tekmar 423 Universal Reset Module - Manual (Page 22)

© 2007 D 423 - 08/07 22 of 36
Boiler Fire Delay
The Boiler Fire Delay is the time delay that occurs between
the time that the control closes the boiler contact to fire the
boiler and when the burner fires.
•
• Locate the Boiler Fire Delay setting in the Adjust Menu.
Boiler Contact Closed
Time
Fire Delay
Burner On
On-Off Boiler(s) Operation
If the heat source is an On-Off Boiler(s), the Boil On-Off / Mod
DIP switch must be set to On-Off.
Differential
An on / off heat source must be operated with a differential
in order to prevent short cycling. With the control, either
a fixed or an auto differential may be selected. The boiler
differential is divided around the boiler target temperature.
The first stage contact closes when the supply water
temperature is 1/2 of the differential setting below the boiler
target temperature. The second stage is operated if the first
stage is unable to bring the supply water temperature up to
the boiler target temperature at a reasonable rate. As the
supply temperature reaches 1/2 of the differential above
the boiler target temperature, the stages are staged off.
•
• Locate the Boiler Differential setting in the Adjust Menu.
Differential = 10°F (6°C)
Target + 1/2 Differential
Target – 1/2 Differential
Target
165°F (74°C)
160°F (71°C)
155°F (68°C)
Boiler
On
Boiler
On
Fixed Differential
If the user desires to have a fixed differential, this is set
using the Boiler Differential setting in the Adjust Menu.
Stage Delay
The Stage Delay is the minimum time delay between the
firing of the first stage and the second stage. After this
delay has expired the control can fire the second stage if it
is required. This setting can be adjusted manually or set to
an automatic setting. When the automatic setting is used,
the control determines the best stage delay based on the
operation of the system.
•
• Locate the Stage Delay setting in the Adjust Menu.
Auto Differential
In order to decrease temperature swings and increase boiler
efficiency, the Auto Differential feature automatically changes
the on / off differential of the boiler based on the heating
load. As the load increases, the differential will decrease to
minimize temperature swings. As the load decreases, the
differential will increase to prevent short cycling.
Off
Differential
Time
Heating Load
On
Modulating Boiler Operation
The 423 can operate up to two modulating boilers. This
requires the use of the Mod 1 (dc) and Mod 2 (dc) outputs
on the 423.
To operate modulating boilers, the Boil On-Off / Mod DIP
switch must be set to Mod. The control operates each boiler
by first closing the stage contact to allow the modulating
boiler to go through the ignition sequence (the stage
contact may not be required on all modulating boilers).
Then, a 0-10 V (dc) analog signal is used to modulate the
boiler firing rate from the Minimum Modulation setting using
Proportional, Integral and Derivative (PID) logic in order
to satisfy the boiler target temperature. The second stage
is operated if the first stage is unable to bring the supply
water temperature up to the boiler target temperature at a
reasonable rate.
Modulating boilers require all the same settings as on-off
boilers in addition to the settings below.
Modulating Boiler Differential
Modulating boilers must be operated with a differential
while operating in low fire. The boiler differential is divided
around the boiler target temperature. The boiler burner
ignites at low fire when the supply water temperature is
1/2 of the Boiler Differential setting below the boiler target
temperature. The boiler is shut off in low fire as the supply
temperature reaches at least 1/2 of the differential above
the boiler target temperature. With the control, either a fixed
or an auto differential may be selected.
When the boilers are modulating above low fire, the differential
does not apply. Instead, the modulation output signal is
determined using Proportional, Integral and Derivative (PID)
logic in order to satisfy the boiler target temperature.