EP4244539A1

EP4244539A1 - Hot water circulation system and method for operating the same

Info

Publication number: EP4244539A1
Application number: EP21892441.3A
Authority: EP
Inventors: Willy Ossiansson
Original assignee: Energybooster AB
Current assignee: Energybooster AB
Priority date: 2020-11-16
Filing date: 2021-11-16
Publication date: 2023-09-20
Also published as: EP4244539A4; SE544546C2; WO2022103323A1; SE2051338A1

Abstract

Hot water circulation system (200) for a building, said system comprising a hot tap water circulation circuit (210); a circulation pump (211); water taps (220-224); a cold water inlet (240) to said circulation circuit; a heat exchanger (230), arranged to heat the water using an externally provided heat medium; a first conduit (213), leading a first share of water from said pump to said taps via said heat exchanger; a temperature sensor (251), arranged downstream of said heat exchanger; and a control device (250), arranged to control a flow of said heat medium. The invention is characterised in that the circulation circuit comprises a second conduit (214), leading a second share of water from said pump to said taps in parallel to said first conduit, in that the first share is at least smaller than said second share as long as no cold water is provided to the circulation circuit, and in that the circulation system further comprises a heat pump (260), heating the water. The invention also relates to a method.

Description

Hot water circulation system and method for operating the same

The present invention relates to hot water circulation system, in particular a hot water circulation system exploiting district heating for heating the circulated tap water. The 5 present invention also relates to a method for operating such a hot water circulation system.

In larger buildings, such as apartment buildings and public buildings, it is common to use a hot water circulation system. Such a system is designed to constantly circulate heated tap w water in the building with the purpose of minimising the flushing time required before hot water is available in a given tap in said building. Namely, in a large building with long hot water conduits, if hot water has not been flushed for some time the water in the conduit will have cooled, and before hot water can reach the tap in question the cooled water first needs to be flushed out. By circulating the hot water in a hot water circulation system, hot is water is instead available immediately at the tap.

Figure 1 illustrates a conventional hot water circulation system 100, which would typically be installed in a building (not shown) in order to deliver hot tap water to taps 120, 121, 122, 123, 124 in said building. 0

The system comprises a main circulation circuit 110, in which hot water is constantly circulated using a circulation pump 111. The hot water passes some type of heat source, such as a heat exchanger 130 in which the circulated water in the circuit 110 is heated by district heating heat medium flowing from a centrally located district heating facility (not5 shown), arriving to the heat exchanger 130 in lead conduit 132 and leaving the heat exchanger 130 in return conduit 131.

The circuit 110 is pressurized, such a via a cold water lead conduit 140 which in turn is pressurized by a cold water source such as a domestic cold water network. When a user0 flushes one of the taps 120-124, the pressure in circuit 110 drops and is as a result replenished by an inflow of cold water via lead conduit 140. Since the water is constantly circu- lated past heat exchanger 130, it over time assumes a desired hot temperature for use as hot tap water.

There are a number of problems with conventional hot water circulation systems, such as s the one illustrated in Figure 1.

Firstly, thermal losses may be significant. There are some estimations concluding that up to half of the total hot water heating energy requirements may be lost due to non-useful heat dissipation from the hot tap water circulating irrespectively of if hot tap water is w currently used or not.

Secondly, in case the heat source used is a district heating heat exchanger, it is often desired that the cooled heating medium leaving the heat exchanger via return line 131 is as cool as possible. Namely, the return medium entering the district heating plant is is normally used as a cooling agent used to cool hot material, such as reaction products from some type of exothermal process. For instance, the returning heat medium may be used to cool flue gases from a combustion process, such as in a combined heat and power plant. As a cooling agent, the cooling will be more thermally efficient the cooler the incoming return heat medium is. Therefore, from a whole system efficiency point of view0 the larger the temperature difference between the heat medium in conduits 131 and 132 the better. Since the hot tap water in circuit 110 typically only changes its temperature gradually and/or intermittently, the heat medium flowing past heat exchanger 130 will in a normal operating mode most often be cooled only slightly, which leads to thermal inefficiencies on the large system scale. 5

The present invention solves the above described problems.

