Abstract:
Methods and apparatus for controlling a climate control system for an enclosure, including a controller for operating a cooling system and a humidification system. The cooling system is operated to maintain the temperature of the air within the enclosure at a specified value, and the humidification system is operated to maintain the humidity of the air within the enclosure at a specified value. Provisions are made to help ensure that the humidification system does not provide water to the air during periods when the minimum value of the temperature of the air provided by the cooling system is below the dew point temperature of the air.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to methods and devices for controlling a climate control system for an enclosure. More particularly, the present invention relates to methods and devices for operating a cooling system and a humidifier for cooling and humidifying the air that is provided to the enclosure. 
   BACKGROUND OF THE INVENTION 
   Conventional thermostats control the operation of cooling systems in response to an increase or decrease in the temperature of the air within an enclosure. Typically, the occupant of the enclosure specifies a temperature set point that the thermostat attempts to maintain by operating the climate control system. During the cooling mode of operation, the thermostat activates the cooling system when the temperature of the air within the enclosure rises above the occupant specified temperature set point, and de-activates, or suppresses, the cooling system when the temperature of the air within the enclosure falls below the occupant specified temperature set point. 
   In moderate moist climate regions, the cooling system often includes one or more cooling coils for cooling the air that is provided to the enclosure. A compressor is typically used to provide refrigerant to the coils when cooling is desired. A humidifier, if present, is typically not used during the cooling season. 
   In hot and arid climatic regions, the cooling system often include a cooler as described above, or an air washer or “swamp cooler” for cooling and humidifying the air within the enclosure. In an air washer system, the warm and often dry air is passed through a chamber having one or more banks of spray nozzles, a sump, an externally mounted pump, and one or more staggered metal baffles at the chamber&#39;s exit. When the thermostat within the enclosure indicates a need for cooling, water is withdrawn from the sump by the external pump and sprayed into the chamber in fine droplets. Air withdrawn from the enclosure and/or from the external environment is blown through the chamber and thereby exposed to the water spray therein. The warm air flowing through the chamber is subjected to evaporative cooling and some humidification. The one or more staggered metal baffles, often called “eliminator plates”, at the exit of the chamber help minimize physical carry-over of water droplets with the air steam. In an air washer system, there is typically no provision for controlling the amount of water that&#39;s added to the air stream. Other cooling systems are also commonly used. 
   One disadvantage of many cooling systems is that if too much water is added to the system, condensation of the water may occur within the ductwork of the system and/or within the enclosure itself. If insufficient water is added to the system, the air within the enclosure can become too dry. The presence of too much or too little moisture can encourage growth of mold and mildew, cause health problems, and/or in some cases, damage the structure, furnishings and other contents of the enclosure. 
   SUMMARY OF THE INVENTION 
   The present invention provides methods and devices for cooling and humidifying the air within the enclosure. In one illustrative embodiment of the present invention, an air stream is passed through a cooling system, a humidifier, and ultimately to the enclosure. The cooling system is used to cool the air that is provided to the enclosure, and the humidifier is used to add water to the air that is provided to the enclosure. To help control the amount of water that is added to the air, and in one illustrative embodiment, a measure of the dew point temperature and a measure of the temperature of the air may be determined. If the temperature of the air is below the dew point temperature, the humidifier may be suppressed. If, however, the temperature of the air is above the dew point temperature, the humidifier may not be suppressed. In some cases, the humidification may be suppressed when the cooling system is activated, and not suppressed after the cooling system is deactivated. 
