EP4033146A1

EP4033146A1 - Heat recovery device

Info

Publication number: EP4033146A1
Application number: EP21153485.4A
Authority: EP
Inventors: John Dieterman; Natalia Myjak
Original assignee: BDR Thermea Group BV
Current assignee: BDR Thermea Group BV
Priority date: 2021-01-26
Filing date: 2021-01-26
Publication date: 2022-07-27
Also published as: WO2022161968A1; EP4285052A1

Abstract

The invention relates to a heat recovery device, in particular for a boiler, the heat recovery device comprising a water storage device comprising an outer wall, an inner wall delimiting an inner space of the water storage device for receiving water, wherein the inner space is fluidically connectable to a transfer conduit, in particular for transferring water received in the water storage device to the boiler, an exhaust gas line for receiving exhaust gas from the boiler comprising a line inlet portion for inletting the exhaust gas into the heat recovery device, a line outlet portion for outputting the received exhaust gas from the heat recovery device and a line middle portion that is fluidically arranged between the line inlet portion and the line outlet portion, wherein the line middle portion is arranged between the outer wall and the inner wall and the inner wall provides thermal contact between the inner space and the line middle portion.

Description

The invention relates to a heat recovery device and a heating system with such a heat recovery device. Additionally, the invention relates to a method of operating such a heating system.
Gas boilers combust gas fuel to heat water for domestic use and/or central heating systems in buildings. Exhaust flue gas is generated by this combustion. Usually, a central heating water circuit is heated, as well as a hot water supply. It is desirable to reduce the amount of gas used by a boiler in order to reduce greenhouse gas emissions and to lower costs for the operator. It is particularly desirable to reduce the amount of gas utilised, whilst not compromising on the amount of useful heat obtained from the boiler (i.e. to increase the overall efficiency of the conversion of chemical energy stored in the gas fuel to useful heat energy).
WO2011060524A1 is directed to providing a water heating system which ameliorates at least some of the needs of the prior art such as a water heating system suited for applications involving large draws of water, which can supply hot water quickly while providing adequate control of the temperature of the water and which is energy efficient and has reduced exhaust emissions and discloses a water heating system having a boiler, a chimney connected to the boiler and at least one conduit connected to a municipal water supply by a valve and positioned such that heat from the exhaust gases in the chimney is transferred to water in the at least one conduit.
US6564755B1 is directed to providing an improved heat recovery system for extracting waste heat from an exhaust gas and discloses a heat recovery system including a heat exchanger surrounding a flue pipe from a furnace for preheating water. The heat exchanger includes a sleeve surrounding the flue pipe to define an annular space and form a water jacket in direct contact with the flue pipe. The system includes water tanks that are heated by residual heat passing through the sleeve. When hot water is needed, the water is drawn from holding tanks through the annular space where water is heated by direct contact with the outer surface of the flue pipe. The preheated water exits the heat exchanger through a conduit outlet, which can be directed, to a conventional water heater, storage tank or domestic water supply.
US2019154359A1 is directed to making the transfer of heat from the combustion process in a domestic boiler more efficient, in order to reduce the amount of fuel used to achieve the desired heating of the supply water and discloses a preheater including a flue box including a combustion gas inlet to receive hot combustion gas from a boiler, and a combustion air inlet to receive air for combustion in a boiler. The preheater includes a condenser including a mains cold water inlet and a mains water outlet arranged such that mains water flows through the condenser prior to being supplied to a boiler combustion chamber. The condenser includes a central heating water return and a central heating water flow outlet arranged such that central heating water flows through the condenser prior to being supplied to the boiler combustion chamber. The condenser includes connections that enable the condenser to be connected to preheated fluid supply pipework from a source of preheated fluid, the preheated fluid including fluid heated by heat from at least one of the combustion gas and a renewable energy source.
GB2459879B is directed to providing an inexpensive and reliable heat recovery device to recover heat from condensate and discloses a condensate heat exchanger in combination with a condensing boiler. The exchanger comprises a vessel arranged to collect condensate from the boiler via an inlet. A fluid flow path carrying mains water is in thermal contact with condensate in the vessel. Said condensate heat exchanger only operates usefully when there is a demand for hot water.
EP1809949A1 is directed to providing a water system which is able to cope with short term high flow rate demands for hot water which would be well beyond the capability of the water heater to service if it received its water solely from the cold main and discloses a system for delivering warmed fluids. The system comprises a storage vessel and storage vessel heating means for heating the fluid in the storage vessel. The storage heating means are arranged within an inner space of the storage vessel.
The devices that are discussed above provide devices and systems that are complicated to manufacture and take up a significant amount of space. Such devices also have a limited amount of compatibility with existing boilers that are commercially available.
The object of the invention is to provide a heat recovery device that is easy to manufacture, takes up less amount of space and that is compatible with existing boilers. The object is solved by a heat recovery device, in particular for a boiler, the heat recovery device comprising:

a water storage device comprising an outer wall, an inner wall delimiting an inner space of the water storage device for receiving water, wherein the inner space is fluidically connectable to a transfer conduit, in particular for transferring water received in the water storage device to the boiler,
an exhaust gas line for receiving exhaust gas from the boiler comprising a line inlet portion for inletting the exhaust gas into the heat recovery device, a line outlet portion for outputting the received exhaust gas from the heat recovery device and a line middle portion that is fluidically arranged between the line inlet portion and the line outlet portion,

The inventive embodiment has the advantage that the heat recovery device is easy to manufacture and that it does not take up a significant amount of space, in particular mounting space. Additionally, the heat recovery device can easily be connected with existing boilers. These advantages result therefrom that it was recognized to arrange the line middle portion within the outer wall of the water storage device and that an inner wall provides thermal contact between the fluid conduit and the inner space. That means, the inner wall enables to heat the water arranged within the inner space by the exhaust gas flowing in the line middle portion.
The heat recovery device uses hot exhaust gas to heat water that can be used as domestic hot water prior to entering the boiler and therefore reduces the amount of the work that the boiler needs to do in order to heat water to a hot water set point. In effect, the heat recovery device takes advantage of the heat generated to e.g. heat a central heating system (that may also be supplied by a water supply) to assist in heating water. Furthermore, the water storage device captures heat from the exhaust gas during the mode of operation where there is a central heating demand but no demand for heated water.
The boiler can be a gas boiler. In particular, the boiler can be a condensing boiler.
The inner wall corresponds with the part of the water storage device that limits the inner space in which water is arranged. The inner wall limits the inner space of the water storage device in at least two, in particular three, space directions. The outer wall at least partly, in particular fully, surrounds the inner wall. That means, in a plane being perpendicular to a length axis of the heat recovery device, the outer wall is arranged further away from the length axis than the inner wall. Due to such an arrangement of the outer wall and the inner space a space is formed between the outer wall and the inner wall. Said space corresponds with the line middle portion of the exhaust gas line.
The line inlet portion is a part of the exhaust gas line through which exhaust gas of the boiler is inserted into the heat recovery device. The line outlet portion is a part of the exhaust gas line through which the inserted exhaust gas leaves the heat recovery device. The exhaust gas can flow out into the environment by means of the line outlet portion. The exhaust gas can be flue that results from a gas combustion in the boiler.
Thermal contact means that the inner wall is arranged and configured such that a heat transfer occurs between the line middle portion, in particular the exhaust gas that flows within the line middle portion, and the inner space, in particular the water arranged within the inner space.
The heat recovery device can advantageously be easily retrofitted to existing boilers, for example, by being mounted on top of the boiler or at any location where exhaust gas is emitted by the boiler.
According to an embodiment of the invention the outer wall and/or the inner wall can limit the line middle portion. That means, the inner wall and/or the outer wall defines the line middle portion. The inner wall is arranged between the inner space and the line middle portion. Thus, the exhaust gas flowing within the line middle portion is separated from the inner space, in particular, the water arranged in the inner space.
The inner wall comprises or can be made of a thermally conductive material. In particular, the thermally conductive material can have a thermal conductivity of at least 8 W/m*K (Watt/meter Kelvin), preferably at least 10 W/m*K, in particular 13 W/m*K. This value refers to an atmospheric pressure and 25 degrees centigrade. Such thermal conductivity enables a good heat transfer between the exhaust gas and the water arranged within the inner space. For example, the inner wall can comprise or be made of stainless steel, in particular stainless steel type 316 or 316L (ASTM A240). Alternatively, the inner wall can comprise or be made of other material like aluminium that has a high thermal conductivity. The inner wall material can have a thermal conductivity of or up to 430 W/m*K.
The outer wall can have thermal conductivity that is lower than the thermal conductivity of the inner wall. This has the advantage that the heat recovery device does not lose significant heat to the environment. The outer wall can comprise or is made of a thermally conductive material having a thermal conductivity less than or equal to 1 W/m*K, preferably between 0,008 W/m*K and 0,5 W/m*K.
The thermal conductivity is defined as the rate at which heat is transferred by conduction through a unit cross-section area of a material, when a temperature gradient exits perpendicular to the area.
The line middle portion can be arranged fluidically downstream the line inlet portion and/or can be arranged fluidically upstream the line outlet portion. Additionally, the line middle portion can be formed such that it is not fluidically connected with the inner space and/or that the line middle portion is exclusively arranged between the outer wall and the inner wall. Therefore, it is easily secured that the exhaust gas does not come in contact with the water stored in the inner space of the water storage device.
The line middle portion can partially or fully surround the inner space of the water storage device. In an embodiment, the line middle portion can extend helically along a length axis of the heat recovery device. The provision of the aforementioned line middle portions results in an efficient heat recovery device as an area for the heat transfer between the exhaust gas and the stored water is provided and the stored water is directly heated by the exhaust gas by means of the inner wall.
The water storage device can have a cylindrical form. This has the additional advantage of constructively simple way to provide additional structural strength in case of a pressurized water storage device. In a further embodiment, the water storage device can be configured to store water that is pressurised to at least 0.5 bar. Typically, the water can be pressurised up to 11 bar (gauge pressure).