Hence, the invention relates to a hot water circulation system, arranged to circulate hot tap water in at least one building, said system comprising a hot tap water circulation0 circuit; a circulation pump, arranged to circulate water in said circulation circuit; a plurality of water taps, arranged for tapping water from said circulation circuit; a cold water inlet, arranged to supply cold water to said circulation circuit; a heat exchanger, arranged to heat water being circulated in said circulation circuit using an externally provided heat medium flowing past said heat exchanger; a first conduit of said circulation circuit, arranged to lead a first share of said water from said circulation pump to said plurality of 5 water taps via said heat exchanger, whereby the water flowing through said first conduit thermally interacts with said heat exchanger; a temperature sensor, arranged to measure a temperature of water flowing through said first conduit, downstream of said heat exchanger; and a control device, arranged to control a flow of said externally provided heat medium through said heat exchanger, which system is characterised in that the w circulation circuit comprises a second conduit, arranged to lead a second share of said water from said circulation pump to said plurality of water taps in parallel to said first conduit without the water thermally interacting with said heat exchanger, in that the first share is smaller than said second share as long as no cold water is provided to the circulation circuit via said cold water inlet, and in that the circulation system further comprises a is heat pump, arranged to heat the water circulated in said circulation circuit.

Moreover, the invention relates to a method for operating a hot water circulation system, said circulation system being arranged to circulate hot tap water in at least one building and comprising a hot tap water circulation circuit; a circulation pump, arranged to circu-0 late water in said circulation circuit; a plurality of water taps arranged for tapping water from said circulation circuit; a cold water inlet, arranged to supply cold water to said circulation circuit; a heat exchanger, arranged to heat water being circulated in said circulation circuit using an externally provided heat medium flowing past said heat exchanger; a first conduit of said circulation circuit, arranged to lead a first share of said5 water from said circulation pump to said plurality of water taps via said heat exchanger, whereby the water flowing through said first conduit thermally interacts with said heat exchanger; a temperature sensor, arranged to measure a temperature of water flowing through said first conduit, downstream of said heat exchanger; and a control device, arranged to control a flow of said externally provided heat medium through said heat0 exchanger, which method is characterised in that the method comprises in a first state of the circulation system, in which all of said water taps are closed, circulating a second share of said water in a second conduit, from said circulation pump to said plurality of water taps in parallel to said first conduit without the water thermally interacting with said heat exchanger, said first share being smaller than said second share, and heating the water circulated in said circulation circuit using a heat pump comprised in said circulation sys-

5 tern; and in a second state of the circulation system, in which at least one of said water taps is open, replenishing the circulation circuit using cold water from said cold water inlet.

In the following, the invention will be described in detail, with reference to an exemplify- w ing embodiment of the invention shown in Figures 2a and 2b.

Hence, Figures 2a and 2b illustrates a hot water circulation system 200 according to the invention. Figures 2a and 2b share the same reference numerals with Figure 1 for corresponding parts, but the reference numerals used in Figures 2a and 2b start with a "2" is while the corresponding reference numerals in Figure 1 start with a "1".

Figure 2a illustrates a system 200 according to the present invention in a first state, while Figure 2b illustrates the same system 200 in a second state. 0 Similarly to the system 100 shown in Figure 1, the hot water circulation system 200 shown in Figures 2a and 2b is arranged to circulate hot tap water in at least one building. The one or several buildings being provided by tap water by said system 200 is not shown in Figures 2a and 2b, but it is realized that they can vary in terms of their constitution. For instance, one and the same system 200 may provide rapidly available hot tap water to5 several apartments in an apartment building; to several rooms in a public building, such as an office building, a school or a hospital; or to several smaller buildings. It is also possible to use a system according to the present invention in a single house, such as in a villa.

The system 200 comprises a hot tap water circulation circuit 210, arranged to circulate0 heated (hot) tap water so that it is rapidly available for a plurality of water taps 220, 221, 222, 223, 224 arranged for tapping water from the circulation circuit 210. It is understood that such tapped water is then hot tap water. In other words, a water supply system for the one or several buildings may also comprise a cold water conduit, which is not part of the present system 200 but a separate system for providing cold water, such as using the same water taps 220-224 that may then be mixer taps. The circulation of heated tap water s in circulation circuit 210 may be constant, or at least intermittently constant. If nothing else is stated herein, the terms "tap water", "hot water" and "heated water" all relate to hot/heated tap water circulating in the circulation circuit 210.

