Thermostat with heat and/or cool fan delays controlled by thermostat output

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

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.

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.

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.

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.

It is therefore an object of the present invention to provide an improved forced air comfort system control apparatus and method.

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.

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.

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.

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.

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

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.

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

FIG. 1 is a schematic illustration of a furnace and air conditioner installation into which the present invention has been incorporated.

FIG. 2 is a wiring diagram showing the thermostat as it is connected to the furnace and the air conditioner.

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.

FIG. 4 is a flow chart showing the function of the thermostat in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

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.

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.

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.

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.

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.

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.

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.

Referring now to FIG. 3, the various delay features of the signals from the thermostat 29 are shown.

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.

With the present invention, however, a fan delay is introduced, such that at time T₁, the thermostat 29 provides a signal from its W terminal for the furnace heater to turn on. At time T2, the thermostat 29 provides a signal from its G terminal for the fan 25 to be turned on. The on-delay time of T2-T₁ 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.

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 T3 and the blower motor 15 is turned off at a later time, T₄. The off delay time of T4-T3 allows for the economical distribution of heat within the heat exchanger that might otherwise be lost.

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 T₅ and T₇ 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 T₆ and turn off at time T₈ to provide a similar on-delay of time T₆-T₅ and an off-delay of time T₈-T₇. 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 T₇.

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.

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.

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.

In the case of cooling operation, the on and off delay times will operate in substantially the same way as described hereinabove.

Claims

1. A thermostat for energizing and de-energizing a forced air comfort system having a furnace and/or air conditioning system with a respective heater or compressor and an air circulating fan comprising:

means within said thermostat for receiving a demand signal and for responsively generating a first signal for energizing said heater or compressor;

means within said thermostat for generating a delay signal of a predetermined time period; and

means within said thermostat for generating a second signal for energizing said circulation fan upon the passing of said predetermined time period following the energizing of said heater or compressor.

2. A thermostat as set forth in claim 1 and further comprising:

means within said thermostat for generating a third signal for de-energizing said heater or compressor;

means within said thermostat for generating a off-delay signal of a predetermined time period; and

means within said thermostat for generating a fourth signal for de-energizing said circulation fan upon the passing of said predetermined time-off period following the de-energizing of said heater or compressor.

3. A method of operating a forced air comfort system having a furnace and/or air conditioner system with a respective heater or compressor and an air circulation fan all of which are turned on and off by signals from the thermostat, comprising the steps of:

sensing a need for heating or cooling and sending a corresponding demand signal to said thermostat;

responsively generating within said thermostat a first energizing signal for energizing said heater or compressor;

in response to said energizing signal, generating within said thermostat an energizing delay signal of a desired time-on period;

waiting for said desired time-on period following the energization of said heater or compressor; and

generating within said thermostat a second energizing signal for responsively energizing said air circulation fan.

4. A method as set forth in claim 3 and including the further steps of generating within said thermostat a first de-energizing signal for de-energizing said heater or compressor;

in response to said de-energizing signal, generating within said thermostat a de-energizing delay signal of a desired time-off period;

waiting for said desired time-off period following the de-energizing of said heater or compressor; and

generating within said thermostat a second de-energizing signal for responsively de-energizing said air circulation fan.

5. A thermostat for energizing and de-energizing a forced air comfort system having a furnace and/or air conditioning system with a respective heater or compressor and an air circulating fan comprising:

a first signal generator for generating a delay signal which causes the air circulation fan to be activated only after a predetermined time period following the energization of the heater or compressor.

6. A thermostat as set forth in claim 5 including a second signal generator for generating an off delay signal which causes the air circulation fan to be deactivated only after a predetermined time period following the de-energization of the heater of compressor.

7. A thermostat as set forth in claim 1 wherein said forced air comfort system is a furnace and said circulation fan is turned on a predetermined time after said heater is energized.

8. A thermostat as set forth in claim 1 wherein said forced air comfort system is an air conditioner and said circulation fan is turned on a predetermined time after said compression is energized.