US3880224A

US3880224A - 3-Stream S-wheel and cooling mode operation

Info

Publication number: US3880224A
Application number: US118196A
Authority: US
Inventors: Sanford A Weil
Original assignee: GAS DEV CORP
Current assignee: Gas Developments Corp; GAS DEV CORP
Priority date: 1971-02-23
Filing date: 1971-02-23
Publication date: 1975-04-29
Anticipated expiration: 1992-04-29

Abstract

An improved adiabatic saturation cooling machine of the opencycle type and method of operation in which the capacity of the machine is increased by routing by-pass streams of air through either the S-wheel alone or both the S- and the L-wheel. The amount of these by-pass streams are from 0 to 100 percent that of the main exhaust stream of air passing from the room through the S-wheel. In the first embodiment the by-pass air is outside air and is directed to the regenerative ''''side'''' of the S-wheel. Such a by-pass stream ranging from 95*F to 80*F will cool the air from the S-wheel an additional 2.6* to 5.9*F below that capable by the room air exhaust stream alone. The outside air by-pass stream may be passed directly through the S-wheel or pretreated by passing through an E-pad. In the second embodiment, where there is sufficient air supplied to the burner section to regenerate the L-wheel, a portion of the primary room exhaust air stream is recirculated as a by-pass stream to the input face of the L-wheel. A third embodiment is directed to incoming air bypassing the E-pads from the cooling side of the S-wheel. A fourth embodiment is directed to a return by-pass for directing the first stream of incoming L-wheel air back out the regenerative ''''side'''' of the L-wheel.

Description

United States Patent Weil [ Apr. 29, 1975 3-STREAM S-WHEEL AND COOLING MODE OPERATION [75] Inventor: Sanford A. Weil, Chicago. Ill.

[73] Assignee: Gas Developments Corporation,

Chicago. 111.

[22] Filed: Feb. 23, 1971 [211 App]. No.: 118,196

Related US. Application Data [63] Continuation of Scr. No. 791.000. Feb. 23. 1971.

Primary E.\'uminerCharles Sukalo Attorney, Agent. or FirmMolinare Allegretti, Newitt & Witcoff TV /CAL OUTS/DE FRESH A/R DRYBl/LB- 95'E WETBULB- 80F [57] ABSTRACT An improved adiabatic saturation cooling machine of the opencycle type and method of operation in which the capacity of the machine is increased by routing bypass streams of air through either the S-wheel alone or both the S- and the L-wheel. The amount of these bypass streams are from 0 to 100 percent that of the main exhaust stream of air passing from the room through the S-wheel. 1n the first embodiment the bypass air is outside air and is directed to the regenerative side of the S-wheel. Such a by-pass stream ranging from 95F to 80F will cool the air from the S-wheel an additional 2.6 to 59F below that capable by the room air exhaust stream alone. The outside air by-pass stream may be passed directly through the S- wheel or pretreated by passing through an E-pad. 1n the second embodiment. where there is sufficient air supplied to the burner section to regenerate the L- wheel, a portion of the primary room exhaust air stream is recirculated as a by-pass stream to the input face of the L-wheel. A third embodiment is directed to incoming air bypassing the E-pads from the cooling side of the S-wheel. A fourth embodiment is directed to a return by-pass for directing the first stream of incoming L-wheel air back out the regenerative side of the L-wheel.

18 Claims, 5 Drawing Figures BYPASS PRECOOL ING A/R i l i 30 I I /2 2 4- HEEL i ROTATION 2 I r ,5, 1 BURNER fi:::: GAS

ROTATION 4 S-h HEEL p Li if 33 l l E AP0/f7?AT/VE1 I :P 7 l3 l 1 I 6 it Q TYP/CAL ROOM A/R 0R) BULB 75'5 WET BULB 63 F 3-STREAM S-WHEEL AND COOLING- MODE OPERATION This application is a continuation of application No. 791,000 filed Feb. 23, I971 and now abandoned.

