INTEGRATED CONTROL SYSTEM USING ~ MICROPROCESSOR
BACKGROUND OF THE INVENTION
Even though prior art heating and cooling apparatuses had fuel valve controls, plenum air temperature sensors, air circulatin~ fans, induced draft blowers for the exhaust gases of a furnace, ignition and flame sensor appaxatus for proving that the ignition of the fuel in the burner takes place, and many other parameter sensors, all of which were 10 a part of a control system or a furnace or ai.r conditioning .~
co~pressor supplying heated or cooled air to a space in wnlch a thermostat was contained, there has ~een a continual need fo.r improvement in such control systems. With the advent of increased ener~y costs, an even greater demand has been s~own for more efficient heating and cooling appaxatuses and sy,stems, especially for homes and dwellings wherein an individual :Eurnace and air conditioning system suppli.es the heated or cooled air to the home as required.by a space thermostat.
Coincidental with the increased cost of energy, the advent of low cos~ microprocessors has made it possible for the gathering of parameter data and the control of various components of a control system in many new manners which provide the long-awaited increased efficiency and thus cost saving in the operation of a furnace and air conditioning apparatus~
SUMMARY OF THE PRESENT INVENTION
The present invention is concerned with the prevention or reduction in the amount of flame "roll out" and thus to provide a longer time to prove the ignition of a gas flame.
By the operation of the induced draft blower durin~ the initial start up of the furn~ce at a high speed and the operation of the gas valve at a low fuel flow stage, the air to fuel ratio is maintained high during the ignition period of the fuel to avoid the roll out condition. After flame is proven, the gas flow can be at a high rate for the initial heating of the furnace to prevent rusting due to condensation and then a reduction of the fuel flow to low fire with a low induced draft blower speed for regular operation.
In accordance with the present invention there is provided an improvement :in a control system for a furnace having a multispeed induced draft blower, a multistage gas control valve means for furnishing gas to a burner with a predetermined air to fuel ratio, and a gas ignition apparatus, the improvement comprising, means, upon the starting of an operation of the furnace, for energizing said induced draft blower at a speed to provide a large amount of air to the combustion chamber of the furnace and for energizing said gas valve for providing a low gas flow into said combustion chamber so that the air -to gas ratio .is higher than normally maintained so that upon said means energizing said gas ignition apparatus to ignite the gas of the burner, the gas in the combustion chamber is not ignited and "roll out" of the combustion flame is minimized even after long ignition delays.
In accordance with the present invention there is further provided in a method of controlling the operation of a gas fired furnace having an induced draft blower for inducing the air flow into the combustion chamber and out through an exhaust stack at various rates and a fuel valve for admitting fuel to a~ burner in the combustion chamber at a low rate and ~3f~37 a high rate ha~ing the following steps upon the call for operation of the furnace by a space temperature responsive means, energizing the induced draft blower means at a high rate to provide an excessive amount of air into the combustion chamber, energizing the gas valve furnishing gas to the burner at a low fuel flow rate whereby a normal air to fuel ratio e~ists at the burner and a high air to fuel ratio exists in the combustion chamber downstream of the burner, igniting the fuel at the burner wherein a normal air to fuel ratio exists, sensing the presence of a flame and thus the combustion of the fuel in the combustion chamber, and upon the presence of combustlon, operat-ing the blower means at its low rate.
Brief Description of the Drawings The invention is shown in the enclosed drawings of which:
Figure 1 is a schematic showing of a conventional forced air heating and cooling system~
Figure 2A to 2D (~our) disclose the circuit diagram of a control module connecting the various components of the system to a microprocessor to provide the integrated control system.
E'igure 3 is a composite of Figures 2A to 2D.
