LAARS SC 12 - Install and Operating Manual - Manual (Page 19)

Page 19 Laars Sequencing Controls
OUTDOOR RESET SETTINGS
CALCULATED (CAL)
• This is the water temperature the SC will stage units to hold. It is based on Outdoor temperature, the Reset Ratio, the Offset, the
Setback/Shutdown values (see pg. 24 and the DHW input (see pg. 25).
• The Calculated water temperature can not be less than the minimum water temperature setting (see pg. 8).
• If either the System or Outdoor sensor is reading a fault condition, all stages will immediately turn off. The Calculated water
temperature display will show OFF to indicate this condition. OFF OFF
• If the outdoor temperature is above the Outdoor Cutoff, the SC will not activate stages. The Calculated display will show OFF
to indicate this condition.
• A DHW call (see pg. 25) will override the Outdoor Cutoff. During a DHW call, the Calculated temperature will be 200°F.
•
Calculated temperature.
• The Calculated temperature is the average temperature the SC will maintain. The system can be expected to fl uctuate above and
below the Calculated temperature. The size of the fl uctuation depends on the number of stages, the size of each stage, the system
load, and the Sequencing options.
• The Calculated temperature is based on all the parameters described above. The Calculated value can not be changed by
pressing the UP or UP UP DOWN button while it is displayed. DOWN DOWN
OUTDOOR TEMPERATURE (OUt) No Adjustment - Display Only
• The Outdoor Sensor must be installed for the Outdoor Reset function to work. If the sensor shows OPn for open or SHt for
short, no stages will be activated.
OUTDOOR CUTOFF (COF) Default: 60°F
• The Outdoor Cutoff sets at what outdoor temperature the SC will begin heating. This setting will only be available if the SC does
not register a fault from the Outdoor sensor (OPn Open or SHt short).
• For heating, when the Outdoor temperature drops below the Outdoor Cutoff temperature, the SC will begin to Sequence stages
for heat. It will continue to Sequence until the Outdoor temperature rises to 2°F above the Outdoor Cutoff temperature.
• The Outdoor Cutoff temperature can be set from 40 to 100°F. In addition, an ON setting is provided to override the Outdoor
Cutoff for continuous Sequencing, and an OFF setting can be used to temporarily prevent any Sequencing.
• The Outdoor Cutoff has a built in 2°F differential.
• If the Outdoor temperature rises 2°F above the Outdoor Cutoff, the SC will not activate stages and the Set Point will read OFF,
unless there is a DHW call.
• If the building is too cold before the system starts, raise the Outdoor Cutoff
temperature.
RESET RATIO (RSt) Default: 7
• The Reset Ratio controls how much heat will be added based on outdoor
temperature. The Reset Ratios are shown as Outdoor Temperature:Water
Temperature.
• A 1:1 Reset Ratio signifi es for each degree it gets colder outside, the Calculated
water temperature will raise 1 degree.
• The other Reset Ratios available are shown on the right.
• The Reset Ratio curves start at 70°F. At 70°F the SC will require 100°F water.
Note that this is not the point where the SC will begin giving heat. That point
is determined by the Outdoor Cutoff. Also note that this starting point can be
changed by adjusting the Offset as shown below.
• For new installations with standard baseboard heating, begin with a Reset Ratio
curve of 7.
• For new installations with radiant heat, begin with a Reset Ratio curve of 4 or 5.
• Adjust the Reset Ratio value in cold weather. If the ambient indoor temperatures
are cold in the cold weather, pick the next higher Reset Ratio (that is, go from 7 to
8). If the ambient building temperatures are warm in the cold weather, pick the next
lower Reset Ratio.
• Wait at least 24 hours before making another Reset Ratio adjustment.
• The Reset Ratio can be set from 1 to 12.
Outdoor Temperature (in °F)
70 60 50 40 20 30 0 -10 10 -20
W
at
er
Te
m
pe
ra
tu
re
(in
°F
)
100
120
110
130
140
150
160
180
170
190
200
210
220
12 11 10 9
8
7
6
4
3
2
5
1
1:4 1:3 1:2 1:1.5
1:1.25
1:1
1.25:1
1.5:1
2:1
3:1
4:1
8:1
NOTICE
The SC will not compute a
Calculated water temperature
below the minimum water
temperature setting.