Method and apparatus for conditioning air

WO 2012/082093 PCT/US2010/060037

METHOD AND APPARATUS FOR CONDITIONING AIR

TECHNICAL FIELD

Various embodiments of the invention relate todehumification and humidification in heating, ventilating, andair conditioning systems.

BACKGROUND

Heating, ventilating, and air-conditioning (HVAC)systems provide temperature and humidity controlled air toresidential, commercial, and industrial buildings. Airprovided by the HVAC system may need to be at a specifiedtemperature or humidified or dehumidified to meet comfortlevels for occupancy, or to be within a range for electronics,or the like. Typically outside air is dehumidified and cooledif using an air conditioning system, and it is humidified andheated if using a heating system. The temperature andhumidity mechanisms may be integrated or separate.

For example, with some conventional air conditioningsystems, air is cooled below its dew point by passing it overcooling coils such that water is condensed out of the air.This usually results in air at a temperature below a comfortzone temperature. The air is then heated to bring it to adesired comfort zone temperature by mixing it with warmer airalready in the space being cooled or by passing it over a 1 WO 2012/082093 PCT/US2010/060037 heating coil. The excess cooling used to dehumidify the airdecreases efficiency.

If a desiccant type dehumidifier is used in an airconditioning system, the desiccant removes water to dehumidifyair in the dehumidification section. The dried air can thenbe cooled using a cooling coil to a desired comfort zonetemperature. The desiccant is regenerated in a regenerationsection where water is removed from the desiccant. Thedesiccant can then be reused in the dehumidification section.Depending on the capacity and type of the dehumidification andregeneration sections, desiccant can be blown out of thesections at high air flow rates. A high flow rate of airflowing through the chamber containing the desiccant contactsthe desiccant, entrains desiccant droplets or vapor, andcauses desiccant to be lost from the HVAC system. The loss ofdesiccant through blow-out from the chamber during high airflow rate conditions can impair the function of thedehumidifier if insufficient desiccant is present, or cancause other problems .

SUMMARY

In some embodiments of the invention, an apparatusfor conditioning air is provided with a quantity of liquiddesiccant. A first contact volume is provided in which afirst portion of a first airflow is received such that itcontacts a first portion of the liquid desiccant. A secondcontact volume is in parallel with the first contact volume inwhich a second portion of the first airflow is received. A 2 WO 2012/082093 PCT/US2010/060037 third contact volume is provided in which at least a portionof a second airflow is brought into contact with a secondportion of the liquid desiccant. A first heat exchanger isassociated with the first portion of the liquid desiccant andconfigured to transfer heat between the first portion of theliquid desiccant and a first medium. A second heat exchangeris associated with the second portion of the liquid desiccantand configured to transfer heat between the second portion ofthe liquid desiccant and a second medium.

In another embodiment, an apparatus for conditioningair is provided with a first chamber having an inlet and anoutlet for a first flow of a first fluid. The first chambercontains a first portion of a liquid desiccant for removingwater from the first flow moving through the chamber. Asecond chamber has an inlet and an outlet for a first flow ofa second fluid and contains a second portion of the liquiddesiccant for evaporating water from the desiccant to thesecond fluid. The second chamber is in fluid communicationwith the first chamber such that the desiccant is capable offlowing between the first and second chambers. A thirdchamber has an inlet and an outlet for a second flow of thesecond fluid, and is in parallel with the second chamber.

In yet another embodiment, a method of conditioninga fluid using a system having a first chamber, a secondchamber, and a third chamber is provided. A first portion ofa first fluid flows through the first chamber. The firstportion of the first fluid interacts with a portion of adesiccant and transfers water between the first portion of thefirst fluid and the portion of the desiccant. A second 3 WO 2012/082093 PCT/US2010/060037 portion of a first fluid flows through the second chamber.The second portion of the first fluid bypasses the firstchamber. A second fluid flows through the third chamber. Thesecond fluid interacts with at least a portion of thedesiccant and transfers water between the second fluid and theat least a portion of the desiccant. The first and secondportions of the first fluid are combined after the firstportion of the first fluid exits the first chamber and thesecond portion of the first fluid exits the second chamber.

