IE86946B1 - A safety cooling circuit for a solid fuel boiler - Google Patents

Abstract

This invention relates to a safety cooling circuit for a solid fuel boiler and a domestic heating system incorporating such a safety cooling circuit. The safety cooling circuit comprises a plate heat exchanger having a primary side and a secondary side. The primary side has a primary charging inlet for reception of a heating fluid supplied by the solid fuel boiler, and a primary discharge outlet for delivery of the heating fluid back to the boiler. The secondary side has a secondary charging inlet for reception of a cooling liquid and a secondary discharge outlet for delivery of the cooling liquid from the heat exchanger to a drain. A temperature controlled valve is operable to permit the cooling liquid to flow through the secondary side to the drain on the temperature of the heating fluid supplied by the boiler exceeding a predetermined temperature. In this way, a relatively simple and inexpensive yet effective arrangement of safety cooling system is provided. Furthermore, the arrangement can be modified with relative ease to provide practically instantaneous hot water to the domicile.

Description

"A safety cooling circuit for a solid fuel boiler" Introduction This invention relates to a safety cooling circuit for a solid fuel boiler and a domestic heating system incorporating such a safety cooling circuit.

Solid fuel boilers are commonly found in domestic heating systems. One problem with the integration of a solid fuel boiler into a domestic heating system is that extensive safety measures must be put in place to allow dissipation of heat from the solid fuel boiler. When the heat from the solid fuel boiler is no longer required in the domestic heating system or when it is no longer possible to pump the heat from the solid fuel boiler to the domestic heating system, such as in the case of a power failure, it is important to be able to dissipate the heat from the solid fuel boiler. Failure to dissipate the heat effectively can result in catastrophic consequences including the solid fuel boiler exploding and significant damage being done to the remaining components of the domestic heating system.

Unlike other types of boilers such as gas or oil fired boilers, solid fuel boilers cannot be made to quickly reduce the amount of heat that they are producing at the flick of a switch or during a power failure. The solid fuel boiler will often continue to generate significant amounts of heat for a substantial period of time after the heat is no longer required or after it is no longer possible to pump the heat away from the solid fuel boiler. Accordingly, special safety measures must be put in place in order to dissipate excess heat away from the solid fuel boiler when necessary. These safety measures typically include one or more of an open vent to atmosphere routed through a heat dump circuit and a heating header tank that operates according to the principles of thermosyphoning.

There are however problems with the known safety measures. First of all, in relation to the open vent to atmosphere routed through a heat dump circuit, the heat dump circuit often comprises one or more dedicated radiators in the residence. Installing additional radiators in a residence is costly and inconvenient. Furthermore, unless the additional radiators are located in an area not normally occupied such as an unconverted attic, an area of the residence with the additional dedicated radiators will continue to be heated -2for some time after it is desired to stop the supply of heat. Secondly, in relation to the implementation of a heating header tank, this solution is not entirely satisfactory as the excess heat in such a system can result in the water reaching boiling point. If the water is allowed to reach such temperatures, it can cause substantial damage to the components of the system. Furthermore, at these temperatures the water will turn to steam and may escape from the system. If the water escapes from the system it must be replenished which is undesirable as newly introduced, oxygenated water will corrode the components of the domestic heating system.

GB2470748 (Dedicated Pressure Systems Ltd) discloses an overheat protection system for a thermal store. However, GB2470748 does not disclose connecting an overheat protection system to a solid fuel boiler or indeed how such an overheat protection system could be connected to a solid fuel boiler.

It is an object of the present invention to provide a safety cooling circuit and a domestic heating system incorporating such a safety cooling circuit that overcome at least some of the difficulties with the known systems.

Statements of Invention According to the invention there is provided a safety cooling circuit for a solid fuel boiler, the safety cooling circuit comprising a plate heat exchanger having a primary side and a secondary side, the primary side having a primary charging inlet for reception of a heating fluid supplied by the solid fuel boiler and a primary discharge outlet for delivery of the heating fluid back to the solid fuel boiler, the secondary side having a secondary charging inlet for reception of a cooling liquid supplied from a cooling liquid supply and a secondary discharge outlet for delivery of the cooling liquid from the plate heat exchanger to a drain, and in which there is provided a temperature controlled valve operable to permit the cooling liquid to flow from the cooling liquid supply through the secondary side to the drain on the temperature of the heating fluid supplied by the solid fuel boiler exceeding a predetermined temperature.

By having such a safety cooling circuit, the safety cooling circuit can be installed with the minimum amount of disruption and expense. The plate heat exchanger can be used to -3cool the heating fluid in the solid fuel boiler down in a simple and effective manner. Furthermore, the safety cooling circuit will operate even during a power failure and will prevent the temperature of the heating fluid reaching levels where it is likely to cause damage to the components of the domestic heating system.

In one embodiment of the invention there is provided a safety cooling circuit in which there is provided a rapid water heating assembly coupled to the safety cooling circuit for supplying heated water to a hot water cylinder, the rapid water heating assembly comprising a flow pipe for connection to and delivery of water from the water cylinder, a return pipe for connection to and delivery of water to the water cylinder, and a pump for circulating water through the water heating assembly, the flow pipe being coupled to the secondary charging inlet and the return pipe being coupled to the secondary discharge outlet of the safety cooling circuit.

