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Bypass control system to maintain a constant air supply pressure in a HVAC duct system

  • US 4,487,363 A
  • Filed: 02/28/1983
  • Issued: 12/11/1984
  • Est. Priority Date: 10/14/1982
  • Status: Expired due to Fees
First Claim
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1. In a system for providing conditioned air from a single zone HVAC unit to a plurality of zones through a duct system having a motorized zone damper associated with each zone which modulates open and closed in response to a zone thermostat in each zone, the HVAC unit including a fan and electrical motor for discharging conditioned air into the outlet of the HVAC unit and a bypass duct communicating between the outlet and the return air intake of the HVAC unit, the improvement comprising a motorized bypass damper located in said bypass duct having a damper blade movable between opened and closed positions and intermediate positions therebetween, a bypass monitor connected to said bypass damper for controlling the operation of the motor of said damper and thereby the movement of said damper blade to selected said positions, a sensor coupled between said electric motor driving said fan and said bypass monitor for providing information indicative of the amount of work being performed by said electrical motor driving said fan to said monitor, said electrical motor driving said fan performing less work when one or more of said zone dampers modulate closed thereby causing an increase in the static air pressure in the duct system, said monitor controlling said bypass damper to move its said damper blade more open to correspondingly compensate for the increase in the static air pressure by bypassing more air from said outlet to said inlet of said HVAC unit thereby maintaining the air pressure supplied by said HVAC unit to said duct system generally constant.

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