Abstract:
The invention relates to a method for conditioning air by means of a ventilation system, in which in order to set a specified target air state characterized by air humidity and air temperature, air having an initial air state is cooled and optionally dehumidified with the aid of an air cooler ( 10 ), by a coolant supply apparatus assigned to the air cooler ( 10 ) for a coolant supplied to the air cooler ( 10 ) regulating both a coolant mass flux and a coolant inlet temperature in accordance with the initial air state and the specified target air state. Moreover, the invention relates to an apparatus for air conditioning is provided.

Description:
FIELD OF TECHNOLOGY 
       [0001]    The invention relates to a method and an apparatus for cooling and dehumidifying air. 
       BACKGROUND 
       [0002]    Ventilation systems for workplaces and meeting rooms are frequently used for maintaining not only the air quality of the room, but also the thermal comfort level. To this end these systems are typically equipped with system components such that admit at least three thermodynamic air treatment processes can be carried out: heating, cooling and dehumidification. The systems must be regulated and controlled in such a manner that both objectives (maintenance of the quality and thermal comfort level) are achieved, although widely varying thermal loads and airborne substances may be present in the room, and for the people present in the room a fresh-air mass flow necessary for reasons of hygiene must be maintained. 
         [0003]    The comfort range in air-conditioned workplaces is defined with respect to the temperature and the air humidity. Thus in the applicable standard of 2006, DIN EN ISO 7730, the operative temperature for the cooling mode for offices of Category B is specified in a range of 24.5° C.±1.5 K. For moisture content for the summer months DIN EN 13779 of 2007 proposes a range between 6 and 12 g/kg. 
         [0004]    For reasons of energy conservation and reduction in operating costs, the room air temperature and the relative humidity should be managed over the year according to a programme of target values, which specifies higher values for the room air temperature in summer and also higher values for the relative humidity than in winter. This tracked operation allows the seasonally determined cooling and moisture loads to be taken into account. 
         [0005]    The thermodynamics of the humid air is referred to as psychrometry. The air in this case represents a gas-vapour mixture, in which the term vapour refers to the component which can condense either as a liquid or a solid in the temperature and pressure range. The remaining components are grouped together to form the component group “Gas” and remain unchanged in terms of their quantity for the relevant temperature range. 
         [0006]    In the temperature and pressure range occurring in process and room ventilation engineering, moist air can be regarded as a mixture of ideal gases. Since at the given temperature non-arbitrary quantities of vapour mix with the non-condensing gas, three states are distinguished. In the unsaturated state, only the gas phase is present. The partial pressure of the vapour is less than the saturation pressure of the vapour in the mixture. In the saturated state the partial pressure of the vapour corresponds exactly to the saturation pressure of the vapour in the mixture. The gas phase and beginning condensate phase have the same temperature T (thermal equilibrium) and the same total pressure (mechanical equilibrium). In the oversaturated state the gas and condensate phase are present. In the gas phase the relationships of the saturated state apply. 
         [0007]    To represent the air states of moist air and the state changes, various diagrams are used. The best known diagrams are the Mollier diagram (Europe) and the Carrier diagram (America). In the case of Mollier the enthalpy (h 1+x ) of the mixture is chosen as the ordinate and the moisture content x as the abscissa. The enthalpy depends linearly on the temperature both for the unsaturated region and for the oversaturated region.  FIG. 1  shows a schematic representation of a simplified Mollier diagram for a given total pressure. 
         [0008]    The cooling and the dehumidification of the air in central ventilation systems is effected typically by means of air coolers which are permeated by a coolant. The power is regulated either on the air side or coolant side by means of a suitable hydraulic circuit. In the case of hydraulic power regulation, this is typically implemented by variation of the coolant flow at constant coolant feed temperature (quantity-regulated cooling). Less frequently, a regulation option known from heating engineering is used, in which the coolant feed temperature is regulated by means of intermixing with the coolant return (mixture-regulated cooling). 
