EP4624827A1

EP4624827A1 - System for providing domestic hot water and space heating within a building

Info

Publication number: EP4624827A1
Application number: EP24165856.6A
Authority: EP
Inventors: James Freeman
Original assignee: Mitsubishi Electric R&D Centre Europe BV; Mitsubishi Electric Corp; Mitsubishi Electric R&D Centre Europe BV Netherlands
Current assignee: Mitsubishi Electric Corp
Priority date: 2024-03-25
Filing date: 2024-03-25
Publication date: 2025-10-01
Also published as: JP2025148251A

Abstract

A system for providing domestic hot water (DHW) and space heating (SH) within a building is provided, comprising a cold water mains inlet, a heat pump connected to a primary heat transfer fluid circuit line of the system, a domestic hot water cylinder unit fluidly connected to the cold water mains inlet and fluidly connected to a hot water outlet, a domestic hot water heat exchanger, a thermal storage vessel containing a heat transfer fluid, and a controller. The thermal storage vessel comprises a pre-heating heat exchanger which is fluidly connected to the domestic hot water cylinder unit and is fluidly connectable to the cold water mains inlet. The pre-heating heat exchanger is suitable for exchanging heat energy between the heat transfer fluid of the thermal storage vessel and water flowing from the cold water mains inlet to the domestic hot water cylinder unit. The system prevents a wasteful loss of heat energy and allows a more energy-efficient, more economical and more ecological operation.

Description

A system for providing domestic hot water (DHW) and space heating (SH) within a building is provided, comprising a cold water mains inlet, a heat pump connected to a primary heat transfer fluid circuit line of the system, a domestic hot water cylinder unit fluidly connected to the cold water mains inlet and fluidly connected to a hot water outlet, a domestic hot water heat exchanger, a thermal storage vessel containing a heat transfer fluid, and a controller. The thermal storage vessel comprises a pre-heating heat exchanger which is fluidly connected to the domestic hot water cylinder unit and is fluidly connectable to the cold water mains inlet. The pre-heating heat exchanger is suitable for exchanging heat energy between the heat transfer fluid of the thermal storage vessel and water flowing from the cold water mains inlet to the domestic hot water cylinder unit. The system prevents a wasteful loss of heat energy and allows a more energy-efficient, more economical and more ecological operation.
Systems for providing domestic hot water (DHW) and space heating (SH) within a building are known in the prior art (see e.g. "Ecodan ATW Databook", Mitsubishi Electric, vol.5.3, R32, issued in Dec. 2020 M-P0798C SIZ2008<MEE>, pages 152-154) (see also present Figures 1 and 2).
If said systems known in the prior art comprise a thermal storage vessel (see e.g. Figure 2), they have the disadvantage that the thermal storage vessel is limited in its use, i.e. can only be used for space heating. This is connected to the problem that the energy stored in the thermal storage vessel is only useful during periods where there is a frequent demand for space heating (e.g. a daily demand and not only a monthly or even only a half-yearly demand). During warmer seasons, for example, there is no demand for space heating. This means that, with the systems according to the prior art, any heat that is stored in the thermal storage vessel is not used and thus eventually dissipates to the environment in a wasteful manner during these times. Hence, the systems of the prior art are not very energy efficient.
Moreover, the operation of the systems of the prior art is not very economical and ecological. The reason is that, on the one hand, thermal energy is wasted by said systems (due to dissipation of heat to the environment in a wasteful manner) and, on the other hand, said systems necessarily rely on an operation of their heat pump during periods of a high demand for domestic hot water. In said periods of high demand for domestic hot water, electricity for operating the heat pump can be expensive and/or can originate from a non-ecological source. For example, the necessary electricity can only be available from the electrical grid at an expensive tariff and/or might not originate from a renewable energy source (like e.g. a PV device). During morning and evening hours, when domestic hot water demand is usually highest, both of these situations can apply which leaves room for improvement of the operation of the system in economical and ecological terms.
Starting from the above, it was the objective of the present invention to provide a system for providing domestic hot water (DHW) and space heating (SH) within a building which overcomes at least one disadvantage of the prior art. Preferably, the provided system should prevent a wasteful loss of heat energy, thereby allowing a more energy-efficient, more economical and/or more ecological provision of domestic hot water and space heating within a building.
The objective is solved by the system having the features of claim 1. The dependent claims show advantageous embodiments.
According to the invention, a system for providing domestic hot water and space heating within a building is provided, comprising:

