Blower mixing tee

Details Blower mixing tee Blower mixing tee

2002-10-25

2003-09-23

Lu, Jiping (Department: 3749)

Liquid heaters and vaporizers

Stand boiler

C122S017100, C122S172000, C122S018310, C122SDIG007, C126S080000

Reexamination Certificate

active

06622660

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention is directed to a blower assembly for use in expelling exhaust gases from a gas or oil fired burner, such as a water heater. More specifically, the present invention is directed to a unique exhaust configuration for expelling exhaust gases from a water heater and mixing the exhaust gases with dilution air.
Water heaters have been around for numerous years to provide hot water for both commercial and consumer usage. A water heater is commonly produced with a gas or oil fired burner. The burner produces a flame that heats the base of the water heater and the hot gases generated by the burner are channeled through the center of the water heater in a flue. The heat from the hot exhaust gases in the flue is transferred to the surrounding water to extract the maximum amount of heat to increase the fuel efficiency of the water heater.
To maximize the amount of heat transferred from the flue to the water, the flue is typically produced with baffles to provide the most tortured path allowable. The amount of baffles in a flow path is limited by the required flow throughput of the flue to prevent the harmful build up of carbon monoxide within the room because of incomplete combustion of the spent gases. The limited amount of baffles in a regular water heater caused several undesirable side effects, the most important of which was a maximum overall operating efficiency limited to approximately 58 percent.
The low efficiency of the water heater is caused by the gases exiting the water heater at a higher than desired temperature because of the required throughput of the exhaust flue. This created large stand-by losses when the heated water was not being used because the heat from the water transferred back out through the flue due to drafts, thereby causing increased fuel usage to maintain water temperature in the standby mode.
The problems identified above were addressed by adding a blower to the water heater. The use of a blower induces a draft through the exhaust flue which allows a more tortured path for the exhaust flue, thereby allowing a transfer of a greater amount of heat from the flue gases to the water. The blower would turn on only when the burner was on, thereby drawing the spent exhaust gases from the flue. Without the aid of a blower, the flow through the flue is dramatically reduced, which can cause a potential back up of spent exhaust gases at the burner.
With the use of a blower, the overall efficiency of a water heater can be increased to about 68 percent. This increase is mainly achieved through the reduced heat losses in the standby mode and the more efficient transfer of heat during the heating mode. The decrease in losses during the standby mode was achieved because there is little flow through the flue without the presence of extremely hot gases and the blower motor running. With reduced air flow through the flue in the standby mode, heat transfer losses were effectively reduced.
An additional benefit of the use of a blower on a water heater was that the temperatures of the exhaust gases exiting the flue were reduced because of more efficient heat scrubbing. In naturally aspirated water heaters, the exhaust gases contained in the flue that exited the water heater were relatively hot. This required the use of steel exhaust tubing that needed to be vented to the outside of the home or building in a nearly vertical manner for safety reasons. The use of a blower reduced the temperatures of the spent exhaust gases to the point that wider selections of materials were available for exhaust piping. Specifically, the use of a blower allowed for the safe use of PVC piping and the horizontal venting through the nearest wall to vent the exhaust gases to the outside atmosphere.
However, the use of a blower with a water heater presented several engineering challenges. The exhaust gases in the flue, while much lower in temperature than normally aspirated water heaters, were still above ideal temperatures for the direct venting through a PVC pipe. To reduce the exhaust gases to a desired temperature, the hot exhaust gases are mixed with dilution air at ambient temperature.
A prior art solution to adding dilution air to exhaust gases was the use of a T-connection attached to the flue with dilution air being drawn through one side of the T-connection and the blower assembly attached on the opposing side. When the blower motor is operated, the blower draws both exhaust gases from the water heater and dilution air into contact with each other to cool the exhaust gases before the exhaust gas/dilution air mixture is exhausted from the blower assembly through the PVC exhaust pipe.
A problem associated with the use of a T-connection for mixing dilution air with expelled exhaust gases from the water heater is the sizing and operation of the blower assembly for both maximum and minimum vent lengths. Any exhaust system design, and specifically the blower assembly, must be able to perform within agency-set standards at both a minimum vent length and a maximum vent length, as well as vent lengths in between.
The agency standard that impacts the minimum length flue pipe operation is the maximum allowable exhaust temperatures. Typically, the maximum allowable exhaust temperature is 157 degrees Fahrenheit wall temperature for the PVC piping attached to the blower. During minimum vent length applications, the blower assembly sees less resistance to drawing air into the blower housing and thus has a tendency to over-draw the burner system. The overdrawing of the burner results in an increased volume of flue gases moving too quickly past the water heaters baffle system, resulting in excessive exhaust temperatures entering into the blower.
During maximum length flue pipe operations, the agency standard that impacts the operation of a blower system is the maximum allowable carbon monoxide levels. During maximum length flue pipe operation, the blower motor has a tendency to under-draw the flue gases from the water heater. Since the blower motor is under-drawing the flue gases, the gases leaving the water heater have a higher concentration of carbon monoxide.
Therefore, it is an object of the present invention to provide a unique exhaust system for a gas or oil fired burner that reduces the amount of exhaust gases drawn through the flue pipe of the water heater during minimum vent length applications while maximizing the amount of flue gases drawn through the burner system during a maximum vent length application. Further, it is an object of the present invention to provide such an exhaust system that utilizes current operating components without increasing the cost and complexity of the exhaust system.
SUMMARY OF THE INVENTION
The present invention is an exhaust system for withdrawing a supply of exhaust gases from an exhaust flue of a gas or oil fired burner and mixing the withdrawn exhaust gases with dilution air prior to expelling the exhaust gases to atmosphere at a remote location. The present invention is particularly useful with a water heater having an oil or gas fired burner.
The exhaust system of the present invention includes a blower assembly having an outer housing including an inlet opening and an exhaust outlet. The blower assembly includes an impeller mounted to an electric motor for rotation within the open blower housing. As the impeller rotates within the open blower housing, the impeller creates a source of negative pressure. The exhaust outlet of the blower housing is coupled to an exhaust pipe for discharging gases to atmosphere from within the open blower housing.
The exhaust system further includes a dilution air inlet pipe having a first end configured to receive a supply of dilution air and a second end in communication with the inlet opening of the blower housing. The dilution air inlet pipe generally extends along a longitudinal axis from the first end to the second end. As the impeller of the blower assembly rotates, the source of negative air pressure in the blower housing draws a flow of dilution air into the blower housing

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