GB2510802A

GB2510802A - Fluid-heating apparatus

Info

Publication number: GB2510802A
Application number: GB1220195.0A
Authority: GB
Inventors: James Grace; Richard Hanson-Graville
Original assignee: SYNERGY CONSULTING ENGINEERS Ltd; Thermal Integration Ltd
Current assignee: SYNERGY CONSULTING ENGINEERS Ltd; Thermal Integration Ltd
Priority date: 2012-11-09
Filing date: 2012-11-09
Publication date: 2014-08-20
Also published as: WO2014072512A2; WO2014072512A3; GB201220195D0

Abstract

A fluid-heating apparatus comprises a heat exchanger 3 for transferring heat from a primary fluid to a secondary fluid, a first supply 5 for supplying a primary fluid at a higher temperature to the heat exchanger 3 and a second supply 7 for supplying the primary fluid at a lower temperature to the heat exchanger. A controller 11, in use, controls flow rate of the primary fluid from each supply 5, 7 to the heat exchanger 3, in response to a control signal. The first supply 5 may be high-grade heat source, eg a gas boiler, while the second supply 7 may be a low-grade heat source, eg a heat pump. The controller 11 may control a four-port mixing valve 15. The primary circuit 23 may be split into two branches (129, 131, fig.2) to heat mains pressure water and central heating water, respectively. In a further embodiment, fig.4, a heat pump (203) delivers water to a lower section (215) or a higher section (217) of a water tank (205) under the control of a controller.

Description

FLUID-HEATING APPARATUS

This invention relates to a fluid-heating apparatus, a method of heating a fluid and related kits.

Background to the Invention

Domestic and industrial water-heating systems frequently employ a primary water circuit and a secondary water circuit. In the primary water circuit, a water heater heats the watei up to a desired temperature and the heated water is stored in a hot water tank or a thermal store. When required, the stored hot water circulates through a heat exchanger to transfer heat to water in the secondary water circuit, such as mains-pressure water or central heating water.

The water heater is typically a boiler such as a gas boiler. However, other heat sources, such as a solar water heater or a heat pump can be used to heat water in the primary circuit.

A heat pump operates by transferring thermal energy from a heat source to a heat sink, against a thermal gradient. A heat pump uses a volatile refrigerant as an intermediate fluid to absorb heat where it vaporises, in an evaporator, and then to release heat where the refrigerant condenses, in a condenser.

Typically, a compressor in the heat pump compresses the refrigerant to make it hotter on the side to be warmed, and releases the pressure at the side where heat is absorbed. The heat source for a heat pump is typically the air (an air-source heat pump) or the ground (a ground-source heat pump).

A heat pump (powered by mains electricity) does not cause local gas emissions and can be efficient, providing a high coefficient of performance, typically in excess of 3 (3kWh of heat transferred for every 1 kWh of electrical power consumed). However, the efficiency of a heat pump decreases as the temperature difference between the heat source and the heat sink increases.

In addition, maximum output temperatures from a heat pump are not as high as for a gas boiler and so a heat pump is often described as a low grade heat source (in contrast to a high grade heat source e.g. a boiler). Consequently! if there is a particularly high demand for hot water, or if environmental conditions are not favourable, a heat pump may not be able to heat the water in the primary circuit sufficiently to meet demand.

Summary of the invention

This invention provides fluid-heating apparatus, methods for heating a tluid and kits as defined in appended independent claims to which reference should now be made. Advantageous or preferred features are set forth in dependent claims.

Accordingly, the invention may thus provide a fluid-heating apparatus or system. The apparatus or system may comprise a heat exchanger for transferring heat from a primary fluid to a secondary fluid; a first supply or source for supplying the primary fluid at a higher temperature to the heat exchanger; and a second supply or source for supplying the primary fluid at a lower temperature to the heat exchanger; in which the apparatus is arranged to control a flow rate of the primary fluid from each supply to the heat exchanger, in response to a control signal.

In one embodiment, each of the first and second supplies may comprise a respective tank or store for storing heated primary fluid, as described further below.

The term flow rate as used here may refer to volumetric flow rate. Thus, the apparatus may be arranged to control relative volumes or quantities of the primary fluid drawn from each supply.

Preferably, the apparatus comprises a controller for controlling the flow rate of the primary fluid from each supply to the heat exchanger, in response to the control signal.

The primary fluid may circulate in a primary circuit. The primary circuit may connect each of the first and second supplies to the heat exchanger. The secondary fluid may circulate in a secondary circuit, such as a mains-pressure water circuit or a central heating circuit.

Advantageously, the apparatus may be adaptable to changes in secondary fluid output. The changes in output may reflect a varying demand for secondary fluid or a varying desired temperature of the secondary fluid.

For example, at certain times, there may be a greater demand for higher temperature secondary fluid than at other times. Also, at certain times there may be a demand for a higher quantity of heated secondary fluid or a higher flow rate of the heated secondary fluid, than at other times. The apparatus, in use, may adjust the relative flow rates of the primary fluid from the first supply and from the second supply in response to the demand. In this way, the apparatus may use primary fluid at the higher temperature only when necessary, with the second supply being the default supply under normal (or non-peak) operating conditions.

The apparatus may mix the primary fluid from each supply at varying relative volumes, or flow rates, to allow the primary fluid entering the heat exchanger to adopt a range of possible temperatures. Ultimately, this may make the apparatus more efficient and save energy costs.

The first supply may comprise, or be heated by, a heater (for example, a first heater) for heating the primary fluid. Preferably, the first heater is a high grade heat source. For example, the first heater may be a boiler such as a gas boiler or it may be a wood burner. The first heater may utilise combustion to heat the primary fluid. Preferably, the first heater is capable of heating the primary fluid to a temperature of 65°C or higher.

