CA2919753C

CA2919753C - Thermal connection of a geothermal source to a district heating network

Info

Publication number: CA2919753C
Application number: CA2919753A
Authority: CA
Inventors: Uwe Lenk; Florian REISSNER; Jochen Schafer
Original assignee: Siemens AG
Current assignee: Siemens Energy Global GmbH and Co KG
Priority date: 2013-07-30
Filing date: 2014-07-21
Publication date: 2018-07-03
Anticipated expiration: 2034-07-21
Also published as: DE102013214891A1; CA2919753A1; JP6133508B2; JP2016525669A; KR20160036618A; US20160370017A1; KR101775568B1; CN105431686B; WO2015014648A1; CN105431686A; EP2994699B1; EP2994699A1

Abstract

The invention relates to a method and an arrangement for providing heat (Q
out) for a district heating supply (40): Heat (Q in) at a first temperature level (T41, T42) is provided by means of a thermal water conveying system (20) from a geothermal source (41). By operating a high-temperature heat pump (43) and thermally connecting same to the geothermal source (41), the thermal water can be conducted through the evaporator (431) of the high-temperature heat pump (43) and the heat (Q in) thereof can be transferred to the evaporator (431) of the high-temperature heat pump (43). The condenser (433) of the high-temperature heat pump (43) then supplies heat (Q out) at a second, higher temperature level (T43, T47) to the district heating network (40). A high-temperature compression heat pump (43) is preferably used as the high-temperature heat pump (43). The second, higher temperature level (T43, T47) achieved in this manner is above 100°C.

Description

Thermal connection of a geothermal source to a district heating network TECHNICAL FIELD
The present invention relates to a method for providing heat for a district heating supply and to the arrangement of a district heating network with a geothermal source.
BACKGROUND
Up until now, district heating supplies have predominantly been based on the burning of fossil energy sources. Most of the existing district heating networks use the waste heat of fossil-fueled plants for electrical power generation. With combined heat and power (cogeneration), the energy content of the fuel is used largely completely. Alternatively, district heating networks are for example connected to refuse incineration combined heat and power plants.
For environmental and climate protection reasons, the burning of fossil energy sources is at present being reduced and in the future will increasingly be reduced to reduce the CO2 emissions. Electrical power is increasingly being generated as primary energy, such as for example by means of wind turbines or by photovoltaics. No usable waste heat is produced thereby.
Since many district heating networks exist at present, they must also continue to be supplied with heat. However, this heat is also to originate as far as possible exclusively from renewable sources of energy. Existing urban district heating networks sometimes have over 800 km of district heating lines and an annual heating output of 4 TWh. They are used for

2 supplying district heat to consumers such as private households, commercial and industrial facilities and various public users. In the year 2012, around 90% of district heat was still being generated by means of heating power plants that burn fossil energy sources.
In order to change over to renewable sources of energy for heat generation as well as for electrical power generation, accordingly existing district heating networks must be connected to new, alternative heat sources; up until now, this has happened for example by burning biomass, one of the disadvantages of this being that the capacity of the existing biomass is very small. As an alternative to this, there is the use of electrical resistance heating systems, the efficiency of which however is very low.
A further alternative heat source for district heating networks is that of geothermal sources. Depending on geographical and geological conditions, however, no thermal water sources of a temperature that would be sufficient for supplying a district heating network are reached even by deep drilling operations.
In Figure 1, for example, there is shown a section through a region such as may be found for example in the German Alpine uplands. The limestone bed carrying thermal water in this case lies up to 4000 m below the surface of the Earth. At depths of between 1000 m and 2000 m below mean sea level, there may be thermal water temperatures of around 65 C. This is an entirely sufficient temperature for example for material use of the thermal water in thermal baths. For thermal use, however, the temperature level would have to be higher. Up until now, the additional necessary thermal energy has been provided by means

3 of what is known as additional firing. For example, heat from burning natural gas is used, which however is to be avoided in the future.
Consequently, it is ecologically necessary to propose an improved solution that manages without CO2 emissions and is based purely on renewable sources of energy. It is found to be desirable for supplying existing district heating networks predominantly to make local geothermal sources usable.
SUMMARY
One embodiment provides a method for providing heat for a district heating supply, comprising the following method steps:
extracting thermal water for providing heat at a first temperature level from a geothermal source, providing and operating a high-temperature heat pump, thermally connecting the geothermal source to the high-temperature heat pump, conducting the thermal water through the evaporator of the high-temperature heat pump, thermally transmitting heat of the first temperature level from the thermal water to the evaporator of the high-temperature heat pump and providing heat at a second, higher temperature level through the condenser of the high-temperature heat pump.
In a further embodiment, a high-temperature compression heat pump is used as the high-temperature heat pump.
In a further embodiment, the second, higher temperature level is at least 100 C, e.g., at least 110 C.
In a further embodiment, a working medium from the family of fluoroketones is used in the high-temperature heat pump.