This invention relates to air conditioning, and in particular to improvedefficiency of cooling involving improved process and apparatus for an open-cycle air conditioning unit.

Open-cycle air conditioners are well known in the art. One system. known as the Munters environmental control system (MEC) unit, is described in US. Pat. No. 2,926,502. Basically, open-cycle air conditioners operate by dehumidification and subsequent cooling of air wherein moist air is conditioned by a 3-stage process to produce cool relatively dry air.

Open-cycle air conditioning systems comprise essentially four sections, considered in order from the interior room in which the air is to be conditioned toward the exterior: 1) an adiabatic evaporating section designated an E-pad, 2) a S-wheel section, for transfer of sensible heat to and from air, 3) a heating section, and 4) a L-wheel section for transfer of latent heat of condensation and evaporation. MEC units are fuel gas or electrically-operated environmental control systems which provide cooling in the summer, heating in the winter, year-around control of humidity, and effective removal of dust and pollen. The principle involved in the cooling effect of the system is that dry, warm air can be simultaneously cooled and humidified by contacting it with water. In geographic areas where the air is both warm and humid, it must be dried before it can be cooled by evaporation. During the heating season of autumn, winter and spring, the unit can be used to warm and humidify cold, dry air by making minor changes in the units operating cycle.

However, the present Munters type of units suffer from an inadequate cooling step involved in the S- wheel section of the machine. The present S-wheels used in this type of machine are approximately 90 percent efficient. For example, air from the dehydrating L-wheel has an average temperature on the order of 190F and is cooled to 75.7F by the S-wheel during the cooling half of the cycle. In turn, the S-wheel is regenerated, i.e., recooled after taking up heat from the incoming air, by a 63F stream of air exhausting from the room during the regenerative half of the cycle. This rather high temperature of the conditioned air from the S-wheel (75.7F) is limited primarily by the wheel efficiency and, to some degree, to the outside ambient air temperature and humidity.

It is therefore an object of this invention to provide an improved open-cycle air conditioner assembly in which the cooling efficiency of the S-wheel is increased.

It is another object of this invention to provide an improved process of conditioning air whereby lower con ditioned air temperatures are achieved, and recirculation of room air is possible when so desired.

Another object of this invention is to provide improved process and apparatus for rejecting a first segment of moist air input through the L -wheel back out through the regenerative side of said wheel;

Another object of this invention is to provide improved process and apparatus for bypassing air from the outside through the 'S-wheel, or first through an E-pad and then the S-wheel, or from the exit side of the S-wheel to the input side of the Lwheel, or from the cooling side of the S-wheel to the room without passing through an E-pad, and the various combinations of bypasses thereof.

Additional objects of this invention will be evident from the detailed description which follows.

The objects of this invention are achieved by directing streams of air through either the regenerative side of the S-wheel, and/or the input face of the L-wheel. In the first embodiment, the S-wheel is precooled by directing a stream of outside air through the wheel prior to passing the primary or main cooling stream of air exhausting from the room through the wheel. In the apparatus .and method of this invention, as the S-wheel passes through the regenerative portion of the cycle, a first, precooling, stream of air is passed through the wheel. This precooling, or secondary air, may be ambient outside air and can be an amount less, as large, or larger than, the amount of the room exhaust air. The secondary air amount can be varied to achieve the desired final conditioned air temperature, and will be typically an amount of 20-100 percent of the main stream passing through from I to 50 percent, and preferably 5 to 30 percent, of the surface area of the S-wheel. The particular area value within this range may be determined to avoid excessive blower power requirements. Thereafter the room exhaust air stream. called the main or primary stream, is passed through an appropriately proportioned fraction of the S-wheel. Usually the amount of primary air exhausted is equivalent to the amount entering the room, but may be more or less as inside an outside environmental factors permit depending on the machine capacity.

In a second embodiment, which is preferably operated in conjunction with a bypass stream of outside air, a portion of the primary exhaust stream is directed as a bypass stream to the input face of the L-wheel.

