Abstract:
An evaporative cooler includes an arrangement of a combination of fluid components including flow control valves, spray bars, spray bar orifices, spray bar distribution channels, and distribution caps that produce a water application profile on the media that is adjusted to match the heat load introduced to the media by the air to be evaporatively cooled. The water evaporation rate is a direct function of this heat load profile. Applying water in this profile takes advantage of the wicking rate and flow through time constant of evaporative cooling media to effectively distribute the water through the media. This results in a once through system that allows the volume of water being applied be the lowered such that water not evaporated and exiting the media is limited and does so at very high cycles of concentration while maintaining high levels of cooling effectiveness and scale free media.

Description:
CROSS REFERENCE TO RELATED PATENT 
       [0001]    The present application is related to and claims priority to a provisional application entitled “Evaporative Cooler With Dual Water Inflow” filed Jan. 18, 2007 and assigned Ser. No. 60/885,557 and the present application is related to and incorporates by reference the disclosure contained in an application entitled “Water Distribution System For Evaporative Cooler” filed Dec. 21, 2006 and assigned Ser. No. 11/569,944. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to water distribution systems for evaporative coolers and, more particularly, to a water distribution system for controlling distribution of water uniformly across a media to avoid dry spots, scaling, streaking and distribution of excess water. 
         [0004]    2. Description of Related Art 
         [0005]    Evaporative cooling appears to be a simple process of passing hot dry air through a wet pad or media to evaporate the water with the latent heat of the air and inherently the air becomes cooler and more humid. In reality, there are three complex mechanical and chemical processes taking place in an evaporative cooler. The first process is the air system which is controlled by the psychrometric chart and the efficiency of the media. The second process is the water delivery system that has to ensure that the media has sufficient water for evaporation and that the media is uniformly wetted. The third process is the water chemistry system where the water for evaporation is controlled so that the naturally occurring dissolved solids in the water remain in solution and are disposed of prior to being deposited on the media. Almost all evaporative coolers built to date have made only first order approximations for one or more of the processes and have either ignored or been unaware of the others. 
         [0006]    The air around us is essentially a constant composition of gases (nitrogen oxygen, carbon dioxide and others) and varying amounts of water vapor. It also contains solid impurities such as dust and organic material, which will be ignored in the following discussion. The gas component of air behaves in accordance with Boyle&#39;s and Charles&#39; laws (e.g., the volume of the gas varies inversely with the absolute pressure and directly with the absolute temperature, respectively). The water vapor portion of air does not behave as a perfect gas. The amount of moisture in the air is dependent on the amount of moisture available and is limited to a maximum saturation value based on the air temperature and pressure. As moisture is added to or removed from the air, water is either evaporated or condensed. This change in phase captures or releases energy. In evaporative cooling applications, the evaporation of water absorbs heat. The movement of the heat from the air to the water vapor happens without a change in air volume or air pressure and results in a lowering of the temperature of the air. The relationships between pressure, temperature, humidity, density and heat content are most commonly shown graphically on psychrometric charts. These relationships are very well defined and have been the subject o extensive research. Applying the psychrometric chart to the evaporative cooling process is easy for any one particular set of operating conditions. If one knows the entering air temperature (inlet dry bulb), the relative humidity of the inlet air, the barometric pressure and the volume of air being cooled one can calculate the theoretical amount of moisture that can be evaporated into the airstream and the resulting temperature reduction. 
         [0007]    Actual operating conditions change constantly. The inlet air temperature, the relative humidity and barometric pressure are the detailed measurements of what is generally referred to as the “Weather.” Most evaporative cooler manufacturers design their equipment to handle a specific air flow rate at standard conditions and size the evaporation media for this flow rate. The efficiency of the evaporative cooler is determined by the air flow rate over the chosen media. Each media type has physical characteristics that determine how fast and thoroughly the water can be evaporated into the airstream. The most common evaporative cooling media in use today is a corrugated Kraft type paper. The market leader in this type of media is Munters Corporation which markets its media under the trademarks Cel Dek and Glacier-Cor. Depending upon the thickness of the media used and the velocity of the air flowing through the media, the saturation effectiveness (efficiency) can range from less than 60 percent to about 98 or 99 percent. 
