WO2019220106A1

WO2019220106A1 - A heating system for providing hot fluid, and a method of operating a heater

Info

Publication number: WO2019220106A1
Application number: PCT/GB2019/051327
Authority: WO
Inventors: Chris Farrell
Original assignee: Canetis Technologies Limited
Priority date: 2018-05-16
Filing date: 2019-05-15
Publication date: 2019-11-21
Also published as: GB2573780A; GB201807970D0

Abstract

When a boiler is instructed to supply hot water for washing and the like, the boiler adapts a fuel use strategy based on reaching a target hot water temperature as fast as possible. Where a boiler has access to a store of thermal energy, and/or where transport through delivery pipework can give rise to delays and losses, the normal fuel use strategy may result in more fuel being burnt than necessary and potentially excessive amounts of very hot water being left to cool in the delivery pipework.

Description

A HEATTNG SYSTEM FOR PROVIDING HOT FLUID. AND A METHOD

OF OPERATING A HEATER

FIELD

The present disclosure relates to an improved heating system for delivering a warmed fluid. Such a heating system may deliver hot water for washing, showering and the like in a home, a factory, a hotel and so on.

BACKGROUND

The UK has an installed base of over 23 million gas boilers, the majority of which are classified as condensing combination boilers, being boilers that provide space heating and on demand instantaneous hot water.

It is known that the fitment of a stored passive flue gas heat recovery device can improve energy efficiency of such boilers and can reduce costs in the production of domestic hot water through the combined benefits of direct and indirect flue gas heat recovery.

As used herein "direct flue gas heat recovery" refers to the recovered energy from flue gases during the production of domestic hot water while "indirect flue gas heat recovery" refers to the energy from flue gases captured and stored for later use from the boiler while heating the home.

Modem boilers are now able to take advantage of these additional energy efficiency opportunities however, the inventor realised that control systems of the boilers have yet to be adapted to improve their efficiency in the production of domestic hot water.

SUMMARY

According to a first aspect of the present disclosure there is provided a fluid heating system comprising: a heater; a thermal store; a temperature sensor or estimator for indicating a temperature of the thermal store; and a controller, wherein when a demand for warmed fluid is made, the controller calculates a modified energy use profde for the heater based on the temperature of the thermal store.

It is thus possible to reduce the energy consumed by the boiler in a ramp up phase by, for example, waiting to ignite the burner until after preheated water from the thermal store has reached the boiler, and/or modifying the target hot water temperature as a function of time.

According to a second aspect of the present disclosure there is provided a method of controlling a gas or oil burning boiler having a flue gas heat recovery device acting as a thermal store, and a temperature sensor or energy estimator for estimating the temperature of the thermal store, the method comprising receiving a demand for hot water, and in response to the demand using an estimate of the usable energy in the thermal store to modify a fuel use profile.

According to a third aspect of the present invention there is provided a heating system comprising a controller and a water heater, the controller adapted to modulate operation of the heater to reduce lukewarm water rejection or energy wasted due to operation in less efficient heating modes where the heat imported therein in predominantly lost to warming a distribution network.

According to a fourth aspect of the present invention there is provided a heating system including a sensor system for identifying operation of a specific valve or tap, or operating of a valve or tap within a group of such valves or taps, and using knowledge about the length of the distribution network or thermal properties thereof between the boiler and valve or tap to vary an energy consumption profile of the boiler.

Stored flue gas heat recovery devices or other types of thermal store present a new opportunity to improve the energy efficiency of boilers when providing hot water.

In an embodiment of this disclosure a flue gas heat recovery device recovers heat from boiler flue heat losses and stores the recovered energy for subsequent use in pre-heating the cold- water supply to the boiler. On each hot-water cycle of the boiler, there are efficiency losses from lukewarm water rejection (water that is below required temperature), heat exchanger losses, and boiler ramp up losses. By instrumenting or estimating the stored energy (e.g. a temperature sensor in store) and providing real time information about the energy content of the store, the boiler controller can improve or optimise resource efficiency, that is, the usage of water, electricity or gas for each hot water tapping cycle.

If there is energy in the store that can be used for a specific hot water cycle (such as a shower) then the boiler does not need to ramp as quickly. This enables a boiler controller to control the ignition timing or rate of heat input, improving the energy efficiency in heating water and as a consequence, reducing the volume of rejected lukewarm water.

The control for the heat input rate to domestic hot water of the boiler can be further adjusted to take into account the static volume of water and heat exchanger characteristics within the boiler’s primary burner and pipework that sits between the stored flue gas heat recovery device and the domestic hot water plate heat exchanger.

