GB2097908A - Heating water in a domestic water circuit - Google Patents

Abstract

The system comprises a refrigerating circuit, which acts as a heat pump and includes an electric compressor (48), a condenser, a throttling element (58), and an evaporator, and a line (24, 30) for supplying liquid from supply to a user take off. The condenser of the refrigerating circuit is constituted by one section of a heat exchanger, the other section of which is traversed by the supply line (24, 30) for the liquid at the desired temperature for use. The system further includes a waste line (36) for hot used liquid, which passes in succession through one section of a heat exchanger (14) the other section of which is traversed by a feedline between a supply and the exchanger of which the condenser forms part, and one section of a heat exchanger (44) the other section of which is the evaporator of the refrigerating circuit. The whole system is contained in a parallelepiped casing (86) subdivided internally into side-by-side compartments (88, 90) hot water insulated storage chamber (26) being provided in compartment (90). <IMAGE>

Description

SPECIFICATION Liquid heating system The present invention relates to a liquid heating system, particularly for providing hot water, of the type comprising a refrigerating circuit, which acts as a heat pump and includes an electric compressor, a condenser, a throttling element, and an evaporator in series with each other, and a line for supplying liquid from an output supply to a user take-off, in which the condenser of the refrigerating circuit comprises one section of a heat exchanger (called on exchanger-condenser) the other section of which is traversed by the supply line for the liquid at the desired temperature for use, the system further including a waste line for hot used liquid, which passes in succession through one section of a heat exchanger (called an exchanger-preheater) the other section of which is transversed by a feed line between a supply and the exchange-condenser, and one section (42) of a heat exchanger (called an exchanger-evaporator) the other section of which is the evaporator of the refrigerating circuit.

Swiss Patent Specification No. 233,376 to Sulzer diagramatically shows a system of this type.

The object of the invention is to provide a system based on the same principle of Sulzer, and which has a very high energy efficiency and is in the form of a compact unit adapted to be placed, for example, under a sink, wash basin or similar sanitary apparatus to recover heat from the used hot water which flows out from the waste pipe.

According to the invention this object is achieved by means of a system of the aforementioned type, characterised in that it includes a substantially rectangular parallelepiped casing subdivded internally into side-by-side first and second compartments, the second compartment having insulated walls; in that the casing has and upper wall defined by the exchanger-preheater which is in the form of a flattened box; in that the electric compressor is of the hermetic type and is situated in the first compartment; in that the exchanger-evaporator is situated in the first compartment (88) and comprises two coaxial heat exchange tubes which are wound into a helix with closed coils to surround the casing of the electric compressor in the first compartment; in that the exchanger-condenser comprises two helically-wound coaxial tubes enciosed in the second compartment; in that the throttling element is situated in the second compartment within the helix of the coaxial tubes of the exchanger-condenser; and in that the second compartment also houses a storage chamber for the hot liquid, which is interposed in the liquid supply line between the exchangercondenser and the user take-off.

As will be better understood from the description made with reference to the drawings, all the above-listed features contribute to both the compactness and the high energy efficiency of the system according to the invention.

Although the invention, as stated above, has been developed in relation to a system for providing hot water, its concept is not limited to the specific application and indeed extends to any system usable for the rapid heating of a liquid.

The invention will be better understood from reading the detailed description which follows, made with reference to the appended drawings which are given by way of non-limiting example and in which: Figure 1 is a schematic representation of the hydraulic circuit and the refrigerating circuit of a system for providing hot water; Figure 2 is a diagram of the electrical part of the system; Figure 3 is a schematic section of a thremostatic expansion valve incorporated in the refrigerating circuit of the system; Figure 4 is a cut-away perspective view of a preferred embodiment of the system; Figure 5 is a section taken in the vertical plane indicated by the line V-V in Figure 4; Figure 6 is a section taken in the horizontal plane indicated by line Vl-Vl in Figure 5;; Figure 7 is a section taken in the plane VIll-VIll of Figure 5; Figure 8 is a partly cut-away perspective view of coaxial pipes used to form the exchangerevaporator and the exchanger-condenser of the system of Figures 4 to 8, and Figure 9 is a section of the exchanger-preheater of the same system, taken in the horizontal plane indicated by the line IX-IX in Figure 5.

