SYSTEM. COOLING DESCRIPTION OF THE INVENTION This invention relates to cooling systems, more particularly to those that include a closed circuit evaporative heat exchanger of the forced ventilation configuration. Closed loop evaporative heat exchangers are used in a variety of industrial schemes to provide cooling or condensation of refrigerants. Very broadly, cooling is provided by means of a cooling fluid which extracts the heat from the area to be cooled and transports it to a heat exchanger where the fluid is cooled again. In the case of a refrigerant condensing system, as part of a refrigeration process, the refrigerant vapor enters the heat exchanger where it is condensed and leaves the heat exchanger as a liquid. In both cases air is blown on the heat exchanger coils to remove heat from the liquid or steam. The cooling process is reinforced by spraying water on the coils so that a proportion of the water evaporates through the air stream. In such systems, most of the water sprayed on the heat exchanger coils in the air distribution enclosure does not evaporate but drains into a collector at the bottom of the air distribution enclosure. From there it is pumped through a filter back to the spray nozzles to be recycled. Typically, evaporative heat exchange products are designed to utilize parts which are common to both closed loop and open cooling towers. The collector in conventional closed loop towers is therefore of a capacity large enough to be able to be used in an open tower as well as in a closed circuit configuration. As mentioned in the above, the cooling provided by the heat exchanger is reinforced by spraying water on the coils of the heat exchanger. However, such reinforced cooling is not always necessary. For example, during the winter months sufficient cooling can be achieved without the evaporative effect of the water, that is, the so-called "dry operation" is possible. However, dry operation requires that the collector be drained since the water it contains could otherwise freeze and cause system damage as a result of the forced flow of cold air over it. This is problematic since the processes of draining and replenishing the collector are time consuming, and typically take several hours.
In addition, it is usually necessary to turn off the cooling system during at least part of the draining or replenishment period, to prepare the manifold for dry or wet operation, respectively, by ensuring the arrangement of the valve floats, the level controls etc. therefore, it is not considered practical or economically feasible to drain and replenish the collector every day. This means that the dry operation can only be carried out for a short proportion of each year in which even during the day, the temperatures are predictably low enough so that the "wet" operation is not required. As a result, it will be appreciated that the potential water and energy savings required to operate the water pump and any collector heater are seriously reduced. It is also known that in some closed circuit evaporative heat exchanger systems a manifold located away from the air distribution enclosure is provided. Most of the non-evaporated water is drained or pumped continuously to the remote manifold during wet operation, and then pumped from the remote manifold back to again be sprayed onto the heat exchanger coils. The advantage of such a remote manifold is that it is not necessary to drain the entire body of water from a manifold in the air distribution enclosure to achieve dry operation since only a small amount of the water remains in the air distribution enclosure and it can drain relatively quickly. The water inside the remote manifold is not subjected to the cold air flow in the air distribution enclosure and thus can be prevented from freezing by means of suitable heaters. There are several disadvantages, however, for a remote collector. First, an additional space is required to accommodate it, which is usually expensive. Second, more powerful pumps are required to justify the additional static weight through which the water must be pumped. Third, the global number of required components and the installation cost are also increased. Together these factors can more than overcome any cost savings so that it is possible for the system to operate more efficiently with respect to water consumption and spray pumping energy. It may be, however, that a remote manifold is necessary to allow dry operation and avoid over cooling in some circumstances. Another problem with the arrangements of the conventional closed-circuit evaporative heat exchanger is that it is necessary to stop the operation of the system to carry out routine maintenance such as inspection, functional tests, cleaning, etc. , of the parts inside the air distribution enclosure. This is a particular problem for conventional systems without a remote collector since the equipment within the collector and the water integration system will also be affected. Such a regular interruption of the operation of the system is obviously harmful and costly. It is an object of the present invention to provide an evaporative heat exchanger in which the problems set forth in the above are alleviated at least partially. When viewed from a first aspect, the present invention provides a closed-circuit evaporative heat exchanger comprising an air distribution enclosure, means for spraying water on the enclosure and a collection surface for collecting non-evaporated water that is sprayed on the enclosure, so that such water is ready to be drained to a collector inside the enclosure, without it remaining substantially on the collection surface. In this way, it will be observed by those skilled in the art that a manifold is still provided within the main air distribution enclosure, although the collector is not used to collect the non-evaporated water, but instead, a surface of collecting drains inside the collector. This means that the collector can be at least partly thermally insulated from the main part of the enclosure. This makes it possible to prevent the water in it from freezing when the ambient air temperatures are below the freezing point, since this is not feasible with the conventional collector arrangement in which it is exposed to the air flow in the enclosure . Such arrangements have the advantage of substantial flexibility in that they are able to be exchanged between a wet and dry operation quickly and each time it is required, but without the disadvantages of providing a remotely located collector. The collector is arranged in such a way that the water contained in it is prevented from freezing during operation in cold weather. This can be achieved by ensuring a sufficient degree of thermal insulation and by providing the heating means, preferably thermostatically controlled. This also allows for variant ambient temperatures to be taken into account. The harvesting surface could simply be arranged to drain into the collector below it, that is, the arrangement could effectively be similar to a conventional one but with a cover or something similar covering the collector and including a drilling or drainage perforations. In this case the upper surface of the lid would form the collection surface.
