EP0096822B1 - Method of operating a bivalent absorption heat pump, and absorption heat pump for carrying out this method - Google Patents

Abstract

In an absorption heat pump capable of bivalent operation, to make possible a combined operation in addition to the pure heat pump operation and the pure boiler operation, it is proposed to divide the refrigerant stream after the condenser and the stream of weak solution leaving the boiler, with one component stream of the refrigerant being fed through the refrigerant throttle and the vaporizer to a low-pressure absorber, into which a component stream of the weak solution is introduced through the temperature changer and the solvent throttle, while the other component stream of the refrigerant is fed either directly to the boiler or to a high-pressure absorber, to which the other component stream of the weak solution is fed directly in both cases, and to feed the strong solution from the low-pressure absorber through the temperature changer and/or the reflux condenser to the boiler, but on the other hand to feed the solution from the high-pressure absorber directly to the boiler.

Description

The invention relates to a method for operating a bivalent-operated absorption pump, as described in the preamble of claim 1.

The invention further relates to a bivalent absorption pump for carrying out this method with the features of the preamble of claim 7.

Absorption heat pumps can only be used effectively for heating purposes if the air temperature has a certain value, e.g. + 3 ° C. not less. At lower temperatures, the performance figure drops sharply, especially due to the icing of the evaporator.

It is already known to switch the absorption heat pump under these unfavorable operating conditions so that it can be operated in pure boiler mode, i.e. H. by means of the refrigerant and / or the solvent, the heat supplied to the cooker from a heat source is fed directly to a heat exchanger surface via which the heating medium is heated (DE-A-28 56 767; DE-A-27 58 773).

These known absorption heat pumps can only be operated either in pure heat pump operation or in pure boiler operation, the changeover from one operating mode to the other being associated with considerable regulation and control expenditure and taking up a considerable amount of time. In the case of pure boiler operation, there is an overall incomplete utilization of the primary energy, which can be attributed to losses in the circulatory system. Finally, in this operation, a switch from pure heat pump operation to pure boiler operation must already take place at a temperature at which heat could still be extracted from the surroundings via the evaporator, if not to a sufficient extent for pure heat pump operation. If, in the known systems, a switch is made to the pure boiler operation at this temperature, the supply of the heat still available per se on the evaporator must be completely dispensed with.

An absorption heat pump system is also already known, with which three different operating modes are optionally possible, namely a heat pump operation, a boiler operation or a mixed operation (DE-A-2 908 423). In heat pump operation, an absorber is used as a low-pressure absorber, which is also used in boiler operation, but as a high-pressure absorber. The mixed operation takes place in that a further absorber is switched on in the stream of the rich solution leaving the first absorber. The entire rich solution leaving the first absorber is brought to the high pressure prevailing in the cooker by means of a pump and then again passed through an absorber in which the rich solution is mixed with a branched-off partial flow of the refrigerant. In this known solution, the two absorbers are therefore connected in series with respect to the supply of the poor solution. This changes the low pressure and the evaporation temperature accordingly in mixed operation. This mode of operation can, for example in the case of a brine-loaded evaporator, lead to considerable malfunctions due to the risk of icing. In addition, in the known method, the coefficient of performance of the heat pump component is reduced by the decrease in the concentration in mixed operation, since the coefficient of performance decreases with decreasing solution concentration.

Starting from this prior art, it is an object of the invention to improve a method for operating an absorption heat pump such that, in addition to pure heat pump operation and pure boiler operation, mixed operation with an increased coefficient of performance can be made possible in a simple manner.

This object is achieved in a method of the type described in the introduction by the features specified in the characterizing part of claim 1.

According to the invention, an absorption heat pump with the features of claim 7 is proposed for carrying out this method.

According to the invention, for mixed operation, the solvent flow from the cooker to the absorber and the refrigerant flow leaving the condenser are each split into two partial flows. A partial flow of the solvent and a partial flow of the refrigerant are carried out in the manner typical for pure heat pump operation, while the other other partial flows are conducted in the manner typical for pure boiler operation. To make this possible, the absorber is divided into a low-pressure absorber, which is used purely for heat pump operation, and a high-pressure absorber, which serves purely for boiler operation.

