Patent Application
20090048714
1. Field of the Invention
The subject invention relates to a system and a method for operating air handling fans for vent hoods.
2. Description of the Related Art
Ventilation hoods, i.e., vent hoods, are commonly used in buildings to ventilate air to the outside. These vent hoods are often installed in kitchens above cooking ranges, both in commercial and residential applications. As such, these vent hoods exhaust not only uncomfortably warm air, but also the smoke that often accompanies food preparation.
In the past, these vent hoods were mostly manually operated. That is, a user would turn a fan on using a switch or button and turn it off when complete. Unfortunately, these manually operated vent hoods are often left on, even when not needed, and therefore wasted energy. Furthermore, a user, e.g., a cook, are often too busy with other tasks to turn the vent hood on or increase its speed from low to high. Moreover, automatically operated vent hoods often switch erratically between different speeds based on a sudden cooling that occurs when the fan is turned on or is increased form a low speed to a high speed.
Therefore, there remains an opportunity for a method for operating a vent hood which is automatically operated and operates in a non-erratic fashion.
The subject invention provides a method of controlling an air handling fan for a vent hood where the fan has at least a first speed and a second speed. The method includes the step of receiving a first temperature setpoint from a user. The first temperature setpoint corresponds to a temperature at which the speed of the fan is changed from the first speed to the second speed. The method further includes the step of storing the first temperature setpoint in a memory. The method further includes receiving a first temperature deadband range from a user. The first temperature deadband range is then stored in the memory. The method continues with the step of obtaining a temperature of air in the vent hood. The temperature of air is then compared to the first temperature setpoint. The speed of the air handling fan is changed from the first speed to the second speed in response to the temperature of air being greater than the first temperature setpoint. The method further includes the step of computing a first deadband temperature setpoint based on the first temperature setpoint and the temperature deadband range. The method also includes the step of changing the speed of the air handling fan from the second speed to the first speed in response to the temperature of air being less than the first deadband temperature setpoint.
By utilizing the deadband range to computer the deadband setpoint, the subject invention provides a method that helps eliminate repetitive, unnecessary, and sometimes harmful switching of the speed of the fan. As the switching of the motor speed may cause damage to various electrical components, such as relays and transistors, the method serves to prevent quick switching of the fan back to the first speed. The method also promotes proper operation of electrical components, e.g., preventing chattering and buzzing relays.
Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
Referring to the Figures, wherein like numerals indicate corresponding parts throughout the several views, a control system 10 is shown for controlling an air handling fan 12 for a vent hood 14. The vent hood 14 may be positioned in a kitchen, particularly above a cooking surface. An electric motor 16 operatively connected to the fan 12 for turning the fan 12, as is well known to those skilled in the art. The fan 12 generates an airflow to move air though the vent hood 14 and, typically, to exhaust the air to the atmosphere.
A motor controller 18 is electrically connected to the electric motor 16 for controlling the application of electric current to the electric motor 16. In the preferred embodiment, the motor controller 18 is a variable speed drive capable of operating the motor 16 at a variety of speeds. Consequently, the speed of the fan 12 and the rate of air flow generated by the fan 12, are also variable. More preferably, the motor controller 18 is a variable frequency drive (VFD) as is well known to those skilled in the art.
In the preferred embodiment, the fan 12 is operated at a first speed, a second speed, or a third speed. The first speed is “off”, where no electricity is applied to the motor 16 to turn the fan 12. The second speed is “low”, where the motor 16 and fan 12 generate an airflow. The third speed is “high”, where the motor 16 is operated at a maximum, i.e., full speed to generate more airflow than at the second speed. Of course, the fan may be operated at different speed definitions in alternative embodiments than those outlined above.
The control system 10 includes a processor 20 in communication with the motor controller 18 for controlling operation of the motor controller 18. In the preferred embodiment, the processor 20 is a microprocessor-based device. More specifically, the processor 20 is implemented with an MSP430F423 microcontroller manufactured by Texas Instruments, headquartered in Dallas, Tex. Of course, other suitable model of microcontrollers or other devices may be suitable to perform the functions of the processor 20.