Two other embodiments involve, respectively, passing incoming air directly to the room from the cooling side of the S-wheel without passing through an E- pad, in order to achieve humidity control and rejecting a first segment of moist air input through the L-wheel from the outside back out through the regenerative side of the L-wheel.

In the Figures like numbers in different figures indicate similar or equivalent parts. The arrows show the air flow paths and are indicated in dashed lines where the air passes through an E-pad, a wheel, or a duct not shown in cross-section. All ducts are shown in diagrammatic cross-section except the portion between the re generative side E-pad and S-wheel and a portion of the recycle duct, which are shown in plan view, and the duct of FIG. 5 which is shown in perspective.

FIG. 1 shows diagrammatically one embodiment of an open-cycle air conditioning system of this invention wherein the Swheel is precooled by a stream of secondary, bypass air;

FIG. 2 shows digrammatically another embodiment of an opencycle air conditioning system of this invention employing a pretreated stream of precooled bypass air;

FIG. 3 is an exploded perspective view of the interior face of an S-wheel showing qualitatively the portions of the wheel exposed to the precooling bypass stream and the primary cooling air streams respectively;

FIG. 4 shows diagrammatically another embodiment employing ducting for recirculation of room air; and

FIG. 5 shows a perspective view partly in section of a return conduit for passing input air back out the L- wheel regenerative side.

Referring now to FIG. 1, a conventional open-cycle system operating in the cooling mode may be described as follows: The incoming outdoor air is shown by the downwardly pointing arrow on the left side of the diagrammatic representation of an open-cycle unit 1. To start the cooling half of the cycle, the warm, moist outside air is drawn into the unit by means of a fan 2 and passed through the input side 30 of a hot, dry L-wheel 3 which serves the function of taking up (sorbing) moisture from the air. In the figures the L-wheels rotate clockwise, from left to right as seen from the top. A major portion of the latent heat of condensation liberated by the water in being absorbed in the L-wheel is taken up by the air as it passes through the wheel.

The air leaving the L-wheel is not uniform in temperature or humidity. I have found that air which first passes through the L-wheel after the wheel has left the regenerative half of the cycle should not continue on to the S-wheel but be diverted into the regenerative stream. 1 have discovered that this portion of air serves primarily to cool the L-wheel with very little dehydration of the air. I have determined that at usual air velocities (about 200 feet per minute through the L-wheel rotating at a representative speed of 34 minutes per revolution), about a fifth of a minute for each 6 inches of wheel depth is required for this cooling section. This may also be expressed as the equivalent angle of rotation, 0, of between about l7-24 per 6 inches wheel depth. The efficiency of the machine is enhanced if this portion of the air stream leaving the L-wheel is sent into the regenerative stream immediately upstream of the burner, as shown in FIG. 5. FIG. 5 shows that the first portion of incoming air passing through a segment of the L-wheel identified by the angle 6 is diverted in a bypass duct 40 back through the regenerative side of the L-wheel by means of baffle 41 as shown by the arrow 42. As shown it can be diverted through the preceeding segment of the L-wheel 3 in the regenerative half of the cycle, or alternatively through other segments of the L-wheel, for example, the first segment of the wheel rotating into the regenerative half of the cycle, as shown in phantom lines 43. Alternatively, the portion of the duct protruding into the regenerative side may be eliminated with the rejected air segment mingling with the exiting regenerative air stream. The remaining portion of the air stream leaving the L-wheel while still hot, is sufficiently dry for the purposes of the machine up to a period of 2 minutes for each 6 inches of wheel depth in mild climate region such as Chicago. This dry segment is only 1.5 minutes in more severe humidity areas such as Texas.

The hot, dry incoming air, I, then passes through the cool portion 4 of a rotating S-wheel wherein it gives up most of its sensible heat to the wheel. For best S-whee] operation, the S-wheel should rotate in a direction opposite to the L-wheel. The two wheels may rotate in the same or opposite directions, and clockwise rotation of the L-wheel is not an absolute requirement. Since the S-wheel is water impervious and relatively cool, the air is cooled with no change in moisture content. In the ordinary cycle, at usual design conditions, the average temperture of the air incoming to the S-wheel at 5 after having passed through the L-wheel is on the order of about 190F. Typically, a well-designed S-wheel is capable of on the order of percent efficiency. With the S-wheel 90 percent efficiency, in the conventional systems, the incoming hot dry air from the L-wheel at 5 during the cooling half of the cycle is thus cooled to about 75.7F at 6 prior to passage through the evaporative pad 7 and then into the room 8.

