config-ured to detect a DHW demand if the freshwater flow through the sec-30 ondary part of the thermal transfer element exceeds a pre-determinedminimum flow.Patentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025

[0021] Optionally, the hydronic system may further comprise an electricheater being arranged in the load feed circuit section of the hydronic system downstream of the feed connection point and upstream of the primary part of the thermal transfer element, wherein the control elec- 5 tronics is configured to add, depending on an electric heating mode, heating power to the load flow by the electric heater, wherein the heat-ing power is added to a sum of a heat pump thermal power providedby the heat pump flow and a storage thermal power provided by the storage flow to meet the DHW demand.

[22] Optionally, the control electronics may be configured to controloperation of the load circuit pump for driving the load flow qL to be apre-determined factor RHEX of the freshwater flow qFW, i.e. ^^ = ^^^^ ∗ ^^^.15

[0023] Optionally, the control electronics may be configured to providea DHW demand signal to a signal-connectable or signal-connected heat pump control for ramping up the heat pump, wherein the control electronics may be configured to ramp up the heat pump flow so that aheat pump thermal power provided by the heat pump flow is already20 used during the ramp-up phase of the heat pump.

[0024] Optionally, the hydronic system may further comprise a load re-turn circuit section for returning the load flow downstream of the primarypart of the thermal transfer element, wherein the load return circuit sec- tion divides into a heat pump return circuit section towards the heatpump and a storage return circuit section towards the thermal energy storage tank.

[25] Optionally, the hydronic system may be an integrated water cir-30 cuit, IWC, unit, wherein the IWC unit comprises: -a heat pump port for connecting the heat pump feed circuit sectionwith the heat pump,Patentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025- a storage port for connecting the storage feed circuit section withthe thermal energy storage tank or for connecting a storage returncircuit section with a load return circuit section,- a cold freshwater inlet port for connecting the secondary part of the5 thermal transfer element with a freshwater supply, and- a hot freshwater outlet port for connecting the secondary part of thethermal transfer element with a hot water consumer.

[26] It is very beneficial to provide the hydronic system in form a pre-10 assembled IWC unit being at least part of an indoor unit of the heat pump. A minimum number of four ports, i.e. the heat pump port, the stor- age port and the two freshwater ports, is needed to connect an external heat pump unit, an external thermal energy storage tank, the freshwater supply and the hot water consumer. If the thermal energy storage tankand a load return circuit section back towards the heat pump and thethermal energy storage tank is integrated into the IWC, the storage portconnects the storage return circuit section and the load return circuitsection with an external heat pump return circuit section. The load returncircuit section from the thermal transfer element may be arranged exter-20 nally of the IWC unit. In that case, another return outlet port may be needed to connect to the external load return circuit section.

[27] Optionally, the hydronic system may further comprise a storagetank temperature sensor being arranged within the thermal energy stor- age tank, wherein the control electronics may be configured to deter-mine a charging level of the thermal energy storage tank based on a measured value of the storage tank temperature sensor.

[28] The thermal transfer element of the DHW system may preferably30 be a heat exchanger. Alternatively, the thermal transfer element of the DHW system may comprise a coil as primary part and a freshwater tank as secondary part. Compared to a freshwater tank, a heat exchanger has the advantage that no freshwater reservoir must be kept above 55°CPatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025 for reducing the risk of legionella contamination. Furthermore, a heat ex- changer consumes less space than a freshwater tank or a bypass flow tank. 5

[0029] The electric heater of the hydronic system may be arranged atthe load feed circuit section downstream of the feed connection pointand upstream of the primary part of the thermal transfer element. Thecontrol electronics may be configured to control gradually or in one ormore steps a heating power of the electric heater for adding thermal10 energy to the load flow. The electric heater is particularly beneficial incombination with the DHW system to provide quickly sufficient comfort when a thermal energy demand during a DHW demand event is very high and the heat pump is still ramping up. It may be more efficient tocover short periods of high thermal energy demand with the electric heater rather than sizing the heat pump and / or the thermal energy stor- age tank to be oversized for most of the time. If the thermal output power of the heat pump together with the thermal output power of the thermal energy storage tank is not sufficient to satisfy a high thermal energy de- mand during a DHW demand event, the electric heater can be switched20 on and / or turned up to a sufficient degree to add heating power to theload flow by increasing the load flow feed temperature. Thus, the electricheater has the advantage of providing a choice between using threedifferent energy sources individually or in combination, in particular dur- ing a DHW demand event. A relatively short DHW demand event maybe met by the storage flow alone. The electric heater may be switchedon in addition, if needed. A longer DHW demand event may require thatthe heat pump circuit pump is switched on and ramped up, so that boththe heat pump flow and the storage flow mix into the load flow. The elec-tric heater may be switched on in addition, but only as much as needed.30

[30] Optionally, when the thermal transfer element is a heat ex-changer, the DHW system of the hydronic system may further comprisePatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025- a flow sensor being arranged at a freshwater circuit section formeasuring the freshwater flow, and -a hot water temperature sensor being arranged at the freshwatercircuit section downstream of the heat exchanger, 5wherein the control electronics is configured to determine a DHW de-mand based on measured values of the flow sensor and the hot watertemperature sensor. This is a very convenient embodiment to save afreshwater tank, which consumes a lot of space and requires a minimum temperature of 55°C in the freshwater tank to reduce the risk of legionella contamination. As an alternative to a flow sensor, temperature sensorsfor measuring the input temperature and the output temperature of the fresh water in the secondary part of the heat exchanger may be used to estimate the freshwater flow if the input temperature and the output temperature of the load flow through in the primary part of the heat ex-15 changer and the load flow itself is known. A detected freshwater flow exceeding a certain threshold may trigger a DHW demand event.

[31] Optionally, when the thermal transfer element is a heat ex-changer, the control electronics may be configured to determine a DHW20 demand based on at least two pre-determined hot water consumption profiles. A first hot water consumption profile of the at least two pre-de-termined hot water consumption profiles may be a “showering” profileindicated by a relatively high freshwater flow, e.g. at or above 7 li- tres / min, wherein a first target hot water temperature is set relatively low, e.g. 42 °C. This is useful to reduce the need for mixing cold water into thehot freshwater flow to obtain a desired showering temperature. A sec- ond hot water consumption profile of the at least two pre-determinedhot water consumption profiles may be a “kitchen” profile indicated bya relatively low freshwater flow, e.g. below 7 litres / min, wherein a second 30 target hot water temperature is set relatively high, e.g.55 °C. This is useful to provide sufficiently hot water for a kitchen sink, for example. Each of the at least two pre-determined hot water consumption profiles may bePatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025time dependent based on experienced usage behaviour. As the hot wa-ter consumption profiles are usually similar on the same days of the week,e.g. working days and weekend days, it is useful to have the thermal en- ergy storage tank charged well before a DHW demand event can be5 expected according to the at least two pre-determined hot water con- sumption profiles.

[32] Optionally, the hydronic system may further comprise a storageflow feed temperature sensor being arranged in a storage feed circuit10 section for measuring a storage flow feed temperature of the storageflow before it mixes with the heat pump flow.

[0033] Optionally, the hydronic system may further comprise a storagetank temperature sensor being arranged within the thermal energy stor- age tank, wherein the control electronics is configured to determine acharging level of the thermal energy storage tank based on a measuredvalue of the storage tank temperature sensor. Preferably, the storagetank temperature sensor may be arranged in an upper section of thethermal energy storage tank where the storage flow is preferably with-20 drawn from the thermal energy storage tank. If the storage tank temper-ature sensor detects a temperature drop from a setpoint storage tanktemperature, the charging level of the thermal energy storage tank is low. Preferably, a second storage tank temperature sensor may be ar-ranged in a lower section of the thermal energy storage tank where the storage flow is preferably returned into the thermal energy storage tank. If said second storage tank temperature sensor measures the setpointstorage tank temperature, the charging level of the thermal energy stor-age tank is high.30

[0034] Optionally, the thermal energy storage tank may be integratedinto the hydronic system being an integrated water circuit, IWC, unit.Patentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025

[0035] Optionally, the control electronics may comprise a communica-tion interface for communication with a heat pump control, wherein the communication interface is configured to -receive a heat pump flow value,5 - send a start / stop command to the heat pump,- receive a heat pump flow feed temperature and a heat pump flowreturn temperature, and / or -send a reference control value to the heat pump for setting theheat pump flow feed temperature and / or a difference between10 the heat pump flow feed temperature and the heat pump flow re-turn temperature.

[36] Optionally, the hydronic system may further comprise:- the heat pump, and / or- the thermal energy storage tank, and / or- at least one thermal energy load, e.g. radiator(s) or underfloorheating(s).

[37] The method disclosed herein may be implemented in form of20 compiled or uncompiled software code that is stored on a computer- readable medium with instructions for executing the method. Alterna- tively, or in addition, the method may be executed by software in acloud-based system and / or a building management system (BMS), e.g. in control electronics disclosed herein.

[38] The present invention may be a system, a method, and / or a com-puter program product at any possible technical detail level of integra- tion. The computer program product may include a computer readable storage medium (or media) having computer readable program instruc- 30 tions thereon for causing a processor to carry out aspects of the present invention.Patentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025

[0039] The computer readable storage medium can be a tangible de-vice that can retain and store instructions for use by an instruction execu- tion device. The computer readable storage medium may be, for exam- ple, but is not limited to, an electronic storage device, a magnetic stor- 5 age device, an optical storage device, an electromagnetic storage de- vice, a semiconductor storage device, or any suitable combination of the foregoing. A non-exhaustive list of more specific examples of the computer readable storage medium includes the following: a portable computer diskette, a hard disk, a random access memory (RAM), a read- 10 only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanically encoded de- vice such as punch-cards or raised structures in a groove having instruc- tions recorded thereon, and any suitable combination of the foregoing. A computer readable storage medium, as used herein, is not to be con- strued as being transitory signals per se, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through a waveguide or other transmission media (e.g., light20 pulses passing through a fibre-optic cable), or electrical signals transmit- ted through a wire.