It is preferred, however, that the drainage interface between the collecting surface and the manifold be arranged to form a liquid seal between the two, so that a non-uniform air pressure can be maintained between them. The benefit of this feature is that the collector can then be maintained at a substantially atmospheric pressure, while the main part of the enclosure is at an elevated pressure resulting from the forced air flow. The physical isolation of the interior of the collector from the interior of the main air distribution enclosure also avoids contact with water sprays. These two factors allow at least access to the manifold for maintenance even when the system is in operation with the associated fans in operation. It will be appreciated that this capability gives it a significant advantage over the prior art systems, which have to be removed from the operation even for routine maintenance. The amount of water used in the cycle spray system through the manifold, as in the prior art, can be of a volume similar to that associated with a manifold used in an open tower cooling system. However, it has been appreciated that since, in accordance with the invention, a new collector shape is contemplated, the small benefit of the community among the collector modules is lost, although this means that the volume restriction imposed when using a common collector is no longer needed and that in fact an additional benefit can be achieved by using less water. Thus, in the preferred embodiments, the evaporative water spray system is arranged to operate with barely enough water for wet operation. In an exemplary embodiment, the system operates with approximately 90 liters of water per square meter of coil area. This contrasts with a conventional system in which a volume of approximately 240 L / m2 is used (which is consistent with the use of a standard size collector). The use of a significantly reduced volume of water not only saves water, but also means that the collector may be smaller than it would be if it were otherwise, less powerful heaters are required to prevent it from freezing, and treatment is required of water with fewer chemicals, all of which helps reduce costs. The preferred embodiment of the invention set forth above is understood to involve using the minimum volume of water necessary for the evaporation process. In practice, this minimum amount depends on the capacity of the water distribution system, including plumbing, the proportion of water that is falling through the air distribution enclosure at any time, and the minimum amount of water required by the water distribution system. pumping to operate properly. This must be contrasted with the prior art in which volumes significantly larger than the minimum are used for the wet operation and in fact in which it has not previously been given consideration to this minimum quantity required. It will be appreciated that in practice, in accordance with the invention, the means for replenishing the water lost through evaporation will be provided. Any means well known in the art can be used, such as a valve operated by float, an electronic sensor, an optical sensor, etc. Such water replenishment may have some inherent hysteresis so that the actual volume of water in the system at any time can cycle between a predetermined maximum and minimum. BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a sectional view of a conventional closed-circuit evaporative heat exchanger. which is shown only for reference purposes; and Figures 2a and 2b are end and side views in section, respectively, of a closed circuit evaporative heat exchanger according to the invention. Returning first to Figure 1, a closed-circuit evaporative heat exchanger of the prior art can be seen. A sealed heat exchanger coil A is provided through which the coolant passes in a distribution enclosure B of B. A fan system C driven by a motor D is provided at one end of the enclosure B. At the top of the enclosure B are a series of nozzles E which are arranged to sprinkle water on coil A heat exchanger. A manifold F is provided at the bottom of the enclosure B with a capacity of 240 liters per square meter of coil area and a pump G is provided to pump water upwards from the collector F towards the spray nozzles E. A water replenishment system H using a float valve ensures that a minimum amount of water is maintained within the manifold. In operation, the refrigerant liquid or refrigerant vapor is fed into the heat exchanger coil A where the heat is extracted from it to cool or condense it before it is returned, as is well known in the art. The fan C forces a rapid flow of air over the heat exchanger coil A in the air distribution enclosure B to extract heat from the cooling fluid or vapor. Evaporative cooling is provided by the water spray system which extracts water from the collector F using the pump G. Part of the water sprayed from the nozzles E will evaporate. The rest of the water is collected inside the collector F from where it is recycled upwards towards the spray nozzles E. The water lost through evaporation is replaced by the system H of water replenishment. To gain access to the collector F to carry out the inspection and maintenance, it is necessary to close the system and turn off the fan C, thus limiting the frequency with which this can be carried out in practice. In addition, if the ambient temperature is such that an additional cooling effect of the water spray system is not required, all water must be drained from the collector F to prevent it from freezing due to the cooling effect of the forced cold air flow. This consumes so much time that it could only be carried out when the operator is sure that the temperature will not rise sufficiently again to require wet operation for a considerable time (ie, over a period of more than one day). One embodiment of the present invention can now be seen in Figures 2a and 2b. As in the apparatus described with reference to Figure 1, the closed-circuit evaporative heat exchanger comprises a heat exchanger coil 2 arranged in an air distribution enclosure 4 and conveying a cooling or cooling fluid to and from an area which is to be cooled (not shown) by the pipe couplings 6. At one end of the air