DE102006056979B4 - Apparatus for heat recovery - Google Patents

Abstract

Apparatus (1) for heat recovery, the apparatus (1) comprising at least one boiler (2) containing a temperature-layered liquid, the boiler (2) having a cold side (8) at the bottom and a hot side (7) at the top, wherein for heating the liquid in the boiler (2) a heat exchanger (10) having a primary side (12) and a secondary side (11) is provided, wherein the secondary side (11) on the one hand with the cold side (8) of the boiler (2) and on the other is connected to the hot side (7) of the boiler (2) and with the boiler (2) forms a closed, driven exclusively by the heat input in the heat exchanger (10) outgoing convection circuit, wherein the primary side (12) of the heat exchanger (10 ) is flowed through by a heat transfer condensing heat transfer medium (14), which removes heat from a heat source (21) with a lower temperature than the hot side (7) of the boiler (2) and thereby verd in which the heat source (21) is followed by at least one compressor (23) which brings the heat transfer medium (14) to a temperature higher than that of the hot side (7) of the boiler (2), the flow rate of the compressor (23) is influenced by a regulating device (29) which is dependent on the temperature of the heat transfer medium (14) between the outlet of the compressor (23) and an outlet line (15) of the heat exchanger (10) and / or the heat exchanger ( 10) and / or boiler (2) is influenced, wherein the control device (29) is influenced by the condensation temperature of the heat transfer medium (14).

Description

The invention relates to a device for heat recovery according to claim 1.

From the DE 28 35 072 C2 a water heater is known, which is formed by a memory and a surrounding heat exchanger. The heat exchanger stands with the memory in konvektionsgebundener connection, wherein the hot water from the heat exchanger is introduced from above into the memory. This results in a favorable temperature stratification of the water in the memory.

From the DE 80 17 626 U1 Another memory is known, which carries on its jacket a countercurrent heat exchanger. This countercurrent heat exchanger can directly introduce heat into the lower area of the store. This results in the memory no temperature stratification, so that the memory must be fully charged to remove hot water can.

From the DE 27 29 668 A1 a device for heat recovery from industrial waste heat is known, comprising a boiler and a heat exchanger associated therewith. The secondary side of the heat exchanger is connected on the one hand with a cold side and on the other hand with a hot side of the boiler, so that a closed circuit between the boiler and the heat exchanger is formed. The primary side of the heat exchanger is flowed through by a heat transfer medium, which is fed by industrial waste heat. In plants where large amounts of industrial waste heat are available, this waste heat is easily enough to not only heat the water of the boiler but at the same time maintain convective flow between the boiler and the heat exchanger. Thus, no circulation pump in this cycle is required, which would destroy the desired temperature stratification within the boiler at too high a flow. This known device has been well proven in practice and forms the starting point of the present invention.

The DE 10 2004 018 034 A1 discloses a service water storage for heat pumps. The hot water tank includes a heat exchanger. If the power of a heat pump is not sufficient to heat the hot water, the heat supply can be throttled or blocked via a 2-way valve, so as not to cool water in the upper part of the hot water tank.

The invention has for its object to provide a device for heat recovery of the type mentioned, which is characterized by a high efficiency and wide usability of available heat sources.

This object is achieved with the features of claim 1.

The device according to claim 1 is used for heat recovery. It has at least one boiler containing a temperature-layered liquid. In general, the boiler is filled with water, with any other heat transfer medium is suitable. The liquid in the boiler is temperature-stratified, so that there is always at least one layer of cold liquid in the boiler and above it at least one layer of warm liquid. In general, an inflow for the liquid, in particular cold water is provided on the cold side of the boiler, while on the hot side, a drain for heated liquid, in particular hot water is provided. The heated liquid is used in particular for heating purposes, with alternatively or additionally also hot water for household purposes can be removed. For heating the liquid in the boiler, a heat exchanger is provided, the secondary side is connected on the one hand to the cold side and on the other hand to the hot side of the boiler. The secondary side of the heat exchanger therefore forms a self-contained circuit with the boiler. This circuit is driven solely by convection of the liquid in the boiler, so that no active circulation pump is provided. The control device is influenced by the condensation temperature of the heat transfer medium. This arrangement has the advantage that the flow rate of the liquid is coupled in this circuit directly to the heat input. It is therefore impossible that the liquid is circulated in this cycle, without a sufficiently high heat input occurs. Such a revolution would result in the total destruction of the temperature stratification of the liquid in the boiler, so that the withdrawal temperature of the boiler would decrease accordingly. On the other hand, the purely convection-bound flow of this cycle requires a relatively intense heating of the liquid, since too low heating convection does not get going.

