Two Stage Cooler

Abstract

A two stage evaporative cooling device has a central chamber, divided into an upper chamber and a lower chamber by a divider. one or more heat exchange units surrounding the central chamber; an upper fan arranged above the upper chamber and a lower fan arranged below the lower chamber; and a water circuit; wherein each heat exchange unit comprises an evaporative cooling element and an air to water pre-cooler, the pre-cooler being placed ahead of a lower portion of the cooling element and the water circuit is arranged to irrigate the cooling element and collect the irrigated water below the cooling element for delivery to the pre-cooler whereby pre-cooled air may be drawn inwardly through the pre-cooler and the lower part of the cooling element by the lower fan and ambient air may be drawn inwardly through the upper part of the cooling element by the upper fan.

Claims

1. An evaporative cooling device comprising: a central chamber, the central chamber defining an upper chamber and a lower chamber separated by a divider; one or more heat exchange units surrounding the central chamber; an upper fan arranged above the upper chamber and a lower fan arranged below the lower chamber; and a water circuit; wherein each heat exchange unit comprises an evaporative cooling element and an air to water pre-cooler, the pre-cooler being placed ahead of only a lower portion of the cooling element and the water circuit is arranged to irrigate the cooling element and collect the irrigated water below the cooling element for delivery to the pre-cooler whereby pre-cooled air may be drawn inwardly through the pre-cooler and the lower part of the cooling element by the lower fan and ambient air may be drawn inwardly through the upper part of the cooling element by the upper fan.

2. The device according to claim 1, wherein the water circuit comprises a sump for collection of the irrigated water, the sump comprising an annular channel surrounding the lower fan.

3. The device according to claim 1, wherein four heat exchange units are arranged in a square around the central chamber.

4. The device according to claim 1, wherein the a single heat exchange unit surrounds the central chamber.

5. The device according to any of claim 1, comprising a housing, defining a lower outlet from the lower chamber and an upper outlet from the upper chamber and having an outer periphery provided with inlet openings.

6. The device of claim 5, comprising removable screens located across the inlet openings.

7. The device according to claim 1, wherein the one or more evaporative cooling elements each comprise a stack of finned plates of aluminium material.

8. The device of claim 7, wherein the plates are arranged to extend vertically and inwardly and are spaced from each other laterally.

9. The device of claim 8, wherein the fins are formed by slits through the plate extending vertically and the fins are displaced laterally from the plate.

10. The device according to claim 1, wherein the one or more evaporative cooling elements are provided with a water retaining coating.

11. The device of claim 10, wherein the water retaining coating comprises an open fibrous structure.

12. The device according to claim 1, wherein the divider is movable whereby the relative sizes of the upper chamber and lower chamber can be varied.

13. The device according to claim 1, wherein the water circuit comprises a pump, arranged to cause circulation of water through the pre-cooler for delivery to the evaporative cooling element.

14. A method of operating an evaporative cooling device to deliver a supply of cooled air to a habitable space, the method comprising: trickling water over an evaporative cooling element; passing a first volume of air only through a first portion of the evaporative cooling element to cool the water and exhausting the first volume of air to ambient in a first axial direction; delivering the cooling water to an air to water pre-cooler; passing a second volume of air through the pre-cooler and through a second portion of the evaporative cooling element and exhausting the second volume of air to the habitable space in a second axial direction opposite to the first axial direction.

15. The method of claim 14, wherein the evaporative cooling device comprises: a central chamber, the central chamber defining an upper chamber and a lower chamber separated by a divider; one or more heat exchange units surrounding the central chamber; an upper fan arranged above the upper chamber and a lower fan arranged below the lower chamber; and a water circuit; wherein each heat exchange unit comprises an evaporative cooling element and an air to water pre-cooler, the pre-cooler being placed ahead of only a lower portion of the cooling element and the water circuit is arranged to irrigate the cooling element and collect the irrigated water below the cooling element for delivery to the pre-cooler whereby pre-cooled air may be drawn inwardly through the pre-cooler and the lower part of the cooling element by the lower fan and ambient air may be drawn inwardly through the upper part of the cooling element by the upper fan.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The features and advantages of the invention will be appreciated upon reference to the following drawings of a number of exemplary embodiments, in which:

[0021] FIG. 1 shows a prior art configuration of a direct evaporative cooler;

[0022] FIG. 2 shows the enthalpy diagram for the cooler of FIG. 1;

[0023] FIG. 3 shows the use of a pre-cooler in combination with the cooler of FIG. 1;

[0024] FIG. 4 shows the enthalpy diagram for the two-stage cooler of FIG. 3

[0025] FIG. 5 shows a perspective view of an evaporative cooling device according to the invention; and

[0026] FIGS. 6 to 9 show cross-sections through the device of FIG. 5 in various modes of operation.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0027] FIG. 1 shows a schematic view of operation of a conventional direct evaporative cooler such as the above mentioned Oxyvap pad described in WO2013095105. Hot dry air 1 is passed through the pad 8 to which water is supplied by water circuit 7 including pump 3 and sump 5. The air is humidified by the water as it passes through the pad 8 and exits as colder and more humid air 2 at the wet-bulb temperature (or close thereto). In FIG. 2, it may be seen that air having an initial dry-bulb temperature of 38 C. and 21% humidity can be cooled to around the wet bulb temperature of 21 C. In actual practice, 90% efficiency may be achieved and the outlet temperature may be around 1.7 C. higher than the wet-bulb temperature. Due to the cooling effect, the water exiting the pad 8 and collected in the sump 5 is also at the wet bulb temperature.