The heat exchange with the heating system takes place in the condenser and in both absorbers. In this way, it is possible to use both the advantages of pure heat pump operation and the advantages of pure boiler operation together, the proportion of pure heat pump operation relative to the proportion of pure boiler operation being continuously adjustable according to the ratio of the splitting of the two flows into partial flows .

It is advantageous if, in mixed operation, the throttling effect of the two throttles is increased compared to pure heat pump operation, so that the throttling effect can be adapted to the lower flow rate throughput of the heat pump circuit.

It is also advantageous if you are in Mixed operation leads the partial flow of the refrigerant only through part of the evaporator.

In mixed operation, the gas flow cross section of the evaporator is preferably reduced compared to pure heat pump operation. Due to the smaller active area of the evaporator, it is possible to keep it free of ice and effectively for longer, so that heat pump operation can be maintained down to lower temperatures.

It can be provided that the poor solution and the refrigerant are combined in the low-pressure absorber in pure heat pump operation and the resulting rich solution is then passed through the high-pressure absorber. In this case, both absorbers are used for heat exchange even in pure heat pump operation.

In order to make the throttling effect of the throttles in the refrigerant line and in the solvent line variable, they can be designed as expansion valves that are variable in volume flow. In a modified exemplary embodiment it can be provided that the chokes comprise at least two parallel lines with throttle valves, the parallel lines being able to be opened alternately or together by switching valves. Through a suitable choice of the throttle strengths in the individual parallel lines, the throttling effects of one line or the throttling effect of the parallel lines can be jointly used by switching.

In an advantageous embodiment of the invention, it is provided that the high-pressure absorber can be switched on in the pure heat pump mode between the low-pressure absorber and the first return line.

• Figur 1 eine schematische Darstellung einer Absorptionspumpe zur Durchführung des erfindungsgemäBen Verfahrens und
• Figur 2 eine Ansicht ähnlich Fig. '1 mit einer anderen Ausgestaltung der Kältemitteldrossei und der Lösungsmittetdrossei.

The following description of preferred embodiments of the invention serves in conjunction with the drawing for a more detailed explanation. Show it :

• Figure 1 is a schematic representation of an absorption pump for performing the inventive method and
• Figure 2 is a view similar to Fig. '1 with a different embodiment of the refrigerant dosing and the solvent dosing.

The heat pump shown in the drawing comprises, in the manner customary for heat pumps, a stove or expeller 1, in which a refrigerant-solvent mixture is heated by means of a heating source not shown in the drawing. The evaporating refrigerant is fed via a refrigerant line 2 through a reflux condenser 3 to a condenser 4 and from there in the liquid state it passes through a heat exchanger 5 via a refrigerant throttle 6 to an evaporator 7. The refrigerant which has been evaporated again and is now under low pressure fed in countercurrent through the heat exchanger 5 to a first absorber 8, which is referred to below as a low-pressure absorber.

A solvent line 9 leads from the cooker 1 through a temperature changer 10 and via a solvent throttle 11 to the first absorber 8, in which the refrigerant supplied via the refrigerant line 2 and the solvent supplied via the solvent line 9 are combined.

From the outlet 12 of the first absorber 8, a first return line 13, into which a feed pump 14 is switched on, leads to a branch 15. From this branch, a first line 16 leads in counterflow through the temperature changer 10 to the cooker 1, while a second line 17 the return cooler 3 is led to the cooker 1.

The parts of the absorption heat pump described so far correspond to the usual structure with branched return of the rich solution. According to the invention, in addition to the low-pressure absorber 8, a second absorber 18 is provided, which is referred to below as a high-pressure absorber. A by-pass line 19 leads into this high-pressure absorber, which feeds the solution from the cooker 1 directly to the high-pressure absorber 18, bypassing the temperature changer 10 and the solvent throttle 11.

