Claims
- 1. In an evaporative cooler including,
- a housing having an upright side,
- an opening in said upright side defined by upper, lower and lateral edges,
- an air pervious, liquid absorbing evaporation pad adjacent said opening and having opposed horizontal edges, opposed upright edges and spaced apart normal inlet and outlet sides surfaces, and
- blower means for drawing a stream of air at a normal velocity through said pad from said inlet side surface in a normal path having a direction generally perpendicular to the side surfaces of said pad,
- improvements therein for balancing the pressure drop of said air stream across said pad and for increasing the evaporative efficiency of said cooler, said improvements comprising:
- shroud means for diverting said air stream from said normal path thereof to a circuitous path to increase the length of travel of said air stream through said pad, said shroud means including
- (a) inlet control means for directing the entrance of said stream of air into said pad through a predetermined inlet portion of the inlet side thereof, said inlet control means having
- (i) an air impervious outer shroud for masking the entrance of said stream of air into said pad, and
- (ii) an air inlet formed in said outer shroud in registry with the inlet portion of said pad; and
- (b) outlet control means for directing the exit of said stream of air from said pad through a predetermined outlet portion thereof, said outlet control means having
- (i) an air impervious inner shroud masking the exit of said stream of air from said pad, and
- (ii) an air outlet formed in said inner shroud in registry with the outlet portion of said pad; said predetermined outlet portion being displaced laterally from said inlet portion with respect to the direction of said normal path of said stream of air.
- 2. The improvements of claim 1, wherein the inlet portion of said pad is generally elongate having spaced apart longitudinal edges and a longitudinal axis extending generally parallel to one of the edges of said pad.
- 3. The improvements of claim 2, wherein said one of the edges of said pad is one of the upright edges.
- 4. The improvements of claim 2, wherein said one of the edges of said pad is one of the horizontal edges.
- 5. The improvements of claim 2, wherein:
- (a) said inlet portion is spaced from one of the edges of said pad; and
- (b) said outlet portion
- i. is generally elongate having a longitudinal axis substantially parallel to the axis of said inlet portion, and
- ii. resides intermediate said inlet portion and said one of the edges of said pad.
- 6. The improvements of claim 5, wherein said inlet portion is the terminal portion of the inlet side of said pad adjacent the edge opposed to said one of the edges of said pad, one of the longitudinal edges of said inlet portion being coincident with said edge opposed to said one of the edges of said pad.
- 7. The improvements of claim 6, wherein said outlet portion is the terminal portion of the outlet side surface of said pad adjacent said one of the edges of said pad, one of the longitudinal edges of said outlet portion being coincident with said one of the edges of said pad.
- 8. The improvements of claim 5, further including:
- (a) a second outlet portion defined on the outlet side of said pad and residing intermediate said inlet portion and the edge opposed to said one of the edges of said pad; and
- (b) a second air outlet formed in said inner shroud in registry with said second inlet portion.
- 9. The improvements of claim 8, wherein said second outlet portion is generally elongate having spaced apart longitudinal edges and a longitudinal axis generally parallel to the first said outlet portion.
- 10. The improvements of claim 9, wherein:
- (a) said first outlet portion is the terminal portion of the outlet side surface of said pad adjacent said one of the edges of said pad, one of the longitudinal edges of said outlet portion being coincident with said one of the edges of said pad;
- (b) said second outlet portion is the terminal portion of the outlet side of said pad adjacent said one of the edges of said pad, one of the edges of said second outlet portion being coincident with said one of the edges of said pad; and
- (c) said inlet portion resides at the approximate mid point of the inlet sides surface of said pad.
- 11. The improvements of claim 1, wherein:
- (a) said inlet portion resides proximate the mid point of the inlet side surface of said pad; and
- (b) said outlet portion of said pad encircles said inlet portion.
- 12. The improvements of claim 11, wherein said inlet portion is defined by opposed horizontal edges and opposed upright edges, the edges of said inlet portion being parallel to and equally spaced from the respective edges of said pad.
- 13. The improvements of claim 11, wherein said outlet portion is defined by:
- (a) a substantially continuous outer edge coincident with the edges of said pad; and
- (b) a substantially continuous inner edge spaced from said outer edge.
- 14. The improvements of claim 11, wherein said outlet portion lies between the inlet and the outlet side surfaces of said pad.
