Abstract:
A controller controls operation of a HVAC&amp;R device to reduce an interior humidity level for a structure to provide comfort for occupants of the structure. The controller includes a first sensor for sensing a temperature inside a structure and a second sensor for sensing a humidity level inside the structure. A controller is responsive to the first and second sensors for the HVAC&amp;R device operating in a cooling mode to reduce the humidity level inside the structure. The controller calculates a temperature correction to a predetermined temperature setting for the HVAC&amp;R device, the temperature correction calculation being obtained by subtracting the sensed humidity level from a predetermined humidity level and dividing the result by a predetermined factor. The controller initiates operation of the HVAC&amp;R device when the sum of the sensed temperature and the temperature correction is greater than the predetermined temperature.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates generally to a control application for a HVAC&amp;R system. More specifically, the present invention relates to a system and method for humidity control in a HVAC&amp;R system.  
         [0002]     To achieve climate control for a structure or enclosed space, a heating, ventilation, air conditioning and refrigeration (HVAC&amp;R) or air treatment system is commonly used. The HVAC&amp;R system is typically thermostat controlled to provide temperature control for the interior space of the structure. However, in addition to temperature, other parameters are significant for providing comfort to the occupants within the structure. For example, relative humidity, or the ratio of the amount of water vapor actually present in the air to the greatest amount possible at the same temperature, is one such parameter. At increased levels of relative humidity, the temperature must be lowered to provide an equivalent level of comfort for an individual. Complicating matters, individual sensitivity to changes in humidity and temperature differ, so that it is not possible to provide a definitive temperature correction when humidity levels are elevated.  
         [0003]     Several techniques have been used to control humidity within a structure. These techniques typically include a combination of reheating and/or cooling the air. Cooling the air, such as by passing the air through evaporator coils, removes moisture from the air since an amount of the air moisture collects and condenses on the evaporator coils. Heating may then need to be performed to raise the air temperature to a level that is comfortable to the occupant. Having both heating and cooling adds HVAC&amp;R components, complexity and cost.  
         [0004]     What is needed is a control for use with HVAC&amp;R systems that is simple to operate, and which can provide an individualized temperature/humidity correction inside a structure in response to elevated humidity levels.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention is directed to a method for controlling humidity in a structure with a HVAC&amp;R system. The method steps include: sensing a temperature and a humidity level inside a structure; calculating a temperature correction value in response to a predetermined humidity level, the sensed humidity level and a predetermined humidity sensitivity factor; comparing a predetermined temperature setting for a HVAC&amp;R device with the sum of the sensed temperature and the temperature correction value; and initiating operation of the HVAC&amp;R device to reduce the humidity level inside the structure when the sum of the sensed temperature and the temperature correction value is greater than the predetermined temperature setting.  
         [0006]     The present invention further includes a controller for controlling humidity in a structure with a HVAC&amp;R system. The controller includes a first sensor for sensing a temperature inside a structure and a second sensor for sensing a humidity level inside the structure. A controller is responsive to the first and second sensors for a HVAC&amp;R device, the controller calculating a temperature correction value in response to a predetermined humidity level, the sensed humidity level and a predetermined humidity sensitivity factor. The controller initiates operation of the HVAC&amp;R device to reduce the humidity level inside the structure when the sum of the sensed temperature and the temperature correction value is greater than the predetermined temperature setting.  
         [0007]     One advantage of the present invention is that it reduces elevated humidity levels within a structure.  
         [0008]     Another advantage of the present invention is that it can provide a selectable relationship between temperature and elevated humidity levels within a structure.  
         [0009]     A further advantage of the present invention is that it requires a minimum amount of memory to operate.  
         [0010]     A yet further advantage of the present invention is that it is extremely simple to operate.  
         [0011]     Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  illustrates schematically an embodiment of a heating, ventilation and air conditioning or refrigeration system for use with the present invention.  
         [0013]      FIG. 2  illustrates a flow chart detailing the humidity control method of the present invention. 
