DK178567B1

DK178567B1 - A water tank system, a method for operating a water tank system and use of a water tank system

Info

Publication number: DK178567B1
Application number: DKPA201470686A
Authority: DK
Inventors: Henrik Lynghus
Original assignee: Henrik Lynghus
Priority date: 2014-11-11
Filing date: 2014-11-11
Publication date: 2016-06-27
Also published as: DK201470686A1

Abstract

Disclosed is a water tank system (1) comprising a water tank (2) arranged below a ground surface (3), wherein the water tank (2) is arranged for collecting rain water from an above ground surface (21, 22) during a rain fall. The water tank system (1) further comprises a drainage conduit (4) enabling fluid communication between the water tank (2) and a water distributing facility (5) and drainage means (6) arranged to control the fluid communication. The water tank system (1) also comprises a heat pump (7) arranged to use water in the wa-ter tank (2) as a heat source, and control means (8) comprising calendar means (9), where-in the control means (8) is arranged to control the drainage means (6) in accordance with the calendar means (9) so that the drainage means (6) is only activated if a current date of the calendar means (9) is within a predefined time period. A method for operating a water tank system (1) and use of a water tank system (1) is also disclosed.

Description

A WATER TANK SYSTEM, A METHOD FOR OPERATING A WATER TANK SYSTEM AND USE

OF A WATER TANK SYSTEM

Field of the invention

The invention relates to a water tank system comprising a water tank arranged below a ground surface, wherein the water tank is arranged for collecting rain water from an above ground surface during a rain fall. The invention also relates to a method for operating a water tank system and to use of a water tank system.

Background of the invention

Heavy rainfall such as cloudbursts is known to cause flooding problems and particularly in urban areas - industrial or residential areas - such flooding can entail substantial damages and financial costs.

It is therefore known to use some sort of cloudburst rain water storage in residential areas to collect rain water during cloudbursts and then drain the water from this water storage gradually afterwards to even out the load on the sewerage system and/or other water distributing facilities as best as possible over time.

A cloudburst rain water storage used in relation with e.g. a residential property will typically comprise a water tank buried in the ground surrounding the property. The water tank will be connected to different ground surface drains to collect rain water during rainfall. After the rainfall the collected rain water is drained from the water tank e.g. to the sewer system or a fascine to ensure that the tank is quickly prepared for the next cloudburst. Such a water tank system is known from the patent applications EP 2 465 005 Al, KR 20100060769 A and WO 2009/123458 Al.

However, e.g. in northern Europa cloudbursts typically only occurs from May to September and outside this period the cloudburst rain water storage is more or less idling.

An object of the invention is therefore to provide for an advantageous technique for increasing the usability of a water tank system.

The invention

The invention provides for a water tank system comprising a water tank arranged below a ground surface, wherein the water tank is arranged for collecting rain water from an above ground surface during a rain fall. The water tank system further comprises a drainage conduit enabling fluid communication between the water tank and a water distributing facility and drainage means arranged to control the fluid communication, characterized in that the water tank system also comprises a heat pump arranged to use water in the water tank as a heat source, and control means comprising calendar means, wherein the control means is arranged to control the drainage means in accordance with the calendar means so that the drainage means is only activated if a current date of the calendar means is within a predefined time period.

Water is an excellent heat conductor and a buried water tank will have a large contact area with the surrounding ground thus enabling that the water in a buried water tank is an excellent heat source for a heat pump. However, as previously explained the water tank of a cloudburst rain water storage has to be emptied as quickly as possible so that it is prepared for the next cloudburst and normally the collected water can therefore not act as a heat source. But by providing the water tank system with control means comprising calendar means to control the drainage means it is possible to ensure that the tank is only emptied during a predefined cloudburst season whereas the rest of the year - where the risk of cloudburst is almost non-existent - the water tank can remain full so that the water may act as an efficient heat source for a heat pump e.g. supplying heat to a nearby facility.

In this context the term “drainage means” should be understood as any kind of draining device capable of draining or at least enable draining water out of the water tank - i.e. any kind of pump, valve, hatch etc.