[40] Computer readable program instructions described herein can bedownloaded to respective computing / processing devices from a com-puter readable storage medium or to an external computer or external storage device via a network, for example, the Internet, a local area net- work, a wide area network and / or a wireless network. The network may comprise copper transmission cables, optical transmission fibres, wireless transmission, routers, firewalls, switches, gateway computers and / or edge30 servers. A network adapter card or network interface in each compu- ting / processing device receives computer readable program instructionsPatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025 from the network and forwards the computer readable program instruc- tions for storage in a computer readable storage medium within the re- spective computing / processing device. 5 SUMMARY OF THE DRAWINGS

[41] Embodiments of the present disclosure will now be described byway of example with reference to the following figures of which: 10 Fig. 1 shows schematically an embodiment of the hydronic system dis- closed herein in the feed line configuration; Fig. 2 shows schematically another embodiment of the hydronic systemdisclosed herein in the feed line configuration;Fig. 3 shows schematically another embodiment of the hydronic systemdisclosed herein in the feed line configuration; Fig. 4 shows schematically another embodiment of the hydronic system20 disclosed herein in the feed line configuration;Fig. 5 shows schematically another embodiment of the hydronic systemdisclosed herein in the return line configuration;Fig. 6 shows schematically another embodiment of the hydronic systemdisclosed herein in the return line configuration;Fig. 7 shows schematically another embodiment of the hydronic systemdisclosed herein in the return line configuration;30 Fig. 8 shows schematically another embodiment of the hydronic systemdisclosed herein in the feed line configuration with a freshwater tank asa thermal energy transfer element;Patentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025Fig. 9 shows schematically another embodiment of the hydronic systemdisclosed herein in the return line configuration with a freshwater tankas a thermal energy transfer element; 5 Fig. 10 a flow chart of an embodiment of the inventive DHW production method when the hydronic system is operated in the fourth operation mode; 10 Fig. 11 a flow chart of an embodiment of the inventive DHW production method when the hydronic system is operated in the second operation mode; and Figs. 12-14 show diagrams of flow q, power P and temperature T overtime t during a DHW demand event when the hydronic system was in a heating mode at reduced thermal power provided by the heat pump and wherein the electric heater is operated in comfort mode; Figs. 15-17 show diagrams of flow q, power P and temperature T over20 time t during a DHW demand event when the hydronic system was in a heating mode at reduced thermal power provided by the heat pump and wherein the electric heater is operated in volume mode; Figs. 18-20 show diagrams of flow q, power P and temperature T overtime t during a DHW demand event when the heat pump was stopped; and Figs. 20-23 show diagrams of flow q, power P and temperature T overtime t during a DHW demand event when the hydronic system was in a30 cooling mode at reduced thermal power provided by the heat pump.Patentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025 DETAILED DESCRIPTION

[42] Fig. 1 shows an embodiment of a hydronic system 1 for transferringthermal energy from a heat pump 3 to at least one thermal energy load 5 5. All figures show embodiments of the hydronic system 1 as part of a domestic heating system with the heat pump 3 as a heat source and radiators and / or underfloor heating as thermal energy loads 5. A skilled reader will readily understand that the hydronic system 1 may be used in analogy as a cooling system, for example as part of an HVAC-System. 10 The hydronic system 1 comprises a heat pump circuit section 7, 9 for transporting a heat pump flow qH that goes through the heat pump 3. The heat pump circuit section 7, 9 comprises a heat pump feed circuit section 7 arranged downstream of the heat pump 3 for providing the heat pump flow qH within the hydronic system 1. Furthermore, the heat pump circuit section 7, 9 comprises a heat pump return circuit section 9for returning the heat pump flow qH from the hydronic system 1 back to the heat pump 3. The temperature TH of the thermal energy transporting medium, e.g. water, is higher in the heat pump feed circuit section 7 than in the heat pump return circuit section 9 when the heat pump 3 is used 20 as a heat source in a heating system. The heat pump flow qH is driven by a heat pump circuit pump 11 that may be installed upstream of the heat pump feed circuit section 7 or in the heat pump return circuit section 9, or within the heat pump 3.

[43] The hydronic system 1 further comprises a load circuit section 13,15 for transporting a load flow qL that goes through the at least one ther- mal energy load 5. The load flow qL is driven by a load circuit pump 17being arranged at the load circuit section 13, 15. The load circuit section 13, 15 comprises a load feed circuit section 13 and a load return circuit30 section 15, wherein the load feed circuit section 13 is arranged down- stream of the heat pump feed circuit section 7 and the load return circuit section 15 is arranged downstream of the at least one thermal energy load 5.Patentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025

[0044] The hydronic system 1 further comprises a storage circuit section19, 21 for transporting a storage flow qS that goes through a thermal en- ergy storage tank 23. It should be noted that the storage flow qS in the5 storage circuit section 19, 21 is bidirectional and the flow direction of thestorage flow qS depends on the operation mode of the hydronic system1. The storage flow qS is selectively directable in a charging directionwhen the thermal energy storage tank 23 is charged with a thermal en- ergy and in a discharging direction when the thermal energy is dis- charged from the thermal energy storage tank 23. The storage circuit section 19, 21 comprises a storage feed circuit section 19 and a storagereturn circuit section 21, wherein the storage feed circuit section 19 isconnected to an upper, hotter part of the thermal energy storage tank23 and the storage return circuit section 21 is connected to a lower,15 cooler part of the thermal energy storage tank 23.

[0045] The hydronic system 1 further comprises a storage valve arrange-ment 25 being arranged at a connection point 27, 29, where the heatpump circuit section 7, 9, the load circuit section 13, 15, and the storage20 circuit section 19, 21 are connected. It should be noted that the connec- tion point 27, 29 may be a feed connection point 27 in a feed line con- figuration as shown in Figs. 1 to 4, where the heat pump feed circuit sec-tion 7, the load feed circuit section 13 and the storage feed circuit sec-tion 19 are connected. Alternatively, the connection point 27, 29, may be a return connection point 29, where the heat pump return circuit sec- tion 9, the load return circuit section 15 and the storage return circuit section 21 are connected in a return line configuration. It should benoted that the valve arrangement 25 is an optional feature and the op- eration modes of the hydronic system 1 may be established by a speed 30 control of the load circuit pump 17 and the heat pump circuit pump 11 alone. However, a controlled storage valve arrangement 25 is preferred.Patentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025

[0046] In the feed line configuration of the storage valve arrangement25, as shown in Fig. 1, the storage valve arrangement 25 is arranged atthe feed connection point 27, e.g. in form of a motor-controlled three-way valve, comprising a storage valve inlet 31, a storage valve storage5 port 33 and a storage valve outlet 35. The storage valve inlet 31 is con-nected to the heat pump feed circuit section 7 and receives the heat pump flow qH from the heat pump 3. The storage valve outlet 35 is con- nected to the load feed circuit section 13 to guide the load flow qL intothe load feed circuit section 13. Depending on the operation mode of10 the hydronic system 1, the storage valve storage port 33 serves as an inletor outlet to or from the storage feed circuit section 19.

[0047] The hydronic system 1 further comprises control electronics 20 (seeFig. 2) that is preferably configured to control the storage valve arrange-ment 25 and the load circuit pump 17 such that the storage flow in the storage circuit section 19, 21 is selectively directed in the charging direc- tion or in the discharging direction.

[48] It should be noted that the configuration of the hydronic system 120 in the feed line configuration or in the return line configuration dependson whether the storage valve arrangement 25 is arranged in a feed line configuration, i.e. at the feed connection point 27, or in a return line con- figuration, i.e. at the return connection point 29. Irrespective of the con-figuration of the storage valve arrangement 25, the load circuit pump 17may be arranged in a feed line configuration, in which the load circuit pump 17 is arranged upstream of the at least one thermal energy load 5 at the load feed circuit section 13 (as shown in Figs. 1-6, 8 and 9), or in areturn line configuration, in which the load circuit pump 17 is arranged downstream of the at least one thermal energy load 5 in the load return30 circuit section 15 (as shown in Fig. 7). It is possible to combine differentcombinations of configurations of the load circuit pump 17 and the stor-age valve arrangement 25.Patentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025

[0049] It is preferred that the hydronic system 1 is an integrated watercircuit, IWC, unit 37 as a part of an indoor unit 39. The IWC unit 37 maybe arranged within a housing 41 of the indoor unit 39. The IWC unit 37comprises at least three ports 43, 45, 47, i.e. a heat pump port 43 for con- 5necting the heat pump circuit section 7, 9 with the heat pump 3, a stor-age port 45 for connecting the storage circuit section 19, 21 with thethermal energy storage tank 23, and a load port 47 for connecting the load feed circuit section 13, 15 with the at least one thermal energy load5.

[50] In the return line configuration (see Figs. 5 and 6), the heat pumpport 43 of the IWC unit 37 may be a heat pump return port 43a for con- necting the heat pump return circuit section 9 with the heat pump 3. An additional heat pump feed port 43b may then be needed to connect15 the heat pump feed circuit section 7 with the heat pump 3. In the feed line configuration (see Figs. 2 to 4), the heat pump port 43 may be the heat pump feed port 43b for connecting the heat pump feed circuit section 7 with the heat pump 3 without a need for a heat pump return port 43a. 20

[51] The storage port 45 of the IWC unit 37 may be a storage returnport 45a for connecting the storage return circuit section 21 with the ther- mal energy storage tank 23 (see Figs.4 and 5). If the thermal energy stor- age tank 23 is not entirely integrated into the IWC unit 37 (as shown in Figs. 2, 3 and 5), the storage port may be a storage feed port 45b toconnect the storage feed circuit section 19 with the thermal energy stor- age tank 23. The embodiment shown in Fig.5 comprises both the storage return port 45b and the storage feed port 45b. The embodiment shown in Fig.6 comprises no storage port 45, i.e. neither the storage return port 30 45b nor the storage feed port 45b, because the thermal energy storage tank 43 is there fully integrated in the return line configuration.

