Abstract:
A method and apparatus for mounting a water heater on the roof of a building or at another location outside of the building. A roof curb surrounds a hole in the roof, and a base member is mounted to the roof curb. Alternatively, the base member is mounted on a concrete pad at ground level. A water tank is mounted to the base member with the longitudinal axis of the water tank extending horizontally. Support rails are mounted to the base member, and wedge-shaped supports are mounted to the support rails. The wedge-shaped supports are interconnected with tank mounted brackets that are mounted to the sides of the water tank. Thermally insulated spacers are interposed between the wedge-shaped supports and the tank mounting brackets.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 09/732,472, filed Dec. 7, 2000, the entire contents of which are incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to water heaters, and more particularly to water heaters adapted to be mounted on the roof of a building. 
     BACKGROUND 
     It is known to provide a water heater within a building, and to mount other equipment (e.g., HVAC equipment) on the roof of a building. A primary concern with rooftop equipment is the load imposed on the roof by the weight of the equipment. Most rooftop equipment is supported on the roof by a roof curb. The roof curb provides a weather-tight seal between the equipment and the roof, and distributes the weight load of the equipment to the building&#39;s roof. The roof curb also prevents leakage of water into the building and equipment in the event of a roof flood. Roof curbs are typically built to match the pitch of the roof so that the equipment mounts on a level surface. Rooftop equipment is typically raised to the roof with a crane and set on the roof curb. A foam sealing tape is often used between the bottom of the equipment and the roof curb to provide a weather-tight seal. 
     Many commercial buildings include a wall around the rooftop to screen the rooftop equipment from view. Much of the HVAC equipment currently installed on rooftops is enclosed in a rectangular cabinet, and has a sufficiently low profile to be not visible from the ground level. 
     SUMMARY 
     The present invention identifies several advantages to providing a water heater on the roof of a building. In commercial applications, one factor affecting many aspects of some businesses, and particularly retail and restaurant businesses, is floor space. Moving a water heater out of a building and positioning it on the building&#39;s roof may permit more floor space to be used for conducting business. In addition to potentially freeing up floor space and the need for a separate boiler room in a building, the present invention provides other advantages over interior water heaters. For example, the design of interior water heaters must account for such considerations as flooding, CO generation, interior noise, some fire hazards arising from flammable vapors, building depressurization, and exhaust venting. While interior water heaters are sometimes limited to a significant degree by such design concerns, a rooftop water heater embodying the present invention is typically not affected to the same extent. This may make design and maintenance of the rooftop water heater simpler and cheaper in some instances when compared to the design and maintenance of interior water heaters. 
     Several design parameters are imposed on the design of a rooftop water heater by weather conditions and the expectations of potential purchasers of such water heaters. The water heater must first account for weather conditions not normally encountered by interior water heaters. It would be desirable to mount the water heater on a weather-tight roof curb that would support the water heater above expected water levels in the event of a roof flood. The roof curb would also provide the required weight load distribution to the roof. Because roof curbs are already used to support other rooftop equipment, it is convenient to use a roof curb to support a rooftop water heater as well. 
     To maintain the aesthetics of their buildings, purchasers would likely want equipment that cannot be ordinarily seen from the ground level. The water heater therefore must have a sufficiently low profile and be of substantially the same height as most HVAC equipment to meet the expected demands of purchasers. 
     In light of the foregoing considerations, the present invention provides a rooftop water heater that includes a water tank mounted on a base member which is in turn mounted on a roof curb. The base member includes a drain communicating with the building&#39;s sewage system so that water leaking or otherwise flowing out of the water tank is drained away from the water heater without causing damage to the roof or the water heater itself. A pair of rails may be mounted under the base member such that the water heater and base member may be moved with a fork lift. The rails also include holes for accepting the hooks of a lifting crane for raising the water heater to the roof of the building. 
     The water tank is preferably generally cylindrical in shape with a longitudinal axis extending substantially horizontally. In this regard, the tank has a low profile compared to a tank having its longitudinal axis extending vertically. A head encloses one end of the tank. A plurality of water pipes extend up through the roof curb and through a water pipe aperture in the base member. A vertical wall surrounds the water pipe aperture. A grommet fits over the vertical wall and seals the water pipes with respect to the base member. 