The system 200 is arranged to control the temperature of the water circulated in the hot w water circulation circuit 210, as will be described hereinbelow. The circulated water may have a temperature of at least 50°C, such as at least 55°C, at least in a part of the circulation circuit 210 leading up to the taps 220-224. It is important from a health perspective that the temperature of the heated tap water, at least at some point in the circulation along the circulation circuit 210, and in particular when available at the taps 220-224, is holds a temperature of at least 50°C, or even at least 55°C.

The system 200 comprises a control device 250, which may comprise control logic implemented in per se conventional hardware and/or software, such as a suitably programmed piece of hardware comprising a CPU, a RAM memory and a computer bus, and which may0 use a setpoint temperature, of at least 50 °C, such as at least 55 °C, against which it regulates a temperature of the water circulating in said circulation circuit 210 and in particular in said part of the circulation circuit 210 leading up to the taps 220-224. The control device 250 may be implemented as a discreet piece of hardware, communicating with controlled entities via a suitable wired or wireless interface, or the control device 2505 may be implemented as a part of an existing control device (in a retrofit scenario), in the latter case preferably completely using software.

Furthermore, the system 200 comprises a circulation pump 211, arranged to circulate said hot tap water in the circulation circuit 210. The circulation circuit 210 may be or comprise0 a closed loop circuit, circulating the heated tap water endlessly round said loop. The system 200 also comprises a cold water inlet 240, arranged to supply fresh cold water to the circulation circuit 210. For instance, the cold water inlet 240 may supply water from a municipal fresh water distribution system. s The system 200 comprises a heat exchanger 230, arranged to heat said tap water being circulated in the circulation circuit 210 using an externally provided heat medium flowing past said heat exchanger 230. The externally provided heat medium may be a district heating heat medium, flowing from a centrally located district heating facility (not shown), arriving to the heat exchanger 230 in lead conduit 232 and leaving the heat exchanger 230 w in return conduit 231. The temperature of the externally provided heat medium, upon arrival at the heat exchanger 230 and when being circulated, may be at least 80 °C, such as at least 90 °C. The heat medium may be any suitable heat medium, such as water or water with any desired additive, such as an anti-freeze additive. It is noted that such a district heating system itself is generally not part of the present system 200, but is considered to is be an external system.

The heat exchanger 230 may also be a part of such a district heating system. It may be an existing heat exchanger 230, and may form part of an existing district heating providing mechanism already installed for delivering heat to the one or several buildings. From this0 perspective, the installation of part of the system 200, or of the entire system 200, may be a retrofitting of a system 200 according to the invention. For instance, the circulation circuit 210 may also be already existing as such, as may be the case for the pump 211, the cold water supply 240 and taps 220-224, before modifying the already existing installation so as to be in accordance with the present invention. 5

Moreover, the system 200 comprises a first conduit 213 of the circulation circuit 210, being arranged to lead a first share of the circulated tap water in the circulation circuit 210 from the circulation pump 211 to the water taps 220-224 via the heat exchanger 230, whereby the circulated tap water flowing through the first conduit 213 thermally interacts0 with the heat exchanger 230. That the circulated tap water "thermally interacts" with the heat exchanger 230 means, herein, that the circulated tap water, while passing through first conduit 213, absorbs thermal energy from the heat medium circulating in conduits 232, 231 and through the heat exchanger 230. Preferably, the first conduit 213 comprises a passage through the heat exchanger 230 as a part of the first conduit 213 in question. Hence, the first conduit 213 is arranged to bring tap water past the heat exchanger 230 so that the tap water is thereby heated by heat exchange with said heat medium. It is realized that this heating will depend on a flow magnitude of heat medium through conduits 232, 231 and through the heat exchanger 230.

The system 200 also comprises a temperature sensor 251, arranged to measure a temperature of heated tap water flowing through said first conduit 213, at a location downstream of the heat exchanger 230. Said control device 250 is arranged to control a flow of said externally provided heat medium through the heat exchanger 230. This control may be performed based on the read temperature from temperature sensor 251, as will be described hereinbelow.

