GB2361295A

GB2361295A - Water heating apparatus

Info

Publication number: GB2361295A
Application number: GB0006036A
Authority: GB
Inventors: Kam Shing Philip Siu; Man Fai Sham
Original assignee: Hong Kong and China Gas Co Ltd
Current assignee: Hong Kong and China Gas Co Ltd
Priority date: 2000-03-13
Filing date: 2000-03-13
Publication date: 2001-10-17
Also published as: GB0006036D0; TW473606B

Abstract

The apparatus (100) comprises a single gas burner (106), a single heat exchanger (118), control valves (122, 136, 158), a mixer (124) and a pump (142). The apparatus supplies heated water at one temperature to heating appliances (152) and at a lower temperature to water outlets (132) via two circulation loops (150, 130) respectively. A microprocessor controller (156) operates the control valves (122, 136, 158) according to the demands for heated water for either the heating appliances (152) or the outlets (132). When no water is required at the outlets (132) control valves (122, 158) are closed and valve (136) only allows circulation in loop (150). When warm water is required at the outlets (132) valves (122, 158) open and valve (136) operates to only allow circulation in loop (130). Hot water passing through valve (122) is mixed with cold water from supply pipe (108) by mixer (124) to achieve the desired temperature for the outlets (132). This embodiment allows circulation in either loop but not simultaneously. A second embodiment includes a further control valve which allows water to circulate in both loops simultaneously.

Description

2361295 A Heating Apparatus This invention relates to a heating apparatus

and, in particular a heating apparatus which can be powered by gas, and which can supply warm water for consumption as well as hot water for providing heat energy to be used by heating applications.

There are a variety of water heaters. The primary function of a water heater is to heat up water contained in a water tank or a set of convoluted water pipes from which warm water may be drawn. A traditional design for a natural gas water heater includes at least a burner, contained in a heat exchanger and/or a water tank.

Some water heaters are adapted to also serve as a heat source for air heaters and/or dehumidifiers. For example, a newer design of heating apparatus has two independent heat exchangers heated by two independent burners, in which one is dedicated to heating water for consumption and the other is dedicated to heating water which is in turn to heat up air via.a fan coil for warming an indoor environment. While this type of heating apparatus is more versatile, there are a number of disadvantages. For instance, their size is usually quite bulky because the presence of dual chambers in a heating apparatus, and may therefore not be suitable for use in small city apartments. In addition, the cost for manufacturing a heating apparatus of this type is usually high.

2 It is thus an object of the present invention to provide a heating apparatus in which the above shortcomings are mitigated, or at least to provide a useful alternative to the public.

According to the present invention, there is provided a water heating apparatus comprising a single heating source and a continuous water circulation system, wherein the apparatus comprises means for delivering water at a first temperature to at least one water outlet, and means for delivering water at a second temperature for providing heating energy to be used in conjunction with heating means.

Preferably, the second temperature is higher than the first temperature.

Preferably, the water circulation system includes a high temperature loop for delivering water for providing heating energy to be used in conjunction with the heating means and a low temperature loop for delivering water to at least one of the water outlets.

Preferably, means are provided to allow water to circulate in either the high temperature loop or the low temperature loop but not both loops simultaneously.

Preferably, the water circulation system includes a water pump and the loops meet at a junction upstream of the water pump, valve means being provided at the junction that allows water to flow from only one of the loops at a time to the pump and closes the other the loop.

Preferably, when both water at a first temperature and water at a second temperature are required, priority is given to the supply of the water at a first temperature.

Preferably, means are provided to allow water to circulate in both of the loops simultaneously.

3 Preferably, the water circulation system includes a water pump and the loops meet at a junction upstream of the pump, valve means being provided at or upstream of the junction that allows water to flow from both of the loops to the pump simultaneously.

Preferably, the low temperature loop includes a mixer for mixing high temperature water with cold water to produce warm water of a temperature suitable to be drawn by a user.

Preferably, cold water is drawn from a cold water supply through regulator means.

