CA2224963A1 - Wireless thermostat - Google Patents

Abstract

A wireless controller for controlling the application of electrical power to a temperature modifying load (HVAC) having a wireless thermostat which has a temperature sensor for sensing the ambient temperature and a comparison means for comparing the ambient temperature with a predetermined setpoint temperature. Thecomparison means provides an air signal as a function of the difference between the ambient temperature and the predetermined setpoint temperature. The transmitter transmits the air signal to a control means wherein the control means controls the temperature modifying load (HVAC) in accordance with the air signal. The wireless controller may further comprise a solar cell and a storage capacitor for providing power to the wireless thermostat and coding means and decoding means for providing identification of the wireless thermostat.

Description

WIRELESS THERMOSTAT
FIELD OF THE INVENTION
This invention relates to thermostats. More specifically, it relates to wirelessand, in one embodiment, batteryless thermostats.

BACKGROUND OF THE INVENTION
Thermostats are common in almost all commercial and residential settings. It is well known that thermostats are a vital control for HVAC systems. For the purpose of simplifying the description and to increase the ease of understanding the invention, 10 Applicant will describe the invention for use in a residential home. However, it should be understood that this invention is also applicable to commercial settings.
Most residential homes utilize a single thermostat which is located in an area away from direct sunlight. The HVAC's heating and cooling units, such as a furnace, a boiler or an air conditioner, are generally located in a different location such as in a 15 basement utility room or in the case of air conditioners and heat pumps, outside. The thermostat is generally hardwired to the heating and/or cooling units, allowing for the control of these devices by the thermostat.
When remodeling an older home, or in the case of upgrading a thermostat, the process can be overly burdensome. To install the new thermostat, the party remodeling 20 or upgrading may be required to run new wiring to the heating and/or cooling units.
This process is extremely difficult if the retrofit installation involves plaster walls or penetrating stone or brick.
A second disadvantage of most hardwired thermostats is that they sense temperature in a single location of the home and are therefore unable to accurately 25 control the temperature in other rooms of the home. By way of explanation, in a home which is a two-story home with a basement, if the thermostat is located in an upstairs hallway, the thermostat is unable to accurately control the heating and cooling in the basement. One solution which has been utilized is to locate thermostats in different zones and provide damper controls for a zone-controlled HVAC system. However, 30 zone-controlled HVAC systems are quite expensive and often difficult to install, if not prohibitive to install in established homes.

Applicant's invention provides a thermostat which is easy to install and does not require hardwiring to the heating or cooling unit. Further, Applicant's invention enables the owner of the home to accurately control the heating and cooling in whichever room the owner of the home desires.

SUMMARY OF THE INVENTION
Applicant's invention is a wireless thermostat which communicates with the HVAC unit via RF signals. The wireless thermostat allows for control of the heating or cooling in a room specified by the occupant. The wireless thermostat is powered by either long life batteries, or by high efficiency solar cells and a storage capacitor.
In one embodiment, the thermostat is capable of sending temperature and other related thermostat information to a remote receiver normally located at the HVAC unit.
The tr~n~mi~ions are originated at the opening or closing of a mercury switch on a bi-metal strip and contain digital coded information to identify the unit from other potential units in the system. The receiver contains decoding circuitry to identify an individual unit code and perform the previously established function.
In a more advanced embodiment, the RF circuitry would be integrated into a setback thermostat and would have the capability of sending timing and temperature data over the RF link to the HVAC receiving unit. Setback thermostats are well known in the art. An example of setback thermostats can be found in U.S. Patent 4,314,665 issued to Michael R. Levine and hereby incorporated by reference. The capability also exists to incorporate multiple temperature transmitting units, communicating to single or multiple receiving units and two-way communications.
As stated earlier, the thermostat can be powered by either a long life lithium battery for continuous operation of more than 5 years, or more preferably by a high efficiency solar cell which charges a large memory backup capacitor. High efficiency solar cells would provide power to the therrnostat and prevent problems associated with dead batteries. However, because the thermostat requires light energy to charge the capacitor, the storage capacitor may discharge if the solar cell is not exposed to sufficient light. Therefore, a low power detection circuit is incorporated to prevent the thermostat from transmitting during a low power situation.