A branch 20 is provided in the refrigerant line 2 downstream of the condenser; here, a bypass line 21 branches off from the refrigerant line 2, which either opens directly into the cooker or preferably according to the broken line in the high-pressure absorber 18. At the outlet 22 of the high-pressure absorber 18 there is a second return line 23, into which a second feed pump 24 is switched on. The second return line 23 opens directly into the cooker 1.

A completely closable metering valve 25 is located in the solvent line 9, and a completely closable metering valve 26 is likewise arranged in the by-pass line 19. Another fully closable metering valve 27 is switched into the bypass line 21.

A further fully closable metering valve 28 is located in the refrigerant line downstream of the branch 20.

Closing valves 29 and 30 are arranged in the return lines 13 and 23, respectively, and the outlet 22 of the absorber 18 is connected downstream of the closing valve 29 by means of a connecting line 31, in which a closing valve 32 is located.

A branch line provided with a closing valve 33 branches off from the by-pass line 19 to the first absorber 8; A further closing valve 35 is arranged in the by-pass line downstream of this branch.

A further connecting line 36, in which a closing valve 37 is arranged, connects the outlet 12 of the first absorber 8 to the inlet of the second absorber 18.

The two throttles 6 and 11 are adjustable in their throttling action, this is in the drawing indicated by a motorized actuator. These throttles can also be designed as expansion valves variable in volume flow.

Another possible configuration of the chokes results from the exemplary embodiment in FIG. 2, which differs from the exemplary embodiment in FIG. 1 only in the configuration of the chokes. Corresponding parts therefore have the same reference numerals.

In the exemplary embodiment in FIG. 2, the refrigerant throttle 6 comprises two parallel lines 38 and 39. In each of these lines, a closing valve 40 or 41 is connected in series with a throttle valve 42 or 43 with a fixed throttle effect.

In the same way, the solvent throttle 11 comprises two parallel lines 44 and 45, in each of which a closing valve 46 or 47 and a throttle valve 48 or 49 with a fixed throttle effect are switched on.

The heat pump shown in the drawing can be operated in three different ways, which are explained below.

In pure heat pump operation, the valves 26, 27, 30, 32, 33, 35 and 37 are closed, while only the valves 25, 28 and 29 are open. In this operation, the refrigerant evaporated by the cooker is supplied to the low-pressure absorber 8 through the refrigerant line 2 via the condenser, the refrigerant throttle and the evaporator. The poor solution passes from the cooker through the solvent line 9 through the temperature changer, the solvent throttle 11 also into the low pressure absorber. After the two components have been combined, the rich solution is fed back to the cooker via the first return line 13 and the two lines 16 and 17.

In the line routing described, the rich solution only penetrates the low-pressure absorber 8; the high-pressure absorber 18 is not switched into the circuit in this operating mode.

In an alternative mode of operation of pure heat pump operation, the valve 29 is closed while the valves 32 and 37 are opened. The rich solution then flows through the high-pressure absorber 18 before entering the first return line 13, so that heat can also be exchanged with the heating system in this high-pressure absorber.

In pure boiler operation, valves 25, 28, 29, 32, 33 and 37 are closed, while valves 26, 27, 30 and 35 are open. In this case, the refrigerant leaving the cooker passes via the bypass line 21 either directly into the cooker or into the high-pressure absorber 18. The refrigerant throttle and the evaporator are bypassed because of the closed valve 28.

The solvent passes via the by-pass line 19 directly into the high-pressure absorber 18, the temperature changer 10 and the solvent throttle 11 being bridged. In the high-pressure absorber, the heat is exchanged with the heating system, and the cooled solvent, to which the coolant, which is also cooled, is added, then reaches the cooker via the second return line 23. Since both the refrigerant choke and the solvent choke are bridged, the pressure in the entire circuit is the same as in the stove, i.e. a relatively high pressure. The pump 24 is therefore designed as a pure circulation pump, while the pump 14 is designed in the manner customary in absorption heat pumps as a pressure pump which has to work against the pressure in the stove.