     A plurality of panels, including a cabinet door and a top, are preferably interconnected with and supported by the base member to substantially weather-tightly enclose the water tank. The top and cabinet door may be removed from the other panels to permit access to the water tank. 
     A U-shaped flue tube is preferably contained within the water tank. A baffle or turbulator is positioned within one of the legs of the U-shaped flue tube. The ends of the flue tube extend through the head of the tank. The legs each include a longitudinal axis, and the longitudinal axes together define a flue plane that may be disposed substantially vertically, or may be angled with respect to vertical. Preferably, the flue plane is angled in the range of 30-60° with respect to vertical. 
     The water heater also includes inlet and outlet tubes for providing cold water to the tank and drawing hot water from the tank, respectively. The inlet and outlet tubes extend substantially the entire inside length of the tank, and preferably include a plurality of apertures facing in a single direction. The outlet tube is positioned in the top portion of the tank with its apertures facing up while the inlet tube is positioned in the bottom portion of the tank with its apertures facing down. Preferably, the inlet and outlet tubes extend through the head of the tank, but in an alternative construction, the inlet and outlet tubes include elbows that extend through the tank shell. 
     Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a water heater embodying the present invention. 
     FIG. 2 is a view of the water heater of FIG. 1 from a different perspective. 
     FIG. 3 is an exploded view of the cabinet of the water heater of FIG.  1 . 
     FIG. 4 is a perspective view of the tank assembly of the water heater of FIG.  1 . 
     FIG. 5 is a schematic illustration of the piping system associated with the tank assembly of FIG.  4 . 
     FIG. 6 is a cross-section view taken along line  6 — 6  in FIG.  4 . 
     FIG. 7 is a perspective view of the tank assembly of FIG. 4 with selected elements removed for the purpose of illustration. 
     FIG. 8 is an exploded view of the tank assembly of FIGS. 4 and 7. 
     FIG. 9 is an end view of the tank assembly of FIGS. 4 and 7. 
     FIG. 10 is a side cross-section view of the tank assembly taken along line  10 — 10  in FIG.  9 . 
     FIG. 11 is a view of the outlet tube taken along line  11 — 11  in FIG.  10 . 
     FIG. 12 is an end view of a tank assembly of an alternative construction. 
     FIG. 13 is a side cross-section view taken along line  13 — 13  in FIG.  12 . 
    
    
     Before one embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The use of “consisting of” and variations thereof herein is meant to encompass only the items listed thereafter. The use of letters to identify elements of a method or process is simply for identification and is not meant to indicate that the elements should be performed in a particular order. 
     DETAILED DESCRIPTION 
     The present invention is embodied in a water heater including a cabinet  10  illustrated in FIGS. 1-3 and a tank assembly  14  illustrated in FIGS. 4-13. A first construction of the tank assembly  14  is illustrated in FIGS. 4-11. With particular reference to FIGS. 9 and 10, the tank assembly  14  includes a tank  18  having a substantially cylindrical shape and a horizontally-extending longitudinal axis  22 . The tank  18  includes a shell  24  that is closed at one end by a head  26 . A U-shaped flue tube  30  is positioned within the tank  18 . The U-shaped flue tube  30  includes two legs  31 ,  32  communicating through a curved or bent portion  33 . The legs  31 ,  32  terminate in a burner end  34  and an exhaust end  38 , respectively, both of which extend through the head  26 . 
     Turning to FIGS. 1-3, the cabinet  10  is mounted on a roof curb  42  on a rooftop  46  of a building, and encloses the tank assembly  14 . The cabinet  10  is generally rectangular in shape, having its major axis extending generally horizontally. In this regard, the cabinet  10  has a generally low profile and is similar to other rooftop units such as typical HVAC (e.g., air conditioning) units. As used herein, “low profile” means that the rooftop water heater cabinet  10  cannot typically be seen by a person of average height standing at ground level from a distance of about one city block. The low profile therefore permits the unit to be mounted on a rooftop without detracting from the aesthetics of the building. Roof rails and a pitch pocket or small roof curb may be used as an alternative mounting structure to the roof curb  42  illustrated. 
