OPEN DRAFT HOOD FURNACE CONTROL USING INDUCED DRAFT BLOWER AND EXHAUST STACK FLOW RATE SENSING

摘要

OPEN DRAFT HOOD FURNACE CONTROL USINGINDUCED DRAFT BLOWER AND EXHAUSTSTACK FLOW RATE SENSINGAbstractApparatus is provided for modifying an open drafthood furnace and its control system, to produce an induceddraft furnace having increased efficiency. A blowerlocated in the furnace exhaust stack is used to inducemovement of air and combustion products into and throughthe draft hood . A flow-limiting orifice located in theexhaust stack upstream from the blower causes a region ofreduced pressure to exist downstream from the orifice. Apressure signal representative of the flow rate of exhauststack gases is sensed on the downstream side of theorifice and is communicated by a conduit to a pressureswitch connected to a gas valve, which together controlgas to the burner. No gas is permitted to flow to theburner unless a predetermined reduced pressure level isachieved at the downstream side of the oxifice. A smallopening in the conduit permits a small flow of flushingair to enter the conduit.-24-