Background of the invention

[0001] The invention relates to a heat exchange apparatus and/or method, in particular to cool a process fluid by means of a heat exchanger in which an air flow removes heat from the process fluid.

[0002] Specifically, but not exclusively, the invention can be applied to a process fluid consisting of a liquid, a gas, a condensing cooler, or any other fluid to which heat must be removed.

[0003] In particular, reference is made to an apparatus and/or a method in which a heat exchanger includes a pipe system in which a process fluid to be cooled flows and in which, when the temperature of gas usable for cooling (generally air at ambient temperature) is greater than the temperature at which the process fluid is required to cool, it is provided the use of at least one evaporative body (generally a body made of a cellulose material, in particular formed in a shape of a panel) which is placed in the air flow before the heat exchanger and which is supplied with an evaporative liquid (water) in order to humidify and cooling the air, in particular to bring the ambient air to the wet bulb temperature.

[0004] Patent publication EP 1698847 A1 discloses a system for extracting heat from a process fluid, in which at low temperatures heat is extracted in a first heat exchange section with dry forced convection, and at higher temperatures an evaporative liquid is dispensed over a second heat exchange section in which the air flow is first saturated adiabatically with the evaporative liquid, so as to cool the air below its dry bulb temperature before entering the first heat exchange section, and in which the evaporative liquid flow is controlled by a humidity/temperature sensor that controls the air conditions before entering the first heat exchange section after passing through the second heat exchange section (adiabatic section).

[0005] Patent publication WO 2018/148460 A1 discloses an adiabatic cooling device with a water dispensing system, a discharge water sensor and a controller that controls a modulation valve to adjust the amount of water dispensed based on the aforementioned sensor.

[0006] Patent publication WO 2015/108603 A1 discloses an adiabatic cooler or condenser, with an adiabatic pad supplied with water to cool the ambient air before entering a condensation or cooling battery, with a temperature or humidity sensor upstream of the pad and a temperature or humidity sensor downstream of the pad and before the battery, and with a controller that controls the amount of water supplied to the adiabatic pad.

[0007] Patent publication EP 3306247 A1 discloses an air-water heat exchanger comprising at least one heat exchange finned battery and at least one adiabatic unit with means for spraying water on the battery so as to cause water to evaporate, while non- evaporated water is continuously recovered, circulated and sprayed on the adiabatic unit.

Summary of the invention

[0008] An aim of the invention is to provide a heat exchange apparatus and/or method that is alternative with respect to those in the prior art.

[0009] An aim of the invention is to make available an alternative solution to the problem of cooling a process fluid in an air heat exchanger even when ambient air temperature is higher than the desired temperature at which it is required to cool the process fluid.

[0010] An advantage is to realize a heat exchange apparatus and/or method of in which a compromise can be achieved between saving energy for moving air used to cool the process fluid and saving water for wetting the evaporative means used to humidify the air.

[0011] An advantage is to provide a heat exchange apparatus, in particular a dry cooler, which is constructively simple and inexpensive.

[0012] These aims and advantages, and still others, are achieved by an apparatus and/or a method according to one or more of the claims below.

[0013] In one embodiment, a heat exchange apparatus comprises a heat exchanger for cooling a process fluid, ventilation means for generating a cooling gas flow to the heat exchanger, at least one evaporative body that is traversed by the flow before the heat exchanger, supply means for supplying an evaporative liquid to wet the evaporative body, a temperature sensor for measuring the process fluid temperature at the outlet of the heat exchanger, and control means for controlling the evaporative liquid supply means based on the temperature measured by the temperature sensor.

[0014] The control means may be configured, in particular, to receive a lower limit of the cooling gas flow and to control the ventilation means and the evaporative liquid supply means based on the temperature measured by the temperature sensor so that, when the cooling gas flow is higher than the aforementioned lower limit and the evaporative liquid flow is not null, if the measured temperature is less than or equal to a predetermined value, then the cooling gas flow is lowered without lowering the evaporative liquid flow.

[0015] The control means may be configured, in particular, to receive a lower limit of the cooling gas flow and to control the ventilation means and the evaporative liquid supply means based on the temperature measured by the temperature sensor so that, when the cooling gas flow is equal to the aforementioned lower limit and the supply flow of the evaporative liquid is not null, if the measured temperature is less than or equal to a predetermined value, then the evaporative liquid flow is lowered without lowering the cooling gas flow.