Description of the Preferred Embodiment of the Invention _ Referring to Figure 1, a conventional temperature con-ditioning apparatus or furnace 10 is shown. The furnace receives fuel to a burner 9 from a gas source connected to pipe 11 and the fuel supply is controlled by a gas valve 12. The air to fuel ratio of the burner is normally fi~ed by the manufacturer's design. Gas valve 12 of a variable capacity may be of several types such as the VR854 for two s-tage direct spark con-trol and the VR852 for two stage intermitteni pilot control, both made and s~ld by Honeywell ~nc. and shown in brochure 60-2447-2 of May 1980. The gas is ignited and a - 2a -~3~
flame is sensed by a conventional igniter and flame sPnsor 13 such as the Q354 made and sold by Honeywell Inc. and sho~rn in brochure 60~2053-8 of July 1980. The e~haust gases from the furnace combustion chamber 81 downstream of burner 9 are forced out of a stack 14 by a blower 15 to provide an induced draft blower (IDBI furnace. Blower 15 is driven by a conventional shaded pole 120 volt A.C. motor having a Hall effect sensor mounted on the motor shaft to provide a pulse each revolution for a speed sensor and control circuit.
The temperature in the bonnet or plenum is sensed by a temperature responsive element 20 such as a C800 Platinum resinate sensor made and sold by Honeywell Inc. and shown in brochure 60-2484-1, Nov. 1979. Temperature condl~ioned rnedium or air is circulated through the plen~m from a return . .. .
duct to the space 21 by blower 22 in a conventior,al manner or by a circulator sump for a hydronic system. The temperature responsive element or thermostat 23 such as a T87F thermostat made by ~oneywell Inc. is located in the space connected to controls fox the furnace. A conventional refrigeration compressor or heat pump 26 has an outdoor heat exchanger or coil 27 and an indoor heat exchanger or coil 28. A fan driven by motor 29 removes heat from coil 27. Coil 28 is in the furnace plenum to deliver cool air during the air conditioning operation. Coils 27 and 28 have temperature sensors 36 and 37, respectively, of the C800 type. An integrated system control module 24 which is supplied with power from a transformer 25 connected to a source of power 30, has all of the mentioned apparatus connected thereto for controlling the furnace and compressor.
Referring to Figure 2, which is made up of ~ composite of Figures 2A to 2D, the schematic circuit of the integrated system control module 24 is shown in more detail. In Figure 2A, transformer 25, which is connected to the power source 30, supplies power to a conventional power supply 40 which has one output 41 connected to a timing signal generator 42, in Figur~
2D, which provides a 60 Hz signal available over conductor 43.
A thermostat 23 is connected over the six wire conductor 44 to the module 24.
The module 24 has a microprocessor 45 of a conventional type known as the 8049 microprocessor which is made and sold by several different companies such as Intel, National Semi Conductor, and Nippon Electric Company. The microprocessor which is shown in Figures 2C and 2D is programmed as shown in Appendix II. The microprocessor receives the signal from the timing signal generator 42 over conductor 43 at pin P14 shown in Figure 2E. Similarly, the output of the thermostat 23 is connected through switching circuit 50 over the input conductors 51 to the microprocessor at pins P10, Pll and P12.
The induced draft blower 15 has two connections to the control module 24 (see Figure 1). A first connection 52 is from the motor speed sensor in the blower which comprises a conventional Hall effect transducer for providing a pulse on each revolution of the motor shaft and thus providing a revolutions per minuke (rpm) signal or input 52. Two other colmections 53 and 54 which are shown in Figure 2G connect motor speed con-trol 55 of the control module to the induced draft blower motor. The motor speed control receives a signal over the conductor 60 from pin P26 of microprocessor 45.
Re~erri.ng to Figure 2B, an input is provided at 61 for a conventional analyzer which would be connected to a buffer 80 to the microprocessor for analyzing the operation of the system. Input circuit 62 connects plenum temperature responsive element or sensor 20. Input 63 connects a temperature responsive element or sensor 36 which senses the temperature of an air conditioning discharge coil when the refrigeration system is used. Input 64 connects temperature responsive element or sensor 37 from the indoor coil when the air conditioning system is used. Connection 65 is a common connection for many of the input circuits.