It should also be noted that in this context the term “control means” should be understood as any kind of controller capable of controlling at least parts of the operation of the water tank system - i.e. any kind of PC (Personal Computer), PLC (Programmable Logic Controller), hardwired control circuit, processor or other.

Furthermore, it should be noted that in this context the term “calendar means” should be understood as any kind of calendar enabling that the control means can be controlled in accordance with one or more specific dates. I.e. the term “calendar means” includes any kind of internal device capable of keeping track of the current date i.e. any kind of timer and any kind of device capable of obtaining information regarding the current date from an external source i.e. any kind of device e.g. communicating via Wi-Fi means, phone means or other communication means.

Even further, it should be noted that in this context the term “water distributing facilities” should be understood as any kind of facility capable of leading the water away - i.e. any kind of fascine, sewer system, lower located lake or stream, further water storage tanks, evaporation facilities, percolation facilities or other.

It should also be noted that in this context the term “heat pump” should be understood as a device that provides heat energy from a heat source to a destination. A heat pump is designed to move thermal energy opposite to the direction of spontaneous heat flow by absorbing heat from a cold space and releasing it to a warmer one. A heat pump uses some amount of external power - typically in the form of electrical power - to accomplish the work of transferring the gained energy from the heat source to where the heat is to be dissipated. In principle the heat pump functions as a reversed refrigerator in which a refrigerant is used as an intermediate fluid to absorb heat. The fluid is then vaporized, in an evaporator, and then to release heat the refrigerant condenses in a condenser. The refrigerant typically flows through insulated pipes between the evaporator and the condenser, allowing for efficient thermal energy transfer even at relatively long distances.

In an aspect of the invention, the water tank system comprises water tank level means arranged for determining a water level in the water tank.

Providing the water tank with water tank level means is advantageous in that it hereby is possible to easily monitor the water level even if the tank is inaccessible.

In this context the term “water tank level means” should be understood as any kind of level sensor capable of determining the water level in the water tank - i.e. any kind of sensor e.g. using microwaves, ultrasound, flotation devices, capacitive detection or other for detecting the water level.

In an aspect of the invention, the control means are arranged to activate the drainage means to drain water from the water tank to the water distributing facility if the water tank level means determines that a water level in the water tank is above a predefined level.

There is no point in collecting the rain water in the water tank if the water in the tank is always and immediately drained to a water distributing facility. It is therefore advantageous to provide control the drainage of the tank in correspondence with the water level in the tank so that the tank e.g. during a cloudburst is only drained if a predefined level of water is reached in the tank. The water level means and the control means can also ensure that the water tank system knows when the water tank is sufficiently full to function as heat source for the heat pump - e.g. outside the cloudburst season - e.g. to direct rain water elsewhere during this period.

In an aspect of the invention, the water tank system further comprises water distributing facility status means for determining if the water distributing facilities is capable of receiving water from the water tank.

During a cloudburst the water distributing facilities will often be overloaded or at least severely strained and there is therefore no point in directing water from the water tank system to the water distributing facilities if these does not currently have the capacity to receive the water or if this would only move the flooding problem to a different area. On the other hand it is also important that the water tank is drained as soon as possible and if the water distributing facility actually is capable of receiving water during a cloudburst it would be advantageous to drain the water tank even during the cloudburst to increase its efficiency in relation to preventing flooding. It is therefore advantageous to make the water tank system comprise water distributing facility status means.

In this context the term “water distributing facility status means” should be understood as any kind of water distributing facility status sensor capable of determining if the water distributing facilities is capable of receiving water from the water tank - i.e. control means capable of receiving e.g. an on-off signal from control means of the water distributing facility indicating its readiness or e.g. any kind of sensor e.g. using microwaves, ultrasound, flotation devices, capacitive detection or other for detecting a water level or in other ways determining the current capacity of the water distributing facility.

In an aspect of the invention, the control means are arranged to activate the drainage means, to drain water from the water tank to the water distributing facility, only if the water distributing facility status means determines that the water distributing facilities is capable of receiving water.

Making the control means of the water tank system control the drainage of the water tank at least also in response to input from water distributing facility status means is advantageous in that it ensures a more efficient and safe operation of the water tank system.