         [0009]    This results in two different hydraulic circuits for the hydraulic regulation of the cooling power, which also induce different changes of state in the air during the permeation of the heat exchanger (air cooler). One of these is a system in which the air cooler is provided with a quantity regulation system. At a constant coolant feed temperature the quantity of coolant supplied to the air cooler is regulated. Alternatively, systems are known in which the air cooler is provided by mixture regulation. In this case the feed temperature of the coolant fed into the air cooler is regulated. 
         [0010]    In a quantity-regulated air cooler, for a water vapour loading above a threshold which is dependent on the feed temperature of the coolant among other things, a dehumidification always takes place in the cooling mode, since the coolant feed temperature, regardless of the cooling load of the building, can be assumed to be constant (cf.  FIG. 2 , line  1 - 4 ). Consequently the surface temperature of the air cooler at the coolant intake is close to the feed temperature of the cold water provided by the cooling unit. Typically this feed temperature is approximately 6° C. in conventional systems. The end point of the change of state of the mixed partial currents of the air lies theoretically on the connecting line between the state point of the air flow upstream of the cooler (point  1  in  FIG. 2 ) and the effective surface temperature of the air cooler (point t O,eff  in  FIG. 2 ). For a given cooler construction the gradient of the state change in the Mollier diagram for each initial point of the moist air therefore depends only on the initial point itself and on the effective surface temperature of the air cooler (point t O,eff  in  FIG. 2 ). 
         [0011]    In this known circuit type two operating modes can be differentiated. Either, the desired level of the dehumidification determines the air output temperature from the air cooler, or the cooling required determines the dehumidification level of the air. The desired end point for temperature and humidity cannot therefore be set with absolute precision with the air cooler alone. In order to obtain a specific air state, the air flow downstream of the air cooler must therefore either be heated (dehumidification determines the cooling), or the air flow must be humidified (cooling determines the dehumidification). 
         [0012]    With a mixture-regulated air cooler an air flow is fully cooled without dehumidification, if the inlet temperature of the coolant medium into the air cooler does not fall below the dew-point temperature of the moist air (cf.  FIG. 2 , line  1 - 2 ). Only when the coolant feed temperature is below the dew-point temperature of the moist air, due to restriction of the coolant return mixture, does condensation of water vapour occur, that is to say, dehumidification for a partial flow of air, (cf.  FIG. 2 , line  2 - 3 ). 
         [0013]    In idealised terms, the result is that with permanent coolant mass flow the entire mass flow of air must be cooled as far as the dew-point, before the dehumidification process can begin at all. According to this conception, if water vapour condenses out of the mass flow of air, then the entire quantity of air must be cooled to the dew-point of the desired moisture content, which typically results in an under-cooling of the air mass flow and is consequently unfavourable from an energy point of view (cf.  FIG. 2 , points  3  and  4 ). The necessary heating of the super-cooled air mass flow requires additional energy, which means the cost-effectiveness of a mixture-regulated cooler is further degraded. 
         [0014]    To regulate the power of the air cooler each of the two known circuits changes exactly one variable of the coolant flow. In the quantity-regulated circuit it is the mass flow (the quantity) that is regulated. In the mixture-regulated circuit the coolant feed temperature is regulated according to the power requirements. To achieve a desired air state with regard to temperature and water vapour content, both known circuits have advantages and disadvantages. In the case of the quantity-regulated air cooler, either post-heating of the air flow or humidification of the air may be necessary, depending on the air state desired. In the case of a mixture-regulated air cooler, in dehumidification mode deeper cooling is almost always needed than is required by the cooling load. The operation of a post-heater is therefore absolutely necessary, in order to obtain the desired air state. 
       SUMMARY 
       [0015]    The object of the invention is to specify a method and an apparatus for cooling and dehumidifying air by means of a ventilation system, which enables an accurate and energy efficient setting of a target air state characterized by air humidity and air temperature. 
