US2843324A - Damper control for unit ventilator - Google Patents

Description

July 15, 1958A F. G. BAKERA DAMPER CONTROL `FOR UNIT VENTILATOR Filed April so, 1954 INVENTOR.

ATTY

United States Patent O DAMPER CONTROL FOR UNIT VENTILATOR Forrest G. Baker, Davenport, Iowa, assiguor to American Air Filter Company, Inc., Louisville, Ky., a corporation of Delaware Application April so, 1954, serial No. 426,770

z claims. (c1. 236-49) This invention relates to self-contained room ventilating units. The invention has particular reference to a control system for a room Ventilating unit of the type designed to maintain the room temperature within a narrow -predetermined range by supplying heated and unheated air to the room respectively when the room temperature falls below and rises above said range or a particular value within that range.

Units of the type to which this invention relates comprises: a damper movable between a damper closed or room-heating position-i. e. one extreme position in which it closes an` inlet opening for unheated air and fully exposes or uncovers a heater to permit circulation of room air through it-to a damper open or roomcooling position-its other extreme position in which it closes oit the room heater and fully exposes or uncovers the unheated air opening-control means normally set for a predetermined room temperature condition and normally operative in response to room temperature conditions rising above and falling below said predetermined temperature conditions to move the damper in the opening and closing directions respectively, the control means including an electrical control circuit and being normally operative when said circuit is energized, and a main switch unit for energizing and deenergizing the control circuit. During normal room occupancy periods, these controls are quite satisfactory. During `those intervals in which the use of the unit is not desired, it may be shut down either manually by a manually operable main switch unit or automatically by a main switch unit in the form of the so called day-night control. When shut down it will leave the damper in whatever position the damper may occupy at `that time and this is undesirable since the damper should be closed during the shut down period.

The principal object of this invention is to provide a Ventilating unit of this general character in which the damper will move automatically to its closed position when the unit is shut down either manually or automatically.

Another object is to provide an extremely simple and inexpensive means for electing the closure of the damper upon shutting down the unit.

The invention is illustrated in the accompanying drawings wherein:` Y

Figure l more or less schematically illustrates a conventional Ventilating unit to which this invention may be applied; and

Figure 2 illustrates a control system for the unit of Figure 1, this system embodying the present invention.

The structure illustrated in Figure 1 conventionally comprises: an outside building wall 1 having an air inlet opening 2; and a Ventilating unit 3 having a blower 4 for drawing air from its inlet chamber 5 through an air lter 6 and the blower intake 7 so as to discharge that air at 8 into the room. The blower 4 is operated by a motor 4a (Figure 2). The inlet chamber 5 of the Unit contains .aA damper 10 mounted for movement from y 2,843,324 ICC Patented Jury-15, 195s one extreme damper closed position-i. e. the full line position illustrated in Figure l-to a damper open position--i. e. the dotted line position illustrated in Figure 1.

. With the damper closed, the blower 4 operates to draw room air into the inlet chamber 5 through heater 9 so that heated air is supplied to the room. With the damper open, the blower 4 operates to `draw only unheated outside air through the opening 2. When the damper is in an intermediate position, it will draw both heated and unheated air in quantities depending upon the position it occupies.

The control for the Figure 1 structure is shown in Figure 2. lt broadly comprises: a control means normally set for a predetermined temperature condition and normally operative, in response to temperature conditions respectively rising above and falling below said predetermined temperature conditions, to move said damper in the opening and closing directions, said control means including an electrical control circuit and being normally operative when said circuit is energized; and a main switch unit for energizing and deenergizing said control circuit. More specically it includes: a damper operating motor; an electric motor-operating circuit system for operating the motor in accordance with the position of a motor control switch means, which is movable from a neutral position to damper closing and opening positions on opposite sides of neutral; balance means normally operative at a predetermined temperature condition to hold said switch means in neutral, said balance means i11- cluding yieldable means urging said switch means to its` damper closing position and a normally energized thermostatically responsive electric control circuit system yieldably urging said switch means in opposition to said yield-v able means, said energized control circuit system being responsive to temperature conditions rising above `said predetermined temperature condition to move said switch means toward its damper opening position; and a power connection for both of the operating and control systems, including a main switch unit for energizing and deenergizing said control system.

DAMPER MOTOR The damper operating motor is indicated at 15 and, as indicated, has a shaft 16 operatively connected to theA damper 10 through a linkage including an arm or crank 17.

