US3090423A

US3090423A - Gas burner control

Info

Publication number: US3090423A
Application number: US735165A
Authority: US
Inventors: Claude M Garner; Jr John C Atterbury
Original assignee: White Rodgers Co
Current assignee: White Rodgers Co
Priority date: 1958-05-14
Filing date: 1958-05-14
Publication date: 1963-05-21
Anticipated expiration: 1980-05-21

Description

May 21, 1963 C. M. GARNER ETAL 3,090,423

GAS BURNER CONTROL Filed May 14, 1958 2 Sheets-Sheet 1 FIG. 2

INVENTORS LAUDE M GARNER SOHN C ATTERBURY JR THEIR AGENT C. M. GARN AL 3,090,423 GAS BURNER CONTROL 2 Sheets 5 2 V I 54 42 3 62 38 I 6 ATTERBURY JR.

BYWZ

THEIR 'AGEN United States Patent 3,090,423 GAS BURNER CONTROL Claude M. Garner, Clayton, and John C. Atterbury, .lr.,

Richmond Heights, Mo., assignors, by mesne assignments, to White-Rodgers Company, a corporation of Missouri Filed May 14, 1958, Ser. No. 735,165 4 Claims. (Cl. 158-125) This invention relates to controls for gaseous fuel burners, and more particularly to means for automatically operating the burner in an on and off manner over a wide range of heat output rates while maintaining high thermal eificiency of the burner.

It is customary to control the flow of gas to a burner by means of a valve spaced at some distance from the burner and to provide a restricting orifice posterior to the valve and at the base or inlet to the burner mixing tube in order to create a relatively high-velocity fuel stream or jet for aspirating combustion air into the burner tube. In this arrangement if the fuel flow is throttled at the valve in order to effect a reduction in the heat output rate of the burner, the pressure on the upstream side of the fuel orifice and, consequently, the velocity of the fuel jet will be reduced.

It has been found that any substantial variation in the velocity of the aspirating fuel jet afieots the quality of the burner flame. As the velocity of the fuel jet is increased over the optimum for a given burner design, the air-fuel mixture becomes leaner and the burning rate slower until a point is reached wherein the flame lifts from the burner port. On the other hand, as the velocity is reduced below the optimum, the flame becomes soft and yellowish indicating insuflicient combustion air, and when the point is reached wherein the velocity of the air-fuel mixture falls below the rate of flame propa gation, the flame will drop back and burning may occur at the orifice. If, however, the fuel flow to the burner port is varied by varying the effective area of the restricting orifice, the flame volume, and consequently burner heat output, may be varied over a wide range with out these objectionable results.

The present invention has for an object the provision of an automatic control system for gas-fired clothes dryers which operates the burner at full heat output capacity until a predetermined temperature is reached and thereafter operates the burner at a reduced heat output rate.

A further object is to provide a control for gas burners wherein a fuel metering orifice at the base of the burner determines the heat output rate of the burner and a temperature responsive valve spaced anteriorly of the burner controls operation of the burner in an on and off manner as the temperature of the space being heated falls below or rises above a preselected temperature, and wherein additional means responsive to the temperature of the space reduces the effective area of the fuel metering orifice as the temperature of the space, when being heated, approaches the preselected temperature.

A further object is the provision of an automatic control system for gas-fired clothes dryers in which a high temperature thermostat operates the burner at a reduced heat output rate and a low temperature thermostat increases the heat output rate of the burner, and in which means is provided to maintain the higher heat output rate of the burner, once it is initiated, until the high temperature thermostat responds to cut off operation of the burner.

These and further objects and advantages will become apparent when reading the following description in connection with the accompanying drawings.

In the drawings:

FIG. 1 is a plan view of a gas burner having associated therewith fuel metering and control valve mechanism constructed in accordance with the present invention;

FIG. 2 is an enlarged sectional view taken on line 2-2 of FIG. 1;

FIG. 3 is an enlarged sectional view taken on line 3-3 of FIG. 1;

FIG. 4 is a still further enlarged fragmentary detail view of the fuel orifice and metering needle;

FIG. 5 is a cross-sectional view taken on line 55 of FIG. 4; and

FIG. 6 is a diagrammatic view of the entire control system.

