GB2097900A

GB2097900A - Liquid heating apparatus

Info

Publication number: GB2097900A
Application number: GB8212555A
Authority: GB
Original assignee: BIRMINGHAM HEAT PUMPS Ltd
Current assignee: BIRMINGHAM HEAT PUMPS Ltd
Priority date: 1981-05-06
Filing date: 1982-04-30
Publication date: 1982-11-10
Also published as: GB2097900B

Abstract

Apparatus for heating water in a domestic hot water supply, utilising a heat pump for collecting heat from the environment, for example ambient air, comprises an unpressurised tank 6 with condenser coils 36, 37 and a ball valve controlling the inlet 11, which tank is adapted for connection to a storage cylinder by supply and return lines and a pump 19 is provided for circulating the liquid between the tank and cylinder when the liquid in the tank is heated to a predetermined temperature. <IMAGE>

Description

SPECIFICATION Liquid heating apparatus This invention concerns improvements in or relating to liquid heating apparatus and in particular, though not exclusively, to apparatus for and a method of heating water, for example for heating the domestic hot water supply.

In general the domestic hot water supply consists of a storage cylinder having an inlet pipe for cold water supplied from a feed tank connected to the mains supply and a branched outlet pipe for supplying water to the various outlet points, for example taps, shower heads etc.

Conventionally the water contained in the storage cylinder has been heated by an electric immersion heater or by a gas, coal or oil fired boiler. However, the recent rapid escalation in the price of such forms of energy has led to proposals for the use of alternative forms of energy as a heat source, for example for heating the domestic hot water supply. One such alternative form of energy is solar radiation and there has been considerable activity in the development of systems utilising this naturally occurring heat source.Nevertheless an inherent disadvantage of such systems is their dependence on the amount of solar radiation received with the result that to date, even with the most efficient collectors their use has been restricted in all but those countries where there is a high level of sunshine throughout the year, to applications where they are used in conjunction with conventional methods of heating rather than as a direct replacement.

It is an object of the present invention to provide apparatus for and a method of heating liquid which avoids the abovementioned disadvantage of systems relying on solar radiation and which may be used in place of conventional methods of heating.

According to one aspect of the present invention liquid heating apparatus comprises an unpressurised tank for a liquid to be heated and a heat pump having an evaporator for collecting heat from the environment and a condenser positioned within the tank for transferring heat to liquid contained within the tank.

Preferably the evaporator is arranged to collect heat from a gas, e.g. ambient air or hot waste gases, passed over it, for example under the influence of a fan.

Preferably the tank has an inlet at the upper end for connection to a supply of liquid, for example the mains cold water supply, an outlet at the lower end for supply of heated liquid and means for controlling the level of liquid within the tank e.g. a ball valve. In addition the tank includes a further outlet above the normal liquid level for connection to the usual overflow line.

The outlet from the tank may supply one or more outlet points for the heated liquid directly but more preferably is adapted for connection to a storage cylinder which in turn supplies one or more outlet points and means is provided to circulate liquid between the tank and storage cylinder when liquid contained in the tank is heated to a predetermined temperature.

Preferably the means for circulating liquid between the tank and the storage cylinder comprises a pump which is thermostatically controlled, for example by a temperature adjustable thermostat arranged to sense the temperature of the liquid in the tank. Preferably the pump is provided in a return line from the storage cylinder to the tank. The return line may conveniently be provided by an expansion or vent line from the storage cylinder and in such instances the pump is of the type having a through line which is continuously open ta allow passage of liquid when the pump is not in operation. In a preferred arrangement in which the tank is provided with a removable lid for access the return line is connected to an inlet to the tank which is positioned above the overflow outlet.

Preferably the tarik and, where provided, lid are insulated, for example by an outer cover of polyurethane, to reduce heat loss.

The heat pump comprises a closed circuit made, for example, of copper tube containing a vaporisable heat transfer medium, for example Arcton F12 (Registered Trade Mark) ex l.C.I. which is circulated by means of a compressor provided between the evaporator and the condenser.

Preferably the circuit includes a device for monitoring the pressure of the heat transfer medium in the circuit which is operational to switch off the compressor in the event of there being a loss of the heat transfer medium, for example due to leakage.

The evaporator is preferably of looped construction to provide a large surface area for collecting heat from the heat source, e.g. ambient air and preferably is finned to improve further heat collection.