Brief description of the drawings

[0016] The invention will be better understood and implemented with reference to the accompanying drawings which illustrate a non-limiting embodiment, in which:

Figure 1 is a perspective view of an example of a heat exchange apparatus made according to the present invention;

Figure 2 shows a diagram of a section of the Figure 1 apparatus performed according to a vertical section plane.

Detailed description

[0017] With reference to the aforementioned figures, a heat exchange apparatus has been indicated as a whole with 1. The heat exchange apparatus 1 includes, in particular, a dry cooler, or air cooler.

[0018] The apparatus 1 is configured, in particular, to cool a process fluid by means of a cooling gas flow. The process fluid may comprise, in particular, a liquid, a gas, a condensation cooler, or any other fluid to which heat must be removed. The cooling gas may comprise, in particular, air, for example air taken from the ambient.

[0019] The heat exchange apparatus 1 may include, in particular, at least one heat exchanger 2 including tube means provided with at least one inlet 3 of the process fluid to be cooled and at least one outlet 4 of the cooled process fluid. The air-cooled heat exchanger 2 removes heat from the process fluid, or working fluid, transferring heat to the air. The heat exchanger 2 tune means may include, in particular, at least two tube batteries arranged in a V-shape. The tube means may include, in particular, tube means provided with fins.

[0020] In particular, the tube means may include, as in the specific example, at least one tube battery, for example finned, (in the specific example a right battery and a left battery arranged in a V-shape), at least one inlet manifold 5 (for example, an inlet manifold for each battery), at least one outlet manifold 6 (for example, an outlet manifold for each battery), at least one inlet connection 7 (for example, an inlet connection for each battery), at least one outlet connection 8 (for example, an outlet connection for each battery). [0021] The tube means may be made, in particular, of copper, aluminum, stainless steel, or other metals covered with special anti-corrosion paints. The tube means fins may be made, in particular, of copper, aluminum, or other materials which can be painted, or provided with particular treatments to resist corrosion (for example salt corrosion).

[0022] The heat exchange apparatus 1 may include, in particular, ventilation means 9 configured to generate a flow of a cooling gas (air) which passes through the tube means. The ventilation means 9 may comprise, in particular, at least one fan. In the specific example, the ventilation means 9 comprises four fans. However, it is possible to provide for the use of ventilation means with a different number of fans.

[0023] In use, hot process fluid flows inside the heat exchanger 2 tube means. Cooling gas (air) is passed between the heat exchanger 2 tube means, moved by the ventilation means 9, removing heat from the process fluid.

[0024] The heat exchange apparatus 1 may comprise, in particular, adiabatic means that is configured to receive (and be wetted by) an evaporative liquid and is arranged to be traversed by the cooling gas flow before the heat exchanger 2. The adiabatic means may comprise, in particular, at least one evaporative body 10 arranged before the heat exchanger 2 to be traversed by the cooling gas flow. The adiabatic means may comprise, in particular, two or more evaporative bodies 10, for example at least one evaporative body for each tube battery. Each evaporative body 10 may comprise, in particular, a body made of cellulosic material, or aluminum (aluminum mesh), or another material, for example a body made of paper or cardboard, in particular a body comprising an open mesh structure to receive the flow of cooling gas (air). Each evaporative body 10 may comprise, in particular, a body permeable to the flow of cooling gas (air). Each evaporative body 10 may comprise, in particular, an adiabatic pad. Each evaporative body 10 may comprise, in particular, a body in a form of a slab or panel (adiabatic panel), that is with a dimension (thickness) much lower than the other two dimensions. In the specific example, the evaporative bodies 10, in the form of panels, are arranged in a vertical position.

[0025] The heat exchange apparatus 1 may comprise, in particular, supply means for supplying an evaporative liquid for wetting the evaporative body(s) 10 so as to humidify the cooling gas flow passing through the wet evaporative body 10.

[0026] The supply means may include, in particular, an evaporative liquid supplying circuit 11 and/or at least one inlet 12 of the evaporative liquid and/or at least one outlet 13 of the evaporative liquid. The supply means may include, in particular, dispensing means including, for example, at least one evaporative liquid dispenser 14 operatively associated with a respective evaporative body 10. The supply means may include, in particular, flow rate control means configured to control the evaporative liquid flow rate in the supplying circuit. The flow rate control means may comprise, in particular, at least one flow control valve 15 arranged to adjust the flow of the evaporative liquid which is supplied to the dispensing means. It is possible to provide, in other embodiments not shown, flow rate control means that includes a pump, for example a variable delivery pump. The use of a pump may be provided, in particular, in a supply circuit (in not shown examples) which includes an evaporative liquid recirculation system.

