SYSTEMS AND METHODS FOR CONTROLLING LOCAL ENVIRONMENT

Abstract: Incoming air enters a contactor (100) where the air contacts water distributed on the contact media (106). After passing through the contactor (100), the air is saturated at a temperature equal or close to that of the water. Water temperature is controlled by a refrigeration system (146). The air is passed through a temperature controlled heater (138) and a desired dry-bulb temperature and humidity are obtained. Before exiting, the air may be passed through a filter (152).

Description: SYSTEMS AND METHODS FOR CONTROLLING LOCAL ENVIRONMENT The present invention relates in general to the control of local environment, and in particular, to systems and methods for controlling the temperature, humidity, and cleanliness of gas such as air delivered to semiconductor equipment. Background of the Invention There are many applications in semiconductor manufacturing where tight control of temperature, relative humidity, and particles of a process gas such as air becomes critical. See Chang & Sze, ULSI Technology (1996), which is hereby incorporated by reference. Foundries, including metrology, lithography, and track areas where photoresist and developer is applied to silicon wafers, may require air having a relative humidity of 45%+ 0.5% at 24+0.1 C, while other cleanroom areas may require a relative humidity of 45%+ 5% at 24+0.5 C. For example, the humidity of air delivered to a photoresist spin station must be controlled because it affects the evaporation rate of solvent of the resist. To avoid particle contamination, the process areas may also require Class 1 (at 0.12 microns) while the surrounding areas may only require Class 1000 (at 0.3 microns). The velocity of air is in laminar flow region such as 0.35 m/sec. Foundries must control other parameters affecting the quality of air, including hydrocarbons and other external contaminants, out-gassing of materials contacting the air, the pressure of the air, and the electrostatic discharge of the system delivering the air to the process. Because of these requirements, especially for cleanliness, some foundries seek to control the local or mini-environments of critical processes, rather than the entire cleanroom, and transport wafers outside mini-environments in SMIF pods (standard mechanical interfaces). Chang & Sze, at pages 12-13. The mini-environments are cost-effective, but require delivery of precisely controlled gas such as air. In an air-water system, humidification and dehumidification involves transfer of water between a liquid water phase and a fixed air phase, which is insoluble in the water. Heat and mass transfer effects influence one another so that the temperature and relative humidity are coupled together. The specific humidity is defined as the mass of water vapor carried by a unit mass of dry air. Relative humidity is defined as the ratio of the partial pressure of the water vapor to the vapor pressure of the water at the gas temperature, and is expressed on a percentage basis so that 100 percent relative humidity means saturated air and 0 percent means dry air. Accurate regulation of temperature and humidity requires use of closed-loop control to compensate for disturbances such as changes in the ambient air conditions. The coupling between temperature and relative humidity presents challenges to the design of the closed-loop controller. The semiconductor industry has attempted to control the temperature and the relative humidity of process air in three stages: first, a chiller lowers the temperature and humidity of the incoming air below the desired values; second, a heater raises the temperature of the air to a desired value, and, third, a steam source humidifies the air to achieve the required relative humidity. However, boiling water at the steam source is an unstable complex process, and it is difficult to provide controlled boiling that generates the required amount of water vapor to control humidity within the required tolerances + 0.5% RH. Furthermore, the response time of humidity levels resulting from change in the heater power supply is too slow and unpredictable. Because the temperature and relative humidity are coupled and it is difficult to precisely controlling the amount of steam used to humidify the air, this conventional approach has significant drawbacks. Summary of the Invention The present invention provides a robust and cost-effective alternative to the systems used previously because final humidity and temperature can be treated as decoupled parameters. In a preferred embodiment, a gas-liquid contactor brings liquid into intimate contact with gas so the gas leaves the contactor at the saturation temperature, a heater heats the gas to a desired temperature, and the absolute humidity of the gas is fixed by the inlet liquid temperature to the contactor. In a preferred embodiment, the system avoids the difficulty of controlling coupled temperature and humidity outputs. In an air-water system, the thermodynamics of moist air dictates the dry bulb and saturation temperatures of the air determine its relative humidity. With the use of steam tables, the problem of controlling temperature and relative humidity can be transformed into one of controlling dry bulb and saturation temperature. Because there is no direct coupling in the control of these parameters, the invention permits precise control of local environments used in the ULSI technology. Brief Description of the Drawings Figure 1 is a schematic diagram of one embodiment of the system of the present invention. Figure 2 illustrates an embodiment of the Direct Contact Cooler-Condenser (DCCC) suitable for use in an air-water system. Figure 3A is a top view of one embodiment of the sprinkler located in the cylindrical housing of the DCCC. Figure 3B is a cross-section of a sprinkler arm taken on the line A-A of Figure 3A. Figure 3C is a cross-section of a sprinkler arm taken on the line B-B of Figure 3B. Figure 3D is a perspective view of a sprinkler arm illustrating the direction and spacing of the orifices. Figure 3E is cross-section of the sprinkler arm showing its internal structure. Figure 4 illustrates an embodiment of the control system suitable for use with the present invention. Figures 5A-5F are a set of tasks performed by one embodiment of software implementing the present invention. Figure 6 illustrates an alternative embodiment of the control system. Figure 7 is a psychrometric chart showing a process path for humidifying air in the system of the present invention. Figure 8 is a psychrometric chart showing a process path for dehumidifying air in the system of the present invention. Figure 9 is a graph illustrating the results of decoupling relative humidity from temperature. Detailed Description of the Preferred Embodiments The present invention relates to a system for controlling the local environment of a gas-liquid system. In a preferred embodiment, the system uses a gas-liquid contactor 100 for humidifying or dehumidifying the gas. As shown in Figure 1 , the gas-liquid contactor 100 includes a housing filled with a contact media 106, a gas inlet 102 below the contact media 106, a gas outlet 107 above the contact media 106, a