In another embodiment, an apparatus for conditioningair is provided with a quantity of liquid desiccant, a firstcontact volume in which a first portion of a first airflow isreceived such that it contacts a first portion of the liquiddesiccant, a second contact volume in parallel with the firstcontact volume in which a second portion of the first airflowis received, and a third contact volume in which at least aportion of a second airflow is brought into contact with asecond portion of the liquid desiccant. A first heatexchanger is in contact with the first portion of the liquiddesiccant and configured to transfer heat between the firstportion of the liquid desiccant and a first medium. A secondheat exchanger is in contact with the second portion of theliquid desiccant and configured to transfer heat between thesecond portion of the liquid desiccant and a second medium. Avapor compression system includes a compressor, a third heatexchanger not in contact with the liquid desiccant, and arefrigerant. 4 WO 2012/082093 PCT/US2010/060037

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a schematic of a unit for conditioning air according to an embodiment of the invention; and FIGURE 2 is a schematic of unit for conditioning airaccording to another embodiment of the invention.

DETAILED DESCRIPTION

As required, detailed embodiments of the presentinvention are disclosed herein; however, it is to beunderstood that the disclosed embodiments are merely exemplaryof the invention that may be embodied in various andalternative forms. The figures are not necessarily to scale;some features may be exaggerated or minimized to show detailsof particular components. Therefore, specific structural andfunctional details disclosed herein are not to be interpretedas limiting, but merely as a representative basis for theclaims and/or as a representative basis for teaching oneskilled in the art to variously employ the present invention. A heating, ventilating, and air conditioning (HVAC)system 10 is shown schematically in Figure 1. The system 10has a dehumidification section or side 14 and a regenerationsection or side 16, and uses a desiccant system 12 to changethe humidity level of air flowing through the system 10. The 5 WO 2012/082093 PCT/US2010/060037 dehumidification side 14 may be used as a dehumidifier toprovide drier air, or as an air conditioner to provide drier,cooler air. Alternatively, the regeneration side 16 may beused as a heating system to provide warmer, higher humidityair. The desiccant is a lithium chloride salt solution.Alternatively, the desiccant includes lithium bromide,magnesium chloride, calcium chloride, sodium chloride, or thelike .

The desiccant system 12 has a dehumidificationchamber 18 on the dehumidification side 14 of the system 10,where a desiccant within the chamber 18 absorbs water from airflowing through the chamber 18 and contacting the desiccant.The air flowing through the chamber 18 is provided through anair inlet 20 to the dehumidification side 14. Only a portionof air entering through inlet 20 flows through thedehumidification chamber 18, and the remainder of air bypassesthe chamber 18 and flows through ducting parallel to thedehumidification chamber 18 thus allowing for higher flowrates required to achieve the desired cooling in a given spaceor better control of the humidity level of the air exiting thedehumidification side 14. Alternatively, all of the airentering through inlet 20 flows through the dehumidificationchamber 18.

The desiccant system 12 also has a regenerationchamber 22 on the regeneration side 16 of the system 10, wherewater is removed from the desiccant through absorption intoair flowing through the chamber 22. The air flowing throughthe chamber 22 is provided through an air inlet 24 to theregeneration side 16. Only a portion of air entering through 6 WO 2012/082093 PCT/US2010/060037 inlet 24 flows through the regeneration chamber 22, and theremainder of air bypasses the chamber 22 and flows throughducting parallel to the chamber 22, thus allowing for higherair flow rates or better control of the humidity of airexiting the regeneration side 16. Alternatively, all of theair entering through inlet 24 flows through the regenerationchamber 22.

The dehumidification chamber 18 and the regenerationchamber 22 are connected such that a liquid desiccant may flowbetween the two. The desiccant with a higher water contentfrom the dehumidification chamber 18 is exchanged withdesiccant with a lower or no water content from theregeneration chamber 22. The desiccant is transported viadiffusion flow from differences in desiccant concentration,pumped flow using one or more pumps, gravitational flow usinga controlled overflow, or the like.

Moist air flows through inlet 20 and through thedehumidification, or process, side 14. Inlet 20 draws airfrom inside a building or draws outside air to add to abuilding HVAC system. A fan (not shown) or other device isused to create a pressure difference to provide the air flowthrough the side 14. A set of dampers, or additional fans,divides and controls the air flow from the inlet 20 into twoair streams.

