CA1162981A - Method and apparatus for power load shedding - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A method and apparatus for the control of power consumption in individual space-conditioning loads fed by an electric power network utilizes a commandable, programmable temperature control device which gradually, substantially continually changes the control setpoint in response to an external signal to reduce power consumption such that tem-perature changes go relatively unnoticed by the occupants.
A radio receiver or the like is utilized to receive a signal from the power utility company and, in response to the sig-nal, the setpoint function of the thermostat associated with the load becomes an electronically simulated function in accordance with the invention and the user-control setpoint is removed from the control loop. The effective load shedding is also greatly enhanced by the provision of an integral reset function in addition to the conventional pro-portional control within the temperature control system.
The use of a plurality of such systems enables the power utility to control electric power network peak load with a minimum impact on the comfort of individuals in the conditioned spaces.
In the cooling mode, the temperature setpoint is caused to be slowly raised or ramped in a substantially con tinuous manner to a predetermined maximum temperature during the peak power consumption hours and, thereafter, is ramped back down to the fixed rate until the conditioned space is returned to its original temperature at which point control is returned to the user. Conversely, in the heating mode, the setpoint is ramped downward to a predetermined minimum temperature limit during peak power consumption hours and, thereafter, ramped back upward to its original setpoint at which time control is also returned to the user.

Description

METHOD AND APPARATUS FOR POWER LOAD SH~DDIN~

NTION
Field o$ the Invention The present invention relates generally to a meth-~d` o~ controlling the peak power demand in a~ electrLcal power distriblltion network by controlling the peak power consumption of individual loads such as air conditioning loads and, more particularly, to a method and apparatus for controlling the thermostats of individual space condl" ioning apparatus in a predetermined manner based on external commands Description of the Prior Art One of the most serious problems confronting elec-tric utility companies today is the great variance i~ total electrical demand on a network between peak and o~f-peak times during the day. The so-c,alled peak demand periods or load shedding intervals are periods of very ~igh demand on the power generating equipment where load shedding~may be necessary to maintain propPr servic~ to the network~ These occur, ~or example~, during hot summèr days occasioned by the~
widespread simultaneous usage of electric air condîtioning devices. Typically the load shedding interval may last many hours and ~ormally occurs~during the hottest part of the day . , such as between ~the hours of noon and 6:00 p~m. Peaks may also occur during the coldest winter months in areas where i ~he usage of elec~rical heating equipmPnt is prevalent. In Il ~ ' " ~.
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the past, in order to accommodate the very high peak demands, electric utility companles have been forced to spend tremendous amounts of money either in investing in additional power generating capacity and equipment or in buying so caIled "pea~" power from other utilities which have made such investments.
More recently, electric utility companies have turned to load shedding as a means of controlling peak demand and this has led to the use of the term "load shedding interval. It is desirable that a load shedding device reduce power demand uniformly over the entlre load shedding interval because the actual peak of power demana on the total utility grid could occur at any time during the load shedding interval.
In the prior art, several basic strategies and devices have been utilized for :load shedding in order to limit the peak power demand on the power generating capacity of electric utility companies. One such mode lnvolves sending signals either over the power lines or by utilizing a radio-~ype signal emanating from the utility to disconnect or interrupt the use of certain selected electric loads such as air conditioning compressors when the demand has reached a certain point. While this type o~ direct control of power consumption by the utility achieves usage cutbacks during peak periods which prevent the power network from becoming overloaded, in many cases, the great inconvenience to the user who may ind his power disconnected for an inordinately .

~ ~6298~
long time may weLl outweigh the benefits of the load sheddingO
An alternate method of control employed by utility companies to reduce peak power consumption on given networks involves the concept of duty cycling. This involves a time ~harin~ over the network of-certain amounts of the power during peak periods such that service is intexrupted to selected devices on a time sharing basis. Thus, for exam-ple, on a ten minute per one-half hour duty cycle, aLl of the devices for which service is to be interrupted have their servlce interrupted ten minutes out o~ each one-half hour on a rotating basis with each ten minutes involving one-third of the device population. While this method does accomplish some load shedding, it has several disadvantages.
Flrst, duty cycling tends to destroy natural diversity. Natural diversity may be defined by the following. A large group of air conditioning or heating machines which contlnually cycle ON and OFF to maintain com~
fort conditions in a space have a natural tendency to oper-ate such that the cycling pattern of each machine is in ran-~i dom phase wi~th the cycling pattern of all other such machines in the power network. In this fashion, there is ~` but a random llke;llhood that all of the air conditioning compreesors or heating machines will be operating at the ; same instant. The tendency for this random operation Is then called natural diversity. Any load shedding strategy which te ds to synchronl u the runni g periods of all the ... .

~ ~L ~compressors or heaters in the utility service network reduces natural diversity. Sy~chronizat~ion causes signifi-cant spikes in power demand durirlg the on cycles of these dévices and negates much of the benefits of the load shedding. lf the devices to be interrupted are electrie air eonditioning and coollng unlts, for example, the chances are that all sueh units whose power supply has been interrupted will be calling for power at the end of the off e~cle sueh that a spike in power demand will occur upon switching of the interrupted units at the end of eaeh cycle.
Also, this method of load shedding may be defeated or overcome by the eustomer by the installation of an oversized air conditioning or heatlng unit such that it may maintain the temperature of the environment utilizing only that portion of time allotted to it. The net effect, of eourse, is that no real power is shed.
The general problems assoeiated with a~l sueh prior art methods and devices is that while they may aeeom-plish a certain amount of load shedding whieh benefits the electrie utility, they largely ignore a very important fae-tor - the impact of one or more modes of interrupted serviee on the customer or user. Abrupt or large ehanges in the environmental temperature of a eonditional space are very undesirable from the standpolnt of the customer.
Other prior art methods of load shedding include the timed resetting of thermostats to a higher setting in the summer during the air-conditioning season and to a lower ' '`' _~_ . -

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setpoint during the heating season for a speciEied period ornumber of hours during the peak demand part oE the day~
Thls step chanqe does result in a great deal of load shedding insoEar as power utility is concerned. However, again it represents an abrupt change in the temperature of ~he environment which is sensed by the inhabitants who are~
required to endure uncomfortable temperatures for this lengthy period of time. What has Long been needed is a device which can achieve the required network load shedding with a minimum lmpact on occupants of the conditioned space.

SUMMARY OF THE INVENTION
. . .
By means of the presen~ invention, the abilit~ to control electrical power network peak load is achieved with a minimum impact on the comfort of individuals in the conditioned space. The present invention contemplates the control of power consumption in individual space-conditioning loads fed ~y an electric power network by means of a commandable, programmable temperature control device which gradually changes the control setpoint in a ;

predetermined manner in response to an external signal such t~at temperature changes go relatively unnoticed by the cus-tomer. In the cooling mode, the temperature control setpoint is slowly raised in a substantially continuous man-ner or "ramped" upward to a predetermined maximum tempera~
tur limit durlng peak power consumption hours and, there-a~ter, ramped back down at a fixed rate until the conditioned space is returned to its origlnal temperature at ~ . .
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which point control is returned ~o the user and the normal manually adjustable thermostat mode. Conversely, in the heating mode, in response to an external slgnal the setpoint is ramped downward to a predetermlned minimum temperature limit during peak power cons~mption hours and, thereafter, ramped ~ack upward to its original setpoint after the peak power consumption hours have passed such that con~rol is then returned to the user and the ori~inal control mode. In the case of air conditioning, the amount of load shedding may be somewhat enhanced by initially precooling the envi-ronment several degrees prior to startin~ the upward ramp cycle and, in the heating mode, the environmental tempera-ture may be raised several degrees prior to the ramping down of the setpoint. This adds additional potential dynamic load shed.
The entire load shedding operation may be accom-plished electronically. A radio receiver or other such means is utilized to receive a signal rom the power utility company. In response to the signal, the setpoint function of the thermostat associated with such load becomes an elec-tronically simulated function in accordance with the present invention and the user-controlled setpoint is removed from the control loop. The effective load shedding is also greatly enhanced by the provlsion of an inte~ral reset function in addit~on to the conventional proportional con-trol within the temperature control system. This enables the thermostat to control the conditioned space at a temper-.