According to the present invention, the circulation circuit 210 further comprises a second conduit 214, arranged to lead a second share of the heated tap water from the circulation pump 211 to said plurality of water taps 220-224 in a flow which is parallel to the one via said first conduit 213. The flow of the second share of the heated tap water through the second conduit 214 takes place without the heated tap water thermally interacting with the heat exchanger 230.

That the heated tap water flows through the second conduit "without thermally interacting with the heat exchanger 230" means, herein, that the second conduit 214 does not pass the heat exchanger 230 in a way offering significant enough thermal connection between, on the one hand, the heat medium flowing through conduits 232, 231 and the heat exchanger 230 and, one the other hand, the heated tap water flowing through the second conduit 214, so as to heat the heated tap water to any significant degree. Prefera- bly, the second conduit 214 does not pass neither through, nor close to the heat exchanger 230. Further preferably, the second conduit 214 has at least 10 cm of insulation, such as in the form of a solid-state insulation or air, between the second conduit 214 and the heat exchanger 230.

Further according to the invention, the first share is smaller than the second share, such as at least five times less than said second share, such as at least ten times less than said second share, as long as no cold water is provided via said cold water inlet 240. In other words, the amount of heated tap water passing through the first conduit 213 at any given point in time will always be less than the amount of heated tap water passing through the second conduit 214, as long as no additional cold water is being supplied. When fresh cold water is provided to the circulating circuit 210, more water may flow through the first conduit 213 (see below). At any rate, it is preferred that, at a point along the circulating circuit 210 at which a main conduit 215 for the tap water splits into the first and said second share flows (in first 213 and second 214 conduits, respectively), at least a majority of, such as at least five times as much, or even ten times as much, tap water per time unit flows into the second conduit 214 as compared to the amount of water per time unit that instead flows into the first conduit 213.

This means that the second conduit 214 is a main subpart of the circulation circuit 210, since a majority of the heated tap water passes therethrough on its way around the circulation circuit 210 from the pump 211, past the taps 220-224 and back again to the pump 211. Correspondingly, the first conduit 213 is a control conduit, through which a smaller share of the heated tap water on its way around the circulation circuit 210, past the heat exchanger 230 and the temperature sensor 251.

The tap water may hence be circulated in a loop defined by the circulation circuit 210, and in this circulation 90% of the tap water is conveyed via the second conduit 214 while a small share of the tap water is instead routed via the first conduit 213, the first conduit 213 constituting a control flow past the cold water inlet 240 and the heat exchanger 230, with the purpose of continuously being able to measure the temperature of the tap water flowing out from the heat exchanger 230 and to control the heat exchanger 230 based on the measured temperature. s Also according to the present invention, the circulation system 200 further comprises a heat pump 260, arranged to heat the heated tap water circulated in said circulation circuit 210. The heat pump 260 is preferably not arranged along the first conduit 213. The heat pump 260 is preferably not arranged along the second conduit 214. Instead, the heat pump 260 is advantageously arranged along a common part of the circulation circuit 210, w so that all heated tap water (both the first and the second share) passes the heat pump 260 on its way around the circulation circuit 210. The heat pump 260 is not a part of the district heating system, but locally arranged in or in connection to the one or several buildings mentioned above. is The heat pump 260 may be arranged to heat the tap water circulating in the circulation circuit 210 to said desired setpoint temperature. To achieve this, the heat pump 260 may be controlled by the control device 250, or be subject to an independent temperature control of the heated tap water. 0 Furthermore, the heat pump 260 may heat the heated tap water independently from the heat exchanger 230, meaning that the heat pump 260 is not controlled directly based on the amount of heating provided by said heat exchanger 230 (it is realized that there may be an indirect control in some cases, such as when the heat exchanger 230 is about to stop heating, and due to inertia of the external heat medium). 5

The system 200 may be configured, such as via control by the control device 250, to only, or substantially only, heat the tap water using the heat pump 260 as long as the taps 220- 224 are all closed, and to heat the tap water using also (or exclusively) the heat exchanger 230 when one or several taps 220-224 are open. The open/closed state of the taps 220-0 HA may be measured indirectly based on the temperature measured by the temperature sensor 251, in the sense that when the measured temperature is below a predetermined value the heating from the heat exchanger may be switched on or increased. Such relatively low measured circulating tap water temperature will occur when cold water is provided from the cold water inlet 240, so that part of, or all, tap water circulating past the temperature sensor 251 originates from the cold water inlet 240. Preferably, the s system 200 is not arranged to measure an open/closed state of the taps 220-224 directly, such as using a sensor at the tap in question.

