Pneumatic temperature reset differential pressure controller
First Claim
1. A control for a variable air flow volume conditioned air distribution system of the kind having an air flow duct for supplying conditioned air to a room, a movable member in the duct for regulating the volume of air flowing through the duct, and an air powered actuator connected to position the movable member, said control comprising,valve means for varying the pressure of the air supplied to the actuator,air flow velocity sensing means for sensing the air flow velocity in the duct and connected to the valve means for applying a flow velocity force to the valve means in response to the sensed air flow velocity,bias spring means connected to the valve means for applying a spring force to the valve means in opposition to the flow velocity force of the air flow velocity sensing means to determine the air flow velocity set point of the controller,room temperature sensing means for sensing the temperature of the air in the room and connected to the bias spring means for applying a room temperature force to the bias spring means in response to the sensed temperature to change the air flow velocity set point of the control in response to changes in the room air temperature so that the control maintains a constantly regulated amount of air flow into the room in proportion to the room'"'"'s temperature demands, andincluding calibration means for calibrating the air flow velocity set point of the controller.
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Abstract
An air flow velocity controller in a variable air volume control system interlocks a room temperature signal from a thermostat with the velocity set point so that the velocity controller maintains a constantly regulated amount of air into a room in proportion to the room'"'"'s thermostat demands and independent of variations in the static pressure in the duct.
The controller includes a maximum lift cam and a movable spring fulcrum which are both mounted in a common cam housing to permit the maximum velocity setting to be adjusted for varying room requirements while maintaining a constant spring range regardless of the maximum velocity setting.
The controller is constructed to provide automatic compensation for control offset produced by changes in the static air pressure in the duct.
The controller includes the ability to control the air flow at a minimum velocity so that the air can be economically reheated or a minimum volume of air flow can be maintained for ventilation requirements.
78 Citations
21 Claims
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1. A control for a variable air flow volume conditioned air distribution system of the kind having an air flow duct for supplying conditioned air to a room, a movable member in the duct for regulating the volume of air flowing through the duct, and an air powered actuator connected to position the movable member, said control comprising,
valve means for varying the pressure of the air supplied to the actuator, air flow velocity sensing means for sensing the air flow velocity in the duct and connected to the valve means for applying a flow velocity force to the valve means in response to the sensed air flow velocity, bias spring means connected to the valve means for applying a spring force to the valve means in opposition to the flow velocity force of the air flow velocity sensing means to determine the air flow velocity set point of the controller, room temperature sensing means for sensing the temperature of the air in the room and connected to the bias spring means for applying a room temperature force to the bias spring means in response to the sensed temperature to change the air flow velocity set point of the control in response to changes in the room air temperature so that the control maintains a constantly regulated amount of air flow into the room in proportion to the room'"'"'s temperature demands, and including calibration means for calibrating the air flow velocity set point of the controller.
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2. A control for a variable air flow volume conditioned air distribution system of the kind having an air flow duct for supplying conditioned air to a room, a movable member in the duct for regulating the volume of air flowing through the duct, and an air powered actuator connected to position the movable member, said control comprising,
valve means for varying the pressure of the air supplied to the actuator, air flow velocity sensing means for sensing the air flow velocity in the duct and connected to the valve means for applying a flow velocity force to the valve means in response to the sensed air flow velocity, bias spring means connected to the valve means for applying a spring force to the valve means in opposition to the flow velocity force of the air flow velocity sensing means to determine the air flow velocity set point of the controller, room temperature sensing means for sensing the temperature of the air in the room and connected to the bias spring means for applying a room temperature force to the bias spring means in response to the sensed temperature to change the air flow velocity set point of the control in response to changes in the room air temperature so that the control maintains a constantly regulated amount of air flow into the room in proportion to the room'"'"'s temperature demands, and including a reset arm connected to the bias spring means and wherein the temperature sensing means include a reset piston connected to the reset arm.
