Understanding Operation Concept; Pid Operation; Oss Operation - heat-timer SQ-Elite-8S Installation And Operation Instruction Manual

understandIng operatIon concept

The SQ-Elite-8S has multiple operating modes that satisfy most steam systems. It can sequence stages to achieve an adjustable Set Point.
Moreover, when used with the 4-20mA EMS Interface (HT# 926741-00) it can accept a 4-20mA signal as a set point. The 4-20mA EMS
Interface must be purchased separately. This gives the SQ-Elite-8S the capability of being controlled remotely.

pId operatIon

PID control logic is primarily used for building heating. The logic will utilize two primary settings to add or subtract stages. The Reaction
Time is used to turn on/energize stages. On the other hand, the Minimum Runtime is used to turn off/de-energize stages. On a call for
heat, by either closing the TSTAT input or opening the SHUTDOWN input, and when the outdoor temperature is below the Outdoor
Cutoff, the SQ-Elite-8S will turn on/energize the Lead Boiler's lowest firing stage to start the Purge Delay. After the elapse of the purge
period, the SQ-Elite-8S will start calculating the Reaction Period. If after a full Reaction Time the control logic foresees additional stages
are needed, the SQ-Elite-8S will energize the following stage. If that stage was another boiler, that boiler has to go through a full Purge
Delay before starting to calculate the Reaction Time for that stage. Otherwise, if the next stage was the higher firing stage on the same
boiler, the Reaction Time will start from the moment the higher firing stage relay is energized.
When the SQ-Elite-8S PID logic foresees that the system will overshoot, regardless of the current system and target values, it will make
sure that the last stage turned on/energized elapsed a full Minimum Runtime before it is turned off/de-energized. Except for the lead
stage, no additional stages will be turned off/de-energized until another full Minimum Runtime is elapsed. On the other hand, if the
last stage is a lead stage, it will remain energized until the system reading exceeds the target set point by the Last Stage Hold value in
addition to satisfying the Minimum Runtime condition. That is, if the Set Point was 10 PSI and the Last Stage Hold was set to 2 PSI,
the lead stage will remain energized until the system reaches 12 PSI and a full Minimum Runtime elapses. This is useful in protecting
the lead stages from short cycling.

oss operatIon

OSS is used in fast reacting application as in process applications, where maintaining a set point is critical. The OSS utilizes the Throttle
setting, as a mean to calculate the number of stages the SQ-Elite-8S shall have on at any point. For every Throttle Range below the set
point an additional stage shall be turned on/energized. That is, if the set point was 50 Psi and the Throttle setting was 5 Psi, if the System
dropped below 45 Psi (50 Psi - 5 Psi), the lead stage will energize. With further decrease in the system value to 40 Psi (50 Psi - 5 Psi - 5
Psi), the second stage will energize.
As the system pressure rises towards the set point, stages will turn off. Using the previous example, when the system rise to 45 Psi boiler
B will de-energize leaving only boiler A on. Boiler A will remain on until the system rises a one full Throttle range above the set point.
This will leave the lead boiler A on until the pressure rises to 55 Psi then turn off/de-energize.
set point = 50 psi
system
throttle
ranges
pressure
55 Psi -1
50 Psi 0
45 Psi 1
41 - 44 Psi 1
40 Psi 2
35 Psi 3
30 Psi 4
25 Psi 5
20 Psi 6
15 Psi 7
throttle = 5 psi boilers (a, b, c, d, e, and F)
Falling pressure
stages turned on
----
----
A
----
B
C
D
E
F
----
SQ-Elite-8S & SQ-Elite-EXT Installation Manual
stages on
None
None
A
A
A + B
A + B +C
A + B +C + D
A + B +C + D + E
A + B +C + D + E + F
A + B +C + D + E + F
lead stage =<a>
rising pressure
stages turned off
A
----
B
----
C
D
E
F
---- A + B +C + D + E + F
---- A + B +C + D + E + F
5
stages on
None
A
A
A + B
A + B
A + B +C
A + B +C + D
A + B +C + D + E