Command and Residual Priority Control of Loads

The present invention relates to the use of command and residual priorities for the control of loads. This invention is particularly useful in building automation control systems.

Building automation control systems are used for controlling air conditioning equipment, including chillers, fans, dampers, humidifiers, heating plants and the like, in larger buildings or building complexes. A typical building automation control system includes a central processor located in a control room and manned by a human operator and a plurality of air conditioning loads connected over a common communication channel to the central processor. Energy management program packages can be stored in the memory of the central processor for controlling the remote loads according to energy management routines.

Such routines can include a demand routine for turning loads on and off upon demand, a duty cycle routine for cycling loads on and off according to a duty cycle to reduce power consumption, an optimum start/stop routine for turning the air conditioning equipment off at an amount of time before non-occupancy to allow the temperature within the building to drift to a night setback temperature and to turn the equipment on in the morning an amount of time before occupancy to bring the temperature back to the desired level for occupancy, a zero energy band routine for providing neither heating nor cooling when the actual temperature within a zone is within a comfort range, and the like.

Since there are more than one routine which can control a load, it often happens that more than one routine will compete for the control of any given load, at any given time. It becomes apparent that, because of the competition between programs for control of loads, a mechanism must be established for determining which of the competing programs should be allowed to control the load.

One possible solution to this problem is to establish a priority hierarchy between the programs which are stored in the central processor such that the program having the highest priority among the programs competing for control of the load is the program selected to control the load. As a practical matter, there is always a routine or program presently controlling a load. Thus, when a new program wants to control a load, its priority must be compared to the priority of the program presently controlling the load. If the program wanting the control of the load has a priority higher than the priority of the program controlling the load, then the program wanting control is allowed to take over control of the load. However, if the program wanting control has a lower priority than the program controlling the load, the program controlling the load is allowed to continue to control the load.

In order to implement this solution, it is necessary to store the priority of the program currently controlling the load. Thus, if the program wanting control of the load has a lower priority than the priority of the program controlling the load, the priority of the program controlling the load is maintained in memory because control remains with the program having control. However, if the program wanting control of the load has a priority higher than the program currently controlling the load, then the program wanting control of the load is allowed to control the load and its priority is stored in memory. As can be seen from this operation, only programs having a priority higher than that stored in memory can control a load and only their priorities are then stored in memory. Thus, the stored priority keeps increasing until the highest priority program controls the load and lower priority programs are excluded. If a higher priority program no longer needs control of the load once its routine has been accomplished, lower priority programs cannot take over control of the load without some sort of special resetting operation to lower the priority stored in memory. The present invention solves this problem.

The present invention is directed to a system for controlling a plurality of loads based upon command and residual priorities. The system includes a plurality of loads, a controller for controlling the loads according to at least two programs, each program having a command priority used when it wants control of a load and a residual priority retained for it when it is allowed control, the controller comparing the command priority of the program wanting control of the load to the residual priority of the program having control for thereby providing a command instruction to the load if the command priority of the program wanting control is greater than or equal to the residual priority of the program having control, and a communication channel connected between the controller and the loads for communicating the command instruction to the loads.

Thus, each program has a command and a residual priority. The command priority of the program wanting control is compared to the residual priority of the program having control. If the command priority of the program wanting control is greater than or equal to the residual priority of the program having control, the program wanting control is then allowed to control the load and its residual priority replaces the residual priority of the displaced program. If the program wanting control has a lower command priority than the residual priority of the program having control, the residual priority of the program having control is retained and the residual priority of the program wanting control is ignored.

FIG. 1 shows a circuit diagram of a system for using the present invention;

FIG. 2 shows a flow chart of the portion of the invention which relates to the selection between competing programs; and,

FIG. 3 shows an example of selected programs and the priorities which might be established for those programs.

Control system 10 shown in FIG. 1 includes central processor computer 11 which can be located in a control room and may include various man machine interfaces so that an operator can visually observe the control and alarm functioning of the system. As shown, central computer 11 can be a Honeywell Level 6 Computer.

