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Modulating furnace having improved low stage characteristics

  • US 6,283,115 B1
  • Filed: 07/31/2000
  • Issued: 09/04/2001
  • Est. Priority Date: 09/27/1999
  • Status: Expired due to Term
First Claim
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1. An improved gas-fired induced-draft furnace which has a low, a medium and a high firing rate, said furnace being of the type which includes a burner, a circulating air blower for establishing a flow of circulating air, an inducer blower for establishing a flow of combustion air, and a heat exchanger having a boundary wall, and which is adapted to operate in conjunction with temperature sensing means for sensing the temperature of a space to be heated and generating call-for-heat signals that correspond to one of said high, medium, and low firing rates;

  • comprising;

    gas flow control means for controlling the rate at which gas is supplied to said burner, said gas flow control means serving to supply gas to said burner at one of said high, medium and low firing rates;

    pressure sensing means for generating one or more differential pressure signals that vary in accordance with the pressure across said heat exchanger;

    furnace control means, responsive to said differential pressure signals and to said call-for-heat signals, for;

    (i) controlling the rate at which said gas flow control means supplies gas to said burner;

    (ii) applying, to said circulating air blower, blower control signals which cause said circulating air blower to establish circulating airflows having magnitudes which correspond to said high, medium and low firing rates;

    (iii) applying, to said inducer blower, inducer control signals which cause said inducer blower to establish combustion airflows having magnitudes which correspond to said high and low firing rates;

    wherein the magnitudes of the combustion airflows which are established by said inducer blower during steady state operation of the furnace at said low and medium firing rates are so related to one another, and to the magnitudes of the circulating airflows which are established by said circulating air blower during steady state operation of said furnace at said low and medium firing rates, that all parts of said wall remain at temperatures high enough to prevent cold spot corrosion.

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