Using the heat pump 260 to heat the heated tap water achieves that the heat exchanger

230 will be used to lesser extent, or preferably not at all, when no hot tap water is used. w This will typically be the case most of the time. This has the advantageous effect that a runtime of the heat exchanger 230 with a relatively small low temperature difference between the heat medium flowing through conduit 232 as compared to through conduit

231 is minimised, which in turn makes the larger system more energy-efficient. is However, when cold water is being supplied via inlet 240, this cold water can be heated efficiently using the heat exchanger 230 before reaching the taps 220-224, while providing a high temperature difference between external heat medium flowing through conduits 231 and 232 on either side of the heat exchanger 230. Preferably, the heat exchanger 230 is dimensioned to heat the supplied cold water up to said setpoint temperature as it

20 passes (one time) through the heat exchanger 230.

Furthermore, the addition of the heat pump 260 according to the present invention increases the total tap water heating capacity of the system 200. During periods of peak load, such as when many taps 220-224 are used at the same time, both the heat exchanges er 230 and the heat pump 260 may be used at the same time, such as under the joint control of the control device 250 or under independent/individual control as described above. Hence, the present system and method provides higher peak heating capacity without having to increase the capacity of the heat exchanger 230.

30 The capacity of the heat pump 260 is preferably between 10% and 100% of the capacity of the heat exchanger 230 in terms of heating power of the tap water. The cold water inlet 240 may be arranged to supply said cold water to the circulation circuit 210 via, such as exclusively via, said first conduit 213. The cold water inlet may furthermore be arranged upstream of a point along said first conduit 213 at which the tap s water thermally interacts with the heat exchanger 230. This means that the supplied cold water is released into the circulation circuit 210 and then passes the heat exchanger 230. Given the fact that only a small amount of tap water passes through the first conduit 213 as long as no cold water is provided, when cold water in fact is provided the provided cold water can constitute most, or even all, of the water flowing through the first conduit 213 w between the cold water inlet 240 and the heat exchanger 230. This minimises the temperature of the tap water flowing through the heat exchanger 230 when the cold water is being supplied, in turn maximising the temperature difference of the heat medium flowing through conduits 232 and 231. is The circulation circuit 210 as a whole may be pressurized by the cold water inlet 240, by the cold water inlet 240 being connected without interruption to said circulation circuit 210, via an open connection. As long as no taps 220-224 are open there is pressure equilibrium between the cold water inlet 240 and the circulation circuit 210, why no cold water flows into the circulation circuit 210 from the cold water inlet 240. However, as the0 tap water pressure drops in the circulation circuit 210, due to a tap 220-224 being opened for flushing, fresh cold water is immediately supplied due to the accrued pressure difference, driven by the accrued pressure gradient.

The first conduit 213 may comprise a flow reducing valve 212, achieving the above-5 described difference between the tap water flow through the first 213 and the second 214 conduits. The flow reducing valve 212 may be of any conventional type, and may furthermore also be or comprise a check valve, only allowing tap water to flow in a direction from the pump 211 to the heat exchanger 230 and not the other way. This forces all cold water supplied from the cold water supply 240 to flow past the heat exchanger 230 before0 reaching the taps 220-224. Such a check valve may also be arranged as a separate component along the first conduit 213. The control device 250 may be arranged to control said flow of the externally provided heat medium through the heat exchanger 230 by controlling a flow valve 252, which is also comprised in the system 200, based on said temperature read by said temperature s sensor 251. The operation of the heat exchanger 230 (on/off or over a continuous power scale) may hence be effectuated by controlling a flow of said external heat medium through the heat exchanger 230. Then, a "decrease" in the heating power of the heat exchanger 230 means that the flow of external heat medium is decreased, and a "stop" of the heat exchanger 230 heating operation means that the flow of external heat medium is w halted.