Preferably a section of the heat pump circuit downstream of the condenser, i.e. in the return line carrying the liquid transfer medium, is associated with the evaporator so that the ambient air passes over this section prior to or during passage through the evaporator.

Preferably this section is of looped and finned construction similar to the evaporator to enhance heat transfer to the ambient air and in a preferred arrangement comprises a single row of loops disposed between two successive rows of evaporator loops. In this way residual heat retained by the heat transfer medium after passing through the condenser is used to heat the ambient air passing through the evaporator simultaneously sub-cooling the heat transfer medium. This heating has two advantages, firstly it increases the efficiency of the heat pump by both collecting a portion at least of any such residual heat and increasing the heat collecting capacity of the heat transfer medium after passing through the expansion valve.Secondly, at low ambient temperatures it assists in preventing moisture in the ambient air which condenses on the evaporator from freezing with the result that the heat pump may continue to operate at low temperatures, e.g. in the region of OOC.

The condenser is preferably of coiled construction with successive coils axially offset to provide a large surface area for heat transfer to the liquid in the tank. Preferably the heat transfer medium is delivered to the bottom condenser coil and exists from the top condenser coil, i.e. the heat transfer medium flows upwards through the condenser whereby the heat transfer medium which condenses during passage through the condenser coils forms a column of liquid in the condenser. As a result the residence time of the condensed liquid in the condenser coils is greatly increased and a greater proportion of the heat carried by the heat transfer medium is given up to the liquid contained in the tank as compared with known arrangements in which the heat transfer medium flows downwards through the condenser allowing condensed liquid to drain rapidly out of the coils.Preferably means is provided to prevent condensed liquid in the coil flowing back to the evaporator in the event the heat pump is switched off.

It has been found that by reversing the direction of flow of the heat transfer medium through the condenser coils and by using any residual heat carried by the heat transfer medium on leaving the condenser to heat the evaporator heat source a significant improvement in the efficiency of the heat pump is obtained.

According to a further preferred feature of the heat pump the compressor is insulated and the condenser is divided into two sections, a first section to which the vaporised heat transfer medium from the evaporator is delivered and a second section to which the liquid transfer medium leaving the first section is delivered after returning to the compressor to collect heat from the oil of the compressor thereby preventing overheating of the insulated compressor and providing a further improvement in efficiency of the heat pump.

Conveniently the components of the heat pump, the fan and the liquid recirculating pump are contained in a rectangular housing having an air inlet opening in one face and an outlet in the opposite face. Preferably means, e.g. a drip tray, is provided for collecting moisture which condenses on the evaporator. Means may be provided for returning collected moisture to the environment to maintain the humidity level in the adjacent surroundings. For example a fabric wick may be provided extending from the drip tray across the path of the ambient air passing through the apparatus. Alternatively the collected moisture may be drained via an outlet from the drip tray.

According to a further aspect of the present invention a method of heating a liquid comprises collecting heat from the environment and transferring the heat collected to a liquid contained in an unpressurised tank by means of a heat pump.

Preferably the method further includes the steps of heating the liquid to a predetermined temperature in the tank and circulating liquid between the tank and a storage cylinder when the liquid in the tank is heated to said predetermined temperature.

According to yet another aspect of the present invention a heat pump includes an evaporator for collecting heat from a heat source, a primary condenser for transferring collected heat to a fluid and a secondary condenser in the return line from the primary condenser associated with the evaporator for heating the evaporator heat source.

The heat pump may be used to transfer the heat to a liquid e.g. to provide hot water in a domestic hot water supply or central heating system.

According to yet a further aspect of the present invention a heat pump includes an evaporator for collecting heat from a heat source and a condenser for transferring collected heat to a fluid wherein the condenser is constructed and arranged so that in use heat transfer medium flows upwards through the condenser.

The invention will now be described in more detail, by way of example only, with reference to the accompanying schematic drawings, wherein Figure 1 shows the layout of a doinestic hot water supply incorporating liquid heating apparatus in accordance with the present invention; Figures 2 and 3 are front and side views, to an enlarged scale and partly in section, of the liquid heating apparatus shown in Figure 1; Figure 4 is a front view, to an enlarged scale of the evaporator/secondary condenser assembly shown in Figures 2 and 3; Figure 5 is a side view, to an enlarged scale, of the primary condenser shown in Figures 2 and 3; and Figure 6 is a schematic layout of the heat transfer circuit.

