Conveying Temperature Information in a Controlled Variable Speed Heating, Ventilation, and Air Conditioning (HVAC) System
The present invention provides methods and apparatuses that support the transfer of data from a thermostat unit to a controller unit to control a variable speed heating, ventilation, and air conditioning (HVAC) system. The duty cycle of a signal (that is sent from a thermostat unit to a controller unit) is adjusted in accordance with a temperature difference between the ambient temperature of an environmentally controlled space and a set temperature. The controller unit measures the duty cycle to determine the temperature difference and adjusts the speed of a blower motor or compressor in accordance with the temperature difference. The signal is switched on and off, in which the AC waveform is conducted and blocked by the thermostat unit and received by the controller unit. The controller unit measures the duty cycle of the received signal, determines the temperature from the duty cycle, and adjusts the speed from a predetermined relationship.
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The present invention relates generally to the field of controlling a variable speed heating, ventilation, and air conditioning (HVAC) system, and more particularly to sending a signal that conveys a temperature difference from a thermostat unit to a controller unit.
BACKGROUND OF THE INVENTIONWith the price of energy steadily increasing, there is an increasing need to enhance the efficiency of heating, ventilation, and air conditioning (HVAC) systems. One approach to increase the efficiency of a HVAC system is to incorporate a variable speed controlled compressor in the system for the cooling function. The latest technology typically employs a sophisticated microprocessor controller unit (MCU) and a digital signal processor (DSP) to support a high performance inverter type variable speed controlled compressor. The speed (revolutions per unit time) of a variable speed controlled compressor depends on the temperature difference of the set temperature (typically set at a thermostat) and the ambient temperature of the temperature-controlled room. In general for the cooling function when the ambient temperature is higher than the set temperature, the higher the temperature difference, the faster the compressor should run.
A typical thermostat can provide only a simple ON/OFF control of the 24V AC to a compressor controller that controls that compressor. However, with this control mechanism, a variable speed controlled compressor will not typically function at their maximum efficiency. Consequently, there is a need for apparatuses and methods that enable the typical thermostat to properly control a variable speed controlled compressor.
SUMMARY OF THE INVENTIONThe present invention provides methods and apparatuses that support the transfer of data from a thermostat unit to a controller unit to control the speed of a compressor of an air conditioner unit or a blower motor of a furnace.
With an aspect of the invention, the duty cycle of a signal that is sent from a thermostat unit to a compressor controller unit is adjusted in accordance with a temperature difference between the ambient temperature of an environmentally controlled space and a set temperature. The compressor controller unit measures the duty cycle to determine the temperature difference and adjusts the compressor speed in accordance with the temperature difference.
With another aspect of the invention, the duty cycle of a signal that is sent from a thermostat unit to a furnace controller unit is adjusted in accordance with a temperature difference between the ambient temperature of an environmentally controlled space and a set temperature. The furnace controller unit measures the duty cycle to determine the temperature difference and adjusts the speed of a blower motor in accordance with the temperature difference.
With another aspect of the invention, the change in hardware at both the thermostat side and the compressor controller side is minimized. An AC line (e.g., 24 volts) is used to transfer data in a signal sent from the thermostat side to the compressor controller side. The signal is switched on and off, in which the AC waveform is conducted and blocked by the thermostat unit and received by the compressor controller. Consequently, existing wiring can be used without modifications.
With another aspect of the invention, a thermostat unit instructs a compressor controller unit to stop operation immediately in an emergency situation by sending a signal with a pulse or pulses having a short time duration.
With another aspect of the invention, a compressor controller unit measures the duty cycle of a received signal, determines the temperature from the duty cycle, and adjusts the compressor speed from a predetermined relationship. The compressor speed is related to the temperature difference, in which the compressor controller unit may access a lookup table using an address determined by the temperature difference.
With another aspect of the invention, a pulse width modulated (PWM) controller is instructed by a microprocessor control unit to generate control pulses for the compressor so that the compressor runs at a desired speed. The PWM controller configures an IGBT (insulated-gate bipolar transistor) array so that an appropriate pulse stream is provided to the compressor.