     
    
       [0014]     Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0015]     One embodiment of the heating, ventilation and air conditioning or refrigeration (HVAC&amp;R) system  10  of the present invention is depicted in  FIG. 1 . Compressor  12  is connected to a motor  14  and inverter or variable speed drive (VSD)  16 , for selectively controlling operational parameters, such as rotational speed, of the compressor  12 . Compressor  12  is typically a positive displacement compressor, such as screw, reciprocating or scroll, having a wide range of cooling capacity, although any type of compressor can also be used. The controller  20  includes logic devices, such as a microprocessor or other electronic components, for controlling the operating parameters of compressor  12  by controlling VSD  16  and motor  14 . AC electrical power received from an electrical power source  18  is rectified from AC to DC, and then inverted from DC back to variable frequency AC by VSD  16  for driving compressor motor  14 . The compressor motor  14  is typically an AC induction motor, but might also be brushless permanent magnet motor or switched reluctance motor.  
         [0016]     Refrigerant gas that is compressed by compressor  12  is directed to the condenser  22 , which enters into a heat exchange relationship with a fluid, preferably water, flowing through a heat-exchanger coil  24  connected to a cooling tower  26 . The refrigerant vapor in the condenser  22  undergoes a phase change to a refrigerant liquid as a result of the heat exchange relationship with the liquid in the heat-exchanger coil  24 . The condensed liquid refrigerant from condenser  22  flows to an expansion device  28 , which lowers the pressure of the refrigerant before entering the evaporator  30 . Alternately, the condenser  22  can reject the heat directly into the atmosphere through the use of air movement across a series of finned surfaces (direct expansion condenser).  
         [0017]     The evaporator  30  can include a heat-exchanger coil  34  having a supply line  34 S and a return line  34 R connected to a cooling load  36 . The heat-exchanger coil  34  can include a plurality of tube bundles within the evaporator  30 . Water or any other suitable secondary refrigerant, e.g., ethylene, calcium chloride brine or sodium chloride brine, travels into the evaporator  30  via return line  34 R and exits the evaporator  30  via supply line  34 S. The liquid refrigerant in the evaporator  30  enters into a heat exchange relationship with the water in the heat-exchanger coil  34  to chill the temperature of the water in the heat-exchanger coil  34 . The refrigerant liquid in the evaporator  30  undergoes a phase change to a refrigerant gas as a result of the heat exchange relationship with the liquid in the heat-exchanger coil  34 . The gas refrigerant in the evaporator  30  then returns to the compressor  12 .  
         [0018]     Controller  20 , which controls the operations of HVAC&amp;R system  10 , employs continuous feedback from indoor temperature sensor  38  and humidity sensor  40  to continuously determine whether to incorporate a temperature correction to achieve a reduction in the humidity level within the structure being cooled by the system  10 . In other words, the humidity reduction control of the present invention is preferably used when the HVAC&amp;R system  10  is in a cooling mode.  
         [0019]     The HVAC&amp;R system  10  is first discussed without considering the humidity sensor  40 . An operator initially inputs a desired temperature setting “T D ”, or settings if multiple temperatures are to be achieved at different times of the day or different days, which are typically referred to as programmed settings. Once the desired temperature setting(s) T D  have been input, the sensed temperature inside a structure “T S ” as sensed by the indoor temperature sensor  38  is compared to the desired temperature setting T D  which was previously input into the controller  20  by the operator. When the inside temperature T S  of the structure as sensed by the indoor temperature sensor  38  is greater than the desired temperature setting T D , the controller  20  activates the HVAC&amp;R system  10  to operate in cooling mode. The HVAC&amp;R system  10  continues to operate in cooling mode until the desired temperature setting is achieved, wherein upon achieving the desired setting, the HVAC&amp;R system  10  is deactivated. This process is then repeated to provide temperature control inside of the structure.  
         [0020]     While providing temperature control of the temperature inside of the structure, other parameters important to the comfort of the occupants of the structure, such as humidity control, are not taken into account in the above-referenced process. The HVAC&amp;R system  10  is again discussed, with the addition of the humidity sensor  40 , which senses a relative humidity percentage inside the structure “H S ”, and a corresponding control algorithm that is programmed into the controller  20 . In addition to initially inputting a desired temperature setting(s) T D , an operator additionally inputs a desired relative humidity percentage “H D ” and a humidity sensitivity factor “H stv ”. A humidity sensitivity factor “H stv ” is a correction factor that correlates an excess in percentage of the relative humidity inside the structure to a reduction of the temperature inside the structure, which reduction in temperature being referred to as a temperature correction “T C ”. More specifically, the temperature correction T C  can be calculated by subtracting the desired relative humidity percentage H D  from the sensed relative humidity H S , and dividing that result by the humidity sensitivity factor H stv  as shown in equation 1. 
