Low-cost wireless HVAC systems

Communication between the various elements of HVAC systems is effected by means of low-cost, low-power, narrow-band AM SAW-stabilized transmitters 21, 27, 39, 86 and receivers 18, 28, 47, 89. A residential embodiment (FIG. 1) transmits temperature information from each room of the house to a master control 24, which is used to control the HVAC demand and to control the damper in the corresponding room. In a first commercial building embodiment (FIGS. 2 and 3), thermostat/transceiver 61-66 assemblies transmit not only demand and control information from the corresponding thermostat 78 (with switches), but relay information transmitted from other thermostat/transceiver assemblies, whereby messages are retransmitted from one floor to the next to overcome the high attenuation of commercial building construction in reaching rooftop HVAC systems 71-76. In a second commercial building embodiment (FIG. 4), messages are transmitted from a thermostat/transceiver assembly 92 in each floor to a relaying transceiver assembly 96 in a stairwell, the transmissions to rooftop units 93, 97 being made with little attenuation through the stairwell and the roof. Message protocols with or without acknowledgement may be used. Relative humidity and CO.sub.2 level may be controlled as well as temperature.

TECHNICAL FIELD 
This invention relates to low-cost wireless communication linking elements 
of heating, ventilating and air conditioning systems (HVAC), in both 
residential and commercial building embodiments, utilizing low-cost, 
surface acoustic wave (SAW) stabilized, amplitude modulated (AM) radio 
receivers and transmitters. 
BACKGROUND ART 
Most present HVAC systems have the elements thereof linked together 
directly by wire to transmit analog signals indicative of sensed 
characteristics such as temperature relative humidity, or CO.sub.2 level, 
discrete signals indicative of demand for heating or cooling, relative 
humidity, or CO.sub.2 level, and fan operation, and/or digital signals 
indicative of actual and desired conditions within the system. 
A wireless HVAC system is disclosed in U.S. Pat. No. 5,224,648. The system 
therein utilizes spread spectrum frequency modulated (FM) transmission 
which can be utilized with output power of on the order of one watt in the 
900 megahertz regime without the need of an FCC site license. While spread 
spectrum FM provides a high degree of noise immunity, there also are a 
large number of competing transmitters, including wireless telephones, 
wireless local area networks, and other devices. Therefore, 
interference-free operation may require additional system sophistication, 
and therefore greater cost. While the power of spread spectrum systems 
allows communication on the order of a city block or more, and permits 
transmission through the elements of commercial buildings (such as steel 
reinforced concrete flooring), the power consumption is such as to require 
each element to be dynamically powered through an AC outlet or by 
batteries. If batteries are used in such a system, batteries need be 
large, bulky, expensive, or suffer from battery life which is too short to 
be practical (weeks or months). 
DISCLOSURE OF INVENTION 
Objects of the invention include provision of a wireless HVAC system which 
is low in cost and can be operated for long periods of time on small, 
common batteries. 
This invention is predicated in part on the concept that narrow band 
amplitude modulated AM transmission can provide adequate noise immunity 
when operating in a regulated low-power spectrum without a site license, 
in part on the concept that an HVAC system can be implemented utilizing RF 
transmission with merely enough power to penetrate through a single level 
of a multi-level building by retransmitting the signal from each level to 
the next, and in part on the concept that the capabilities of a 
sophisticated system are not really necessary for communications in HVAC 
systems, which systems are, after all, extremely simple to control. This 
invention is also predicated on the concept that HVAC systems are 
generally non-critical, and with very slow response times (on the order of 
minutes), and therefore can operate with relatively few, 
randomly-transmitted messages. 
According to the present invention, a wireless HVAC system employs low 
cost, low power, surface acoustic wave SAW-stabilized, narrow band AM 
radio transmitters and receivers as communication links between the 
operative elements thereof. In accordance with the invention, low power, 
low cost, SAW-stabilized, narrow band AM radio transceivers are utilized 
as relays to transmit signals from one level of a building to the next 
level of the building so that the low powered signals will ultimately 
reach through several levels of a building, even when the levels are 
separated by steel and concrete. The invention may be used to control 
temperature, CO.sub.2 level and/or humidity. 