4 In a further embodiment, a non-toxic working medium is used in the high-temperature heat pump.
In a further embodiment, a working medium of which the critical temperature lies above 160 C is used in the high-temperature heat pump.
In a further embodiment, at least one thermal store for taking up and storing the heat of the first temperature level from the thermal water or the heat of the second, higher temperature level from the condenser of the high-temperature heat pump is used.
In a further embodiment, at least two high-temperature heat pumps are coupled in a series connection.
Another embodiment provides an arrangement for providing heat for a district heating network at a temperature level of at least 100 C comprising at least one thermal water extraction device and a high-temperature heat pump.
In a further embodiment, the high-temperature heat pump is a high-temperature compression heat pump.
In a further embodiment, the high-temperature heat pump contains a working medium that is from the family of fluoroketones.
In a further embodiment, the high-temperature heat pump contains a working medium of which the critical temperature lies above 160 C.
In a further embodiment, the arrangement includes at least one thermal store, which is designed for taking up and storing heat of a first temperature level from the thermal water or heat of a second, higher temperature level from the condenser of the high-temperature heat pump.
=
In a further embodiment, the arrangement includes at least two

5 high-temperature heat pumps in a series connection.
According to one aspect, there is provided a method for providing heat for a district heating supply, comprising: extracting thermal water from a geothermal source, operating a high-temperature heat pump, thermally connecting the geothermal source to the high-temperature heat pump, conducting the thermal water through a heat exchanger which transmits heat to a heat transporting medium, thereby providing a heated heat transporting medium, returning the thermal water cooled in the heat exchanger via a reinjection line to the geothermal source, passing a first flow of the heated heat transporting medium to an evaporator of the high-temperature heat pump, thermally transmitting heat at a first temperature level from the first flow of the heated heat transporting medium to the evaporator of the high-temperature heat pump, passing a second flow of the heated heat transporting medium to a condenser of the high-temperature heat pump, and thermally transmitting heat at a Second temperature level higher than the first temperature level and at least 100 C via the condenser to the second flow of heated heat transporting. medium passed to the condenser.
According to another aspect, there is provided a system for providing heat fora district heating network at a temperature level of at least 100 C, the system comprising: at least one thermal water extraction device configured to extract thermal water, a high-temperature heat pump comprising an evaporator and a condenser, a heat exchanger configured to transmit heat from

6 the extracted thermal water to a heat transporting medium to thereby provide a heated heat transporting medium, a thermal water transporting line configured to pass the extracted thermal water to the heat exchanger, a reinjection line for returning the thermal water cooled in the heat exchanger to the geothermal source, and a first supply line configured to conducting the heated heat transporting medium from the heat exchanger to the evaporator of the high-temperature. heat pump, and a second supply line configured to conducting the heated heat transporting medium from the heat exchanger to the condenser of the high-temperature heat pump, wherein the condenser provides heat to a flow of the heated heat transporting medium passed to the condenser via the second supply line.
BRIEF DESCRIPTION OF THE DRAWINGS
Example embodiments of the present invention are described in detail blow with reference to the drawings, in which:
Figure 1 shows a North-South section through a region given as an example, Figure 2 shows a method diagram of a geothermal heating plant with an absorption heat pump, Figure 3 shows a method diagram of an absorption heat pump, Figure 4 shows a method diagram for raising the temperature with a compression heat pump, Figure 5 shows a method diagram for raising the temperature with a compression heat pump and thermal buffer stores,