Referring to the drawings in more detail, the numeral 10 generally indicates a main gas burner to which a combination dual valve and metering device generally indicated at 12 and a pilot burner generally indicated at 14 are attached by means of a bracket 16. The bracket 16 also serves as a means of rigidly mounting the burner and fuel control assembly in an appliance such as a clothes dryer. The dual valve and fuel metering device includes an elongated, hollow valve body 18 having an axial fuel inlet 20 at one end, a lateral main burner fuel outlet 22 at the other end, and a lateral intermediate pilot burner outlet 24. The hollow valve body is divided by partitions into three chambers, namely, the fuel inlet chamber 26, an intermediate chamber 23 from which fuel flows to the pilot burner through the outlet 24, and a main outlet chamber 30 from which fuel flows to the main burner through the outlet 22. The inlet and

intermediate chambers

26 and 28 are in communication through a port 32, and the intermediate and

outlet chambers

28 and 30 are in communication through a port 34. The ports 32 and 34 are provided with valve seats 36 and 38, respectively.

A pair of

valves

40 and 42 are provided for cooperation with the valve seats 36 and 38, respectively. The

valves

40 and 42 are normally biased on their respective seats by springs 44 and 46, and are opened by

solenoid actuators

48 and 50, respectively, when these actuators are energized. The solenoid actuators each comprise a winding, 'a central sleeve open at its lower end, and a plunger arranged for reciprocation in the sleeve and having one of the valves attached to its lower end. These elements of the solenoid actuators are respectively designated as 48a, 48b, and 480, and 50a, 50b, and 500. i

The main burner .10 comprises an elongated mixing tube 52 with an enlarged cylindrical chamber 54 at its base which has an axial opening 56 for the introduction of fuel and lateral ports 58 for admission of air. An adjustable sleeve 60 is provided for varying the area of air ports 58. A short tube 62 is provided for conducting fuel from fuel outlet 22 to the base of burner 10. The tube 62 is in axial alignment with outlet 22 and is attached at one end in any suitable manner to one side of the valve body. The other end of tube 62 is necked down and internally threaded to receive a threaded orifice plug 64 having an orifice 64a. The necked down end of tube 62 and the orifice plug 64 enter the axial opening 56 and extend into the base portion 54 of the main burner.

The valve body 18 is provided with an aperture 6-6 in the wall opposite to and in axial alignment with the outlet 22. The aperture 66 is counterbored and threaded to receive in threaded engagement a solenoid actuator 68. The actuator 68 is provided with the usual winding 68a, central guide sleeve 63b, and plunger 63c arranged to reciprocate in the guide sleeve. Attached at one end to the solenoid plunger 63c and extending in axial alignment therewith is a metering rod 70 which extends transversely through the valve body, through the tube 62, and into the orifice plug 64-. The orifice plug 64 has a tapered bore '72, and one end of the rod 70 is provided Patented May 21, 1963 S with a tapered point of which the included angle is slightly less than the included angle of the tapered bore 72 The end of rod 79 is additionally provided with flat surfaces 74, as indicated in FIGS. 4 and 5, so that when the tapered end of rod 74 is seated at the intersection of orifice 64a and tapered bore 72, there will be two passages, one on each side of the rod 70. The fiat surfaces '74 diverge inwardly from the end of rod 7% at such angle as to effect substantially the same percentage of flow reduction through the orifice 6411 when orifice plugs having larger or smaller diameter orifices are substituted. It is necessary to vary the diameter of orifice 64a to compensate for fuels of different calorific values, and the foregoing arrangement provides for maintaining the same percentage of reduction in heat output of the burner for fuels of different heat value as the rod 70 is moved from its withdrawn position of FIG. 3 to its seating position on line -5 of H6. 4. The rod 70* is further provided with a collar 76 at its other end, against which a spring 78 bears so as to bias the rod in a seated position when the solenoid 68 is tie-energized. When solenoid 68 is energized, the rod 79 is retracted from the orifice plug, thereby to permit the maximum passage of fuel through the straight bore portion of the orifice.