Preferably, the apparatus includes a water supply pipe for delivering cold water to a heat exchanger and a hot water pipe supplying hot water output from the heat exchanger, and wherein the water circulation system includes a first loop comprising a warm water outlet pipe that on demand of a user by opening a warm water outlet draws hot water from the hot water outlet pipe, a mixer for mixing hot water drawn from said hot water pipe with cold water drawn from the water supply pipe to generate warm water, and a warm water return pipe, and a second loop comprising a hot water outlet that draws water from the hot water pipe for providing heating energy to be used in conjunction with the heating means upon activation of the heating means and a hot water return pipe, and wherein the water circulation system further comprises a pump and a third water return pipe for returning hot and/or warm water to the water supply pipe.

Preferably, the warm water return pipe and the hot water return pipe meet at a junction upstream of the pump.

Preferably, valve means are provided at the junction whereby water from only one of the hot water return pipe or the warm water return pipe may flow to the pump whereby only one of the loops may be open at a time.

4 Preferably, when both warm air and water are required simultaneously, priority is given to said warm water loop.

Preferably, valve means are provided in said hot water and warm water return pipes at or upstream of said junction whereby water may flow from either or both of said hot and warm water return pipes to said pump simultaneously.

Preferably, the heat source of the apparatus is a gas burner.

Preferably, the heating means used in conjunction with the apparatus is controlled by a microprocessor.

The invention will now be described, by way of examples only, with reference to the accompanying drawings, in which: - Fig. 1 is a diagram showing a first design of a heating apparatus according to the present invention; and Fig. 2 is a diagram showing a second design of the heating apparatus according to the present invention.

A first embodiment of a heating apparatus according to the present invention is shown in Fig. 1, and generally designated as 100. The heating apparatus 100 comprises a gas incoming pipe 102 supplying gas to a burner 106 located in the heating unit 104. Adjacent to the burner 106 is located a coiled water pipe 116 within which passing water may be heated. The burner 106 and coiled water pipe 116 form an area for heat exchanging (hereinafter referred as heat exchanger 118). The apparatus 100 further includes a water pipe 108, a one-way valve 110, a two-way valve 136, two water regulators (servo valves) 122, 158, three temperature sensors 114, 120, 126, a mixer 124 and a circulation pump 142.

The heating apparatus 100 is generally constructed with two loops, namely a warm water delivering loop 130 and a hot water delivering loop 150. The warm water delivering loop 130 may provide warm water to at least one of the water outlets 132 (e.g. for bathing or showering) via a warm water supply pipe 128 while the hot water delivering loop 150 may provide heating energy to be used in conjunction with a heating application 152. The heating application 152 may be a floor heater, dehumidifier or fan coil unit connected to the hot water delivering loop 150 connected at a hot water outlet 148. For instance, when a fan coil unit is used, air may be heated by the heating application 152. Heated air (warm air) may then be released at an air outlet for increasing an indoor room temperature. The water temperature required for bathing or showering is usually in the range of 35-50T while the water temperature for providing heat energy to the heating apparatus 152 is usually 65-85T. As shown in Fig. 1, all water pipes are connected in a continuous system.

The warm water delivering loop 130 comprises a plurality of water pipes connected in such a way that water heated at the heat exchanger 118 may flow through the water servo valve 122 and water mixer 124 and reach the water outlets 132. The function of the water mixer 124 is to allow hightemperature heated water (usually of 65-85T after passing through the heat exchanger 118) to mix with cold water from the water supply that passes through the water servo regulator 158. The mixing of the heated and cold water lowers the temperature of heated water so that water (warm water with a temperature in the range of 35-50T) passing through warm water pipe 128 and coming out from the water outlets 132 will be suitable for use and will not be too hot. In use, when a water outlet 132 is open, the water pressures at 6 water servo valves 122, 158 drop naturally, which triggers both water servo valves 122, 158 to open. Opening of 122, 158 then allows heated water and cold water to flow through 122, 158. The heated and cold water are then mixed at the mixer 124 as explained above. Upon passing of water at the water servo valves 122, 158, flow sensor 112 senses the water flow and as a result provides signals (according to the flow rate) to circuit board (PC13) 156 which in turn triggers the operation of the heating unit 104. Water is accordingly heated at the heat exchanger 118 to approximately 65-85T. The passing of heated water to the water mixer 124 is regulated by the water servo valve 122. The PCB 156 controls the temperature of mixed water at the mixer 124. This is achieved by using a computerised algorithm contained in the PCB 156 to achieve the temperature as selected by a user. When water ceases to be drawn from the water outlets 132, the heating unit 104 ceases to operate under the control of the PCB 156. Located on water supply pipe 108 is the one-way valve 110 which prevents heated water contained in the water pipe 116 from flowing back to the water supply 108.