a) a cold water mains inlet which is fluidly connected to a cold water mains line of the system;
b) an air-to-water heat pump comprising a heat pump heat exchanger, wherein the heat pump heat exchanger is fluidly connected to a primary heat transfer fluid circuit line of the system;
c) a domestic hot water cylinder unit which is fluidly connected to the cold water mains inlet via the cold water mains line and is fluidly connected to a domestic hot water outlet of the system for providing domestic hot water;
d) a domestic hot water heat exchanger which is suitable for exchanging heat energy between the domestic hot water cylinder unit and the primary heat transfer fluid circuit line;
e) a thermal storage vessel containing a heat transfer fluid, wherein the thermal storage vessel is fluidly connected to a secondary heat transfer fluid circuit line and fluidly connected to a heat emitter circuit line;
f) a first valve in the primary heat transfer fluid circuit line;
g) a second valve in the cold water mains line;
h) a controller;

wherein the secondary heat transfer fluid circuit line is fluidly connectable to the primary heat transfer fluid circuit line via switching of the first valve (i.e. the controller of the system can be configured to establish said connection by switching the first valve),
wherein the heat emitter circuit line is connected to at least one heat emitter for providing space heating within a building,
characterized in that the thermal storage vessel contains a pre-heating heat exchanger which is fluidly connected to the domestic hot water cylinder unit and is fluidly connectable to the cold water mains inlet via switching of the second valve (i.e. the controller of the system can be configured to establish said connection by switching the second valve),
wherein the pre-heating heat exchanger is suitable for exchanging heat energy between the heat transfer fluid of the thermal storage vessel and water flowing from the cold water mains inlet to the domestic hot water cylinder unit.

The system according to the invention allows a more effective utilization of the energy storage flexibility offered by the thermal storage vessel, without incurring a wasteful loss of heat energy and allows a more energy-efficient, more economical and more ecological provision of domestic hot water and space heating within a building.
In fact, with the pre-heating heat exchanger of the system, it is possible to recover heat from the thermal storage vessel to pre-heat mains water flowing from the cold water mains inlet to the domestic hot water cylinder unit. This is beneficial, for example, when there is heat stored in the thermal storage vessel and there is no demand for space heating, but a demand for domestic hot water.
Unlike a demand for space heating, which predominates during the summer season (i.e. only during certain months within a year), a demand for domestic hot water is usually consistent throughout the year (i.e. there is usually a daily demand for domestic hot water throughout the year). Thus, using the thermal storage vessel not only for providing thermal energy for space heating, but also for providing thermal energy to domestic hot water is beneficial because it allows the energy storage flexibility provided by the thermal storage vessel to be utilized without incurring a wasteful loss of thermal energy by the thermal storage vessel (especially during summer months). This allows the system to operate in a more energy-efficient, more economic and more ecologic manner.
Apart from the above, a peak demand for domestic hot water typically occurs in the morning and evening. It is likely that the domestic hot water cylinder unit will require charging by the heat pump during said peak-demand hours. An ability to time-shift the heat pump operation is usually limited by the volume of the domestic hot water cylinder unit. A further advantage of the system according to the invention is that it allows "accessing" the additional heat storage capacity of the thermal storage vessel for transferring heat energy to mains water during said times of peak domestic hot water demand. This prevents unnecessarily frequent operations of the heat pump and allows the system to operate in a more energy-efficient, more economic and more ecologic manner.
Besides, there are also other occasions when it is preferable to use the heat energy stored in the thermal storage vessel for pre-heating of domestic hot water, for example days on which an expected demand for domestic hot water is unusually high (e.g. days on which many persons use domestic hot water). Also during these times, thermal energy can be drawn from the thermal storage vessel and an unnecessary operation of the heat pump of the system can be prevented. Put differently, the thermal storage vessel of the system acts as a "buffer" for reducing intermittent operation of the heat pump due to variations in space heating demand and/or hot water demand. This also allows the system to operate in a more energy-efficient, more economic and more ecologic manner.
Furthermore, the ability of the system according to the invention to provide a required heating energy for heating domestic hot water during certain times without a necessity to operate the heat pump during said times (i.e. a capability of a time-shift operation of the heat pump) allows to operate the heat pump to a greater extent during times in which cheap electricity is available. The cheap electricity can be electricity from an electrical grid during times when cheap electricity tariffs are available and/or can be electricity from a renewable energy source providing cheap and ecologic electrical energy. This allows the system to operate in a more economic manner.
The heat transfer fluid can comprise or consist of water. Moreover, the heat transfer fluid can comprise, on the one hand, water and, on the other hand, an antifreeze agent (e.g. glycol) and/or a corrosion inhibitor.
Moreover, the thermal storage vessel can comprise a phase change material, preferably an encapsulated phase change material. The encapsulated phase change material can be suspended in the heat transfer fluid of the thermal storage vessel.
In the system, the second valve can be suitable to switch between