In one embodiment of the invention, temperature within each room of a 
multi-room residential HVAC system, wherein each room comprises a zone, is 
transmitted by a corresponding low power, low cost, SAW-stabilized, narrow 
band, AM radio transmitter to a receiver on a master controller, and a 
similar transmitter on the master controller will transmit a corresponding 
desired response to a similar receiver on a damper regulating HVAC system 
airflow into the corresponding room. In another form of the invention, the 
temperature signal is relayed by low power, low cost, SAW-stabilized, 
narrow band, AM radio transceivers, the receiving portion of which is 
utilized to provide an acknowledgement signal, thereby providing integrity 
of transmission even though only providing one signal transmission for 
each change in condition. 
In further accord with the invention, transceivers are utilized as relays 
such that every transmitted signal gets retransmitted by one or more 
transceivers at each level of a building, thereby ensuring that the 
transmission will be received even though there is prohibitive attenuation 
between the point of original transmission and the point of ultimate 
reception. 
In accordance with another aspect of the present invention, low powered SAW 
transmitters may be utilized to transmit HVAC control messages within the 
low RF attenuating stairwells of buildings which have high RF attenuation 
between one floor and the next. 
The invention may be implemented with readily available low power, low 
cost, SAW-stabilized, narrow band, AM radio receivers and transmitters 
which are utilizable without site license under FCC Part 15 regulations. 
The invention utilizes transmitters and receivers as well as very simple 
microprocessors, the power consumption of which is sufficiently small that 
ordinary common batteries may be utilized with a suitably long useful life 
(on the order of a year). The invention is practiced utilizing only 
apparatus and techniques which are well within the skill of the art, in 
the light of the teachings which follow hereinafter. 
Other objects, features and advantages of the present invention will become 
more apparent in the light of the following detailed description of 
exemplary embodiments thereof, as illustrated in the accompanying drawing.

BEST MODE FOR CARRYING OUT THE INVENTION 
In FIG. 1, an HVAC unit 9 supplies conditioned (heated or cooled) air 
through a duct 10 to a plurality of dampers 11, there being one damper in 
each room of the corresponding building, which may typically be a 
residence. Air is returned from the rooms through return inlets (not 
shown) and a return duct 12. Each room of the building is considered a 
zone M . . . N for HVAC purposes. 
The functions of the HVAC 9 (heating, cooling and air motion) are effected 
in response to signals on a trunk of lines 15 from a microprocessor 16, 
which in turn receives commands over a line 17 from a SAW receiver 18. The 
microprocessor 16 responds to signals from the receiver 18 which are sent 
thereto by a SAW transmitter 21 in response to signals on a line 22 from a 
microprocessor 23 in a master control 24. In response to recognition of 
command signals sent thereto, the microprocessor 16 may provide signals on 
a line 26 to cause a SAW transmitter 27 to transmit an acknowledgement to 
a SAW receiver 28 connected to the microprocessor 23 by signal lines 29. 
The microprocessor 23 has a plurality of temperature set point inputs 32, 
one corresponding to each of the zones M . . . N, to define the desired 
temperature for the corresponding zone. 
Each zone has a temperature sensor 35 which provides an input over a signal 
line 36 to a corresponding microprocessor 37. In the present embodiment, 
whenever one of the microprocessors 37 determines that the temperature has 
changed by some threshold amount from a previous temperature which has 
been communicated to the master control 24, the new temperature will be 
formulated in a message sent over signal lines 38 for transmission by a 
SAW transmitter 39 to the SAW receiver 28 in the master control 24. In 
order to identify the zone related to the temperature indicated in the 
message, the transmitted message includes a zone address provided by the 
microprocessor 37 in response to suitable signals on lines 42 from a zone 
address switch 43 connected to each microprocessor 37. In order to receive 
acknowledgement signals, if desired, the microprocessors 37 also have 
signal lines 46 connecting them with corresponding SAW receivers 47. 