liquid sprinkler 108 above the contact media 106, and a liquid reservoir 110 below the housing with an outlet 112. In a preferred embodiment, the gas-liquid contactor 100 is a direct-contact cooler condenser that operates like a cooling tower, but instead the liquid is heated and the gas is cooled. The governing equations and solutions are similar. Cooling tower theory is dealt with by Mills & Irwin, Heat and Mass Transfer (1995), which is incorporated by reference. In a preferred embodiment, the contact media 106 is material with a large surface area/volume of material, chemically inert to the liquid and gas, which brings the liquid and gas into intimate contact for sufficient heat and mass transfer to saturate the gas with the liquid after the contact. Some suitable materials are tower packing, refrigerated coils, and tubes. McCabe & Smith, Unit Operations (1976 & later editions) and Perry's Handbook of Chemical Engineering (1973 & later editions) provide suitable contact media and are incorporated by reference. Conventional cooling tower packing typically has large hydraulic diameters in order to reduce pressure drop, but if there is little space, compactness of the DCCC 100 may be more important than avoiding greater than typical pressure drop. Whatever tower packing is selected, it clearly is preferably to have a large surface area per volume. The liquid from the outlet 112 enters an inlet 116 of a heat exchanger 114 connected to a refrigeration system 146. The chiller, including the refrigeration system 146 and the heat exchanger 114, chills the liquid. The liquid returns from outlet 118 to a pump 120, moves through the flowmeter 140, and enters the gas-liquid contactor 100 at the inlet 104 to the sprinkler 108 forming a closed-loop circulation. Closed-loop circulation is preferred because the liquid temperature does not deviate as much and can be more quickly returned to operating conditions by the chiller. Further, closed-loop circulation lowers the expense of purifying water, but even so humidification requires make-up and dehumidification removal. Thus, in the preferred embodiment, the system provides a make-up inlet 178 and a removal outlet 179 at the reservoir 110, and high and low reservoir sensors 174, 176 indicating when removal or make-up liquid is required. A suitable high and low sensor is the NCG Multipoint Level Switch made by Kobold Instruments, Inc. A percentage of the liquid in the "closed-loop" is preferably refreshed to meet the purity requirements. The capacity of the chiller to bring the liquid to operating conditions and the cost of purification sets the appropriate percentage of liquid to add to the "closed-loop" through the make-up inlet 178. A preferred percentage might be 50% of the circulating liquid per hour. It is preferred that the sprinkler 108 distributes liquid uniformly over the contact media 106. In one embodiment, the system includes temperature sensors 128 and 126 to measure the temperature of the liquid entering and leaving the heat exchanger 114, but the system may in another embodiment include only the gas temperature sensors 122 and 144 for control. In the embodiment of Figure 1 , a blower 136 moves the gas to a valve 134, a positive flow displacement meter (PDFM) 132, and a gas inlet 102 below the contact media 106. In another embodiment shown in Figure 2, the gas enters inlet 202 from the surroundings, the blower 236 is placed downstream of the contrator, and valve 134 and flowmeter 132 are not used. In the preferred embodiment, the gas travels up through the contact media 106 countercurrent to liquid flowing down. However, it is not strictly necessary to have countercurrent flow because any gas-liquid contact achieving the saturated gas at the outlet is satisfactory. After contacting the liquid, the gas leaves at outlet 107 saturated with vapor and goes to a heater 138 with a heater coil 142 where the gas temperature increases to a desired value. A suitable heating coil 142 is a Watlow Gordon 1/16 inch diameter cable heater arranged in a snake-like pattern in two layers to form a heating grid. As shown in Figure 1 , the system includes the gas temperature sensors 124 and 122 to measure the gas entering and leaving the gas- liquid contactor 100. Thus, the preferred embodiments include two stages. In the first stage, the gas passes through contact media where it is cooled and humidified or dehumidified by direct contact with the flow of chilled liquid. In this stage, it is important that there is sufficient contact media surface area per unit volume to bring the gas and the chilled liquid to thermal equilibrium at full saturation by heating the liquid and cooling the gas. In the second stage, the gas is heated to the desired dry-bulb temperature maintaining its specific humidity unchanged, at which the desired relative humidity is achieved because the desired specific humidity was achieved in the first stage. From the desired relative humidity and dry-bulb temperature, one can extract the corresponding specific humidity and its saturation temperature. Saturation temperature can be controlled by controlling the temperature of the liquid independently from the dry bulb temperature. Similarly, controlling the temperature of the gas in second stage will not impact the specific humidity achieved in the first stage. Note the leading digit of the part numbers indicates the Figure showing the part in question, while the trailing digits indicate like parts are involved. Thus, contact media 106 and 206, shown in Figure 1 and Figure 2, respectively, have the same function. Figure 2 illustrates a Direct Contact Cooler-Condenser (DCCC) 200 suitable for an air-water system. The DCCC 200 preferably includes a cylindrical-shaped housing, an air inlet 202, a distributing air space at the bottom of the housing, a water inlet 204 and a sprinkler 208 at the top, a reservoir 210 with a water outlet 212 near the bottom, a removal outlet 279 below that, a make-up inlet 278 at the top of the reservoir 210, and a contact media 206, such as the tower packing mentioned earlier. The housing of the DCCC 200 is preferably chemically inert, not off-gassing or exceeding hydrocarbon limits in operation. In one preferred embodiment, the internal diameter of the housing of the DCCC 200 is 12 inches in diameter and 24 inches in height. The water lines are preferably an inert tough material such as Vz inch in diameter Teflon tubing. The inner wall of the reservoir 210 is larger in diameter than the outer wall of the DCCC 200 forming an inlet 202 around the circumference of the DCCC 200 to allow uniform airflow into the tower. The contact media 206 is tower packing 18 inches in height, leaving an open space above of 6 inches. The tower packing is chemically inert, not off-gassing, and contains adequate passages to avoid excessive liquid holdup or pressure drop. Some suitable tower packings for air-water are tower packing media CF650 made by Brentwood Industries, Inc.; black oxidized copper wire cloth; cloth of anodized aluminum wire, or Teflon filaments. If the contact media 206 is tower packing, it may be held by supporting screens (not shown) or held in place by friction of the tower packing against the walls of the