| 摘要 |
An induced draft, fuel-fired upflow furnace is provided with a compact, high efficiency heat exchanger having horizontally spaced apart inlet and outlet manifold structures which are innerconnected by a horizontally spaced series of vertically serpentined, relatively small diameter flow transfer tubes. Larger diameter inlet flow tubes are positioned beneath the balance of the heat exchanger, extend parallel to the transfer tubes, and have upturned discharge ends connected to the underside of the inlet manifold. The heat exchanger is configured so that its total vertically facing peripheral surface area is considerably larger than its total horizontally facing peripheral surface area, thereby significantly reducing undesirable outward heat loss through the vertically extending furnace housing side walls upon burner shut off and increasing the overall efficiency rating of the furnace. The small diameter, serpentined transfer tubes create a significant flow restriction within the heat exchanger to thereby increase heat transfer to the continuing supply air flow through the furnace after burner shut off. The reduced mass of the heat exchanger, compared to conventional clamshell heat exchangers, also desirably lessens its cold start up "dwell time" to inhibit internal heat exchanger corrosion. A pilot bypass system is provided to inhibit internal heat exchanger corrosion potentially caused by the continuously generated combustion products of a standing pilot flame within the furnace housing by venting such combustion products directly through the draft inducer fan outlet section and into the exhaust flue, thereby bypassing the heat exchanger, during idle periods of the furnace.
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