Greenheck VSU Installation, Operation And Maintenance Manual page 16

Set the Burner Air Pressure Differential
With the fan running and discharging 70ºF (21ºC) air,
connect a U-Tube manometer to the outer sensing
probes (see below) and measure the static pressure
across the burner.
Outer Sensing Probes
Pressure Switch
U-Tube Manometer
Measuring the Pressure Drop
The proper static pressure should be
between 0.625 and 0.675 inches
wg (155.68 and 168.64 Pa). If
needed, evenly adjust the
baffles above and below the
burner, keeping the burner
centered in the opening until the
required pressure is obtained.
IMPORTANT
Proper air velocity over the burner is critical on direct-
fired gas units. If the air velocity is not within the unit
specifications, the unit will not operate efficiently,
may have sporadic shutdowns, and may produce
excessive carbon monoxide (CO) or other gases.
Burner
Adjustable
Baffle
Airflow
Burner and Baffles
16 Model VSU Make-Up Air
7
0.625 - 0.675 in. wc
6
Adjustable
Baffle
Airflow
The pressure drop was set at the factory and may not
need adjustment.
When required pressure is obtained, be sure to
reconnect the outer sensing probes.
IMPORTANT
This process may need to be repeated until the proper
pressure is achieved. This adjustment will change the
air quantity delivered by the unit and therefore the air
quantity delivered should be rechecked. Refer to the
Blower Start-Up section.
To increase the static pressure decrease the opening.
To decrease the static pressure increase the opening.
Set the Maximum Firing Rate
Monitor the unit's actual temperature rise by placing
a thermocouple in the unit's inlet and a second in the
discharge, three duct diameters downstream of the burner.
Send the unit to maximum fire by disconnecting and
isolating the wire connected to Terminal 3 on the Maxitrol
14 or the Maxitrol 44. See images on page 18.
While monitoring the units temperature rise, set the
maximum firing rate by adjusting the regulator until the
designed temperature rise is achieved. After setting the
maximum firing rate, reconnect the wire to the amplifier.
Do not set the burner maximum firing rate based on gas
pressure. It should be set based on the unit's designed
temperature rise shown on the direct gas label.
MIN GAS
PRESSURE
" WC
PRESSION DE GAZ
MIN BURNER
PRESSURE DROP
" WC
PERTE MIN DE PRESSION
DANS LE BRULEUR
TYPE OF GAS
NATURE DU GAZ
EQUIPPED FOR AGAINST
SCFM
CONCU POUR CONTE
Direct Gas Nameplate
Combined Regulator Valve
NOTE
NOTE
NOTE
NOTE
MAX GAS
PRESSURE
PRESSION DE GAZ
MAX
MAX BURNER
PRESSURE DROP
PERTE MAX DE PRESSION
DANS LE BRULEUR
DESIGN ΔT
ΔT NORMALE
EXTERNAL STATIC PRESSURE
" WC
PRESSION STATIQUE EXTERIEURE
Maximum firing
rate adjustment
" WC
PSI
F
®