[0027] Each evaporative body 10 may be wet and/or saturated by dripping evaporative liquid (for example falling from the dispensing means) on one end (in particular, upper end) of the evaporative body 10.

[0028] Air taken from ambient may be passed through the adiabatic means, thereby air will come into contact with the water which adiabatic means are impregnated of, and will increase its humidity, for example up to a saturation degree determined by the adiabatic means, so that the air downstream of adiabatic means will have a higher humidity than ambient air. This enables to obtain an adiabatic operation mode in which air, passing through the adiabatic means, decreases its temperature, in particular down to the wet bulb temperature relative to the humidity transferred by the adiabatic means, and then passes through the tube means, thereby the heat exchanger can use cooling air at a lower temperature than ambient air temperature.

[0029] The heat exchange apparatus 1 may comprise, in particular, at least one temperature sensor 16 arranged to measure the temperature Tout of the (cooled) process fluid at the outlet of the tube means. The temperature sensor 16 may be arranged, for example, at or near an outlet connection 8, or an outlet manifold 6, or at the outlet 4 of the process fluid. It is possible to provide, in other examples, the use of two or more temperature sensors arranged, in particular, in two or more different points of the path of the process fluid.

[0030] The heat exchange apparatus 1 may include, in particular, control means 17 configured to control the various actuators of the apparatus itself. The control means 17 may include, in particular, programmable electronic control means. The control means 17 may include, for example, a CPU. The control means 17 may be configured, in particular, to control the evaporative liquid supply means based on the temperature Tout measured by the temperature sensor 16. The control means 17 may be configured, in particular, by computer program instructions. The control means 17 may comprise, in particular, feedback control means. The type of control may include, in particular, a PID, or PI, or other type of control.

[0031] The supply means 15 may be configured so as to be able to assume two or more configurations in which it supplies, respectively, two or more not null values, different from each other, of an evaporative liquid flow rate. The control means 17 may be configured, in particular, to modulate the supply means 15 corresponding to the aforementioned two or more configurations.

[0032] The heat exchange apparatus 1 may comprise, in particular, first sensor means 18 for measuring the cooling gas humidity before passing through the evaporative body 10. The first sensor means 18 may include, in particular, at least one humidity sensor arranged to detect the cooling gas humidity upstream of the adiabatic means. The first sensor means 18 may be configured, in particular, to measure relative humidity and/or absolute humidity and/or specific humidity. In the specific example, the first sensor means 18 comprises at least one sensor arranged to measure the ambient air relative humidity.

[0033] The control means 17 may be configured, in particular, to control the evaporative liquid supply means on the basis of the humidity measured by the first sensor means 18 so that the evaporative liquid flow rate is null if humidity measured by the first sensor means 18 is greater than or equal to a predetermined maximum value.

[0034] The heat exchange apparatus 1 may comprise, in particular, second sensor means 19 for measuring the cooling gas humidity between the adiabatic means (evaporative body(s) 10) and the tube means. The second sensor means 19 may comprise, in particular, at least one humidity sensor arranged to detect cooling gas humidity downstream of the adiabatic means and upstream of the tube means. The second sensor means 19 may be configured, in particular, to measure relative humidity and/or absolute humidity and/or specific humidity. In the specific example the second sensor means 19 comprises a sensor for measuring relative humidity of the air which has passed through the adiabatic means and has not yet crossed the tube means.

[0035] The control means 17 may be configured, in particular, to control the evaporative liquid supply means based on the humidity measured by the second sensor means 19, for example so as to act on the evaporative liquid flow rate (in particular to block the flow, or to prevent it from increasing, or to decrease it, or to nullify it) if the humidity measured by the second sensor means 19 is greater than or equal to a predetermined value.

[0036] To remove heat from the process fluid, process fluid temperature must be greater than cooling gas temperature. The greater the difference in temperature between cooling gas and process fluid, the lower the cooling gas flow rate required to remove heat, cooling gas flow rate provided by the ventilation means 9, so, consequently, the less will be the power absorbed by the ventilation means 9.

