Automatic temperature and humidity regulation – Miscellaneous – Burner controls with automatic cutoff
Reexamination Certificate
1999-11-08
2001-06-12
Wayner, William (Department: 3744)
Automatic temperature and humidity regulation
Miscellaneous
Burner controls with automatic cutoff
C236S011000, C165S256000
Reexamination Certificate
active
06244515
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to gas furnace controls and more specifically to controls for furnaces having two different gas burning rates, or stages.
BACKGROUND OF THE INVENTION
The use of two stage gas furnaces has become quite pervasive recently. Two stage gas furnaces essentially burn gas at two rates, one low and the other is high. In most situations, the low combustion rate is sufficient to satisfy the heat loss from a conditioned environment (e.g., a home). However, when the outdoor environment becomes quite cold the second high combustion rate is used to satisfy the increased demand. The greatest advantage to the two stage furnace is that it allows the furnace to maintain the conditioned environment in a more stable manner. For example, a single stage heating system for a home may be designed to maintain the indoor temperature at 70° F. while the outdoor temperature is 0° F. Depending on the insulation factors and the size of the relevant building, this could require a 100,000 BTU/Hr combustion rate on the furnace. However, if the outdoor temperature is 45° F., the capacity (above the actual need) of this furnace will cause the temperature to exceed a selected desired setting, such as 70° F., in the home (actually caused by the latent heat stored in the heat exchanger of the furnace). The two stage furnace corrects this over-temperature problem by operating at a low fire condition (approximately 50,000 BTU/hr for a 100,000 BTU/hr furnace). This improves the efficiency and comfort level in the home.
In the prior art, two stage gas furnaces required the use of a two stage room thermostat in which the second stage of the furnace is engaged when the second stage of the room thermostat is energized (a separate set of contacts set to close 2° F. below the first stage setting). Another approach is disclosed in U.S. Pat. No. 5,271,556. In this patent, a jumper is placed between the first stage signal (W
1
) and the second stage signal (W
2
) to the furnace. The control within the furnace then detects the simultaneity of the two signals when a single stage thermostat is used. The furnace then delays the operation of the second stage of combustion for 5 minutes. This allows the home owner to use a single stage room thermostat with a two stage gas furnace.
The former approach requires a special thermostat while the latter approach complicates wiring and increases the possibility of mistakes being made when the system installer is adding or replacing the jumper.
SUMMARY OF THE INVENTION
An object of the invention is to overcome the prior art limitations noted above. Another object of the invention is to provide a two stage gas furnace ignition control which can be used with either a two stage or a single stage room thermostat. Yet another object is the provision of a two stage gas furnace ignition control which is less subject to installation mistakes than prior art two stage controls.
Briefly, in accordance with the invention, since the second (higher) stage combustion is only required due to low outdoor ambient temperature or by changing the thermostat setting a certain amount higher, e.g., 10° F., the improved control monitors the length of time the first, low combustion, stage is energized. If this time exceeds a selected period, e.g., 10 minutes, the second, high combustion, stage is energized, independently of the type of room thermostat used (single or two stage) and with no jumper required between the two stage signals (W
1
and W
2
) to energize the second stage ignition with a single stage thermostat. According to a feature of the invention, if the second stage signal (W
2
) is energized, the measurement of the time that the first stage is on is circumvented and the second stage ignition is immediately begun. This allows the features associated with a two stage room thermostat to be utilized as well by the control/furnace combination (for example, if the two stage room thermostat is moved to a selected delta degrees, such as 10° higher setting, both stages will be energized as soon as possible).
As an added benefit, fault tolerance is added to the system. If the wire to the second stage (W
2
) is broken or becomes loose the furnace/control will still function as a two stage gas combustion system as described above. It also removes the possibility of mistakes which could occur when the system installer is adding or replacing the prior art jumper mentioned above.
Additional objects and advantageous of the invention will be set forth in part in the description which follows and in part will be obvious from the description. The objects and advantages of the invention may be realized and attained by means of the instrumentalities, combinations and methods particularly pointed out in the appended claims.
REFERENCES:
patent: 4638942 (1987-01-01), Ballard et al.
patent: 5271556 (1993-12-01), Helt et al.
patent: 5806760 (1998-09-01), Maiello
patent: 5902099 (1999-05-01), Rowlette et al.
Eifler Mark A.
Rowlette Mitchell R.
Baumann Russell E.
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
Wayner William
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