US 4,374,569 AGranted

Furnace draft control system with electronic loss-of-draft timer

AssigneeJohnson Controls GmbH

InventorThomas E. Hayes

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Abstract

The system includes a damper plate equipped with a draft controller or sensing switch and a motor for positioning the damper plate to control the furnace draft. Upon generation of a call-for-heat signal, an initialization signal drives the damper off its closed position. From then on, draft must be sensed by the draft controller switch to complete the cycle to open the damper plate. When the damper plate is fully opened, a fuel and ignition control circuit is energized to supply fuel to the furnace, and an electronic timer is energized to generate a signal which establishes a trial-for-draft period. When the fuel is ignited, the draft will increase and energize the motor to move the damper plate off the fully open position during the trial-for-draft period, and thereafter, the position of the damper plate is controlled by the draft controller switch to achieve a proper draft within design range. If draft is lost at any time, the controller moves the damper to the full open position and a loss-of-draft safety timing period commences. If draft is not re-established during this period, the system shuts off the fuel and locks out. When the call for heat is satisfied, the system closes the damper and is prepared for another operating cycle. All operating elements, both electronic and mechanical, are tested in a full operating cycle because operation of a subsequent cycle cannot commence unless the damper plate is returned to the fully closed position which also reduces heat loss during periods of non-use. A failure of any component locks the system out.

Claims8

Dependent claims

In combination with a furnace having a firebox and adapted to be connected to a source of fuel by means of fuel control means, a movable element movable between a closed and an open position for controlling the flow of air through a firebox of said furnace, and a thermostat for generating a call-for-heat signal from a space to be heated by said furnace, the improvement comprising:

flue means for communicating combustion gases from said firebox to a chimney and substantially free of losses to the atmosphere between said firebox and chimney;
motor means responsive to a run open signal for operating said movable element toward said open position and responsive to a run closed signal for operating said element toward said close position;
first limit switch means actuated when said movable element is in said open position;
second limit switch means actuated when said movable element is in said closed position;
holding circuit means responsive to a call-for-heat signal only when said second limit switch means is actuated for generating an initial run open signal to said motor means;
controller means including pressure sensing means responsive to the pressure in said flue means for generating a run open signal when the draft in said flue means is less than a first predetermined value, and for generating a run close signal when the draft in said flue means is greater than a second predetermined value, said controller means generating neither of said signals when the draft is between said first and second predetermined values;
electronic timer circuit means responsive to the actuation of said first limit switch means when said movable element is in said open position following a predetermined time interval after said holding means is actuated for generating a timing signal of predetermined duration representative of a trial-for-draft period;
first enable circuit means energized by said timer circuit means during said trial-for-draft period for energizing said fuel control means and for enabling said controller means to couple said run open and run close signals to said motor means;
said timer circuit means being connected in circuit with said first limit switch to de-energize said first enable circuit means if said controller means senses no draft in said flue means during said trial-for-ignition period.

6 more elements

In combination with a furnace having a firebox and adapted to be connected to a source of fuel by means of fuel control means, a damper element movable between a closed and an open position for controlling the flow of air through a firebox of said furnace, and a thermostat for generating a call-for-heat signal from a space to be heated by said furnace, the combination comprising:

flue means for communicating combustion gases from said firebox to a chimney and substantially free of losses to the atmosphere between said firebox and chimney;
motor means responsive to a run open signal for operating said damper element toward said open position and responsive to a run close signal for operating said damper element toward said closed position;
first limit switch means actuated when said damper element is in said open position;
second limit switch means actuated when said damper element is in said closed position;
holding circuit means responsive to a call-for-heat signal only when said second limit switch means is actuated for generating an initial run open signal to said motor means;
controller means including pressure sensing means responsive to the pressure in said flue means for generating a run open signal when the draft in said flue means is less than a first predetermined value, and for generating a run close signal when the draft in said flue means is greater than a second predetermined value, said controller means generating neither of said signals when the draft is between said first and second predetermined values;
timer circuit means responsive to said damper element's reaching said open position for generating a trial-for-draft signal of predetermined duration, said trial-for-draft signal being of greater magnitude only if said timer circuit means is actuated a predetermined time after said holding circuit means is actuated;
and enabling circuit means responsive only to said trial-for-draft signal of said greater magnitude for communicating said call-for-heat signal to said fuel control means and for coupling said controller means in operative relation with said motor means, said timer circuit means including means responsive to said damper element's moving off said closed position to sustain said trial-for-draft signal beyond said predetermined period and thereby continue to energize said enabling circuit means.

5 more elements

Dependencies are inferred from the claim text.