7 Figure 6 shows a COP temperature diagram of the high-temperature heat pump (Coefficient of Performance, rate of performance), Figure 7 shows a COP temperature diagram for estimating the potential in the megawatt power range, Figure 8 shows a temperature entropy diagram of a transcritical heat pump process, and Figure 9 shows a temperature entropy diagram of a subcritical heat pump process.
DETAILED DESCRIPTION
Some embodiments of the invention provide a method for providing heat for a district heating supply, which includes the following steps: first, extracting thermal water for providing heat from a geothermal source, the temperature of which is at a first temperature level. Then, providing and operating a high-temperature heat pump, and also thermally connecting the geothermal source to the high-temperature heat pump. This is followed by conducting the thermal water through the evaporator of the high-temperature heat pump and thermally transmitting heat of the first temperature level from the thermal water to the evaporator of the high-temperature heat pump. Finally, there is also providing heat at a second, higher temperature level through the condenser of the high-temperature heat pump.
This method of combining a district heating supply with a geothermal source and suitably connecting them by way of a high-temperature heat pump has the advantage of ensuring a

8 decarbonized heat supply. The geothermal source is therefore used as a heat source for the evaporator of the heat pump. Heat can then be provided in the condenser of the heat pump at a higher temperature level for supplying heat consumers in a district heating network. Heat consumers may be for example towns or urban districts, which along with public users may predominantly comprise residential buildings and private consumers, as well as industrial users.
The method may provide an enhancement of the heat of a geothermal source.
A high-temperature compression heat pump may be used as a high-temperature heat pump. Apart from the heat source for the evaporator, this only requires an electrical energy source for operating the compressor. This may take place via electrical power from regenerative sources of energy, for example by means of electrical power from a photovoltaic or wind turbine installation.
Depending on the location and the depth of the bore, geothermal sources are often not at sufficiently high temperatures for a district heating supply. Especially in the vicinity of towns or directly in the urban area, where most of the consumers are located, it is not possible to switch to any sources, no matter how far away they are, or to any bores, no matter how deep they are, on the basis of the geological site. The heat of geothermal sources that are available often lies at a temperature level between 60 C and 95 C, which could perhaps be sufficient for a district heating supply in the summer months, but especially in the winter season is not sufficient at the

9 temperate latitudes. Then, district heating flow temperatures of at least 100 C, e.g., about 130 C, are necessary.
Typically, the second, higher temperature level lies at at least 100 C, in particular at at least 110 C. For example, the second, higher temperature level may be at least 120 C or in some embodiments at least 130 C.
In one embodiment of the invention, in the method working media from the family of fluoroketones are used in the high-temperature heat pump. Exclusively non-toxic working media may be used, e.g., environmentally friendly, safe working media. A working medium of which the critical temperature lies above 140 C, e.g., above 150 C and in some embodiments above 160 C, may be used in the high-temperature heat pump.
Especially environmentally friendly, non-toxic and safe working media are often distinguished by very specific thermodynamic properties, such as for example a high critical temperature.
The high critical temperature of the working medium used has the advantage that a subcritical heat pump process can be operated and an almost isothermal heat output can take place.
According to one embodiment of the invention, it is provided that the thermal water is first conducted through a first heat exchanger and the cooled thermal water is returned to the rock bed by way of a reinjection line. The first heat exchanger is adjoined by a heat transporting circuit, in which a heat transporting medium, e.g., water, transports the heat. From this heat exchanger, heat at a temperature level that lies only a little below the temperature of the geothermal source is passed on the one hand to the evaporator and on the other hand to the condenser of the high-temperature heat pump by way of two lines. By means of the high-temperature heat pump, the heat transporting medium is brought to the required flow temperature for the district heating network. For example, the district heating return and the return from the evaporator of the heat 5 pump may be brought together again and mixed before the heat transporting medium reaches the first heat exchanger again. The return temperatures of heat transporting media to district heating networks usually lie at 45 C or below. The return temperature downstream of the evaporator is much higher,

10 depending on the temperature of the geothermal source, and, given the mixing with the district heating return, can consequently already provide an increased mixing temperature before the heat transporting medium takes up heat again from the geothermal source by way of the first heat exchanger.
According to a further embodiment of the invention, it is provided to use in the method at least one thermal store for taking up and storing the heat of the first temperature level from the thermal water or the heat of the second, higher temperature level from the condenser of the high-temperature heat pump. For this purpose, at least one thermal store is arranged with the first heat exchanger at the geothermal source or downstream of the condenser of the heat pump, so that in each case the heat pump can access the thermal store of the geothermal source temperature level or the district heating network can access the thermal store of the heat pump outlet temperature level. This method has the advantage of severing the link between the times at which power and heat are demanded and the times at which power and heat are provided. On the one hand, when there is a surplus supply of power in the network, as occurs as a result of the increased use of regenerative