In particular, the control device 250 may be arranged to control said flow of the externally provided heat medium through the heat exchanger 230 so that said flow is decreased or, preferably, stopped entirely, when the temperature read by said temperature sensor 251 is is equal to or above the above-mentioned temperature setpoint.

The circulation pump 211 may be arranged along said main conduit 215 of the circulation circuit 210, the main conduit 215 being part neither of the first conduit 213 nor of said second conduit 214. Preferably, the pump 211 is arranged between the taps 220-224 and0 the above-mentioned split point of the main conduit 215 and said first 213 and second 214 conduits.

The heat pump 260 may be arranged along said main conduit 215 also. In Figures 2a and 2b, the heat pump 260 is shown to be located upstream, along the main conduit 215, in5 relation to the pump 211, but it is realized that the heat pump 260 may also be arranged downstream of the pump 211 along the main conduit 215.

However, it is preferred that all tap water flowing through the circulation circuit 210 passes the heat pump 260 each lap around the circulation circuit 210. 0 Moreover, the heat pump 260 may be a gas-to-liquid heat pump, arranged to heat the tap water using thermal energy from air surrounding the heat pump 260. Hence, "gas-to- liquid" may in practise mean "air-to-tap water". How such heat pumps work is completely conventional as such, and will not be described herein in any detail. However, it may be s worthwhile mentioning that such a heat pump uses electric power to circulate an internal heat carrier past a compressor and an expansion valve to transfer thermal energy from the gas to the liquid, effectively cooling the gas and concurrently heating the liquid using the harvested thermal energy. The heat pump cycle achieves a thermal transfer that typically has a higher power than the supplied electric power, as measured by the so- w called COP (Coefficient Of Performance) value of the heat exchanger.

In particular, the heat pump 260 may be arranged in a closed indoors space 270, such as a machine room for said one or several buildings. Then, the heat exchanger 230 may also be arranged in said closed space 270. Since the provision of the heat medium via conduit 232 is to the heat exchanger 230 will lead to certain heating of the closed space 270, the closed space 270 will typically need cooling. At any rate, heating of the closed space 270 resulting from the externally supplied heat medium will normally constitute an energy waste. By the heat pump 260 using the same air inside the closed space 270 as is heated by the externally provided heat medium, via heat exchanger 230 or directly via part of the0 conduit 232 being arranged inside said closed space, the heat pump 260 both provides cooling to said closed space 270 and will operate under efficient thermal conditions, using a relatively warm gas as the gas from which heat is harvested.

In some embodiments, the closed space 270 may also comprise additional electric equip-5 ment 271, not forming part of the system 200 but used to operated said at least one building and emitting heat in the process. Such additional electric equipment may comprise ventilation equipment, computer equipment, electric grid equipment and similar. The control device 250 itself may also be provided in said closed space, adding to the heating of the closed space 270. Hence, using the heat pump 260 in the same closed0 space, this waste heat is exploited to heat the circulating tap water. It is noted that the circulation circuit 210 is at least partly arranged outside of the closed space 270, and in particular at least one or several of said taps 220-224 may be arranged outside of the closed space 270. But the circulation circuit 210 itself may pass through the closed space 270. Hence, the heated tap water will typically be cooled when circulating in the circulation circuit 210 from the heat pump 260 and again back to the heat pump 260.

Therefore, the heating by the heat pump 260 constitutes a maintenance heating of the heated tap water, with the goal of maintaining the setpoint temperature for rapid delivery to the taps 220-224 upon need. The return temperature of the tap water arriving at the heat pump 260 may be between 40-50°C.

Figure 3 illustrates a method according to the invention, for operating a hot water circulation system 200 of the present type, being arranged to circulate hot tap water in at least one building and comprising the circulation circuit 210, the pump 211, the taps 220-224, the cold water inlet 240, the heat exchanger 230, the first conduit 213, the second conduit 214, the control device 250 and the heat pump 260.

In a first step, the method starts.

