Abstract:
A forced-air HVAC system has an induction motor that drives its fan or blower. The motor is controlled by a circuit that causes the speed of the fan or blower to vary continuously whenever the HVAC system operates. The controller circuit includes temperature sensors that continuously monitor the temperature of the air the system is delivering. These sensors signal the controller circuit to vary the speed of the fan or blower motor in order to maintain at an optimal level the air temperature in the spaces heated or cooled by the system.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to controlling the flow of air in a forced-air HVAC system. In particular, this invention offers a means to monitor the system temperature and, in response thereto, to vary continuously the speed of the fan or blower whenever the system operates. 
   Present forced-air HVAC systems control the speed of a fan or blower motor, generally an induction motor, in one of three ways: (1) the fan runs at full speed, (2) the fan speed is stepped, or (3) the fan cycles on and off when the system operates. In these systems, the flow of forced air is discontinuous. It does not start until well after the system has called for the flow of heated or cooled air. Thus premises with more than one room that are served by a single HVAC system can develop hot and cold air pockets throughout the occupied space. Therefore, for optimal comfort, there is need for a continuous flow of air, circulating at varying velocities, to mix air above and below the thermostatically set level and eliminate pockets at non-optimal temperatures, thereby bringing to a substantially single optimal temperature the entire space to be heated or cooled. Depending on the season, both heating and cooling may be required during a single period to keep the space at the substantially single optimal temperature set by at least one thermostat. 
   Most forced-air HVAC systems use the air temperature of only one occupied space to cycle the fan or blower on and off. Other systems use the difference between the respective air temperatures in a plenum and in a return to turn the fan or blower on and off, e.g., U.S. Pat. No. 6,684,944 to Byrnes et al. These systems cause a delay in supplying air at an optimal temperature. Still other systems open and close dampers to control temperature in the space to be heated or cooled. In none of these systems of the prior art does the blower/fan motor operate continuously. Thus, to obtain an optimal temperature, there is a need to monitor continuously the heating plenum and/or cooling coil and to adjust accordingly the blower/fan motor speed continuously to overcome the drawbacks of the prior art and keep the space at a substantially single and stable optimal temperature. 
   OBJECTS AND SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a system of forced-air HVAC system control that overcomes the drawbacks of the prior art by operating the blower/fan motor continuously. 
   A further object of the present invention is to vary the velocity of a continuous air flow in a forced-air HVAC system, because a system that uses HEPA or UV filtering requires a constant flow of air to maximize filtration. 
   Yet another object of the present invention is to vary the velocity of a continuous air flow in a forced-air HVAC system and thus maintain a substantially stable optimal temperature in the space served by the system. 
   Still a further object of the present invention is to ensure that, in the event the return air and plenum temperatures are equal, but are either higher or lower than an optimal room temperature, the speed of the fan or blower motor will continue to increase or decrease, thereby allowing the air in the ducts and in the occupied space to mix until a substantially single, stable optimal temperature is established throughout the entire system. 
   Briefly stated, the present invention provides a forced-air HVAC system with an induction motor that drives its fan or blower. The motor is controlled by a circuit that causes the speed of the fan or blower to vary continuously whenever the HVAC system operates. The controller circuit includes temperature sensors that continuously monitor the temperature of the air the system is delivering. These sensors signal the controller circuit to vary the speed of the fan or blower motor in order to maintain at a substantially single, stable optimal level the air temperature in the spaces heated or cooled by the system. 
   According to an embodiment of the invention, a method of controlling a blower/fan motor in a forced-air HVAC system to maintain a substantially optimal temperature in an interior comprises the steps of: measuring a temperature in the interior space; communicating the substantially optimal temperature to a controller; when the substantially optimal temperature is higher than the temperature in the interior space, causing the controller to call for heated air from the system; when the substantially optimal temperature is lower than the temperature in the interior space, causing the controller to call for cooled air from the system; varying continuously a speed of the blower/fan motor in response to the call for the heated or the cooled air, whereby the blower/fan motor runs substantially continuously once it starts; the step of varying being responsive to a temperature sensed in a plenum chamber of the system when the call is for the heated air; and the step of varying being responsive to a temperature sensed in a cooling coil of the system when the call is for the cooled air. 
   According to a feature of the invention, apparatus for controlling a blower/fan motor in a forced-air HVAC system to maintain a substantially optimal temperature in an interior space comprises: means for measuring a temperature in the interior space; means for communicating the substantially optimal temperature to a controller; when the substantially optimal temperature is higher than the temperature in the interior space, the controller being effective to call for heated air from the system; when the substantially optimal temperature is lower than the temperature in the interior space, the controller being effective to call for cooled air from the system; the controller being effective to vary continuously a speed of the blower/fan motor in response to the call for the heated or the cooled air, whereby the blower/fan motor runs substantially continuously once it starts; the controller being further effective to vary the speed of the blower/fan motor in response to a temperature sensed in a plenum chamber of the system when the call is for the heated air; and the controller being further effective to vary the speed of the blower/fan motor in response to a temperature sensed in a cooling coil of the system when the call is for the cooled air. 