The second supply may comprise or be heated by a heater (for example, a second heater) for heating the primary fluid. Preferably, the second heater is a low grade heat source. For example, the low grade heat source may be a heat pump, such as a ground-source heat pump or an air-source heat pump. The second heater preferably does not use combustion in order to heat the primary fluid. Preferably, the second heater heats the primary fluid to a maximum temperature that is lower than 65°C. The maximum temperature may be about 60°C or below, or about or 55°C or below. The second heater may not be able to heat the primary fluid to a temperature as high as the first heater can.

Advantageously, a low grade heat source, such as a heat pump, may be able to meet the demands of the secondary fluid output under normal, or non-peak, operating conditions. Under these conditions, using primary fluid which has been heated by the heat pump may be more efficient and more economical than using fluid from a high-grade heat source. However, under peak operating conditions when demand is high, the primary fluid which has been heated by the heat pump may not be able to heat the second fluid adequately, for example to a high enough temperature or at a fast enough rate. In these conditions, the primary fluid heated by the first heater (which may be able to heat the primary fluid to a higher temperature than the second heater) would meet the increase in demand.

If, for example, the heat pump is an air-source heat pump, efficiency may reduce considerably if the external or outside temperature is particularly low. In such conditions, it may be preferable to use primary fluid heated by. for example, a gas boiler rather than by a heat pump.

The controller may receive the control signal as an input. An output from the controller may then affect the flow rates of the primary fluid from each supply, to the heat exchanger. The controller may be configured, programmed or programmable to receive the control signal input and to generate an appropriate output.

The apparatus may comprise a means for generating a control signal.

Preferably, this comprises a temperature sensor or a console (as described below). However, it may comprise a flow sensor for measuring a flow rate of a fluid.

The control signal may indicate a temperature of the secondary fluid. For example, the apparatus may comprise a temperature sensor arranged to measure the temperature of the secondary fluid. The temperature sensor may be arranged to measure the temperature of the secondary fluid exiting the heat exchanger. The controller may be programmed or programmable to ensure that the secondary fluid is heated to a target, pre-determined or set-point temperature. The pie-deteimined tempelature may be adjustable depending on the application of the secondary fluid.

If, for example, the tenipelatule sensoi senses a secondary fluid temperatule above the set-point temperature, the controller may effect a reduction in the flow rate of the primary fluid from the first supply and increase the flow rate of the primary fluid from the second supply. If the temperature sensor senses a secondaiy fluid temperature below the set-point temperature, the controller may affect an increase in the flow rate of the primary fluid from the first supply and a decrease in the flow rate of primary fluid from the second supply.

For example, if the secondary fluid enteling the heat exchangei is paiticularly cool, such as if the outside temperature is cool, primary fluid from the second supply may not be able to heat the secondary fluid sufficiently. To maintain a set-point temperature or target temperature, the flow rate of the primaly fluid from the first supply may then be controlled to be higher than the flow rate of primary fluid from the second supply.

The relative flow lates of the plimary fluid from each souice may also reflect changes in a flow rate of the secondary fluid through the heat exchanger. For example, under a normal flow rate, and at a moderate target temperature, the controllei may ensure that heating of the secondary fluid is achieved almost entirely using primary fluid from the second supply. However, if the flow rate of the secondary fluid through the heat exchanger incleases to a level above normal, fluid from the second supply (which may be at a lower temperature than the primary fluid from the first supply) may not be able to heat the secondary fluid adequately. In this instance, the flow rate of the primary fluid from the first supply may increase in preference to the primary fluid from the second supply.

The controller may be able to control the flow of primary fluid by switching between the first and second supplies, so that primary fluid flows to the heat exchanger from either the first or second supply, But, preferably, the controller is able to affect the relative flow rates of the primary fluid from each supply to the heat exchanger, such that the flow rate from each supply is variable. The apparatus may be configured such that there is a relationship between the flow rates of the primary fluid from each supply. For example, increasing the flow rate of the primary fluid from one supply may result in a relative or coiiesponding deciease in the flow rate of the primaly fluid from the other supply.

The controller may be responsive to a control signal indicating an aft temperature, such as an external oi outdooi air temperature. Thus, the apparatus may comprise a temperature sensor or thermometer arranged to measure the air temperature. Advantageously, the apparatus may thus be able to compensate for changable weather conditions. This may be particularly applicable if the secondaiy fluid is foi central heating. For example, the controller may set a target temperature for the secondary fluid that is dependent on the air temperature. If the air temperature is mild, the target temperature may be low, say about 30°C, so that the cential heating only heats at a low level. This target temperature may be achievable by taking primary fluid only from the second supply. The flow rate of the primary fluid from the first supply may thus be zero or at least negligible. If the air temperature is cold, the controller may adjust the taiget temperature so that it is highei, say about 55-60°C. The controller may achieve this by increasing the flow rate of the primary fluid from the first supply and decreasing the flow rate of the primary fluid from the second supply.

The control signal may be a manual control signal. Thus, the appalatus may comprise a console for generating the manual control signal. For example, a user may use the console to program the controller.

The controller may be configured to receive a plurality of control signals. For example, the controller may receive one or more of the control signals exemplified above.

The apparatus may comprise a means for varying the flow rate of the primary fluid from each supply. In one embodiment, this may be provided by a separate pump for each supply. Each pump may have a variable pump speed.

However, in a preferred embodiment, the apparatus comprises a valve or valves for varying the flow rate of the primary fluid from each supply. The controller may control the or each valve in response to the control signal. Thus, the or each valve may be responsive to an output from the controller. For example, there may be a first valve for controlling the flow rate of the primary fluid from the first supply and a second valve for controlling the flow rate of the primary fluid from the second supply.

In a particularly preferred embodiment, the apparatus comprises a valve for mixing the primary fluid from the first supply and the primary fluid from the second supply. The valve may permit the mixing of the primary fluid from each supply in varying quantities, or at varying flow rates. The valve may permit mixing of the primary fluid from each supply prior to entry of the primary fluid into the heat exchanger.

