Technical Field

This invention relates to a method and system for controlling a heating/air conditioning unit. More particularly, this invention relates to a control unit which detects the presence of one or more gases produced by the heating/air conditioning unit.

Background Art

Many homes employ a heating unit which oper¬ ates by the combustion of supplied gas, and the distri¬ bution of the heat produced to the various rooms in the home by a network of forced air ducts and air return ducts. These central heating units can, under certain operating conditions exhaust undesirable levels of supplied gas and gas which is a byproduct of combustion, such as carbon monoxide, into the forced air ducts.

Further, many central heating units operate in conjunction with a central air conditioning unit. These units generally operate by pumping heat from the house to an outdoor heatsink by means of a closed compres¬ sion/evaporation system operating on a refrigerant. If a leak occurs in this closed system, refrigerant can be exhausted into the forced air ducts.

Prior art devices, such as the device dis¬ closed in U.S. Patent number 4,893,113 issued to Park et al . are capable of detecting the presence of carbon

monoxide in the air surrounding a heating unit and activating an alarm.

Further, Japanese patent number 62-225829 discloses a control device for a heating unit which calculates the concentration of carbon monoxide in the room the heating unit is placed in and terminates combustion based upon this calculated concentration. These prior art devices do not disable the heating unit in response to the detection of undesired gases.

U.S. Patent No. 5,239,980 issued to Hilt et al . ("the Hilt '980 patent") discloses a forced air furnace control system and method of operation. The system and method include a carbon monoxide (CO) sensor mounted in the furnace plenum for detecting a threshold concentration of CO and disabling the furnace if that threshold is exceeded. A reset circuit is also provided to manually re-enable the furnace. Significantly, the number of times that the furnace may be re-set is not restricted. That is, a building owner/operator may repeatedly re-enable the furnace regardless of the CO concentration present, thereby defeating the purpose of preventing exposure to dangerous CO concentrations.

This safety problem may be overcome by posi¬ tioning or configuring the re-set circuit of the Hilt '980 patent such that it is operable only by a properly trained service technician. However, with such re¬ stricted operation of the re-set circuit, a service technician will always be needed to re-enable the furnace, even where a dangerous CO concentration has been falsely indicated. Such false CO indications and the resulting furnace shut-down can be inconvenient, if

not dangerous, during winter periods where building heat may be absolutely necessary.

Moreover, sensing gas concentrations in the furnace plenum also requires a skilled service techni- cian for proper installation of the appropriate sensor or sensors and the wiring associated therewith. As a result, the cost and inconvenience of such a method and system increases, especially where such a system must be retrofit in an existing building. Higher costs and inconvenience decrease the likelihood that such a method and system will be used, thereby eliminating the very safety benefits sought.

Further, while sensing gas concentrations in the furnace plenum may provide the most rapid detection of higher than normal concentrations, depending upon the threshold levels used for comparison purposes, such a location may also result in a heating/air conditioning unit being disabled falsely or prematurely. That is, the gas concentration present in the actual living/working spaces of a building may be normal even though the concentration present in the plenum appears higher than normal .

Thus, a need exists for a method and system for sensing higher than normal gas concentrations away from the plenum and disabling a heating/air conditioning unit in that event which may be conveniently and econom¬ ically installed. Such a method and system, however, would still be capable of safely and accurately sensing gas concentrations in the very living/working spaces where those concentrations are most critical, and would provide a limited reset feature, thereby solving the

problems of false or premature disablement of a heat¬ ing/air conditioning unit described above.

Summary Of The Invention

According to the present invention, then, a method and system are provided for controlling a unit for heating a building having a plurality of liv¬ ing/working spaces, the heating unit operating by the combustion of a fuel. The method of the present inven¬ tion comprises sensing the concentration of a gas in at least one of the plurality of living/working spaces, and comparing the sensed gas concentration to a selected threshold. The method further comprises transmitting a control signal when the sensed gas concentration exceeds the selected threshold, receiving the control signal at a remote location, and disabling the heating unit in response to receipt of the control signal.

Similarly, the system of the present invention comprises means for sensing the concentration of a gas in at least one of the plurality of living/working spaces, and means for comparing the sensed gas concen¬ tration to a selected threshold. The system further comprises means for transmitting a control signal when the sensed gas concentration exceeds the selected threshold, means for receiving the control signal at a remote location, and means for disabling the heating unit in response to receipt of the control signal.

An object of the present invention is to detect the presence of multiple gases including supply gas and refrigerant and provides a separate indication for each gas. This indication can aid in the diagnostic

procedure during servicing of the heating/air condition¬ ing unit.

A further object of the present invention is to provide disabling of the central heating/air condi- tioning unit after a preset number of faults. Means are provided for reset of the control unit only upon actions taken by knowledgeable service personnel . This prevents the user from continually resetting the heating/air conditioning unit based upon continuing fault condi- tions.

Moreover, an object of the present invention is to provide a means for disabling the central heat¬ ing/air conditioning unit based upon the activation of one or more smoke alarms.

