Ventilation fan control

Apparatus for ventilating a structure comprising:

• a variable speed exhaust fan mountable in an exhaust port in the structure, said structure permitting the admission of external environmental air;
• means including a triggerable semiconductor switching device for energizing said fan from a.c. suppy means;
• first sensing means for sensing air temperature at said exhaust port;
• second sensing means for sensing the temperature of external environmental air;
• first control means including a comparator responsive to said sensing means and including analog feedback providing hysteresis for enabling triggering of said switching device when
• A) the sensed air temperature rises above a first preselectable temperature and
• B) the external environmental air temperature is below the air temperature at said exhaust port and
• for disabling triggering of said switching device when the sensed air temperature falls below a second preselected temperature lower than said first temperature;
• and second control means for varying the phase angle of triggering of said switching device responsive to said sensing means for varying the speed of said fan for sensed air temperatures between said first temperature and a third preselectable temperature, said fan speed increasing progressively from about one-half full speed at said first temperature to full speed at said third temperature, said fan speed being essentially constant between said first and second temperatures.

Apparatus for ventilating a structure comprising:

• a variable speed exhaust fan mountable in an exhaust port in the structure, said structure permitting the admission of external environmental air;
• means including a triggerable semiconductor switching device for energizing said fan from a.c. suppy means;
• first sensing means for sensing air temperature at said exhaust port;
• second sensing means for sensing the temperature of external environmental air;
• first control means including a comparator responsive to said sensing means and including analog feedback providing hysteresis for enabling triggering of said switching device when
• A) the sensed air temperature rises above a first preselectable temperature and
• B) the external environmental air temperature is below the air temperature at said exhaust port and
• for disabling energization of said fan when the sensed air temperature falls below a second preselected temperature lower than said first temperature or when outside environmental air temperature rises above inside air temperature by a preselected amount;
• and second control means for varying the phase angle of triggering of said switching device responsive to said sensing means for varying the speed of said fan for sensed air temperatures between said first temperature and a third preselectable temperature, said fan speed increasing progressively from about one-half full speed at said first temperature to full speed at said third temperature, said fan speed being essentially constant between said first and second temperatures.

Apparatus for ventilating a structure comprising:

• an a.c. motor powered variable speed exhaust fan mountable in an exhaust port in the structure, said structure permitting the admission of external environmental air;
• circuit means including a triggerable semiconductor switching device for selectively energizing the fan motor from a.c. supply leads;
• first sensing means for sensing air temperature at said exhaust port;
• second sensing means for sensing the temperature of external environmental air;
• first control means including at least one comparator circuit means interconnected with said first and second sensing means for enabling triggering of said switching device to effect energization of said fan when
• A) the sensed air temperature rises above a first preselectable temperature and
• B) the external environmental air temperature is below the air temperature at said exhaust port and said comparator circuit means includes analog feedback providing hysteresis for disabling energization of said fan by disabling triggering of said switching device when the sensed air temperature falls below a second preselected temperature lower than said first temperature;
• and
• second control means responsive to said first sensing means for controlling the phase angle of triggering of said semiconductor switching device for varying the speed of said fan for sensed air temperatures between said first temperature and a third preselectable temperature, said fan speed increasing progressively from about one-half full speed at said first temperature to full speed at said third temperature, said fan speed being essentially constant between said first and second temperatures.