 
 T   C =( H   S   −H   D )/ H   stv   [1]
 
         [0021]     Stated another way, a humidity sensitivity factor of 5, for example, means that for every 5 percent the sensed humidity percentage H S , as sensed by the humidity sensor  40 , exceeds the desired relative humidity percentage H S , the temperature correction T C  inside the structure must be lowered by one ° F. to achieve a similar level of comfort due to the humidity. The humidity sensitivity factor H stv  is subjective, possibly differing for each individual, and can range from about 1 up to about 10, although typically it is about 5 or less.  
         [0022]     In operational example, assume the following input values: desired relative humidity percentage H D  is 50 percent, the humidity sensitivity factor H stv  is 5, the desired temperature setting TD is 70° F. and a maximum correction temperature “T CMAX” is  5. The maximum correction temperature T CMAX  is an operator-input maximum deviation temperature from the desired temperature T D . Further assume a sensed relative humidity H S  of 80 percent and a sensed inside structure temperature T S  of 70° F. In a conventional HVAC&amp;R system, since the sensed inside structure temperature T S  and the desired temperature setting T D  are equal, the HVAC&amp;R system would remain deactivated. However, since the sensed relative humidity H S  is greater than the desired relative humidity H D , occupants within the structure can be made more comfortable by cooling the temperature within the structure as provided by the control algorithm. The temperature correction T C  as provided by equation [1] is calculated as follows: (80−50)/5, which simplifies to 6° F. However, in this example, the maximum correction temperature T CMAX  is 5, or 5° F., so the maximum correction temperature value is applied in place of the calculated correction temperature. By application of the control algorithm in this example, the equivalent temperature inside the structure is reduced by the maximum correction temperature T CMAX , so that the HVAC&amp;R system is activated to operate until the temperature inside the structure is lowered to 65° F., at which point the HVAC&amp;R system is deactivated.  
         [0023]     In summary, for the above example, occupants inside the structure are made more comfortable by operation of the control algorithm, since the elevated level of relative humidity is reduced as the air inside the structure is passed through the evaporator coils for the additional time required to cool the structure by the amount of temperature correction T C . This process is then repeated to provide temperature and humidity control inside of the structure.  
         [0024]     After the control algorithm completes a cycle, especially when the sensed relative humidity H S  is significantly greater than the desired relative humidity H D , the reduction of the sensed relative humidity H S  is typically sufficient to likewise reduce the amount of temperature correction T C . In the above example, after the temperature inside the structure is lowered to 65° F., if the relative humidity inside the structure is reduced to 70 percent, the temperature correction of equation [1] is calculated as follows: (70−50)/5, which simplifies to 4° F. By application of the algorithm, the equivalent temperature inside the structure is reduced by less than the maximum correction temperature T CMAX , or 4° F. Thus, upon the temperature inside the structure being sufficiently raised to activate the HVAC&amp;R system, the HVAC&amp;R system operates until the temperature inside the structure is lowered to 66° F., at which point the HVAC&amp;R system is deactivated. In other words, so long as the control algorithm removes more moisture from the air inside the structure than is added, such as by activities of the occupants or by moisture producing processes occurring within the structure, the temperature correction should continue to decrease. As the relative humidity inside the structure is reduced to the desired humidity level, the temperature correction approaches zero.  
         [0025]     Although the desired relative humidity level could be set to an extremely low level, such as thirty percent or less, there is typically little benefit, from a comfort standpoint, to reduce the humidity below a level of about 45 percent.  
