Patent Application
20070051359
The present invention generally relates to fuel-fired fluid heating devices and, in representatively illustrated embodiments thereof, more particularly provides a fuel-fired water heater having a specially designed multi-pass condensing type heat exchanger incorporated therein.
Conventional fuel-fired water heaters are typically of a “single pass”, non-condensing configuration, meaning that the hot combustion gases used to heat the tank-stored water are subjected to only a single pass through a heat exchanger structure (usually a vertical flue) within the tank before being discharged from the water heater to, for example, an external vent structure, and that flue gas condensation does not occur to any appreciable degree in the heat exchanger structure within the water heater tank. In this conventional type of fuel-fired water heater, the overall thermal efficiency is typically limited to about 80-85%. Various proposals have been made to provide fuel-fired water heaters with condensing type single-pass heat exchangers (i.e., in which flue gases condense within the heat exchanger). However, previously proposed single-pass condensing type heat exchange structures incorporated in fuel-fired water heaters typically provide the water heaters with thermal efficiencies limited to the 85-90% range.
In an attempt to increase this thermal efficiency to above 95%, multi-pass condensing heat exchangers of varying configurations and types have been proposed for installation within the tank portions of fuel-fired water heaters. While such previously proposed multi-pass condensing type heat exchangers have met this thermal efficiency goal, they have also undesirably presented various problems, limitations and disadvantages. These include increased heat exchanger complexity, higher material and fabricational costs, condensate management problems, increased operational noise, and reduced heat exchanger operational life.
It would thus be desirable to provide a fuel-fired water heater, or other type of fuel-fired fluid heating device, with an improved multi-pass condensing type heat exchanger. It is to this goal that the present invention is primarily directed.
In carrying out principles of the present invention, in accordance with representative embodiments thereof, a fuel-fired fluid heating apparatus is provided that is representatively a fuel-fired commercial water heater, but could alternatively be another type of fuel-fired water heater or another type of fuel-fired fluid heating apparatus such as, for example, a boiler.
In general, the apparatus comprises a tank for holding a fluid to be heated, and a heat exchanger disposed in the tank and having an interior combustion gas flow path defined by (1) a first pass section having an inlet portion and an outlet portion spaced apart from the inlet portion of the first pass section in a first direction, (2) a central collector plenum coupled to the outlet portion of the first pass section, (3) a second pass section having an inlet portion coupled to the central collector plenum and an outlet portion spaced apart from the inlet portion of the second pass section in a second direction opposite from the first direction, (4) a third pass section having an inlet portion coupled to the outlet portion of the second pass section and an outlet portion spaced apart from the inlet portion of the third pass section in the first direction, (5) an outer collector plenum circumscribing the collector plenum and being coupled to the outlet portion of the third pass section, and (6) an exhaust section coupled to the outer collector plenum. Additionally, the apparatus comprises a combustion system operative to flow hot combustion gases into the inlet portion of the first pass section and then through the balance of the heat exchanger.
In a first embodiment thereof, the apparatus is a fuel-fired water heater comprising a tank for holding water to be heated, and a condensing type multi-pass heat exchanger disposed within the tank. The heat exchanger includes (1) a vertically extending flue having an upper inlet end and a lower outlet end, (2) a central collector plenum coupled to the lower outlet end of the flue, (3) an outer collector plenum horizontally circumscribing the central collector plenum, (4) a plurality of vertically extending inverted U-tubes horizontally spaced around the flue, each inverted U-tube having a lower inlet end coupled to the central collector plenum, and a lower outlet end coupled to the outer collector plenum, and (5) an exhaust pipe having an inlet portion coupled to the outer collector plenum. The water heater also comprises a fuel burner (which may be either a powered fuel burner or a non-powered burner) having an outlet coupled to the upper inlet end of said flue, the fuel burner being operative to flow combustion gases through the flue and then the balance of the condensing type heat exchanger.
