EP4624809A1

EP4624809A1 - System for heating at least one space and for providing domestic hot water and method for operating the system

Info

Publication number: EP4624809A1
Application number: EP24165976.2A
Authority: EP
Inventors: Dr. Christopher OLKIS; Dr. 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: JP2025148248A

Abstract

The present invention is directed to a system for heating at least one space and for providing domestic hot water. The system comprises a heat transfer device for providing domestic hot water, at least one emitter for heating the at least one space, the at least one emitter being provided within the at least one space, a reconfigurable fluid network for transferring a first heat transfer fluid, a first heat exchanger for transferring heat between the first heat transfer fluid and a second heat transfer fluid, a second heat exchanger for pre-heating water to be further heated by the heat transfer device to obtain domestic hot water, and a controller. The reconfigurable fluid network comprises a heat pump unit, at least one valve, and pipes, the heat pump unit comprising a compressor and at least one expansion valve. The reconfigurable fluid network is configurable by the controller in a plurality of specific configurations and the controller is configured such that it can operate the system in a plurality of specific modes. Furthermore, the present invention also applies to a method for operating a system.

Description

The present invention is directed to a system for heating at least one space and for providing domestic hot water. The system comprises a heat transfer device for providing domestic hot water, at least one emitter for heating the at least one space, the at least one emitter being provided within the at least one space, a reconfigurable fluid network for transferring a first heat transfer fluid, a first heat exchanger for transferring heat between the first heat transfer fluid and a second heat transfer fluid, a second heat exchanger for pre-heating water to be further heated by the heat transfer device to obtain domestic hot water, and a controller. The reconfigurable fluid network comprises a heat pump unit, at least one valve, and pipes, the heat pump unit comprising a compressor and at least one expansion valve. The reconfigurable fluid network is configurable by the controller in a plurality of specific configurations and the controller is configured such that it can operate the system in a plurality of specific modes. Furthermore, the present invention also applies to a method for operating a system.
Water-to-water heat pumps are increasingly installed in multi-residential apartments. They are installed in individual apartments to deliver hot water and heating and can be connected to a heat network such as a 5th Generation ambient temperature district heat network, which is deployed throughout the building. These water-to-water heat pump systems combine a heat pump refrigerant circuit and a domestic hot water (DHW) thermal energy storage (TES) in the indoor unit, whereas a typical air-to-water heat pump has the heat pump refrigerant circuit in the outdoor unit and the TES in the indoor unit. In a water-to-water heat pump system, the heat pump is often at the bottom of the indoor unit and in the top section is a cylinder for domestic hot water (DHW) provision.
Current water-to-water heat pump systems often have a large indoor unit and thus require a lot of indoor space, which is mostly due to the DHW storage cylinder. However, residential apartments are very space constrained so that it could be difficult to install a heat pump indoor unit with integrated DHW storage cylinder in a residential apartment due to lack of space.
Starting from this, it was the objective of the present invention to provide a system for providing domestic hot water and heating at least one space that can be realised in a small and compact design so that it requires only a relatively small amount of indoor space (for installation).
This objective is achieved with respect to a system for heating at least one space and for providing domestic hot water by the features of claim 1 and with respect to a method for operating such system by the features of claim 13. The dependent claims represent advantageous further developments.
In accordance with the present invention, a system for heating at least one space and for providing domestic hot water is provided, the system comprising

a heat transfer device for providing domestic hot water, at least one (heat) emitter for heating the at least one space, the at least one (heat) emitter being provided within the at least one space,
a reconfigurable fluid network for transferring a first heat transfer fluid, the reconfigurable fluid network comprising a heat pump unit, at least one valve, and pipes, the heat pump unit comprising a compressor and at least one expansion valve, wherein the reconfigurable fluid network is configurable by a controller in a plurality of configurations comprising a first configuration, in which the reconfigurable fluid network is configured to transfer the first heat transfer fluid from the heat pump unit to the heat transfer device and not to the at least one (heat) emitter, and a second configuration, in which the reconfigurable fluid network is configured to transfer the first heat transfer fluid from the heat pump unit to the at least one (heat) emitter and not to the heat transfer device,
a first heat exchanger for transferring heat between the first heat transfer fluid and a second heat transfer fluid, the second heat transfer fluid being external to the reconfigurable fluid network, wherein the first heat exchanger is external to the heat pump unit,
a second heat exchanger for pre-heating mains water (to a preheated mains water temperature, the preheated mains water) to be further heated (to a domestic hot water outlet temperature) by the heat transfer device to obtain domestic hot water,
and
the controller, wherein the controller is configured such that it can operate the system in a plurality of modes comprising a (first) mode for providing domestic hot water, in which the reconfigurable fluid network is configured in the first configuration, and a (second) mode for heating the at least one space, in which the reconfigurable fluid network is configured in the second configuration.

