US2289206A

US2289206A - Unit heater

Info

Publication number: US2289206A
Application number: US292903A
Authority: US
Inventors: Clarence W Nessell
Original assignee: Honeywell Inc
Current assignee: Honeywell Inc
Priority date: 1939-08-31
Filing date: 1939-08-31
Publication date: 1942-07-07
Anticipated expiration: 1959-07-07

Description

'July 7, 19,42. c. w. NEssEL-L 2,239,206 UNIT HEATER Fnedug. s1, 1959 (54 ,ss (sa 31,V soal 52' m W o 116/' h( 3g (No, l nvcnfor Clerenvce WZ Nessell mfom@ Patented .my 7, 1942- UNITED STATES, PATENT OFFICE UNIT HEATER. Clarence W. essell, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application August s1, 1939, serial No. 292,903

10 Claims.

My invention relates to the automatic control of heating appliances commonly known in the art as unit heaters, and is especially concerned with the control of high capacity' unit heaters wherein air is forced downwardly over the heating element. Heating units of this latter type are used more commonly in large industrial es` tablishments and the like where there are large spaces to be heated, and in order to do so with a small compact unit, it must be a high capacity heater with a high rate of air flow over the unit. Usually the airis directed downwardly and a high air velocity is used to insure that -the floor area is properly heated and that as wide a range as possible is covered,

The problem ofcontrolling a unit ofl the type described isa more or less specialized one, there being various limitations to be met. Due to the starting the unit from a temperature indicative that the unit has properly cooled down, and shutting down the unit in response to a discharge air temperature value indicative that the proper temperature of air being heated has been reached.

Another obj ect is to prevent excessive temperatures in high capacity unit heaters by starting an air circulating fan at the same time that heating is started, and terminating heatingfrom the temperature of air being heated.

Another object'is'to improve the eiciency andv render the operation of unit heaters more satisfactory by means of no vel control arrangements therefor. A

' Other objects will appear from the accompanying drawing' and detailed specification.

The single iigure of the drawing. represents high heating capacity of the unit, the air circulating means mustbe operated .whenever heating is in `progress to avoid damage to the unit from overheating. There is limited space for .application of controls to the units and for efliciency t there should be proper cycling operation, it being desirable that the unit cool of! after each cycle` before the next cycle is begun.

With my control arrangement, a cycle is started when the stack temperature indicates that the unit has cooled downsuitably' after the preceding cycle. An air circulating fan begins operating as soon as heating commences. Heating continues until the discharge temperature reaches a predetermined value at which'a switch opens. There is normally a deiiniterise in temperature of the air as it passes through a unit of the type described, an'd the said switch'is set to open at a temperature value equal to the desired space temperature plus the amount of the known lrise through the unit. Heating will terminate therefore when the air going to the v'unit reaches the desired space temperature. I provide for continued fan operation after heating has been terminated until the unit cools down considerably. An object of 'my invention is to provide improved control means for aheating unit wherein there is normally a deilnite rise in air temperatue through the unit, the control means shutting down the unit when the discharge air temperaarrangement of my invention applied thereto.

' The unit heater itselfis designated by numeral I0 on the drawing. It comprises a combustion chamber II having a stack I2 and an air jacket' or casing I3 enclosing the combustion chamber.

The clearance between the air jacket and the through and consequently a relatively high rate of heat transfer between the combustion chamber and the air being heated. For forcing a circulation of air through the air jacket Idprovide a fan I4 which is4 driven by an electric motor I5, the fan drawing air from the space which is to be heated and discharging it into the casing I3.

ture is at a value substantially equal to the desired temperature plus the amount of the rise through the unit.