To achieve universal applicability of the heat recovery device, it is important to be able to use also heat sources whose temperature is lower than the hot side of the boiler. For this purpose, a heat transfer medium is used, which is evaporated by the heat source. Subsequently, the heat transport medium is compressed by a compressor, which brings the heat transfer medium including the heat contained therein to a higher temperature. The heat transport medium is then passed through the primary side of the heat exchanger where it heats the boiler fluid. At the same time, the heat transfer medium condenses, the heat of vaporization for the heat exchanger being released to the boiler fluid. The liquid heat transfer medium is then fed back to the heat source, where it can absorb heat again. In this way, heat is transported from the low temperature heat source to the higher temperature heat exchanger. However, it has been found that the operation of such a heat pump along with a convection-based heat exchanger is quite problematic.

In contrast to the use of industrial waste heat, heat pump operation requires high system efficiency because of the associated energy consumption. If the heat input of the heat pump into the heat exchanger is too low, the convection in the boiler circuit does not start. On the other hand, if the heat input is too high, the compressor consumes a lot of energy without the heating of the liquid in the boiler being noticeably increased.

To solve this problem, a compressor is used whose flow rate is influenced by a control device. This control device is influenced by the temperature of the heat transfer medium between the output of the compressor and the output line of the heat exchanger or by the temperature of the liquid of the heat exchanger or boiler. By this measure it is achieved that the throughput of the heat transport medium is dependent by the compressor of the heat output of the heat transfer medium in the heat exchanger. When starting up the device, therefore, the compressor is used at relatively low power to give the convection on the secondary side of the heat exchanger time to build up accordingly. With increasing Konvektionsströmung the compressor is raised in its performance, since then the heat output of the heat transfer medium increases in the heat exchanger accordingly. In this way, optimum heat utilization of the heat source results in relatively low energy consumption, so that the entire device has a surprisingly high efficiency.

To achieve the lowest possible heat loss, it is advantageous according to claim 2, when the heat exchanger is designed as a countercurrent heat exchanger. As a result, the boiler fluid is heated almost to the temperature of the heat transfer medium. Thus, the heat transfer only leads to a very low temperature loss. If the heat exchanger is provided within a heat insulation of the boiler, the result is particularly low heat losses. Preferably, the heat exchanger is arranged around the boiler, so that heat radiation losses of the boiler are partly regenerated in the heat exchanger.

In order to maintain the most effective convection, it is favorable according to claim 3, when the heat exchanger on the secondary side has a larger line cross-section than the primary side. This leads to a lower line resistance on the secondary side, so that even a relatively small temperature difference within the heat exchanger leads to an effective convection flow. On the primary side, a large line cross-section is not required because the heat transfer medium is forcibly circulated anyway by the action of the compressor.

To achieve a sensitive control, it is advantageous according to claim 4, when the control device is influenced by the condensation temperature of the heat transfer medium after the heat exchanger. The condensation temperature is a material-dependent function of the pressure, so that only the pressure of the heat transfer medium after the heat exchanger must be measured to determine the condensation temperature in known heat transport medium. This measured pressure can then be converted to a condensation temperature using the vapor pressure curve of the heat transfer medium. The knowledge of the condensation temperature is important because an incomplete condensation of the heat transfer medium would result in incomplete heat transfer into the heat exchanger and possibly an unstable control, so that the energy consumption of the compressor is too high. The influence of the condensation temperature on the control therefore improves the efficiency of the device.