The foregoing summary of the invention, as well as the following detailed description of exemplary embodiments of the invention, is better understood when read in conjunction with the accompanying drawings, which are included by way of example, and not by way of limitation with regard to the claimed invention.
Microprocessor control unit 107 measures the ambient temperature of the controlled space with thermistor 109, which is situated in an appropriate point of the controlled space. Microprocessor control unit 107 consequently determines a difference temperature (Tdiff) by subtracting the set temperature (Tset) from the ambient temperature (Tamb):
Tdiff=Tamb−Tset (EQ. 1)
In the embodiment shown in
Because switching module 105 is either on or off, only two states are directly supported. However, in accordance with an aspect of the invention, information that is indicative of Tdiff is transmitted from thermostat unit 100 to compressor controller unit 300 (as shown in
In an embodiment of an invention, thermostat unit 100 sends a special signal that has a short pulse duration to notify a furnace/air conditioner controller to immediately stop operation. For example, the special signal can be four consecutive pulses with 1 second on and 1 second off.
During each time period 201, 203, 205, signal 200 is being electrically conducted during an activated time duration (Ton) (e.g., activated time duration 201a for time period 201) and electrically blocked during an deactivated time duration (Toff) (e.g., deactivated time duration 201b for time period 201). During activated time duration 201a, AC power (corresponding to a 24 volts AC waveform) is conducted. During deactivated time duration 201b, AC power is not conducted. The corresponding duty cycle is determined by:
In an embodiment of the invention, thermostat unit 100 notifies compressor unit 300 the value of Tmax by sending a configuration signal having a preamble followed by a number of pulses, in which the number of pulses is indicative of the value of Tmax. In an exemplary embodiment, the preamble comprises a predetermined pulse sequence of two ON time periods followed by two OFF time periods, each time period being one second. For each ON time period, a pulse is generated for 0.5 second during an ON time period and not generated during an OFF time period. The value of Tmax (degrees Fahrenheit) is determined from the number of pulses following the preamble by:
Tmax=2(number of pulses+5) (EQ. 3)
Referring to
The duty cycle of signal 200 conveys information about the temperature difference (Tdiff) as determined by microprocessor control unit 107. As suggested by
In an embodiment of the invention, the temperature difference (Tdiff) is encoded by the duty cycle as follows:
Duty_Cycle=Tdiff/Tmax*50%+50% (EQ. 4)
Ton=(Tdiff/Tmax*50%+50%)*Tcycle (EQ. 5)
where Tcycle=Ton+Toff
However, if the temperature difference if greater than Tmax−Δtemp or less than −Tmax+Δtemp, the temperature difference is limited as follows:
Tdiff=Tmax−1 if Tdiff>=Tmax−Δtemp (EQ. 6a)
Tdiff=−Tmax+1 if Tdiff<=−Tmax+Δtemp (EQ. 6b)
Tmax−Δtemp corresponds to maximum value 409 of the duty cycle and −Tmax+Δtemp corresponds to minimum value 407 of the duty cycle as shown in
Referring to
Tdiff=(Measured_Duty_Cycle−50%)/50%*Tmax (EQ. 7)
If Tdiff is positive, variable speed compressor 303 should turn faster based on a predetermined relationship, e.g., relationship 503 as shown in
In an embodiment of the invention, compressor control unit 300 obtains Tmax by a user entering Tmax through keypad 309. While compressor controller unit 300 may obtain the value of Tmax from a configuration signal sent by thermostat unit 100, as previously discussed, the value of Tmax may be entered into keypad 111 by the user. Other embodiments of the invention may utilize a predetermined value of Tmax that is stored in memory.
Microprocessor control unit 301 may access lookup data structure 317 in order to determine the temperature difference (Tdiff) and the compressor speed. (As will be discussed, the compressor speed is determined as a function of the temperature difference as shown in
With the exemplary embodiment, compressor controller unit 300 functions with a traditional thermostat design but with software modifications as will be discussed.