In the mixed operation according to the invention, in which both a heat pump effect and a boiler effect are achieved, only the valves 32, 33 and 37 are closed, the other valves 25, 26, 27, 28, 29, 30 and 35 are open. This divides both the refrigerant flow and the solvent flow. Part of the refrigerant flow reaches the low-pressure absorber via the refrigerant line, the refrigerant throttle 6 and the evaporator 7, the other part of the refrigerant is supplied to either the cooker 1 or the high-pressure absorber 18 via the bypass line 21.

Part of the solvent reaches the low-pressure absorber 8 via the solvent line 9, the temperature changer 10 and the solvent throttle 11, the other partial flow flows directly to the high-pressure absorber 8 via the by-pass line 19. The poor solution emerging from the low-pressure absorber is returned to the cooker via the first return line 13 by the pump 14, the solution emerging from the high-pressure absorber 18, which is optionally mixed with refrigerant, returns to the cooker via the second return line 23 by means of the circulation pump 24 1.

Heat is exchanged with the heating system in the condenser and in both absorbers. In this case, the heating system in the condenser and in the high-pressure absorber is supplied directly with heat which comes from the heating of the cooker, while the heating in the low-pressure absorber is supplied with heat which is taken from the surroundings via the evaporator.

The ratio of the two partial refrigerant flows to one another and the ratio of the two partial solvent flows to one another can be adjusted continuously by a suitable choice of the opening of the valves 27 and 28 or 25 and 26 assigned to one another from pure heat pump operation to pure boiler operation. The throttling effect of the refrigerant throttle 6 and the solvent throttle 11 is to be changed in accordance with the size of the partial flow flowing through the throttles, so that the relaxation required for the heat pump effect occurs.

This can be done differently in the manner mentioned above, depending on the type of chokes 2, this throttling is achieved by opening or closing the closing valves 40 and 41 or 46 and 47 accordingly.

In order to be able to continuously control the described heat pump between the pure heat pump operation and the pure boiler operation, it is sufficient to continuously change the opening state of the valves 25 and 26 or 27 and 28 and to open or close the valves 29, 30 and 35. Furthermore, the throttling effect of the throttles 6 and 11 must be adjusted in accordance with the open state of the valves 25, 26, 27 and 28. No further changes are necessary.

Since the change can take place continuously between the two extreme operating states, the entire system can be optimally adapted to the external conditions, in particular it is possible at any time to choose a larger proportion of heat pumps and a lower proportion of the boiler in mixed operation or vice versa.

In the case of pure boiler operation, it would also be possible to additionally pass the solvent through the low-pressure absorber 8 in order to enable heat exchange with the heating system there as well. In this case, valve 35 is closed while valves 33 and 37 are opened.

In pure boiler operation, the throughput of both the refrigerant expelled from the cooker and the poor solution flowing from the cooker to the absorber is not controlled in a manner known per se by control valves with a variable throttle effect, but by a different pumping capacity of the circulation pump or pumps in the Return lines 13 and 23. For this purpose, these pumps can advantageously be of multi-stage or volumetric flow. The main advantage here is that there is no pressure drop in the line caused by controllable throttle valves, but the pressure level in the entire line system is approximately the same. To circulate the solution, therefore, only low pumping capacities are required, which are altogether significantly lower than those which had to be applied in conventional processes in which the throughput was achieved by different throttling of the flows.

This measure also avoids complicated control fittings that could give rise to faults. The control of the circulation pumps can be accomplished in the simplest way and can therefore be optimally adapted to the respective requirements.

Claims (12)

1. A method of operating a two-way operable absorption heat pump, in which, during heat-pump-only operation, the refrigerant expelled in the boiler is supplied via a liquefier, a refrigerant throttle, and an evaporator to an absorber, is combined there with a lean solution supplied from the boiler to the absorber via a temperature changer and a solvent throttle, and the resulting rich solution is supplied to the boiler via the temperature changer, and if required, via a reflux condenser for cooling the stream of refrigerant leaving the boiler, whereas during boiler-only operation the refrigerant expelled from the boiler on leaving the liquefier is supplied directly to the absorber, the lean solution from the boiler is supplied directly to the absorber, and the rich solution leaving the absorber is supplied directly to the boiler, characterised in that during mixed operation the stream of refrigerant leaving the liquefier and the stream of lean solution leaving the boiler are divided, a partial stream of refrigerant being supplied through the refrigerant throttle and the evaporator to a low-pressure absorber in which a partial stream of the lean solution is supplied via the temperature changer and the solvent throttle, whereas the other partial stream of refrigerant is supplied either directly to the boiler or to a high-pressure absorber which in both cases is directly supplied with the other partial stream of lean solution, and the rich solution from the low-pressure absorber is sent through the temperature changer and/or the reflux condenser whereas the solution from the high-pressure absorber is sent directly to the boiler.