A wireless thermostat retrofit installation of thermostat is relatively simple. The installer need only install a receiving unit at the HVAC control and program thethermostat. The operator can secure the thermostat as one would a conventional thermostat. However, as the thermostat is now wireless, it need not be permanently secured to the wall of the home. The operator is now able to transport the thermostat with them to whichever room they are (;ullellLly occupying, in essence, providing an inexpensive zone control system.
The thermostat may be further enhanced by providing an algorithm in the HVAC controller which cycles the HVAC on and off with a predetermined duty cycle.
The battery powered thermostat is programmed to transmit at an upper and lower temperature limit. If the predetermined duty cycle of the HVAC does not m~intz~in the temperature within these limits, the thermostat transmits data to alter the duty cycle accordingly. In doing this, the thermostat only fine tunes the self cycling HVACcontroller. An example of a HVAC controller operated under this principle can befound in U.S. Patent 5,248,083 and in U.S. Patent 5,307,990, both of which issued to Adams, et al., and are hereby incorporated by reference. Further, in order to prevent the furnace from being controlled outside normal temperatures, the HVAC controller can be provided with a safety monitor. This safety monitor would operate to override the temperature signals coming from the wireless thermostat in the event that the wireless thermostat provided erroneous or no information. As an example, if the operator were to remove the wireless thermostat from the home and place it outdoors on a cold day, the furnace would essentially be locked in an "on" position until the override temperature controller turned the furnace off.

BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 illustrates a block diagram of the complete system.
Figure 2 illustrates the logic and sensing control for the thermostat.
Figure 3 illustrates the RF portion of the thermostat.
Figure 4 illustrates the RF portion of the HVAC controller.
Figure 5 illustrates the logic and control means for the HVAC controller.
Figures 6A & 6B illustrates a second embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Figure 1 illustrates the general concept of the wireless controller. Wireless thermostat 1 comprises general control elements 10, RF transmitter 20, and antenna 30.
General control element 10 comprises a temperature sensor for sensing ambient 5 temperature. The ambient temperature is compared to a predetermined set point by a comparison means. The comparison means provides an error signal as a function of the difference between the ambient temperature and the predetermined set point temperature. RF transmitter then transmits the error signal to a control means.
Transmitter 20 may also comprise an RF receiver in the event two-way transmissions 10 are desired.
Figure 1 illustrates two possible control means which would receive data from and possibly transmit data to thermostat 1. HVAC controller 80 represents a conventional controller which is located on or near the temperature modifying load.
The temperature modifying load, may be a HVAC coolant or heating unit but need not 15 be so limited. For example the temperature modifying load could include means for providing circulation of outside air into the structure or be as simple as a fan. However, for simplification the temperature modifying load shall be referred to as the HVAC
system. HVAC controller 80 comprises antenna 32, RF receiver 85 and controller circuitry 90. Control circuitry 90 is hardwired to the HVAC system and operates to turn 20 on and off the HVAC system. A second embodiment of the control means involves the use of a home control system 60, such as the Honeywell Total HomeTM Control System, or a p.c. based home control system. RF receiving unit 65 receives from and transmits to wireless thermostat 1 through antenna 34. Control circuitry 68 and the software incorporated therein operates to control many parameters within the home. One of these 25 parameters being the internal temperature of the home. In the second embodiment, controller 60 would generally be hardwired to the HVAC controller 80, although home control 60 may also transmit and receive RF signals with HVAC controller 80.
Figure 2 illustrates the logic necessary to control the timing and informationalcontent of the transmissions. Mercury switch 5 of the temperature sensing means 8 30 thermostat triggers clock/divider 11 which controls the transmitter power up, data rate, message link and interval between messages. Temperature sensing means 8 illustrates a simple temperature sensor, it would be simple for one of ordinary skill in the art to replace temperature sensing means 8 with a programrnable setback thermostat.
Temperature sensing means 8 further provides an input to shift registers 13 and 14.
Clock/divider 11 clocks shift registers 13 &14 and bi-phase codes the 16 bits of data and serially sends the data through data line 12 to transmitter 20. Two 4 bit words comprise the information and 4 additional bits are used as checksum. The rem~ining bits provide synchronization in the receiver or are unused. The 16 bit word is transmitted eight times at three second intervals to insure reliability. Low voltage detector 15 is also added to insure the transmitter does not lock in the transmit mode and low voltages do not allow the solar cells to recharge the capacitor. A transmit enable is provided on line 16 when sufficient power is present to transmit.
Figure 3 illustrates the RF portion of the transmitter which contains solar power cell 22, crystal RF oscillator 25, frequency multiplier 26 and output filter 27.Transmitter 20 is powered up for 50 ms for each tr~n~mis~ion the error signal and is frequency shift keyed by the data in the shift register. The frequency is modulated by modulator 24. The helical filter 29 at the output insures a clean tr~n~mi~ion of spurious emlsslons.
Solar cell 22 and storage capacitor 23 are designed to provide power to the wireless thermostat 1 at a constant voltage level. Though solar cell 22 and storage capacitor 23, are shown as the power source, a long life lithium battery can be substituted with no circuitry changes. This may be desirable in locations which have very low light conditions over prolonged periods.
Figure 4 illustrates the analog portion of the receiver and data squaring circuit.
A crystal oscillator 81, multiplier 83 and helical filter 82 similar to that of transmitter 20 are used as the first RF oscillator which is frequency offset by 45 MHz from transmitter 20. An input helical 84 is inserted between the antenna 32 and the first mixer to minimi7~ interference from high powered licensed transmitters. The 45 MHz I/F from the first mixer is filtered, amplified and mixed again to 455KHz where it is filtered again, amplified, limited and detected before being squared at the output and sent to the receive logic. The steps are accomplished l1tili7ing second oscillator/mixer 86, second IF filter 87 and FM amplifier/limiter/discriminator 88. The output of FM
amplifier/limiter/discrimin~tor 88 is provided to data squaring circuit 89.

