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Evaporative cooler with dual water inflow

Evaporative cooler with dual water inflow description/claims

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.

1. Field of the Invention

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.

2. Description of Related Art

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.

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's and Charles' 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Various prior art evaporative cooler systems are described in the patents listed below.

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.

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.

• Provisional Patent
• Utility Patent

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