Mechanical draft systems

Abstract

A representative mechanical draft system for drawing exhaust gasses from a chimney includes: an exhaust fan assembly having: a housing defining a chamber and having opposing openings, the opposing openings having a centerline extending therebetween, a first of the openings being operative to intake a flow of gasses, a second of the openings being operative to exhaust the flow of gasses from the chamber; and a centrifugal fan having a motor and an impeller, the motor being mounted external to the housing, the impeller being positioned within the chamber, a rotational axis of the impeller being inclined with respect to the centerline extending between the openings of the housing.

1 . A mechanical draft system for drawing exhaust gasses from a chimney comprising:
 an exhaust fan assembly comprising:
 a housing defining a chamber and having opposing openings, the opposing openings having a centerline extending therebetween, a first of the openings being operative to intake a flow of gasses, a second of the openings being operative to exhaust the flow of gasses from the chamber; and 
 a centrifugal fan having a motor and an impeller, the motor being mounted external to the housing, the impeller being positioned within the chamber, a rotational axis of the impeller being inclined with respect to a linear flow path extending between the openings of the housing. 
   
     
     
         2 . The system of  claim 1 , wherein an exterior of the housing has a recessed portion and the centrifugal fan is mounted at the recessed portion. 
     
     
         3 . The system of  claim 2 , wherein the recessed portion has a mounting platform to which the centrifugal fan is mounted, the mounting platform providing the incline of the rotational axis of the impeller. 
     
     
         4 . The system of  claim 1 , wherein the rotational axis of the motor intersects the centerline. 
     
     
         5 . The system of  claim 1 , further comprising a divider positioned within the housing and being operative to partition the chamber into an intake compartment, communicating with the first of the openings, and an exhaust compartment, communicating with the second of the openings, the partition being further operative to restrict gases from the intake chamber from leaving the housing without flowing through the impeller. 
     
     
         6 . The system of  claim 1 , further comprising the chimney to which the exhaust fan assembly is mounted. 
     
     
         7 . The system of  claim 1 , further comprising a heat recovery unit mounted to the chimney, the heat recovery unit being operative to extract heat from exhaust gases passing therethrough. 
     
     
         8 . The system of  claim 7 , wherein the heat recovery unit is attached to the exhaust fan assembly. 
     
     
         9 . The system of  claim 7 , wherein the heat recovery unit has a unit housing and a heat exchanger, the heat exchanger being operative to receive a variable flow of operating fluid for extracting the heat from the exhaust gasses. 
     
     
         10 . The system of  claim 7 , wherein the heat recovery unit is operative to selectively move between a heat exchange position, in which the heat exchanger is located along the flow of gasses, and a bypass position, in which the heat exchanger is displaced from the flow of gasses. 
     
     
         11 . The system of  claim 10 , further comprising an actuator operative to move the heat recovery unit between the heat exchange position and the bypass position. 
     
     
         12 . The system of  claim 7 , wherein the exhaust fan assembly is located downstream of the heat recovery unit. 
     
     
         13 . The system of  claim 7 , further comprising:
 a first appliance operative to provide exhaust gasses to the chimney;   a second appliance operative to provide exhaust gasses to the chimney; and   a controller operative to adjust an operating speed of the centrifugal fan such that, responsive to a change in pressure in the chimney, the controller adjusts the operating speed of the centrifugal fan to maintain a desired pressure in the chimney.   
     
     
         14 . The system of  claim 13 , wherein the controller is further operative to adjust a flow of the operating fluid to the heat recovery unit. 
     
     
         15 . The system of  claim 1 , further comprising:
 a first appliance operative to provide exhaust gasses to the chimney;   a second appliance operative to provide exhaust gasses to the chimney; and   a controller operative to adjust an operating speed of the centrifugal fan such that, responsive to a change in pressure in the chimney, the controller adjusts the operating speed of the centrifugal fan to maintain a desired pressure in the chimney.   
     
     
         16 . The system of  claim 15 , wherein the centrifugal fan is a single fan of the system. 
     
     
         17 . The system of  claim 1 , wherein the housing, in a vicinity of the first opening, has a circular cross-section. 
     
     
         18 . The system of  claim 1 , wherein less than approximately 75% of a length of the motor protrudes beyond a radial extent of the housing. 
     
     
         19 . The system of  claim 18 , wherein less than approximately 50% of a length of the motor protrudes beyond a radial extent of the housing.