Electronic control and method for increasing efficiency of heating

A method of increasing the efficiency of a hot air furnace by measuring the temperature differential across the heated air inlet and outlet plenums which occurs during normal operation of the furnace to raise the room temperature from its turn on point to its turn off point. The plenum temperature differential is then used to time cycle the burner.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to the area of heating and cooling 
systems, and more specifically to electronic control systems designed to 
increase the efficiency of central heating and cooling air conditioning 
systems. 
2. Description of the Prior Art 
Heretofore, temperature control systems for use with heating and air 
conditioning units, hereinafter referred to as "HVACs," have consisted of 
thermostats which turn the heating or cooling unit on or off when a given 
temperature is reached. Further improvements have been accomplished 
through the use of timers which limit the period of use of the HVAC. 
Additional improvements have included controls using a relay together with 
a time delay in conjunction with a thermostat, so that the fan operates 
for a preset time after the HVAC unit is turned off, thereby clearing the 
duct of any available warm or cool air. Applicant is unaware of any prior 
art teaching a device or method which combines a differential thermostat 
sensing both the supply and return duct temperatures with a computerized 
control unit having the unique features as taught herein. 
SUMMARY OF THE INVENTION 
The present invention comprises a control unit for use with HVAC's which is 
designed to increase energy efficiency during operation of existing 
equipment. The control unit is operationally positioned between the room 
thermostat which would normally control the HVAC unit and the HVAC unit 
itself, so that it is in a position to control the HVAC. The control unit 
could be modified to include a thermostat function and thus obviate a 
separate thermostat. The control unit is capable of deactivating the HVAC 
equipment even though the thermostat is in an "on" condition; however, 
unless the thermostat indicates a demand, the control unit will not 
activate the HVAC unit except for operation of the fan as discussed 
herein. In connecting the control unit, the operator disconnects the 
thermostat and connects the control unit in place of the thermostat. The 
thermostat is then connected to the control unit as shown in the drawings 
and discussed later herein. The control unit senses temperature at both 
the supply duct and the return duct of the HVAC system, compares the two 
temperatures, computes the rise and modifies operation of the system on 
the basis of the computed data. The rise referred to herein is the 
mathematical difference between the temperatures in the supply duct and 
the return duct. On the basis of the computed data, the control unit 
cycles the burner or compressor of the HVAC unit on and off, increasing 
the efficiency of the system. As it performs this function, it also senses 
the supply and return duct temperatures and continues to operate the fan 
after the burner or compressor of the HVAC unit is deactivated. The fan 
continues to operate until the temperature difference between the supply 
and return ducts ("rise") is reduced to a computed level. The control unit 
does not operate on absolute temperature variations in either of the 
ducts, but rather on the differential ("rise") between the ducts. Then, 
having read the demand, it operates the HVAC unit. 
In operating the HVAC in the heating mode, the control unit increases 
efficiency by preventing the heat exchanger from exceeding saturation 
(that is, the point at which the temperatures of the inside and outside 
surfaces of the heat exchanger wall are substantially equal), thereby 
limiting the loss of heat through a flue. Exceeding saturation 
dramatically reduces efficiency. Efficiency is further increased because 
the control unit leaves the fan on to clear the flue of warm air after the 
burner is deactivated. 
In operating the HVAC in the cooling mode, the control unit operates the 
compressor in the HVAC in its most efficient mode by cycling on and off, 
allowing head pressure to be equalized, and by evaporating moisture on the 
cooling coils, and by clearing the ducts of the remaining cool air during 
a "coasting" period with the evaporator fan on and the compressor off. 
One of the objects of the present invention is to provide an electronic 
control unit which is capable of increasing the efficiency of an HVAC 
system. 
Another object of the present invention is to provide a control unit for 
HVAC systems which is relatively inexpensive to build and to operate. 
A further object of the present invention is to provide a method of 
controlling HVAC systems so as to maximize efficiency at a minimum cost. 
A further object of the present invention is to provide a control unit for 
use with HVAC systems which increases efficiency dramatically. 
