Condensing boiler

A condensing boiler including a heat exchanger,

• wherein the heat exchanger comprises at least a first and second set of cassettes, the cassettes within each set of cassettes in fluid communication with each other via a number of fluid flow connectors, at least one of the at least first and second set of cassettes including at least a first fluid flow cassette and a second fluid flow cassette, each fluid flow cassette comprising first and second sheets, at least one of the number of the fluid flow connectors further connecting a fluid flow passageway in the first fluid flow cassette to a fluid flow passageway in the second fluid flow cassette,
• wherein a first fluid flow connector is connected to a first end of the first fluid flow cassette, and a second fluid flow connector is connected to a second, opposite end of the first fluid cassette, such that fluid sent via the first connector flows along the first cassette from the first fluid flow connector to the second fluid flow connector, and wherein of the second fluid flow connector is arranged to reverse the flow of the fluid such that the fluid is able to flow out of the first fluid flow cassette in one direction, through the second fluid flow connector and then flow into the second fluid flow cassette in substantially the opposite direction,
• wherein at least each of the first sheets has corrugations along a length of the sheet so as to form a number of grooves extending across a width of the sheet,
• wherein each of the second sheets is attached against the first sheet so as to enclose the grooves to form a number of fluid flow passageways extending across a width of the fluid flow cassette in between the first and second sheets, and
• wherein each fluid flow cassette is substantially curved across its width such that
• the fluid flow passageways are substantially curved along their length.

A method of manufacturing a heat exchanger unit or condensing boiler comprising a heat exchanger within the heat exchanger unit, wherein the heat exchanger comprises at least first, second and third fluid flow cassettes with each fluid flow cassette comprising first and second sheets, the method comprising the following steps:

• providing a first sheet for each fluid flow cassette with corrugations along its length so as to form a number of grooves extending across a width of the sheet, and
• attaching a second sheet against the first sheet so as to form each fluid flow cassette and to enclose the grooves to form a number of fluid flow passageways extending across a width of each fluid flow cassette in between the first and second sheets, wherein each fluid flow cassette is substantially curved across its width such that the fluid flow passageways are substantially curved along their length,
• wherein the first cassette and the third cassette are configured to abut a first end of the heat exchanger unit and wherein the second cassette is configured to abut a second, opposite end of the heat exchanger unit,
• wherein the gas to be cooled by the heat exchanger flows along a length of the heat exchanger in a gap between the first and second fluid flow cassettes in a first direction and between the second and third cassettes in a second opposite direction and wherein gas flow is reversed around the second cassette.

A method of manufacturing a heat exchanger or condensing boiler wherein the heat exchanger comprises at least a first and second set of cassettes, the cassettes within each set of cassettes in fluid communication with each other via a number of fluid flow connectors, each one of the at least first and second set of cassettes including a first fluid flow cassette and a second fluid flow cassette with each fluid flow cassette comprising first and second sheets, and the number of fluid flow connectors further connecting a fluid flow passageway in a first fluid flow cassette to a fluid flow passageway in a second fluid flow cassette, wherein the fluid flow connectors are arranged to reverse the flow of the fluid such that the fluid is able to flow out of the first fluid flow cassette in one direction, through a fluid flow connector and then flow into a second fluid flow cassette in substantially the opposite direction, the method comprising the following steps:

• providing a first sheet in each fluid flow cassette with corrugations along its length so as to form a number of grooves extending across a width of the sheet, and
• attaching a second sheet against the first sheet so as to form each fluid flow cassette and to enclose the grooves to form a number of fluid flow passageways extending across a width of each fluid flow cassette in between the first and second sheets, wherein each fluid flow cassette is substantially curved across its width such that the fluid flow passageways are substantially curved along their length.