The inner space can be fluidically connectable to a water supply conduit. The water supply conduit can be connected at one end with a water supply source of a municipal water supplier. Thereto, the outer wall can comprise a through hole through which the water supply conduit extends. Thus, water can be easily supplied into the water storage. This can be necessary when in an operation mode water is removed from the water storage device. This is explained later more in detail. In a further embodiment, the outer wall through hole can further comprise a seal. In a further embodiment, the water supply conduit is connected to the inner wall by way of a water tight connection, such as for example by way of a welded joint with the inner wall. This has the additional advantage of constructively simple means to secure water-tightness of the water supply conduit.
According to an embodiment, the heat recovery device can comprise a heat exchanger that is fluidically connected with the line inlet portion and the water storage device. The heat exchanger can be arranged fluidically downstream of the line inlet portion and/or can be arranged fluidically upstream the line middle portion. Additionally, the heat exchanger can be fluidically connectable with the transfer conduit and/or the heat exchanger can be arranged such that a heat transfer occurs between the exhaust gas of the boiler and water flown out of the water storage device before the water is supplied to the boiler. This has the advantage that the water can be heated up by the exhaust gas before it is supplied to the boiler and additionally further increases the amount of useful heat transferred to the water from the boiler waste combustion products, particularly during all modes of operation of a boiler.
The water storage device can be arranged coaxially to line inlet portion and/or the line outlet portion and/or the heat exchanger. This enables a compact heat recovery device in radial direction of the heat recover device. Alternatively, the line outlet portion can extend in a horizontal direction. The horizontal placement of the line outlet portion avoids the need for a bend in the gas outlet to the horizontal, which may be necessitated where the line outlet portion initially extends in an upwards direction.
The heat recovery device can comprise a device air box case wherein the water storage device and/or the heat exchanger is arranged within the device air box case. The device air box case provides protection for the other components of the heat recovery device. Additionally, the device air box case enables that the heat recovery device is formed as a module. That means, all parts of the heat recovery device can be transported as whole.
The heat recovery device can comprise a ventilation device wherein at least a part of the line gas portion is arranged within the ventilation device. A cross section of the line outlet portion is smaller than a cross section of the ventilation device. Thus, there is space between the line outlet portion and the ventilation device through which air can be sucked into the heat recovery device by means of e.g. a boiler fan.
A particularly advantageous embodiment is a heating system with an inventive heat recovery device and a boiler. The boiler is fluidically connected with the heat recovery device. A fluid connection means that a fluid can flow from one component, e.g. the boiler, to another component, e.g. the heat recovery device, in particular into the gas inlet, or vice versa.
The heat recovery device can be arranged above the boiler. In particular, the heat recovery device can be placed on the boiler, in particular, a top surface of the boiler. The top surface of the boiler comprises a boiler outlet through which the exhaust gas can flow out of the boiler. The line inlet portion, the line middle portion and line outlet portion are configured to vent exhaust gas emitted from the boiler outlet on the top surface of the boiler. Typically, the heat recovery device is attached to the top surface of the boiler, at a location corresponding to the boiler outlet, via a duct or adaptor.
The boiler can comprise a boiler air box case wherein at least a part of the heat recovery device is arranged within the boiler air box case. In particular, at least a part of the exhaust gas line, the heat exchanger and the water storage device are arranged within the boiler air box case. Such a heating system is compact.
According to an aspect of the invention a method of operating a heating system is provided. The method is characterized in that in an operation mode in which a central heating system is heated, the boiler combusts gas to heat a central heating system and the heat recovery device transfers heat from the exhaust gas generated by the gas combustion to water stored in the water storage device and that in a further operation mode the heat recovery device transfers water from the water storage device to the boiler by means of the transfer conduit.
The central heating system can be heated after the heating system receives a heating demand. The further operation mode can be executed after the heating system receives a demand that a domestic needs water, in particular hot water. In the further operation mode, the central heating system can be heated. Additionally, the further operation can be executed subsequently to the operation mode.
During the further operation mode, the heat recovery device can transfer water from the water storage device to the boiler via the heat exchanger. The heat exchanger transfers heat from the exhaust gas generated by the gas combustion to heat the water flowing out the water storage device. The heat exchangers and the water storage device can be located such that exhaust gas contacts the heat exchanger before it contacts the water storage device.
According to an operation the heating system can capture heat from exhaust flue gas for heating water, even when there is no hot water demand. In other words, the device enables harvesting of heat from exhaust gas during multiple modes of operation, in particular, whether or not there is a hot water demand by e.g. a domestic home.
It is anticipated that the heat recovery device can be utilised with boilers that either combust gas fossil fuels such as natural gas and liquefied petroleum gas, or, combust hydrogen gas fuels including mixtures of hydrogen gas and fossil fuels.
In the figures, the subject-matter of the invention is schematically shown, wherein identical or similarly acting elements are usually provided with the same reference signs.

