Operating Instructions

Controlling Laboratory Air Flow
Siemens Building Technologies, Inc. 3-5
Inaccurate flow reading
It is possible that one of the flow values used by the LRC is not accurate. Examine the values
displayed by the Pressurization report. This report is available through CIS, the field panel
and Insight. If any of the values appear to be incorrect, take steps to calibrate or correct
them. A Siemens Building Technologies, Inc. representative can help you with this process.
Setting Limits on Supply and General Exhaust Flow
At times, it may be necessary to adjust specified limits on airflow through the supply terminal
or the general exhaust terminal. Possible reasons include:
• Changes in the minimum ventilation required, possibly due to new information about
the work done in the room
• Attempts to extend the capacity of an overloaded fan system
• Changes in the amount of cooling required for a particular room
When adjusting the limits, the Facility Engineer must consider the mechanical capability of
the particular equipment to operate at the new limits.
• Will the terminal deliver the maximum desired airflow?
• Will the damper regulate effectively at the desired minimum airflow?
• Will the airflow sensors stay within their effective ranges?
The Facility Engineer must also consider the effect on the room air balance. Is it possible to
reach the new limits without upsetting the pressurization of the room? Moving the limits
usually does not cause the LRC to violate pressurization, but if the changes are not balanced,
they might not have the intended effect. For example, the supply flow maximum could be
increased to get more cooling capacity, but the system may still be limited by the general
exhaust. If the laboratory requires more cooling, the supply flow tracks the amount of exhaust
air leaving the space, even though it may be well below the supply maximum. Although
pressurization is not lost, the temperature control is not achieved unless the general exhaust
volume is increased.
With that in mind, you can adjust the flow limits by setting values for the points in Table 3-2.
These points are conveniently accessed using the Start-up report. This report is available
through CIS, the field panel and Insight. Notice that there are two sets of limits, one for
occupied periods and one for unoccupied periods. If the unoccupied ventilation rates are not
used, set both the occupied and unoccupied rates to the same value. For more information
on setting back ventilation rates for unoccupied periods, see
Setting the Unoccupied Flow
Rates
in this chapter.