The domestic hot water supply shown in Figure 1 of the accompanying drawings comprises water heating apparatus 1 situated in the loft 2, a storage cylinder 3 for water heated by the apparatus 1 and a branched outlet 4 from the cylinder 3 for supplying hot water to various outlet points 5 around the house.

The heating apparatus 1 comprises a cylindrical tank 6 supplied with cold water from the mains supply 7 and a heat pump 8 for collecting heat from the ambient air in the loft and transferring it to water contained in the tank 6.

As shown in more detail in Figures 2 and 3 the tank 6 is unpressurised having a removable lid 9 to allow access to the tank interior to facilitate maintenance and allow the tank to act as a feed and expansion tank. The external surface of the tank 6 and lid 9 is thermally insulated by a polyurethane cover 10. The tank 6 has an inlet 11 adjacent to the upper end for connection to the mains supply 7 (Figure 1) and a ball valve assembly 12 for controlling the level 13 of water within the tank 6. An overflow outlet 1 4 is provided above the normal water level 1 3 for connection to an overflow pipe 1 5 (Figure 1).In addition the tank 6 has an outlet 1 6 adjacent to the lower end for connection to a supply pipe 1 7 (Figure 1) leading to the storage cylinder 3 and an inlet 1 8 at the upper end above the level of the overflow outlet 1 4 for connection via a water recirculating pump 19 to a return pipe 20 (Figure 1) from the storage cylinder 3. The pump 1 9 is of a type having a through line which is open at all times so that the return pipe 20 may operate as a vent line when the pump 19 is not operating.

The heat pump 8 comprises a closed circuit made of copper tube containing Arcton F12 which acts as a vaporisable heat transfer medium. The circuit includes an evaporator 21, a thermally insulated compressor 22 having start and run capacitors (not shown), a secondary condenser 23, a thermostatic expansion valve 24 and a filter dryer 25 mounted in a rectangular housing 26 positioned below the tank 6 and a primary condenser 27 located in the tank 6.

The evaporator 21 and secondary condenser 23, both of looped construction, are combined in a casing 28 open to the rear and having an annular opening 29 in the front face in which a fan 30 driven by an electric motor 31 is mounted. The evaporator comprises three rows 32 of closely spaced loops enclosed by fins 33 (Figure 4) to improve heat collection and the secondary condenser comprises a single row 34 of closely spaced loops enclosed by fins disposed between the first two rows of the evaporator as viewed in the direction of air flow indicated by arrows A (Figure 3). A drip tray 35 positioned below the evaporator 21-and secondary condenser 23 assembly serves to collect moisture that condenses on the evaporator and the liquid collected is drained via an outlet from the bottom of the drip tray.

The primary condenser 27 which is of coiled, seamless and jointless construction with successive coils axially offset is divided into two sections (Figure 5), a lower section 36 and an upper section 37 each having an inlet 36a and 37a respectively leading to the bottom coil thereof and an outlet 36b and 376 respecitvely leading from the top coil thereof i.e. the flow of heat transfer medium through both sections 36, 37 is in an upwards direction. In addition inlet 36a to the lower section 36 passes to the top of the condenser before returning to the bottom coil of the lower section so that fluid condensing in the lower section is prevented from flowing back to the compressor.

The temperature of the water in the tank 6 is monitored by a temperature adjustable thermostat which senses the temperature in the vicinity of the uppermost coil of the primary condenser 27. The thermostat incorporates a switch 38 mounted in the housing 26 which is operable when the water in the tank 6 reaches a predetermined temperature to switch off the compressor 22 and fan 30 and actuate the recirculating pump 19 mounted in the housing 26 to transfer water from the storage cylinder 3 to the tank 6 and simultaneously transfer the heated water from the tank 6 to the cylinder 3.Located alongside the switch 38 in the housing 26 is a safety switch 39 of a low pressure sensorforthe liquid transfer medium of the heat pump which is operable to switch off the compressor 22 if any leak occurs in the closed circuit causing a loss of the liquid transfer medium.