Figure 1: shows a schematic representation of a heating system with an inventive heat recovery device according to a first embodiment.
Figure 2: shows a schematic representation of the heating system of fig. 1 in which the boiler is shown more in detail,
Figure 3: shows a schematic representation of a heating system with an inventive heat recovery device according to a second embodiment and
Figures 4a, 4b, and 4c: show a schematic representation of a system utilising the heat system shown in Figure 1 or 2 to supply heat to a central heating system and to supply hot water during different modes of operation.

With reference to Figure 1, a heating system 17 comprising a heat recovery device 1 and a boiler 2 is shown. The heat recovery device 1 is fluidically connected with the boiler 2 and comprises an exhaust gas line for receiving exhaust gas from the boiler 2. The exhaust gas line has a line inlet portion 3 for receiving exhaust gas from the boiler 2, a line outlet portion 4 for outputting the received exhaust gas to the environment and a line middle portion 8 that is fluidically arranged between the line inlet portion 3 and line outlet portion 4. Thus, the line middle portion 8 is arranged downstream of the line inlet portion 3 and upstream of the outlet portion 4 with respect to an exhaust gas flow. The exhaust gas flow is shown by arrows in fig. 1.
Additionally, the heat recovery device 1 comprises a water storage device 5. The water storage device 5 comprises an outer wall 6 and an inner space 7 for receiving water 20. The line middle portion 8 is arranged between the outer wall 6 and an inner wall 9, wherein the inner wall 9 provides thermal contact between the inner space 7 and the line middle portion 8. The inner wall 9 is the wall that is at least partly in contact with the water 20 arranged in the inner space 7. Thus, the water 20 arranged in the inner space is heated by the exhaust gas flowing in the line middle portion 8. This is possible as the innerwall 9 comprises or is made of thermally conductive material. Additionally, the outer wall 6 can comprise or can be made of a thermally insulating material.
The inner space 7 is fluidically connected with a transfer conduit 10. Thereto, the outer wall 6 can comprise a through hole through which the transfer conduit 10 extends. The transfer conduit 10 is fluidically connected with the boiler 2 so that the transfer conduit 10 transfers water 20 from the water storage device 5 to the boiler 2.
The heat recovery device 1 comprises a heat exchanger 15. The heat exchanger 15 is fluidically arranged between the line inlet portion 3 and the line middle portion 8. That means, the exhaust gas has to flow through the heat exchanger 15. Additionally, the heat exchanger 15 is fluidically connected with the inner space 7 and the transfer conduit 10. The heat exchanger 15 is configured to transfer heat form the exhaust gas entered into the exhaust gas line to the water 20 flowing out the inner space 7. The water 20 flowing out the inner space 7 is heated by the heat exchanger 15 before it is supplied to the boiler 2.
The heat exchanger 15 may be any type of heat exchanger suitable for exchanging heat between hot exhaust gas on one side and water on the other side. For example, heat exchanger 15 may comprise a series of stainless steel plates that are bonded together, for example, a heat exchanger that is known as a plate heat exchanger. Plate heat exchangers utilise a "cross flow" design, meaning that exhaust gas passes either side of plates in thermal contact with water. As hot exhaust gas goes through the heat exchanger 15, heat is transferred to the water 20 flowing through the heat exchanger 15. Alternatively, the heat exchanger 15 may have a "tube and fin" design, where tubes are pressed into a series of fine plates forming fins. In operation, exhaust gas passes between the fins, whilst water passes through the tubes. The heat exchanger 15 may be referred to as an "instant heat exchanger" because it transfers heat from exhaust gas that is generated at the same time as water is entering the boiler 2 for heating.
The water storage device 5 is preferably a cylinder in order to provide suitable strength for holding the water 20. A cylindrical shape is also found to provide a suitable size surface area for providing sufficient heat transfer between the exhaust gas and stored water 20. Additionally, the cylindrical shape has the additional advantage of constructively simple way to provide additional structural strength in case of a pressurized water storage device. The water storage device 5 is not necessarily a cylinder and may instead be any three dimensional shape that is suitable for containing water. The water within the water storage device 5 is typically pressurised to at least 0.5 bar (gauge pressure).