In an aspect of the invention, the control means are arranged to activate the drainage means, to drain water from the water tank to the water distributing facility, wherein the flow rate through said drainage means is adjusted in accordance with input from said water distributing facility status means measurements regarding the water distributing facilities capability to receive said water.

In an aspect of the invention, the time period is predefined according to empirical studies of dates of local cloudbursts.

Everywhere on the planet where distinct seasons exist (i.e. winter, spring, summer and fall) the risk of cloudbursts will be considerably higher within a specific period of the year. It is therefore advantageous to predefine the period in which the water tank system shall run in cloudburst season mode and the period it shall run in heating mode on the basis of known facts regarding the local cloudburst season.

In this context the term “local” should be understood as local in relation to the specific implemented water tank system.

In an aspect of the invention, the water tank system further comprises temperature means for detecting the temperature of the outside air above the ground surface.

Empirical studies of dates of local cloudbursts is fine as a basis for determining a local cloudburst season but sometimes there are extreme variations and it is therefore advantageous to supplement the predefined period with actual measurements of the actual outside air temperature, so that the water tank system will not change e.g. from operating in heating mode to operating in cloudburst season mode unless e.g. the average 24 hour temperature is above a predefined level even if the predefined time period states that cloudburst season mode should be commenced.

In an aspect of the invention, the water tank is located in a basement of a building and wherein the heat pump is arranged to supply heat to heat consumers in the building.

Arranging the water tank in the basement of a building is advantageous in that it reduces installation cost and simplifies the heat integration and exchange between the water tank system and the building.

In an aspect of the invention, the water tank system comprises heat exchange means arranged to exchange heat with domestic or industrial facilities of the building.

Heating the water in the water tank by means of waste heat or surplus heat from domestic or industrial facilities such as tumble dryers, ventilation systems, wastewater or other is advantageous in that it will increase the output of the heat pump and thus increase the value and efficiency of the water tank system when operating in heating mode.

In an aspect of the invention, the water tank further comprises stirring means.

Providing the water tank with stirring means is advantageous in that it hereby is possible to distribute the heat in the tank more evenly to increase the efficiency of the heat pump when operating in heating mode.

In an aspect of the invention, the drainage means comprises a valve driven by an actuator.

Particularly, if the water tank is arranged higher than the water distributing facility it is advantageous to control the fluid communication between the water tank and the water distributing facility simply by opening or closing a valve arranged at the drainage conduit by means of the actuator e.g. in response to a signal from the control means.

The invention further provides for a method for operating a water tank system comprising a water tank arranged below a ground surface, wherein the water tank system operates in cloudburst season mode or in heating mode, wherein the following steps are performed in the cloudburst season mode: • collecting rain water in the water tank from an above ground surface during a rain fall, and • reducing the amount of water in the water tank by directing at least a part of the water in the water tank to a water distributing facility, and the following steps are performed in the heating mode: • collecting water in the water tank from an external water source, • using the water in the water tank as a heat source for a heat pump, • supplying heat from the heat pump to a building, wherein the water tank system is operating in cloudburst season mode or heating mode at least in response to one or more predetermined time periods.

Operating the water tank system in two distinct operational modes is advantageous in that outside the cloudburst season, the water tank hereby can be used as a heat source for a heat pump thus increasing the value and applicability of the water tank system substantially without compromising increasing the risk of the water tank not being ready - i.e. empty - if a cloudburst should occur.

In an aspect of the invention, the switch between the cloudburst season mode and the heating mode is also controlled at least in response to a temperature measurement of the outside above ground air. Hereby it is possible to optimise the efficiency of the water tank system.

In an aspect of the invention, the water collected in the water tank when operating in heating mode is rain water.

When the water tank is filled at the start of the heating mode this water will not be drained for a long time and it could therefore be advantageous if the tank was filled with clean tap water when starting heating mode. Furthermore, if it does not rain for a long while at the start of the change to heating mode the heat pump will be ineffective. Nevertheless, it is also advantageous to fill the tank with rain water when changing to heating mode in that this is inexpensive and since rain water typically is readily available.