Exiting from the S-wheel at 6, relatively cool, relatively dry air passes over or through evaporative pads 7, where water is evaporated and the air is humidified. Simultaneously, the latent heat of vaporization is extracted from the air (in order to evaporate the water into the air), thereby cooling the air. The resulting air issuing into a room or space to be conditioned 8 is typically at a lower dry bulb temperature than the outside air with about percent relative humidity. This cooled, moist air is thus conditioned for room comfort. If desired, a preselected humidity level can be achieved by passing a controlled portion of stream 6 around the E-pad 7, e.g. via bypass duct 33 (FIG. 1).

The regenerative half of the cycle commences with typical room air passing through evaporative pads 7' where the air is cooled while evaporating water from the pad. The resultant cool, relatively moist air is then passed over the hot portion 4 of the S-wheel which is cooled thereby. It should be recalled that the Swheel has been heated by taking up sensible heat from the hot dry air produced from the L-wheel, the dehydrating wheel. The air incoming to the S-wheel after passing through the evaporative pads is ordinarily on the order of 63F.

Continuing with the regenerative half of the cycle, the moist air passing through the right side of the S- wheel 4, while cooling the rotating S-wheel so that it may repeat its portion of the cooling half of the cycle at 4, is warmed. This warm, moist air then passes through a heating section 9. This heating section typically employs a gas burner or other heat source where the temperature is greatly increaseed, producing very hot air, of low relative humidity, typically on the order of 325F. This very hot air, because of the heat, has a low relative humidity which, when passed through the moist portion of the L-wheel 3 dries the wheel. The very hot air is then exhausted to the outside 10 completing the regenerative half of the cycle. Meanwhile, the heated, dried L-wheel rotates into position to function in the cooling half of the cycle where it again sorbs moisture from incoming outdoor air.

In one embodiment of this invention (still referring to FIG. 1), a stream of bypass air 15 (secondary air) is drawn in by means of fan 11 (or optionally by fan 11 shown in phantom lines) into the duct 12 shown at one side of the apparatus. The air shown by the dashed arrow BP is directed by suitable ducting 13 through a portion of the S-wheel. The portion of the S-wheel which receives the bypass air from the outside is on the order of from l50 percent. of the surface area of the regeneration side of the S-Wheel, preferably 5-30 percent; that segment is identified as segment B in FIG. 3. As shown in the figures, that portion is preferably a portion of the rightside of the S-wheel, but may be partially or entirely on the left side.

The term side has the meaning here of portion, and the regenerative side need not be identical to half the S-wheel, as shown in FIG. 3 by the phantom line 14. For example, ducting to and from the. wheel faces may be arranged to divide the wheel faces area into any desired number of parts and proportons, including radial (angular) or concentric annular portions, or the like. Where the wheel faces area is divided into three segments for l the input air being conditioned, 2) the secondary precooling air, and 3) the primary exhaust air, respectively, only the input air portion would be termed the input side, with the remaining portions constituting the regenerative side" even though they may constitute, say, 2/3 of the wheel area.

Continuing with the regenerative portion of the method and apparatus of this invention, 100 percent of the room exhaust air (the main or primary air stream indicated by dashed arrow M in the figures) is directed through the remaining portions of the regenerative side or portion of the S-wheel as shown in segment creased capacity of the machine. Where an improved machine of this invention is to have the original capacity, the blower requirements can actually be lower than the original machine.

