Energy Management Control Systems 1 Introduction Energy management

Energy Management Control Systems 1

Introduction • Energy management control systems (EMCS) – relatively recent advance in computer technology – use of microprocessor directly connected to devices – control loads and reduce energy costs • Energy Conservation • Peak Lopping • Load Shifting to Off-Peak e. g. MU ice-storage

• Systems have several components • Simple systems - one of each item • Large systems - many modules Figure: Energy Management Control System Functions of an Energy Management Unit

System components • Sensors – monitor what is happening? • E. g. Conditions in MU lecture theaters • Overall power consumption • – provides EMCS with knowledge of the current status Actuators – Provides means for EMCS to change status via valves, dampers, contactors • e. g. turn on air-con, fans, ice-storage etc. • – Send alarm if there is a problem Data Link allows information exchange between the components of the system. Electric link for small installations: Fibre-optic link for larger installations telecommunications network allows access to system from a remote office in another country. – Satellite terminals allow access from literally anywhere. – –

System components • Energy Management Unit – – – self-contained unit programmed by supervisor processes information from sensors and makes decisions creates logs of previous problems builds up history of system loads • e. g. time history of electrical load profile • e. g. timetabling • Supervisor Console – controls the overall programming of all the EMUs. – from this location it is possible to change time settings and operational parameters. – reports on performance over a period of time can also be generated

System Components • Terminal – capacity for several terminals to be connected to network so that other users: • are aware of the system performance and functioning. • have access to the system to modify performance or shutdown equipment • Remote Terminal – use of modems onto the data link – access the system via e. g. phone systems, mobile networks, satellites. – alarm conditions to be dealt with by a qualified person from their own home – diagnostic work on a system be performed by someone in a different country.

Control Strategies • Daily scheduling – Multiple start and stop schedules for each piece of equipment for each day of the week. • Holiday Programming – program into the controller the dates of public holidays over the year – shut down unnecessary equipment for those days. • Yearly Scheduling – e. g. allow set points for thermostats to vary depending on season • Minimum On - Minimum Off Times – ensures mechanical equipment runs for required minimum run time and stays off for any required off-time – reduced maintenance costs • Optimum Start/Stop – e. g. outside conditions and rate of heat gain and loss in the building used to optimize – the starting and stopping of heating and cooling systems.

Optimum Start/Stop • E. g. Automatic optimization of air conditioning on and off times. – specify that building must be at the correct conditions between certain hours – “learns” how quickly indoor conditions reach comfort criteria based on outdoor conditions – if cool morning in summer then turning on is left as late as possible – turn off is done before building is vacated and relies on thermal inertia of the building to carry on an extra half hour or so.

Optimum Start/Stop • Duty Cycling – temperature compensated • cycle a piece of equipment on and off to maintain a setpoint within a dead band • program dead-bands into EMCS – time dependent • cycle on and off for distinct time periods • Minimum On/Off times may dictate duty cycling

Optimum Start/Stop – Peak Demand Limiting • Tariffs more expensive in peak periods • Penalties for exceeding peak limits – EMCS can control loads to reduce costs • energy conservation • peak load levelling (lopping) • peak load shifting

Energy Conservation • Better system performance – e. g. optimum enthalpy control • More efficient appliances

Peak load leveling • Load is shifted to the shoulder period. • Achieved by detailed knowledge of the building systems. – Load shedding – Duty cycling

Peak Load Shifting • e. g. heating water overnight for process heating during the day. • e. g. generating ice overnight for chilled water during peak hours • can reduce the cost but can in fact increase the energy use.

Determination of the Peak Load • When to apply energy savings techniques? – how to know if peak energy consumption for a period is going to be exceeded? • The basic problem is one of trying to determine what the energy consumption is going to be at the end of a time interval given the power being drawn at present and the energy used up to the present time.

Limiting Peak Power • limit the peak power at any instant. – – easy to apply reliable (conservative) always underestimates the possible energy permitted. actual energy consumed is below the ideal situation.

Limiting Peak Energy • limit the peak energy at any instant. – Don’t have to worry about the power consumed – may run out of energy by the end of the time period and have to shut down almost everything to achieve goal

Limiting Deviation in Consumption • • allow deviation from the desired energy consumption limit this within bounds that can be controlled by the EMCS system. no losing out on potential energy usage no last minute major power limiting

Requirements • Switchable loads • Need to have element of storage to allow for power switching off • Air-conditioning, heating, refrigeration • Lighting

Specific strategies • Night setback – Allowing temp. in a conditioned space to drop to specified setpoint when not occupied – 2% energy savings per degree of setback • Hot water reset – varies the temperature of the hot water in a loop so that the temperature is reduced as the heating requirement decreases. • Boiler Optimization – schedules multiple boilers giving preference to most efficient units and minimizing partial loading.

Control Strategies • Chilled Water Reset – varies temp. of the chilled water in a loop so that the temperature is increased as the cooling requirement decreases. • Chiller Optimization – schedules multiple chillers giving preference to most efficient units. • Chiller Demand Limiting – limit chiller demand by interfacing the EMCS with the chiller controls to reduce the maximum available cooling capacity in several fixed steps.

Control Strategies • Free Cooling – use of outside air to augment air conditioning or to ventilate a building when enthalpy (total heat content) of outside air is less than that of internal air and cooling load exists. • Recirculation – provides rapid startup in heating or cooling by keeping outside air dampers fully closed and return air dampers fully opened • Motor Speed Control – vary the speed of fans and pumps to reduce air and water velocities as demand for heating or cooling decreases

Other uses of Energy Management Control Systems (EMCS) • Generation of sophisticated reports – Trend reports indicate changes in use of energy – Separate billing of users in building complex – Smart systems learn from previous behavior • Alarm monitoring and recording – equipment failure, temperatures out of range etc – Alerts for unusual events • Duty logs – For use by operators – Historical records that can be archived • Manual Override – allows direct control of equipment for specific periods of time

Maintenance Optimization • Maintenance scheduled according to the system performance – no longer necessary to schedule according to set run hours or for a person to go and check on meters, gauges etc – EMU alerts supervisor when certain condition reached – E. g. filter cleaning in an air-conditioning plant could be alerted by the pressure drop across them rather than the run time of the plant.

EMCS - Negatives • Cost – though significant saver for high energy consumers – useful demarcation in multi-tenant buildings • Reliability – relies on regular calibration of sensors – potential problem if everything controlled by one unit • Complexity – vast amounts of data to handle – significant training required to use it to full potential

Tutorial Questions • How can an energy management control system reduce maintenance costs? • What are three key components in an energy management control system? • List four functions that an energy management control system can perform and describe how these reduce the energy cost.