WO2018162729A1

WO2018162729A1 - A domestic hot water installation and method of operating same

Info

Publication number: WO2018162729A1
Application number: PCT/EP2018/055941
Authority: WO
Inventors: Terence William Madigan; Terence Gerard Madigan
Original assignee: Systemlink Aquaeco Limited
Priority date: 2017-03-09
Filing date: 2018-03-09
Publication date: 2018-09-13
Also published as: GB2560359A; GB201703786D0

Abstract

This invention relates to a domestic hot water installation and a method of operating same. The domestic hot water installation comprises an external heating circuit. The external heating circuit includes a heat source and a heat exchanger. The heat source is either a boiler or a heat pump. A controller receives temperature readings from a plurality of temperature sensors and controls a pair of variable speed pumps, one on the primary side of the heat exchanger and one on the secondary side of the heat exchanger, to provide hot water to a hot water outlet, which may comprise a hot water cylinder, a hot water tap module or the like, at a desired temperature in a tightly controlled manner. The pumps are operated so that changes in the additional equipment connected to the heat source will not have an adverse effect on the provision of the hot water in the domestic hot water installation.

Description

Title of Invention:

"A domestic hot water installation and method of operating same" Technical Field:

This invention relates to a domestic hot water installation and a method of operating same. More specifically, the present invention relates to a domestic hot water installation having an external heating circuit comprising a heat source and a heat exchanger, and a method of operating such an installation. The heat source comprises either a boiler or a heat pump.

Background Art: Domestic hot water installations that incorporate an external heating circuit comprising a boiler and a heat exchanger are very useful as they provide an almost instantaneous hot water supply in the household. They obviate the delays associated with immersion heaters and in many cases provide a cost effective way of satisfying the household's hot water requirements. One such installation is that described in the applicants own PCT Patent Application Publication No. WO2015/082708. WO2015/082708 describes a method and system that allow for the amount of hot water stored in a hot water cylinder to be known to a high degree of accuracy and reduces avoidable waste. Other similar arrangements are known for the provision of underfloor heating. There are however problems with many of the known offerings. Heretofore, many of the known arrangements rely on the use of a mixing valve on the primary side of the heat exchanger to ensure that hot water at a stable delivery temperature is provided. This is highly disadvantageous as mixing valves and the control equipment associated therewith are often prohibitively expensive for domestic applications in particular and can add significant complexity to the system. Other arrangements provide a mixing valve or a throttle valve on the secondary side of the heat exchanger however these too are deemed too expensive and complex for application in a domestic hot water installation. Another problem with many of the known methods and systems is that they are relatively slow to react to changes in the temperature of the heating fluid being delivered from the boiler. These changes may for example be due to a heating circuit being turned on or off or variations in the firing profile of the particular type of boiler. Sudden changes in the heating fluid temperature may result in significant deviation from the desired set temperature of the supplied hot water. This is also highly undesirable. Again, these problems can be addressed to a degree by the use of suitable mixing valves on the secondary side however these solutions are not suitable for domestic applications in particular due to additional cost and complexity.

In more recent times, heat pumps have become popular in domestic installations to reduce the cost of heating in the home. There is however a problem with the use of a heat pump to provide hot water in the domestic hot water installation due to the varying output of the heat pump, caused in part by the varying weather conditions on which they rely. As a consequence, complex and expensive control solutions are necessary to implement such solutions in a domestic hot water installation. UK Patent Application Publication No. GB2406901 in the name of EC Power A/S describes a combined heat and power unit with a feedback conduit for temperature regulation. This configuration requires the use of mixing valves and therefore is seen as unsatisfactory for use in a domestic hot water installation. German Patent Application Publication No. DE4313276 in the name of Koenig describes a solar power installation and a method of operating same. This configuration incorporates throttle valves and mixing valves and is seen as unsuitable for use in a domestic hot water installation. It is an object of the present invention to provide a domestic hot water installationand method that overcome at least some of these problems and offer a useful choice to the consumer.