By way of example, the various potential gains through use of a bypass stream of this invention can be illustrated in the following table which relates the total water consumption, the blower power requirements, the delivered temperature, and the amount of bypass air used as compared to conventional machines of same capacity. In this example the bypass stream is precooled as in FIG. 2, and the amount of the precooled bypass stream is expressed in terms of a ratio of its mass relative to that of the primary or room exhaust stream C of FIG. 3. For example, in this embodiment, where 5 mass.

Table I Ratio Rclative Temperature Relative Relative Bypass of Conditioned Air Total Water Total Blower Air/Room Delivered to E-pad, F Consumption, Power, Exhaust Air (at 6 in FIG. 2) Ratio Ratio 0 l.() l.() [/9 -2.8 .92 .76 2/8 4.7 .90 .69 3/7 5.6 .95 .72 4/6 5.9 1.05 .77 l 5.9 1.16 .97

the room exhaust or primary air stream and the input air stream passing from 5 to 6 are volumetrically equal, and the secondary bypass air stream passing through segment B of the S-wheel (see FIG. 3) is on the order of 95F, the l90F stream passing inwardly from 5 via face 31 through segment A of the S-wheel (see FIG. 3) will be cooled to about 73.1F at 6. In contrast, where no bypass air stream is used, only 75.7F would be achieved at 6. Thus, this embodiment of the invention resulted in about a 2.6F drop at 6, and a corresponding efficiency increase.

Referring now to FIG. 2, a second embodiment of the invention employs a bypass air stream 15 routed first through an evaporative pad 32, via ducting 13 before passing through an appropriate portion of the S-wheel 4. In passing first through the evaporative pad, a 95F bypass air stream is evaporatively cooled to about 80F at 16. The water vapor added may be preselected in amount up to adiabatic saturation. This results in an improvement in the cooling of the conditioned stream 6 of 59F over that acheived without the bypass, where the same main and input air stream as above are used. This 5.9F improvement corresponds to an increase of 24 percent in machine capacity if no other changes are made.

As can be seen from FIG. 3, the bypass air stream BP from the outside passing through the appropriate B of the S-wheel operates to precool the S-wheel since the wheel rotates first into the bypass segment B from the cooling half cycle portion or side 4. Thus, the S-wheel of this invention employs the use of three streams of air, the added one being outside air, either untreated or evaporatively precooled. The apparatus of this invention thus has an equivalent cooling efficiency of over 95 percent, in cooling the hot air I incoming from the L-wheel at 5, as compared to efficiency figures of on the order of 90 percent for MEC units not employing the bypass of this invention.

Although the use of a third stream increases the blower requirements, the increase is offset by the in- When the bypass airzprimary exhaust air ratio is greater than 2 3, the room exhaust air may be recirculated as shown in the embodiment of FIG. 4. In this embodiment the burner air is supplied completely by the bypass air. Even where there is less than 2 3 ratio, a portion of the room exhaust air can be recirculated. Under mild conditions, where full burner operation is not used, full recirculation is possible even though the ratio is less than 2 3.

Referring now to FIG. 4, this embodiment of this invention employs a bypass stream routed by duct 13 as in the embodiment of FIG. 2 described above. The room exhaust stream, instead of going to the L-wheel on the regenerative side, is directed, via

suitable ducts

20, 21, 22 to the input side of the L-wheel. When not in use, louvre 23, pivotable at 24, is disposed in its closed position 25 and the flow-through louvres 26 in duct 20 opened to provide operation as in the device of FIG. 2. The machine of this embodiment is adjustable between zero and full recirculation, e.g. by adjustment of the louvres 23 and/or 26. Thus advantage may be taken of greater efficiency on mild days without the use of this recirculation method, while on severely hot and humid days recirculation permits greatest efficiency.

