LAARS M4-LHS - Installation Manual - Manual (Page 32)

HT# 059295-00
A
32
M4-LHS installation and Operation Manual
• The System Run-On time should be set based on the size and type of the boilers and
pumps used. In general, when setting the System Run-On consult the boiler and pump
manufacturers for the best setting.
• When the System relay is in the Run-On period, the Message Display Line will indicate that
status and the remaining time.
Lead Boiler rotation
Adjustable Manual, Time (1 hr to 60 Days), Last-On Default: Time (24Hours)
Button: MENU/<System Settings>/Lead Rotation
• The Lead Boiler is the first boiler brought on when an output is needed.
• The Lead Boiler can be rotated automatically every specified time period, manually, or
based on Last-On. Time rotation is recommended.
• The Lead Group Lead Boiler is shown in bracket layers on the main display. The Lag
Group lead Boiler is shown in a single bracket. See "Boiler Status" on page 38.
• Only boilers which are set to Auto Mode can be Lead. Therefore, not all the boilers may be
available when manually selecting a new Lead Boiler.
-- LEAD ROTATION --
24hrs
[ ]
BACK ▲ ▼ SAVE
-- LEAD ROTATION --
Manual
Time
Last-On
BACK ▲ ▼ SAVE
Standby Time
Adjustable from 1 min to 60 min Default: 10 min
Button: MENU/<System Settings>/<More Settings>/Standby Time
• Standby boilers are used for backup or extreme load conditions only. A Standby boiler can
never be a Lead Boiler.
• The Standby Time only applies to boilers set to Standby.
• A boiler can be set to be a Standby boiler using the Stage Menu. See "Mode" on page 39.
• A Standby boiler can only be activated after all the boilers in Auto Mode have run at 100%
modulation for the full Standby Time.
-- STANDBY TIME --
10 min
[ ]
BACK ▲ ▼ SAVE
• The full Standby Time must always elapse regardless of what happens to the system
temperature. Therefore, shorter Standby Times will result in smoother set point operation in
extreme conditions. On the other hand, longer Standby Times may prevent a Standby boiler
from firing if the other boilers can eventually meet the load, or if the load decreases.
Last Stage Hold
Adjustable from 0F°/0C° to 30F°/17C° Default: 5F°/3C°
Button: MENU/<System Settings>/<More Settings>/Last Stg Hold
• The Last Stage Hold prevents short cycling of the Lead Stage during low demand periods.
• In these conditions, the system might require less output than the lowest lead Stage. When
the M4-LHS brings on the Lead Stage, the Set Point is quickly exceeded, and the M4-LHS
turns the Lead Stage off.
• To prolong the run time during this type of condition, use the Last Stage Hold setting to let
the system temperature exceed the Set Point by the number of degrees selected.
• For example, with a Set Point of 160°F and a Last Stage Hold setting of 10°F, the Lead
Stage boiler will de-energize after the Set Point exceeds 170°F (160°F + 10°F).
• In many cases, it is better to overshoot slightly than to short cycle a boiler.
• When Soft-Off is set to other than 0 seconds, the Lead Boiler will need to remain at or
exceed the Last Stage Hold for the Soft-Off period before turning off.
LAST STAGE HOLD
5 o F
[ ]
BACK ▲ ▼ SAVE
Lead Stages
Condensing Lead, Non-Condensing Lead Default: 1st boiler in the Group
Button: MENU/<System Settings>/<More Settings>/Lead Stages
• In addition to having a lead group, each group of boilers, Condensing Group and
Non-Condensing Group, will have its own lead boiler that can be selected from this menu.
• After assigning the lead boiler for each group, the lead will rotate based on the Lead
Rotation option selected. See "Lead Boiler Rotation" on page 32.
• The Lead Group Lead Boiler can be identified by the two brackets <<A>>.
• The Lag Group Lead Boiler can be identified by the one bracket <C>.
--- LEAD STAGES ---
Cond Lead A
Non-Cond Lead C
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