Another object of the invention is to produce eicie'nt cycling operation of a unit -heater by 55 In the lower part of the combustion chamber is a gas burner I6 to which gas is supplied through a conduit I'I, there beingan electric control valve I8 interposed in the conduit I l. Adjacent the burner I6 is a small pilot burner I9 to which gas is continually fed through a tube 20 communicating with'the conduit I1 aheadof the valve I8. Numeral 24 designates a safety pilot of conventional type comprising a bimetal element 25 stack falls to a value which may be for example 110 for this particular unit and opens when the stack temperature has risen to 150. Another control device 33 is provided which comprises two

mercury switches

34 and 35 both of which are actuable by a helical thermostatic element 36 disposed in the discharge duct of the air casing I3. The mercury switch 35 closes upon a rise in -ternperature in the discharge duct t 110 for example and serves to control the fan lli as will presently be described. The mercury switch 34 normally acts to cut off the supply of gas to the burner, this switch opening at a temperature in the discharge duct of 180 for example, in this particular unit. Numeral designates an electrical relay comprising a winding 39 cooperating with an armature arranged to actuate switch blades 40, 4I and 42, the switch blades moving to the left when the winding 39 is energized, into engagement with xed electrical contacts 43, 44, and 45, respectively.

Power for the system is supplied by line conductors 46 and 41 there being a double pole single throw switch 48 controlling the power in the line conductors. Low voltage for operation of the relay 38 is provided by a transformer 49 which is of the step-down type having a primary winding 50 and secondary winding 5I, the primary winding having a greater number of turns than the secondary winding.

Due to the high capacity of the unit heater I0, there normally being a high velocity of air ow therethrough during operation, it is necessary that the fan be operating whenever heating is in progress in order to prevent the temperature of the heater from rising to excessively high values. Even momentary stopping of the fan while heating is in progress would be apt to cause the temperature to rise to such a high value as to damage the heater. With this unit heater the air normally experiences a definite rise in temperature as it passes through the heater, the rise in this particular unit being 110. In operation the unit is started from the switch 30, this switch closing at a temperature, as pointed out above, of 110, for example, which indicates that the heat generated during the previous operating cycle has nbeen substantially dissipated from the heater, the average temperature of the heater being around 90 when switch 30 closes. At the time that switch 30 closes, mercury switch 34 will be in closed position because at this time the air in the discharge duct has had an opportunity to fall to a value substantially below 180. 'Ihe primary of transformer 49 will therefore be energized through the following circuit: from line conductor 46, through a wire 52, wire 53, meraasaace switch 4I completes a. circuit for energizing and opening the valve I 0 as follows: from line conductor 46 through'wlre 62, switch blade Ill, iixed contact 44, wire 63, safety pilot 24, wire 6G, valve I 3, and wire back to line conductor il. As soon as valve I8 is opened heating commences and at the same time, by reason oi closure of switch 42 a circuit is completed for energizing the fan motor I5 as follows: from line conductor 40 through a wire 6G, switch blade 4Z, iixed contact 45, wire 6l, wire 68, motor l5, and wire 69 back to line conductor d?. Heated air being discharged through the discharge duct of the casing I3 will cause the thermostatic element 3S to operate in a direction tending to close mercury switch and at a temperature in the discharge duct of for example, for this particular unit, mercury switch 35 will close completing a circuit for the fan motor I5 which is independent of the relay 38, this circuit being as follows: from line conductor 136 through wire 52, wire l0, mercury switch 35, wire 'II, wire Sii, motor i5. and wire 69 back to line conductor ci'. Heating will continue until the temperature in the discharge duct reaches at which ternperature mercury switch 36 will be opened. Switch 3i opens at a stack temperature of 150 for example. After switch 3l has opened relay 38 will remain energized through its holding circuit but after relay 38 is deenergized it cannot be reenergized until the stack temperature has fallen enough to close switch 3l. When the temperature in the discharge duct is at this value the air in the spaces to be lheated has reached the desired value. That is, for example, ifit is desired that the space temperature be 70, when the air at this temperature is being admitted or forced into the unit by fan I 4 it will experience a rise of 110 in passing through the unit as pointed out above so .that its temperature in the discharge duct will be 180. When mercury switch 34 opens transformer 49 is deenergized thereby discontinuing the supply of power for relay 38 which causes deenergization of the relay. All of the circuits except the fan motor circuit controlled by mercury switch 35 are now interrupted. Heating will be discontinued as far as operation of burner I6 is concerned but the fan will continue in operation until the temperature in the discharge duct has fallen to approximately 110, at which mercury switch 35 will open and fan operation will be terminated. In mentioning temperature values at which the various switches are operated it is to be understood that these switches have normal operating diierentials as well understood in the art. When the cury switch 34, wire 54, primary Winding 50, and