In the event that the water outlets 132 are closed, the water servo valves 122, 146 stay closed by default. The circulation pump 142 may be operating at a lower capacity so that warm water continues to circulate in the warm water delivering loop 130. Under this warm water circulation mode, warm water is standing by to be drained at the outlets 132. The operation in this mode is explained in more detail as follows.

As described, a user can turn on the warm water circulation mode for maintaining the temperature in the warm water delivering loop 130 in between 7 drawing of warm water. Under this circulation mode, the PCB 156 sets 2- way valve 136 in a flow direction that conveys water from warm water return pipe 134 to the circulation pump 142 and closes water regulator 158 to prevent water from returning to water inlet 108. The PCB 156 monitors the water temperature measured by temperature sensor 126. When the water temperature drops to a certain level as selected by the user, the PCB 156 activates the circulation pump 142 to draw water in the warm water delivery loop 130 to heating exchanger 118 via warm water return pipe 134 and the water pipe 144. The PCB 156 computes the data collected from the flow sensors 112, 120 and temperature sensors 114, 126. According to the computed values, the PCB 156 modulates gas input to the burner 106 of the heating unit 104 and the speed of the circulation pump 142 so as to achieve the water temperature as selected by the user. When the water temperature as selected by user is reached, the heating unit 104 and the circulation pump 142 cease to operate under the control of the PCB 156. The PCB 156 continues to monitor the temperature measured by the temperature sensor 126 in order to determine when to initiate the warm water circulation in the warm water delivering loop 130.

Turning to the hot water delivering loop 150, when the heating application 152 is activated, a signal is sent to the PCB 156 to start a hot water circulation mode. The PCB 156 sets the 2-way valve 136 to a flow direction that conveys water from hot water return pipe 154 to circulation pump 142 only and closes water regulator 122 to prevent hot water flowing to the warm water delivering loop 130. The PCB 156 activates the circulation pump 142. Water of lower temperature after passing the heating application 152 is pumped from the hot water return pipe 154 to the heating exchanger 118 by the circulation pump 142, and heated by the heating unit 104 at the 8 heat exchanger 104 to a temperature of 65-85T as suitable to the heating application connected. Hot water is then returned to the hot water outlet 148. The PCB 156 computes the data collected from the flow sensor 112 and the temperature sensors 114, 120, and the temperature sensor 120. According to the computed values, the PCB 156 modulates gas input to the burner 106 and the speed of circulation pump 142 to circulate hot water in hot water delivery loop 150 for providing heat energy to the heating application 152. When the heating application 152 is turned off, a signal is sent to the PCB 156 to cease the heating operation.

As can be seen, the heating apparatus 100 interlocks with the heating application 152 which, as described, may be in the form of any suitable heat exchanging means such as a floor heater, dehumidifier or fan coil unit. Hot water is delivered through hot water pipe 146 in the hot water delivering loop 150.

As illustrated above, the warm water delivering loop and the hot water delivering loop are connected in a continuous system in which only one heating source, the burner 106, is required. The warm water delivering loop 130 and hot water delivering loop 150 share the heating effect at the heat exchanger 118. Warm water with temperature in the range of 35- 50T may be provided at the water outlets 132.