During the heating season, the MEC unit of this invention has the capability of delivering heated, filtered and controlled humidification of air to the space to be conditioned. Conversion of the unit from cooling to heating is accomplished very simply by stopping rotation of the S-wheel and increasing the speed of rotation of the L-wheel. During the heating cycle, exhaust air from the conditioned space is heated by the gas burner and this heat is then transferred to the rotating L-wheel as exhaust air passes through the L-wheel to the outside. The heat thus stored in the L-wheel is utilized when relatively cold outside air is drawn through the L-wheel, which in this mode of operation functions as a very efficient heat exchanger. Moisture generated by combustion of gas is recycled to the incoming air to provide humidity levels adequate in most cases. Air

heated by the L-wheel then passes through the stationary S-wheel. If necessary, the air may be passed through a water curtain or evaporative pad where dust or pollen is removed and the air is further humidified to a desired level before it is delivered to the conditioned space. Optionally, all the air may pass directly to the space via bypass conduit 33. In this mode of operation the

bypass air system

11, 12, 13 shown in FIGS. 1, 2 and 4 is not utilized.

Such open cycle environmental control systems in both the heating and cooling modes can utilize 100 percent outside air, unlike most air conditioning systems, which, except on mild days, must recycle inside air. Because of the water curtain or evaporative pads employed, all such air is subject to removal of dust and pollen before it enters the conditioned space.

I claim:

1. In a method for cyclic conditioning of air including the steps of:

l. passing outside air as a first air stream through a first portion of a rotating dehydrating L-wheel to produce relatively dry air;

2. passing said relatively dry air through a first portion of a rotating sensible heat exchanging S-wheel to produce relatively cool dry air, for use in an enclosed space;

3. withdrawing a primary stream of exhaust air from said conditioned space through an evaporative pad;

4. passing said exhaust air as a second air stream through a second portion of said S-wheel whereby.

said S-wheel is cooled;

5. passing a portion of said exhaust air through a heating section;

6. passing said exhaust air through a second portion of said L-wheel to be exhausted to the outdoors;

said

steps

1 and 2 comprising the cooling half of said conditioning cycle and said steps 46 comprise the regenerative half of said conditioning cycle, the improvement which comprises in combination the added step of:

7. directing a stream of bypass air as a third air stream through a portion of said S-wheel prior to being cooled by said primary exhaust air stream whereby heat is exchanged between said three streams, said S-wheel is precooled, and its effciency increased without an increase in its mass.

2. A method as in claim 1 wherein said third stream of bypass air is supplied in an amount of from about to 100 percent of the primary room exhaust air stream.

3. A method as in claim 1 which includes the added step of passing a portion of said primary exhaust stream exiting from said second portion of said S-wheel to said first portion of said L-wheel.

4. A method as in claim 1 which includes the added step of passing the hot air exiting from that portion of said L-wheel which is rotating from said regenerative half of said cycle into said cooling half of said cycle back through said second portion of said L-wheel.

5. A method as in claim 1 which includes the added step of passing a portion of said relatively cool dry air exiting from said first portion of said S-wheel through an evaporative pad.

6. A method as in claim 1 which includes the step of passing a portion of said third stream of bypass air through an evaporative pad prior to being directed through said S-wheel.

7. A method as in claim 6 wherein said third stream of bypass air is suppled in an amount of from about 20 to percent of the room exhaust air.

8. A method as in claim 6 which includes the added step of passing the hot air exiting from the portion of said L-wheel which is rotating from said regenerative half of said cycle into said cooling half of said cycle back through said second portion of said L-wheel.

9. A method as in claim 6 which includes the added step of passing a portion of said relatively cool dry air exiting from said first portion of said S-wheel through an evaporative pad.

10. A method as in claim 3 which includes the added step of passing a portion of said relatively cool dry air exiting from said first portion of said S-wheel through an evaporative pad.

11. A method as in claim 4 which includes the added step of passing a portion of said primary exhaust stream exiting from said second side of said S-wheel to said first portion of said L-wheel.

12. A method as in claim 6 which includes the added step of passing a portion of said primary exhaust stream exiting from said second portion of said S-wheel to said first portion of said L-wheel.

