Operating Instructions

Controlling Laboratory Air Flow
Siemens Building Technologies, Inc. 3-9
Table 3-3
Descriptor Number Function
OCC SUP MAX 31 Maximum supply in occupied mode.
OCC SUP MIN 32 Minimum supply in occupied mode.
OCC GEX MAX 33 Maximum general exhaust in occupied mode.
OCC GEX MIN 34 Minimum general exhaust in occupied mode.
UOC SUP MAX 71 Maximum supply in unoccupied mode.
UOC SUP MIN 72 Minimum supply in unoccupied mode.
UOC GEX MAX 67 Maximum general exhaust in unoccupied mode.
UOC GEX MIN 68 Minimum general exhaust in unoccupied mode.
The LRC selects one of these two sets of limits to apply at any moment. The selected values
are displayed by the points in Table 3-4. Do not override these settings to implement a
ventilation setback strategy. Instead, let the controller set them. Overriding the points will
make it impossible for the controller to apply the proper limits according to occupancy.
Table 3-4
Descriptor Number Function
SUP MAX 76 The currently active maximum supply.
SUP MIN 77 The currently active minimum supply.
GEX MAX 74 The currently active maximum general exhaust.
GEX MIN 75 The currently active minimum general exhaust.
Determining Occupancy
Determining occupancy in a laboratory greatly depends on whether the laboratory works on a
schedule or is available to personnel at undetermined times. If the laboratory has a set
schedule, the LRC can be programmed to switch between occupied and unoccupied modes.
However, if the laboratory is available to personnel at their discretion, it will be necessary to
make the controller respond to the occupants themselves. Methods for this type of control
include occupancy sensors, monitored light switches, a button used by the occupant, and
monitoring the position of fume hood sashes. The LRC supports the following approaches
and certain combinations of them:
• Schedule (implemented over the network)
• Light switch or other two-position switch in the room
• Push button on the thermostat
• Fume hood opening
• Occupancy sensor
The LRC also supports a custom-programmed occupancy scheme, implemented over the
network.