Patent Application
20170108251
1. Field of the Invention
The present invention is directed to improvements in evaporative cooling systems, and particularly to direct evaporative cooling systems. Evaporative cooling systems can be considered conditioning systems that utilize thermodynamic laws to cool a fluid. In evaporative cooling systems, a change of a fluid from a liquid phase to a vapor phase can result in a reduction in temperature due to the heat of vaporization involved in the phase change.
2. Related Background Art
Evaporative coolers typically include a contact pad or media made of structured corrugated fill composed of cellulose, glass fiber, or other media. This fill is used to act as an extended surface for the contact of cooling fluid with the air that passes through the media. Examples of this product go by the trade names CELdek® and GLASdek®. In a typical evaporative cooler, raw water is supplied to or recirculated through a heat exchanger and is vaporized by extracting heat from supply air flowing through the heat exchanger. In particular, a cooling fluid such as water is applied to the top area of the heat exchanger and the liquid flows downward by gravity over the surfaces of the media. Air is passed through the media and a portion of the water evaporates from the surface of the media into the air stream.
In a recirculating evaporative cooling system, excess water supplied to the heat exchanger that has not evaporated is collected in a reservoir and then pumped back to the heat exchanger. As the water evaporates from heat exchange, minerals and salts dissolved in the raw water remain, building in concentration as the water volume decreases. Make-up water is supplied to the system to compensate for the evaporated water, but the salts and minerals remain and can become deposited on the heat exchanger as scalants if the concentration is too high.
In order to alleviate high concentrations of scalants, most evaporative cooling devices that use water incorporate a water bleed to drain to control salt and mineral content in the reservoir. The techniques to determine an effective amount of bleed are varied and well-known. In general, the amount of bleed is dependent on the level of mineral contamination in the feed water and water chemistry, but varies from as low as about 10% of the feed water for very fresh water to as much as 50% or more of the feed water where mineral content is high. Even where chemical treatment is utilized to extend solubility of the minerals, bleed is still required to replace water saturated with minerals with fresh water to prevent scaling within the evaporative process.
In direct evaporative cooling systems, the bled water is directed to drain and is otherwise not used. Such can result in substantial waste of cooling water. This waste can significantly increase the cost of operating the system and also place a significant burden on water supplies, particularly in areas where fresh water is scarce.
The present invention can improve the efficiency and effectiveness of evaporative cooling systems by utilizing energy available in the incoming water supply to create a recirculating loop to increase the water applied to the top of the media.
In one aspect of the present invention, an evaporative cooling system includes a heat exchange medium for receiving cooling fluid to cool supply air flowing past the heat exchange medium, a cooling fluid source for supplying fresh cooling fluid, a supply line communicating with the cooling fluid source for supplying the cooling fluid to the heat exchange medium, a return reservoir for collecting the cooling fluid supplied to the heat exchange medium, and a pump provided in the supply line for recirculating the cooling fluid collected in the reservoir into the supply line so as to provide recirculated cooling fluid along with fresh cooling fluid to the heat exchange medium.
In another aspect of the present invention, a gas conditioning system includes a conditioning unit configured to condition a gas flowing therethrough, the conditioning unit utilizing a conditioning fluid to condition the flowing gas, a conditioning fluid source for supplying fresh conditioning fluid, a supply line communicating with the conditioning fluid source for supplying the conditioning fluid to the conditioning unit, a return reservoir for collecting the conditioning fluid supplied to the conditioning unit, and a pump provided in the supply line for recirculating the conditioning fluid collected in the return reservoir into the supply line so as to provide recirculated conditioning fluid along with fresh conditioning fluid to the conditioning unit.
In yet another aspect of the present invention, a method of cooling supply air in an evaporative cooling system includes supplying fresh cooling fluid from a cooling fluid source to a heat exchange medium through a supply line, collecting at least a portion of the fresh cooling fluid supplied to and having passed through the heat exchange medium in a return reservoir, recirculating the collected cooling fluid to the supply line to be supplied along with the fresh cooling fluid, and flowing the supply air through the primary heat exchange medium and the secondary heat exchange medium.