DAMPER MOTOR CIRCUIT SYSTEM open position, in4 accordance with a demand for cool airto lower the room temperature; and contact 25 of the` motor control switch. The counterclockwise damper closing circuit includes, `from lead line 20: motor winding 22` for counterclockwise rotation; a limit switch 24, which opens when the damper 10 has moved to its fully closed position iu accordance with a demand for hot air to raise the room temperature; and contact 26 of the motor sition of the switch; and contact arm 28 pivoted forr movement from the neutral position either to `adamper opening position on one side of neutral in which it 'en- The clockwise damper open-` 3 gages `contact 25 of the damper opening circuit to complete that circuit to lead line30, or, tov a damper closing position on the other side of neutral in which it engages contact 26 of the damper closing circuit to complete that circuit to lead 1ine.30.

BALANCE MEANS The balance means includes a yieldable means urging the switch means toward the room heating or damper closing position and a normally energized thermostatically responsive'electric control circuit system yieldably urging the switch in the opposite direction toward the room cooling or damper opening position.

Yieldnble means The -yieldable means comprises a spring 31 urging switch arm 28 toward damper closing contact 26. When unopposed, this spring is strong enough to pull arm 28 past the neutral position arm 27 over into engagement with contact 26.

Control circuit system The control circuit system conventionally includes: a relay coil 35 for operating the` motor control switch; an amplifier 36 for operating the relay coil; and a potentiometeror Wheatstone bridge 45 for operating the amplifier.

The relay coil 35, when energized, magnetically urges switch arm 28 toward the damper opening position. Under low room temperature conditions, coil 35 is energized by a weak current so that the magnetic force it exerts is overcome by the spring 31. Consequently, arm 2.8will engage, and remain in contact with, damper closing contact 26. With an intermediate degree of energization, which corresponds to normal room temperature, the coil 35 will overcome spring 31 sufficiently to pull arm 28 over to the neutral position where it engages neutral arm 27. With strong energization corresponding to high room temperatureconditions, the coil 35 will overcome both spring 31 and the resiliently held arm 27 to pull arm 28 over into engagement with contact 25 inthe, damper opening circuit. It may be noted that the switch means in the motor operating circuit and coil 35 in the control circuit are conventionally shown in the form of a relay.

The amplifier 36 is of a conventional type which, when energized through a power connection, operates to magnify or amplify the energy it receives from the Wheatstone bridge and energize coil 35 accordingly. Since it is of a conventional type, it. should suice to say that l' it has power terminals 37 and 38 for connection to power and control terminals 39 and 40 for connectionto the Wheatstone bridge. Terminal 39 is a ground connection while terminal 40 is connected to the Wheatstone bridge through line 41.

The Wheatstone bridge is of a conventional type which, when energized, operates in response to low, predetermined and high room temperatures to feed relatively low, intermediate and strong currents to the amplifier. Accordingly, the bridge has power receiving terminals 46 and 47 and energy delivering terminals 48 and 49. The power receiving terminals 46 and 47 are connected by lines, not shown, to the secondary winding terminals of a transformer 45a forming a part of the amplifier transformer which, in turn, is connected to power through terminals 37 and 38. The power delivering terminal 48 1s connected through ground to the grounded terminal 39 of the amplifier while bridge terminal 49 is connected through line 41 to the amplifier terminal 40. One leg. of the bridge 45 contains room thermostat 50 of the teslstance type whilel the diagonally opposite portion of the other leg of the bridge contains a blower outlet thermostat 51 also ot the resistance type, this latter thermostat being, located in the outlet air stream of blower 4 as shown inFigure 1.

POWER CONNECTION The motor 4a which drives blower 4, the amplifier 36, the Wheatstone bridge are all connected through a main switch unit 55 to incoming power lines 56 and 57. In conventional operation, the damper motor lead lines 20 and 30 are also connected through 55 to power. The main switch unit 55 may` be of any conventional hand-controlled single pole type or automatic type which is operated by one or more independent room thermostats to apply power when the room temperature vfalls below a minimum value during the nighttime.

CONVENTIONAL OPERATION We assume that the main switch unit 55 is closed, that the room temperature is at a normal predetermined value, and that the damper is at its mid-position. With this assumption, the bridge 45 will be unbalanced to an intermediate degree feeding an intermediate current to` the amplifier which, in turn, energizes the relay coil 35 to an intermediate degree holding arm 28 of the motor switch means in the neutral position.

With this assumption, if the room temperature rises above the normal predetermined value, the resistance of room thermostat will also rise increasing the bridge unbalance and correspondingly increasing the current flow from the bridge to` the amplifier with a resultant increase in the energization of coil 35. If this rise in room temperature is suicient, the motor switch will close the room-cooling damper-opening circuit to actuater the damper in the opening direction. But this actuation will be relatively small because the damper actuating mechanism will operate, through the conventional bridge readjuster 60, to change the resistance in the other leg of the bridge and thereby reduce the unbalance enough to open the room-cooling damper-opening circuit and bring the system once again to a relatively stable condition. However, if the room temperature continues to rise, the foregoing operation will be repeated.

