26
Heat-Timer Corp.
last stage Hold
(available in pId only)
Adjustable 0
º
F/0
º
C - 30
º
F/17
º
C
Default: 5
º
F/3
º
C
Hold Button:
MENU/<SEQ Settings>/<System Settings>/<Stage Settings>/Last Stage Hold
• The Last Stage Hold prevents short cycling of the Lead Stage during low load conditions
where the system might have a load that is significantly less than the output of one stage.
LAST STAGE HOLD
5 F
[
]
BACK SAVE
• When the SQ-Elite-MV brings on the Lead Stage, the Set Point is quickly exceeded, and the Lead Stage is turned off. To prolong
the run time during this type of condition, use the Last Stage Hold setting.
• The SQ-Elite-MV will allow the system temperature to exceed the Set Point by the number of degrees selected, before the Lead
Stage is turned off.
(See PID Operation under Control Logic on page
• For example, with a Set Point of 160°F and a Last Stage Hold setting of 10°F, the Lead Stage boiler will remain on, until the Set
Point reaches 170°F
then turn off.
During that period, the display will show "
Hold Until 170F
".
tHrottle
(available in oss only)
Adjustable 2
º
F/1
º
C - 20
º
F/11
º
C
Default: 2
º
F/1
º
C
Hold Button:
MENU/<SEQ Settings>/<System Settings>/<Stage Settings>/Throttle
• The Throttling Range sets a temperature band around the Set Point that controls when
stages will be turned on or off.
-- THROTTLE RANGE --
2 F
[
]
BACK SAVE
• For example, in the Oversize (OSS) heating mode, no stages will be activated until the temperature falls one full Throttling range
below the Set Point. A second stage will be activated when the temperature falls to two full Throttling ranges below the Set Point,
and so on, with one extra stage being turned on for every additional throttling below the Set Point the System temperature reaches.
• Stages will be turned off as the temperature rises toward the Set Point with one full throttling range as a differential.
• The last stage to be turned off will be allowed to exceed the Set Point by a full Throttle before it is turned off. This helps prevent
the last stage from short cycling when the load is low or when the stage is oversized.
throttling example
set point = 180
°
f
throttling = 5
°
f
4 Boiler stages, a, B, c, and d
falling temperature
rising temperature
temperature
calculation
stage turned on
stages on
stage turned off
stages on
185
°
F
180 + (1)
THR
None
None
A
None
180
°
F
180 - (0)THR
None
None
None
A
175
°
F
180 - (1)THR
A
A
B
A
171 to 174
°
F
---
---
A
---
A,B
170
°
F
180 - (2)THR
B
A,B
C
A,B
166 to 169
°
F
---
---
A,B
---
A,B,C
165
°
F
180 - (3)THR
C
A,B,C
D
A,B,C
161 to 165
°
F
---
---
A,B,C
None
A,B,C,D
160
°
F
180 - (4)THR
D
A,B,C,D
None
A,B,C,D
avoiding conflicting Boiler limits
• The temperature limits set on the boilers MUST be set considerably higher than the
SQ-Elite-MV’s SEQ Set Point for the reasons detailed below.
• The SQ-Elite-MV SEQ System sensor is located in a header some distance from the boilers.
• As the temperature rises in the header and before reaching the sensor location, energy is
dissipated. Therefore, the header temperature could be lower than that at the boilers.
• In addition to the normal drop experienced between the boiler temperature and that read by
the SEQ System sensor, the Last Stage Hold setting must be accounted for. The boiler
warnIng
The temperature limits set on
the boilers must be higher than
the SQ-Elite-MV Set Point.
Read the section at left for
details that will prevent erratic
system operation.
limit must be set above the SEQ Set Point PLUS the Last Stage Hold PLUS the normal drop experienced in the piping.
• Using the previous example of a 10°F Last Stage Hold with a 160°F SEQ Set Point, the boilers’ limits must be set high enough
over 170°F to prevent the boilers’ internal limits from being reached. In this situation, the boiler high limit should be set at
approximately 180°F to prevent the difference in boiler temperature vs. header temperature causing erratic operation.