These and other aspects and advantages will become apparent when the description below is read in conjunction with the accompanying drawings.
Several factors can influence the selection of the cooling fluid flow rate applied to the top surface of the evaporative pad in an evaporative cooling system. Preferably, sufficient cooling fluid is applied to the media so that at no location within the media does all of the cooling fluid evaporate before it can reach the bottom of the media. As the cooling fluid evaporates, the mineral content is concentrated in the remaining cooling fluid. Sufficient excess flow must be applied to ensure that the mineral content in no region becomes high enough that scale is deposited or precipitates out on the surface of the media. Scale deposits can eventually foul the surface and prevent sufficient or even air flow through the media.
Guidelines have been published to help designers choose a cooling fluid flow that will provide reliable performance. Examples include Munters Bulletin EB-IDI-0405, Munters Bulletin EB-WTM-0408, and Munters Bulletin EB-IDI-0712, which provide extensive design considerations for the application of direct evaporative media including water flow rates and which are incorporated herein by reference. As a general rule, water flow is typically specified in flow rate per unit area of media top surface. From Table 1 in the latter-mentioned Munters Bulletin, a low threshold value can be 0.75 gpm per foot of length of 14 inch deep media. This equates to a flow of 0.64 gpm/ft2 (25.8 1 pm/m2) at media top area.
To achieve the proper flow rate, as discussed above with respect to
The amount of bleed required to control the recirculated water quality is based on many factors involving the incoming water quality and its ability to be “cycled up” or concentrated without mineral precipitation. A good explanation of how the water quality affects the scaling indexes and the determination of an appropriate Cycles of Concentration (CoC) can be found in Munters Bulletin EB-WTGT-0406, which is also incorporated herein by reference. Cycles of concentration is a measure that compares the level of solids of the recirculating water to the level of solids of the original raw make-up water. For example, if the circulating water has four times the solids concentration than that of the make-up water, then the cycles of concentration is 4.
A lower cost system, termed “direct water,” does away with the pump and applies water directly from the water source to the top of the pad. These systems attempt to use as little water as possible by setting the flow rate to the lowest possible flow that will achieve even and complete media coverage. However, this generally requires that substantial excess water be applied as compared to the evaporation rate, resulting in a significant waste of water.
The present invention is directed to a direct water system which uses energy available in an incoming cooling fluid supply to create a recirculating loop to increase the cooling fluid applied to the top of the media. This is accomplished through the use of an eductor, or venturi pump, to entrain water from the sump of the system into the direct water stream to increase the flow to the top of the media.
Evaporative pad 218 can be CELdek® or GLASdek® media available from Munters Corp., and the size of the media can be selected based on the needs of the particular system. Examples of cooling effectiveness and pressure drop per selected thicknesses over various parameters are shown in the graphs of
In the example of
Given a 50 psi water supply, an eductor can be designed to more than triple the volume of flow to the top of the evaporative media. The operation of an example of an eductor is described in Penberthy Jet Pump Technical Data Bulletin 1200 issued in May 1987, which is incorporated herein by reference. The chart on page 6 demonstrates that given a lift requirement of 10′ of discharge head and utilizing a 50 psi water source, an entrained rate or suction capacity (Qs) of nearly double the motive rate (Qm) of inlet water can be achieved, in this case 33 gpm entrained with 17 gpm motive for a nominal sized eductor. (Note that smaller flows are possible with a smaller sized eductor.) With this multiple, a make-up water flow approaching the excess flow required for evaporation and bleed may be approached, especially during hot times and in cases where required Cycles of Concentration are low.