On the other hand, with the original assumption, if the room temperature decreases, the bridge will be unbalanced in the opposite direction decreasing the current fed by the bridge into the amplifier with a resultant decrease in the energization of coil 35. Itf this decreasev is pronounced enough, spring 31 will effect the closureof the room-heating damper-closing circuit. Again, however, the closing movement of the damper will be restricted by the rebalancing'of the bridge` through readjuster 60. v

The outlet thermostat 51 exercises less authoritythan the room thermostat 50. It is said to exercise 10% authority when it requires a l0 degree change in temperature to change its resistance as much as a l degree changev in room temperature changes the resistance of theroom thermostat. Furthermore, since room thermostat 50 and outlet thermostat 51 are located in diagonally opposite sections of the bridge,.the unbalance produced by an increase in the resistance of room thermostat 50..corresponding to a l degree rise in room temperature is counterbalanced by a fallin the resistance of outlet thermostat 51 corresponding to a l0 degree decrease in the outlet temperature. Consequently, if the room temperature rises sayl degree` and causes room temperature thermostat 50 to open the damper and if'the ensuing temperature of the air stream, discharged by blower 4,

falls 10 degrees, the resistance ofthe outlet thermostat 51 will decrease enough to eiect a compensating closing movement of the damper.

Before passing, it may be noted that the foregoingl control system is normally designedy to bring about a full closure of the damper when the room temperature reaches a low value of say 71.0"` to hold the damper in thatv posi-V holds it fully open duringall room Vtemperatures above-7 that` value.Y Between these limits, it operates to hold tha damper at some intermediate position and it resets itself to different predetermined temperature values with each operation of the room thermrstat and readjuster 60. For example, if it holds a temperature of 72 when the outside temperature falls and causes the room temperature to drop, it will close the damper slightly and the readjuster will then reset the Wheatstone bridge to a value corresponding to room temperature of say 71.8 instead of 72. With a further lowering of the outside temperature, this resetting action will be repeated until the bridge is reset to a value corresponding to a room temperature of 71.0. Here the damper is fully closed.

Heretofore, if the Ventilating unit were shut down by opening or interrupting power supply lines 56 and 57, the entire system would be rendered inoperative leaving the damper in whatever position it chanced to be at the time the interruption occurred. This is extremely objectionable because, with the damper open at the time of the shut down, the outside air is free to pass into the room through the unit ventilator. With a drastic drop in outside air temperature, the room temperature could drop accordingly.

IMPROVEMENT In accordance with the present invention, the damper motor circuit is connected to power independently of the main switch unit 55 so that a deenergization of the control circuit system does not effect the supply of power to, and the continued operation of, the damper motor circuit. Consequently, when the switch unit 55 is operated to shut down the Ventilating unit and deenergize the control circuit system, the spring 3l immediately becomes effective to move switch arm 28 to the damper closing position and, since the damper motor circuit is then con- .nected to power, it becomes immediately operative to close the damper and then shut down automatically through travel limit switch 24.

I claim as my invention:

1. A control system for a ventilator having a damper to close and open an air flow opening and a motor for operating said damper comprising a selectively energizable control circuit, including temperature sensing means, for providing electrical signals indicative of a sensed temperature departure from a predetermined desired value thereof, a normally energized damper motor operating circuit, switching means included in said damper motor operating circuit responsive to said electrical signals for selectively operating said motor to progressively displace said damper in a direction to return the sensed temperature to said predetermined desired value, means included in said switching means responsive to deenergization of said control circuit for operating said motor to displace said damper to a limiting position closing said air flow opening, and means responsive to said last mentioned means for deenergizing said damper motor operating circuit when said damper reaches said limiting position.

2. A control system for a ventilator having a motor operated damper to close and open an air ilow opening, comprising: an electric operating circuit system for operating the motor in accordance with the position of motor control switch means movable from a neutral position to damper closing and opening positions on opposite sides of neutral; balance means normally operative at a predetermined temperaturc condition to hold said switch means in neutral, said balance means including means yieldably urging said switch means to its damper closing position and a normally energized thermostatically responsive electric control circuit system yieldably urging said switch in opposition to said yieldable means, said energized circuit system being responsive to temperature conditions rising above said predetermined temperature condition to move said switch means toward its damper opening position; and a power connection for both systems including a main switch unit for energizing and deenergizing said control circuit system; said yieldable means and operating circuit system being operable, upon the deenergization of said control system, respectively to move said switch means to its damper closing position and to operate the damper in the closing directio v References Cited in the tile of this patent UNITED STATES PATENTS

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