However, if no acknowledgement signal is necessary in the implementation 
of the present invention, the SAW receivers 47 and/or the SAW transmitter 
27 need not be utilized. The sensors 35 could include, or instead be, 
CO.sub.2 or humidity sensors. 
Operation of this embodiment may take a variety of forms. Typically, the 
master control will compare received temperature messages with 
corresponding setpoints for the various zones, and when a temperature 
message indicates that a zone has veered from a desired temperature by a 
threshold amount, the microprocessor 23 will send a message to the 
microprocessor 16 to cause the proper conditioning of the air (heating or 
cooling) so that such air passing through the damper 11 of the 
corresponding zone will tend to correct the temperature. In the embodiment 
shown in FIG. 1, it is assumed that each microprocessor 37 is directly 
wired to the corresponding damper 11. However, whenever this is not 
possible, each damper may have associated therewith its own microprocessor 
and SAW receiver (along with a SAW transmitter for acknowledgment 
messages, if desired). Within each zone, the microprocessor will operate 
the damper to permit maximum, minimum, or some in-between amount of air as 
determined by the difference in the temperature sensed in the zone and the 
temperature of the air in the duct 10. In the embodiment of FIG. 1, this 
is achieved by the microprocessor 23 sending a message to the related 
microprocessor 37 to regulate the damper accordingly. In other embodiments 
of the invention, the microprocessor may also respond to a temperature 
sensor in the duct 10 immediately adjacent the damper 11, whereby it can 
determine the correct setting for the damper by comparing the setpoint 
temperature with actual temperature, and with the duct temperature, in a 
well-known fashion. Or, each damper may be controlled directly by the 
temperature sensor 37, or a thermostat, directly associated therewith, 
through RF transmissions. As is known, in the event that one zone requires 
heat while the other zone requires cooling, the microprocessor 23 will 
respond to the comparison of setpoint inputs 32 with the temperature 
messages received to cause the HVAC 9 to cycle between heating and cooling 
in response to messages sent through the microprocessor 16. The sensors 
could also, or instead, comprise CO.sub.2 level sensors and/or relative 
humidity sensors. Most HVACs include humidifiers; the return duct 12 may 
have a fresh air inlet damper 49, controlled by a microprocessor (such as 
37) communicating with a transmitter (such as 39) and/or a receiver (such 
as 47), in response to CO.sub.2 level. All of this is well known in the 
art and forms no part of the present invention. 
In the present embodiment, it is assumed that the SAW transmitters and 
receivers are narrow-band, 418 MHz AM, transmitting randomly and 
infrequently with on the order of a milliwatt of output power, to permit 
operation without any site licenses under FCC Part 15.231. It is also 
assumed in this embodiment that messages being transmitted are formatted 
in the known Echelon Lon Works communication protocol, or in a simplified 
communications protocol that will serve the purpose herein. Because 
temperature response of a temperature sensor in a room fed with 
conditioned air is on the order of minutes, the transmissions of 
temperature from any given zone, in response to changes of a threshold 
magnitude therein, will occur no more frequently than once every few 
minutes, except in response to strong perturbations (such as initial 
opening of an outside door or window during extreme temperature 
conditions). 
The SAW transmitters, SAW receivers, microprocessors and associated 
circuitry for each of the zones, for the master controller, and for the 
HVAC may, of course, be integrated into suitable single units. The SAW 
transmitters may be formulated utilizing RF Monolithics, Inc. type HX1003 
integrated circuits (ICs), and the SAW receivers may be formulated by 
utilizing RF Monolithics, Inc. type RX1300 ICs, all as is known in the 
art. 