This is seen as a highly advantageous aspect of the present invention. As well as operating as a safety cooling circuit, the present invention may also be used to provide hot water to a water cylinder. Due to the fact that a plate heat exchanger is used to transfer heat indirectly from a solid fuel source, the water will be heated very quickly and the secondary water will be suitable for use in the hot water cylinder. The rapid water heating assembly will provide hot water practically instantaneously at any time the solid fuel boiler is in operation provided that the heating fluid supplied by the solid fuel boiler is below the predetermined temperature of the temperature controlled valve.

In one embodiment of the invention there is provided a safety cooling circuit in which the plate heat exchanger is a three sided plate heat exchanger further comprising a tertiary side having a tertiary charging inlet for connection to the return side of a pressurized domestic heating installation and a tertiary discharge outlet for connection to a flow side of a pressurized domestic heating installation. This is seen as a useful, compact implementation of the system. By using a three sided heat exchanger, the same heat exchanger can also be used to connect the solid fuel boiler to the pressurized domestic heating installation.

In one embodiment of the invention there is provided a safety cooling circuit in which there is provided a second plate heat exchanger also having a primary side and a -4secondary side, the primary side of the second plate heat exchanger having a primary charging inlet for reception of a heating fluid supplied by the solid fuel boiler and a primary discharge outlet for delivery of heating fluid back to the solid fuel boiler, the secondary side of the second plate heat exchanger having a secondary charging inlet for connection to a return side of a pressurized domestic heating installation and a secondary discharge outlet for connection to the flow side of a pressurized domestic heating installation. This is seen as a useful alternative to providing a three sided heat exchanger that will also allow the solid fuel boiler to be connected up to the pressurized domestic heating installation. It is envisaged that this implementation may be less expensive than a three sided heat exchanger implementation.

In one embodiment of the invention there is provided a safety cooling circuit in which the first and second plate heat exchangers are connected in series so that the primary charging inlet of one of the first and second plate heat exchangers is for reception of a heating fluid supplied by the solid fuel boiler and the primary discharge outlet of that plate heat exchanger is connected to the primary charging inlet of the other of the first and second plate heat exchangers and the primary discharge outlet of the other plate heat exchanger is for delivery of heating fluid back to the solid fuel boiler. By having such an arrangement, this will simplify the piping to the heat exchanger.

In one embodiment of the invention there is provided a safety cooling circuit in which there is provided a heating liquid short circuit intermediate the primary charging inlet for reception of the heating fluid supplied by the solid fuel boiler and the primary discharge outlet for delivery of the heating fluid back to the solid fuel boiler, the heating liquid short circuit comprising a fluid conduit, a valve and a pump mounted on the fluid conduit. This is seen as a particularly preferred implementation of the present invention. By implementing such a configuration, a heat source connected up to the pressurized domestic heating installation can be used to rapidly heat the water in the hot water cylinder through the heat exchanger.

In one embodiment of the invention there is provided a safety cooling circuit in which there is provided a diverter valve at the intersection of the cooling liquid supply, the secondary side charging inlet and the flow pipe of the rapid water heating assembly. The diverter valve will prevent the cooling liquid supply being supplied to the secondary side -5charging inlet unless the temperature controlled valve is open. Instead, water from the hot water cylinder can be provided through the flow pipe of the rapid water heating assembly. As soon as the temperature controlled valve is opened, the diverter valve will stop water flowing from the hot water cylinder and instead cause the cooling liquid to be supplied.

In one embodiment of the invention there is provided a safety cooling circuit in which the temperature controlled valve is a mechanically operated valve. This is particularly effective as it will ensure that the valve will operate during a power outage which is particularly desirable.

In one embodiment of the invention there is provided a safety cooling circuit in which the cooling liquid supply is the water mains. Alternatively, the cooling liquid supply could be a mains fed reservoir.

In one embodiment of the invention there is provided a domestic heating system comprising a pressurized domestic heating installation and an unpressurized solid fuel boiler, the pressurized domestic heating installation comprising a heat source and a plurality of heat sinks, a flow side for delivery of heated water from the heat source to the heat sinks and a return side for delivery of cooled water from the heat sinks to the heat source, and a hot water cylinder, the domestic heating installation comprising a plate heat exchanger coupling the unpressurized solid fuel boiler to the pressurized heating system, and in which the unpressurized solid fuel boiler comprises a safety cooling circuit as claimed.

In one embodiment of the invention there is provided a domestic heating system in which the plate heat exchanger of the domestic heating system is provided by way of the plate heat exchanger of the safety cooling circuit.