   In some embodiments of the present invention, the climate control system may include provisions for fan over-run whereby the indoor air circulation fan is permitted to continue operating for a duration of time after de-activating the cooling system and before activating the humidifier. In such an embodiment, the air stream through the cooling system may continue to be cooled by cooling energy stored within the thermal mass of the cooling system. The air stream may also be evaporatively cooled by water condensate on the one or more cooling coils, and any residual condensate in the coil drip pans, if present. The humidifier may then be activated if a need for humidification is indicated, and if the temperature of the air stream exiting the last of the one or more cooling coils during a cooling cycle is greater than the dew-point temperature of the air. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates an enclosure climate control system of the present invention; 
       FIG. 2  is an overview of the cooling and humidification process; 
       FIG. 3  illustrates the next level of detail for the process of  FIG. 2 ; 
       FIG. 4  is a flowchart for one embodiment of the present invention; 
       FIG. 5  illustrates the process for another embodiment of the present invention; 
       FIG. 6  is a flowchart for yet another embodiment of the present invention; and 
       FIG. 7  illustrates the process for yet another embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The following detailed description should be read with reference to the drawings, in which like elements in different drawings are numbered in like fashion. The drawings, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention. Those skilled in the art will recognize that many of the examples provided may have suitable alternatives that could be utilized without departing from the spirit of the present invention. 
     FIG. 1  illustrates one illustrative embodiment of the present invention as implemented in a controller  25  of a climate control system for an enclosure  12  in a hot and arid climatic region. Enclosure  12  receives conditioned air from a conventional air conditioning unit  19  and a conventional humidification unit  22  through ductwork  69 . 
   Air conditioning unit  19  operates on externally supplied AC power provided on conductors  42  to control element  23 . Control element  23  switches power to compressor  17  and blower  20  on conductors  38  and  39  respectively, thereby providing sequencing as needed for their operation. Compressor  17  provides liquid coolant to evaporator (or cooling coil)  18  located within plenum  21  along with blower  20  and humidifier  58 . Cooling coil  18  may include one or more evaporators, although only one cooling coil is shown for illustration purposes. Air conditioning unit  19  operates while a demand signal is present on path  26 . The demand signal on path  26  closes switch  29 , allowing control current supplied by a 24 VAC source on path  40  to flow to the air conditioning unit controller  23  on path  41 . 
   Humidification unit  22  operates on power provided on path  64 . Humidifier  58  is shown located in plenum  21  and operates to humidify the air passing through plenum  21  to duct  69 . Control element  54  switches power to humidifier  58  on conductor  56 , thereby providing sequencing as needed for operating humidifier  58 . Humidifier  58  may include, and is not limited to one or more of the following: steam, water spray, pad, drip mesh, etc. Humidifier  58  operates when a demand signal is present on path  60 . The demand signal on path  60  closes switch  62 , allowing control current supplied by a 24 VAC source on path  66  to flow to humidifier controller  54  on path  64 . 
   While air conditioning unit  19  is operating, fan  20  first forces air  10  across cooling coil  18  to cool, and dehumidify air  10  (if it contains excess water), and then across humidifier  58  to add water to air  10  if and as needed as directed by the presence or absence of a demand signal on path  60 . Air  10  may include re-circulation air drawn from enclosure  12 , and/or air drawn from the external environment interacting with enclosure  12 , and/or a combination of re-circulation air and air from the external environment. The conditioned air then flows into enclosure  12  through duct  69  to maintain both the desired temperature and humidity of the air within enclosure  12 . 
   The demand signals on paths  26  and  60  are provided by controller  25 . Controller  25  will typically be attached to a wall of enclosure  12  in the manner done for conventional thermostats. Controller  25  may include memory  27  which can store digital data, and processor  28  which can perform computation and comparison operations on data supplied to it from both memory  27  and from external sources. Processor  28  also includes an instruction memory element. In one embodiment, a conventional micro-controller may be used to function as memory  27  and processor  28 . 