In a second embodiment thereof, the apparatus is a fuel-fired water heater comprising a tank for holding water to be heated, a transfer plenum disposed exteriorly of he tank at an upper end portion thereof, and a condensing type multi-pass heat exchanger disposed within the tank. The heat exchanger includes (1) a vertically extending flue having an upper inlet end and a lower outlet end, (2) a central collector plenum coupled to said lower outlet end of said flue, (3) an outer collector plenum horizontally circumscribing the central collector plenum, (4) a first plurality of vertical tubes horizontally spaced around the flue and having lower inlet ends coupled to the central collector plenum, and upper outlet ends coupled to the transfer plenum, (5) a second plurality of vertical tubes disposed horizontally outwardly of and horizontally spaced around the first plurality of vertical tubes, the second plurality of vertical tubes having upper inlet ends coupled to the transfer plenum, and lower outlet ends coupled to the outer collector plenum, and (6) an exhaust pipe having an inlet portion coupled to the outer collector plenum. The water heater also comprises a fuel burner (which may be either a powered fuel burner or a non-powered fuel burner) having an outlet coupled to the upper inlet end of the flue, the fuel burner being operative to flow combustion gases through the flue and then the balance of the condensing type heat exchanger.
According to other aspects of the invention a portion of the central collector plenum extends downwardly past the outer collector plenum, the outer collector plenum has vertically sloped lower side having a lowermost portion to which an inlet portion of the exhaust pipe is connected, the bottom side of the central collector plenum has a downwardly domed configuration, and a sloped condensate drain line extends within the tank from the bottom side of the central collector plenum to an inlet portion of the exhaust pipe within the tank.
Schematically illustrated in cross-section in
During firing of the water heater 10, hot flue gases 18 from a fuel burner 20 atop the water heater are flowed through the heat exchanger 12 to transfer combustion heat, with a thermal efficiency of 95% or above, to the stored water 14. Burner 20 may be either a powered fuel burner or a non-powered fuel burner. On demand, pressurized heated water 14 stored in the tank 16 may be withdrawn therefrom through a tank-mounted outlet fitting 21. Automatically, the withdrawn water 14 is replaced with pressurized cold water, from a source thereof, through a tank-mounted inlet fitting 23.
The heat exchanger 12 is of a three-pass configuration and includes a vertical flue portion 22 connected at its upper end to the outlet of the burner 20 and connected at its lower end to an inverted dome-shaped central primary flue gas collector plenum 24 horizontally circumscribed by an annular secondary flue gas collector plenum 26 that has a bottom wall which is vertically sloped downwardly and rightwardly as indicated by the slope arrow 27 in
During firing of the water heater 10, the flue gas 18 discharged from the burner 20 sequentially makes a first pass downwardly through the vertical central flue portion 22, a second pass from the central plenum 24 upwardly through the U-tube legs 28a, and a third pass downwardly through the U-tube legs 28b into the annular outer plenum 26, with condensation 35 from the flue gas 18 being formed within the U-tube legs 28b as shown. Condensate from the annular plenum 26 flows into the exhaust pipe 30, and any condensate which may be in the central plenum 24 also flows into the exhaust pipe 30 via the submerged, sloped condensate line 34.
The modified water heater 10a shown in
During firing of the water heater 10a, flue gases 18 from the burner 20 sequentially flow downwardly through the vertical central flue portion 22 into the central plenum 24, upwardly from the plenum 24 through the vertical tubes 36 into the top plenum 40, and then downwardly from the top plenum 40 through the vertical tubes 38 into the bottom annular plenum 26 from which they are discharged via the exhaust pipe 30. Condensate 35 formed in the third pass tubes 38 is discharged from the heat exchanger 12a in a manner similar to that previously described in conjunction with the
Compared to conventional multi-pass condensing type heat exchangers utilized in fuel-fired water heaters, the heat exchangers 12,12a representatively illustrated and described herein provide a variety of advantages which may include, for example, the capability of providing their associated water heaters with thermal efficiencies well above 95%, simplified heat exchanger configuration, reduced material and fabricational costs, quieter operation, increased heat exchanger life, and improved condensate management.
As will be readily appreciated by those of skill in this particular art, the representatively illustrated heat exchangers 12 and 12a, could have other orientations within their associated water heaters 10 and 10a without departing from principles of the present invention. For example, the heat exchangers 12 and 12a, with minor modifications thereto, could alternatively be horizontally oriented within their associated water heaters 10 and 10a.
The foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims.
