Reset Ratio; Custom Reset Ratio; Offset - heat-timer DIGI-SPAN Elite MC Series Installation And Operation Manual

reset ratio

(Available when Control Mode = Outdoor Reset)
Options: From 1(8.00º/1.00º) to 12(1.00º/4.00º), Custom
/<Out. Reset>/Reset Ratio
SET
• The Reset Ratio changes the Target temperature based on the outdoor temperature.
The colder it gets outside, the hotter the Target will be. The Ratio is measured as;
Outdoor (O): System Water (S). See "Reset Ratio Concept" on page 4.
• With a 1.00:4.00 ratio, the System water temperature will increase rapidly as the
outside temperature falls hitting the maximum default water temperature of 240°F at
35°F outdoor temperature. With a 4.00:1.00 ratio, the System water temperature will
increase slowly as the outside temperature falls.
• The Reset Ratio controls the amount of heat entering the heating system based
on the outdoor temperature. A higher numbered Reset Ratio will result in a higher
Calculated water temperature. If the application has radiant heat, a lower numbered
Reset Ratio curve should be selected. See "Radiation Type Settings" on page 4.
• If required: Adjust the Reset Ratio in cold weather. If the ambient building
temperatures is too cold in cold weather, move the ratio to a higher selection. That
is, if 1.00:1.00 was initially selected, change the selection to 1.00:1.25. If the
building temperature is too warm in cold weather, move the ratio to a lower selection.
That is, if 1.00:1.00 was initially selected, change the selection to 1.25:1.00.
• The Custom option gives the user the capability of creating a specialized Reset Ratio
curve. The Offset, Minimum Target and Maximum Target settings will still apply to
the customized curve.

Custom reset ratio

Options: SYS Temp 1, 2 (-10ºF/21ºC) to (210ºF/99ºC)
Options: OD Temp 1, 2 (-10ºF/-23ºC) to (100ºF/38ºC)
SET /<Out. Reset>/Reset Ratio/Custom
• Use the Custom option when the standard reset ratios do not provide the perfect
building heat-loss equilibrium.
• The Custom Reset Ratio requires the assignment of two points on the reset ratio
diagram and use the line connecting the two points as the customized reset ratio
curve. Each of the two points will need a specific System and Outdoor Temperature
to identify it on the diagram. To Specify the first point, set Sys Temp 1 and OD Temp
1. Then, set Sys Temp 2 and OD Temp 2 to set the second point on the curve.
• The chart shows a customized curve 6(O):5(S). If the outdoor temperature reaches
30ºF, the system target will be 145ºF.
• Remember that the Min Target and Max Target apply to all reset ratios including the
custom reset ratio ones.

Offset

(Available when Startup Control Mode = Outdoor Reset)
Options: From -40ºF/-22ºC to +40ºF/+22ºC
SET /<Out. Reset>/Offset
• The Offset setting adds or subtracts a fixed number of degree to the Target. For
example, if the Set Point temperature was 130°F and the Offset was changed from
0° to +10°, then the Set Point temperature would increase to 140°F.
• If required: Adjust the Water Offset in mild weather.
• If the ambient building temperature is too warm in the mild weather, decrease the
Offset. If the ambient building temperature is too cold in the mild weather, increase
the Offset. The rule of thumb for baseboard radiation is to change the Offset 4°F for
every 1°F you wish to change the building temperature. In radiant heat applications,
change the Offset 1°F or 2°F for every 1°F you wish to change the building
temperature. See "Radiation Type Settings" on page 4.
14
Default: 7(1.00º/1.00º)
Default: 1(100ºF/38ºC)
Default: 2(171ºF/77ºC)
Default: 1(70ºF/21ºC)
Default: 2(0ºF/-18ºC)
Default: 0ºF/0ºC
MC-Elite Installation and Operation Manual
Reset Ratio O/S:
Custom
1(8.00 / 1.00)
2(4.00 / 1.00)
3(3.00 / 1.00)
4(2.00 / 1.00)
5(1.50 / 1.00)
6(1.25 / 1.00)
7(1.00 / 1.00)
8(1.00 / 1.25)
9(1.00 / 1.50)
10(1.00 / 2.00)
11(1.00 / 3.00)
12(1.00 / 4.00)
Set SYS Temp 1:
100 F
At OD Temp 1:
70 F
Point1: System=120°F Point2: System=170°F
Oudoor=60°F Oudoor=0°F
Max Target
180
170
160
150
140
130
Point1
120 Min Target
110
100
70 60 50 40 30 20 10 0
Outdoor Temperature (in °F)
Custom Reset Ratio
Offset:
+0 F
Offset=10°F Min Target=120°F
Reset Ratio=1.5 : 1.0 Max Target=170°F
180
170
Max Target
160
150
140
130
Min Target
120
110
100
70 60 50 40 30 20 10 0 -10
Outdoor Temperature (in °F)
Target Offset
Point2
-10 -20
-20