US3026041A - Conditioned air distribution - Google Patents

Description

March 20, 1962 A. P. JENTOFT Filed May 6, 1960 -PNEUMATIC FLOW CONTROLLER 3| 4; Sheets-Sheet 1 I I 5 2| I Z "I l 5, {/20 l 2 I 11 I L8. I 1 l q I PNEUMATIC I blg E 25 I THERMOSTAT I I 23 I I l I3 I L I PRIOR f ART THERMOSTAT PRESSURE HIGH STATIC AIR PRESSURE IN FLOW HOT AIR INLET HOT All-7 D o 0 [NORMAL RA N65! THERMOSTAT PRESSURE INVENTOR.

ARTHUR P. JENTOFT BY 6 I March 20, 1962 A. P. JENTOFT CONDITIONED AIR DISTRIBUTION 4 Sheets-Sheet 2 Filed May 6, 1960 PNEUMATIC FLOW CONTROLLER n y MO M UR u m PT NORMAL RANGEI THERMOSTAT PRESSURE INVENTOR.

ARTHUR P. JEN TOF'I A TORNEY March 20, 1962 A. P. JENTOFT 3,026,041

CONDITIONED AIR DISTRIBUTION Filed May 6, 1960 4 Sheets-Sheet 3 3| PNEUMATIC FLOW CONTROLLER PNEUMATIC THERMOSTAT LOW LOW STATIC STATIC AIR PRESSURE IN AIR PRESSURE IN FLOW HOT AIR FLOW HOT AIR NLET \wm/n INLET \HOTA/R 0 Q O [NORMAL RANGE! O I/VOl-PMAL RANGEI THERMOSTAT PRESSURE THERMOSTAT PRESSURE INVENTOR.

ARTHUR P. JENTOFT BY 4 fl.

ATTORNEY Filed May 6, 1960 A. P. JENTOFT CONDITIONED AIR DISTRIBUTION 4 Sheets-Sheet 4 GQ QT 3| PNEUMATIC FLOW CONTROLLER 34 f F A 4 H PNEUMATIC 1:; i9 THERMOSTAT 14 INVENTOR.

ARTHUR P. JENTOFT T R EY United States Patent Office 3,026,041 Patented Mar. 20, 1952 3,026,041 CONDITIONED AIR DISTRIBUTION Arthur P. Jentoft, Wexford, Pa., assignor to H. H. Robertson Company Filed May 6, 1960, Ser. No. 27,411 3 Claims. (Cl. 23613) This invention relates to air conditioning systems and more particularly to a method and apparatus for automatic regulation of room temperature and inlet volume of air flow in a two stream air conditioning system.

Air conditioning systems employing two separate streams of air, hot and cold, are well known in the art. See, for example, US. Patent 2,729,429. Such air conditioning systems operate by providing separate streams of air which are distributed throughout a building for blending prior to discharge into the rooms of the building. One of these streams is maintained at a temperature substantially above the temperature which it is desired to maintain within the rooms. The other stream is maintained at a temperature which is substantially below the temperature which it is desired to maintain in the rooms. By independently throttling the two streams, a resultant blended stream of conditioned air can be provided for discharge into the rooms at a blended temperature which will maintain the desired conditions within the rooms of the building. Good ventilation practice dictates that the conditioned air should be supplied to the individual rooms at a substantially constant volume of flow.

For a clear understanding of the present invention and of problems presented by two stream conditioned air systems, reference should be had to the accompanying drawings in which:

FIGURE 1 is a schematic illustration of a prior art mixer box having automatic controls suitable for normal operation of two-stream air conditioning systems;

FIGURE 2 is a graphical representation of the normal operation of the mixer box illustrated in FIGURE 1;

FIGURE 3 is a graphical illustration of one defect which is inherent in the operation of the prior art mixer box shown in FIGURE 1;

FIGURE 4 is a schematic illustration of a mixer box according to one embodiment of the present invention which offsets the inherent defect illustrated in FIGURE 3;

FIGURE 5 is a cross-section illustration of a shuttle valve which is shown schematically in FIGURE 4;