The control system 10 also includes an analog-to-digital converter 22 (ADC). The ADC 22 is in communication with the processor 20 for providing digital data to the processor 20 corresponding to an analog signal. In the preferred embodiment, the ADC 22 is integrated with the processor 20. That is, the microcontroller includes a built-in ADC 22. However, those skilled in the art realize that the ADC 22 may be an independent component, separate from the processor 20.
A temperature sensing circuit 24 is electrically connected to the ADC 22. The temperature sensing circuit 24 provides a temperature to the ADC 22, and accordingly, to the processor 20. The processor may then control operation of the motor controller 18 based on temperature, as described in greater detail below.
The temperature sensing circuit 24 includes a temperature sensor 26. The temperature sensor 26 may be mounted in the vent hood 14 or other suitable locations. In the preferred embodiment, the temperature sensor 26 is implemented as a resistance temperature detector (RTD) 28. As is known to those skilled in the art, the electrical resistance of the RTD 28 varies based on its temperature. Of course, in alternate embodiments, the temperature sensor 26 may be implemented with other devices, including, but not limited to, a thermocouple.
The temperature sensing circuit 24 of the preferred embodiment also includes a constant current circuit 30. The constant current circuit 30 is electrically connected to the RTD 28 and provides a constant current to the RTD 28. As the current to the RTD 28 is held constant, the voltage drop across the RTD 28 will also vary according to the temperature of the RTD 28. The RTD 28 is electrically connected to the ADC 22 such that the ADC 22 translates the voltage drop across the RTD 28 into the temperature of the RTD 28.
Specifically, in the preferred embodiment, as shown in
Referring again to
In the preferred embodiment, as shown in
As shown in
The control system 10 preferably includes a power circuit 38 for supplying electrical power to the various electrical components of the control system 10. More preferably, the power circuit 38 receives AC power and supplies DC power to the various components. Specifically, in the illustrated embodiment shown in
The control system 10 preferably includes an output interface 45 for interfacing the processor 20 to the motor controller 18. In the preferred embodiment, as shown in
The first and second conditioning circuits 46, 48 each include, respectively, a first and second op-amp 47, 49. The non-inverting input of each op-amp 47, 49 is electrically connected to separate outputs of the processor 20. A first relay 50 is electrically connected to the first conditioning circuit 46 and a second relay 52 is electrically connected to the second conditioning circuit 48. Specifically, the conditioning circuits 46, 48 are each connected to a coil (not numbered) of the respective relays 50, 52. The motor controller 18 is then electrically connected to the contacts (not numbered) of each relay 50, 52. This allows electrical isolation between the motor controller 18 on one side and the processor 20 and the power circuit 38 on the other side.
The subject invention also includes a method of controlling the air handling fan 12. The method is preferably implemented with the control system 10 described above. However, those skilled in the art realize that alternative techniques for implementing the method may be utilized.
The method includes the steps of receiving temperature setpoints from a user and storing these temperature setpoints in a memory (not shown) of the processor 20. In the preferred embodiment, the temperature setpoints include a first temperature setpoint and a second temperature setpoint. The first temperature setpoint corresponds to a temperature at which the speed of the fan 12 is changed from the first speed to the second speed. The second temperature setpoint corresponds to a temperature at which the speed of the fan 12 is changed from the second speed to the third speed.
The method also includes the steps of receiving at least one temperature deadband range from a user and storing this temperature deadband range in the memory of the processor 20. In the preferred embodiment, the temperature deadband range is a value from 2 degrees Fahrenheit to 99 degrees Fahrenheit. Of course, other values for the temperature deadband range may be utilized in alternate embodiments. Furthermore, other temperature measuring conventions, such as Celsius, may also be utilized.
In the preferred embodiment, the temperature setpoints and temperature deadband range may be received and stored at any time. Therefore, operation of the fan 12 can be changed “on the fly” by the user as a desired operation of the fan 12 changes
The method also preferably computes a first deadband temperature setpoint and a second deadband temperature setpoint. The first deadband temperature setpoint is based on the first temperature setpoint and the temperature deadband range while the second deadband temperature setpoint is based on the second temperature setpoint and the temperature deadband range. Specifically, in the preferred embodiment, the first deadband temperature setpoint is computed by subtracting the temperature deadband range from the first temperature setpoint. Likewise, in the preferred embodiment, the second deadband temperature setpoint is computed by subtracting the temperature deadband range from the second temperature setpoint. Of course, in other embodiments, the deadband temperature setpoints may be computed by alternate techniques.
