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applications usually require a lower curve. An external T-Stat input can be used to shut
the heating system down when the thermostat is satisfied. Another, is a Setback input that
will switch the heating system to a lower set point determined by the Set Back setting.
Type of Radiation in Building
Radiators (Steel & Cast Iron)
Baseboard (Finned copper tube& Cast Iron)
Radiant (High Mass/Concrete)
Radiant (Low Mass/Joists)
Fan Coils & Air Handlers
An optional domestic hot water input is provided for systems where an indirect tank
provides DHW. During a DHW call, the SEQ-3 will maintain a constant set point of
200°F or the Maximum Water Temperature setting, whichever is lower, regardless of
outdoor temperature or the status of the heating system. If 1-On/Off+2-Pumps Output
Mode option was selected, the DHW pump will be enabled whenever there is a call for
DHW. In addition, the heating system pump can be programmed to turn off during a
DHW call for up to 120 minutes to satisfy the DHW demand quicker while withholding
building heat.
Operation Concept
The SEQ-3 has multiple Output Modes of operation. It can control any three output boiler-and-pump variety ranging from a single
On/Off boiler with a system pump to three individual boilers. In addition, it can accepts a DHW call signal to raise the target set point.
Moreover, if "1-On/Off+2-Pump" is selected as an Output Mode, it will control the DHW pump allowing it to energize on a DHW
call. (See Operating Mode Table under the Startup Menu on page 5.)
Boiler Operation
• When a single On/Off boiler is selected as the primary function of the SEQ-3, the boiler relay will energize when the System
Sensor reading is below the Target temperature less the Differential. Moreover, the Outdoor Sensor reading must be below the
Outdoor Cutoff setting and the EXT+/EXT- (Enable/Disable) terminals must be shorted using a dry-contact switch or a jumper. If
the System temperature exceeds the Target, the boiler relay will de-energize.
• If sequencing multiple stages or boilers are the primary function of the SEQ-3, the SEQ-3 will use the Purge Delay (See Purge
Delay on page 12.) to start the lead boiler. Then, it will use the Reaction Time (See Reaction Time on page 11.) to add additional
stages or boilers. When subtracting stages, the SEQ-3 will use only the Minimum Run Time. (See Minimum Runtime on page 12.)
System Pump Operation
• When the SEQ-3 is in one of the Output Modes that control the System Pump relay while the EXT+/EXT- (Enable/Disable)
terminals are shorted using a dry-contact switch or a jumper, the System Pump relay will energize, as long as the Outdoor Sensor
reading is below the Outdoor Cutoff setting. However, upon the opening of the EXT+/EXT- (Enable/Disable) terminals or if the
Outdoor Sensor reading rises two degrees above the Outdoor Cutoff setting, all boiler relays will de-energize and the System Pump
relay will remain energized for the Run-On delay period before de-energizing.
• If DHW Priority was set to other than "NO", a DHW call using terminals T3+/T3- (DHW call Input) will de-energize the System
Pump relay for the period of the DHW priority or the termination of the DHW call, whichever comes first. This will ensure all
boiler outputs are directed to produce domestic hot water.
• If DHW Priority was set to "NO", then a DHW call will not have any effect on the System Pump relay.
DHW Pump Operation
• When the SEQ-3 is controlling the DHW Pump relay by selecting "1-On/Off+2-Pump" mode from the Output Modes, a DHW
call using terminals T3+/T3- (DHW call Input) will energize the DHW Pump relay. In addition, the SEQ-3 will raise the Target
temperature to the lower of 200˚F or the Maximum Water temperature Setting.
• When the SEQ-3 is in Outdoor Cutoff or when the EXT+/EXT- (Enable/Disable) terminals are open, a DHW call will energize only
the DHW Pump relay in a DHW Priority setting. See Output Mode Table on page 5. However, if No DHW Priority was selected,
both the System and DHW Pumps will energize on a DHW call.
2
Reset Ratio
Offset
0˚F
1.00 (O) : 1.00 (S)
0˚F
1.00 (O) : 1.00 (S)
-10˚F
4.00 (O) : 1.00 (S)
-10˚F
2.00 (O) : 1.00 (S)
20˚F
1.00 (O) : 1.00 (S)
1:4 1:3
1:2
12 11
10
220
210
200
190
180
170
160
150
140
130
120
110
100
70
60
50
40
30
20
10
0
Outdoor Temperature (in °F)
Reset Ratio Curves
Reset Ratios are presented as
Outdoor : Water
1:1.5
9
8
1:1.25
7
1:1
6
1.25:1
5
1.5:1
4
2:1
3
3:1
2
4:1
1
8:1
-10
-20
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