US3257816A

US3257816A - Air conditioning apparatus

Info

Publication number: US3257816A
Application number: US335050A
Authority: US
Inventors: Charles W Parce
Original assignee: Individual
Current assignee: Individual
Priority date: 1964-01-02
Filing date: 1964-01-02
Publication date: 1966-06-28
Anticipated expiration: 1983-06-28

Description

June 28, 1966 c. w. PARCE 3,257,816

AIR CONDITIONING APPARATUS Filed Jan. 2, 1964 32 3 4 3| 0241M PA/v F/LTEE INVENTOR g Ckar/er/Z a/ce Q E 5 5 :5

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ATTORNEYS United States Patent This invention relates to air conditioning systems, and more particularly to systems providing conditioned air to an environmental room on a continuous basis without having to shut down the system for defrosting of the cooling coils.

Where air must be conditioned below 32 F., and especially dehumidified below a dew point of 32 F., it is wellknown that frost will accumulate upon the cooling coils of the conditioning system, thereby insulating the coil and restricting the air flow causing a loss of efficiency in the conditioning system and lOSs of control of desired conditions. At such times as frost forms upon the cooling coils, it is imperative that it be completely removed with a minimum amount of down time for the conditioning system while maintaining a precise control of the environmental room. The present invention contemplates an air conditioning system that permits defrosting while precisely conditioned air is delivered on a continuous basis.

An object of this invention is, therefore, to provide an apparatus for conditioning air, particularly when the air must be conditioned to a temperature below its dew point whether the dew point be above or below the freezing point of water.

Another object of this invention is to provide an apparatus which will allow air that has been conditioned below its dew point to be delivered on a continuous basis without shutting down the conditioning system to remove accumulated frost that will have formed upon the cooling coils during operation.

Another object is the provision of an apparatus and control for conditioning air that utilizes independent cooling units operating in close conjunction with one another to provide a continuous flow of conditioned air within very close tolerance of temperature and humidity.

Other objects, advantages and capabilities of the invention will become apparent from the following description taken in conjunction with the accompanying drawings showing only a preferred embodiment of the invention.

In the drawings:

. The figure shows a diagrammatic view of a preferred and practical embodiment'of an air conditioning system according to this invention.

Referring to the drawing, wherein like reference characters designate corresponding parts throughout the figure, the air conditioning chamber is generally indicated by reference numeral and comprises a return air filter 11 mounted in the lower end of the chamber '10 through which air is re-circulated into the system to be reconditioned.

To provide cooling of the air, chamber 10 has mounted therein two

separate cooling units

12, 13 which may be mounted, as shown in the drawing, in a spaced vertical relation. Chamber walls 14 of the

cooling units

12, 13 may, if desired, have a hollow core and be filled with a suitable insulation (not shown) to prevent excessive heat transfer from the outside ambient air through the walls 14.

The lowermost cooling unit, designated by numeral 12, comprises an air inlet opening 15 and an air discharge opening 16 which allows air, being drawn in through filter 11 and opening 15, to be circulated over cooling coil 17 and conditioned a desired amount before being discharged through opening 16. The damper system, comprising a pair of dampers 18a and 18b, is adapted to close over the openings 15 and 16 respectively to prevent air from entering cooling unit 12 for reasons later to be discussed, and

therefore, the air being unable to pass through unti 12 must pass through the by-pass plenum 19 without being conditioned by cooling unit 12.

Within the bottom panel, or lower wall 21 of cooling unit 12, is a drain pan defrost heater 22 comprising a plurality of resistance heating coils, indicated by 22a and 22b, which, upon energization at desired times, will impart heat to interior portion 23 of the wall 21 to remove any ice that may form in the integral drain pan 23a which is so constructed to effect removal of water whenever cool ing coil 17 is defrosted and is provided with a suitable drain opening (not shown) to allow exit of the melted frost. Suitably embedded within coil 17 are internal resistance heating elements, denoted as 17a, which melt any accrued frost upon the coil 17 which tends to impede the travel of air therethrough.

Cooling unit 13 is mounted generally vertically of the cooling unit 12 and the two units are basically identical in construction, and especially this is so with respect to the defrosting systems. The unit 13 comprises an air inlet opening 24 and an air discharge opening 25 which allows air moving upwardly in the by-pass plenum 1? to flow over cooling coil 26 at such times as the dampers 27a and 27b may be in an open position, thereby blocking all or a portion of the by-pass plenum 19 and necessitating the flow of air through chamber 13 and over coil 26.

