US2321242A - Method and apparatus for - Google Patents

Description

June s, 1943. `M A, RAMSEY 2,321,242

METHOD AND APPARATUS FOR CONDITIONING AIR Filed Nov. 14, 1939 Patented June 8, 1943 METHOD AND APPARATUS FR CONDITIONING AIR.

Melvin Atkinson Ramsey, Buenos Aires, Argentina Application November 14, 1939, Serial No. 304,317 In Argentina `uly 6, 1939 (Cil ca -12s) 4 Claims.

The present invention relates to air conditioning and in particular to air conditioning methods and apparatus in which a portion of the recirculated air is by-passed with respect to the air conditioning devices.

It has been recognised for some time that the by-passing of a portion ofthe main stream of recirculated air in such manner that the by-passed portion is not subjected to the action of the cooling and dehumidifying devices allows desirable conditions to be obtained which cannot otherwise be achieved. According to known methods the proportion of air by-passed has been controlled by a variety of instrumentalities all of which have been either directly or indirectly responsive to a factor present in the air in the conditioned space or in the return duct. Generally other means have been provided for maintaining constant the temperature of the cooling medium by varying the degree of refrigeration thereof. In water cooled apparatus, the volume of cooling medium (water) available is generally such that the refrigerator can be satisfactorily operated by a thermostat device controlling the capacity of the refrigerator plant, because the relatively large Volume ofswater will allow the refrigerator to operate for reasonably long periods with reasonably long intervals. If, however, direct expansion coils are used as the cooling medium, the system just described fails because the capacity variations available in such a type of cooling and dehumidifying device are very limited in practice. Consequently the control apparatus responsive to air conditions used to control the proportion of by-passed air to recirculated air will by varying the demand of the cooling medium cause the capacity of one such cooling device to vary with considerable and objectionable frequency, or, if more than one com- .pressor is used to secure variation in the refrigeration capacity by cutting compressors in and out of circuit, the effect of the aforementioned control apparatus will be to stop one compressor are never met in practice.

in other words, a large number of compressors, so that the installation would become disproportionately huge and expensive. Again, a direct expansion cooling plant composed of a small number of units could be efficiently controlled by known methods'provided that the cooling demand always varied in steps substantially equal to the capacity of each unit, but such conditions As is well-known by-passing is used in the ar of air-conditioning for a variety of objects, but fundamentally the purpose is essentially to dilute a volume of freshly conditioned air with a volume of air withdrawn from the conditioned space (recirculated air) but not subjected to conditioning before being reintroduced into the conditioned space, in orderto obtain the desired constancy of the temperature and humidity factors in the conditioned space. Seasonal and other circumstantial variations call for adjustment of the proportion of by-passed air to freshly conditioned air, particularly when the freshly conditioned air includes a proportion of outside air. The humidity factor is controlled principally by means of the cooling device which actsto alter the water content of the air passing therethrough in dependence on the relation between the temperature of the said air andthe temperature of when the temperature of the refrigerant falls slightly, thereby causing a rise in said temperature to occur immediately, whereupon the control apparatus will again start the compressor, probably only a few seconds after it has been stopped. Such frequent starting and stopping of the compressors is highly undesirable.

Theoretically, of course, it would be possible to adapt a direct expansion cooling plant so as to enable the known type of control apparatus to be used. but such adaptation would involve providing a very large number of unit steps, or

the effective element of the cooling means. In a dehumidifying device in which the medium is water, a sufficient volume of medium isl generally available or can readily be made available so as to render the device insensitive to transitory alteratons in the aforesaid temperature relationship while keeping it sufliciently sensitive to changes which demand a readjustment of the treatment conditions. Thus on the supposition that the installation comprises two sources of cooling water in one of which provision is made,l for local refrigeration and that the conditions in the circulating air have demanded a change over to the refrigerated supply of water, there will, owing to the volume of cooling medium, be a sufficient lag before equilibrium is again established or over-shot to prevent a demand Abeing made with undesirable rapidity fora change back to the original treatment conditions.

Heretofore the proportion of recirculated air to intensively dehumidied and cooled air has been controlled in dependence on the temperature of the space to be conditioned, hereinafter called the room temperature, and the capacity of the cooling and dehumidifying medium has been adjusted in accordance with ,the temperature variations therein. As already stated suc'h an "y arrangement is satisfactory in cases in which the response of the cooling medium to changes of capacity is relatively slow as in water-cooling, but is unsuitable in practice when it is desired to use direct expansion coils as the cooling medium. The setting of the recirculation dampers as determined by the device responsive to room temperature may be and very frequently is such that the capacity of the cooling plant at the time when the setting is effected, is insufficient to deal with the volume of air to be intensively cooled but that the addition of the next step of capacity is excessive. In these circumstances, the undesirable conditions of rapid cutting in and out of the compressor motor associated with the additional step will prevail.