The system according to the present invention comprises a specific reconfigurable fluid network comprising a heat pump unit, wherein the heat transfer device, the at least one emitter for heating the at least one space, and the first heat exchanger for transferring heat between the first heat transfer fluid and the second heat transfer fluid are all connected to the reconfigurable fluid network. The reconfigurable fluid network is configurable by a controller in a plurality of configurations in which the first transfer fluid can be transferred between different components of the system via the pipes of the reconfigurable fluid network. For example, the at least one valve (which is e.g. at least one three-way valve) can be switched by the controller to change the configuration of the reconfigurable fluid network.
The plurality of configurations comprise at least two configurations. In the first configuration, the reconfigurable fluid network is configured to transfer the first heat transfer fluid from (a high pressure side of) the heat pump unit to the heat transfer device (and back) but not to the at least one emitter. In the second configuration, the reconfigurable fluid network is configured to transfer the first heat transfer fluid from (a high pressure side of) the heat pump unit to the at least one emitter (and back) but not to the heat transfer device.
In the system according to the present invention, mains water is preheated by the second heat exchanger to a preheated mains water temperature. The preheated mains water is then further heated to a domestic hot water outlet temperature by the heat transfer device.
Since the system according to the present invention comprises the second heat exchanger for pre-heating mains water to be further heated by the heat transfer device to obtain domestic hot water, the mains water heated by the heat transfer device to provide domestic hot water is already preheated and does not need to be heated as much so that the heat transfer device does not need to be a large thermal energy storage device to provide domestic hot water. Instead, it is sufficient to use a smaller device as the heat transfer device, such as e.g. a (third) heat exchanger or a small thermal energy storage device. As a result, a small device can be used as the heat transfer device in the system according to the present invention, so that also the system itself can be designed smaller and more compact. Thus, the system can be realised in a small and compact design so that it requires only a relatively small amount of indoor space (for installation). In particular, the system can be present in the form of a small and compact unit, e.g. a small and compact indoor unit.
For example, cold mains water could be pre-heated by the second heat exchanger which is itself heated by a heat network, with e.g. 25 - 40 °C heat network temperature. In this exemplary case, the water-to-water heat pump does not require a 170 L DHW cylinder to provide DHW but instead two alternatives are possible: The heat pump can heat the mains water directly to a supply temperature of at least 40°C via a (third) heat exchanger used as the heat transfer device. Or a small thermal energy storage device used as the heat transfer device can improve the heat pump efficiency by preventing very short heat pump compressor on-off cycles for small DHW discharges. The small thermal energy storage device can be designed for discharges of 5 - 50 L, preferably 5 - 20 L. The small thermal energy storage device is preferably comprised of PCM as thermal energy storage material but can also be comprised of a sensible heat store like a small DHW cylinder.
Since the specific reconfigurable fluid network comprises the heat pump unit and is connected to the heat transfer device, the at least one emitter, and the first heat exchanger, and since the first heat exchanger is external to the heat pump unit, a simplified and flexible system is obtained that can be operated in a plurality of specific modes comprising a mode for providing domestic hot water and a mode for heating the at least one space. Preferably, the plurality of modes also comprises a mode for both cooling the at least one space and providing domestic hot water (i.e. a mode in which the at least one space is cooled and domestic hot water is provided) wherein the heat removed from the at least one space is used for heating domestic hot water.
The plurality of modes comprise a (first) mode for providing domestic hot water and at least one (second) mode for heating the at least one space. In the at least one (first) mode for providing domestic hot water, the reconfigurable fluid network is configured in the first configuration. In the (second) mode for heating the at least one space, the reconfigurable fluid network is configured in the second configuration.
Due to the presence of the specific reconfigurable fluid network and the first heat exchanger, which is external to the heat pump unit, a flexible system is obtained in which a packaged heat pump (i.e. monobloc heat pump) or split-type heat pump can be used and which can be used in several modes.
The first heat exchanger for transferring heat between the first heat transfer fluid and a second heat transfer fluid can also be referred to as first external heat exchanger.
The second heat exchanger for pre-heating mains water to be further heated by the heat transfer device to obtain domestic hot water can also be referred to as second external heat exchanger.