- 15. The improvements of claim 2, wherein:
- (a) said inlet portion is spaced from one of the edges of said pad; and
- (b) said outlet portion
- i. is generally elongate having a longitudinal axis substantially parallel to the axis of said inlet portion, and
- ii. resides at one of the edges of said pad intermediate the inlet and the outlet side surfaces thereof.
- 16. The improvements of claim 15, further including:
- (a) a second generally elongate outlet portion having a longitudinal axis generally parallel to the axis of said inlet portion and residing at the edge opposed to said one of the edges of said pad intermediate the inlet and outlet surfaces thereof; and
- (b) a second air outlet formed in said inner shroud in registry with said second outlet portion.
- 17. The improvements of claim 16, wherein said inlet portion is substantially equidistant from the opposed horizontal edges of said pad.
- 18. The improvements of claim 16, wherein said inlet portion is substantially equidistant from the opposed upright edges of said pad.
CROSS REFERENCE TO RELATED APPLICATIONS
The instant application is a divisional of copending application Ser. No. 907,852, filed Sept. 15, 1986 and issued as U.S. Pat. No. 4,752,419, which in turn is a divisional of copending application Ser. No. 480,861, filed Mar. 31, 1983 and now abandoned, which in turn is a divisional of application Ser. No. 295,638, filed Aug. 24, 1981, and issued Apr. 12, 1983, as U.S. Pat. No. 4,379,712.
This invention relates to air conditioning devices.
In a further aspect, the present invention relates to evaporative coolers of the type having wettable, air permeable pads.
More particularly, the instant invention concerns means for increasing the efficiency and utility of evaporative coolers.
The evaporative cooler is a common means of providing cool air to a space, usually an enclosure such as a residence. Due to certain inherent desirable characteristics, such as the requirement for substantially less energy input than compressor operated refrigeration units, the evaporative cooler is exceedingly popular, especially in arid or semi-arid regions. Other desirable features include periodic air exchange within the space and the introduction of moisture into overly desiccated air. Evaporative coolers are also relatively inexpensive to purchase and comparatively simple and economical to install and maintain.
In general, evaporative coolers are available in two primary configurations. Based upon discharge direction of the cooled air, evaporative coolers are broadly classified as either down-draft delivery or side-draft delivery. Down-draft delivery coolers are usually mounted upon a building or other structure, discharging cooled air downwardly through an opening in the roof. Side-draft coolers, which are especially adapted for attachment to an upright surface, are also employed in open areas to direct air to a designated locale such as a work station. With suitable ducting, down-draft and side-draft coolers are interchangeably employable.
Commonly, conventional commercially available evaporative coolers include a generally box-like housing which serves as the main frame. Angular corners, extending between the top and the bottom, define upright open sides. A pad assembly, including a louvered frame holding a water wettable, air permeable pad, spans the opening in each side. The pads are fabricated of a saturatable material such as aspen fiber.
The bottom, having an upturned peripheral edge upon which the pad assemblies rest, functions as a reservoir for retaining the coolant liquid, usually water. A pump transfers the liquid from the reservoir to a distribution system for delivery to the pads. Traditionally, a trough extends along the upper portion of each louvered frame. Water, flowing from a delivery tube, passes through spaced openings in the bottom of the trough and gravitates downwardly through the pad.
Located within the housing is a blower which draws a stream of air through each of the several pads and discharges the air through a common duct communicating with the space to be cooled. The typical blower includes a centrifugal impeller rotatably mounted within a housing having an air inlet aligned with either end of the impeller. An electric motor, usually mounted upon the housing, rotates the impeller by means of a belt drive. The blower and the pump are energized simultaneously in response to the closing of a remote switch. The switch may be activated manually or in response to an environmentally sensitive control.
Theoretically, the pads are of uniform density and saturated with water. As the air moves through the pads, water is evaporated to absorb a portion of the heat within the air. Moisture content of the air is also raised. A float, sensing the water level within the reservoir, controls an inlet valve to compensate for losses due to evaporation.
In addition to designation by design configuration based upon direction of air delivery, evaporative coolers are referenced by a size related to the air flow capacity. The capacity is given in cubic feet per minute (cfm). The designated, or rated cfm, however, is the nominal value and may vary significantly from the certified capacity.
For a more comprehensive understanding of prior art evaporative coolers, example is made of a statistic test model. The model incorporates a specific unit currently being produced by a major manufacturer. The exemplary unit is mounted upon the roof of a typical private residence in accordance with techniques considered to be standard within the art. The geographical setting is Phoenix, Arizona.