As previously discussed, a duty cycle between minimum value 407 and maximum value 409 is utilized in order to facilitate the detection of signal edges by microprocessor control unit 301. In an embodiment of the invention, microprocessor control unit 301 analyzes signal 200 in a time-interrupt basis as shown in
In step 801, microprocessor control unit 301 determines if signal 200 is conducting AC power (typically 24 volts AC) during Ton. If not, the Toff counter is incremented in step 817. (In flow diagram 800, Toff counter and Ton counter are appropriately incremented so that the duty cycle can be determined when flow diagram is respectively executed during the current timer period. Once the current time period is completed, the duty cycle is determined by step 807 as will be discussed.) The process will exit (i.e., flow diagram 800 determines that the air conditioner is not active).
If microprocessor control unit 301 determines that signal 200 is conducting AC power during Ton in step 801, microprocessor control unit 301 determines if signal 200 was previously in a non-conductive state (i.e., deactivated time duration 201b for time period 201) in step 805. If not, the Ton counter is incremented in step 819, and process 800 is exited. If so, a rising signal edge is detected and step 807 is executed.
In step 807 (corresponding to a rising edge just being detected), the temperature difference is determined in accordance with EQ. 7 for the time period that has just completed. The Ton counter and the Toff counter are then reset. In step 811, microprocessor control unit 301 determines the speed of compressor 303 in accordance with a predetermined function f(Tdiff), e.g., relationship 503 as shown in
Compressor 303 is powered by AC power lines 905a, 905b through rectifier bridge 907 and IGBT array 307. PWM controller 305 configures IGBT array 307 to control compressor 303 at the desired compressor speed. PWM controller 305 includes microcontroller 901 and gate drivers 903a-903c. The speed of compressor 303 is controlled by PWM controller 305, in which the voltage-to-frequency ratio is adjusted with a speed feedback configuration.
Embodiments of the invention support a heating function in a HVAC system. When supporting the heating function a controller unit, in conjunction with a thermostat unit, couples with a variable blower motor of a furnace. The speed of the variable blower motor is varied in accordance with characteristics of the motor and thermodynamics considerations.
As can be appreciated by one skilled in the art, a computer system with an associated computer-readable medium containing instructions for controlling the computer system can be utilized to implement the exemplary embodiments that are disclosed herein. The computer system may include at least one computer such as a microprocessor, digital signal processor, and associated peripheral electronic circuitry.
Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.
Claims
1. A system for controlling an air conditioning unit, the air conditioning unit including a variable speed compressor, the system comprising:
- a thermostat unit including: a temperature sensor measuring an ambient temperature of an environmentally controlled space; a switching module controlling conduction of a signal over a controlled time interval; and a thermostat processing module determining a temperature difference between the ambient temperature and a set temperature, determines a duty cycle corresponding to the temperature difference, and controlling the switching module in accordance with the duty cycle, the signal being electrically conducted during an activated time duration and electrically blocked during an deactivated time duration over a time period, the duty cycle specifying the activated time duration and the deactivated time duration; and
- a compressor controller unit including: a signal interface module monitoring the signal from the thermostat unit; and a compressor controller processing module determining the duty cycle from the signal, determining the temperature difference from the duty cycle, and determining an updated compressor speed from the temperature difference, and instructing the variable speed compressor to function at the updated compressor speed.
2. The system of claim 1, the switching module including an electrical component that electrically closes during the activated time duration and electrically opens during the deactivated time duration.
3. The system of claim 1, the thermostat processing module processing the temperature difference between a range between Tmax and −Tmax.
4. The system of claim 3, thermostat processing module determining the duty cycle from the temperature difference divided by said Tmax times 50% plus 50%.
5. The system of claim 4, the thermostat processing module setting the temperature difference to a positive limited value when the temperature difference is greater than approximately Tmax and setting the temperature difference to a negative limited value when the temperature is less than approximately −Tmax.
6. The system of claim 3, the thermostat processing module sending a pulse having a pulse duration less than a minimum value when decoding the duty cycle as zero, the pulse being conveyed by the signal.
7. The system of claim 6, the compressor controller processing module decoding the signal corresponding to the duty cycle as being zero when the pulse duration is less than the minimum value.
8. The system of claim 3, the thermostat processing module sending a predetermined pulse pattern that designates an emergency stop, the predetermined pulse pattern being conveyed on the signal.
9. The system of claim 8, the compressor controller processing module decoding the signal corresponding to the emergency stop and instructing the variable speed compressor to stop rotating.