Therefore, a boiler controller that is aware of the amount of stored energy and the hot water characteristics of the boiler can improve both the energy efficiency in hot water generation while reducing the amount of lukewarm water losses, which would be otherwise classified as wasted energy.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure will now be described, by way of non-limiting examples, with reference to the accompanying Figures, in which:

Figure 1 is a schematic representation of a combination gas boiler used to provide hot water for space heating and hot water for washing;

Figure 2 repeats Figure 1, but identified pipe lengths that introduce a transport delay; Figure 3 shows a typical profile of temperature versus time at an output of a boiler.

Figure 4 shows an embodiment of the present disclosure;

Figure 5 shows a multiport manifold; and

Figure 6 shows a domestic system with acoustic sensing.

DESCRIPTION OF SOME EMBODIMENT

Figure 1 schematically illustrates the connections around a combination boiler, generally designated 2. The combination boiler comprises a primary heat exchanger 4 which comprises a primary coil 6 in the vicinity of the gas burner 8 such that the water within the primary coil becomes heated by the hot gas flow resulting from operation of the burner 8. The hot water from the primary heat exchanger flows towards a diverter valve 10 which can divert the hot water along a first path 12 to the space heating system or along a second path 14 to a secondary heat exchanger 16, generally in the form of a plate heat exchanger, to provide domestic hot water to a hot water outlet 20. A pump 22 circulates the water through the primary heat exchanger, and either be space heating system or plate heat exchanger 16 depending on whether the boiler is in space heating mode or is providing domestic hot water for washing or the like.

In a conventional boiler system, an input port of the plate heat exchanger 16 would receive cold water directly from a cold main 30. However in heating systems associated with a thermal store, for example in the form of a flue gas heat recovery device 40, such as the GAS SAVER™ a cold water path from the cold main can then exist by way of the thermal store 40.

Cold water from the cold main passes through a thermal store heat exchanger 42 which is in contact with the volume of water or flue gas condensate 44 held within the thermal store 40. Warmed water exiting the thermal store 40 can be supplied directly to the input of the boiler or more generally is mixed with water from the cold main by way of a blending valve 50. The blending valve 50 may be a thermostatic valve set to obtain a desired target temperature, for example in the range of 23 °C to 30°C, or it may be an electrically operated valve under the influence of a valve controller (not shown).

Figure 2 repeats Figure 1, but has some additional information. In particular, it shows that between the cold main and the thermal store 40 there is a length of pipe Ll having an internal cross-section Al . Within the thermal store there is the heat exchanger which for the purposes of this discussion will be represented by a length of pipe L2 having an internal cross-section A2. Between the outlet of the thermal store 40 and the blending valve there is a length of pipe L3 having internal cross section A3, and then between the blending valve and the plate heat exchanger there is a length of pipe L4 having an internal cross-section A4.

We can see that once a tap (faucet) 60 is opened, water is admitted into the boiler and the plate heat exchanger. In a boiler without a flue gas heat recovery system or thermal store, the operation of the tap 60 causes a pressure change which instructs the boiler to ignite the gas burner and start warming fluid in the primary heat exchanger 6. Similarly the diverter valve 10 is operated to make sure the boiler is in domestic hot water mode and then the boiler starts to commence heating the water. There is inevitably time lag whilst the water in the primary heat exchanger passes through the secondary heat exchanger and these become warmed to the extent that they can provide useful heat for warming the water from the cold main.

Given that users want hot water as fast as possible, the boiler generally operates at a "full power" mode to provide the maximum heat, although this can be relatively inefficient.

If we turn to consider the heating system shown in Figures 1 and 2, it can be seem that upon opening the tap 60, a slug of cold water having the volume L3 - A3 and a volume of cold water L4· A4 flows towards the plate heat exchanger 16 and then to the tap. Meanwhile water from the cold main is displacing water in the thermal store heat exchanger 42. As a result there is a volume of warm water whose volume is L2-A2 and whose temperature is that of a thermal store which travels towards the plate heat exchanger, and then after that there is water at a reduced temperature being the water from the cold main that is warmed as it passes through the thermal store. It would be advantageous for the boiler controller to take account of the arrival of the warm water coming from the thermal store, even though that is associated with a transport delay.

Figure 3 shows the typical heat to water temperature rise over time for a standard condensing combination boiler, as installed in millions of UK homes.

In this example, we can see that the horizontal axis, time, and vertical axis, temperature show a range of outcomes identified by regions A to E, where;

A is the energy contribution of the pre-heat value

B is the recovered energy contribution for the hot water generation strategy

C is the non-optimised recovered energy benefit

D is the indirect benefit of the stored passive flue gas heat recovery device

E is the standard boiler heat to water profile

It is known that a standard boiler operates in both heating and domestic hot water and there is a close integration between these two modes of operation. This interaction provides a means by which a flue gas heat recovery device can store and keep hot waste flue heat energy from the space heating operation.

As well as space heating, the boiler also produces on demand domestic hot water for showers, baths and sinks. The process of domestic hot water generation is currently not included in an industry bimodal test strategy, so there is no correlation between recovered energy in space heating and recognised levels of efficiency in the generation of domestic hot water.