Located upstream from the conventional centrifugal blower 28 and discharge opening 29 is an electric resistance heating element 31 suitably placed to provide the conditioned air from the plenum '19 with a degree of reheat that may be deemed to be proper at the time. The function of the heater 31 and its operation will be later described, but sufiice it to say that the heater 31 provides reheat to the conditioned air which, after passing through the

cooling chamber

12 or 13, may have been cooled more than the desired degree due to cooling required for dehumidification, or it may provide heat to raise the temperature of the environmental room,

If a particular conditioning application or environmental room calls for the conditioned air to have a certain amount of humidification over and beyond that of the ambient air, or if in cooling the air in one of the

cooling units

12 or 13 the humidity is lowered, then sufficient humidification may be supplied by automatically injecting steam into the air discharged from discharge opening 29 from steam line 32 through the automatic modulated steam valve 33. It should be noted that the steam must be injected into chamber 10 beyond the vicinity of the

cooling units

12 and 13 to prevent the build-up of ice about the walls and cooling coils 17 and 26 of the cooling units when operating below 32 F. In order to accomplish this purpose a specially designed distributor duct 34 is installed to provide proper distribution of the admitted steam to the discharge air flowing through discharge opening 29. By the provision of modulating steam valve 33 and specially designed distributor duct 34 the steam for humidification will be evenly distributed so it will mix with the condi-- tioned air flowing out of discharge 29 thereby providing a highly precise amount of humidification for a wide range of operating conditions. The proper distribution of the steam is accomplished by the provision of a duct 34 located just below the discharge opening 29 and by a perforated steam pipe 35, which introduces the correct amount of steam into the duct 34. The duct 34 and pipe 35 normally extend the full width of the discharge opening 29 in order that the steam flowing through duct opening 34a becomes entrained with air flowing out of the conditioning units which, at the time the humidifier is operating, is below the saturation point. If it is desired that the humidifier be located other than directly below and in front of the discharge opening 29, it may be equipped with a small blower (not shown) to blow room air over the top of the duct 34 to entrain the steam.

For automatic control of the present conditioning system there is provided an electronic temperature controller 36 and an electronic humidity controller 37, both of conventional design and more conveniently called thermostat and hygrostat respectively. To indicate the environmental room temperature a temperature sensitive sensor 38 is placed at a convenient location and is connected by an electronic lead 39, or any other suitable information transmission means, to thermostat 36. In a similar manner the relative humidity of the environmental room is conveyed by a humidity sensor 41 through line 42 to the hygrostat 37. The room humidity sensor 41 should preferably be placed in or within close proximity with the return air stream. Such a location may be within the chamber 10 behind filter 11 in order that a precise reading of the humidity of the return air may be had so as to closely modulate the steam injection from valve 33 if increased humidity is called for. When a reduction of humidity is required by conditions of the environmental room the humidity sensor 41 indicates to the hygrostat the degree of dehumidification needed.

To operate the pair of damper doors 18a and 18b of cooling unit 12, there is provided, as shown schematically in the figure, an electronic motor 43 responsive to control from thermostat 36. Additionally, an electric motor 44 that is responsive to control from hygrostat 37 is provided to operate the dampers 18a, 18b in close conjunction with temperature responsive motor 43. To combine the outputs from motors 43, 44 into a workable damper control, a differential gearing system 45 differentially combines the outputs from motors 43, 44 and causes drive shaft 46 and

damper door linkages

47a, 47b to move in a manner suitable to modulate the damper doors 18a, 1812 open and shut about

pivotal hinges

48a, 48b in whatever degree of movement is necessary to achieve a desired condition in the environmental room.

The damper doors 27a, 27b of cooling unit 13 are Operated in a manner similar as the damper doors 18a, 18b of unit 12, and an identical operating mechanism is provided which includes temperature responsive motor 51 responsive to thermostat 36, humidity responsive motor 52 responsive to hygrostat 37, differential gearing system 53, drive shaft 54 and damper door linkagesSSa, 55b.

In the

present invention motors

43, 44, 51 and 52 are understood to be not limited to any particular type or design of motor as other types of motors, whether electric, pneumatic or hydraulic, may be used with equally satisfactory results in controlling

damper doors

18a, 18b and 27a, 27b.

