EP2320189B1 - Method for operating a recooling circuit with a hybrid cooler for an assembly with discontinuous heat discharge - Google Patents

Description

The invention relates to a method for operating a recooling circuit with a hybrid cooler for an adsorption refrigerator with an intermittent heat output according to claim 1.

Recoolers and recooling circuits are used to dissipate heat from a heat source to the environment. A recooling medium is used to conduct the heat from the heat source to a heat exchange surface that is in thermal contact with the surroundings. A large number of different configurations are known for this. The heat is released to the environment either via a dry recooler, in which the recooling medium flows through pipes within the heat exchange surface and thus transfers the heat to the environment, or via a wet cooler, in which the recooling medium, which is predominantly in the form of water, evaporates or evaporates directly , as is the case with a cooling tower, for example.

The principle of dry recooling and wet cooling is combined in a hybrid cooler. This involves dry recooling, which is supported by water spraying, sprinkling or wetting the cooling surfaces or the surrounding air.

The conventional control of the operation of a hybrid cooler is carried out in such a way that the spraying is started when a certain temperature is established in the supply air or at the outlet of the recooler. When the spray is activated, a valve is opened and water is continuously sprayed into the supply air flow. The resulting lowering of the temperature in the supply air enables higher heat dissipation in the recooling circuit. Spraying is usually controlled by detecting the temperature at the cooler outlet. This is compared with a specified target value.

This control method has the disadvantage that the water consumption during spraying and thus the efficiency of the spraying of the back cooler can only be influenced to a very limited extent. The known control method is designed for continuous spraying. The water consumption is therefore disproportionate, the constant spraying also leads to dirt and lime deposits in the recooler. This further deteriorates the efficiency of the recooling and in turn leads to an additional water consumption during the spraying.

In addition, the control of the spraying of the recooler proves to be variable only to a very limited extent in the currently known methods. For technical reasons, it has a fixed hysteresis, which prevents the spraying from being switched on and off in a timely manner. The entire control process is therefore very sluggish.

The disadvantages mentioned become particularly serious when systems have to be recooled which have a discontinuous heat output which, moreover, changes within relatively short time cycles. In this case, the conventional control methods of recooling mean that the spraying remains useless in operation whenever there is no or only a small amount of heat to be dissipated from the system. The known control method of spraying is not able because of its inertia react to the changing cyclical heat loads of the plant. This makes the recooling of such a system inefficient.

In US 7 021 070 B2 describes a compressor cooling with a cooling subsystem. This is a hybrid cooler with water cooling. A water supply is regulated or controlled depending on the operating parameters of the cooling system. For this purpose, sensors are arranged in the cooling subsystem or in the hybrid cooler. Spraying with water is started when a certain temperature is reached in the supply air or at the outlet of the recooler.

The task is to design a recooling circuit with a hybrid cooler in such a way that it is particularly suitable for systems with discontinuous heat emission. The recooling circuit should be particularly suitable for systems in which the heat output changes within comparatively short time cycles. The recooling circuit should have a reduced water consumption during the spraying, increase the efficiency of the recooling and ensure an increased service life of the components present in the recooling circuit, in particular the hybrid cooler itself. In connection with this, the operating and maintenance costs of the recooling circuit and beyond that of the system are to be reduced and optimized.

The object is achieved in terms of the method aspect according to the teaching for operating a recooling circuit with the features of claim 1.

According to the invention, the method for operating a recooling circuit with a hybrid cooler for an adsorption refrigerator with discontinuous heat emission is characterized by spray control of the hybrid cooler with the following method steps:
The spray control of the hybrid cooler relates to a working cycle of the adsorption refrigerator, the working cycle being repeated periodically essentially over time:
A current operating parameter is continuously recorded within the adsorption refrigerator. The operating parameter recorded in this way is compared with a predetermined first value in a control unit. A spraying device of the hybrid cooler is activated when the predetermined value is reached and / or exceeded by the currently recorded operating parameter until a predetermined second value has been reached and / or fallen below.

The spraying device remains activated as long as the relevant operating parameter is exceeded. The spraying device is then deactivated by closing a valve. The valve is open or closed during a fixed interval, so that the hybrid cooler is sprayed at intervals.