wire 55 back to line conductor 41. Closure of mercury switch 3l will now completea circuit energizing relay winding 39 as follows: from secondary winding 5I of transformer 49 through wire 56, wire 5,1, mercury switch 3|-, wire 58, winding 39, and wire 59 back to secondary winding 5I. As soon as winding 39 is energized switch blades 40, 4I and 42 are moved into engagement with their respective fixed contacts. Closure of switch 40 completes a maintaining circuit for relay winding 39 so that the energization of this winding becomes independent of switch III, the circuit being as follows: from secondary winding 5I through wire 56, wire 60, switch'blade 40, xed contact 43, wire 5I. winding 39, and wire 59 back to sfgindary' winding 5I. Closure of cycle will then be as described above.

From the foregoing it should be apparent to f those skilled in the art that I have devised a control arrangement and sequence particularly adapted to unit heaters, the arrangement havingl a number of outstanding advantages. My particular control system insures that the cycling operation will be elcient and with the arrangein a relatively large space by means of a small high capacity unit heater. The arrangement utilizes a simple combination of controls but produces a maximum `in operating advantages in that the danger of overheating of theunit is precluded and the desired temperature is maintained without departing from desirably emcient cycling operation.

The single embodiment of myr invention which I have disclosed is `representative and the scope of the invention is not to be limited by my disclosure but only in accordance with the appended claimss' I claim as my invention:

1. In apparatus of the-character described, for heating a uid medium to a desired temperature, in combination, a fluid heating unit adapted to heat said iiuid medium, `means for circulating said uidmedium in heat exchange relation with said unit, 'said iiuid medium undergoing a definite temperature rise in passing said unit, automatic means for initiating an operating cycle by accelerating heatingv at said unit, said automatic -means starting said iiuid circulating means at the same time that heating is accelerated, and control means'including a device responsive to the temperature of fluid medium being discharged fromsaid unit, said device controlling heating after initiation of an operating cycle, said device being arranged to decelerate heating at a iirst predetermined temperature value equal to the desired temperatureof said medium plus the amount of the definite rise through the unit, and means responsive to heat generated at said unit for causing said luid'circulating means to conf t-inue in operationafter heating is de celerated until the temperature of the iiuid medium being discharged has dropped to a second temperature value.

2. In apparatus of the character described, in combination, a heating unit comprising a combustion chamber having a stack and fuel supplying means, means -comprising a fah for circulating air in heat exchange relation with said unit, contro1 apparatus comprising meansresponsive to the temperature oi said stack and means responsive to the temperature of air being discharged from said unit, said control means being arranged to ,startthe supply of fuel to said combustion chamber and the operation of said fan stack switch and a relay controlled thereby, said relay controlling heating at said unit and operation of said fan, a switch responsive to temperature oi' air being discharged-from said unit, electrical connections whereby said stack switch can energize said relay, energization of said relay initiating a cycle of operation of said unit, and

-electrical lconnections whereby upon energization of.said relay a maintaining circuit therefor is" established through said discharge air temperature responsive switch.

5. In apparatus of the character described, in combination, an air heating unit comprising a combustion chamberhaving a stack, means comprising a fan for circulating air in heat exchange relation with the combustion chamber, control means comprising al temperature responsive stack switch and a relay controlled thereby, said relay controlling heating at said unit and operation of said fan, a switch responsive to temperature of air being' discharged from said unit, electrical connections whereby said stack switch can energize said relay, energization of said relay initiating a cycle of operation of said unit, elec- 'trical connections whereby-upon energization of 5 said relay a maintaining vcircuit therefor is established through said discharge air temperature responsive switch, and another switch responsive to discharge air temperature for controlling said fan independently of said relay.