11 sources of energy, this can be used to charge the heat store at the second, higher temperature level: power-to-heat principle.
Alternatively, when there is an increased demand for power, it is possible to dispense with operating the pump for a certain period of time, in which the district heating network accesses the store. For this period of time, the heat that originates from the geothermal source is then kept in a further heat store, to which the heat pump can resort at a later point in time (Demand Side Management).
At sites at which there are only very low thermal water temperatures, for example on account of the geographical conditions, the coupling of two heat pumps may be performed for example to enhance the geothermal heat source. The heat pumps may be combined in a series connection, in order in this way to generate sufficiently high temperatures.
Some embodiments provide an arrangement for providing heat for a district heating network at a temperature level of at least 100 C, which arrangement comprises at least one thermal water extraction device and a high-temperature heat pump. In particular, heat is provided at a temperature level of at least 100 C, for example of at least 120 C and in some embodiments at least 130 C. This arrangement of a high-temperature heat pump with a geothermal source and a district heating network has the advantage of ensuring a decarbonized heat supply, reducing CO, emissions and reducing the dependence on imported fossil energy sources.
Typically, the high-temperature heat pump is a high-temperature compression heat pump.

12 The high-temperature heat pump may contain a working medium that is from the family of fluoroketones. Typically, the working medium in the high-temperature heat pump is at a critical temperature above 140 C, e.g., above 150 C and in some embodiments above 160 C. Environmentally friendly, non-toxic and safe working media may be contained by the high-temperature heat_ pump.
The compressor of the high-temperature heat pump is typically operated with electrical energy from regenerative energy sources, for example a photovoltaic installation or a wind turbine installation.
In one embodiment of the invention, the arrangement for providing heat for a district heating network comprises a thermal store, which is designed for taking up and storing heat of a first temperature level from the thermal water or heat of a second, higher temperature level from the condenser of the high-temperature heat pump. The arrangement may include a first thermal store for taking up and storing heat of the first temperature level from the thermal water and a second thermal store for taking up and storing heat of a second, higher temperature level from the condenser of the high-temperature heat pump. The first thermal store may be arranged between the geothermal source and the heat pump, so that the evaporator of the heat pump can access this first thermal store. The second thermal store is typically arranged between the condenser of the high-temperature heat pump and the district heating network or the district heating consumers, so that it can be charged with heat from the condenser of the high-temperature heat pump and the district heating network can be fed from it.

13 In a further embodiment, the arrangement comprises at least two high-temperature heat pumps in a series connection, i.e. that they are coupled one downstream of the other in such a way that heat from thermal water sources of very low temperature can also be enhanced to the extent that a temperature level that is suitable for supplying district heat is achieved.
In Figure 1 there is shown, as already mentioned at the beginning, a North-South section through a region of ground such as occurs for example in the German Alpine uplands. In this case, the limestone bed M carrying thermal water descends from the North to the South, so that in the South it can only be reached by bores that become increasingly deeper. While the thermal water temperature Tl in the Northern region is around 35 C, the temperature T4 in the South, and accordingly with the limestone bed M lying very much deeper, is around 140 C. In between, in the case of bores at depths of between 1000 m and 3000 m below mean sea level, thermal water temperatures T2/3 of around 65 C to 100 C are encountered. If the ground heat is then to be made usable for the new district heating supply 40, this cross section illustrates the problem that a temperature that is usable for the district heating is not achieved without additionally raising the temperature level. Typically, the temperature T7 of a district heating flow 27 lies between 70 C
and 110 C, but depending on the time of year even much higher.
In winter, the temperature T7 of the district heating flow 27 may be between 90 C and 180 C. Generally, a temperature T7 of the district heating flow 27 of around 130 C is sufficient.
In Figure 2 there is shown a method diagram known from the prior art for using ground heat in a district heating