The heat pump unit can comprise a complete heat pump comprising the compressor, a first heat pump heat exchanger, the at least one expansion valve, and a second heat pump heat exchanger, or the heat pump unit can be a heat pump subunit comprising only a part of a heat pump (e.g. comprising the compressor and the at least one expansion valve but not comprising any heat exchanger). If the heat pump unit is a heat pump subunit that does not comprise any heat exchanger, heat exchangers of the system arranged external of the heat pump unit can act as evaporator and condenser of the heat pump, so that a system similar to a split-type air-conditioning system (i.e. a traditional air-to-air air conditioning system) is provided, where the (e.g. wall mounted) heating and air conditioning unit is supplied with refrigerant from an outdoor unit (of the traditional air-to-air air conditioning system) and can act as evaporator during cooling and condenser during heating mode. Such heat exchangers of the system arranged external of the heat pump unit can be, e.g. the heat exchanger for transferring heat between the first heat transfer fluid and a second heat transfer fluid, the at least one emitter, and/or a heat exchanger of the heat transfer device.
The pipes of the reconfigurable fluid network can comprise pipes that are external to the heat pump unit and pipes that are internal to the heat pump unit. The pipes that are internal to the heat pump unit can also be designated as (internal) pipes of the heat pump unit. The pipes that are external to the heat pump unit can also be designated as distribution circuit.
A preferred embodiment of the system according to the present invention is characterized in that the heat pump unit is a water source heat pump unit.
A further preferred embodiment of the system according to the present invention is characterized in that the first heat transfer fluid comprises or consists of water or a refrigerant different from water.
A further preferred embodiment of the system according to the present invention is characterized in that the heat transfer device is a (third) heat exchanger or is a thermal energy storage device preferably having a storage volume of not more than 50 l of domestic hot water, more preferably of 5 to 20 l of domestic hot water, wherein the thermal energy storage device preferably comprises a phase change material and more preferably having a storage capacity equivalent to not more than 50 l of domestic hot water, preferably 5 to 20 l of domestic hot water, and/or allows simultaneous charging (of the thermal energy storage device from a first hot fluid stream) and discharging of the thermal energy storage device (to a second cold fluid stream that is entirely isolated from the first hot fluid stream). By using a phase change material, the system has a higher energy storage density, which further reduces the system size. The (third) heat exchanger that might be used as heat transfer device can also be referred to as third external heat exchanger.
A further preferred embodiment of the system according to the present invention is characterized in that, when the heat transfer device is the thermal energy storage device, the system further comprises a state of charge analyser for determining the state of charge of the thermal energy storage device, wherein preferably the controller is configured to operate the system in consideration of the state of charge of the thermal energy storage device determined by the state of charge analyser.
A further preferred embodiment of the system according to the present invention is characterized in that the second heat transfer fluid comprises (or is) water, preferably water from a heat network, more preferably water from a district heat network. The district heat network is preferably a low temperature heat network, more preferably a low temperature heat network with a supply temperature of at least 20 °C, even more preferably at least 30 °C, most preferably at least 40 °C.
A further preferred embodiment of the system according to the present invention is characterized in that the first heat exchanger and/or the second heat exchanger is/are connected to a heat network comprising a heat transfer fluid circuit (in which the second heat transfer fluid is flowing), wherein the heat network is preferably a low temperature heat network, more preferably a low temperature heat network with a supply temperature of at least 20 °C, even more preferably at least 30 °C, most preferably at least 40 °C.
A further preferred embodiment of the system according to the present invention is characterized in that the plurality of configurations further comprises a further configuration in which the reconfigurable fluid network is configured to transfer the first heat transfer fluid from the heat network to the at least one emitter and not to the heat pump unit, wherein the plurality of modes further comprise a mode for heating the at least one space by directly transferring thermal energy from a heat network to the at least one emitter, while bypassing the heat pump unit to conserve electricity, in which mode the reconfigurable fluid network is configured in the further configuration.
A further preferred embodiment of the system according to the present invention is characterized in that the system further comprises at an outlet for domestic hot water of the heat transfer device