i) a fluid connection of the cold water mains inlet with the domestic hot water cylinder unit via the pre-heating heat exchanger of the thermal storage vessel; and
ii) a fluid connection of the cold water mains inlet with the domestic hot water cylinder unit by bypassing the pre-heating heat exchanger of the thermal storage vessel.

Preferably, the second valve is a 2-position valve (e.g. a three-way valve).
Moreover, the second valve can be connected to a first line which connects a first opening of the second valve with the cold water mains inlet.
Furthermore, the second valve can be connected to a second line which connects a second opening of the second valve with a first opening of a pre-heating heat exchanger of the thermal storage vessel.
Besides, the second valve can be connected to a third line which connects a third opening of the second valve, by bypassing the pre-heating heat exchanger of the thermal storage vessel, with an opening of the domestic hot water cylinder unit.
The primary heat transfer fluid circuit line of the system can comprise a pump for circulating heat transfer fluid within the primary heat transfer fluid circuit line.
The system can comprise a domestic hot water circuit line which fluidly connects the domestic hot water cylinder unit with the domestic hot water heat exchanger, wherein the domestic hot water circuit line comprises a pump for circulating water within the domestic hot water circuit line.
Moreover, the first valve can be suitable to switch between

i) a fluid connection of the heat pump heat exchanger with the domestic hot water heat exchanger (via the primary heat transfer fluid circuit line); and
ii) a fluid connection of the heat pump heat exchanger with the thermal storage vessel (via the secondary heat transfer fluid circuit line).