One of the air streams from the inlet 20 flowsthrough the dehumidification chamber 18 where water is removedfrom the air by the desiccant. The desiccant is a liquiddesiccant and may be sprayed, contained on a sponge like 7 WO 2012/082093 PCT/US2010/060037 material, or used as is known in the art to dehumidify the airstream. The stream of air flowing through thedehumidification chamber 18 leaves the chamber 18 with a lowerwater content, as a dry air portion.

The other portion of air from inlet 20 is cooled bya heat exchanger 26, such as a cold water coil or a glycolcoil. The heat exchanger 26 may be directly connected to agroundwater source, or may be integrated into a larger coolingsystem 28 or thermodynamic system 29, such as a vaporcompression cycle. The dry air portion and the other cooledportion of air are recombined before exiting thedehumidification side 14. Heat exchanger 30 is a part of thevapor compression cycle 29, or alternatively, is connected toa ground water source and integrated into cooling system 28.The heat exchanger 30 is located on the regeneration side 16to keep the lines in vapor compression cycle 29 on theregeneration side 16, and out of the dehumidification side 14.The air flow is conditioned on the dehumidification side 14through cooling and the removal of water moisture. Vaporcompression cycle 29 has a compressor 31 to circulate arefrigerant fluid through the cycle 29, and additionally has athrottle (not shown). The heat exchangers described withinthe system 10 are associated with a medium such as variousflows of air, desiccant, or circulating fluids, meaning thatthere is either direct heat transfer between a fluid flowingthrough the heat exchanger and the medium or there is indirectheat transfer between the fluid flowing through the heatexchanger and the medium using intermediary heat exchangers oradditional mediums. - 8 - WO 2012/082093 PCT/US2010/060037

Alternatively, after the water removal in thedehumidification chamber 18, the dry air portion and the otherportion of air from inlet 20 are recombined and then flowacross and are cooled by a medium flowing in the heatexchanger 26.

By reducing the air flow through the chamber 18 byproviding a bypassed air portion, blow-out of desiccant fromthe chamber 18 is prevented or reduced and higher flow ratesare attainable. The flow rate through the chamber 18 islimited based on when the air flowing through the chamberbegins to entrain desiccant. The flow rate of air through thedehumidification side 14 is increased by bypassing air aroundthe chamber 18, thereby providing an air flow that is greaterthan what is attainable using the chamber 18 alone.

If a cooling system 28 is present, a flow of coolingfluid, such as glycol or another refrigerant, leaves the heatexchanger 30 and flows in parallel or in series to heatexchanger 26 and heat exchanger 32. The cooling fluid in heatexchanger 32 may be used to cool the desiccant before use inthe dehumidification chamber 18, which additionally cools theair . A second flow of air enters through inlet 24 andthrough the regeneration side 16 of the system 10. Inlet 24may draw air from outside a building if the system 10 is usedas an air conditioning system. A fan (not shown) or otherdevice is used to create a pressure difference to provide theair flow through side 16. The air is preheated by a medium inheat exchanger 34 before it enters the regeneration chamber 22 9 WO 2012/082093 PCT/US2010/060037 containing the desiccant. The air is preheated to increasethe amount of water that may be evaporated into the air fromthe desiccant. Heat exchanger 34 is a part of the vapor-compression cycle 29, or alternatively, is connected to anexternal heat source. The air flows through the regenerationchamber 24 where water is removed from the desiccant. Thedesiccant may be sprayed, contained on a sponge like material,or used otherwise as is known in the art. The desiccant isheated by a medium in heat exchanger 36 before entering theregeneration chamber 22 to aid in the evaporation water fromthe desiccant. Heat exchanger 36 is connected into vaporcompression cycle 29, or alternatively, is connected to anexternal heat source. The heated air flowing through theregeneration chamber 22 leaves the chamber 22 as moist airwith an increased water content.

In an embodiment, a set of dampers, or additionalfans, divides the air flow through inlet 24 into two airstreams, often after the heat exchanger 34. One of the airstreams flows through the regeneration chamber 22, while theother air stream bypasses the chamber 22. By limiting the airflow through the chamber 22, blow-out of desiccant from thechamber 22 is prevented or reduced. The flow rate of airthrough the regeneration side 16 is increased by bypassing airaround the chamber 22, thereby providing an air flow that isgreater than what is attainable using the chamber 22 alone.The two air streams may be recombined in a mixing chamber orthe like downstream of the regeneration chamber 22.

