GB2073862A - Heat Actuated Heat Pump and Turbine - Google Patents

Abstract

A heating system comprises: (i) a power circuit (A) having a continuous flow path (10) for working fluid, a heater (14) for heating the working fluid at supercritical condition in one part of said circuit, a turbine (16) in the circuit arranged so as to be driven by the working fluid passing around the circuit, a condenser (20) in another part of the circuit for discharging heat from the working fluid, and a feed pump (22) downstream of said condenser to raise the pressure of the working fluid before it is returned to the heater; (ii) a heat pump circuit (B) having a continuous flow path (12) for a respective working fluid, and including an evaporator (24), a condenser (28) and a compressor (26) for the fluid, the compressor being arranged to be driven by said turbine (16), the turbine and compressor being mounted on a common rotor shaft (34) which is supported by gas bearings. A regenerator (18) is arranged to extract part of the sensible heat in the working fluid passing from the turbine (16) to said condenser (20) and transfer it to the working fluid passing from the condenser (20) to the heater (14). The system can provide a directly fired heat pump heating system of improved fuel efficiency, and other cost and operating advantages. The design of the turbine (Figs. 2 and 3) and the heater (Fig. 4) assist in providing these advantages. <IMAGE>

Description

SPECIFICATION Heat Actuated Heat Pump and Turbine and Fluid Heater Therefor This invention relates to heating systems. It is particularly applicable for providing space, water or other heating in buildings, especially domestic buildings, but may also be usefully employed in commercial and industrial buildings.

The heat pump has long been used in environmental temperature control, but primarily for "air conditioning". Its use in primary heating systems, while theoretically attractive, has in general encountered various practical problems and disadvantages. An electrically driven domestic heat pump has in general poor reliability, excessive noise, part load operation, and a negligible saving to the householder in energy costs when compared with conventional fossil fuel fired boilers. Electrical energy, as currently generated, has a fuel utilisation coefficient of only about 0.28 (i.e. for every unit of energy consumed in generating the electricity, only 0.28 units of electricity are available for use after generation and transmission losses). A conventional fossil fuel fired boiler has a fuel utilisation coefficient of about 0.7, and a unit gas heater about 0.75.The fuel utilisation coefficient of electricity can be dramatically improved by the use of a heat pump, since the coefficient of performance of a heat pump may be as high as 3, and this would then give an overall fuel utilisation coefficient of about 0.84. However, the equipment involved in an electrically driven heat pump is rather elaborate, requiring for example fans, pumps and electric defrost for the evaporator, and this makes a capital cost high and also reduces the overall fuel utilisation coefficient as a result of the power required to operate the ancillary equipment.

It is an object of the present invention to provide a directly fired heat pump heating system which is potentially capable of higher fuel utilisation coefficients than those indicated above, and has various other advantages as will be indicated below.

A heat pump for domestic installation should aim to provide the following features: a) a high level of reliability, with minimal maintenance operation; b) minimisation of lubrication or wear problems; c) minimal noise or vibration in operation; d) minimal pollution; e) potential for being powered by different fuels; f) high energy conservation potential to produce a short pay-back period; g) small physical size.

There are various methods of powering a domestic directly fired heat pump. The main methods are by internal combustion engine, external combustion engine and Rankine-type engines. The present invention adopts the latter type of prime mover, usiny a turbine in the power cycle to drive the compressor for the heat pump.

By mounting the turbine and compressor on a common rotor shaft, the prime mover need only have a single moving part.

The present invention provides a heating system comprising: (i) a power circuit having a continuous flow path for working fluid, a heater for heating the working fluid at supercritical condition in one part of said circuit, a turbine in the circuit arranged so as to be driven by the working fluid passing around the circuit, a condenser in another part of the circuit for discharging heat from the working fluid, and a feed pump downstream of said condenser to raise the pressure of the working fluid before it is returned to the heater; (ii) a heat pump circuit having a continuous flow path for a respective working fluid, and including an evaporator, a condenser and a compressor for the fluid, the compressor being arranged to be driven by said turbine, the turbine and compressor being mounted on a common rotor shaft which is supported by gas bearings.