FIGURE 6 is a graphical illustration showing the results achieved by operation of the mixer box of FIG- URE 4;

FIGURE 7 is a graphical illustration showing another defect which is inherent in the operation of the prior art mixer box of FIGURE 1;

FIGURE 8 is a schematic illustration of an alternative embodiment of the present invention which ofisets the inherent defect illustrated in FIGURE 7;

FIGURE 9 is a cross-section illustration of a shuttle valve which is illustrated schematically in FIGURE 8;

FIGURE 10 is a graphical illustration showing the results achieved by the operation of the mixer box of FIG- URE 8; and

FIGURE 11 is a schematic illustration of a preferred embodiment of the mixer box of this invention including the features ah'eady shown in FIGURES 4 and 8.

Every room, group of rooms or portion of a single room in a building may be considered as a relatively confined zone for the purposes of air conditioning. A continuous supply of conditioned air is introduced into each room (control zone) and a corresponding quantity of air is removed from the room (control zone) for dissipation or reconditioning and recirculation.

As shown in FIGURE 1, an individual room or control zone is indicated by the numeral 10.

Two streams of conditioned air are provided throughout the building and are represented by the numerals 11 (cold air inlet) and 12 (hot air inlet). The two air inlets communicate with a mixer box 13 which is shown in cross-section. A pair of partitions 14, 15 extend across the cavity of the mixer box 13 and divided the cavity into an inlet blending chamber 16, a mixing chamber 17 and a distribution chamber 18. The partition 14 separates the inlet blending chamber 16 from the mixing chamber 17 and has a plurality of directional mixing vanes 19 which create some turbulence as air passes through the portion 14 to provide a uniformly mixed stream of blended air. The partition 15 separates the mixing chamber 17 from the distribution chamber 18 and has a perforate plate 20 through which air may experience streamline flow. The perforate plate 26 may be a screen, perforated sheet, netting, mesh and the like. Imperforate plates 21 are provided in a slidable mounting in which they may be extended or retracted to'regulate the cross-sectional area of the perforate plate 21 to regulate the flow of air therethrough.

A pair of pneumatically controlled valves 22, 23 is provided in the cold air inlet 11 and the hot air inlet 12 respectively to throttle the fioWs of air issuing into the inlet blending chamber 16. Air is discharged from the inlets 11 and 12 into the inlet blending chamber 16 whence it passes between the vanes 19 for uniformity of mixing within the mixing chamber 17. Uniformly blended air passes through the perforate plate 213 into the distribution chamber 18 whence it is discharged into the control zone 10 through conduits 24, 25. Additional conduits 26 may be provided to discharge additional air to other rooms or to different locations of the same room. The entire air discharge from the distribution chamber 18 enters the control zone albeit several different rooms may reeive the discharge.

An exit conduit 27 is provided to withdraw air from the control zone 10 for dissipation or reconditioning and recirculation.

A pneumatic thermostat 28 is maintained within the control zone 10 for continuous observation of the temperature therein. A supply stream of pressurized air is introduced into the thermostat 28 through a supply conduit 29. The thermostat 28 regulates the pressure of the supply air, usually by bleeding a portion of the air, according to the deviation of the actual temperature within the control Zone 10 from a predetermined temperature setting of the thermostat 28. Thus a temperature regulated pressure of the throttled supply air is introduced into a conduit 36 which communicates with and operates the pneumatically controlled valve 23 in the hot air inlet 12. Normally the supply air in the conduit 29 is maintained at a pressure of about 17 to 20 pounds per square inch. The temperature regulated pressure in the conduit 30 normally has a range of about 5 pounds per square inch, that is, from about 8 pounds per square inch to about 13 pounds per square inch. Hereinafter any conduit which confines the temperature regulated pressure and which extends between the thermostat 28 and any other element in the system will be identified as the thermostat conduit.

