GB2305235A

GB2305235A - An ejector device for use in a heat pump

Info

Publication number: GB2305235A
Application number: GB9519012A
Authority: GB
Inventors: Trevor Ward
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-09-16
Filing date: 1995-09-16
Publication date: 1997-04-02
Also published as: GB9519012D0

Abstract

A heat pump comprising a closed circuit including an evaporator (17) and a condenser (13) and containing a refrigerant fluid, includes means causing circulatory flow of fluid in the circuit, wherein said means for causing flow of fluid includes an ejector device (12). Refrigerant liquid from a receiver (14) is pumped via a pump (15) to a vapour generator (11). Refrigerant fluid is expanded in the ejector nozzle to a high velocity and low pressure, inducing fluid from the evaporator. The heat pump system may include a compressor, the ejector only operating at peak loads, or vice-versa. The heat pump may operate in cascade with a refrigeration system or a second ejector-driven heat pump circuit. The heat pump may use two refrigerant fluids which are immiscible with one another.

Description

Title: HEAT PUMPS Description of Invention This invention relates to heat pumps. Heat pumps in accordance with the invention may be utilised wherever transfer of heat energy from one or more positions or locations to one or more other positions or locations is required, whether such transfer of energy is for the purposes of providing a heating or cooling effect. For example, the invention may find application in refrigeration systems, air conditioning systems, or heating systems, or any combination thereof.

More particularly, the invention relates to a heat pump of the kind comprising a closed circuit in which heat energy is taken up by a refrigerant fluid in an evaporator and released by such fluid in a condenser, the fluid being caused to circulate between the evaporator and condenser so that it carries the heat energy therebetween.

Most known heat pumps of this type utilise a compressor to cause the refrigerant fluid to flow in the circuit. The external energy input which causes the heat pump to operate is by way of an electric motor or some other form of motor driving the compressor, but compressors generally are complex, expensive and bulky devices and represent a potential source of failure in the heat pump.

Heat pumps are known, and commonly used in refrigerators, of the absorption system type. They utilise ammonia and water as operating fluids, but have the disadvantage that they are relatively inefficient and ammonia is corrosive and toxic.

It is broadly the object of the present invention to provide a heat pump in which one or more of these disadvantages are overcome or reduced.

According to the present invention, I provide a heat pump comprising a closed circuit including an evaporator and a condenser and containing a refrigerant fluid, and means for causing circulatory flow of said fluid in the circuit, wherein said means for causing flow of said fluid includes an ejector device. The ejector device may utilise a portion of said refrigerant fluid as a driving fluid to cause flow of the rest of said refrigerant fluid, or may utilise another fluid as a driving fluid.

When it is a portion of the refrigerant fluid which constitutes the driving fluid of the ejector, it is preferably derived from the condensed refrigerant fluid (following the condenser in the circuit) by a pump and a vapour generator (boiler) which has an input of heat energy from an external source.

Where it is another fluid which is utilised as the driving fluid for the ejector, it is preferably provided to the ejector, under conditions suitable for its utilisation as a driving fluid, by a pump and a vapour generator which has an input of heat energy from an external source.

The amount of external energy required to pump the refrigerant or other fluid in liquid form to the vapour generator is relatively low, and the input of thermal energy into the vapour generator to cause evaporation of the refrigerant fluid to drive the ejector can be derived from a relatively low grade heat source, e.g. thermal energy, e.g. a solar energy collector, or the like, although it will be appreciated that the energy input could be provided by an electrical heater or a fuel-burning heater.

In referring herein to an ejector, I intend to include all fluid flow pumping devices wherein flow of a fluid is used to induce flow of the same or another fluid. For example, there are fluid flow pumping devices utilising the coanda effect, and such devices are intended to be within the scope of the term "ejector".

These and other features of the invention will now be described by way of example with reference to the accompanying drawings, of which Figures 1 to 8 show diagrammatically different embodiments of heat pump in accordance with the invention. In all the embodiments described hereafter, corresponding components of the heat pumps are identified by the same reference numerals throughout.