The valve may be a three-port valve. In use, a first port may receive the primary fluid from the first supply, a second port may receive primary fluid from the second supply, and a third port may be an output for the primary fluid.

Depending on the type of valve used, the primary fluid flowing from the third port may be a mixture of primary fluid from the first supply and primary fluid from the second supply. The relative proportions or the relative flow rates from each supply may be adjustable to affect the temperature of the primary fluid exiting the third port, and subsequently entering the heat exchanger.

In a preferred embodiment, the apparatus comprises a pump or pumps for pumping the primary fluid from the first and second supplies through the heat exchanger.

The first supply may comprise a fluid tank or store for storing the primaly fluid heated by the first heater. The second supply may comprise a fluid tank or store for storing the primary fluid heated by the second heater. Primary fluid from the first heater may be stored in a first store and primary fluid from the second heater may be stored in a second store.

The or each store, or at least one of the stores, is preferably a thermal store.

Preferably, the or each store, or at least one of the stores, is arranged to enable a temperature stratification of the primary fluid within the store, such that warmer fluid is nearer the top of the store and cooler fluid is nearer the bottom of the store. Fluid may be delivered from a lower part of the store to the respective first fluid heater or second fluid heater and, once heated, may be delivered to a higher part of the store. In use, warmer fluid from the higher part of the store may be delivered to the heat exchanger, and once heat transfer has occurred, the cooler fluid may return to the lower part of the store.

Alternatively, the primary fluid from the first heater and the primary fluid from the second heater may be stored in the same store, which is preferably thermal store, most preferably a temperature stratified thermal store. Primary fluid from the second heater may be delivered to a lower part of the store than primary fluid from the first heater, in order to maintain temperature stratification. The apparatus may be arranged to deliver primary fluid to the heat exchanger from the lower part and/or from the higher pad in varying quantities, or at varying flow rates, in response to the control signal.

The or each store, or at least one of the stores, may comprise an immersion heater.

In a preferred embodiment, the apparatus comprises a third supply for supplying the primary fluid to the heat exchanger. The third supply may contain or consist of primary fluid which has already passed from the first and/or second supply, through the heat exchanger, but which still retains a usefully elevated temperature Preferably, the controller controls the flow rate of the primary fluid entering the heat exchanger from the third supply in response to the control signal. Preferably, a temperature of the primary fluid from the third supply is lower than the temperature of the primary fluid from the first supply and is equal to or lower than the temperature of the primary fluid from the second supply. Preferably, the third supply supplies primary fluid to the heat exchanger without it being heated since it previously passed through the heat exchanger.

In a particularly preferred embodiment, the third supply comprises a recirculation circuit or bypass. In use, the bypass may take primary fluid from the heat exchanger and recirculate it to the heat exchanger, without being heated by a water heater.

The controller may control the relative flow rates of the three fluid supplies depending on the control signal. At a peak output of heated secondary fluid, the apparatus may draw primary fluid from the first supply. As the required output drops, the apparatus may draw more primary fluid from the second supply and less from the first supply. Further drops in the required output may result in the apparatus drawing fluid only from the second supply, with no fluid being drawn from the first supply. At even lower required outputs, the apparatus may begin to draw more primary fluid from the third supply and less from the second supply. When the apparatus draws the primary fluid exclusively from the third supply, the water-heating function of the apparatus may be said to be switched off. Advantageously, the third supply may allow the first and second supplies to remain unused and prevent waste.

Preferably, the apparatus is configured such that the primary fluid from the first supply can mix with the primary fluid from the second supply and such that the primary fluid from the second supply can mix with the primary fluid from the third supply. The apparatus may be configured such that the fluid from the first supply cannot mix with the fluid from the third supply.

To receive the three fluid supplies, the apparatus may comprise a four-port mixing valve. The four port mixing valve may operate in substantially the same way as the three-pod mixing valve described above, except that the valve comprises a fourth port for receiving primary fluid from the third supply. The relative proportions or the relative flow rates from each of the three supplies may be adjustable to affect the temperature of the primary fluid exiting the third port, and subsequently entering the heat exchanger.

The bypass (provided by the third supply) may advantageously allow the pump for pumping the primary fluid through the primary circuit to run continuously.

There may be no need to control the pump speed or to switch off the pump in response to demand. Continual flow of the primary fluid through the heat exchanger may prevent the pump from burning out.

The bypass may comprise a valve to limit flow rate of the primary fluid to a low level, sufficient to satisfy the continually-running pump and which is enough to permit reaction of any sensors in the apparatus to further changes in demand for output.

In an alternative embodiment, the apparatus may be arranged such that the first supply for supplying the primary fluid to the heat exchanger comprises a fluid heater. The second supply may comprise a bypass circuit for re-circulating the first fluid through the heat exchanger, as described above. The second source may thus not necessarily supply primary fluid heated by a heater, such as a heat pump.

The heat exchanger is preferably a plate heat exchanger. The heat exchanger is preferably external to any fluid store.

The apparatus may comprise a plurality of heat exchangers. For example, the apparatus may comprise two heat exchangers, a first heat exchanger and a second heat exchanger. Each heat exchanger may carry out a different function. For example! the first heat exchanger may heat mains-pressure water and the second heat exchanger may heat central heating water. The apparatus may then be arranged in any form as described above, but in respect of each heat exchanger. Thus, the primary circuit may have a plurality of branches or sub-circuits, each branch for circulating primary fluid to one of the heat exchangers. The branches may operate in parallel and may be independently controlled.

Preferably, the primary fluid comprises water. Preferably, the secondary fluid comprises water.

According to the invention! there may be provided a method for heating a fluid.

The method may comprise supplying a primary fluid to a heat exchanger to heat a secondary fluid; and controlling the relative quantities of the primary fluid supplied to the heat exchanger from a first supply and from a second supply, in response to a control signal. The primary fluid from the first supply may be at a higher temperature than the primary fluid from the second supply.