In contrast to the conventional control of the spraying device, which is fed back to the temperature value at the output of the recooler, an operating parameter, for example a temperature value, from the adsorption refrigerator itself is used to regulate the spraying device. The operation of the spraying device is thus directly related to the operational processes the adsorption chiller and thus coupled with the heat-generating process running there. The spraying device thus reacts directly to the operational processes and thus to the heat generation within the system. This significantly shortens the response times of the control of the spraying device, so that a real discontinuous and / or cyclical operation of the spraying device can be carried out in accordance with the discontinuous heat generation within the adsorption refrigerator. The spraying device thereby reacts in particular to operating cycles occurring within the adsorption refrigerator and is coupled to them. In this way, the amount of water used for spraying and thus the stress on the hybrid cooler is sustainably reduced and the recooling cycle is effectively adjusted to the heat load supplied by the adsorption chiller.

The system is designed as an adsorption chiller. The currently recorded operating parameters are recorded within an evaporator in a cold water circuit or a condenser in the adsorption refrigeration machine.

Adsorption chillers are characterized by a discontinuously generated and cyclical heat emission. The recooling circuit operated according to the invention is therefore particularly advantageous for such purposes.

The method and an exemplary device for carrying out the method are to be explained in more detail below on the basis of exemplary embodiments. The serve to clarify Figures 1 to 5 . The same reference numerals are used for identical and / or equivalent parts.

Fig. 1

eine Darstellung einer zyklischen Arbeitsweise einer Adsorptionskältemaschine,

Fig. 2

eine Darstellung eines beispielhaften Rückkühlkreislaufs im Überblick,

Fig. 3

eine zweckmäßige Ausführungsform eines beispielhaften Hybridkühlers,

Fig. 4

eine Darstellung eines Temperaturverlaufs am Austritt eines Hybridkühlers unter dem Einfluss einer zeitlich diskontinuierlichen Wärmelast mit und ohne Besprühungsintervalle und

Fig. 5

eine Darstellung einer Maschinenarbeitszahl einer rückgekühlten Adsorptionskältemaschine in Abhängigkeit von einer Außentemperatur mit und ohne Besprühung.

Here show:

Fig. 1

a representation of a cyclic operation of an adsorption refrigerator,

Fig. 2

an overview of an exemplary recooling circuit,

Fig. 3

an expedient embodiment of an exemplary hybrid cooler,

Fig. 4

a representation of a temperature curve at the outlet of a hybrid cooler under the influence of a temporally discontinuous heat load with and without spraying intervals and

Fig. 5

a representation of a machine performance factor of a recooled adsorption refrigerator as a function of an outside temperature with and without spraying.

A method based on the operation of a recooling circuit coupled to an adsorption refrigeration machine, in particular a recooling water circuit, is shown as an example below. As for all thermally driven refrigeration systems, an efficient and efficient recooling of the supplied drive energy and the generated cooling energy is also of great importance for such systems. The recooling energy in the form of heat that can no longer be used by the machine must therefore be efficiently dissipated via the recooling circuit and heat exchange. For this purpose, a heat transfer medium, which consists, for example, of water or a mixture of water and glycol, circulates in the recooling circuit.

The heat transfer temperature in the recooling circuit increases due to the heat absorption in the machine. The heat transfer medium is cooled again to a lower temperature level along the recooling circuit and in particular on a cooler designed as a heat exchanger. It is then available to the refrigeration system for renewed heat absorption. The efficiency and performance of the recooling circuit depend on the outside temperature, the type of cooler used, its peripheral components and the refrigeration system itself.

Fig. 1 shows a representation of the cyclic operation of an adsorption refrigerator. The characteristic discontinuous mode of operation of the machine is characterized by the structure and the changing processes of adsorption and desorption. In order for the machine to run as continuously as possible, adsorption and desorption processes are carried out alternately in two adsorbers. At the outlet temperature of a heat transfer circuit shown in curve C, the fluctuations are extremely steep and occur cyclically. These fluctuations can also be seen in a damped form at the inlet temperature of the heat transfer circuit on curve D. The cyclic operation of the machine is particularly clearly expressed in the course of a cooling capacity shown by curve E. In the example shown here, a maximum cooling capacity of 8 kW and a minimum cooling capacity of 2 kW are achieved.

The outside temperature represented by curve F shows a course with natural fluctuations up to a point X. The sudden rise in outside temperature in point X is due to incident solar radiation. The rise in the outside temperature results in a delayed rise in the inlet temperature in curve D and the outlet temperature in curve C of the heat transfer circuit. The reduction in cooling capacity at curve E after point X is due to the temperature increase in the circuit.