   According to another feature of the invention, apparatus for controlling a blower/fan motor in a forced-air HVAC system to maintain a substantially optimal temperature in an interior space comprises: a controller effective for varying continuously a speed of the blower/fan motor, whereby the blower/fan motor runs substantially continuously once it starts; the controller being responsive to at least one of a plenum temperature and a cooling coil temperature; and the controller being further responsive to a temperature sensor in the interior space, whereby the interior space is kept at a temperature substantially optimal and stable. 
   The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagram of the controller circuit of the present invention. 
       FIG. 2  graphs the response of a forced-air HVAC system controlled by the present invention when only heating is called for. 
       FIG. 3  graphs the response of a forced-air HVAC system controlled by the present invention when only cooling is called for. 
       FIG. 4  graphs the response of a forced-air HVAC system controlled by the present invention when both heating and cooling are called for. 
       FIG. 5  is a flow chart that shows the operation of the controller of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1 , 120V AC enters a circuit  100  of the present invention at a point  101  and returns through a point  102  kept at neutral. Circuit  100  is connected to a ground  104  through a point  103 . A motor is connected through points  105  and  106  to be controlled by circuit  100 . 
   The AC that enters circuit  100  passes through a fuse  201  and enters a voltage conditioning circuit formed by resistors  203  and  205  and capacitors  204  and  206  that snub out transient voltages. An AC load resistor  207  stabilizes circuit  100 &#39;s output. An alternistor  202  provides a gated line voltage. 
   Control of this gated line voltage is provided by a combination of resistors  301 ,  303 ,  306 ,  307 ,  308 ,  309 , and  310  together with a bridge  302 , a capacitor  304 , and a diode  305 . 
   A diode  401  and a capacitor  403  provide a peak high-voltage DC supply for feeding both electrical energy and reference voltage to the circuit. A resistor  402  is connected across capacitor  403  to detect a brownout. 
   An optically-controlled mathematical processor (MPD), configured to accept multiple inputs and furnish a single output, comprises four LEDs  508 ,  803 ,  904 , and  1011  for inputs and resistor  310  for output of the gated line voltage. 
   A network comprising resistor  501  and capacitor  503  provides a time-constant voltage to a comparator  506 , which compares it to a reference voltage provided by resistors  504  and  505 . At power-up, this network provides, via a pull-up resistor  507 , a signal that elevates the output RMS voltage to the load. A resistor  502  bleeds voltage from the time-constant voltage network when the system is de-energized. A resistor  509  limits the current input to the MPD. 
   A diode  602  and a capacitor  603  provide a low-voltage, regulated DC supply, which is stepped down by resistors  601  and  604 . A pair of resistors  701  and  702 , a diode  703 , and a capacitor  704  provide a regulated DC voltage for sensing temperature. 
   To sense the heating temperature, a network of resistors  801 ,  802 ,  806 , and  807  comprises a resistive bridge  810 . Resistors  802 ,  806  are thermistors that do the actual sensing of the heating temperature. Resistive bridge  810  provides an input signal to the MPD, which in turn sends a control signal to the gate control circuit. A resistor  805  limits the current entering the MPD. A diode  804  provides a reverse clamping voltage to protect the MPD. 
   To sense the cooling temperature, a network of resistors  901 ,  902 ,  906 , and  907  comprises a resistive bridge  910 . Resistors  902 ,  906  are thermistors that do the actual sensing of the cooling temperature. Resistive bridge  910  provides another input signal to the MPD, which in turn sends a control signal to the gate control circuit. A resistor  903  limits the current entering the MPD. A diode  905  provides a reverse clamping voltage to protect the MPD. 
   To sense a fault in the system, especially a brownout, a network, comprised of resistors  1001 ,  1002 ,  1003 ,  1004 ,  1005 ,  1006 ,  1007 , and  1009 , capacitor  1013 , and transistors  1008  and  1010 , sends an inversely proportional signal as an input to the MPD, which in turn sends a control signal to the gate control circuit. A resistor  1012  limits the current entering the MPD. 
     FIG. 2  graphs the performance of a forced-air HVAC system controlled by the present invention when the system calls for heating only. The horizontal axis is temperature in degrees Fahrenheit. The right-hand vertical axis is the true RMS voltage delivered to the blower/fan motor. The left-hand vertical axis is the percentage of maximum blower/fan motor speed. 