The method may comprise controlling the relative quantities of the primary fluid supplied to the heat exchanger from a first supply, a second supply and a third supply, in response toa control signal, as described above.

According to the invention, there may be provided a kit. The kit may comprise a means for varying a flow rate of a primary fluid from a first supply and for varying a flow rate of the primary fluid from a second supply; a controller for controlling the means for varying the flow rates in response to a control signal; and a means for generating a control signal.

The means for varying the flow rates may be in any form as described above, but is preferably a valve. Most preferably, the valve is a three-port or four-port valve.

The means for generating a control signal may be in any form as described above, but is preferably a temperature sensor for measuring a temperature of a secondary fluid or for measuring an air temperature, or comprises a console for generating a manual control signal.

The kit may comprise a set of instructions for installing an apparatus as defined in any form above.

The kit may comprise one or more of a heat exchanger for heating a secondary fluid by the primary fluid; a pump for circulating the primary fluid through the heat exchanger; a heater or heaters for heating the primary fluid; and a tank or tanks for storing the plimary fluid.

Accordingly, in another aspect, the invention may thus provide a fluid-heating apparatus or system, comprising: a heater for heating a fluid, such as the primary fluid; a heater circuit for delivering or distributing the fluid from the heater to a first section of a fluid store and to a second section of a fluid store; and a controller for controlling flow or flow rate of the fluid to each section in response to a control signal.

The heater circuit may selectively deliver the fluid to the first section and/or to the second section.

This fluid heating apparatus is most preferably used in conjunction with, or as part of, an apparatus described in any form above. For example, the apparatus may be used with an apparatus comprising: a heat exchanger for transferring heat from a primary fluid to a secondary fluid; a first supply for supplying a primary fluid at a higher temperature to the heat exchanger; a second supply for supplying the primary fluid at a lower temperature to the heat exchanger; and a controller for, in use, controlling flow rate of the primary fluid from each supply to the heat exchanger, in response to a control signal.

The heater circuit may permit circulation of the fluid between the heater and the fluid store sections.

In a preferred arrangement, the heater is a low-grade source, such as a heat pump, and is able to deliver heated fluid (e.g. the primary fluid) to a first section of a fluid store and to a second section of a fluid store. Flow of the fluid to each section is preferably controlled in response to a control signal or control signals. A heater circuit, such as a heat pump circuit, may circulate primary fluid between the water heater and the store. The controller may permit and/or prevent flow of the fluid to each section.

The first section is preferably maintained at a lower temperature than the second section. Thus, advantageously, the apparatus may create a temperature differential within the store or between sections of different stores.

The fluid from the first section may be used to heat central heating water. The fluid from the second section may be used to heat mains-pressure water.

The first section may be in a first stole and the second section may be in a second store. Alternatively, the first section and the second section may be in the same store. If they are in the same store, the first section may be lower than the second section. The store, stores or at least one of the stores may be a thermal store.

The flow or flow rate of the fluid to the first section and/or to the second section may be controlled by a controller. The control signal (or control signals), supplied or input to the controller may indicate a particular parameter in the system such as a temperature of the fluid flowing from the heater (such as the temperature of the fluid exiting the heater), a temperature or temperatures of the fluid at a pre-determined position or positions in the store and/or an external air temperature. Consequently, the apparatus may comprise a parameter sensor such as temperature sensor or temperature sensors for measuring parameters such as temperature or flow rate. The control signal may also indicate a manual control signal e.g. generated by a console or a user control.

If the control signal indicates that a parameter is above a pre-determined value or is below a pre-determined value, the controller may control flow of the fluid to the first section or to the second section, or optionally to neither section.

The controller output may control the operation of a valve or valves in the heater circuit. The valve or valves may be three-port valves. The controller output may configure the valve or valves to circulate fluid to the first section of the store, to the second section of the store or to neither section of the store.

The controller may thus be in electrical connection with the valve or valves.

The heater circuit may also permit circulation of water through the water heater without water being drawn from, or delivered to, the store. For example, the heater circuit may comprise a bypass. This may occur if the heater cannot heat the fluid to a desired temperature. The valve or valves may be controllable to enable the fluid to bypass the store.

The heater circuit preferably comprises a pump. The controller may also control operation of the pump and/or the heater, in response to the control signal or control signals. For example, the controller may switch off the heat pump and the pump if a desired temperature is achieved.

In a preferred embodiment, the apparatus comprises a first temperature sensor for measuring the temperature of the fluid at the first section of the store and/or the apparatus comprises a second temperature sensor for measuring the temperature of the fluid at the second section of the store.

The controller may control flow or flow rate of the fluid to the first section or to the second section of the store in response to a temperature of the fluid flowing from the heater and/or in response to a temperature of the fluid in the store.

For example, if a temperature of a fluid exiting the heater is below a pre-determined temperature, the controller may prevent flow or reduce flow rate to a particular section in the store. If the temperature is above the pre-determined temperature, the controller may permit flow or increase flow rate to that section.

Alternatively or additionally, if the temperature of fluid at a section of the store (e.g. the first or second section) is below a pre-determined temperature, the controller may permit flow or increase flow rate of heated fluid to that section, whereas if the temperature is above the pre-determined temperature, the controller may prevent flow or decrease flow rate to that section.

The controller may act in response to a particular combination of control signals. For example, if the fluid exiting the heater is above a pre-determined temperature and the temperature at a section of the store is below the pre-determined temperature, the controller may permit flow or increase flow rate of heated fluid to that section of the store.

There may be more than one pre-determined temperature. For example! there may be a first pre-determined temperature and a second pre-determined temperature. Depending on whether the temperature of the fluid exiting the heater and/or the temperature of the fluid in the store is above or below each pre-determined temperature, the controller may direct delivery of fluid to the first section, to the second section or to neither section.