[52] The load port 47 of the IWC unit 37 is in all shown embodiments aload feed port 47b for connecting the load feed circuit section 13 withPatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025 the at least one thermal energy load 5. In the return line configuration as shown in Figs.5 and 6, an additional load return port 43a may be needed to connect the load return circuit section 15 with the at least one thermal energy load 5. The IWC unit 47 needs further ports if it comprises a do-5 mestic hot water, DHW, system 49 as described below.

[53] All embodiments of the hydronic system 1 shown in the figurescomprise a domestic hot water, DHW, system 49. The DHW system 49 isvery beneficial to use the hydronic system 1 for providing hot water to a10 hot water consumer 51, e.g. a faucet, shower or bathtub. The DHW sys- tem 49 comprises a DHW freshwater circuit section 53, 55 for transportinga freshwater flow qFW coming from a fresh water supply towards the atleast one hot water consumer 51. The DHW system 49 further comprises a bypass circuit section 57, 59 for transporting a bypass flow qB as at least part of the load flow qL. Furthermore, the DWH system 49 comprises athermal transfer element 61 (in Figs. 1 to 7 shown as a heat exchanger)being arranged to thermally couple the bypass flow qB with the freshwa-ter flow qFW. Finally, the DHW system 49 comprises a bypass valve ar-rangement 63 being arranged at a bypass connection point 65, 67, 20 where the load circuit section 13, 15 and the bypass circuit section 57, 59 are connected. It should be noted that, independent of the configura-tion of the storage valve arrangement 25 and / or the load circuit pump 17, the bypass valve arrangement 63 may be arranged in a feed line configuration at a bypass feed connection point 65 where the load feedcircuit section 13 and the bypass feed circuit section 57 are connected, or in a return line configuration at the bypass return connection point 67 where the load return circuit section 15 and the bypass return circuit sec- tion 59 are connected. It should be noted that the bypass valve arrange-ment 63 is not used to control the bypass flow qB during a DHW demand 30 event, because the load flow qL is preferably fully directed as bypass flow qB through the bypass circuit section 57, 59 during a DHW demand event.Patentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025

[0054] The control electronics 20 is further configured to control, outsideof a DHW demand event, the bypass valve arrangement 63 such that atleast part of the load flow is used as the bypass flow qB. The embodimentsof the hydronic system 1 shown in Figs. 1 to 7 show the thermal transfer 5 element 61 as a heat exchanger having a primary heat exchanger part transporting the bypass flow qBand a secondary heat exchanger part transporting the freshwater flow qFW. The embodiments of Figs. 8 and 9show the thermal transfer element 61 as a freshwater tank being in ther- mal contact with a coil 69 transporting the bypass flow qB. Yet another10 option for an embodiment for the thermal transfer element 61 is a bypass flow tank (not shown) in thermal contact with a coil transporting the freshwater flow qFW.

[0055] In case of the thermal transfer element 61 is a heat exchanger,the hydronic system 1 preferably comprises a flow sensor 71 being ar- ranged in the DHW freshwater circuit section 53, 55 for measuring the freshwater flow qFW. Additionally, the hydronic system 1 may comprise ahot water temperature sensor 73 being arranged at the DHW freshwater circuit section 55 downstream of the heat exchanger 61. The control20 electronics 20 is configured to detect a DHW demand event based onmeasured values of the flow sensor 71 and the hot water temperature sensor 73. In case the thermal transfer element 61 is a freshwater tank (as shown in Figs. 8 and 9) or a bypass flow tank, the hydronic system 1 mayfurther comprise a DHW temperature sensor 75 being arranged at the thermal transfer element 61 for measuring a DHW temperature. The con- trol electronics 20 may then be configured to control, outside of a DHWdemand event, the bypass valve arrangement 63 such that the DWHtemperature is kept above a settable minimum DHW temperature. For example, in case of a freshwater tank 61, the DHW temperature should30 be kept above 55°C for reducing the risk of legionella contamination.

[56] A further feature of all embodiments of the hydronic system 1shown in the figures is an electric heater 77 being arranged at the loadPatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025 feed circuit section 13 downstream of the feed connection point 27 and upstream of the bypass feed connection point 65. The control electronics 20 is further configured to control gradually or in one or more steps thepower of the electric heater 77 for adding heating power PBUH to the load5 flow qL in the load feed circuit section 13. The hydronic system 1 may further comprise a load flow feed temperature sensor 79 being arrangedat the load feed circuit section 13 upstream of the bypass feed connec- tion point 65 and preferably upstream of the electric heater 77. The con- trol electronics 20 is configured to control stepwise or gradually a heating10 power PBUH of the electric heater 77 based on measured values of the load flow feed temperature sensor 79 and based on a load flow qL meas-ured by a load flow sensor (not shown) or estimated on the basis of op-erating values of the load circuit pump 17. The estimation is preferred tosave a load flow sensor. The electric heater 77 is useful to provide suffi-cient comfort at peak times of high thermal energy demand and toavoid dimensioning of the heat pump 3 and the thermal storage tank 23that would be oversized for most of the time outside such peak times of high thermal energy demand. The electric heater 77 may also allow asetup of the hydronic system 1, in which the temperature Ts in the thermal20 energy tank storage tank 23 can be kept at the load flow feed temper-ature TL of the at least one thermal energy load 5 during times of no DHWdemand. In case of an underfloor heating as the at least one thermal energy load 5, such load flow feed temperature TL can be relatively low. In this manner, a significant dissipation power loss from the thermal en- ergy storage tank 23 can be avoided. The electric heater 77 is preferablyonly needed to provide a higher load flow feed temperature TL duringtimes of DHW demand.

[57] Preferably, the control electronics 20 receives a heat pump circuit30 pressure value via the communication interface 88 from the heat pump 3. However, if this is not available, the hydronic system 1 may further com- prise a pressure sensor 80 being arranged in the heat pump feed circuit section 7. The control electronics 20 may preferably be configured toPatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025control the storage valve arrangement 25 and the load circuit pump 17based on measured values of the pressure sensor 80.

[0058] The hydronic system 1 may further comprise a safety valve 81 at5 the load feed circuit section 13, an expansion vessel 82 at the heat pumpfeed circuit section 7, and / or an air powered purge 83 at the load feedcircuit section 13 as shown in Fig. 2. The hydronic system 1 further com-prises a storage flow feed temperature sensor 85 being arranged in the storage feed circuit section 19 for measuring the storage flow feed tem-10 perature TS in the discharging direction into the load flow qL. It may befurther beneficial for the hydronic system 1 to comprise a storage tank temperature sensor 87 being arranged within the thermal energy storage tank 23, wherein the control electronics 20 is configured to determine acharging level of the thermal energy storage tank 23 based on meas-ured value of the storage tank temperature sensor 87. The thermal en-ergy storage tank 23 may be arranged outside of the hydronic system 1 (as shown in Fig. 3) or integrated into the hydronic system 1 as part of theintegrated water circuit, IWC, unit 37 as shown in Fig. 4.20

[0059] Preferably, the control electronics 20 comprises a communicationinterface 88 for a communication 90 with a heat pump control of theheat pump 3. The communication interface 88 may be configured toreceive a heat pump flow value qH that is measured by means of a heatpump flow sensor (not shown) or estimated on the basis of operating val-ues of the heat pump circuit pump 11. The communication interface 88 may be further configured to send a start / stop command to the heat pump 3, and / or to receive a heat pump flow feed temperature TH meas-ured by a heat pump flow feed temperature sensor 89 and a heat pump flow return temperature THR measured by a heat pump return flow tem- 30 perature sensor 91. The heat pump flow feed temperature sensor 89 may be integrated into the heat pump 3 or arranged at the heat pump feed circuit section 7 of the hydronic system 1. Analogously, the heat pump flow return temperature sensor 91 may be integrated into the heat pumpPatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025 3 or arranged at the heat pump return circuit section 9 that may be in- ternal or external to the hydronic system 1. Furthermore, the communi- cation interface 88 may be configured to send a reference control value to the heat pump 3 for setting the heat pump flow feed temperature TH 5 and / or a difference TH-THR between the heat pump flow feed tempera- ture TH and the heat pump flow return temperature THR.

[0060] The control electronics 20 is preferably configured to control thestorage valve arrangement 25 and / or both the load circuit pump 17 and10 the heat pump circuit pump 11 to operate the hydronic system 1 selec- tively in the following operation modes: a) a first operation mode in which only the heat pump flow providesthe load flow, b) a second operation mode ion which the heat pump flow and thestorage flow in the discharging direction from the thermal energy storage tank 23 are merged into the load flow,c) a third operation mode in which the heat pump flow splits into theload flow and the storage flow in the charging direction, d) a fourth operation mode, in which only the storage flow in the dis-20 charging direction provides the load flow, and e) a fifth operation mode in which are the heat pump flow is fully usedas the storage flow in the charging direction

[61] In the first operation mode, there is no charging or discharging ofthermal energy to or from the thermal energy storage tank 23, because there is no storage flow in the storage circuit section 19, 21 and prefera-bly the storage valve storage port 33 of the valve arrangement 25 is closed. This first operation mode is useful if the thermal energy storagetank 23 has a low charging level and the electricity price is high. There-30 fore, it is currently too expensive to charge the thermal energy storagetank 23. Due to the low charging level of the thermal energy storage tank 23, it cannot be used to support the heat pump 3 in providing a required load flow. The first operation mode is also useful if the electricity price isPatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025 low and the thermal energy storage tank 23 has a maximum charging level. It may therefore be more economic to save the thermal energy in the thermal energy storage tank 23 for times of higher electricity prices.As the thermal energy storage tank 23 is already fully charged, the op- 5portunity of charging the thermal energy storage tank 23 at low electric-ity prices cannot be seized. The first operation mode is usually not usedduring a DHW demand.