In the embodiment of FIG. 1, it is assumed that all of the information 
processing to determine what the HVAC should do, and whether any dampers 
should more open or more closed is achieved in the microprocessor 23. On 
the other hand, it should be understood that the particular place where 
the majority of signal processing occurs is irrelevant to the present 
invention, which relates only to the manner of transmission between 
elements of the HVAC system. Further, the setpoint inputs could be in each 
zone and transmitted to any processor which responds thereto to manifest 
the demand. 
Referring now to FIG. 2, a building 50 comprises a plurality of zones 
51-56, each having a corresponding thermostat/transceiver assembly 61-66 
disposed therein for communicating commands to a related rooftop HVAC 
system 71-76, for controlling the temperature and air flow within the 
related zone 51-56. In FIG. 3, each of the thermostat/transceiver 
assemblies include a wall mounted thermostat 78 which has a service 
selection switch 79 to command cooling, heating or neither, a fan switch 
80 to cause the fan to be on all the time or to turn on only when a demand 
is being met, a setpoint control 81, and, possibly, a visible thermometer 
82. Within the wall mounted thermostat 78, thermo-responsive means will 
provide signals indicating when there is a demand for the indicated 
service (that is, it is too warm when cooling is required or it is too 
cool when heating is required). The wall mounted thermostat 78 is 
therefore equivalent to the temperature sensors 35, the setpoint inputs 
32, and the routines of the microprocessor 23 which generate a condition 
demand indicating signal for transmission to the HVAC. This signal is 
provided along with the discrete signals from the switches 79, 80 through 
signal lines 83 to a microprocessor 84. The microprocessor 84 will 
formulate a message and send it over signal lines 85 to a SAW transmitter 
86 for transmission, in order to cause the related HVAC system 71-76 to 
respond appropriately. The microprocessor 84 also receives signals on 
lines 88 from a SAW receiver 89 which may comprise commands from others of 
the thermostat/transceiver devices 61-66, or, depending upon the protocol 
used, may comprise an acknowledgment signal from the related HVAC system 
71-76. Any message received with an address different from that of the 
microprocessor 84 (which comprise all received messages except 
acknowledgement messages for the microprocessor 84) will be retransmitted 
by the SAW transmitter 86. This is the relay aspect of the present 
invention. 
In FIG. 2, each of the HVAC systems 71-76 is assumed to include the 
apparatus (not shown) associated with the HVAC 9 in FIG. 1, that is, a 
microprocessor, a SAW transmitter, and a SAW receiver. A low powered 
narrow band AM radio transmission on the order of 1 milliwatt is 
sufficient to transcend the various barriers represented by the building 
structure. For instance, the floors 91-93 may each comprise 
steel-reinforced concrete or concrete over steel, and the wall structures 
between zones may include stairwells, restrooms and the like, and may 
comprise more than a single wall structure. However, according to the 
invention, it has been determined that transmissions of narrow band AM at 
418 MHz on the order of one milliwatt will penetrate a single wall or 
floor structure of a concrete building such that the signal can be passed 
from one unit 61 to another unit 62, and so forth, in a relay fashion. As 
depicted in FIG. 2, the signals can also be transferred from one unit 61 
to another unit 64 and a third unit 65, and so forth. By using a basic 
methodology that receives signals and only changes stored signals 
representative of conditions in the system when the received signals 
indicate a change therein, it is irrelevant how many times a particular 
HVAC system 71-76 may receive the same message due to being relayed 
through many of the assemblies 61-66. The messages may in fact be received 
from the original transmitter as well as from a relaying transmitter, in 
some cases. However, depending on the message protocol used, it would be 
simple to have each assembly (e.g., 62) retransmit only messages received 
from an assembly (e.g., 61) farther from the HVACs 71-76. Or, the 
transmissions could all be unicast--e.g., 61 to 62, 62 to 63, etc., by 
using specific addresses, for initial transmissions and for 
retransmissions. All of this is well within the skill of the art. 