The known practice may therefore be summarized as consisting in operating the recirculation dampers by means of a device responsive to the room conditions in order to maintain the room temperature constant, and maintaining constant the temperature of the cooling medium by varying the capacity of the refrigerator.

I have found, however, that the objections to which reference has been made may be overcome and substantially equal conditioning effects achieved in an air conditioning plant in which direct expansion coils Iare used, if the capacity of the refrigerator be controlled in accordance with variations in the room temperature and the dampers be operated by a device responsive to a function of the surface temperature of the refrigverator.

The room temperature will generally fluctuate at a very slow rate so that the demands for extra capacity will not be frequent on this score. On the other hand, a device responsive to a function of the surface temperature of the refrigerator and arranged to control 'the dampers, can adjust the relative proportions of recirculated and conditioned air so as to maintain constant conditions in the room, without calling for changes in capacity, at least until such a degree of disparity between the conditions in the room and the setting of the capacity controlling device has arisen as to cause the latterto respond.

It is therefore the principal object of the present invention to provide an improved method of air conditioning in which direct expansion coils are utilised as the cooling medium; and in which f the cutting in and out with objectionable frequency of the compressor motors shall be avoided.

Another object of the present invention is to provide a method of air conditioning including the by-passing of air for recirculation without reconditioning, and the control of the proportion of by-passed air by means of dampers, in which direct expansion coils are utilized as the cooling medium and in which the settingof the dampers is controlled by a device responsive to a function of the surface temperature oi said coils, the refrigeration capacity being controlled in response to variations in the conditions in the air conditioned space.

A further object of the present invention is to provide a method of air conditioning including the by-passing of. air for recirculation without reconditioning, and the control of the proportion of by-passed air by means of dampers, in which direct-l expansion coils are used as the cooling and dehumidifying medium, and in which the dampers are adapted to be adjusted to vary the proportion of by-passed air by means of a device responsive to the surface temperature of said coils, said device comprising setting adjustment means operatively associated with means responsive to the room conditions, whereby the setting of the said device may automatically be altered to meet abnormal conditions, the refrigeration capacity being controlled in response to variations in the room conditions.

These and other objects and advantages of the present invention will appear more clearly in the course of the following description thereof.

In the drawing: I Fig. 1 is a diagram illustrating one embodiment of the present invention, and Figs. 2 and 3 are diagrams of portions of the plant illustrating certain modifications.

With particular reference to Fig. 1 air from the room I0 to be conditioned is drawn through a return duct I2 into a suction space I4 by means of a fan I6 which discharges the air into room III. The part of the air withdrawn from the room IIJ into the suction space I4 (hereinafter referred to as recirculated air) may reach the suction space I4 either directly or by passing first through a refrigerating and dehumidifying zone. In the latter event, the recirculated air passes through an opening I8 near the end of the return duct remote from the room I0, into a space 20, where fresh air entering through a fresh air duct 22 may be added to the recirculated air, and then passes over the direct expansion units 24 into a mixing zone 26 immediately in front of the suction space I4. Alternatively the recirculated air may reach the suction space I4, through a by-pass duct 28 which discharges into the said mixing zone 26. For controlling the proportion of air by-passed a damper 30 is provided in the by-pass duct 28 and a second damper 32 is located at the air entrance to the direct expansion units. The dampers may be of any suitable known kind, but for convenience the louvre type has been used, in which damper 32 consists of a plurality of vanes 36 pivoted between frame members 38 and adapted to be moved by an actuating bar 40 and damper 30 consists of a plurality of vanes 33 pivoted between frame members 34 and adapted to be moved by an actuating bar 35. If desired dampers 42, 44 may likewise be installed in the recirculated air duct I8 and in the mouth of the fresh air inlet 22 if such inlet is provided. These additional or optional dampers 42, 44 may be manually adjustable whereas the dampers 30 and 32 are adapted to have their setting automatically adjusted in response to variations in the surface temperature of the refrigeration means or to a function there- As indicated in the drawing, a direct expansion unit is connected to one or more compressors 46a, 4Gb and 46c by means of a single suction line 48 and branch suction lines 48a, 48h and 48e and to a condenser 41 by means of a liquid line 49 through a valve 5I. Instead of using more than one compressor for variable refrigerating capacity, a single compressor of variable capacity may be used. Valve 5I may be a thermostatically controlled expansion valve, a refrigerant float valve or any other known means of controlling the flow of refrigerant between the condenser 41 and the evaporator or direct expansion unit 24. It is immaterial whether each compressor has its separate condenser or all compressors discharge into one condenser as shown so long as the liquidlines of all the condensers enter a common liquid line before supplying the direct expansion unit. There may be one or more direct expansion units so long asv they all are fed with refrigerant from a single liquid line through one or more refrigerant control valves and the evaporated refrigerant from all enters a common suction line. The important factor is that if more than one coil is used, they are connected so that all are in use whenever there is any refrigeration.