Detailed Description of the Invention The invention will now be more clearly understood from the following description of some embodiments thereof given by way of example only with reference to the accompanying drawings, in which:-6Figure 1 is a diagrammatic representation of a domestic heating system known in the art; Figure 2 is a diagrammatic representation view of a domestic heating system according to the invention; Figure 3 is a diagrammatic representation of the parts of the domestic heating system concerned with providing a virtually instantaneous hot water supply; Figure 4 is a diagrammatic representation of the parts of the domestic heating system comprising the safety cooling circuit; Figure 5 is a diagrammatic representation of the domestic heating system with parts of the safety cooling circuit and the unpressurized solid fuel boiler components removed; Figure 6 is a diagrammatic representation of an embodiment of plate heat exchanger used in the safety cooling circuit according to the invention; Figure 7 is a diagrammatic representation, similar to Figure 5, of a second embodiment of domestic heating system with parts of the safety cooling circuit and the unpressurized solid fuel boiler components removed; Figure 8 is a diagrammatic representation of a third embodiment of a domestic heating system; Figure 9 is a diagrammatic representation of a fourth embodiment of a domestic heating system; Figure 10 is a diagrammatic representation of a fifth embodiment of a domestic heating system; -7Figure 11 is a diagrammatic representation of a sixth embodiment of a domestic heating system; Figure 12 is a diagrammatic representation view of a seventh embodiment of a domestic heating system; Figure 13 is a diagrammatic representation of an eighth embodiment of a domestic heating system; Figure 14 is a diagrammatic representation of a ninth embodiment of a domestic heating system; Figure 15 is a diagrammatic representation of a tenth embodiment of a domestic heating system; Figure 16 is a diagrammatic representation of an eleventh embodiment of a domestic heating system; Figure 17 is a diagrammatic representation of a twelfth embodiment of a domestic heating system; Figure 18 is a diagrammatic representation of a thirteenth embodiment of a domestic heating system; Figure 19 is a diagrammatic representation of a fourteenth embodiment of a domestic heating system; Figure 20 is a diagrammatic representation of a domestic heating system demonstrating the flow of fluid during thermosyphoning protection; Figure 21 is a diagrammatic representation of a domestic heating system demonstrating the flow of fluid during capillary valve protection; -8Figure 22 is a diagrammatic representation of a domestic heating system demonstrating the flow of fluid during pitching protection; Figure 23 is a diagrammatic representation of a domestic heating system demonstrating the flow of fluid when the gas/oil boiler is being used to heat zones; Figure 24 is a diagrammatic representation of a domestic heating system demonstrating the flow of fluid when the solid fuel boiler is being used to rapidly heat the cylinder; Figure 25 is a diagrammatic representation of a domestic heating system demonstrating the flow of fluid when the solid fuel boiler is being used to heat zones; and Figure 26 is a diagrammatic representation of a domestic heating system according to the invention.

Referring to Figure 1, there is shown a domestic heating system known in the art, indicated generally by the reference numeral 1, comprising a pressurized domestic heating installation 3 surrounded in dashed outline, and an unpressurized solid fuel boiler system 5 outside the dashed outline. The pressurized domestic heating installation 3 comprises a heat source 7, in this case a gas boiler, and a plurality of heat sinks represented by radiator banks 9, 11 and a hot water cylinder 13. The heat source 7 transfers heat to the heat sinks via a manifold 15. The manifold comprises a hot chamber or flow side 14 from which hot water is received from the heat source and delivered out to the heat sinks and a cold chamber or return side 16 from which water is received back from the heat sinks and passed onwards to the heat source for re-heating. The operation of the manifold 15 is well understood in the art and further description is deemed unnecessary for the understanding of the present invention. An expansion vessel 17, a double check filling loop 19 and various valves and pumps are also provided to ensure smooth circulation of heating fluid in the domestic heating system. -9The unpressurized solid fuel boiler system 5 comprises a solid fuel boiler 21 and an associated safety cooling circuitry comprising a heat leak radiator 23 and a heating header tank 25. The unpressurized solid fuel boiler system 5 is coupled to the pressurized domestic heating installation through a heat exchanger 27 having a primary side 29 and a secondary side 31. The solid fuel boiler 21 is connected to the primary side 29 of the heat exchanger and the secondary side 31 of the heat exchanger is connected to the manifold 15. A pump 33 is provided to pump heating fluid between the manifold 15 and the heat exchanger 27.

In use, the solid fuel boiler 7, when in operation, passes a heating fluid through the primary side 29 of the heat exchanger 27. The heating fluid in the primary side of the heat exchanger heats any heating fluid in the secondary side 31 of the heat exchanger 27. The pump 33 controls the amount of heating fluid pumped through the secondary side 31 of the heat exchanger and the speed of flow of heating fluid through the secondary side 31 of the heat exchanger will determine the temperature gain of the heating fluid as it passes through the secondary side 31 of the heat exchanger 27. The heating fluid from the secondary side 31 of the heat exchanger 27 is passed to the manifold 15 from where it may be distributed to the heat sinks 9, 11, 13 in the residence.

In the event of a power failure, or in the event of the heating system being shut down by the resident, pump 33 will cease pumping heating fluid to and from the heat exchanger 27. The solid fuel boiler 21 will however continue to generate heat and this heat must be dissipated and not allowed to build up to dangerous levels. Heat from the solid fuel boiler is instead routed to the heat leak radiator 23, effectively a heat dump circuit, and/or the heating header tank 25 through thermosyphoning. This arrangement suffers from the disadvantages outlined above.