Preferably, the first valve is a 2-position valve (e.g. a three-way valve).
The first valve can be connected to a first line which connects a first opening of the first valve with an opening of the heat pump heat exchanger.
Moreover, the first valve can be connected to a second line which connects a second opening of the first valve with an opening of the domestic hot water heat exchanger.
Furthermore, the first valve can be connected to a third line which connects a third opening of the first valve with an opening of the thermal storage vessel.
The system can comprise a hot water supply line which fluidly connects the pre-heating heat exchanger of the thermal storage vessel with the domestic hot water cylinder unit. Said hot water supply line preferably connects the opening of the domestic hot water cylinder unit to a second opening of the pre-heating heat exchanger.
The heat emitter circuit line can be connected to a plurality of heat emitters. The at least one heat emitter of the system and/or the plurality of heat emitters of the system is/are preferably selected from the group consisting of radiators, fan-coil units and underfloor heating.
Moreover, the heat emitter circuit line can comprise a pump for circulating heat transfer fluid within the heat emitter circuit line.
The pre-heating heat exchanger of the system can be located at least partially, optionally completely, in an internal space of the thermal storage vessel, wherein the pre-heating heat exchanger is preferably a coil-type heat exchanger. Alternatively, the pre-heating heat exchanger of the system can be located at least partially, optionally completely, externally to the thermal storage vessel, wherein the pre-heating heat exchanger is preferably a plate-type heat exchanger, wherein the system optionally comprises a pump for circulating water of thermal storage vessel through the plate-type heat exchanger.
The controller of the system can be configured to switch the second valve to establish a fluid connection of the cold water mains inlet with the domestic hot water cylinder unit via the pre-heating heat exchanger of the thermal storage vessel, when no demand for space heating is expected. No demand for space heating is preferably expected when an outdoors temperature is equal to or above a predefined threshold value.
Moreover, the controller of the system can be configured to switch the second valve to establish a fluid connection of the cold water mains inlet with the domestic hot water cylinder unit by bypassing the pre-heating heat exchanger of the thermal storage vessel, when a demand for space heating is expected. A demand for space heating is preferably expected when an outdoors temperature falls below a predefined threshold value.
Furthermore, the controller of the system can be configured to switch the first valve to establish a fluid connection of the heat pump heat exchanger with the domestic hot water heat exchanger of the system, and to operate the heat pump to heat the domestic hot water cylinder unit of the system, when

i) a surplus of cheap electricity is available and the domestic hot water cylinder unit is not fully charged; and/or
ii) a high demand of domestic hot water is expected and the domestic hot water cylinder unit is not fully charged; and/or
iii) there is requirement to reheat the domestic hot water cylinder unit of the system, preferably in a normal operation mode of the heat pump, wherein said requirement is more preferably met when a temperature of the domestic hot water cylinder unit drops below a predefined temperature setpoint value.

Besides, the controller of the system can be configured to switch the first valve to establish a fluid connection of the heat pump heat exchanger with the thermal storage vessel of the system, and to operate the heat pump to heat the thermal storage vessel of the system, when

i) a surplus of cheap electricity is available and the domestic hot water cylinder unit is fully charged; and/or
ii) a high demand of domestic hot water is expected and the domestic hot water cylinder unit is fully charged; and/or
iii) there is a requirement for space heating, preferably in a normal operation mode of the heat pump, and the heat pump is not currently providing heating energy to the domestic hot water cylinder unit.