[0037] The control means 17 may be configured, in particular, by inserting a set point value Tset of the process fluid temperature at the heat exchanger outlet. The control means 17 may be configured, in particular, so as to vary the speed of the ventilation means 9, thus varying the cooling gas flow rate, based on the comparison between the value Tout measured by the temperature sensor 16 and the set point value Tset.

Example of “dry” operation

[0038] Inlet temperature of the hot process fluid is, for example, 40 °C. The desired set point value Tset of the outlet temperature is, for example, 35 °C. The ambient air temperature is, for example, 20 °C. The control means 17 adjusts the ventilation means 9, for example, at 40% of ventilation means 9 maximum power. Process fluid flows inside the tube means which is traversed by a flow of air at 20 °C, thereby the process fluid can be cooled down to the desired temperature of 35 °C.

[0039] If ambient air temperature increases, the temperature sensor Tout will detect an increase in the process fluid temperature at the outlet of the heat exchanger, for example 36 °C. The control means 17, consequently, will increase the air flow rate moved by the ventilation means 9 (for example by adjusting the ventilation means 9 to 60% of maximum power thereof). The temperature Tout detected by the process fluid output temperature sensor 16 will be restored to the set point value of 35 °C.

[0040] It is possible to provide the “dry” operation as long as the ambient temperature is lower than the set point value. If the ambient air temperature reaches 35 °C it is no longer possible to cool the process fluid in a “dry” mode. In an example of operation, dry air, that is, without the use of the evaporative liquid, is used for cooling the process fluid as long as possible, and then, only when it is no longer possible to use dry air for cooling the process fluid, the use of evaporative liquid is provided (transition to “adiabatic” mode). Examples of “adiabatic” operation

[0041] In these examples the process fluid can be cooled even if the ambient air temperature is higher than the set point temperature, in particular by bringing air to the wet bulb temperature.

[0042] The first sensor means 18 (ambient air humidity sensor) allows to activate the adiabatic mode only if the ambient humidity URamb is lower than a certain value URtg (target value), so that this mode is advantageous. It is understood that the activation of the adiabatic mode actually takes place when the supply flow rate of the evaporative liquid (water) to the adiabatic means, that is, to at least one evaporative body 10 (adiabatic panel or pad) is non-zero. The activation of the adiabatic mode essentially means that at least one evaporative body 10 is wetted with evaporative liquid.

[0043] Activation of the adiabatic mode can take place, in particular, only when the ambient humidity URamb is less than or equal to the preset value URtg. In addition to or alternatively to the aforementioned condition (URamb < URtg), activation of the adiabatic mode can take place, in particular, only when ambient air temperature Tamb is greater than or equal to a predetermined value Ttrs (threshold value, for example Ttrs = 15 °C). In addition to or alternatively to one and/or the other of the aforementioned conditions (URamb < URtg and/or Tamb > Ttrs), it is possible to provide that the activation of the adiabatic mode can take place only when the set point temperature Tset of the process fluid at the outlet of the heat exchanger 2 is greater than or equal to a predetermined maximum value Tmax, where Tmax may be, for example, a value set by the manufacturer, or a value that can be set by the user.

[0044] The aforementioned reference value URtg for air humidity may include, in particular, a saturation maximum value which air can have after having been treated by adiabatic means (evaporative body(s) 10). URtg value may be, in particular, a constant value defined by the manufacturer, for example a value equal to an 80% of relative humidity.

[0045] If humidity URamb read by the first sensor means 18 is lower than the URtg value (target value or reference value), if ventilation V supplied by the ventilation means 9 is greater than or equal to a threshold value Vsup (upper ventilation threshold), if temperature Tout of the process fluid read by the temperature sensor 16 is greater than or equal to a predetermined threshold value Tsup (upper evaporator threshold), then the control means 17 controls activation of the evaporative liquid supply means (that is, in this specific case, the opening of the flow control valve 15). In particular, the evaporative liquid supply means may be activated so as to perform a step control of the evaporative liquid flow rate, even if it is possible to provide a type of control of another type (for example a PID type, or PI type, or other type feedback control). In the specific case, the supply means is controlled so as to dispense a first flow rate step.