an electric booster heater, and/or
an adjustable valve for adjusting the flow rate and/or temperature of domestic hot water.

With the electric booster heater and/or the adjustable valve, a desired outlet temperature of the domestic hot water can be ensured. For example, the adjustable valve can adjust the domestic hot water flow rate to meet a domestic hot water setpoint of preferably 40 to 50 °, e.g. 45 °C.
A further preferred embodiment of the system according to the present invention is characterized in that the at least one valve is at least one three-way valve and/or the at least one valve is switchable by the controller (to change the configuration of the reconfigurable fluid network).
A further preferred embodiment of the system according to the present invention is characterized in that the reconfigurable fluid network comprises a least one pump, preferably at least two pumps, and/or the at least one valve comprises at least two valves, preferably at least four valves. Preferably, the valves are three-way valves and/or are switchable by the controller (to change the configuration of the reconfigurable fluid network).
A further preferred embodiment of the system according to the present invention is characterized in that the system is also capable for cooling the at least one space, wherein

the heat pump unit is a reversible heat pump unit, and/or
the plurality of configurations further comprises a third configuration in which the reconfigurable fluid network is configured to transfer the first heat transfer fluid from the heat pump unit to the at least one emitter and from the heat pump unit to the heat transfer device, wherein the plurality of modes further comprise a mode for cooling the at least one space and providing domestic hot water, in which the reconfigurable fluid network is configured in the third configuration.

In the third configuration, the reconfigurable fluid network is configured to transfer the first heat transfer fluid from (a low pressure side of) the heat pump unit to the at least one emitter (and back) and also to transfer the first heat transfer fluid from (a high pressure side of) the heat pump unit to the heat transfer device (and back). In order to achieve the third configuration, pipes of the reconfigurable fluid network, which are external to the heat pump unit, can be (or are) connected to both sides of the heat pump unit (i.e. a high pressure side and a low pressure side of the heat pump unit), e.g. to heat pump heat exchangers used as evaporator and condenser or to internal pipes of the heat pump unit on both sides of the heat pump unit.
Since in the mode for cooling the at least one space and providing domestic hot water, the reconfigurable fluid network is configured in the third configuration in which third configuration the reconfigurable fluid network is configured to transfer the first heat transfer fluid from the heat pump unit to the at least one emitter and from the heat pump unit to the first thermal energy storage device, (heat) energy (or heat) obtained by cooling the at least one space can be used for heating the heat transfer device and thus providing domestic hot water instead of rejecting the heat to the ambient through an air heat exchanger, which results in an energy efficient provision of domestic hot water without wasting the heat obtained by space cooling. Thus, the system according to the present invention is an energy efficient system that allows providing domestic hot water, heating at least one space, and cooling the at least one space.
A reversible heat pump can be obtained e.g. by the heat pump unit comprising a four-way valve that is arranged such that the heat pump cycle can be reversed.
A further preferred embodiment of the system according to the present invention is characterized in that the heat pump unit

comprises an internal refrigerant circuit circulating a third heat transfer fluid, the internal refrigerant circuit comprising the compressor, a first heat pump heat exchanger, the at least one expansion valve, and a second heat pump heat exchanger, wherein at least one of the first heat pump heat exchanger and the second heat pump heat exchanger is connected to pipes of the reconfigurable fluid network which are external to the heat pump unit, wherein preferably the first heat pump heat exchanger and the second heat pump heat exchanger are each connected to pipes of the reconfigurable fluid network which are external to the heat pump unit, or
(is a heat pump subunit and) comprises internal pipes for transferring the first heat transfer medium to the compressor and away from the compressor and for transferring the first heat transfer medium to the at least one expansion valve and away from the at least one expansion valve.