At least one of the pre-determined temperatures may be variable and may be dependent on, for example, an air temperature. In a particularly preferred embodiment, the apparatus is configured or programmed such that a temperature sensor or thermometer measures an air temperature, such as an external air temperature. From this, the controller may calculate a desired flow temperature (or a first pre-determined temperature). For example, if the outside temperature is particularly cold, the desired flow temperature may be higher, say 40-50°C. If the outside temperature is warmer, the desired flow temperature may be lower, say about 30°C. The desired flow temperature may be for delivering heat through a heat exchanger to a central heating system or to a central heating system directly.

If the temperature of the fluid at the first section of the store is less than the first pre-determined temperature and the temperature of the fluid exiting the heater is lower than the first pre-determined temperature, the controller may control flow in the heater circuit e.g. by configuring the valve or valves, such that thefluid in the heater circuit is not delivered to the store or drawn from the store. However, if the temperature of the fluid exiting the heater is at or above the first pre-determined temperature, the control ensures that the fluid circulates to the first section of the store. For example, the fluid may be taken from a lower, or cooler section of the store, such as the bottom of the store.

If the temperature of the fluid at the second section is below a second pre-determined temperature e.g. 55-60°C and the temperature of the fluid exiting the heater is lower than the second pre-determined temperature (and optionally the temperature of the fluid at the first section of the store is greater then or equal to the first pre-determined temperature) the controller may control flow in the heater circuit such that the fluid in the heater circuit is not delivered to the the store or drawn from the store. However! if the temperature of fluid exiting the heater is at or above the second pre-determined temperature, the controller ensures that the fluid circulates to the second section of the store. For example, the fluid may be drawn from a lower or cooler section of the store, such as the first section of the store or the bottom of the store.

If the fluid at the first section of the stole is at or above the first pie-determined temperature and the fluid at the second section of the store is at or above the second pie-determined temperature, the controller may prevent the heater circuit from delivering fluid to the store or drawing fluid from the store. The controller may also turn off the heat pump and may turn off the pump in the heater circuit.

If the heater is a heat pump, fluid at the second section may be at a temperature that is the maximum temperature achievable by the heat pump.

The temperature may be 50-60°C, or about 55°C. The temperature at the first section may thus be lower, and may be, for example, 25-50°C. Preferably, the temperature at the first section is variable. To get maximum performance (coefficient of performance) 1 may be desiraLe to heat the fluid to the temperature it needs to be, rather than heating the fluid to a hotter temperature and mixing it with cooler fluid in order to bring the temperature down.

The fluid from the first section (e.g. the fluid from the first section being a first supply) may be used to heat central heating water (using a heat exchanger, such as a plate heat exchanger), or may itself, be circulated through the central heating circuit or system.

The fluid from the first section (or first supply) may be mixed with fluid from another section of the store, from a different store or from a different supply (e.g. a second supply). For example, fluid from the first section may be mixed with fluid heated by another water heater, such as a boiler, to achieve a desired central heating temperature. The boiler may heat the fluid up to a temperature greater than or equal to 60°C, 65°C, 70°C or 80°C. This may occur if the heat pump is not able to heat the fluid up to a desired temperature.

The fluid at the hottest temperature may thus only be used when required.

Similarly, fluid from the second section may be mixed with fluid at a higher temperature e.g. fluid heated by a boiler. fluid from the second section of the store may be used to heat mains-pressure water, for example, to a temperature of about 6000. If the temperature of water at the second section is not adequate, fluid at a higher temperature (for example from the top of the fluid store) may be mixed with the fluid from the second section.

The invention may provide a method for heating a fluid, comprising heating the fluid using a fluid heater; and controlling flow or flow rate of the fluid to a first section of a fluid store and to a second section of a fluid store, in response to a control signal.

The invention may provide a kit, comprising a valve or valves for effecting flow of a fluid to a first section of a fluid store and/or a second section of a fluid store; a controller for controlling the valves in response to a control signal; and a sensor, such as a temperature sensor for measuring a fluid temperature or an air temperature and for generating a control signal.

The kit may also comprise one or more of the following: a fluid heater such as a heat pump for heating the fluid; a fluid store or fluid stores for storing the fluid; a pump for pumping the fluid in a fluid heater circuit between the fluid heater and the fluid store or stores.

Description of specific embodiments

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a schematic diagram of a system according to a first embodiment of the invention; Figure 2 is a schematic diagram of a system according to a second embodiment of the invention; Figure 3 is a graph showing the operational characteristics of a four-port valve used in the embodiments of figures 1 and 2, in conjunction with schematic representations of the valve; Figure 4 is a schematic diagram of a system according to a third embodiment of the invention; and Figure 5 is a table showing the operation of the system of figure 4.

A water heating system 1, as shown in figure 1, has a high-grade temperature-stratified thermal store 5 and a low-grade temperature stratified thermal store 7. The high-grade store has a water outlet 5a located at the top and a water inlet 5b located at the bottom. Similarly, the low-grade store has a water outlet 7a at the top and a water outlet at the bottom lb. A gas boiler (not shown) is connected to the high-grade store, whereas a heat pump (not shown) is connected to the low-grade store.

A primary water circuit 23 formed from a network of piping is arranged between the water outlets 5a, 7a of the high grade and low grade stores 5, 7 and the water inlets Sb, lb of the high grade and low grade stores. The primary water circuit passes through a four-port mixing valve 15, a plate heat exchanger 3 and a pump 9.

A bypass 17 is arranged within the primary water circuit 23 between the mixing valve 15 and a position between the pump 9 and the water inlet 7b of the low-grade store 7. The bypass has a bypass valve 19.

A secondary circuit in the form of a mains-pressure water circuit 25 passes through the heat exchanger 3. A temperature sensor 13 is positioned within the secondary circuit. A controller 11 is in electrical connection with the temperature sensor and the mixing valve 11.

In use, the high-grade store 5 contains water that has been heated by the gas boiler (not shown). Water from the bottom of the high-grade store is circulated through the boiler and is delivered to the top of the high-grade store. Thus, the hottest water is found at the top of the high-grade store. The temperature of the water at the top of the high-grade store is approximately 80°C.