In an aspect of the invention, the water collected in the water tank in the heating mode is collected from a roof area of the building.

Rain water collected from paved areas or planted will often flush dirt and other along which will reduce the capacity of the tank and the water quality in the water tank system during heating mode. Water collected from the roof of buildings is typically cleaner and it is therefore advantageous to fill the tank at the change to heating mode with water collected from the roof area of the building.

In an aspect of the invention, the amount of water in the water tank is only directed to the water distributing facility if it is detected that the water distributing facility has available capacity in the cloudburst season mode.

To avoid moving the flooding risk or problem to another location and to ensure the efficiency of the water tank system by enabling that the tank can be emptied as soon as possible it is advantageous to only lead water from the water tank to the water distributing facility when the water distributing facility actually has available capacity in the cloudburst season mode to receive the water.

In an aspect of the invention, the predetermined time periods comprise a consecutive period of at least three months wherein the water tank system is operating only in heating mode.

At the start of the heating mode the water tank has to contain water for the tank to efficiently act as a heat source for the heat pump. Preferably the tank is full of water, but the tank may also efficiently act as a heat source for the water pump if the tank is only partly full of water, i.e. such as 1/3 full, half full, 2/3 full, 3/4 full or other. However, if this is done by means of tap water it can be expensive and if it is done by means of collected rain water it could take some time for the tank to be fully operational as a heat source. It is therefore advantageous that the water tank system is not frequently changed back and for the between operating in cloudburst season mode or in heating mode and it is advantageous that once changed to running in heating mode the system is not changed back to cloudburst season mode for at least three month to increase the efficiency of the system.

In an aspect of the invention, the method is a method for operating a water tank system according to any of the previously mentioned water tank systems.

Hereby is achieved an advantageous embodiment of the invention.

Even further, the invention provides for use of a water tank system according to any of the previously mentioned water tank systems for operating a water tank system as a cloudburst rain water storage within a predefined time period and as a heat source within another predefined time period.

Determining the use and functionality of a water tank system on the basis of a predefined time period is advantageous in that it hereby is possible to best adapt the use of the water tank system to the specific time of year.

Figures

The invention will be described in the following with reference to the figures in which fig. 1 illustrates a water tank system with the water tank located in the basement of a building, as seen from the side, fig. 2 illustrates a water tank system with a buried water tank and heat pump, as seen from the side, and fig. 3 illustrates a water tank system with a buried water tank and heat pump located in a basement, as seen from the side.

Detailed description

Fig. 1 illustrates a water tank system 1 with the water tank 2 located in the basement 13 of a building 14, as seen from the side.

In this embodiment the water tank 2 is placed in a basement 13 of a building 14 so that the water tank 2 is arranged below the surface 3 of the surrounding ground 22. It is important that the water tank 2 in arranged so low that the rain water gathered from drains 23 in the surrounding outdoor area 22 will flow to the water tank 2 purely by means of gravity.

Thus, in this embodiment the water tank 2 is filled by means of rain water collected from local drains 23 arranged in the surrounding outdoor area 22 and by rain water collected on the roof area 21 of the building 14 in which the water tank 2 is arranged. However, in another embodiment the rain water could also or instead be collected from the roof 21 of neighbouring buildings, from nearby streams, drains or other areas.

In this embodiment the water tank 2 is arranged in fluid communication with a water distributing facility 5 by means of a drainage conduit 4 which in this embodiment is a buried pipe.

In this embodiment the water distributing facilities 5 is a underground sewer pipe but in another embodiment the water distributing facilities 5 could also or instead be a fascine, a lower located lake or stream or other facilities capable of diverting water from the water tank system 1.

To control the fluid communication between the water tank 2 and the water distributing facilities 5, the water tank system 1 is in this embodiment provided with drainage means 6, which in this embodiment is a valve. In this embodiment the valve is a ball type valve enabling that the size of the flow between the water tank 2 and the water distributing facilities 5 can be regulated and the status of the valve - i.e. how open-closed - is driven by an actuator 20 in the form of a step motor. However, it is evident to the skilled person that in another embodiment the valve could be of another type and/or it could be actuated differently.