An additional object of the present invention is to provide a means for indicating inefficient combus¬ tion in a heating/air conditioning unit -- detected by measuring the pressure of higher than normal levels of exhaust gases.

These and other objects, features and advan¬ tages will be readily apparent upon consideration of the following detailed description in conjunction with the accompanying drawings .

Brief Description Of The Drawings

FIGURE 1 is a flow chart representation of one embodiment of the present invention;

FIGURE 2 is a block diagram representation of one embodiment of the system of the present invention;

FIGURE 3 is a block diagram representation of an alternate embodiment of the system of the present invention;

FIGURE 4 is a flow chart representation of an alternate embodiment of the present invention;

FIGURE 5 is a block diagram representation of an alternate embodiment of the system of the present invention;

FIGURE 6 is a flow chart representation of an alternate embodiment of the method of the present invention;

FIGURE 7a is a schematic representation of an alternate embodiment of the system of the present invention;

FIGURE 7b is a timing diagram which describes the operation of the circuit in FIGURE 7a;

FIGURE 7c is a schematic representation of an alternate embodiment of the system of the present invention;

Figure 7d is a schematic representation of an alternative embodiment of the system of the present invention;

Figure 7e is a schematic representation of an alternative embodiment of the system of the present invention;

FIGURE 8 is a block diagram representation of a standard heating/air conditioning unit and thermostat with connections to the system of one embodiment of the present invention;

FIGURE 9a is a block diagram representation of the smoke detector monitoring system of one embodiment of the present invention;

FIGURE 9b is a block diagram representation of the smoke detector processor of one embodiment of the present invention;

FIGURE 9c is a block diagram representation of an alternate embodiment of the smoke detector processor for one embodiment of the present invention; and

FIGURE 9d is a block diagram representation of a second alternate embodiment of the smoke detector processor for one embodiment of the present invention.

Best Mode For Carrying Out The Invention

Referring to Figure 1, a flow chart represen¬ tation of one embodiment of the method of the present invention is shown. The concentration of a selected gas is sensed as supplied by a heating or heating/air conditioning unit as shown in step 10. This gas concen¬ tration is compared with a selected threshold as shown in step 12. If the gas concentration exceeds the

selected threshold, the heating unit or heating/air conditioning unit is disabled as shown in step 14. If however, the gas concentration does not exceed the threshold, the gas concentration is continued to be sensed as shown in step 10.

It should be noted that, in the event the gas concentration exceeds the threshold, an audible alarm may also be generated. Such an alarm could be a conven¬ tional tone, as with commercially available smoke or carbon monoxide sensors, or a voice communication. Such a voice communication could be pre-recorded or syntheti¬ cally generated, and could be modified by the user to include appropriate instructions. It should also be noted that an alarm could be transmitted to appropriate emergency personnel in order to minimize response time. Such an alarm could be programmed for transmission only in certain situations, such as where the building is temporarily unoccupied.

The selected gas to be sensed could be carbon monoxide, radon or other potentially harmful gases. The selected gas to be sensed could also be the supply gas used for combustion in a combustion-type gas heating unit or the gas produced by a liquid combustion fuel such as fuel oil vapor. Further, the selected gas to be sensed could be the refrigerant used for air condition¬ ing in a heating/air conditioning unit.

It should also be noted that the gas could be sensed in an area immediately adjacent to the heating or heating/air conditioning unit. Alternately, the gas could be sensed within the forced air ducts of a forced air heating or heating/air conditioning unit. The

sensing of gas in these regions provides rapid detection of higher than normal concentrations of the selected gas.

As previously indicated, however, sensing gas concentrations at such locations requires a skilled service technician for proper installation of the appropriate sensor or sensors and the wiring associated therewith. As a result, the cost and inconvenience of such a method and system increases, especially where such a system must be retrofit in an existing building. Higher costs and inconvenience decrease the likelihood that such a method and system will be used, thereby eliminating the very safety benefits sought.

Moreover, while such gas sensing locations may provide the most rapid detection of higher than normal gas concentrations, depending upon the threshold levels used for comparison purposes, such locations may also result in a heating/air conditioning unit being disabled prematurely. That is, the gas concentration present in the actual living/working spaces of a building may be normal even though the concentration present more proximate the heating/air conditioning unit appears higher than normal .

To solve the cost and inconvenience problems associated with the method and system described above, appropriate gas sensor units capable of sensing the concentrations of one or more gasses and communicating with a controller for disabling a heating/air condition¬ ing unit may alternatively be placed in one or more living/working spaces of a building. Such units may be

ceiling or wall mounted, and powered by a battery and/or by the building power supply itself.

Preferably, such units are simply plugged into an existing building power outlet and include a battery back-up to allow for continued operation in the event of a blown fuse or tripped circuit breaker controlling the power outlet involved. Similar units are known in the art which sense a gas concentration in a building living/working space and sound an alarm if that concen- tration exceeds a threshold. Such units, however, lack both a battery back-up for continued operation in the event of a blown fuse or tripped circuit breaker, as well as the ability to communicate with a controller to disable a heating/air conditioning unit and prevent further buildup of that gas concentration.