Another object of the present invention is to compute and determine the 
equipment's present level of energy efficiency (fuel utilization) and the 
increased efficiency resulting from the use of the control unit, and then 
to display the savings realized in percentage form. 
The foregoing objects, as well as other objects and benefits of the present 
invention, are made more apparent by the descriptions and claims which 
follow.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows a perspective view of an HVAC 14 with flue 11 and having an 
outlet, supply duct 12, and an inlet, return duct 13. Though such is not 
shown in the drawings, HVAC 14 includes a burner for heating, an 
evaporator and condenser coils for cooling, an air circulating fan, and a 
transformer. For purposes of simplicity, a room thermostat 16 is shown 
beside HVAC 14. Room thermostat 16 would normally be connected to HVAC 14 
through lines 17 and 18. However, in the present invention, a control unit 
15 is connected to HVAC 14 by line 17, and room thermostat 16 is connected 
to control unit 15 by line 18. Control unit 15 is also attached by lines 
19 and 42 to a temperature sensing means, temperature sensor 21, in the 
supply duct 12 of HVAC 14, and through lines 20 and 43 to a temperature 
sensing means, temperature sensor 22, in return duct 13 of HVAC 14. 
Control unit 15 senses temperatures in supply duct 12 and return duct 13 
and modifies the operation of HVAC 14 on the basis of computed variations 
between those temperatures. Thermostat 16 is used by control unit 15 to 
determine when demand is present, whether the demand is for heat, cool or 
manual fan, and when the demand is satisfied. While thermostat 16 is here 
used as a switch to indicate demand, a manually operated switch could be 
connected in place of thermostat 16 if desired. Control unit 15 is also 
usable with a convection or gravity heater rather than an HVAC, in which 
case a fan may or may not be used. 
FIGS. 2 and 3 show control unit 15 and its connection to room thermostat 16 
and HVAC 14. The actual construction of one embodiment of control unit 15 
is shown in FIG. 3 of the drawings. Control unit 15 consists of a 
microprocessor 36 connected through line 47 to a RAM chip 38. RAM chip 38 
is connected to EPROM memory chip 39 through lines 48. In one variation, 
the microprocessor 36 has an internal RAM which takes the place of RAM 
chip 38. Basic programming of the functioning of the unit is provided by 
EPROM memory chip 39. Display 34 is provided to monitor operation of 
control unit 15, and is attached to microprocessor 36 by lines 44. 
Microprocessor 36 is connected to input buffer 37 through line 49. Input 
buffer 37 is utilized to input data from room thermostat 16, and monitors 
heat demand through line 23, cooling demand through line 24, and the fan 
of HVAC 14 through line 26. Input buffer 37 further monitors temperature 
sensor 21 in supply duct 12 through lines 19 and 42, and temperature 
sensor 22 in return duct 13 through lines 20 and 43. Output buffer 40 is 
attached to microprocessor 36 by line 50, and controls HVAC 14 through the 
use of relays 25, 30 and 32, which route power to the burner, fan and 
compressor of HVAC 14 through lines 28, 29 and 31, specifically 
controlling heating through line 28, cooling through line 29, and fan 
through line 31. Control voltage to operate relays 25, 30 and 32, which 
actuate HVAC 14 through lines 28, 29 and 31, is provided by line 60, which 
is attached to line 27, which is connected to a transformer in HVAC 14 or 
other appropriate power supply. Output buffer 40 is connected to constant 
known voltage source 41 through line 51, and directs voltage to 
temperature sensor 21 through line 42 and to temperature sensor 22 through 
line 43. Power is provided to power supply 33 by line 27, which is 
connected to a 24-volt transformer in HVAC 14. Power supply 33 provides 
power through line 46 to operate microprocessor 36, as well as other 
components in control unit 15. 
OPERATION 
Control unit 15 is connected to the components of HVAC 14 and to room 
thermostat 16 and temperature sensors 21 and 22 in supply duct 12 and 
return duct 22 as shown in the drawings. EPROM memory chip 39 is 
programmed to establish optimal operation (i.e., cycling) of HVAC 14 to 
substantially increase efficiency in all types of weather conditions. 