Referring to Figure 1, a pipeline 10 is connected to a water mains or like supply of cold water. A solenoid valve 12, the purpose of which will be clarified below, is inserted in the pipeline 10. The pipeline 10 terminates at a heat exchanger 14 which is called an exchangerpreheater. In the exchanger-preheater 14, the water passes through the section indicated 1 6.

The outlet from the section 1 6 is connected by means of a pipeline 18, to one of the sections, indicated 20, of a further heat exchanger 22 which is called an exchanger-condenser. The outlet from the section 20 is connected, by means of a pipeline 24, to an insulated storage chamber 26 provided with an electrical resistance heating element 28.

The chamber 26 is connected by a pipeline 30 to a user take-off represented conventionally by an ordinary tap 32. A vessel 34, such as a wash basin, a shower-head, or the like, is associated with the tap 32. The waste pipe 36 for hot water used in the vessel 34 terminates in the other section 38 of the exchanger-preheater 14. The outlet of the section 38 is connected by a pipeline 40 to one of the sections, indicated 42, of a further heat exchanger 44 which is called an exchanger-evaporator. The outlet of the section 42 is connected to the drainage system or the like by means of a pipeline 46.

The waste line 36, 38, 40, 42, 46 has a descending path so as to allow the used water from the vessel 34 to flow to the drainage system under gravity. More particularly, the exchanger preheater 14 is at a higher level than the exchanger-evaporator 44.

A refrigerating circuit, which acts as a heat pump is associated with the water circuit described above, this refrigerating circuit incorporates an electric compressor 48 of the hermetic type normally used in domestic conditioning systems. The feed pipeline 50 of the compressor 48 terminates in a condenser 52 which constitutes the other section of the exchanger-condenser 22. The outlet of the section 52 is connected by a pipeline 54 to an evaporator 56 which constitutes the other section of the exchanger-evaporator 44. In the pipeline 54 is inserted, as a throttling element, a thermostatically-controlled expansion valve 58 which will be described with reference to Figure 3.

The outlet of the section 56 is connected to the intake pipeline 58 of the compressor 48. The direction of circulation of the refrigerant fluid ("Freon") in the refrigerating circuit is indicated by the arrows in Figure 1.

In Figure 2 shows the electrical circuit which forms part of the system of Figure 1. By L1 and L2 are indicated a pair of electrical feedlines which are connectible to a mains supply, for example, a 220V, 50Hz supply, by means of a bipolar general switch SW.

The electric motor of the electric compressor 48 is indicated M. The heating resistance of the storage chamber 26 is indicated 28. The motor M and the resistance 28 are supplied electrically through respective normally-open contacts C1,C2 of remote control switches, the excitation coils of which are indicated B1, B2 respectively.

The coils B1, B2 are in series with respective manually-controlled push-button switches P1, P2.

Furthermore, the coils B1, B2 are in parallel with respective pilot lights L1, L2 with which respective load resistors R1, R2 are associated.

The coil of the solenoid valve 12 of Figure 1, which is in series with the switch P1, is indicated B3.

A temperature sensor, is associated with the evaporator 56 (Figure 1) and controls a relay including a normally-closed contactTS11 in series with the coil B1 and the coil B3.

Associated with the condenser 52 is a temperature sensor TS2 (Figure 1) which controls a thermostat including a pair of normally-open contacts TS21 in series with the coil B3.

A temperature sensor TS3 is associated with the feed pipeline 50 of the compressor 48 (Figure 1) and controls a thermostat including a pair of normally-closed contacts TS31 in series with the coil B1.

A temperature sensor TS4 is located in the storage chamber 26 and controls a thermostat having a pair of normally-closed contacts TS41 in series with the coil B2.

The operation of the system of Figures 1 and 2 will now be described.