10. The system of claim 1, the switching module controlling the signal having a switched alternating current (AC) waveform.
11. The system of claim 1, the compressor controller processing module determining the time period as a time value between raising edges of consecutive time durations.
12. The system of claim 1, the thermostat unit sending configuration information to the compressor controller unit.
13. The system of claim 12, the thermostat unit encoding a value of Tmax in the configuration information.
14. The system of claim 1, the compressor controller unit further including:
- a data structure that maps the temperature difference to the updated compressor speed; and
- the compressor controller processing module access the data structure to determine an updated compressor speed.
15. A thermostat unit for controlling an air conditioning unit, the air conditioning unit including a variable speed compressor, the thermostat unit comprising:
- a temperature sensor measuring an ambient temperature of an environmentally controlled space;
- a switching module controlling conduction of a signal over a controlled time interval, the signal having a switched alternating current (AC) waveform; and
- a thermostat processing module determining a temperature difference between the ambient temperature and a set temperature, determines a duty cycle corresponding to the temperature difference, and controlling the switching module in accordance with the duty cycle, the signal being electrically conducted during an activated time duration and electrically blocked during an deactivated time duration over a time period, the duty cycle specifying the activated time duration and the deactivated time duration.
16. A thermostat unit of claim 15, the thermostat processing unit determining the duty cycle from the temperature difference divided by Tmax times 50% plus 50%.
17. A thermostat unit of claim 15, the switching module including an electrical component that electrically closes during the activated time duration and electrically opens during the deactivated time duration.
18. A compressor controller unit for controlling an air conditioning unit, the air conditioning unit including a variable speed compressor, the compressor controller unit comprising:
- a signal interface module monitoring a signal from a thermostat unit, the signal having a switched alternating current (AC) waveform and being characterized by a duty cycle; and
- a compressor controller processing module determining the duty cycle from the signal, determining the temperature difference from the duty cycle, and determining an updated compressor speed from the temperature difference, and instructing the variable speed compressor to function at the updated compressor speed.
19. A compressor controller unit of claim 18, the compressor controller processing module decoding the signal by determining that the temperature difference equals the duty cycle minus 50% divided by 50% times Tmax.
20. A compressor controller unit of claim 18, further comprising:
- a pulse width modulation controller controlling a pulse width of at least one control pulse in accordance with the temperature difference and a feedback signal from the variable speed compressor, the feedback signal being indicative of a difference between a target compressor speed and an actual compressor speed; and
- an array providing at least one control signal to the variable speed compressor in accordance with the pulse width of the at least one control pulse from the pulse width modulation controller.
21. A system for controlling a furnace, the furnace including a variable speed blower motor, the system comprising:
- a thermostat unit including: a temperature sensor measuring an ambient temperature of an environmentally controlled space; a switching module controlling conduction of a signal over a controlled time interval; and a thermostat processing module determining a temperature difference between the ambient temperature and a set temperature, determines a duty cycle corresponding to the temperature difference, and controlling the switching module in accordance with the duty cycle, the signal being electrically conducted during an activated time duration and electrically blocked during an deactivated time duration over a time period, the duty cycle specifying the activated time duration and the deactivated time duration; and
- a furnace controller unit including: a signal interface module monitoring the signal from the thermostat unit; and a furnace controller processing module determining the duty cycle from the signal, determining the temperature difference from the duty cycle, and determining an updated speed of the variable speed blower motor from the temperature difference, and instructing the variable speed blower motor to function at the updated compressor speed.
22. The system of claim 21, the thermostat processing module processing the temperature difference between a range between Tmax and −Tmax.
23. The system of claim 22, the thermostat processing module determining the duty cycle from the temperature difference divided by said Tmax times 50% plus 50%.
Type: Application
Filed: Jun 28, 2006
Publication Date: Jan 3, 2008
Applicant: Computime, Ltd. (Kowloon)
Inventors: Wai-Leung Ha (Hong Kong), Chung Ming Cheng (Hong Kong), Kairy Kei Lei (Shen Zhen City)
Application Number: 11/427,161
International Classification: F24F 7/00 (20060101); F25B 49/00 (20060101);