The characteristics described below, in connection with the unit, are taken from literature supplied by the manufacturer. Other input parameters are gathered from various public sources and from empirical observation. Output, or performance data, is the result of a computer model based upon the foregoing. The data, set forth as exemplary of the current state of the art, is herein presented for immediate purposes of orientation and subsequent purposes of providing a standard of comparison in connection with the ensuring description of the improvements contemplated by the present invention.
The specific evaporative cooler unit selected for discussion is a down-delivery type having a designated or nominal capacity of 6500 cfm. Literature supplied by the manufacturer sets forth the certified air flow at 4900 cfm. Being generally cubical, the housing carries a pad in each of the four upright sides. Water level within the reservoir is maintained by a float actuated valve. Supplied with water from perforate overhead troughs at a rate to maintain wetness, the pads are exposed on one side to the environment.
Air is moved by an impeller driven by a 0.75 horsepower electric motor. Being of conventional configuration, the impeller receives air through a circular opening, or eye, at either end. Air is discharged centrifugally into an encircling housing having an outlet. The eyes of the impeller embrace an area of 427 square inches, through which the air passes at a velocity of 1652 feet per minute. The velocity of air measured in the approximate 400 square inch outlet duct is 1764 feet per minute.
The inlet area, the total measurement of openings in the four sides normally spanned by the water absorbing, air permeable pads, is 4244 square inches. Assuming a uniform air flow, velocity through the 1.5 inch average thickness pads is 166 feet per minute. Calculated transit time, residence duration of air within the pads, is 0.045 seconds.
Standards for space cooling systems are established by the American Society of Heating Refrigerating and Air-Conditioning Engineers (ASHRAE). Based upon the ASHRAE 1% criteria, a system for Phoenix, Arizona includes a design dry bulb rating of 109.degree. F. and a mean coincident wet bulb rating of 71.degree. F. Also assumed is standard barometric pressure of 28.86 inches of mercury. An evaporative cooler, the type chosen for discussion having a 4900 cfm fan capacity, is commonly used in connection with a typical residential heat load of 3 tons. The specific air flow, given by the formula fan capacity in cfm/heat load in tons, equals 4900/3 or 1633 cfm/ton.
An evaporative cooler is a relative cooling device. That is, an evaporative cooler cannot receive ambient air of any existing condition and cool the air to any selected temperature. An evaporative cooler can produce a maximum temperature drop limited by the ambient air wet bulb temperature. The foregoing described test unit, operating under conditions as set forth above, has a rated temperature drop of 30.4.degree. F. for an output temperature of 78.6.degree. F., according to the manufacturer's published data.
The conventional definition of evaporative efficiency is given by the formula: ##EQU1## where: Tdb=ambient air dry bulb temperature
Evaporative coolers are not generally used in connection with recirculating air systems. The cooled air from the unit is usually vented to atmosphere at a location opposite the inlet location of the space to be cooled. As a result of absorbing the heat within the space, the temperature of the air is increased. Assuming a typical residential heat load of 3 tons in Phoenix, Arizona, with the above design criteria, the room exit temperature of the air will be 86.1.degree. F., reflecting a rise of 7.5.degree. F. The wet bulb temperature within the space will be 73.1.degree. F.
Utilizing the foregoing data, the theoretical limits for an evaporative cooler operating at 100% efficiency can be calculated. Such a cooler, unknown at this time, would decrease the temperature of the ambient air 38.0.degree. F. to provide a discharge of 71.0.degree. F. Passing through the space to be cooled, the air would rise 7.3.degree. F. to an exit temperature of 78.3.degree. F. The wet bulb reading taken within the cooled space would be 73.0.degree. F.
Various factors are responsible for the discrepancy between the ideal limits of 100% evaporative efficiency and the industry standard of 80% evaporative efficiency. Certain differences are due, at least in part, to the inherent characteristics of conventional prior art coolers. Significant among these are pad thickness, air velocity through the pads, and transit time of the air through the evaporative media. The standard 80% evaporative efficiency assumes optimum operating conditions for the test unit evaporative cooler. Other factors impair the function and serve to decrease performance to a level substantially below optimum. Exemplary are various factors such as air and water-borne chemicals and particulates and direct and reflected radiation which deteriorate the pads, materially reducing the absorption ability and disturbing the air flow characteristics.