It is assumed that the system is at rest with the switch P2 closed, and that the chamber 26 contains hot water from previous operations. The coil B2 is excited and the contacts C2 are closed by the switch P2, whereby the resistance heating element 28, which is of low power, is supplied solely to compensate for heat loss from the chamber 28.

In order to set the system in operation and obtain hot water from the tap 32, the general switch SW and the push-button switch P1 are closed. The coil B1 is excited and closes the contacts C,, to start the motor M of the compressor 48.

The refrigerant fluid compressed by the compressor is heated progressively and heats the water in the section 20 of the condenser 52.

When the sensor2 (Figure 2) detects that the predetermined temperature (for example, 450C) has been reached in the condenser 52, it causes closure of the contacts TS21, exciting the coil B3 and opening the solenoid valve 12 to permit hot water to be drawn from the tap 32.

The operation of the two thermostats controlled by the sensors TS1, TS3 is a safety measure. The sensorTS1contrnls the temperature of the refrigerant fluid in the evaporator 56, which must not fall below OOC, the freezing point of the water. When there is a risk of freezing, the sensorTS1 causes opening of the contacts TS11, de-activating the coil B1 and the compressor. The sensor1 also causes the deactivation of the coil B3, resulting in closure of the solenoid valve 12.

The sensorTS3 controls the temperature of the refrigerant fluid at the outlet of the compressor 48, which must not rise above a safety value. If this value is exceeded, the contacts TS31 are opened, again de-activating the compressor. The maximum thermostat TS4 opens the contacts TS when the temperature in the chamber 26 reaches the predetermined value, which substantially coincides with the heating temperature of the water in the exchanger-condenser 22. When the switch P1 is open, the coils B1 and B3 are deactivated, resulting in the simultaneous deactivation of the compressor M and the solenoid valve 12.

Referring to Figure 3, the thermostatic expansion valve 58 is controlled by a temperature sensorTS5 which, as illustrated in Figure 1, is situated on the pipeline 58 at the outlet of the evaporator 56. The sensorTS5 comprises a bulb containing a gas, which communicates through a pipe 60 with a capsule 62 subdivided by a diaphragm 64 into two compartments 66, 58, one compartment 66 of which contains the gas o- the sensor TS5.

The body of the valve includes an inlet 70 and an outlet 72 by which the valve is interposed in the pipeline 54. Between the inlet 70 and the outlet 72 is a valve seat 74 with a cooperating shutter member 76 which is biassed into the closed position by a helical spring 78. A calibration screw 80 is associated with the spring 78.

The shutter member 76 is connected mechanically to the disphragm 64 by means of a small rod 82. The outlet 72 or outlet chamber communicates with the chamber 68 of the capsule 62 through a passage 84. It will be appreciated that the arrangement of the valve 58 and its sensor5 is such that the valve opens wider as the temperature of the refrigerant fluid at the outlet of the evaporator 56 becomes higher, and vice versa. Thus, regulation of the intake pressure of the compressor 48 is achieved, so as to minimise over-heating of the inducted refrigerant fluid.

The used hot water gives up heat in the preheating exchanger 14 to the cold water fed in.

Assuming that the cold mains water is at a temperature of 100 to 1 50C and the used hot water is at a temperature of the order of 400 to 450C, it may be arranged that the preheated water in the section 1 6 reaches the exchangercondenser 22 at a temperature of 28 0--33 0 C.

The compressor need only provide enough energy to increase the temperature of water by 120 to 170C.

In Figures 4 to 7 is shown a very compact practical embodiment of the system described above, which is ready for installation wherever it is required to provide a user take-off, such as a shower, a wash basin or a sink, with a continuous supply of clean hot water. The same system may be used to provide hot clean fluids of other types, for example, in medical or industrial apparatus.

Referring to Figures 4 to 7, the system is contained in a parallelepiped casing or box 86 (in Figure 1 the casing is shown schematically by the box 86).

The casing 86 is subdivided into two adjacent compartments 88, 90. The compartment 88 is not insulated and contains, in correspondence with the front panel, the general switch SW, the pushbutton switches P1, P2 with their pilot lights, as well as the thermostats, generally indicated TS.