Water from the top of the high-grade store can circulate through the primary circuit 23, from the outlet 5a, through the mixing valve 15, the heat exchanger 3 and finally the pump 9, before entering the low-grade store 7 at the water inlet7b.

The low-grade store 7 contains water that has been heated by the heat pump (not shown). Water from the bottom of the heat pump is circulated through the heat pump and is delivered to the top of the low-grade store. Thus, as with the high-grade store, the hottest water is found at the top. The temperature of the water at the top of the low-grade store is approximately 60°C.

Water from the top of the low-grade store 7 can circulate through the primary circuit 23. from the water outlet 7a, through the mixing valve 15, the heat exchanger 3 and finally the pump 9, before entering the low-grade store 7 at the water inlet 7b. When water enters the low-grade store through the water inlet, water from the top of the low-grade store is displaced and flows through the water outlet 7a and in to the water inlet Sb of the high-grade store 5. A non-return valve (not shown) ensures that water cannot flow out of the water inlet of the high-grade store.

Alternatively, instead of the water in the primary circuit 23 entering the low-grade store through its water inlet 7b, the water may flow through the bypass 17 and re-circulate through the mixing valve 15, the heat exchanger 3 and the pump 9. The bypass thus functions as a third supply for primary fluid.

The controller 11 controls circulation of water through the primary circuit 23.

The temperature sensor 13 in the secondary circuit senses the temperature of the water leaving the heat exchanger 3 and sends an input signal to the controller. The controller is programmed to ensure that the temperature of the water in the secondary circuit is heated to a pre-determined temperature (typically 60°C). The controller achieves this by affecting the operation of the mixing valve 15. The valve is arranged such that it can vary the relative flow rates of the water from the high-grade stole 5, the low grade store 7 and the bypass 17 in response to a varying output in the secondary circuit 25.

At peak output, the valve will draw water substantially only from the high-grade store 5. If output requirement drops, the valve is controlled to alter its configuration (by changing its opening angle) to draw less water from the high-grade store, and more water from the low grade store 7. As output requirement drops further, the valve will be controlled to alter its configuration to stop drawing water from the high-grade store, drawing its water entirely from the low grade store. Further decreases in output requirement will result in the valve altering its configuration to draw more water from the bypass 17, and less from the low-grade store. Figure 3 illustrates the varying configurations of the mixing valve and demonstrates how an increase in the flow rate of water from, for example, the high grade store, results in a decrease in the flow rate of water from the low grade store.

The bypass valve 19 in the bypass 17 limits the flow rate of water through the bypass to a minimum, that is enough to permit reaction of the system's sensors to further changes in secondary circuit output and to enable the pump 9 to operate continuously, if desired.

An alternative water heating system 1 is shown in Figure 2. Similar features have been assigned like reference numerals. The system is substantially the same as the system shown in figure 1 and described above, except that the primary circuit 23 is split into two branches, a first branch 129 and a second branch 131. Both branches operate in parallel.

The first branch 129 is arranged as described above in relation to figure 1, and is used to heat mains-pressure water. The second branch 131 is arranged to heat the central heating water.

The second branch 131 contains an additional heat exchanger, 103, pump 109, controller 111, water temperature sensor 113, four-port mixing valve 115, bypass 117, and bypass valve 119. These additional features are arranged in the same way as the corresponding features in the first branch 129. However, the second branch contains a thermometer 121 for measuring an external air temperature and the thermometer is in electrical connection with the controller.

The additional heat exchanger 103 is connected to an alternative secondary circuit in the form of a central heating circuit 125. The water temperature sensor 113 is arranged to measure the temperature of the central heating water exiting the heat exchanger.

The first and second branches 129, 131 of the primary circuit 23 convey water between the high-grade store 5 and the low-grade store 7. Each branch draws water from the high-grade store outlet 5a and the low-grade store outlet 7a.

However, whereas the first branch 129 delivers water to the low-grade store inlet 7b, the second branch delivers water to an additional low-grade store inlet 107b at the bottom of the low-grade store.

In use, the first branch 129 operates in the same way as described above in relation to the embodiment in figure 1. The second branch also operates in a very similar way to the embodiment in figure 1, except that the controller receives an input signal from the temperature sensor 113 and the thermometer 121. The thermometer provides the controller with an indication of the external air temperature. According to the external air temperature, the controller affects the operation of the mixing valve 115 to allow for weather compensation. The controller alters the predetermined temperature for the central heating water exiting the heat exchanger 103, according to the outside temperature. If the outside temperature is particularly cold, the controller will increase the predetermined temperature, so that the central heating output temperature increases. This, in turn, will result in the valve 115 drawing more water from the high-grade store than the low-grade store. If the outside temperature is mild, the controller will decrease the pre-determined temperature so that the central heating output temperature decreases. The valve will draw more water from the high-grade store than the low-grade store.

A water heating system 201 as shown in Figure 4 has a heat pump 203 connected to a water store or tank 205 by a heat pump circuit 227. The heat pump circuit connects the heat pump to a bottom section 213 of the store, a first section 215 of the store (higher than the bottom section) and a second section 217 of the store (higher than the first section). The heat pump circuit has a first heat pump circuit valve (3-port) 207 and a second heat pump circuit valve (3-port) 209. The heat pump circuit has a pump 228.

The system 201 has a boilers 231 connected to the store 205 by a boiler water circuit 229. The boiler water circuit connects the boiler to the second section 217 of the store and a third section or the top 219 of the store (which is higher than the second section). The boiler water circuit has a pump 230.

The system 201 has a central heating circuit 241. The central heating circuit connects a central heating appliance 242 to the bottom 213 of the store 205 and to the first section 215 of the store. The central heating circuit has a temperature sensor 245 and a mixing valve 243 (3-port) that connects the central heating circuit to the top section 219 of the store. The central heating circuit has a pump 244.