The inner space 7 is fluidically connected with a water supply conduit 14. Thereto, the outer wall 6 comprises a through hole through which the water supply conduit 14 extends. Thus, it is possible to supply water into the water storage device 5. The water supply conduit 14 is fluidically connected with a water supply source of a municipal water provider that is not shown in the figures.
An end of the line middle portion 8 is fluidically connected with the line inlet portion 3 and another end of the line middle portion 8 is fluidically connected with the line outlet portion 4. The line middle portion 8 is arranged in the outer wall 6 and is not fluidically connected with the inner space 7 of the water storage device 5 so that there is no contamination of the exhaust gas with the water 20 arranged in the inner space 7.
The line outlet portion 4 is arranged within a ventilation device 28 of the heat recovery device 1. The line outlet portion 4 has a smaller cross section in a plane located perpendicular to a length axis of the heating system 17 than the ventilation device 28 so that there is a space between line outlet portion 4 and the ventilation device 28.
The line outlet portion 4 is represented as being located in an upwards direction relative to the boiler 2. However, the line outlet portion 4 is not limited to said direction. For example, the line outlet portion 4 may extend in a substantially horizontal direction from a portion of the outer wall 6 that extends in vertical direction. A horizontal placement of the line outlet portion 4 can be more suitable where the boiler 2 is located away from a ceiling and therefore the line outlet portion 4 must pass through a sidewall of a building (not shown). Substantially horizontal placement of the line outlet portion 4 also avoids the need for a bend in the gas outlet to the horizontal, which may be necessitated where the line outlet portion 4 initially extends in an upwards direction.
As shown in Figure 1, the heat recovery device 1 is mounted above the boiler 2. Typically, the heat recovery device 1 is attached to a top surface of the boiler 2 via an adaptor or duct. The top surface comprises a boiler outlet 21 to provide an outlet for exhaust gas that is lighter than atmospheric air.
The heat exchanger 15 is mounted above the boiler outlet 21 in order that exhaust gas reaches the heat exchanger 15 before the exhaust gas can reduce in temperature significantly. The water storage device 5 is mounted directly above the heat exchanger 15 to recover further heat from the exhaust gas by heating the stored water 20.
Some exhaust gas will condense to form an exhaust condensate within the heat recovery device 1. The exhaust condensate contains water and combustion waste products of the boiler combustion process. The exhaust condensate is allowed to flow out of the heat recovery device 1 and is not exposed to any water arranged within the water storage device 5. Typically, the exhaust condensate flows through the heat exchanger 15 into a condensate circuit (not shown). The exhaust condensate is typically eventually discharged from the boiler 2 via a condensate discharge pipe (not shown).
The heat recovery device 1 is configured to provide recovery of heat from the hot exhaust gases whether or not there is a domestic hot water demand. A domestic hot water demand occurs when a user demands hot water, for example, by opening a hot water tap.
In a mode of operation when there is no domestic hot water demand, water enters and is stored in the water storage device 5. The boiler 2 is typically operable to combust gas fuel for heating water that is circulated through radiators in a central heating system (not shown) during a central heating demand. This combustion generates hot exhaust gas. Therefore, during a central heating demand, hot exhaust gas flows into the heat recovery device 1 by means of the line inlet portion 3. The hot exhaust gas is in thermal contact with the water 20 that is stored in the inner space 7 by means of the inner wall 9 that is arranged between the line middle portion 8 and the inner space 7.