When the temperature Within the control zone It) is below the predetermined value, the temperature regulated pressure in the thermostat conduit 30 is reduced; when the temperature in the control zone 10 is above the predetermined value, the temperature regulated pressure in the thermostat conduit 30 is increased. The pneumatically responsive valve 23 operates to be opened when confronted with relatively low pressures and to be closed when confronted with relatively high pressures. Thus the amount of hot air issuing from hot air inlet 12 into the inlet blending chamber 16 is controlled in response to deviations of the actual temperature within the control zone 19 from a predetermined value.

A substantially constant volume discharge of blended conditioned air into the distribution chamber 18 is achieved by means of a pneumatic flow controller such as a differential pressure regulator 31. It will be observed that the perforate plate 24) in the baflie 15 serves as a flow measuring orifice. A pair of static pressure sensing tape 32, 33 is provided to observe the static pressure on each side of the baffie 15 and to transmit these static pressures to the differential pressure regulator 31. So long as a constant volume of air passes through the perforate plate 20, a predetermined constant pressure differential will exist between the pressure taps 32, 33. If the volume of air passing through the perforate plate 24) exceeds the predetermined value, the pressure differential existing between the pressure taps 32, 33 will increase. Similarly if the volume of air passing through the perforate plate 2i) is less than the predetermined value, the pressure diflferential existing between the pressure taps 32, 33 will decrease. Accordingly the differential pressure regulator 31 serves to regulate a supply of pressurized air from a conduit 34, usually by bleeding a portion of the air, in response to deviations in the observed difierential pressure from a predetermined constant value. Thus a flow regulated pressure of the throttled supply air is introduced into a conduit 35. Hereinafter any conduit which confines the flow regulated pressure and which extends between the differential pressure regulator 31 and any other element in the system will be identified as a pressure regulator conduit. If the observed differential pressure is greater than the predetermined value, the flow regulated pressure maintained in the pressure regulated conduit 35 increases. It the observed differential pressure is less than the predetermined value, the flow regulated pressure maintained in the pressure regulator conduit 35 is decreased.

The perforate plate 20 serves principally to promote a uniform flow of air from the mixing chamber 17 to the distribution chamber in order that the pressure diiierential existing between the chambers 17 and 18 may be accurately measured by suitable pressure differential measuring apparatus. The pressure regulator conduit 35 communicates with and operates the pneumatically controlled valve 22 in the cold air inlet 11. Normally the range of the flow regulated pressure maintained within the pressure regulator conduit 35 will be about 5 pounds per square inch, that is, from about 3 pounds per square inch to about 8 pounds per square inch. High air pressures in the pressure regulator conduit 35 tend to close the pneumatically controlled valve 22. Low air pressures in the pressure regulator conduit 35 tend to open the pneumatically controlled valve 22.

It is thus apparent that the how of hot air from the hot air inlet 12 is regulated in response to the thermostat 28 in such manner that greater quantities of hot air will be discharged into the inlet blending chamber 16 when the actual temperature in the control Zone is below the predetermined temperature setting. The amount of cold air discharged into the inlet blending chamber 16 from the cold air inlet 11 will be sufiicient so that the combination of the hot air and cold air which passes through the perforate plate 20 is a predetermined volume.

The normal operation of the system illustrated in FIGURE 1 can be described by the graphical representation shown in FIGURE 2. The vertical axis represents the flow of air from each of the two inlets 11, 12. An arrow A indicates the predetermined constant volume of air which is desired in the control zone It The horizontal axis indicates the temperature regulated pressure (thermostat pressure) maintained within the temperature regulated conduit 39. It will be observed that increasing thermostat pressure results in a decreased volume of hot air entering into the inlet blending charnher 16. The amount of cold air discharged into the inlet blending chamber 16 is supplementarily dependent upon the amount of hot air and is such that the summation of the cold air and the hot air is equal to the predetermined constant volume which is indicated by the arrow A. The arrow B indicates the flow of hot air which is achieved when the pneumatically controlled valve 23 is fully opened with a normal static pressure being maintained in the hot air inlet 12. The arrow C indicates that there is no hot air admitted into the inlet blending chamber 16 when the pneumatically controlled valve 23 is completely closed, corresponding to a high temperature regulated pressure appearing within the conduit 3%). Under normal operatin conditions, the system illustrated in FIGURE 1 will perform entirely within the normal range indicated in FIGURE 2. That is, some quantity of air will be admitted into the inlet blending chamber 16 from each of the inlets 11 and 12.