Operation of the above-described hot water supply is as follows, assuming the tank 6 and storage cylinder 3 are filled with cold water, a control switch for the compressor 22 and fan 30 is actuated either manually or automatically by means of a time clock. The fan 30 draws ambient air through an air inlet opening in one face of the housing 26 and directs it through the secondary condenser 23 and evaporator 21 and out of an outlet opening in the opposite face of the housing 26. The evaporator collects heat from the air to vaporise the heat transfer medium which passes via line 40 to the compressor 22 where it is compressed thereby increasing its temperature and passed via line 41 to the lower section 36 of the primary condenser where it gives up a major proportion of its heat to the water in the tank 6.

The heat transfer medium leaving the lower section 36 of the primary condenser 27 is returned to the oil cooler of the compressor via line 42 where it absorbs heat from the oil and passes via line 43 to the upper section 37 of the primary condenser where it gives up a further proportion of its heat to the water in the tank 6 before returning via line 44 to the secondary condenser 23 where it gives up any residual heat to the ambient air passed through it by the fan 30 thereby heating the air before returning to the evaporator.In this way not only is maximum use made of the energy available for heating the water in the tank 6 but un-used heat re-cycled to heat the incoming ambient air thereby decreasing the occurrence of moisture in the air freezing on the evaporator and enabling the heat pump to continue operation at low temperatures e.g. in the region of OOC. The above heating cycle is repeated continuously until the water in the tank 6 is heated to a predetermined temperature, for example 600C, at which temperature the switch 38 operates to switch off the compressor 22 and fan 30 and actuate the pump 1 9 causing cold water to be transferred from the storage cylinder 3 to the tank 6 and the hot water in the tank 6 to be transferred to the storage cylinder 3.The above transfer takes place relatively rapidly following which the switch 38 operates to switch off pump 1 9 and actuate compressor 22 and fan 30 to re start the heating cycle. The above operation is repeated until the water in the storage cylinder 3 and the tank 6 is heated to the predetermined temperature.

Water may be drawn off from the storage cylinder 3 via the outlet 4 at any time, the removed water being replaced by water from the tank 6 which is replenished from the mains supply 7.

It will be appreciated that the sole heat source for the above-described liquid heating apparatus is the ambient air contained in the loft which is heated by heat exchange through the roof, and by waste heat from inside the house, the latter being not inconsiderable even where the loft space is insulated. In addition the air in the loft which is cooled by operation of the liquid heating apparatus is continuously being replaced by warmer air entering the loft space.

It has been found that the above-described liquid heating apparatus is capable of heating the water for domestic use without requiring any additional method of heating and the amount of energy which has to be put into the system to operate the compressor, fan etc is considerably less than that required to heat an equivalent volume of water by conventional methods thereby providing a saving in operation costs. In addition to cost saving a further advantage of the apparatus when used in combination with a storage cylinder as above-described is that the available capacity of hot water is increased as not only is the water in the tank 6 heated to the required temperature but also that contained in the storage cylinder 3.

Although the liquid heating apparatus in accordance with the present invention has been described with particular reference to its application for heating a domestic hot water supply it will be apprecaited that it is not restricted to such application but may be used for heating water for industrial use and also for heating liquids other than water. Furthermore the apparatus may be used for heating water for a central heating system.

The apparatus may be positioned in locations other than the loft although for domestic applications such a position has the advantage that no use is made of useful heat for heating the liquid, i.e. heat used to heat the house itself.

Other modifications to the above-described liquid heating apparatus include positioning the primary condenser sections one inside the other, forming the primary condenser in one section only, arranging the flow of heat transfer medium to be in a downwards direction through the primary condenser, positioning the secondary condenser in front of the evaporator, varying the number of rows forming the evaporator and secondary condenser, using alternative evaporator heat sources, e.g. hot waste gases (boiler flue gases, steam etc), omitting the secondary condenser, using a check valve or similar in the line from the compressor to the primary condenser to prevent backflow of condensed liquid.

Finally while the liquid heating apparatus of the present invention is ideally suited for modifying an existing domestic hot water supply incorporating a storage cylinder by connecting the tank to the mains supply and overflow and to the supply and return lines to and from the storage cylinder together with the wiring connection to a main control switch, it will be understood that the apparatus may be used on its own by connecting the outlet from the tank to the various outlet points.

