GB2045906A - Heat pumps - Google Patents

Abstract

A heat pump system comprising a single evaporator system (20) in association with a plurality of condenser units (21) for heating a space or spaces, the evaporator system being arranged to take up heat from ambient air or the ground. A condenser is described comprising a coil over which the air to be heated is directed through successive portions of the coil in the direction of flow of heat exchange medium, a first portion containing superheated vapour, a second portion containing condensing vapour and a third portion containing condensed liquid. <IMAGE>

Description

SPECIFICATION Heat pumps This invention relates to various aspects of heat pumps for use in space and other heating applications.

It is an object of the present invention to provide an improved heat pump system for such application.

In one aspect the invention provides a multi-point heat pump system in which a plurality of condenser units are provided to give up heat into various spaces to be heated, operative with a common evaporator unit arranged to take heat either from the ambient air, or from the ground.

In another aspect the present invention provides an expansion device for use in such a heat pump system, or in other heat pump systems, in which the expansion is controlled in accordance with the temperature immediately upstream of the expansion device, a temperature drop at that point causing the expansion device to reduce the flow of heat exchange medium.

According to a further aspect the present invention provides a flooded evaporator for use in heat pump systems.

According to a further aspect the invention provides a condenser for use in heat pump systems.

According to a further aspect the invention provides a collection and distribution device for use in a multipoint heat pump system.

According to a further aspect the present invention provides a centrifugal oil separator for use in a heat pump system.

According to a further aspect the present invention provides a de-humidifier system utilising a heat pump.

In order to promote a fuller understanding of the above and other aspects of the present invention, some embodiments will now be described by way of example only, with reference to the accompanying drawings, in which Figure 1 shows an overall schematic diagram of a multi-point heat pump system, Figure 1a shows a schematic diagram of one of the room units of the system of Figure 1, Figure 2 shows a collection and distribution vessel for the system of Figure 1, Figure 3 shows an oil separator for use in the unit of Figure 1a, Figure 4 shows a schematic cross-section of an evaporator construction, Figure 5 shows a similar view to that of Figure 4 of the evaporator in Figure 1, Figure 6 shows in schematic outline a condenser for the unit of Figure 1 a, Figure 7 shows a detailed construction of a condenser of Figure 6, Figure 8 shows an alternative construction of the condenser of Figure 6, and Figure 9 shows in schematic outline a further heat pump system.

Referring first to Figures 1 and 1 a, there is shown in schematic outline a heat pump system for domestic or industrial room heating. The system includes an evaporator indicated generally at 20 which is arranged to be positioned outside the space to be heated in ambient air, and a plurality of condenser units indicated generally at 21, and which is shown in more detail in Figure la. The system also includes an accumulator arrangement indicated at 22 and a distributor and collection unit indicated generally at 23.

Each condenser unit 21 comprises a condenser coil 30 with an associated fan unit 31 arranged to derive room air through the coil 30. Connected between an inlet line for heat exchange medium indicated at 32 and the evaporator coil 30 is a compressor unit 33 which is of conventional designperse.

An oil separator unit 34 is also provided on the output line from the compressor. The outlet side of the condenser coil 30 is connected by way of a heat exchanger 35 on the inlet line 32 to an outlet 36 from the unit 21. The inlet line 32 and the outlet line 36 of the condenser units 21 are all connected respectively to a suction vapour line 40 and a liquid return line 41 indicated in Figure 1, these lines preferably being arranged one inside the other to effect heat exchange from the liquid return line to the suction vapour line.

The return line continues through a heat exchanger 42 in the accumulator 22, then through either or both of two expansion devices 43 according to the setting of flow control valves 44 and 45 through either or both arms 46 and 47 of the evaporator 20 back to the accumulator 22 through a line 48. A fan unit 49 is provided to drive external ambient air through the evaporator 20.

