
VAV-PRC011M-EN 93
DDC Controls
savings of a VAV system. A flow tracking system in a given zone consists of a standard Space
Comfort Control VAV (see B) unit plus a single-duct, cooling-only, exhaust VAV unit (see C). As the
supply VAV unit modulates the supply airflow through the air valve to maintain space comfort, the
exhaust box modulates a similar amount to maintain the required CFM differential. This is a simple,
reliable means of pressurization control, which meets the requirements of the majority of zone
pressurization control applications. Typical applications include:
• School and University laboratories
• Industrial laboratories
• Hospital operating rooms
• Hospital patient rooms
• Research and Development facilities
•And many more…
The CFM offset is assured and can be monitored and documented when connected to a Trane
Tracer Building Automation System. Flow Tracking Control is designed to meet most pressurization
control projects. If an application calls for pressure control other than flow tracking, contact your
local Trane Sales Office for technical support.
LONMARK Direct Digital Controller—Unit Control Module (VV550)
Figure 5. How does it operate?
B
A
C
Exhaust
Communication link
Supply VAV
To other VAVs or
Main Control Panel
How Does It Operate?
T
Primary Air
from Main
AHU
Occupied Space
The Trane LONMARK
®
direct digital controller Unit Control Module (DDC-
UCM) is a microprocessor-based terminal unit with non-volatile memory
which provides accurate airflow and room temperature control of Trane and
non-Trane VAV air terminal units. provides a simple open protocol to allow
integration of Trane VAV units and controls into other existing control
systems. The UCM can operate in pressure-independent or pressure-
dependent mode and uses a proportional plus integral control algorithm.
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