The system may also be installed with an overflow line 234 to drain 236 to allow an overflow or bleed stream. This overflow or bleed stream can measured by a flow sensor 238 in overflow line 234 and the measured flow can then be compared to an inflow of source water from source 228, either measured directly through another sensor (not shown), or indirectly through a timer and assumed flow rate. The inflow and overflow values can then be used to calculate a Cycles of Concentration. The incoming flow can then be pulsed to reduce the primary flow as a means to decrease the ratio of bled water to incoming water as a means to achieve a target Cycles of Concentration. In the present embodiment, in order to control the fresh cooling fluid flow, a supply valve 240 is provided in supply line 212 upstream of eductor 230. Supply valve 240 can be variable or simply on/off and be controllable by a controller 242. Controller 242 can be any suitable systems microcontroller. The supply valve can be adjusted according to system conditions. A signal from flow sensor 238 to controller 242 can be analyzed so that controller 242 controls supply valve 240 to increase, decrease, or pulse the cooling fluid as the amount of overflow changes.
An example of a simple evaporative system operating with 10,000 m3/hr of airflow at an incoming condition of 35° C. and 0.010 g/kg follows. In this example, the evaporative media is Munters GLASdek® having a depth of 200 mm. The evaporative efficiency of the media is given by the manufacture as 85%. Thus, air leaving conditions will be approximately 23.2° C. and 0.01493 g/kg.
In the example above, the system is evaporating 59.2 kg/hr of water (10,000 m3/hr×1.2 kg/m3×(0.01493−0.010) kg water/kg air) or 1.0 1 pm (59.2 kg/hr×1 1/kg×1 hr/60 min). Let us assume that this system is running in a location where the water has a mildly high hardness and a maximum Cycles of Concentration of 3 should be used. In this example an additional ⅓ or 33% bleed should be designed into the system in order to control the mineral content in the recirculated water. Thus, the system will need a total make-up flow of 1.33 1 pm.
In the above example, the media is being operated at a typical face velocity of 2.5 m/s and has dimensions of 1.1 m in height and 0.75 m in width. The top area of the media is 0.15 2. Using the minimum best practices from the Munters Bulletin of 25.8 1 pm/m2, the minimum amount of water to be applied to the top of the media to insure good water distribution and prevent mineral deposits is 3.9 1 pm (0.15 m2×25.8 1 pm/m2).
The 1.33 1 pm make-up water at 50 psi acts as motive flow to drive additional recirculated flow through the supply line 212 using eductor 230. The Penberthy document teaches a roughly 2:1 ratio of entrained fluid to motive fluid if acting against a total lift of 10′. Thus, in this example, a total of 1.33+1.33×2 =3.99 1 pm will be delivered to the top surface of the evaporative media. This flow meets the minimum flow requirements of 3.9 1 pm calculated above.
The evaporation rate will change based on the air entering conditions. When the evaporation rate is less, if the incoming motive flow is left the same there will be excess flow that will go to drain. The mineral content in the sump will decrease to a lower level, the CoC will be reduced, and water will be wasted. In these cases the incoming flow can be reduced to prevent the excess bleed. If the flow were reduced by reducing its pressure, the ratio of supply water to motive water would be reduced. This has the negative effect of reducing the top water flow to below the desired minimum flow for good distribution and scale prevention. In order to reduce the bleed flow, the motive flow is intermittently interrupted, or pulsed, to reduce the excess bleed flow. In this manner, when the water is flowing, it will flow at full rate and thus the distribution system will operate as designed. As water flows rather slowly down the surface of the wetted media, for example, on the order of 1 m per minute, short periods of no flow will not be apparent on the media. Water flow can be shut off for periods up to 1 minute with little noticeable effect.
It should be noted that in a preferred embodiment, an eductor is used to provide the motive force for the recirculation. However, the energy in the incoming water could also be used to power a mechanical pump, such as a diaphragm pump, a piston pump, or a rotary vane pump. These solutions may be less efficient as they will have mechanical losses.
Thus, there have been shown and described new and useful evaporative cooling systems. Although this invention has been exemplified for purposes of illustration and description by reference to certain specific embodiments, it will be apparent to those skilled in the art that various modifications, alterations, and equivalents of the illustrated examples are possible.
This application claims the benefit of U.S. Provisional Patent Application No. 62/242,569, filed Oct. 16, 2015.
| Number | Date | Country | |
|---|---|---|---|
| 62242569 | Oct 2015 | US |