The system illustrated in FIGURE 1 exhibits inherent defects in two circumstances:

Circumstance ].When the control zone 10 is cold and a high static pressure exists in the hot air inlet 12.

Circumstance 2.When the control zone iii is cold and a low static pressure exists in the hot air inlet 12.

According to the present invention, mixer box controls are presented which overcome the inherent defects in the two described circumstances. To offset circumstance 1, a shuttle valve is provided in the thermostat conduit which permits the differential pressure regulator to override the thermostat as the control parameter for the pneumatically controlled valve in the hot air inlet. To compensate for circumstance 2, a shuttle valve is provided in the pressure regulator conduit which causes closure of the pneumatically controlled valve in the cold air inlet in respose to pressurized supply air when the thermostat pressure falls below its normal operating range.

The principal obiect of this invention is to provide a mixer box and controls therefor which will automatically regulate the flow of air from a two-stream air conditioning system to maintain a predetermined temperature within a control zone while providing ventilation at a substantially constant volume rate.

A further object of this invention is to provide a mixer box and control system therefor to regulate the flow or" air from a two-stream air conditioning system regardless of the static pressure fluctuations in the streams.

These and other objects and advantages of the present invention will become apparent from the following detailed description.

Circumstance I.When the control zone 10 is cold and a high static pressure exists in the hot air inlet 12.

Consider the system shown in FIGURE 1 when the control zone 10 is cold, i.e., at a temperature below tr e predetermined temperature. Decreased temperature regulated pressure in the thermostat conduit 30 will cause the pneumatically controlled valve 23 to move to fully open position. If, at this time, the static pressure within the hot air inlet 12 is excessive, it is possible that the hot air issuing into the inlet blending chamber 16 has a greater volume than the predetermined volume which is controlled by the differential pressure regulator 31. Accordingly the pressure taps 32, 33 will sense an excessive differential pressure; hence an increasing flow regulated pressure will appear in the pressure regulator conduit 35 to cause the pneumatically controlled valve 22 to close completely. The differential pressure regulator 31 at that point has fully compensated the dependent variable which it controls yet has not limited the volume of air flowing through the perforate plate 20 to the predetermined value. The result is as shown in FIGURE 3 where it appears from the arrow D that the flow of cold air has been terminated yet the total flow, representing exclusively hot air, exceeds the predetermined value (indicated by the arrow A) as shown by the shaded area 34. Thus when circumstance 1 develops, an excessive volume of air is introduced into the control zone 18 through the conduits 24, 25.

The embodiment of this invention illustrated in FIG- URE 4 avoids the difi'iculties just described with reference to circumstance l. The essential elements of FIG- URE 4 are the same as those illustrated in FIGURE 1 and corresponding numerals refer to corresponding elements.

A shuttle valve 40 is provided having two inlet connections and one outlet connection. A thermostat conduit 30a connects the thermostat 28 with one of the inlet connections of the shuttle valve 40. A pressure regulator conduit 41 extends from the pressure regulator conduit 35 to the other inlet connection of the shuttle valve 49. A pneumatic valve operating conduit 42 connects the outlet of the shuttle valve 40 with the pneumatically controlled valve 23.

The shuttle valve 40 is more clearly illustrated in FIG- URE 5. Essentially the shuttle valve 49 is formed from two casing halves 43 and 44 which are joined together by means of bolts 45. A flexible diaphragm 46 separates the casing halves 43 and 44. Cavities in each of the casing halves 43 and 44 form a right hand chamber 47 and a left hand chamber 48 separated by the flexible diaphragm 46. A conduit 49 is provided in the casing half 43 for communication between the thermostat conduit 39a and the right hand chamber 47. A conduit 50 is provided in the casing half 44 for communicating between the pressure regulator conduit 41 and the left hand chamber 48. A conduit 51 extends through both of the casing halves 43, 44 and communicates between the right hand chamber 47 and the pneumatic valve operating conduit 42. A threaded needle adjustment screw 52 extends through the casing half 43 to provide an adjustable restriction in the conduit 51. A conduit 53 is provided in the casing half 44 between the left hand chamber 48 and the pneumatic valve operating conduit 42. A central boss 54, 55 extends inwardly from each of the casing halves 43, 44 respectively.