As is readily apparent, sensor units such as those associated with the method and system of the present invention may be easily and conveniently in¬ stalled, particularly in existing buildings. Moreover, in contrast to prior art methods and systems wherein a single sensor is located proximate the heating/air conditioning unit, a sensor unit may be installed in any number of living/working spaces desired in the building. Still further, such units are still capable of safely and accurately sensing gas concentrations. Indeed, such units sense gas concentrations in the very liv¬ ing/working spaces where those concentrations are most critical, thereby solving the problem of premature disablement of a heating/air conditioning unit associat- ed with the previously described method and system.

The selected threshold could correspond to a selected gas concentration which would be harmful to persons serviced by the heating or heating/air condi¬ tioning unit. Moreover, the selected threshold could correspond to a selected gas concentration representa¬ tive of inefficiency or improper combustion present in the heating or heating/air conditioning unit. Particu¬ larly, the presence of refrigerant could indicate the presence of a leak in an air conditioning unit. Fur- ther, the presence of supply gas or carbon monoxide at above normal concentrations would correspond to incom¬ plete or improper combustion in a combustion-type heating unit .

Moreover, the selected threshold could vary with the sample interval. Given the sensing of carbon monoxide, for a sample interval of one minute, a concen¬ tration of 300 ppm might be used and for a sample interval of 5 minutes a concentration of 100 ppm might be used.

Turning now to Figure 2, a block diagram representation of one embodiment of the system of the present invention is shown. The air 22 in proximity to heating/air conditioning unit 20 is sensed via gas sensor 24. Gas sensor 24 determines the concentration of a selected gas and compares that concentration to a selected threshold. As will be described in greater detail below, sensor 24 is provided with a transmitter (not shown) for transmitting a high frequency control signal to thermostat/controller 26 via communication link 28.

Thermostat/controller 26 contains the elements of a standard thermostat for a heating/air conditioning unit. Thermostat/controller 26 also contains receiver and controller circuitry (not shown) which are respon- sive to a signal transmitter by sensor 24 in order to disable the operation of the heating/air conditioning unit 20 based upon a gas concentration above the select¬ ed threshold.

Turning now to Figure 3, an alternate embodi- ment of the system of the present invention is shown. The air 32 as supplied by heating unit 30 is sensed by gas sensor 34 in a manner similar to the embodiment of the present invention shown in Figure 2. However, the thermostat/controller unit 26 of Figure 2 is shown as two separate units, thermostat 38 and controller 36. Thermostat 38 performs all of the functions associated with a normal heating/air conditioning unit thermostat including the activation of the heating unit upon a drop in temperature below the user selected temperature threshold if the heating mode is selected, and the activation of the air conditioning unit upon a tempera¬ ture rise above a user selected temperature threshold if the thermostat is in the cooling mode. Controller 36 accepts an electrical signal generated by sensor 34 indicative of whether or not the gas concentration is above the selected threshold. The presence or absence of this signal is used to trigger the disabling of heating/air conditioning unit 30. Once again, as is readily apparent to those of ordinary skill in the art, sensor 34 and controller 36 are provided with a trans¬ mitter and receiver, respectively (not shown) .

In any of the embodiments presented, a display could be included. This display could indicate such parameters as the current gas concentration level, the peak gas concentration which triggered a disabling of the heating or heating/air conditioning unit or more generally the status of the controller in a "normal" or "disabled" mode.

It should be noted from the configuration in Figure 3 that controller 36 can be located separately from thermostat 38. Thus, controller 36 could be located for instance, in close proximity to the heat¬ ing/air conditioning unit 30 or the sensor 34.

Turning now to Figure 4, a flow chart repre¬ sentation of one embodiment of the method of the present invention is presented. In this embodiment, monitor 40 monitors the alarm status of one or more smoke alarms which are located in proximity to a heating unit or directly within the forced air ducts in a forced-air system. If one or more of the smoke alarms are deter- mined to be in the alarm status -- indicating that a presence of smoke has been detected by the smoke alarms -- then the heating unit is disabled as shown in block 44. If however, none of the smoke alarms are determined to be in an alarm status, the present invention contin- ues to monitor smoke alarms as indicated by block 42 and block 40.

The operation of the present invention, in detecting the alarm status of one or more smoke alarms and disabling a heating unit based upon this alarm status, provides an important function. The operation of a forced air heating or heating/air conditioning unit

during a fire, can serve to promote the spreading of the fire by means of the air movement produced. Further, in certain circumstances, the operation of a forced air heating or heating/air conditioning unit during a fire can serve to supply additional oxygen to an existing fire which has the effect of increasing the magnitude of the fire in progress. Moreover, the operation of a forced-air system during a fire can cause smoke damage throughout a building by transporting smoke to areas uneffected by the fire.