14 network 40. The thermal water is extracted from a rock depth of for example 2300 m via a thermal water line 20 and is at a temperature T2 of around 65 C. The thermal water is then for example passed to a heat exchanger 22, which directly sends part of the thermal water at a temperature T2 of around 65 C
further in the direction of the district heating flow 27 and provides a cooled part of the thermal water at a temperature level T5 of around 40 C to 45 C to a thermal bath 25. This is a known, very popular material use of the thermal source. Heat exchangers 22 used in such a way lie in a power range of for example around 2 MW. The heat exchanger 22 also has fluidic connections to a heat pump 23, only the use of absorption heat pumps 23 being known up until now in the prior art. These operate for example in a power range of around 7 MW. An absorption heat pump 23 in this case represents a reheating solution. Alternatively, the burning of biomass or natural gas or electrical reheating is used for example for the additional firing. The heat pump 23 has an outflow to the district heating flow 27, and also an outflow with very greatly cooled water to a consumer 26. The cooled water is at a temperature T6 of for example around 20 C and is passed on for material use, thus for use as a drinking water supply, for example for households.
This outgoing line to the consumer 26 may for example have a fluidic connection to the line to the thermal bath 25.
Furthermore, the heat pump 23 has an inflow for cold water, which is for example partly supplied from the district heating return 28. Furthermore, in the method diagram in Figure 2 there is shown a combustion vessel 24 for natural gas, which operates for example in the range of 10 MW and can balance out peak loads, and consequently represents a further necessary component for increasing the temperature of the district heating flow 27. The temperature T7 of the district heating flow 27 realized in this way is in this case between 70 C
and 110 C. The temperature of 130 C that is necessary for winter operation in most district heating networks 40 cannot be 5 accomplished with this type of geothermal heating plant. Shown downstream of the heat user 29 are supply lines to heat consumers 40, such as for example a town S with residential buildings and various public users, as well as alternatively to industrial users I. The district heating return 28 is at a 10 temperature level Tu of generally between 40 C and 45 C.
In Figure 3 there is additionally also shown in detail the method diagram of an absorption heat pump 23, used for example in Figure 2. In the case of this pump, the heat input Qin takes place to an evaporator 31 and the heat output Qout takes place

15 at the liquefier 28 of the absorption heat pump 23. The refrigerant circuit is identified by arrows. On the left side of the circuit, the refrigerant K1 is liquid and, downstream of the evaporator 31, the refrigerant Kg is vaporous. This is the form in which it reaches the thermal compressor 37. In the latter, the vaporous refrigerant Kg first runs through the absorber 32 and is then transported further by way of a pump 33 to the generator 34. The return connection between the generator 34 and the absorber 32 has a pressure reducing valve 36. The generator 34 is heated by means of burning natural gas, so that the refrigerant Kg leaves the generator 34 again in a vaporous form. Downstream of the thermal compressor 37, the refrigerant Kg reaches the liquefier 38, at which the heat output Qõt takes place. The return connection between the liquefier 38 and the evaporator 31 has in turn a pressure reducing valve 39. Heat pump installations 23 of this

16 type known up until now and also compression heat pumps known up until now from the prior art are not currently capable of reliably achieving temperatures above 90 C. Individual prototypes achieve up to 100 C, but are not commercially available and are based on transcritical processes. The majority of the heat pumps used deliver temperatures in the low temperature range of around 55 C to 60 C and in the high temperature range of around 70 C to 75 C.
In Figures 4 and 5 there is shown the concept for raising the temperature of a geothermal source 41 by means of a compression heat pump 43. The heat pump 43 in this case respectively acts as a link between the geothermal source 41 and the district heating network 40. For this purpose, the heat pump 43 is thermally coupled to both: the extracted thermal water from the geothermal source 41 is for example at a temperature T41 of 93 C. The extracted thermal water is passed by way of a thermal water transporting line 411 to a heat exchanger 42. The outflow of the heat exchanger 42 is configured as a reinjection line 412 and brings the cooled water back into the deep rock beds G. By way of the heat exchanger 42, a further circuit Is supplied with heat of the thermal water. A transporting medium, in particular water, can be conducted through a first supply line 421 to the evaporator 431 of the high-temperature heat pump 43 and by way of a second supply line 422 to the condenser 433 of the high-temperature heat pump 43. The outflow from the evaporator 431 then carries water at an already reduced temperature T431 of for example about 80 C. The temperature T42 of the flow to the evaporator 431 is for example around 90 C. The return from the evaporator 431 is in particular brought together with the return 48 of the district