The system 10 is described previously as an airconditioning unit where the dehumidification side 14 provides 10 WO 2012/082093 PCT/US2010/060037 a high flow rate of cooler air at an appropriate humiditylevel to a building, and the regeneration side 16 is used tocycle desiccant for reuse in the desiccant system 12. Inother embodiments, the system 10 as described above is used asa heating unit with the regeneration side 16 providing a highflow rate of warmer air at an appropriate humidity level to abuilding, and the dehumidification side cycling the desiccantfor reuse in the desiccant system 12. The system 10 may beused to provide air as a HVAC system using the side 14, 16which corresponds to the HVAC purpose or requirements.

Figure 2 illustrates another HVAC system 50 having adehumidifying chamber 52 and a regenerator unit 54. Thedehumidifying chamber 52 and the regenerator unit 54 providechambers or contact volumes where air interacts and comes intocontact with a desiccant. In one embodiment, the system 50provides cooler, drier, conditioned air from the dehumidifyingchamber 52, while the desiccant is regenerated in unit 54 forreuse. In another embodiment, the system 50 provides warmer,moister, conditioned air from the regenerator unit 54, whilethe desiccant is regenerated using the chamber 52 for reuse.The system 50 is described below as an air conditioning unit;however, the use of the system as a heater or ventilator iscontemplated and functionally would also operate as describedbelow. Differences between the system 50 as an airconditioner and as a heater are the sources of inlet air forthe chamber 52 and the unit 54, and where the air from thechamber 52 and unit 54 is directed after leaving the system50 . 11 WO 2012/082093 PCT/US2010/060037

Moist air enters the dehumidifying chamber 52through a moist air inlet 56, and cooler, dried air orpartially dried air exits chamber 52 through a dry air outlet58. A bypass duct 60 allows a portion of the air enteringthrough inlet 56 to be bypassed around the dehumidifyingchamber 52. The bypass duct 60 acts as a chamber or contactvolume for the bypassed portion of air. A series of fan ordampers 62 control the relative portions of air flowingthrough the chamber 52 and the duct 60. The respectiveportions of air may be recombined using a mixing chamber 64downstream of the chamber 52 and the duct 60. The bypass duct60 allows for a higher flow rate of air (cubic feet perminute, cfm) to be provided by outlet 58 and to flow throughthe system 50. The addition of the duct 60 provides amechanism to obtain higher overall flow rates at outlet 58,while maintaining air flow through the chamber 52 at a lowerflow rate. The flow rate through chamber 52 is limited bywhen the desiccant begins to be entrained by the air flowingthrough the chamber 52. Without a bypass duct 60 and at highflow rates, desiccant from chamber 52 blows out of the chamberand is entrained in the exiting air at outlet 58.

Desiccant 66 is pumped from a desiccant reservoir 70through a pipe 72 to a series of nozzles 74 using a pump 68.The nozzles 74 spray the desiccant into the interior ofchamber 52. The chamber 52 may be filled with a cellulosesponge material through which the desiccant percolatesdownward to the reservoir 70. The portion of moist airentering the chamber 52 through inlet 56 contacts thedesiccant droplets. The hygroscopic desiccant absorbs watervapor from the moist air. Drier air exits the chamber 52, 12 WO 2012/082093 PCT/US2010/060037 mixes with the bypass air from duct 60, and exits throughoutlet 58.

The desiccant in the sump 70 connected to chamber 52increases in water content as air is dried. The desiccant isregenerated for reuse by having water removed from it in aregeneration unit 54. Air enters through inlet 76 of theregeneration unit 54 and exits through outlet 78. The airflow may be divided into two portions, with one portionflowing through the regeneration unit 54, and the otherportion flowing through a bypass duct 80. The bypass duct 80acts as a chamber or contact volume for the bypassed portionof air. A series of dampers 82 or fans are used to controlthe relative portions of air between the unit 54 and the duct80. The portion of air flowing through the unit 54 carriesaway moisture evaporated from the desiccant through outlet 78.The portions of air flowing through the unit 54 and the bypassduct 60 may be recombined in a mixing chamber 84 beforeexiting the outlet 78.