Turning now to Figure 5, a block diagram representation of an alternate embodiment of the system of the present invention is presented. The air 52 in proximity to heating/air conditioning unit 50 controlled by thermostat 62 is sensed by means of sensors 1-K 54. This plurality of sensors 54 is used to detect the presence of a plurality of different gas in proximity to heating/air conditioning unit 50. Specifically, each sensor 54 is present to detect the concentration of a respective gas. Alternatively, each of the respective sensors 54 could produce an electrical output signal to controller 58 based upon differing thresholds for a common gas .

Controller 58 disables heating/air condition- ing unit 50 based upon the detection of an alarm status from smoke alarm 56, or based upon the exceeding of one or more thresholds for the gas concentration for one or more gases as detected by sensors 54. Once again, as is readily apparent to those of ordinary skill in the art, sensors 54 and controller 58 are provided with transmit¬ ters and a receiver, respectively (not shown) .

Indicators 1-K 60 provide an indication of the status of each of the sensors 1-K 54. By this means, if heating/air conditioning unit 50 is disabled by control¬ ler 58, a user could determine which of the plurality of sensors caused the respective fault condition. For instance, if the sensors 54 corresponded to different gases, a user could determine which gas was present in unacceptable levels so as to cause the disabling of heating/air conditioning unit 50. Further, indicator 64 is provided to indicate a fault condition triggered by smoke alarm 56.

It should be noted that a wide variety of different display/indication means could be used to implement indicators 60 and 64. In the preferred embodiment, a duo-chromatic light-emitting diode would be used to provide this indication. If the light- emitting diode were a first color, this would indicate that the status of each of the sensors and the smoke alarm were normal -- meaning that the smoke alarm was not in the alarm status, and each of the sensors was not detecting a gas concentration above the respective threshold. The second color of the light-emitting diode would correspond to a fault condition for its corre¬ sponding sensor or smoke alarm.

Those with ordinary skill in the art will recognize that a wide variety of different sensors could be used in the present invention. For instance, the use of metallic oxide semiconductor sensors for the detec¬ tion of various gases and vapors is well known. For many years, a Japanese company, Figaro Engineering Company Inc. of Osaka, Japan, has been manufacturing and marketing a family of such sensors based upon tin oxide

for gas detection as described in U.S. Patent No. 3, 676,820.

In practice, the resistance of the tin oxide is measured, usually while it is heated. The resistance of the sensor changes dramatically when even small amounts of organic vapors, carbon monoxide, or even water vapor are present. U.S. Patent No. 4,896,143 further describes a gas concentration sensor with dose monitoring which cancels the effects of ambient tempera- ture and humidity in calculating the concentration of carbon monoxide. By this means, an integer value is generated which is proportional to the concentration of the sensed gas in parts per million. Further, the patent discloses a system whereby an alarm is issued if the concentration value reaches a predetermined level . The triggering of a binary signal in response to this alarm condition, could be used in the present invention to perform the functions described by any of the sensors described previously.

Referring again to Figures 2, 3 and 5, sensors

24, 34, and 54 are provided in communication with controllers 26, 36, and 58, respectively. As previously described, sensors 24, 34, and 54 may be wall or ceiling mounted units within one or more living/working spaces of a building. In addition to direct electrical wiring or a fiber optic link, communication between sensors 24, 34, and 54 and controllers 26, 36, and 58, respectively, may alternatively be provided by a radio frequency (RF) link, with sensors 24, 34, and 54 including a transmit- ter (not shown) and controllers 26, 36, and 58 including a receiver (not shown) . Such RF communication links are well known in the art and examples thereof are described

in detail in U.S. Patent Nos. 4,538,973; and 4,818,920, which are hereby incorporated by reference.

Alternatively, sensors 24, 34, and 54 may be units plugged into an existing building power outlet . Communication with controllers 26, 36, and 58, respec¬ tively, may be provided via the building power system wiring itself, by transmitting a modulated high frequen¬ cy control signal via a carrier wave over that wiring as is commonly done in the home security art area. In that regard, the control signal preferably has a frequency of approximately one order of magnitude greater than that of the building power supply, i.e. approximately 600 Hertz. Exemplary communication links of this type are described in detail in U.S. Patent Nos. 4,885,563; 4,755,792; 4,744,093; 4,737,769 and 4,697,166, which are hereby incorporated by reference.

An RF communication link may be also be provided as a back-up, again in the event of a blown fuse or tripped circuit breaker controlling the power outlet or outlets involved. Indeed, where sensors 24, 34, and 54 are wall or ceiling mounted units located in one or more living/working spaces of a building, such RF or power system wiring communication links are prefera¬ ble, since they permit the method and system of the present invention to be economically and conveniently installed and used.

