The invention relates to an air-conditioning system, where incoming air is led through a heat ex- changer and through the same heat exchanger exhaust air is led in the opposite direction. The object of this generally known system ^' is to recover heat from the ex¬ haust air. In the summer, there is no need for this, on the contrary, the incoming air is usually desired, to be cooled.

One known cooling manner is to use compressor mechanisms operating on the heating pump principle. As the air volumes to be handled are usually big, the com¬ pressor mechanism is also big and both its purchase and operation costs, especially consumption of electric power, are big.

Another known cooling manner is to humidify the air. The cooling effect is based on the fact that the vaporization heat of water is high. When water vaporizes, it binds heat form the air and cools it. The drawback with this method is that the relative humidity of the air increases. A high humidity causes easily damages to buildings, furniture etc. and creates favourable culture circumstances for, e.g., blight, bacteri etc., which adds to the damage risk for buildings and furniture as well as causes health risks for people. Furthermore, the real cooling effect stays smaller than what could be imagined directly on the basis of a fall in tempera¬ ture. The heat regulation of man is based on evaporation, that is, on sweating. A high air humidity makes sweating more difficult and the more humid the air is, the hotter it feels. According to researches, a temperature of 25°C the relative humidity being 100 % is felt as equally hot as a temperature of 30°C the humidity being 50 %. Despite this, a cooling based on humidifying is generally used, for example, in industry, when the volume streams

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to be dealt with are so big that the costs for com¬ pressor cooling would rise to the excessive. It is also general in countries, where the air is very dry

(so-called desert cooler) . It has been proved in practice that in addition to said drawbacks of principle, it is almost impossible to regulate the system. This is because too many factors effect the desired final result, that is, the in-blow-te perature, which factors are not depending on each other, viz. temperature of incoming air, humidity of incoming air, temperature of water and humidification percentage, which in itself is very difficult to adjust. The most important advan¬ tages of the system are a simple construction and because of this a low price as well as low running costs. The object of the invention is to provide, on the basis of the system described at the beginning, a new air-conditioning system where the heat exchanger is, when required, used for cooling the incoming air.

The object is attained with an air-conditioning system according to the invention, which is characterized in that in the flow path of the exhaust air, before the heat exchanger, is arranged a moistening element for cooling the air flowing through by vaporizing aqueous vapour into it and trhough which at least part of the exhaust air can be led, for cooling the incoming air in the heat exchanger by means of the exhaust air.

The system of the invention is thus based on an economically preferable humidification but it has not the drawbacks of known humidification cooling systems. The basic idea is that incoming air is not directly humidified, but exhaust air is used which is humidified and thus cooled air is used for cooling incoming air. Hence the humidity of air-conditioning air does not increase and the drawbacks caused by humidity are avoided. The adjustment is essentially facilitated because, instead of humidification, mass flows can be regulated

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and dew-point humidification can be used all the time_.

With the conception "exhaust air" is in this patent application generally meant air which flows through the heat exchanger in the opposite direction to the incoming air; in. such a cooling situation, in which the heat load of the space to be air-conditioned is so big that the temperature of air leaving the space is higher than the temperature of incoming air, it is preferable to blow the actual exhaust air directly out and instead lead part of the incoming air back into the heat exchanger through the moistening element.

.In an especially preferable embodiment of the' invention, the moistening element comprised in the system is used for moistening incoming air in the winter, when the out-of-door air is very dry. Then exhaust air is led directly into the heat exchanger and incoming air is led into the space to be air-conditioned partly or wholly through the moistening element.

Said realizations are defined in claims 3 to 5 and they also appear from the following detailed de¬ scription in which references are made to the enclosed drawing.

Figure 1 shows the basic solution of a system according to the invention as a diagram. Figures 2 and 3 show versions of the solution in Figure 1.

Figure 4 shows an especially preferable embodiment of the invention.

In the examples of the drawing, the incoming air flow is designated with reference numeral 1 and the exhaust air flow with numeral 2, and corresponding fans with numerals 3 and 4. Numeral 5 denotes a heat exchanger, through which incoming and exhaust air flows in opposite directions. 6 is the moistening element positioned before the heat exchanger, in which element exhaust air is cooled by vaporizing aqueous vapor into it through

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nozzles 7. With the thus cooled air, incoming air is cooled in the heat exchanger 5, which air from here flows through a pipe 8 to be further treated or into the space to be air-conditioned. A thermostat 9 posi- tioned in the channel 8 regulates the cooling effect and controls a regulating motor 11 of a regulating plate 10. The basic solution shown in Figure 1 can naturally be varied as to its details, the regulating plate 10 can be positioned between the moistening element and the heat exchanger 5 or between the exchanger 5 and the fan 4, or also after the fan 4- The position of the fans 3 and 4 can also be freely varied in the system, etc.

Instead of the plate 10 another regulating manner for secondary air volume can be used. The plate can, for example, be replaced by a guide blade regulator or by using a fan with adjustable blades, by regulating the rotation rate of the fans, etc.

The adjustment can be realized also by passing the heat exchanger. Such a solution is shown in Figure 2. Otherwise the system functions as the one shown in Figure 1 , but the plate 10 is moved to the air-condi¬ tioning air channel and a by-pass regulating plate 12 and a by-pass channel 13 are added to the system. A motor 14 regulates simultaneously the plates 10 and 12 which are cross-connected so that when the plate 10 opens the plate 12 closes. Part of the air flow is guided through the channel 13 past the heat exchanger 5, whereat it is not cooled, and is after the heat exchanger mixed into the air cooled in the heat exchanger. Thus it is easy to reach the desired temperature by regulating the proportion of air flows to be suitable.