Also, in another embodiment the drainage means 6 could also or instead be a pump actively pumping the water out of the water tank 2 - e.g. if the water distributing facilities 5 was located higher than the water tank 2.

In this embodiment the water tank system 1 is provided with a heat pump 7 arranged to use water in the water tank 2 as a heat source. The gained heat is in this embodiment used for heating purposes in the building 14 simply by being supplied to heat consumers 15 in the building 14, which in this embodiment are one or more radiators 24. However, in another embodiment the heat could instead or also be used by other types of heat consumers 15 and/or in another building, in or on the outside area 22 or the heat could be transformed e.g. to electricity or it could be used in another way.

In another embodiment the heat pump 7 could also be arranged to supplement the heat from the water tank 2 - or even replace this in certain periods of the year - with some sort of geothermal heat.

To ensure high efficiency of the water tank system 1 the water tank 2 is in this embodiment arranged to exchange heat with domestic or industrial facilities 17 of the building 14 - i.e. in this embodiment exhaust air from tumble driers, wastewater drains and ventilation systems are directed through the water tank 2 to dissipate heat before the exhaust air is released to the surroundings. However, in another embodiment the exhausted air or wastewater from the domestic or industrial facilities 17 could simply be used for heating the room 13 in which the tank 2 is located, which in turn will heat the water in the tank 2, the water tank 2 could be arranged to exchange - i.e. receive - heat from other domestic or industrial facilities 17 of this or other buildings and the heat change could be arranged in a number of ways known to the skilled person. It should also be noted that even if the water tank 2 is located in a room in the basement 13 of a building 14 it will in most embodiments still receive a lot of heat from the surrounding ground - i.e. the cold water tank 2 will be heated by the warmer floor and walls of the basement 13 during a heating season.

To ensure an even heat distribution in the water tank 2 the tank 2 is in this embodiment provided with stirring means in the form of a propeller agitator.

However, in another embodiment the stirring means 18 could also or instead comprise jets arranged to induce flow inside the tank 2, vibration means or other means arranged to ensure a uniform temperature in the tank 2.

In this embodiment the water tank system 1 comprises water distributing facility status means 11 in the form of an ultrasonic sensor capable of determining if the water distributing facility 5 is capable of receiving water from the water tank 2 by measuring the actual water level in the water distributing facility 5. However it is known to the skilled person that the water distributing facility status means 11 could be enabled in several other ways and by other means.

In this embodiment the water tank system 1 also comprises water tank level means 10 also in the form of an ultrasonic sensor capable of determining the actual water level in the water tank 2. However it is known to the skilled person that the water tank level means 10 could be enabled in several other ways and by other means.

In this embodiment the water tank system 1 also comprises temperature means 12 for detecting the temperature of the outside air. In this embodiment the temperature means 12 is based on a simple Bi-metallic thermostat but in another embodiment the temperature means 12 could also or instead comprise a thermistor, Resistive Temperature Detectors (RTD), a Thermocouple, infra-red sensors or other.

In this embodiment the water tank system 1 comprises control means 8 including calendar means 9, wherein the control means is arranged to keep track of the current date and time so that the control means 8 may control the water tank system 1 in accordance with the current date.

In this embodiment the control means 8 is connected to the drainage means 6 to control if water is drained from the tank 2. The control means 8 is in this embodiment also connected to the heat pump 7 to the operation of the heat pump 7 e.g. to enable that the heat pump 7 is turned off in cloud burst season mode. However in another embodiment the heat pump 7 could also or instead comprise its own control means or it could be controlled by other control means.

In this embodiment the control means 8 is also arranged to control the operation of the stirring means 18 but in another embodiment the stirring means 18 could comprise its own control means.

In another embodiment the control means 8 could be arranged to control further elements or devices, such as heat consumers 15, domestic or industrial facilities 17, directional valves controlling if rain water from drains 23 is being directed to the water tank 2 or to the water distributing facility 5 or other.