As seen in Figure 2, controller 26 is inte¬ grated with a thermostat . It should be noted that sensor 24 may also be integrated with ther- mostat/controller 26, and may then be powered by the same battery powering the thermostat or ther-

mostat/controller 26. As with any other remote wall or ceiling mounted sensor, sensor 24 integrated with thermostat/controller 26 would sense gas concentrations in the ambient living/working space air, in this case the air at the thermostat/controller 26. Thereafter, sensor 24 or thermostat/controller 26 would compare the sensed gas concentration to a selected threshold, and generate a control signal when the sensed gas concentra¬ tion exceeds the selected threshold. Thermo- stat/controller 26 would then disable the heating unit via the thermostat in response to the control signal. Alternatively, a routing and sampling system may also be employed to route air samples from any location in a building to any sensor. Such a routing and sampling system would, however, increase costs associated with the present invention.

As seen in Figures 3 and 5, controllers 36 and 58 are remotely located from heating/air conditioning units 20 and 50, respectively. As with sensor 24 and thermostat/controller 26 in Figure 2, it should be noted that controllers 36 and 58 may also be integrated with heating/air conditioning units 20 and 50. Indeed, any number of various combinations of heating/air condition¬ ing units, sensor, thermostats and controllers will be readily apparent to those of ordinary skill in the art.

One with ordinary skill in the art will also recognize that sensors of this type can be used to generate a logic signal which is indicative of a spec¬ trum of different gas thresholds based upon a corre- sponding measurement time interval. For instance, a gas sensor can easily be sent to trigger a binary signal if a concentration of gas is a first selected level for a

first selected time period. A second concentration level for a second selected time interval, and a third concentration level at a third selected time interval. This mode of operation is referred to as a "dosed-type sensing mode" as one of ordinary skill in the art will recognize.

One such dosed type sensor is produced by Asahi Electronics, Inc. of Markham, Ontario. The Asahi COS-200B sensing unit operates with a 9-volt DC alkaline battery. The sensor measures gas conditions at six minute intervals and generates a latch on alarm condi¬ tion which could easily be adapted to generate a binary logic signal in a case where: (1) the sensor is exposed to 120 parts per million to 200 parts per million of carbon monoxide gas for more than 30 minutes; (2) the sensor is exposed to 200 parts per million to 300 parts per million carbon monoxide gas for more than 18 min¬ utes; (3) the sensor is exposed to 300 parts per million to 400 parts per million carbon monoxide gas for more than 12 minutes; or (4) the sensor is exposed to more than 400 parts per million carbon monoxide gas for more than six minutes. One of ordinary skill in the art will recognize that the signal from the sensor which illumi¬ nates its LED output could easily be adapted for the generation of a binary logic signal necessary for performing the functions of the sensor in the present invention.

One with ordinary skill in the art will further recognize that a wide variety of other gas sensor and gas sensor units could be used to perform the functions of the previously described sensor of the present invention. Such gas sensors exist to measure

the concentrations of not only carbon monoxide, but carbon dioxide, oxygen and a wide variety of hydrocar¬ bons, halogens and other gases.

Turning now to Figure 6, a flow chart repre- sentation of an alternate embodiment of the method of the present invention is presented. After the heating or heating/air conditioning unit has been disabled by the controller of the present invention, due to the detection of alarm status in the smoke alarms or the presence of a gas concentration above a selected thresh¬ old, the heating or heating/air conditioning unit can be reenabled by the user. However, after the heating or heating/air conditioning unit is disabled X times by the controller, it can only be reenabled by the activation of a separate switch.

In reference to Figure 6, a counter is ini¬ tially set to zero as indicated by step 70. The output from the sensor or sensors or smoke alarm is monitored as shown in step 72. If one of these sensors yields a logic high output indicating a gas concentration level above the selected threshold or indicating that one or more smoke alarms is in the alarm status as shown in step 74 , the counter is incremented by one as shown in step 76. Furthermore, the heating or heating/air conditioning unit is disabled as shown in step 78.

The user has an opportunity to reenable the heating or heating/air conditioning unit by means of a first switch. The first switch is monitored as shown in step 80. If the switch is pressed, the counter value is checked to determine if it is greater than or equal to a selected value X as shown in step 82. If the counter

value does not meet or exceed the value of X, the heating or heating/air conditioning unit is reenabled as shown in step 84. If however, the value of the counter meets or exceeds the value of X, the activation of a separate switch is required as shown in step 86 to reenable the heating or heating/air conditioning unit as shown in step 88.

The goal behind this aspect of the present invention is to only allow a user to reenable the heating or heating/air conditioning unit a selected number of times in the presence of a fault condition. The second switch could be designed or located in such a manner such that it would not be obvious to the user that the heating or heating/air conditioning unit could be reenabled in this manner. Rather, switch number two could only be activated by means known only to competent service personnel. Thus, the heating or heating/air conditioning unit user would not be able to continuously reenable the heating or heating/air conditioning unit if the controller were sensing gas concentration levels above a selected threshold. The user would be required to contact competent service personnel who would deter¬ mine the cause of the fault and hopefully, correct the fault before the heating or heating/air conditioning unit were reenabled.

One with ordinary skill in the art will recognize that the second switch could be implemented in many ways. This second switch could be implemented with a magnetic reed switch activated by placing a magnet in proximity to the switch. A special key or tool could be required to activate the switch. Alternatively, an

electronic key could be required -- such as a resistor placed across two terminals.