For

automaticallycontrolling cooling units

12, 13 independently of one another a central control timer mechanism 56 is provided to periodically energize temperature responsive motors 51, 43 to open damper doors 27a, 27b of cooling unit 13 and close damper doors 18a, 18b of cooling unit 12 whenever a sufficient amount of frost has accumulated upon coil 17, and in addition the timer will energize the electric defrost heater 22 to speed in the rapid removal of frost. The timer 56 has numerous other functions to perform in the overall refrigeration system of the present invention as will become evident in the description of a typical cycle of operation.

The cooling coils 17, 26 are supplied with a suitable refrigerant through conduit 57, and shutoff valves 58 and 59 are situated between inlet 61 and cooling coils 17, 26 respectively. Each valve 58, 59 may be independently operated upon signal from timer 56 indicating shut down time for defrosting. The refrigerant, after coursing through the open cooling coil and pre-cooling it (the exact one depends upon the particular operating cycle at that time) exits through conduit 62.

In operation, assuming the refrigeration system of the present invention to be initially in a steady state condition, the desired environmental room conditions of temperature and humidity are normally preset in the electrical controller 36 for temperature and the electrical humidity controller 37 for humidity. With the damper doors 18a and 18b in the position shown in the figure and with a suitable refrigerant flowing through open valve 58 into cooling coil 17 a portion of the air that is being drawn through filter 11 is being conditioned as to humidity and temperature by flowing through opening 15 across cooling coil 17 and thence out into the plenum 19, where it is mixed with the air flowing through the by-pass plenum that has not been forced into unit 12 by the damper doors 18a, 18b, subsequently directed into blower 28 and discharged into the environmental room that is to be con ditioned.

If the environmental room temperature rises and additional cooling is required the temperature sensitive sensor 38 senses the rise in temperature and transmits this information to thermostat 36 which controls through the timer 56 temperature responsive motor 43. The motor 43 will operate throughfdifierentiator gear system 45, draft shaft 46 and

linkages

47a, 47b to modulate damper doors 18a, 18b open to a greater degree in order to block a greater portion of the partially opened plenum 19 or to close it completely. If the plenum 19 is blocked completely, then the complete intake flow of air from the environmental room is allowed to flow over cooling coil 17. The damper doors will continue to modulate until sutficient cooling, as indicated by sensor 38, has been obtained to reduce the environmental room temperature to the desired degree.

When a reduction in humidity is indicated the humidity sensor 41 located in the return air duct relays to the hygrostat 37 the present relative humidity reading of air being returned through the filter 11, the hygrostat 37 operates the humidity responsive motor 44 which in turn modulates doors 18a, 18b to allow more air to pass over cooling coil 17 which will remove moisture from the air by condensing it upon the cooling coils 17.

In the event that a temperature drop in the environmental chamber, as indicated by sensor 38, the thermostat will operate motor 43 to energize the electrical resistance heating element 31 to provide the temperature increase to bring the environmental room to the set conditions. Because dehumidification also acts to lower the temperature of the air blowing across the cooling coils there will be normally needed a certain amount of reheat imparted to the air in order that the environmental room temperature may be kept constant. This reheat function is provided by the resistance heating element 31 at such time as the temperature sensor 38 indicated that the air undergoing dehumidification is also undergoing an unwanted drop in temperature.

When the environmental room temperature rises due to a high load in the environmental room, the refrigeration system will respond to this increase in temperature rise by providing greater cooling capacity in unit 12 and it will be seen that a corresponding decrease of humidity will take place when the air is being passed over the cooling coil .17 for temperature reduction. Upon the happening of such a condition the humidity of the environmental room is brought back to its preset condition by injecting steam through modulating valve 33 into perforated pipe 35 and thence into duct 34 and out through opening 34a wherein the injected steam thoroughly and completely mixes with the conditioned air being discharged. The amount of steam to be injected is controlled by humidistat 37 upon information received by the humidity sensor 41 located in the returning air duct.

In the normal course of operations it will be seen that both the humidity and temperature of the environmental room will tend to change constantly necessitating that the air being conditioned must be continuously and simultaneously conditioned as to both temperature and humidity. Such continuous conditioning is provided for by the incorporation into the present invention of motor 43 responsive only to temperature and motor 44 responsive only to humidity, both of which act through differential gearing system 4 5 which algebraically adds the respective imputs of these two motors and modulates the damper doors 13a, 18b to a balanced degree of humidity and temperature. When this'balanced degree does not precisely match the preset conditions of the environmental room additional temperature and humidity is supplied by heater 31 and steam modulating valve 33 respectively. With this method of control the damper doors are modulated to position so that the cooling, heating dehumidification and reheat exactly balance the environmental room load, and after temperature and humidity conditions called for by the precise conditions of the environmental room are achieved the damper doors remain practically motionless until a change in room load whereupon the damper doors shift slightly to balance the new load.