These sensors, that is the plenum sensor 20, air conditioning discharge sensor 36, air conditioning indoor coil sensor 37, are all connected to a conventional CMOS
multiplexer 69 (see Figure 2B) which provides an output over conductor 71 to a conventional analogue to digital dual slope con~erter 72 providing the input to terminals Tl and ALE of the microprocessor over conductors 72 of Figure 2D.
An optional selection circuit 73 is shown on Figure 2s which provides for different arrangements of the circuit to the multiplexer in accordance with a selection table I as Appendix I. The optional selection can be accomplished by making different circuit connections either by breaking jumpers or using conventional pins to make selected connections.
Referring to Figure 2C, a shift register 80 has an output at 81 connected to a safety switch r~lay 82 and Kl.
Referring to Figure 2D, input 90 provides the connection from the flame igniter and flame sensor 13 and is connected to the flame sensor circuit 91 of the type S825C made and sold by ~loneywell Inc. and shown in brochure 60-2053-8 of July 1980 for providing a xedundant signal over conductors 92 to the pins Pl3 and Pl5 of the microprocessor. Inputs 93, 94 and 95 are connected to the gas valve 12 and provide fox a control of the pilot valve and main valve (a multi or t~o stage control) S and high fire valve (see Figure 2I) when two stage burner operation is used. Output lOl and 102 for low speed and high speed operation are connected to a circulator for a hydronic system or circulation fan 22, Output 103 is connected to the ignitex 130 The ou~.put of the microprocessor from conductors 104 are eonnected to control a plurality of relays-K2, K3, K4~ KS and K6, which have associated contacts wi~h similar labels for controlling the various components connected to output circuits 94~ 95, lO0, lOl, 102 and 103.
-OPERATION OE' THE PREFERRE~D EMBO~IMENT OF THE INVEl\lTI~I
1 5 ~
Referring,to-Figure 1, when the space thermostat 23---calls for operation of the furnace, the induced draft blower 15 and the yas valve 12 are energized. With the normal fuel to air ratio, such a furnace is normally te~ted by Underwriters Laboratory to ensure that ignition of the burner takes place before the accumulation of gas is sufficient that the "roll out" of the burner occurs. "Roll out" is a result of the flame moving outside of the combustion chamber when a large accumulation of air and gas mixture downstream of the burner ignites. To ensure that such "rol] out" doesn't take ,place, especially where a longer time for ignition and the proving of the existence of a flame is desired, the blower is operated at a high speed to have an over abundance of air and the valve 12 is energized at a low fuel flow or first stage.
A normal (premixed) air to fuel ratio exists at the bu~ner by design 9; with excessive air ¢yreater than 100~ pro~ided by the induced draft blower, downstream of the burner in the combustion chamber 81, a high air to fuel ratio e~ists.
Ignition of the gas at the burner takes place in a normal manner, but since the air to fuel ratio downstrearn of the burner is high, the gas in that area does not ignite and "roll out" does not occur even after excessive ignition delays. Such lends itsel to direct ignition of the burner.
The accumulatlon of gas in the combustion chamber is then ~0 limited and with the excessive air, when ignition does take place, "roll out" of the flame is a minimum.
As soon as the flame proving apparatus 13 senses the presence of combustion, the speed of the induced draft blower: i.s left at high speed and the gas valve is operated at high fire ~second stage~ to ensure that the combustion chamber heats up as-fast as possi~le to minimize r~sting of the furnace by removing moisture from the furnace which is condensed by combustion products at the beginning of the combustion operation. After some predetermined time such as ninety seconds, when the combustion chamber is up to temperature, the gas valve 12 would be returned to the first stage of operation, or low fire, and the blower speed is reduced to its corresponding low speed (first stage of operation) to enhance efficiency.