[62] In the second operation mode, thermal energy is withdrawn from10 the thermal energy storage tank 23 to support the heat pump 3 in provid- ing the load flow. In this situation, the storage flow in the storage feedcircuit section 19 is in the discharging direction to merge into the heatpump flow at the feed connection point 25. Both, the thermal energystorage tank 23 as well the heat pump 3 act as a thermal energy source in the second operation mode. The second operation mode is useful when the thermal energy demand of the load flow is higher than whatcan be delivered by the heat pump 3 or the thermal energy storage tank 23 alone. Another scenario for applying the second operation mode iswhen the temperature in the thermal energy storage tank 23 and / or20 downstream in the storage load circuit section 19 in discharging direc- tion of the storage flow is above a required load flow feed temperature.This may, for example, be the case if the thermal energy load 5 is an underfloor heating that requires relatively low loaf flow feed tempera- tures. The heat pump flow at a lower temperature may be used to mix the colder heat pump flow into the hotter storage flow to obtain the ref- erence load flow feed temperature in the load feed circuit section 13.The second operation mode is a preferred operation mode for produc- ing DHW when there is a DHW demand.30

[0063] In the third operation mode, the heat pump 3 serves as a thermalenergy source to provide the load flow as well as the storage flow in the charging direction to fill the thermal energy storage tank 23. The heat flow is therefore split up at the feed connection point 25 into the storagePatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025 flow and the load flow. The storage flow is in this situation directed into the charging direction in the storage feed circuit section 19. This is usefulwhen the electricity prices are low, and the charging level of the thermalenergy storage tank 23 is low during a moderate thermal energy de- 5mand of the thermal energy loads 5. In this situation, it is economic toseize the opportunity of low electricity prices and to run the heat pump3 at a higher power than needed by the thermal energy load(s) 5 andto charge the thermal energy storage tank 23 with thermal energy. The control electronics 20 commands the load circuit pump 17 in this situa-10 tion to provide a load flow that is lower than the heat pump flow pro- vided by the heat pump circuit pump 11 so that the flow difference re-sults in the storage flow in the charging direction. Irrespective of whether the heat pump circuit pump 11 is arranged in an outdoor unit of the heat pump 3 or integrated into the IWC unit 37 as part of the indoor unit 39,the control electronics 20 may be configured to directly or indirectly con-trol the speed of the heat pump circuit pump 11. However, a direct con-trol of the heat pump circuit pump 11 is not preferred if the heat pumpcircuit pump 11 is integrated in the external heat pump 3. Preferably, itthen the heat pump 3 that controls directly the speed of the heat pump 20 circuit pump 11. The control electronics 20 preferably sets a heat pump flow differential reference temperature for the heat pump 3 to achieve.Thereby, the control electronics 20 is able to indirectly control the speedof the heat pump circuit pump 11 and thus to indirectly control the heat pump flow. The third operation mode is usually not used during a DHWdemand.

[64] In the fourth operation mode, the heat pump flow in the heatpump circuit section 7, 9 is zero, so that the storage flow in the discharg- ing direction in the storage feed circuit section 19 provides the full load30 flow alone. The fourth operation mode is useful when the electricity price is high and the thermal energy storage tank 23 is sufficiently charged with thermal energy. It is useful to save one or more start / stop cycles of thePatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025 heat pump. Therefore, it is a further scenario for applying the fourth op- eration mode when the thermal energy demand of the thermal energy loads 5 is so low that the required load flow is below a minimum heat pump flow for the heat pump 3 to properly work. The fourth operation 5mode is therefore very useful to save a significant number of start / stopcycles of the heat pump 3, which prolongs the lifetime and efficiency of the heat pump 3. The fourth operation mode is a preferred operationmode for producing DHW when there is a DHW demand.10

[0065] In the fifth operation mode, there is no thermal energy demand ofthe thermal energy loads 5, so that the load flow is zero. In the situation, it is useful to run the hydronic system 1 in the fifth operation mode when the electricity price is low, and the thermal energy storage tank 23 is not fully charged. This is particularly useful during summer months when the thermal energy demand is less continuous and comes mainly from the DHW system 49. The thermal energy storage tank 23 can be chargedduring times of no thermal energy demand and discharged, preferably in the fourth operation mode, when the DHW system 49 demands ther-mal energy. This can significantly reduce the number of start / stop cycles 20 of the heat pump 3 during the summer months, which is advantageous for the lifetime and efficiency of the heat pump 3. The fifth operationmode is usually not used during a DHW demand.

[66] The control electronics 20 is further configured to check in the firstfour operation modes whether the load flow feed temperature in the load feed circuit section 13 as measured by the load flow feed temper- ature sensor 70 is sufficient to satisfy the thermal energy demand of the thermal energy load(s) 5 and / or the DHW system 49. If this is not the case,the control electronics 20 is configured to switch on and / or turn up, grad-30 ually and / or in steps, the power of the electric heater 77 to obtain theneeded load flow feed temperature in the load feed circuit section 13. The control electronics 20 may be configured to balance the fractions ofthermal energy coming from the heat pump 3, from the thermal energyPatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025 storage tank 23 and the electric heater 77 depending on the electricity price, the thermal energy demand and the charging level of the thermal energy storage tank 23. The flexibility of mixing the thermal energy con- tributions of the heat pump 3, the thermal energy storage tank 23 and 5 the electric heater 77 allows a smaller dimensioning of all three compo- nents and allows the most economic operation of the hydronic system 1. Preferably, the electric heater 77 is only used in the second and fourth operation mode during during a DHW demand.

[67] The above-mentioned operation modes are applicable for all em-bodiments shown in the figures. Fig. 1 shows the hydronic system 1 in thefeed line configuration, wherein the storage valve arrangement 25 is ar- ranged at the feed connection point 25, the load circuit pump 17 is ar- ranged at the load feed circuit section 13 and the bypass valve arrange- 15 ment 63 is arranged at the bypass feed connection point 65.

[68] Fig. 2 and 3 show the embodiment of Fig. 1 in form of an inte-grated water circuit, IWC, unit 37 as part of an indoor unit 39, wherein thehydronic system 1 is arranged within the housing 41 of the indoor unit 39.20 The IWC unit 37 comprises the heat pump port 43 for connecting the heatpump feed circuit section 7 with the heat pump 3 and the storage portfor connecting the storage feed circuit section 19 with the thermal en- ergy storage tank 23. In the feed line configuration, the heat pump port 43 may be a heat pump feed port 44b. The load port 47, here a load feed port 47b, of the IWC unit 37 is used to connect the load feed circuitsection 13 with the at least one thermal energy load 5. The DHW system 49 requires in the feed line configuration of Figs. 1 to 4 three additionalports 86, 84, 92, namely a cold freshwater inlet port 86, a hot freshwateroutlet port 84 and a bypass return outlet port 92. The cold freshwater inlet30 port 86 is used to connect the DHW freshwater circuit section 53 with a freshwater supply. The hot freshwater outlet port 84 is used to connectthe DHW freshwater circuit section 55 with the hot water consumer 51.Patentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025The bypass return outlet port 92 is used to connect the bypass return cir-cuit section 59 with the load return circuit section 15.

[69] In Fig. 4, the thermal energy storage tank 23 is integrated into the5 IWC circuit 37, so that the storage port 45, here a storage return port 45a,is used to connect the storage return circuit section 21 with the return connection point 29 where the load return circuit section 15 and the heat pump return circuit section 9 are connected.10

[0070] In Fig. 5, the hydronic system 1 is in a return line configuration, be-cause the storage valve arrangement 25 is arranged at the return con-nection point 29. The bypass valve arrangement 63 is here also arranged in the return line configuration, because it is arranged at the bypass re- turn connection point 67. The load circuit pump 17 is here in the feed line configuration, because it is arranged at the load feed circuit section 13. In this embodiment, the load return circuit section 15 is fully integrated into the IWC unit 37. The IWC unit 37 then needs two ports 43a,b, 45a,b,47a,b, 86, 84 each for the thermal energy storage tank 23, for the heatpump 3, for the thermal energy load(s) 5, and for the DHW system 49. 20

[71] As shown in Fig. 6, the two ports 43a,b to the thermal energy stor-age tank 23 can be saved if the thermal energy storage tank 23 is fullyintegrated into the IWC unit 37. Fig. 7 shows that the load circuit pump17 may be arranged, in a return line configuration, at the load return cir-cuit section 15. If the load return circuit section 15 is fully integrated intothe IWC unit 37, for example when the storage valve arrangement 25and / or the bypass valve arrangement 63 are in the return line configura- tion, the return line configuration of the load circuit pump 17 may be beneficial, because the return temperature in the load return circuit sec-30 tion 15 is lower than the load flow feed temperature in the load feed circuit section 13.Patentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025

[0072] The embodiment shown in Fig. 8 is a feed line configuration for allthe storage valve arrangement 25, the load circuit pump 17, and thebypass valve arrangement 63, wherein the thermal transfer element 61 of the DHW system 49 is a freshwater tank. The DHW flow is guided 5 through the coil 69 arranged within the freshwater tank 61 in order to heat up the fresh water within the freshwater tank 61 to a desired DHWtemperature. The flow sensor 71 may measure a freshwater flow qFW, butthis is not needed. The DHW temperature senor 75 being arranged withinthe freshwater tank 61 may be used to measure the DHW temperature 10 to indicate a hot water demand. The freshwater tank 61 is heated up as soon as the DHW temperature falls below a pre-determined lower thresh- old. The heating up of the freshwater tank 61 is stopped as soon as the DHW temperature reaches a pre-determined upper threshold. The con- trol electronics 20 may thus be configured to control, outside of a DHWdemand event, the bypass valve arrangement 63 such that the DHWtemperature is at least kept above a settable minimum DHW tempera- ture, e.g. above 55°C for reducing the risk of legionella contamination.Fig. 9 shows the DHW system 49 with a freshwater tank 61 in combinationwith a hydronic system 1 having the storage valve arrangement 25 and20 the bypass valve arrangement 63 in the return line configuration.