It will be apparent that the air pressure of the thermostat conduit 33a is presented in the right hand chamber 47 through the conduit 49 whereas the air pressure of the pressure re ulator conduit 41 is presented in the left hand chamber 48 through the conduit 50. Under normal operating conditions, the pressure in the right hand chamber 47 will exceed the pressure in the left hand chamber 48 and consequently the diaphragm 46 will be displaced to the left to cover the chamber openings of the conduits 50, 53 which are presented in the left hand chamber 48 in the boss 55. Accordingly the conduits 49, 51 will be in communication with the right hand chamber 47 and the air pressure of the thermostat conduit 3% will be transmitted through the conduit 49, the right hand chamber 47, the conduit 51 to the pneumatic valve operating conduit 42. In effect, under normal operating conditions, there is a direct conduit connection between the thermostat 28 and the pneumatically controlled valve 23 and hence the system shown in FIGURE 4 normally functions exactly as the system shown in FIGURE 1.

However when circumstance l is presented, i.e., the temperature within the control zone 16 is below the predetermined value and a high static pressure exists in the hot air inlet 12, the inherent defect illustrated in FIG- URE 3 is ofiset by the apparatus shown in FIGURE 4. The defect is offset in the following manner. Because of the low temperature existing in the control zone 10, the air pressure in the thermostat conduit 34a is a low value tending to open the pneumatically controlled valve 23 to a maximum open position. Similarly the air pressure in the pressure regulator conduit 35 is a maximum tending to close the pneumatically operated valve 22. Once the pneumatically operated valve 22 is fully closed, the differential pressure regulator 31 will continue to increase the air pressure in the pressure regulator conduit 35 in an effort to correct for the excessive differential pressure which is being sensed through the pressure taps 32, 33. The further increasing pressure is transmitted through the conduit 41 into the shuttle valve 40 through the conduit 50. When the pressure in the left hand chamber 43 exceeds the pressure in the right hand chamber 47, the diaphragm 46 moves from left to right covering the boss 54 and opening the boss 55, Thus the increased pressure from the conduit 41 is transmitted through the conduit 5% into the left hand chamber 48 through the conduit 5;: to the pneumatic valve operating conduit 42 where it exerts a pressure against the pneumatically operated valve 23 tending to cause it to move toward a closed position until only the predetermined volume of air is issuing through the perforate plate 20.

Normal operation is restored when the static pressure in the hot air inlet 12 is reduced to a normal value or when the temperature in the control zone 10 rises to a value closer to the predetermined value. If the static pressure in the hot air inlet 12 decreases to a normal value, the air issuing from the conduit 12 into the inlet blending chamber 16 will be less than the predetermined value and the air pressure in the pressure regulator conduits 35 and 41 will decrease to allow the diaphragm 46 to move against the boss 55 as in normal operation. Alternatively a closer approach to the predetermined temperature in the control zone 1% will result in an increase in the air pressure in the thermostat conduit 30a which will cause the diaphragm 46 to move against the boss 55 and at the same time exert a closing tendency through the pneumatic valve operating conduit 42 against the pneumatically operated valve 23.

The correction achieved by the system illustrated in FIGURE 4 is shown graphically in FIGURE 6. When the flow of cold air has been terminated completely (see the arrow D), the shuttle valve 40 automatically switches the control parameter from the thermostat to the differential pressure regulator so that the desired volume of air, as indicated by the arrow A, is not exceeded.

A typical situation which might create circumstance 1 would be presented when an individual within the control zone 10 opens a window or a door in cold weather to allow a substantial quantity of cold air to enter the control zone 10 and create a decrease in the actual temperature therein. If this situation should develop at a time when an excessive static pressure appears in the hot air inlet 12, circumstance 1 would be presented.