[0046] For ventilation V it may be understood, in particular, a parameter indicative of the cooling gas flow rate supplied by the ventilation means 9, such as, for example, the operating speed of the supply means 9 and/or the power absorbed by the ventilation means 9 and/or the actual flow rate of the cooling gas passing through the heat exchanger 2, and so on. Therefore, in the present description the term “ventilation” V indicates any parameter indicative of the cooling gas flow rate generated by the ventilation means 9. [0047] The aforementioned threshold value Vsup (ventilation upper threshold) may be, in particular, less than or equal to the maximum ventilation value, corresponding to the value of maximum speed and/or absorbed power of the ventilation means 9 (that is, in particular, the maximum rotation speed value of blade-holder rotors of the fans).

[0048] When the evaporative liquid supply means (flow rate adjustment means or flow control valve 15) receives the activation control (valve 15 opening), then it is controlled so as to supply a flow rate value corresponding to the first step, by flowing the evaporative liquid (water) to the adiabatic means (evaporative bodies 10).

[0049] External ambient air passes through the adiabatic means (evaporative bodies 10) and humidifies. The second sensor means 19 (internal humidity sensor URint) will detect a humidity higher than external ambient air humidity URamb.

[0050] It is possible to provide, in particular, that the control means 17 be configured so as to send an anomaly signal if the second sensor means 19 (internal humidity sensor URint) does not detect an increase in humidity with respect to the external ambient air humidity URamb after a set time period. In this case, in fact, the adiabatic means (evaporative bodies 10) could be consumed with use. The anomaly signal emitted by the control means 17 could comprise, for example, a warning or alarm signal, in particular a signal on a user interface (for example a display) to indicate to an operator the need to perform maintenance of the adiabatic means (for example cleaning or replacing an evaporative body 10). The anomaly signal emitted by the control means 17 could include, for example, a control signal for controlling the evaporative liquid supply means, for example to interrupt the supplying, by closing the flow control valve 15.

[0051] It is possible to provide, in particular, that the control means 17 controls the supply means (flow control valve 15) so that the evaporative liquid flow rate to be introduced into the adiabatic means is as little as possible to maintain the temperature Tout of the process fluid equal to the desired value Tset. To this end, the control means 17 is configured in such a way that, if after a predetermined period of time DT (for example DT > 1 min., or DT > 5 min., or DT > 10 min., or DT >20 min.), the temperature Tout is still greater than or equal to Tset value, or to Tsup value (evaporator upper threshold), then the supply means (valve 15) is controlled to increase the evaporative liquid flow by another step.

[0052] This control action (gradual increase in flow rate, for example by one step at a time) is repeated if the temperature Tout remains above a predetermined value (for example Tset or Tsup), possibly until a maximum supply flow rate is reached (valve 15 full open). The number of adjustment steps of the evaporative liquid flow rate may be greater than 5, or greater than 4, or greater than 3, or greater than 2, or greater than 1.

[0053] If, during the adiabatic phase (in which evaporative liquid flow rate is nonzero), the process fluid temperature Tout drops below a predetermined value (for example the set point temperature Tset or a Tinf < Tset value), then it is possible to provide a decrease in ventilation V (slowing down of ventilation rotor(s)) down to a certain ventilation lower threshold value Vinf, so as to facilitate a precise control of process fluid temperature.

[0054] The control means 17 may be configured, in particular, so that, when the ventilation V reaches the (ventilation lower threshold) value Vinf and the process fluid temperature Tout, read by the sensor, drops below a predetermined value, for example below Tset or below the Tinf value (evaporator lower threshold), then the evaporative liquid supply means is controlled so as to gradually reduce (for example by one step) the evaporative liquid flow rate.

[0055] If, after a predetermined time period DT (equal for example to the aforementioned time period DT), the temperature Tout read by the temperature sensor still remains lower than a predetermined value (for example Tset, or Tinf = evaporator lower threshold), then the evaporative liquid supply means is controlled to further decrease (for example by another step) the evaporative liquid flow rate.

[0056] This control action (gradual reduction of the flow rate, for example by one step at a time) is repeated if the temperature Tout remains below a predetermined value (for example Tset, or Tinf), possibly down to zero supply flow rate (valve 15 full closed).