If the heat pump is a heat pump subunit, it comprises only a part of a heat pump (e.g. comprises the compressor and the at least one expansion valve but does not comprise any heat exchanger). If the heat pump unit is a heat pump subunit that does not comprise any heat exchanger, heat exchangers of the system arranged external of the heat pump unit can act as evaporator and condenser of the heat pump, so that a system similar to a split-type air-conditioning system (i.e. a traditional air-to-air air conditioning system) is provided, where the (e.g. wall mounted) heating and air conditioning unit is supplied with refrigerant from an outdoor unit (of the traditional air-to-air air conditioning system) and can act as evaporator during cooling and condenser during heating mode. Such heat exchangers of the system arranged external of the heat pump unit can be, e.g. the heat exchanger for transferring heat between the first heat transfer fluid and a second heat transfer fluid, the at least one emitter, and/or a heat exchanger of the heat transfer device.
If the heat pump unit is a heat pump subunit and/or comprises internal pipes for transferring the first heat transfer medium to the compressor and away from the compressor and for transferring the first heat transfer medium to the at least one expansion valve and away from the at least one expansion valve, it is preferred that the first heat transfer fluid is a refrigerant different from water.
If the heat pump unit comprises an internal refrigerant circuit circulating a third heat transfer fluid, it is preferred that the first heat transfer fluid is water and/or the third heat transfer fluid is a refrigerant different from water.
Preferably, the third heat transfer fluid is a refrigerant different from water (especially if liquid-vapour phase change is intended).
A further preferred embodiment of the system according to the present invention is characterized in that the system further comprises a further heat transfer device which is a solar heat transfer device, wherein the further heat transfer device is connected to the reconfigurable fluid network, and wherein preferably the further heat transfer device comprises at least one solar thermal collector and/or at least one photovoltaic thermal hybrid solar collector.
A further preferred embodiment of the system according to the present invention is characterized in that the system further comprises an additional thermal energy storage device, wherein the additional thermal energy storage device is connected to the reconfigurable fluid network, and wherein preferably the additional thermal energy storage device comprises a phase change material. By using a phase change material in the additional thermal energy storage device, the system has a higher energy storage density, which further reduces the system size.
A further preferred embodiment of the system according to the present invention is characterized in that the at least one (heat) emitter for heating and cooling the at least one space comprises

fan coil units (FCU), and/or
wall-mounted HVAC (Heating, Ventilation and Air Conditioning) units and/or ceiling cassettes, and/or
underfloor heating.

For systems featuring at least two heating spaces and/or heating-only applications underfloor heating can also be advantageous. Underfloor heating is one of the most efficient heat emitter systems, but it can be uncomfortably cold for the feet to use underfloor heating for space cooling. Thus, if at least two heating spaces are present, at least one space can be fitted with FCU for heating and cooling, while the at least one other space can be fitted with underfloor heating for space heating at high efficiency and low fan noise.
A further preferred embodiment of the system according to the present invention is characterized in that the heat transfer device, the reconfigurable fluid network (and thus also the heat pump unit), the first heat exchanger, the second heat exchanger are arranged within one indoor unit.
The present invention also relates to a method for operating the system according to the present invention, in which method the controller operates the system at least in a mode for providing domestic hot water and/or in a mode for heating the at least one space.
A further preferred embodiment of the method according to the present invention is characterized in that the controller additionally operates the system in a mode for cooling the at least one space, preferably in a mode for cooling the at least one space and providing domestic hot water.
A further preferred embodiment of the method according to the present invention is characterized in that the controller additionally operates the system in a mode for heating the at least one space by directly transferring thermal energy from a heat network to the at least one emitter, while bypassing the heat pump unit to conserve electricity. Preferably the first heat exchanger and/or the second heat exchanger is/are connected to the heat network, wherein the heat network comprises a heat transfer fluid circuit (in which the second heat transfer fluid is flowing), wherein the heat network is more preferably a low temperature heat network, even more preferably a low temperature heat network with a supply temperature of at least 20 °C, even more preferably at least 30 °C, most preferably at least 40 °C.
The preferred embodiments of the system described above also correspondingly apply to the method according to the present invention.
The present invention will be explained in more detail with reference to the following figures and examples without restricting it to the specific embodiments and parameters shown here.