Central computer 11 is connected by communication channel 12 to a plurality of Honeywell 560 Intelligent Data Gathering Panels (IDGP) 13, 14, and 15. Since all IDGPs can be arranged similary, only IDGP 14 is shown in more detail.

IDGP 14 is connected to memory 16 which may contain the various programs which are used for controlling the loads of building automation system 10. There are four programs A-D shown in memory 16 and these programs may be related to the programs shown in FIG. 3. In addition, the memory also contains a point data file 17 which stores all of the data necessary for the control and supervision of remote loads. In this case, a point is defined as a remote load. Such information may include alarm limits, setpoints, last readings, change of state information, and the like. A further piece of information stored for each point is the residual priority of the program currently controlling that point or load.

IDGP 14 is in turn connected over communication bus 18 to a plurality of 540 multiplexers 21, 22, and 23. Since all multiplexers can be connected to various sensors and loads and are essentially alike, only the loads and sensors connected to multiplexer 21 are shown. Thus, various sensors 24, 25 and 26, which may be temperature sensors, humidity sensors, pressure sensors, air motion sensors and the like, are shown connected to multiplexer 21. Multiplexer 21 is in turn connected to a plurality of loads 27, 28, and 29 which are to be controlled by system 10.

Thus, when 560 IDGP 14 receives a temperature, for example, from sensor 24 through multiplexer 21 indicating a deviation from setpoint, IDGP 14 will issue an instruction to load 27 to bring the temperature of the zone in which sensor 24 is located back to setpoint. This control function can also reside alternatively or concurrently in central computer 11. Likewise, programs A-D in memory 16 and point data file 17 can alternatively or concurrently be stored in a memory attached to central computer 11. Furthermore, although separate memories 16 and 17 are shown in FIG. 1, these memories may be different memory locations of the same memory.

For each program A-D, there is assigned a command priority and a residual priority. The residual priority of the program presently controlling a load is stored in the point data file 17. Thus, each point or load has stored in memory 17 a residual priority of the program presently controlling that point. When a different program wants to take control of a point or load, controller 14 will compare the command priority of that program to the residual priority of the program currently in control of the load, which residual priority has been stored in the point data file for that load, and will allow the program wanting control to assume control of the load if its command priority is greater than or equal to the residual priority stored in the point data file. If the program wanting control of the load takes control of the load, then the residual priority associated with that program replaces the old residual priority in the point data file. If, on the other hand, the priority of the program wanting control is less than the residual priority stored in the point data file, the residual priority stored in the point data file remains and no changes are made. In this latter case, the program concurrently controlling the load continues to control that load.

FIG. 2 shows this operation in flow chart form. When two programs compete for control of a load, the command priority of the new command, that is the command priority of the program wanting control, is compared to the residual priority of the last issued command, that is the residual priority of the program having control. If the command priority of the program wanting control is not greater than or equal to the residual priority of the program having control, the comparison operation exits and no action is taken. If, on the other hand, the command priority of the program wanting control is greater than or equal to the residual priority of the program having control, then the residual priority of the program wanting control replaces the residual priority of the program having control for subsequent comparison operations. Also, the new command or command instruction is issued.

FIG. 3 shows an example of selected energy management programs which can compete for control of the load, the command and residual priorities established for each program, and the direction of control depending upon a comparison of those priorities. The blank spaces in this chart represent areas where no comparison is made. For example, certain intersecting programs never compete for the control of certain loads and, therefore, the blocks at these intersections are left blank. Another example is that the common blocks to a program, such as the column and row duty cycle blocks, are left blank.

This chart shows at the top those programs wanting to control a load and the command priorities used when those programs want control. Four programs have been used as examples including the duty cycle program, the demand program, the optimum start/stop program, and the zero energy band program. The manual section merely indicates that a human operator has intervened to take over control of a load.

