EP0055263A1

EP0055263A1 - Heat pump

Info

Publication number: EP0055263A1
Application number: EP19810901694
Authority: EP
Inventors: John Nickels
Original assignee: THERMO HEATING Ltd
Current assignee: THERMO HEATING Ltd
Priority date: 1980-06-25
Filing date: 1981-06-25
Publication date: 1982-07-07
Also published as: WO1982000053A1

Abstract

Dans et pour une pompe a chaleur, un condenseur possede un echangeur de chaleur (10) comprenant un cylindre (12) dans lequel et hors duquel un liquide de refrigeration s'ecoule. Deux ou plusieurs tubes coaxiaux (13, 14, 15) sont prevus pour definir au travers du cylindre un passage en forme de serpentin forme par les espaces annulaires (16) entre les tubes et le cylindre avec un serpentin d'eau continu (17) enroule en spirale au travers de ceux-ci. Des pressions et des temperatures de condensation du liquide de refrigeration sont commandees par un circuit de refrigeration avec prechauffage (24) comprenant une serie de tubes (22) montes dans un evaporateur (23), Le circuit se trouve du cote de la sortie du condenseur et est mis en fonctionnement lorsqu'un regulateur a pression constante (25) est mis en marche lorsqu'une pression determinee est atteinte. Une vanne anti-retour (29) est prevue pour empecher le retour d'ecoulement du liquide refrigerant lorsque le regulateur est ferme.In and for a heat pump, a condenser has a heat exchanger (10) comprising a cylinder (12) into and out of which a coolant flows. Two or more coaxial tubes (13, 14, 15) are provided to define through the cylinder a serpentine-shaped passage formed by the annular spaces (16) between the tubes and the cylinder with a continuous water coil (17) winds in a spiral through them. Condensing pressures and temperatures of the coolant are controlled by a preheating refrigeration circuit (24) comprising a series of tubes (22) mounted in an evaporator (23), The circuit is on the side of the condenser outlet and is activated when a constant pressure regulator (25) is started when a determined pressure is reached. A non-return valve (29) is provided to prevent the return of coolant flow when the regulator is closed.

Description

DESCRIPTION

HEAT PUMP

This invention relates to an air-to-water heat pump and to a heat exchanger theretofor.

Heretofore an air-to-water heat pump has a closed refrigerant circuit in which a gaseous refrigerant at low pressure is fed to a compressor, to be compressed and fed therefrom at high pressure to a condenser consisting of a heat exchanger from which it leaves in liquid form having given up heat. The liquid refrigerant flows from the heat exchanger to an expansion valve thence to an evaporator in which the refrigerant boils, changing from liquid to low pressure gas taking in heat from the atmosphere and is fed to the compressor. A water circuit passes through the heat exchanger in counterflow to the refrigerant and the water therein is heated by the refrigerant as it passes through the circuit. One of the problems with existing heat pumps is the fact that to obtain water temperatures above 60° C. (140° F. ) requires very high condensing temperatures with a resultant loss of efficiency due to the wide temperature differences between the condensing and evaporating temperatures. Also, a further problem is one of compressor design in that presently existing compressors cannot operate satisfactorily at condensing temperatures above a maximum of 65° C. (150° F. ) this in effect means that heat pumps are presently regarded as a low temperature heat source with a resultant very restricted market. The refrigerant gases, when compressed, leave the compressor at temperatures much higher than actual condensing temperatures, therefore, if this high amount of heat can be transferred to the water with an efficient heat exchanger, the water can be heated to a temperature higher than normal condensing temperatures.

An object of the present invention is to provide a heat pump which can give initial. flow water temperatures of 82° C. (180° F. ) at a relatively low condensing temperature of 55° C. (130° F. ) .

According to a first aspect of the present invention, there is provided a heat pump in which the condenser consists of at least one first heat exchanger which comprises a cylinder into and out of which refrigerant flows, and in which there are two or more co-axial tubes arranged to define through the cylinder a snake-like passage formed by the annular gaps between the tubes and cylinder with a continuous water coil spirally wound therethrough, the coil and tubes being of heat-conductive material.