The accumulator 22 is of conventional designper se, with the line 48 leading into a vapour space 50 in the top of the accumulator. The vapour suction line 40 is connected by way of a U-tube 51 also to the vapour space 50. Liquid heat exchange medium collects in the bottom of the accumulator and the heat exchanger 42 is positioned to fall in the collected liquid. The U-tube 51 is perforated as indicated at 52 so that a small quantity of liquid medium is drawn out through the U-tube.

The collection and distribution device 23 is shown in more detail in Figure 2. The device 23 comprises an annular outer chamber 60 arranged around an inner chamber 62. The inner chamber 62 is connected at the top of the outlet line 36 of the unit 21 connected to the system. Thus liquid heat exchange medium collects as indicated at 63 in the bottom of the chamber, and the liquid return line 41 is arranged to extend into the chamber 62 to the bottom thereof to collect such liquid. The outer chamber 60 is provided with a series of U-tubes 64 each arranged to connect the upper part of the chamber 60 to a respective inlet line 32 of a condensing unit 21.The U-tubes 64 extend down through the bottom of the chamber 60 and are perforated at that point as indicated at 65 to draw a small amount of liquid heat exchange medium which collects in the bottom of the chamber 60 with the vapour passing to the units 21, and also to draw a small amount of oil in with such vapour, the oil being that which is provided in the system in known mannerperse for lubricating the compressors 33, and which in operation tend to collect in the bottom of the chamber 60.

As mentioned above, the evaporator 20 comprises two banks 46 and 47, flow through which is controlled by the valves 44 and 45, according to the heat demand at any given time and the number of units 21 which are operational. Thus if a greater heat demand is present both the valves 44 and 45 would be open so that both banks of the evaporator were brought into operation. The expansion devices 43 are arranged to be temperature responsive under the control of temperature sensing elements 43a positioned on the pipeline immediately upstream of them. The devices 43 are arranged so that a temper azure drop sensed by the detectors 43a causes the valve to close and vice versa. The devices 43 may be of a type which has a bleed passage which remains open when they are fully closed, or they may be short-circuited by a capillary bleed passage indicated at43b.

Figure 4 shows in schematic outline one bank 46 of the evaporator 20. The bank comprises an upper header 70 and a lower header 72. Extending between the headers are a series of heat exchange tubes 73 of which only one is shown. The tubes 73 are provided with fins 74 in known mannerperse. The evaporator is arranged to operate it in the flooded mode and in order to reduce the total volume of heat exchange medium in the system, while not affecting the performance of the evaporator, the tubes 73 are each provided with a core 75 to leave only a small annular space for the flow of heat exchange medium. The lower header 72 is provided also with a hollow core 76 arranged to receive an electrical heating element 77 for defrosting purposes.It is to be noted that the provision of the heating element in the bottom header 72 provides for extremely efficient defrosting since heat is conducted from the elements 77 by convection up the tubes 73. It is to be noted further that the provision of the core 75 in the tubes 73 also enhances the velocity of flow through the evaporator improving heat exchange and ensuring that lubricating oil in the heat exchange medium does not collect and remain in the evaporator.

Figure 5 shows in very brief outline how the two banks of the heat exchanger 20 may be arranged in a housing 80 with a single fan 81 provided in the top of the housing through the circulation of air through the banks 46 and 47. Louvres can be arranged in the housing 80 to ensure the correct air flow through the banks.

Figure 6 shows in schematic detail the condenser coil 30 of a condensing unit 21. Heat exchange medium flows as compressed vapour from the compressor 33 to the inlet end 90 of the coil 30 and out through the outlet end 91. The vapour is superheated at the entry 90 and through the initial portion 91 of the coil cools without condensation. Through the next portion 92 condensation takes place, and finally through the last portion 93 the condensed liquid is sub-cooled before passing back to the accumulator via the heat exchanger 35 and the device 23.

The bulk of the heat given out by the heat exchange medium in the condenser 30 is of course during condensation in the portion 92, and this in a typical arrangement takes place at 105"F. In the condenser of this embodiment of the invention, advantage is taken of the heat available in the superheated vapourto provide a higher output air temperature than would be possible normally for a given condensation temperature. As shown in Figure 7, the various portions of the condenser coil 30 are arranged in the air flow so that the air passes first through the portion 93, then through the portion 92 and finally leaves via the portion 91 of the coil 30.