tower. Preferably, the tower packing has sufficient surface area per unit volume to provide good contact between the water and the air for high heat and mass transfer rates; and to bring the air and the water into intimate contact necessary to achieve thermal equilibrium in a single pass whether parallel or countercurrent flow. As shown in Figure 2, a non-corrosive chemically compatible pump 220, sitting on support 272, withdraws water from the reservoir 210 through the line 212 and moves the water through line 216 to a heat exchanger 214. One suitable heat exchanger 214 includes a matrix of approximately 100 TECs (thermal electric chips) sandwiched between two copper plates such that the cold side of the TECs face the same plate and the hot side of the TECs face another plate. Copper tubing with snake-like pattern is brazed on the opposite surface of the copper plate that is in contact with the cold surfaces of the TECs. Water delivered to the DCCC 200 circulates through the copper tubing. Another copper tubing with snake-like pattern is brazed on the opposite surface of the copper plate that is in contact with the hot surfaces of the TECs. Separate water runs through this tubing to extract the heat from the TECs. The heat exchanger can be remote if desired from the mini-environment to avoid any disturbances. A suitable TEC is part no. CP 2.8- 32-06L made by Melcor Materials Electronic Products Corp. The chilled water leaving the heat exchanger 214 at the outlet 218 is delivered through the line 204 to the sprinkler 208, which distributes the water on the contact media 206. It is important to introduce the water on the contact media 206 so as not to generate mist, or water particulates. It is also preferred not to have any liquid water phase in the air departing the DCCC 200. The air should carry water in its vapor-phase only. The sprinkler 208 has a set of sprinkler arms 244, 246, and 248, attached to a hub 250 capable of free rotation, and preferably, parallel and close to the contact media 206 such as one inch or closer, and about four inches or more below a gas outlet 207. The relative spacing and the direction of the orifices 399 (Figure 3) help to prevent entrainment of mist in the air outlet 261. Thus, the air leaves at the outlet 261 saturated and free from water particulates. An example of a suitable environment for the embodiment of Figure 2, is an air-water system with the following conditions: • Ambient air temperature: 18-25 C • Maximum rate of temperature change: + 3 C/hour • Ambient relative humidity: 35-50% RH • Maximum rate of relative humidity change: + 5% RH/hour • Maximum static pressure at output: 1 inch of water • Temperature control range: 18-24 C + 0.1 C • Relative humidity: 35 to 50% RH + 0.5% • Maximum air capacity: 150 CFM Figure 3A is a top view of one embodiment of the rotatable sprinkler 308 in the cylindrical tower of the DCCC. As shown, in this embodiment, the sprinkler arms 344, 346, and 348 attached to a hub 350 are 120 degrees from each other and the outer tips of the arms are preferably close, e.g., 1/8 inch from the tower walls 385. This arrangement when combined with the rotation of the arms promotes uniform distribution of the liquid on the tower packing in the cylindrical tower (Figures 1-2). It is recognized that other arrangements and number(s) of sprinkler arms, such as one or more, e.g., four arms in a cross pattern would be also suitable to achieve uniform liquid distribution. Further, it is not necessary that the "sprinkler" rotate as it might be a non-rotating shower head, e.g., shaped like a disk whose major surfaces are parallel to the contact media. Figure 3B is a cross-section of the sprinkler arm 344 taken on line A-A of Figure 3A. As shown in Figure 3B, an orifice 399 is angled downward, not down or sideways, but between, for the following reasons. If the orifice points straight down at the contact media it will reduce the mist entrainment in the outlet gas, but will exert no component of rotational force on the sprinkler. If, however, the orifices 399 are at an angle as shown in Figures 3B, 3D, and 3E, the mist entrainment can be prevented, plus the component of reactive force directed about the hub can exert rotational force to the sprinkler arm such that the sprinkler distributes the liquid uniformly over the contact media without the need for a separate motor. Figure 3C is a cross-section of a sprinkler arm 344 taken on line B-B of Figure 3B, showing the tightly spaced orifices 399 which enhance the uniform distribution of the liquid on the contact media. Figure 3D is a perspective view of the sprinkler arm 344 illustrating the direction and spacing of the orifices 399. In a preferred embodiment, the sprinkler 308 has a plurality of tightly space orifices 399, e.g., each 1/8 inch apart and 0.050 inches in diameter. Figure 3E is a cross-section of the sprinkler arm 344 showing its internal structure, including the common passage in the arm 344 for each of the orifices 399. Referring again to Figure 2, the gas leaving at the outlet 261 enters a duct 207. The air in the duct 207 travels to a heater 238 close to the exit of the duct 207. The heater 238 raises the air temperature to a desired value. The air is pulled into a blower 236, leaves duct 207 and enters a diffuser box 265, which has a sloped wall 267 such that the air exiting from the diffuser box 267 through a filter 252 is uniformly distributed on the process below the hood 255. Suitable filters for use in an air-water system include a HEPA filter with the required efficiency, or an ULPA (Ultra Low Penetration Air) filter having an efficiency of 99.9995% or more for particulate diameters greater than 0.12 microns or another high efficiency air filter. The objective of the control system is to regulate the temperature and the relative humidity of the gas to user-defined set points, the desired values required by the process, and to adjust for disturbances to the system such as changes in the temperature of the gas from the cleanroom or another supply source. The control systems are now discussed. In the first embodiment, a user sitting a computer 464 such as an IBM compatible computer with software described below and a conventional analog-to-digital (A/D) converter such as the AT-MIO-16DE-10 from National Instruments, which includes software, enters desired values for T set point and RH set point, by the keyboard and display monitor. As shown in Figure 1 , the temperature sensors 122 and 144 measure T saturation and T dry bulb of the gas and output analog feedback signals proportional to the temperatures to the analog-to-digital (A/D) converter associated with the computer 464. In one embodiment, the dry bulb temperature and relative humidity have been measured after the heater 138 and filter 152 with a combined temperature and humidity sensor 144 and 130 such as the HMP233 from Vaisala, Inc. This combined sensor 144 and 130 is preferably placed approximately 6 inches downstream of the filter 152 outlet. Although a relative humidity feedback signal is not used in the control, it is entered into the computer 464 for monitoring purposes. T saturation of the gas out shown in Figure 1 is determined indirectly by measuring