Example 1

Fig. 1 shows a schematic view of a first example (Example 1) of the system according to the present invention. The system comprises a heat transfer device 19 for providing domestic hot water, heat emitters 14 for heating (and optionally cooling) at least one space, a reconfigurable fluid network for transferring a first heat transfer fluid, a first heat exchanger 15, a second heat exchanger 21, and a controller (not shown in Fig. 1). In this example, the first heat transfer fluid is water.
The reconfigurable fluid network comprises a heat pump unit 1, two pumps 8, 9, four three-way valves, and pipes. The heat pump unit 1 is a water-to-water heat pump unit comprising a (complete) water-to-water heat pump. The heat pump unit 1 comprises an internal refrigerant circuit circulating a third heat transfer fluid, the internal refrigerant circuit comprising a first heat pump heat exchanger 2, two expansion valves 3a, 3b, a refrigerant receiver 4, a second heat pump heat exchanger 5, a four-way valve 6, and a compressor 7, wherein the first heat pump heat exchanger 2 and the second heat pump heat exchanger 5 are each connected to pipes of the reconfigurable fluid network which are external to the heat pump unit 1. The third heat transfer fluid is a refrigerant different from water.
The expansion valves are e.g. linear expansion valves. The compressor is preferably a hermetic scroll or reciprocating type. The first and second heat pump heat exchangers 2, 5 are preferably plate heat exchangers due to their high efficiencies and compactness.
The first heat exchanger 15 is a heat exchanger for transferring heat between the first heat transfer fluid and a second heat transfer fluid, the second heat transfer fluid being external to the reconfigurable fluid network, wherein the first heat exchanger 15 is external to the heat pump unit 1. In this example, the second heat transfer fluid comprises (or is) water (e.g. from a district heating network).
The second heat exchanger 21 is a heat exchanger for pre-heating mains water to be further heated by the heat transfer device 19 to obtain domestic hot water.
The first heat exchanger 15 and/or the second heat exchanger 21 are connected to a low temperature heat network 20 (e.g. a district heating network) via the same refrigerant circuit wherein the low temperature heat network has a supply temperature of at least 20 °C, preferably at least 30 °C, more preferably at least 40 °C.
The heat transfer device 19 is a small thermal energy storage device (DHW-TES) having a storage capacity equivalent to not more than 50 l, or a heat exchanger. If the heat transfer device 19 is a small thermal energy storage device, the small thermal energy storage device preferably comprises a phase change material (PCM) as energy storage means. If the heat transfer device 19 is a small thermal energy storage device, the small thermal energy storage device can be linked to a state-of-charge (SOC) analyser (not shown in Fig. 1) that is configured to determine the state of charge of the first thermal energy storage device.
Furthermore, the system according to Example 1 allows direct use of thermal energy from the heat network for space heating, while bypassing the heat pump unit to conserve electricity. The heat emitters 14 can be directly connected to heat exchanger 15 through the reconfigurable fluid network and pump 8.
A part of the system according to Example 1 is comprised in a compact indoor unit. In detail, the reconfigurable fluid network with the heat pump unit, the heat transfer device, and the first and second heat exchangers are comprised in the compact indoor unit. In Fig. 2, an exemplary arrangement of the components is shown. According to this exemplary arrangement, the heat transfer device, which is a small thermal energy storage device having a storage capacity equivalent to not more than 50 l (DHW-TES) in this case, is arranged at the bottom of the indoor unit while the first and second heat exchangers (HEX) are arranged next to each other at the top of the indoor unit. Furthermore, the reconfigurable fluid network with the heat pump unit, which comprises a water-to-water heat pump, is located at the middle of the indoor unit, i.e. between the heat transfer device and the two heat exchangers.
The controller of the system according to Example 1 is configured such that it can operate the system in a plurality of modes (operating modes), wherein the reconfigurable fluid network is configurable by the controller in a plurality of configurations. The four three-way valves are switchable by the controller to change the configuration of the reconfigurable fluid network.
Fig. 3, Fig. 4, and Fig. 5 show schematic views of a control strategy and of two operating modes DHW-1 and DHW-2 of the system according to Example 1, wherein in this case the heat transfer device 19 is a small thermal energy storage device (DHW-TES) having a domestic hot water discharge volume capacity of not more than 50 l. Fig. 3 shows the control strategy. In Fig. 3, "Y" means "Yes", "N" means "No", "SOC" is the state of charge of the DHW-TES, "SOC-threshold" is a threshold for the state of charge of the DHW-TES, "T-HEX2" is the temperature of the first heat pump heat exchanger 2, and "T-Threshold" is a threshold for the temperature of the first heat pump heat exchanger 2. Furthermore, "Is charging?" refers to current charging of the DHW-TES in mode DHW-2 in the previous loop iteration.
Fig. 4 shows a schematic view of mode DHW-1 of the system according to Example 1. In mode DHW-1, the state of charge of the DHW-TES drops below a SOC-threshold, which can be in the range of 40 - 90 %, but is preferably in the range of 40 - 70 %. The heat pump unit is turned on and the internal refrigerant circuit of the heat pump unit 1 is preheated until the temperature in the first heat pump heat exchanger 2 reaches a threshold temperature. The system is then switched over to a mode DHW-2. It can be beneficial, if the heat emitters can be bypassed in the heat emitter circuit in mode DHW-1. The bypass would enable faster heating of the internal refrigerant circuit of the heat pump unit 1 to reach the temperature threshold in a shorter period of time.
Fig. 5 shows a schematic view of mode DHW-2 of the system according to Example 1. In mode DHW-2, the heat pump charges the DHW-TES and/or heats mains water to the desired domestic hot water outlet temperature.
The system performance depends on the desired DHW flow rate and the temperature of the preheated mains water according to: $Q_{HP} = V_{w} ρ_{w} c_{p, w} (T_{dhw} - T_{pm})$ where V_w is the DHW flow rate, ρ_w is the density of water, c_p,w is the specific heat capacity of water, T_dhw is the DHW outlet temperature, i.e. 45 °C in this example, and T_pm is the preheated mains water temperature. In this example, the heat pump has a heating capacity of Q_HP = 8 kW. The dependence of the system performance on the desired DHW flow rate also arises from the diagrams shown in Fig. 6a and 6b.
The diagrams in Fig. 6a and 6b show:

a) To achieve a DHW temperature of 45°C, the heat pump capacity depends on the DHW flow rate and the pre-heated water temperature. For example, the preheated mains temperature would have to be at least 26 °C at a DHW flow rate of 6 l/min to heat water to 45 °C at the DHW outlet. In addition, the plot shows that without the pre-heating HEX a 20 kW heat pump would be needed to deliver 8 l/min of DHW at 45 °C.
b) Heat source temperature requirements to achieve a DHW outlet temperature of 45°C assuming a heat exchanger effectiveness of 85 % in the preheating heat exchanger. The analysis indicates that a source temperature of approximately 35°C would be required to deliver 8 l/min with an 8 kW heat pump without a storage tank to achieve an outlet temperature of 45 °C.

For heat networks providing temperatures below 30 °C, the system could be modified by the following measures to meet the DHW temperature requirement:

Increase of the size of the DHW-TES.
A proportional valve at the DHW outlet, which adjusts the DHW flow rate to meet a DHW setpoint, e.g. 45°C, according to the equation shown above
An electric booster heater at the DHW outlet to increase the temperature to desired DHW setpoint, e.g. 45°C. The booster heater can be beneficial if no DHW-TES is present or to reduce the size of the DHW-TES even further.

Reference signs

1: Heat pump unit
2: First heat pump heat exchanger
3a, 3b: Expansion valve
4: Refrigerant receiver
5: Second heat pump heat exchanger
6: Four-way valve
7: Compressor
8, 9: Pump
14: Heat emitters
15: First heat exchanger
19: Heat transfer device
20: Low temperature heat network
21: Second heat exchanger

Claims

System for heating at least one space and for providing domestic hot water, comprising
a heat transfer device (19) for providing domestic hot water,

at least one emitter (14) for heating the at least one space, the at least one emitter being provided within the at least one space,

a reconfigurable fluid network for transferring a first heat transfer fluid, the reconfigurable fluid network comprising a heat pump unit (1), at least one valve, and pipes, the heat pump unit (1) comprising a compressor (7) and at least one expansion valve (3a, 3b), wherein the reconfigurable fluid network is configurable by a controller in a plurality of configurations comprising a first configuration, in which the reconfigurable fluid network is configured to transfer the first heat transfer fluid from the heat pump unit (1) to the heat transfer device (19) and not to the at least one emitter (14), and a second configuration, in which the reconfigurable fluid network is configured to transfer the first heat transfer fluid from the heat pump unit (1) to the at least one emitter (14) and not to the heat transfer device (19),

a first heat exchanger (15) for transferring heat between the first heat transfer fluid and a second heat transfer fluid, the second heat transfer fluid being external to the reconfigurable fluid network, wherein the first heat exchanger (15) is external to the heat pump unit (1),

a second heat exchanger (21) for pre-heating mains water to be further heated by the heat transfer device (19) to obtain domestic hot water,
and