Apart from the above, the controller of the system can be configured to switch the air-to-water heat pump to a normal operation mode when no surplus of cheap electricity is available and no high demand of domestic hot water is expected.
The thermal storage vessel can have an internal volume in the range of 100 to 1000 dm³. Especially if the internal volume is in said range, energy storage is normally limited to "intra-day" periods, i.e. periods of a few hours, and an internal volume in said range is most suitable for systems comprising a photovoltaic device for producing electrical energy, e.g. a surplus energy in the middle of the day. This surplus energy can be used to run the heat pump of the system to charge the thermal storage vessel with thermal energy, which can then be used during night-time hours for space heating and/or can be used throughout the year for contributing heating energy for providing domestic hot water.
In a preferred embodiment of the system, the system comprises a photovoltaic device which is suitable to provide electrical energy to the air-to-water heat pump of the system. This allows the system to operate in an even more economic and even more ecological manner.
With reference to the following Figures and Example, the subject-matter according to the invention is intended to be explained in more detail without wishing to restrict said subject-matter to the specific embodiments shown here. Figures 1 and 2 show no systems according to the invention, but systems which are helpful to understand certain aspects of the invention.
Figure 1 shows a typical air-to-water heat pump system of the prior art for providing space heating and domestic hot water. In a first system operation (charging the domestic hot water cylinder unit DHWCU), the heat pump HP operates to heat domestic hot water in the domestic hot water cylinder unit DHWCU via the domestic hot water heat exchanger HEX2 (e.g. a plate heat exchanger) in the indoor unit that transfers heat from the primary heat transfer fluid circuit line PWCL (i.e. the primary circulating water) to the domestic hot water circuit line DHWCL (i.e. to the sanitary water of the domestic hot water cylinder unit DHWCU). In a second system operation (provision of domestic hot water), hot water is extracted at the domestic hot water outlet DHWO and from the top of the domestic hot water cylinder unit and replaced by fresh water from a cold-water mains inlet CWMI fed in at the bottom of the domestic hot water cylinder unit DHWCU. Principally, it is not necessary to operate the compressor of the heat pump HP during extraction of domestic hot water. In a third system operation (provision of space heating), the position of the 3-way valve MV1 changes to allow hot water circulated by the pump P1 to circulate in a closed loop between the outdoor unit and the heat emitters HE, wherein the closed loop is formed by the secondary heat transfer fluid circuit line SWCL and the heat emitter circuit line HECL.
Figure 2 shows a further typical air-to-water heat pump system of the prior art for providing space heating and domestic hot water. Unlike the system shown in Figure 1, this system comprises a thermal storage vessel TSV which is located in between the heat pump HP indoor unit and the heat emitter circuit line HECL. The thermal storage vessel TSV contains a primary heating fluid, not potable water for supply of domestic hot water. In this system, the heat pump HP can be operated to store energy in the thermal storage vessel TSV when there is no demand for space heating (charging the thermal storage vessel). If there is no simultaneous demand for space heating, then this energy is stored in the thermal storage vessel TSV until such a time when there is a demand for space heating. If there is a demand for space heating, the heating circulator pump P3 is switched on to distribute heat from the thermal storage vessel TSV to the space via the heat emitter circuit line HECL (SH provision by thermal storage vessel). The heat pump HP may also be operated to provide space heating both by the heat pump HP and the thermal storage vessel TSV, with the thermal storage vessel serving effectively as an intermediate buffer (SH provision by thermal storage vessel and heat pump). In this case, pumps P1 and P3 both operate at the same time.
Figure 3 shows an air-to-water heat pump system according to the present invention for providing space heating and domestic hot water. The system is identical to the system shown in Figure 2 with the difference that said system comprises a pre-heating heat exchanger HEX3 (here: an internal coil heat exchanger) within the thermal storage vessel TSV, and a two-position valve MV2 (e.g. a motorized 3-way valve) in the cold water mains line CWMLofthe system.
Figure 4 shows, in a system according to the invention, a domestic hot water extraction with a preheating of cold-water main water by the pre-heating heat exchanger HEX3 of the thermal storage vessel TSV. Said extraction is performed when stored thermal energy is available in the thermal storage vessel TSV and it is desired to use the stored thermal energy for preheating mains water flowing from the cold water mains inlet CMWI to the domestic hot water cylinder unit DHWCU. To this end, the second valve MV2 switches to the position shown in Figure 4, and cold mains water is diverted through the pre-heating heat exchanger HEX3 (see arrow), where it is heated to a temperature approaching the top temperature in the thermal storage vessel TSV. The pre-heated mains water exiting the pre-heating heat exchanger HEX3 is then fed to the bottom of the domestic hot water cylinder unit DHWCU to be heated to its final supply temperature (see arrow). This represents a typical summertime operation of the system.
Figure 5 shows, in a system according to the invention, a domestic hot water extraction without preheating of cold water mains water. Said extraction is performed when it is preferable not to use the stored heat in the thermal storage vessel TSV for pre-heating domestic hot water. In this case, the second valve MV2 switches to its default position, in which cold mains water bypasses the pre-heating heat exchanger HEX3 and is fed directly to the inlet of the domestic hot water cylinder unit DHWCU (see arrow). This represents a typical winter-time operation of the system where it is preferable to use any stored heat in the thermal store for space heating.
Figure 6 shows, in a system according to the invention, an operation of the system in which the heat pump provides heat energy to the domestic hot water cylinder unit DHWCU. The first valve MV1 is switched to a first state in which water is pumped only through the primary heat transfer fluid circuit line PWCL (see arrows). The system comprises a domestic hot water circuit line DHWCL which fluidly connects the domestic hot water cylinder unit DHWCI with the domestic hot water heat exchanger HEX2. The domestic hot water circuit line DHWCL comprises a pump P2 for circulating water within the domestic hot water circuit line DHWCL. The domestic hot water heat exchanger HEX2 is suitable for exchanging heat energy between the domestic hot water cylinder unit DHWCU (specifically: the domestic hot water circuit line DHWCL) and the primary heat transfer fluid circuit line PWCL.
Figure 7 shows, in a system according to the invention, an operation of the system in which the heat pump provides heat energy to the thermal storage vessel TSV. The first valve MV1 is switched to a second state in which water is pumped through the primary heat transfer fluid circuit line PWCL and through the secondary heat transfer fluid circuit line SWCL and thus to the thermal storage vessel TSV (i.e. the domestic hot water heat exchanger HEX2 is bypassed) (see arrows). The pump P2 for circulating water within the domestic hot water circuit line DHWCL is turned off.
Figure 8 shows a possible configuration of the controller of the system according to the present invention.