The method further includes the step of sensing a temperature of air in the vent hood. As stated above, in the preferred embodiment, an RTD 28, a temperature sensing circuit 24, and an ADC 22 work in concert to provide a sensed temperature to the processor 20. Of course, those skilled in the art realize other suitable techniques to sense the temperature of air.
The sensed temperature may be utilized directly by the processor 20 as the actual temperature of air in the vent hood. However, seemingly random variations, spikes, etc. may occur in the electrical signal received by the processor 20 due to electrical interference or other factors. As such, the system 10 may use one or more techniques to obtain a more accurate temperature of the vent hood. For instance, in the preferred embodiment, transient temperature readings are filtered out of the readings obtained by the RTD 28. Furthermore, in the preferred embodiment, a plurality of temperature readings are averaged to compute the actual temperature of air in the vent hood.
The method also includes the step of determining the current speed of the air handling fan 12. This step may be accomplished using several techniques. In one technique, the speed of the air handling fan 12 is stored in the memory of the processor 20 when the speed of the air handling fan 12 is changed. That is, whatever speed the processor 20 previously ordered for the air handling fan 12 is considered the current speed of the air handling fan 12. In another technique, a current sensor (not shown) is utilized to sense the amount of electrical current applied to the motor. This electric current corresponds to the current speed of the fan 12. In yet another technique, an airflow sensor (not shown) is utilized to sense the amount of air being drawn by the fan 12. The amount of airflow corresponds to the current speed of the fan 12. Of course, other techniques will be recognized by those skilled in the art.
The method progresses based on the current speed of the air handling fan 12. When the current speed of the air handling fan 12 is the first speed, the temperature of the air is compared to the first temperature setpoint. If the temperature of the air is greater than the first temperature setpoint, then the speed of the air handling fan 12 is changed from the first speed to the second speed. Therefore, in the preferred embodiment, when the fan 12 is off, and the temperature exceeds the first setpoint, then fan 12 is turned on at the low speed.
When the current speed of the fan 12 is the second speed, the temperature of the air is compared to the first deadband temperatures setpoint and the second temperature setpoint. If the air temperature is less than the first deadband temperature setpoint, then the speed of the air handling fan 12 is changed from the second speed to the first speed. If the air temperature is greater than the second temperature setpoint, then the speed of the air handling fan 12 is changed from the second speed to the third speed. Said another way, if the air temperature rises past the second temperature setpoint, the fan 12 speed increases to the high speed while if the air temperature declines lower than the first deadband temperature setpoint, then the fan 12 is turned off. Otherwise, when the air temperature is between the first deadband temperature setpoint and the second temperature setpoint, the fan 12 continues to operate at the low speed.
When the current speed of the fan 12 is the third speed, the temperature of air is compared to the second deadband temperature setpoint. If the air temperature is less than the second deadband temperature setpoint, then the speed of the air handling fan 12 is changed from the third speed to the second speed. That is, if the air temperature falls lower than the second deadband temperature setpoint, then the fan 12 speed decreases to the low speed.
By utilizing the deadband temperature setpoints, which, in the preferred embodiment, are lower than the corresponding temperature setpoints, the method prevents fast switching of speeds of the fan 12 based on sudden drops in temperature of only one or two degrees. As such, wear and tear on the motor 16, motor controller 18, and relays 50, 52. Furthermore, the annoyance to a user of hearing the fan 12 frequently change speeds is also reduced.
The present invention has been described herein in an illustrative manner, and it is to be understood that the terminology that has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the invention are possible in light of the above teachings. The invention may be practiced otherwise than as specifically described within the scope of the appended claims.
This application claims the benefit of U.S. Provisional Application No. 60/956,548 filed Aug. 17, 2007.
| Number | Date | Country | |
|---|---|---|---|
| 60956548 | Aug 2007 | US |