13. In a method for cyclic conditioning of air including the steps of:

3. withdrawing a primary stream of exhaust air from said space through an evaporative pad;

4. passing said exhaust air as a second air stream through a second portion of said S-wheel whereby said S-wheel is cooled;

5. passing a portion of said exhaust air through a heating section;

said

steps

1 and 2 comprising the cooling half of said conditioning cycle and said steps 46 comprising the regenerative half of said conditioning cycle, the improvement which comprises in combination the added step of:

7. passing a portion of said primary exhaust stream exiting from said second portion of said S-wheel to said first portion of said L-wheel as part of said first 7 air stream.

14. A method as in claim 13 which includes the added step of passing the hot air exiting from that portion of said L-wheel which is rotating fron said regenerative half of said cycle into said cooling half of said cycle back through said second portion of said L- wheel.

15. A method as in claim 4 wherein said air from said first portion is the amount passing through from l724 angular rotation of said L-wheel per 6 inches L-wheel depth.

16. A method as in claim 1 wherein said S- and L- wheels are rotated in opposite directions.

17. A method as in claim 13 wherein said 5- and L- wheels are rotated in opposite directions.

18. A method as in claim 4 wherein said 5- and L- wheels are rotated in opposite directions.

Claims

1. In a method for cyclic conditioning of air including the steps of: 1. passing outside air as a first air stream through a first portion of a rotating dehydrating L-wheel to produce relatively dry air; 2. passing said relatively dry air through a first portion of a rotating sensible heat exchanging S-wheel to produce relatively cool dry air, for use in an enclosed spAce; 3. withdrawing a primary stream of exhaust air from said conditioned space through an evaporative pad; 4. passing said exhaust air as a second air stream through a second portion of said S-wheel whereby said S-wheel is cooled; 5. passing a portion of said exhaust air through a heating section; 6. passing said exhaust air through a second portion of said Lwheel to be exhausted to the outdoors; said steps 1 and 2 comprising the cooling half of said conditioning cycle and said steps 4-6 comprise the regenerative half of said conditioning cycle, the improvement which comprises in combination the added step of: 7. directing a stream of bypass air as a third air stream through a portion of said S-wheel prior to being cooled by said primary exhaust air stream whereby heat is exchanged between said three streams, said S-wheel is precooled, and its efficiency increased without an increase in its mass.

2. A method as in claim 1 wherein said third stream of bypass air is supplied in an amount of from about 20 to 100 percent of the primary room exhaust air stream.

5. passing a portion of said exhaust air through a heating section;

6. passing said exhaust air through a second portion of said L-wheel to be exhausted to the outdoors; said steps 1 and 2 comprising the cooling half of said conditioning cycle and said steps 4-6 comprise the regenerative half of said conditioning cycle, the improvement which comprises in combination the added step of:

6. passing said exhaust air through a second portion of said L-wheel to bE exhausted to the outdoors; said steps 1 and 2 comprising the cooling half of said conditioning cycle and said steps 4-6 comprising the regenerative half of said conditioning cycle, the improvement which comprises in combination the added step of:

7. passing a portion of said primary exhaust stream exiting from said second portion of said S-wheel to said first portion of said L-wheel as part of said first air stream.

7. A method as in claim 6 wherein said third stream of bypass air is suppled in an amount of from about 20 to 100 percent of the room exhaust air.

7. directing a stream of bypass air as a third air stream through a portion of said S-wheel prior to being cooled by said primary exhaust air stream whereby heat is exchanged between said three streams, said S-wheel is precooled, and its efficiency increased without an increase in its mass.

13. In a method for cyclic conditioning of air including the steps of:

14. A method as in claim 13 which includes the added step of passing the hot air exiting from that portion of said L-wheel which is rotating fron said regenerative half of said cycle into said cooling half of said cycle back through said second portion of said L-wheel.

15. A method as in claim 4 wherein said air from said first portion is the amount passing through from 17*-24* angular rotation of said L-wheel per 6 inches L-wheel depth.

16. A method as in claim 1 wherein said S- and L-wheels are rotated in opposite directions.

17. A method as in claim 13 wherein said S- and L-wheels are rotated in opposite directions.

18. A method as in claim 4 wherein said S- and L-wheels are rotated in opposite directions.