Apparatus and method for monitoring and controlling heating and/or cooling systems

This invention relates to an apparatus and method for monitoring and controlling a heating and/or cooling system which controls the temperature of air in a conditioned space within a building and to such an apparatus and method capable of indicating the performance of such a system and effectuating control over the system for maximizing the operating efficiency of the system. As compared with a conventional control system, additional temperature sensors are provided to sense the temperatures of air drawn into and discharged from a temperature modifying unit such as an air handling unit having a heat exchange coil. The sensed temperatures are then used as a basis for determining the differential attained by flowing air through the unit, and compared with a desired differential taken as indicating an optimal condition, with the percentage of attainment of the optimal differential being visually displayed for an operator of the system. The attainment or non-attainment of certain target differentials within certain predetermined time intervals is used to control the operation of the system by either stopping such operation and draw attention to a clearly defective system or cycling the system to operate a satisfactory system in the most economical way. Application to systems other than circulating air systems is suggested.

FIELD AND BACKGROUND OF INVENTION 
This invention relates to an apparatus and method for monitoring and 
controlling a heating and/or cooling system which controls the temperature 
of air in a conditioned space within a building or a commercial freezer or 
refrigeration unit. More particularly, this invention relates to such an 
apparatus and method capable of indicating the performance of such a 
system and effectuating control over the system for maximizing the 
operating performance of the system. 
Most dwellings and commercial buildings now in use are serviced by systems 
for circulating a flow of air through the spaces within the building and 
controlling the temperature of the circulating flow of air. Such systems 
may use various means of heating and/or cooling the flow of air, including 
combustion of fuels, mechanical refrigeration systems circulating liquids, 
and dual cycle systems of the types known as heat pumps. Such systems 
conventionally have temperature sensors in the conditioned spaces for 
sensing air temperatures in those spaces (often known as thermostats) and 
control systems responsive to the temperature sensors for changing the 
temperature of flowing air to reach and maintain a desired temperature in 
the conditioned space. 
It has been recognized heretofore that such systems may have varying 
performance, and that maintenance of satisfactory system performance 
(herein sometimes also referred to as operating efficiency) is beneficial 
in minimizing the costs of maintaining the desired temperature effects 
within a building. It has been proposed heretofore that certain additional 
temperature measurements may be used to monitor the operation of a system, 
or that system performance may be somewhat controlled by the provision of 
timing controls which govern the intervals of operation of a system. 
However, such proposals typically do not assure than an operator of a 
system be advised of the performance attained or not attained, in order 
that preventative maintenance be applied to sustain system performance. 
BRIEF DESCRIPTION OF INVENTION 
With the foregoing in mind, it is an object of this invention to provide, 
in a control system for a temperature modifying system such as a heating 
and/or air conditioning system, an improved apparatus for monitoring the 
system performance and providing a visual indication of the useful output 
attained by the system. In realizing this object of the present invention, 
additional temperature sensors are provided to sense the temperatures of 
air drawn into and discharged from a temperature modifying unit such as an 
air handling unit having a heat exchange coil. The sensed temperatures are 
then used as a basis for determining the differential attained by flowing 
air through the unit, and compared with a desired differential taken as 
indicating an optimal condition, with the percentage of attainment of the 
optimal differential being visually displayed for an operator of the 
system. 
Yet a further object of this invention is to provide, in a performance 
monitoring system of the type described, a means for assuring that 
performance is monitored at times when it is appropriate for such 
monitoring to occur. More particularly, with a forced air system, it is 
appropriate to monitor system performance only when there is a circulating 
flow of air. Accordingly, in realizing this object of the present 
invention, provision is made for sensing the movement of the heated or 
cooled circulating fluid (in the usual case, air). 
