Automatic temperature and humidity regulation – Hot-air furnace – Air and fire control
Reexamination Certificate
2000-01-20
2001-05-15
Wayner, William (Department: 3744)
Automatic temperature and humidity regulation
Hot-air furnace
Air and fire control
C236S0010EA, C236S094000, C165S262000, C062S175000
Reexamination Certificate
active
06230979
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a controller for a two-stage heat source that can be used with either a single or a two-stage thermostat.
There are two types of commonly available, gas-fired, warm air furnaces in the marketplace: those with a single gas flow rate, and those with two or more gas flow rates. These are referred to as single and multistage furnaces, respectively. Multistage furnaces are frequently selected by homeowners for replacement furnaces because they offer increased performance and comfort. In retrofit applications there is typically a thermostat and wiring in place. It can be troublesome to install a multistage thermostat in a retrofit application with a single stage thermostat already in place because of the need to add additional wiring. For simple and economical installation, it is desirable to be able to continue to use a single stage thermostat and single stage thermostat wiring with a replacement multistage furnace.
Several attempts have been made to utilize a single stage thermostat with two-stage furnaces. One method, disclosed in U.S. Pat. No. 5,271,556, ties the first stage and second stage terminals on the controller together. The controller recognizes a simultaneous call for first stage and second stage heat as a single stage thermostat, and operates in the first stage only. If the demand for heat is not satisfied within a predetermined time (typically ten minutes), the controller switches to second stage heating. Another method, disclosed in U.S. Pat. No. 5,806,760, includes a time delay relay in the first stage terminal. After the expiration of the time for the time-delay relay, the controller switches to the second stage heating.
SUMMARY OF THE INVENTION
The controller of the present invention permits a multistage heating plant, such as a two stage gas furnace, to be operated with either a single or a multi stage thermostat. This allows fast, easy, and inexpensive replacement of an existing single stage heating plant with a modern multistage heating plant, without replacing the thermostat and/or adding additional thermostat wiring.
Generally the controller of the present invention has a first terminal for connection to a single stage thermostat, or the first stage of a multistage thermostat, and a second terminal for connection to the second stage of a multistage thermostat. The controller also comprises an indicator for selecting the type of thermostat (single stage or multistage) that is connected to the controller. This indicator can be, for example, a contact bar with three contacts that are appropriately connected by the installer to indicate to the controller the type of thermostat connected to the controller. Alternatively, the controller could be programmed to assume that the thermostat is a single stage thermostat, unless and until the thermostat receives a demand for second stage heating which indicates that the controller is connected to a multistage thermostat.
The controller initiates a second stage delay timer, and the timer continues to count down unless reset, until it reaches zero and second stage heating is initiated. The second stage delay timer can be reset by several events, including the satisfaction of the demand for first stage heat; a demand for second stage heat; or the absence of a demand for second stage heat when the controller is connected to a multistage thermostat.
REFERENCES:
patent: 5022460 (1991-06-01), Brown
patent: 5271556 (1993-12-01), Helt et al.
patent: 5806760 (1998-09-01), Maiello
Butler William P.
Cenedella David M.
Vendt Stephen J.
Emerson Electric Co.
Harness Dickey & Pierce
Wayner William
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