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For example, assume the following settings:
Item | Display | Value |
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Setpoint 1 | SP1 | 160 |
Low Temp Differential | HyS1 | |
High Temp Differential | HyS3 | 12 |
Low Temp Setpoint | SPL | 150 |
High Temp Setpoint | SPH | 195 |
The boiler will modulate to try to maintain 160 o F. If the temperature increases to 172 o F which is Set- point 1 (SP1) 160 + High Temp Differential (HyS3) 12, it will shut off. Once it shuts off, it will not re- start until the temperature drops to 155 o F which is Setpoint 1 (SP1) 160 + Low Temp Differential (Hys1)
Alternate Setpoint
The control must be configured for night setback. (See the configuration menu.) When the Alternate Setpoint contact is closed the boiler switches to its alternate setpoint.
The alternate setpoint can be determined by several different values. It can be a fixed alternate setpoint SP2. It can be a fixed differential from SP1 called dsP. dsP will “offset” the main setpoint SP1 by the value of dsP. dsP can be positive or negative.
The Alternate Setpoint can also be determined by an external analog source such as a
Outdoor Air Reset
The control must be configured for outdoor air reset. (See the configuration menu.)
The setpoint of the boiler is controlled by an out- door temperature sensor. As the outdoor tempera- ture falls the setpoint of the boiler is increased.
The boiler modulates to maintain this setpoint. The boiler functions as indicated in internal setpoint; however, SP1 is determined by the outdoor air tem- perature.
The setpoint SP1 is reset using a linear relationship with outdoor air temperature. As the outdoor air temperature drops the setpoint SP1 is increased a proportional amount. This increase is determined by the Heating Slope H. (See Table 1 at the end of this section.) For example if H is set at 1 then for every degree the outdoor air temp drops, the set- point SP1 will increase 1 degree.
This heating curve has a reference temperature of 68°. This reference can be offset using the Parallel shift parameter P. (See Table 1 at the end of this section.) If P is set to 0 the setpoint SP1 will be 68° when the outdoor temp is 68°. If P is set to 10, the setpoint SP1 will be 78° when the outdoor temp is 68°. The minimum setpoint of the boiler is limited by the control. In the above example the actual set- point SP1 of the boiler will not go below 150°.
Analog Input Setpoint
The control must be configured for external set- point. (See the configuration menu.)
The setpoint of the boiler is controlled by an exter- nal signal. The boiler functions as described with the internal setpoint, using the value determined by the external analog signal.
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