6. In apparatus of the character described, .in combination, .an air heating unit comprising a combustion chamber, ,fuel supplying means associated with the combustion chamber and means for circulating air around the outsidejof said chamber so as to absorb heat generated therein,

said unit being 'adapted for cycling operation and being oi' a type wherein there is a denite rise in air temperature passing therethrough, a y.

single means for starting a cycle of operation of said unit, said. last means being responsive to a temperature indicative that the unit has substantiallyrdissipated heat generated during f the preceding cycle, means responsive to temat a predetermined vtemperature of said stack, l

combination, an-air heating unit, fuel supplying means for said unit, means for circulating air in `heat exchange relation with the unit, automatic means effective only f or starting a cycle Yof operation' oi` said unit, and control means including av device viresponsive to temperature of the air heated by said unit, said "control means being eective only to control operation of said unit after it has beenk started byfsaid automatic means and being operable to terminate the supply of v fuel by said fuel supplying means.

4. In apparatus of the character described,

combination, an air heating kunit comprising a combustion chamberhaving a stack, means comprising a fan for lcirculating air in heat exchange relation with thecombustion chamber, control means comprising a temperature responsive sponsivey isedi perature of air being discharged from said unit,

and control means whereby after a cycle of op eration of ald unit has been started control is transferred to said discharge air temperature responsive means, said last means discontinuing heating when the discharge air temperature'is at f a predetermined value indicative that the air being admitted. tothe unit is at the desired temperature which temperature plus the amount of the rise through the unit equalssaid value. 7. In apparatus of the character described, in combination, an air heating unit comprising a `combustion chamber having a'stack, means for circulating air in heat exchange relation with the combustion chamber, control means comprisinga temperature responsive stack switch for initiating operation of said heating unit,

-means-resp0nsive toV temperature of air being discharged from said unit, and means whereby after operation of said unit has been initiated it continues in operationuntil said means reto temperature ofdischarge air is sat- 8., A system for maintaining the temperature of -a space `at a desired value, comprising in' combination, a heater, means for circulating the air of said space Lin heat exchange relation with said heater, said' heater andA said circulating produce a deiinite temperature rise'in the air means cooperating vunder normal conditions to circulating` past' said heater, and control means for causing cycling operation of said heater including a single switch for initiating operation of said heater, said switch being responsive to a condition indicative of the temperature within said heater, and a switch for maintaining said heater in operation, and a device responsive to the temperature of the air being discharged from said heater for opening said maintaining switch when said discharge air temperature is substantially equal to said desired value plus said denite temperature rise.

9. A system for maintaining the temperature of a space at a desired value, comprising in combination, a heater, means for circulating the air of said Space in heat exchange relation with said heater, said heater and said circulating means cooperating under normal conditions to produce a deinite temperature rise in the air circulating past said heater, and control means for causing cycling operation of said heater, said control means comprising a single switch responsive to a condition indicative of the temperature within said heater for initiating operation of said heater and said circulating means, a iirst switch responsive to the temperature of the air discharged from said heater for terminating operation of said heater when said discharge air is above a first predetermined temperature, and a. second switch responsive to said discharge air temperature for terminating operation of said circulating means when said heater is not operating and said discharge air is below a second predetermined temperature.

10. An air heating unit comprising in combination, a heater, means for circulating air downward over said heater, means including a duct for discharging heated air from said heater in e, downward direction, means for simultaneously initiating operation of said heater and said circulating means, a thermostatic device responsive to the air temperature in said duct, a first control means operated by said device for stopping operation of said heater at a predetermined temperature,l and a second control means operated by said device fo'r stopping operation of said circulating means at a second predetermined temperature after said heater has been stopped.

CLARENCE W. NESSELL.