US2504798A - Unit heater - Google Patents

Description

H. F. BRIN EN UNIT HEATER April 18, 1950 2 Sheets-Sheet 1 Filed Feb. 9, 1946 April 18, 1950 H. F. BRINEN 2,504,798

UNIT HEATER Filed Feb. 9, 1946 2 Sheets-Sheet 2 Zwar/72% Patented Apr. 18, 1950 UNIT HEATER Howard F. Brinen, Racine, Wis., assignor to Young Radiator Company, Racine, Wis., a corporation oi Wisconsin Application February 9, 1946, Serial No. 6416*.660

3 Claims. (Cl. 257-137) This invention relates to unit heaters of the type generally known as vertical or projected In the heating of certain types of buildings, such as factories, shops, laboratories, and sometimes expansive oillces. it is the practice to project the heat vertically downward from unit heaters suspended from the ceiling. These heaters as a rule combine a heating coil and a motor-driven propeller fan. The coil receives heat from a remote central heating plant. The i source of heat may be either steam or hot water. The former is by far the more desirable and practical. The fan draws the air in and around the heating coil and directs it downwardly toward the oor below. The fan motor, of necessity, must be mounted in close proximity to the heating coil. This presents a problem in protecting the motor windings against temperatures that tend to deteriorate the wiring insulation and render the motor ineffective is not inoperative. The earlier practice of using the so-called open type motor, wherein the end bells of the motor are slotted or otherwise formed with openings. has not provided the solution of the aforesaid problem. The air stream passing through such openings over the motor windings has caused grease. lint, dust, and other deleterious materials to collect on the motor windings. This has resulted in insulating or short-circuiting electrical contacts or building up a general thermal insulation that prevents the intended dissipation of heat. resulting from electrical losses, to the air stream flowing through these end bell openings. All too frequently, where motors of this type were used with unit heaters of the aforesaid type, they have burned out.

These facts resulted in the manufacturers of fan motors standardizing on the so-called fan du or "totally enclosed" motor, for installations of this kind. In that type of motor, heat caused by electrical losses is conducted to the motor housing with the expectation that it will be absorbed in the air stream pulled around the.

housing by the fan. To keep such a motor, operating at full load, properly cooled requires an air velocity in excess of 500 F. P. M. with the air at the ordinary room temperature.

Unit heaters of the type in question have steam supplied to the heating coil at a pressure of between 80 and 100 p. s. i. Generally the heat is supplied continuously. The operation ofthe motor as a rule is intermittent, being controlled by a room thermostat. Thus, when there is no fus ' demand for elevating the room temperature the 55 2 motor is idle. Under certain conditions this might be for an extended period of time.

During the operation of the fan the intensive heat of the steam under such pressures is rather rapidly dissipated by the comparatively cooler air as it is drawn through the coil and around the motor. However, the velocity of the air current around the motor housing must materially exceed the minimum of 500 F. P. M. if there is to be an adequate dissipation of the heat caused by electrical losses in the motor operation. In many of the fan-motor and heating-coil combinations, heretofore provided, that is not a very diiicult matter.

The more acute problem, however, is the overheating of the motor through failure to properly dissipate the heat generated by the coil when the motor is not running and there is no forced air ow around the motor housing. 'I'he motor remaining idle in the center of the temperatures generated by the heating coil containing steam at 80 to 100 p. s. i., the windings are too often subjected to temperatures greater than they can long resist without injury thereto.

Heretofore, various valve arrangements have been developed for cutting off the steam supply to the heating coil when the motor is idle. However, these have proven expensive, hence not very often resorted to by those responsible for the installation of heating systems of this type.