After cooling unit 12 has been in operation for a period of time under conditions requiring operation below a 32 F. dew point of the chamber air, and especially when the unit 12 has been conditioning air that has a high relative humidity, the water condensed out of the air passing through the cooling coil v17 will have accumulated as frost about the tubes of the coil, thereby limiting the volume of air that may pass, and thus the efficiency of the cooling coil is impaired. Periodically the central control timer 56 will close down cooling unit 12 and open cooling unit 13 in order that the accumulated frost may be removed from coil 17. The time interval between frost removals may be preset into timer 56 or the timer may be sophisticated enough to have programmed into it a defrosting schedule that would be dependent upon the operating temperature and humidity conditions of the cooling chamber then in operation. The timer 56 also pre-cools the defrosted coil after termination of the defrosting period by opening a refrigerant control valve 59.

At the desired time for defrosting coil 17, assuming unit 12 is in operation, the timer will first open refrigerant control valve 59 to admit refrigerant to coil 26 of unit 13. Because the idle coil is pre-cooled it is possible to shift the conditioning load to unit 13 without any loss of efficiency. Timer 56 also operates temperature motor 51 and humidity motor 52 to open damper doors 27a, 27b to allow\the air flowing through plenum 19 to be admitted to the unit 13. Simultaneously the damper doors 18a, 1812 are modulating shut at generally the same rate doors 27a, 2% are opening so as not to over or under condition the air.

Once damper 13a, 1812 have completely shut, valve 58 is closed to prevent refrigerant from flowing through coil 17 and the defrost heater system 22 is automatically turned on by the timer 56 to apply heat to chamber 12 and coil 17 for the purpose of melting frost. The heaters remain on until the coil is completely defrosted as determined by thermostat sensing element (not shown) located within the confines of coil 17. Once the frost is melted and the water has drained from drain pan 23 the heaters are turned off by timer 56 which in turn opens valve 58 to reduce the temperatureof'coil 17 in a manner similar to that described for coil 26 and unit 13.

At the end of the pre-set cycle the timer 56 will act to shut valve 5 9 and modulate open doors 18a, 181; and

simultaneously close doors 27a, 27b. The frost that has' accumulated in unit 13 during the operation while unit 12 was being defrosted will be allowed to melt naturally and have the water drained off through a drain in the bottom of the unit similar 'to the drain pan 23 of unit 12. Or in the alternative it is within the scope of this invention that defrost heaters may be provided in the bottom wall of unit 13 in a manner similar to that of unit 12.

With this method of control the damper doors of the cooling units 12, 113 are continuously modulated to a position so that the cooling, heating, dehumidification,

and reheat exactly balance the room loading. Experience shows that this system provides extremely uniform room conditions over extended periods due to its ability to match room loads exactly yet promptly adjust itself to any change in room load, and also its ability to provide frost free cooling. The unique modulating condition system of the present invention provides extremely accurate continuous control of temperature and humidity over ranges of -25 -F. to +125 F. and 20% to relative humidity.

While I have particularly shown and described 'one particular embodiment of the invention, it is distinctly understood that the invention is not limited thereto but that modifications may be made within the scope of the invention and such variations as are covered by the scope of the appended claims.

What is ciaimed is:

1. In an air conditioning apparatus comprising a housing having an air inlet and an air outlet, first and second cooling units, means for selectively supplying refrigerant to said cooling units, said second cooling unit being mounted in a spaced vertical relation with respect to said first cooling unit and having a common wall therebetween, electrical defrosting means integral with said first cooling unit, by-pass duct means connecting said housing air inlet and air outlet, each of said cooling units having a plurality of air openings, said air openings being in communication with said duct means, each of said cooling unitsbeing adapted to be individually and completely isolated from the passage of air which flows through the duct means and said housing, a movable damper door mounted in conjunction with each of said air openings and adapted to control the proportion of air flowing through saidd-uct means and said cooling units, means for moving air through said housing, heating means associated with the downstream portion of said by-pass duct means, thermostatic means downstream with respect to said heating means, hygrostat means upstream with respect to said first cooling unit, motive means for adjusting said damper doors, said motive means comprising for each of said cooling units a motor responsive to said thermostatic means and a motor responsive to said hygrostatic means and having the outputs of the motors of each cooling unit differentially connected for adjusting said damper doors of the respective cooling unit.