         [0016]    This object is achieved according to the invention by a method for cooling and dehumidifying air according to the independent Claim  1  and an apparatus for air conditioning according to the independent claim  7 . Advantageous configurations of the invention are the subject matter of dependent claims. 
         [0017]    According to one aspect of the invention, a method for cooling and dehumidifying air is created by means of a ventilation system, in which in order to set a specified target air state characterized by air humidity and air temperature, air having an initial air state is cooled and optionally dehumidified with the aid of an air cooler, by a coolant supply apparatus assigned to the air cooler for a coolant supplied to the air cooler regulating both a coolant mass flow and a coolant inlet temperature in accordance with the initial air state and the specified target air state. 
         [0018]    According to a further aspect of the invention, an apparatus for cooling and dehumidifying air is created, which comprises the following features: an air cooler which is configured, in order to set a specified target air state characterized by air humidity and air temperature, to cool and optionally dehumidify air with an initial air state, and a coolant supply apparatus connected to the air cooler for a coolant to be supplied to the air cooler, which is configured to regulate both a coolant mass flow and a coolant inlet temperature in accordance with the initial air state and the specified target air state. 
         [0019]    With the aid of the proposed techniques, air conditioning, in particular room air conditioning, is achieved. 
         [0020]    Air coolers with conventional hydraulic circuits, when in cooling mode, are only capable of setting desired air states in a limited manner Known quantity-regulated air coolers are energy-inefficient when the desired cooling performance leads to an unnecessarily high dehumidification performance. By contrast, mixture-regulated air coolers always waste cooling energy when, in addition to pure cooling performance, dehumidification becomes necessary. With the invention, these disadvantages are now overcome. In the proposed method and in the apparatus, a precise regulation of air cooling and dehumidification is performed in a combined manner in the coolant supply apparatus. Both the quantity and the inlet temperature of the coolant for the air cooler are regulated in the coolant supply apparatus. This facilitates a precise setting of a desired target air state in an energy-efficient manner. 
         [0021]    A preferred embodiment of the invention provides that the regulation of the coolant mass flow and of the coolant inlet temperature is carried out with the aid of a hydraulic circuit of the coolant supply apparatus. 
         [0022]    In an advantageous embodiment of the invention the regulation of the coolant mass flow and the coolant inlet temperature is carried out with the aid of an integrated regulator circuit forming part of the coolant supply apparatus, in which a mixture-regulated circuit is formed with a feed-quantity regulated pumping apparatus. In this embodiment an integrated regulator circuit is formed which represents an integration of the mixture-regulated circuit and the quantity-regulated circuit. The coolant supplied to the air cooler is determined by the feed-quantity regulated pump with regard to the quantity (coolant mass flow) and by the coolant return mixture with regard to temperature. 
         [0023]    An advantageous embodiment of the invention provides that the regulation of the coolant mass flow and the coolant inlet temperature is carried out using a series connection of a mixture-regulated and a quantity-regulated circuit which forms part of the coolant supply apparatus. It can be provided that the coolant supply apparatus consists only of the mixture-regulated and the quantity-regulated circuit. 
         [0024]    In one embodiment of the invention it can be provided that the regulation of the coolant mass flow and the coolant inlet temperature is carried out with the aid of an integrated regulator circuit forming part of the coolant supply apparatus, in which a pump device with constant feed pressure and a valve regulation device are formed. 
         [0025]    A preferred embodiment of the invention provides that the regulation of the coolant mass flow and the coolant inlet temperature is carried out with the aid of an integrated regulator circuit forming part of the coolant supply apparatus, in which a pump device with constant rotation rate and a bypass device is formed. The bypass device preferably comprises a regulated bypass. 
     
