LAARS M4-Ext - Installation Manual - Manual (Page 27)

Installation Manual 27
OPERATiNg STAgiNg BOiLER SETTiNgS
REACTiON TiME
Adjustable from 1 to 10 minutes Default: 2 minutes
Button: MENU////Reaction Time
• It is the amount of time it takes a single stage to affect the system.
• After the M4-CNC turns on a stage trying to meet a set point, it will not turn on another
stage until the Reaction Time has elapsed.
• To determine the optimum time, start with a hot system. Then, turn on a single stage and
calculate how long it takes until the system begins to respond to that stage. That period
should be set as the Reaction Time.
- STAGE SETTINGS -
Reaction Time 2min
Minimum Runtime 2min
BACK ▲ ▼ SAVE
-- REATION TIME --
2 min
[ ]
BACK ▲ ▼ SAVE
MiNiMUM RUNTiME
Adjustable from 1 to 60 minutes Default: 2 minutes
Button: MENU////Min Runtime
• This is the minimum amount of time any stage will run.
• For the lowest stage of a unit, the Minimum Runtime starts after the purge cycle.
• The Runtime does not apply to the last stage online. The Last Stage Hold applies in that
case.
• Initially, set the Minimum Runtime to half the Reaction Time.
• If the system tends to overshoot, reduce the Minimum Runtime. However, if boilers tend to
short cycle, increase the Minimum Runtime.
- MINIMUM RUNTIME -
2 min
[ ]
BACK ▲ ▼ SAVE
AvOidiNg CONFLiCTiNg BOiLER LiMiTS
• The temperature limits set on the boilers MUST be set considerably higher than the
M4-CNC's Set Point for the reasons detailed below.
• The M4-CNC sensor is located in a common header some distance from the boilers.
• As the temperature rises in the header and before reaching the sensor location, energy is
dissipated. Therefore, the temperature in the header could be lower than that registered by
boiler sensors.
• In addition to the normal drop experienced between the boiler’s temperature and that
read by the M4-CNC sensor, the Last Stage Hold setting must be accounted for. The boiler
limit must be set above the 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 Set Point, the boilers’
limits must be set enough over 170°F to prevent the boilers’ internal limits being reached. In
this situation, the boiler high limit should be set at approximately 180°F or higher to prevent
the difference in boiler temperature vs. header temperature causing erratic operation.
WARNiNg
The temperature limits set on
the boilers must be higher than
the M4-CNC Max Water Temp.
Read the section at left for
details that will prevent erratic
system operation.
LAARS Modulating Controls M4 & M4-EXT
HT# 059104-00 B