Warm up method for two stage furnace

• US 5,326,025 A
• Filed: 07/08/1993
• Issued: 07/05/1994
• Est. Priority Date: 07/08/1993
• Status: Expired due to Term

• Current Assignee: Carrier Corporation (Carrier Global Corporation)
• Original Assignee: Carrier Corporation (Carrier Global Corporation)
• Inventors: Thompson, Kevin D., Dempsey, Daniel J.
• Primary Examiner(s): Tanner, Harry B.
• Application Number:
  US08/089,792
• Time in Patent Office: 362 Days
• Field of Search: 236/11, 236/10, 236/1 E, 236/1 EA, 236/1 EB, 236/46 E, 236/DIG. 9, 165/12
• US Class Current: 236/11
• CPC Class Codes: F23N 2227/06 Postpurge
• CPC Class Codes: F23N 2229/00 Flame sensors
• CPC Class Codes: F23N 2233/08 with variable speed
• CPC Class Codes: F23N 2235/14 electromagnetically operated
• CPC Class Codes: F23N 2237/10 High or low fire
• CPC Class Codes: F23N 5/203 using electronic means
• CPC Class Codes: F24H 15/254 Room temperature
• CPC Class Codes: F24H 15/345 Control of fans, e.g. on-off control control of fans of heat pump units F24H15/375
• CPC Class Codes: F24H 15/36 of burners
• CPC Class Codes: F24H 9/0036 Dispositions against condensation of combustion products
• CPC Class Codes: F24H 9/2085 using fluid fuel
• CPC Class Codes: Y10S 236/09 Fan control

Abstract

A two-stage furnace is operable at a high fire full rate mode and at a low fire partial rate mode when there is a call for high heat or low heat, respectively. In order for the furnace to be less prone to vent gas condensate formation when operating at low fire, and to permit the heat exchanger and vent pipe to reach equilibrium as soon as possible on both low fire and high fire, a shorter blower-on delay is provided for high fire and longer blower-on delay is provided on low fire.

Claims

1. In a furnace for supplying circulating heated air to an interior comfort space and in which at least one burner sends heated combustion products through a heat exchanger which are exhausted therefrom through an exhaust vent to an outside environment, the burner being actuable into a high-fire full heat mode, a low-fire partial heat mode, and shut off;

a circulation blower is operative to force return air drawn from said comfort space through said heat exchanger to absorb heat from said combustion products, from where the air is returned as heated circulation air to said comfort space;

controller means responsive to a thermostat in said comfort space and operative to select a call for low heat or a call for high heat depending on heating conditions in said comfort space, including means for actuating said at least one burner at said high-fire mode when there is a call for high heat and at said low-fire mode when there is a call for low heat, and for shutting off said at least one burner when said thermostat is satisfied; and

blower delay timer means for delaying energization of said circulation blower by a first predetermined delay period after actuation of said at least one burner into said high-fire mode to permit the vent gases to heat up suitably before said blower forces said return air therethrough;

the improvement wherein said blower delay timer means is operative for delaying energization of said circulation blower by a second time delay period, longer than said first time delay period, after actuation of said at least one burner into said low-fire mode to permit said vent gases to heat up suitably under low heat operation before said blower forces said return air therethrough.

2. The improved furnace according to claim 1 wherein said at least one burner is supplied with a fuel gas, and said furnace includes a flame sensor that proves flame from said at least one burner to commence operation of said blower delay timer means.

3. The improved furnace according to claim 1 wherein said heat exchanger includes a primary heat exchanger stage receiving the combustion products from said at least one burner, and a secondary condensing heat exchanger stage following said primary heat exchanger stage, and wherein an inducer following said secondary stage induces flow of said combustion products through said heat exchanger.