Patent Application
20060010891
The present invention relates generally to a control application for a HVAC&R system. More specifically, the present invention relates to a system and method for humidity control in a HVAC&R system.
To achieve climate control for a structure or enclosed space, a heating, ventilation, air conditioning and refrigeration (HVAC&R) or air treatment system is commonly used. The HVAC&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.
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&R components, complexity and cost.
What is needed is a control for use with HVAC&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.
The present invention is directed to a method for controlling humidity in a structure with a HVAC&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&R device with the sum of the sensed temperature and the temperature correction value; and initiating operation of the HVAC&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.
The present invention further includes a controller for controlling humidity in a structure with a HVAC&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&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&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.
One advantage of the present invention is that it reduces elevated humidity levels within a structure.
Another advantage of the present invention is that it can provide a selectable relationship between temperature and elevated humidity levels within a structure.
A further advantage of the present invention is that it requires a minimum amount of memory to operate.
A yet further advantage of the present invention is that it is extremely simple to operate.
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.
Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
One embodiment of the heating, ventilation and air conditioning or refrigeration (HVAC&R) system 10 of the present invention is depicted in
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).
The evaporator 30 can include a heat-exchanger coil 34 having a supply line 34S and a return line 34R 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 34R and exits the evaporator 30 via supply line 34S. 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.
Controller 20, which controls the operations of HVAC&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&R system 10 is in a cooling mode.
The HVAC&R system 10 is first discussed without considering the humidity sensor 40. An operator initially inputs a desired temperature setting “TD”, 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) TD have been input, the sensed temperature inside a structure “TS” as sensed by the indoor temperature sensor 38 is compared to the desired temperature setting TD which was previously input into the controller 20 by the operator. When the inside temperature TS of the structure as sensed by the indoor temperature sensor 38 is greater than the desired temperature setting TD, the controller 20 activates the HVAC&R system 10 to operate in cooling mode. The HVAC&R system 10 continues to operate in cooling mode until the desired temperature setting is achieved, wherein upon achieving the desired setting, the HVAC&R system 10 is deactivated. This process is then repeated to provide temperature control inside of the structure.
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&R system 10 is again discussed, with the addition of the humidity sensor 40, which senses a relative humidity percentage inside the structure “HS”, and a corresponding control algorithm that is programmed into the controller 20. In addition to initially inputting a desired temperature setting(s) TD, an operator additionally inputs a desired relative humidity percentage “HD” and a humidity sensitivity factor “Hstv”. A humidity sensitivity factor “Hstv” 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 “TC”. More specifically, the temperature correction TC can be calculated by subtracting the desired relative humidity percentage HD from the sensed relative humidity HS, and dividing that result by the humidity sensitivity factor Hstv as shown in equation 1.
TC=(HS−HD)/Hstv [1]
Stated another way, a humidity sensitivity factor of 5, for example, means that for every 5 percent the sensed humidity percentage HS, as sensed by the humidity sensor 40, exceeds the desired relative humidity percentage HS, the temperature correction TC inside the structure must be lowered by one ° F. to achieve a similar level of comfort due to the humidity. The humidity sensitivity factor Hstv 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.
In operational example, assume the following input values: desired relative humidity percentage HD is 50 percent, the humidity sensitivity factor Hstv is 5, the desired temperature setting TD is 70° F. and a maximum correction temperature “TCMAX” is 5. The maximum correction temperature TCMAX is an operator-input maximum deviation temperature from the desired temperature TD. Further assume a sensed relative humidity HS of 80 percent and a sensed inside structure temperature TS of 70° F. In a conventional HVAC&R system, since the sensed inside structure temperature TS and the desired temperature setting TD are equal, the HVAC&R system would remain deactivated. However, since the sensed relative humidity HS is greater than the desired relative humidity HD, 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 TC 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 TCMAX 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 TCMAX, so that the HVAC&R system is activated to operate until the temperature inside the structure is lowered to 65° F., at which point the HVAC&R system is deactivated.
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 TC. This process is then repeated to provide temperature and humidity control inside of the structure.
After the control algorithm completes a cycle, especially when the sensed relative humidity HS is significantly greater than the desired relative humidity HD, the reduction of the sensed relative humidity HS is typically sufficient to likewise reduce the amount of temperature correction TC. 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 TCMAX, or 4° F. Thus, upon the temperature inside the structure being sufficiently raised to activate the HVAC&R system, the HVAC&R system operates until the temperature inside the structure is lowered to 66° F., at which point the HVAC&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.
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.
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&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.
In step 120, if the sensed relative humidity HS is greater than the desired humidity percentage HD, then a calculation is performed to determine the humidity correction temperature TC in step 125. However, if in step 120, the sensed relative humidity HS is not greater than the desired humidity percentage HD, a humidity temperature correction is not greater than zero, the humidity temperature correction TC is set to zero in step 140 and control of the process is returned to step 145.
Once the humidity temperature correction TC in step 125 has been calculated, the humidity temperature correction TC is compared to the maximum temperature correction TCMAX in step 130. If the humidity correction temperature TC is greater than the maximum temperature correction TCMAX in step 130, the humidity temperature correction TC is set equal to the maximum temperature correction TCMAX in step 135 and control of the process is returned to step 145. However, if the humidity temperature correction TC is not greater than the maximum temperature correction TCMAX in step 130, the value of the humidity temperature correction TC is retained, and control of the process is returned to step 145.
In step 145, the desired temperature TD is compared to the resulting value obtained by adding the humidity temperature correction TC and the sensed temperature inside the structure TS. If the desired temperature TD is less than the resulting value obtained by adding the humidity correction temperature TC and the sensed temperature inside the structure TS, the HVAC&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 TD is greater than the resulting value obtained by adding the humidity correction temperature TC and the sensed temperature inside the structure TS, a query is performed as to whether the HVAC&R system 10 is activated in step 155. If the HVAC&R system 10 is activated, the HVAC&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&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.
In another embodiment, after activating the HVAC&R system 10 in step 150, the control can return to step 115 and steps 115-160 can be repeated.
In addition to use with commercial HVAC&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.
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.