Having described the fuel control valves and fuel metering device, the arrangement and operation of the entire control system as diagrammatically illustrated in FIG. 6 will now be described. In addition to the main and pilot burners and 14, respectively, and the dual valve and metering device 12, the system further includes as primary elements a low-temperature space thermostat 82 which opens on a rise in temperature a high-temperature space thermostat 84 which opens on a rise in temperature an electrical resistance igniter coil 36, an igniter transformer 88, a flame sensitive switch 90 sensitive .to

flame at the pilot burner, current reducing

resistors

92 and 94, and a three-position manual selector switch 96 comprises a rotatable switch generally indicated at 96. The switch blades 98 and 100, both fixed on a rotatable shaft 102, and therefore they rotate in unison as the shaft 102 is manually rotated. The three positions of switch 96 are indicated as H for high fire, L for low fire, and A for automatic operation, or more specifically, for an automatic sequence of operation in which the burner initially operates at high fire and continues to operate in this manner, regardless of the response of low temperature thermostat 82, until the space being heated has attained a predetermined temperature, and thereafter operates in an on-and-oif manner at low fire under control of the high temperature thermostat to maintain this temperature. This method of burner operation is particularly useful in a clothes dryer wherein it is desirable to heat the load from room temperature to a predetermined drying temperature as quickly as practical, whereafter the heating load diminishes as the moisture evaporates from the :wet clothes and the drying temperature can readily be maintained on low fire.

Terminals 104 and 106 are provided for connection to a power source such as 110 volt, 60 cycle, A.C., and a line switch 108 is provided for primary control of the circuits which energize the electrically operated components. The winding 43a of solenoid actuator 48 is connected across the terminals 1ti4'106 as follows: a lead 110, line switch 108, a lead :112, a lead 114, Winding 48a, a lead 116, a lead 118, the flame sensitive switch 90 (when in the cold, solid line position shown), and a lead 120. When flame sensitive switch 90 moves to its hot dotted line position in response to the presence of a pilot flame, a partial energization of winding 48a is maintained through the resistor 92, which is connected in parallel with the cold side contacts of switch 90. This amount of energization is sufficient to hold the valve 40 in an open position once the solenoid plunger is in an attracted position, but is insufiicient'to attract the solenoid plunger from its de-energized position and thereby move the valve from a closed to an open position,

When selector switch '96 is in high fire position H, solenoid actuator winding 50a is connected across the terminals 164-166 as follows: lead 110, switch :108, lead 112, switch blade 98, contact H, a lead 122, high temper-attire thermostat 84, a lead 124, a lead 126, winding 50a, a lead 128, a lead 130, flame sensitive switch (when in hot, dotted line position), and lead When selector switch 96 is in low fire position L, solenoid actuator winding 50a is connected across the terminals 104106 as follows: lead 110, switch 108, lead 112, switch blade 98, contact L, a lead 132, a lead 134, low temperature thermostat 82, a lead 136, a lead 138, lead 126, winding 50a, lead 123, lead 130, flame sensitive switch 90 (when in hot, dotted line position), and lead 120.

When selector switch 96 is in automatic position A, solenoid actuator winding 50:; is connected across the power source terminals 104-106 in the same manner as when selector switch 96 is in high fire position H, due to the provision of a lead which connects selector switch contact A of the lefthand switch section to the lead 122.

When selector switch 96 is in high fire position H, the metering pin actuator winding 68a is connected across the terminals 104-406 as follows: lead 110, switch 108, lead 112, a lead 142, switch blade 100, a lead 144, winding 68a, lead 130, flame sensitive switch 90 (when in a hot, dotted line position), and lead 120.

When selector switch 96 is in a low fire position L, the just described circuit for the metering pin actuator winding 68a is broken by movement of selector switch blade 160 to L position.

When selector switch 96 is in automatic position A," the metering pin actuator winding 68a is connected across terminals 104106 as follows: lead 110, switch 108, lead 112, blade 98 and contact A of switch 96, lead 140, lead 122, high temperature thermostat 84, lead 124, lead 138, lead 136, low temperature thermostat 82, lead 134, lead 132, lead 146, contact A, blade 100, lead 144, winding 68a, lead 130, flame sensitive switch 90 (when in a hot, dotted line position), and lead 120'. Metering pin actuator winding 68a is also connected across the power source when in A position through a resistor 94, which is connected in parallel with the low-temperature thermostat 82. The resistance of winding 94 is such as to provide suflicient energization of winding 68a to hold in the metering pin 70 in a retracted position once it has been moved there, but is insuflicient to retract the pin from its normally biased position in the orifice 64.