Motor manufacturers, aware of this problem, have sought to lessen its acuteness by developing and applyingl insulating varnishes to the motor windings capable of withstanding greater temperatures than is the varnish ordinarilyy applied to motorwindings for other types of service. Where this has met with any degree of success it has resulted in a material increase in the cost of motors. This has not met with favor among purchasers and' installers of heating equipment.. l

As a consequence of all this, manufacturers of this type of unit heater have undertaken to alleviate the problem by providing a motor mounting that would aiord measurable protection of the motor against being dangerously overheated when standing idle, as well as ensure a dissipation of the heat generated within the motor resulting from electrical losses during its operation.

The main objects of -this invention, therefore, are to provide an improved construction and relative arrangement of the heating coil and fan motor for u'nit heaters of the vertical or projected type; to provide in a unit heater of this kind an improved form and arrangement of a stack or duct for the motor which, at all times; will directly protect the motor from the heat l generated by the heating coil and supplement that with an adequate volume and velocity of air current around the motor; and to provide an improved structure of this kind which is simple and economical in construction and which is highly efllcient in operation. even under the least favorable circumstances.

A preferred embodiment of this invention is I shown in the accompanying drawings, in which:

Fig. 1 is a top plan view of such an improved vertical type unit heater;

Fig. 2 is a transverse central sectional view;

Fig. 3 is a diagrammatic illustration of the demonstrated air flow currents during the opera- 1 tion of the fan: and

Fig. 4 is a diagrammatic illustration of the demonstrated air flow currents when the fan motor is idle.

A vertical type unit heater constructed in accordance with this invention comprises, a housing 5 formed of the plates 6 and 1 wherein is supported a heating coil 8 through and around which coil air is drawn and directed downwardly by means of the fan 9 driven by the motor I0 protectively mounted in the stack or duct II supported on the plates 6 and 1.

The upper housing plate 6 is in the form of a disc. A flange I2 is formed along its outer edge to provide reinforcement. A central opening I3 is `formed to receive the stack Il, as will more fully hereinafter appear. Channel bars Il are secured to the upper face of the plate to provide i further reinforcements.

The lower housing plate 1 is likewise provided with a reinforcing ange I5 around its outer perimeter. The central portion of this lowei housing plate is cut out and the perimetrical part spun axially outwardly to form a flange or` shroud I6 around a central opening I1. A series of short channel bars I8 are secured on the inner face of the plate 6, just inwardly of the shroud I6, so as to provide reinforcement for the plate. l

The vertical spacing of the plates 6 and 1 provides an annular chamber 61 communicating exteriorly of said housing through the opening I1 and with a perimetrical opening I9, inwardly of which is mounted the heating coil 8.

The heating coil 8 comprises a pair of headers 20 and 2| connected by a series of tubes 22 on which are supported the conventional, closelyspaced heat-dissipating fins 23.

These several parts of the heating coil are assembled by first placing the fins 29. on the tubes 22 and-.expanding the tubes slightly by drawing balls axially through the tubes. This is` extends down through plate 1 and has the endv threaded for connection with the returnl to the source of heat.

The fan 9 may be of any suitable construction. Its diameter is slightly less than the internal diameter of the lower end of the flange or shroud I6. Preferably lt is positioned so that the plane .f the lower edges of the blades is in the plane of the perimeter of the flange or shroud I6.

The motor I0 Is preferably of the fan duty or "totally enclosed" type. It is supported on a b'aket 24 concentrically within the stack or duc The stack or duct I I is concentrically mounted on the plates 6 and 1 by means of angle brackets 25 and rods 26. The brackets have the vertical legs thereof welded to opposite points on the exterior of the stack Il and have the shorter legs thereof bolted at 21 to the plate 6. The rods 26 have their inner ends bolted at 28 to the stack II and their outer ends inserted in apertures 29 in the plate 'l (see Fig. l).

The stack II is of such a length and is positloned relative to the plates 6 and 1 so that it spans the annular chamber ,61. In this particular embodiment the lower end of thestack is practically in the plane of the plate 1 whereas the upper end thereof extends above the plate 8 a little more than the spacing between the plates 6 and 1. The motor I0 has the bracket 24 secured to a plate 30, bolted to the interior of the stack II, so that the ends of the motor bearings are within the respective ends of the stack I I.