Referring now to Figures 2 to 6 inclusive, there is shown some representations of a domestic heating system incorporating a safety cooling circuit and its most important components according to the present invention that overcome at least some of the difficulties with the known system. For reasons of clarity, like parts have been given the same reference numerals as before. The domestic heating system, indicated generally by the reference numeral 41 comprises a pressurized domestic heating installation 3 to the left side of the dashed line 43, and an unpressurized solid fuel boiler system 5 - 10located on the right side of the dashed line 43. The unpressurized solid fuel boiler system comprises a safety cooling circuit which in turn comprises a plate heat exchanger 45 having a primary side 47 and a secondary side 49. The plate heat exchanger forms part of the safety cooling circuit of the domestic heating system.

Referring specifically to Figure 6, it can be seen that the plate heat exchanger’s primary side 47 has a primary charging inlet 51 for reception of a heating fluid supplied by the solid fuel boiler 21 and a primary discharge outlet 53 for delivery of the heating fluid back to the solid fuel boiler. The secondary side 49 has a secondary charging inlet 55 for reception of a cooling liquid supplied from a cooling liquid supply, in this instance a mains water supply 57 and a secondary discharge outlet 59 for delivery of the cooling liquid from the plate heat exchanger 47 to a drain 61. There is provided a temperature controlled valve 63 operable to permit the cooling liquid, in this case water, to flow from the mains supply 57 through the secondary side 49 to the drain 61 on the temperature of the heating fluid supplied by the solid fuel boiler 21 exceeding a predetermined temperature. The temperature controlled valve 63 in this embodiment comprises a wax bulb 65 and capillary action operated valve that opens when the wax bulb is heated to a melting temperature. Preferably, the wax bulb has a melting point in the region of between 95°C and 97°C.

In use, the solid fuel boiler 21 provides heating fluid to the primary side 47 of the heat exchanger 45. If the temperature in the wax bulb reaches the predetermined temperature which is equivalent to the melting temperature of the wax bulb 65, the wax bulb 65 will melt thereby causing the valve 63 to open. When the valve opens, mains water will flow from the mains supply 57 through the secondary side 49 of the plate heat exchanger and out to the drain 61. As the water passes through the secondary side 49 of the heat exchanger 45, it cools the heating fluid in the primary side 47 of the heat exchanger which in turn keeps the temperature of the heating fluid in the unpressurized solid fuel boiler system 5 within an acceptable temperature range.

The heat exchanger 45 is in fact a three sided heat exchanger and there is provided a tertiary side 67 having a tertiary charging inlet 69 for connection to the return side 16 of a pressurized domestic heating installation and a tertiary discharge outlet 71 for connection to a flow side 14 of a pressurized domestic heating installation. In this way, -11 during normal operation, as well as having a safety cooling circuit ready to operate to cool the unpressurized solid fuel boiler system 5, the heat exchanger is also used to transfer heat from the solid fuel boiler 21 to the manifold 15 and the pressurized domestic heating installation.

The safety cooling circuit further comprises a rapid water heating assembly coupled to the safety cooling circuit for supplying heated water to the hot water cylinder 13. The rapid water heating assembly comprising a flow pipe 73 for connection to and delivery of water from the water cylinder 13, a return pipe 75 for connection to and delivery of water to the water cylinder 13, and a pump 77 for circulating water through the water heating assembly. The flow pipe 73 is coupled to the secondary charging inlet 55 and the return pipe 75 is coupled to the secondary discharge outlet 59 of the plate heat exchanger 45 of the safety cooling circuit. A diverter control valve 79, in this case a Termobac ® valve, is used to control the source of water being delivered to the secondary side 49 of the plate heat exchanger 45. In other words, whether the water entering the secondary side is sourced from the mains supply 57 or the hot water cylinder 13.

In this way, during normal heating operation of the domestic heating system (i.e. when the safety cooling circuit is not operable with the valve 63 open to flood the plate heat exchanger and cool the heating fluid in the unpressurized solid fuel boiler system), water may be drawn from the bottom of the hot water cylinder 13 through the flow pipe 73 and pumped into the secondary side of the plate heat exchanger, thereby heating the water using the heating fluid in the primary side 47, before the heated water is then pumped out through the return pipe 75 and delivered into the top of the hot water cylinder 13. By doing this, the water being heated in the heat exchanger will be heated almost instantaneously. Provided that the solid fuel boiler is up to temperature, it will be possible to provide hot water in this manner practically instantaneously which is highly advantageous. It is believed that a standard hot water cylinder could be filled three to five times faster using this method than the methods currently used in the art.

Figure 3, shows the components of the system required to provide practically instantaneous hot water to the hot water cylinder 13. This view represents the components that are in use when the safety valve 63 (not shown) is closed and the temperature of the heating fluid from the solid fuel boiler is below the predetermined - 12temperature. Referring specifically to Figure 5, there is shown a view of the connection of a three sided plate heat exchanger to both the manifold 15 and the hot water cylinder 13.