In this embodiment the control means 8 is arranged to receive input from both the water distributing facility status means 11, water tank level means 10 and temperature means 12 but in another embodiment the control means 8 could be arranged to receive input from none or only some of these sensors 10, 11, 12 and/or the control means 8 could also or instead be arranged to receive inputs from further sensors and devices of the water tank system 1 and/or external sensors and devices.

In this embodiment the control means 8 comprises a predefined setting so that between 1 May and 31 September the water tank system 1 will operate in so-called cloudburst season mode in which the control means 8 will control the drainage means 6 to disable fluid communication to the water distributing facility 5 so that rain water is collected in the water tank 2 e.g. during a cloudburst. In another embodiment the control means 8 could be arranged to activate the drainage means 6 - i.e. enable draining of the tank 2 - e.g. for half an hour e.g. once every 24 hours but in this embodiment the water tank 2 is provided with water tank level means 10 so that the control means 8 will activate the drainage means 6 to disable fluid communication to the water distributing facility 5 and thus drain the tank when the water tank level means 10 has detected that the water in the tank 2 is above a specific level - when the system 1 operates in cloudburst season mode.

In another embodiment the water distributing facility 5 would always be able to receive water from the tank 2 or the water tank system 1 would lead water to the water distributing facility 5 no matter if the water distributing facility 5 is able to handle the water of not. However, in this embodiment the control means 8 will only initiate opening of the fluid communication between the tank 2 and the water distributing facility 5 if the water distributing facility status means 11 provides a signal to the control means 8 indicating that the water distributing facility 5 has capacity to receive the water.

In another embodiment the control means 8 could be arranged to operate in cloudburst season mode in another time period of the year such as between March and October, between June and August, between January and April or between one or more other periods e.g. in dependence of the specific heating need, empirical studies of dates of local cloudbursts, the local seasonal changes or other.

Thus, when the end of the specific time period in cloudburst season mode has been reached the control means 8 will change its operation to heating mode. In heating mode the control means 8 will not activate the drainage means 6 to drain the tank 2 -not even if e.g. the water tank level means 10 detects that the tank 2 is full. I.e. in this mode water is collected in the water tank 2 from an external water source such as rain water, tap water, water from another water tank or other.

The water stored in the water tank 2 is then used as a heat source for a heat pump 7 and the heat produced by the heat pump 7 is supplied to a building 14.

Once the control means 8 - by means of the calendar means 9 - detects that a new period in cloudburst season mode has to start the control means 8 will activate the drainage means 6 so that the tank 2 can be drained and thus be ready in case a cloudburst should occur.

Fig. 2 illustrates a water tank system 1 with a buried water tank 2 and heat pump 7, as seen from the side.

In this embodiment the water tank is buried under ground surface 3 of the outdoor area 22 surrounding the building 14 to which the heat produced by the heat pump 7 is supplied.

In this embodiment the heat pump 7 is arranged at the water tank 2 so that e.g. hot water will be circulated between the heat pump 7 and the building 14.

In this embodiment the water tank 2 is divided into four sub-tanks 25 enabling that an intermediate operational mode in which the sub-tank 25 next to the heat pump 7 would remain full and thus act as a heat source for the heat pump 7 will the remaining three sub-tanks would be drained regularly to act as a cloudburst water storage. Another advantage would be that if the sub-tank 25 next to the heat pump 7 was filled first - when initiating heating mode - the heat pump 7 would more quickly become more efficient.

In an embodiment the tank arranged in the basement as illustrated in fig. 1 could also be divided into a number of sub-tanks 25 e.g. to simplify installation.

Fig. 3 illustrates a water tank system 1 with a buried water tank 2 and heat pump 7 located in a basement 13, as seen from the side.

In this embodiment the heat pump 7 is arranged in the basement 13 of the building 14 so that the heat pump would be connected to the water tank 2 through a circulating fluid drawing heat from the water and delivering it to the heat pump 7.

In another embodiment a main water tank 2 would be buried in the surrounding ground. This main tank 2 would then be arranged to circulate water with a sub-tank (not shown) arranged in the basement 13. In such an embodiment the heat pump 7 would use the sub-tank as a heat-source.