In this embodiment, when warm water is being drawn at the water outlets 132, the warm water delivering loop is activated as explained above. In particular, when warm water is being drawn at the water outlets 132, the valve 136 only allows water to flow from water pipe 134 to the circulation pump 142 and does not allow water to 4 9 flow from the heating application 152 to flow to the circulation pump 142. Hence, heating at the heating application 152 while warm water is being drawn at water outlets 132 is hindered as constant circulation of heated water in the warm air generating loop is disallowed. In other words, providing warm water has a higher priority in this embodiment, given that a finite amount of heating power output is provided by the burner 106.

An additional valve 140 located upstream of the one-way valve 138 and downstream of the circulation pump 142 is used to release excess pressure built up in the water circulation system.

The following illustrates three circumstances under which the apparatus 100 may operate.

Circumstance (1) - Warm water is drawn momentarily, while warm water circulation is required and heating application is off.

When warm water is drawn from the water outlet 132, the PCB 156 operates in the warm water delivery mode. The PCB 156 sets the 2-way valve 136 in a flow direction that prepares to convey water from the warm water return pipe 134 to the circulation pump 142, while the circulation pump 142 is not in motion. When warm water is not drawn from the water outlet 132, the PCB 156 switches to the warm water circulation mode. Hence, switching between the warm water circulation mode and warm water delivering mode mode is triggered by drawing of warm water at the warm water outlet 132.

Circumstance (2) - Warm water is drawn momentarily, while warm water circulation is not required and heating application is on.

When warm water is drawn from the water outlet 132, the heating apparatus 100 initiates the warm water delivery mode. The PCB 156 sets the 2way valve 136 in a flow direction that allows water to flow from the hot water return 154 to circulation pump 142, while circulation pump 142 is not in motion. In the moment warm water is not drawn, the PCB 156 switches to the hot water circulation mode. Hence, switching between the hot water circulation mode and the warm water delivering mode is also triggered by drawing of warm water at the warm water outlet 132.

Circumstance (3) - Warm water is drawn momentarily, while warm water circulation is required and heating operation is on.

In the moment warm water is drawn from water outlet 13 2, the heating apparatus 100 operates in a warm water delivery mode. The PCB 156 set the 2-way valve 136 in a flow direction that allows water to flow from the hot water return pipe 154 to circulation pump 142, while circulation pump 142 is not in motion. When warm water is not drawn, the PCB 156 initiates to the warm water circulation mode. When water temperature measured by temperature sensor 126 drops below a certain level of the user selected temperature, the PCB 156 initiates to the hot water circulation mode. The PCB 142 immediately switches to the warm water delivery mode when water is drawn from water outlet 132, when water is drawn fiom the water outlets 132. When warm water is not drawn, switching between the warm water circulation mode and hot water circulation mode is triggered by the temperature measured by the temperature sensor 126.

A second embodiment of a heating apparatus according to the present invention is shown in Fig. 2, and generally designated as 200. The heating apparatus 200 comprises a natural gas incoming pipe 202 supplying natural gas to a burner 206. The burner 206 and water pipe 216 form an area for heat exchanging (hereinafter referred as heat exchanger 218). Adjacent to the burner 206 is located the water pipe 216 within which passing water may be heated. The apparatus 200 further includes a water supply pipe 208, a water return pipe 244, an air heating unit 204 for controlling the burner 213, two one-way valves 210, 238, water outlets 232, one water pump 242, two water mixers 224, 260, four water regulators 222, 235, 237, 258 and an air outlet 240. The water regulators 235, 237 are solenoid valves while the water regulators 222, 258 are servo valves. The arrangement and function of these components are explained in more detail as follow.

The heating apparatus 200, similar to the heating apparatus 100, is also constructed with two loops, namely the warm water delivering loop 230 and hot water delivering loop 250. The warm water delivering loop 230 may provide warm water at water outlets 232 while the hot water delivering loop 250 may provide heat energy to be used in conjunction with a heating application 252. The heating application 252 may be a floor heater, dehumidifier or fan coil unit connected to the hot water delivering loop 250 at a hot water outlet 248. For instance, when a fan coil unit is used, air may be heated by the heating application 252. Heated air (warm air) may then be released at an air outlet for increasing an indoor room temperature. The water temperature required for bathing or showering is usually in the range of 35-50T while the water temperature for providing heat energy to the heating application 252 12 is usually 65-85T. As shown in Fig. 1, all water pipes are connected in a continuous system.