The compressor 48 is disposed centrally in the compartment 88 and is surrounded by the exchanger-evaporator 44. The latter (Figure 8) comprises a pair of coaxial outer and inner copper tubes 92, 94. The outer surface of the inner tube 94 has a helical projection 96 which acts as a fin to improve the heat transfer.

The water flows through the inner tube 94, which defines the section 20 of Figure 1, and the refrigerant fluid flows in the opposite direction through the space between the two tubes. The internal surface of the inner tube 94 is polished to avoid the formation of deposits.

The exchanger-evaporator 44 is wound into a helix, with a vertical axis and closed coils, which surrounds the casing of the compressor 48 so that the refrigerant fluid flowing through the space helps to cool the compressor.

Some hermetic compressors incorporate a cooling coil (a so-called "oil cooler") through which refrigerant fluid usually flows. In use of a compressor of this type, the feed water may flow through the coil before the exchanger-condenser both to cool the compressor and to provide an advantageous supplementary preheating of the water itself.

The solenoid inlet valve 1 2 is also located in the compartment 88.

The compartment 90 has insulating walls and houses the exchanger-condenser 22. The latter has the same structure as the exchangerevaporator 44 illustrated in Figure 8, and is wound in a helix with a horizontal axis and closed coils. In the exchanger-condenser 22, the refrigerant fluid flows through the space between the two coaxial tubes and the used water passes through the inner tube, which preferably has a polished internal surface to avoid the formation of deposits.

Surrounded by the coils of the exchangercondenser 22 is the thermostatic expansion valve 58 and a filter drier 98 for the refrigerant fluid ("Freon").

The storage chamber 26 is next to the exchanger-condenser 22 and has inlet and pipelines 24, 30 respectively.

The exchanger-preheater 14 is in the form of a flattened box which constitutes the upper wall of the casing 86.

As is best seen in Figure 9, the box is subdivided internally by transverse septa 100 which define a labyrinthine passage. This passage comprises the section 1 6 of Figure 1 through which the cold inlet water flows. Within the labyrinthine passage extends a serpentine tube 102, with fins and a smooth internal surface, through which the used hot water from the waste pipe 36 flows in the opposite direction, before flowing under gravity through the inner tube of the exchanger-evaporator 44.

Alternatively, the exchanger-preheater 1 4 may comprise two coaxial tubes. In this case, the inner tube would still be a metallic tube with a polished internal surface through which the hot used water passes, while the cold inlet water would flow in the opposite direction through the space between the tubes. The outer tube could be a tube of reinforced plastics material or the like fitted over the longitudinal external fins of the inner tube. The pair of coaxial tubes could, for example, be serpentine in shape like the tube 102, or wound in a flattened spiral.

A system like that illustrated in Figures 4 to 9 has been made with a casing or box 86 60 cm long, cm wide, and 33 cm high. These dimensions make it suitable for positioning under a wash-basin or sink, for example.

The power of the electric compressor 48 is about 1050 watts.

With a water flow rate of 300 litres/hour, a temperature increase of 30oC is obtained in the water.

The operational logic of the various thermostats allows water to be provided in the shortest possible time: - 0 seconds for intervals of use of less than 1 5 minutes; - 25 to 50 seconds for intervals of up to 2 hours.

In order to achieve these results, the storage chamber 26 has a capacity of twice that occupied by the used water in the preheating exchanger 14, that is, in the section 38. It has been found, however, that it is advantageous for the storage chamber 26 to have a volume at least equal to the said volume occupied by the used liquid.

The resistance heating element 28 in the storage chamber 26 has a power of 13 watts.

From tests carried out, it is found that the so called COP of the system (a dimensional ratio between the energy supplied to the water and that absorbed by the compressor) was 8-9, while the COP of a traditional boiler with an electrical resistance heater having the same performance was about 0.9.

