Reznor RPBL, Installation, Operation And Maintenance Manual

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62 SSCBL-RPBL-IOM (10-22) 149159-C
ADJUSTMENTS—CONTINUED
Adjust Heat Stage Controllers (Option AG41 or AG42)
NOTE: Unit sizes 500, 600, and 800 with two furnace sections have two heat stage controllers. Unit
size 1200 with three furnace sections has four heat stage controllers.
Units with option AG41 and AG42 have heat stage controllers that control operation of the two-stage furnace based
on outside air temperature setpoints . Proper setpoints are important to ensure that the modulating furnace ( Heat
Stage 1
) is always in control and avoids cycling . The proper setpoint for each controller must be determined from
basic design information as follows:
1 . Calculate controller settings:
a . For
Heat Stage 2
and
Heat Stage 3
in system with two furnace sections, use following formulas in which
T
SP
= setpoints of heat stage controllers (T
SP2
and T
SP3
) , T
SA
= desired supply air temperature , and T
D
=
design (minimum) entering air temperature
:
Setpoint for heat stage 2: T
SP2
= T
SA
− 0.46 (T
SA
− T
D
)
Setpoint for heat stage 3: T
SP3
= T
SA
− 0.73 (T
SA
− T
D
)
EXAMPLE: With 3,600 CFM, power-vented, 100% outside air, −10°F outdoor winter design, and 75°F desired
supply air:
T
SP2
= 75 − [0.46 × (75 − (−10))] = 75 − (0.46 × 85) = 35.9
T
SP3
= 75 − [0.73 × (75 − (−10))] = 75 − (0.73 × 85) = 12.9
Set Heat #2 controller to 36°F
Set Heat #3 controller to 13°F
b . For Heat Stage 2 , Heat Stage 3 , Heat Stage 4 , and Heat Stage 5 in system with three furnace sections, use
the following formulas in which
T
SP
= setpoints of heat stage controllers (T
SP2
, T
SP3
, T
SP4
, and T
SP5
)
,
T
SA
=
desired supply air temperature , and T
D
= design (minimum) entering air temperature :
Setpoint for heat stage 2: T
SP2
= T
SA
− 0.30 (T
SA
− T
D
)
Setpoint for heat stage 3: T
SP3
= T
SA
− 0.49 (T
SA
− T
D
)
Setpoint for heat stage 4: T
SP4
= T
SA
− 0.65 (T
SA
− T
D
)
Setpoint for heat stage 5: T
SP5
= T
SA
− 0.82 (T
SA
− T
D
)
EXAMPLE: With 8,850 CFM, power-vented, 100% outside air, −10°F outdoor winter design, and 75°F desired
supply air:
T
SP2
= 75 − [0.30 × (75 − (−10))] = 75 − (0.30 × 85) = 49.5
T
SP3
= 75 − [0.49 × (75 − (−10))] = 75 − (0.49 × 85) = 33.3
T
SP4
= 75 − [0.65 × (75 − (−10))] = 75 − (0.65 × 85) = 19.8
T
SP5
= 75 − [0.82 × (75 − (−10))] = 75 − (0.82 × 85) = 5.3
Set Heat #2 controller to 49°F
Set Heat #3 controller to 33°F
Set Heat #4 controller to 20°F
Set Heat #5 controller to 5°F
2 . Locate heat stage controllers marked Heat #2 and Heat #3 (for two furnaces) or Heat #2 , Heat #3 , Heat #4 , and
Heat #5
(for three furnaces) in inlet air section .
NOTE: The same type of controller may also be used as the optional high ambient limit control
(option BN2) and as the mixed air controller that is part of air control options AR12, AR13, AR15,
and AR16.
3 . Adjust each controller to setpoint as determined by calculation in step 1 .