    
     
       BRIEF DESCRIPTION 
         [0026]    The invention is described in detail in the following by way of preferred embodiments with reference to the figures. The figures show: 
           [0027]      FIG. 1  a schematic view of a known Mollier diagram for a specified total pressure, 
           [0028]      FIG. 2  a schematic view of the known change of state from moist air when cooling occurs, 
           [0029]      FIG. 3  a schematic view of an apparatus for cooling and dehumidifying air, having an integrated hydraulic circuit consisting of a mixture-regulated circuit with a pump device that is directly feed-quantity regulated, 
           [0030]      FIG. 4  a schematic view of an apparatus for cooling and dehumidifying air, having an integrated hydraulic circuit consisting of a mixture-regulated circuit with a pump device that is indirectly feed-quantity regulated, 
           [0031]      FIG. 5  a schematic view of an apparatus for cooling and dehumidifying air having an integrated hydraulic circuit consisting of a mixture-regulated circuit with an unregulated pump device with regulated bypass, 
           [0032]      FIG. 6  a schematic view of an apparatus for cooling and dehumidifying air having an integrated hydraulic circuit consisting of a series circuit composed of a mixture-regulated circuit with an unregulated pump device and a quantity-regulated circuit, 
           [0033]      FIG. 7  Symbols for elements of the system diagram in  FIG. 3 to 6  and  FIG. 8   
           [0034]      FIG. 8  a simplified system diagram of an air-only system with waste heat recovery and a circulating air path, wherein a humidification process takes place by means of a vapour humidifier, 
           [0035]      FIG. 9  a schematic view of a regulation strategy for the apparatuses for cooling and dehumidifying air in  FIGS. 3 to 6  in the simplified Mollier diagram, 
           [0036]      FIG. 10  a simplified regulation scheme for the hydraulic circuit according to  FIG. 3   
           [0037]      FIG. 11  another simplified regulation scheme for the hydraulic circuit according to  FIG. 3   
           [0038]      FIG. 12  another simplified regulation scheme for the hydraulic circuit according to  FIG. 3   
           [0039]      FIG. 13  another simplified regulation scheme for the hydraulic circuit according to  FIG. 3 , and 
           [0040]      FIG. 14  another simplified regulation scheme for the hydraulic circuit according to  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0041]      FIG. 3  shows a schematic view of an apparatus for conditioning air (cooling and dehumidification) having an integrated regulator circuit, in which a feed-quantity regulated pump device is integrated into a mixture-regulated circuit. The integrated circuit is embodied in the exemplary embodiment shown as a hydraulic circuit, which can also be referred to as an “Optimized Dehumidification Control Loop” (OpDeCoLo), which enables the accurate setting of a target air state characterized by air humidity and air temperature with the aid of a liquid-cooled air cooler with the least possible energy input (cooling and pumping energy). 
         [0042]    In the apparatus in  FIG. 3  a coolant supply apparatus  11 , which is formed with a mixing valve  12  and a rotation-speed regulated pump  13 , is coupled to an air cooler  10 . The mixing valve  12  connects a cold water feed  14  provided by a cooling unit (not shown) with the intermixture of a coolant return  15  to the coolant feed  16  to be fed into the air cooler  10  at the desired temperature and quantity. The state of the air emerging from the air cooler  10  is recorded by means of a temperature measuring device  17  and an air humidity measuring device  18 . 
         [0043]    The circuit in  FIG. 3  corresponds to the mixture-regulated circuit, but in which instead of a pump with constant feed quantity, the rotation-speed regulated pump  13  is installed. The mixing valve  12 , which defines three paths, is fitted with an actuator  19 . 
         [0044]    The rotation speed regulation of the rotation-speed regulated pump  13  (cf.  FIG. 3 ) can be effected with the aid of a frequency converter (not shown). In the case where dry cooling is desired, the air cooler  10  and the coolant mass flow are designed such that the cooling power is delivered at a coolant inlet temperature above the respective dew-point of the moist air. In many cases this requires a larger air cooler than in the case of a quantity-regulated hydraulic circuit or a mixture-regulated circuit with wet cooling. 
         [0045]    Alternatively to this, either a pump  40  with constant feed pressure together with a regulated straight-way valve  41  (cf.  FIG. 4 ) or a pump  50  with constant rotation rate with a bypass  51  (cf.  FIG. 5 ) can be provided, which is preferably regulated. Expressed in very simplified terms the dehumidification of the air is specified by the selection of the cold water inlet temperature, while the cooling power is specified by means of the coolant mass flow. The respective total cooling power delivered by the cooling and dehumidification of the air cooler  10  is therefore given as a combination of the coolant mass flow and coolant inlet temperature. 
         [0046]    With the proposed circuits, state changes can be achieved which can also be implemented in a different embodiment with a series circuit formed from a quantity-regulated and a mixture-regulated circuit element (cf.  FIG. 6 ), but with markedly reduced energy expenditure.  FIG. 6  shows a schematic representation of an apparatus for conditioning air (cooling and dehumidification) having an integrated regulator circuit, consisting of a series circuit formed of a mixture-regulated circuit  60  with a non-feed quantity regulated pumping device  61  and a quantity-regulated circuit  62 . In  FIG. 6  equivalent features are assigned the sane reference labels as in  FIGS. 3 to 5 . 
         [0047]    From an energy point of view the quantity-regulated air cooler when dehumidification is required is very much more efficient than the mixture-regulated air cooler. The economy potential of the air conditioning apparatus according to  FIGS. 3 to 6  relative to the known quantity-regulated air cooler is obtained in particular for the following cases:
       For all initial air states which require cooling and of which the moisture content is less than the maximum moisture content in the target state, for example for reasons of comfort, and the dew-point of which is above the coolant inlet temperature of a conventional quantity-regulated hydraulic circuit. Precisely in this area, in which for reasons of comfort no dehumidification is required, a mixture-regulated air cooler would be more favourable from an energy point of view than a quantity-regulated air cooler.   For initial air states, the moisture content of which is above the maximum air humidity in the target air state. Here the difference between the moisture content of the initial air state and the maximally permitted moisture content and the temperature of the target area are key factors in determining the potential for economies. In the case of the quantity-regulated circuit, initial air states with high air temperature but low dehumidification load typically lead to an excessive dehumidification.       
 
