Setback; Last Stage Hold - heat-timer Mini-Extension Installation And Operations

20 Heat-Timer Corp.
• A common use for the System Run-On is to control a system pump in a heating system. The extra time helps transfer the heat
from the boilers to the heating system.
• The System Run-On time should be set based on the size and type of the boilers and pumps. In general, a boiler with low
water content and high horsepower will need a longer System Run-On than a boiler with the same horsepower and more water
content. (Refer to boiler manufacturer recommendation)

SETBACK

Adjustable 0°F to 75°F
Button: MENU/<System Settings>/<More Settings>/Setback
• The Setback feature can be used to provide the Mini-MOD with a lower temperature Set
Point when less load is required.
• The lower Set Point will appear on the main display indicating this condition.
• For example, if the calculated temperature is 180°F and the Setback is 20°F, then when
in Setback, the Mini-MOD will hold a Set Point of 160°F.
• A typical use for Setback is to provide less system temperature to a building during the
night or on the weekends when building is not occupied, but heat is still required.
• The amount of Setback selected is subtracted from the Set Point when a Setback External Signal is received or the Night Time
schedule setting started.
• If External Signal is selected as a Setback Mode (See Startup menu), the Setback will not be activated unless a dry contact
signal source is wired into the Shutdown/Setback terminals (31 and 32) and the Mini-MOD receives a SHORT signal.
• If Day/Night Schedules is selected as a Setback Mode (See Startup menu), the Setback will be activated only when Night
Schedule time has started.
When using Soft-Off and Last Stage Hold, the last boiler stage will not turn off
until both parameters have elapsed. In this case, Soft-Off will start after the Last
Stage Hold.

LAST STAGE HOLD

Adjustable 0°F to 30°F
Button: MENU/<System Settings>/<More Settings>/Last Stg Hold
• The Last Stage Hold prevents short cycling of the Lead Stage during low load periods.
• In low load conditions, the system might require only 5% of the output of one Stage.
When the Mini-MOD brings on the Lead Stage, the Set Point is quickly exceeded, and
the Mini-MOD turns the Lead Stage off.
• To prolong the run time during this type of condition, use the Last Stage Hold setting.
• The Mini-MOD will let the system temperature exceed the Set Point by the number of
degrees selected, before the Lead Stage is turned off.
• 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, at low modulation, until the Set Point reaches 170°F.
• From an efficiency standpoint, it is better to overshoot slightly than to short cycle a
boiler.
Avoiding Conflicting Boiler Limits
• The temperature limits set on the boilers MUST be set considerably higher than the
Mini-MOD's Set Point for the reasons detailed below.
• The Mini-MOD 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
CAUTION
--- --- ---- ---- SET BAC K -- ---- ---- -
Default: 0°F
[
BACK
- ---- - LA ST S TAG E HO LD -- --- -
Default: 0°F
[
BAC K
The temperature limits set on
the boilers must be higher than
the Mini-MOD Set Point. Read
the section at left for details
that will prevent erratic system
operation.
0
F
]
SAVE
0
F
]
SA VE
WARNING