In a subsequent step, the system 200 is operated in a first state, in which all of the water taps 220-224 are closed. In this state, the second share of the tap water is circulated in the second conduit 214, from the circulation pump 211 to the taps 220-224 in parallel to the first conduit 213 without the water thermally interacting with said heat exchanger 230, as described above. As also described above, in this first state the first share of the tap water is at least smaller than the second share, as no cold water is supplied via cold water inlet 240. Also in this first state, the tap water being circulated in the circulation circuit 210 is heated using the heat pump 260.

This first state is illustrated in Figure 2a, in which white arrows symbolise flow direction of a relatively small flow amount per time unit of tap water, whereas black arrows symbolise flow direction of a relatively large amount per time unit of tap water. In a subsequent step, the system 200 is operated in a second state, in which at least one of the water taps 220-224 is open. In this second state, the circulation circuit 210 is automatically replenished using cold water from the cold water inlet 240, as described above.

Thereafter, the method may switch between said first and second states multiple times, depending on the current open/closed state of the taps 220-224. It is realized that, using the principles described herein, the switch between the first and the second state is completely automatic. It is dictated by the state of the taps 220-224 and effected by said automatic control of the heat exchanger 230 and the heat pump 260, as described above.

In a subsequent step, the method ends.

As discussed above, in said first state the control device 250 may read a measured tem- perature from the temperature sensor 251 and then determine that the read temperature is equal to or above said temperature setpoint. As a result, the control device 250 may decrease or stop a flow of said externally provided heat medium past the heat exchanger 230. Correspondingly, in said second state the control device 250 may read a measured temperature from the temperature sensor 251 and then determine that the read temperature, due to the addition of said cold water via cold water inlet 240 as a result of at least one tap 220-224 being open, is below said temperature setpoint, and may as a result increase a flow of the externally provided heat medium past the heat exchanger 230.

The heat pump 260 may, at any or all times, be operated to try to achieve or maintain a predetermined minimum temperature of the tap water flowing past the heat pump 260 in question. Above, preferred embodiments have been described. However, it is apparent to the skilled person that many modifications can be made to the disclosed embodiments without departing from the basic idea of the invention. For instance, the system 200 may comprise additional parts, in addition to the ones disclosed in the Figures.

In general, everything which has been described in relation to the present system is equally applicable to the present method.

Several different possible embodiments have been described herein, in connection to Figures 2a, 2b and 3, that sometimes differ in the details. The described embodiments have been selected to provide a clear description of the invention and how it can be varied. Pending compatibility, such embodiments are freely combinable in any manner.

Hence, the invention is not limited to the described embodiments, but can be varied within the scope of the enclosed claims.

Claims

C L A I M S

1. Hot water circulation system (200), arranged to circulate hot tap water in at least one building, said system comprising s a hot tap water circulation circuit (210); a circulation pump (211), arranged to circulate water in said circulation circuit (210); a plurality of water taps (220;221;222;223;224) arranged for tapping water from said circulation circuit (210); a cold water inlet (240), arranged to supply cold water to said circulation circuit (210); w a heat exchanger (230), arranged to heat water being circulated in said circulation circuit (210) using an externally provided heat medium flowing past said heat exchanger (230); a first conduit (213) of said circulation circuit (210), arranged to lead a first share of said water from said circulation pump (211) to said plurality of water taps (220;221;222;223;224) via said heat exchanger (230), whereby the water flowing through is said first conduit (213) thermally interacts with said heat exchanger (230); a temperature sensor (251), arranged to measure a temperature of water flowing through said first conduit (213), downstream of said heat exchanger (230); and a control device (250), arranged to control a flow of said externally provided heat medium through said heat exchanger (230), wherein 0 the circulation circuit (210) comprises a second conduit (214), arranged to lead a second share of said water from said circulation pump (211) to said plurality of water taps (220;221;222;223;224) in parallel to said first conduit (213) without the water thermally interacting with said heat exchanger (230), wherein the first share is smaller than said second share as long as no cold water is provided to the5 circulation circuit (210) via said cold water inlet (240), c h a r a c t e r i s e d i n that the circulation system (200) further comprises a heat pump (260), arranged to heat the water circulated in said circulation circuit (210), and in that the heat pump (260) is arranged along a main conduit (215) of the circulation circuit (210),0 said main conduit (215) not being part of said first conduit (213).

2. Hot water circulation system (200) according to claim 1, wherein said heat medium is provided from a district heating system.