Yet a further object of the invention is to operate a system of the type 
described in accordance with a method in which the attainment of 
predetermined differentials across the intake and discharge of an air 
temperature modifying unit, as a function of time, is used to control 
operation of the system. In realizing this object of the invention, the 
attainment or non-attainment of certain target differentials within 
certain predetermined time intervals is used to control the operation of 
the system by either stopping such operation to prevent damage to and 
generate an error signal to call attention to a clearly defective system 
or cycling the system to operate a satisfactory system in the most 
economical way.

DETAILED DESCRIPTION OF INVENTION 
While the present invention will be described more fully hereinafter with 
reference to the accompanying drawings, in which a preferred embodiment of 
the present invention is shown, it is to be understood at the outset of 
the description which follows that persons of skill in the appropriate 
arts may modify the invention here described while still achieving the 
favorable results of this invention. Accordingly, the description which 
follows is to be understood as being a broad, teaching disclosure directed 
to persons of skill in the appropriate arts, and not as limiting upon the 
present invention. 
Referring now more particularly to the drawings, an apparatus as 
contemplated by this invention is there represented in two different 
ways--by the largely schematic diagram of FIG. 1 and a more explicit 
diagram of FIG. 2. It is to be understood at the outset that the diagram 
of FIG. 2 is one expression of a circuit which is capable of performing as 
indicated by FIG. 1, and that other forms may function in accordance with 
the description which follows. It is also to be understood that the 
diagrams are somewhat incomplete, in that certain components which are 
well known in the art are not shown. Thus, persons of skill in the 
appropriate arts will be able to understand that a complete apparatus 
incorporating this invention will include an air handling unit (not shown) 
having a fan for drawing a flow of air from a conditioned space into and 
through the unit and means for changing the temperature of the air as it 
passes through the unit. The means for changing the temperature of the air 
may be any suitable controllable source of heating or cooling, such as an 
evaporator or condenser coil for a mechanical refrigeration system, or a 
gas or oil fired heat exchanger. Interested readers needing further 
description of such systems are referred to the widely available 
commercial literature or prior patents for further descriptions of such 
apparatus. 
As indicated, the apparatus in accordance with this invention includes a 
first temperature sensing means in the conditioned space for sensing the 
temperature of air in that space, generally known as a thermostat and 
indicated in FIGS. 1 and 2 at 20. It is typically the case in 
installations of the types with which this invention is used that 
provision is made for using a single thermostat for both heating and 
cooling, and such thermostats conventionally have switches for selecting a 
heating function, a cooling function, and providing manual control over 
the running of the fan. At least some systems may use dual thermostats or 
two stage thermostats, and such systems may be adapted to the present 
invention to be described hereinafter by using multiple systems in 
accordance with the invention. Control over the fan, heating source and 
cooling source is conventionally established by electrical relays or by 
valves, with such relays being indicated generally in the diagrams as fan 
relay 21; heating relay 22; and cooling relay 23. The thermostat also 
includes a temperature responsive switch which is settable for a desired 
temperature within the conditioned space and will open or close to 
indicate a need for modification of the temperature of air supplied to the 
space by the air handling unit. 
Those elements described to this point, and their operation together, are 
essentially conventional. 
In accordance with certain features of this invention as they relate to the 
preferred embodiment shown in the drawings, apparatus in accordance with 
this invention has, in addition to the first temperature sensor provided 
by the thermostat 20, second and third temperature sensors 30, 31 for 
sensing the temperatures of return air drawn to the unit and supply air 
expelled from the unit. These additional sensors provide signals, 
preferably analog electrical signals such as voltages which vary with 
temperature, which are supplied to and used by a processor means which, in 
the form shown in FIG. 2, takes the form of a group of TTL devices or 
chips connected together to perform certain functions described in greater 
detail hereinafter. As will be addressed hereinafter, the present 
invention contemplates that a microprocessor CPU chip operating under 
suitable programs or any other comparable type of device may be used 
instead of the TTL devices shown and described. 