Example - Possible components of the system

The system can comprise (e.g. in an outdoor unit of the system):

a compressor
a fan-assisted evaporator heat exchanger
an expansion device (e.g. a linear expansion valve, LEV)
a condenser heat exchanger (refrigerant to water, HEX1)
a 4-way reversing valve

Furthermore, the system can comprise (e.g. in an indoor unit of the system):

a domestic hot water cylinder unit (DHWCU)
a primary heat transfer fluid circulation pump (P1)
a domestic hot water circulation pump (P2)
a primary heat transfer fluid to DHW heat exchanger (HEX2)
a 3-way valve (MV1) for switching between DHW and space heating
a DHW tank temperature sensor

Moreover, the system can comprise (e.g. in a heat emitter circuit of the system):

an array of heat emitters (e.g. radiators, fan-coil units and/or underfloor heating)
a heat transfer fluid pump (P3)

List of abbreviations and reference signs

CWMI:: a cold water mains inlet;
CWML:: cold water mains line;
HP:: air-to-water heat pump;
HEX1:: heat pump heat exchanger;
PWCL:: primary heat transfer fluid circuit line;
DHWCU:: domestic hot water cylinder unit;
DHWO:: domestic hot water outlet;
DHW:: domestic hot water;
HEX2:: domestic hot water heat exchanger;
TSV:: thermal storage vessel;
SWCL:: secondary heat transfer fluid circuit line;
MV1:: first valve;
HECL:: heat emitter circuit line;
HE:: heat emitter;
SH:: space heating;
HEX3:: pre-heating heat exchanger;
MV2:: second valve;
P1:: pump for circulating heat transfer fluid within the primary heat transfer fluid circuit line;
DHWCL:: domestic hot water circuit line;
P2:: pump for circulating water within the domestic hot water circuit line;
HWSL:: hot water supply line;
P3:: pump for circulating heat transfer fluid within the heat emitter circuit line.

Claims

A system for providing domestic hot water (DHW) and space heating (SH) within a building, comprising:
a) a cold water mains inlet (CWMI) which is fluidly connected to a cold water mains line (CWML) of the system;

b) an air-to-water heat pump (HP) comprising a heat pump heat exchanger (HEX1), wherein the heat pump heat exchanger (HEX1) is fluidly connected to a primary heat transfer fluid circuit line (PWCL) of the system;

c) a domestic hot water cylinder unit (DHWCU) which is fluidly connected to the cold water mains inlet (CWMI) via the cold water mains line (CWML) and is fluidly connected to a domestic hot water outlet (DHWO) of the system for providing domestic hot water (DHW);