Circumstance 2.When the control zone 10 is cold and a low static pressure exists in the hot air inlet 12.

Referring once again to the apparatus shown in FIG- URE l, in this circumstance the thermostat 28 develops an increasing temperature regulated pressure in the thermostat conduit 39 causing the pneumatically operated valve 23 to open to a full position. Because of the inadequate static pressure in the hot air inlet 12, less than the predetermined total volume of air is discharged from the hot air inlet 12 into the inlet blending chamber 16. Accordingly the differential pressure regulator 31 reduces the flow regulated pressure in the pressure regulator conduit 35 causing the pneumatically operated valve 22 to move in an open position. As a result, a blend of air from the cold air inlet 11 and the hot air inlet 12 is introduced into the inlet blending chamber 16 and thence through the mixing chamber 17 to the distribution chamber 18 and into the control zone 1% despite the fact that the control zone 10 already is at a temperature below the predetermined value.

This condition is illustrated graphically in FIGURE 7 where the arrow E indicates the maximum flow of hot air attainable with a fully opened valve 23. Because the value indicated by the arrow B is less than the predeterined value indicated by the arrow A, a quantity of cold air indicated by the shaded area 61 will enter the control Zone 10.

According to a further embodiment of the present invention as illustrated in FIGURE 8, the difiiculties described as circumstance 2 can be obviated. The elements of the mixer box shown in FIGURE 8 are essentially the same as those shown in FIGURE 1. merals are employed to indicate corresponding elements.

. The principal change is the provision of a shuttle valve 62 having two inlet ports 63, 64, one outlet port 65, and one control port 66. A source of supply air is introduced into a conduit 67 to the inlet port 63. The pressure regulator conduit 35a joins the differential pressure regulator 31 with the inlet port 64. A valve operating conduit 68 joins the outlet port 65 with the pneumatically operated valve 22. A shuttle valve operating conduit 69 connects the thermostat conduit 30 with the shuttle valve operating inlet port 66.

The shuttle valve 62 is more fully illustrated in FIG- URE 9.

The valve 62 comprises a hollow casing 70 having an internal chamber 71 and the previously mentioned inlet ports 63, 64 and outlet port 65. An annular boss 72 is provided externally of the casing 70 surrounding a plunger port 73 which extends through the casing 70. A resilient diaphragm 74 is secured across the outer surface of the annular boss 72 by peripheral sealing of a cover plate 75. The diaphragm 74 comprises the common wall of two chambers 76 and 77 which are respectively a shuttle valve operating chamber 76 and a vent chamber 77. The shuttle valve operating port 66 appears in the cover plate 75. Secured to the diaphragm 74 is a flat metal plate 78 and, mounted normally thereto, an operating plunger 79 which extends through the plunger port 73. A bleed port 88, opening to the atmosphere, extends through the annular boss 72 from the vent chamber 77.

Within the shuttle valve chamber 71 and pivotally mounted about a pin 81 is a flapper 82 suitably formed from a fiat piece of metal and having at its extreme end a pair of pads 83, 84 of rubber or similar resilient material. A normally compressed spring 85 is positioned with relation to the flapper 82 to exert a force tending to cause counterclockwise movement of the flapper 32 whereby the pad 83 covers the tip 86 of the pressure regulator conduit 35a and the pad 84 is displaced from the tip 87 of the supply air conduit 67. Opposing the counterclockwise force presented by the normally compressed spring 85 is the plunger 79 which bears against the flapper 82 exerting a clockwise force about the pivot pin 81. The force exerted by the plunger 79 is determined by the pressure maintained within the operating chamber 76, i.e., the pressure within the thermostat conduit 69.