Preferably, two first heat exchangers are provided in series. Preferably also, the condenser includes a second heat exchanger.

According to a second aspect of the present invention, there is provided a heat exchanger comprising a cylinder into and out of which refrigerant flows, and in which there are two or more co-axial tubes arranged to define through the cylinder a snake-like passage formed by the annular gaps between the tubes and cylinder with a continuous water coil spirally wound therethrough, the coil and tubes being of a heat-conductive material. Preferably, three tubes are provided. The turns of the coil are preferably in abutment with each other and with the tubes and cylinder.

According to a third aspect of the present invention, there is provided in or for a heat pump, means to control condensing pressures and temperatures of a refrigerant, the means comprising a pre-heater refrigerant circuit comprising a series run of tubing provided in the evaporator, the circuit being on the outlet side of the condenser and being brought into use on operation of a constant pressure regulator actuable on a determined discharge pressure being reached, and a non-return valve being provided to prevent back-flow of refrigerant when the regulator is closed.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Fig. 1 is a circuit diagram of a heat pump according to the present invention;

Fig. 2 is a schematic cross-sectional view of a heat exchanger for the heat pump; and

Fig. 3 is a schematic cross-sectional view on the line III-III of Fig. 2.

Referring to the drawings, a heat pump has a condenser consisting of a first heat exchanger 10 and a second heat exchanger 11. The first heat exchanger 10 comprises a cylinder 12 into and out of which gaseous refrigerant flows. Mounted inside and co-axially with the cylinder 12 are three co-axial tubes 13, 14, and 15. The annular gap 16 between adjacent tubes and cylinder 12 is the same width. Tube 13 is closed at both ends, and tubes 14 and 15 are closed at alternate ends 14A and 15A, tube 14 being open at the inlet end of the cylinder 12. The gaps 16 and open ends of tubes 14 and 15 form a snake-like passage which houses a continuous water coil 17 spirally wound lengthwise of each gap 16. The inlet end of the coil 17 is at 'one end of the cylinder 12 and the coil 17 is wound along the gap between the cylinder 12 and tube 15 towards the other end of the cylinder 12 into the gap between tubes 14 and 15, therealong, into the gap between tubes 13 and 14 and therealong to exit from the cylinder at the opposite end of the cylinder from its entrance. The tubes and coil 17 are of heat-conductive material, for example copper, and the cylinder 12 is of steel, insulated on the outside, for example by a glass reinforced plastics cover. The coil 17 is tightly wound with each turn touching the other, and touching the sides of the tubes and cylinder. The second heat exchanger 11 is a tank 18 through which a coil 19 carrying refrigerant is located, water being fed from a source by piping 20 into the tank 18 at the bottom and exhausting by piping 21 from adjacent to the top thereof, the piping 21 being connected to the inlet of the coil 17.

Means to control condensing pressures and temperatures of the refrigerant are provided and comprise a pre-heater refrigerant circuit 24 consisting of a series run of tubing 22 which is provided in a finned block (not shown) of an evaporator 23. The circuit 24 is on the outlet side of the second heat exchanger 11 from piping 30 and is brought into use on operation of a constant pressure regulator 25 actuable on a determined discharge pressure being reached in the output flow of refrigerant from a compressor 26. A pressure line 27 is provided from pipe 28 from the compressor 26 to cylinder 12, to control the constant pressure regulator 25. A non-return valve 29 is provided to prevent back-flow of refrigerant when the regulator is closed, the circuit 24 being reconnected to piping 31 connecting piping 30 to a drier 32. The outlet of drier 32 is connected by piping 33 to an expansion valve 34 which feeds via piping 37 into the evaporator 23. A bleed line 35 having a solenoid 36 interposed therein connects piping 28 to piping 37 to provide hot gas to defrost evaporator 23, the solenoid 36 being actuated by a time clock at preset intervals. A line 38 is connected from expansion valve 34 and is a thermostatic sensor to control expansion valve 34 to govern flow of liquid refrigerant from the evaporator 23. Piping 39 connects evaporator 23 to a suction accumulator 40. Piping 41 connects this accumulator 40 to the compressor 26. In the event of expansion valve 34 malfunctioning and allowing liquid refrigerant to flow through piping 9, the suction accumulator 40 converts the liquid refrigerant to a gaseous form before allowing it to flow on to the compressor 26.