Desiccant 66 is pumped by a pump 86 from a desiccantreservoir 88 through a pipe 90 to a series of nozzles 92. Thenozzles 92 spray the desiccant into the interior of unit 54,which may be filled with a cellulose sponge material throughwhich the desiccant percolates downward to reservoir 88. Theportion of air entering the unit 54 through inlet 76 contactsthe moisture laden desiccant droplets. Water vapor isevaporated from the desiccant into the drier air, and moistair exits the chamber 54, mixes with the bypass air, and exitsthrough outlet 78. By reducing the water content in the 13 WO 2012/082093 PCT/US2010/060037 desiccant, the desiccant 66 is regenerated for reuse in thedehumidifying chamber 52.

The bypass duct 80 allows for a higher flow rate ofair (cubic feet per minute, cfm) to be provided by outlet 78.The addition of the duct 80 provides a mechanism to obtainhigher overall flow rates at outlet 78, while maintaining airflow through the unit 54 at a lower flow rate which preventsdesiccant from becoming entrained into the air flowing throughthe unit 54. Without a bypass duct 80 and at high air flowrates, desiccant may blow-out of unit 54 and be entrained inthe exiting air. A heat transfer mechanism often occurs between thedesiccant flowing through the dehumidifying side and theregenerative side. For example, a vapor compression cycle 94,such as a heat pump or refrigeration cycle, is used for theheat transfer between the high and low water contentdesiccants and is additionally used to cool or heat airflowing through the system 50. Of course, other cycles orheat exchangers operating independently using heat sources andsinks are also contemplated. The heat exchangers describedwithin the system 50 are associated with a medium such asvarious flows of air, desiccant, or circulating fluids,meaning that there is either direct heat transfer between twomediums flowing through the heat exchanger or there isindirect heat transfer between two mediums flowing through theheat exchanger through intermediary heat exchangers oradditional mediums. 14 WO 2012/082093 PCT/US2010/060037

The vapor compression cycle 94 includes a compressor96, a first condenser 98, a second condenser 100, a throttleor expansion valve 102, and an evaporator 102. The heat pump94 uses a refrigerant such as R-134a, R-1234, or others as areknown in the art. The compressor 96 circulates therefrigerant through the cycle 94. The first condenser 98 actsas a heat exchanger to heat the desiccant in pipe 98. Bypreheating the desiccant before regenerating it in unit 54,water is more easily evaporated from the desiccant. Thesecond condenser 100 acts as a heat exchanger to heat the airflowing through inlet 76. Warmer air flowing through unit 54is able to retain a higher level of moisture or water at ahigher temperature, which additionally assists regeneration ofthe desiccant 66. The evaporator 104 provides a heatexchanger which acts as a heat sink to directly or indirectlycool desiccant and air on the dehumidifying side of the system50 .

The order of the first and second condensers 98, 100may be reversed depending on the heating requirements of theair and the desiccant. Additionally, the second heatexchanger 100 could be positioned to heat only the portion ofair flowing through the unit 54, as opposed to the air flowingthrough inlet 76.

The evaporator 104 may be a two-stage evaporator, ortwo evaporators in series to directly cool the desiccant andthe air on the dehumidifying side of the system 50.Alternatively, the evaporator 104 is connected to a coolingloop 106, which contains glycol, water, or another fluid.Flow within the cooling loop 106 leaves the evaporator 104, 15 WO 2012/082093 PCT/US2010/060037 and divides at valve 108. One line in the cooling loop 106flows through a heat exchanger 110, which is directly orindirectly in contact with the desiccant in the pipe 72 topre-cool the desiccant before it enters chamber 52. The otherline in the cooling loop 106 flows through a heat exchanger112, in parallel with the first heat exchanger 110. Themedium in the heat exchanger 112 cools the air in the bypassduct 60. By cooling the air in the bypass duct, cooler moistair from duct 60 is mixed with drier air from chamber 52 atmixing chamber 64, which allows for control over the airtemperature and humidity level at outlet 58 through use of thedampers 62, fans, and a controller (not shown). Heatexchanger 112 may also be positioned at inlet 56 to cool allof the air flowing through the dehumidifying side of thesystem 50. Other cooling loops 106 are also contemplated,such as those having heat exchangers in series.

Cooling the desiccant on the dehumidifying side withheat exchanger 110, reduces the temperature of the desiccantin chamber 52, which contacts the air being dried in thechamber 52 and additionally reduces the temperature of thedried air.

Alternatively, the heat exchangers in the vaporcompression cycle 94 and cooling loop 106 may be directlyplumbed to heat sinks or sources, such as groundwater or wasteheat from an associated air-conditioner or other system.