2. A method according to claim 1, characterised in that during mixed operation the throttling action of the two throttles is made greater than during heat-pump-only operation.

3. A method according to claim 1 or 2, characterised in that during mixed operation the partial stream of refrigerant is sent through only part of the evaporator.

4. A method according to any of the preceding claims, characterised in that during mixed operation the gas flow cross-section of the evaporator is made less than during heat-pump-only operation.

5. A method according to any of the preceding claims, characterised in that during heat-pump-only operation the lean solution and the refrigerant are combined in the low-pressure absorber and the resulting rich solution is then conveyed through the high-pressure absorber.

6. A method according to any of the preceding claims, characterised in that during boiler-only operation the flow rate of refrigerant expelled from the boiler and the flow rate of lean solution flowing from the boiler to the absorber are not adjusted by means of throttle valves but are controlled by varying the delivery of the circulating pump or pumps conveying the rich solution leaving the absorber.

7. A two-way operable absorption heat pump for working the method according to claims 1 to 5, comprising a refrigerant line leading from a boiler to an absorber and containing a liquefier, a refrigerant throttle, and an evaporator in series, a solvent line supplying a lean solution from the boiler to the absorber via a temperature changer and a solvent throttle, a return line supplying the rich solution from the absorber to the boiler via the temperature changer and/or a reflux condenser for cooling the refrigerant expelled from the boiler, the return line containing a feed pump, a closable by-pass line through which the coolant leaving the liquefier outlet can be conveyed directly to the boiler or absorber so as to by-pass the coolant throttle and evaporator, and an additional closable by-pass line for supplying the lean solution directly to the absorber by-passing the temperature changer and the solvent throttle, characterised in that the absorber is divided into a low-pressure absorber (8) and a high-pressure absorber (18), the refrigerant line (2) coming from the evaporator (7) opens into the low-pressure absorber (8) and the by-pass line (21) opens into the boiler (1) or the high-pressure absorber (18), the solvent line (9) opens into the low-pressure absorber (8) whereas as the by-pass line (19) opens into the high-pressure absorber (18) a second return line (23) leads directly to the boiler (1) and comprises a second feed pump (24) and is connectable to the outlet (22) of the high-pressure absorber (18) whereas the first return line (13) is connectable to the low-pressure absorber (8), and on-off valves (25, 26, 27, 28, 30, 32) are disposed in the refrigerant line (2) after the branching-off (20) of the by-pass line (21), in the by-pass line (21), in the solvent line (9) after the branching-off of the by-pass line (19), in the by- pass line (19), and in both return lines (13 and 23).

8. A heat pump according to claim 7, characterised in that the throttling action of the throttles (6, 11) in the refrigerant line (2) and the solvent line (9) is variable.

9. A heat pump according to claim 8, characterised in that the throttles (6, 11) are expansion valves having a variable volumetric flow.

10. A heat pump according to claim 8, characterised in that the throttles (6, 11) comprise at least two parallel lines (38, 39: 44, 45) with throttle valves (42, 43 ; 48, 49), the parallel lines (38, 39 ; 44, 45) being openable alternately or together by on-off valves (40, 41 ; 46, 47).

11. A heat pump according to any of claims 7 to 10, characterised in that in heat-pump-only operation the high-pressure absorber (18) is insertable between the low-pressure absorber (8) and the first return line (13).

12. A heat pump according to any of claims 7 to 11, characterised in that the feed pumps (14, 24) are multi-stage or have a variable volumetric flow.

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