Figure 5 illustrates the logic decoder and AC power control. The CiL~;Uilly for the data decoder is implemented in microprocessor 91 which contains logic for the data synchronization ch~;uilly, serial to parallel conversion, checksum and word redundancy check. The output from data squaring circuit 89 is provided to microprocessor 91. The decoded output controls optical isolator 93 which controls triac 92. Triac 92 operates the temperature modifying load. Power supply 94 provides power to receiver 85 and control means 90.
In a second embodiment the majority of the components are replaced by surface mounted integrated circuits. Figures 6A and 6B illustrate the second embodiment.Figure 6A illustrates wireless thermostat 1. Wireless thermostat 1 of the secondembodiment still utilizes temperature sensing means 8 and solar cell 22. However, general control element 110 is a Microchip PIC 12C54. General control element 10replaces most of the discrete components of Fig. 2. The Microchip PIC 12C54 is an 8-bit CMOS microcontroller. Transmitter 20 in the second embodiment is replaced bytransmitter 120. Transmitter 120 is a RF Monolithics, Inc. HX1000 transmitter.
Figure 6B illustrates control means 80 for the second embodiment. For the second embodiment control means 80 is powered by a standard wall transformer 194that rectifies and steps the voltage down. Receiver 185 is a RF Monolithics, Inc.
RX1000 receiver. The received error signal is processed by control circuit 190 which is a second Microchip PIC 12C54. The output of control circuit 190 controls triac 92 which in turn controls the temperature modifying load.
A further benefit of lltili7ing microprocessors 91 and 190 is that the system can be set up to self cycle the temperature modifying load. By self cycling the temperature modifying load wireless thermostat 1 need only transmit when the ambient temperature is above or below the predetermined temperature, dependent upon the application (i.e.
heating or cooling).
It would be obvious to one of ordinary skill in the art that wireless thermostat 1 need not be limited to simple temperature sensing. One of ordinary skill in the art could easily adapt any thermostat to communicate in the manner disclosed in the invention.
Thus allowing humidity, co2, and other commonly sensed conditions to be controlled through wireless thermostat 1.

Claims (6)

1. A wireless controller for controlling the application of electrical power to a temperature modifying load comprising:
at least one wireless thermostat comprising, a temperature sensor for sensing ambient temperature, comparison means for comparing ambient temperature with a predetermined setpoint temperature, said comparison means providing an error signal as a function of their difference, transmission means for transmitting said error signal;
control means for generating a control signal for said temperature modifying device, said control means further comprising receiving means for receiving said error signal and providing said error signal to said control means, wherein said control means generates said control signal as a function of said error signal.

2. The wireless controller of claim 1 wherein said wireless thermostat further comprises a solar cell and a storage capacitor for providing power to said wireless thermostat.

3. The wireless controller of claim 1 wherein said wireless thermostat further comprises coding means, and said control means further comprise decoding means for identifying said wireless thermostat.

4. The wireless controller of claim 3 further comprising multiple wireless thermostats, each of said thermostats having a distinct identification code provided by said coding means, said decoding means utilizing said identification code to identify said wireless thermostat.

5. The wireless controller of claim 1 wherein said control means cycles said temperature modifying means based on a predetermined cycle rate, wherein when said error signal is received by said control means said predetermined cycle rate is modified in accordance with said error signal.

6. The wireless controller of claim 1 further comprising a second temperature sensor for sensing ambient temperature, wherein said second temperature sensor provides an override signal to said control means if said ambient temperature is above a high set point limit or below a low set point limit.