         [0050]    By contrast, initial states with high moisture content but where there is only a small temperature difference relative to the target area, lead to an under-cooling of the air mass flow with all hydraulic circuits, which needs to be compensated by post-heating. 
         [0051]    Below, the effects of the hydraulic circuit of the air cooler on the specific cooling energy demand are examined for a ventilation system. 
         [0052]    For the comparison an air-only system (cf.  FIG. 8 ) with recuperative waste heat recovery and air recirculation controller (Economizer Mode) was chosen. The economy potential of the air conditioning apparatus according to  FIG. 3  is related both to the mixture-regulated and the quantity-regulated air cooler. For simplicity, any energy requirements appropriate to post-heating or humidification are not considered in this comparison, a fact which reduces the calculated potential economy relative to the actual case. 
         [0053]    A air-only system with regenerative waste heat recovery (WRG) and a recirculated air valve controller corresponds to the state of the art for ventilation systems which have to dissipate high thermal loads under conditions of varying levels of human occupancy. For this comparison a combined heat-/cooling recovery system was chosen for the heat recovery, which can be easily bypassed as required by switching off the pump and furthermore offers the facility to guide the external air flow and outgoing air flow in a spatially separate manner Available systems are frequently retrofitted with such systems. 
         [0000]    
       
         
               
             
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Boundary conditions for determining the energy required for air 
               
               
                 cooling according to the hydraulic circuit of the air cooler. 
               
             
          
           
               
                 Identifier 
                 Value 
               
               
                   
               
               
                 Room air temperature 
                 25° C. 
               
               
                 Room air loading 
                 1 g/kg above outside air 
               
               
                 Air heating by ventilators 
                 1K in each case 
               
               
                 Air temperature after air cooler (target) 
                 18° C. 
               
               
                 Loading after cooler (target) 
                 6 to 10 g/kg 
               
               
                 Recovered heat figure WRG 
                 0.5 
               
               
                 Recirculated air proportion 
                 0 or 50% 
               
               
                 Coolant feed temperature 
                 6° C. 
               
               
                 Coolant return temperature 
                 12° C. 
               