All the tanks 2 illustrated in figs 1-3 are shown without access hole or other facilities enabling access to the inside of the tank 2 from the outside - e.g. to enable cleaning or repair. However, in a real embodiment of a water tank 2 such access means would most likely be provided in the tank 2 and in case of a buried tank 2 as illustrated in figs. 2 and 3 a passage way would also be formed from the ground surface 3 or from a nearby building 14 to enable access to the tank 2, piping and/or the heat pump 7.

Also in another embodiment the water tank 2 would be provided with overflow means (not shown). The overflow means will direct the surplus water from the tank 2 to e.g. water distributing facility 5 when the water tank 2 is full.

The invention has been exemplified above with reference to specific examples of water tank systems 1, water tanks 2, water distributing facilities 5 and other. However, it should be understood that the invention is not limited to the particular examples described above but may be designed and altered in a multitude of varieties within the scope of the invention as specified in the claims.

List 1. Water tank system 2. Water tank 3. Ground surface 4. Drainage conduit 5. Water distributing facility 6. Drainage means 7. Heat pump 8. Control means 9. Calendar means 10. Water tank level means 11. Water distributing facility status means 12. Temperature means 13. Basement 14. Building 15. Heat consumer 16. Heat exchange means 17. Domestic or industrial facilities 18. Stirring means 19. Valve 20. Actuator 21. Roof area of building 22. Outdoor area 23. Drain 24. Radiator 25. Sub-tank

Claims

A water tank system (1) comprising a water tank (2) disposed beneath a ground surface (3), wherein the water tank (2) is adapted to collect rainwater from a surface above the ground (21, 22) during a rainstorm, a drainage channel (4) which allows fluid connection between the water tank (2) and a water distribution system (5), drain means (6) arranged to control said fluid connection, characterized in that the water tank system (1) further comprises a heat pump (7) which is adapted to use water in the water tank (2) as a heat source, and control means (8) comprising calendar means (9), and wherein said control means (8) are arranged for controlling said drainage means (6) in in accordance with said calendar means (9), so that said bottling means (6) are activated only if a current date in said calendar means (9) is within a predefined period.

The water tank system (1) according to claim, wherein the water tank system (1) comprises water tank level means (10) adapted to determine a water level in the water tank (2).

A water tank system (1) according to claim 2, wherein said control means (8) is adapted to activate said drainage means (6) for draining water from the water tank (2) to the water distribution system (5), if said water tank level means (10) determine that the water level in the water tank (2) is above a predefined level.

Water tank system (1) according to any one of the preceding claims, wherein the time period is predefined according to empirical studies of local cloudburst dates.

Water tank system (1) according to any one of the preceding claims, wherein the water tank (2) is arranged in a basement (13) of a building (14) and wherein the heat pump (7) is arranged to supply heat to heat consumers. (15) in the building (14).

The water tank system (1) of claim 5, wherein the water tank system (1) comprises heat exchange means (16) adapted to exchange heat with private or industrial plants (17) in the building (14).

A method of operating a water tank system (1) comprising a water tank (2) disposed below a ground surface (3), wherein the water tank system (1) operates in cloudburst season mode or in heating mode, wherein the following steps are performed in cloudburst season mode: collecting rainwater in the water tank (2) from a surface above the ground (21, 22) during a rainstorm, and • reducing the amount of water in the water tank (2) by directing at least a portion of the water in the water tank (2) to a water distribution system (5) and the following steps are performed in the heating mode: • collecting water in the water tank (2) from an external water source, • using the water in the water tank (2) as a heat source for a heat pump (7), • supplying heat from the heat pump (7) to a building (14) wherein the water tank system (1) runs in the cloudburst season or heating state at least in response to one or more predetermined periods of time.

A method according to claim 7, wherein the amount of water in the water tank (2) is directed to the water distribution system (5) only if it is detected that the water distribution system (5) has available capacity in the cloudburst season state.

The method of claim 7 or 8, wherein the predetermined periods comprise a continuous period of at least three months, wherein the water tank system (1) operates only in the heating mode.

Use of a water tank system (1) according to any one of claims 1-7 for operating a water tank system (1) as a cloudburst rainwater storage site within a predefined period and as a heat source within another predefined period.