         [0008]    The majority of existing evaporative coolers are controlled by a downstream thermostat and the evaporative coolers are either on or off. The efficiency of the evaporative cooler changes with the weather and the water system pressure. The conventional evaporative cooler does not attempt to control any of these process variables of demised efficiency. 
         [0009]    To obtain maximum evaporation, the media must be adequately wetted. Most conventional evaporative coolers have a large basement or sump filled with water that is pumped to a perforated header pipe at the top of the media. The water is sprayed from the header pipe up to a deflector shield and runs down onto the top of the media. Excess water is applied to ensure saturation of the media. The water not evaporated drains into the sump to be reused. All recirculating evaporative coolers manufacturers recommend that a portion of the recirculating water be discarded and replaced with fresh water added to the sump to keep the water quality at a minimum quality level. 
         [0010]    The media removes significant amounts of airborne contaminants from the air as the air passes through the media and the return water rinses a portion of the contaminants off the media and carries them to the sump. In addition, naturally occurring salts in the water supply become concentrated on the surface of the media and are partially rinsed into the sump. While some of these contaminants and precipitated salts settle to the bottom of the sump, a significant amount are entrained at the pump inlet and are recirculated back onto the media. 
         [0011]    The pumps used in most recirulating type evaporative coolers are submersible centrifugal pumps. These inexpressive pumps are not precision pieces of equipment when new and wear quickly as the debris is recirculated. This deterioration of the pump leads to fairly rapid changes in the delivery head for the pump. This change in the output of the pump renders it difficult to regulate the water flow across the media. The distribution header pipe uses large holes on relatively large hole spacing to minimize debris from fouling and plugging the holes. The end result is an uneven water distribution and occasionally dry strips on the media. Constant maintenance is required to adjust and maintain an adequate supply of water for the media. Often, these systems attempt to cure uneven water flow by pumping an excess amount of water to the media. This excess amount of water can cause the cellulose media to deteriorate prematurely with associated poor performance and costly early media replacement. 
         [0012]    The most overlooked aspect of evaporative cooling is controlling the concentration of dissolved solids in the water being evaporated on the media. The water supply for evaporative coolers is typically domestic water which contains a number of compounds as dissolved solids. Water is evaporated by the warm air and leaves behind all of the dissolved solids in a small volume of water on the media. Each type of dissolved solid has a solubility limit. That is, when the concentration of a particular compound reaches a known concentration, the compound precipitates out. In evaporative coolers the most common form of precipitate is calcium carbonate scale on the media. This hard water scale does not re-dissolve when rewetted. Once formed on the media, it reduces the saturation efficiency and clogs the water distribution channels. 
         [0013]    Recirculating evaporative coolers reapply the sump water to the media. Each time the water is applied some of it evaporates and the dissolved solids build up in the water. All evaporative cooler manufactures either bleed some of the recirculating water off to try and reduce the concentration of the dissolved solids (called cycles of concentration in the industry) or dump the sump water occasionally to eliminate as much of the dissolved solids as possible. Most sumps have a float actuated make up valve to add water to the sump. This mixes the fresh water with the concentrated dissolved solids in the water and reduces the concentration. As a practical matter however the resulting water being distributed on the media will always have higher levels of dissolved solids than the inlet water. 
         [0014]    If the water distribution system allows the water in any area to become too concentrated with dissolved solids before it leaves the media, the media will start to scale. Once scaling begins, the process threshold for additional scaling is reduced such that the crystals will grow whenever the surrounding water is just near the precipitation point. This occurs after scaling starts and the recirculating water must be kept at a lower dissolved solids concentration than would be allowed if the scale had not started. 
         [0015]    While the step of bleeding slows the build-up of scale it does not eliminate it or control it. To date, the best solution is that of eliminating a recirculating system in favor of a single water pass system. The single pass systems provide water to the top of the media and lets it flow through the media and the flow therefrom is drained. Several problems arise. First, one must incorporate on/off controls to regulate the water introduced to the media. Second, the flow volume of water must be sufficient to wet the media completely and yet the flow must be periodically shut off to avoid wasting large amounts of water. Some existing systems use a timer based controller to regulate the water flow. Another type of system uses a single temperature sensor within the media coupled with a timer to control the flow of water. These systems typically fail prematurely either form using too much water or from using insufficient water resulting in drying out and scaling of the media. Neither of these two types of systems are widely commercially acceptable. 