[73] The control electronics 20 is preferably integrated into the IWC unit37 as part of the indoor unit 39. Preferably, at least parts of electronicsalready available in the indoor unit 39 may be programmed or updatedto be used to function as the control electronics 20 of the IWC unit 37.The control electronics 20 may alternatively be arranged on extra hard-ware components arranged within the housing 41 of the indoor unit 39. Such extra hardware components may be in communication connec-tion with other electronic hardware components 93 of the indoor unit 39,30 such as a human machine interface and / or a display of the indoor unit39. As an alternative, or in addition, the control electronics 20 may bepart of a cloud-based system and / or a building management system (BMS) external of the IWC unit 37.Patentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025

[0074] The control to establish a reference load flow feed temperature isnow explained with reference to Fig. 1 in more detail. However, it shouldbe noted that the control to establish the reference load flow feed tem- 5 perature applies to all embodiments of Figs.1 to 9.

[75] The following situation may apply. There is no DHW demand andthe hydronic system 1 is operated in the first operation mode in which only the heat pump 3 provides thermal power PH to the at least one ther-10 mal energy load 5. In this situation, the output power of the thermal en- ergy storage tank PS is zero and the thermal energy consumption PL of the at least one thermal energy load 5 equals the thermal output power PH of the heat pump 3. The heat pump flow qH equals the load flow qL and the load flow feed temperature TL equals the heat pump flow feed temperature TH. The following equations apply in this situation: wherein ^ ist the density of the thermal energy transferring medium, e.g.water, and cp is the specific heat capacity of the thermal energy trans- ferring medium, e.g. water. The load circuit pump 17 may be switched20 off in this situation, because the heat pump circuit pump 11 may pro- vide alone the load flow qL that equals the heat pump flow qH. Thecontrol electronics 20 directly controls the speed of the heat pump cir-cuit pump 11 to obtain a load flow qL requested by the at least one thermal energy load 5. Alternatively, the control electronics 20 may seta heat pump differential TH-THR so that the heat pump 3 sets the speed of the heat pump circuit pump 11 accordingly to provide the re- quested heat pump differential TH-THR. thereby, the control electronics20 indirectly controls the speed of the heat pump circuit pump 11. Theopening degree of the bypass valve arrangement 65 is, outside of a30 DHW demand event, controlled to obtain a desired bypass flow qB forestablishing a desired heat pump flow return temperature THR that is de- termined by the following equation: Patentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025 wherein TLR is the load flow return temperature. The speed of the heat pump circuit pump 11 is then varied until a deviation of the load flow feed temperature TL from the reference load flow feed temperature isminimised. 5

[76] Another situation may apply as follows. There is no DHW demandand the hydronic system 1 is operated in the second operation mode in which both the heat pump 3 and the thermal energy storage tank 23simultaneously provide thermal power to the at least one thermal energy 10 load 5. In this situation, the output power of the thermal energy storage tank PS adds to the output power of the heat pump PH. The thermal en- ergy consumption PL of the at least one thermal energy load 5 then equals the sum of the output power of the thermal energy storage tankPS and the thermal output power PH of the heat pump 3. The speed ofthe load circuit pump 17 is set to provide a requested load flow qL. The speed of the heat pump circuit pump 11 is varied until a deviation of the load flow feed temperature TL from the reference load flow feed tem-perature is minimised. The following equations apply in this situation: 20 This means that the needed heat pump flow qH can be found to establish the reference load flow feed temperature. In the first, second and fourthoperation mode, i.e. when the storage flow is zero or in discharging di- rection, TBLR is equal to the known heat pump flow return temperature THR.

[77] In another situation, the hydronic system 1 may be operated in thethird operation mode in which the heat pump 3 supplies thermal energy simultaneously to both the thermal energy storage tank 23 and to the at 30 least one thermal energy load 5. The following equations apply in this situation: ^^ = ^^ + ^^Patentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025 wherein TBLR is a load flow return temperature after mixing with the bypass 5flow qB. This means that the needed heat pump flow qH can be found toestablish the reference load flow feed temperature.

[0078] Embodiments of the inventive DHW production are explained withreference to Figs.10 and 11 in combination with Fig.1. However, it should10 be noted that the inventive DHW production is applicable for all embod-iments of Figs. 1 to 9.

[79] Fig. 10 shows an example of the inventive method of transferringthermal energy from the heat pump 3 to produce DHW, wherein the hydronic system 1 is operated in the fourth operation mode, in whichthe heat pump flow is zero and the storage flow provides the full load flow. The following operating variables are known, measured or esti- mated: a storage flow feed temperature TS which may be determined by the storage flow feed temperature sensor 85 and / or the storage20 tank temperature sensor 87; a freshwater flow qFW which may be deter-mined by the flow sensor 71 or deduced from the bypass flow qB and temperature differentials across the primary and secondary parts of the heat exchanger 61; a hot water temperature TDHW of the freshwaterflow as measured by the hot water temperature sensor 73; and load flow qL as measured by a load flow sensor or preferably estimated based on the current speed and power consumption of the load flow circuit pump 17. It should be noted that, during a DHW demand event,the load flow qL is preferably directed fully into the bypass flow qB, so that the bypass flow qB through the primary part of the heat exchanger30 61 equals the load flow qL. The flow through other thermal energyload(s) 5 is then zero during a DHW demand event.Patentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025

[0080] In step 1001, it is checked if the freshwater flow qFW exceeds a startthreshold value qstart, e.g.1 litre / min, for triggering a DHW demand event. It is also regularly, e.g. every 50 ms, or constantly checked in step 1001 if 5 the freshwater flow has dropped below a stop threshold value qstop, e.g. 1litre / min, for ending a DHW demand event. The threshold values qstartand qstop may be identical or differ from each other. If the freshwater flow qFW is below the threshold(s) qstart or qstop for having a DHW demandevent, the DHW production stops at step 1003 by stopping the electric10 heater 77 (and the load circuit pump 17 if there is currently no other ther- mal energy load 5 demanding a load flow qL).

[81] If, however, there is a DHW demand event ongoing, the methodproceeds to step 1005 in which a reference temperature differential ^THEXref between the primary part and the secondary part of the heat ex-changer 61, a reference hot water temperature TDHWref, and a referenceload flow qLref is determined. The reference load flow qLref depends on the freshwater flow qFW and a desirable thermal transfer element ratio RHEX for operating the heat exchanger 61 efficiently. A heat exchanger20 ratio RHEX about one is usually most efficient, e.g. RHEX=1.15. The heat ex- changer ratio RHEX may be a pre-defined constant or a pre-defined func- tion of temperatures and / or flows. Anyway, the reference load flow qLref is fully defined by the known freshwater flow qFW.

[82] The reference hot water temperature TDHWref is defined by the fol-lowing equation: ^^^^^^^ = −^^^ ∙ ^^^ + ^^^wherein ^^^and ^^^are pre-determined parameters of a linear rela-30 tionship between the reference hot water temperature TDHWref and thefreshwater flow qFW. The rationale is here to have a lower reference hotwater temperature TDHWref when a high freshwater flow qFW is detected.The aim is here to extend the maximum duration of a DHW demandevent for a given charging level of the thermal energy storage tank 23Patentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025when the freshwater flow qFW is high. A high freshwater flow qFW is mostlikely requested by an open shower tap or a bathtub tap. However, asshowers and bathtubs nowadays use a thermostat to mix cold waterwith hot water, there is no need for very hot water during a DHW de-5 mand event of a shower or bathtub. The lower the reference hot watertemperature TDHWrefis, the longer the DHW demand event can be with- out the help of the heat pump flow. The relationship between refer- ence hot water temperature TDHWref and the freshwater flow qFW couldalso be given by a lookup table, wherein a fixed low reference hot wa-10 ter temperature TDHWref could be used for high freshwater flows qFW, e.g.at or above 66% of a maximum freshwater flow qFW, and another fixedhigher reference hot water temperature TDHWref could be used for low freshwater flows qFW, e.g. below 66% of the maximum freshwater flowqFW.

[83] The reference temperature differential ^THEXref between the pri-mary part and the secondary part of the heat exchanger 61 is definedby the following equation: ∆^^^^^^^ = −^∆^^^^ ∙ ^^^ + ^∆^^^^20 wherein ^∆^^^^and ^∆^^^^are pre-determined parameters of a linear relationship between the reference temperature differential ^THEXref andthe freshwater flow qFW. The rationale is here is to make a best guess forthe required temperature lift ^THEXref that the heat exchanger 61 must pro-vide. The heat exchanger 61 has a flow-dependent specific temperaturelift, because the efficiency of the heat transfer from the primary part tothe secondary part of the heat exchanger 61 is dependent on the flowspassing through both the primary and secondary parts of the heat ex-changer 61. A high flow passing through the heat exchanger 61 is moreturbulent than a low flow and turbulent flow provides a higher efficiency30 of the heat transfer. Therefore, a lower hex temperature lift is needed for high freshwater flows. It follows that the bypass flow qB in the bypass feedcircuit section 57 must be at a reference temperature THEXref that is thePatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025reference hot water temperature TDHWref plus the reference temperaturedifferential ^THEXref.