2 ~ 8 ~

ature closer to that of the setpoint such that -the best advantage may be taken of the ramping function in either the cooling or heating mode.
By means of the system of the present invention, not only in almost all c~ses, is more load shed during the critical peak power demand hours, but it is also done in a manner which practically elim-inates the impact of physical discomfort on the persons occupying the conditioned space during the time hours the temperature is being ramped. As a guideline, it has been found that a gradual temperature change of up to about 1.5F goes generally unnoticed by persons in the controlled environment. This amount of ramping accomplishes a great deal of load shedding at the same time. Ramping with reference to the heating mode may be carried on up to 2F per hour conveniently with little change noticed by the occupants.
In accordance with the present invention, there is provided a method of controlling electrical power demand of a space-condition-ing load comprising the steps of: assuming control of the setpoint function of the space-conditioning thermostat associated with said load; causing a simulated value representing the setpoint of said space-conditioning thermostat associated with said load to change substantially continuously with time at a first rate to a first pre-determined space temperature limit wherein said first rate is a func-; tion of the difference between said simulated set point at the time - control is assumed and such first predetermined temperature limits and the predetermined electrical power demand control interval; and returning control of said setpint function to said thermostat.
ln accordance with the present invention, there is further provided an apparatus for controlling the operation of a -thermostat-~: :
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~ ' 1 162~1 ically controlled space-conditioning load comprising: means for es-tablishing control over the function of the setpoint of the thermo-stat controlling the operation of said electric space-conditioning load; means causing a simulated value representing said setpoint to change substantially continually with time at a Eirst rate in a first direction until a first predetermined temperature limit is achieved wherein said firs-t rate is a function of the difference between the value of said simulated setpoint at the time control is assumed and said first predetermined temperature limit and -the predetermined electrical power demand control interval; and means for relinquishing control over said setpoint function after said setpoint reaches said ~: second predetermined temperature limit.
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`~ Description of the Drawing : In the drawings wherein like numerals are utilized to designate like parts throughout the same:
:` :
: ~igure 1 is a~general bIock diagram of the temperature con-~ trol system of the invention; ;:

:~ Figure 2 includes schematic diagrams of an external time:' ~ clock and typical thermostats which~may be used with the system of , 0~ : the invention;
: Figure:3 i:s~a schematic block diagram of the thermostat control system of the inveDtion;

~: : ~ : :

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~ IGS. 4, 4A, and ~B dPp1~ct an electrical schematic diagram of the control system of FIG. 3;
FIG. 5 is a theoretical plot of comfort ternpera-ture versus the time of day for an air conditioning apparatus controlled in accordance with the invention~
: ~IGS. 5A and 5B depic~ theoretical cycle average power consumption versus time of day plot for an air conditioning system comparing results between a thermostat having a fixed 76 F setpoint and one controlled in accor-dance with FIG. 5 ~or a 105.1F maximum outdoor temperature day and a 90F maximum temperature day, respectively;
FIG. 6 is simllar to FIG. 5 but including a 3 precool period;
FIG. 6A is a theoretical plot similar to FIGS. 5A
and 5B of cycle average power versus time of day with the cycle of FIG. 6 compared with the cycle of the fixed 76F
~ setpoint;
: FIG. 7 is a theoretical plot of a comparison between control point and fixed setpoint illustrating a typ-: ical "droop" effect in thermostats wlthout an integral reset function;
FIG. 7A shows the same plot as FIG. 7 with inte-~ral reset control .function added to the thermostat, FIG. 7B is a theoretical plot of comfort tempera-: ture and setpoint versus time of day for the thermostat of FIG. 7 stepped up in discrete steps during the peak power interval;

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FIG. 7C is similar to FI~. 7B for a ramped function uslng the thermostat of FIG. 7 havlng no i.ntegral reset;
~ IGS. 7D and 7E are plots of cycle average power versus time of day as in FIGS. 5A and 5B showing comparative cycle a~erage power usage of an air conditioning system controlled at a fixed 76 setpoint, utilizing the ramping function without a precool cycle, and having the setpoint stepped up in discrete steps each hour;
FIG. 7E is similar to FIG. 7D except the compari~
son is made between ramping with integral reset and ramping with a conventional thermostat not hav;ng integral reset; `
FIGS. 8, 8A, 8B, and ~C show plots of theoretical temperature versus time for various prior art duty cycle modes of load shedding along with corresponding cycle aver-age power consumption versus time of day plots for the respective duty cycling; .
FIGS. 9 and g~ depict cycle average power consump-tion versus time o~ day comparing a ten-minute duty c~cle .
: concept w~th a fixed 76 setpoint and a ramping cycle .
without precooling showing the relative amounts of load shed at two different maximum outdoor temperature days.

DESCRIPTION OF_THE PREFERRED_EMBODIMENT
~: The basic concept of the present invention allows an electric power utility to control individual air conditioning or heating load.s with.in a given power network such that it may accomplish the necessary load shed commen-' , ~.
_ g _ , ~ .. . .

29~
surate with the peak power demand of the system with min7mum effect on space occupants. Control by the power company may be established by a remote signalling system utiLizing radio frequency, power line carrier signals or the like.
Çenerally, upon recelpt of a command signal from the power utility, each individual thermostat controlled in accordance with the present invention has its manual setpoint control lever func~ion overridden by another actuated control system. The initial control point or starting setpoint is normally set equal to the sensed conditioned space temperature. These two events preclude effects caused_both by the occupant changing the setpolnt during the load shedding period or changing the thermostat setpoint just prior to the known peak load times such as the 12:30 p.m. to 6:30 pOm. interval which is typical of the air conditioning season.
After control i5 assumed by the system of the present invention, the setpoint of the load shedding thermo-stat is ramped continuously from the initial point to a predetermined value which is stored in a microprocessor mem-ory ~nd which is typically 82F for air conditioning and 62F for heating. The basic ramp rates used may be given by the following formulas: :

(1) Upward Ramp Rate ( COQ1 ing) 82.0 ~F) or Other Selected Max. - Initial SPaCe TemP. (F) Load Shed Time (llouis) ~2) Downward Ramp ~ate (Heating) 1 ~6~9~1 Initial Space Temp. - 62F or Other Min.
~oad Shed Time ( Hour s

(3) Typical Recovery Rate 1.5F/Hour Cooling, 2.0F in Heating Mode If the above ramp rate ~s neqative, i.eD, if ~e-space temperature is already over 82F or below 62F, then the rate is set to zero and nothlng happens inasmuch as sys-tem has already equaled exceeded its maximum allowable com-fort setting extremes with respect to the occupants of the conditioned space. If the rate is greater than maximum val-ue per hour, it is then limlted to maxlmum value per hour to keep the rate of warming or coolin~ below the threshold of awareness for most people. If the rate of the equation is between zero and maximum value per hour, the formula value is used. In thls way, the setpoint is moved or ramped con-tinuously over the entire~load shedding period to affect the maximum continual load relie~.
As the setpoint is ramped up or down, the space temperature sensor is continually monitored. If the sensor reads 82F or higher or 62F or lower, the ramping is a~ain stopped because the allowable space temperature extremes are limited on both the high and low side to preserve the basic comfort of ~the occupants of the conditioned space. This, of course, maintains the load sheddlng/comfort balance in accordance with the invention.
.: : -... ...

After the predetermined load shedding perlod is over, the setpoint is ramped back to the original occupant specified setpoint at the constant recovery rate.
Continuous ramping of the setpoint sheds loads both dynamically and statically. The static load shed comes rom the fact that the cooIin~ or heating load is roughIy proportional to the difference between indoor and outdoor air temperature. Thus, the closer the setpoint is to the outdoor temperature, of course the lower lS the required load to satlsfy the conditloning of the space. If thls were the only mechanism of load shedding, the best strategy of load shedding ~ould be one of the prior art's strategies, i.e., to move the setpoint directly to the maximum or mini-mum allowable comfort temperature and hold it there for the entire demand period. However, the static or temperature -differential load shedding effect is not the only load shedding effect to be considered~.
In addition to the static or kemperature differen-tial load shedding e~fect, there ls normally a rather large dynamic load shedding effect whlch comes from the cooling ef~ect or hea',ing effect stored in the mass of the bulldlng :
and its contents which can be utilized to the advantaga of a load shedding situation. As the setpoint ls continually ramped, the average air temperature moves up or down with the ramping. As the air warms or cools relative to th~
contents and structure mass, the cooler masses return stored cooling effects to the alr or, conversely~ the heated masses ' , ......
' . . ~ .

~ ~298~
returns stored heating effects to the air. This pheno~enon partially offsets the demands of the air condltloning or heating load.
I~ the setpoint is incremented in larger discrete steps, all thls dynamic load sheddlng happens at once or-in - rather large increments. After such a step, the demand goes off comp~etely until all the latent dynamic potent~al is used up for that step. At thls point, the coollng or heating plant again comes on and is a~le to draw only upon the static load release.
As explained above, stepping the setpoint up or down in either a single or large discrete steps also has the disadvanta~e that it tends to destroy natural dlversity and synchronize the running period of all of the air conditionlng or heating loads involved in the step change.
Thls, of cource, means that when all such units are off aEter a step change in the thermostat setting, the demand is very low. However, at the end of this interval, a spike in demand occurs~hich is one of the very things the power com-pany seeks to prevent by load shedding.
- ~ A distinct advantage of the present invention is that the continuous ramping strategy causes no loss in natu-ral diversity of loads because the setpoint is never abrupt-ly moved enough to cause all the air conditioners or heatin~
units to cycle at once and thereby become synchronlzed.
Conversely, at the end of the critical load shedding interval, the reverse is true. Thus, if all t~he . .

setpoints were again abruptly set back to the original position or stepped toward that position abruptly, a rather large spike in demand would occur causing a serious demand overshootO This is prevented in accordance with the present inve~tio~ b~ cau~ing the temperature setpoint to be ramped .
bac~ he original setpoint at ~he fixed predetermined-rate.
At the end of the period of peak power demand, the static load relief has reached its maximum. When the setpoint begins to ramp back to the original setting, of course, the dynamic load relief whlch had been added to the static load re~ief during the peak power demand period must be recovered. However, by allowing it to be recovered at an off peak period, the total power demand on the network never exceeds capacity. Thusr whereas other power load shedding techniques may ultimately reduce the total power consumption an amount equal to that of the present invention, none com-bine dramatic peak period load shedding with occupant com-fort control as does that of the present invention.
A more detailed description of a preferred embodiment of the present invention ls given in conjunction with the drawings. It is understood, of course, that the system applies equally as well to electric heating systems during the winter months as to air condition~ng systems in the summer months. ~lowever, peak power demand problems associated with widespread use of electric air conditioning are unlversal throughout the country, whereas, electric '. . :' : , ' ' ~ . ' , ' ' ~ .