Conventional means of wetting the pads further contributes to the inefficiency of the typical cooler. Sections of the pad, intermediate the openings in the trough, are not provided with adequate water. Originating from finite sources, the water tends to define a plurality of rivulets, the paths of which decrease in width as the pad ages and deteriorates. Further, observation has shown that continuous wetting is not optimum.
In addition to the foregoing, evaporative coolers mounted in close proximity to certain other structures, such as a unit resting upon the roof of a residence, are additionally burdened. Temperatures immediately above the roof are substantially elevated above ambient. Empirical observation indicates that the air received by a roof mounted unit is approximately 6.degree. to 7.degree. F. warmer than the air received by a remotely located unit. Since the unit is responsible for a given change in humidity ratio, the elevated inlet temperature is reflected in the outlet temperature. The elevated inlet temperature coupled with the previously noted decreased efficiency, results in a normal operating temperature substantially above the 78.6.degree. F. calculated for operation under optimum conditions.
Air temperature and humidity affect human comfort. An accepted guide for evaluating comfort factors is the temperature humidity index which is given by the formula:
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.
Accordingly, it is an object of the present invention to provide improvements in the art of evaporative space cooling systems.
Another object of the invention is the provision of means for increasing the evaporative efficiency of conventional type evaporative coolers.
And another object of this invention is to provide an evaporative cooler which will yield a greater temperature drop.
Still another object of this invention is the provision of means for decreasing the temperature humidity index number in connection with evaporative coolers.
Yet another object of the instant invention is to provide means for maintaining the continued performance of an evaporative cooler at a level nearer optimum than possible with prior art devices.
Yet still another object of the invention is the provision of a cooler having improved air flow characteristics.
And a further object of the immediate invention is to provide means to preserve the integrity of the pad and prevent undue deterioration thereof.
Still a further object of the invention is the provision of means to decrease the temperature of the inlet air to an evaporative cooler in certain unusual and common situations.
Yet a further object of the invention is to provide improvements of the above type which may be practiced in connection with commercially available prior art evaporative coolers.
And still another object of this invention is the provision of an evaporative cooler which is selectively spatially orientatable.
Yet still another object of the subject invention is to provide improved means for wetting the pads of an evaporative cooler.
Briefly, to achieve the desired objects of the instant invention, first provided are means for increasing the length of travel of the air stream through the pad. In accordance with a preferred embodiment of the invention, the length of travel of the air stream is increased by shroud means which divert the air stream from the normal path thereof to a circuitous path through the pad. In a more specific embodiment of the invention, the shroud means includes inlet control means for directing the entrance of the air stream into the pad through a predetermined inlet portion of the pad and outlet control means for directing the exit of the air stream from the pad through a predetermined outlet portion. The inlet control means includes an air impervious outer shroud for masking the entrance of the air stream into the pad and an air inlet formed therein in registry with the inlet portion of the pad. The air outlet control means includes an air impervious inner shroud masking the exit of the air from the pad and an air outlet formed in the inner shroud in registry with the outlet portion of the pad. Preferrably, the outlet portion of the pad is laterally displaced from the inlet portion of the pad whereby at least a portion of the circuitous path is in a direction generally perpendicular to the normal direction of the stream of air through the pad. Cooperating therewith are means, such as a higher speed or larger blower means, for moving the air stream in the circuitous path at a greater velocity then the velocity of the air stream in the prior art normal path. In addition, it is suggested that the width of the path be increased.
The foregoing improvements are responsible, when practiced in connection with the previously described prior art test model, for an increase in inlet air velocity from the standard 166 feet per minute to approximately 1208 feet per minute. The circuitous path extends the length of the air flow through the pad from the current 1.5 inches to approximately 13.6 inches. It is seen, therefore, that the air inlet velocity increases by a factor of 7.3 to 1 while the air flow length is increased by a factor of 9.1 to 1. Specific air flow remains relatively constant at 1633 cfm/ton. Air transit time within the pad is increased by 24% from the standard 0.045 seconds to 0.056 seconds.
Wet bulb depression error, a well known measure of evaporative efficiency, decreases as velocity increases. A graph illustrating the effects of air velocity on wet bulb depression error well known to those skilled in the art is the modified Arnold theory devised in 1936. According to the graph, the wet bulb depression error for air at the standard velocity of 166 feet per minute is approximately 8.0%. The wet bulb depression error for an air velocity of 1208 feet per minute, as suggested by the instant invention, is 0.85.