the controller, wherein the controller is configured such that it can operate the system in a plurality of modes comprising a mode for providing domestic hot water, in which the reconfigurable fluid network is configured in the first configuration, and a mode for heating the at least one space, in which the reconfigurable fluid network is configured in the second configuration.
System according to claim 1, characterized in that the heat pump unit (1) is a water source heat pump unit.
System according to any one of the preceding claims, characterized in that the first heat transfer fluid comprises or consists of water or a refrigerant different from water.
System according to any one of the preceding claims, characterized in that the heat transfer device (19) is a heat exchanger or is a thermal energy storage device, wherein the thermal energy storage device preferably comprises a phase change material and/or allows simultaneous charging and discharging of the thermal energy storage device.
System according to any one of the preceding claims, characterized in that, when the heat transfer device (19) is the thermal energy storage device, the system further comprises a state of charge analyser for determining the state of charge of the thermal energy storage device (19), wherein preferably the controller is configured to operate the system in consideration of the state of charge of the thermal energy storage device (19) determined by the state of charge analyser.
System according to any one of the preceding claims, characterized in that the second heat transfer fluid comprises water, preferably water from a heat network, more preferably water from a district heat network.
System according to any one of the preceding claims, characterized in that the first heat exchanger (15) and/or the second heat exchanger (21) is/are connected to a heat network comprising a heat transfer fluid circuit, wherein the heat network is preferably a low temperature heat network (20), more preferably a low temperature heat network (20) with a supply temperature of at least 20 °C, even more preferably at least 30 °C, most preferably at least 40 °C.
System according to claim 7, characterized in that the plurality of configurations further comprises a further configuration in which the reconfigurable fluid network is configured to transfer the first heat transfer fluid from the heat network to the at least one emitter (14) and not to the heat pump unit (1), wherein the plurality of modes further comprise a mode for heating the at least one space by directly transferring thermal energy from a heat network to the at least one emitter, while bypassing the heat pump unit to conserve electricity, in which mode the reconfigurable fluid network is configured in the further configuration.
System according to any one of the preceding claims, characterized in that the system further comprises at an outlet for domestic hot water of the heat transfer device (19)
- an electric booster heater, and/or

- a valve for adjusting the flow rate and/or temperature of domestic hot water.
System according to any one of the preceding claims, characterized in that the reconfigurable fluid network comprises a least one pump (8, 9), preferably at least two pumps (8, 9), and/or the at least one valve comprises at least two valves, preferably at least four valves.
System according to any one of the preceding claims, characterized in that the system is also capable for cooling the at least one space, wherein
- the heat pump unit (1) is a reversible heat pump unit, and/or

- the plurality of configurations further comprises a third configuration in which the reconfigurable fluid network is configured to transfer the first heat transfer fluid from the heat pump unit (1) to the at least one emitter (14) and from the heat pump unit (1) to the heat transfer device (19), wherein the plurality of modes further comprise a mode for cooling the at least one space and providing domestic hot water, in which the reconfigurable fluid network is configured in the third configuration.
System according to any one of the preceding claims, characterized in that the heat pump unit (1)
- comprises an internal refrigerant circuit circulating a third heat transfer fluid, the internal refrigerant circuit comprising the compressor (7), a first heat pump heat exchanger (2), the at least one expansion valve (3a, 3b), and a second heat pump heat exchanger (5), wherein at least one of the first heat pump heat exchanger (2) and the second heat pump heat exchanger (5) is connected to pipes of the reconfigurable fluid network which are external to the heat pump unit (1), wherein preferably the first heat pump heat exchanger (2) and the second heat pump heat exchanger (5) are each connected to pipes of the reconfigurable fluid network which are external to the heat pump unit, or

- comprises internal pipes for transferring the first heat transfer medium to the compressor (7) and away from the compressor (7) and for transferring the first heat transfer medium to the at least one expansion valve (3a, 3b) and away from the at least one expansion valve (3a, 3b).
Method for operating a system according to any one of the preceding claims, in which the controller operates the system at least in a mode for providing domestic hot water and/or in a mode for heating the at least one space.
Method according to claim 13, characterized in that the controller additionally operates the system in a mode for cooling the at least one space, preferably in a mode for cooling the at least one space and providing domestic hot water.
Method according to claim 13 or 14, characterized in that the controller additionally operates the system in a mode for heating the at least one space by directly transferring thermal energy from a heat network to the at least one emitter, while bypassing the heat pump unit to conserve electricity.