~ 16~9~ I
heating, while more prevalent in Europe, is generally localized to portlons of this country where other forms o~
central heating are less economlcal.
In the drawings and, ln particular, FIG. 1 thereof there i5 shown a general block diayram of the system of the present inventlon. This includes ~he controlling electr-ic power utility represented by 100 which communicates with the load shedding system, as by remote radio signal or the like, through a signal recelving unit 101. In the case of an air conditioning compressor, the receiving unit may be located outside of the building structure in the vicinity of the compressor. Responsive to the command of the power utility, the load shedding control 102 establishes control over the internal space conditioning thermostat 103. This, In turn, controls the electrical space condltioning load 104.
FIG. 2 depicts two space thermostats which are adapted to connect with the control system of FIGS. 3 and 4 r 4A and 4B. The space thermostat labeled Thermostat A is one typically designed for use in a resident7al environment in accordance with the present invention. That thermostat is a basically solld state control device which includes a key board 110 through which data may be entered into a clock program chip lll which may control an LCD display. Time is kept by a crystal oscillator circuit 112. Utility informa t~on and batiery backup clrcuitry are indicated at 113.

. ; .
Other common thermostat functions provided incl~de a manual setpoint adjust as at 114, a manual setup/back adjust ~or --1 >--.~} . : .

automatically timed energy savlng as step changes such as night setback at 116 and an environment or room temperature sensor 117. Mode selectlon deslgnations for heating, off, cool, and the status as to whether the associated circula-~i~nr~a-n is under automat;c control or the ON mode are also . . .
provl~ed. Electrical conductors which coordinate with FIGS.
3 and 4 include DC supply line C2, setpolnt connection C3r mode status connectlons C4~ and temperature sensor connections C5, respectively, and a common line.
The second space thermostat, Thermostat "B," is a typical commercial version. Thermostat "B" like the resl-dential Thermostat "A" has heat off and cool modes and fan or blower control which can be operated on an ON or automat-ic status. The~rmostat "B" also includes a separate manual heatin~ setpoint adjustment lever as at 120, and cooling setpoint adjust at lZl. A room temperature sensor is shown at 122. A light emitting diode as at 123 is utilized to indicate when the particular thermostat is under the control o$ the utility during the load shedding interval. The ther-mostat has conductors like those of thermostat A whlch coor-dinate with ~IG. 3 and 4, 4A and 4B at C2, C3, C4, C5, and common.
Unlike the typical residential thermostat system, however r the typical commercial thermostat system has an external time clock as at 125 for controlling setup and set-back functions. This is shown connected at Cl.

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.
FIG. 3 deplcts a schematic block diagram of the thermostat control system of the.invetltion which connects to the thermostat to be controlled. The system includes a remote control input receiving unlt such as a ~adlo recei.ver deplcted at 130 wlth associated radlo receiver buf~ers - indicated by ~31.
The illustrated conductors Cl-C5 associated with thermostats A and B and the external clock 125 of FIG. 2 continue at Cl-C5 o:E the dlagram of FIG. 3. The control system of FIG. 3 may be integral with or located separately from the associated thermostat shown ln FIG. 2.
The connectlons Cl connect the external time clock with the system microprocessor 132 through input buffers ; 133. The "thermostat jumper" connection "A" or "B" is a permanent internal ~umper which s connected for either a typical residential or commerclal thermostat when the use of the system of FIG. 3 has been determined. An additlonal ~umper may be used to select whether or not precoollng wlll be utilized in conjunction wlth the ramping load sheddlng strategy of the inventlon~ Inputs lndicative of the type of use and whether or not precooling/preheating is desi.red al~o become inputs to the mlcroprocessor 132 through the input :: ~
: buf~ers 133.
: The DC supply from the regulated DC voltage source 134 is supplled to~a designated thermostat as controlled by the microprocessor 132 through the DC supply line C2. The power source is also utilized to control the varlous power .

: ~17-lB2~81 and fan relays of ~IG. 3 as controlled by the microprocessor 132 through relay drivers 135 in a well known fashion.
Temperature informat1on received from the thermo-stat of interest which includes the value of the heating or ---- ~Qolin$ setpoint C3, the information indicating the mode ,.~. ~ , .
status 5shown in more detail in FIG. 4) is contained on line C4 and the sensed space temperature signal on line C5. This information is processed for use by the microprocessor 132 by a system wh~ch ~ncludes multiplexer 136, constant current source 137, analog-to-digital converter 138 which has addi-t70nal inputs from buf~ers 139 and A/D control logic gates 140, and finally interfaces with the microprocessor 132 through the flip-flops and counter (A/D control) at 141.
Time ~or coordinatin~ the s~stem is kept by a crystal oscii-lator 142~
In addition, a watchdog mon7tor C7 rcuit 143 is provided which assures the existence of proper input voltage power to the system and automatically resets the micro-processor if a low input voltage is sensed~ The watchdog monitor also acts as an automatic reset lf it is se~sed that the program is not going through its normal sequence of pro-gram c,ycles.
The opt1onal logic analyzer jack 144 is utilized to provide an interEace between an external logic analyzer and the data bus of the microprocessor 132. For example, if .
desired, the contents of the RAM of the microprocessor can be made visible via a cathode ray tube. All of the func-,. ~ .; . . . .

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tional blocks associated with the schematic block diagram of FIG. 3 are shown in greater detail in the electrical circuit diagram of FIGS. 4, 4~, and 4~.
In conjunction with both the schematic block dia-gram of FIG. 3 and the electrlcal schematic dlagram o~ FIGS.

, . .

4, 4A, and 4B, the generaI operation of a mi`croprocessor-controlled system oE the present invention depends on the condition of various discrete, decoded, and sensed inp~ts.
These include the input C5 from the space temperature sensor of the connected thermostat as at 117 or 123. This space temperature is typically sensed by a platinum thick~film sensor which has a characteristic resistance whlch varies linearly with temperature over the range of temperatures utilized. The setpoint input C3 is typically a variable resistance whic~ may-be set at the thermostat manually with reference to a dial that reads in degrees F, typically from about 45F to 85F. The mode status input provides informa-tion which tells the system whether the thermostat is ln the heating, off or cooling mode and whether the clrculating fan switch is in the automatic or constantly runnlng ON
position. In additioni where setup/setback adjustmen~s are not available on the thermostat involved, i.e. thermostat "B," the amount of setback selected is typically indicated by the different input lines C~ as more distinctly labeled in FIG. 4. In thermostat "A" this is a variable resistance ~set at the thermostat with a lever that slides from 0-15F.

.

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The external clock setup/setback timing indicates information as to when the normal setpoint is to be adjusted by the amount indicated setup or setback in thermostat "B."
In the case of the residentlal thermostat "A" the timing is done internally with the amount of setup or setback showing ~........................ . . .
p~n the line when this information is sampled.
The precool (preheat) or no precool (preheat) jumper~ a~ain, is another internal jumper which instructs the mlcroprocessor whether or not the precool segments of the load shedding sequence in accordance with the present invention should be initiated when the utilit~ controlled "Start Siqnal" is initlally received.

~ . . .
The radio receivPd utility commands include the command to start the mlcroprocessor on the entire load shedding sequence, a recover command whlch indicates a :
return to normal control via a recovery ramp, a hold command which indicates a holding of the existing space temperature ~usually occurs during a rampin~ interval) ~and an emergency off command which, in the case of a brownout or other power emergency will s~mply shut the power off to the heating or cooling loadsO
All these signals after proper interface processing form~the~later basis for certain outputs from the ~mlcroprocessor or microcomputer 132. The microcomputer 132 controls the relay drivers which control the heating and cooling means, i.e. furnace~heating control or the air :
conditIoning compressor control and also ~he fan control as . .