17 heating network 40. The return temperature To of the district heating network 40 is in this case a maximum of around 45 C.
The brought-together return then again reaches the heat exchanger 42.
By way of the evaporator 431, the heat Qh, which is made available by the geothermal source 41, is passed on to the heat pump 43. Apart from the evaporator 431 and the condenser 433, this comprises a compressor 432 and also an expansion valve 434. The use of particularly suitable working media in the high-temperature heat pump 43 makes it possible to give off at the condenser 433 heat Qout at a temperature level 143 of around 130 C, which can be made available to various consumers by way of a district heating network circuit 40.
The compressor 432 of the high-temperature heat pump 43 is operated with electrical power, which according to the invention has been obtained from regenerative energy sources.
Consequently, the overall arrangement comprising the geothermal source 41 or thermal water extraction 411, high-temperature heat pump 43 and district heating network 40 is as it were decarbonized and ensures a reliable supply of heat for a district heating network 40 by means of ground heat.
In the method diagram in Figure 5, thermal stores 51, 52 have been added to the concept as it is represented in Figure 4. The first thermal store 51 serves as a buffer between the geothermal source 41 and the arrangement of the district heating network 40 with the heat pump 43. In this first thermal store 51, heat at a temperature level 141 of around 90 C is stored and can be given off as and when required to the high-temperature heat pump 43.

18 A second thermal store 52 is arranged between the high-temperature heat pump 43 and the district heating network 40 and is designed in such a way that heat at a temperature level 143 of around 130 C can be buffer-stored and given off as and when required to the district heating flow 47. These possibilities for storing heat make it possible to sever the link between the times at which power and heat are demanded by the customer and the times at which it is possible to supply the heat. If, therefore, there is a reduced demand for heat from the district heating network 40, this heat can first be buffer-stored in the second store 52 without being lost. In addition, this offers an option of providing negative control power (Power to Heat): in this way, a contribution can be made to balancing out fluctuating power production. There is in particular the possibility of taking up regeneratively produced surplus power from the power network with increased use of regenerative power sources such as wind turbines or photovoltaics. The power surplus can thus be compensated quickly, reliably and inexpensively and is available to the district heating network 40 at any desired later point in time in the form of heat from the energy store 52.
It is similarly possible for a limited period of time to dispense with drawing power from the network for operating the heat pump 43, in order first to deplete the store 52 (Demand Side Management). In this way it can therefore be ensured that the link is severed between the time that heat is supplied and the time that the heat pump 43 is operated. In the time period in which the heat pump 43 is not operated, the heat of the geothermal source 41 can be kept in the first thermal store 51.

19 In Figures 6 and 7, COP-T diagrams are shown. COP stands here for Coefficient of Performance and is the rate of performance of the heat pump 43, which represents the heat output per electrical drive input:
COP = heat output electrical drive input The temperature T1-1,7 plotted in the diagram is the temperature of the heat output of the heat pump 43 to the district heating network 40. Measured values of a high-temperature compression heat pump 43, which is operated with a working medium such as for example Novec 649 (dodecafluoro-2-methylpentan-3-one), are plotted. For this purpose, the temperature Tc) of the source, or the evaporation temperature, was varied between 40 C and 90 C.
In dependence on the compressor power of the high-temperature compression heat pump 43, different temperature swings TH of between 30 K and 60 K were realized. With an increasing temperature swing TH, the rate of performance COP of the heat pump 43 falls. However, with a temperature swing TH of 50 K, for instance, heat at a temperature level T43 of 130 C, as is necessary for the district heating supply 40, can be ensured with the high-temperature compression heat pump 43 at a rate of performance COP of around 3.8.
In Figure 7 there is shown an estimate of the potential for high-temperature heat pump installations 43 in the megawatt range: the given measured values 73 with Novec 649 relate to a demonstrator with a thermal capacity of only 10 kW.
Alternatively, Novec 524 (decafluoro-3-methylbutan-2-one) may also be used as the working medium. Also depicted in the diagram of Figure 7 is the thermodynamic limit 70 on the basis of the Carnot efficiency. The expectation values 71 for plants in the megawatt power range lie at 55% to 65% of the Carnot efficiency 70. The estimates 71 are based on extrapolations 5 such as are to be expected according to experience as a result of higher efficiencies in the case of large plants with a greater volume and lower heat losses, and also greater compressors. The efficiency, that is to say the rate of performance COP, falls with increasing temperature TFw of the 10 heat output, or the condensation temperature of the pump. The values shown in Figure 7 apply for a heat source temperature of 80 C.
In Figures 8 and 9, two temperature entropy diagrams are shown.
These are intended to illustrate the difference between a 15 transcritical heat pump process 80, as often occurs in the prior art, as indeed especially in the case of a known heat pump that only achieves a heat output of up to 90 C, and a subcritical heat pump process 90. The transcritical process 80 does not allow the output of heat Qout to be maintained

