LAARS M4-Ext - Installation Manual - Manual (Page 7)

Installation Manual 7
OUTdOOR RESET CONCEPT
The M4-CNC has multiple operating modes that satisfy most hydronic systems. It changes
the System Set Point based on outdoor temperature (Outdoor Reset). The M4-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 M4-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 ° F Water Temp. For example with
a 1.00 (OD):1.00 (SYS) ratio, if the outdoor temperature is 50 ° F, this means the
temperature has fallen 20 ° from the starting point of 70 ° F. Therefore, the heating
water temperature will increase 20 ° to 120 ° F.
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 M4-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 Reset Ratio Offset
Radiators (Steel & Cast Iron) 1.00 (OD) : 1.00 (SYS) 0˚F
Baseboard (Finned copper tube& Cast Iron) 1.00 (OD) : 1.00 (SYS) 0˚F
Radiant (High Mass/Concrete) 4.00 (OD) : 1.00 (SYS) -10˚F
Radiant (Low Mass/Joists) 2.00 (OD) : 1.00 (SYS) -10˚F
Fan Coils & Air Handlers 1.00 (OD) : 1.00 (SYS) 20˚F
Outdoor Temperature
W
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er
T
em
pe
ra
tu
re
70 40 50 60
130
120
110
100
Outdoor Temperature
W
at
er
T
em
pe
ra
tu
re
70 40 50 60
110
100
90
80
Outdoor Temperature
W
at
er
Te
m
pe
ra
tu
re
70 40 50 60
150
140
130
120
1:4
With a 0° Offset, the
Reset curves begin at
100° Water Temperature.
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
1:4 1:1
1:1
1:1
4:1
4:1
4:1
90
100
+20 Offset
-20 Offset
Outdoor Temperature
W
at
er
T
em
pe
ra
tu
re
70 40 50 60
130
120
110
100
1:4 1:1
4:1
Colder
Warmer
Outdoor Temperature (in °F)
70 60 50 40 20 30 0 -10 10 -20
100
120
110
130
140
150
160
180
170
190
200
210
220
1:3 1:2 1:1.5
1:1.25
1:1
1.25:1
1.5:1
2:1
3:1
4:1
W
ater
Temperature (in °F)
Reset Ratio Curves
Reset Ratio is Presented as
Outdoor Temp. : Water Temp. Ratio
1:4
LAARS Modulating Controls M4 & M4-EXT
HT# 059104-00 B