The igniter transformer 88 is connected across terminals 104106 as follows: lead 110, switch 108, lead 112, lead 148, the transformer primary winding 88a, lead 150, flame sensitive switch 90 (when in a cold, solid line position), and the lead 120.

Operation When it is desired to operate the burner at high fire, the selector switch 96 is rotated to position H. Upon closure of line switch 108, the solenoid winding 48a will be energized through the cold side contact of flame sensitive switch 90. This will effect opening of the valve 48 and admit fuel through outlet 24 to pilot burner 14. At the same time, igniter transformer primary 88a will be energized through the described circuit, which includes switch 90 in a cold position, and will effect ignition of fuel issuing from the pilot burner. When flame sensitive switch 90 responds to the presence of flame at pilot burner 14, it moves from its cold, solid line position to its hot, dotted line position thereby breaking the igniter circuit at lead and the circuit for solenoid winding 48a at lead 118. Valve 40 will remain open, however, to supply fuel to the pilot burner due to the described shunt resistor 92. The movement of switch 90 to its dotted line position completes the described circuit for the solenoid winding 50a extending through selector switch blade and contact H, and through the high temperature thermostat 84. The main burner will now continue to operate at full output under the on and off control of high-temperature thermostat 84.

If for any reason the electrical power source is interrupted during operation of the main burner, both

valves

40 and 42 will close immediately, thereby extinguishing both pilot and main burner. Even though the power interruption be only momentary with a full restoration of power in a matter of a few seconds, and before the flame sensitive switch 90 has had time to respond to the no-fiame condition to break the energizing circuit for main burner valve winding 50a, fuel will not again be permitted to fiow to the main burner, or the pilot burner for that matter, until the flame sensitive switch 90 has had time to move to its cold, solid line position in which energization of the igniter 88 is again completed. This power failure, safety feature is set forth in more detail in the application of Claude M. Garner, Serial No. 648,174 filed March 25, 1957, now abandoned for Burner Control System.

When it is desired to operate the burner at low fire, the selector switch 96 is rotated to position L. This action breaks the energizing circuit for the metering pin actuator winding 68a at switch blade 100 and contact and permits metering pin 70 to be seated in the orifice plug 64, thereby reducing the flow of fuel to the main burner. At the same time, switch blade 98 is moved to position L so as to connect the main burner valve winding 50a through the low temperature thermostat 82 via lead 132. The burner will now continue to operate in an on and olf manner at a reduced heat output rate under control of the low-temperature thermostat 82.

When it is desired to initially operate the burner at high fire when the heating load is heavy and then automatically efiect a reduction in heat output rate when a desired temperature is reached, the selector switch 96 is moved to position A. When the selector switch is in this position, main burner valve winding 50a is connected through the high temperature thermostat 84 via switch blade 98, contact A and the lead 140, and metering pin actuator winding 68a is connected through the high-temperature thermostat 84, the low-temperature thermostat 82, and the parallel resistor 94. When operation of the burner is initiated, the metering rod 70 is retracted and the burner operates at high fire. When the temperature of the space to which the

thermostats

82 and 84 are sensitive reaches the point wherein low-temperature thermostat 82 opens, the electrical current through winding 68a will be limited by the resistor 94. The value of resistor 94 is such as to permit sufficient energization of winding 68a to hold the metering rod 70 retracted, but not suflicient energization to effect its withdrawal from a seated position in orifice 64. The burner will therefore continue to operate in an on and off manner under control of thermostat 84 at a high heat output rate until a higher space temperature is reached at the high-temperature thermostat 84 opens.

When high-temperature thermostat 84 opens, the circuit therethrough for energization of winding '68:: is broken and pin 70 drops into its seat in orifice 64, so that when the thermostat 84 again closes, the burner will be operated at a low heat output rate. If, however, the heating load again increases to the point wherein the space temperature drops under the low heat output to a point wherein the low-temperature thermostat 82 again closes, the circuit for winding 68a will again be completed and the burner will again operate at a high heat output rate.