[0084] In step 1007, a heating power PBUH of the electric heater 77 is de-5 termined. If the known storage flow feed temperature TS is below THEXref, the electric heater 77 is needed to heat up the load flow qL. A reference heating power PBUHref of the electric heater 77 can be determined by: The electric heater 77 may have only three discrete heating power steps 10 to choose, in which one, two or three power phases of the electric heater 77 may be activated. In order to select the needed number of activated power phases, the smallest whole-numbered multiple of a third of the maximum heating power PBUHmax may be selected to run the electric heater 77 with a certain heating power PBUH, i.e.: The electric heater 77 is activated in step 1009 accordingly to providethe heating power PBUH.

[85] The reference load flow qLref is then used as an input into a feed-20 forward control of the speed of the load circuit pump 17. However, the reference load flow qLref is compensated using a PI controller in a closed-loop control in step 1011. In step 1011, a PI reference load flow qLPIref is determined to minimise a deviation of the hot water temperature TDHW from the reference hot water temperature TDHWref. The PI reference load flow qLPIref is added to the feed-forward reference load flow qLref to yielda compensated reference load flow qLcompref that is used in step 1013 as a reference for controlling the speed of the load circuit pump 17 to ob- tain a load flow qL that equals the compensated reference load flow qLcompref. Thereby, the hydronic system 1 is most efficiently operated to30 produce DHW using the storage flow qS alone as the load flow qL.Patentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025

[0086] Fig. 11 shows an example of the inventive method of transferringthermal energy from the heat pump 3 to produce DHW, wherein the hy- dronic system 1 is operated in the second operation mode in which the heat pump flow and the storage flow mix to provide together simultane- 5ously the load flow. The DHW production method is very similar to thesituation described in Fig. 10. The feed-forward control part of the speed of the load circuit pump 17 is the same, but the closed-loop control part is different. There is also another operating variable of the hydronic sys- tem 1 available, namely the load flow feed temperature TL. 10

[87] In step 1101, it is checked if the freshwater flow qFW exceeds a startthreshold value qstart, e.g.1 litre / min, for triggering a DHW demand event. It is also regularly, e.g. every 50 ms, or constantly checked in step 1101 ifthe freshwater flow has dropped below a stop threshold value qstop, e.g. 1 litre / min, for ending a DHW demand event. The threshold values qstart and qstop may be identical or differ from each other. If the freshwater flow is below the threshold(s) qstart or qstop for having a DHW demand event,the DHW production stops at step 1103 by stopping the electric heater 77 (and the load circuit pump 17 if there is currently no other thermal20 energy load 5 demanding a load flow qL).

[88] If, however, there is a DHW demand event ongoing, the methodproceeds to step 1105 in which a reference temperature differential ^THEXref between the primary part and the secondary part of the heat ex- changer 61, a reference hot water temperature TDHWref, and a reference load flow qLref is determined. The reference load flow qLref depends on the freshwater flow qFW and a desirable thermal transfer element ratio RHEX for operating the heat exchanger 61 efficiently. A heat exchanger ratio RHEX about one is usually most efficient, e.g. RHEX=1.15. The heat ex-30 changer ratio RHEX may be a pre-defined constant or a pre-defined func- tion of temperatures and / or flows. Anyway, the reference load flow qLref is fully defined by the known freshwater flow qFW.Patentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025

[0089] The reference hot water temperature TDHWref is defined by the fol-lowing equation: ^^^^^^^ = −^^^ ∙ ^^^ + ^^^wherein ^^^and ^^^are pre-determined parameters of a linear rela- 5tionship between the reference hot water temperature TDHWref and thefreshwater flow qFW. The rationale is here to have a lower reference hotwater temperature TDHWref when a high freshwater flow qFW is detected.The aim is here to extend the maximum duration of a DHW demandevent for a given charging level of the thermal energy storage tank 2310 when the freshwater flow qFW is high. A high freshwater flow qFW is mostlikely requested by an open shower tap or a bathtub tap. However, asshowers and bathtubs nowadays use a thermostat to mix cold waterwith hot water, there will is no need for very hot water during a DHW de-mand event of a shower or bathtub. The lower the reference hot watertemperature TDHWref is, the longer the DHW demand event can be with- out the help of the heat pump flow. The relationship between refer- ence hot water temperature TDHWref and the freshwater flow qFW couldalso be given by a lookup table, wherein a fixed low reference hot wa-ter temperature TDHWref could be used for high freshwater flows qFW, e.g.20 at or above 66% of a maximum freshwater flow qFW, and another fixedhigher reference hot water temperature TDHWref could be used for low freshwater flows qFW, e.g. below 66% of the maximum freshwater flowqFW.

[90] The reference temperature differential ^THEXref between the pri-mary part and the secondary part of the heat exchanger 61 is definedby the following equation: ∆^^^^^^^ = −^∆^^^^ ∙ ^^^ + ^∆^^^^wherein ^∆^^^^and ^∆^^^^are pre-determined parameters of a linear30 relationship between the reference temperature differential ^THEXref andthe freshwater flow qFW. The rationale is here is to make a best guess forthe required temperature lift ^THEXref that the heat exchanger 61 must pro-vide. The heat exchanger 61 has a flow-dependent specific temperaturePatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025lift, because the efficiency of the heat transfer from the primary part tothe secondary part of the heat exchanger 61 is dependent on the flowspassing through both the primary and secondary parts of the heat ex-changer 61. A high flow passing through the heat exchanger 61 is more5 turbulent than a low flow and turbulent flow provides a higher efficiencyof the heat transfer. Therefore, a lower hex temperature lift is needed for high freshwater flows. It follows that the bypass flow qB in the bypass feedcircuit section 57 must be at a reference temperature THEXref that is the reference hot water temperature TDHWref plus the reference temperature10 differential ^THEXref.

[91] In step 1107, a heating power PBUH of the electric heater 77 is de-termined. If the known storage flow feed temperature TS is below THEXref, the electric heater 77 is needed to heat up the load flow qL. A reference heating power PBUHref of the electric heater 77 can be determined by: ^^^^^^^ = ^ ∙ ^^ ∙ ^^ ∙ ^^^^^^^^ − ^^^The electric heater 77 may have only three discrete heating power steps to choose, in which one, two or three power phases of the electric heater 77 may be activated. In order to select the needed number of activated 20 power phases, the smallest whole-numbered multiple of a third of the maximum heating power PBUHmax may be selected to run the electric heater 77 with a certain heating power PBUH, i.e.: The electric heater 77 is activated in step 1109 accordingly to provide the heating power PBUH.

[92] The reference load flow qLref is then used as an input into a feed-forward control of the speed of the load circuit pump 17. The reference load flow qLref is used in step 1113 as a reference for controlling the speed30 of the load circuit pump 17 to obtain a load flow qL that equals the ref- erence load flow qLref.Patentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025

[0093] In step 1115, a reference load flow feed temperature TLref is deter-mined by: 5

[0094] In step 1117, a PI reference load flow feed temperature TLPIref is de-termined in a closed-loop control by a PI controller that minimises a de- viation of the hot water temperature TDHW from the reference hot water temperature TDHWref. That PI reference load flow feed temperature TLPIref is added to the reference load flow feed temperature TLref to yield a com-10 pensated reference load flow feed temperature TLcompref that is used instep 1119 as a reference for controlling the speed of the heat pump cir-cuit pump 11 to obtain a load flow feed temperature TL that equals thecompensated reference load flow feed temperature TLcompref. Thereby,the hydronic system 1 is most efficiently operated to produce DHW using the storage flow and the heat pump flow mixed together as the load flow.

[95] Figs. 12-23 show diagrams of flow q, power P, and temperature Tover time t during a typical DHW demand event as outlined in Fig. 11 in 20 different scenarios. Figs. 12-14 shows an example situation in which the hydronic system 1 was operating in the first operation mode before the DHW demand event started at time t=0. In the shown example of Figs. 12-14, the heat pump 3 was being operated at time t=0 with reduced power, e.g. 3 kW, to provide thermal energy to the thermal energyload(s) 5 for heating with a heat pump flow feed temperature TH of 38°Cto achieve a heating ^T of 8 °C. The heat pump 3 has a maximum powerof 9 kW in this example. At time t=0, the DHW system 49 detects a fresh-water flow qFW above qstart, i.e. 1 litre / min. The freshwater flow qFW is here 9 litres / min and assumed to be constant over the full DHW demand event 30 that extends over 250 seconds or more in the shown example. The heat exchanger ratio RHEX is 1.15 in this example, so that a reference load flow qLrefis set to 10.35 litres / min. The control electronics 20 thus controls thePatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025 load circuit pump 17 to quickly ramp up to drive a load flow qL of 10.35 litres / min as quickly as possible. As shown in Fig. 12, the reference load flow qLref is reached within a few seconds. Following the control logic ofFig. 11, the control electronics 20 sets here the reference hot water tem- 5perature TDHWref to 42°C. The compensated reference load flow feedtemperature TLcomprefis determined to be 47°C. The storage flow feed temperature TS is here 56°C and assumed to be constant during the whole DHW demand event, i.e. the charging level of the thermal energy storage tank 23 is sufficient to operate in the second operation mode 10 during the entire DHW demand event. The volume of the thermal energy storage tank 23 is 80 litres in this example.