Referring specifically to Figure 4, there is shown a view of the components of the system required to cool the heating fluid during a power outage or if desired by the resident. This view represents the components that are in use when the safety valve 63 is open and the temperature of the heating fluid from the solid fuel boiler is above the predetermined temperature of the valve. The valve 63 opens thereby allowing water from the mains 57 to flow through the secondary side 49 of the plate heat exchanger 45 and cool the heating fluid in the primary side 47 of the plate heat exchanger 45 down.

Referring now to Figure 7, there is shown an alternative embodiment of domestic heating system according to the present invention, indicated generally by the reference numeral 81, where like parts have been given the same reference numerals as before. Some parts of the present system 81, which are identical to like parts in the previously described system 41, such as, for example, the unpressurized solid fuel boiler system, have been omitted for clarity to emphasize those parts that have in fact been modified. The domestic heating system comprises a third radiator bank 83 connected to the manifold 15. The coil 85 in the hot water cylinder is instead connected up to a solar panel array (not shown) instead of to the manifold. By far the most important difference however between the system 81 and the previously described system 41 is the heating liquid short circuit 87 intermediate the primary charging inlet 51 for reception of the heating fluid supplied by the solid fuel boiler (not shown) and the primary discharge outlet 53 for delivery of the heating fluid back to the solid fuel boiler. The heating liquid short circuit 87 comprises a fluid conduit 89 bridging the primary charging inlet 51 and the primary discharge outlet 53, a valve 91 and a pump 93 mounted on the fluid conduit 89.

The main advantage of this configuration of heating liquid short circuit 87 is that the heat source 7 may also be used to provide hot water practically instantaneously to the hot water cylinder 13. This may be desirable if the solid fuel boiler is either not operating or is not yet up to temperature. In order to provide hot water from the heat source 7 practically instantaneously using this arrangement of heating liquid short circuit 87, the -13pump 33 is operated to pump water from the return side 16 of the manifold 15 to the tertiary side 67 of the plate heat exchanger. As well as operating pump 33, pump 93 is operated to circulate heating fluid through the primary side 47 of the plate heat exchanger. In other words, the heating fluid in the tertiary side 67 of the plate heat exchanger 45 is now being used to heat the heating fluid in the primary side 47 of the plate heat exchanger 45. In addition to pumps 33 and 93 being operated, the pump 77 is operated to pump water from the bottom of the hot water cylinder 13 through the flow pipe 73 and into the secondary side 49 of the three sided plate heat exchanger 45. The heating fluid in the primary side 47, that has itself been heated by the heating fluid in the tertiary side 67, will in turn heat the water in the secondary side before it is pumped by pump 77 back to the top of the hot water cylinder 13.

It will be seen from the above embodiment that the heating fluid from the tertiary side is coming from the return side of the manifold, in other words, the colder side of the manifold. Although the water is coming from the return side of the manifold, the water in the return side of the manifold may still be in the range of approximately between 60°C to 71 °C which is sufficient to heat up water for the hot water cylinder which only needs to be approximately in the range of 30°C to 45°C for a shower, for example. As an alternative to the above, a suitable piping and valve system along with complementary controls could be provided to switch the direction of flow of the heating fluid passed into the tertiary side so that it comes from the flow (hot) side 14 of the manifold and returns to the return (cold) side 16 of the manifold.

Another advantage of the heating liquid short circuit 87 and pump 93 is that the pump can be used to prevent heated water flowing to and heating up the solid fuel boiler. The arrangement shown provides for the transfer of heat from the solid fuel boiler side using the pump 93. The pump 93 is used as a bridge between circuits and provides the means to transfer heat from the secondary side to the tertiary side while preventing the water circulating and heating up the unlit solid fuel boiler with all the attendant losses of energy. This is a significant problem that has been overcome. There are numerous installations that suffer from the problem of hot boiler water from the gas/oil system heating the solid fuel boiler when unlit thus wasting the heat from the gas/oil system. - 14Referring to Figure 8, there is shown a diagrammatic representation of a third embodiment of a domestic heating system according to the present invention, indicated generally by the reference numeral 101, where like parts have been given the same reference numeral as before. The domestic heating system 101 differs from those previously presented and in particular that shown in Figure 7 in that the remaining parts of the unpressurized solid fuel boiler system including the solid fuel boiler 21 and the remaining safety cooling circuit components including the valve 63 and cold water supply 57 are shown once more. In addition to these components, most importantly, the system 101 differs from the previously shown systems in that there is provided a pair of plate heat exchangers 103, 105 instead of a three sided heat exchanger.

The first plate heat exchanger 103 has a primary side and a secondary side. The second plate heat exchanger 105 also has a primary side and a secondary side. The primary side of the first plate heat exchanger 103 has a primary charging inlet 51 for reception of a heating fluid supplied by the solid fuel boiler 21 and a primary discharge outlet 107 for delivery of heating fluid back to the solid fuel boiler, the secondary side of the first plate heat exchanger 103 has a secondary charging inlet 69 for connection to a return side 16 of a pressurized domestic heating installation and a secondary discharge outlet 71 for connection to the flow side 14 of a pressurized domestic heating installation. The primary side of the second plate heat exchanger 105 has a primary charging inlet 109 for reception of a heating fluid supplied by the solid fuel boiler 21 and a primary discharge outlet 53 for delivery of heating fluid back to the solid fuel boiler, the secondary side of the second plate heat exchanger 105 has a secondary charging inlet 55 for selective connection to one of the cold water supply 57 and the flow pipe 73 from the hot water cylinder 13 and a secondary discharge outlet 59 for selective connection to the drain 61 and the return pipe 75 to the hot water cylinder 13.