The exhaust gas remains at a relatively high temperature after passing across the heat exchanger 15 in this mode of operation, since there is no flow of water through the heat exchanger 15 (there is no domestic hot water demand). Therefore, a high level of the heat from the hot exhaust gas is transferred to the water in the water storage device 5. The overall temperature of water 20 in the water storage device 5 is raised. Normally, the temperature of the water storage device 5 will be raised until a thermal equilibrium, which will vary according to the heat load and/or heating set point of the boiler 2.
The temperature of the water storage device 5 is mainly related to the temperature that is set for the central heating system. The water storage device 5 can normally be heated to the equilibrium level (i.e. charged) within a predefined time, such as for example about one or two hours, during a central heating demand. The heating set point of the boiler 2 may be limited to ensure that the exhaust gas does not exceed a maximum temperature in order to prevent the temperature of the stored water in the water storage device 5 from reaching excessive levels.
When the water storage device 5 is charged and has stored heat (in thermal equilibrium), the heating system 17 can utilise the heated water when operating under a different mode of operation, which is when there is a domestic hot water demand, for example, when a hot water tap is opened. During a domestic hot water demand, heated water 20 flows from the water storage device 5, and through the heat exchanger 15. The heat exchanger 15 transfers additional heat from the exhaust gas to the heated water and additional gains to the temperature of the heated water are attained by the heat exchanger.
The water entering the boiler 2 is at a higher temperature than water supplied to the inner space 7 by means of the water supply conduit 14. Therefore, the boiler 2 needs to do less work to reach the hot water set point. For example, if in embodiments known form the prior art water of 10 degrees centigrade from a water supply conduit is directly fed to the boiler 2, and the set point (by the user) is adjusted to 50 degrees centigrade, then the water must be raised by a total of 40 degrees centigrade by the boiler 2 alone. Using the heat recovery device 1 as discussed above, water may enter the boiler at for example 40 degrees centigrade, and the boiler therefore would only need to work to raise the water temperature by 10 degrees centigrade. The amount of work that needs to be undertaken by the boiler 2 is significantly reduced. Water that is heated by the boiler 2 is supplied to a hot water supply via boiler water conduit 22.
If there is a long domestic hot water demand, then the water storage reservoir 5 may be depleted of water that has been heated during a previous heating demand. In this case, the water is still heated to a lesser degree as it flows through the water storage device 5, and additionally when flowing through the heat exchanger 15. Some heat of the exhaust gas is transferred to the water by the heat exchanger 15. Therefore, useful heat is still recovered from the exhaust gas and the work that needs to be undertaken by the boiler 2 is still reduced.
The disclosure advantageously provides for heat to be recovered from exhaust gas exhaust whether or not there is a hot water demand.
The heat recovery device 1 comprises a device air box case 16 wherein the water storage device 5 is arranged within the device air box case 16. Additionally, a part of the exhaust gas line is also arranged within the device air box case 16. The boiler 2 comprises a boiler air box case 18. The aforementioned parts of the boiler 2 are arranged within the boiler air box case 18. As is evident from figure 1 the device air box case 16 and the boiler air box case 18 are separate cases.
Figure 2 shows a schematic representation of the heating system 17 of fig. 1 in which the boiler 2 is shown more in detail.
The boiler 2 comprises a boiler domestic hot water heat exchanger 23. The boiler domestic hot water heat exchanger 23 is fluidically connected with the transfer conduit 10 and with the boiler water conduit 22. Additionally, the boiler 2 comprises a further main gas to water heat exchanger 24, which is connected with its own separate primary water circuit 22 to the domestic hot water heat exchanger 23. The main gas to water heat exchanger 24 is used to transfer heat resulting from a gas combustion process to the water supplied by the primary water circuit 22 The heated water leaves the further heat exchanger 24 via the primary water conduit 22.
