Adjusting Burner Profile Pressure Differential - Modine MDB Série Manuel D'installation Et De Maintenance

start-uP Procedure

adjusting Burner Profile Pressure differential

WarninG
Proper air velocity over the burner is critical. If the velocity
is not within the unit specifications, the unit will not operate
efficiently, may have nuisance shutdowns, and may produce
excessive carbon monoxide (CO) or other gases.
imPortant
1. On model configurations that allow adjustments to the
burner profile plates, the only adjustment permitted is
repositioning within the range of the adjustment slots to
increase or decrease air velocity across the burner. No
other modifications are permitted.
2. Repositioning of burner profile plates is only available on
select models, as indicated in the instructions. Do NOT
attempt to alter or reposition the plates in models not
setup to accommodate adjustments.
3. The burner profile pressure differential has been
factory set based on the unit configuration and operating
characteristics on the original unit order. If the profile
pressure differential is outside the allowable range, every
effort should be made to correct the condition without
changing the profile plate positions.
4. Changes to the position of the burner profile plates may
impact the temperature rise of the unit.
To adjust the position of the burner profile plates, the unit MUST
meet the following criteria:
• Digits 1-3 of the Model Number must be "MDB".
• Serial Number Digit 18 must be "A".
If the unit does not meet BOTH of these criteria, do not attempt
to alter or adjust the burner profile plates.
Before adjusting the burner profile plates, it is important to
understand why the pressure is outside what is shown in Table
19.2. Based on the design airflow and total static pressure,
the unit is set at the factory to provide the correct burner profile
pressure drop, which is a result of the correct airflow (air
velocity). The following are common causes for incorrect airflow:
• Low burner profile pressure drop is often a result of the
external static pressure (typically ductwork) being higher
than originally designed. The high external static will cause
a reduction in airflow which may result in the low airflow
proving switch not closing, disabling the burner.
• High burner profile pressure drop is often a result of the
external static pressure (typically ductwork) being lower
than originally designed. The low external static will cause
an increase in airflow which may result in the high airflow
cutoff switch opening, disabling the burner.
To account for an increase or decrease in airflow, the unit
needs to be balanced. Before attempting to adjust the burner
profile plates, the following should be completed:
• Correct any ductwork or duct termination design issues that may
be creating external static pressure differences from design.
• Adjust the fan RPM by adjusting the sheave on the motor as
described in the "Blower/Motor Adjustment" section on page 21.
22
• If the supply fan is driven by a factory supplied variable
frequency drive, it may be possible, depending on actual
conditions, to adjust the blower speed via the VFD.
Contact Modine Technical Service for guidance.
If the steps above have been completed and it is desired to
make additional adjustments via the adjustable burner profile
plates, the following is the process for adjustment:
1. Turn power on to the unit. With the unit running and the
gas controls set to discharge at 70°F, measure the burner
profile differential pressure, as outlined in step 26 on
page 19, to determine if the pressure differential must be
increased or decreased to match what is shown in Table
19.2.
2.
Once the measurement has been made, disconnect power
to the unit and open the burner access door.
3. Remove the screws as indicated in Figure 23.1. Note that
the quantity of screws to be removed will vary by unit size
and the quantity shown in Figure 23.1 is for reference only.
4.
To adjust the position of the burner profile plates, loosen
the remaining 2 screws in the slots of each plate and
carefully move the plates to the desired position, then
retightening the 2 screws in the slots of each plate.
Since small changes can have a significant impact, it is
recommended that plates be moved approximately 1/16" to
1/8". Both top and bottom plates should be moved equally
to maintain consistent top and bottom clearance to the
burner. To determine which direction to move the plates,
review the following:
• To decrease the pressure differential, the open area
around the burner needs to increase by moving the top
plate up and the bottom plate down.
• To increase the pressure differential, the open area
around the burner needs to decrease by moving the top
plate down and the bottom plate up.
The range of adjustability will vary based on the unit
configuration and factory setting. Some configurations will allow
adjustment to increase or decrease the opening size. Other
units will allow adjustment in only one direction. The following
rules apply:
• When adjusting to decrease the open area (top plate moved
down, bottom plate moved up), the top of the top plate and
the bottom of the bottom plate must overlap a minimum of
3/4" with the sheet metal material behind the plate to allow
enough material for attaching with the screws.
• When moving the plates closer to the burner, there must be
a minimum of 1/2" clearance between the edge of the plate
to the top or bottom of the burner mixing plates.
5. With the adjustment made, close the burner door.
6. Repeat steps 1 through 5 until the measured pressure
differential meets the requirement of Table 19.2.
7. Once the profile pressure differential meets the required
reading of Table 19.2, disconnect power to the unit,
open the burner access door, and replace all the screws
removed in step 3 above. To replace the screws, use the
holes in the burner profile plates as a guide to drill pilot
holes in the sheet metal behind the plates.
8. Close the burner access door.
7-500.10