Referring now to FIG. 4, another embodiment of the invention utilizes the 
stairwell 90 of a building 91 as a low attenuation path for transmitting 
HVAC control messages between thermostat-receiver assemblies 92 in each 
zone of the building and corresponding HVAC systems 93 on the rooftop of 
the building. Transmission is effected between one of the assemblies 92 
and a corresponding relay transceiver 96 disposed adjacent thereto on the 
same building level within the stairwell 90, and corresponding 
transceivers 97 on the rooftop. In this case, no relay operation is 
required between the transceiver assemblies 92 or between transceiver 
assemblies 96 since the transmission can easily be effected in the open 
stairwell 90. Thus, each related pair of transceiver assemblies 92 and 96 
form an independent communication channel. Of course, if the stairwell 
attenuates the signals too much, relay function may be provided by the 
transceivers 96. In the embodiment of FIG. 4, each of the HVAC systems 93 
has a corresponding transceiver 97 on the rooftop; however, in a suitable 
situation, only a single rooftop transceiver and microprocessor is 
required on the rooftop, the microprocessor sorting out the signals and 
providing them to the correct, corresponding HVAC system, in each case. 
In the embodiment of FIG. 4, the transceiver assemblies 97 are shown 
hard-wired to the corresponding HVAC systems 93; the invention may as well 
be practiced, however, utilizing transceivers at the HVAC systems 93, as 
in the embodiment of FIG. 1, for communication with one or more 
transceivers 97 on the rooftop. 
As is common in the industry, the term "air conditioning" usually refers to 
air cooling with its attendant dehumidification, but sometimes include 
humidity control as such, and freshness control (CO.sub.2 level); but the 
term "conditioning air" usually means heating, cooling, controlling the 
humidity or freshness of air, and it is used in that way herein. The 
present invention may be used in an air conditioning and/or heating and 
ventilating system: that is, it may be used in a central heating system 
which does not provide cooling and it may be used in a central cooling 
system which does not provide heat; it may be used with or without 
humidity or freshness control. 
In the embodiment of FIG. 1, the temperature sensors 35 are separate from 
the temperature setpoint inputs 32, and the microprocessor will respond to 
manifestations from each in order to provide a condition demand indicating 
signal to control the manner in which the HVAC conditions air. In the 
embodiments of FIGS. 2-4, the setpoint is manifested by adjusting the 
positional bias of a thermostatic switch, and the temperature is 
manifested by thermostatic switch motion responsive to temperature to 
cause it to actuate appropriately, in dependence upon the setpoint. In 
this case, the switch itself provides the condition demand indicating 
signal to control the manner in which the HVAC conditions the air. 
In the embodiment of FIGS. 2-4, the thermostat and switch assembly 78 
processes all the necessary information to provide simple demand signals 
on the lines 83, which, absent the invention, would go to the appropriate 
parts of the corresponding HVAC system 71-76 directly by wire. In a 
commercial embodiment wherein other than an analog, wall mounted 
thermostat/switch assembly 78 is utilized, temperature sensors may be 
utilized and processing may be achieved in the microprocessor 84 of each 
of the assemblies 61-66 or in the corresponding processor in each of the 
HVAC systems 71-76. Such is irrelevant to the invention, which relates 
only to the manner of transmission of the manifestations (setpoint, 
temperature and corresponding demand), as well as heat/cool/off and fan 
on/auto discretes. 
In the embodiments of FIGS. 2-4, infrequent, random transmissions are 
achieved by transmitting a signal only when the demand signal changes from 
demanding heating and cooling to cessation thereof, or changes from there 
being no demand to a demand for heating or cooling. 
Thus, although the invention has been shown and described with respect to 
exemplary embodiments thereof, it should be understood by those skilled in 
the art that the foregoing and various other changes, omissions and 
additions may be made therein and thereto without departing from the 
spirit and scope of the invention.