     As seen in FIG. 3, the cabinet  10  includes two side panels  50 ,  54  arranged generally parallel to each other and at right angles to a third side panel or end panel  58 . A second end panel or cabinet door  62  is releasably attached at right angles to the two side panels  50 ,  54  and generally parallel to the end panel  58 . The door  62  includes a cutout  66  and a recessed or raised handle  70  to facilitate removal of the door  62  from the rest of the cabinet  10  without the use of tools. An upper panel or top  74  is releasably affixed to the top edges of the other panels  50 ,  54 ,  58 ,  62  of the cabinet  10 . The top  74  is preferably removable from the rest of the cabinet  10  without the use of tools. Preferably the door  62  and top  74  are locked to the other panels  50 ,  54 ,  58  to resist tampering with the tank assembly  14 . 
     A base member  78  supports the cabinet panels  50 ,  54 ,  58 ,  62 ,  74  and provides the bottom of the cabinet  10 . The base member  78  is supported by the roof curb  42 , and a foam tape or other sealing member is preferably interposed between the roof curb  42  and the base member  78  to create a water-tight seal therebetween. A pair of rails  82  are mounted to the underside of the base member  78  and straddle the roof curb  42 . The rails  82  define channels along their lengths into which the prongs of a conventional fork lift may be inserted for lifting and lowering the water heater, and also include slots  86  to insert the forklift prongs transverse to the channels. The rails  82  also include apertures  90  for attaching the hooks of a lifting crane to facilitate lifting the water heater to the roof  46  of the building. 
     When the top and door  74 ,  62  are removed, the tank assembly  14  is sufficiently exposed to permit a service technician to perform service on the water heater. An electrical disconnect button  94  (FIG. 1) is mounted to one of the side panels  50 . The disconnect button  94  permits the service technician to conveniently connect and disconnect power to the water heater while the technician is on the rooftop  46 . An electrical outlet  98  (FIG. 1) is also provided to accommodate a service technician&#39;s power tools and electric lights. Another feature of the water heater is the provision of local and remote controllers  99 ,  100 , respectively, that include thermostats. The local controller  99  may be mounted on the side panel  50  as illustrated, or it may be mounted within the cabinet  10 . The remote controller  100  is mounted in a desirable place within the building. The local and remote controllers  99 ,  100  each include a digital display of the water temperature within the tank  18 , and permit adjustment of the temperature. Thus, the water heater may be monitored and controlled from both the rooftop  46  and from within the building. This arrangement creates convenience for both the building owner or occupant within the building and a service technician on the rooftop  46 . 
     The cabinet panels  50 ,  54 ,  58 ,  62 ,  74  are joined together around the tank assembly  14  in a weather-tight fashion. As used herein, “weather-tight” means that rain or other precipitation falling on the cabinet  10  from above are substantially prevented from entering the cabinet  10  and interfering with the operation of the water heater. For example, one of the side panels  54  includes an air inlet vent  102  that opens downwardly to cause precipitation to run off the cabinet  10 , and the other side panel  50  includes a downwardly-opening exhaust vent  106 . In addition to being weather-tight, the edges of the cabinet panels  50 ,  54 ,  58 ,  62 ,  74  are preferably substantially water-tightly joined to each other (e.g., by welding or with gasket material) to resist or prevent water from entering the cabinet  10  and interfering with the operation of the water heater. 
     Turning now to FIG. 4, the tank assembly  14  will be discussed in more detail. A fan or combustion blower  110  communicates with the air inlet vent  102  through an inlet duct  112  to deliver air from outside the cabinet  10  to a gas fuel burner  114  positioned at the burner end  34  of the flue tube  30 . Gas fuel is also delivered to the burner  114  via a gas pipe  118  and regulator  122 . The burner  114  causes combustion of the air and gas fuel, and the products of combustion are forced through the flue tube  30  by the combustion blower  110 . The products of combustion heat the water in the tank  18  through the wall of the flue tube  30 , and then exit the exhaust end  38  of the flue tube  30 . The exhaust vent  106  communicates with the exhaust end  38  of the flue tube  30  through an exhaust duct  123  to permit the spent products of combustion to be exhausted to the surrounding atmosphere. 