[0057] It is possible to provide that, in the active adiabatic mode, if the process fluid temperature Tout is lower than a predetermined value (for example Tset or Tinf), then the ventilation means 9 is slowed down to decrease ventilation V to lower threshold value Vinf. When the ventilation V reaches the lower threshold value Vinf, then the control means 17 stops slowing down and the ventilation V is kept constant at the value Vinf, while the evaporative liquid supply means is controlled to decrease the evaporative liquid flow rate. If Tout remains lower than a predetermined value (for example Tset or Tinf), then the evaporative liquid flow rate may be nullified (valve 15 full closed), thus ceasing the adiabatic mode. If Tout is still lower than the preset value (Tset or Tinf) even after the adiabatic mode has ceased (that is, with no evaporative liquid flow rate), then the control means 17 may further decrease the ventilation V below the minimum threshold value Vinf. [0058] The value of Tsup (evaporator upper threshold) may be, in particular, greater than the value of Tinf (evaporator lower threshold). It is however possible to provide that the value of Tsup is equal to the value of Tinf.

[0059] The value of Tsup (evaporator upper threshold) may be, in particular, greater than or equal to the set point value Tset. The value of Tinf (evaporator lower threshold) may be, in particular, less than or equal to the set point value Tset.

[0060] It is possible to provide, in specific examples, Tsup = Tset + 1 °C and Tinf = Tset - 1 °C, or Tsup = Tset and Tinf = Tset - 2 °C, or Tsup = Tset + 2 °C and Tinf = Tset, or Tsup = Tset + 2 °C and Tinf = Tset - 2 °C, or Tsup = Tset and Tinf = Tset - 4 °C, or Tsup = Tset + 4 °C and Tinf = Tset, etc.

[0061] As mentioned, the flow control valve 15 opens and closes with stepped movements, but it could also operate through an opening and closing system with fine adjustment, controlled for example by a feedback adjustment system, for example PID, or PI, or PD, or other adjustment systems.

[0062] Moreover, when the humidity value URint measured by the second sensor means 19 reaches a predetermined humidity value URtg (target value), then the control means 17 may be configured to control the evaporative liquid supply means so as to prevent the evaporative liquid flow rate from increasing, in particular so as to interrupt opening of the valve 15 (valve 15 blocked), so as not to waste evaporative liquid (water). [0063] Furthermore, if, during the adiabatic operation, the first sensor means 18 (ambient humidity sensor) measures a humidity URamb greater than the value of URtg, then the control means 17 may control the evaporative liquid supply means to interrupt, or in any case, not to dispense evaporative liquid (valve 15 closed), in order not to wet the adiabatic means (evaporative body(s) 10) if the surrounding environment is already sufficiently damp.

[0064] The heat exchange apparatus 1 may comprise, in particular, at least one discharge valve 20 which is controlled by the control means 17 so as to be open when the evaporative liquid flow rate is zero (flow control valve 15 closed) and, conversely, it is controlled to be closed when the evaporative liquid flow rate is non-zero (flow control valve 15 open). In this way, when the adiabatic mode is not used, pipes that supply the adiabatic means are discharged, since the evaporative liquid present in the pipes can be discharged (by falling) through the discharge valve 20, to avoid liquid stagnation and reduce risk of presence and formation of bacteria (such as the legionella bacterium).

[0065] In the heat exchange apparatus 1 , the evaporative liquid (water) used to wet the adiabatic means (evaporative body(s) 10) may be supplied, in particular, with a “lose” system, that is, it may not be provided recovering and recirculating the exhaust liquid, which is discharged and no longer reused, so as not to have to perform any treatment on the exhaust liquid. It is however possible to provide that the apparatus 1 is provided with an evaporative liquid recirculation system.

[0066] The control means 17 may be configured, in particular, to receive a lower limit of the cooling gas flow (the value of the cooling gas flow may be correlated, for example, to the value of the ventilation V, since the operation of the ventilation means is closely related to the cooling gas flow, thereby the aforementioned lower limit of the cooling gas flow could be, for example, the aforementioned Vinf value) and to control the ventilation means 9 and the evaporative liquid supply means based on the temperature Tout measured by the temperature sensor 16 so that, when the flow rate V of the cooling gas is higher than the aforementioned lower limit Vinf and the evaporative liquid flow rate is non-zero, if the measured temperature Tout is less than or equal to a predetermined minimum value (for example Tset or Tinf), then the cooling gas flow V is lowered, while the flow rate of the evaporative liquid supply is not lowered.

[0067] The control means 17 may be configured, in particular, to receive a lower limit Vinf of the cooling gas flow and to control the ventilation means 9 and the evaporative liquid supply means based on the temperature Tout measured by the temperature sensor 16 so that, when the cooling gas flow V is equal to the aforementioned lower limit Vinf and the flow rate of the evaporative liquid supply is non-zero, if the measured temperature Tout is less than or equal to a predetermined minimum value (for example Tset or Tinf), then the flow rate of the evaporative liquid supply is lowered, while the cooling gas flow V is not lowered.