               
                   
               
             
          
         
       
     
         [0054]    The ventilation system is to be operated such that in summer the WRG is only active when the temperature of the outside air (ODA) exceeds that of the outgoing air (EHA). The pre-treated outside air (PODA) after the WRG is then intermixed with recirculated air (RCA) in the mixing chamber only when the recirculated air has a lower temperature than the pre-treated outside air flow (PODA). The moisture content of the recirculated air has been assumed to be in each case 1 g/kg higher than that of the outside air, on account of sources of moisture in the room. The boundary conditions of the comparison are set out in Table 1. 
         [0055]    The intermixture of recirculated air reduces not only the temperature reduction to be provided by the air cooler, but also decreases the difference between the moisture content of the outside air and the target value after the air cooler. 
         [0056]    The calculation of the air states that apply after the air cooler is based on simplified methods. For the mixture-regulated air cooler, it was assumed that the cooling process takes place until the dew-point temperature is reached without condensate being produced. In the case of additional cooling the change of state follows the saturation line. In the case of the quantity-regulated air cooler it was assumed that the change of state in each case lies on a straight line between the initial point and a temperature proportional to the effective surface temperature of the cooler t O,eff . The air-conditioning apparatus according to  FIG. 3  creates a combination of both types of circuit, wherein in the boundary region either a mixture-regulated or a quantity-regulated cooler is present. 
         [0057]      FIG. 7  shows symbols for elements of the system diagram in  FIGS. 3 to 6  and  FIG. 8 . Here an air-only system with heat recovery and recirculated air path is shown in simplified form, wherein a humidification process takes place by means of a vapour humidifier. 
         [0058]    Although  FIG. 8  shows a complete air-only system, the estimation of the energy economising potential only includes the cooling energy demand (air cooling and dehumidification). Neither post-heating nor humidification power is taken into account in this comparison. Also not considered were the energy costs for operating the pumps. Here also the hydraulic circuit shown in  FIG. 3  performs better than the two base circuits and the circuits of  FIGS. 4 to 6 . 
         [0059]    For the present system type the cooling energy demand for three hydraulic circuits was examined for different German climates. For this purpose, statistical weather data from 2003 according to DIN 4710 was chosen for the outside air values and the annual specific cooling energy demands were compared with one another. The results for Mannheim are summarised below (cf. Table 2). 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Specific annual cooling energy demand for an air 
               
               
                 mass flow of 1 kg/h for climate data for Mannheim 
               
             
          
           
               
                   
                 Annual cooling energy demand n terms of the 
               
               
                 Daily operating 
                 mixture-regulated cooler in % 
               
             
          
           
               
                 time of the 
                 mixture-regulated 
                 quantity-regulated 
                   
               
               
                 A/C system 
                 cooler 
                 cooler 
                 OpDeCoLo 
               
               
                   
               
               
                 24 h 
                 100 
                 96 
                 90 
               
               
                 (0 to 24 hours) 
               
               
                 12 h 
                 100 
                 98 
                 90 
               
               
                 (6 to 18 hours) 
               
               
                   
               
             
          
         
       
     