[96] Fig. 12 show the flows q over time t of the DHW demand event.The load flow qL reaches the reference load flow qLref of 10.35 litres / minwithin seconds and remains constant for the rest of the DHW demand event. The heat pump circuit pump 11 was already running at t=0 to drive aheat pump flow qH of about 5.35 litres / min for heating the thermal en-ergy load(s) 5 in the first operation mode. Once the DHW demand event started, the heat pump 3 gets a command to ramp up its power PH as 20 shown in Fig. 13, which takes about 40 seconds to reach the maximum heat power of 9kW. During the ramp-up phase of the heat pump 3, the heat pump circuit pump 11 is slowly ramped up. The flow difference be- tween the load flow qL driven by the load circuit pump 17 and the heat pump flow qH driven by the heat pump circuit pump 11 is the resulting storage flow qS with which thermal energy is withdrawn from the thermal energy storage tank 23. With the quick ramp-up of the load circuit pump 17, the storage flow qS quickly rises to 5 litres / min and then reduces as the heat pump circuit pump 11 is slowly ramped up during the ramp-up phase of the heat pump 3. Once the heat pump 3 is fully ramped up 30 after 40 seconds, the storage flow qS settles at about 4.4 litres / min and the heat pump flow qH settles at 6.95 litres / min to mix at the feed con- nection point 27 and yield in sum the load flow qL of 10.35 litres / min.Patentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025

[0097] Fig. 13 shows the power P over time t of said DHW demand event.To meet the DHW demand, the thermal transfer element 61 must transfer 20kW thermal power PDHW to the freshwater flow qFW as quickly as possi- ble. During the ramp-up phase of the heat pump 3, the DHW demand5 cannot be met without the help of the electric heater 77. In Figs. 12-14, the electric heater 77 is operated in a comfort mode that shall ensure reaching the reference hot water temperature TDHWref of 42°C within sec- onds, i.e. significantly before the end of the ramp-up phase of the heat pump 3. The electric heater 77 is thus controlled to add heating powerPBUH during the ramp-up phase of the heat pump 3. The added heatingpower PBUH is controlled to be at its maximum of 6kW at the start of the DHW demand event and then stepwise reduced during the ramp-up phase of the heat pump 3. Thereby, the desired thermal power PDHW of 20kW is quickly reach within seconds and fluctuates slightly about 20kW15 during the ramp-up phase of the heat pump 3.

[98] Fig. 14 shows the temperatures T over time t of said DHW demandevent. The hot water temperature TDHW quickly reaches the desired refer- ence value TDHWref of 42°C and fluctuates about 42°C during the the20 ramp-up phase of the heat pump 3. The heat pump flow feed tempera- ture TH initially drops with the ramp up of the heat pump circuit pump 11 before the heat pump 3 can compensate that by its own ramp-up. The added heating power PBUH of the electric heater 77, however, compen- sates that in the first seconds of the DHW demand event. As the heat pump 3 ramps up further, the heat pump flow feed temperature TH rises to 41°C, which leads to a rise of the load flow feed temperature TL to the desired value TLcompref of 47°C. The storage flow feed temperature TS isconstantly at 57°C during the whole DHW demand event.30

[0099] One main advantage of the inventive method and system to pro-vide DHW as shown in Figs. 11 to 23 by an operation of the hydronic sys- tem 1 in the second operation mode is a saving in consumption from the thermal energy storage tank 23, which can thus be designed smaller. APatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025 thermal energy storage tank 23 having a volume of 80 litres can be used to meet a DHW demand of more than 160 litres. Fig. 12 shows that the storage flow qS is significantly less than the required load flow qL. 5

[0100] Figs. 15-17 show the three diagrams of flow q, power P and tem-perature t over time t when the electric heater 77 is set to volume mode. The rationale is here to achieve a maximum of storage flow saving to meet a maximum volume DHW demand event, e.g. filling a bathtub. As shown in Fig. 16, the electric heater 77 is operated at maximum power10 PBUH of 6kW during the whole DHW demand event. This means that muchless storage flow qS is required and the heat pump flow qH can be much higher. In the shown example of Fig. 15, the storage flow qS setlles to about 2 litres / min, whereas the heat pump flow qH reaches 8.35 litres / min to yield in sum the required load flow qL of 10.35 litres / min. It should benoted that the load flow feed temperature TL is measured here by the load flow feed temperature sensor 79 being installed upstream of theelectric heater 77 as shown in Fig.1. Thus, the hot water temperature TDHW is higher than the load flow feed temperature TL, because heating power PBUH of 6kW is added by the electric heater 77 downstream of the load20 flow feed temperature sensor 79.

[101] Figs. 18-20 show the three diagrams of flow q, power P and tem-perature t over time t when the electric heater 77 is set to comfort mode as in Figs. 12-14. In Figs. 18-20, however, the heat pump 3 was switched off at the beginning of the DHW demand event. The ramp-up phase is thus longer and takes now about 170 seconds. The heat pump 3 does not provide any heating power PH during the first 90 seconds, so that the cool heat pump flow qH cools the storage flow qS to achieve a load flow feed temperature TL that equals the desired load flow feed temperature 30 TLcompref of 47°C. The electric heater 77 is only switched on shortly in the first seconds of the DHW demand event, because the storage flow qS is hot enough. Of course, the thermal energy consumption from the ther- mal energy storage tank 23 is high during the first 90 seconds. Once thePatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025 heat pump 3 is ramped up to 3 kW to contribute heating power, the sit- uation continues similarly as described in Figs. 12-14.

[102] Figs. 21-23 show the three diagrams of flow q, power P and tem-5 perature t over time t when the electric heater 77 is set to comfort mode as in Figs.12-14 and 18-20. In Figs.21-23, however, the heat pump 3 was providing (negative) cooling power of PH=-3kW to the thermal energyload(s) 5 at the beginning of the DHW demand event. As long as theheat pump thermal power PHis negative, the electric heater 77 is 10 switched to maximum heating power PBUH of 6kW and the heat pump flow qH is quickly reduced. The ramp-up phase of the heat pump 3 is sim- ilarly long as when the heat pump 3 was switched off as shown in Figs. 18-20. The electric heater 77 is operated at 5kW during a plateau phase when the heat pump 3 does not contribute heat pump power PH. Thereby, the storage flow qS can be kept relatively low at about 6 li- tres / min during the ramp-up phase of the heat pump 3. The heat pump flow qH is thus controlled to be about 4.35 litres / min during the ramp-up phase of the heat pump 3. Once the heat pump 3 starts contributing positive thermal power PH, the added heating power PBUH of the electric 20 heater 77 is reduced stepwise to zero. The heat pump flow qH is gradually increased together with the increase of the heat pump flow fee temper- ature TH to about 6 litres / min, so that the storage flow qS reduces to about 4.35 litres / min.

[103] Where, in the foregoing description, integers or elements are men-tioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Referenceshould be made to the claims for determining the true scope of the pre- sent disclosure, which should be construed so as to encompass any such30 equivalents. It will also be appreciated by the reader that integers or fea-tures of the disclosure that are described as optional, preferable, advan- tageous, convenient or the like are optional and do not limit the scope of the independent claims.Patentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025

[0104] The above embodiments are to be understood as illustrative ex-amples of the disclosure. It is to be understood that any feature de-scribed in relation to any one embodiment may be used alone, or in 5 combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. While at least oneexemplary embodiment has been shown and described, it should be un- derstood that other modifications, substitutions and alternatives are ap- 10 parent to one of ordinary skill in the art and may be changed without departing from the scope of the subject matter described herein, and this application is intended to cover any adaptations or variations of the specific embodiments discussed herein.

[105] In addition, "comprising" does not exclude other elements or steps,and "a" or "one" does not exclude a plural number. Furthermore, charac-teristics or steps which have been described with reference to one of the above exemplary embodiments may also be used in combination with other characteristics or steps of other exemplary embodiments de-20 scribed above. Method steps may be applied in any order or in parallelor may constitute a part or a more detailed version of another method step. It should be understood that there should be embodied within thescope of the patent warranted hereon all such modifications as reason- ably and properly come within the scope of the contribution to the art. Such modifications, substitutions and alternatives can be made without departing from the spirit and scope of the disclosure, which should be determined from the appended claims and their legal equivalents.