     With additional reference to FIG. 8, a baffle or turbulator  124  is positioned within one of the legs  31 ,  32  of the U-shaped flue tube  30 , and preferably in the upper leg  32 . The legs  31 ,  32  each include a longitudinal axis  125  (FIG.  10 ), and the longitudinal axes  125  together define a flue plane FP (FIG. 9) that may be disposed substantially vertically, or may be angled with respect to vertical an angle labeled α. Preferably, the angle α is between 30-60° with respect to vertical. 
     Referring to FIGS. 8-11, an inlet tube  126  and outlet tube  130  are also mounted in the head  26 , and extend substantially parallel to the longitudinal axis  22  of the tank  18 . The inlet tube  126  is positioned in the bottom portion of the tank  18  below the longitudinal axis  22 , and the outlet tube  130  is positioned in the top portion of the tank  18  above the longitudinal axis  22 . Preferably, the inlet tube  126 , outlet tube  130 , and longitudinal axis  22  of the tank  18  are aligned parallel to each other in a vertical plane. This arrangement is made possible in part because the flue plane angle α is greater than zero (i.e., the flue plane FP is non-vertical), which moves the legs  31 ,  32  of the flue tube  30  from a position in which they would interfere with the extension of the inlet and outlet tubes  126 ,  130 . The tubes  126 ,  130  are substantially identical to each other and preferably have a length  132  (FIG. 11) slightly shorter than or substantially the same as the interior length  134  of the tank  18  so that cold water is provided and hot water is removed along the entire interior length  134  of the tank  18 . The preferred length  132  is between about 37 and 38 inches, but the length  132  will vary depending on the dimensions of the water tank  18 . A threaded end  138  is attached at one end of the tubes  126 ,  130 . The threaded end  138  is threaded into a threaded spud  142  in the tank head  26 , and includes additional threads to receive a nipple, water pipe, or other plumbing fixture. In a less preferred embodiment, one or both of the tubes  126 ,  130  may be significantly shorter than illustrated, or the outlet tube  130  may be removed, leaving only the conventional spud  142  to which the building&#39;s hot water pipe communicates. 
     The end  146  opposite the threaded end  138  is closed. The tubes  126 ,  130  include a plurality of holes, apertures, or openings  150  along their lengths. The tubes  126 ,  130  preferably have an outer diameter of about one inch, with the holes  150  having a diameter of about 0.25 inches. The hole spacing  154  is preferably about five inches, with the last hole being spaced from the closed end  146  a distance  158  of about 0.5 inches. 
     In the illustrated construction, all of the openings  150  in the inlet tube  126  face down and all of the openings  150  in the outlet tube  130  face up. Thus, the inlet tube  126  directs cold water toward the bottom of the tank  18  and the outlet tube  130  draws hot water from the top of the tank  18 . This is advantageous because the hottest possible water is drawn from the top by the outlet tube  130  while the inlet tube  126  introduces cold water directly at the bottom of the tank  18 . The inlet tube  126  therefore evenly distributes water at the bottom of the tank to minimize mixing and thereby maximize heated water drawn from the tank  18 . In alternative less preferred constructions, the openings  150  may be arranged around the periphery of the tubes  126 ,  130  instead of opening in only one direction. 
     As can be seen in FIGS. 3,  4 , and  6 , the base member  78  includes a water pipe aperture  162  surrounded by a vertical wall  166 . Four water pipes  168   a ,  168   b ,  168   c ,  168   d  (collectively referred to as  168 ) extend up from the building, through the roof curb  42 , and through the aperture  162 , and communicate with the water tank  18 . A grommet  170  includes apertures  174  water-tightly slip fit around the water pipes  168 , and has a depending wall  178  (FIG. 6) water-tightly slip fit over the vertical wall  166 . The grommet  170  therefore provides a water-tight seal between the pipes  168  and the base member  78 . Suitable clamps  182  can be employed to further tighten the grommet  170  around the vertical wall  166  and pipes  168 . 
     FIGS. 4-6 illustrate the piping system associated with the tank assembly  14 . One of the water pipes  168   a  provides cold water to the water inlet tube  126 . Another water pipe  168   b  removes hot water from the tank  18  through the outlet tube  130 , and this hot water is used for dishwashers and other applications requiring very hot water (e.g., between about 120° F. and about 150° F., or a higher temperature if necessary). Another water pipe  168   c  communicates with a mixing valve  186 , and delivers a mixture of hot water and cold water to the warm water faucet of the building&#39;s bathrooms and kitchen sink. 