Figure 2 1 shows an exemplary recooling circuit 1 provided for the adsorption chiller, Figure 3 an exemplary embodiment of a hybrid cooler connected in the circuit.

The recooling circuit contains a hybrid cooler 2, which is expediently arranged outdoors, and a system 3, for example an adsorption refrigerator with the in Fig. 1 shown operating cycles, which discontinuously gives off heat to the recooling circuit. The heat transfer medium flowing in the recooling circuit flows from the system into the hybrid cooler via a feed line 4. There it transfers the heat absorbed by the system to the ambient air. For this purpose, a cooling element 5 is provided in a lamella construction, which offers particularly good thermal contact with the surroundings.

The heat carrier cooled in the hybrid cooler flows back to the system via a return 6. A pump 7 is provided for circulating the heat transfer medium within the cooling circuit. The flow of the heat transfer medium in the recooling circuit can be regulated via a series of valves. If necessary, the flow can be blocked via blocking valves 10 arranged in the vicinity of the pump. A storage and expansion tank 11 connected to the recooling circuit compensates for pressure fluctuations.

A process medium flows within a process circuit within the system cooled by the recooling circuit. In the case of an adsorption refrigeration machine, the process cycle corresponds to the cycle of the adsorbed and desorbed refrigerant which is customary in such systems. This exchanges heat via heat exchangers arranged in the circuit, in particular one Condenser 13, two adsorbers 14 and an evaporator 15 with adjacent operating components.

For this purpose, the evaporator 15 is thermally coupled to an external cold water circuit, not shown here. This includes, for example, a cooling ceiling or a cooling spiral. These facilities are not shown here.

The adsorbers 14 are in turn thermally coupled to an external hot water circuit, which contains, for example, a solar storage, not shown here, a district heating device or a waste heat device of a combined heat and power plant.

Temperature sensors 16 are provided at various points on the secondary sides of the heat exchangers or also in the recooling circuit, in particular in the region of the condenser, the evaporator and / or the adsorbers. These transfer the operating parameters recorded at these points, i.e. the temperature values measured in this example to a control unit 17.

The already mentioned hybrid cooler is a dry hybrid cooler with a spraying device 18 and a ventilation 19. The spraying device consists of a nozzle arrangement 20 arranged under the cooling element 5, which is supplied with cold water by an inlet line 21. The water supply via the feed line can be released or shut off via a check valve 22. The opening state of the check valve is determined by the control unit 17 via a control line 17a and the electrical switching signals transmitted via this line. For this purpose, the check valve is designed as an electrically switchable valve, for example as a solenoid valve.

In the present construction of the hybrid cooler, ambient air is sucked in by the ventilation. This flows through the cooling element and exits the hybrid cooler. In the dry recooler with spraying in the ventilation direction, the nozzle arrangement is in the form of a nozzle assembly under the cooling element. The ambient air sucked in first flows through the nozzle assembly and pulls the water sprayed in there with it. By spraying water in the direction of flow of the air volume flow, the cooling element is wetted on its surface. An evaporation effect occurring on the one hand in the air volume flow and on the other on the surface of the finned heat exchanger wall of the cooling element enables the heat carrier to be cooled to a temperature which is below the ambient temperature. This intensifies the cooling of the heat transfer medium in the recooling circuit. Spraying can be activated or deactivated via the switching status of the shut-off valve, thus adjusting the effectiveness of the cooling.

Fig. 4 shows the effect of discontinuous spraying using an exemplary diagram. The diagram shows the time course of an outlet temperature at the recooler under the influence of a discontinuous heat load during a working cycle of the adsorption chiller. This essentially repeats periodically over time.

Curve A shows the temperature profile of the outlet temperature from the recooler without spraying, curve B shows the temperature profile of the outlet temperature with spraying. In the example shown here, the spraying is carried out within two time intervals t _S1 during the working cycle. It can be seen from the course of curve A that the temperature at the outlet of the recooler initially reaches a maximum, which over time drops asymptotically against a limit value due to the onset of the recooler.

As the course of curve B shows, the initial temperature maximum is considerably reduced by the spraying taking place during the first time interval t _S1 . The temperature curve then shows a much flatter course. In contrast to the temperature profile in curve A, the initial temperature present at time t = 0 can be achieved by spraying later, again within a time interval t _S1 can be reached again quickly. The brief spraying in the two time intervals is therefore sufficient to smooth the temperature profile at the outlet of the hybrid cooler and thus to ensure a constant cooling capacity of the hybrid cooler with a discontinuous heat load. The spraying, which is only carried out within the time intervals, is sufficient to effectively dissipate the discontinuously introduced heat.