[106] List of reference numerals:30 1hydronic system3 heat pump5 thermal energy loadsPatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 20257 heat pump feed circuit section9 heat pump return circuit section11 heat pump circuit pump13 load feed circuit section5 15 load return circuit section17 load circuit pump19 storage feed circuit section20 control electronics21 storage return circuit section10 23 thermal energy storage tank25 storage valve arrangement27 feed connection point29 return connection point31 storage valve inlet33 storage valve storage port35 storage valve outlet37 integrated water circuit, IWC 39 indoor unit41 housing of indoor unit20 43 heat pump port43a heat pump return port43b heat pump feed port45 storage port45a storage return port45b storage feed port47 load port47a load return port47b load feed port49 DHW system30 51 hot water consumer53 cold DHW freshwater circuit section55 hot DHW freshwater circuit section57 bypass feed circuit sectionPatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 202559 bypass return circuit section61 thermal transfer element63 bypass valve arrangement65 bypass feed connection point5 67 bypass return connection point69 coil71 flow sensor73 hot water temperature sensor75 DHW temperature sensor10 77 electric heater79 load flow feed temperature sensor80 pressure sensor81 safety valve82 expansion vessel83 air purge84 hot freshwater outlet port85 storage flow feed temperature sensor86 cold freshwater inlet port87 storage tank temperature sensor20 88 communication interface89 heat pump flow feed temperature sensor90 communication91 heat pump return temperature sensor92 bypass return outlet port93 electronic hardware components of the indoor unitPS thermal output power of the storage tank PH thermal output power of the heat pump PL thermal power consumption of the at least one thermal energy load 30 PDHW thermal power consumption of the thermal transfer element PBUH heating power of the electric heater qS storage flow qH heat pump flowPatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025 qL load flow qB bypass flow qFW freshwater flow TS storage flow feed temperature 5 TSR storage flow return temperature TLload flow feed temperature TLR load flow return temperature TH heat pump flow feed temperature THR heat pump flow return temperature 10 TBLR load flow return temperature after mixing with the bypass flow TDHW hot water temperature of the freshwater flowPatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025

Claims

1. Claims 1. A method for providing domestic hot water, DHW, by a hydronicsystem (1) comprising a heat pump (3), a thermal energy storage tank (23) and a DHW system (49) with a thermal transfer element5 (61), wherein the method comprises:- identifying a DHW demand event,- controlling, in case of an identified DHW demand event, oper-ation of a load circuit pump (17) for driving a load flow (qL)along a load feed circuit section (13) of the hydronic system (1)10 through a primary part of the thermal transfer element (61), -controlling operation of a heat pump circuit pump (11) for driv-ing a heat pump flow (qH) through the heat pump (3) along a heat pump feed circuit section (7) of the hydronic system (1), -withdrawing a storage flow (qS) from the thermal energy stor-age tank (23) along a storage feed circuit section (19) of the hydronic system (1), and -mixing the heat pump flow (qH) with the storage flow (qS) at afeed connection point (27) where the heat pump feed circuit section (7), the load feed circuit section (13) and the storage 20 feed circuit section (19) are connected upstream of the primary part of the thermal transfer element (61), wherein the storage flow (qS) results from the controlled operation of the heat pump circuit pump (11) and of the load circuit pump (17) so that the sum of the heat pump flow (qH) and the storage flow (qS) yields the load flow (qL) through the primary part of thethermal transfer element (61).

2. The method of claim 1, further comprising determining a load flowfeed temperature (TL) of the load flow (qL) by a load flow feed tem-30 perature sensor (79), wherein the load flow feed temperature sen- sor (79) is arranged at the load feed circuit section (13), and wherein said controlling of the operation of the heat pump circuitatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025 pump (11) adjusts the mixing so that a deviation of the load flow feed temperature (TL) from a reference load flow feed temperature (TLcompref) is minimised.

53. The method of claim 1 or 2, further comprising measuring or esti-mating the freshwater flow (qFW) through the secondary part of thethermal transfer element (61), wherein the DHW demand event is identified if a freshwater flow (qFW) through the secondary part ofthe thermal transfer element (61) exceeds a pre-determined mini-mum flow.

4. The method of any of the preceding claims, further comprisingadding, depending on an electric heating mode, heating power(PBUH) to the load flow (qL) by an electric heater (77) being arranged15 in the load feed circuit section (13) of the hydronic system (1) down- stream of the feed connection point (27) and upstream of the pri- mary part of the thermal transfer element (61), wherein the heating power (PBUH) is added to a sum of a heat pump thermal power (PH) provided by the heat pump flow (qH) and a storage thermal power20 (PS) provided by the storage flow (qS) to meet a DHW demand ofthe identified DHW demand event.

5. The method of any of the preceding claims, wherein said control-ling operation of the load circuit pump (17) comprises driving theload flow (qL) to be a pre-determined factor (RHEX) of a freshwater flow (qFW) through the secondary part of the thermal transfer ele-ment (61), i.e. ^^ = ^^^^ ∗ ^^^.

6. The method of any of the preceding claims, further comprising30 providing a DHW demand signal to a signal-connectable or signal- connected heat pump control for ramping up the heat pump (3), wherein said controlling operation of the heat pump circuit pump (11) ramps up the heat pump flow (qH) so that a heat pump thermalatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025 power (PH) provided by the heat pump flow (qH) is used already during the ramp-up phase of the heat pump (3).

7. The method of any of the preceding claims, further comprising re-5 turning the load flow (qL) along a load return circuit section (15) ofthe hydronic system (1) downstream of the primary part of the ther- mal transfer element (61), wherein the returned load flow (qL) is split up into the storage flow (qS) and the heat pump flow (qH) at a return connection point (29) where the load return circuit section (15) di-10 vides into a heat pump return circuit section (9) of the hydronic sys-tem (1) towards the heat pump (3) and a storage return circuit sec- tion (21) of the hydronic system (1) towards the thermal energy stor- age tank (23).

8. A hydronic system (1) for providing domestic hot water, DHW,wherein the hydronic system (1) comprises:- a DHW system (49) comprising a thermal transfer element (61),wherein the thermal transfer element (61) comprises a primarypart and secondary part being thermally coupled to each 20 other, wherein the DHW system (49) is configured to identify a DHW demand event, -a load feed circuit section (13) for transporting a load flow (qL)through the primary part of the thermal transfer element (61), -a load circuit pump (17) for driving the load flow (qL) along theload feed circuit section (13), -a heat pump feed circuit section (7) for transporting a heatpump flow (qH) through a connectable or connected heat pump (3), -a heat pump circuit pump (11) for driving the heat pump flow30(qH), -a storage feed circuit section (19) for transporting a storage flow(qS) out of a connectable or connected thermal energy storagetank (23), andatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025- control electronics (20),wherein the control electronics (20) is configured to control opera-tion of the heat pump circuit pump (11) and of the load circuit pump (17) for mixing the heat pump flow (qH) with the storage flow 5 (qS) at a feed connection point (27) where the heat pump feed circuit section (7), the load feed circuit section (13) and the storage feed circuit section (19) are connected upstream of the primary part of the thermal transfer element (61), wherein the storage flow (qS) results from the controlled operation of the heat pump circuit 10 pump (11) and of the load circuit pump (17) so that the sum of the heat pump flow (qH) and the storage flow (qS) yields the load flow (qL) through the primary part of the thermal transfer element (61).

9. The hydronic system (1) of claim 8, further comprising a load flowfeed temperature sensor (79) for determining a load flow feed tem- perature (TL) of the load flow (qL), wherein the load flow feed tem- perature sensor (79) is arranged at the load feed circuit section (13), and wherein the control electronics (20) is configured to control theoperation of the heat pump circuit pump (11) so that the mixing is 20 adjusted to minimise a deviation of the load flow feed temperature (TL) from a reference load flow feed temperature (TLcompref).

10. The hydronic system (1) of claims 8 or 9, wherein the DHW system(49) is configured to measured or estimate the freshwater flow (qFW) through the secondary part of the thermal transfer element (61),wherein the control electronics (20) are configured to identify the DHW demand event if a freshwater flow (qFW) through the second- ary part of the thermal transfer element (61) exceeds a pre-deter-mined minimum flow. 30 11. The hydronic system (1) of any of the claims 8 to 10, further compris-ing an electric heater (77) being arranged in the load feed circuitatentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025 section (13) of the hydronic system (1) downstream of the feed con- nection point (27) and upstream of the primary part of the thermal transfer element (61), wherein the control electronics (20) is config- ured to add, depending on an electric heating mode, heating 5power (PBUH) to the load flow (qL) by the electric heater (77),wherein the heating power (PBUH) is added to a sum of a heat pump thermal power (PH) provided by the heat pump flow (qH) and a stor- age thermal power (PS) provided by the storage flow (qS) to meet a DHW demand of the identified DHW demand event.

12. The hydronic system (1) of any of the claims 8 to 11, wherein thecontrol electronics (20) is configured to control operation of the load circuit pump (17) for driving the load flow (qL) to be a pre- determined factor (RHEX) of a freshwater flow (qFW) through the sec-15 ondary part of the thermal transfer element (61), i.e. ^^ = ^^^^ ∗ ^^^.

13. The hydronic system (1) of any of the claims 8 to 12, wherein thecontrol electronics (20) is configured to provide a DHW demand signal to a signal-connectable or signal-connected heat pump20 control for ramping up the heat pump (3), wherein the control elec- tronics (20) is configured to ramp up the heat pump flow (qH) sothat a heat pump thermal power (PH) provided by the heat pump flow (qH) is used already during a ramp-up phase of the heat pump(3).

14. The hydronic system (1) of any of the claims 8 to 13, further compris-ing a load return circuit section (15) for returning the load flow (qL)downstream of the primary part of the thermal transfer element (61), wherein the load return circuit section (15) divides into a heat 30 pump return circuit section (9) towards the heat pump (3) and a storage return circuit section (21) towards the thermal energy stor- age tank (23).atentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 202515. The hydronic system (1) of any of the claims 8 to 14, wherein thehydronic system (1) is an integrated water circuit, IWC, unit (37),wherein the IWC unit (37) comprises: -a heat pump port (43) for connecting the heat pump feed cir-5 cuit section (7) with the heat pump (3);- a storage port (45) for connecting the storage feed circuit sec-tion (19) with the thermal energy storage tank (23) or for con-necting a storage return circuit section (21) with a load returncircuit section (15);10 - a cold freshwater inlet port (86) for connecting the secondarypart of the thermal transfer element (61) with a freshwater sup- ply; and -a hot freshwater outlet port (84) for connecting the secondarypart of the thermal transfer element (61) with a hot water con- sumer (51).

16. The hydronic system (1) of any of the claims 8 to 15, further compris-ing a storage tank temperature sensor (87) being arranged withinthe thermal energy storage tank (23), wherein the control electron-20 ics (20) is configured to determine a charging level of the thermalenergy storage tank (23) based on a measured value of the stor-age tank temperature sensor (87).atentanwälte Hemmer Lindfeld Frese GP 3907 WO, 10 / 10 / 2025

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