Figure 3 shows that when the stored indirect energy from space heating is introduced to the production of domestic hot water, there is an opportunity for the boiler to produce hotter water faster, when compared with the standard boiler that does not have the indirect stored energy benefits. In Figure 3 this is the difference between regions C and E, where E is the boiler’s standard rate of hot water generation and C is the same rate with the added benefit of the indirect stored flue heat recovery from space heating. Area C shows us that there is a range of hot water outcomes, all above the output of E.

The key points about areas C and E are that they have the same ignition sequence and in the instance of Figure 3, are set to immediately burn gas on receiving hot water demand from the user. Therefore, it is possible to see that the boiler 2 will automatically provide hotter water than is required at the same rate of gas heat input, until such a time as the boiler has heated the water sufficiently to allow modulation of the heat input to a lower level.

Alternatively, in this example, we can see that the benefit of area D can also be used to improve efficiency further by enabling the boiler to monitor the temperature of the heat store 40 and estimate the energy content of the indirect stored energy benefit. This benefit could then be realised when the boiler controller is adapted to include the concept of static water volumes held within the boiler's internal pipework and the time it takes for the heat exchanger 42 to heat the incoming cold water to an optimum target temperature of about 30°C. 30°C represents both the point at which hot water is considered useful and is the most advantageous temperature from which to heat water via a modern gas boiler.

Therefore, when the user requires domestic hot water, the boiler controller can be arranged to judge both the time it should wait before burning gas and the rate of gas heat input required to suit the variables of the domestic hot water temperature setting, incoming cold water supply temperature and flow rate.

The flow rate information may be of further use in deterring the boiler’s domestic hot water generating logic in estimating whether the domestic hot water requirement is for a shower or sink, where B may be a variable outcome based either from the optimised heat input to hot water output over time, or where the boiler may decide that it will set a different domestic hot water target temperature until a few seconds have passed so as to ensure that it does not waste heating water that would otherwise lose heat in the domestic hot water pipework. This point becomes apparent when considering that there are three types of domestic hot water;

1 ) Cold water in the hot pipework.

2) Lukewarm water, water that has some added heat input but is not sufficiently hot enough for use.

3) Domestic hot water supply.

A user who requires domestic hot water to a bathroom sink for washing their hands may only operate the tap for a very short period, however, in today’s boilers this would lead to the boiler behaving in the same operation as though the requirement was for a sustained shower. The short hot water operation would therefore, lead to the use of the stored indirect energy and additional heat input to water, only to lose this heat energy as cooling water that remained in the hot water pipework.

Therefore, a boiler may have a controller to optimise the use of both the stored indirect energy and heat input that seeks to further reduce the waste associated with short domestic hot water requirements, i.e. bathroom sinks.

Figure 5 shows an embodiment of the present disclosure in which a temperature sensor 60 has been provided to measure the temperature of the thermal store and provide this information to a boiler controller 62.

The boiler controller may be a controller provided as part of the boiler and arranged to control the operation of the boiler, such as the diverter valve 10 and a gas modulation valve 65. Alternatively, in a retro-fit installation the boilers own internal controller may be left unmodified and the controller 62 is provided as further controller to vary the demanded water temperature, thereby being able to reduce the demand temperature when it wants to inhibit the boiler, and vary the temperature during the start-up phase. The temperature sensor may be moved to a position along the pipe between the store 40 and the mixer valve 50, but then the controller has to wait for the slug of hot water exiting the heat exchanger 42 to reach the temperature sensor.

As a further option, the temperature sensor 42 could be omitted, and the controller 62 could work to estimate the temperature of the store base don previous use of the boiler and a temperature delay equation.

In order to take advantage of modifying the boiler's gas or oil burn rate to take account for the distribution network between the boiler and the tap, it becomes desirable to know which tap, shower, faucet is being operated. One way of achieving this is to divide the outlet manifold of the boiler into a plurality of ports. Such an arrangement is shown in Figure 5 where the outlet manifold, generally designated 80 is divided into outlet ports 82, 84 and 86. Each port can be connected to a different pipe, or grouping of pipes such that taps which are close to the boiler are connected to one port, taps which are remote from the boiler are connected to another port and intermediate taps are connected to a third port. Alternatively, high flow rate devices, such as a bath might be connected to one port, a shower might be connected to another port, and the remainder of the taps connected to a third port. Of course the number of ports can be increased or decreased as appropriate. Each port can be associated with a flow rate sensor. The flow rate sensors, designated 88 in Figure 5 may be adapted to give an estimated flow rate, or may simply be switches associated with a moveable diaphragm or similar such that a flow/no-flow signal is given from each port. The controller then also needs to be programmed with an estimate of the fluid volume and/or thermal properties of the delivery network between the boiler and the appropriate tap such that it can estimate how much energy will be lost to warming the delivery network to the useable hot water output temperature.

