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UNDERSTANDING OPERATION CONCEPT
The BSC has multiple operating modes that satisfy most hydronic systems. It can change the
System Set Point based on outdoor temperature (Outdoor Reset) or it can modulate its stages
In Outdoor Reset, the BSC controls a hot water heating system to provide a building with
comfortable and even heat levels. The BSC varies the temperature of the circulating heating
water in response to changes in the outdoor temperature. The heating water temperature is
controlled through the modulation of the stages.
The BSC also controls the system circulating pump with an adjustable Outdoor Cutoff. When
the outdoor temperature is above Outdoor Cutoff, the pump is off and no heating water is
circulated through the system. When the outdoor temperature drops below the Outdoor Cutoff,
the system pump relay is activated and the heating water circulates through the system. The
temperature of the heating water is controlled by the Reset Ratio, Water Offset, and the Outdoor
temperature.
RESET RATIO/OUTDOOR RESET
When a building is being heated, heat escapes through the walls, doors, and windows
to the colder outside air. The colder the outside temperature, the more heat escapes. If
you can input heat into the building at the same rate that it is lost out of the building,
then the building temperature will remain constant. The Reset Ratio is an adjustment
that lets you achieve this equilibrium between heat input and heat loss.
temperature drops, the temperature of the heating water will increase one degree. The
starting point of the curves is adjustable, but comes factory selected at 70
Temperature and 100
°
ratio, if the outdoor temperature is 50
the starting point of 70
F. Therefore, the heating water temperature will increase 20
°
120
F.
°
Each building has different heat loss characteristics. A very well insulated building will
2 degrees to increase the water temperature 1 degree. On the other hand, a poorly
temperature will increase 2 degrees. The BSC has a full range of Reset Ratios to match
any buildings heat loss characteristics.
A heating curve that relies not only on Outdoor temperature but also on type of radiation
will improve heat comfort. The following are suggested initial settings for different
types of radiation based on average building insulation and heat loss. The contractor
Type of Radiation in Building
Radiators (Steel & Cast Iron)
Baseboard (Finned copper tube& Cast Iron)
Radiant (High Mass/Concrete)
Radiant (Low Mass/Joists)
Fan Coils & Air Handlers
BSC Installation and Operation Manual
F, this means the temperature has fallen 20
°
Reset Ratio
1.00 (OD) : 1.00 (SYS)
1.00 (OD) : 1.00 (SYS)
4.00 (OD) : 1.00 (SYS)
2.00 (OD) : 1.00 (SYS)
1.00 (OD) : 1.00 (SYS)
220
210
200
190
180
170
160
150
140
130
120
110
100
Reset Ratio Curves
With a 0° Offset, the
ratio curves begin at
100° Water Temperature.
F Outdoor
°
from
°
With a -20° Offset, the
ratio curves begin at
to
°
80° Water Temperature.
With a +20° Offset, the
ratio curves begin at
120° Water Temperature.
Offset
When controlling a non condensing
boiler directly without the use of a
mixing valve, minimum boiler water
temperature must be set to boiler
case, system temperature must not go
below such temperature.
1:4
1:3
1:2
1:1.5
50
30
0
-10
70
60
40
20
10
-20
Outdoor Temperature (in °F)
Reset Ratio is Presented as
Outdoor Temp. : Water Temp. Ratio
1:4
130
120
110
100
70
60
50
Outdoor Temperature
1:4
110
100
90
-20 Offset
80
70
60
50
Outdoor Temperature
1:4
150
140
130
120
90
+20 Offset
100
70
60
50
Outdoor Temperature
WARNING
1:1.25
1:1
1.25:1
1.5:1
2:1
3:1
4:1
1:1
4:1
40
1:1
4:1
40
1:1
4:1
40
5
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