The choice of the value of X could be based upon several factors. These factors include the type and nature of the heating or heating/air conditioning unit being controlled, the level of sophistication of a specific heating or heating/air conditioning unit user, the level of sophistication of a general heating or heating/air conditioning unit user, the respective gas concentration threshold set for the various gases being sensed, or based upon some other similar criteria.

In one modification of the embodiment of the present invention described above, any disabling of the heating unit which occurred more than a selected time Y from the present time, would not be counted in calculat¬ ing X. Thus, a failure that happened a long time period previously, such as one week, would not count. However, if X failures occurred within a period shorter than Y, the heating unit would no longer respond to the first switch.

Turning now to Figure 7a, a schematic diagram of a circuit which implements the features described in Figure 6 is shown. Upon power-up of the system, flip flop 102 is reset via resistor 106 and capacitor 108 such that the Q output 148 is a logic zero and the Q output 138 is a logic one. Similarly, flip flops 124, 126 and 128 are reset upon power-up by resistor 136 and capacitor 132 making their respective Q outputs 150, 152 and 154 a logic zero. Thus, each of the inputs to AND gate 122 are logic zero, yielding an output 140 which is logic one. Thus, during this power-up state, Q output

138 of flip flop 102, which is logic one, is input to

NAND gate 104 along with NAND 122 output 140, which is logic one, yielding output 142, which is logic zero.

This logic zero level at line 142 is coupled through optoisolator 112 to normally closed relay 116 which remains in the closed position. Clamping diode 114 is present to dissipate transient voltages generated by the solenoid of relay 116. Light emitting diode 120 is similarly in a deactivated state when line 142 is at a logic zero level.

The logic states of the various inputs and outputs of the circuit are represented by the timing diagram shown in FIGURE 7B. The initial power-up states of the system are represented by time T ₀ . The remainder of the timing diagram illustrates the operation of the circuit under various conditions.

At time T ₁ sensor 100 generates a positive voltage pulse indicating the presence of a gas above a selected threshold or an alarm status for one or more smoke alarms. The rising edge of the pulse on line 101 triggers a latching of a logic one on the Q output 148 of flip flop 102 and a logic zero on Q output 138. This logic zero to logic one transition of line 148 triggers the latching of a logic one level of Q output 150 of flip flop 124, as well as the latching of logic zero levels on Q outputs 152 and 154 of flip flops 126 and 128, respectively. The output 140 of NAND gate 122 is thus a logic one. The logic one from output 140 is combined with the logic zero from output 138 which is input to NAND gate 104. This yields an output 142 which is a logic one. This logic one voltage supplies current to light emitting diode 120 via current limiting resis-

tor 118. This serves to illuminate light emitting diode 120 indicating the presence of a fault condition. Further, the logic one voltage at line 142 activates the solenoid of relay 116 via optoisolator 112, causing the contacts to open. Thus, at this point nodes a and β are open circuited. The open circuit condition of nodes a and β could be used to disable the heating or heat¬ ing/air conditioning unit such that the operation of the unit would cease.

The disabled state of the heating or heat¬ ing/air conditioning unit is maintained until switch 110 is activated. When the switch is closed, reset input 144 of flip flop 102 is connected to ground. This changes Q output 148 to a logic zero and Q output 138 to a logic one. The inputs 138 and 140 to NAND gate 104 are thus both high yielding a low output on 142 which deactivates LED 120 and the solenoid to relay 116 causing nodes a and β to be once again connected.

At time T ₃ , a second sensor pulse is generated on line 101 corresponding to a second fault condition. This fault condition causes line 142 to take on a logic high level which illuminates LED 120 and opens relay 116 as before. Further, Q output 152 of flip flop 126 takes on a logic zero level in a manner similar to the transi- tion of output 150 of flip flop 124 at time T ₂ .

If switch 110 is momentarily closed at time T ₄ , this again serves to deactivated LED 120 and relay 116 in a manner similar to the actions of the circuit at time T ₂ . If, however, a third sensor pulse is received on line 101 at time T ₅ , and the relay 116 is opened and LED 120 activated, the circuit cannot be reset by a

third activation of switch 110. The sensor pulse at T ₅ causes Q output 154 of flip flop 128 to take on a logic one level. Thus, the output 140 of NAND gate 122 is a logic zero. This logic zero input to NAND gate 104 insures that no actions of flip flop 102 will be able to change the state of output 142 from its logic one level. The third activation of switch 110 at time T ₆ causes Q output 148 of flip flop 102 to switch to a logic zero level and Q output 138 to switch to a logic one level. However, the combination of a logic one level on line 38 and a logic zero level on line 140 causes the output 142 of NAND gate 104 to be logic one. The only way to deactivate the solenoid to relay 116 and the LED 120 is to momentarily press switch 134 which couples reset line 146 to flip flops 124, 126 and 128 to ground. This resets the Q outputs 150, 152 and 154 of flip flops 124, 126 and 128, respectively, to the logic zero level which they attained upon power up of the system. Thus, the relay 116 and LED 120 can be deactivated twice again by switch 110 before switch 134 and activation of switch 134 is required to reset the circuit.