In Figures 1 and 2 the heat exchanger is shown as a conventional cross ^" flow - reverse flow exchanger, but the invention is of course not limited only to this, but all generally known heat exchangers are possible.

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In Figure 3 a solution is shown, in which the heat ex¬ change is carried out by means of a medium, e.g. water, which a ;pump 15 circulates through heat exchangers 16 and 17. The regulating plate is in this system replaced by a three-way valve 18 which, regulates the quantity of the circulating medium. Other regulating manners are of course possible, e.g. the rotation rate of the pump 15 can be adjustable, a three-way valve can be used, instead of the water the air volume can be adjusted as in Figure 1 , etc. In Figure 4 an especially preferable embodiment of the invention is shown where, in the winter, the heat exchanger is used for recovering heat from exhaust air and, in the summer, for cooling, as well as where the moistening element is used for cooling in the summer and for humidifying in the winter, when the out-of-door air very dry.

From the incoming air channel 8 there is a connec¬ tion to the moistening element 6 through a regulating plate 18 and behind the moistening element 6 a connection 20 is formed through a regulating plate 19 back to the incoming air channel 8. A plate 21 regulates the flow from the moistening element 6 to the heat exchanger 5. Further, a connection 22 is formed to the exhaust air channel past the moistening element, whereat the stream quantities going to the moistening element and respectively past it are regulated by means of plates 23 and 24. Exhaust air going past the moistening element 6 can in its turn be led to the heat exchanger 5 through a regu¬ lating plate 25 or directly out through a regulating plate 26. 27 denotes a fan with a regulating plate 28 and a regulating plate 29 regulates the incoming air volume going directly from the heat exchanger 5 to the space to be air-conditioned.

In the following, the operation of the system shown in Figure 4 is described.

In the winter when the heat exchanger 5 is used for recovering heat and the moistening element 6 for

humidifying air-conditioning air, the regulating plates 21., 23, 26 and 28 are closed. The regulating plates 24 and 25 are fully open, so exhaust air sucked from the air-conditioning system by the exhaust f n 4 streams through the plates 24 and 25 to the heat exchanger 5 where the heat content of the exhaust air is transferred to the air-conditioning air. After this, the exhaust air streams out. Air-conditioning air is blown by the fan 3 through the heat exchanger 5 and the ^" regulating plate 29 into the space to be air-conditioned. If humidification is needed, the plate 29 begins to close and the regulating plates 18 and 19 to open. Part of the air then streams through the plate 18 to the moistening element 6 where it is humidified. The humidified air is directed back through the plate 19 and is mixed into the ^* air-conditioning air after the plate 29. The desired humidification rate is attained by regulating the pro¬ portion of air streams streaming through the plates 18 and 29. When the out-of-door temperature rises in -the spring (or in the autumn) , the regulating plate 25 begins to close and the regulating plate 26 to open. Thus the exhaust air volume streaming through the heat exchanger 5 decreases, because of which the amount of heat trans- ferring into the air-condition air decreases and the desired in-blow-temperature is attained despite the rising temperature out-of-doors. When the out-of-door temperature has risen to the same as the desired in-blow-temperature, the plate 25 is closed. Also during this stage, the moistening element 6 can be used for humidifying incoming air.

The out-of-door temperature still rising, a need for cooling begins to appear and then the regulating plate

24 begins to close and the plates 21 and 23 to open. The plates 18, 19 and 28 must then be closed, so the system can no longer be used for humidifying.- Usually this is.

however, not even necessary because as the out-of-door temperature rises, its aqueous content increases, and upon cooling the relative humidity increases, so that usually a ^' sufficient humidity is attained. When the plates 21 and 23 open, part of the exhaust air streams to the moistening element 6, where it is cooled, and further to the heat exchanger 5, where it cools the air- conditioning air. When the maximum cooling need appears, the plate 24 is fully closed and the plates 21 and 23 are fully open.

When the heat load of the space to be air-condi¬ tioned is so big that the temperature of the exhaust air is higher than the temperature of the out-of-door air, it is more preferable to use out-of-door air than exhaust air for the cooling. The auxiliary fan 27 makes this possible. By means of it, the operation of the system can be made more efficient also in such a way that the air volume of the auxiliary fan 27 is bigger than that of the exhaust air fan 4, whereat the cooling effect increases. First, the system can be used so that the auxiliary fan 27 is started when the plate 23 is fully open, that is, the cooling effect is not sufficient any more when using exhaust air. When the fan 27 starts, the plate 23 must close and the plate 24 open fully. Another possibility is to use only out-of-door air for the cooling. Then the fan 27 starts immediately when a cooling need appears. The plates 23 and 24 can thus be left out. Such an embodiment is especially use¬ ful when a heat exchanger according to Figure 3 is used, because the exhaust and the blowing in can be positioned far apart.

For the sake of clarity, the control system is left out of Figure 4 ₇ in principle it is similar to the ones shown in Figures 1 to 3. It comprises a thermostat which, depending on the number of plates, controls one or-several regulating motors or other regulating devices.

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What is said in connection with Figures 1 to 3 about different variation possibilities, naturally also holds good for the case in. Figure 4. The position of the components can be another than the one shown in the Figure, a by-pass regulation can be used, the heat ex¬ changer type can be of any known type, etc. Further¬ more, for humidifying t_lιe air any known humidification system can be used. Parts can of course be left out of the system in Figure 4. Instead of the cooling operating only on out-of-door air described above, a cooling operating only on exhaust air can be used, whereat the fan 27 and the plate 28 are left out. The possibility to use humidification in the winter can also be left out, whereat the plates 18, 19, 21 and 29 are not needed. All connecting possibilities based on prior-art technology are of course included in the scope of the invention.

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