~ 20--.~

~ lS298~
shown at 145 of FIG. 3. The microprocessor also controls the supply voltage and current ~.o operate the releva~t connected thermostat through the DC supply lines C2.
Signals are also sent to the thermostats whlch indicate to the user that the system is under u~ility control as rndi~ate~ at u~ltty ind~cati.on I23 o~ thermostat "B"~ A
truth table associated with a typical microprocessor In accordance with the presen~ lnvention appears as Append x A
at the end of this specification.
The various system control hlocks which have been brie~ly pointed out in ~onnectlon with our discussion of ~IG. 3 are shown tn greater detail ln the schematic electri-_.
cal circuit diagram of FIGS. 4, 4A, and 4B. Of course, theconductors labeled Al, A2, ~tc., and Bl, B2, etc., are i~tended to connected directly between the three sheets included in FIG. 4, 4A, and 4B.
The power supply 134~is designed to transform the input voltage which ~s nominally 24 volt ~C 60 Hz power supplied from a normal control t:ransformer into the three working voltages of the system circuit. These voltages .
include regulated ~5 and 15 Yolt supplies 150 and 151 and an ~unregulated relay drive voltage which is approximatel~ equal to 20 volts. The supplles are regulated by a 15 -volt regb-., : lator 1S2 and 5-volt regulator 153, respectively. In addi-tion, a very large (nominally 22,000) microfarad capacitor 154 is provided at the input of the 5~volt regulator 153 so that the 5-vo:lt supply stays regulated through power:inter-, ~, .

` ``` ~ 1~2~ ~

ruptions of up to one full second~ Transient currents and voltages are controlled utilizing a varister as at 155 ln conjunction wlth a capaci-tor 156 in a well known manner~
The multiplexer unit 136 is supplied with a con- `.
stant current from the constant current source 137. The constant current is nomlnally 1.17 milliamps to the se~ec~ed channel of the maltiplexer which is properly addressed by the microprocessor 132. The unknown resistance at the Input of the multiplexer 136 may represent either the setpo~nt, space temperature, or the mode sta~us of the thermostat is converted to an unknown voltage at the output of the opera-tional amplifier 160 of the constant current source 137.
The analog-to-digital converter un~t 138 includes four solid state switches 170, 171, 172, and 173 which are controlIed by the microprocessor through a bus output 174 at.
pin 16 o~ the microprocessor 132. These switches are also controlled in conjunction wIth Logic gates 1~0, 181, 18~, and 183 associated with the A tv D control logic 140. These gates also operate through line 174 in conjunction with the output of the comparator 175. The output of comparator 175, :
in effect, tells the rest of the circult when each A/D cyc.le is completed.
: Each AJD cycle begins wlth the output of.the microprocessor at pin 16 (line 174) going high. This signal closes the appropriate switches so that the unknown voltage ; is integrated for a known period o~ time. After this period of time t the output of p~n 16 at line 174 goes low so that -22~
.: .

the integrator begins to integrate a known voltage, i~eO
ground. Thus, a known slope is inItiated In the direction opposite from that initiated ln reference to the unknow~-voltage. This continues for an unknown period of time until the output of the integrator reaches a voltage level at which the w~ole cycl`e started, at which po-int the Integra-tion shuts itself off for that cycle.
The unknown reslstance is converted into the desired unit by looking at the status of a counter. This counter started from zero at the point where the A/D started the integration of the known Yoltage and incrementation thereof stopped when the inte9ration shut off upon the com-pletion of the A/D cycle. The number of counts allowed to accumulate is directly related to the unknown voltage lni-tially integrated. Thus, the larger the resistance, th~
longer the interval or the ~reater the number of counts.
This converted signal is then used by the microprocessor in conjunction with the program of the present invention.
The flip-flop and counter (A/D control) 141 oper-ate in conjunction with the A/D timing sequence. The count-I er 190 simply designed to 7nterrupt the microprocessor every 10l2 counts of the output clock which connects with the microprocessor on line 191. This reestabl~shes the program of the microprocessor into a regular cyclical routine n a well known mannerO The flip-flops 192 and 193 perform a division by three routine coun-ts o~ the counter 190 and feed ' ~:

,~, .

~ ~ 6 ~
every third pulse into the counter which In turn holds the number which is eventually converted i~ltO the desired units.
The buffers shown at 131 of FIG. 3 include the radlo input buffers associated with the radio lnput signals on lines 200 and 201. Thus, the radio input signals are essentially Eed directly into the microprocessor 132 through the buffers, such that when the input port is tested by the program, appropriate action can be taken. The inputs on these lines can only be hi~h or low, not continuous, as is the case for the multlplexed inputs which were discussed in reference to the A/D conversion. The two radio inputs are capable of delivering form commands such as binary commands which are stmply whether or not thè relay contacts on the externAl receiver are opened or closed. The effects of the form of the command is made compatible with and under the control of the particular power utllity involved as discussed in greater detail belo~.
As previously discussed, the commercial/residential jumper tells ~he microprocessor which thermostat is connected to the system. Normal program operation differs between the restdential and the commercial thermostat. For example, the setup/setback F amount indicated in FIG. 4 is in line in the case of the residen-tial thermostat only when selected and it is always n line but only used when the external clock contacts are closèd in the case of the commerclal thermostat.

~ -2~

The watchdog moni~or circuit 143 serves a dual ~unctionO It operates both as an automatic reset to the microprocessor if a low input voltage is sensed and, ln addltlon, also acts as an automatic reset system i~ it is sensed that the program for some reason is not going through r~s nor~-aI se~uence o~ program cycles. The main component in the circu~t is a dual one-shot integrated circuit including one-shots 210 and 211. In normal operation, both the clear pins of the one shots are i~ the "hlgh'l posltion indicating that no reset is necessary and the low voltage detect transistor 212 (FIG. 4A) is "on" which keeps the input at pin A of one-shot 210 low.
If for any reason the input voltage through the

5-volt regulator 153 drops below seven volts, the translstor 212 turns off which forces the A input to the one shot 210 to ~o high. This triggers the n output of the one shot 210 to pulse low which, in turn, pulses the reset of clear pin of the one shot 211. This forces a Q output of the one shot 211 to go low and reset the m'croprocessor via line B2 which enters the microprocessor at the reset pin 4.
At ~he same time the Q output of the one shot 211 is low, the Q output of the one shot 211 is high which turns on the transistor ~13~ This transistor draws the current which would otherwise turn the relays on during a power-up situation. This situation exlsts because a characteristic of the microprocessor is that, during a reset condltion, all `~ 329$ ~
ports are initialized hlgh which normally ls the state that would turn on all the control relays.
The circult that controls the reset when the pro-qram malfunctions samples the outpu~ of the "PROG" pin 25 of the microprocessor 132. This pin is normally low and is - pu~sed every time the microprocessor pro~rarn goes ~hrough a new sequenced cycle. If these pulses do not routinely come, the Q output of the one~-shot ~11 returns to the low state and resets the microprocessor.
The output relays are controlled by the relay drivers 135 in a well known manner in conjunction with the outputs of the microprocessor which feed into the relay sys-tem. These, of course, control the power to the loads involved.
The Thermostat ~umper "A" or "B" indicated in FIG.
3 corresponds to the commercial/resldential jumper input of FIG. 4. Inasmuch as the system of the invention is designed to be compatible with either commercial or residential thermostats, the jumper is provided internally in the pro-cessor unit to tell the microprocessor in fact wh1ch type of thermostat is connected to the system. `Thi5 is necessary because the~microprocessor program expects different inputs and gives correspondlngly different outputs depending on whether it is connected to a commercial thermostat or resi-dential thermostat. This, of course, facili~tates ease of lnterchangeability in appllcat~on for the coDtrol system of the inventlon.

`

,~

29~ .

As previously discussed, the device of the present inventlon must execute a control~Led set point ~amping from the sensed temperature level at the start vf the load shedding lnterval to the upper comfort limit of ~2F or 6~F
upon cooling. It ls well known that thermostats without an ~n~e~ra~ reset function tend to control the conditioned space temperature off of the control setpoint as much as two or three degrees. This normal characterlstic is inherent in the steady state operation of proportional controls as well as on~off controls such as room thermostats. In the cooling mode, then, such a controller tends to allow the temperature to drift upward and be controlled somewhat above the setpoint as shown and dlscussed below in regard to FIGS. 7, 7B, and 7C. In the heating mode! the reverse is true and the space temperature tends to be controlled at a point somewhat below the room thermostat setpoint.
Because the load shedding strategy of the present invention involves moving the setpoint over a discrete range during a discrete interval of time, in conjunction with limiting itself to a maximum change in the temperature of , the conditioned space to provide ~reater comfort to the occupants, the drooping characterlstic tends to limit the load shedding relief afforded by the strategy by narrowing the band of temperature change available to it. Under n~r-mal circumstances, the droop error can be compensated for by simply manlpulating ~he setpolnt such that the space temper-~` .
-~7 . ..

9 ~ ~
ature is actually controlled at the deslred temperature wlth the setpolnt somewhat offset from the desired vaLue.
Wlth the present inventlon, lt is desirable that the actual conditloned space temperature coincide as much as possible with the setpoint temperature so that the maximum temperature change range is available to the load sheddlng strateqy. Thus, the preferred embodiment in addition to the normal proportlonal control afforded by a typlcal space conditioning thermostat also employs an lntegral reset function ln arrlving at the electxlcal signal which represents the sampled setpoint at any given lnstant in time. This integral reset is incorporated into the program of the microprocessor 132 which is also g~ven in Append7x ~.
!' The operation of an integral reset functlon in a control system is well known in other art applications and -need not be discussed in detall here. An excellent çxplana-tion~of both pr~oportlonal and proportional plus lntegral :
control systems is ound in a standard textbook on the sub-ject such as Raven, Francis H., Au~omatic Control Engineering, McGraw-Hl~l Book Company,~New~

, ~ , York (19~8), pp. 89-110.
In conjunction wlth~the operation of the load shedding device of the present invention, certain parameters are normally arbi~trarily selected and~fixed wlthin t:he m~croprocessor 132. These may be represented by the ~following:

.