Claims (11)

1. Liquid heating system, particularly for providing hot water, of the type comprising a refrigerating circuit, which acts as a heat pump and includes an electric compressor, a condenser, a throttling element, and an evaporator in series with each other, and a line for supplying liquid from an output supply to a user take-off, in which the condenser of the refrigerating circuit comprises one section of a heat exchanger (called an exchanger-condenser) the other section of which is traversed by the supply line for the liquid at the desired temperature for use, the system further including a waste line for hot used liquid, which passes in succession through one section of a heat exchanger (called an exchanger-preheater) the other section of which is traversed by a feedline between a supply and the exchangercondenser, and one section (42) of a heat exchanger (called an exchanger-evaporator) the other section of which is the evaporator of the refrigerating circuit, characterised in that it includes a substantially rectangular parallelepiped casing (86) subdivided internally into side-by-side first and second compartments (88, 90), the second compartment (90) having insulated walls; in that the casing has an upper wall defined by the exchanger-preheater (14) which is in the form of a flattened box; in that the electric compressor (48) is of the hermetic type and is situated in the first compartment (88); in that the exchangerevaporator (44) is situated in the first compartment (88) and comprises two coaxial heat exchange tubes (92, 94) which are wound into a helix with closed coils to surround the casing of the electric compressor (48) in the first compartment (88); in that the exchangercondenser (22) comprises two helically-wound coaxial tubes (92, 94) enclosed in the second compartment (90); in that the throttling element (58) is situated in the second compartment (90) within the helix of the coaxial tubes of the exchanger-condenser (22); and in that the second compartment (90) also houses a storage chamber (26) for the hot liquid, which is interposed in the liquid supply line (24, 30) between the exchangercondenser (22) and the user take-off (32).

2. System according to Claim 1, characterised in that in the exchanger-preheater (14) the flattened box has internal septa (100) defining a labyrinthine passage for inlet liquid, and in that an externally-finned tube (102) with an internally polished surface extends along the labyrinthine passage,the used liquid flowing through said tube (102) in the opposite direction to the inlet liquid.

3. System according to Claim 1, characterised in that in the exchanger-preheater (14) the flattened box contains a pair of coaxial tubes, the tube, through which the used liquid flows, being metallic with external longitudinal fins and a polished internal surface, and the outer tube being made from plastics or like material and fitted over the fins of the inner tube, the inlet liquid flowing through the space between the tubes in the opposite direction to the used liquid.

4. System according to Claim 1, characterised in that in the exchanger-evaporator (44) the inner coaxial tube (24) has a polished internal surface and is traversed by the used liquid, and the refrigerant fluid flows through the space between the two coaxial tubes (92, 94) in the opposite direction to the used liquid.

5. System according to any of Claims 1 to 4, characterised in that the waste line (36, 38, 40, 42, 46) has a descending path, which allows the used liquid to flow under gravity.

6. System according to Claim 1, characterised in that in the exchanger-condenser (22) the inner coaxial tube (94) has a polished internal surface and is transversed by the liquid to be heated, and the refrigerant fluid flows through the space between the two coaxial tubes (92, 94) in the opposite direction to the liquid.

7. System according to Claim 1, characterised in that the throttling member is a thermostatic expansion valve (58) controlled by a temperature sensor (TS5) associated with the outlet of the evaporator (56), so that the valve (58) opens wider the more the refrigerant fluid is overheated at the outlet of the evaporator (56), and vice versa.

8. System according to Claim 1, characterised in that a solenoid cut-off valve (12) is interposed in the feedline (10) and a temperature sensor (TS2 which controls the solenoid valve (12) is associated with the condenser (52), so that the solenoid valve is opened when the refrigerant fluid in the condenser (52) exceeds a predetermined temperature.

9. System according to Claim 1, characterised in that the storage chamber (26) is provided with at least one electrical resistance heating element (28) which is thermostatically controlled so that the element (28) is energised only to compensate for heat loss from the chamber (26).

10. System according to Claim 9 or Claim 10, characterised in that the volume of the storage chamber (26) is at least equal to the volume occupied by the used liquid in the exchanger preheater (14).

11. System according to Claim 1, characterised in that the electric compressor (48) is of the hermetic type provided with an internal cooling coil, and in that the feedline (1 8) for the liquid traverses the coil.