Summary of Invention

According to the invention there is provided a domestic hot water installation comprising: a water inlet and a hot water outlet; an external heating circuit, the external heating circuit comprising a heat source and a heat exchanger; a pipe network connecting the water inlet and the hot water outlet to the heat exchanger and connecting the heat source to the heat exchanger; a first pump operable to deliver heating fluid from the heat source, through a primary side of the heat exchanger and back to the heat source; a second pump operable to deliver water from the water inlet, through a secondary side of the heat exchanger and back to the hot water outlet; a plurality of temperature sensors including: a first temperature sensor in thermal communication with the water being delivered from the water inlet upstream of the heat exchanger, a second temperature sensor in thermal communication with the water being delivered back to the hot water outlet downstream of the heat exchanger, a third temperature sensor in thermal communication with the heating fluid being delivered from the heat source upstream of the heat exchanger; and a controller in communication with the first pump, the second pump and the plurality of temperature sensors, the controller having: a processor for processing the data received from the temperature sensors; an accessible memory for storage of a domestic hot water installation operating program; and means to operate the first and second pumps in accordance with the domestic hot water installation operating program.

By having such a system, it will not be necessary to provide a mixing valve or the associated control circuitry. This will significantly reduce the cost and complexity of the system. Instead, the installation has a plurality of temperature sensors and a pair of pumps to closely control the temperature and flow of heating fluid and water to and from the heat exchanger. The arrangement will also be able to react quicker to changes in the heating fluid temperature without a significant deviation from the set temperature of the delivered hot water. Furthermore, in those instances in which the heat source is a boiler, by having a temperature sensor in thermal communication with the heating fluid being delivered from the boiler upstream of the heat exchanger, it is possible to allow the boiler get up to temperature before starting to draw water from the water inlet for heating or indeed before circulating water back to the boiler through the heat exchanger. This can result in substantial savings.

In one embodiment of the invention there is provided a domestic hot water installation in which there is provided a fourth temperature sensor in thermal communication with the heating fluid being delivered back to the heat source downstream of the heat exchanger. This is seen as a particularly preferred embodiment of the present invention. By having such an arrangement, when the heat source is a boiler, it is possible to ensure that the heating fluid being returned to the boiler is within the desired operating range of the boiler. If the return temperature of the heating fluid returning to an oil boiler is too low, the flue gases of the boiler may produce sulphurous acid and other corrosive agents which can damage the boiler and the flue with often catastrophic consequences. Similarly, when the heat source is a heat pump, it is possible to ensure that the heating fluid being returned to the heat pump is above a predetermined minimum temperature to reduce the temperature gap and thereby improve the coefficient of performance (COP) of the heat pump. By having the fourth temperature sensor, the first pump may be operated at an appropriate speed to ensure that the heating fluid is above the desired temperature when it is returned to the heat source.

In one embodiment of the invention there is provided a domestic hot water installation in which at least one of the temperature sensors is mounted at a port of the heat exchanger. By mounting the temperature sensor at the port of the heat exchanger, a more compact assembly may be provided. This will also be simpler to install than alternative configurations. ln one embodiment of the invention there is provided a domestic hot water installation in which the first pump is a variable speed pump and the means to operate the first pump comprises means to vary the speed of the first pump in addition to turning the first pump on or off. The variable speed pump may be a single or twin head pump. This is seen as a particularly useful embodiment of the present invention. By being able to vary the speed of the pump, this will enable the assembly to react more effectively to other heating circuits in the household being turned on or off and will enable closer control over the resultant temperature of the hot water returned to the hot water outlet. In one embodiment of the invention there is provided a domestic hot water installation in which the second pump is a variable speed pump and the means to operate the second pump comprises means to vary the speed of the second pump in addition to turning the second pump on or off. Again, this is seen as a particularly useful embodiment of the invention that will allow closer control over the temperature of the hot water returned to the hot water outlet from the heat exchanger.