Figure 6 shows an alternative arrangement where a single port from a boiler is used to connect the boiler to a domestic hot water network 90 which has outputs 92, 94 and 96 at different distances, and with different use regimes, from the boiler 2. The distribution network is associated with an acoustic sensor 100, e.g. a microphone, connected to boiler controller 102. The microphone and controller can be adapted to learn an acoustic signature associated with operation of the taps. For example the signature of water exiting a bath tap is likely to be different from the signature of water exiting the sink tap, and different again from the signature of water exiting a shower head. The microphone connected to the hot water delivery circuit can pick up the sounds associated with operation of the various taps, showers and the like and feed acoustic signal to the controller 102. The acoustic signal can then be analysed by the controller in order to determine which water consuming device is operative. The technology suitable for performing the acoustic measurement exists, and is disclosed in PCT/GB2017/051036 where it was used in the context of identifying the type of gas meter installed in a premises and the flow rate of the gas meter. Alternatively each tap may be modified to make a distinct sound, such as a click pattern when operated.

It is thus possible to use knowledge about the volume of water entrained in pipework between a boiler and the point of use where that water is required to modify the water heating profde of the boiler so as to reduce the time that it spends operating in an inefficient mode where the heat imparted during that operation is likely to be unusable either because the water gives up its heat to the pipe network between the boiler and the point of use, or because at the desired point of use the water will not have reached an acceptable temperature. It is further possible to modify the heating profile of a boiler to take account for heat stored within a thermal store that is available to the boiler. The thermal store can be used to recover waste heat from the flue gas of a boiler and/or waste heat from other processes or heat from other input sources. Thus, for example, the thermal store may contain heat provided by a solar panel or heat recovered from grey water, for example heat recovered from a previous shower or bath or heat recovered from the output of a device such as a dishwasher or a washing machine. The techniques described herein can be used alone or in combination.

With the introduction of "smart meters" gas suppliers can impose time varying tariffs to users. The controller may be programmed with the knowledge of the tariffs and may have a programmed or learnt usage pattern of water use, and can use this information to inform its decision to take water from the thermal store or to inhibit use of the thermal store, for example by closing a valve in the path to or from the thermal store, so as to save energy for later when the tariff is greater.

Claims

1. A fluid heating system comprising:

a heater;

a thermal store;

a temperature sensor or estimator for indicating a temperature of the thermal store; and

a controller, wherein when a demand for warmed fluid is made, the controller calculates a modified energy use profile for the heater based on the temperature of the thermal store.

2. A fluid heating system as claimed in claim 1, in which further comprising means for estimating or identifying a type of warmed fluid demand, and modifying the energy use profile based on the type of the fluid demand.

3. A fluid heating system as claimed in any preceding claim, in which the means for estimating the type of demand comprises a flow rate meter.

4. A fluid heating system as claimed in any preceding claim, wherein the means for estimating the type of demand comprises an outlet manifold with a plurality of ports, and pressure sensors or flow rate sensors operative to identify which port is delivering fluid.

5. A fluid heating system as claimed in any preceding claim, where the means for estimating the type of demand comprises an acoustic sensor and a processor for identifying an acoustic signature specific to a given delivery control valve.

6. A fluid heating system as claimed in any preceding claim, in which the heater is a gas boiler, and the rate of gas bum can be varied.

7. A fluid heating system as claimed in any preceding claim, in which the heating system delivers domestic hot water.

8. A fluid heating system as claimed in claim 6, in which the thermal store comprises a flue gas heat recovery device.

9. A fluid heating system as claimed in any preceding claim, comprising a blending device for blending liquid that has passed through the thermal store to warm it or which has been removed from the thermal store with liquid from a supply pipe to form warmed liquid at an input to the heater.

10. A fluid heating system further comprising a timer and fuel tariff memory and a processor adapted to estimate whether heat should be removed from the thermal store or saved for later use.

11. A method of controlling a gas or oil burning boiler having a flue gas heat recovery device acting as a thermal store, and a temperature sensor or energy estimator for estimating the temperature of the thermal store, the method comprising receiving a demand for hot water, and in response to the demand using an estimate of the usable energy in the thermal store to modify a fuel use profile.

12. A heating system comprising a controller and a water heater, the controller adapted to modulate operation of the heater to reduce lukewarm water rejection or energy wasted due to operation in less efficient heating modes where the heat imparted therein in predominantly lost to warming a distribution network.

13. A heating system including a sensor system for identifying operation of a specific valve or tap, or operating of a valve or tap within a group of such valves or taps, and using knowledge about the length of the distributed network or thermal properties thereof between the boiler and valve or tap to vary an energy consumption profile of the boiler.