Abstract:
A thermostat includes within its circuitry a delay signal generator for delaying the activation and deactivation of an air circulation fan for a predetermined time period after which a heater or compressor is activated or deactivated.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates generally to thermostats and, more particularly, to a thermostat method and apparatus for introducing delays in the energizing and de-energizing of an air circulating fan of a forced air comfort system.  
         [0002]     In a forced air comfort system that may include a furnace and/or an air conditioner, an electrically driven air circulation fan is used to move the conditioned air to the space for which the air being conditioned. In older furnaces and air conditioning systems, and in lower end systems being manufactured today, the air circulating fan is energized and de-energized at the same time that the furnace heater or the air conditioning system compressor is energized or de-energized. This results in the circulation of air that is not properly conditioned or to the non-circulation of air that is properly conditioned. That is, in the case of a furnace, non-heated or inadequately heated air is circulated at start up, and when the furnace shuts down, the air that has been heated is not circulated, thereby causing inefficiencies. Similarly, for an air conditioning system, warm unconditioned air is circulated at the beginning of a cycle, and cool conditioned air is not circulated at the end of the cycle.  
         [0003]     In high end furnaces and air conditioners of today, it is common to include control features within the system control board to introduce delays in the turning on and off of the circulating fan so as to overcome the problems discussed hereinabove. However, these features are not available in older furnaces/air conditioners or low end furnaces/air conditioners. Accordingly, in order to obtain these features it is presently necessary to purchase a new system.  
         [0004]     Further, even in those systems where the delay functions can be included in the system control apparatus, the delays will be set according to generalized time periods which may not be appropriate for the particular installation and would not be adjustable to other times except possibly by a service person who would need to make the individual changes in each of the cooling and heating systems.  
         [0005]     It is therefore an object of the present invention to provide an improved forced air comfort system control apparatus and method.  
         [0006]     Another object of the present invention is the provision in a forced air comfort system for greater comfort and efficiency in older and/or less expensive furnace/air conditioning systems.  
         [0007]     Yet another object of the present invention is the provision in such forced air comfort systems for initiating delays in the turning on and off of the air circulation fan without upgrading the furnace/air conditioning system.  
         [0008]     Another object of the present invention is the provision for a homeowner to easily adjust delay times to either or both of the heating and cooling systems by adjusting a single thermostat to meet the needs of a particular system as installed.  
         [0009]     Still another object of the present invention is the provision in a forced air comfort system for a thermostat which is economical to manufacture and effective and efficient in use.  
         [0010]     These objects and other features and advantages become more readily apparent upon reference to the following descriptions when taken in conjunction with the appended drawings.  
       SUMMARY OF THE INVENTION  
       [0011]     Briefly, in accordance with one aspect of the invention, a thermostat includes within its internal control features, signal generating means for introducing a delay between the time in which a signal is sent to turn on the heater or compressor of a comfort system and the time in which the associated air circulation fan is turned on or off. In this way, greater comfort and efficiencies are obtained without the need for upgrading the furnace/air conditioner.  
         [0012]     In the drawings as hereinafter described, a preferred embodiment is depicted; however various other modifications and alternate constructions can be made thereto without departing from the true sprit and scope of the invention.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a schematic illustration of a furnace and air conditioner installation into which the present invention has been incorporated.  
         [0014]      FIG. 2  is a wiring diagram showing the thermostat as it is connected to the furnace and the air conditioner.  
         [0015]      FIG. 3  is a timing diagram of the various thermostat signals for turning on and off the components of the furnace and air conditioner in accordance with the present invention.  
         [0016]      FIG. 4  is a flow chart showing the function of the thermostat in accordance with the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]     Referring now to  FIG. 1 , there is shown a plan view of an enclosure  10  with an installed furnace  11  and air conditioner or heat pump  12 . The furnace  11  is mounted such that cold air from the enclosure is received by the furnace through cold air return  13  and thereafter hot air from the furnace is supplied to the enclosure  10  through supply ducts  14  and hot/cold air supply duct  16  to the enclosure  10 . The furnace has a blower  17  for circulating the air from the enclosure through the cold air return  13  to the furnace  11  and through the furnace heat exchangers  18 , through supply duct  14  and back to the enclosure through hot/cold air supply duct  16 .  
         [0018]     The air conditioner or heat pump  12  is mounted such that the indoor coil  19  is contained within supply duct  14  in communication with the enclosure air being circulated by the furnace blower, and that the outdoor coil  21  is mounted outside the enclosure in communication with the ambient air  22 . The indoor coil  19  and the outdoor coil  21  are connected through a reversing valve  23  to a compressor  24 . The outdoor fan  26  is powered by an outdoor fan motor  27  located such that the ambient air is circulated through the outdoor coil  21 .  