I lB2~
Parameter Cool_ng Mod~ _ t 1. Upper Temperature 82E~ Original Set Limit Point 2. Lower Temperature Origi,lal Set 62~
I.imlt Point 3. Maximum Deviation 9F 9F
fr~m Starting Space ~emperature 4. Hours for Load Shed 6 Hours 4 Hours Ramp 5. Maximum Rate of 1.5F Per Hour 2.0F Per Hour Change

6. Recover~ Rate of 1.5F Per Hour 3.0F Per Hour Change

7. Maximum Precool or 3F 4F
Preheat

8. Xate of Preheat or 1.5F Per ~our 2.0F Per Hour Precool Ramp Other parameters may be determined for certain models having speclfied applications as desired.
In normal operation, the particular power utility involved initiates a utility command signal which, in the pre~erred embodiment, is a radio signal which init~alizes the system. This is known as a "Start Shed" or "Resume Shedding" Operation signal. This signal is carried ~rom the radio inputs along lines 200 and 201 as indicated in FIG 4B
to the microprocessor which then responds to the start com-mand. Immediately, the current space temperature value is monitored through the l ine C5 and stored in memory. In addition, through the microprocessor through the inputs and outputs begins to continually monitor the status o~ certain parameters including the positions of various system .
~ 29 ~ ' ''' '`

. .

switches, s lectable jumpers such as the jumpers involved in determlnlng whether a resldential or commercial ~hermostat is being used whether precool or preheat are beiny us~d, etc. Space temperatures are contlnually monitored, radio command inputs and, in the case of the commercial thermo-~tat-~ tfie exter~al timè clock rela~ is continua-l-ly ~=
monl~tored. In addition, any manual setpoint changes are ignored.
If the status of the mode switch ls on "Cool" and precool is not selected, the system then remains under user control for the two hour precool period and there is no ~ndication of utility control durlng that perlod. After the precool period has passed, the base temperature is again sensed and stored and the ramp rate is determined by taking the difference between the limlted maximum temperature/ ~ e.
8~F, and the space temperature in determining the rate at which the setpoint must be lncreased ln order to reach the maximum allowablé temperatu~e at the end of the load shedding lnterval. If the ramp rate determined ls less than the allowable max~mum per hour, the actual calculated rate is used~ However, if the~determined rate is higher tha~ the maxlmum per hour, the maximum per hour rate is used over the load shedding interval. At the end of the load sheddlng interval, the recovery portion of the cycle ls initiated e~ther by the ~nternal program or by a new external command by the power utility in which the control setpoint is again .

~ -30-:

slowly ramped down at the recovery rate until the value of the oriqinal pre-recorded setpoir~t is reache~.
If the precool jumper is in the position such that precool is added to the ramping cyclet as soon as the system is initialized by the slgnal from the power utility, the .:, set~oint beglns ramping down at 1.5 per hour for the 3F-two hour precool. After the precool period, the cycle operates as in the case of the no-precool sequence In the heatlng mode, the temperature ls ramped-downward toward a limit rather than being ramped upward and the precool period becomes a preheat period ~n which the temperature s ramped up before belng ramped down.
At 'the end of the recovery cycle, when the existing setpoint is reached or the space temperature that was stored at the beginning of the utility c~ntrol cycle is reached, the utility indication turns off and control of the system is returned to the user.
If the "Start She~" signal is received after an interruption other than the normal cycling sequence, the space temperature originally recorded in memory is utilized and the ramping function ~s resumed or continued in the , appropriate direction from which it was moving at the time of the interruption~ ` ' In addition to the normal functions of the system, an "emergency ofE" sequence may be provided such-that, if necessary, the utility may shut all the loads off on an emergency basis. Thus, if the emergency off message occurs ' .

1 1~29~ J
whi.le the system is under the control of thP usPr I the s~s-tem of the inventlon immediately shu~s off all the power relays, except the fan relay, such tha~ ~he space conditioning load is completely off. rrhis status is held for the duratlon of a command or unti~. a di~ferent command i5 received from the power utllity.
the emergency off occurs ~7hen the system is under the command of the load-sheddlng apparatus, the refer- .
ence temperature stored at the beginning of the load-shedding cycle is retained and all power relays are opened such that the entire load is disconnected. This sta-tus is also retained for the duration of the command or until a differe~t command is received from the utility.
A start command following an emergency o~f command is treated as a normal start command if the system has been under user control. However, lf the system was under utlli-ty co~trol and it was, in fact, already pursuing its load-shedding programr the load shedding ramp is restarted based on the then existing space temperature and the orig~-nally calculated ramping eate. To protect the occupants, if the system has drifted beyond the limits while ~n the emer-gency off mode, it controls at the predetermined temperature limit and holds there until the time for the normal recovery ramping i5 reached.
The system can also be made responsive to a ~Ihold~
command. Under the hold command, the exlsting space temper-ature becomes the control temperature for the duration of : .

8 ~

the command. The previously stored referenc~ temperature is retained as the future ramp rate re~erence point~
Of course, if deslred, other command sequences can be contained ln any partlcular embodiment of the present ~n~Tention without deviating from the basic l~ad-shedding - ~trate~y.
The electrical components utilized in the diagrams of FIGS. 3 and 4 are standard components available from various manufacturers. Certain parts not labeled on FIGS. 3 and 4 include:

; Reference Number Component 132 ~8048 Microcomputer 135 MC 1413P Dual Buffer Array 139 MC 1413P Dual Buffer Array 160 798 Dual Op-amp 170-173 4066B Quad Switch 175 79~ Dual Op-amp lB0-183 40:LlB Quad NAND ~ate 190 ~ 4020B Counter 192,193 4013B Flip-flop FIG. 5-9 represent theoretical performancP plots depicting and comparing the load sheddrng method of the present invention w7th that of a fixed setpoint or certain prlor art load shedding methods in a manner whlch rev~als both the e~fect on the conditloned space and the theoretical load shed accomplished by the various methods, The plots ; -33-:

9 ~ ~

are theoretlcal and were produced using a digital simulation of a 1440 square foot buildlng~ The bullding model was a typical California-style residential home using typical con~
struction for that part of the country. The particular type ~me was chosen because that part of the country repr~sents . .... .
~ ., ~ne ~n whl~h l~ad shed~in~,ls presently of a prlmary concern to the power utility companles.
In the model chosen, the house was built over a crawl space having stuccoed exterior walls and an attic having an uncooled crawl space. Assumptions were made that the walls contained 3-1/2 lnches of fiberglass insulation, the roof 6 inches of flberglass in,sulation, and single pane windows were assumed. The absorptlon of the roof was assumed to be 50 percent. The alr conditioning system for the home had 3 tons of nominal cool~ng capacity.
The outdoor weather conditions on the graphs uti-ed 105~1 or 90 days are based on actual weather data from a local weather bureau in Fresno, Cal'ifornia in August, 1965.
The other assumptlons made were typlcal for such buildlng construction. The attic crawl space was assumed to be heated indirectly by the solar flux on the xoof surface.
The distribution ducting was located ln the attic crawl space and heat flow from the crawl space into the ductlng was simulated. The buildlng had approximately 25 percent oE
its exterlor walls ln windows and doors and the solar flux was assumed to penetrate the window openings. Overhanging .

, . . .

~ ~629~1 eaves were modeled around the perlrne~er of ~he roof and the resultlng shadows afected the solar flux on the walls and wlndows. ~ constant infiltratlon rate of one alr change per hour was assumed for the conditioned space and that for the attlc crawl space and the Eloor crawl space were chosen at A . .
typical values for natural ventilation of such areas. Radi~
ation heat exchange between the interior wall surfaces and floor and ceilings was also modeled.
In order to more carefully evaluate the value of the dynamic load sheddlng, much care was taken in assuring correct calculation of the internal thermal mass and the thermal mass of the structure. Each wall surface was broken down into its constituent construction materials and modeled by a separate thermal resistance appropriate to each materl-alr The thermal mass of each layer of each wall was modeled by a thermal capacltance and a differential equation~
accord ng to the thermal capacitance was wrltten for each thermal mass in the structure. These differential equations represent the storage of enerqy wlthin the structure and content of the building. Approximately 2~ ordinary, linear ~ifferential equations were required to simulate the build-ing modeled.
The air conditioning plant was a Lennox 3 ton cen-tral air conditioning system with a separate outdoor condensor and indoor evaporator. The model of the air conditioner was a non-linear curve of the performance data available from the manufacturer's literature. Thus, the ; _35_ :, :

29%~ .

power requlred in the cooling capacity varied with indoor and outdoor alr temperature conditions and the capacity of the air conditioner for latent cooling was also simulated thereby accounting for the effect of moisture buildup within the conditionlng space.
- The thermostats (both conventional and commandable) utilized were modeled in a manner which included all internal dynamics. The thermo.stat model required two ordinary differential equations to simulate its behavlor. In the model of the build ! ng, the thermostat as well as the air conditioning plant were combined to form a complete system of differential equations. In this manner, the complete interactions of the bulldtng, control system, air conditioning plantr and the outdoor weather conditions were properly modeled.
Such techniques have been used by the assignee of the present invention successfully ~n designln~ other con-trol systems and in simulating other model conditions.
~ IG. 5 depicts a plot of "comfort" temperature ` versus time utiltzing commandable setpoint control tn accor-dance with the present invention. As used in the plots and dlscussion herein, "comfort" temperature is defined to be a weighted average of the indoor dry-bulb temperature (1/2~
and the radlation temperature of the four walls, floor, and ceillng in the condltioned space (1/12 each~. The typical sawtooth wave form is the normal varlatlon ln comfort tem-: ` `

.