The boiler 2 also comprises a fan 29 used to provide air for the combustion process with the main gas to water heat exchanger 24. The airflow of the air is shown in fig. 2 by arrows. As can be seen from fig. 2 air drawn in via the ventilation device 28 and further drawn into the heat recovery device 1 and flows form the heat recovery device 1 into the boiler 2. Air can be drawn into the heat recovery device 1 via the ventilation device 28, in particular the space between the ventilation device 28 and the line outlet portion 4.
Figure 3 shows a schematic representation of a heating system 17 with an inventive heat recovery device 1 according to a second embodiment. The second embodiment differs from the first embodiment shown in fig 1 and 2 in that the boiler air box case 18 is formed such that in addition to the boiler 2 components discussed above at least a part of the heat recovery device 1 is arranged within the boiler air box case 18. In particular, the water storage device 5, the heat exchanger 15 and a part of the exhaust gas line are arranged within the boiler air box case 18.
Figures 4a, 4b, and 4c show a schematic representation of a system utilising the heating system 17 of Figures 1-3 to supply heat to a central heating system and to supply hot water during different modes of operation.
The boiler 2 can supply heat to both a hot water supply 25 and a central heating system 19. The two systems are not fluidically connected with each other. Arrows in these figures represent the flow of central heating fluid to be supplied to the central heating system 19 and water to be supplied to the hot water supply 25.
With reference to Figure 4a, in an operation mode the boiler 2 may be operated to heat the central heating system 19 via the circulating heat transfer fluid flowing through the circulating pipes 27 (typically non-potable water). The hot water supply 25 is switched off. During this condition, the water storage reservoir 5 in the heat recovery device 1 is charging, i.e. storing heat that is obtained from the exhaust gas generated to power the central heating system 19.
In Figure 4b, the operation mode is finished, i.e. the central heating system may be switched off. The heat transfer fluid is no longer circulating through circulating pipes 27 and the boiler 2 is switched off. The heat recovery device 1 is storing heated water in the water storage device 5.
Figure 4c shows a further operation mode, wherein a user may demand hot water by opening a hot water supply 25 such as a hot water tap causing the boiler (if not already firing) to ignite for heating domestic hot water to a set point temperature. The central heating system 19 may be switched on or remain off. Heated water flows from the water storage reservoir 5 within the heat recovery device 1 into the boiler 2. The boiler 2 advantageously needs to do less work to heat the water to a set point temperature.
The water storage device 5 within the heat recovery device 1 is replenished with cold water from the water supply conduits 14. Eventually, the temperature in the water storage device 5 will be reduced as it is topped up with cold mains water that has not had time to heat. The water in the water storage reservoir 5 will be preheated to some degree due to the continued influence of hot exhaust gas flowing around the sides of the outer wall 6. However, the boiler 2 will need to work harder to heat the cooler water to the set point temperature. This is at least partially mitigated by operation of the heat exchanger 15 as discussed above with respect to Figure 1. Similarly, if the boiler 2 has not been operated for a significant amount of time, the water 20 stored in the water storage reservoir 5 within the heat recovery device 1 will have reduced in temperature and therefore during a subsequent hot water demand, the incoming domestic water to the boiler 2 is influenced by instant exhaust gas flowing around the water storage device 5 and by the heat exchanger 15.
This disclosure is not limited to examples including both the gas boiler 2 and the heat recovery device 1. The heat recovery device 1 may be supplied separately to a gas boiler 2 and may be suitable for retrofitting to existing gas boilers 2.
The term "domestic hot water" has been used to refer to water that is heated for use for domestic purposes such as drinking or cleaning/showering. However, this could refer to water used for such purposes in a setting that is not necessarily in a domestic home, such as for example on industrial or commercial premises.

