Fume hood ventilation control system
First Claim
1. In a fume hood having an opening, a movable sash for controlling the area of the opening that is exposed, and adjustable ventilating means for ventilating the fume hood, the improvement comprising:
- means for sensing the velocity of air entering the fume hood opening;
means responsive to the sash position for sensing the exposed area of the fume hood opening;
means for adjusting said ventilating means in a manner to maintain the velocity of air entering the opening at a substantially constant preselected level when the exposed area of the opening is greater than a preselected area; and
means for adjusting said ventilating means in a manner to maintain the volume rate of air entering the opening at a substantially constant preselected rate when the exposed area of the opening is less than said preselected area.
1 Assignment
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Accused Products
Abstract
A method and apparatus for controlling ventilation of a laboratory fume hood. The face velocity of air entering the fume hood is sensed by a velocity sensor, and a stepping motor controls damper blades in the exhaust duct to normally maintain the face velocity at a nearly constant level. A potentiometer senses the position of a sash that controls the fume hood face opening. When the sash is 40% open or less, the damper blades are adjusted to keep the volume rate of flow through the fume hood nearly constant. An alarm signal is generated if the flow is unduly low. The damper blades are fully opened either if a switch is operated or if the sash is abruptly opened. An unoccupied mode permits reduced air flow when the sash is nearly closed and the laboratory is unoccupied.
66 Citations
18 Claims
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1. In a fume hood having an opening, a movable sash for controlling the area of the opening that is exposed, and adjustable ventilating means for ventilating the fume hood, the improvement comprising:
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means for sensing the velocity of air entering the fume hood opening; means responsive to the sash position for sensing the exposed area of the fume hood opening; means for adjusting said ventilating means in a manner to maintain the velocity of air entering the opening at a substantially constant preselected level when the exposed area of the opening is greater than a preselected area; and means for adjusting said ventilating means in a manner to maintain the volume rate of air entering the opening at a substantially constant preselected rate when the exposed area of the opening is less than said preselected area. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A method of controlling ventilation of a fume hood having an opening and a movable sash for controlling exposure of said opening, said method comprising the steps of:
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sensing the velocity of the air entering the fume hood through said opening; sensing the sash position to detect the exposed area of the opening; maintaining the velocity of air flowing into said opening substantially constant when the exposed area of the opening is greater than a preselected area; and maintaining the volume rate of air flow into said opening substantially constant when the exposed area of the opening is less than said preselected area. - View Dependent Claims (14, 15, 16, 17)
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18. In a fume hood having an opening, a movable sash for controlling the area of the opening that is exposed, an exhaust duct, and a damper in the exhaust duct movable between a fully open position and a fully closed position, the improvement comprising:
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means for sensing the speed of movement of the sash; and means for effecting immediate movement of the damper to the fully open position thereof in response to movement of the sash above a preselected speed in a direction to increase the exposure of the opening.
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Specification