Desiccant may be transferred between the tworeservoirs 70, 88 using a diffusive aperture 114, pumps, afloat system, or the like. Desiccant in reservoir 70 16 WO 2012/082093 PCT/US2010/060037 increases in water content as the dehumidifying chamber 52operates compared to the desiccant in reservoir 88, whichequates to a higher concentration of desiccant in reservoir 88than in reservoir 70. The desiccant needs to be regeneratedfor the efficiency and drying capacity of the dehumidifyingchamber 52.

In the system 50 as shown in Figure 2, the desiccantis transferred between the dehumidifying reservoir 70 and theregeneration reservoir 88 through diffusion transport.Alternatively, pumping or another system may be used.

Aperture 114 allows for transfer of ions of water anddesiccant salt between the reservoirs while minimizing theamount of heat transfer between the reservoirs. Thedehumidifying chamber 52 continuously adds water content tothe desiccant 66 in the reservoir 70. The regenerating unit54 continuously removes water from the desiccant. Duringoperation, the concentration of salt ions in the reservoir 88is generally higher than that in reservoir 70 because thedesiccant the regeneration reservoir 88 is being concentratedwhile the desiccant in reservoir 70 is being diluted. Thedifference in concentration causes a flow of salt ions fromreservoir 88 to reservoir 70 by diffusive transport, throughaperture 114, which is balanced by the flow of water ions fromreservoir 70 to reservoir 88 caused by the flow of solution inthis direction. This results in steady state levels ofdesiccant concentrations, although during changing air flowrate, start up conditions, or other system 50 transients,there will be corresponding transient period for the desiccantconcentrations . 17 WO 2012/082093 PCT/US2010/060037

In one embodiment, the system 50 has a dehumidifyingchamber (or contact volume) 52 and a regeneration chamber 54.A bypass duct (or contact volume) 60 is provided in parallelwith the dehumidifying chamber 52. Liquid desiccant 66 isused in the chambers 52, 54 to change the humidity level ofair flowing through the chambers 52, 54. A portion of anairflow entering inlet 56 flows into chamber 52 such that itcontacts a first portion of the liquid desiccant 66 and isdehumidified. A second portion of an airflow entering inlet56 flows through the bypass duct 60. At least a portion of asecond airflow entering through inlet 76 flows into chamber 54such that it contact a second portion of the liquid desiccant66 and water is removed from the desiccant to regenerate thedesiccant. The system 50 has a heat exchanger 110 in contactwith the first portion of the liquid desiccant 66. Anotherheat exchanger 98 is in contact with the second portion of theliquid desiccant 66. Yet another heat exchanger 112 is not incontact with the liquid desiccant 66. In one embodiment, theheat exchanger 112 is in contact with the second portion ofthe first airflow in bypass duct 60. In some embodiments, thesystem has a vapor compression system 94 including heatexchangers 110, 98, 112, a compressor 96, and a refrigerant.In other embodiments, the heat exchangers 110, 112, 98 may berun to independent heat sources or sinks. Alternatively, theheat exchangers 110, 112 are a part of a cooling loop 106 incommunication with the vapor compression cycle 94. Heatexchangers 110, 112 are arranged in parallel such that therefrigerant or cooling fluid flows in parallel to the heatexchangers 100, 112. 18 WO 2012/082093 PCT/US2010/060037

Heat exchanger 110 transfers heat from the desiccant66 to the vapor compression cycle 94. Heat exchanger 112transfers heat from the bypass air in duct 60 to the vaporcompression cycle 94. This provides two sources of heat tothe vapor compression cycle 94, the bypass air in duct 60 andthe desiccant flowing through piping 72. The increased energytransferred into the vapor compression leads to additionalenergy (or heat) that may be transferred or used on theregeneration side, increasing the heat capacity available forregeneration. This additionally increases the system 50efficiency and allows for higher airflows through the system50. By arranging the heat exchangers 110, 112 in parallel, ahigher airflow may be attained through inlet 56 and outlet 58without blow-out of the desiccant 66 from the chamber 52.

While embodiments of the invention have beenillustrated and described, it is not intended that theseembodiments illustrate and describe all possible forms of theinvention. Rather, the words used in the specification arewords of description rather than limitation, and it isunderstood that various changes may be made without departingfrom the spirit and scope of the invention. Additionally,features of various implementing embodiments may be combinedto form further embodiments of the invention. 19