In one embodiment of the invention there is provided a domestic hot water installation in which there is provided a hot water cylinder and in which the water inlet and the hot water outlet are connected to the hot water cylinder. This is seen as a particularly beneficial aspect of the present invention. The water heated in the heat exchanger can be returned to the top of the hot water cylinder through the hot water outlet and the water fed to the heat exchanger can be delivered from the bottom of the hot water cylinder through the water inlet. In this way, hot water at a predetermined temperature can be provided in the hot water cylinder.

In one embodiment of the invention there is provided a method of operating a domestic hot water installation of the type claimed in any preceding claim in which the method further comprises the step of: the controller using the third temperature sensor to monitor the temperature of the heating fluid being delivered from the heat source to the heat exchanger; and the controller turning the second pump off when the temperature of the heating fluid being delivered from the heat source to the heat exchanger is below a first threshold temperature and turning the second pump on when the temperature of the heating fluid is above the first threshold temperature.

By having such a method, this will prevent waste of energy and electricity from unnecessary circulation of water from the water inlet for heating before the heating fluid from the heat source is up to temperature. This is a simple and effective way of improving the overall efficiency of the method.

In one embodiment of the invention there is provided a method of operating a domestic hot water installation in which the method further comprises the step of: the controller using the fourth temperature sensor to monitor the temperature of the heating fluid being delivered back from the heat exchanger to the heat source; and the controller varying the speed of the first pump in response to the output of the fourth temperature sensor to maintain the temperature of the heating fluid returning to the heat source from the heat exchanger above a second threshold temperature.

By monitoring the temperature of the heating fluid returning to the heat source, it is possible to ensure that the heating fluid does not drop below a desired temperature of returning heating fluid. This can be important as it will ensure that a gas or an oil boiler will stay in condensing mode. Furthermore, in oil-fired boilers, this will prevent sulphurous acid being created in the exhaust flue gases and will protect against damage to the oil-fired boiler and the flue over time. For heat pump implementations, this will enable the heat pump to be operated at a desired COP level.

In one embodiment of the invention there is provided a method of operating a domestic hot water installation in which the method further comprises the steps of: the controller using the first temperature sensor to monitor the temperature of the water being delivered from the water inlet to the heat exchanger; the controller using the second temperature sensor to monitor the temperature of the water being delivered back to the hot water outlet from the heat exchanger; and the controller varying the speed of the second pump in response to the outputs of the first and second temperature sensors to maintain the temperature of the water returning to the hot water outlet from the heat exchanger at a given temperature. This is seen as an important embodiment of the present invention, particularly when the water inlet and hot water outlet are connected to a hot water cylinder. The temperature of the water entering the heat exchanger from the water inlet or the hot water cylinder was heretofore largely ignored. However, by providing such a method, the temperature of the water coming from the water inlet or the hot water cylinder is carefully monitored and the length of time that the water has to spend in the heat exchanger to get up to temperature will depend to a large extent on the temperature of the water before it enters the heat exchanger. This will enable a more effective method that will heat the water to the desired temperature in the shortest time possible. In one embodiment of the invention there is provided a method of operating a domestic hot water installation in which the method further comprises the step of: the controller varying the speed of the second pump in response to the output of the third temperature sensor to maintain the temperature of the water returning to the hot water outlet from the heat exchanger at a given temperature.

In this way, if there is a drop in the temperature of the heating fluid coming from the heat source, the water in the secondary side of the heat exchanger can be kept for longer in the heat exchanger to ensure that it gets up to the set temperature. This method will ensure that the system is quick to react to changes in the operating conditions of the heat source and that there are little or no substantial deviations from the set temperature of the heated water. This will allow for very accurate control over the delivery of the hot water to the hot water outlet or hot water cylinder if one is provided connected to the hot water outlet. Brief Description of the Drawings:

The invention will now be more clearly understood from the following description of some embodiments thereof given by way of example only with reference to the accompanying drawings, in which:-

Figure 1 is a diagrammatic representation of a first embodiment of a hot water installation according to the invention; and Figure 2 is a diagrammatic representation of a second embodiment of a hot water installation according to the invention.