The warm water delivering loop comprises a plurality of water pipes connected in such a way so that water heated at the heat exchanger 218 may flow through the water mixer 224 and reach the water outlets 232. The function of the water mixer 224 is to allow heated water (usually of 6585T or above after passing the heat exchanger 218 and water regulator 222) to mix with cold water from the water supply after passing the water regulator 258. The mixing of the heated and cold water lowers the actual temperature of the heated water so that water (warm water with a temperature in the range of 35-50T) drawn at outlets 232 will be suitable for use and will not be too hot. In use, when a water outlet 232 is open, the water pressures at water regulators 222, 258 naturally drop which triggers both water regulators 222, 258 to open. Opening of the regulators 222, 258 then allows heated water and cold water to flow through regulators 222, 258 respectively, which are then mixed at the mixer 224 as explained above. Located on water supply pipe 208 is the one- way valve 210 which that ensures water contained therein flows away from the water supply.

In the event that water outlets 232 are closed, regulators 222, 258 stay closed by default. The pump 242 may be operating at a lower capacity so that warm water continues to circulate in the warm water delivering loop 230. Warm water will be ready to be drained at the outlets 232.

13 Turning to the hot water delivering loop 250, when the heating application 252 is switched on, the circulation pump 242 is correspondingly activated at a higher capacity. The water regulator 222 is then triggered to close. Water heated at the heat exchanger 218 will flow through water pipe 246 and reach the heating application 252. As the heated water passes through the water pipe 248 towards the heating application 252, heat exchanging takes place. After heated water passes the heating application 252, it will then flow through the valve 235 and the circulation pump 242. The valve 235 is a one-way valve which allows water to flow away the heating application 252 to the circulation pump 242 and prevents any back-flow. The presence of both valves 235, 237 allows water in water pipes 252, 234 to flow pass to the pump 242 simultaneously when both valves 235, 237 are open. The valve 237 also prevents heated water from hot water return pipe 254 of the hot water delivering loop 250 to be drained at water outlets 232. Once water flows through the pump 242, it is returned to the heat exchanger 218 via the water pipe 244 for re-heating and recirculation.

An additional valve 240 located upstream of one-way valves 235, 237 and downstream of the circulation pump 242 is used to release pressure built up in the water circulation system. A further mixer 260 controls the amount of water from the water supply at 208 and water from the water return pipe 244 to flow to the heat exchanger 218.

The following illustrates the three modes under which the apparatus 200 may operate.

14 Warm Water DelivM Mode When water is drawn at the water outlet 232, water flows through water inlet pipe 208 and is measured by flow sensor 212. Signals from flow sensor 212 trigger the PCB 256 to start water-heating operation. Heated water flows to the warm water delivering loop 230 through the water regulator 222, while the water regulator 258 is in close position. The water regulator 222 regulates the flow of heated water to mix with cold water regulated by the water regulator 258 in the mixer 224. The PCB 256 controls the temperature of the mixed water with a computerized algorithm to achieve the temperature as selected by user. The PCB 256 computes the data collected from the flow sensor 212 and the temperature sensor 214, and the temperature sensor 226. According to the computed values, the PCB 256 modulates gas input to the burner 206 and regulates the volume of heated water and cold water passing through the water servo valves 222, 258 to achieve the water temperature as selected by the user. When water ceases to be drawn from the water outlet 232, the heating unit 204 ceases to operate under the control of the PCB 256.