Self-acting herringbone groove gas bearings around a circumferential part of the rotor, provide radial support, and suitably a blocked spiral groove gas thrust bearing or possibly externally pressurised gas thrust bearing provides axial support. A gas thrust bearing is preferably provided at the compressor end of the rotor, the turbine suitable being of a mixed axial and radial flow type with an axial shroud over the turbine blades. The power circuit preferably includes a regenerator arranged to extract part of the sensible heat in the working fluid passing from the turbine to said condenser and transfer it to the working fluid passing from said condenser to the heater.

Both the condenser in the power circuit and the condenser in the heat pump circuit can be used to provide heating, e.g. domestic space heating or hot water or both.

The working fluid is preferably the same in both the circuits, and preferred working fluids are chlorofluorohydrocarbons or pure fluorocarbons.

The heater preferably takes the form of a through passage for hot heating fluid and a conduit for the working fluid arranged in the passage so that over a final length of conduit leading up to its exit from the passage the working fluid therein will travel in the same general direction as that of the flow of the heating fluid, whereas in an earlier length of the conduit before said final length the working fluid will travel in a general direction opposite to that of the heating fluid. Said earlier length and said final length of the conduit are preferably arranged to occupy a common length of the passage, and the conduit preferably has a further preiiminary length thereof in another part of the passage in which the working fluid flows in a general direction opposite to that of the heating fluid.

In order that the invention may be more readily understood, a specific embodiment will now be described with reference to the accompanying drawings, wherein: Figure 1 shows diagrammatically the layout of the heating system, Figure 2 shows a perspective exploded view of the rotor carrying the turbine and compressor, Figure 3 shows diagrammatically a longitudinal cross-section through the turbine and compressor, Figure 4 shows diagrammatically a longitudinal cross-section view through the primary heater, and Figure 5 shows graphically the operation of the heater.

Referring firstly to Figure 1; the heater comprises a power circuit A and a heat pump circuit B, each comprising a continuous flow path 10, 12 respectively for working fluid.

The power circuit A comprises, in succession, a fluid heater 14, a turbine 16, the heat output side of a heat regenerator 18, a condenser heat exchanger 20, a feed pump 22 and the feed input side of the regenerator. The heat pump circuit comprises, in succession, an evaporator 24, a compressor 26, a condenser 28 and an expansion valve 30. The condensers 20, 28 of the two circuits are shown as being arranged to provide a sensible heat output to a domestic central heatinc circuit 32, but they could be arranged to supply other heating requirements.

The turbine 16 and compressor 26 are interconnected by a common rotor shaft 34, so that the turbine of the power circuit drives the compressor of the heat pump circuit. The turbine could also be used to power any other component such as an electric generator or pump.

In operation, the working fluid of power circuit A is heated by the heater 14, and passes at high temperature and high pressure to the turbine 16, where it experiences a pressure and temperature drop in driving the turbine. It then passes to the regenerator 18 where it gives up part of its sensible heat to the working fluid in a later part of the circuit about to return to the heater 14, thus preheating the working fluid. In between the two sides of the regenerator, the working fluid passes first through the condenser 20 where it gives up further heat in condensing, and from there it passes to a small feed pump 22 which raises the pressure of the condensed fluid to above its critical pressure so that there is no change in phase of the fluid as it passes through the regenerator 1 8 and heater 14.

In the heat pump circuit the compressor 26, driven by the turbine 16, compresses the working fluid, raising its temperature and pressure before it passes through the condenser 28, where it gives up heat to the circuit 32. The fluid then passes through the expansion valve 30 which cools the fluid so that it absorbs heat from the ambient environment as it passes through the evaporator 24. The evaporator is located in an environment which can provide external low grade energy, for example in the outdoor air or in a river.