         [0016]    In general, the evaporative cooler market has become a commodity market, with market conditions forcing the manufacturers to produce less expensive coolers. Without clear standards on how to rate the units and an uneducated consumer base, a lot of the evaporative coolers are rated at a nominal air flow rate without reference to the efficiency of the unit. As a result, the consumer makes his decision primarily on cost rather than performance or return on investment. 
         [0017]    Various prior art evaporative cooler systems are described in the patents listed below. 
         [0018]    U.S. Pat. No. 4,968,457 describes a non-circulating control for an evaporative cooler. The water flow is metered by a simple solenoid value which does not take into consideration changes in flow rate as a function of inlet line pressure. Therefore, the amount of water delivered at different times of the day will vary with changes in domestic water line pressure. Furthermore, there is no understanding of the need for a change of the water flow rate as a function of the hardness of the inlet water, nor is there a discussion of providing more water than is evaporated to keep the media from scaling. A sensor for controlling operation of a solenoid valve is placed downstream of spray nozzles ejecting water to the media to sense the temperature or the humidity. There is no understanding that the cooling process is primarily dependent on the inlet air conditions. 
         [0019]    U.S. Pat. No. 5,775,580 is directed to a non-circulating evaporative cooler for primarily eliminating the dripping of water from the media. This will result in at least a part of the media becoming dry with resulting deposit of salts and compromise of the integrity of the media and its effectiveness unless pure water is used. 
         [0020]    U.S. Pat. No. 6,367,277 discloses the use of fresh water makeup to minimize scaling in a recirculating evaporative cooler system. There is no disclosure relating to controlling the hardness of the water at the point of evaporation on the media nor does this system minimize the amount of water used. It also requires bleed of a substantial amount of the recirculating water to keep the minerals form precipitating out. No understanding of the varying conditions from location to location and the effect thereof on the efficiency of the evaporative cooler is set forth. 
         [0021]    There are several types of problems associated with heavy scale formation on the media in an evaporative cooler where evaporative cooling occurs. First, there is a decreased air flow through the media because the air channels therewithin become more or less plugged. To maintain an adequate air volume, the velocity of the air through the media must increase. At speeds above 650 feet per minute, small droplets of water become entrained in the airstream. These droplets may super saturate the airstream to the point that moisture may condense downstream of the media and create other problems unacceptable to the user. Second, at localized concentrations of salts, the pH in those areas increases dramatically. The high pH will allow the water to leach the resin and delignify the cellulose in the media and cause premature structural failure of the media. 
         [0022]    Indoor air quality has become a growing concern as modern office and industrial buildings become more energy efficient and better insulated. Various regulations cover how much fresh outside air must be introduced into the HVAC system in a building. This outside air is rarely at the desired temperature and relative humidity. In the southwest of the United States, the air is generally much dryer and hotter than desired. This means that the makeup air requires cooling and humidification before it can be introduced into the building. Conventional chilled water systems in large commercial buildings use large cooling towers and chillers to supply the cooling for the building. These systems are usually on or off and when on use considerable electricity to operate. Direct evaporative cooling has been used to reduce the electrical demand by evaporatively cooling the makeup air prior to use. These applications have been plagued by the same scaling and lack of control problems described above. 
         [0023]    Evaporative cooling is often used in dusty industrial environments. Historically, recirculating evaporative coolers become plugged with dust. Often pre-filters are installed upstream of the evaporative cooler to remove the dust present in the air. Poor maintenance often results in filter overloading, filter failure and media plugging. One approach to this problem of dust has been that of using an excess water flow controlled by only a timer for dust control. 
         [0024]    These prior are results were not particularly successful. A further unit uses a fresh water makeup header to try to control the dust buildup, but a timer is used to activate the flush and it is not particularly effective. 