[0068] The aforementioned lower limit Vinf may be, in particular, a value of the cooling gas flow V greater than zero, in particular a value greater than 50% of the maximum value of the cooling gas flow, that is, the value V corresponding to the maximum power of the ventilation means 9. The correlation between the cooling gas flow and the ventilation power may be determined, for example, empirically.

[0069] The control means 17 may be configured, in particular, to receive an upper limit of the cooling gas flow (the aforementioned upper limit of the cooling gas flow could be, for example, the above mentioned Vsup value) and to control the ventilation means 9 and the evaporative liquid supply means based on the temperature Tout measured by the temperature sensor 16 so that, when the cooling gas flow V is lower than the aforementioned upper limit Vsup, if the measured temperature Tout is greater than or equal to a predetermined maximum value (for example Tset or Tsup), then the cooling gas flow V is increased, while the liquid supply flow rate is not increased.

[0070] The control means 17 may be configured, in particular, to receive an upper limit Vsup of the cooling gas flow and to control the ventilation means 9 and the evaporative liquid supply means based on the temperature Tout measured by the sensor temperature 16 so that, when the cooling gas flow V reaches the aforementioned upper limit Vsup, if the measured temperature Tout is greater than or equal to a predetermined maximum value (for example Tset or Tsup), then the evaporative liquid flow rate is increased, while the cooling gas flow rate is not increased.

[0071] The control means 17 may be configured, in particular, to control the evaporative liquid supply means so as to increase the evaporative liquid flow rate if the measured temperature Tout is greater than or equal to a predetermined maximum value (for example Tset or Tsup) and/or so as to decrease the evaporative liquid flow rate if the measured temperature Tout is less than or equal to a predetermined minimum value (for example Tset or Tinf). [0072] The control means 17 may be configured, in particular, to receive the upper limit Vsup of the cooling gas flow (where the upper limit Vsup may be, in particular, lower than the maximum value of the flow which can be dispensed by the ventilation means 9 to its maximum power), and to increase the cooling gas flow V when it is verified that: the cooling gas flow V is equal to the upper limit Vsup; the evaporative liquid flow rate is equal to a maximum flow rate value dispensable by the supply means (for example valve 15 full open); the measured temperature Tout is greater than or equal to a predetermined value (for example Tset or Tsup).

[0073] The control means 17 may be configured, in particular, to increase the evaporative liquid flow rate, without increasing the cooling gas flow V, when it is verified that: the cooling gas flow V is equal to the upper limit Vsup (where, as already mentioned, the upper limit Vsup of the cooling gas flow is lower than the maximum value of the flow that can be dispensed by the ventilation means 9); the evaporative liquid flow rate is zero; the measured temperature Tout is greater than or equal to a predetermined value (for example Tset or Tsup). [0074] The control means 17 may be configured, in particular, to decrease the supplying of the evaporative liquid (for example, decreasing by a predetermined step, or by means of a PID or PI algorithm) when, for a predetermined period T (for example, T > 1 min., or T > 5 min., or T > 10 min.), it is verified that: the evaporative liquid flow rate is equal to a maximum flow rate value that can be delivered by the supply means 15; the cooling gas flow V is greater than or equal to the upper limit Vsup (where Vsup may be, as mentioned, lower than the maximum value that can be supplied by the ventilation means 9); and the temperature Tout measured by the temperature sensor 16 remains between a predetermined upper value (for example Tsup) and a predetermined lower value (for example Tinf). After another predetermined period of time T (for example T > 1 min., or T > 5 min., or T > 10 min.) from the aforementioned decrease in the evaporative liquid flow rate, the control means 17 may be configured, in particular, to check if the temperature Tout measured by the temperature sensor 16 remains between a predetermined upper value (for example Tsup) and a predetermined lower value (for example Tinf): if Tinf < Tout < Tsup, that means that, effectively, a certain saving of water has already been obtained, and possibly, and it is possible to provide reiterating the aforementioned action of reducing the evaporative liquid flow rate; if Tout > Tsup, then the supply means 15 is controlled so as to increase the flow rate of the evaporative liquid; if Tout < Tinf then the ventilation means 9 will be controlled so as to decrease the ventilation V.