Modine MDB Série Manuel D'installation Et De Maintenance page 26

control aPPlications - return air units - model mrB
Tables 26.1 through 26.2 show the sequence of operation for Return Air Two-Position and Floating Airflow Control Options and
associated Control Types. Note that in all cases, the controlling thermostat is based on the gas controls selected and the firing rate
control is not controlled by the night setback thermostat. For additional information on gas controls options, please see page 13-14.
Model MRB units feature outside air bypass and return air dampers and either a two-position damper actuator or a floating damper
actuator with a remote mounted room to outside air photohelic pressure controller. The function of the dampers are as follows:
• As the outside air bypass dampers are opened and the return air dampers closed more outside air is introduced to the building
(less return air).
• As the outside air bypass dampers are closed and the return air dampers opened less outside air is introduced to the building
(more return air).
The maximum return air is based on the Return Air/Outside Air ratio selected. Available ratios are 75/25 or 70/30.
table 26.1 - two Position (75/25 or 70/30 return air/outside air ratio) control types
changeover
switch setting
Occupied
Unoccupied
changeover
switch setting
Occupied
Unoccupied
time clock
mode
Occupied
Unoccupied
table 26.2 - Floating Position outside air Bypass and return air dampers for Building Pressurization control types
changeover
switch setting
N/A
changeover
switch setting
Occupied
Unoccupied
time clock
mode
Occupied
Unoccupied
A separate inlet or discharge air damper is required if 100% shut-off of outside air is required when the unit is not operating.
j
26
control type "a" - manual occupied/unoccupied switch
Blower
operation
Continuous
Continuous
control type "B" - manual occupied/unoccupied switch
with night setback stat
Blower
operation
Continuous
Intermittent j
control type "c" - time clock with night setback stat
Blower
operation
Continuous
Intermittent j
control type "a" - continuous operation
Blower
operation
Continuous
control type "B" - manual occupied/unoccupied switch
with night setback stat
Blower
operation
Continuous
Intermittent j
control type "c" - time clock with night setback stat
Blower
operation
Continuous
Intermittent j
7-500.10
air
delivery
100% OA
Minimum OA
air
delivery
100% OA
Minimum OA
air
delivery
100% OA
Minimum OA
air
delivery
Floating 25% to 100% OA
air
delivery
Floating 25% to 100% OA
25% OA, 75% RA
air
delivery
Floating 25% to 100% OA
25% OA, 75% RA
controlling
thermostat
Per Gas Controls
Per Gas Controls
controlling
thermostat
Per Gas Controls
Per Gas Controls (Enabled by
Night Setback Stat)
controlling
thermostat
Per Gas Controls
Per Gas Controls (Enabled by
Night Setback Stat)
delivery
thermostat
Per Gas Controls
controlling
thermostat
Per Gas Controls
Per Gas Controls (Enabled by
Night setback Stat)
controlling
thermostat
Per Gas Controls
Per Gas Controls (Enabled by
Night Setback Stat)