Referring firstly to Figure 1 of the drawings, this illustrates diagrammatically a heat pump whose principal operative components are a vapour generator or boiler 11, an ejector 12, a condenser 13, a receiver 14 for liquid refrigerant, a pump 15, an evaporation control valve 16, and an evaporator 17.

These components are connected in a closed system of suitable pipes or the like, the entire system containing a refrigerant fluid of a type which is readily evaporated and condensed under the conditions pertaining at different parts of the system.

The normal directions of flow of the refrigerant fluid in the system are as shown by the arrows drawn on the lines connecting the above described components and representing the appropriate pipework. The mode of operation of the illustrated heat pump is that a proportion of the refrigerant fluid is drawn from the receiver 14 by pump 15 and fed to the generator 11. Heat energy from an external source is supplied to the fluid in the generator, which causes evaporation thereof at a relatively high temperature and pressure. Such vapour forms the driving fluid for the ejector 12. The ejector is a device of well known type in which the driving fluid is expanded in a nozzle to flow at a high velocity and hence a low pressure, which causes it to induce flow of a (possibly relatively great) quantity of fluid (in the present case vapour) at relatively low pressure.

The mixture of the driving fluid and the entrained fluid pass through a diffuser which decreases the velocity of flow and increases the pressure thereof.

The liquid refrigerant fluid from the reservoir 14, which is not fed by the pump 15 to the generator 11, passes through an evaporation control valve 16 and an evaporator 17. Evaporation of the fluid takes place in the evaporator 17 and takes in heat energy.

After the ejector 12, the entire quantity of refrigerant fluid therefrom passes to the condenser 13 in which it is condensed and gives up heat energy.

Thus the system transfers heat energy from the evaporator 17 to the condenser 13, the external energy input being that required to drive the pump 15 and that required for the generator 11.

The pump 15 may be of a type which, instead of being driven by a separate external energy input, is driven by the refrigerant fluid at a position in the system at which its temperature and pressure conditions render it suitable for such usage. For example, some refrigerant fluid may be taken from a position between the generator 11 and ejector 12 for pump driving, after which it is returned to the system downstream of the ejector. The pump may be, for example, of a reciprocating type or a rotary type with appropriately dimensioned driving and pumping sections to enable it to feed the refrigerant fluid to the generator 11 at the required pressure.

Referring now to Figure 2 of the drawings, this shows a heat pump in which a system as above described is combined with a conventional compressor driven system. The combined system comprises the components above described in relation to Figure 1, but with the addition of a shut-off valve 19, a compressor 18, and check valves 20, 21. From the evaporator 17, refrigerant fluid is able to flow to the condenser 13 either by way of check valve 20 and ejector 12 or by way of compressor 18 and check valve 21.

Circulation of the refrigerant fluid in the system can thus be provided by the ejector 12 and/or the compressor 18. The compressor can have its size determined to suit normal operating conditions, and the ejector can be brought into operation additionally if peak loads require a greater flow of the refrigerant fluid to be provided. Alternatively, the ejector can provide for operation under normal conditions and the compressor can be brought into operation for peak loads. The ejector may be operated when a suitable energy input for the generator 11 is available, for example from solar radiation during daytime, whilst the compressor can be operated when such energy is not available, e.g. at night.

Because of the simplicity and robustness of an ejector, it can be used as a back-up system should the compressor fail, for example if the heat pump forms part of a refrigeration system for, for example, a sea container.

When the compressor 18 is not in operation, check valve 21 prevents refrigerant fluid from condensing in the compressor. When the ejector is not in operation, the shut off valve 19 is closed and the check valve 20 remains closed.

For control purposes, valve 19 may be a solenoid-operated valve and valve 20 may also be controlled by a solenoid to cause it to remain closed or be allowed to be opened by differential pressure across the valve.