         [0019]     A control box  28  is arranged to control by way of signals on line  30  from a thermostat  29 , the furnace blower motor  15  by way of line  31 , the heater or gas ignition system  20  by way of line  32 , the compressor  24  by way of line  33 , and the outdoor fan motor  27  by way of line  34 , respectively. An outdoor temperature sensor  36  can also be provided for sensing the temperature and sending it to the control box  28  by line  37  and then to the thermostat  29  by line  30 .  
         [0020]     Referring now to  FIG. 2 , the thermostat  29 , the furnace  11  and the air conditioning system  12  are shown by their respective blocks with the various electrical interconnections being shown between the three units. For simplicity, the interconnections of the control board  28  are not shown since the signals to and from the thermostat  28  are designed to communicate directly with the components of the furnace  11  and the air conditioning system  12 .  
         [0021]     As will be seen, the W terminal of the thermostat  28  is intended to provide signals to the W terminal of the furnace  11  so as to selectively activate and deactivate the heater or gas ignition system  20 . Similarly, the G terminal of the thermostat  29  is intended to communicate with the G terminal of the furnace  11  to selectively activate and deactivate the blower motor  15 .  
         [0022]     When the system is operating in the air conditioning or heat pump mode, the thermostat  29  communicates with the air conditioning by way of the respective Y terminals in order to activate and deactivate the compressor  24  as shown. The cooled air is circulated, of course, by the blower  17 , and thus the blower motor  15  is again activated by way of communication between the respective G terminals as shown.  
         [0023]     The R and C terminals of the respective thermostat  29 , furnace  11  and air conditioner  12  are used for various 24 volt input control signals such as are used to operate the reversing valve  23 , for example.  
         [0024]     Referring now to  FIG. 3 , the various delay features of the signals from the thermostat  29  are shown.  
         [0025]     As will be seen, for normal operation of the thermostat, the signals for turning on and off the heater and the fan in the case heating operation, and for turning on and off the air conditioner and fan in the case of cooling, both occur at the same time.  
         [0026]     With the present invention, however, a fan delay is introduced, such that at time T 1 , the thermostat  29  provides a signal from its W terminal for the furnace heater to turn on. At time T 2 , the thermostat  29  provides a signal from its G terminal for the fan  25  to be turned on. The on-delay time of T 2 -T 1  is thus provided for the furnace heat exchangers to be heated up prior to the fan being turned on such that cold air is not caused to be circulated into the enclosure  10 , but rather, the fan comes on only after the furnace heat exchangers have been heated up to a satisfactory temperature.  
         [0027]     When the thermostat receives an indication that the temperature of the enclosure  10  has been heated to a predetermined level, the furnace is then turned off. A similar delay is provided at this time in order to allow the fan to continue to operate after the furnace heater  18  has been shut off in order to obtain the benefit of the residual heat in the heat exchangers. That is, the heater is turned off at time T 3  and the blower motor  15  is turned off at a later time, T 4 . The off delay time of T 4 -T 3  allows for the economical distribution of heat within the heat exchanger that might otherwise be lost.  
         [0028]     In a similar manner, the air conditioner compressor  24  is activated and deactivated by signals from the Y terminal of the thermostat  29  at times T 5  and T 7  as shown. Again, the signals to the fan motor  15 , as received from terminal G of the thermostat  29  cause the fan to turn on at time T 6  and turn off at time T 8  to provide a similar on-delay of time T 6 -T 5  and an off-delay of time T 8 -T 7 . The on-delay allows for the air conditioning system to be operational for a sufficient time such that when the blower motor  15  comes on, it is cooled air rather then hot air that is circulated. Similarly, the off-delay allows for the continued circulation of the residual cool air in the system after the air conditioner is turned off at time T 7 .  
         [0029]     Referring now to  FIG. 4 , a flow chart of the present system is shown during the heating operation wherein a demand signal is generated at step  38  as determined by the difference between the said point of the thermostat and the actual temperature as indicated by the thermostat. If the demand is greater than the specified off set as established by the operator and set into the thermostat, then the heat is turned on as shown in steps  39  and  41 .  
         [0030]     If the on-delay timer is set in step  42  as discussed hereinabove, then the system will wait for the on-delay time, after which is will turn on the fan in step  43 .  
         [0031]     When the demand is finally determined to be zero in step  44 , the heater will be turned off at step  46 . Again, if the off-delay timer is set in step  47 , then the system will wait until the off-delay time has expired, after which the fan will be turned at step  48 .  
         [0032]     In the case of cooling operation, the on and off delay times will operate in substantially the same way as described hereinabove.