Table of Contents
Advertisement
outdoor reset concept
The Mini-MOD-CNC has multiple operating modes that satisfy most hydronic systems.
It changes the System Set Point based on outdoor temperature (Outdoor Reset). The
Mini-MOD-CNC 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 or sequencing of the stages.
The Mini-MOD-CNC also controls the system circulating pump with an adjustable Outdoor
Cutoff. When the outdoor temperature is above the 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 changes with 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 temperatures will remain constant. The Reset Ratio is an adjustment that
lets you achieve this equilibrium between heat input and heat loss.
The starting point for most systems is the 1.00 (OD):1.00 (SYS) (Outdoor
Temperature : Heating Water Temperature) ratio. This means that for every
degree the outdoor temperature drops, the temperature of the heating water will
increase one degree. The starting point of the curve is adjustable, but comes
factory selected at 70
F Outdoor Temp. and 100
°
a 1.00 (OD):1.00 (SYS) ratio, if the outdoor temperature is 50
temperature has fallen 20
from the starting point of 70
°
water temperature will increase 20
Each building has different heat loss characteristics. A very well insulated
building will not lose much heat to the outside air, and may need a Reset Ratio
of 2.00 (OD):1.00 (SYS) (Outdoor:Water). This means the outdoor temperature
would have to drop 2 degrees to increase the water temperature 1 degree. On
the other hand, a poorly insulated building with insufficient radiation may need
a Reset Ratio of 1.00 (OD):2.00 (SYS). This means that for each degree the
outdoor temperature dropped the water temperature will increase 2 degrees. The
Mini-MOD-CNC 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 the 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 can fine tune these adjustments based on the specific building need.
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
Mini-MOD-CNC & Mini-Extension Installation Manual
F Water Temp. For example with
°
F. Therefore, the heating
°
to 120
F.
°
°
reset ratio
130
1.00 (OD) : 1.00 (SYS)
120
1.00 (OD) : 1.00 (SYS)
4.00 (OD) : 1.00 (SYS)
110
2.00 (OD) : 1.00 (SYS)
100
1.00 (OD) : 1.00 (SYS)
70
Outdoor Temperature
With a 0° Offset, the
Reset curves begin at
100° Water Temperature.
F, this means the
°
With a -20° Offset, the
Reset curves begin at
80° Water Temperature.
With a +20° Offset, the
Reset curves begin at
120° Water Temperature.
1:4
1:1
offset
Warmer
0˚F
0˚F
Colder
-10˚F
4:1
-10˚F
20˚F
60
50
40
1:4
1:3
1:2
1:1.5
220
210
200
190
180
170
160
150
140
130
120
110
100
50
30
0
-10
70
60
40
20
10
Outdoor Temperature (in °F)
Reset Ratio is Presented as
Outdoor Temp. : Water Temp. Ratio
Reset Ratio Curves
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
7
1:1.25
1:1
1.25:1
1.5:1
2:1
3:1
4:1
-20
1:1
4:1
40
1:1
4:1
40
1:1
4:1
40
Advertisement
Table of Contents
