User Guide

7
EM-40-SM Service Manual
STAGE DELAY (STG DLY)
The stage delay is the minimum time between firing first
to second stage, second to third stage, and third to fourth
stage and is determined by the Stage Delay setting. It can
b
e manually set, or it can be set to automatic in which the
boiler mass determines the stage delay time.
BOILER MASS (BOIL MASS)
The boiler mass setting allows the installer to adjust the
control to the thermal mass of different types of heat sources
used. The boiler mass setting automatically determines the
stage delay on, stage delay off, minimum on time and
minimum off time of the stages. A higher thermal mass
setting provides slower staging, while a lower thermal mass
provides faster staging.
Pr
oportional (P)
Proportional staging, also known as step staging, is based
on manually adjusted settings that determine when the
next stage is required to turn on. These manual settings are
based on temperature and time. The interstage differential
sets the temperature drop at which the next stage turns on.
However, in order for a stage to fire, the interstage delay
on and minimum off times must first elapse.
Interstage Differential (STG DIFF)
The interstage differential is the temperature drop at which
the next stage will turn on. Once a stage turns on, the
next stage cannot turn on until the temperature drops
the interstage differential below the temperature at which
the previous stage turned on. The interstage differential
is adjustable through the STG DIFF setting in the Adjust
menu.
Interstage On Delay (ON DLY)
The interstage on delay is the amount of time that must
elapse before turning on the next stage. Once a stage turns
on, the ne
xt stage cannot tur
n on until the interstage dela
y
on time elapses. The interstage on delay is adjustable
through the ON DLY setting in the Adjust men
u.
Interstage Off Delay (OFF DLY)
The interstage off delay is the amount of time that must
elapse before turning off the next stage. Once a stage turns
off, the next stage cannot turn off until the interstage delay
off time elapses. The interstage off delay is adjustable
through the OFF DLY setting in the Adjust menu.
Minimum On Time (MIN ON)
The minimum on time is the minimum amount of time that
a stage must be on before it is allowed to turn off. Once a
stage tur
ns on, it cannot tur
n off until a minimum on time
elapses. The minimum on time is adjustable through the
MIN ON setting in the Adjust menu.
Minimum Off Time (MIN OFF)
The minimum off time is the minimum amount of time that
a stage must be off before it is allowed to turn on. Once a
stage turns off, it cannot turn on until a minimum off time
e
lapses. The minimum off time is adjustable through the
MIN OFF setting in the Adjust menu.
BOILER DIFFERENTIAL (DIFF)
A heat source must be operated with a differential in order to
reduce short cycling. The boiler differential is divided around
the boiler target temperature. The first stage
contact will close once the water temperature at the
operating sensor is 1/2 of the differential setting below the
boiler target temperature, and will open once the water
temperature at the operating sensor is 1/2 of the
differential setting above the boiler target temperature.
Manual Differential
The differential can be manually set using the DIFF setting
in the Adjust menu.
A
uto Differential
A
uto diff
erential is only a
v
ailable when using PID staging.
If the Auto Differential is selected, the control automatically
determines the best differential as the load changes,
thereby improving efficiency. During light loads, the
differential is increased to allow longer on and off times to
reduce the potential for short cycling. During large loads, the
differential is narrowed thereby improving comfort in heating
spaces by reducing temperature swing.
P
roportional Staging
A Minimum On Time
B Minimum Off Time
C Interstage On Delay
D Interstage Off Delay
A B C D
Fixed Differential
Differential
Des ired Temperature
Desired Temperature
Increasing
Temperature
Increasing Time
O
NON
OFF
OFF
Automatic Differential
Differential
Low
Heat
Load
ON
ON
OFF
OFF
Differential
High
Heat
Load
ON
ON
FFOFFO
Partial Outdoor Reset
Decreasing Outdoor Air Temperature
Increasing Water Temperature
B oil MAXBoil MAX
B oil MINBoil MIN
WWS DWWSD
D
Proportional Staging
A Minimum On Time
B Minimum Off Time
C Interstage On Delay
D Interstage Off Delay
A B C D
Fixed Differential
Differential
Des ired Temperature
Desired Temperature
Increasing
Temperature
Increasing Time
ON ON
OFF
OFF
Automatic Differential
Differential
Low
Heat
Load
ON
ON
OFF
OFF
Differential
High
Heat
Load
ON
ON
FFOFFO
Partial Outdoor Reset
erature
B oil MAXBoil MAX
B
Proportional Staging
A Minimum On Time
B Minimum Off Time
C Interstage On Delay
D Interstage Off Delay
A B C D
Fixed Differential
Differential
Des ired Temperature
Desired Temperature
Increasing
Temperature
Increasing Time
ON ON
OFF
OFF
Automatic Differential
Differential
Low
Heat
Load
ON
ON
OFF
OFF
Differential
High
Heat
Load
ON
ON
FFOFFO