To achieve optimal efficiency, it is favorable according to claim 5, when the control device adjusts the temperature of the heat transfer medium after flowing through the heat exchanger to a temperature which is a predetermined temperature range below the condensation temperature of the heat transfer medium. The heat transfer medium is undercooled in this case, so that the heat of vaporization has been completely discharged through the heat exchanger to the boiler fluid. If the heat output in the heat exchanger increases, this results in a drop in the temperature of the heat transport medium at the outlet of the heat exchanger relative to the condensation temperature. In this case, the control ensures an increase in the flow through the compressor. Thus, the increased heat capacity of the heat exchanger can be used directly to increase the performance of the device. In addition, the regulation remains stable over the entire operating range.

For the temperature range, a range between 1K and 10K has been proven according to claim 6. At a temperature range of less than 1K there is a risk that the condensation of the heat transfer medium is no longer complete in the event of disturbances, so that heat is pumped unused circle. In addition, this can result in difficult to control control oscillations. A choice of the temperature range of over 10K is impractical, since this would result in a limitation of available heat sources. Depending on the usable heat source, however, a larger temperature range is possible. Preferably, the temperature range between 3K and 7K is selected to achieve the most sensitive and efficient control possible.

In order to use the device in a wide power range, it is advantageous according to claim 7, if at least one expansion valve is provided between the heat exchanger and the heat source. This expansion valve ensures a relaxation of the heat transport medium and thus keeps the pressure conditions of the heat transfer medium in the region of the heat exchanger in approximately constant.

In order to achieve that the device achieves optimum efficiency under all conditions, it is advantageous according to claim 8, when the expansion valve is in operative connection with a control device influenced by the pressure of the heat transfer medium. In this way, constant properties of the heat transport medium can be realized over a wide operating range.

In particular, in heat sources with very low temperature, it is advantageous according to claim 9 nachordnen the heat exchanger and at least one container which is in thermal contact with the vaporized heat transfer medium. Thus, the heat transfer medium is additionally cooled to improve the heat absorption. In addition, the recoverable from the compressor end temperature increases.

The subject invention is exemplified with reference to the drawing, without limiting the scope.

The single figure shows a schematic representation of a device 1 for heat recovery. The device 1 has a boiler 2 on that with water 3 is filled.

The boiler 2 has a feed 4 for cold water and a drain 5 for hot water. Inside the boiler 2 turns a layer boundary 6 one in which a warm side 7 on a cold side 8th lies. Between the warm side 7 and the cold side 8th Only a very small mixing takes place, so that the water 3 the warm side 7 can be removed with almost constant temperature. In particular, the temperature of the water depends 3 at the expiration 5 practically not from the height of the layer boundary 6 from.

The boiler 2 is via lines 9 with a countercurrent heat exchanger 10 connected. The water 3 flows through a secondary side 11 of the heat exchanger 10 , This secondary side 11 has a larger wire cross-section than a primary side 12 of the heat exchanger 10 to switch between the boiler 2 and the heat exchanger 10 over the wires 9 To be able to realize a free convection flow without circulating pump. To achieve the lowest possible heat loss of the heat exchanger 10 inside a thermal insulation 13 of the boiler 2 intended. In addition, the radiant heat of the boiler 2 to make usable, the heat exchanger extends 10 around the boiler 2 around.

In addition, in the boiler could 2 - Deviating from the representation - nor heat sources, such as heat exchangers from fossil fuel heaters or be housed by high-temperature solar thermal systems. Such additional heat sources in the boiler 2 However, they have nothing to do with the subject invention itself and are therefore not shown.

In addition, depending on the application, the heat exchanger 10 from the boiler 2 be thermally decoupled by an additional heat insulating layer. Depending on the application is alternatively also thought, the partition between the heat exchanger 10 and the boiler 2 to be provided with openings or omit altogether, so that in this way an improved convection is formed.