Detailed Description of the Drawings: Referring to Figure 1 , there is shown a domestic hot water installation, indicated generally by the reference numeral 1 , comprising a water inlet 2, a hot water outlet 4, a hot water cylinder 3, an external heating circuit 5 comprising a heat source 7 (in this instance a boiler) and a heat exchanger 9, and a pipe network of pipes 11 (a)-1 1 (d) connecting the water inlet 2, the water outlet 4 and by extension the hot water cylinder 3 to the heat exchanger 9, and the boiler 7 to the heat exchanger 9. The boiler 7 is connected to the primary side 13 of the heat exchanger 9 and the hot water cylinder is connected to the secondary side 15 of the heat exchanger.

A first pump 17 is provided to deliver heating fluid from the boiler 7 along a flow pipe 1 1 (c) to a flow port 19 of the primary side 13 of the heat exchanger 9. The heating fluid passes through the primary side 13 of the heat exchanger before exiting through a return port 21 of the primary side of the heat exchanger, along the return pipe 1 1 (d) and back to the boiler 7. The first pump 17 is a variable speed pump, the operation of which will be described in more detail below.

A second pump 23 is provided to deliver water from a point adjacent the base of the hot water cylinder 3 along a flow pipe 1 1 (a) to a flow port 25 of the secondary side 15 of the heat exchanger 9. The water passes through the secondary side 15 of the heat exchanger before exiting through a return port 27 of the secondary side of the heat exchanger, along a return pipe 1 1 (b) and back to the hot water cylinder 3 to a point adjacent the top of the hot water cylinder. The second pump 23 is also a variable speed pump, the operation of which will be described in more detail below. There are provided three temperature sensors including a first temperature sensor 29 located adjacent the flow port 25 of the secondary side of the heat exchanger, a second temperature sensor 31 located adjacent to the return port 27 of the secondary side of the heat exchanger, and a third temperature sensor 33 located adjacent to the flow port 19 of the primary side of the heat exchanger.

In addition to the foregoing, there is provided a controller 35 in communication with each of the first pump 17, the second pump 23 and the three temperature sensors 29, 31 , 33. The communication links between the controller 35 and the pumps 17, 23 and the controller 35 and the temperature sensors 29, 31 , 33 are illustrated by way of dashed lines 37(a)-37(e). The temperature sensors 29, 31 , 33 communicate the temperature of the fluid or water passing through their respective ports back to the controller 35 over communication links 37(c), 37(d) and 37(e) and the controller sends control instructions to operate the pumps 17, 23 over communication links 37(a), 37(b). The communication links 37(a)-37(e) could be provided by wired and/or wireless links. The controller 35 comprises a processor 39 for processing the data received from the temperature sensors, an accessible memory 41 for storage of a domestic hot water installation operating program, and means 43 to operate the first and second pumps 17, 23 in accordance with the domestic hot water installation operating program. In use, pumps 17 and 23 are initially turned off. The boiler and the pump 17 are turned on and the temperature of the heating fluid from the boiler is monitored by temperature sensor 33. It will be understood that the boiler 7 may be 50 metres away from the heat exchanger 9 and therefore the temperature sensor 33 is provided adjacent to the heat exchanger in order to detect the temperature of the heating fluid entering the heat exchanger. If desired, an additional temperature sensor may be provided at the outlet of the boiler operable to detect the temperature of the heating fluid exiting the boiler. By monitoring the temperature in these two positions simultaneously, it is possible to measure the temperature drop between the locations. This may allow for improved control of the system by adjusting the primary pump speed to enable better "condensing" temperatures. Once the temperature of the heating fluid at the heat exchanger gets "up to temperature", typically in the region of 70°C, the second pump 23 is turned on and the first pump circulates heating fluid through the primary side 13 of the heat exchanger from the boiler 7 and the second pump 23 circulates water from the hot water cylinder 3 through the secondary side 15 of the heat exchanger. The heating fluid circulating in the primary side 13 of the heat exchanger from the boiler 7 heats the water in the secondary side 15 of the heat exchanger and the heated water in the secondary side 15 returns to the hot water cylinder 3. The speed of the pump 23 is controlled to ensure that the water remains in the secondary side 13 for a period of time sufficient to heat the water to the desired set temperature, which may, for example, be of the order of 60°C. In this way, cooler water is gradually fed from the bottom of the hot water cylinder through the heat exchanger where it is heated and then returned to the top of the hot water cylinder from where it may be drawn through pipework (not shown) for use in a shower, bath, sink or the like. Advantageously, the temperature of the water entering and exiting the secondary side of the heat exchanger is known and the temperature of the heating fluid is known. This allows for a very accurate and controlled method of heating the hot water. The speed of the pump 17 may also be regulated to ensure that the heating fluid does not remain in the heat exchanger for too long, which may result in too great a drop in the temperature of the heating fluid before it is returned to the boiler.