the temperature of the saturated gas leaving the contactor 100 by temperature sensor 122 located just inside the gas-liquid contactor 100. One suitable temperature sensor is a resistive-temperature-device (RTD) such as the Style RB from Watlow Gordon. Figure 4 illustrates the first embodiment of the control system suitable for use with the present invention. As shown in Figure 4, in the first embodiment, the control system includes an algorithm consisting of two feedback loops 466, 468, and a feedforward element 462, which transforms the T set point and RH set point into a corresponding saturation temperature set point 470 sent to comparator 460. The comparator 460 takes the difference between set point 470 and the feedback signal 468, and outputs an error signal to a proportional-integral-derivative (PID) compensator 456 which in turn outputs a command signal to the chiller 414 to adjust its cooling rate. As is known, a PID takes the error signal: (1) multiplies it by a first constant; (2) integrates the error signal, and multiplies it by a second constant; and (3) takes the error signal's derivative, multiplies it by a third constant, and sums (1), (2), and (3), which provides accurate and responsive control over a wide range of conditions. See Weber, An Introduction to Process Dynamics and Control (1973), which discusses PID controllers in more detail, and is hereby incorporated by reference. Similarly, the comparator 458 takes the difference between T set point and feedback signal 466 and outputs an error signal to a PID compensator 454, which outputs a command signal to the heater 438 to adjust its heating rate. In one embodiment, the transformation to the saturation temperature set point 470 is achieved by use of empirical 'steam table' equations, which can be found in texts such as Irvine & Liley, Steam and Gas Tables with Computer Equations. Academic Press, 1984, which is hereby incorporated by reference. The two feedback loops 466, 468, regulate the T dry bulb and T saturation of the outlet gas, while the feedforward 462 ensures T dry bulb and T saturation yield the desired relative humidity RH set point defined by the user. One embodiment of real-time control software written in the C language is shown in the program listing below. The software includes a cooperative multitasking scheduler that executes six tasks. In a cooperative multitasking environment, the scheduler allocates use of the CPU to each of tasks so each task is given processing time and passes back control to scheduler after completion of the task. Each task is divided into states which execute in a short time period, so no single task monopolizes the CPU, and the tasks appear to be performed simultaneously. The software architecture is preferably simple to facilitate migration from a PC to an advanced microcontroller such as the Microchip PIC17C756 by Microchip Technology, Inc. since all required hardware and software can be contained in a compact package. Figures 5A-5F show six tasks in state transition logic form performed by one embodiment of software implementing the present invention: • Task 0 maintains a simple user interface for entering the T and RH set points and displaying T dry bulb, RH, and T saturation on the computer monitor and permitting shut down of the scheduler if the user presses the escape key on the computer. This turns off the chiller 414 and heater 438 and exits the control software. • Task 1 includes a wait state 507 to initialize the system, including establishing communication with the sensors 144 and 130 before initiating control. After the system is initialized 509, Task 1 moves into control state 511 where Task 1 executes the algorithm described in connection with Figure 4, including feedforward 462 and feedback loops 466, 468. • Task 2 also includes a wait state 513 for the same reasons as for wait state 507. In this embodiment, temperature and humidity sensors 144 and 130 generate serial data so Task 2 must acquire both serial data and the analog signals of sensor 122. The preferred embodiment use only analog sensors because this provides faster sensor response and simplifies the code needed in Task 2. • Tasks 3 and 4 convert the outputs from heater PID 454 and chiller PID 456 shown in Figure 4 into pulse-width-modulated (PWM) signals. Horowitz & Hill, The Art of Electronics (1989) describes PWM signals and is incorporated by reference. The PWM signals permit the heater 438 and chiller 414 to interface to the computer 464 by conventional solid state relays appropriate for the heater 438 and the chiller 414 selected such as those readily available from Continental Industries, Inc. or any appropriate power switching device. Considerations for selecting solid state relays for the heater and chiller are AC versus DC, maximum voltage, maximum current, and switching speed. The PWM signals have been generated in software, but a more appropriate method would be to use a microcontroller with built-in PWM hardware. • Task 5 includes wait state 541 until the user at the computer 464 presses an appropriate key to enable the logging of data, T dry bulb, RH, and T saturation. Once logging is enabled, Task 5 moves to states 545 where it continuously writes the data to the computer hard disk. Another key press disables the logging and Task 5 moves back to the wait state. Whether control is implemented on a PC or a microcontroller, it is not necessary to have Task 5. As mentioned previously, the microcontroller embodiment may be preferable to replace the personal computer to reduce cost and size. The user interface could be reduced to a LCD screen and push buttons. The computational requirements of the algorithm have been kept low enough to be performed by inexpensive microcontroller such as the Microchip Technology's part no. PIC17C756. Figure 6 illustrates a second embodiment of control system suitable for use with the present invention. In this embodiment, the system controls T dry bulb and RH with two independent feedback loops 666 and 668. A controller 668 and 670 implement the comparators 658, 660, the compensation of PID 654 and 656, and PWM signals driving the heater 638 and chiller 614. Honeywell IAC Division makes suitable single- loop controllers such as the UDC1000 controller. Since this control system does not compensate for the coupling of the temperature and relative humidity, it is likely to have decreased stability. The advantage of the second embodiment is that it can be readily constructed using commercially available components. The same type of temperature/humidity sensor discussed in the first embodiment can be used. The controllers 668 and 670 contain simple functions for setting the set points and reading the temperature and humidity sensor. T saturation temperature is not used and need not be measured. The outputs of the controllers 668 and 670 are PWM signals which interface with the heater 638 and the chiller 614 as described in the first embodiment. Figure 7, a psychrometric chart, shows humification and relates dry bulb temperature of air (abscissa) to specific humidity (ordinate) and % relative humidity. As shown in Figure 2 and 7, the air entering inlet 202 of the DCCC 200 has a relative humidity of 30% at an