It can be seen that the two plate heat exchangers 103, 105 are arranged in series. In other words, the discharge outlet 107 of the first plate heat exchanger 103 is connected to the charging inlet 109 of the second plate heat exchanger. However, if desired, the discharge outlet 107 of the first plate heat exchanger 103 could be connected back to the solid fuel boiler 21 and the charging inlet 109 of the second plate heat exchanger 105 may be fed directly from the solid fuel boiler 21. -15Referring to Figure 9, there is shown a diagrammatic representation of a fourth embodiment of a domestic heating system according to the invention, indicated generally by the reference numeral 121, where like parts have been given the same reference numeral as before. The domestic heating system 121 differs from the domestic heating system shown in Figure 8 in that instead of a manifold, a mechanical valve and pump arrangement, encircled by the dashed line 123, is provided instead.

Referring to Figure 10, there is shown a diagrammatic representation of a fifth embodiment of a domestic heating system according to the invention, indicated generally by the reference numeral 141, where like parts have been given the same reference numeral as before. The domestic heating system 141 differs from the domestic heating system shown in Figure 9 in that the coil in the hot water cylinder is connected to the heat source 7 through the valve and pump arrangement 123. Furthermore, the domestic heating system 141 differs from the domestic heating system shown in Figure 9 in that the heating liquid short circuit 87 has been omitted. Therefore, the domestic heating system 141 shown in Figure 10 will not permit the same rapid heating of the water from the hot water cylinder by the heat source 7 but instead will only permit rapid heating of the hot water from the hot water cylinder by the solid fuel boiler 21. Even though the coil in the hot water cylinder is heated by the heat source 7, the coil will have to heat the entire body of water simultaneously rather than smaller quantities as is the case when the plate heat exchanger is used to heat the water. Therefore, the heat source 7 is not considered to permit rapid heating of the hot water in the hot water cylinder within the meaning of the application in suit.

Referring to Figure 11, there is shown a further embodiment of a domestic heating system according to the invention. The domestic heating system, indicated generally by the reference numeral 161, is similar in construction to the embodiments hereinbefore described with the exception that it further comprises a shell and tube type heat exchanger 163.

Referring to Figure 12, there is shown a further embodiment of a domestic heating system according to the invention. The domestic heating system, indicated generally by the reference numeral 171, is similar in construction to the embodiments hereinbefore described and like parts have been given the same reference numeral as before. The - 16domestic heating system 171 differs from the other embodiments described above in that the system is pressurised on both sides of the heat exchanger and instead of a heating header tank, there is provided a further expansion vessel 173 and double check filling loop 175.

In addition to the cooling mechanisms described above, there will be a further safety feature that may be introduced into the systems that will be activated prior to the safety valve being called upon. This feature is where the cylinder will thermosyphon and circulate the water through the heat exchanger whilst the solid fuel system is also thermosyphoning. This allows the transfer of heat from the solid fuel system to the cylinder without the need for any pump and operates before the safety valve ever gets called upon. This provides two levels or three levels of safety depending on whether the system is open or closed. To operate in this way, the heating system must be set up in a particular way with the heat exchanger above the solid fuel source (e.g. a stove) and the cylinder above both the heat exchanger and the solid fuel source. Furthermore, all pipe work must rise continuously to allow the thermosyphoning effect to operate. The order of safety operation for an open system is therefore 1) Thermosyphoning; 2) Safety valve operation and 3) Open vent to header tank. The closed system will be the same order but without the header tank safety option.

The thermosyphoning or gravity safety aspect is important when there is no cold water storage in the roof space as for example on a farm/dwelling that relies totally on a well pump. Should the pump or electricity fail there would be no "mains" water available to cool the solid fuel circuit. Furthermore, there would be no cold "storage" water in the roof space available to cool the solid fuel boiler either. In this situation the gravity circuit is the sole means of safety for the solid fuel boiler. The thermosyphoning action is illustrated in the arrangement 201 shown in Figure 15.

Referring to Figure 13, there is shown a further embodiment of a domestic heating system according to the invention. The domestic heating system, indicated generally by the reference numeral 181, is similar in construction to the embodiments hereinbefore described with the exception that it further comprises a mechanically operated or motorised valve 183. This motorised valve is a useful alternative to the temperature controlled thermostatic capillary valve described in the embodiments above. The - 17mechanically operated valve is operable to prevent flow of water when it is supplied with electricity. Once the electricity supply is cut, for example in a power cut, the mechanically operated valve opens thereby allowing the cooling liquid to flow through the heat exchanger. It is envisaged that a solenoid could be used in such an arrangement to operate the valve. Other implementations of valve that do not rely on temperature could be used instead also to ensure that the cooling circuit operates during a power failure. This solution is not seen as optimum as the valve will open and allow water to flow as soon as there is a power failure without taking into account the temperature of the water in the solid fuel appliance. This perhaps would not be a popular way to provide safety due to the increased amount of water going to waste however it illustrates an iteration of what can be implemented.