   Referring to  FIG. 2 , plenum air temperature is plotted against airflow and blower/fan motor speed when the controller of the present invention is set for heating only. The graph shows an increasing airflow with increasing temperature sensed within the plenum airflow and decreasing flow with decreasing temperature sensed within the plenum airflow, as called for by the controller of the present invention. The graph also shows that, when the sensed temperature is normal room temperature, the blower/fan motor runs at its minimum speed. Similarly, when the sensed temperature is at 125 degrees F. or higher, the blower/fan motor runs at its maximum speed until the plenum air equilibrates approximately with the desired temperature, at which point the blower/fan motor returns to minimum speed. 
     FIG. 3  graphs the performance of a forced-air HVAC system when the controller of the present invention calls for cooling only. The horizontal axis is temperature in degrees Fahrenheit. The right-hand vertical axis is true RMS voltage delivered to the blower/fan motor. The left-hand vertical axis is the percentage of maximum blower/fan motor speed. 
   Referring to  FIG. 3 , cooling-coil temperature is plotted against airflow and blower/fan motor speed when the controller of the present invention is set for cooling only. The graph shows an increasing change in airflow with decreasing temperature sensed on the cooling coil and decreasing flow with increasing temperature sensed on the cooling coil, as called for by the controller of the present invention. The graph also shows that, when the sensed temperature is at normal room temperature, the blower/fan motor runs at its minimum speed. Similarly, when the sensed temperature is at 40 degrees F. or lower, the blower/fan motor remains at its maximum speed until the cooling coil equilibrates approximately with the desired temperature, at which point the blower/fan motor returns to minimum speed. 
     FIG. 4  graphs the performance of a forced-air HVAC system when the controller of the present invention calls for both heating and cooling. The horizontal axis is temperature in degrees Fahrenheit. The right-hand vertical axis is true RMS voltage delivered to the blower/fan motor. The left-hand vertical axis is the percentage of maximum blower/fan motor speed. 
   Referring to  FIG. 4 , the composite plenum air/cooling coil temperature is plotted against airflow and blower/fan motor speed of a controller of the present invention that calls for both heating and cooling. The graph shows the changes in airflow with increasing and decreasing temperature sensed within/on the plenum airflow and cooling coil, as called for by the controller of the present invention. The graph also shows that, when the sensed temperature is at normal room temperature the blower/fan motor remains at its minimum speed. Similarly, when the sensed temperature is at either 125 degrees F. or higher or 40 degrees F. or lower, the blower/fan motor remains at its maximum speed until the plenum air or cooling coil equilibrates approximately with the desired temperature, at which point the blower/fan motor returns to minimum speed. 
     FIG. 5  shows the steps carried out by the controller of the present invention in response to its setting. The flow begins with a step  10  of system power energizing. 120-volt line voltage is applied to point  101  (see  FIG. 1 ). The system power travels over a conduit  20  to immediately charge capacitor  403 . In a step  30 , this triggers a 3–10 second RC time-constant charge of the network comprising resistor  501  and capacitor  503 . This RC time-constant charge is applied, via a conduit  40 , to the comparing input of comparator  506  to provide a timed latched/de-latching trigger to LED  508 , i.e., an input signal to the MPD. 
   In a step  50 , LED  508  and resistor  310  deliver an output resistance for the gate control circuitry that initially elevates and then de-elevates the fan/blower motor speed to its maximum then minimum preset level. The fan/blower motor speed controller system remains at the minimum preset level and monitors input line voltage, plenum temperature, and cooling coil temperature via a conduit  60 . If the input line voltage drops approximately 5 to 10 volts, in a step  70 , the network comprising resistors  1001 ,  1002 ,  1003 ,  1004 ,  1005 ,  1006 ,  1007 , and  1009 , capacitor  1013 , and transistors  1008  and  1010  begin to provide a control signal. The magnitude of this control signal, flowing over a conduit  80 , is continuously altered in response to the deviation from full line voltage. In a step  130 , this control signal is applied to the MPD, thereby delivering an output resistance for the gate control circuitry that elevates and then de-elevates the fan/blower motor speed. When 120 volts, full line voltage is re-established at point  101 , a conduit  140  keeps the fan/blower motor speed controller at the minimum preset level. 
   If resistors  802  and  806 , which are both thermistors, detect an elevated plenum temperature of 85 degrees F. or higher, a control signal is generated in a step  90 . If resistors  902  and  906  (thermistors) detect a decreased cooling coil temperature of 60 degrees F. or lower, a control signal is generated in a step  110 . The magnitude of this control signal, which travels over a conduit  160 , is continuously adjusted to respond to the temperature when it deviates from a normalized room value. In a step  120 , this control signal is applied to the MPD to deliver an output resistance for the gate control circuitry that elevates and then de-elevates the fan/blower motor speed. When the plenum/cooling coil temperature normalizes to room value, the fan/blower motor speed controller system returns via a conduit  150  to the minimum preset level. 
   Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.