initial dry bulb temperature of 17 C. This is point A shown in Figure 7. As discussed earlier, the air travels through the DCCC 200, loses sensible heat, and gains vapor from the water contacting it until the air is fully saturated. The air leaves the DCCC 200 at outlet 207 at T saturation. This is point B shown in Figure 7. The wavy dotted line from A to B indicates that the actual temperature-humidity path is not known, nor is it necessary as long as air leaves the DCCC 200 at outlet 207 at T saturation, that is, point B. Next, the heater 238 heats the outlet air from the DCCC 200 to the desired dry bulb temperature T dry bulb and relative humidity RH shown as point C in Figure 7, which corresponds to T dry bulb and T saturation shown in the control diagram of Figure 4. Figure 8, a psychrometric chart, shows dehumidification of air in a system of the present invention. As shown in Figure 2 and 8, the air entering inlet 202 of the DCCC 200 has a relative humidity of 50% at a dry bulb temperature of 26 C. This is point X shown in Figure 8. As discussed earlier, the inlet air travels through the DCCC 200, loses sensible heat, and gains vapor from the water contacting it until the air is fully saturated. The air leaves DCCC 200 at outlet 207 at temperature, T saturation. This is point Y shown in Figure 8. The wavy dotted line from X to Y indicates that the actual temperature humidity path is not known, nor is it necessary as long as the air leaves at outlet 207 at T saturation, that is, point B. Next, the heater 238 shown in Figure 1 heats the outlet air from the DCCC 200 to desired dry bulb temperature T dry bulb and relative humidity RH, that is, point Z shown in Figure 8. It should be noted that point Z also corresponds to T dry bulb and T saturation shown in Figure 4. Figure 9 is a graph illustrating the results of decoupling relative humidity from temperature of air in the embodiment shown in Figure 2. As shown in Figure 9, the user defines RH set point and T set point (see Figures 4 and 6) and tolerances of the air at a relative humidity of 45% + 0.5% at 24 +0.1 C. Although T dry bulb, the actual temperature of the air delivered at t = 0 meets the user requirements, the actual relative humidity of air, RH, is 46%, and therefore fails to meet requirements. After less than about 10 minutes of control, however, the system brings relative humidity, RH, of the air within the tolerances established by the user. The temperature- humidity path of the air shown in Figure 9 is the logged data obtained by execution of Task 5 of the software computer or microcontroller shown in Figure 5. if (task[fgQueue[ι]] timeLeft The following is a program listing of the <= 0){ software source code in C: stack[++stacklndex]=fgQueue[i], , , 0 { "Period C", 17, 10, 10, 5000, if (TairZerolnt || fabs(TaιrError)>TAIR_ILIM){ &PerιodChιller}, TaιrErrorlnt=0 , { "Enable", 20, 1, 0, } 1, &CollectData} Compute D term*/ }. TairErrorDeπv = (TairError - #defιne NUM_OUT 11 TaιrErrorPrev)/((float)( task[1 ] tιmeSιnceLast)/1000), struct ScreenOutputltem outltem[NUM_OUT]--{ TairErrorPrev = TairError, { "RH Meas", 5.NULL, &RHMeasured}, /"Compute Feedforward*/ { "Tair Meas",4,NULL, 8TaιrMeasured}, DutyHeaterPredicted = KFHEAT1*(TaιrSetpoιnt- { "Tsat Meas",6,NULL, &TsatMeasured}, (1 +KFHEAT2)"TsatMeasured-KFHEAT3), { "Tair lntgr",9,NULL, &TaιrErrorlnt}, /"Compute Output*/ { "H Duty * ",10,NULL, 8.DutyHeaterPredιcted}, DutyHeater = KPTAIR*TaιrError + { "Tsat Setpt",12,NULL, &TsatSetpoιnt}, KITAIR'TairErrorlnt + KDTAIR*TaιrErrorDerιv { "Tsat lntgr", 13.NULL, 8.TsatErrorlnt}, + DutyHeaterPredicted, { "C Duty * ", 14.NULL, &DutyChιllerPredιcted}, if (DutyHeater<0) DutyHeater=0 , { "H Duty",17,NULL, SDutyHeater}, else if (DutyHeater>1 ) DutyHeater=1 , { "C Duty",18,NULL, SDutyChiller}, { "Data Count",20, &DataCount, //////// SAT TEMPERATURE CONTROL PID w/ FF /// NULL} /'Determine Tsat }. Setpoint * / //begin \askO TsatSetpoint = void taskOstateO(){ static cont = FALSE, Tsat_steamTable(RHSetpoιnt 100 * Psat_steamTable(TaιrSetpoι if (cont=--FALSE){ nt+273 16))-273 16, cont=TRUE, /"Compute P term //begin ENTRY function 7 SetupScreen(msg,NUM_MSG, TsatError = TsatSetpoint - TsatMeasured, ιnltem,NUM_IN, outltem,NUM_OUT, "Compute I term */ &escKeyHιt, NULL), TsatErrorlnt += //end ENTRY function TsatError * (float)(task[1] tιmeSιnceLast)/1000, } if (TsatZerolnt || fabs(TsatError)>TSAT_ILIM){ //begin ACTION function TsatErrorlnt=0 , DoScreenlnputO, } DoScreenOutputf), /"Compute D term //end ACTION function */ if (escKeyHιt){ TsatErrorDeπv = (TsatError - //begin EXIT function TsatErrorPrev)/((ftoat)(task[1] tιmeSιnceLast)/1000), StopSchedulιng(USER_STOP), TsatErrorPrev = TsatError, //end EXIT function /"Compute cont=FALSE, Feedforward */ task[0] nextState -- taskOstateO, DutyChillerPredicted = KFCHILL1 'TsatSetpoint + } KFCHILL2, if (!Commlnιtιalιzed){ /"Compute Output //begin EXIT function */ StopSchedulιng(COMM_STOP), DutyChiller = KPTSAT*TsatError + //end EXIT FUNCTION KITSAT'TsatErrorlnt + KDTSATTsatErrorDeπv cont=FALSE, + DutyChillerPredicted, task[0] nextState = taskOstateO, if (DutyChιller<0) DutyChιlIer=0 , } else if (DutyChιller>1 ) DutyChιller=1 0, } //end ACTION function //begin taskl if (FALSE) void taskl state0(){ static cont = FALSE, { if (cont==FALSE){ //begin EXIT function cont=TRUE, //end EXIT function //begin ENTRY function cont=FALSE, //end ENTRY function task[1] nextState = tasklstatel , } } //begin ACTION function } //end ACTION function //begin tos\<2 if (Commlnιtιalιzed){ void task2state0(){ static cont = FALSE, //begin EXIT function if (cont==FALSE){ //end EXIT function cont=TRUE, cont=FALSE, //begin ENTRY function task[1 } nextState = taskl statel , //end ENTRY function } } } //begin ACTION function void taskl statel (){ static cont = FALSE, //end ACTION function if (cont==FALSE){ if (Commlnιtιalιzed){ cont=TRUE, //begin EXIT function //begin ENTRY function //end EXIT function //end ENTRY function cont=FALSE, } task[2] nextState = task2state1 , //begin ACTION function } /// DRY BULB TEMPERATURE CONTROL PID w/ } FF// void task2state1 (){ static cont = FALSE, / • Compute P term */ if (cont==FALSE){ TairError = TairSetpoint-TairMeasured, cont=TRUE, / • Compute I term*/ //begin ENTRY function TairErrorlnt += txCharCS 1 ), TaιrError * (float)(task[1 ] timeSιnceLast)/1000, txChar('E'), txChar('N'), } txChar('D'), if (TιmerHeater>TιmeOffHeater && DutyHeater<1 ){ txChar(CR), //begin EXIT function //end ENTRY function //end EXIT function } cont--FALSE, //begin ACTION function task[3] nextState = task3state2, //end ACTION function ) if (TRUE){ if (EnableHeater<1){ //begin EXIT function //begin EXIT function if //end EXIT function (getHMP230Readιngs(&RHMeasured,&TaιrMeasured)) { con-=FALSE, task[3] nextState = task3state0, StopSchedulιng(COMM_STOP), } //end EXIT function void task3state2(){ static cont = FALSE, cont=FALSE, if (cont=--FALSE){ task[2] nextState = task2state2, cont=TRUE, } //begin ENTRY function } Pιn2to(), void task2state2(){ static cont = FALSE, OutputHeater=0, if (cont=--FALSE){ //end ENTRY function cont--TRUE, } //begin ENTRY function //begin ACTION function ALCIear(ALDEVICE), TιmerHeater+= (float)task[3] timeSinceLast, //end ACTION function AI_Read(ALDEVICE,AI_CHAN,AI_GAIN,&value), if (TιmerHeater>PerιodHeater && DutyHeater<=0){ //begin EXIT function AI_VScale(AI_DEVICE,AI_CHAN,ALGAIN,1 ,0 O.val //end EXIT function ue.