According to the present invention the compressors are controlled by a device responsive to the room conditions. This may take the form of a gas filled bulb 54 and a bellows 50 so connected that a rise in temperature will expand the bellows moving arm 56 and contactor 58 in a clockwise direction around axis 55, successively contacting points 60a, 60h and 60e thus closing circuits and in a manner which those skilled in the art will readily understand, successively starting compressors 66a, 46h and llSc. The device described for controlling the compressors is one form of temperature control or thermostat, but the device may be any known form of temperature control such as a thermostat. i

The device for controlling dampers 30 and 32 so as to govern the proportion of by-pass recirculated air and conditioned air is shown as a bulb 82 in contact with the surface of the direct expansion unit 2t and being connected to a bellows 52. The bulb contains a fluid which expands with a rise in temperature thus distending the bellows and causing the arms to rotate in a counter-clockwise direction around axis 53, (in the drawing) with the result that bar 40 moves upward moving damper 32 more tdward the closed position and bar 35 moves to the right carrying damper 30 more towardthe open position. This device may, of course, be replaced by any known device for moving dampers in response to a sensitive element, such as the bulb 62, either directly or indirectly such as pneumatically, electrically or in any other form. The sensitive element or bulb may be located in any position where it will be responsive to a temperature function of the expansion unit surface temperature.

For the better understanding of the present invention, the expression function of the surface temperature of the refrigerator coils will now be more fully explained with reference to 26 which has been hereinbefore referred to as the mixing zone.-

Thus the sensitive member 62 may be located as shown in Fig. 1 in close contact with the surv face of the coils of the direct expansion unit, within the coils themselves, or the suction pipe 48 or its branches 48a, 48h, 48e so as to be affected by the temperature therein, or at a point between the direct expansion units and the mixing zone so as to be affected by the temperature at that point.

As will readilyv be seen from the drawing, the system Vdescribed is designed to operate on the principle of maintaining substantially constant the coil surface temperature of the direct expansion units by adjusting the relative proportions of by-passed air to intensively conditioned air in accordance with the varying values of a function of said surface temperature, whereas v the capacity of the refrigerator plant is altered in accordance with variations in room conditions. For a given setting of the devices 50 and 52, and while the norma conditions corresponding to such setting obtain in room Hl, the dampers 30 and 32 will be adjusted so that the mixture discharged by fan i6 will maintain substantially constant said normal conditions. If the room l0 is untenanted, that is to say, if there be no factor present tending to disturb the conditions obtaining therein, damper 30 will be substantially fully open and damper 32 will be substantially fully closed, the compressor motors will not be operating, so that the direct expansion units will not be refrigerating and substantially the whole of the reclrculated air will be by-passed. If, through infiltration of heat or moisture or through the occupancy of the room, the conditions therein are slowly or more rapidly altered so as to reach a point within the range for which device 5|! has been set, the said device will respond to start up the first compressor motor, whereupon the surface temperature of the corresponding coils will be very rapidly lowered to within the range for which the damper control rdevice 52 is set. This will then operate to adjust 'the dampers so as to decrease the proportion of Fig. l to Fig. 3. In Fig. 1 the sensitive member 62 is shown in direct contact with the surface of the refrigerator, so that the function is an identity. The word function is to be understood in the sense usually given it in mathematics, so that the conditionsI for example the temperature, inside the coils (Fig. 3) or in the air leaving the coils a short distance away from the coils (Fig. 2) may all be said to be functions of the surface temperature since in each case the conditions bear some specific relationship to the said surface temperature. For example, the temperature inside the coils will differ from the surface temperature at least by the conduction gradient of the material of the coil walls. The conditions at a point a short distance away from the coils on the side thereof nearest to the fan i5 will have been so little disturbed, as to make them substantially equal to those in close proximity to the coils, and these latter obviously depend in a close manner from the surface temperature. By a short distance away from thecoils is meant a distance far enough to involve spatial separation but not far enough to bring the point (or the sensitive member) within the influence of the stream of by-pressed air. The zone of influence of the by-passed air is the zone by-passed air and to increase the amount of intensively conditioned air, in order to counteract the chilling of the coils. The factor tending to restore the conditions in room i0 to normal is the proportion of lintensively conditioned air, and this depends on the extent to which a given volume of recirculated air can maintain the coil surface temperature within the predetermined limits of constancy. The capacity controlling device 50 will tend to keep the first compressor `motor running until normal conditions have been restored in room l0, but the longer the compressor motor runs the more pronounced will be the refrigeration effect in the coils, so that in order to maintain the coil surface temperature constant, a greater volume of recirculated air (intensively conditioned air) will be required. Hence the damper control device 52 will continue to close the damper 30 and to open damper 32 until the volume of intensively conditioned air is such that equilibrium is established. In these circumstances a restoring factor will be injected into room I0 but owing to the relation between the volume of the return duct and that of the room space, a certain time will elapse before normal conditions are fully restored or until a point is reached at which the capacity controlling deconditioned air to be governed not by room conditions but by the coil surface temperature of ditioning has passed. If the condition disturbing factor in room I is such that its effects continually increase, then a point will be reached at which the device 50 will operate to connect a second compressor motor in circuit so that for this second compressor the same sequence of events will hold good in relation to the dampers and the damper controlling device as was described for the rst motor. Thus it will be seen that the second, and similarly the third or any other stage, compressor motor will be running and resting for reasonable periods which do not give rise to objectionable results so far as the motors are concerned. At the same time, the damper controlling device 52 by actuating the dampers as described will ensure that the motors are running for only the minimum time consistent with economy and satisfactory air conditioning.

