CONTROL FUNCTIONS
RESET RATIO
The Reset Ratio setting determines how much the Target Temperature will increase as the outdoor temperature drops. The Reset Ratio is expressed in the following manner:
X:Y | X - change in outdoor temperature |
| Y - change in Target Temperature |
The first number in the ratio refers to the change in outdoor temperature in degrees Fahren- heit below outdoor cutoff while the second refers to the change in the computed Target Temperature in degrees Fahrenheit. A Reset Ratio of 2:1 means that for every 2°F drop in outdoor temperature from 70°F, the Target Temperature will increase 1°F.
For example:
Assume a Reset Ratio setting of 2:1 and a Set Point of 120°F.
When the outdoor temperature drops from 70°F to 20°F, the Target Temperature will in- crease from 120°F to 145°F. (With an outdoor to target ratio of 2:1, a 50°F outdoor tem- perature decrease results in a 25°F Target Temperature increase). See Reset Ratio Chart (pg. 20) for more information.
The Reset Ratio is adjustable from 0.12:1 to 8.0:1.
Recommended Initial Setting for Reset Ratio is 1:1.
Suggested Settings
| Typical | Reset Ratio Setpoint at Design Temp: | |||||
RADIATION | Temp @ | Temp. @ | 40°F | 20°F | 0°F | - 20°F | |
Design Cond. | 70°F | ||||||
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Standing | 190 | 105 | 0.3:1 | 0.6:1 | 0.8:1 | 1.1:1 | |
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Convection or | 200 | 105 | 0.3:1 | 0.5:1 | 0.7:1 | 0.9:1 | |
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Fan Coil - Heating | 190 | 105 | 0.3:1 | 0.6:1 | 0.8:1 | 1.1:1 | |
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Fan Coil - Heat & Cool | 140 | 105 | 0.9:1 | 1.4:1 | 2.0:1 | 2.6:1 | |
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Radiant Floor | 120 | 105 | 2.0:1 | 3.3:1 | 4.7:1 | 6.0:1 | |
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Radiant Ceiling | 120 | 105 | 2.0:1 | 3.3:1 | 4.7:1 | 6.0:1 | |
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The selection of the correct ratio is dependent on the initial temperature Set Point and the desired system water temperature. If the building is too cold, move the ratio knob
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