The system 201 also has a heat exchanger circuit 233 comprising a plate heat exchanger 235, a temperature sensor 239 and a mixing valve 237. The heat exchanger circuit connects the heat exchanger to the bottom section 213 of the store 205, the second section 217 of the store and the top section 219 of the store. The heat exchanger circuit has a pump 234.

The store 205 has a first temperature sensor 221 situated at the first section 215 of the store; a second temperature sensor 223 situated at the second section of the store; and a third temperature sensor 225, situated at the top 219 of the store.

In use, the heat pump 203 heats water and delivers it to either the first section 215 of the store 205 or the second section 217 of the store. Circulation of water from the heat pump to the first or second section is controlled by a controller (not shown). The controller controls the operation of the first heat pump circuit valve 207 and the second heat pump circuit valve 209 in response to input signals from the first temperature sensor 221, the second temperature sensor 223, the heat pump water temperature sensor 211 that measures the temperature of the water leaving the heat pump, and a thermometer (not shown) that is arranged to measure an external air temperature.

Figure 5 summarises the control of the valves in response to the input signals.

The thermometer measures an external air temperature and this temperature sets a desired flow temperature, which in this case is about 30°C, but is variable depending on the external temperature.

If the first temperature sensor 221 of the first section 215 of the store 205 measures the water temperature as less than 30°C and the heat pump water temperature sensor 211 measures the temperature as less than 30°C, the first and second heat pump circuit control valves 207, 209 are configured by the controller such that water circulates within the heat pump circuit 227 without delivering water to, or drawing water from, the store. However, if the heat pump water temperature sensor measures the temperature as greater than or equal to 30°C, the first and second heat pump circuit control valves are configured such that water circulates from the bottom section 213 of the store, through the heat pump 203, to the first section 215 of the store.

If the first temperature sensor 221 at the first section 215 of the store 205 measures the water temperature as greater than or equal to 30°C; the second temperature sensor 223 at the second section 217 of the store measures the water temperature as less than 55°C (representing a maximum temperature that can be achieved by the heat pump); and the heat pump water temperature sensor 211 measures the temperature less than 55°C, the first and second heat pump circuit control valves 207, 209 are configured by the controller such that water circulates within the heat pump circuit without delivering water to or drawing water from the store. However, if the heat pump water temperature sensor measures a temperature greater than or equal to 55°C, the first and second heat pump circuit control valves are configured such that water circulates from the first section 215 of the store, through the heat pump 203, to the second section 217 of the store.

If the first temperature sensor 221 measures the temperature greater than or equal to 30°C and the second temperature sensor measures the temperature greater than or equal to 55°C, the heat pump circuit control valves are configured such that water cannot be drawn from or delivered to the store 205.

The heat pump 203 and the pump 228 in the heat pump circuit are also switched off.

Advantageously, the control of the heat pump circuit 227 can thus create a temperature differential between the first section 215 of the store 205 and the second section 217 of the store.

Water at the first section 215 of the store 205, which is at 30°C can then be circulated through the central heating circuit 241, the water in the central heating circuit being heated to the desired flow temperature. The temperature sensor 245 in the central heating circuit can measure the temperature of the water in the central heating circuit to check whether it is at the desired tlow temperature e.g. 30°C. If the temperature of the water is lower than the desired temperature, a controller (not shown) controls the central heating circuit mixing valve 243 so that water may be drawn from the top section 219 of the store and mixed with water from the first section at appropriate flow rates to achieve the desired temperature. The central heating circuit delivers water back to the bottom section 213 of the store. Alternatively, water from the second section may be directed to a plate heat exchanger (not shown) to heat the central heating water indirectly.

The boiler water circuit 229 circulates water from the second section 217 of the store 205 to the top section 219 of the store. The boiler heats the water to about 85°C. The third temperature sensor 22 measures the temperature of the water at the top section of the store. A signal from the third temperature sensor is used to control the boiler in order to maintain the temperature at 85°C.

The heat exchanger circuit 233 circulates water from the top section 219 of the store 205 and water from the second section 217 of the store, through the heat exchanger 235, to the bottom section 213 of the store. The circulating water heats mains-pressure water in a secondary circuit 247 at the heat exchanger, for example for a domestic hot water supply. The temperature sensor 239 measures the temperature of the water entering the heat exchanger and provides an input to a controller (not shown). The controller configures the mixing valve 237 in the heat exchanger circuit such that the flows of water from the top section and the second section through the heat exchanger are suitably controlled to achieve the target temperature of about 60°C to be obtained, for example for supply to hot taps.