'I'he device 50 will control the capacity of refrigeration and the damper controlling device will ensure that such capacity will be efficiently utilized to secure the desired correct proportion of latent to sensible heat.

Iclaim:

l. In an air conditioning system comprising a room to be conditioned. a return duct for recirculated air having a spent air inlet end and a spent air discharge end, a mixing zone, a refrigerating and dehumidifying zone communicating with said mixing zone, a fan communicating on its suction side with said mixing zone and on its exhaust side with said room, said return duct communicating with its spent air inlet end with said room and with its discharge end with said refrigerating and dehumidifying zone on the sde thereof remote from said mixing zone to direct recirculated air through saidrefrigerating and dehumidifying zone, direct expansion refrigeration means in said refrigeration and dehumidifying zone adapted to treat recirculated air and comprising compressors and' motors to drive said compressors, a by-pass connecting said return duct with and defining said mixing zone and 'adapted to by-pass untreated recirculated air, a

by-pass baffle on said by-pass a main baille between said spent air discharge end and said refrigerating means, means including means responsive to a function of the surface temperature of said refrigerating means operatively associated with said by-pass baille and said main baille to vary the relative positions thereof in response to variations in said function and means including means responsive to room conditions operatively associated with said motors to vary the capacity of said refrigerating means in response to room conditions.

2. The method of Ventilating and conditioning a room which includes withdrawing air from the room, conditioning said air by causing it to pass over the surface of a direct expansion refrigeration means of variable capacity, adding bypassed withdrawn air of a different condition to said conditioned air and adjusting in response to air conditions in the room the capacity of the vrefrigeration means and adjusting in response to a function of the surface temperature of said refrigeration means the proportion of bypassed withdrawn air and conditioned air and delivering this mixture of bypassed withdrawn air and conditioned air to the room in order to vary the conditions in the room.

3. The method of Ventilating and conditioning a room which includes withdrawing air from the room, conditioning said air by causing it to pass over the surface of a direct expansion refrigeration means of variable capacity, vadding bypass withdrawn air of a different condition to said conditioned air and adjusting in response to air conditions in the room the capacity of the refrigeration means and adjusting in response to a function of the surface temperature of said refrigeratlon means the proportion of bypassed withdrawn air and conditioned air and'delivering this mixture of bypassed withdrawn air and conditioned air to the room in order to vary the conditions in the room.

4. In an air conditioning system comprising a room to be conditioned, a return duct for recirculating air having a return air inlet end and a return air discharge end, a mixing zone, a refrigerating and dehumidifying z one communicating with said mixing zone, a fan communieating on its suction side with said mixing zone and on itsdischarge side with said room. said return duct communicating with its return air inlet end with said room and with its discharge end with said refrigerating and dehumidifying zone on the side thereof remote from said mixing zone; direct expansion refrigeration means in said refrigeration and dehumidifying zone adapted to treat recirculated air and comprising compressors and motors to drive said compressors, a bypass connecting said return duct with `and ydefining said mixing zone and adapted to bypass untreated recirculated air, a bypass baille on said bypass, a main baille between said return air discharge end and said refrigeration means, means including means responsive to a function of the surface temperature of said refrigerating means operatively associated with said bypass baille and said main baille to vary the relative positions thereof in response to variations in said function and means including means responsive to room conditions operatively associated with said motors to vary the capacity of said refrigerating means in response to room-

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