The top priority that can be assigned to a routine is 1 and the lowest priority which can be assigned is 31. It is to be noted here that the higher the priority, the smaller the number. Of course this can be inverted so that the higher the priority, the larger the number. The manual portion of the routine has a command priority of 1 which means that any time the human operator wants to take manual control of the load, his manual instructions will always be obeyed. On the other hand, the manual routine has a residual priority of 31 which means that most programs wanting to control the load will be permitted to control the load. However, the letter C on the chart indicates that a comparison is not permitted per program logic. There may be several reasons for this. For example, if a manual instruction has turned a load on, the residual priority 31 is then stored in the point data file for that load. If a demand routine desires to turn that load off, the load will be turned off because the demand routine has a higher command priority than the residual priority of the manual routine and because to conserve energy it is desired to turn loads off which are not in demand, (i.e. are not essential). But, if a manual instruction has turned a load off and a demand routine desires to turn the fan on, normally the load would be turned on because the demand routine has a higher command priority than the residual priority of the manual routine. However, it is presumed that the human operator made the right choice in turning off the fan or load and the demand routine will not be permitted by the program logic to turn the load back on even though its command priority is higher than the residual priority of the manual instruction because this kind of operation does not result in energy savings. This reasoning is also applicable to a comparison between manual and duty cycle. In the cases of optimum start/stop and zero energy band routines, however, these routines are always allowed to override manual control because both programs are designed for always operating in an energy efficient manner.

As another example, if a duty cycle routine wants to turn a fan off which has previously been turned on by a demand routine, the duty cycle program will control because its command priority is higher than the residual priority of the demand routine. On the other hand, if a duty cycle program wants to turn a fan on which has previously been turned off by a demand program, the demand program is allowed to continue control because its residual priority is higher than the command priority of the duty cycle routine. In this latter case, if there is no demand for that fan to be turned on, it would be wasteful in energy to allow the duty cycle routine to turn the fan on. If the duty cycle program wants to turn a fan off which had been previously turned off by a demand program, of course the fan would still remain off. However, the demand program would be allowed to maintain control of that fan because its residual priority has a higher priority than the command priority of the duty cycle routine thus requiring a routine having a higher priority to take control of the fan. By allowing the higher residual priority to remain in the point data file, energy is saved because the fan is not unnecessarily operated. A comparison between the duty cycle fan ON and demand fan ON is not permitted because an ON command to a load currently on is only permitted if the demand program had itself issued the last command. Thus, the designation C is used depending upon the desirable operation between the programs competing for loads and may be changed depending upon installation.

As another example, when the optimum start/stop program wants control of the fan, heating, and cooling equipment, it has a fairly high command priority which means that in most cases it will assume control of that equipment. The fan, heating, and cooling equipment during a optimum start/stop routine is given a residual priority of 5 until the temperature within the building reaches the non-occupancy or occupancy temperatures depending on whether stop or start operations are being followed to prevent any other program assuming control of those loads. The equipment is then given a residual priority of 31 once the correct temperature has been reached so that any of the other programs can assume control. When controller 14 issues a heat enable control instruction indicating the beginning of an optimum start/stop routine, a local controller is allowed to assume control of the heating equipment. For example, the local controller may include one thermostat for a nighttime temperature and a second thermostat for the occupancy temperature. As another example, controller 14 may issue one setpoint for occupancy and a second setpoint for a non-occupancy using a single thermostat. The heating and cooling disable instructions have not been shown since they are merely duplicative and essentially have the same command priority as the enabling routines.

The 560 IDGPs and the 540 multiplexers may all be supplied by Honeywell. The program listing according to the flow chart of FIG. 2 is attached as an appendix.

The chart shown in FIG. 3 is merely demonstrative. The actual priorities established for the programs can be changed according to the desire of the user and the specific comparison operations between selected routines (represented by the letter C in the chart) can also be altered as desired. Such modifications still fall within the scope of the present invention. ##SPC1## ##SPC2## ##SPC3## ##SPC4## ##SPC5## ##SPC6## ##SPC7## ##SPC8## ##SPC9## ##SPC10## ##SPC11## ##SPC12## ##SPC13##