d) a domestic hot water heat exchanger (HEX2) which is suitable for exchanging heat energy between the domestic hot water cylinder unit (DHWCU) and the primary heat transfer fluid circuit line (PWCL);

e) a thermal storage vessel (TSV) containing a heat transfer fluid, wherein the thermal storage vessel (TSV) is fluidly connected to a secondary heat transfer fluid circuit line (SWCL) and fluidly connected to a heat emitter circuit line (HECL);

f) a first valve (MV1) in the primary heat transfer fluid circuit line (PWCL);

g) a second valve (MV2) in the cold water mains line (CWML);

h) a controller;

wherein the secondary heat transfer fluid circuit line (SWCL) is fluidly connectable to the primary heat transfer fluid circuit line (PWCL) via switching of the first valve (MV1),

wherein the heat emitter circuit line (HECL) is connected to at least one heat emitter (HE) for providing space heating (SH) within a building,

characterized in that the thermal storage vessel (TSV) comprises a pre-heating heat exchanger (HEX3) which is fluidly connected to the domestic hot water cylinder unit (DHWCU) and is fluidly connectable to the cold water mains inlet (CWMI) via switching of the second valve (MV2), and

wherein the pre-heating heat exchanger (HEX3) is suitable for exchanging heat energy between the heat transfer fluid of the thermal storage vessel (TSV) and water flowing from the cold water mains inlet (CWMI) to the domestic hot water cylinder unit (DHWCU).
System according to the preceding claim, characterized in that the second valve (MV2) is suitable to switch between
i) a fluid connection of the cold water mains inlet (CWMI) with the domestic hot water cylinder unit (DHWCU) via the pre-heating heat exchanger (HEX3) of the thermal storage vessel (TSV); and

ii) a fluid connection of the cold water mains inlet (CWMI) with the domestic hot water cylinder unit (DHWCU) by bypassing the pre-heating heat exchanger (HEX3) of the thermal storage vessel (TSV);
wherein the second valve (MV2) is preferably a 2-position valve.
System according to the preceding claim, characterized in that the second valve (MV2) is connected to
i) a first line which connects a first opening of the second valve (MV2) with the cold water mains inlet (CWMI); and/or

ii) a second line which connects a second opening of the second valve (MV2) with a first opening of a pre-heating heat exchanger (HEX3) of the thermal storage vessel (TSV); and/or

iii) a third line which connects a third opening of the second valve (MV2), by bypassing the pre-heating heat exchanger (HEX3) of the thermal storage vessel (TSV), with an opening of the domestic hot water cylinder unit (DHWCU).
System according to any one of the preceding claims, characterized in that the primary heat transfer fluid circuit line (PWCL) comprises a pump (P1) for circulating heat transfer fluid within the primary heat transfer fluid circuit line (PWCL).
System according to any one of the preceding claims, characterized in that the system comprises a domestic hot water circuit line (DHWCL) which fluidly connects the domestic hot water cylinder unit (DHWCI) with the domestic hot water heat exchanger (HEX2), wherein the domestic hot water circuit line (DHWCL) comprises a pump (P2) for circulating water within the domestic hot water circuit line.
System according to any one of the preceding claims, characterized in that the first valve (MV1) is suitable to switch between
i) a fluid connection of the heat pump heat exchanger (HEX1) with the domestic hot water heat exchanger (HEX2); and

ii) a fluid connection of the heat pump heat exchanger (HEX1) with the thermal storage vessel (TSV);
wherein the first valve (MV1) is preferably a 2-position valve.
System according to the preceding claim, characterized in that the first valve (MV1) is connected to
i) a first line which connects a first opening of the first valve (MV1) with an opening of the heat pump heat exchanger (HEX1); and/or

ii) a second line which connects a second opening of the first valve (MV1) with an opening of the domestic hot water heat exchanger (HEX2); and/or