Normally the pressure in the operating chamber 76 is sufficient to cause the plunger 7 to overcome the resiliency of the normally compressed spring 85 whereby, under normal conditions, the pad 84 is compressed against the tip 87 of the supply air conduit 67 so that a direct flow passageway is provided from the pressure regulator con duit 35a through its tip 86 and into the pneumatic controlled valve operating conduit 68. When the temperature regulated pressure in the thermostat conduit 69 falls below a predetermined value, the resilient spring 85 causes counterclockwise movement of the flapper 82 whereby the supply air conduit 67 is free to introduce its pressure directly into the conduit 68. The pressure of the air in the supply conduit 67 is at all times in excess of that appearing in the pressure regulator conduit 35a. Under normal conditions the supply air conduit pressure will be from about 17 to 20 pounds per square inch. The pressure in the how regulated pressure regulator conduit 35a will have a range of about pounds per square inch, for example from about 3 to about 8 pounds per square inch. Since the normal range of pressures in the thermostat conduits 3t), 69 is from about 8 to 13 pounds per square inch, the resilient spring 85 produces counterclockwise movement of the flapper 82 only when the pressure in the operating chamber 76 falls below about 8 pounds per Corresponding nusquare inch. The spring tension of the spring is adjusted to the lower pressure of the operating range of the pressures in the thermostat conduit 30.

Returning to FIGURE 8, it will be observed that the system operates satisfactorily under circumstance 2. That is, under normal conditions, the system shown in FIG- URE 8 performs exactly as the system shown in FIG- URE '1.

Where, however, the low pressure maintained in the thermostat conduit 30 results in a fully opened valve 23, that same low pressure will activate the shuttle valve 62 whereby the supply air from the conduit 67 will be introduced into the conduit 68 to operate the pneumatically controlled valve 22. By virtue of its normal pressure of 17 to 20 pounds per square inch, the pressure from the supply air conduit 67 will cause the pneumatically controlled valve 22 to close completely.

Accordingly the characteristics of the system illustrated in FIGURE 8 can be graphically represented as shown in FIGURE 10. When the temperature regulated pressure from the thermostat decreases to a value below its normal operating range, the pneumatically controlled valve 23 becomes fully opened and, with a constant static pressure existing in the hot air inlet 12, the resulting air flow through the hot air inlet 12 will be constant as shown by the arrow F. Because of the postulated low static pressure in the hot air inlet 12, the flow of air therefrom at fully opened position is less than the predetermined flow of air as indicated by the arrow A. Nevertheless, because the thermostatic pressure is below its normal range, the further inflow of cold air is prevented and exclusively hot air is introduced into the inlet blending chamber 16. Admittedly the total flow of air from the system shown in FIGURE 8 does not, in this one isolated circumstance, have a constant value.

A typical situation giving rise to the circumstance 2 occurs in the early morning in buildings which have been mantained at lower than normal temperatures throughout the preceding evening during which the building was relatively unoccupied. In the early morning, every room or control zone 10 presents a temperature below the predetermined value and accordingly every room or control zone requires substantial quantities of hot air until the predetermined temperature is attained. Because of the universal demand upon the hot air supply, certain periods of low duct pressure may occur in the hot air inlets 12 through the inability of the hot air supply system to provide the peak load requirements. Thus the system illustrated in FIGURE 8 compensates for a problem which occurs daily in the operation of dual duct air conditioning systems.

Having now described its elements the preferred embodiment of the present invention may now be quickly illustrated by reference to FIGURE 11. The apparatus shown in FIGURE 11 embodies that previously shown in FIGURES 4 and 8., Corresponding numerals are employed to indicate corresponding elements.

As shown in FIGURE 11, both the shuttle valve 40 and the shuttle valve 62 are included in the preferred embodiment. The system shown in FIGURE 11 operates exactly, with respect to the shuttle valve 40, as the system illustrated in FIGURE 4. The system, with respect to the shuttle valve 62, operates exactly as that shown in FIG- URE 8. The conduit 30a joins the thermostat 28 with the shuttle valve 46. In the preferred embodiment, the shuttle valve operating conduit 69 joins the thermostat conduit 30a with the operating port 66 of the shuttle valve 62. Similarly the pressure regulator conduit conduit 35a joins the difierential pressure regulator 31 with the inlet port 64 of the shuttle valve 62. In the preferred embodiment the pressure regulator conduit 41 joins the pressure regulator conduit 35a with the inlet port of the shuttle valve 40.