Initially, in a calibration mode, control unit 15 operates HVAC 14 in an 
uncycled or uncontrolled standard mode based on demand indicated by room 
thermostat 16 while monitoring information and recording it in RAM chip 
38. In this mode it notes various performance data during normal operation 
of the HVAC 14. This includes temperature variation between the supply 
duct 12 and return duct 13 during normal operation of the system. Using 
information gathered and the program in EPROM memory chip 39, it creates 
its own program variables, based upon collected data, and calculations. 
Thus, utilizing the program in EPROM chip 39, it adjusts the equipment's 
operation to match the building, equipment used, occupants, temperature 
settings desired, type of fuel used and exterior weather conditions to 
provide the most fuel-efficient and economical mode of operation. 
Data monitored and recorded include return duct temperature, supply duct 
temperature, temperature differential between supply and return ducts, 
demand time, total time during which fuel is consumed, energy-used 
coefficient (to determine savings), and rise maximum during a preset 
period. 
Monitoring is automatically performed during the calibration mode when no 
data are present in RAM chip 38. This occurs at the time of installation, 
any time power is interrupted, or whenever recalibration to maintain 
efficiency is desired (normally weekly). 
When monitoring is complete, one of two programs--for either heating or 
cooling--will be used to maximize efficiency. 
For heating, the program cycles the HVAC's burner "on" until the 
temperature differential between supply and return ducts reaches a first 
percentage (e.g., 85%) of the rise in a preset period of time (e.g., 5 
minutes) as recorded previously during monitoring, and "off" until the 
temperature differential between supply and return ducts reaches a second 
percentage (e.g., 60%), lower than the aforementioned first percentage of 
the rise. This cycling continues until room thermostat 16 indicates the 
demand has been satisfied. To further enhance efficiency, the fan is held 
"on" until demand indicated by room thermostat 16 is satisfied and the 
supply duct temperature drops below a preset temperature (e.g., 100 
degrees Fahrenheit). 
With the system in the cooling mode, for purposes of calibration the 
program of control unit 15 activates the air conditioner and continues 
operation until the demand indicated by room thermostat 16 is satisfied. 
Data are monitored as previously noted and logged into memory. When demand 
is again indicated by room thermostat 16, the program cycles the air 
conditioner compressor on and off for preset segments of calibrated time 
periods; for example, on for one-fifth of the time required to satisfy the 
demand indicated by room thermostat 16 in the calibration mode and off for 
a minimum of three minutes or a sufficient time to allow the compressor 
head pressure to equalize. The program continues to operate the fan during 
each "off" period until a preset temperature (e.g., 66 degrees Fahrenheit) 
is reached in the supply duct, at which point, if sufficient time has 
elapsed to allow the compressor head pressure to equalize, it reactivates 
the compressor. Control unit 15 continues to cycle the air conditioner 
compressor on and off until the demand indicated by the room thermostat 16 
is satisfied. When the demand is satisfied, the compressor is deactivated 
and the program holds the fan on until the air in the supply duct reaches 
a preset temperature (e.g., 68 degrees Fahrenheit). Efficiency is gained 
partly as a result of clearing the ducts of cooler air, and also through 
the evaporation of moisture on the cooling coils which occurs during the 
"coasting" period. 
The program utilized also provides for displaying the calculated percentage 
of savings. This figure is determined with calculations performed on the 
basis of efficiency realized during the calibration period versus 
efficiency realized during operation utilizing the techniques taught 
herein. This calculation, which is performed by the control unit 15, is 
based on the following formulae: 
##EQU1## 
While the foregoing description of the invention has shown a preferred 
embodiment using specific terms, such description is presented for 
illustrative purposes only. It is applicant's intention that changes and 
variations may be made without departure from the spirit or scope of the 
following claims, and this disclosure is not intended to limit applicant's 
protection in any way.