Thus the air is pre-heated in the portion 93 taking heat from the condensed heat exchange medium, receives the bulk of its heat from the condensing heat exchange medium in the portion 92, and is finally raised to a temperature which can approximate that of the condensing vapour, in the portion 91 by taking thesuper-heatfrom the vapour.

This arrangement is in contrast to prior art systems in which the condenser coil 30 is not arranged in the above fashion, but the air flows indiscriminately through the whole condenser coil. This arrangement enables the ultimate utilisation of the heat available in the compressed vapour.

Figure 8 shows an alternative arrangement of the condenser 30 which in construction is generally similar to the evaporator shown in Figure 4. However in order to guide the air flow through the condenser coil so that it passes over the various parts of the coil in the required sequence, a series of baffles are arranged around the fins associated with the tubes so that the air is confined to flow from an inlet to an outlet end over the various parts of the coil as discussed above.

Figure 3 shows in schematic cross-section an oil separator unit for use in the condenser units 21. The separator shown generally at 34 comprises a cylindrical chamber which a tangential inlet passage 100 and an axial outlet passage 101. The arrangement is such that the vapour entering the separator from the compressor via the passage 100 is caused to swirl around the interior of the passage before leaving through the outlet 101 to the condenser 30. About mid-way along the passage an oil collecting gallery 102 is provided covered buy a gauze ring 103. In opera ation the oil carried with the vapour is separated by centrifugal action to be spread out on the surface of the chamber thus to collect in the gallery 102 and be lead back to the compressor via a line 104.

The general mode of operation of the heat pump system described above is in broad principle similar to conventional heat pumps. The heat exchange medium which is a suitable refrigerant gas is circu lated through the system with a cycle of compression release of heat, expansion absorption of heat and recompression. Each individual condenser unit 21 is provided with its own compressor unit to draw vapour from the accumulator 22 as described above.

The fan motor 31 and compressor 33 of each con denser unit is provided with a room thermostat control so that the unit is brought into operation to heat a particular space as required. Vapour is drawn into the condenser unit 21, compressed to raise its energy level, and is then passed through the con denser coil to give up its super-heat, its latent heat, and some of its sensible heat content as described above in the condenser coil 30. Further heat is extracted from the condensed liquid medium in the heat exchanger 35, and put back into the incoming vapour. Liquid heat exchange medium is carried via the device 23 through the heat exchange coil 42 in the accumulator where it gives up further heat to collected liquid heat exchange medium in the accumulator.It passes from the heat exchanger 42 through an expansion device 43, to the evaporator coil 20 where heat is taken in from the ambient atmosphere and a mixture of vapour and liquid passes to the accumulator 22. The control of the expansion devices 43 is such that as the liquid level in the accumulator rises, a greater part of the heat exchanger 42 becoming covered so that more heat is extracted into the liquid in the accumulator with the result that the temperature of the liquid reaching the expansion device is lower, the temperature sensing device 43a causes the expansion device 43 to close.

In this fashion the level of liquid in the accumulator is controlled according to the demand upon the system.

As discussed above each condenser unit 21 drawn vapour from the accumulator via the distribution device 23.

In a typical system such as that shown in Figure 1, the medium leaves the evaporator at a temperature of some 20"F and enters the compressors of the condenser units 21 at some 40"F having passed through the accumulator and the line 40. This charged temperature from the compressor would be of the order of 140 to 1700F with as mentioned above, a condensation temperature in the condenser of 105 F. The liquid medium would leave the outlet of the con denser coil at some 80 F and enter the accumulator having given up heat during passage down the line 41 at some 60 F. Heat exchange within the accumulator would reduce the temperature of the liquid medium to some 32"F at the entry to the expansion device. Evaporation in the evaporator 20 would take place at some 20"F.