According to the provisions of the patent statutes, I have explained the principle, preferred embodiment and mode of operation of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. In an air conditioning mixing and distributing box having a hot air inlet, a cold air inlet and at least one outlet conduit for discharging a blended stream of conditioned air into a relatively confined zone, a fluid pressure operated valve in each of said inlet conduits, a source of supply air under pressure, flow responsive means adapted to control the pressure of a first supply air source as aflow regulated pressure in accordance with the flow rate of said blended air stream, temperature responsive means within said relatively confined zone adapted to control the pressure of a second supply air source as a temperature regulated pressure in accordance with the temperature existing within said relatively confined zone, shuttle valve means having two fluid inlets and one fluid outlet adapted to communicate the said fluid outlet with that fluid inlet having the greater static pressure, conduit means communicating the said temperature regulated pressure and the said flow regulated pressure respectively to the said two fluid inlets and for connecting the said fluid outlet to the said fluid pressure operated valve in the said hot air inlet, and conduit means communicating said flow regulated pressure to said fluid operated valve in said cold air inlet.

2. In an air conditioning mixing and distributing box having a hot air inlet, a cold air inlet and at least one outlet conduit for discharging a blended stream of conditioned air into a relatively confined zone, a fluid pressure operated valve in each of said inlet conduits, a source of supply air under premure, flow responsive means adapted to control the pressure of a first supply air source as a flow regulates pressure in accordance with the flow rate of said blended air stream, temperature responsive means within said relatively confined zone adapted to control the pressure of a second supply air source as a temperature regulated pressure in accordance with the temperature existing within said relatively confined zone, conduit means communicating the said temperature regulated pressure to the said fluid pressure operated valve in the said hot air inlet, shuttle valve means having two inlet ports and one outlet port, means within said shuttle valve means responsive to the pressure of said temperature regulated pressure to communicate said outlet port with only one of said inlet ports, conduit means connecting a third supply air source to one of said inlet ports and communicating said flow regulated pressure to the other of said fluid inlet ports and for connecting said outlet port to said fluid operated valve in said cold air inlet.

3. In an air conditioning mixing and distributing box having a hot air inlet, a cold air inlet and at least one outlet conduit for discharging a blended stream of conditioned air into a relatively confined zone, a fluid pressure operated valve in each of said inlet conduits, a source of supply air under pressure, flow responsive means adapted to control the pressure of a first supply air source as a flow regulated pressure in accordance with the flow rate of said blended air stream, temperature responsive means Within said relatively confined zone adapted to control the pressure of a second supply air source as a temperature regulated pressure in accordance with the temperature ex isting within said relatively confined zone, first shuttle valve means having two fluid inlets and one fluid outlet adapted to communicate the said fluid outlet with that fluid inlet having the greater static pressure, conduit means communicating the said temperature regulated pressure and the said flow regulated pressure respectively to the said two fluid inlets and for connecting the said fiuid outlet to the said fluid pressure operated valve in the said hot air inlet, second shuttle valve means having two inlet ports and one outlet port, means within said second shuttle valve means responsive to the pressure of said temperature regulated pressure to communicate said outlet port with only one of said inlet ports, conduit means connecting a third supply air source to one of said inlet ports and communicating said flow regulated pressure to the other of said fluid inlet ports and for connecting said outlet port to said fluid operated valve in said cold air inlet.

References Cited in the file of this patent UNITED STATES PATENTS 2,793,812 McDonald May 28, 1957 2,815,915 Salerno Dec. 10, 1957 2,821,343 Payne Ian. 28, 1958 Disclaimer 3,026,04L-Arthur P. J entoft, Wexford, Pa. CONDITIONED AIR DISTRIBUTION. Patent dated Mar. 20, 1962. Disclaimer filed Sept. 13, 1962, by the assignee, H. H. Robertson Company. Hereb enters this disclaimer to claim 1 of said patent.

Gazette October 25, 1962.]

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