We claim:

1. In a burner control system, a burner, a fuel supply conduit to said burner, first and second electromagnetically operated valves in said supply conduit arranged in series, said first valve being operative between fully open and fully closed positions and said second valve being operative between fully open and partially closed positions, said first valve having a normally fully closed position when de-energized and said second valve having a normally partially closed position when de-energized, and when in said partially closed position being effective to restrict the flow of fuel to the burner, a source of power, an energizing circuit for said valves including a first, high-temperature thermostat responsive to a drop in the temperature of the space being heated below a first, predetermined point to close and complete the energization and effect the opening of said first valve and a second, low-temperature thermostat responsive to a drop in the temperature of the space being heated below a second, lower, predetermined point to close and complete the energization and opening of said second valve but only if said first, high-temperature thermostat is closed, the circuit arrangement being such that said first valve is connected across the source of power through said first,

high temperature thermostat and said second valve is connected across the source of power through said first and second thermostats in series, and a current limiting conductor connected across said second, low-temperature thermostat, said current limiting conductor having such resistance value as to permit suificient energization of said second electromagnetically operated valve when said second thermostat is open to hold said valve open once it is open, While, on the other hand, restricting energi zation sufficiently when said second thermostat is open to prevent actuation of said second valve from its normal partially closed position to its fully open position, whereby when the space is being heated from a cold condition the maximum flow of fuel to the burner will persist until the space temperature has reached the point wherein said first, high-temperature thermos-tat opens, even though said second, low-temperature thermostat has previously opened at a lower space temperature.

2. In a control system for clothes dryers operable automatically to supply heat at a high rate to the dryer until a predetermined dryer temperature is reached and thereafter to supply heat in an on-and-off manner at a lower rate, an electrically operated heat producer operable at a high heat output rate and at a low heat output rate, a high temperature open-on-rise thermostat which when closed effects operation of the heat producer at a low heat output rate, a low temperature open-on-rise thermostat which when closed increases the heat output rate of the heat producer to its high heat output rate, and holding means rendered operative upon closure of said high temperature thermostat and rendered inoperative only upon the opening of said high temperature thermostat to maintain operation of said heat producer at a high heat output rate once such rate of operation is initiated by the closing of said low temperature thermostat.

3. In a control system for clothes dryers operable automatically to supply heat at a high rate to the dryer until a predetermined dryer temperature is reached and thereafter to supply heat in an on-and-olf manner at a lower rate, an electrically controlled heat producer operable at a high heat output rate and at a low heat output rate, a high temperature open-on-rise thermostat and a low temperature open-on-rise thermostat, said thermostats being responsive to a space being heated by the heat producer, a first circuit completed through said high temperature thermostat for effecting operation of said heat producer at a low heat output rate, means including an electromagnetically operated device which when energized increases the output rate of said heat producer to a high heat output rate, a branched circuit under the control of said high temperature thermostat and completed through said low temperature thermostat for energizing said electromagnetic device, and a holding circuit shunting said low temperature thermostat, said holding circuit including impedance of such value as to reduce the magnetomotive force developed by said electromagnetic device to a value which is suificient to hold said electromagnetic device in an energized position once it 7 has been moved there but is insufficient to operate said device from its rile-energized to energized position, whereby operation of said heat producer at a high heat output rate is maintained once it is established until said high temperature thermostatropens irrespective of the position of said low temperature thermostat.

4. In a burner control system for clothes dryers operable automatically to supply heat at a high rate to the dryer until a predetermined dryer temperature is reached and thereafter to supply heat in an on-and-otf manner at a lower rate, a burner, a fuel supply conduit to said burner, first and second electromagnetically operated valves in said supply conduit arranged in series, said first valve being operative between fully open and fully closed positions and said second valve being operative between fully open and partially closed positions, said first valve having a normally fully closed position when tie-energized and said second valve having a normally partially closed position when de-energized, and when in said partially closed position being effective to restrict the flow of fuel to the burner, a first, high temperature thermostat responsive to a drop in the temperature of a space being heated below a first, predetermined point to efiect energization and opening of said first valve and a second, low temperature thermostat responsive to a drop in the temperature of the space being heated below a second,

lower, predetermined point to efiect the energization and opening oi said second valve, and holding means rendered operative when said high temperature thermostat is in a closed position for holding said second valve open once it has been opened, whereby said burner is operated constantly at a high heat output rate irrespective of the position of said low temperature thermostat until the temperature of the space being heated attains said first predetermined temperature and said high temperature thermostat opens.

