Deep Energy Efficiency

Demand Controlled Ventilation with Demand

Based Scheduling: Campus Applications

Demand Controlled Ventilation

Controlling the amount of ventilation to a space based on demand

Reset based on occupancy: Use carbon dioxide sensors to track space CO2 levels and raise lower supply fan airflow to maintain <700ppmReset based on economizer operation: Lower supply fan airflow based on percentage of outside air in supply air mix

Occupancy sensorsDetermine physical presence of people

CO2 sensorsDetermine quality of air in spaceLocated in return air duct or in conditioned space

Temperature sensorsDetermine whether space needs to be cooled/heated

Variable Speed DrivesAllow a proportional rate of airflow to space based on demand

Control EquipmentUse sensors to determine space need and operate equipment efficientlyGraphical building control systemEffective sequence of operation

Buildings designed before 2001Large spaces with dedicated air handling unitsHigh operating hours/Low usage/Dense occupancySpaces that have wide weekly operating schedules and highly variable actual usage

Performance spacesArt/Music StudiosLecture hallsLarge ClassroomsAuditoriumsComputer LabsMulti-purpose RoomsDining Areas

Potential DCV Retrofit Applications

Demand Based Scheduling

Problem:UCSC facility staff were aware of building equipment that was running when spaces were not occupied

HolidaysClass scheduling changes and reductions to spacesFaculty / Researchers demanded spaces be accessible during a wide range of hours

Legacy building control systems could not be modified quickly and easily

Solution: Demand Based Scheduling

Retrofit legacy BMS controllersInstall Occupancy and CO2 sensorsIf CO2 levels are below setpointAnd temperature is within desired rangeAnd occupancy sensors indicate empty spaceShut off equipment

Demand Based Scheduling

Demand Based Scheduling

Turning OFF air handling equipment whenCO2 levels are below 700ppm ANDSpace is unoccupied ANDTemperature of space is between 64-80 deg F

Sequence of Operation

3 modes of building equipment operation

Occupied Mode: regular building occupancy scheduled hours. Occupancy sensors sense space occupancy. Equipment ONUnoccupied Mode: regular building unoccupied schedule hours. Equipment OFFStandby Mode: regular building occupied hours, space is unoccupied, CO2 and temperature is within desired range. Equipment OFF or at reduced operation

Energy Benefits

Electrical Savings:Variable airflow results in exponential electrical reductionLower equipment runtimeReduce airflow when economizer is in free cooling modeReduced cooling from reduced volume of air to coolReduced cooling from temperature setback (standby mode)

Natural Gas Savings:Reduced heating from temperature setbackReduced heating from reduced volume of air to heat

UCSC Theatre Arts Complex

Annual Energy Savings200,337 kWh28.4 kW15,062 therms

Demand Controlled VentilationDemand Based SchedulingTimer Switches on Fan Coil Units

UCSC Theatre Arts Complex

Main Stage and Second Stage Occupant wanted broad access, but actual usage of

space is low7 days/week, 8am-11pmSpecial Events: Theatre PerformancesHighly variable actual occupancyAirflow rates designed for peak capacity (performances)

Performance StudiosMultiple spaces with operable

windows and dedicated FCUs.7 days/week, 8am-11pmVariable actual occupancyOccupant need for conditioned

air was low

*Main Stage electricity savings

Engineering 2 Auditorium

Engineering 2 Auditorium

Building built in 2004Designed and constructed with DCVTrending of system determined that

DCV was not operation correctlyModified sequence to include demand

based schedulingResolved over pressurization issues

by reducing supply fan airflow and maintaining CO2 levels

Engineering 2 Auditorium pre vs.

post kW trending

Red line shows kW profile before commissioning

Blue line shows kW profile after commissioning

Social Sciences 1

Annual Energy Savings73,286 kWh17.64 kW1,124 therms

Demand Based SchedulingZone Level DCV

Zone Level DCV1) Occupancy Sensor goes

unoccupied2) VAV goes to min position3) Main Supply/Return fan

slow down as VAVs close

Soc Sci 1: Room 110

Exterior classroom with dedicated Air Handling Unit

Weekly schedule: 530am-1100pm,7 days/week

Original BMS didn’t allow for simple schedule modifications

Installed occupancy sensors and changed sequence of operations

June 2011:Scheduled Hours: 525 hoursActual Hours: 78 hours

Reduced hours of operation by 85%

Simple Demand Based Scheduling

Science & Engineering Library Computer Lab

Annual Energy Savings35,066 kWh2.4 kW

DCV and Demand Based Scheduling

Sci & Eng Library Computer lab

*Implemented measures a a part of Monitored Based Commissioning Project (MBCx)*Computer lab has dedicated AHU that ran 24/7*During academic breaks, building was open for staff but

computer lab was closed*Allowed HVAC operation of computer lab during extended

hours*CO2 levels trigger AHU during non-scheduled hours

Science Library Computer Lab AHU Graphic

Lessons Learned

Sequence of operation needs to be commissioned. If too complex or mis-programmed, DCV will not be effective

CO2 sensors need to be appropriately placed. If system shuts off during standby mode, CO2 sensors MUST be placed in space, not return air duct

Integration of lighting and HVAC optimizes retrofit