.

2 ~ 8 ~ .

perature as the cooling plant cycles on and off on thermo-stat command about the setpoint line.
In FIG. 5, the se~point is held constant at 76~
until 12:30 and thereafter continuously ramped upward at approximately 1F per hour until 6.3~. At 6:30 the setpoint is then ramped downward at 1.5 per hour until the origi~al 76 setpo~nt is reached. A comparison with outdoor tempera-ture is also shown.
FIG. 5A depicts a theoretical plot of cycle aver-age power versus t me of day. The "cycle average power" is defined as the average power consumed by the system durlng one complete ON and OFF cycle. The cycle average power is typlcally much less than an instantaneous power demand as upon startup of the air conditioning compressor. While the utilities net air conditioning power demand is made up of the sum of the instantaneous power demands from all the air conditioning units in a given service area, the cycle aver-age power for a typical buildincl is believed to be represen-tative of th~ ensamble average power consumed by a large number of buildings. If the load shedding device does not disturb the natural diversity, the cycle average power, then, is a good measure of the average power demand per building in a given service area. If the natural diversity is destroyed, as in some of the examples herein, however, all the cooling plants wlll be operating at one time which results in a great deal more power than the cycle average power being drawn which could be dlsastrous.

.,.. - :

~ ~629~ `
In each of the example plots as in 5~ and 5B
whereln the cycle average power versus time oE day are depicted, each hortzontal step in the plot represents the level of average power consumed over one complete ON and OFF
cycle. Each method of load savlng is compared to the case of a fixed 76 setpoint whlch represents a typical undisturbed system. The dashed curve in FIG. 5~ represents the cycle average power required if the ramping strategy of FIG. 5 is followed on the same day. The upward ramping interval can be timed to coinclde with the peak power demand of the utility which is typically between 12:30 and 6:30 p.m. on s~uch a day. After the peak demand ~nterval is passed, the downward ramp~ng cools the space gradually back down to the original control point. The additional power required to cool the building a~d contents ~ack down to the orig~nal control point is consumed after the peak demand inteeval which, in efect, shifts the load from the peak demand period to the evening hours when the total network power demand is typically low. The area between the curves, of course, represents the cycle average power reduction of the system during ~he peak hours FIG. 5B depicts the cycle average power versus time of day plot for the load shedding meLhod of FIG. 5 for a 9~ day. While the total load is much less inasmuch as the temperature dif~erence ls less extreme, it may be noted that the average load shed during the peak demand interval is very nearly the same on both days. Thus, the power com-.

pany can expect approximately the same degree oE load sheddi~g durlng the peak demand interval on elther day and the ramping strategy of FIG. 5 is utilized.
FIG. 6 deplcts a comfort temperaturP versus time of day plot similar to that of FIG . 5 with one lmportant difference. In FIG. 6, the setpolnt was ramped down three degrees between the hours of 10:30 and 12:30 at 1.5E` per hour. Thls precooling allows the subsequent upward ramping to take full advantage of the 9 F upward ramp between the hours of 12:30 and 6:30 p.m. at 1.5F per hour. The downward ramping after 6:30 p.m. ls the same as that for FIG. 5. This results in a somewhat lower average tempera-ture for the condltloned space during the time interval without sacriflclng any load shedding during the peak demand .
interval. The regular sawtooth temperature waveform shows no sign of disturbance due to the changing ramp rate and, .
thus, no loss of natural diversity due to the strategy is indicated. Again, the maximum t:emperature o 82 for the conditioned space has been selected :: :
IG. 6A is the corresponding cycle average power versus time o day plot for the load-shedding strategy in accordance with FIG. 6. A comparison of thiS with FIGS. SA
and 5R indicates somewhat greater load shedding during the demand interval but a slightly greater total power consump-tion lnasmuch as the 3 of precool require somewhat more energy.

.

`
~ -3~-~,~ . . .

\
2 9 8 ~

FIG. 7 is a plot of comfort tempera~.ure versus ~ime of day for a conventlonal thermostat having a Eixec1 setpoint. The sawtooth wave~orm of indoor comfort tempera-ture is above the sPtpoint showing the effects of the pro-portional offset or "droop" inherent in conventlo.lal thermostats which have no integral reset function. The tem-perature waveform depicted in FIG. 7A is held nearly con-stant on the setpolnt line by the additlon of integral reset action in the subject device. The offset between the tem perature waveform and the setpolnt line In FIG. 7 increases with the magnitude of the cooling load and at mldday reaches its maximum which may be as much as 3F. While the slightly higher indoor air temperature malntained by .he thermo3tat without integral reset action results in the consumpt;on of less total energy, it also results in less load shedd~ng during the peak demand lnterval because there is far less room for ramping to the preselected maximum temperaturet e.gO 82F. Also, it is conventional for one to manually -lower the fixed setpoint in a 'Idroopin~'' thermostat to achieve the same degree of comfort as with the integral~
reset model.
FIG, 7B is a plot of comfort temperature versus time of day in which the thermostat is incrementally raised in finit~e steps at the start of each hour during the load shedding interval. After the load shedding interval, the , setpoint is incrementally stepped dow~ward to retur.1 to the ori~inal setpoint. As can be seen from the deviation o~ the -~0-2 9 ~ ~

sawtooth waveform, the thermostat used is one without inte~
gral reset. The rather large inltial step at 12:30 p.m.
assumes that the sensor reading is approximately 2 degrees high at that point and this correction is taken in addition ~o the normal step of one-sixth the d7fference between the sensor temperature and 82F. Thls large step turns the air conditioning compressor of for over one-half hour as does each ensuing step o approximately three-quarters of 1F.
Each such incremental step, however, has the effect of synchronizing the operation of each air conditloner thereby destroying the desired natural diversity in the network.
This will cause a serious demand spike following each incremental setup. Also, all the desired setups cannot be utilized inasmuch as the control temperature drlfts above the limited 82F prior to the last two setup steps. Again, at 6:30 p.m.~ the setpoint is incremented downward at 1.5F
per hour ~n the downward increment is repeated each hour until the orig7nal setpoint is reached.
FIG. 7C is again a comfort temperature versus time of day plot util7zing the ramping technique of the present invention but with a thermostat which does not have integral reset. The purpose of this plot is to show that while suc-cessful load shedding does occur utilizing the ramping tech-nique without integral resetl ramping and integral rese~
work together synergistlcally. In FIG. 7C, at 12:30 p.m.
the setpoint is incremented to the sensor readlng as before to defeat setpoint adjustment just before the load shedding ~.

~ ~ ?

~ 1~29~
interval. The ramp rate is determined by the difEerence between the 82F upper limit and the sensor reading at 12:30 p.m. The upward ramplng rate is only approximately 0.7~F per hour because of the original control offset due to the drooping of the thermostat whIch was present at 12:30 p.m. Thls greatly reduces the allowed ramping rate and thereby reduces the positive effects of the load shedding during the load shedding interval. The same strat-egy with integral reset, of course, is shown in FIG. 5.
The initial reset point at 12:30 which synchroni~es the comfort temperature with the setpoint tem-perature also has the effect of synchronizing the air conditloning systems because of this large initial step change. Agaln, th~ proportional offset which has not been cancelled by integral reset devlce in this example causes the sensor readlng to reach the upward limit of 82 well before the setpoint has ramped its entire allowable distance~ Thus, ramplng stops at approxImately 4:00 p.m.
and the setpoint is held constant until the end of the demand nterval. At 6:30 the setpoint is again ramped back to the original level.
FIGS. 7D and E show the cycle average power versus t~me of day curves for ramping a thermostat with lntegral reset versus (1) the setpolnt being stepped up in discrete steps (FIG. 7D) and l2) ràmping with a conventional droop~ng thermostat when the setpoint is reset at 12:30 p.m. (FIG.

`
-~2-.