Referring to Figure 2, there is shown an alternative embodiment of a hot water installation, indicated generally by the reference numeral 51 , where like parts have been given the same reference numeral as before. The hot water installation further comprises a fourth temperature sensor 53 adjacent the return port 21 of the primary side 13 of the heat exchanger. The fourth temperature sensor is in communication with the controller 35 over the communication link 37(f). In use, the fourth temperature sensor monitors the temperature of the heating fluid exiting the primary side of the heat exchanger and returning to the boiler 7. If the temperature of the returning heating fluid is too low, (for example in a boiler that operates in a temperature range of 82°C to 71 °C, below 71 °C would be considered too low), this can impair the efficiency of the boiler and this can cause the creation of sulphurous acid and other corrosive agents in the flue gases of oil boilers. These agents can result in corrosion of the flue and the boiler components with potentially catastrophic consequences. Accordingly, it is preferable to keep the temperature of the heating fluid returning to the boiler at or above the minimum operating temperature. The temperature sensor 53 detects the temperature of the heating fluid returning to the boiler and if the temperature of the heating fluid returning to the boiler should drop to or below the desired minimum operating temperature, the controller 35 will increase the speed of the pump 17 to push heating fluid through the primary side of the heat exchanger faster. If the pump 17 is already operating at maximum speed, the pump 23 may be shut down by the controller 35 until such time that the boiler is in a position to provide heating fluid at an appropriate temperature. More preferably though, the controller 35 will have the ability to shut down or restrict other heating circuits (not shown) in the household and concentrate the efforts of the boiler into heating water in the household.

It will be understood from the foregoing that the system and method according to the invention provide greater control over the operation of the domestic hot water installation. The system and method allow for hot water to be provided almost instantaneously once the boiler is up to temperature. The temperature of the hot water is regulated very closely without the need for mixing valves, choke valves, blending valves, diverting valves or the associated control circuitry. Furthermore, with the particular arrangement, the amount of waste and damage to the equipment is significantly reduced. This is achieved in part by the ability of the system and method to control the speed of the pair of pumps, one of which is on the primary side of the heat exchanger and the other of which is on the secondary side of the heat exchanger. Furthermore, by having the specific arrangement of temperature sensors as described, the system and method are able to monitor the operating parameters of the domestic hot water installation closely and react quickly to any changes to ensure continuity and reliability of supply.