     The last water pipe  168   d  communicates between the building&#39;s hot water pipes and a circulation pump  190 . The circulation pump  190  performs two functions. First, the circulation pump  190  is turned on by the controller  99  (FIG. 1) each time the combustion blower  110  is turned on, and remains active for a set period of time (e.g., about nine minutes) after the combustion blower  110  is turned off. A bypass valve  191  is actuated to route water from the outlet tube  130 , through the circulation pump  190 , and back into the tank  18  through the inlet tube  126 . In this manner, the circulation pump  190  causes hot water to be drawn off the top of the water tank  18  through the outlet tube  130  and recirculated through the cold inlet tube  126  to even out the temperature of the water in the tank  18  and reduce the effects of stacking. 
     The second function of the circulation pump  190  is to maintain a supply of hot water in the pipes of the building. A thermostat  192  (FIG. 5) may be employed to determine when the temperature in the building&#39;s hot water pipes has dropped below an desired temperature (e.g., when a hot water draw has not occurred for an extended period of time). In this case, the bypass valve  191  is turned to permit the circulating pump  190  to circulate the water in the building&#39;s hot water pipes into the inlet pipe  126 , which forces hot water out the outlet pipe  130  and into pipe  168   b . The hot water replaces the water in the building&#39;s hot water pipes. The piping system also includes check valves CV and an adjustable gate valve GV (which may be replaced with a fixed valve). The gate valve GV may be used to control the flow rate of recirculated water into and out of the water tank  18 . 
     Referring again to FIG. 3, the base member  78  also includes a drain opening  194  that receives a drain member  198 . The drain member  198  communicates with a drain pipe  202  (shown in phantom in FIGS. 1,  2 , and  4 ) in the building, and the drain pipe  202  communicates with the building&#39;s sewage system. The drain opening  194  is the only opening in the base member  78  through which water is permitted to flow in the event of a water leak within the cabinet  10 . Thus, any water flowing freely within the cabinet  10  drains through the drain opening  194  and is routed to the building&#39;s sewage. The tank assembly  14  also includes a drain valve  204  (FIG. 5) that permits the tank  18  to be drained. The valve  204  is preferably positioned over the drain opening  194 . 
     As seen in FIGS. 4 and 8, the water heater also includes a temperature and pressure valve  206 , which opens in the event the temperature of the water in the tank  18  becomes too high, or if unacceptable pressure levels are present within the tank  18 . A hose or pipe  210  extends down from the temperature and pressure valve  206 , and terminates above the drain opening  194 . Water is drained from the top of the tank  18  and is fed into the building&#39;s sewage system in the event of an overtemperature or overpressure condition in the tank  18 . 
     Referring again to FIGS. 7 and 8, the water tank assembly  14  also includes a pair of support rails  214  extending transverse to the longitudinal axis  22  of the tank  18 , and a pair of wedge-shaped supports  218  welded or otherwise affixed to each support rail  214 . Tank mounting brackets  222  are attached (e.g., welded) to the tank  18 , and a thermally insulated spacer  226  is interposed between the tank mounting brackets  222  and the wedge-shaped supports  218 . Suitable fasteners couple the supports  218  to the brackets  222 . The tank  18  is surrounded with insulation  230  to reduce heat loss from the tank  18  to the ambient air. The head  26  includes an access opening  234  for cleaning the tank  18  and for applying a glass coating to the inside of the tank  18  during manufacture. An access cover  238  is mounted over the opening  234  and a gasket  242  is employed to prevent leakage of water through the access opening  234 . A thermostat and/or an anode tube are mounted in spuds  246  in the access cover  238 . 
     An alternative construction of the tank assembly  14  is illustrated in FIGS. 12 and 13. Here the flue plane FP is substantially vertical, and alternative inlet and outlet tubes  254 ,  258 , respectively, are positioned below and above, respectively, the flue tube  30 . A 90° elbow  262  is provided on both the inlet and outlet tube  254 ,  258  so that the tubes communicate with the building&#39;s pipes through the cylindrical shell  24  of the tank  18  and through the insulation  230 , rather than through the head  26 .