6|HEAT-TIMER CORP. 059063–00 REV. C
03 UNDERSTANDING OPERATION CONCEPT
The SQ-Elite-8T has multiple operating modes that satisfy most hydronic systems. In
heating when the Outdoor Reset is selected, it can change the System Set Point based
on outdoor temperature. Or, it can be set to Set Point and sequence stages to achieve
a manually adjusted Set Point in either heating or cooling.
In Outdoor Reset, the SQ-Elite-8T controls a hot water heating system to provide a
building with comfortable and even heat levels. The SQ-Elite varies the Target temperature
of the circulating heating water in response to changes in the outdoor temperature.
The SQ-Elite-8T also controls the system circulating pump with an adjustable Outdoor
Cutoff. In heating, when the outdoor temperature is above the Outdoor Cutoff, the
System Pump will be off and no heating water is circulated through the system. When
the outdoor temperature drops below the Outdoor Cutoff, the system pump relay is
energized and the heating water starts to circulate through the system. The temperature
of the heating water is controlled by the Reset Ratio parameters or the Set Point. In
cooling applications, the SQ-Elite-8T turns off the cooling units and System Pump when
the outdoor temperature rises above the Outdoor Cutoff setting.
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 curves 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 SQ-Elite 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
Water Temperature
70 60 50 40
Outdoor Temperature
130
120
110
100
Water Temperature
70 60 50 40
Outdoor Temperature
110
100
90
80
Water Temperature
70 60 50 40
Outdoor Temperature
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
Water Temperature
70 405060
130
120
110
100
1:4 1:1
4:1
Colder
Warmer
70 60 50 40 30 20 10 0 -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
Water Temperature (in °F)
Outdoor Temperature (in °F)
Reset Ratio is Presented as
Outdoor Temp. : Water Temp. Ratio
Reset Ratio Curves
1:4
Water Temperature
70 60 50 40
Outdoor Temperature
130
120
110
100
Water Temperature
70 60 50 40
Outdoor Temperature
110
100
90
80
Water Temperature
70 60 50 40
Outdoor Temperature
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
Water Temperature
70 405060
130
120
110
100
1:4 1:1
4:1
Colder
Warmer
70 60 50 40 30 20 10 0 -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
Water Temperature (in °F)
Outdoor Temperature (in °F)
Reset Ratio is Presented as
Outdoor Temp. : Water Temp. Ratio
Reset Ratio Curves
1:4
WARNING
When controlling a non condensing
boiler, the Minimum Target
temperature must be set to the
boiler manufacturer specifications. In
that case, system temperature must
not go below such temperature.