In a preferred arrangement the evaporator coil is positioned on the building to experience incidence solar radiation. The evaporator coil is housed in a suitably transparent housing to allow sunlight to fall on it and also to allow ambient air to circulate through it. Because of the low temperature of the evaporator, incidence sunlight is more or less totally absorbed with very efficient utilisation of incidence solar energy.

It is anticipated that the overall co-efficient of performance of the system that is to say heat released to space to be heated, divided by the heat equivanent of input power to the various electrical items for operation of the system can be in the range of 2.5 to 4.5 to 1 in typical British weather conditions with an overall seasonal average of 3.3 to 3.75. The expansion device is preferably arranged to keep the temperature of the liquid entering it some 8 to 12"F above the temperature in the evaporator coil. It is anticipated in such a system that the temperature of air entering the condenser units 21 would be of the order of 65"F, and it would be raised to a temperature of some 105"F at the exit.

In an alternative arrangement instead of the evaporator coil 20 being positioned to experience ambient air, it may be buried in the ground to extract geothermal heat. In other respects the operation of the system would be generally similar to that described above.

Figure 9 shows in schematic outline a different heat pump system embodying aspects of the invention. This heat pump system is of particular use in situations having a high humidity content in the ambient air, and where it is desired to reduce that humidity. A typical example of such a situation is in a hall or room housing a swimming pool where evaporation from the pool surface causes high humidity leading to condensation problems within the room.

This heat pump system as shown in Figure 9 comprises an evaporator coil 110, a compressor 111, a condensation coil arrangement 112 and an expansion device 113. The condenser 112 includes a heat exchanger to extract heat from the heat exchange medium and pass it to the water of the swimming pool either by means of a heat exchange coil is indicated at 114, or by a portion of the condenser 112 being actually in the swimming pool itself. If the arrangement shown the flow of swimming pool water through the heat exchange coil 114 is controlled either by valves 115, or by a by-pass control valve 116 provided in the conventional circuit for circulating the swimming pool water through a filter 117 by means of a pump 118. A conventional pool water heater 119 may also be provided in the circuit.

The remaining portion of the condenser 112 is arranged to heat air circulated from the pool hall.

In operation air is drawn from the hall housing the swimming pool or other humid space by means of a fan not shown through the evaporator coil 110, and then out through the air heating portion of the condenser coil 112. The air is cooled in the evaporator coil thus causing water vapour in the air to condense out in the evaporator coil to be drained away and indeed if required returned to the swimming pool, and it is then reheated back to a pleasant temperature in the condenser coil 112 before being passed back to the hall housing the swimming pool. A humidistat and a thermostat are provided to sense the ambient conditions in the pool hall, and the information thus obtained is utilised to control the compressor 111, the expansion 113, and the division of heat output in the condenser 112 between the pool water and the air leaving the system to return to the pool hall. By this means it is possible to control the temperature and humidity of the air in the pool hall, while returning heat extracted back to the swimming pool thus economising on pool heating.

In a typical such system it is anticipated that air from the pool hall would enter the evaporator 110 at some 75"F with a 75% relative humidity, leave the evaporator 110 with a temperature of some 45"F and a relative humidity of 95%, and leave the condenser coil 112 with a temperature of some 105"F and a relative humidity of 35%.

By this means the latent heat in the air above a swimming pool may be returned to the pool while not significantly affecting the sensible heat in the air above the pool.

Claims (4)

1. A heat pump system comprising a single evaporator system in association with a plurality of condenser units for heating a space or spaces, the evaporator system being arranged to take up heat from ambient air or the ground.

2. A heat pump system substantially as herein described with reference to the accompanying drawings.

3. A condenser for a heat pump system, comprising a coil and means for directing air to be heated successively through successive portions of the coil in the direction of flow of heat exchange medium, a first portion containing in operation super heated vapour, a second portion containing in operation condensing vapour, and a third portion containing in operation condensed liquid.

4. A condenser for a heat pump system comprising a finned coil assembly having baffles arranged in association with the fins to direct air through successive spaces between the fins along the length of the coil.