In use, high temperature gases leaving the compressor 26 enter the heat exchanger 10 where it percolates through the passage of annular gaps 16 between the tubes and cylinder, and the high heat is transferred to water circulating in the water coil 17. Considerable heat is removed from the gaseous refrigerant. The cooler gas then enters heat exchanger 11. At the initial start up of the pump, when the water temperature is low, practically all of the heat is removed from the gaseous refrigerant as it leaves heat exchanger 11 turning this refrigerant into liquid form. This liquid refrigerant is then carried to the evaporator 23 via the expansion valve 34 where it becomes a low pressure state and absorbs heat from, the air converting the refrigerant to vapour when is returned to the compressor 26 and the cycle is repeated. As mentioned above, the water circuit is counterflowing in that the water enteis heat exchanger 11 point where it is heated slightly before entering heat exchanger 10 (at the point where the refrigerant leaves heat exchanger 10) . After flowing through beat exchange 10 the water leaves the exchanger 10 at the point of entry of the refrigerant gases where these gases are at their hottest. The water is then pumped through the source to be heated.

When the discharge pressure from the compressor 26 reaches a determined level, for example in a boiler of 270 p.s.i.g., constant pressure regulator 25 opens allowing the refrigerant to flow into the pre-heater circuit 24; at which pressure the condensing temperature reaches 55° C. (130° F.). Due to this circuit 24 being placed in front of the evaporator 23, the air ambient to the finned block causes the pre-heater 24 to become another condenser removing heat from the refrigerant gases thereby controlling the condensing pressure and temperatures. The constant pressure regulator 25 controls the refrigerant flow and the outlet of the pre-heater circuit 24 joins the liquid line 31 and normal flow is achieved. When heat is removed from the gases in the pre-heater circuit 24, this heat is carried in the air-flow to the evaporator 23 with the effect of raising the air temperature before the air reaches the evaporator 23 and therefore raising the evaporator temperature. Because theevaporator temperature is raised, a high efficiency is maintained compared with the outside ambient conditions.

To increase efficiency of the heat pump, two first heat exchangers 10 may be provided in series. A heat exchanger 10 above-described can be used for purposes other than for incorporation into a heat pump, and can be used in a water-to-water circuit.

Claims

1. A heat pump in which the condenser consists of at ast out of which refrigerant flows, and in which there are two or more co-axial tubes arranged to define through the cylinder a snake-like passage formed by the annular gaps between the tubes and cylinder with a continuous water coil spirally wound therethrough, the coil and tubes being of heat-conductive material.

2 . A heat pump according to claim 1, wherein two first heat exchangers are provided in series.

3. A heat pump according to claim 1 or 2, wherein the condenser includes a second heat exchanger.

4. A heat exchanger comprising a cylinder into and out of which refrigerant flows, and in which there are two or more co-axial tubes arranged to define through the cylinder a snake-like passage formed by the annular gaps between the tubes and cylinder with a continuous water coil spirally wound therethrough, the coil and tubes being of a heat-conductive material.

5. A heat exchanger according to claim 4, wherein three tubes are provided.

6. A heat exchanger according to claims 4 or 5, wherein the turns of the coil are in abutment with each other and with the tubes and cylinder.

7. In and for a heat pump, means to control condensing pressures and temperatures of a refrigerant, the means comprising a pre-heater refrigerant circuit comprising a series run of tubing provided in the evaporator, the circuit being on the outlet side of the condenser and being brought into use on operation of a constant pressure regulator actuable on a determined discharge pressure being reached, and a non-return valve being provided to prevent back-flow of refrigerant when the re ulator is closed.