&volts), cont=FALSE, TsatMeasured = TSAT_SLOPE * volts + task[3] nextState = task3state2, TSATJNT, } //end ENTRY function if (TιmerHeater>PerιodHeater && DutyHeater>0){ } //begin EXIT function //begin ACTION function //end EXIT function //end ACTION function cont=FALSE, if (TRUE){ task[3] nextState -- task3state1 , //begin EXIT function } //end EXIT function } cont--FALSE, //begin \asW4 task[2] nextState = task2state1 , void task state0(){ static cont = FALSE, } if (cont==FALSE){ } cont=TRUE, //begin ιas\κ3 //begin ENTRY function void task3state0(){ static cont = FALSE, Pιn3lo(), if (cont--=FALSE){ OutputChilter=0, cont--TRUE, //end ENTRY function //begin ENTRY function } Pιn2lo(), //begin ACTION function OutputHeater=0, //end ACTION function //end ENTRY function if (EnableChιller----1 ){ } //begin EXIT function //begin ACTION function //end EXIT function //end ACTION function cont=FALSE, if (EnableHeater=--1 ){ task[4) nextState -- task state1 , //begin EXIT function } //end EXIT function } cont=FALSE, void task 4 state1 (){ static cont = FALSE, task[3] nextState = task3state1 , if (cont----FALSE){ } cont=TRUE, } //begin ENTRY function void task3state1(){ static cont = FALSE, TιmerChιller--0, if (cont--=FALSE){ T.meOffChιller--Du-yChιller*PeπodChιl.er, cont=TRUE, Pιn3hι(), //begin ENTRY function OutputChιlter=1, TιmerHeater=0, //end ENTRY function } TιmeOffHeater--DutyHeater*PerιodHeater, //begin ACTION function Pιn2hι(), TιmerChιller+-- (float)task[ ] timeSinceLast, OutputHeater=1 , //end ACTION function //end ENTRY function if (TιmerChιller>TιmeOffChιller && DutyChιller>--1 ){ } //begin EXIT function //begin ACTION function //end EXIT function TιmerHeater+= (float)task[3] timeSinceLast, cont=FALSE, //end ACTION function task[ ] nextState = task state1 , if (TιmerHeater>TιmeOffHeater && } DutyHeater>--1 ){ if (TιmerChιller>TιmeOffChιller && DutyChιiler<1 ){ //begin EXIT function //begin EXIT function //end EXIT function //end EXIT function cont=FALSE, cont--FALSE, task[3] nextState = task3state1 , task[4] nextState = task state2, } Commlnιtιalιzed=TRUE, -f (Enab-eChιller<1){ //initialize DAQ //begin EXIT function USE_E_Serιes_AI(), //end EXIT function ALCIear(A DEVICE), cont=FALSE, //initialize Screen task[ ] nextState = task 4 state0, clrscr(), } //begin shutdownTask/////////////////////////////////////////////////// void task state2(){ static cont = FALSE, void shutdownTask() { if (cont----FALSE){ int ix, cont=TRUE, FILE * fp, //begin ENTRY function Pιn3lo(), //Set all outputs low OutputChιller--0, Pιn2lo(), //end ENTRY function Pιn3lo(), } //Write data to file //begin ACTION function fp--fopen("data txt","wt"), TimerChi--er+= (float)task[ ] timeSinceLast, for (ιx=0, ιx<DataCount, ιx++) { //end ACTION function if (TιmerChιller>PerιodChιller && DutyChιl-er<=0){ fprιntf(fp,"%M%ftt%ftt%f\t%f\t%f\t%f\n",Data1[ιx],Data //begin EXIT function 2[ιx],Data3[ιx], //end EXIT function cont=FALSE, Data [ιx],Data5[ιx],Data6[ιx],Data7[ιx]), task[4] nextState -- task4state2, } } fclose(fp), if (TιmerChιller>PerιodChιller && DutyChιller>0){ //begin EXIT function //end EXIT function con-=FALSE, File Screen c task[ ] nextState = task state1 , } Bryan Wade } Creates a simple text ui for real-time systems The interface //begin tasks entities are 1) static messages (e g a title), 2) outputs with void task5state0(){ static cont = FALSE, labels, if (cont==FALSE){ 3) inputs with labels (increment/decrement by user-defined cont=TRUE, amount), and 4) //begin ENTRY function access to the ESC key DataCount=0, Use //end ENTRY function 1 )#ιnclude "screen h" } 2)defιne struct arrays ScreenMsg[],Screenltem[] (inputs) //begin ACTION function Screenltemj] (outputs) DataCount=0, 3)voιd SetupScreen(struct ScreenMsg * msg, int numMsgs, struct //end ACTION function Screenlnputltem input, if (CollectData==TRUE){ int numlnputs, struct ScreenOutputltem* //begin EXIT function output, int numOutpus, int* ESC Iag), //end EXIT function )voιd DoScreenlnputsO, cont=FALSE, process keyboard buffer for input commands task[5] nextState = task5state1 , 5)voιd DoScreenOutputsO, } updates outputs (one output per call) } '7 void task5state1 (){ static cont = FALSE, ftnclude <conιo h> if (cont=--FALSE){ #ιnclude <stdιo h> cont=TRUE, ftnclude "screen h" //begin ENTRY function static struct ScreenMsg* msg, DataTιme=0, static int maxMsglndex, //end ENTRY function static struct Screenlnputltem * inlte , } static int maxlnputlndex, //begin ACTION function static struct ScreenOutputltem* outltem, DataTιme+= (ftoat)(task[5) tιmeSιnceLast)/1000 , static int maxOutputlndex, if (DataCount<MAX_DATA_COUNT) { static int * escFlag, Datal [DataCount]--DataTιme, static int* spaceFlag, Data2[DataCount]--TaιrMeasured, Data3[DataCountj--TaιrSetpoιnt, void DoScreenlnput(){ Data4[DataCountj--TsatMeasured, int o, Da-a5[DataCountj=TsatSetpoιnt, static int ιndex=0, Data6[DataCount]=RHMeasured, whιle(kbhιt()){ Data7[DataCount++]--RHSetpoιnt, c = getch(), } switch (c){ //end ACTION function case UP if (CollectData--=FALSE){ //begin EXIT function gotoxy(INPUT_CURS_COL,ιnltem[ιndex] pos), //end EXIT function cont=FALSE, pπntf(" "), task[5] nextState = task5state0, index = (index =0)' maxlnputlndex ιndex-1 , //begin gotoxy(INPUT_CURS_COL,ιnltem[ιndex] pos), void ιnιtιalιzatιonTask() { //initialize serial comm prιntf(">"), initCommunicationsO, gotoxy(msg[ι] x,msg[ι] y), break, prιntf("%s' ,msg[ι] text), case DOWN } //setup inputs gotoxy(INPUT_CURS_COL,ιnltem[ιndex] pos), for (ι=0, κ=maxlnputlndex, ι++){ pπntff '), gotoxy(INPUT_NAME_COL,ιnltem[ι] pos), prιntf("%s",ιnltem[ι] name), index = (index ----maxlnputlndex)' 0 ιndex+1 , gotoxy(INPUT_VALU_COL,ιnltem[ι] pos), prιntf("%72f",*(ιnltem[ι] address)), gotoxy(INPUT_CURS_COL,ιnltem[ιndex] pos), } prιntf(">"), gotoxy(INPUT_CURS_COL,ιnltem[0] pos), prιntf(">"), break, //setup outputs case LEFT for (ι=0, κ=maxOutputlndex, ι++){ * (ιnltem[ιndex] address)-=inltem[index] delta, gotoxy(OUTPUT_NAME_COL,outltem[ι] pos), if ( * (ιnltem[ιndex] address) < ιnltem[ιndex] mιn){ prιntf("%s",outltem[ι] name), * (ιnltem[ιndex] address) = gotoxy(OUTPUT_VALU_COL,outltem[ι] pos), ιnltem[ιndex] mm,} if (outltem[ι] ιRri=NULL) prιntf("%d ",*(outltem[ι] iRr)), gotoxy(INPUT_VALU_COL,ιnltem[ιndex] pos), else prιntf("%72f ","(outltem[ι] fRr)), prιntf("%72f ",*(ιnltem[ιndex] address)), break, case RIGHT File Thc cns c * (ιnltem[ιndex] address)+=ιnltem[ιndex] delta, Bryan if (*(ιnltem[ιndex) address) > ιnltem[ιndex] max){ Wade This file contains functions for the DCCC controller * (ιnltem[ιndex] address) = This includes the steam table equations and routines for ιπltem[ιndex] max,) communicating with gotoxy(INPUT_VALU_COL,ιnltem[ιndex] pos), the HMP230 sensor prιntf("%72f ", * (ιnltem[ιndex] address)), ftnclude "thc_fcns h" ftnclude <math h> break, ftnclude 'bios h" case ESC ftnclude <strιng h> #defιne COM 0 //0=COM1 , 1 =COM2 * escFlag=1, #defιneTRUE 1 #defιne FALSE 0 break, #defιne CR OxOD case SPACE #defιne NUL 0 a 1 ms interrupt and resets clock last reset last reset & resets to DOS txChar(char ch){ int ShutdownMιllιClock(){ unsigned int status, if (running)! //wait disableQ, status = READY_TO_WRITE & _bιos_serιaicom( setalarm(00), * set back to DOS default * / _COM_STATUS, COM, 0 ), setvect(CK_VECT,old_vect), while ( status ι= RE-ADY_TO_WRITE && 0){ enable(), Status = READY_TO_WRITE & runnιng=0, _bιos_serιalcom (_COM_STATUS, COM, 0), } } return(1), //send char } _bιos_serιalcom( _COM_SEND, COM, ch ), } int Mι!l-Clock(ιnt flag){ int int temp = milliCount,, getHMP230Readιngs(float * rh, float * t) { if (flag==0) milliCount = 0, char ch, buf [10], return temp, unsigned int ιx=0,-rιes, } for (ιx=0,trιes=0, ιx<6,) { ch=rxChar(), void interrupt tιmerJSR(voιd){ if (chl=NUL) { /'manipulate floating point processor stack * / buf[ιx++]=ch, asm sub SP,9 } asm mov BP,SP if (++tπes>40000) { asm fsave[BP] txChar(CR), asm fwait return 0, mιllιCount++, } / • send E0I7 } outport(0x20,0x60), buf[ιx]=NUL, manipulate floating point processor stack*/ if (buf[3] --= ' ') * rh= atof(buf), asm mov BP.SP else asm frstor[BP] return 0, asm add SP,9 for (ιx=0,trιes=0, ιx<5,) { asm fwait ch=rxChar(), } if (chl=NUL) { buf[ιx++]=ch, int setalarm (double ms){ } ιf((ms>00) && (ms<=MAX_MS)){ if (++trιes>40000) { count=(CLOCKFREQ * ms) / 10000 + 05, txChar(CR), outportb(TIMER_CTL, 0x36), return 0, outportb(TIMER, count&OxFF), outportbfTIMER, (count»8)&0xFF), }else if (ms<=00){ int timeLeft, outportb(TIMER_CTL, 0x36), void ( * nextState)(), outportbfTIMER, DOS_COUNT&0xFF), int priority, outportb (TIMER, int timeSinceLast, (DOS_COUNT»8)&0xFF) , } . count=DOS_COUNT, //begin sched function prototypes///////////////////////////////////////////// }else{ void fιlDueues(ιnt* fgQueue.mt* numFG.int* bgQueue.int* return(1),/*error return * / numBG, } return(O) /'normal return*/ unsigned long * taskCount), } void shutdownScheduler( unsigned tang startTime, unsigned r " * — ******** ** — • * — long passes, File LPTJO c Bryan Wade unsigned long* taskCount, int stacklndex), Functions for using parallel port for digital I/O Now that we void StopSchedulιng(ιnt stopType), have the Nl data acquisition board it would be easier to use it for I/O rather than this . v File Tasks h ftnclude <dos h> ******** — " •• " •***** — • » •• / #defιne BASE 0x378 / * Usually Iptl is 0x378 & Ipt2 is 0x278 7 //taskO states prototypes static int dataByte = 0x00, void taskOstateO(), //user interface static int inputByte = 0x00, //taskl state prototypes static int controlByte = 0x00, void taskl stateOO , //go on void Pιn2hι(){ void tasklstatel (), //process control algorithm dataByte |= 0x01 , //task2 state prototypes outportb(BASE+0,dataByte), void task2state0(), //go on } void task2state1 (), //request RH.Tair and wait for response void Pιn2lo(){ void task2state2(), //read Tsat dataByte &= OxFE, //task3 state prototypes outportb(BASE+0,dataByte), void task3state0(), //heater output disabled void task3state1{), //heater PWM hi void Pιn3hι(){ void task3state2(), //heater PWM lo dataByte |= 0x02, //task 4 state prototypes outportb(BASE+0,dataByte) , void task 4 stateO() , //Chiller output disabled } void task 4 state1 (), //Chiller PWM hi void Pιn31o(){ void task state2(), //Chiller PWM lo dataByte &= OxFD, //tasks state prototypes outportb(BASE+0,dataByte), void task5state0(), //Don't collect data } void task5state1 (), //Collect data void Pιn hι(){ //mitalizationTask prototype dataByte |= 0x04, void ιnιtιalιzatιonTask(voιd), outportb(BASE+0,dataByte), //shutdownTask prototype } void shutdownTask(voιd). void Pιn to(){ //end state prototyping///////////////// dataByte &= OxFB, //begin Tasks module defines outportb(BASE+0,dataByte) , extern struct taskStruct taskQ, #defιne FALSE 0 void Pιn5to(){ //inverted #defιneTRUE 1 dataByte |= 0x08, #defιne HUGE 1 0e9 outportb(BASE+0,dataByte), void Pιn5hι(){ //inverted File Screen h dataByte &= 0xF7, outportb(BASE+0,dataByte), #defιne UP '8' #defιne DOWN '2' void Pιn6hι(){ #defιne LEFT '4' dataByte |= 0x10, #defιne RIGHT '6' outportb(BASE+0,dataByte) , #defιne ESC 0x1 b } #defιne SPACE ' ' void Pιn6ta(){ #defιne INPUT_NAME_COL 6 dataByte &= OxEF, #defιne INPUT_CURS_COL5 outportb(BASE+0,dataByte), #defιne INPUT_VALU_COL 18 } #defιne OUTPUT_NAME_COL 49 int ShutdownLPT(){ #defιne OUTPUT_VALU_COL 61 outportb(BASE+0,0x00), void DoScreenlnput(voιd), return(1), void DoScreenOutput(voιd), void SetupScreen(struct ScreenMsg * ,ιnt, struct Screenlnputltem*,ιnt, File Sched h * struct ScreenOutputltem*,ιnt,ιnt * ,ιnt * ), struct Screenlnputltem { //begin sche char name[12], #defιne EMPTY -1 int pos, #defιne EPS 1e-9 float delta, #defιne USER_STOP 1 float mm, #defιne STACK_STOP 2 float max, #defιne FILE_STOP 3 float* address, #defιne STEPPING_STOP 4 }. #defιne COMM_STOP 5 struct ScreenOutputltem { struct taskStructf char name[12], int Tsamp, int pos, int* iPtr; int x; float* fRr; int y; }; ); struct ScreenMsg { Typedef unsigned char BYTE; char text[80];

Claims: What is Claimed: 1. A gas-liquid contact system, comprising: a contactor, including contact media, a gas inlet and a gas outlet, a liquid inlet and a liquid outlet, wherein the liquid inlet admits liquid above the contact media and the gas inlet admits gas below the contact media, and the liquid and gas flow through the contact media such that the gas leaves through the gas outlet in saturated state; a heater; a chiller; a gas outlet line connecting the gas outlet to the heater; a liquid outlet line connecting the liquid outlet to the chiller, wherein the liquid flows in a closed loop through the liquid inlet, the contactor, the liquid outlet and the chiller; a first gas temperature sensor associated with the gas outlet line and upstream of the heater; a second gas temperature sensor associated with the gas outlet line and downstream of the heater; and a controller coupled to the first and second gas temperature sensors and the heater, wherein the controller and adjusts the heater to deliver the gas at a desired temperature and relative humidity. 2. The system of claim 1 , further comprising a sprinkler above the contact media to distribute the liquid uniformly on the contact media, a pump located between the chiller and the sprinkler to supply liquid to the sprinkler, and a gas blower to supply gas to the gas inlet. 3. The system of claim 2, wherein the housing is cylindrical in shape, and the sprinkler includes at least one arm with a plurality of orifices along the arm and pointed between parallel and opposite the top of the contact media and wherein the sprinkler engages in self-rotation from reactive force exerted against the arm(s) from distribution of the liquid from the orifices 4. The system of claim 1 , further comprising a reservoir with a make-up inlet line to introduce liquid into the reservoir and a removal outlet line to remove liquid from the reservoir, a low sensor which generates a signal to a liquid supply means whenever the level of the liquid is low to supply additional liquid through the make-up inlet to the reservoir, a high sensor which generates a signal whenever the level of the liquid is too high to remove liquid through the removal inlet from the reservoir. 5. The system of claim 1 , wherein the controller sends a signal to a liquid supply means to admit fresh liquid from the supply means at periodic times to maintain liquid purity requirements and such that the chiller can maintain the liquid at a desired temperature. 