Filter
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BELLOWS PRESSURE — As the airflow through the unit
changes, the high and low pressures vary proportionately.
Comparing these 2 pressures, the unit volume controller pro-
vides a bellows pressure which in turn inflates the unit air
valve. Bellows pressure varies from near zero at full flow to
plenum or duct pressure at shutoff.
UNIT AIRFLOW DELIVERY — The relationship between
the bellows pressure and the plenum pressure determines the
unit air valve position, which controls unit airflow delivery.
When the pressures become nearly equal, the valve closes
and the unit shuts off. Conversely, as the bellows pressure
approaches zero, the valve opens completely and the unit
delivers maximum flow, as determined by the existing ple-
num pressure. Units normally operate between these ex-
tremes. In constant volume applications, the bellows pres-
sure is automatically adjusted in proportion to the plenum
pressure, providing a constant pre-set flow within the oper-
ating limits of the unit. In variable air volume op-
eration, the bellows pressure is further modulated to reduce
flow below the preset level as load requirements are satis-
fied. After passing through the valve, the primary air flows
down through the diffuser and out to the conditioned space.
CONTROL APPLICATIONS
Introduction —
The Moduline terminal is offered with
a variety of cooling and heating control options which adapt
to many building applications. In this section, the various
control applications are described and the functions they in-
clude are identified. Each application has a function number
which corresponds to the function number shown in
Tables 14 and 15 in the Control Selection section, page 50.
Table 14 describes the functions; Table 15 shows the control
packages required for each function. The part numbers shown
are found on the Moduline air terminal price pages.
Detailed operating sequences for each control application
are found beginning on page 55.
System-Powered Controls
COMPONENTS OF THE SYSTEM-POWERED CON-
TROL SYSTEM — The 37HS system-powered control con-
sists of a set of custom design and manufacturer’s compo-
nents which provide airflow and temperature regulation of a
Moduline air terminal. These devices are interchangeable,
field-installed components which plug into the Moduline unit
without the use of tools.
Figure 36 shows the basic components: Control block (part
of the unit); filter/manifold; volume controller; and thermo-
stat. Figure 37 demonstrates the control air paths in a sec-
tional view of the control system. Note that the high pres-
sure and low pressure pick-ups of theunit are connected through
the control block to the filter and from there to the volume
controller and thermostat.
Figure 38 shows the control filter/manifold; Fig. 39, the
airflow volume controller; Fig. 40, the diffuser thermostat
with aspirator; and Fig. 41, the wall thermostat and alternate
to diffuser mounting.
Fig. 35 — High and Low Pressure Pick-Up Tubes
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