3. Hot water circulation system (200) according to claim 1 or 2, wherein said cold water inlet (240) is arranged to supply said cold water to said first conduit (213).

4. Hot water circulation system (200) according to any one of the preceding claims, wherein the circulation circuit (210) is pressurized by said cold water inlet (240), which is connected without interruption to said circulation circuit (210).

5. Hot water circulation system (200) according to any one of the preceding claims, wherein said first conduit (213) comprises a flow reducing valve (212).

6. Hot water circulation system (200) according to any one of the preceding claims, wherein the control device (250) is arranged to control said flow of the externally provided heat medium through said heat exchanger (230) by controlling a flow valve (252) based on said temperature read by said temperature sensor (251).

7. Hot water circulation system (200) according to any one of the preceding claims, wherein the control device (250) is arranged to control said flow of the externally provided heat medium through said heat exchanger (230) so that said flow is decreased or stopped when the temperature read by said temperature sensor (251) is equal to or above a temperature setpoint. 8. Hot water circulation system (200) according to any one of the preceding claims, wherein the circulation pump (211) is arranged along said main conduit (215) of the circulation circuit (210).

9. Hot water circulation system (200) according to any one of the preceding claims, wherein said main conduit (215) is not part of said second conduit (214). 19

10. Hot water circulation system (200) according to any one of the preceding claims, wherein the heat pump (260) is a gas-to-liquid heat pump, arranged to heat said water using thermal energy from air surrounding the heat pump (260). s 11. Hot water circulation system (200) according to any one of the preceding claims, wherein the heat pump (260) is arranged in a closed space (270), and in that said heat exchanger (230) is also arranged in said closed space (270).

12. Hot water circulation system (200) according to claim 11, wherein the closed space w (270) also comprises electric equipment (271) used to operated said building and emitting heat.

13. Method for operating a hot water circulation system (200), said circulation system (200) being arranged to circulate hot tap water in at least one building and comprising is a hot tap water circulation circuit (210); a circulation pump (211), arranged to circulate water in said circulation circuit (210); a plurality of water taps (220;221;222;223;224) arranged for tapping water from said circulation circuit (210); a cold water inlet (240), arranged to supply cold water to said circulation circuit (210);0 a heat exchanger (230), arranged to heat water being circulated in said circulation circuit (210) using an externally provided heat medium flowing past said heat exchanger (230); a first conduit (213) of said circulation circuit (210), arranged to lead a first share of said water from said circulation pump (211) to said plurality of water taps (220;221;222;223;224) via said heat exchanger (230), whereby the water flowing through5 said first conduit (213) thermally interacts with said heat exchanger (230); a temperature sensor (251), arranged to measure a temperature of water flowing through said first conduit (213), downstream of said heat exchanger (230); and a control device (250), arranged to control a flow of said externally provided heat medium through said heat exchanger (230), 0 c h a r a c t e r i s e d i n that the method comprises in a first state of the circulation system (200), in which all of said water taps (220;221;222;223;224) are closed, circulating a second share of said water in a second 20 conduit (214), from said circulation pump (211) to said plurality of water taps (220;221;222;223;224) in parallel to said first conduit (213) without the water thermally interacting with said heat exchanger (230), said first share being smaller than said second share, and heating the water circulated in said circulation circuit (210) using a heat pump s (260) comprised in said circulation system (200); and in a second state of the circulation system (200), in which at least one of said water taps (220;221;222;223;224) is open, replenishing the circulation circuit (210) using cold water from said cold water inlet (240), and in that the heat pump (260) is arranged along a main conduit (215) of the circulation circuit (210), w said main conduit (215) not being part of said first conduit (213).

14. Method according to claim 13, wherein, in said first state, the control device (250) reads a measured temperature from the temperature sensor (251) and determines that the read temperature is equal to or above a temperature setpoint, and as a result de-

15 creases or stops a flow of said externally provided heat medium past said heat exchanger

(230).

15. Method according to claim 13 or 14, wherein, in said second state, the control device (250) reads a measured temperature from the temperature sensor (251) and0 determines that the read temperature, due to the addition of said cold water, is below a temperature setpoint, and as a result increases a flow of said externally provided heat medium past said heat exchanger (230).