Referring now to Figure 3 of the drawings, this shows a heat pump in which the system as above described with reference to Figure 1 is used in combination with a compressor-driven heat pump. In the upper part of Figure 3, a heat pump is shown as in Figure 1 with the components thereof identified by the same reference numerals as in Figure 1, whilst in the lower part of Figure 3 there is shown the compressor-driven heat pump. This latter comprises a compressor 18 condenser 22, receiver 23 for condensed refrigerant fluid, expansion valve 24, and evaporator 25, all forming a conventional compressordriven heat pump. The evaporator 17 of the ejector-driven heat pump and the condenser 22 of the compressor-driven heat pump are disposed in heat-transfer relationship to one another.

The system shown in Figure 3 transfers heat from the evaporator 25 to the adjacent condenser 22 and evaporator 17, and thence to the condenser 13.

The ejector-driven heat pump may work at an higher average temperature than the compressor-driven heat pump, and different refrigerant fluids may be used in the two heat pumps to suit the conditions pertaining thereto.

If the compressor-driven heat pump is to be run without the ejectordriven heat pump, then an additional condenser (not shown) could be introduced into the compressor heat pump circuit, in parallel with the condenser 22 and could be isolated when the ejector-driven heat pump is in operation.

The system shown in Figure 3 may advantageously be utilised under conditions where for some part of the time when the system is in use there is an increased demand on the performance of the system and potentially a reduced capacity of the system. For example, during daylight hours there is an increased demand on the performance of refrigeration plant for a refrigerated warehouse, because of solar radiation and increased ambient temperature, whilst the capacity of refrigeration plant is decreased due to the higher condensing pressure of the refrigerant also resulting from the increased ambient temperature.

By coupling an ejector-driven heat pump with a conventional compressor-driven heat pump system as shown in Figure 3, the condensing temperature and hence pressure of the compressor-driven heat pump can be reduced, and thus its capacity increased. At the same time, the ejector-driven heat pump can be driven primarily by solar radiation so that the need for large external energy inputs is reduced.

Referring now to Figure 4 of the drawings, this shows a system combining ejector-driven and compressor-driven heat pumps, but different from that of Figure 3 in that the ejector-driven heat pump is the low temperature stage and the compressor-driven heat pump the high temperature stage. The evaporator 25 of a compressor-driven heat pump and the condenser 13 of the ejector-driven heat pump are disposed in heat transfer relationship with one another.

Figure 5 of the drawings shows a system which is generally similar to that of Figure 4 but with the additional feature that in parallel with the condenser 22 of the compressor-driven heat pump there is a further condenser 30 in heat transfer relationship with the generator 11 of the ejector-driven heat pump. Thus some or all of the input of heat energy required by the generator 11 may be derived from condensation of the refrigerant fluid in the compressor-driven heat pump circuit.

By operatively connecting the compressor-driven heat pump with an ejector-driven heat pump, using appropriate refrigerant fluids, the effective temperature range of the combined system can be increased farther than can be effectively achieved by use of a single type of heat pump only.

Referring now to Figure 6 of the drawings, this shows a heat pump which utilises two ejector-driven heat pump circuits arranged for heat transfer therebetween. The entire heat pump comprises two circuits each as shown in Figure 1 and with their components identified by the same reference numerals as used in Figure 1. The components are identified by the suffices "A" and "B", the latter components being in a circuit which operates at a lower temperature than the circuit whose components are identified by the suffix "A". The generator 1 1B of the low temperature circuit has its heat input derived wholly or partly from a part of the condenser 13A of the high temperature circuit, while the condenser 13B of the low temperature circuit is in heat transfer relationship with the evaporator 17A of the high temperature circuit.

Different refrigerant fluids may be used in the two circuits of the heat pump, to suit the temperature conditions prevailing therein.

It would be possible for more than two heat pump circuits to be arranged for heat transfer between them to provide a multiple stage heat pump system. An ejector-driven heat pump or pumps in accordance with the invention may be combined with heat pumps of other types. This may be done in order to provide a higher efficiency than can be attained in a single stage heat pump, for a given temperature range of operation. By appropriate selection of refrigerants, the operating temperature range of such a combined system may be extended, for example to refrigerate to very low temperatures.

