LAARS M4-LHS - Installation Manual - Manual (Page 5)

HT# 059295-00
A
M4-LHS installation and Operation Manual
5
OuTDOOr rESET CONCEPT
The M4-LHS has multiple operating modes that satisfy most hydronic systems. It
changes the System Set Point based on outdoor temperature (Outdoor Reset). The
M4-LHS 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-LHS 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 increases by one
degree. The starting point of the curves is adjustable, but comes factory selected
at 70 ° F Outdoor Temperature and 100 ° F Water Temperature. 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 shall 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° 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 increases by 2°. The M4-LHS 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 improves 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
at
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