Referring to Figures 2 and 3; this shows a preferred form of turbine/compressor for use in the system. The unit comprises a housing, generally indicated in Figure 3 at 36 in which is rotatably mounted the rotor shaft 34 carrying the compressor 26 at one end and the turbine 16 at the other end. As shown in Figure 2, the rotor and compressor can be made in a single piece, with a central stem 38 projecting from the rotor at the turbine end. The turbine blades 40 are provided around an end block 42 which is fitted onto the stem 38 after having first positioned on the stem a shroud 44 for the turbine blades. The block 42 and shroud 44 are secured on the stem 38 by a screw 46. The shroud is associated with a radially outwardly projecting disc 48 around which is provided a series of radial passages 50 which communicate with respective passages between the turbine vanes 40.The ends of the turbine vanes remote from the passages 50 are angled at 52 so that fluid passing along the inter-vane passages imparts a rotational movement to the turbine, as indicated by the arrow X in Figure 2.

The working fluid from the power circuit A is supplied through the housing 36 via an inlet port 54 leading to an annular distribution passage 56 in register with the passages 50 in the turbine disc 48. Fluid ernerging from the turbine vanes escapes through an outlet port 58 in the housing 36.

At the other end of the rotor 34, the compressor comprises a radially projecting disc 60, the face of which remote from the turbine is provided with a series of vanes 62, so that the compressor acts as a centrifugal impeller in compressing the working fluid of the heat pump circuit B. This working fluid enters the housing 36 through an inlet port 64, leading to annular distribution chamber 66 which communicates with the eye of the impeller, and the fluid leaves the periphery of the impeller through an annular diffuser passage 68 leading to an outlet port 70.

The impeller is of the open-face type, the vanes co-operating at close clearance with the adjacent surface 72 of the housing to define the inter-vane passages for the working fluid.

The rotor is rotatably supported by four bearings. Of these, one axial bearing is provided by the rounded head 74 of the screw 46 engaging a graphite bush 76 in the housing. This bearing only operates on start-up, since under normal running conditions the hydraulic effect from the compressor and turbine creates an axial thrust on the rotor towards the compressor end. At that end the other axial thrust bearing is provided by a blocked centre inward pumping spiral groove gas bearing. This takes the form of an end face 78 of the rotor which faces an end face 80 of a cooperating bearing member 82 in the housing. The two faces 78, 80 are accurately machined so as to be exactly parallel and provide little resistance against relative rotation. One of the faces (the face 80, for example, as illustrated) is formed with very shallow spiral grooves 84, which can for example be etched into the face. These grooves extend from the periphery of the face, but terminate short of the centre of the face. The curve of the grooves is arranged so that when the rotor rotates in its intended normal direction (arrow X) gas contained in these spiral passages between the two faces will be swept towards the block inward ends of the passages thereby forming a region of higher pressure at the centre between the faces which establishes a gas cushion between the faces. This thus provides a self-acting end thrust gas bearing for the rotor.It will be apparent that an alternative arrangement would be to have the spiral grooves blocked at their outer ends with a gas entry at the central region, and the shaft rotating so as to sweep the gas contained in the grooves towards their blocked outer ends. Alternatively an externally pressurised gas thrust bearing may be used instead of a self-acting gas bearing.

The length of rotor between the turbine and compressor is radially supported by two rotational gas bearings 86. The peripherai surfaces of this part of the rotor and the mating cylindrical surface of the housing are accurately machined to a small tolerance allowing the rotor to be freely rotatable within the housing. The surface of the rotor in the two bearing regions 86 is etched to provide a series of shallow V-shaped channels 88, of herringbone formation. These channels are arranged so that when the rotor rotates in the chosen direction (arrow X) fluid contained in the channels between the rotor and housing faces will be swept towards the apexes of the channels and there establish a region of relatively high gas pressure which provides, for each bearing, a circumferential gas cushion between the rotor and the housing.This, again, therefore gives a self-acting (hereingbone) gas bearing for the rotor. As with the end thrust gas bearing, the Vchannels could be formed in the housing face rather than the rotor face as shown, but the latter arrangement is likely to be move convenient to manufacture.

The principal advantageous features of this turbine/compressor can be described as follows.