         [0060]    Under the assumptions made for the boundary conditions the superiority of the OpDeCoLo relative to the conventional circuits is clearly shown, because dehumidification is only used when this is really necessary for reasons of comfort. 
         [0061]    To realise the savings potential, with regard to hardware in one of the embodiments described above a rotation-speed regulated pump is used. The design of an associated regulation technique which not only adjusts the coolant mass flow or the coolant inlet temperature, but also the respective optimum composed of the coolant inlet temperature and coolant mass flow, is described below. The rotation speed regulation of the pump can be effected either by a frequency converter (cf.  FIG. 3 ) or, as shown in  FIG. 4 , by varying the flow resistance with the aid of a valve. The hydraulic circuits of  FIG. 5  and  FIG. 6  with unregulated pump devices are also capable of achieving the cooling energy economy according to Table 2, but are characterized by higher pumping energy costs. 
         [0062]      FIG. 9  shows a schematic representation of a regulation strategy for the previously described air coolers in a simplified Mollier diagram. Unlike in conventional regulator circuits of air coolers, in the circuits proposed here both the coolant quantity and also their inlet temperature are always regulated. 
         [0063]    Below, the regulation design is described in more detail. 
         [0064]    In the case of cooling without dehumidification the surface temperature of the cooler must not at any point be equal or below the dew-point temperature of the moist air to be cooled. Therefore, in this case the feed temperature of the coolant fluid for the air cooler must not fall below the dew-point temperature of the moist air. Since the cooling power depends on the mean surface temperature of the air cooler, the air cannot be cooled down as far as the saturation line. Therefore the air cooler in this case is operated at a higher pump rotation rate, wherein the power matching is effected by varying the coolant return mixture. 
         [0065]    With regards to the coolant it follows that: 
         [0000]        {dot over (Q)}   cooling   ={dot over (m)}   coolant   *c   p     Kühlmittel   *( t   return   −t   flow )  (1)
 
         [0000]    with
   {dot over (Q)} cooling  cooling power of the air cooler [W]   {dot over (m)} coolant  coolant mass flow [kg/s]   c pcoolant  specific heat capacity of the coolant [kJ/(kg*K)]   (t return −t flow ) Temperature difference of the coolant upstream and downstream of the air cooler [K]
 
and t flow ≧t dew-point  
   
 
         [0070]    With regards to the air the cooling power is determined according to equation (3), making use of equation (2): 
         [0000]      Δ h   cooling =( x   1 *( r   0   +c   p     D     *t   1 )+ c   p     L     *t   1 )−( x   LK *( r   0   +c   p     D     *t   LK )+ c   p     L     *t   LK )  (2)
 
         [0000]    with
   r 0  latent heat of water at 0° C. [kJ/kg]   c pD  specific heat capacity of the water vapour [kJ/(kg*K)]   c pL  specific heat capacity of the dry air [kJ/(kg*K)]   
 
         [0000]        {dot over (Q)}   cooling   ={dot over (m)}   air   *Δh   cooling   (3)
 
         [0000]    with
   {dot over (m)} air  air mass flow [kg/s]   Δh cooling  Enthalpy difference; here at constant moisture content of the air [kJ/kg]   
 
         [0076]    In the case of cooling with dehumidification, as well as the air outlet temperature from the cooler the water vapour content of the air is also regulated. To do so, both the pump rotation speed and the coolant return mixture are modified such that the target point of the air at the cooler outlet is achieved. The feed mass flow (pump rotation rate) takes over the quantity regulation and the coolant inlet temperature (coolant return mixture) the mixture regulation. Expressed very simply, the pumping mass flow at constant coolant temperature determines the gradient of the change of state in the Mollier diagram; at constant pumping flow the coolant inlet temperature determines the sensible cooling power. However, the two parameters are not independent of each other, since due to the influence on the coolant return temperature when the coolant inlet temperature and the pumping mass flow changes, the effective surface temperature changes—which has an effect both on the sensible cooling power and the dehumidification of the air flow. For a specified outlet air state there is exactly one combination of pumping mass flow and coolant inlet temperature corresponding to the initial state. 
         [0077]      FIGS. 10 to 14  show simplified regulation schemata for the hydraulic circuit according to  FIG. 3 . The letters “R” and “N” refer to a return mixture and a pump rotation rate regulation. Arrows indicated in connection with these control variables show a regulation towards an increase (arrow upwards) or towards a decrease (arrow downwards) of the respective variable. The variables T target  and T actual  refer to a target and an actual temperature of the cooled/de-humidified air. In the same way X target  and X actual  refer to a target and an actual air humidity. The numbers “11”, “21”, . . . are used for reference among the regulation schemata in  FIGS. 10 to 14 . 
         [0078]    The features of the invention disclosed in the present description, claims and the figures can be of significance both individually and in any desired combination for the implementation of the invention in its various embodiments.