As will be apparent from the drawings. the upper end of the stack II is unobstructed and completely open to the space above and surrounding the heating coil 8. Thus a free flow of air is ensured through the stack between the areas below and above said heater. When the fan is operating, the suction thereof will draw the air from above the heating element downwardly through. the stack, as shown in Fig. 3, and thus cool the motor. When the fan is idle, the rising air currents will aspirate air upwardly through the housing Il, as shown in Fig. 4, thus protecting the motor II from the excessive heat of the heating coil 8.

Furthermore, the stack I I is of a diameter such that the annular space 32 between the motor and the stack will permit not less than 5 per cent of the total air drawn by the fan 9 to pass through the stack II around the motor I0, at velocities ranging from 800 to 1020 F. P. M.

Such a unit heater is suspended from-the ceiling by cables or rods attached to the eye bolts 3l.

Various tests have been made with this improved type unit heater to determine heating performance and motor ventilation" capacities. The tests were conducted in accordance with a code developed and approved jointly by the Industrial Unit Heater Association and the American Association of Heating and Ventilating Engineers.

During all tests, steam was applied to the heating coil at between and 100 p. s. i. One test was made with the motor operating for 81/'2 hours. Another test was made with the motor idle for 81/2 hours.

The room temperature during the test, with the motor operating, fiuctuated between 84 and 102 F., with the outdoor temperature ranging from 51 to 37 F. During the test when the motor was idle, the room temperature fluctuated between 83 and 88 F., with the outdoor temperature ranging between 55 and 44 F.

The tests for heating performance" were made with several forms and arrangements of the circular heating coil. The results revealed a very uniformly acceptable efliciency.

In the tests for "motor ventilation the motor ascuas was thermocoupled to determine the heat conditions of both bearings. two points on the windings, and one point on the motor housing.

The temperatures of the motor bearings ranged from 130 to 143 F. The temperatures of the motor windings ranged from 142 to 175 F.

During the 81/2 hour "operating test, the highest temperature attained in the motor windings was 175 F. During the 81/2 hour idle-"test, the highest motor winding temperature attained was 116.4 F. The highesttemperature attained by the air in the stack during the "operating" test was 132 F. The highest stack temperature during the idle test was 112 F.

These temperatures are normal, and troubles l from overload, outside heat, etc., will not usually show up until these windings temperatures exceed 225 F., which is the limit of ordinary so-called Class A insulating varnish with which the wires and other electrical conducting parts are coated.

These temperature tests were supplemented by the conduct of smoke" tests and the making of on-the-spo sketches of reactions. The smoke tests were made for both "operating" and "ldle conditions of the motor. Smoke guns, cigar smoke, and one-minute smoke bombs were employed. Fig. 3 shows the iiow of air currents during the operating condition. Fig. 4 shows the ilow of air currents during the idle" condition.

It is obvious from these diagrammatic illustrations that an eifective movement of air currents is achieved for heating purposes and for keeping the temperature of the motor windings far below a dangerously critical stage. The structure which accounts for this is the horizontal 35 housing with its perimetrical and lower housingplate central openings with the annular heating coil arranged adjacent to the perimetrical opening and the fan motor enclosed in the central stack extending across the horizontal housing chamber and above the same and proportioned in height and diameter to completely enclose the motor and ailord an air flow passage around the motor sumcient to permit not less than 5-'per cent of the air drawn by the fan to pass through the stack and around the motor.

It will be readilyv apparent that the manner of mounting the fan motor, i. e. supporting it solely and rigidly from the cylindrical stack which surrounds it, and the manner in which this stack is supported from the housing of the deviceare important features of this invention. As is well known to those skilled in this art rumbling and drumming noises cannot be tolerated in a unit heater, and since the heater of this invention, being designed to be suspended from the ceiling, must be light, avoidance of such noises presented a sgious problem, especially in the larger sized uni "t By rigidly mounting the fan motor from they stack and rigidly securing the stack to both top and bottom plates or walls of the housing these objectionable noises have been reduced to a minimum.