Referring now to Figure 7 of the drawings, this shows a heat pump wherein two refrigerant fluids which are immiscible with each other are used.

One fluid is used as the driving fluid for the ejector whilst the other fluid is used to take up heat energy in an evaporator and to give up the heat energy in a condenser, circulation of such other fluid being induced by the ejector.

In Figure 7, the arrangement of the heat pump is analogous to that shown in Figure 1 but there are two condensers 13C, 13D and two receivers 14C, 14D. The two refrigerant fluids used are selected so that they condense at different temperatures, and in condenser 13C the first refrigerant fluid which has the higher temperature of condensing is condensed and collected in receiver 14C.

This refrigerant is fed by pump 15 to the generator 11 to act as the driving fluid for the ejector 12. The second refrigerant which has a lower condensing temperature passes through the condenser 13C without being condensed and passes into the condenser 13D where it is condensed at a lower temperature.

This refrigerant is collected in the receiver 14D and fed back to the evaporator 17 by way of the valve 16.

The first refrigerant fluid, which has a higher condensing temperature than the second refrigerant fluid is selected with the characteristic of a lower latent heat of vaporisation, than the other refrigerant, taking into account the entropy values and the vapour volumes/densities when the fluids mix in the ejector, thus potentially increasing the efficiency of the system.

Referring finally now to Figure 8 of the drawings, this shows a system which like that shown in Figure 7 uses two immiscible refrigerant fluids, which condense at different temperatures. In this embodiment, however, the refrigerant which condenses first (at a higher temperature) passes to receiver 14E and thence by way of a further cooler 31 and expansion valve 16 to evaporator 17. The other refrigerant which is still a vapour when it leaves condenser 13E passes to a further condenser 13G and thence to receiver 14G and, by way of pump 15, to generator 11, to be used as the driving fluid for ejector 12.

Heat pump systems as above described may be operable with refrigerant fluids of the type which generally are usable in conventional systems, a suitable refrigerant fluid for any particular system being decided upon in accordance with the conditions prevailing in the system. For example, commercially available refrigerant fluids such as R123, R124, R134A, R600A, may be suitable.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1. A heat pump comprising a closed circuit including an evaporator and a condenser and containing a refrigerant fluid, and means for causing circulatory flow of fluid in the circuit, wherein said means for causing flow of fluid includes an ejector device.

2. A heat pump according to Claim 1 wherein the ejector device utilises a portion of said refrigerant fluid as a driving fluid for the ejector device, to cause flow of the rest of said refrigerant fluid.

3. A heat pump according to Claim 1 wherein the ejector device utilises another fluid as a driving fluid to cause circulation of said refrigerant fluid.

4. A heat pump according to any one of the preceding claims comprising a compressor arranged to cause flow of said refrigerant fluid, said compressor being operable as an alternative or an addition to said ejector.

5. A heat pump according to Claim 2 or Claim 4 as appendant thereto wherein said portion of the refrigerant fluid is derived from the condensed refrigerant fluid by a pump and a vapour generator which has an input of heat energy from an external source.

6. A heat pump according to Claim 3 or Claim 4 as appendant thereto wherein said further fluid is provided to the ejector by a pump and a vapour generator which has an input of heat energy from an external source, said further fluid having been separated from said refrigerant fluid.

7. A heat pump according to Claim 5 or Claim 6 wherein said input of heat energy is derived at least partially by condensation of said refrigerant or other fluid.

8. A heat pump according to claim 5 or claim 6 wherein said input of heat energy is derived at least potentially from solar radiation.

9. A heat pump according to Claim 7 wherein said refrigerant fluid or other fluid is contained in said closed circuit or another closed circuit.

10. A heat pump comprising a heat pump according to any one of the preceding claims and at least one further heat pump, elements of said heat pumps being in heat transfer relationship with one another.

11. A heat pump substantially as hereinbefore described with reference to any one of the accompanying drawings.

12. Any novel feature or novel combination of features described herein and/or in the accompanying drawings.