       SUMMARY OF THE INVENTION 
       [0025]    This invention is an arrangement of a combination of fluid flow components including flow control valves, spray bars, spray bar orifices, spray bar distribution channels, and distribution caps in a manner that results in a water application profile that is adjusted to match the heat load introduced to the media by the air to be evaporatively cooled. The water evaporation rate is a direct function of this heat load profile. Applying water in this profile takes advantage of the wicking rate and flow through time constant of the evaporative cooling media to effectively distribute the water through the pad. This result in a once through system allows the volume of water being applied to be lowered such that water not evaporated and exiting the pad(s) is limited and does so at very high cycles of concentration while maintaining high levels of cooling effectiveness and scale free pad(s). 
         [0026]    It is therefore a primary object of the present invention to provide an effective water distribution for a once through water metering system using the latest equipment capabilities such that little water beyond that evaporated to cool the air is used while avoiding dry spots and scaling to promote effective cooling. 
         [0027]    Another object of the present invention is to distribute water onto evaporative cooling media in a profile that matches the thermal profile and water evaporation rate of the air to be evaporatively cooled as it travels from the front to the back of the media. 
         [0028]    Yet another object of the present invention is to distribute water onto evaporative cooling media in a profile that results in very little or no mineral buildup and scale formation to achieve maximum cooling performance. 
         [0029]    Still another object of the present invention is to distribute water onto evaporative cooling media in a profile that results in significantly higher cycles of concentration of water exiting the media to achieve reduced water bleed or discharge requirements and reduce the water withdrawn and used by an evaporative cooler. 
         [0030]    A further object of the present invention is to distribute water onto evaporative cooling media in a profile that results in longer media life by reducing the water passing over the media and washing out the media regifying agents. 
         [0031]    A yet further object of the present invention is to provide a method for efficiently and effectively using water in an evaporative water. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]      FIG. 1  is a flow diagram of a once through evaporative cooling system; 
           [0033]      FIG. 2  is a cross-sectional view of a pair of spray bars for distributing water to an underlying media; and 
           [0034]      FIG. 3  illustrates a water application profile on the media. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0035]    The psychrometric chart provides that if the inlet dry bulb temperature and the inlet wet bulb temperature are known one can calculate the amount of moisture that can be added to the air and the resulting leaving air dry bulb and wet bulb temperatures for an evaporative cooler. This is known as a mass balance equation. The mass balance equation must be solved for the inlet conditions and the capabilities of the equipment. Further, the rate of water evaporation varies along the air path as it moves through the pad or media and is cooled. This evaporation rate is dependent on the difference between the local conditions and the wet bulb temperature. 
         [0036]    Existing evaporative coolers attempt to measure the outlet temperature, the pad temperature, and the outlet relative humidity or pad relative humidity. It is known that the physical state of the inlet air drives or is responsible for all efforts to achieve evaporative cooling. At one extreme, if the inlet air is at 100 percent relative humidity, the evaporative cooler cannot function because additional moisture cannot be evaporated and hence no reduction in temperature of the outlet air can be achieved. Yet, there are an infinite number of possibilities of inlet conditions and operating parameters that could yield this measured outlet condition. Measuring the inlet conditions permits calculation of the expected results from an evaporative cooler and this calculation can be compared with the measured results to confirm the correct operation of the evaporative cooler. The problem that has existed in applying these concepts to evaporative coolers is that most designs are not able to distribute the water effectively on the pad nor to manage the physical parameters that control the process. The only input parameters attendant most evaporative coolers include a leaving air temperature switch (such as a room thermostat), the area of the wetted media and the nominal air flow. For example, a commercially available unit simply measures the temperature of the outflowing air while another unit measures the inlet air temperature and regulates the on and off time of the water supply at two control points. 
         [0037]    A key factor behind the development of recirculating coolers was the inability to distribute water at the desired volume to the desired location. To compensate for this limitation, additional water was delivered to the top of the pad and then collected and returned to the top of the pad. 
         [0038]    The unique features of the present invention include: 
         [0039]    1. Front and back spray bars that incorporate rows of orifices sized and oriented to produce water jets that distribute the water onto the media at specific volumes uniformly along their length to the front and back of the media and to the associated spray bar distribution channel. 