References Cited in the file of this patent UNITED STATES PATENTS 742,990 Humphrey Nov. 3, 1903 1,602,206 Possons Oct. 5, 1926 1,819,560 Klees Aug. 18, 1931 2,109,862 Kriechbaurn Mar. 1, 1938 2,164,511 Furlong July 4, 1939 2,223,283 Grant et al. Nov. 26, 1940 2,266,563 McCorkle Dec. 16, 1941 2,286,296 McGrath June 16, 1942 2,494,737 Borst Jan. 17, 1950 2,820,130 Dodson .Jan. 14, 1958 2,824,605 Dolby Feb. 25, 1958 2,884,009 Hetherington Apr. 28, 1959 2,978,228 Carlson Apr. 4, 1961

Claims

1. IN A BURNER CONTROL SYSTEM, A BURNER, A FUEL SUPPLY CONDUIT TO SAID BURNER, FIRST AND SECOND ELECTROMAGNETICALLY OPERATED VALVES IN SAID SUPPLY CONDUIT ARRANGED IN SERIES, SAID FIRST VALVE BEING OPERATIVE BETWEEN FULLY OPEN AND FULLY CLOSED POSITIONS AND SAID SECOND VALVE BEING OPERATIVE BETWEEN FULLY OPEN AND PARTIALLY CLOSED POSITIONS, SAID FIRST VALVE HAVING A NORMALLY FULLY CLOSED POSITION WHEN DE-ENERGIZED AND SAID SECOND VALVE HAVING A NORMALLY PARTIALLY CLOSED POSITION WHEN DE-ENERGIZED, AND WHEN IN SAID PARTIALLY CLOSED POSITION WHEN DE-ENERGIZED TO RESTRICT THE FLOW OF FUEL TO THE BURNER, A SOURCE OF POWER, AN ENERGIZING CIRCUIT FOR SAID VALVES INCLUDING A FIRST, HIGH-TEMPERATURE THERMOSTAT RESPONSIVE TO A DROP IN THE TEMPERATURE OF THE SPACE BEING HEATED BELOW A FIRST PREDETERMINED POINT OF CLOSE AND COMPLETE THE ENERGIZATION AND EFFECT THE OPENING OF SAID FIRST VALVE AND A SECOND, LOW-TEMPERATURE THERMOSTAT RESPONSIVE TO A DROP IN THE TEMPERATURE OF THE SPACE BEING HEATED BELOW A SECOND, LOWER, PREDETERMINED POINT TO CLOSE AND COMPLETE THE ENERGIZATION AND OPENING OF SAID SECOND VALVE BUT ONLY IF SAID FIRST, HIGH-TEMPERATURE THERMOSTAT IS CLOSED, THE CIRCUIT ARRANGEMENT BEING SUCH THAT SAID FIRST VALVE IS CONNECTED ACROSS THE SOURCE OF POWER THROUGH SAID FIRST, HIGH TEMPERATURE THERMOSTAT AND SAID SECOND VALVE IS CONNECTED ACROSS THE SOURCE OF POWER THROUGH SAID FIRST AND SECOND THERMOSTATS IN SERIES, AND A CURRENT LIMITING CONDUCTOR CONNECTED ACROSS SAID SECOND, LOW-TEMPERATURE THEMOSTAT, SAID CURRENT LIMITING CONDUCTOR HAVING SUCH RESISTANCE VALVE AS TO PERMIT SUFFICIENT ENERGIZATION OF SAID SECOND ELECTROMAGNETICALLY OPERATED VALVE WHEN SAID SECOND THERMOSTAT IS OPEN TO HOLD SAID VALVE OPEN ONCE IT IS OPEN, WHILE, ON THE OTHER HAND, RESTRICTING ENERGIZATION SUFFICIENTLY WHEN SAID SECOND THERMOSTAT IS OPEN TO PREVENT ACTUATION OF SAID SECOND VALVE FROM ITS NORMAL PARTIALLY CLOSED POSITION TO ITS FULLY OPEN POSITION, WHEREBY WHEN THE SPACE IS BEING HEATED FROM A COLD CONDITION THE MAXIMUM FLOW OF FUEL TO THE BURNER WILL PERSIST UNTIL THE SPACE TEMPERATURE HAS REACHED THE POINT WHEREIN SAID FIRST, HIGH-TEMPERATURE THERMOSTAT OPENS, EVEN THOUGH SAID SECOND, LOW-TEMPERATURE THERMOSTAT HAS PREVIOUSLY OPENED AT A LOWER SPACE TEMPERATURE.