9 ~ ~1 7C). Both are compared with the conventional fixed 76 setpoint curve.
It should be noted that In the case of bo~h the~-mostat systems which do not have integral reset, a great deal of initial load shedding rellef attributed to dynamic . . .
load shed occurs at the first reset polnt. And in the case of FIG. 7Dr discrete spikes of load shedding occur at each stepping point. ~owever, the overall amount of load shed by the ramping thermostat having integral reset is super or either to the discrete stepping up of the thermostat without integral reset or the ramping of a conventional thermostat withvut integral reset. This is especially true in the later hours, i.e. after 4:00 p~m. when the higher control points of the thermostats without integral reset causes the setpoint increase to be curtailed as the comfort temperature reaches 32~F~ Thus, the ramping with the integral reset appears superior both from the standpoint of the amount of load shed dyring the load shedding interval and the average comfort temperature of the conditioned space.
An lmportant conventional method ~f load shedding which has been utilized and contemplated by electric power utilitles involve the concept of duty cyclin~. FIG. g i5 a plot of comfort temperature versus time of day for the duty cycling concept util~zlng three different timed duty cycles.
hese include 10, 15, and 20-minute duty cycles per half hour which denote the amount of time for each one-half hour that the power is shut off to the air conditionin~ compres-.

~~3~

--8 ~
sor or the interval that the compressor is locked out by theduty cycle.
The conventional thermostat detects the Increase in space temperature and calls for coollng. When the ther-mostat calls for cooling, in most residential applications, both the indoor blower and the compressor are turned ON.
The duty cycle device is commonly installed in such a way that only compressor opera-tion is prevented durlng the OFF
time of the duty cycle. Thus, the indoor blower runs con-tinuously during the duty cycle period.
Clearly, both the 20-minute and 15-minute duty cycle strategies allow the indoor comfort temperature to rise above the 82 limit. If the air conditloning compres-sor ln this example had been undersized, the upward excur-slon and air temperature would have been even greater.
This illustrates the fundamental problem with duty cycling which is the lack of comfort temperature control of any klnd during the load shedding interval. FIG. 8C is a plot slmilar to 8A for a 90 day.
FIG. 8A deplcts the cycle average power versus time of day for the 13, 15, and ~0-minute duty cycling concepts of FIG~ 8. As expected by the great degree of tem-perature~ overrun in the 15 and 20-minute duty cycling, a great deal of load is actually shed during the peak demand lnterval and it increases dramatically as the length of the duty cycle is increased. However, the strategy definitely will synchronize the operation of all the air conditioners ,2981 controlled on a speciEic duty cyclo. To counter thls prob-lem, the utilltles must start the duty cycllng stratPgy for sub-grouplngs of the installPd du~y cyclers. Each sub-group is started out of phase wlth each other group in an attempt to maintain the natural diverslty of the control loads.
Thls, of course, requires addltlonal communlcation channels or additlonal communicatlon tlme on a single channel to coordinate all these efforts. Also, as can be seen ln FIG.
8A and 8C~ a tremendous amount of energy over a long term is required for recovery at the end of the duty cycling.
The 10 and 15-minute duty cycle strategles as deplcted for a 90 day ln FIG. 8B do not cause a slgnificant temperature rise in the conditioned space because the coollng loads are much lower and the alr condltionlng com-pressor can almost sat~sfy the cooling load during the allotted period of the duty cycle. Only the 20-minute .
strategy causes a slgnificant rise in indoor comfort temper-ature. In both the example of FIG. 8 and FIG. 8B, it has been assumed that the alr condltlonlng system was propPrly s~zed for the peak load on the 105' day.
;~ Of course, were the air conditioning system oversized, the temperature increase would be lower in all eases because of the better ability to recover. The load ; shed, however, would be greatly reduced or ellmlnated depending on the degree of oversizing because the overs æed system would draw a great deal more powPr when operating.

: :

, :

On the other hand, if the alr condltioning system were undersized, the comfort temperature ~ncrease would have been more dramatic in all cases. Thls ls due, of course, to the fact that the duty cycling device does not sense or con~
trol alr temperature. It is an open loop devlce and as such is completely insens~tlve to the particular needs of the conditioned space.
Of course, one of the essentlal conditlons of the load shedding scheme of the present Invention which makes it more acceptable is that it does not cause undue discomfort for any of the occupants of the conditloned space. If a duty cycling strategy could be ta~lored to each installa-tion, it would perform satlsfactorily in both comfort tem-perature and power control. It would not be practical, how-ever, for utilitles to tailor the strategy of each of the thousands of installations necessary in order for signifl-cant load shedding to be accomplished in a power network.
FIG. 8C is a plot of cycle average power versus time of day for the three load shedding strategies of FIG.
8B, i.o. on a 90 day. As can be seen ln a comparison of FIGS. 8A and 8C, the dut~ cycling strategles yleld far less load shed on a 90 than on a 105 day. In fact, the

10-mlnute and 15-minut~ duty cycling strategy actually increases the demand for power above that for the fixed 76 setpo~nt comparison plot. Under these conditionsJ of course, d~ty cycling ls totally unacceptable.

-~6-,, l 1~2~
An additional drawback to duty cycllng which is not found in the system of the present lnvention i~volvPs the act that duty cycllng devices are typlcally installed on the outdoor unit of a split system air condLtioner and thereby control or cycle the compressor only and not the indoor circulating fan. The existing thermostat retains control of the indoor distribution blower. When the duty eycling strategy causes the indoor air temperature to rise, the thermostat causes for coollng and it turns on the indoor distribution blower. This causes the distribution blower to operat~ even when the compressor is off which is not the case for thermDstatic control alone and therefore there is somewhat of a demand increase over the uncontrol fixed 76 setpoint sltuation. In fact, in cases where the ducts are located in higher temperature portions of the house such as attic erawl spaces, the indoor space temperature may actual-ly be increased due to heat whieh leaks into the distribu-tion duets and is blown into the conditioned space by the ~lower.
FIGS. 9 and 9A again depict cycle average power ve~rsus time of~day ~or two different ~emperatures comparing the 10-minute duty cycling~system (which ~s generally the most aceeptable to the occupants of the conditioned space) with the unreg~ulated fixed 76 setpoint plot and the straight ramping without precooling in accordance with the present invention. It should be noted that the ramping sys-tem produces more load shedding in the load shedding ! ntPr--~7-, .

2 ~ ~ ~
val than the 10-min~te duty cycling system at both ~he 105.1 and the 90 days. This is done with less discomfort to the occupants o~ the conditloned space.

Table 1 . .
Peak Peak Average Peak Indoor Outdoor Load I.oad Energy Comfort Air Temp. Shed Shed Savlngs Temp.
Load Shedding Strategy (F) (%) (~) (%) ~F) Set-polnt Ramplng90.0 40.73 41.03 -6.48 82.1 with Integral Reset 95.0 32.58 34.56 -4.89 82.1 Action and 3F of100.9 24.02 25. 95 -3.92 82.1 Precooling 105 A 1 22.70 24.02 -4.60 82.1 Set Point Ramplng90.0 34 .18 30.90 -2. 72 82.1 w~th Integral Reset 95.0 27. 75 26. 07 -1. 59 82.1 Action and No 100.9 20.02 18.96 -1.74 82.1 Preco~l 105.1 19.76 18.88 -1.99 82.1 .
Set Po~nt Ramping90.0 36.38 18.77 11.99 82.5 with No Integral95.0 28.38 15.44 9.81 82.5 Reset Act~on and100.9 19.50 9.84 6.36- 82.6 No Precool 105.1 19.86 10.13 5.23 82.7 .. .. _ ._ __ _ _~ . _ . _ A _ _ _ _ _ _ -- _ _ _ _ __ _ _ ~ . _ . _ _ _ Thermostat Set Po~nt 90.0 47.92 24.34 14.47 83.7 Stepped Up from95~0 40.10 13.5I 11.61 83.9 76F t~ 82~ over100.9 30031 13.49 %.50 84.3 the Peak Demand105.1 29.55 14.08 7.48 84.3 Inter~val Set Point 90~0 37~55 22.67 12.89 83.0 Incremented Up in95.0 26.87 15.04 8.99 82.5 Disc~ete Steps100~9 21.24 10.39 6.81 82.9 Each Hour Over the 105.1 21.07 10.52 5.80 83.0 Loading Shedding Interval :
-- .

-' ~ :
:

9 ~ ~

10 Min. Per Half 90.0 -6.66 -22.39 -7.04 78.7 Hour Duty Cycle 95.0 -5.69 -6.46 -1.81 78.8 100.9 7.07 14.5~0.29 82.0 105.1 10.86 15.6~-0.0~ 82.6 c . ~ = ~ . ~ . _ __ _ - ~5 Min. Per Half 3~.0 -6.13 ~74 -9.82 ~9.6 ~our Duty Cycle 95.0 5.37 15.75 -2.27 81.7 100.9 26.20 31.413.33 86.6 105.1 27.63 33.19'3.71 ~7.0 ___ . . .
20 Min. Per Half 90~0 15.23 24.92 -6.52 83.5 Hour Duty Cycle 95~0 28.67 37.19 2.34 86.1 lOO.g 45.45 48.818.20 90.~
105.1 46.32 50.248.31 ~1.4 Table 1 summarizes the performance of each of the load shedding-strategies. The performance of each load sheddlng technique is given for operation on four different days having different cooling loads. The peak outdoor air temperature for each of the four days is given in column one. Column two shows the average load shedding expressed as a percentage of the average power demand wh~ch would result without the use of a load shedding device. The aver-age load shed ls averaged over the entire peak demand inter-val. The third column represents the peak load shea expressed as a percentage of the peak load which would occur without the use of a load shedding strategy. The fourth column gives the electrical energy saving due to the use of the load shedding strategy as a percentage of the 24-hour electrlcal energ~ consumption. The ~lfth column is the peak indoor comfort temperature which occurred daring the load sheddlng interval.