Turning now to FIGURE 8, a common interconnec¬ tion between the heating/air conditioning unit 160 and a thermostat 162 is shown. Four lines labelled 164, 166, 168 and 170 interconnect these two units.

Line 66 couples voltage from the heating/air conditioning unit 160 to the thermostat. This voltage is commonly 24 volts AC. Line 168 is circuit ground from the heating/air conditioning unit 163. Lines 164 and 170 are control lines for the heating and air conditioning functions respectively of the heating/air conditioning unit 160.

The thermostat operates by connecting line 166 to line 164 if the ambient temperature of the thermostat falls below a selected temperature threshold and if the thermostat is in a heating mode. Alternatively, line 166 is connected to control line 170 if the ambient temperature of the thermostat rises above a selected temperature threshold and if the thermostat is in a cooling mode.

The heating operation of the heating/air conditioning unit 160 can be disabled by providing an open circuit to nodes a ' and β ' by means of a circuit such as the circuits shown in FIGURES 7a and 7c. Similarly, the cooling operation of the heating/air conditioning unit 160 can be disabled by providing an open circuit to notes a " and β" by means of a circuit such as the circuits shown in FIGURES 7a and 7c.

When the relay is in the closed position, indicative of either no fault condition or a fault condition followed by a valid re-enabling of the cir- cuits shown in FIGURE 7a and 7c, the nodes a and β corresponding to either the connection a ' and β ' , respectively, or the connections α" and β" , respective¬ ly, will be connected thereby enabling the respective function of the thermostat and therefore the heating or heating/air conditioning unit. Further notice that upon the detecting of a binary logic signal generated by sensor 100 on line 101, relay 116 is opened thereby disabling either the heating operation or the air conditioning operation of heating/air conditioning unit 160 in FIGURE 8.

As is readily apparent to those of ordinary skill in the art, where a gas sensor is integrated with and powered by the same battery as thermostat 162 (as discussed previously in conjunction with Figures 2, 3 and 5) , a standard six wire thermostat configuration is necessary. Those of ordinary skill will also recognize, however, that heating/air conditioning unit 160 may still be disabled using an appropriately configured battery powered relay in a fashion similar to that described above in conjunction with Figures 7 and 8.

In the preferred mode of operation, a circuit as shown in FIGURES 7a or 7c implemented with a sensor 100 which is configured for the detection of carbon monoxide would be connected with nodes and β in FIGURE 7a or 7c connected to nodes a ' and β ' as shown in FIGURE 8. Thereby, if the concentration of carbon monoxide were detected to be above a selected threshold, the heating operation of the heating/air conditioning unit 160 in FIGURE 8 would be disabled. Further, a second circuit similar to the circuit shown in FIGURE 7 with sensor 100 configured for the detection of refrigerant, could be connected such that nodes α and β as shown in FIGURE 7a or 7c would be connected to nodes ot" and β " as shown in FIGURE 8. Thereby, if a gas concentration were detected which exceeded a selected threshold, the air conditioning function of the heating/air conditioning unit 60 in FIGURE 8 could be disabled.

One with ordinary skill in the art will also recognize that heating/air conditioning unit 160 in FIGURE 8 could be disabled by means of a circuit such as the circuit shown in FIGURE 7a whereby nodes ot and β were connected in line of line 116. That is, an open

circuit between nodes a and β produced by the control circuit shown in FIGURE 7a would supply an open circuit on line 166 whereby the source of power to the thermo¬ stat would be disabled. This in turn, would disable the operation of heating/air conditioning unit 160.

One with ordinary skill in the art will further recognize that the circuit shown in FIGURE 7a could easily be implemented by means of an algorithm executed by a microprocessor, signal processor, program- mable controller or other similar devices.

One with ordinary skill in the art will recognize that the method described by the flow chart in FIGURE 6 could easily be modified to encompass a condi¬ tion whereby two separate sensor outputs are monitored. The first sensor output could correspond to a condition whereby a binary high signal is generated when the gas concentration exceeds a first selected threshold. The second sensor output could generate a logic high level if the gas concentration exceeded a second selected threshold whereby the second selected threshold is higher than the first selected threshold. The first sensor output could be used as in the method described by the flow chart in FIGURE 6. In addition, the second sensor output could be used to indicate a more serious fault condition which immediately disabled the operation of the heating or heating/air conditioning unit such that the activation of switch number one would not re¬ enable the operation of the heating or heating/air conditioning unit. Rather, the activation of a third switch, similar to the second switch in that its mode of activation would not be readily apparent to the heating or heating/air conditioning unit user. Further, the

functions of this third switch could also be performed by the second switch previously described.