         [0026]     The controller  20  can include an analog to digital (A/D) converter, a microprocessor, a non-volatile memory, and an interface board to control operation of the HVAC&amp;R system  10 . The controller  20  can also be used to control the operation of the VSD  16 , the motor  14  and the compressor  12 . The controller  20  executes a control algorithm(s) or software to control operation of the system  10 . In one embodiment, the control algorithm(s) can be computer programs or software stored in the non-volatile memory of the controller  20  and can include a series of instructions executable by the microprocessor of the controller  20 . While it is preferred that the control algorithm be embodied in a computer program(s) and executed by the microprocessor, it is to be understood that the control algorithm may be implemented and executed using digital and/or analog hardware by those skilled in the art. If hardware is used to execute the control algorithm, the corresponding configuration of the controller  20  can be changed to incorporate the necessary components and to remove any components that may no longer be required.  
         [0027]      FIG. 2  illustrates a flow chart detailing the control process of the present invention relating to cooling control in an HVAC&amp;R system  10 , as shown in  FIG. 1 , wherein control is maintained by the thermostat (not shown). The cooling control process of  FIG. 2  can also be implemented as a separate control program executed by a microprocessor, or control panel, or controller  20  or the control process can be implemented as a sub-program in the control program for the HVAC&amp;R system  10 . Once the process is started in step  105  of  FIG. 2 , values are selected and set for the desired humidity percentage H D , the humidity sensitivity factor H stv , desired temperature T D  and the maximum temperature correction T CMAX  in step  110 . Controller keypads on existing controllers  20  or other suitable entry devices can be used with the control algorithm and can be used to enter all required parameters. After the desired humidity percentage H D , humidity sensitivity factor H stv , desired temperature T D  and maximum temperature correction T CMAX  are set, the temperature inside the structure T S  as sensed by the indoor temperature sensor  38  and the relative humidity H S  as sensed by the humidity sensor  40  are sensed in step  115 . Once the temperature inside the structure T S  and the relative humidity H S  are sensed, the sensed relative humidity H S  is compared to the desired humidity percentage H D  in step  120 .  
         [0028]     In step  120 , if the sensed relative humidity H S  is greater than the desired humidity percentage H D , then a calculation is performed to determine the humidity correction temperature T C  in step  125 . However, if in step  120 , the sensed relative humidity H S  is not greater than the desired humidity percentage H D , a humidity temperature correction is not greater than zero, the humidity temperature correction T C  is set to zero in step  140  and control of the process is returned to step  145 .  
         [0029]     Once the humidity temperature correction T C  in step  125  has been calculated, the humidity temperature correction T C  is compared to the maximum temperature correction T CMAX  in step  130 . If the humidity correction temperature T C  is greater than the maximum temperature correction T CMAX  in step  130 , the humidity temperature correction T C  is set equal to the maximum temperature correction T CMAX  in step  135  and control of the process is returned to step  145 . However, if the humidity temperature correction T C  is not greater than the maximum temperature correction T CMAX  in step  130 , the value of the humidity temperature correction T C  is retained, and control of the process is returned to step  145 .  
         [0030]     In step  145 , the desired temperature T D  is compared to the resulting value obtained by adding the humidity temperature correction T C  and the sensed temperature inside the structure T S . If the desired temperature T D  is less than the resulting value obtained by adding the humidity correction temperature T C  and the sensed temperature inside the structure T S , the HVAC&amp;R system  10  is activated in step  150  and control of the process is returned to step  145 . However, if in step  145  the desired temperature T D  is greater than the resulting value obtained by adding the humidity correction temperature T C  and the sensed temperature inside the structure T S , a query is performed as to whether the HVAC&amp;R system  10  is activated in step  155 . If the HVAC&amp;R system  10  is activated, the HVAC&amp;R system  10  is deactivated in step  160  and control of the process is returned to step  115 , wherein the process between steps  115 - 160  are repeated. However, if the HVAC&amp;R system  10  is not activated in step  155 , control of the process is returned to step  115 , wherein the process between steps  115 - 160  are repeated.  
         [0031]     In another embodiment, after activating the HVAC&amp;R system  10  in step  150 , the control can return to step  115  and steps  115 - 160  can be repeated.  
         [0032]     In addition to use with commercial HVAC&amp;R systems, including roof-mounted configurations, the control process of the present invention can also be used with residential structures. The residential structures include split systems where the condenser is located outside the structure.  
         [0033]     While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.