_~9_ .

~ lB29~1 Wherever a load shed percentage is negative the loads were not reduced but were, In fact, increased by the percentage indicated. Si~milarly, a negative energy savings is an energy loss due to the application of the `load shedding s~rategy under the conditions indicated~
A load shedding device af~ects both power consump~
tion and ~ndoor comEort temperature. If two load shedding strategles yield the same load shed with the same increase in indoor comfort temperature, they are said to be equal in perEormance. The 10-minute duty cycle strategy causes the indoor comEort temperature to reach 82 on both the 100 and 105 day. The setpoint ramping strategies with integral reset action raise the indoor comLort temperature to 82 under all conditions, thus, the load shedding percentage of the 10-minute duty cycle strategy on the 100F and 105F
days can be compared directly w:Lth the load shedding percentages ~or the rampIng strategy.
It l5 noteworthy that the average load shed per-centage is nearly twice as good for the present invention relative to the 10-minute per 1/2~hour duty cycle. The peak load shed percentage lS 20 to 40 percent greater for the present invention.
While ~the 15~and 20 minute per 1/2 hour dùty cycle strategies clearly~shed more load than does the ramplng device, during the load shedding lnterval, the indoor com-fort temperature, however, rises to unacceptable levels with these strategies. Clearly, for a given reasonable upper :

: ' ~ ' ' ~16~
limit on indoor comfort temperal:ure, the ramplng strategies of the present inventlon yield superior load shedding per-formance.
The energy saving column is the estimated energy saved by use of the load sheddlng strategy relative to the - energy consumption for a buildlng wlth a conventional ther-mostat having a fixed setpoint of 76 and no i~tegral reset action. For the ramping strategy, the setpo-nt was assumed to be 76~ also when not in the ramplng mode. It should be noted that the indoor air temperature with integral resPt action ls lower at a given setpo~nt than is the case without integral reset action (FIGS. 7 and 7A). The lower indoor air temperature (closer to the setpoint) requires additional cooling energy over the entire day which oEfsets the energy saving whlch occurs during the load sheddlng interval.
This result is not entlrely valid, however, for all conditions of operation. If the occupants set the con-ventional thermostat to the same value as one with integral reset act~on, then more energy will be consumPd. If the occupants ad~ust the setpoint lever of the conventional thermostat to yield ~he same com~ort conditions, however, the energy ~consumption outside the load shed interval will be nearly the same. During the load shedding interval, the ramping dev~ce saves energy, and hence a net energy saving would result. This comparison is made becausP in the actual applicatlon of the present invention, a conventional therrno-stat wlthout integral reset action would be removed from the ~; -51-~ ~ ~29~ ~
site and the subject invention with integral reset action would replace it.
The average load shed percentage for the ramping device with integral reset and the ramping device without lntegral reset is nearly the same. The peak load shed per~
centage, however, is approximate]y one-half as great for the device wlthout integral reset action. I'his is due to the maldistribution of load shedding which results wlthout the accurate temperature control af~orded by the lntegral reset action. Thus, the two features - ramping and reset action -work synergistically to produce the desired perEormance.
While the step-change thermostat y~elds good aver-age performance, the peak load shed is not quite as great.
Furthermore, the indoor comfort temperature exceeds the 82 limit malcing direct comparison between that devlce and the present invention less valuable. If the step-change were limited to a setting less than 82 so that the comfort tem-perature would not exceed the 82 limit, the load sheddlng performance would be reduced relative to a rampin~ device.
Similarly, the device with incremental setpoint changes in discrete steps on the hour ylelds good average performance and poor peak load shed performance. That, coupled with the tendency to synchronizP the operation of the alr conditionlng plants in the utility service area, makes that device less desirable. The subject device is clearly an improvement over all these examples of attempts at optional load sheddin~.

J~

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Claims (20)

The embodiments of the invention in which an exclusive property or right is claimed are defined as follows:

1. A method of controlling electrical power demand of a space-conditioning load comprising the steps of:
assuming control of the setpoint function of the space-conditioning thermostat associated with said load;
causing a simulated value representing the setpoint of said space-conditioning thermostat associated with said load to change substantially continuously with time at a first rate to a first predetermined space temperature limit wherein said first rate is a function of the difference between said simulated set point at the time control is assumed and such first predetermined temper-ature limits and the predetermined electrical power demand control interval; and returning control of said setpoint function to said thermo-stat.

2. The method of claim 1 further comprising the step of causing said value representing said setpoint of said thermo-stat to change substantially continuously with time in the opposite direction from said first change at a second rate after said first predetermined time interval to a second predetermined temperature limit prior to returning control of said setpoint function to said thermostat.

3. The method of claim 1 further comprising the step of causing the sequence of steps to be responsive to at least one externally controlled command signal.

4. The method of claim 3 wherein said signalling is under the control of the electrical power supplier.

5. The method of claim 4 further comprising the step of signalling a plurality of systems substantially simultaneous-ly.

6. The method of claim 1 further comprising the step of causing said value representing said setpoint to change substantially continuously with time at a predetermined rate in a direction away from the direction to said first predetermined temperature limit prior to causing said value representing said setpoint to change toward said first predetermined temperature limit.

7. The method of claim 1 wherein said step of changing said value representing said setpoint toward said first predeter-mined temperature further comprises:
sensing the conditioned space temperature at the time said control is assumed;
comparing said conditioned space temperature with said first predetermined space temperature limit;
equating said value representing said setpoint with said conditioned space temperature;

comparing said space temperature with said first predeter-mined temperature limit; and changing said value representing said setpoint from said sensed space temperature to said first predetermined space temperature limit at a constant rate equal to the difference between the simulated value representing the setpoint at the time control is assumed and the first predetermined space temperature limit divided by said predetermined power demand control interval.

8. The method of claim 7 wherein said predetermined temperature to which said value representing said setpoint is initially equated is said conditioned space temperature.

9. The method of any of claims 1, 7 or 8 wherein said first predetermined temperature limit in a heating mode is 62°F.

10. The method of any of claims 1, 7 or 8 wherein said first predetermined temperature limit in a cooling mode is 82°F.

11. The method of any of claims 1, 7 or 8 wherein said rate of change of said value representing said setpoint does not exceed a predetermined limit.

12. The method of any of claims 1, 7 or 8 wherein said rate of change of said value representing said setpoint does not exceed a predetermined limit and wherein said predetermined limit of said rate of change is 1.5°F per hour in a cooling mode.

13. The method of any of claims 1, 7 or 8 wherein said rate of change of said value representing said setpoint does not exceed a predetermined limit and wherein said predetermined limit of said rate of change is 20°F. per hour in a heating mode.

14. The method of claim 1 wherein said simulated first rate is a substantially constant rate equal to the difference between the simulated value representing said setpoint at the time control is assumed and said first predetermined space tem-perature limit divided by said predetermined power demand control interval.

15. An apparatus for controlling the operation of a thermostatically controlled space-conditioning load comprising:
means for establishing control over the function of the set-point of the thermostat controlling the operation of said electric space-conditioning load;
means causing a simulated value representing said setpoint to change substantially continually with time at a first rate in a first direction until a first predeter-mined temperature limit is achieved wherein said first rate is a function of the difference between the value of said simulated setpoint at the time control is assumed and said first predetermined temperature limit and the predetermined electrical power demand control interval; and means for relinquishing control over said setpoint function after said setpoint reaches said second predetermined temperature limit.

16. The apparatus of claim 15 further comprising means causing said value representing said setpoint to change substan-tially continuously with time at a second rate until a second predetermined temperature limit has been reached.

17. The apparatus of claim 15 further comprising sig-nal receiving means responsive to at least one externally controlled command signal.

18. The apparatus of claim 17 wherein said signal receiving means is a radio receiver.

19. The apparatus of claim 17 wherein said external signals are under the control of the electrical power supplier.

20. The apparatus of claim 15 wherein said means causing said value representing said thermostat control setpoint to change further comprises:
means for generating a signal indicative of the temperature in said conditioned space;
means for comparing said signal of said sensed temperature in said conditioned space with said first predetermined limit temperature;
means for determining said first rate such that said value representing said thermostat setpoint changes substan-tially continuously at a substantially constant rate with time such that said value representing said ther-mostat setpoint would reach said first predetermined temperature limit at the end of said predetermined time interval; and means for changing said value representing said setpoint at said rate