   Controller  25  further includes sensor  14 , located within enclosure  12 , which provides a dew-point temperature signal on path  30  encoding the dew-point temperature of the air within enclosure  12 , but alternatively may encode the wet-bulb temperature or the relative humidity of the air within enclosure  12 . Temperature sensor  15 , also located within enclosure  12 , encodes a dry-bulb temperature value in an air temperature signal on path  31 . In one embodiment of the present invention, sensor  52 , located within plenum  21  and between humidifier  58  and the last of the one or more cooling coil  18 , may encode on path  16 , a dry-bulb temperature value of the air entering humidifier  58 . In an alternate embodiment, sensor  52  may encode on path  16 , a dew-point temperature value of the air entering humidifier  58 . In another embodiment, sensor  52  may encode on path  16 , a signal representing the presence or absence of water condensate on the one or more cooling coils  18  and/or the presence or absence of water condensate in the drip pans of the one or more cooling coils  18 . In the illustrative embodiment, processor  28  receives these temperature signals and converts them to digital values for internal operations. 
   Paths  33  and  35  carry signals to memory  27  encoding various set point values. Typically the signals on paths  33  and  35  are provided by the person responsible for controlling the climate of enclosure  12 . The set point values may be selected by simply shifting control levers or dials on the exterior of controller  25 . The values may also be selected by a keypad which provides digital values for the set points in the signals on paths  33  and  35 . Path  33  carries a dew-point temperature signal encoding a dew-point temperature set point value representative of the desired dew-point temperature within enclosure  12 . This dew-point temperature set point value may be the actual desired dew-point temperature, or the desired relative humidity, or the desired wet-bulb temperature. Path  35  carries a signal encoding an air (dry-bulb) temperature set point value. Memory  27  records these set point values, and encodes them in set point signals carried to processor  28  on a path  36 . If memory  27  and processor  28  are formed of a conventional microcontroller, the procedures by which these set point values are provided to processor  28 , when needed, are included in further circuitry not shown which provides a conventional control function for the overall operation of such a microcontroller. In some cases, processor unit  28  has internal to it, a read-only memory (ROM) in which a sequence of control instructions are stored and executed by processor unit  28 . 
   Turning now to  FIGS. 2 through 7 , top level overviews and different embodiments of the overall cooling and humidification process are illustrated. It should be noted that the steps for the humidification process are in addition to the temperature control algorithms in a conventional thermostat.  FIG. 2  is a high level overview of the cooling and humidification process. From the conventional thermostat, the operating status of the cooling system is provided in block  200 . The operating status, i.e., “on” or “off”, is next checked in decision block  202 . If the cooling system is “on”, then humidification of the air stream is suppressed as shown in block  204 , and the process control is passed back to decision block  202  for determining the operating status of the cooling system. If, however, the cooling system is “off”, then the humidification system may be enabled in block  206 , and process control is transferred to decision block  202  as described above. 
     FIG. 3  adds additional steps to the process of FIG.  2 . As shown in  FIG. 3 , if decision block  202  indicates that the cooling system is “off”, then the sensed dew-point temperature of the air, T DP,SEN , and the minimum temperature of the air exiting the last of one or more cooling coils of the cooling system, T DIS , are provided as inputs ( 210 ) to the control algorithms. In one embodiment of the present invention, T DIS  may be the minimum temperature of the air from the current or the most recently concluded cooling cycle. In an alternate embodiment of the present invention, T DIS  may be the minimum temperature of the air over a predefined duration of time, for example, 2 hours, 12 hours, or 24 hours. The values of T DP,SEN  and T DIS  are then compared in decision block  208 . If T DIS  is less than T DP,SEN , then the air stream can not be humidified since any addition of water to the air stream will result in condensate on the one or more cooling coils during the subsequent cooling cycle, thereby removing the moisture added by the humidifier. If T DIS  is greater than T DP,SEN , then water may be added to the air stream by enabling the humidifier ( 206 ). Thus, T DIS  effectively becomes the upper limit of the dew point temperature within the space, even if T DIS  is less than the dew-point temperature set-point, T DP,SET . 