The formula for wet bulb depresion, Tdb-Twb, is a significant portion of the formula for evaporative efficiency. Wet bulb depression is approximately equal to the theoretical maximum change in air temperature by the evaporation of water. Therefore, utilizing the above data, the performance of the test unit evaporative cooler, improved in accordance with the teachings of the instant invention, can be calculated. Under the same ASHRAE design criteria as utilized in connection with the test model, the improved evaporative cooler of the instant invention yields a temperature drop of 35.3.degree. F. resulting in a discharge temperature of 73.7.degree. F. Passing through the space to be cooled, the temperature will rise 7.3.degree. F. to 81.0.degree. F. and 73.0.degree. F. wet bulb. Accordingly, the evaporative efficiency is increased to 93%. It is also noted that the temperature humidity index guide member is lowered to a substantially more comfortable 76.6.
Next provided by the instant invention are means for intermittent wetting of the pad. More specifically, the improvement includes timer means for alternating the distribution system between a delivery cycle during which liquid is delivered to the pad and an arrest cycle during which delivery of the liquid to the pad is suspended. The timer means may comprise a timer in series with the conventional pump. The delivery cycle precedes the arrest cycle and is initiated upon activation of the cooler by the conventional thermostat or other switch means. It has been determined, from actual measurements taken in connection with the test model, that the outlet temperature will drop 1.degree. F. to 2.degree. F. within one to two minutes after the flow of water to the pads has been discontinued. The temperature will remain below the normal outlet temperature for approximately 8.5 minutes. Therefore, it is suggested, in accordance with a preferred embodiment of the invention, that the delivery cycle be of approximately 1.5 minute duration and the arrest cycle be of approximately 8.5 minute duration. No technical explanation is known for the foregoing phenomenon other than empirical observation.
Further provided by the instant invention is an upstream shield for screening the pad from radiant energy and airborne contaminants. In accordance with a preferred embodiment of the instant invention, the shield includes a generally upright panel spaced from the pad to intercept the normal path of the air stream, thereby deflecting the stream to a circuitous path to reach the inlet side of the pad. In a more specific embodiment, the shield further includes a lower panel extending between the lower horizontal edge of the upright panel and the evaporative cooler housing and a pair of lateral panels extending between each upright edge of the upright panel and the evaporative cooler. Accordingly, the air is caused to enter at a height approximately equal with the top of the housing of the evaporative cooler. The foregoing improvement is also applicable for use with other types of air conditioning devices to protect the heat exchanger.
The immediate improvement is largely responsible for maintaining optimum operation of the evaporative cooler. Further, receiving air through an elevated opening, more nearly ensures the ingestation of air approximating ambient conditions. In a roof-top installation, as previously referenced, the inlet air will be approximately 6.degree. F. to 7.degree. F. lower than the prior art test model. In addition to preserving the integrity of the pads, the shield minimizes dust and other particulates entering the space to be cooled as is common with prior art devices especially during dust storms as frequently occur in arid and semi-arid regions.
Improved means for evenly distributing the water to the pad is also contemplated by the instant invention. Included is an elongate manifold which receives pressurized coolant liquid from the pump or other supply. Spaced along the upper portion of the manifold are a plurality of orifices for dispensing the water in a plurality of pressurized jets. The jets are directed against a diffuser which dissipates the jets and disseminates the water to the upper edge of the pad. The diffuser, which includes an elongate deflection surface, may be incorporated along the upper inner edge of a conventional pad frame. In accordance with one embodiment of the invention, the manifold is in the form of an elongate tubular element supported by a splash shield depending from either end of the diffuser. Each end of the tubular element is closed and the pressurized water is introduced through a conventional T-arrangement at an intermediate location.
Further provided by the instant invention is an improved evaporative cooler housing usable in connection with the foregoing improvements or conventional prior art components. The improved housing is especially orientatable for discharging cooled air in a preselected vertical or horizontally directed stream. The housing includes a first reservoir for holding water when the side of the housing, including the outlet opening is positioned vertically, and a second reservoir for holding water when the side of the housing is positioned horizontally.
US Referenced Citations (8)
Divisions (3)
|
Number |
Date |
Country |
| Parent |
907852 |
Sep 1986 |
|
| Parent |
480861 |
Mar 1983 |
|
| Parent |
295638 |
Aug 1981 |
|
Patent Grant
4851162
