UC Los Angeles Campus & Medical Center Strategic Energy Plan ...

8.2.3 Air Handler Project 3. Demand Control Ventilation
This project adds a carbon dioxide sensor to air handlers that serve areas with highly variable
occupancies, such as lecture halls, theaters, gymnasiums. Measurement of the carbon dioxide
level is used to reset the minimum outside air flow function of the outside air economizer
according to occupancy requirements. The project includes a carbon dioxide sensor which is
usually located inside the lecture hall or building space. This will result in the heating and
cooling of less outside air when it is not needed for ventilation.
The minimum flow of outside air into the air handler has typically been designed according to full
occupancy of the space. For example, if there are 200 seats in a lecture hall the minimum
outside air flow may have been determined by multiplying 15 cfm per person (or seat) times 200
seats, or 3,000 cfm. The outside air economizer would be adjusted never to drop below this
level.
In the modified case the minimum outside air flow will be allowed to drop to lower levels as long
as adequate ventilation is maintained for the number of people in the room, as indicated by the
carbon dioxide levels. This is a standard control sequence required by Title 24 for new
construction in high density spaces. Title 24 requires a minimum outside air flow rate of at least
0.15 cfm/sf, regardless of occupancy. This level of ventilation removes contaminants not
related to human occupants. This level of outside air supply is typically found in office areas, so
carbon dioxide sensors do not offer significant energy savings potential for offices and other
areas that are never densely occupied.
The savings are calculated for this project through a bin simulation adjusted for local weather,
operating hours, building load characteristics, air handler flows and configuration, and
temperature control strategies.
The cost for implementing this project includes a carbon dioxide sensor, which can be factory
calibrated with no need for additional calibration during its service life, and integration into the
economizer control sequence. The campus can choose to monitor and log the carbon dioxide
levels.
This project does not apply to air handlers serving office areas or other relatively low density
areas. It does not apply to patient handling or laboratory air handlers where other outside air
requirements exist.
8.2.4 Air Handler Project 4. Static Pressure Reset on Variable Air Volume Air Handlers
This project adds a static pressure reset capability to existing VAV air handlers that do not have
direct digital zone controls. The current design static pressure setpoint may be the appropriate
pressure to operate at during hours of high air conditioning load, but it is not necessarily needed
during other hours of operation. This project automatically resets the static pressure to a level
that maintains comfort conditions but is typically lower than the original setpoint.
There are two technologies commonly used to apply this control strategy. If the VAV system
has direct digital controls at the room thermostats it is possible to use information from these
thermostats to automatically reset the supply static pressure. It can be continuously reset so
that a small portion of the VAV boxes are calling for full cooling. This would be an indicator that
the pressure is operating at as low a point possible. For air handlers with DDC at the zones,
2413.01/Reports/UC SEP Final Report – UCLA.doc 8-7 December 31, 2008
Newcomb | Anderson | McCormick