Warm Water Circulation Mode User can turn on warm water circulation mode for maintaining the temperature in the warm water delivering loop 230 in between drawing of warm water. Under this mode, the PCB 256 closes the water servo 258 to prevent water from going back to the water inlet 208 and closes the water regulator 235 to stop water circulating in the hot water delivering loop 250. The PCB 256 monitors the water temperature measured by the temperature sensor 226. When water temperature drops to a certain level below the user-selected temperature, the PCB 256 starts the circulation pump 242 to draw water in the warm water delivering loop 230 back to the heating unit 204 through the warm water return pipe 244. The PCB 256 computes the data collected from flow sensors 212, the temperature sensors 214, 226. According to the computed values, the PCB 256 modulates gas input to the burner 206 and the speed of circulation pump 242 to achieve the water temperature as selected by the user. When the water temperature as selected by user is reached, the heating unit 204 and the circulation pump 242 cease to operate under the control of the PCB 252. The PCB 256 continues to monitor the temperature measured by the temperature sensor 226 to determine when to restart the warm water circulation.

Hot Water Circulation Mode The heating apparatus 200 may be used in conjunction with the heating applications 252. Hot water is delivered through hot water outlet 248 to the heating application 252. After heat energy is transferred, water of lower temperature returns to the hot water return pipe 244.

When the heating application 252 is turned on, a signal is sent to the PCB 256 to start the hot water circulation mode. The PCB 256 closes the water servo 222 and opens the water servo 235 to allow water circulation only in the hot water delivering loop 250. The PCB 256 starts the circulation pump 242 and the heating unit 204. Water is pumped to the heat exchanger 218 by the circulation pump 242. Water is heated at the exchanger 218 to a temperature of 65'C to 85'C as suitable to the heating application(s) connected. Hot water is delivered to hot water pipe 248. The PCB 256 computes the data collected from flow sensor 212, the temperature sensors 214, 220 According to the computed values, the PCB 256 modulates gas input to the burner 206 and the speed of the circulation pump 242 to circulate hot water in the hot water 16 delivering loop 250 for providing heat energy to the heating application 252. When the heating application 252 is turned off, a signal is sent to the PCB 256 to cease heating operation.

Parallel Mode In this embodiment, the heating apparatus 200 can operate to cater for parallel running of warm water delivery, warm water circulating and hot water circulating.

When warm water delivery and hot water circulation are running in parallel, the PCB 256 closes solenoid valve 237. The PCB 256 puts the circulation pump 242 in motion according to the signal received from the heating application 252. In parallel, water is drawn from the water outlet 232. The PCB 256 computes the data collected from the sensors 262, 212 and the temperature sensors 214, 220, 226, 260 to determine the total volume of hot water required. According to the computed values, the PCB 256 modulate the gas input to the burner 206 to provide the required volume of heated water. The PCB 256 regulates the volume of heated water and cold water passing through water regulators 222, 258 from which water is mixed in the mixer 224 to achieve the temperature as selected by the user and deliver to the warm water outlet 232. In parallel, the PCB 256 opens solenoid valve 235 and regulates the speed of the circulation pump 202 to provide heated water to the hot water delivering loop, which is sufficient to recover the heat transferred to the heating application 252. The circulation pump 242 returns water from the hot water return pipe 254. The PCB 256 always gives priority to warm water delivery by reducing the speed of circulation pump 242 to a minimum flow rate such that most of the heated water is delivered to the warm water delivery loop 228, When the total volume of heated water required 17 exceeds the capacity of the heating apparatus 200, the PCB 256 regulates the warm water at the temperature as selected by user of reduced volume. When the water outlet 232 ceases to drawn warm water, the PCB 256 switches to heating water circulation mode.

When warm water circulation and heating water circulation are running in parallel, the PCB 256 always set heated water temperature (usually at a lower level) that meet the temperature selected by user. The PCB 256 opens solenoid valves 235, 237 and the water servo valve 222 to allow the circulation pump 242 to draw water from both the warm water delivery loop 230 and the hot water delivering loop 250. The PCB 256 also close the water servo valve 258 to prevent heated water from flowing to the water inlet 208. The PCB 256 collects data from the temperature sensors 214, 226, 220 and the flow sensor 212. According to the computed values, the PCB 256 modulates the gas input to the burner 206 and sets the circulation pump 242 in full speed to shorten the time required to deliver heated water to the warm water circulation loop 230 at the temperature as selected by the user. When temperature of water in the warm water circulation loop reaches the level as selected by user, the PCB 256 switches to hot water circulation mode. As illustrated above, the warm water delivering loop 230 and the hot water

delivering loop 250 are connected in a continuous system in which only one heating source, the burner 206, is required. The warm water delivering loop 230 and the hot water delivering loop share the heating effect at the heat exchanger 230. Warm water with a temperature in the range 35-STC may be provided at outlets 232.

