Deep Energy Efficiency
Demand Controlled Ventilation
with Demand Based Scheduling:
Campus Applications
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 <700ppm
Reset based on economizer operation: Lower supply fan airflow based on
percentage of outside air in supply air mix
Occupancy sensors
Determine physical presence of people
CO2 sensors
Determine quality of air in space
Located in return air duct or in conditioned space
Temperature sensors
Determine whether space needs to be cooled/heated
Variable Speed Drives
Allow a proportional rate of airflow to space based
on demand
Control Equipment
Use sensors to determine space need and operate
equipment efficiently
Graphical building control system
Effective sequence of operation
Buildings designed before 2001
Large spaces with dedicated air handling units
High operating hours/Low usage/Dense occupancy
Spaces that have wide weekly operating schedules and highly
variable actual usage
Performance spaces
Art/Music Studios
Lecture halls
Large Classrooms
Auditoriums
Computer Labs
Multi-purpose Rooms
Dining Areas
Problem:
UCSC facility staff were aware of building equipment that was
running when spaces were not occupied
Holidays
Class scheduling changes and reductions to spaces
Faculty / 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 controllers
Install Occupancy and CO2 sensors
If CO2 levels are below setpoint
And temperature is within desired range
And occupancy sensors indicate empty space
Shut off equipment
Turning OFF air handling equipment when
CO2 levels are below 700ppm AND
Space is unoccupied AND
Temperature of space is between 64-80 deg F
Occupied Mode: regular building occupancy
scheduled hours. Occupancy sensors sense space
occupancy. Equipment ON
Unoccupied Mode: regular building unoccupied
schedule hours. Equipment OFF
Standby Mode: regular building occupied hours,
space is unoccupied, CO2 and temperature is
within desired range. Equipment OFF or at
reduced operation
Electrical Savings:
Variable airflow results in exponential electrical reduction
Lower equipment runtime
Reduce airflow when economizer is in free cooling mode
Reduced cooling from reduced volume of air to cool
Reduced cooling from temperature setback (standby mode)
Natural Gas Savings:
Reduced heating from temperature setback
Reduced heating from reduced volume of air to heat
Annual Energy Savings
200,337 kWh
28.4 kW
15,062 therms
Demand Controlled Ventilation
Demand Based Scheduling
Timer Switches on Fan Coil Units
Main Stage and Second Stage
Occupant wanted broad access, but actual usage of space is
low
7 days/week, 8am-11pm
Special Events: Theatre Performances
Highly variable actual occupancy
Airflow rates designed for peak capacity (performances)
Performance Studios
Multiple spaces with operable
windows and dedicated FCUs.
7 days/week, 8am-11pm
Variable actual occupancy
Occupant need for conditioned
air was low
*
Building built in 2004
Designed and constructed with DCV
Trending of system determined that DCV
was not operation correctly
Modified sequence to include demand
based scheduling
Resolved over pressurization issues by
reducing supply fan airflow and
maintaining CO2 levels
Red line shows kW
profile before
commissioning
Blue line shows kW
profile after
commissioning
Annual Energy Savings
73,286 kWh
17.64 kW
1,124 therms
Demand Based Scheduling
Zone Level DCV
1) Occupancy Sensor goes
unoccupied
2) VAV goes to min position
3) Main Supply/Return fan slow
down as VAVs close
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 hours
Actual Hours: 78 hours
Reduced hours of operation by 85%
Annual Energy Savings
35,066 kWh
2.4 kW
DCV and Demand Based
Scheduling
* 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
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