30
Fig. 42 — Thermostat Level Detail
NOTE: Maximum inlet pressure
— 3.0-in. wg.
START-UP
Principles of Operation
GENERAL
Units are normally open (bellows deflated). Rise in bellows
pressure closes unit. When thermostat is calling for no flow,
pressure differences between unit plenum (measured at con-
trol filter) and bellows should be less than 0.1-in. wg.
A leak
may cause bellows in circuit to be fully open, partially
open or fully closed depending on location of the leak.
An obstruction
prevents operation of all bellows down-
stream. The inoperative bellows may remain open or closed,
depending on whether air has been trapped in them.
CONSTANT VOLUME OPERATION
Both high-pressure and low-pressure control air from the ple-
num of the master unit passes through the filter to the volume
controller. An adjustable bleed orifice reacting to the relative
change of high and low pressure allows a set amount of con-
trol air to pressurize the bellows until unit air delivery match-
es the controller setting.
VARIABLE AIR VOLUME OPERATION
The constant volume control becomes variable volume con-
trol with the addition of a thermostat. The thermostat enables
the control to sense changes in the room temperature, over-
ride the volume controller and reduce the unit flow to match
the thermostat setting. If room temperature rises, the bellows
will bleed, increasing unit flow until the thermostat is satis-
fied. If room temperature falls, the bellows will inflate, de-
creasing the unit flow until the thermostat is satisfied.
Preliminary System Check
Perform air balancing and control system checkout before
building is occupied but after conditioned spaces are reason-
ably clean. The high induction ratio of 37HS Moduline
®
dif-
fusers can produce ceiling smudges within a few days if con-
struction dirt is present.
Before starting system, thoroughly check the air handling ap-
paratus and controls. Verify that the fan static pressure control
is operating properly so that starting the fan without airflow
at terminals will not cause duct damage from overpressure.
1. Check fan and system controls for proper hookup.
2. Be sure that all dampers, including fan inlet, fan outlet
and outdoor-air and return-air dampers, have proper free-
dom of movement. Lubricate as required.
3. Check fan belts, motors, sheave alignment and fan wheel
rotation. Check bearings for proper lubrication. Refer to
fan manufacturer’s recommendations.
4.
Be sure that fan final filters are in place.
If not, accumu-
lated dirt will be distributed throughout the system and
can accumulate in unit or fall into space. Dirt can also
disrupt air terminal operation.
5. Be sure that fan, coil, filter section and ductwork are
clean and free of any construction debris.
6. Remove protective tape from all diffusers.
Initial Start-Up
GENERAL CHECKOUT
1. Start the variable volume air-supply system and obtain
suitable supply-air temperature and pressure. If design
speed of supply fan is based on a diversified block load,
close zone fire dampers or set Moduline thermostats at
highest setting to obtain sufficient pressure at terminal
being balanced.
2. Check the air terminal system for open control loops.
Noise and excessive airflow at unit may indicate discon-
nected tubes, loose plugs or fittings. Correct the problem
before beginning detailed checkout below.
SERVICE
Gaining Access to Control Area
On standard units, center diffuser is not removable. Remove
ceiling tile or reach through nearby light fixture to gain ac-
cess to controls.
Table 8 — Minimum Static Pressure at Control
(Master) Unit - Units with System-Powered Controls
and Standard Diffusers
AIRFLOW
(cfm)
37HS1
37HS2
37HS4
PLENUM SIZE (in.)
5 X 7
7 X 7
7 X 7
9 X 9
9 X 9
9 X 9
11 X 11
11 X 11
11 X 11
13 X 13
Minimum Static Pressure (in. wg.)
40
50
60
70
0.75
0.75
—
—
80
90
100
0.75
0.75
0.75
—
110
0.90
0.90
0.75
—
120
140
—
—
0.75
—
160
180
200
—
—
0.75
0.75
220
—
—
0.90
0.75
240
280
320
360
400
—
—
—
0.75
440
—
—
—
0.90
Table 9 — Minimum Airflow (cfm)
MINIMUM AIRFLOW (cfm)
37HS1
37HS2
37HS4
40
80
160
THERMOSTAT
LEVER
IN CEILING