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12. A control for a variable air flow volume conditioned air distribution system of the kind having an air flow duct for supplying conditioned air to a room, a movable member in the duct for regulating the volume of air flowing through the duct, and an air powered actuator connected to position the movable member, said control comprising,
valve means for varying the pressure of the air supplied to the actuator, air flow velocity sensing means for sensing the air flow velocity in the duct and connected to the valve means for applying a flow velocity force to the valve means in response to the sensed air flow velocity, bias spring means connected to the valve means for applying a spring force to the valve means in opposition to the flow velocity force of the air flow velocity sensing means to determine the air flow velocity set point of the controller, room temperature sensing means for sensing the temperature of the air in the room and connected to the bias spring means for applying a room temperature force to the bias spring means in response to the sensed temperature to change the air flow velocity set point of the control in response to changes in the room air temperature so that the control maintains a constantly regulated amount of air flow into the room in proportion to the room'"'"'s temperature demands, and including offset compensating means for automatically compensating for offset of the control caused by changes of static air pressure in the duct.
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15. A control for a variable air flow volume conditioned air distribution system of the kind having an air flow duct for supplying conditioned air to a room, a movable member in the duct for regulating the volume of air flowing through the duct, and an air powered actuator connected to position the movable member, said control comprising,
valve means for varying the pressure of the air supplied to the actuator, air flow velocity sensing means for sensing the air flow velocity in the duct and connected to the valve means for applying a flow velocity force to the valve means in response to the sensed air flow velocity, bias spring means connected to the valve means for applying a spring force to the valve means in opposition to the flow velocity force of the air flow velocity sensing means to determine the air flow velocity set point of the controller, and offset compensating means for automatically compensating for offset of the control caused by changes of static air pressure in the duct.
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18. A method of controlling the volume of air flow through a duct in a variable air flow conditioned air distribution system, said method comprising,
regulating the volume of air flow through the duct by an air powered actuator, supplying air under pressure to the actuator through a supply conduit, controlling the pressure of the air supplied to the actuator by a valve associated with the supply conduit, sensing the air flow velocity in the duct and applying a flow velocity force to the valve in one direction in response to the air flow velocity, applying a bias spring force to the valve in opposition to the flow velocity force to determine the air flow velocity set point, sensing the temperature of the room supplied with the conditioned air from the duct, combining a room temperature force with the bias spring force in response to the sensed temperature to change the air flow velocity set point with changes in the room temperature, and including changing the velocity set point in response to changes in static air pressure in the duct to automatically compensate for control offset caused by changes of static air pressure in the duct.
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19. A method of controlling the volume of air flow through a duct in a variable air flow conditioned air distribution system, said method comprising,
regulating the volume of air flow through the duct by an air powered actuator, supplying air under pressure to the actuator through a supply conduit, controlling the pressure of the air supplied to the actuator by a valve associated with the supply conduit, sensing the air flow velocity in the duct and applying a flow velocity force to the valve in response to the air flow velocity, applying a bias spring force to the valve in opposition to the flow velocity force to determine the air flow velocity set point, and changing the velocity set point in response to changes in static air pressure in the duct to automatically compensate for control offset caused by changes in static air pressure in the duct.
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20. A method of compensating for offset of a fluid flow regulating control mechanism caused by a change in one of the pressures sensed by the control mechanism, said method comprising,
positioning a control element of the control mechanism to regulate the volume of fluid flow through a duct, sensing first and second pressures of the fluid flowing in the duct and applying a first flow velocity force to the control element in response to the difference between said pressures, applying a bias spring force to the control element in opposition to the first flow velocity force to determine the fluid flow velocity set point of the control mechanism, and changing the velocity set point in response to changes in one of the sensed pressures to automatically compensate for control offset caused by changes in that sensed pressure.
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21. A flow control mechanism which compensates for offset of the control mechanism caused by a change in one of the pressures sensed by the control, said control mechanism comprising,
a control element for regulating the volume flow of a fluid flowing through a duct, sensing means for sensing first and second pressures of the fluid flowing in the duct and operatively associated with the control element to apply a first flow velocity force to the control element in response to the difference between said pressures, bias spring means connected to the control element for applying a spring force to the control element in opposition to the flow velocity force to determine the fluid flow velocity set point of the control mechanism, and offset compensating means for automatically compensating for offset of the control mechanism caused by changes in one of the pressures sensed by the sensing means.
Specification