The use of self-acting gas bearings for the rotor during normal running eliminates the need for any external gas pressure supply for the bearings, and eliminates the need for any lubricant. The bearings provide high load carrying capacity, with low starting torque. The bearings are easy to manufacture, aid provide high shaft stiffness and excellent control of running clearances. In particular, the herringbone bearings 86 prevent flexing or tilting of the shaft, thereby preventing undue leakages in the turbine or compressor which might result. The end thrust gas bearing provided by the faces 78, 80 establishes an accurate axial datum for the shaft during running, thereby allowing the clearance between the compressor vanes 62 and the mating face 72 of the housing to be kept to a minimum, particularly at the compressor tips.Thermal expansion of the rotor during running will not substantially affect the clearances around the compressor, which is near to the axial datum. The resulting small axial movement at the turbine end will not substantially affect the efficiency of the turbine since the blades 52 are shrouded by the sleeve 44, and the turbine is of the mixed axial-radial flow type; the greater part of the action of the gas on the turbine blades coming from its axial flow rather than its radial flow, and a labyrinth seal 90 being provided by an annular passage in the housing around the shroud sleeve 44 which alows axial movement of the shroud without affecting the seal between the sleeve and housing. Thus, the turbine is largely unaffected by small changes in the axial dimension of the rotor.By shrouding the turbine blades, running clearances are controlled and leakage losses are kept to a minimum, which is especially important with a small mass flow miniature turbine of this kind.

Furthermore, by using the same working fluid, (possibly fluorinated and fluorochlorinated hydrocarbons), in both circuits, the consequences of any leakage of fluid from one circuit to the other through the turbine/compressor are minimised.

Referring to Figure 4; this shows a preferred form of heater 14 for the power circuit. A generally cylindrical housing 92 has a burner 94 axially located at one end, with an air inlet 96 and a gas inlet 98. This provides hot combustion gases to a central plenum chamber 100 defined by a tubular inner wall 102. An intermediate tubular wall 104 is located between the wall 102 and housing 92 and is closed at its end 106 remove from the burner, thereby establishing a sepentine passage for hot gases from the plenum chamber 100 leading to an exhaust outlet 108 at the end of the housing remote from the burner.

Within the inner part 110 and outer part 112 of this serpentine passage is located a spirally formed conduit 114 for the power circuit working fluid. The conduit enters the housing at an inlet 11 6 at the exhaust end of the housing, passes spirally down the outer part 11 2 of the passage then spirally up the inner part 110 of the passage, reversing at the exhaust end of the plenum chamber 110 to pass again spirally down the inner part 110 of the passage and emerge from the housing at an outlet 118 adjacent the burner.

The operation of the heater can be illustrated with reference to the diagram in Figure 5. Hot combustion gases pass to the region C at the exhaust end of the plenum chamber. They then pass over the conduit coils 114, down the inner part 110 of the passage to the region D adjacent the burner, before turning into the outer part 11 2 of the passage, along which the steadily cooling gases pass, over the conduit coils 11 4, to the exhaust region E. The power circuit working fluid entering through the inlet 11 6 first encounters the heat from the burner gases in the exhaust region E, and is gradually preheated as it passes first down the part 112 of the passage to the region D adjacent the burner, and then up the part 110 of the passage to the region C.There it encounters the maximum temperature of the burner gases, but the working fluid continues to increase in temperature as it reverses back down the part 110 of the passage until it reaches its maximum temperature at the outlet 118 in the region D. The graph of Figure 5 shows how the temperature of the working fluid rises steadily from region E, at which it is at temperature To close to the exhaust temperature T4 of the combustion gases, to a somewhat higher temperature T, as it first passes through region D, then to a higher temperature T2 as it reaches region C, and then to a final high temperature T3 as it once again comes back into region D.At region D the temperature T5 of the combustion gases is higher than either of the working fluid temperatures T,, T3 at that point, but the characteristic feature of this arrangement is that the temperature T2 of the working fluid in the region C where it meets the combustion gases at their maximum temperature T6 is rather lower than the final temperature T3 of the working fluid.