The primary side 12 of the heat exchanger 10 is from a heat transfer medium 14 flows through, which is circulated in a separate circuit. The primary side 12 of the heat exchanger 10 is via an output line 15 with a container 15a connected, which is designed as an intermediate heat exchanger. In this container 15a gives the heat transport medium 14 Heat to vaporized heat transfer medium 14 which is the container 15a in a pipe 22 flows through. This measure improves the heat absorption capacity of the heat transport medium 14 ,

After leaving the container 15a enters the heat transport medium 14 in an expansion valve 16 , which is for a reduction of the pressure of the heat transfer medium 14 provides. The expansion valve 16 is about a control device 17 with a pressure gauge 18 in operative connection, which the pressure of the heat transport medium 14 in the output line 15 keeps constant. The control device 17 is a differential amplifier 17b upstream of the measured pressure with a setpoint value of a setpoint generator 17a compares. The comparison result is the controlled variable of the control device 17 , This ensures that inside the heat exchanger 10 approximately constant pressure conditions of the heat transport medium 14 prevail, so that the heat transport medium 14 has approximately a constant condensation temperature.

The expansion valve 16 is over a line 19 with another heat exchanger 20 in operative connection, dealing with a heat source 21 in contact. As a heat source 21 For example, ambient air, but also geothermal or a solar thermal system in question. As a rule, the temperature of the heat source is sufficient 21 do not go to the water directly 3 in the heat exchanger 10 heat. For this purpose, this heat must first be brought to a higher temperature.

For this purpose, the heat transport medium 14 chosen so that it is within the line 19 is liquid and through the heat source 21 evaporated. This steam is over another line 22 through the container 15a where it is in heat exchange with the heat exchanger 10 upcoming heat transport medium 14 stands. The heat transport medium 14 will be approximately at the inlet temperature of the boiler 2 heated.

After leaving the container 15a becomes the heat transport medium 14 a compressor 23 fed, whose flow is adjustable over the speed. The compressor 23 compresses the heat transport medium 14 , which also increases its temperature level. About a line 24 enters the heat transport medium 14 back into the heat exchanger 10 where it transfers its heat to the secondary water 3 emits. The heat transfer medium condenses 14 so that its entire heat of vaporization to the water 3 is delivered.

By the formation of the heat exchanger 10 as a countercurrent heat exchanger is also achieved that the water 3 after leaving the heat exchanger 10 almost the temperature of the incoming heat transport medium 14 having. The temperature loss is very low, as the incoming heat transfer medium 14 initially only the top layer of the water 3 heated, which is almost the temperature of the heat transfer medium 14 has reached. The heat transport medium 14 flows downwards in the heat exchanger and heats colder water layers, causing it to cool down noticeably. It is at a certain point within the heat exchanger 10 the condensation temperature of the heat transport medium 14 achieved, so that instead of further cooling of the heat transfer medium 14 a condensation of the same at constant temperature begins. The condensation of the heat transport medium 14 is complete, so that the entire heat of evaporation is released. In the lower part of the heat exchanger 10 becomes the now liquid heat transport medium 14 cooled even further and then the expansion valve 16 and the heat source 21 fed. In this way results in a very efficient use of energy of the device 1 ,

To operate the device 1 is a temperature sensor 25 in the area of the output line 15 on the output side of the heat exchanger 10 intended. This temperature sensor 25 measures the temperature of the heat transport medium 14 after the heat release in the heat exchanger 10 , About the already mentioned pressure gauge 18 In addition, the pressure of the heat transfer medium 14 in the output line 15 certainly. About a calculation circuit 26 , in which the vapor pressure curve of the heat transport medium 14 is stored, this is the condensation temperature of the heat transfer medium 14 calculated and delivered as an electrical signal. The calculated condensation temperature is combined with the signal from the temperature sensor 25 and a setpoint value of a setpoint generator 27a a differential amplifier 27 supplied from the supercooling of the heat transfer medium 14 in the output line 15 determined under the condensation temperature and compared with the target value.