Referring to Figures 14 and 16, there are shown further embodiments of domestic heating systems according to the invention, indicated generally by the reference numerals 191 and 211 respectively. The systems 191 and 211 are similar in construction to the embodiments hereinbefore described and illustrate further arrangements that are possible.

Referring to Figure 17, there is shown a further embodiment of a domestic heating system according to the invention. The domestic heating system, indicated generally by the reference numeral 221, is similar in construction to the embodiments hereinbefore described with the exception that it further comprises a high flow connection 223 for the hot water on the cylinder dome rather than connecting at the very top of the cylinder. This is simply an iteration of what can be done as some plumbers/installers prefer this method of connection to a cylinder.

Referring to Figures 18 and 19, there are shown further embodiments of domestic heating systems according to the invention, indicated generally by the reference numerals 231 and 241 respectively. The systems 231 and 241 are similar in construction to the embodiments hereinbefore described and illustrate further arrangements that are possible. The systems 231 and 241 differ from those described above in that the cylinder has been removed giving instantaneous water but with no storage. This effectively turns a standard boiler into a combi-boiler. Typically, combi-boilers are installed where there is - 18no need or want for a storage cylinder and they rely purely on the instantaneous heating effect.

Referring to Figures 20 to 22, there are shown various representations of the domestic heating system according to the invention demonstrating the flow of fluid for the protection measures described above, where like parts have been given the same reference numerals as before. Referring first of all to Figure 20, there is shown a representation of domestic heating system 251 in which the system is thermosyphoning in order to dissipate heat from the sold fuel boiler 21. The flow of fluid is represented in the drawing by thicker lines. It can be seen that hot water flows from the solid fuel boiler 21 to the heat exchanger 45 primary side 47 and back again to the solid fuel boiler. At the same time, water is circulated to and from the heat exchanger 45 secondary side 49 and the hot water cylinder 13. In Figure 21, the flow of fluid in a domestic heating system 261 is shown during capillary valve 63 operation. In this implementation, the valve 63 has been activated and water from the mains supply 57 is passed through the secondary side 49 of the heat exchanger 45 and the water flows through the secondary side 49 and out to a drain 61. At the same time, fluid passing through the primary side 47 of the heat exchanger 45 that has been cooled by the water flowing in the secondary side 49 and this fluid circulates through the solid fuel boiler thereby cooling the solid fuel boiler 21 down. In Figure 22, the flow of fluid in a domestic heating system 271 during "pitching" (open vent to heating header tank) is illustrated. In this instance, heated fluid from the solid fuel boiler 21 is circulated through the heating header tank 25.

Referring to Figure 23, there is shown a diagrammatic representation of a domestic heating system, indicated generally by the reference numeral 281 in which the gas/oil boiler 7 is shown heating the zones (radiator banks) 9, 11 as well as the hot water cylinder 13. Again, the flow of fluid in the system 281 is represented in the drawing by thicker lines.

Referring to Figure 24, there is shown a diagrammatic representation of a domestic heating system, indicated generally by the reference numeral 291 in which the solid fuel boiler 21 is shown rapidly heating the water in the hot water cylinder 13. The flow of heating fluid is represented in the drawing by thicker lines. Water is pumped from the hot water cylinder 13 to the secondary side 49 of the plate heat exchanger 45. This water is heated by heating fluid passed from the solid fuel source through the primary side 47 of the plate heat exchanger 45. The flow of fluids is similar to that shown in Figure 20 however in Figure 24, there is power supplied to the pump 77 and the water from the hot water cylinder 13 is pumped through the heat exchanger 45.

Referring to Figure 25, there is shown a diagrammatic representation of a domestic heating system, indicated generally by the reference numeral 301 in which the solid fuel boiler 21 is shown heating the zones (radiator banks) 9, 11 via a manifold 15. Again, the flow of fluid is represented in the drawing by thicker lines.

Referring to Figure 26, there is shown a diagrammatic representation of a domestic heating system, indicated generally by the reference numeral 311. In the domestic heating system 311, it can be seen that there are provided non-return valves 313 on the outward flow pipes when the zones are likely to be higher than the manifold 15. The nonreturn valves are provided in front of the zone’s pump. The non-return valves are provided in order to prevent the creation of a gravity fed, thermosyphoning loop, which would cause a continued supply of heated water to the radiators in that zone, even when the zone’s pump is no longer required and has been shut off.

In the embodiments described, the safety cooler circuit and in particular the plate heat exchanger is a standalone unit external to the solid fuel boiler. This is seen as advantageous as it can be retrofit and can also be used with a large number of disparate types of boiler. It is envisaged that the cooling principles of the present invention could be applied to other areas, for example to a large engine on a boat where the present invention could be applied as a secondary method of cooling the engine by having the heat exchanger in-line with the existing engine cooling circuit.