This means that the working fluid at the region C still has some way to heat up, and hence there is less risk of the fluid being overheated at this critical region, and the working fluid does not reach its maximum temperature T3 until region D, by which time the temperature of the combustion gases has been considerably reduced (to T,). As well as providing a safety factor, the conduit arrangement within the inner part 110 of the passage, where it will be seen that the general direction of travel of the working fluid (as opposed to its circular movement) is first in contra-flow to the combustion gases and then in parallel flow to those gases, provides a closer control of the final temperature of the gases as compared with the more conventional simple contraflow arrangement (as present in the outer part 112 of the passage).This type of heater represents a very compact design with high thermal efficiency.

The invention is not limited to the use of heaters of the type shown in Figure 4, nor indeed to the use of gas as a fuel. The heating system generally described above can be used with other forms of heat source for the power circuit, and the power circuit can be used for production of shaft power for purposes other than driving of a heat pump, or for other purposes in addition to driving a heat pump, for example by connecting to the same turbine shaft a high speed alternator to produce electric power for the ancillary equipment used with the system, and for driving the feed pump in the power circuit.The invention therefore also includes a turbine comprising a shaft rotatably mounted in a housing, a turbine assembly carried by the shaft having vanes arranged to provide a mixed axial and radial flow of driving fluid, and having a shroud over the turbine vanes apertured to receive the driving fluid from an inlet in the housing and to deliver it radially to the turbine vanes, and to extend axially over the vanes to close circumferentially the axial intervane passages along which the fluid flows to drive the turbine. The shroud suitably comprises a radially projecting disc having a series of radial passages along which the driving fluid flows to respective intervane passages in the turbine assembly. The shaft is preferably supported radially in the housing by a self-acting gas bearing, suitably of herringbone groove type. The shaft may also be supported axially by a gas bearing, suitably a self-acting blocked spiral groove gas bearing, suitably at the end of the shaft remote from the turbine assembly.

Claims (12)

Claims

1. A heating system comprising: (i) a power circuit having a continuous flow path for working fluid, a heater for heating the working fluid at supercritical condition in one part of said circuit, a turbine in the circuit arranged so as to be driven by the working fluid passing around the circuit, a condenser in another part of the circuit for discharging heat from the working fluid, and a feed pump downstream of said condenser to raise the pressure of the working fluid before it is returned to the heater; (ii) a heat pump circuit having a continuous flow path for a respective working fluid, and including an evaporator, a condenser and a compressor for the fluid, the compressor being arranged to be driven by said turbine, the turbine and compressor being mounted on a common rotor shaft which is supported by gas bearings.

2. A heating system according to claim 1 wherein circumferential self-acting herringbone groove gas bearings provide radial bearing support for the rotor.

3. A heating system according to claim 1 or claim 2 wherein a blocked spiral groove gas thrust bearing provides axial bearing support for the rotor.

4. A heating system according to any of claims 1, 2 and 3 wherein a gas thrust bearing is provided at the compressor end of the rotor.

5. A heating system according to claim 4 wherein the turbine is of a mixed axial and radial flow type with an axial shroud around the turbine blades.

6. A heating system according to any one of the preceding claims wherein the power circuit includes a regenerator arranged to extract part of the sensible heat in the working fluid passing from the turbine to said condenser and transfer it to the working fluid passing from the condenser to the heater.

7. A heating system according to any one of the preceding claims wherein both the condenser in the power circuit and the condenser in the heat pump circuit are used to provide a useful heat output from the system.

8. A heating system according to any one of the preceding claims wherein the working fluid is the same in both circuits.

9. A heating system according to any one of the preceding claims wherein the heater takes the form of a through passage for hot heating fluid and a conduit for the working fluid arranged in the passage so that over a final length of conduit leading up to its exit from the passage the working fluid therein will travel in the same general direction as that of the flow of the heating fluid, whereas in an earlier length of the conduit before said final length the working fluid will travel in a general direction opposite to that of the heating fluid.

10. A heating system according to claim 9 wherein said earlier length and said final length of the conduit are arranged to occupy a common length of the passage.

11. A heating system according to claim 10 wherein the conduit has a further preliminary length thereof in another part of the passage in which the working fluid flows in a general direction opposite to that of the heating fluid.

12. A heating system substantially as described herein with reference to the drawings.