Claims

1. Liquid heating apparatus comprising an unpressurised tank for a liquid to be heated and a heat pump having an evaporator for collecting heat from the environment and a condenser positioned within the tank for transferring heat to liquid contained within the tank.

2. Apparatus according to claim 1 wherein the evaporator heat source is a gas.

3. Apparatus according to claim 1 or claim 2 wherein the tank has an inlet for connection to a liquid supply and means for controlling the level of liquid within the tank.

4. Apparatus according to any one of the preceding claims including means adopted to circulate liquid between the tank and a storage cylinder when liquid contained within the tank is heated to a predetermined temperature.

5. Apparatus according to claim 4 wherein the means for circulating liquid between the tank and the storage cylinder comprises a pump located in one of a supply line and return line which in use extend between the tank and storage cylinder.

6. Apparatus according to claim 5 wherein the return line enters the tank at a level above the normal liquid level in the tank and an overflow outlet from the tank.

7. Apparatus according to claim 5 or claim 6 wherein the pump is located in the return line from the storage cylinder to the tank.

8. Apparatus according to claim 7 wherein the pump has a through line which is open at all times.

9. Apparatus according to any one of claims 5 to 8 including means for controlling operation of the heat pump and the recirculating pump.

1 0. Apparatus according to claim 9 wherein said means comprises a thermostat for sensing the temperature of liquid in the tank and a switch for actuating either the heat pump or the recirculating pump in response to the liquid temperature sensed by the thermostat.

11. Apparatus according to any one of the preceding claims wherein the tank has a removable lid.

12. Apparatus according to any one of the preceding claims wherein the tank is insulated.

13. Apparatus according to any one of the preceding claims wherein the heat pump comprises a closed circuit containing a vaporisable heat transfer medium circulated by a compressor positioned between the evaporator and condenser.

1 4. Apparatus according to claim 1 3 including means for monitoring the pressure of the liquid heat transfer medium and a switch operable in response to the pressure sensed for controlling operation of the heat pump.

1 5. Apparatus according to claim 13 or claim 14 wherein the heat transfer medium flows in an upwards direction through the condenser positioned in the tank.

1 6. Apparatus according to claim 1 5 wherein the condenser positioned in the tank is divided into two sections.

1 7. Apparatus according to any one of the preceding claims wherein the evaporator is arranged to collect heat from ambient air passed over it by a fan.

1 8. Apparatus according to claim 1 7 wherein the evaporator and fan are located in a housing having opposed air inlet and outlet openings.

1 9. Apparatus according to any one of the preceding claims wherein the heat pump includes a further condenser in the return line from the condenser positioned within the tank, said further condenser being associated with the evaporator.

20. Apparatus according to claim 19 wherein the further condenser is positioned in front of the evaporator.

21. Apparatus according to claim 19 wherein the further condenser is positioned within the evaporator.

22. Apparatus according to any one of the preceding claims including means for collecting moisture condensing on the evaporator.

23. Apparatus according to claim 22 including means for returning collected moisture to the environment.

24. Liquid heating apparatus substantially as hereinbefore described with reference to the accompanying drawings.

25. Liquid heating apparatus according to any one of the preceding claims in combination with a storage cylinder and a liquid supply line and liquid return line between the tank and storage cylinder.

26. A domestic hot water supply incorporating liquid heating apparatus according to any one of the preceding claims.

27. A method of heating a liquid comprises collecting heat from the environment and transferring the heat collected to a liquid contained in an unpressurised tank by means of a heat pump.

28. A method according to claim 27 further including the steps of heating the liquid to a predetermined temperature and circulating liquid between the tank and a storage cylinder when the liquid in the tank is heated to said predetermined temperature.

29. A method of heating a liquid substantially as hereinbefore described with reference to the accompanying drawings.

30. A heat pump including an evaporator for collecting heat from a heat source, a primary condenser for transferring collected heat to a fluid and a secondary condenser in the return line from the primary condenser associated with the evaporator for heating the evaporator heat source.

31. A heat pump as claimed in claim 30 substantially as hereinbefore described with reference to the accompanying drawings.

32. A heat pump including an evaporator for collecting heat from a heat source and a condenser for transferring collected heat to a fluid wherein the condenser is constructed and arranged so that in use heat transfer medium flows upwards through the condenser.

33. A heat pump as claimed in claim 32 substantially as hereinbefore described with reference to the accompanying drawings.