Claims

Claims 1. A fluid-heating apparatus, comprising: a heat exchanger for transferring heat from a primary fluid to a secondary fluid; a first supply for supplying a primary fluid at a higher temperature to the heat exchanger; a second supply for supplying the primary fluid at a lower temperature to the heat exchanger; and a controller for, in use, controlling flow rate of the primary fluid from each supply to the heat exchanger, in response to a control signal.
2. A fluid-heating apparatus according to claim 1, in which the first supply comprises a first heater for heating the primary fluid and the second supply comprises a second heater for heating the primary fluid.
3. An apparatus according to claim 2, in which the first heater is a high-grade heat source.
4. An apparatus according to claim 3, in which the high-grade heat source comprises a boiler.
5. An apparatus according to any of claims 2 to 4, in which the second heater is a low-grade heat source.
6. An apparatus according to claim 5, in which the low-grade heat source comprises a heat pump.
7. An apparatus according to any preceding claim, in which the control signal indicates a temperature of the secondary fluid.
8. An apparatus according to any preceding claim, in which the control signal indicates an air temperature, such as an exterior or outdoor air temperature.
9. An apparatus according to any preceding claim! comprising a valve for mixing the primary fluid from the first supply and the primary fluid from the second supply before the primary fluid is delivered to the heat exchanger, in which the controller controls the valve in response to the control signal to vary the relative flow rates of the primary fluid from each supply.
10. An apparatus according to any preceding claim, comprising a pump for pumping the primary fluid from the first and second supplies through the heat exchanger.
11. An apparatus according to any preceding claim, comprising a tank or store for storing the primary fluid of the first supply.
12. An apparatus according to any preceding claim, comprising a tank or store for storing the primary fluid of the second supply.
13. An apparatus according to any preceding claim comprising a third supply for supplying the primary fluid to the heat exchanger, in which the controller controls the relative quantity of the primary fluid entering the heat exchanger from the third supply in response to the control signal, and in which a temperature of the primary fluid from the third supply is lower than the temperature of the primary fluid from the first supply and is lower than the temperature of the primary fluid from the second supply.
14. An apparatus according to claim 13, in which the third supply comprises a bypass circuit for re-circulating the first fluid through the heat exchanger.
15. An apparatus according to claim 14, in which the bypass circuit comprises a bypass valve for controlling a flow rate of the first fluid through the bypass circuit.
16. An apparatus according to any preceding claim, comprising: a heater for heating the primary fluid; a heater circuit for delivering the primary fluid from the heater to a first section of a fluid store and to a second section of a fluid store; and a controller for controlling flow of the fluid to each section in response to a control signal.
17. A method for heating a fluid, comprising: supplying a primary fluid to a heat exchanger to heat a secondary fluid at the heat exchanger; and controlling the relative quantities of the primary fluid supplied to the heat exchanger from a first supply and from a second supply, in response to a control signal, in which the first fluid from the first supply is at a higher temperature than the first fluid from the second supply.
18. A kit, comprising: a valve for mixing a primary fluid from a first supply with the primary fluid from a second supply; a controller for controlling the mixing of the primary fluid from the first supply and the primary fluid from the second supply in response to a control signal; and a temperature sensor for measuring a temperature of a secondary fluid or for measuring an air temperature.
19. A kit according to claim 18, in which the valve is a four-port mixing valve.
20. A kit according to claim 18 or claim 19, comprising a set of instructions for installing an apparatus as defined in any of claims ito 16.
21. A kit according to any of claims 18 to 20, comprising one or more of the following: a heat exchanger for heating a secondary fluid by the primary fluid; a pump for circulating the primary fluid through the heat exchanger; a heater or heaters for heating the primary fluid; and a tank or tanks for storing the primary fluid.
22. A fluid-heating apparatus, comprising: a fluid heater for heating a fluid; a fluid heater circuit for delivering the fluid from the heater to a first section of a fluid store and to a second section of a fluid store; and a controller for controlling flow of the fluid to each section in response to a control signal.
23. An apparatus according to claim 22, in which the fluid heater is a heat pump.
24. An apparatus according to claim 22 or claim 23, in which the control signal indicates a temperature of the fluid exiting the fluid heater.
25. An apparatus according to any of claims 22 to 24, in which the control signal indicates a temperature of the fluid at a pre-determined location in the fluid store.
26. An apparatus according to claim 25, comprising a first temperature sensor for measuring a fluid temperature at the first section of the fluid store and/or a second temperature sensor for measuring a fluid temperature at the second section of the fluid store.
27. An apparatus according to any of claims 22 to 26, in which the control signal indicates an air temperature, such as an exterior or outdoor air temperature.
28. An apparatus according to any of claims 22 to 27, in which the fluid heater circuit comprises a valve or valves for affecting the flow of the primary fluid to the first or second section, the valve or valves, in use, being controllable by the controller.29. An apparatus according to any of claims 22 to 28, in which the fluid heater circuit is arranged such that the fluid can circulate through the fluid heater without drawing the fluid from, or delivering the fluid to, the fluid store.
29. An apparatus according to any of claims 22 to 28. in which, in use, the fluid is delivered to the first section if the temperature of the fluid at the first section is less than a first pre-determined temperature, and the fluid exiting the fluid heater is at a temperature greater than or equal to the first-pie-determined temperature.
30. An apparatus according to any of claims 22 to 29, in which, in use, the fluid is delivered to the second section if the tempeiature of the fluid at the second section is below a second pre-determined temperature, and the fluid exiting the fluid heater is at a temperature greater than or equal to the second pre-determined temperature.
31. An apparatus according to any of claims 22 to 30, in which the apparatus is arranged to selectively deliver fluid from the first section to a central heating circuit, or to a heat exchanger for heating central heating water.
32. An apparatus according to any of claims 22 to 31, in which the apparatus is arranged to deliver fluid from the second section to a heat exchanger for heating mains-pressure water.
33. An apparatus according to any of claims 22 to 32, comprising: a heat exchanger for transferring heat from the fluid to a secondary fluid; a first supply for supplying the fluid at a higher temperature to the heat exchanger; a second supply for supplying the fluid at a lower temperature to the heat exchanger; and a controller for, in use, controlling flow rate of the primary fluid from each supply to the heat exchanger, in response to a control signal
34. A method for heating a fluid, comprising: heating the fluid using a fluid heater; and controlling flow of the fluid to a first section of a fluid store or to a second section of a fluid store, in response to a control signal.
35. A kit, comprising: a valve or valves for affecting flow of a fluid to a first section of a fluid store and a second section of a fluid store; and a controller for controlling the valves in response to a control signal; and a sensor, such as a temperature sensor for measuring a fluid temperature or an air temperature and for generating a control signal.
36. A kit according to claim 35, comprising one or more of the following: a fluid heater such as a heat pump for heating the fluid; a fluid store or fluid stores for storing the fluid; a pump for pumping the fluid in a fluid heater circuit between the fluid heater and the fluid store or stores.
37. An apparatus substantially as hereinbefore described with reference to the accompanying drawings.
38. A method substantially as hereinbefore described with reference to the accompanying drawings.
39. A kit substantially as hereinbefore described with reference to the accompanying drawings.