20 constantly at the achieved temperature level T7. Depicted in the diagrams is a portion of the phase limit of the respective working medium with its critical point KP, and also the heat pump process 80, 90. In the case of the transcritical heat pump process 80 shown, the achievable temperature T7 that can be delivered to the district heating flow 27 lies far above the critical point KP.
In the case of the high-temperature compression heat pump 43 used according to the invention, the flow temperature Tzp, that is to say the maximum achievable hot water temperature TH20 for

21 the district heating supply 40, lies well below the critical point KP of the working medium, since preferably working media with very high critical temperatures are used. Accordingly, the heat pump process 90 is in the subcritical range, whereby an approximately isothermal heat output at this high temperature level T43 of for example around 130 C is ensured.

Claims

CLAIMS:

1. A method for providing heat for a district heating supply, comprising:
extracting thermal water from a geothermal source, operating a high-temperature heat pump, thermally connecting the geothermal source to the high-temperature heat pump, conducting the thermal water through a heat exchanger which transmits heat to a heat transporting medium, thereby providing a heated heat transporting medium, returning the thermal water cooled in the heat exchanger via a reinjection line to the geothermal source, passing a first flow of the heated heat transporting medium to an evaporator of the high-temperature heat pump, thermally transmitting heat at a first temperature level from the first flow of the heated heat transporting medium to the evaporator of the high-temperature heat pump, passing a second flow of the heated heat transporting medium to a condenser of the high-temperature heat pump, and thermally transmitting heat at a second temperature level higher than the first temperature level and at least 100°C via the condenser to the second flow of heated heat transporting medium passed to the condenser.

2. The method of claim 1, wherein a high-temperature compression heat pump is used as the high-temperature heat pump.

3. The method of claim 1 or claim 2, wherein the second temperature level is at least 110°C.

4. The method of any one of claims 1-3, wherein a working medium comprising a fluoroketone is used in the high-temperature heat pump.

5. The method of any one of claims 1-4, wherein a non-toxic working medium is used in the high-temperature heat pump.

6. The method of any one of claims 1-5, wherein a working medium having a critical temperature above 160°C is used in the high-temperature heat pump.

7. The method of any one of claims 1-6, comprising storing the heat of the first temperature level received from the heated heat transporting medium or the heat of the second temperature level received via the condenser of the high-temperature heat pump in at least one thermal store.

8. The method of any one of claims 1-7, further comprising operating at least two high-temperature heat pumps coupled in series.

9. A system for providing heat for a district heating network at a temperature level of at least 100°C, the system comprising:
at least one thermal water extraction device configured to extract thermal water, a high-temperature heat pump comprising an evaporator and a condenser, a heat exchanger configured to transmit heat from the extracted thermal water to a heat transporting medium to thereby provide a heated heat transporting medium, a thermal water transporting line configured to pass the extracted thermal water to the heat exchanger, a reinjection line for returning the thermal water cooled in the heat exchanger to the geothermal source, and a first supply line configured to conducting the heated heat transporting medium from the heat exchanger to the evaporator of the high-temperature heat pump, and a second supply line configured to conducting the heated heat transporting medium from the heat exchanger to the condenser of the high-temperature heat pump, wherein the condenser provides heat to a flow of the heated heat transporting medium passed to the condenser via the second supply line.

10. The system of claim 9, wherein the high-temperature heat pump comprises a high-temperature compression heat pump.

11. The system of claim 9 or claim 10, wherein the high-temperature heat pump contains a working medium comprising a fluoroketone.

12. The system of any one of claims 9-11, wherein the high-temperature heat pump contains a working medium having a critical temperature above 160°C.

13. The system of any one of claims 9-12, comprising at least one thermal store configured to receive and store heat of a first temperature level from the heated heat transporting medium or heat of a second temperature level, higher than the first temperature level, from the condenser of the high-temperature heat pump.

14. The system of any one of claims 9-13, comprising at least two high-temperature heat pumps connected in series.