18 It should be understood that the above only describes preferred embodiments according to the present invention, and that various modifications and alterations may be made thereto without departing from the spirit of the invention. For example, an apparatus according to the present invention may be powered by electricity instead of natural gas.

Claims

1. A water heating apparatus comprising a single heating source and a continuous water circulation system, wherein said apparatus comprises means for delivering water at a first temperature to at least one water outlet, and means for delivering water at a second temperature for providing heating energy to be used in conjunction with heating means.

A water heating apparatus as claimed in Claim 1 wherein said second temperature is higher than said first temperature.

3. Apparatus as claimed in Claim 1 or 2 wherein said water circulation system includes a high temperature loop for delivering water for providing heating energy to be used in conjunction with said heating means and a low temperature loop for delivering water to at least one of said water outlets.

Apparatus as claimed in Claim 3 wherein means are provided to allow water to circulate in either said high temperature loop or said low temperature loop but not both loops simultaneously.

5. Apparatus as claimed in Claim 4 wherein said water circulation system includes a water pump and said loops meet at a junction upstream of said water pump, valve means being provided at said junction that allows water to flow from only one of said loops at a time to said pump and closes the other said loop.

Apparatus as claimed in Claim 4 or 5 wherein when both water at a first temperature and water at a second temperature are required, priority is given to the supply of said water at a first temperature.

7. Apparatus as claimed in Claim 3 wherein means are provided to allow water to circulate in both said loops simultaneously.

8 Apparatus as claimed in Claim 7 wherein said water circulation system includes a water pump and said loops meet at a junction upstream of said pump, valve means being provided at or upstream of said junction that allows water to flow from both of said loops to said pump simultaneously.

9. Apparatus as claimed in any of Claims 3 to 8 wherein said low temperature loop includes a mixer for mixing high temperature water with cold water to produce warm water of a temperature suitable to be drawn by a user.

10. Apparatus as claimed in Claim 9 wherein said cold water is drawn from a cold water supply through regulator means.

Apparatus as claimed in Claim 1 including a water supply pipe for delivering cold water to a heat exchanger and a hot water pipe supplying hot water output from said heat exchanger, and wherein said water circulation system includes a first loop comprising a warm water outlet pipe that on demand of a user by opening a warm water outlet draws hot water from said hot water pipe, a mixer for mixing hot water drawn by said warm water outlet pipe with cold water drawn from said water supply pipe to generate warm water, and a warm water return pipe, and a second loop comprising a hot water outlet that draws water from said hot water pipe for providing heating energy to be used in conjunction with said heating means upon activation of said heating means and a hot water return pipe, and wherein said water circulation system further comprises a pump and a third water return pipe for returning hot and/or warm water to said water supply pipe.

12.

Apparatus as claimed in Claim 11 wherein said warm water return pipe and said hot water return pipe meet at a junction upstream of said pump.

13, Apparatus as claimed in Claim 12 wherein valve means are provided at said junction whereby water from only one of said hot water return pipe or said 21 warm water return pipe may flow to said pump whereby only one of said loops may be open at a time.

14. Apparatus as claimed in Claim 13 whereby if both warm water and hot water are required simultaneously priority is given to said warm water loop.

15. Apparatus as claimed in Claim 14 wherein valve means are provided in said hot water and warm water return pipes at or upstream of said junction whereby water may flow from either or both of said hot and warm water return pipes to said pump simultaneously.

16. Apparatus as claimed in any preceding claim wherein said heat source is a gas burner.

17. Apparatus as claimed in any preceding claim wherein said heating means is controlled by a microprocessor.

18. A water heating apparatus substantially as hereinbefore described with reference to the embodiment of either Fig. 1 or Fig.2,