The apparatus in accordance with this invention also has, where applied to 
a forced air system, a means for detecting the flow of conditioned air. It 
is known that such an air flow detection means may take a wide variety of 
forms, including such element means as an anemometer or other flow 
responsive device mounted in the system ductwork adjacent a coil face or 
the like. However, in the preferred forms of this invention, it is 
contemplated that the air flow sensing means take the form of a self 
heated or indirectly heated NTC thermistor, a device in which the 
resistance varies with temperature. By determination of the resistance 
value of the device in the presence of a known air stream flowing over the 
device, a calibration may be accomplished by which air flow within a 
predetermined proper range can be identified. As a consequence, should air 
flow drop below that range (as from a filter becoming stopped or a coil 
iced up), a signal may be derived, an appropriate warning annunciator may 
be activated, and the processor signalled that the temperature 
differentials and times being determined are not representative of proper 
operation of the system. As will be appreciated by the thoughtful reader, 
determination of temperature differentials as will be described 
hereinafter will be most effective in providing an indication of system 
performance where the system is in fact performing, i.e. where air is 
flowing. 
The processor means compares the temperatures sensed by said second and 
third temperature sensors, determines the temperature differential 
therebetween and the percentage of a predetermined optimum differential 
between the sensed return air and supply air temperatures which has been 
attained, and generates a percentage signal representative of such 
percentage. In association with timers to be described hereinafter and 
other circuitry, the processor determines (a) whether a predetermined 
percentage of a predetermined optimum differential between the sensed air 
and supply air temperatures has been attained within the first 
predetermined time interval and (b) whether the optimum differential has 
been attained within a second predetermined time interval and (c) whether 
the optimum differential has been attained before a desired temperature 
has been attained in the conditioned space, and functions for (d) 
interrupting operation of the associated temperature modifying unit and 
generating an alarm signal in the event of a determination that the 
predetermined percentage of the optimum differential has not been attained 
within the first predetermined time interval and (e) generating an error 
signal in the event of a determination that the optimum differential has 
not been attained within the second predetermined time interval and, if 
desired, (f) cycling the unit on and off in the event of a determination 
that the desired temperature has not been attained in the conditioned 
space upon the optimum differential being attained. These functions 
contribute to the enhanced performance and improved monitoring of 
operation which are objects of this invention. 
As used in this description, the phrase "optimum differential" refers to a 
determination made after the basic operating conditions for a system have 
been established and using system performance data available from 
component manufacturers. One such procedure is discernible from pages 301 
and 302 of "Refrigeration and Air Conditioning" by W. F. Stoecker 
(McGraw-Hill, 1958) which describe and give an example of a popular method 
of presenting coil performance data, a tabular form. Attention is invited 
to the table set forth as Table 21-1, where entering air conditions, face 
velocities of air flow, refrigerant temperatures, and final dry and wet 
bulb temperatures are set forth. From such a table, the determination of 
"optimum differential" becomes a simple matter, as most of the system 
variables will have been established before the control of the present 
invention is applied. For example, where applicant's apparatus is to be 
used with a 2 row coil, 35 degree refrigerant temperature and 400 fpm face 
velocity, the optimum differential of dry bulb temperatures is between 86 
degree entering air and 69.3 degree exit air. 
In FIG. 1, certain of the processor functions described thus far are 
performed by elements indicated as a differential determiner 32 and 
differential/optimal determiners 34. Circuit components performing these 
functions are similarly indicated in FIG. 2. It will be noted that a 
plurality of differential/optimal determiners 34 are provided. In the 
illustrate form of the invention, each of these elements determines that a 
predetermined percentage of the optimal conditioner has been attained. 
That is, one element or set of elements determines that 10% of the optimal 
differential has been attained; another 50%; a third a percentage which is 
adjustable between 0% and 100%; and a fourth, 100%. These percentages, 
which compared with certain timers, provide "flags" or indicators of 
system performance which control other indications given to an operator. 
It will be appreciated that one step in the determination is the 
conversion of the analog voltage signals derived from the sensors into 
digital signals for further processing, as the subsequent determinations 
are more readily made by such processing as described herein. 