An output signal 28 of the differential amplifier 27 becomes a control device 29 fed to the compressor 23 via a frequency converter 30 controls. In this way it is ensured that the heat transport medium 14 depending on the convection flow of the water 3 always optimally circulated. Thus, on the one hand, the heat source 21 optimally used and on the other hand the energy consumption of the compressor 23 kept to a minimum. In this way, overall results in an optimal efficiency of the device 1 ,

LIST OF REFERENCE NUMBERS

1

device

2

boiler

3

water

4

Intake

5

procedure

6

layer boundary

7

warm side

8th

cold side

9

management

10

heat exchangers

11

secondary side

12

primary

13

thermal insulation

14

Heat transport medium

15

output line

15a

container

16

expansion valve

17

control device

17a

Setpoint encoders

17b

differential amplifier

18

pressure gauge

19

management

20

heat exchangers

21

heat source

22

management

23

compressor

24

management

25

temperature sensor

26

computing circuit

27

differential amplifier

27a

Setpoint encoders

28

output

29

control device

30

frequency converter

Claims (9)

Apparatus (1) for heat recovery, the apparatus (1) comprising at least one boiler (2) containing a temperature-layered liquid, the boiler (2) having a cold side (8) at the bottom and a hot side (7) at the top, wherein for heating the liquid in the boiler (2) a heat exchanger (10) having a primary side (12) and a secondary side (11) is provided, wherein the secondary side (11) on the one hand with the cold side (8) of the boiler (2) and on the other is connected to the hot side (7) of the boiler (2) and with the boiler (2) forms a closed, driven exclusively by the heat input in the heat exchanger (10) outgoing convection circuit, wherein the primary side (12) of the heat exchanger (10 ) is flowed through by a heat transfer condensing heat transfer medium (14), which removes heat from a heat source (21) with a lower temperature than the hot side (7) of the boiler (2) and thereby verd in which the heat source (21) is followed by at least one compressor (23) which brings the heat transfer medium (14) to a temperature higher than that of the hot side (7) of the boiler (2), the flow rate of the compressor (23) is influenced by a regulating device (29) which is dependent on the temperature of the heat transfer medium (14) between the outlet of the compressor (23) and an outlet line (15) of the heat exchanger (10) and / or the heat exchanger ( 10) and / or boiler (2) is influenced, wherein the control device (29) is influenced by the condensation temperature of the heat transfer medium (14). Device (1) according to Claim 1 , characterized in that the heat exchanger (10) is designed as a counterflow heat exchanger and is provided within a heat insulation (13) of the boiler (2). Device (1) according to Claim 1 or 2 , characterized in that the heat exchanger (10) on the secondary side has a larger line cross-section than the primary side. Device according to at least one of Claims 1 to 3 , characterized in that the regulating device (29) is influenced by the condensation temperature of the heat transfer medium (14) after the heat exchanger (10). Device (1) according to at least one of Claims 1 to 4 , characterized in that the regulating device (29) adjusts the temperature of the heat transfer medium (14) after flowing through the heat exchanger (10) to a temperature which is a predetermined temperature range below the condensation temperature of the heat transfer medium (14). Device (1) according to Claim 5 , characterized in that the temperature range is between 1K and 10K, preferably between 3K and 7K. Device (1) according to at least one of Claims 1 to 6 , characterized in that between the heat exchanger (10) and the heat source (21) at least one expansion valve (16) is provided. Device (1) according to Claim 7 , characterized in that the expansion valve (16) is in operative connection with a control device (17) influenced by the pressure of the heat transfer medium (14). Device (1) according to at least one of Claims 1 to 6 , characterized in that the primary side (12) of the heat exchanger (10) at least one container (15a) is arranged downstream, which is in thermal contact with the of the heat source (21) evaporated heat transfer medium (14).

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