Advantageously, the method of control described takes away the many temperature anomalies that occur between the gas fired boilers, oil fired boilers and solid fuel boilers. Solid fuel boilers can and do get damaged if the return temperature is too low. Catastrophic failure is known to happen through corrosion of the boiler if consistent low return temperatures are experienced. There are specific mixing valves on sale for solid fuel boilers to try and cure this problem, however these are expensive to provide. The boiler 7 described herein could be any of those types of boiler and is not limited to one particular type of boiler. For example, in addition to oil, gas and solid fuel boilers, an electric boiler could also be used on the primary side. The method according to the invention ensures that the switching on or off of different zones within a heating system does not result in a sudden loss of the set temperature required in the hot water cylinder. Furthermore it allows for the combination of different sources of heating appliance to be turned on/off at any time seamlessly without loss of set temperature or cooling of the domestic hot water.

The unique controller 35 adjusts a proportional-integral-derivative (PID) controller (not shown) of the pump 17, 23 while also taking into account the differing temperatures parameters of the boiler 7 being used. For example, there are boilers that use a typical flow and return temperature of 82°C and 71 °C respectively. The temperature of hot water required in the hot water cylinder 3 is between 55°C and 65°C. As outlined above, damage can be done to the boiler and the flue if the return temperature of the heating fluid of this type of boiler goes below the 71 °C by allowing the flue gasses in oil boilers to produce sulphurous acids which eat away at the flue and the boilers own fabric potentially resulting in catastrophic failure of the pressurized waterways. The method and system according to the invention obviate the possibility of this damage.

Furthermore, modern condensing gas boilers typically operate under different conditions. It is recommended by some manufacturers to keep the boiler temperature set at the order of 60°C for optimum use. This temperature is fine to supply hot water in a hot water cylinder when you are using a traditional coil in a domestic hot water cylinder. However, when using a brazed heat exchanger or a plate heat exchanger, it is impossible to deliver domestic hot water close to the 60°C required. Additionally, different gas boiler manufacturers adjust the flow temperature up and down constantly at the beginning of the firing sequence in order to try and achieve the best and most efficient temperature to fire to try and take into account the buildings natural heat profile. This profile differs greatly from building to building because of the type of emitters (i.e. radiators) being used in the house, whether they are high output, low water content radiators or steel panel radiators or underfloor heating or forced air circulation type emitters. Boiler manufacturers use different profiles of firing to try and achieve the desired outcome. The method and system according to the invention applies the appropriate control signals to ensure that the domestic hot water temperature is always controlled to the set temperature of between 55°C and 65°C. According to an alternative embodiment of the present invention, the heat source 7 could, instead of being provided by way of a boiler, be provided by way of a heat pump. In other words, in Figures 1 and 2, the heat pump rather than a boiler would be represented by the numeral 7. The first pump 17 on the primary side of the heat exchanger 9 may be incorporated into the heat pump 7 and a separate pump on the primary side of the heat exchanger may not be required. The configuration of the present invention is able to incorporate the heat pump into a domestic hot water installation with relative ease and operate that heat pump with good efficiency. The configuration will enable the first pump 17 (whether integral or separate to the remainder of the heat pump) to be operated in such a way that the COP of the heat pump is within the desired operating range for the heat pump. For example, it may be determined that a temperature drop of more than 5°C would be disadvantageous from a COP perspective, in which case the pump 17 may be operated to ensure that there is not a drop greater than 5°C in the heating fluid returning to the heat pump. For a heat pump implementation that is used to provide domestic hot water, the hot water may be provided to a hot water cylinder at a temperature of the order of 48°C. In order to achieve this, the heat pump will have to provide a heating fluid at no less than of the order of a minimum of 50°C. Alternatively, the hot water produced at a lower temperature could be put to other uses in the household if desired.