[0028] FIG. 3 shows an arrangement in which a pre-cooler 10 has been placed ahead of a lower portion of the Oxyvap pad 8 of FIG. 1. The cooled water collected in the sump 5 is pumped through the pre-cooler 10 before being delivered at 6 to the upper side of the Oxyvap pad 8. A first volume of air 1A passes through the upper portion of the pad 8 without passing through the pre-cooler 10. This first volume of air 1A serves to reduce the temperature of the cooling water descending through the Oxyvap pad 8 and may be discarded to ambient at 2A. A second volume of air 1B is drawn in through the pre-cooler 10 and is cooled without change to its absolute humidity. This air 1B, after passing through the pre-cooler 10, has a lower wet bulb temperature. It is then passed through the lower portion of the Oxyvap pad 8 where it is cooled by humidification and can then be delivered to a user or habitable space at the new, lower wet bulb temperature at 2B.

[0029] FIG. 4 shows the enthalpy diagram for the second volume of air 1B-2B in the configuration of FIG. 3. It shows the cooling of the air at constant absolute humidity from an initial temperature of 38 C. to a dry bulb temperature of around 22 C. As this volume passes through the Oxyvap pad 8, it increases in humidity towards the saturation line and decreases in temperature to around 19 C. The wet bulb efficiency is 112%.

[0030] FIG. 5 shows a perspective view of an evaporative cooling device 100 according to the invention. It comprises a generally square housing 20 having an upper outlet 22 and an outer periphery provided with inlet openings 24 on its four sides. Removable screens 26 are located across the inlet openings. The housing 20 and screens 26 are formed of marine grade powder coated aluminium. The housing 20 is supported on a conical column 28 that provides a lower outlet 30 distributing radially outwards beneath the device 100.

[0031] FIG. 6 shows a cross-section through the device 100 of FIG. 5 in the standby state. Behind each of the screens 26 is located a heat exchange unit 32 comprising an evaporative cooling element 8 and a pre cooler 10. These may be as shown in FIG. 3. In this case, the heat exchange units 32 are arranged around a central chamber 34, which is separated by a divider 36 into an upper chamber 38 and a lower chamber 40. The divider 36 is movable and controlled by an actuator (not shown) to move upward and downwards within the central chamber 34. Also visible are a lower fan 42 and an upper fan 44 in communication with the lower outlet 30 and upper outlet 22 respectively. Elements of the water circuit 7 are visible above the evaporative cooling elements 8 and the sump 5 is provided as an annular trough beneath the evaporative cooling elements 8. Other items are not shown in this view, including a controller to control operation of the device and a pump 3 for the water circuit 7. The conical column 28 is also shown in cross-section.

[0032] In the configuration shown in FIG. 6, the device 100 is in standby mode with both of the fans 42, 44 switched off. The divider 36 may also be moved downwards to close off the lower outlet 30 should this be required, e.g. to prevent air leakage from a habitable space as a winter seal.

[0033] FIG. 7 shows the device 100 in ventilation mode with the lower fan 42 operating to draw air in through the heat exchange units 32 and direct it downwards through the lower outlet 30. The water circuit is not operational.

[0034] FIG. 8 shows the device 100 operating as a direct evaporative cooler. In this state, water is supplied by the water circuit directly to the evaporative cooling element 8, which causes humidification of the air that is directed downwards through the lower outlet 30 by the lower fan 42. The upper fan 44 is switched off. Although not shown, the divider 36 may be moved upwards to allow air to flow through the full area of the evaporative cooling element 8.

[0035] FIG. 9 shows the device operating as a two-stage cooler. In this state, both of the fans 42, 44 are operational and the water circuit and pump (not shown) operate to supply water through the pre-cooler 10. The device operates in the same manner as in FIG. 3, with a first volume of air 1A passing through the upper portion of the evaporative cooling element 8 and the upper chamber 38 to exhaust 2A at the upper outlet 22. A second volume of air 1B is cooled as it passes through the pre-cooler 10 and subsequently humidified and further cooled as it passes through the lower portion of the evaporative cooling element 8. It is exhaust 2B from the lower chamber 40 and lower outlet 30 by the lower fan 42.

[0036] The configuration shown is advantageous in that it can be easily installed in an open space to deliver cool humidified air to the open space. To this end, the column 28 should be of a height such that the device is supported above the level desired to remain cool. Ambient air 1 is drawn in above this level and the humid but slightly warmer waste air 2A is exhaust upwards out of the cooling zone.

[0037] Thus, the invention has been described by reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art. In particular, the shape of the device and the positioning of the heat exchange units may be distinct from the schematically illustrated design.

[0038] Many modifications in addition to those described above may be made to the structures and techniques described herein without departing from the spirit and scope of the invention. Accordingly, although specific embodiments have been described, these are examples only and are not limiting upon the scope of the invention.