Reference Signs

1: heat recovery device
2: boiler
3: line inlet portion
4: line outlet portion
5: water storage device
6: outer wall
7: inner space
8: line middle portion
9: inner wall
10: transfer conduit
14: water supply conduit
15: heat exchanger
16: device air box case
17: heating system
18: boiler air box case
19: central heating system
20: water
21: boiler outlet
22: boiler water conduit
23: boiler heat exchanger
24: further heat exchanger
25: hot water supply
27: circulating pipes
28: ventilation device

Claims

Heat recovery device (1), in particular for a boiler (2), the heat recovery device (1) comprising:
a water storage device (5) comprising an outer wall (6),an inner wall (9) delimiting an inner space (7) of the water storage device (5) for receiving water (20), wherein the inner space (7) is fluidically connectable to a transfer conduit (10), in particular for transferring water (20) received in the water storage device (5) to the boiler (2),

an exhaust gas line for receiving exhaust gas from the boiler (2) comprising a line inlet portion (3) for inletting the exhaust gas into the heat recovery device (1), a line outlet portion (4) for outputting the received exhaust gas from the heat recovery device (1) and a line middle portion (8) that is fluidically arranged between the line inlet portion (3) and the line outlet portion (4),

wherein the line middle portion (8) is arranged between the outer wall (6) and the inner wall (9) and the inner wall (9) provides thermal contact between the inner space (7) and the line middle portion (8).
Heat recovery device (1) according to claim 1, characterized in that
a. the outer wall (6) and/or the inner wall (9) limit the line middle portion (8) and/or

b. the inner wall (9) is arranged between the inner space (7) and the line middle portion (8).
Heat recovery device (1) according to claim 1 or 2, characterized in that
a. the inner wall (9) comprises or is made of a thermally conductive material having a thermal conductivity of at least 8 W/m*K, preferably at least 10 W/m*K, preferably at least 13 W/m*K and/or in that

b. the outer wall (6) comprises or is made of a thermally conductive material having a thermal conductivity less than or equal to 1 W/m*K, preferably between 0,008 W/m*K and 0,5 W/m*K, and/or in that

c. the inner wall (9) is arranged such that heat of the exhaust gas flowing in the line middle portion (8) is directly transferred into the inner space (7) by means of the inner wall (9).
Heat recovery device (1) according to one of the claims 1 to 3, characterized in that
a. the line middle portion (8) is arranged fluidically downstream the line inlet portion (3) and/or is arranged fluidically upstream the line outlet portion (4) and/or in that

b. the line middle portion (8) is not fluidically connected with the inner space (7).
Heat recovery device (1) according to one of the claims 1 to 4, characterized in that the line middle portion (8) partially or fully surrounds the inner space (7) of the water storage device (5).
Heat recovery device (1) according to one of the claims 1 to 5, characterized in that the inner space (7) is fluidically connectable to a water supply conduit (14).
Heat recovery device (1) according to one of the claims 1 to 6, characterized in that the heat recovery device (1) comprises a heat exchanger (15) that is fluidically connected with the line inlet portion (3) and the inner space (7) wherein
a. the heat exchanger (15) is arranged fluidically downstream the line inlet portion (3) and/or is arranged fluidically upstream the line middle portion (8) and/or wherein

b. the heat exchanger (15) is fluidically connectable with the transfer conduit (10) and/or wherein

c. the heat exchanger (15) is arranged such that a heat transfer occurs between the exhaust gas of the boiler (2) and water (20) flowing out of the water storage device (5) before the water (20) is supplied to the boiler (2).
Heat recovery device (1) according to one of the claims 1 to 7, characterized in that the water storage device (5) is arranged coaxially to the line inlet portion (3) and/or the line outlet portion (4) and/or the heat exchanger (15).
Heat recovery device (1) according to one of the claims 1 to 8, characterized in that the heat recovery device (1) comprises a device air box case (16) wherein the water storage device (5) and/or the heat exchanger (15) is arranged within the device air box case (16).
Heat recovery device (1) according to one of the claims 1 to 9, characterized in that the heat recovery device (1) comprises a ventilation device (28) wherein
a. at least a part of the line outlet portion (4) is arranged within the ventilation device (28) and/or wherein

b. a cross section of the line outlet portion (4) is smaller than a cross section of the ventilation device (28).
Heating system (17) with a heat recovery device (1) according to one of the claims 1 to 10 and a boiler (2), wherein the boiler (2) is fluidically connected with the heat recovery device (1).
Heating system (17) according to claim 11, characterized in that
a. the heat recovery device (1) is arranged above the boiler (2) and/or in that

b. the heat recovery device (1) is placed on the boiler (2).
Heating system (17) according to claim 11 or 12, characterized in that the boiler (2) comprises a boiler air box case (18) and wherein at least a part of the heat recovery device (1) is arranged within the boiler air box case (18).
Method of operating a heating system (17) according to one of the claims 11 to 13, characterized in that in an operation mode in which a central heating system (19) is heated, the boiler (2) combusts gas to heat a central heating system (19) and the heat recovery device (1) transfers heat from the exhaust gas generated by the gas combustion to water (20) stored in the water storage device (5) and that in a further operation mode the heat recovery device (1) transfers water (20) from the water storage device (5) to the boiler (2) by means of a transfer conduit (10).
Method according to claim 14, characterized in that
a. during the further operation mode, the heat recovery device (1) transfers water from the water storage device (5) to the boiler (2) via the heat exchanger (15), and wherein the heat exchanger (15) transfers heat from the exhaust gas generated by the gas combustion to heat the water (20) and/or in that

b. the further operation mode is executed subsequently to the operation mode.