6. The system of claim 1 , 2, 3, 4, or 5, wherein the contact media is tower packing. 7. A system of controlling the temperature, the relative humidity, and the cleanliness of air, comprising: an air-water contactor, including a housing with contact media, an air inlet and an air outlet, a water inlet and a water outlet, wherein the water inlet admits a water above the contact media and the air inlet admits air below the contact media, and the water and air flow through the contact media such that the air leaves through the air outlet in saturated state; a heater; a chiller; a filter; an air outlet line connecting the air outlet to the heater; a water outlet line connecting the water outlet to the chiller, wherein the water flows in a closed loop through the contactor and the chiller; a first air temperature sensor associated with the air outlet line and upstream from the heater; a second air temperature sensor associated with the air outlet line and downstream from the heater; and a controller coupled to the first and second air temperature sensors, the heater, and the chiller, wherein the controller adjusts the heater and chiller to deliver air at a desired temperature and relative humidity, and wherein the filter is associated with the air outlet and downstream from the heater. 8. The system of claim 7, further comprising a sprinkler above the contact media to distribute the water uniformly on the contact media, a pump located upstream from the chiller to supply water to the sprinkler, and an air blower located between the heater and the filter. 9. The system of claim 8, wherein the housing is cylindrical in shape, and the sprinkler includes at least one arm with a plurality of orifices along the arm and pointed between parallel and opposite the top of the contact media and wherein the sprinkler engages in self-rotation from reactive force exerted against the arm(s) from distribution of the water from the orifices 10. The system of claim 7, further comprising a reservoir with a make-up inlet line to introduce water into the reservoir and a removal outlet line to remove water from the reservoir, a low sensor which generates a signal to a water supply means whenever the level of the water is low to supply additional water through the make-up inlet to the reservoir, a high sensor which generates a signal whenever the level of the water is too high to remove water through the removal inlet from the reservoir. 11. The system of claim 7, wherein the controller sends a signal to a water supply means to admit fresh water from the supply means at periodic times to maintain water purity requirements and such that the chiller can maintain the water at a desired temperature. 12. The system of claim 7, 8, 9, 10, 11 , wherein the contact media is tower packing. 13. A controller adapted for obtaining gas at a desired temperature and relative humidity from a system, including a gas-liquid contactor, a gas heater connected to the contactor, a liquid chiller connected to the contactor, comprising: a computer, including input means for a temperature set point and a relative humidity set point, a first compensator, a second compensator, a transformer taking the inputs of the temperature set point and relative humidity set point and generating a output to the second compensator, wherein the first and second compensators outputs control the heater and chiller, to obtain gas from the contactor in a desired tolerance of the temperature and relative humidity set points. 14. The controller of claim 13, wherein the computer further comprises a first PWM signal converter, wherein the first compensator is a first PID generating a first output signal, and wherein the first PWM signal converter converts the first PID output signal to a first command signal to adjust the heating rate of the heater. 15. The controller of claim 13, wherein the computer further comprises a second PWM signal converter, wherein the second compensator is a second PID generating a second output signal, and wherein the second PWM signal converter converts the second PID output signal to a second command signal to adjust the cooling rate of the chiller. 16. The controller of claim 13, wherein the transformer generates a saturation temperature set point from the temperature set point and the relative humidity set point, and wherein the computer includes a temperature dry bulb feedback loop, comparing the dry bulb temperature with the temperature set point, and a temperature saturation feedback loop, comparing the saturated temperature with the saturation temperature set point. 17. The controller of claim 13, wherein the computer includes a cooperative multitasking scheduler, which allocates when a task runs in the CPU of the computer so that each task is given processing time and passes back control to scheduler after completion of the task. 18. The controller of claim 13, 14, 15, 16, or 17, wherein the gas is air and the liquid is water. 19. A method for controlling the quality of air delivered to a local environment, comprising the steps of: providing an input for temperature and relative humidity set points; circulating water through a contactor, wherein the contactor includes a water inlet and outlet, an air inlet and outlet; circulating air through the contactor, wherein the air in the contactor is in intimate contact with the water in the contactor, and the air at the air outlet is saturated; measuring the dry bulb temperature of the air delivered to the local environment and the temperature of saturated outlet air; and comparing the dry bulb temperature of the air with the temperature set point and generating a corresponding first signal. 20. The method of claim 19, further comprising the steps of: transforming the temperature set point and the relative humidity set point into a saturation temperature set point; and comparing the saturation temperature set point with the temperature of the saturated outlet air and generating a corresponding second signal; and adjusting the chiller in accordance with the second signal to bring the circulating water to the temperature which results in air delivered to the local environment to the value of the temperature and relative humidity set points. 21. The method of claim 19, further comprising the step of adjusting the heater in accordance with the first signal to bring the air delivered to the local environment to the value of the temperature and relative humidity set points. 22. The method of claim 20, further comprising transforming the first signal by a first PID compensator to a first command signal and converting the first command signal to a first pulse width modulated format for powering the heater. 23. The method of claim 19, further comprising transforming the second signal by a second PID compensator to a second command signal and converting the second command signal to a second pulse width modulated format for poweringthe chiller.

Inventors: BABIKIAN DIKRAN, WADE BRYAN, BABIKIAN, DIKRAN, WADE, BRYAN
Applicants: SILICON VALLEY GROUP, SILICON VALLEY GROUP, INC.
Application year: 2000
Main classification: F24F
IPC codes: F24F5