This invention contemplates that the optimal difference between return air 
and supply air temperatures may be different when heating is called for in 
the conditioned space and when cooling is called for in the conditioned 
space. For this reason, it is significant for the apparatus of this 
invention to distinguish between the two states of heating control and 
cooling control. With a conventional thermostat 20 the switch selection of 
such control or of fan operation provides input signals to the processor 
means which are used to permit determination with appropriate optimal 
differentials. Such signals are in addition to the signal indicating 
whether the first temperature sensor embodied in the thermostat is 
"satisfied" or calling for temperature change in the conditioned space. As 
will be understood, the presence of a heating or cooling demand signal 
will be the only indication of a need for a change in the temperature of 
the conditioned space. 
As mentioned hereinabove, timer means are operatively connected for timing 
intervals of operation of the unit. Preferably, and for convenience in 
achieving the desired operation, and timer means takes the form of a 
plurality of timers. One timer 40 cooperates with one differential optimal 
determiner 34 for determining whether the system has attained a first 
predetermined percentage (in this instance, fifty percent) or the optimal 
differential within a first predetermined time interval (in this instance, 
ten or fifteen minutes). If such percentage is not attained, then the 
temperature modifying element is disabled, by opening of the related 
control relay. At the same time, an audible signal is emitted by an 
annunciator device such as a piezoelectric buzzer 41 and a visual warning 
is given by another annunciator device such as a light emitting diode 42. 
Other timers 44, 45 cooperate with an differential/optimal determiner 34 
for determining whether a second predetermined percentage (in this 
instance, on hundred percent) of the optimal differential has been 
attained within a second predetermined time interval (in this instance, 
fifteen minutes for heating cycles and thirty minutes for cooling cycles). 
In the event that the target differential is not attained within the 
applicable time interval, an error signal is generated and delivered to an 
appropriate annunciator device (in this instance, a light emitting diode) 
to indicate that the heating or cooling equipment needs to be checked for 
maintenance. 
Other timers provide for continuing fan operation in the event that the 
system attains one hundred percent of the optimal differential within a 
predetermined time interval and while the temperature modifying element is 
disabled, and for preventing "short cycling" of a refrigeration producing 
mechanical compressor in such event. More particularly, should the 
differential/optimal determiner distinguishing one hundred percent 
attainment of an optimal differential signal that achievement within a 
predetermined time interval (in this instance, fifteen minutes), then the 
efficient operation of the system results in the heating or cooling system 
being stopped, even though the thermostat 20 may be calling for further 
temperature change in the conditioned space. In the event that the 
thermostat is unsatisfied, the fan of the air handling unit continues 
operation in order to extract from the temperature modifying element all 
of the then stored heat or cold. Thereafter should the thermostat still be 
calling for change in the conditioned area, the system is restarted. In 
such a restart, a further timer assures that the compressor of any 
mechanical refrigeration producer used as a cooling element is protected 
against excessively frequent starting, as such "short cycling" is known to 
be damaging to such compressors. 
The apparatus of the present invention includes provision for visually 
indicating to an operator the relative efficiency of the system. Such a 
means takes the form, in the embodiments illustrated in FIG. 1, of a 
visual display 50. In the form illustrated in FIG. 2, the visual display 
is digital, and composed of three numerical indicators of known types 
capable of presenting a display of a numerical value indicative of the 
percentage of the optimal differential which is then being attained by the 
system. An alternate would be a bar graph analog display, described 
hereinafter. 