iii) a third line which connects a third opening of the first valve (MV1) with an opening of the thermal storage vessel (TSV).
System according to any one of the preceding claims, characterized in that the system comprises a hot water supply line (HWSL) which fluidly connects the pre-heating heat exchanger (HEX3) of the thermal storage vessel (TSV) with the domestic hot water cylinder unit (DHWCU), wherein preferably said hot water supply line (HWSL) connects the opening of the domestic hot water cylinder unit (DHWCU) to a second opening of the pre-heating heat exchanger (HEX3).
System according to any one of the preceding claims, characterized in that the heat emitter circuit line (HECL)
i) is connected to a plurality of heat emitters (HE), wherein the plurality of heat emitters (HE) are preferably selected from the group consisting of radiators, fan-coil units and underfloor heating;
and/or

ii) comprises a pump (P3) for circulating heat transfer fluid within the heat emitter circuit line.
System according to any one of the preceding claims, characterized in that the pre-heating heat exchanger (HEX3) is located at least partially, optionally completely,
i) in an internal space of the thermal storage vessel (TSV), wherein the pre-heating heat exchanger (HEX3) is preferably a coil-type heat exchanger; or

ii) externally to the thermal storage vessel (TSV), wherein the pre-heating heat exchanger (HEX3) is preferably a plate-type heat exchanger, wherein the system optionally comprises a pump for circulating water of thermal storage vessel (TSV) through the plate-type heat exchanger.
System according to any one of the preceding claims, characterized in that the controller is configured to switch the second valve (MV2) to establish a fluid connection of the cold water mains inlet (CWMI) with the domestic hot water cylinder unit (DHWCU) via the pre-heating heat exchanger (HEX3) of the thermal storage vessel (TSV) when no demand for space heating is expected, wherein no demand for space heating is preferably expected when an outdoors temperature is equal to or above a predefined threshold value.
System according to any one of the preceding claims, characterized in that the controller is configured to switch the second valve (MV2) to establish a fluid connection of the cold water mains inlet (CWMI) with the domestic hot water cylinder unit (DHWCU) by bypassing the pre-heating heat exchanger (HEX3) of the thermal storage vessel (TSV) when a demand for space heating is expected, wherein a demand for space heating is preferably expected when an outdoors temperature falls below a predefined threshold value.
System according to any one of the preceding claims, characterized in that the controller is configured to switch the first valve (MV1) to establish a fluid connection of the heat pump heat exchanger (HEX1) with the domestic hot water heat exchanger (HEX2) of the system, and to operate the heat pump (HP) to heat the domestic hot water cylinder unit (DHWCU) of the system, when
i) a surplus of cheap electricity is availaible and the domestic hot water cylinder unit (DHWCU) is not fully charged; and/or

ii) a high demand of domestic hot water is expected and the domestic hot water cylinder unit (DHWCU) is not fully charged; and/or

iii) there is requirement to reheat the domestic hot water cylinder unit (DHWCU) of the system, preferably in a normal operation mode of the heat pump (HP), wherein said requirement is more preferably met when a temperature of the domestic hot water cylinder unit (DHWCU) drops below a predefined temperature setpoint value.
System according to any one of the preceding claims, characterized in that the controller is configured to switch the first valve (MV1) to establish a fluid connection of the a heat pump heat exchanger (HEX1) with the a thermal storage vessel (TSV) of the system, and to operate the heat pump (HP) to heat the thermal storage vessel (TSV) of the system, when
i) a surplus of cheap electricity is available and the domestic hot water cylinder unit (DHWCU) is fully charged; and/or

ii) a high demand of domestic hot water is expected and the domestic hot water cylinder unit (DHWCU) is fully charged; and/or

iii) there is a requirement for space heating, preferably in a normal operation mode of the heat pump (HP), and the heat pump (HP) is not currently providing heating energy to the domestic hot water cylinder unit (DHWCU).
System according to any one of the preceding claims, characterized in that the controller is configured to switch the heat pump (HP) to a normal operation mode when no surplus of cheap electricity is available and no high demand of domestic hot water is expected.