Turning now to FIGURE 7c, a sample circuit for implementing this additional function is presented. The circuit of FIGURE 7c is identical to the circuit in FIGURE 7a (with common elements being labelled with the reference numerals used in FIGURE 7a augmented with the prime (') symbol) except for the following modifica¬ tions. A second output 103 to sensor 100' generates a logic high signal based upon a measured gas concentra¬ tion which is above a selected threshold which is higher than the selected threshold which corresponds with output 101' . This output 103 is fed to flip flop 156 whose Q output 158 is further input to NAND gate 105. Upon power up of the system, Q output 158 is high due to the reset function performed by resistor 130' in capaci¬ tor 132' . If a high gas concentration is sensed, a logic high binary signal is generated on line 103 which latches a logic one level on Q output 158 thereby opening relay 116' and activating LED 120' . Notice that the activation of switch 110' would not re-enable the operation of the controller. Rather, the activation of switch 134' is required to reset flip flop 156 to re¬ enable control operation.

Referring again to Figures 7a and 7c, as previously described, sensors 100 and 100' may be provided in communication with flip-flops 102, 102', and 156 by lines 101, 101', and 103, respectively. In that regard, lines 101, 101' , and 103 may be traditional electrical wiring or fiber optic cables. As also previously described, however, lines 101, 101' , and 103 may also be part of the building power system wiring

itself, provided that wiring is appropriately adapted. Finally, as seen in Figures 7a and 7c, those portions of the circuits configured for re-enabling operation of the heating/air conditioning unit are preferably part of the controllers 26, 36, and 58 depicted in Figures 2, 3, and 5, respectively. Nevertheless, such re-set circuitry may be independent of the controllers 26, 36, and 58, or may be part of heating/air conditioning units 20, 30, and 50 or thermostats 26, 38, and 62.

Referring next to Figures 7d and 7e, schematic representations of alternative embodiments of the system of the present invention are shown. As seen therein, such schematics are similar in most respects to those of Figures 7a and 7c, respectively. The only differences lie in the communication links between sensors 100 and 100' and flip-flops 102, 102', and 156.

More specifically, as seen in Figures 7d and 7e, sensors 100 and 100' include an RF transmitter for transmitting a signal to RF receiver and signal genera- tors 100a and 100a' indicating that the sensed concen¬ tration of a selected gas exceeds a corresponding threshold and that the heating/air conditioning unit should therefore be disabled. As also seen in Figures 7d and 7e, any number of sensors/transmitters 100 and 100' may be placed in any number of building living/- working spaces as desired.

RF receiver and signal generators 100a and

100a' then generate an appropriate control signal for transmission via lines 101, 101' , and 103 as previously described with respect to Figures 7a and 7c. Indeed, the remaining operation of the circuits depicted in

Figures 7d and 7e is exactly the same as that of the circuits depicted in Figures 7a and 7c, respectively, described above.

Turning now to FIGURE 9a, one possible method of interfacing an existing smoke alarm to the controller of the present invention is shown. The audio output 180 of smoke alarm 182 is received by microphone 184. Microphone 184 generates an electrical signal 186 in response to this audio signal. Processor 190 processes electrical signal 186 to generate a logic signal 188 indicative of whether or not the audio output 180 is present from smoke alarm 182.

FIGURES 9b, 9c and 9d show various options for implementing processor 190. In FIGURE 9b, electrical signal 186 is fed to matched filter 200 whose impulse response is given by S(T-t) where S(t) represents the audio signal 180 produced by smoke alarm 182. The output of matched filter 200 is sampled at time t = T by switch 202 and fed to comparator 204. The output of switch 202 is compared with a selected threshold 206 to generate logic signal 188.

An alternate method for implementing processor 190 is shown in FIGURE 9c. Electrical signal 186 is multiplied by S(t) by multiplier 210. This result is integrated from time zero to time T by integrator 112. The integrator result is fed to comparator 214 which compares the integrated result to threshold 216 and generates logic signal 188.

A second alternative for implementing proces- sor 190 is shown in FIGURE 9d. Electrical signal 186 is

fed to band pass filter 220 which is tuned to one or more of the selected frequency components of the audio output 180 of smoke alarm 182. The output of the band pass filter is fed to envelope detector 222 whose output is compared with threshold 226 by comparator 224 to generate logic signal 188.

Those with ordinary skill in the art will recognize that thresholds 206, 216 and 226 would be generated based upon the expected signal levels generat- ed by the audio output of a smoke alarm at the inputs to the comparators in the respective circuits described above. Preferably, these levels would be chosen to be below the minimum expected signal level, yet above the level generated by expected audio noise present in proximity to the smoke alarm or smoke alarms.

Those with ordinary skill in the art will recognize that the systems of the various embodiments of the present invention could include an integral smoke alarm. That is, the system of the present invention could include a smoke alarm circuit which is powered by the power supply of the system. This would eliminate the need for smoke alarm batteries and the various detecting and processing circuits described in FIGURES 9a through 9d. Rather, a logic signal indicative of alarm status of the smoke alarm could be directly fed to the controller of the present invention for disabling the heating or heating/air conditioning unit in response to this alarm condition.

While the best mode for carrying out the invention has been described in detail, those familiar with the art to which this invention relates will

recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.