distribution chamber 4 is a fan 8 driven by a motor 10 by a band 12. The blades of the fan 8 are housed within a coating 14 and thus are not visible in Figure 2a. Unlike the system shown in Figure 1, there is no open collector at the bottom of the air distribution enclosure 4. Instead, the manifold 16 is defined in the lower part of one end of the air distribution enclosure 4 by an inclined diverter wall 18. In this mode, the collector has a capacity of ninety liters per square meter of coil area, but this is purely exemplary and this number depends, for example, on the length of the coil. The diverter wall 18 is downwardly dependent on the rear end wall 20 of the enclosure 4. It ends in such a way as to leave a cavity between its end and the base of the collector 16. The diverter wall 18 extends between the two opposite side walls of the enclosure 4. - in other words, perpendicular to the plane of Figure 2a or from left to right in Figure 2b. The area of the lower part of the air distribution enclosure 4 not occupied by the collector 16 is formed as an inclined base 22. The base 22 is tilted towards the diverter wall 18, but stops just before it so as to leave a small cavity 24 running from one side wall of the enclosure 4 towards the other. The base also extends between the two side walls so that the cavity 24 runs along the width of the enclosure 4. The diverter wall 18 and the base 22 each form collecting surfaces on which the water that falls from the coils 2 Heat exchangers will settle. Within the manifold 16 there is a valve 26 operated by float connected to an inlet spout 28 to maintain a minimum level of water within the manifold 16. This water level is set to be the minimum amount required for the wet operation of the exchanger of heat (taking into account the capacity of the pipes, etc., in the rest of the system). At the base of the manifold 16 is a filter 30 through which the water can be withdrawn from the manifold by a pump 32 and pumped upwards by a vertical pipe 34 outside the rear end 20 of the enclosure, where it re-enters the enclosure 4 to feed a water distribution pipe 36. A series of nozzles 38 are spaced along the water distribution pipe 16 so that the water is forced into a conical spray on the heat exchanger coils 2 under the pressure imparted by the pump 32. A nozzle 38 of that type it can be seen more clearly in the fragmentary detail view above it. Above the water distribution pipe 36 is a series of liquid droppers 40 in suspension one of which is also shown more clearly in a fragmentary detail view. These separate droplets of water entered the air stream, left the heat exchanger and prevented droplets from being lost from the system. Finally, a pair of access doors 42 is provided in the lower part of the end wall 20 of the enclosure to allow external access to the interior of the collector 16. The operation of the apparatus will now be described. As in the prior art system, the fan 8 forces air to flow over the coils 2 heat exchangers to extract heat from the cooling fluid they contain. When additional cooling is required, the pump 32 is operated to draw water from the manifold 16 through the filter 30 and force it through the nozzles 38 to form a fine mist on the heat exchanger coils. A significant cooling effect is achieved by evaporating part of the water. The non-evaporated water falls down towards the bottom of the air distribution chamber 4 and on the collection surfaces formed by either the diverting wall 18 or the inclined base 22. The water that falls on these parts does not remain there but drains into the small cavity 24 between them. As can be seen from Figure 2a, the water level inside the collector is such that the cavity 24 is at least partially filled with water. This forms a water shut-off between the air distribution enclosure 4 and the manifold 16. This water shut-off allows to maintain a differential air pressure between the main part of the enclosure 4 and the collector 16 so that access to the collector 16 can be obtained. , for example, for inspection and maintenance, even if the main fan 8 is still in operation and the system is in operation. During the dry operation, the pump 32 is turned off and the remaining water is drained through the cavity 24 into the manifold 16. Within the manifold 16 the water is no longer in direct contact with the air current generated by the fan 12. It will be appreciated, therefore, that since there is no water remaining in the main part of the air distribution enclosure 4, i.e., in contact with the cold air flow, the probability of it freezing is significantly reduced. Although not shown in Figure 2a, thermostatically controlled heaters are provided to maintain the temperature of the water within the manifold 16 above that of the freezer. Nevertheless, since the collector 16 is relatively small compared to the distribution enclosure 4, and which is separated from the cold air stream by the diversion wall 18, the power required for such heaters is relatively low. It will further be appreciated that the amount of water within the manifold 16 is significantly less than within the manifold F in Figure 1. This not only brings savings in the amount of water that is required to fill the equipment, but also in the cost of the treatment. necessary chemical and the amount of heat that is required to prevent it from freezing. The embodiment described above provides the overall advantage that it is completely flexible in that it can be operated either in wet or dry mode as required, and on the other hand, it can be switched very rapidly between these modes. Example A prototype of apparatus similar to that described in the foregoing was constructed and tested with reference to Figures 2a and 2b. The volume of water inside the collector of the test apparatus was 860 liters and the ventilator gave an air flow of 27 cubic meters per second on the heat exchanger coils. However, a normal atmospheric pressure was maintained inside the collector by virtue of the water lock. When the pump of the evaporative cooling system was turned off and the ambient temperature was reduced to -10 ° C, the collector and the water shutoff remained completely free of ice with a heat input from the collector heater of a modest 4 KW .