2. In an air conditioning apparatus comprising a housing having an air inlet and an air outlet, first and second cooling units, means for selectively supplying refrigerant to said cooling units, said second cooling unit being mounted in a spaced vertical relation with respect to said first cooling unit and having a common wall therebetween, electrical defrosting means integral with said first cooling unit, by-pass duct means connecting said housing air inlet and air outlet, each of said cooling units having a plurality of air opening-s, said air openings being in communication with said duct means, each of said cooling units being adapted to be individually and completely isolated from the passage of air which flows through the duct means and said housing, a movable damper door mounted inconjunction with each of said air openings and adapted to control the proportion of air flowing through said duct means and said cooling units, means for moving air through said housing, heating means. associated with the downstream portion of said bypass duct means, thermostatic means downstream with respect to said heating means, hygrostat means upstream with respect to said first cooling unit, humidifier means located downstream from said second cooling unit in said housing for imparting humidification to the conditioned air after discharge, control means responsive to said thermostatic means and said hygrostatic means, motive means for adjusting said damper doors, said motive means being adapted to be controlled by said control means to selectively position said damper doors of one of said cooling units open while maintaining the damper doors of the other cooling unit closed, said heating means, humidifier means and defrosting means being simultaneously responsive to said control means whereby air flowing through said air conditoning apparatus is conditioned within close tolerances of temperature and humidity on a continuous basis.

3. In the air conditioning apparatus of claim 2 wherein said means for moving air through said housing comprises, an air blower mounted vertically above said cooling units and being in communication with said by-pa-ss duct for moving air through said cooling units and said by-pass duct,

4. In the air conditioning apparatus of claim 2 wherein said heating means comprises, an electrical resistance heating means being mounted in said by-pass duct means whereby a controlled amount of reheat is imparted to the discharged air upon energization of the heating means.

5. In the air conditioning apparatus of claim 2 wherein said humidifier means comprises a steam injecting and diflusing apparatus to completely entrain the steam in the discharged conditioned air thereby preventing any dripping of condensate when the apparatus operates at low temperatures.

6. In an air conditioning apparatus comprising an air outlet, first and second cooling units, means for selectively supplying refrigerant to said cooling units, said second cooling unit being mounted in a spaced vertical relation with respect to said first cooling unit and having a common wall therebetween, electrical defrosting means integral with said first cooling unit, by-pass duct means connecting said housing air inlet and air outlet, each of said cooling units having a plurality of air openings, said air openings being in communication with said duct means, a movable damper door mounted in conjunction with each of said air openings and adapted to control the proportion of air flowing through said duct means and said cooling units, an air blower mounted vertically above said cooling units and being in communication with said by-pass duct for moving air through said cooling units and said by-pass duct, an electrical resistance heating means associated with the downstream portion of said bypass duct means whereby a controlled amount of reheat is imparted to the discharged air upon energization of the heating means, thermostatic means downstream with respect to said electrical resistance heating means, hygrostat means upstream with respect to said first cooling unit, humidifier means located, downstream from said second cooling unit in said housing for imparting excess humidification to the conditioned air after discharge, said humidifier means comprising a steam injecting and diffusing apparatus, control means responsive to said thermostatic means and said hygrostatic means, motive means for adjusting said damper doors, said motive means comprising for each of said cooling units a motor responsive to said thermostatic means and a motor responsive to said hygrostatic means and having the outputs of the motors of each cooling unit differentially connected for adjusting said damper doors of the respective cooling unit, said heating means, humidifier means and defrosting means being simultaneously responsive to said control means whereby air flowing through said air conditioning apparatus is conditioned within close tolerances of temperature and humidity on a continuous basis.