In operation, the apparatus described functions within the context of well 
known methods in which the temperature of air within a conditioned space 
is controlled by circulating a flow of air while sensing the temperature 
of air in the conditioned space and changing the temperature of the 
flowing air in response to any difference between the sensed temperature 
thereof and a desired temperature. The improvements accomplished by the 
present invention lie in monitoring the efficiency of the method and 
controlling the temperature change and, as described above, include the 
steps of sensing the temperatures of return air drawn from the space and 
supply air returned to the space; responding to the sensed return and 
supply temperatures by comparing the return and supply temperatures and 
determining the temperature differential therebetween and the percentage 
of a predetermined optimum differential between the sensed return air and 
supply air temperatures which has been attained; determining whether a 
predetermined percentage of the predetermined optimum differential between 
the sensed return air and supply air temperatures has been attained within 
a predetermined time interval; and interrupting operation of said unit in 
the event of a determination that said predetermined percentage of said 
optimum differential has not been attained within said predetermined time 
interval. The method according to this invention also includes determining 
whether the optimum differential has been attained within a predetermined 
time interval; generating an error signal in the event of a determination 
that the optimum differential has not been attained within the 
predetermined time interval; and responding to the generation of an error 
signal by displaying a warning that the apparatus is operating below a 
desired efficiency. 
As alluded to hereinabove, certain of the indications to an operator are 
displayed at the face of a control in accordance with this invention. Two 
forms of such displays are shown in FIGS. 3 and 4. The principal 
difference between the two is the provision in FIG. 3 for a numerical 
display of percentage figures of efficiency. In FIG. 4, separate heating 
and cooling displays are provided in the form of bar graphs formed by a 
series of light emitting diodes. The bar graph diodes may be appropriately 
colored in the case of FIG. 4, using red color emitting diodes for the 
heating bar graph and green for the cooling. Alternatively, a single bar 
graph display may be provided by bi-color light emitting diodes which emit 
red light in heating and green in cooling. In each instance, a rising line 
of the bar graph indicates increasing efficiency, measured as an 
increasing achievement of the desired optimal differential between return 
and supply air temperatures. Additional indications are provided for 
displaying operation in heating and cooling modes; displaying operation in 
the high efficiency, saving mode where the desired optimal differential is 
attained within a short time interval and fan operation continues; 
displaying signals indicative of a need for maintenance checks of heating 
and cooling; and displaying the occurrence of a protective shutdown. 
As will be understood by the knowledgeable reader, the results described 
may be accomplished with a number of forms or types of digital 
microprocessors capable of receiving and processing electrical signals of 
the types described above. Persons familiar with the selection and design 
of digital microprocessor circuits will be enabled by this discussion to 
select conventionally available circuitry to accomplish the functions of 
monitoring the signals from the temperature sensors described hereinabove 
and developing control signals to be supplied to the heating, cooling and 
fan relays in such a manner as to accomplish the control envisioned for 
the present invention. 
By way of an illustrative example, microprocessors of the types known as 
8013, 8015 and Z-80 may be programmed using machine language or higher 
level languages such as Basic to respond to digital signals received from 
the temperature sensors by processing such signals and developing control 
signals as described above. Specific programs will vary with the 
microprocessor chosen, the types of heating and cooling equipment used, 
and the desired characteristics of operation, all as discussed more fully 
hereinabove. For that reason, no detailed program listing is here given, 
it being considered that a knowledgeable programmer familiar with any of 
the aforementioned microprocessors will be able, from the present 
disclosure, to prepare such a listing and further that inclusion of an 
illustration of such a listing here would occupy an excessive number of 
pages of the present specification. 
As alluded to briefly hereinabove, the present invention has application 
where the circulating fluid as to which the temperatures are sensed at the 
return and supply sides of a temperature modifying unit are other than 
air. More specifically, one contemplated application would be with 
conditioned space systems of the type known as hydronic systems, where the 
circulating fluid is a liquid such as water. With such a system, 
temperature sensing in accordance with this invention, and performance 
monitoring and control, could be accomplished either on the "air side" 
substantially as described hereinabove or, closer to the actual 
temperature modifier, on the "water side". It is believed that person of 
appropriate skill in the applicable arts will be able, from this brief 
discussion, to apply this invention to such systems and to others where 
the usefulness of the invention can be recognized. 
In the drawings and specifications there has been set forth a preferred 
embodiment of the invention and, although specific terms are used, the 
description thus given uses terminology in a generic and descriptive sense 
only and not for purposes of limitation.