Generally any energy management control software shall provide as a minimum the following functions. Each function is detailed separately.
Time Control Modes
There shall be no limit to the number of time schedules each of which can have any point or number of points assigned. Each time programme shall operate over a seven-day week and allow for on/off periods per time programme.
There shall be a facility to cross reference to a core time schedule via a relative schedule allowing an offset of +/- time in minutes based on the core time schedule on/off periods.
A calendar schedule shall allow advance programming defining which time or relative schedules are to be utilized for the advance dates to provide a variable switching pattern over a calendar period.
There shall be no limit to the number of holiday schedules. Any time schedule or number of time schedules may be assigned to any holiday schedule. It shall be possible to programme holiday’s 365 days in advance.
Optimum start/stop control
There shall be no limit to the number of optimum start schedules. Any point can be assigned to any optimizer.
The system shall start the plant at the latest possible time to achieve the desired internal temperature by target time. Configurable, one of two algorithms shall be used:
- by use of a linear algorithm monitoring outdoor air and space temperatures
- by use of a logarithmic algorithm relating to inside temperature only
Similarly the system shall stop the plant at the earliest possible time before the end of the occupancy without ambient conditions deteriorating below pre-set acceptable limits.
This shall operate in heating or cooling mode or a combination of both. The optimizer programme shall be self-adjusting, the amount of adjustment being user defined between 0% and 100%.
The user shall have the option of defining the termination of plant run-up or boost on target temperature being achieved, target time being reached, or whichever occurs first.
The following reports shall be available for selection by the system user as required for each schedule:-
- Report at commencement of run
- Report at termination of run
- Report at commencement of run down
- Report at leaving time
- Report at premature run down
- Report of low temperature stop/start
- Report at start of occupanc
- Anti-condensation/frost protection control
During plant off times the space and outdoor temperature shall be monitored continuously. When the temperature falls to a pre-set low limit, the plant shall start to prevent formation of condensation or water freezing.
It shall be possible to set the differential between plant on and plant off temperature under these conditions to minimise plant cycling.
Enthalpy control mode
For air-conditioned plant it shall be possible to monitor both fresh air enthalpy and extract air enthalpy. It shall be possible for the comparison of fresh air and return air enthalpy to be used to set damper control mode for minimum energy usage.
Night Purge Mode
When plant is operating in a cooling mode the system shall monitor both the external and internal temperatures. Providing the external temperature is less than the desired and actual internal temperatures at a pre-set time, the plant shall operate in a full fresh air mode for fixed time duration. This is in order to “flush” the building with cooler fresh air, thus reducing chiller load at occupancy start and providing fresh air into the building.
Load Cycling
The system shall be capable of cycling loads to reduce electrical consumption. The programme shall have a user defined cycle period and maximum off time.
A temperature detector shall be assigned to each plant on the load cycling programme. Should the space temperature exceed pre-set limits the load cycling shall be overridden and the plant returned to the time control programme until the space temperature has returned to an acceptable level.
User Programmable Software
The system shall have a flexible software package to allow a user with minimal knowledge of software programming to construct unique programs for plant control and management information.
The package shall provide, but not be limited to, the following functions :
- Auto changeover of pumps, fans etc. on time programme, hours run or event (pump trip etc.).
- Damper enthalpy override
- Degree day calculations
- Boiler and fridge efficiency calculations
- Time delays and sequenced interlocks
- Cost savings calculations
Full arithmetic operators shall be available for use in the programs as required e.g.: +, -, /,*, ().
Programs shall permit the use of comparison statements such as: =, >, <, =< etc. Programs shall permit logical operators to be used such as: NOT, AND, OR, XOR AND MASK.
Direct reference to any point shall be available to obtain its current value. Such references shall be using standard language such as, ON, OFF, OPEN, CLOSE, MANUAL, SETPOINT, EXPIRED TIME, PRIORITY, ALARM – e.g.: the programme shall support conditional statements (IF…THEN…ELSE) and branches (GOTO).
It shall be possible to refer to secondary values of points such as in optimisers to determine which mode they are currently operating e.g.: run-up, occupancy, frost, run-down etc.
It shall be possible to refer to time and calendar functions directly such that DATE, TIME, HOUR, MINUTE functions may be used.
It shall be possible to set timers for example so that a timed delay may be produced before an action is carried out.
PID CONTROL
The system shall be capable of performing proportional control, integral control, derivative control or any combination of the three utilising direct digital control techniques.
The primary input to a control loop shall be ether a measured value (°C, %RH, etc.) or a calculated value).
The secondary or reset input shall be either a measured value (°C, or %RH etc.) or a calculated value. The secondary reset input characteristic may be a 3-step segment function. It shall be possible to view this in a graphical format and modify characteristics by mouse control.
Additional sun or wind influence may be input.
The set-point of any control loop shall be capable of being adjusted by time, event or as a result of a calculation.
It shall be possible to reference a number of control loops to the same primary input point to achieve multi- stage control.
Where a step-controlled output is utilized, it shall be possible to rotate the order in which the steps are switched by time, or as the result of a calculation.
Valve and damper control shall be via 0-10 Vdc.
Control loop set-up shall be via a graphical tool to enable sampling test and trend display.
AUTO POWER UP
The system shall sequence the reinstatement of plant after a power failure.
When a standby generator is in operation, the system shall limit the number of plants in operation according to the load on the generator.
It shall be possible to configure a fixed limit in addition to the floating limit determined by generator capacity.
It shall be possible to monitor any overload condition of the standby generator so that if an overload is detected reinstatement of the loads shall be prevented and loads switched off until the condition is cleared.