In this specification the terms "comprise, comprises, comprised and comprising" and the terms "include, includes, included and including" are all deemed totally interchangeable and should be afforded the widest possible interpretation. It will be understood that various modifications could be made to the embodiments hereinbefore described without departing from the spirit of the invention. The invention is in no way limited to the embodiments hereinbefore described but may be varied in both construction and detail within the scope of the claims.

Claims (14)

1. -20Claims: (1) A safety cooling circuit for a solid fuel boiler, the safety cooling circuit comprising a plate heat exchanger having a primary side and a secondary side, the primary side having a primary charging inlet for reception of a heating fluid supplied by the solid fuel boiler and a primary discharge outlet for delivery of the heating fluid back to the solid fuel boiler, the secondary side having a secondary charging inlet for reception of a cooling liquid supplied from a cooling liquid supply and a secondary discharge outlet for delivery of the cooling liquid from the plate heat exchanger to a drain, and in which there is provided a temperature controlled valve operable to permit the cooling liquid to flow from the cooling liquid supply through the secondary side to the drain on the temperature of the heating fluid supplied by the solid fuel boiler exceeding a predetermined temperature.

2. (2) A safety cooling circuit as claimed in claim 1 in which there is provided a rapid water heating assembly coupled to the safety cooling circuit for supplying heated water to a hot water cylinder, the rapid water heating assembly comprising a flow pipe for connection to and delivery of water from the water cylinder, a return pipe for connection to and delivery of water to the water cylinder, and a pump for circulating water through the water heating assembly, the flow pipe being coupled to the secondary charging inlet and the return pipe being coupled to the secondary discharge outlet of the safety cooling circuit.

3. (3) A safety cooling circuit as claimed in claim 1 or 2 in which the plate heat exchanger is a three sided plate heat exchanger further comprising a tertiary side having a tertiary charging inlet for connection to the return side of a pressurized domestic heating installation and a tertiary discharge outlet for connection to a flow side of a pressurized domestic heating installation.

4. (4) A safety cooling circuit as claimed in claim 1 or 2 in which there is provided a second plate heat exchanger also having a primary side and a secondary side, the primary side of the second plate heat exchanger having a primary charging inlet for reception of a heating fluid supplied by the solid fuel boiler and a primary discharge outlet for delivery of heating fluid back to the solid fuel boiler, the -21 secondary side of the second plate heat exchanger having a secondary charging inlet for connection to a return side of a pressurized domestic heating installation and a secondary discharge outlet for connection to the flow side of a pressurized domestic heating installation.

5. (5) A safety cooling circuit as claimed in claim 4 in which the first and second plate heat exchangers are connected in series so that the primary charging inlet of one of the first and second plate heat exchangers is for reception of a heating fluid supplied by the solid fuel boiler and the primary discharge outlet of that plate heat exchanger is connected to the primary charging inlet of the other of the first and second plate heat exchangers and the primary discharge outlet of the other plate heat exchanger is for delivery of heating fluid back to the solid fuel boiler..

6. (6) A safety cooling circuit as claimed in claims 3 to 5 in which there is provided a heating liquid short circuit intermediate the primary charging inlet for reception of the heating fluid supplied by the solid fuel boiler and the primary discharge outlet for delivery of the heating fluid back to the solid fuel boiler, the heating liquid short circuit comprising a fluid conduit, a valve and a pump mounted on the fluid conduit.

7. (7) A safety cooling circuit as claimed in claim 2 in which there is provided a diverter valve at the intersection of the cooling liquid supply, the secondary side charging inlet and the flow pipe of the rapid water heating assembly.

8. (8) A safety cooling circuit as claimed in any preceding claim in which the temperature controlled valve is a mechanically operated valve.

9. (9) A safety cooling circuit as claimed in any preceding claim in which the cooling liquid supply is the water mains.

10. (10) A safety cooling circuit as claimed in any preceding claim in which instead of a temperature controlled valve operable to permit the cooling liquid to flow from the cooling liquid supply through the secondary side to the drain on the temperature of the heating fluid supplied by the solid fuel boiler exceeding a predetermined -22temperature, there is provided a motorized valve operable to permit the cooling liquid to flow from the cooling liquid supply through the secondary side to the drain on the power supply to the motorized valve being interrupted.

11. (11) A domestic heating system comprising a pressurized domestic heating installation and an unpressurized solid fuel boiler, the pressurized domestic heating installation comprising a heat source and a plurality of heat sinks, a flow side for delivery of heated water from the heat source to the heat sinks and a return side for delivery of cooled water from the heat sinks to the heat source, and a hot water cylinder, the domestic heating installation comprising a plate heat exchanger coupling the unpressurized solid fuel boiler to the pressurized heating system, and in which the unpressurized solid fuel boiler comprises a safety cooling circuit as claimed in any of claims 1 to 10.

12. (12) A domestic heating system as claimed in claim 11 in which the plate heat exchanger of the domestic heating system is provided by way of the plate heat exchanger of the safety cooling circuit.

13. (13) A safety cooling circuit substantially as hereinbefore described with reference to and as illustrated by the accompany drawings.

14. (14) A domestic heating system substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.