This effect is caused by the temperature of the ambient air drawn in via the ventilation which is reduced as a result of spraying. The temperature profile of the ambient air is shown by curve B '.

According to the invention, the start and the duration of the respective time intervals t _{S1 are determined} by the control unit. The spraying then starts when the temperature T _to a set value T at a location of the refrigeration cycle of the adsorption reaches or exceeds. It is then turned off and the valve 22 is closed when the predetermined operating parameters _should in this case, the target value T, has fallen again. The strong flattening of the curve B in comparison to A is explained by the fact that spraying of the cooling element in the hybrid cooler begins even before the now more heated heat carrier has reached the cooling element via the flow. As a result, the cooling element is already wetted and can therefore absorb the heat brought in by the heat transfer medium very effectively.

As can also be seen from the diagram, spraying begins at a point in time when the temperature of the heat transfer medium is still rising. The minimum reached in the curve B 'of the air temperature during the time interval t _S1 thus coincides with the increasing section of the curve B of the outlet temperature. The effectiveness of the interval-like spraying regulated by the control unit thus results above all from the fact that the temperature rise of the heat transfer medium in the recooling circuit is counteracted in a timely manner and at the beginning.

An experimental comparison of the spraying method mentioned for the hybrid recooler with the conventional mode of operation of a quasi-continuous spraying shows that a considerably larger amount of water is consumed when the latter is carried out. Compared to the conventional mode of operation, the water consumption during spraying is reduced to approximately one seventh in the method according to the invention.

Fig. 5 shows the beneficial influence of in Fig. 4 shown execution of the spraying on a machine performance factor of an adsorption refrigerator with such a recooling circuit operated at different ambient temperatures. The machine performance figure is a measure of the effectiveness of the adsorption chiller. It indicates the ratio between the heat pumped by the adsorption chiller and the energy required for this. A high machine performance factor therefore means that the refrigeration system is highly effective.

The diagram shows that the machine performance factor decreases as the outside temperature increases. Without spraying, it reaches a value of less than 10 at a temperature of 26 ° C. If the spraying is carried out according to the procedure at this temperature Fig. 3 put into operation, the machine work factor increases significantly to a value of 15 and thus one and a half times.

Reference list

1

Recooling circuit

2nd

Hybrid cooler

3rd

System with discontinuous heat emission

4th

leader

5

Cooling element

6

Rewind

7

pump

10th

Check valves

11

Storage and expansion tank

13

capacitor

14

Adsorber

15

Evaporator

16

Temperature sensor

17th

Control unit

17a

Control line

18th

Spraying device

19th

ventilation

20

Nozzle arrangement

21

Inlet pipe

22

Check valve

A

Outlet temperature without spraying

B

Outlet temperature with interval spraying

B '

Ambient air temperature

C.

cyclically varying outlet temperature in the heat transfer circuit of an AKM

D

Cyclically varying inlet temperature in the heat transfer circuit of the AKM

E

cyclically varying cooling capacity

Claims (1)

1. A method for operating a recooling circuit (1) with a hybrid cooler (2) for an adsorption refrigerator (3) with discontinuous heat discharge, concerning
   a spray control of the hybrid cooler (2) during an operating cycle of the adsorption refrigerator, with the operating cycle repeating substantially periodically in time, including the following method steps:

   - continuously detecting a current operational parameter of the adsorption refrigerator (3), wherein the currently detected operational parameter is a current temperature (3) in the adsorption refrigerator (3) and is detected within a heat carrier circuit,

   - comparing the detected operational parameter to a predefined temperature setpoint in a control unit (17),

   - activating a spray device (18) of the hybrid cooler (2), when the currently detected operational parameter reaches and/or exceeds the temperature setpoint until the temperature setpoint is reached or fallen below,
   wherein

   - the spraying starts when the temperature T at a point in the refrigerating circuit of the adsorption refrigerator has reached or exceeded a setpoint T_soll and during this, a switching signal for opening a valve of the spray device is output,
   and

   - the spraying is performed during the operating cycle within two time intervals t_S1, wherein the start and duration of the respective time intervals t_S1 are determined by the control unit,
   and

   - the spraying is deactivated and the valve is closed when the predefined operating parameter T_soll is fallen below again.

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