         [0040]    2. Flow control valves that deliver a predetermined constant flow rate of water to each spray bar with the front spray bar receiving about twice the volumetric flow rate of the back spray bar. 
         [0041]    3. Spray bar distribution channels configured to accept the water from the spray bar jets directed to them and redistribute this water evenly at each edge of the distribution channel. 
         [0042]    4. Spray bar distribution channels located above the media and formed with a radius that is sized to apply water at desired locations on the top of the media. 
         [0043]    5. Distribution cap that is configured to accept the water from the spray bar jets directed to the front and back of the distribution cap and redistribute this water to the front and back of the media. 
         [0044]    6. Distribution cap that incorporates features to orient and securely configure the spray bars and distribution channels to consistently apply water in a designed profile. 
         [0045]    Referring to  FIG. 1 , there is shown an evaporative cooling system  10  and the controls for operating it efficiently while causing minimal deterioration of the operative aspects of the wetted media. The most common media  12  presently in use is of the corrugated Kraft type paper. A typical media is manufactured by Munters Corporation and sold under the Cel Dek and Glacier-Cor trademarks. A water distribution unit  14  is mounted above the media to uniformly distribute water across the top of the media at a sufficient flow rate to maintain the media wetted during operation of the evaporative cooler. Water dripping from the media is collected in drain tray  16  and discarded through a drain  18 . The water is not recirculated. Thereby, the build-up of dissolved solids in the water used in water recirculating evaporative coolers is eliminated. Air to be cooled is drawn through media  12  by a fan  20 . The air to be cooled, as represented by arrow  22 , is drawn into media  12 . As the air passes through the media, it causes evaporation of some of the water present on the media. Such evaporation draws heat from the air and the air exhausted from the media, as represented by arrow  24 , is cooled. The cooled air is discharged, as represented by arrow  26 , into the environment to be cooled. 
         [0046]    An inlet water supply  30  may be water from a municipal water system or other source of water. A solenoid valve  32  controls the flow of water into evaporative cooling system  10  and ensures that water inflow only occurs during operation of the system. Various shut off controls may be incorporated to ensure cessation of water flow in the event of malfunction of one or another component. The flow rate of the water is controlled by constant flow control valves  34 , These valves ensure that a predetermined flow rate to water distribution unit  14  is constant irrespective of pressure fluctuations that normally occur with respect to any municipal water system as a function of time of day and changing demands. A temperature sensor  36  to sense the temperature of the water flowing to media  12  via water distribution unit  14  is embodied. 
         [0047]    If the water distribution is not uniform across the media and from side to side and in a profile from inlet to exit that matches the water evaporation rate, or if the water application rate is insufficient, there will be dry spots on the media. At each such dry spot, any dissolved solids in the water will collect and build up. Subsequent wetting will not re-dissolve the solids and the efficiency of the media will be compromised. It is well known that evaporation is a function of a number of variables which must be sensed and corrective action taken to ensure that no dry spots on the media exist or come into being. To achieve this end, numerous sensors are employed. Sensor  40  senses the temperature of the air flowing into media  12  and sensor  42  senses the temperature of the air flowing from the media. Sensor  44  senses the relative humidity of the air flowing into the media and sensor  46  senses the relative humidity of the air flowing from the media. Sensor  60  senses the fan speed which is directly related to and used by microprocessor  70  to determine the air flow rate. 
         [0048]    The rate of air flow through media  12  may be varied in response to varying climatological conditions to ensure highest efficiency of evaporative cooling system  10  and the greatest temperature differential between the air flowing into and out of the media. To permit varying the rate of air flow generated by fan  20 , a sensor  60  is used to sense the speed of the fan and a relay  62  may be used to control the operation of the fan. 
         [0049]    The above described sensors are interconnected with microprocessor  70  that receives electrical signals from the sensors. Upon processing the data represented by each of these electrical signals, control signals are generated to control not only the water flow to water distribution unit  14 , but also the rate of flow. Similarly, the speed of fan  20  may be controlled to provide an air flow rate through media  12  that will optimize operation of the evaporative cooler. 
