Make up air controller for use with fume hood systems

• US 4,773,311 A
• Filed: 11/24/1986
• Issued: 09/27/1988
• Est. Priority Date: 11/24/1986
• Status: Expired due to Fees

• Current Assignee: Phoenix Controls Corporation (Honeywell International Inc.)
• Original Assignee: Phoenix Controls Corporation (Honeywell International Inc.)
• Inventors: Sharp, Gordon P.
• Primary Examiner(s): Joyce, Harold
• Application Number:
  US06/933,965
• Time in Patent Office: 673 Days
• Field of Search: 98/33.1, 98/1.5, 98/115.1, 98/115.3, 126/299 R, 126/299 D
• US Class Current: 454/56
• CPC Class Codes: B08B 15/023 Fume cabinets or cupboards, e.g. for laboratories
• CPC Class Codes: F24F 11/74 for controlling air flow rate or air velocity
• CPC Class Codes: F24F 2011/0004 to create overpressure in a room
• CPC Class Codes: F24F 2011/0005 to create underpressure in a room, keeping contamination inside

Abstract

Method and apparatus for varying the make-up air volume of an HVAC system used in conjunction with a laboratory fume hood. The invention maintains a constant difference in air volume between the total air volume exhausted from the laboratory, including the variable fume hood exhaust volume and the make-up and supply air provided by the HVAC system. The invention provides a continuous modulation of the make-up air volume which tracks the exhaust volume to maintain a constant preset differential between the makeup and exhaust volumes. The invention includes a preferred embodiment in which a signal from a sash height transducer is used to control the volume of make-up air.

Claims

1. Apparatus for controlling the volume of make-up air supplied to an area in which is located a fume hood having an exhaust volume which varies as the fume hood sash is opened and closed comprising:

transducer means, responsive to the fume hood sash position, for providing an output signal representative of the area of the sash opening;

make-up air control means, connected to an air supply and responsive to a make-up air command signal, for providing a make-up air flow the volume of which is determined by the make-up air command signal, and

a make-up air controller for providing the make-up air command signal, including;

means for mu1tiplying the transducer means output signal by a scale factor to provide a scaled output signal;

offset means, responsive to the scaled output signal, for subtracting therefrom a signal representative of a desired air flow volume differential between the fume hood exhaust volume and the make-up air volume to provide an output signal representative of a resulting make-up air volume; and

means, responsive to the offset means output signal, for applying a make-up air command signal to the make-up air control means so as to produce a make-up air flow the volume of which equals said resulting make-up air volume.