The manner in which the stack is mounted and especially the way in which it is connected to the bottom wall or plate performs still another important function; it assures coaxiallity between the fan and its shroud since theclamping nuts or the tie rods 26 enable corrective adjustment of alignment inaccuracies inevitable in production.

Variations and modifications in the details of structure and arrangement of the parts may be resorted to within the spirit and coverage of the appended claims.

Iclaim:

1. A vertical type downblast lunit heater, comprising: a housing having horizontally disposed spaced top and bottom walls; an annular heating coil mounted between the outer portions of ,said walls, the housing being open at its sides to permit air to ilow :laterally across the heating coil into or out of the housing, the top and bottom walls having coaxial central openings; a cylindrical stack mounted in the housing and projecting throughl and being contiguous to the edge of the central opening in the top wall and having its lower end adjacent to the plane of the bottom wall; a fan operating in the opening in the bottom wall and having a sweep but slightly smaller than the opening in the bottom wall so as to requireaccurate alignment between the axes ofthe fan and the central openings; a motor for the fan having a shaft to which the fan is secured; means mounting the motor within the cylindrical stack with the motor spaced from the wall of the stack so that air flowing through the stack insulates the motor from the radiant heat of the heating coil, said mounting means securing the motor to and supporting the same solely from the cylindrical stack; means rigidly securing the stack to the top wall of the housing; and spokes rigidly connecting the lower end portion of the stack with the bottom wall of the housing to thereby rigidly secure the cylindrical stack against displacement from the positional relationship with the housing necessary to maintain the required alignment between the axes of the vfan and the central openings in the top and bottom walls ofthe housing.

2. A vertical type downblast unit heater, comprising: a housing having spaced parallel horizontal top and bottom walls of sheet metal, each of which has a central opening, the opening in the bottom wall being larger than the opening in the top wall; a fan shroud extending down from the edge of the opening in the bottom wall, said shroud reinforcing the bottom wall; a circular heating coil mounted in the outer peripheral portion of the housing and extending across vthe space between the top and bottom walls, the

housing being open at its sides to enable air to ow across the heating coil into or out of the housing; an open ended cylindrical stack mounted within the housing and extending through the opening in the top wall, the stack being contiguous to the edge ofthe opening in the top wall; means rigidly securing the stack to the top wall with its upper end projecting a substantial distance above the housing and its lower end pro- `iecting a. short distance into the fan shroud; a vertical fan motor within the cylindrical stack with-its shaft projecting from its lower end; a fan fixed to the shaft and operating in said shroud; mounting means for the motor carried entirely by the cylindrical stack so that the disposition of the stack in the housing determines the concentricity of the fan with respect to its shroud; and radial tie rods rigidly connecting the lower end portion of the cylindrical stack with the bottom wall to rigidly hold the stack against vibration with its fan properly centered with respect to the shroud.

3. In a unit heater of the character described: a round housing having horizontal topV and bottom walls; a circular heating element interposed between the marginal edge portions of said walls and spanning the distance therebetween, each of said walls having a central opening, said openings together providing a vertical air passage l, l through the housing: an open ended cylindrical stack extending through the central opening in 'the top wall and contiguous to the edge of said,

opening, said stack extending a substantial distanoeabove and below the top wall; means rigidly. connecting the cylindrical stack with the top and bottom-walls to hold the stack coaxial with the housing; a vertical fan motor disposed. within the stack and having a shaft projecting downwardly therefrom; a fan mounted on Athe shaft and operating in the opening in the bottom wall; and mounting means for the motor supported solely by the stack. said mounting means holding the motor spaced from the wall of the stackso that air ilowing through the stack insulates the 15 Number motor from the radiant heat of the heating coil.

HOWARD F. BRmEN.

'REFERENCES crrlm The following. references'are of record in the

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