         [0050]      FIG. 2  shows a cross section of the spray bars and the water distribution elements arranged in a configuration that produces a water application profile consistent with the water evaporation profile at design conditions, as shown in  FIG. 3 . A key factor in determining the configuration is the wicking rate of media  12  or the time it takes for the media to wick the water one inch from the time it is applied to the media. To develop the desired profile, given these conditions, flow control valves  34  (see  FIG. 1 ) feeding two spray bars  80 ,  82  are selected such that the flow rate to front spray bar  80  is about twice the flow rate of back spray bar  82 . Orifices  84 ,  86  in front spray bar  80  are evenly spaced (every 1.2 inches) in two rows along the spray bar with the holes in the two rows offset in a triangular pattern to avoid interference between water jets  88 ,  89 . Front spray bar orifaces  84 ,  86  are sized at 0.050 inches to achieve a height of water jet  88 , given the volumetric flow rate through the orifice (approximately 0.027 gpm), adequate to reach distribution cap  90  and spray bar distribution channel  92 . By having an equal number of equally sized orifices in the two rows on the front spray bar, half of this water is applied to the very front of media  12  and half is directed to the spray bar distribution channel where this water is divided equally by the distribution channel and applied to the media. The radius of distribution channel  92  is set and the center of the distribution channel is set to apply this water to the top of the media one inch and three inches, respectively, from the front side of the media. 
         [0051]    Orifices  100  in the front row of back spray bar  82  are spaced evenly at the same distance as the front row of orifice  86  (every 1.2 inches). The number of orifices  102  in the rear row of back spray bar  82  is reduced to half of orifices  100  in the front row (every 2.4 inches). Orifices  100 ,  102  in the two rows are offset in a triangle pattern to avoid interference between water jets  104 ,  106 . The orifices  100 ,  102  in the second spray bar  82  are sized at 0.040 inches to achieve a water jet ( 104 ,  110 , respectively) height, given the volumetric flow rate through the orifice (approximately 0.016 gpm), and oriented to reach the back of the distribution cap  90  and the center of the rear spray bar distribution channel  112 . This configuration of the back spray bar distributes the water such that two thirds of the water is directed to the back spray bar distribution channel and the remaining one third is directed to the back of the distribution cap. Both distribution channels are the same with back spray bar distribution channel  112  being positioned to apply one third of the water into the media five inches from the front of the media and one third into the media seven inches from the front of the media. The back row of orifices  102  apply one third of the water from this spray bar to the back of the media. The resulting water application profile is displayed in  FIG. 3 . This shows the relative distribution of the water from the front of the media to the back of the media. 
         [0052]    In summary,  FIG. 1  illustrates a flow diagram of the preferred embodiment of a once through cooling system incorporating specific features to implement this invention. In this flow diagram, water from the water supply  30  flows through a solenoid valve  32  that opens and closes to meter water onto the media  12  as required to resupply the water evaporated to cool the air with just enough excess to achieve the desired cycles of concentration in the discharge water. Individual flow control valves  34  control the rate of water that flows through the lines to the front and back spray bars when the solenoid valve is open. Microprocessor  70  senses inlet air  22 , temperature  40 , humidity  44  and air flow  60  and uses local values directly input to the microprocessor for altitude and cycles of concentration to compute the air&#39;s wet bulb temperature and heat load profile of installation media  12  and determines the length of time the solenoid valve needs to be open and closed to match the water evaporation rate and achieve the desired cycles of concentration for the water exiting into drain tray  16  and drain  14 . The remaining components and items in the flow diagram are the cooled air  24  exiting the media  12 , the cooler fan  20 , fan discharge air  26 , system differential pressure sensors  64  and  66 , media differential pressure sensors  50  and  52 , air outlet temperature sensor  42 , and air outlet humidity sensor  46 . 
         [0053]    The combination of controls to compute and apply water at a rate that matches the water evaporation rate and the water distribution elements to match the profile of the water evaporation rate as air passes through the evaporative cooler achieves an effective once through evaporation cooler configuration that is able to achieve cooling performance levels beyond those achievable by recirculating coolers, achieve high cycles of concentration limiting the water discharged, achieve long media life by avoiding scale buildup, and achieve long media life by lowering the rate at which regifying agents are washed out of the media.