     FIG. 4  illustrates the process for one embodiment of the present invention. If decision block  202  indicates that the cooling system is “off”, then the sensed dew-point temperature of the air, T DP,SEN , and the dew-point temperature set-point for the air within the enclosure, T DP,SET , are provided as inputs from block  212 . Next, decision block  214  compares the values of T DP,SEN  and T DP,SET . If T DP,SEN  is greater than T DP,SET , then humidification may be suppressed ( 204 ). If T DP,SEN  is not greater than T DP,SET , then any cooling energy stored within the thermal mass of the one or more cooling coils of the cooling system may be extracted by “fan over-run” ( 216 ), i.e., continuing running fan  20  for a period of time after the cooling system is turned “off”. The duration of fan over-run may be for a pre-specified period of time, or may be a function of the temperature of air  10  and the discharge air temperature T DIS , or any other suitable method. At the end of fan over-run, water may be added to the air stream by enabling humidification ( 206 ) by continuing operating fan  20 . It should be noted that fan over-run, in addition to extracting cooling energy stored within the thermal mass of the one or more coils, may extract cooling energy stored within the thermal mass of the ductwork. Furthermore, fan over-run may evaporatively cool and humidify the air steam with any residual water condensate on the one or more cooling coils and their drip pans. 
     FIG. 5  illustrates the process for another embodiment of the present invention. If decision block  202  indicates that the cooling system is “off”, then block  218  provides as inputs: the sensed dry-bulb temperature of the air, T DB,SEN ; the sensed relative humidity of the air, RH SEN ; the dry-bulb temperature set-point for the air within enclosure  12 , T DB,SET ; and the relative humidity set-point for the air within enclosure  12 , RH SET . Next, process block  220  computes the sensed dew-point temperature of the air, T DP,SEN , as a function of T DB,SEN  and RH SEN , and the dew-point temperature set-point for the air within the enclosure, T DP,SET , as a function of T DB,SET  and RH SET . Values of T DP,SEN  and T DP,SET  are compared in decision block  214 . If T DP,SEN  is greater than T DP,SET , then humidification may be suppressed ( 204 ) because it is not required. If T DP,SEN  is not greater than T DP,SET , then fan over-run is initiated ( 216 ) as previously described. 
     FIG. 6  illustrates the process for yet another embodiment of the present invention. If decision block  214  indicates the need for humidification, then fan over-run is initiated ( 216 ). During this period of fan over-run immediately following a cooling cycle, one or more condensate sensors  222  provide input about whether or not water condensate is present on the one or more cooling coils or in their drip-pans. Condensate sensors  222  may include liquid water sensors, or dry-bulb temperature and dew-point temperature sensors, or relative humidity and dry-bulb temperature sensors, or any other suitable sensor or device. If decision block  224  determines the presence of water condensate, then humidification is suppressed by passing control to process block  204 . If decision block  224  indicates the absence of water condensate, then humidification is enabled by passing control to process block  206 . 
     FIG. 7  illustrates the process for another embodiment of the present invention. During each cooling cycle, if decision block  214  indicates the need for humidification, then fan over-run is initiated ( 216 ). During this period of fan over-run, the minimum dry-bulb temperature of the air discharged from the one or more cooling coils, T DIS , during a cooling cycle is provided as input ( 226 ) to decision block  228 . If decision block  228  determines that T DIS  is not greater than T DP,SEN , then humidification is suppressed by passing control to process block  204  since any addition of water to the air stream will result in condensation on the one or more cooling coils during the subsequent cooling cycle, thereby effectively negating humidification. If decision block  228  determines that T DIS  is greater than T DP,SEN , then humidification is enabled by passing control to process block  206 . 
   Although the methods illustrated in  FIGS. 2-7  indicated that humidification is suppressed when the cooling system is “on”, this is not required. For example, if the temperature of the air provided by the cooling system is above the dew point temperature of the air by a preset value, then humidification need not be suppressed. 
   Although the invention has been described in terms of particular embodiments and applications, one of ordinary skill in the art, in light of this teaching, can generate additional embodiments and modifications without departing from the spirit of or exceeding the scope of the claimed invention. Accordingly, it is to be understood that the drawings and descriptions herein are proper by way of example to facilitate comprehension of the inventions and should not be construed to limit the scope thereof.