In the embodiments described, it is envisaged that the heat exchanger is a plate heat exchanger or a brazed heat exchanger. Other heat exchangers can be used such as Shell and Tube heat exchangers. The temperature sensors 29, 31 , 33, 53 may be incorporated into the ports of the heat exchanger for convenience and this will provide a compact unit that is simple and efficient to install. It is envisaged that in addition to providing hot water to a hot water cylinder, the method and system could also be applied to other applications such as an underfloor heating system. In this way, the underfloor heating system could also be run in an efficient and effective manner without the need for mixing valves and the associated control circuitry. ln the embodiments shown, the water inlet 2 is shown connected to the base of a hot water cylinder to take cooler water from the base of the hot water cylinder and the hot water outlet 4 is shown connected feeding hot water back in to the top of the hot water cylinder. It is envisaged that the hot water cylinder 3 could be discarded and the hot water outlet 4 may be connected directly to a tap (not shown) and the water inlet 2 could be connected directly to the mains, a ring main of a domestic hot water installation, or other water supply so that the system and method could be used to provide a hot water supply practically instantaneously to the tap. The tap could be in a kitchen or a bathroom for example. Accordingly, the same principles as described above apply to a High temperature hot water (HTHW) to Medium temperature hot water (MTHW) installation and a MTHW to Low temperature hot water (LTHW) installation that operate without a hot water cylinder and instead have a ring main. For example, in a MTHW installation such as those commonly found in hotels, apartment complexes and the like, the primary water can be at 150°C and it is reduced to LTHW at 80°C. In order to achieve this, a plate heat exchanger or a brazed heat exchanger or a Shell and Tube heat exchanger with a mixing valve to control the heat exchanger would be provided.

Preferably, the controller 35 will also be in communication with other control equipment in such a way that the controller 35 will be able to control one or more other zones in the household so that the hot water supply can be prioritized. The concept of hot water priority is not in itself new. For example, Combi Gas boilers use this idea to enable the switching off of any heating zones in order to direct the full KW power of the boiler to heating the DHW for immediate use by the shower or hot taps. However, heretofore, it is unknown to provide a domestic hot water installation controller which has this built in functionality. According to the present invention, the controller has the ability to switch off all the heating zones while in use should the user call for hot water. Furthermore, if the user has called for a volume of hot water and no heating has been called for but perhaps the programmed heating timer on the controller does attempt to switch on one are all of the heating zones, the controller according to the invention will prevent the heating zones from being switched on until the water "call" has been satisfied. Normal Fossil fuel or solid fuel boilers (with the exception of Combi Boilers) do not have this facility and the functionality of those boilers can be enhanced using the controller according to the present invention. Another advantageous aspect of the present invention is that the controller 35 may operate to ensure that there is always sufficient hot water in the tank for the user. For example, the domestic hot water installation operating program may stipulate that there is always sufficient water (e.g. 100 litres) in the tank for a shower and the controller 35 may operate the pumps in accordance with a domestic hot water installation operating program that ensures that this requirement is fulfilled. The domestic hot water installation operating program may stipulate that if the hot water gets below a certain level, the boiler and the pumps may be operated to bring the hot water level up to a desired level.

In this specification the terms "comprise, comprises, comprised and comprising" and the terms "include, includes, included and including" are all deemed totally interchangeable and should be afforded the widest possible interpretation. The invention is not limited to the embodiments hereinbefore described but may be varied in both construction and detail within the scope of the appended claims.