7. A method of conditioning air to a temperature below the dew point of the air being conditioned comprising the steps of sensing the temperature of air in an environmental chamber, passing the air into a passageway, sensing the humidity of the air being passed into said passageway, adjusting air blocking means associated with a first cooling unit in said passageway in response to the temperature and humidity sensings of the air to block a portion of the flow of air in said passageway, passing the blocked portion of the air through a first cooling coil in said first cooling unit reducing the temperature and humidity of the air, then mixing the air having reduced temperature and humidity with the air flowing in said passageway, then passing the mixed air past a closed second cooling unit, periodically at a predetermined time admitting refrigerant to a cooling coil in said second cooling unit, then closing said first cooling unit air blocking means and simultaneously adjusting passageway air blocking means of said second cooling unit to block a portion of the flow of air in said passageway, then passing a portion of the air through said second cooling coil reducing the temperature and humidity of the air, then mixing the air having reduced temperature and humidity with the air flowing in said passageway, stopping the flow of refrigerant in said first cooling coil and defrosting said first cooling coil during the time said second cooling coil is in operation.

8. A method of conditioning air to a temperature below the dew point of the air being conditioned comprising the steps of sensing the temperature of air in an environmental chamber, passing the air into a passageway, sensing the humidity of the air being passed into said passageway, adjusting air blocking means associated with a first cooling unit in said passageway in response to the temperature and humidity sensings of the air to block a portion of the flow of air in said passageway, passing the blocked portion of the air through a first cooling coil in said first cooling unit reducing the temperature and humidity of the air, then mixing the air having reduced temperature and humidity with the air flowing in said passageway, then passing the mixed air past a closed second cooling unit, periodically at a predetermined time admitting refrigerant to a cooling coil in said second cooling unit, then closing said first cooling unit air blocking means and simultaneously adjusting passageway air blocking means of said second cooling unit to block a portion of the flow of air in said passageway, then passing a portion of the air through said second cooling coil reducing the temperature and humidity of the air, then mixing the air having reduced temperature and humidity with the air flowing in said passageway, stopping the flow of refrigerant in said first cooling coil and defrosting said first cooling coil during the time said second cooling coil is in operation, discharging the conditioned air into an environmental chamber and immediately thereafter causing finely divided particles of steam to become entrained in the air to provide humidification.

References Cited by the Examiner UNITED STATES PATENTS 2,001,704 5/1935 Bulkeley 20 2,207,714 7/1940 Bulkeley 165-2O 2,388,210 10/1945 Hanson et al. 165-21 2,389,440 11/1945 Kucher 16521 3,063,253 11/1962 Dickson et al. 62-276 X 3,065,608 11/1962 Arz'berger 6280 3,091,942 6/1963 Dickson et al, 62-8O ROBERT A. OLEARY, Primary Examiner. MEYER PERLIN, Examiner.

W. E. WAYNER, Assistant Examiner.

Claims

7. A METHOD OF CONDITIONING AIR TO A TEMPERATURE BELOW THE DEW POINT OF THE AIR BEING CONDITIONED COMPRISING THE STEPS OF SENSING THE TEMPERATURE OF AIR IN AN ENVIRONMENTAL CHAMBER, PASSING THE AIR INTO A PASSAGEWAY SENSING THE HUMIDITY OF THE AIR BEING PASSED INTO SAID PASSAGEWAY, ADJUSTING AIR BLOCKING MEANS ASSOCIATED WITH A FIRST COOLING UNIT AND SAID PASSAGEWAY IN RESPONSE TO THE TEMPERATURE AND HUMIDITY SENSING OF THE AIR TO BLOCK A PORTION OF THE FLOW OF AIR IN SAID PASSAGEWAY, PASSING THE BLOCKED PORTION OF THE AIR THROUGH A FIRST COOLING COIL IN SAID FIRST COOLING UNIT REDUCING THE TEMPERATUERE AND HUMIDITY OF THE AIR, THEN MIXING THE AIR HAVING REDUCED TEMPERATURE AND HUMIDITY WITH THE AIR FLOWING IN SAID PASSAGEWAY, THEN PASSING THE MIXED AIR PAST A CLOSED SECOND COOLING UNIT, PERIOCIALLY AT A PREDETERMINED TIME, ADMITTING REFRIGERANT TO A COOLING COIL IN SAID SECOND COOLING UNIT, THEN CLOSING SAID FIRST COOLING UNIT AIR BLOCKING MEANS AND SIMULTANEOUSLY ADJUSTING PASSAGEWAY AIR BLOCKING MEANS OF SAID SECOND COOLING UNIT TO BLOCK A PORTION OF THE FLOW OF AIR IN SAID PASSAGEWAY, THEN PASSING A POR-