Claims

A domestic hot water installation (1 , 51 ) comprising: a water inlet (2) and a hot water outlet (4); an external heating circuit (5), the external heating circuit comprising a heat source (7) and a heat exchanger (9); a pipe network 1 1 (a)-1 1 (d) connecting the water inlet and the hot water outlet to the heat exchanger and connecting the heat source to the heat exchanger; a first pump (17) operable to deliver heating fluid from the heat source, through a primary side (13) of the heat exchanger and back to the heat source; a second pump (23) operable to deliver water from the water inlet, through a secondary side (15) of the heat exchanger and back to the hot water outlet; a plurality of temperature sensors (29, 31 , 33) including: a first temperature sensor (29) in thermal communication with the water being delivered from the water inlet upstream of the heat exchanger, a second temperature sensor (31 ) in thermal communication with the water being delivered back to the hot water outlet downstream of the heat exchanger, a third temperature sensor (33) in thermal communication with the heating fluid being delivered from the heat source upstream of the heat exchanger; and a controller (35) in communication with the first pump, the second pump and the plurality of temperature sensors, the controller having: a processor (39) for processing the data received from the temperature sensors; an accessible memory (41 ) for storage of a domestic hot water installation operating program; and means (43) to operate the first and second pumps in accordance with the domestic hot water installation operating program. (2) A domestic hot water installation (1 , 51 ) as claimed in claim 1 in which there is provided a fourth temperature sensor (53) in thermal communication with the heating fluid being delivered back to the heat source downstream of the heat exchanger.

A domestic hot water installation (1 , 51 ) as claimed in claim 1 or 2 in which at least one of the temperature sensors (29, 31 , 33, 53) is mounted at a port of the heat exchanger.

A domestic hot water installation (1 , 51 ) as claimed in any preceding claim in which the first pump (17) is a variable speed pump and the means to operate the first pump comprises means to vary the speed of the first pump in addition to turning the first pump on or off.

A domestic hot water installation (1 , 51 ) as claimed in any preceding claim in which the second pump (23) is a variable speed pump and the means to operate the second pump comprises means to vary the speed of the second pump in addition to turning the second pump on or off.

A domestic hot water installation (1 , 51 ) as claimed in any preceding claim in which there is provided a hot water cylinder (3) and in which the water inlet (2) and the hot water outlet (4) are connected to the hot water cylinder.

A domestic hot water installation (1 , 51 ) as claimed in any preceding claim in which the heat source (7) is a boiler.

A domestic hot water installation (1 , 51 ) as claimed in claim s 1 to 6 in which the heat source (7) is a heat pump. A domestic hot water installation (1 , 51 ) as claimed in claim 8 in which the first pump (17) is integral with the heat pump.

A method of operating a domestic hot water installation (1 , 51 ) of the type as claimed in any preceding claim, the method comprising the steps of: the controller using the third temperature sensor (33) to monitor the temperature of the heating fluid being delivered from the heat source (7) to the heat exchanger (9); and the controller (35) turning the second pump (23) off when the temperature of the heating fluid being delivered from the heat source (7) to the heat exchanger (9) is below a first threshold temperature and turning the second pump on when the temperature of the heating fluid is above the first threshold temperature.

A method of operating a domestic hot water installation (1 , 51 ) as claimed in claim 10 in which the method further comprises the step of: the controller (35) using the fourth temperature sensor (53) to monitor the temperature of the heating fluid being delivered back from the heat exchanger (9) to the heat source (7); and the controller (35) varying the speed of the first pump (17) in response to the output of the fourth temperature sensor (53) to maintain the temperature of the heating fluid returning to the heat source from the heat exchanger above a second threshold temperature.

A method of operating a domestic hot water installation (1 , 51 ) as claimed in claims 10 or 1 1 in which the method further comprises the steps of: the controller (35) using the first temperature sensor (29) to monitor the temperature of the water being delivered from the water inlet to the heat exchanger; the controller (35) using the second temperature sensor (31 ) to monitor the temperature of the water being delivered back to the hot water outlet from the heat exchanger; and the controller (35) varying the speed of the second pump (23) in response to the outputs of the first and second temperature sensors to maintain the temperature of the water returning to the hot water outlet from the heat exchanger at a given temperature.

A method of operating a domestic hot water installation (1 , 51 ) as claimed in claim 12 in which the method further comprises the step of: the controller (35) varying the speed of the second pump in response to the output of the third temperature sensor (33) to maintain the temperature of the water returning to the hot water outlet (4) from the heat exchanger (9) at a given temperature.