STAGE DELAY
The stage delay is the minimum time delay between the fir- ing of stages. After this delay has expired the control can fire the next stage if it is required. This setting can be adjust- ed manually or set to an automatic setting. When the auto- matic setting is used, the control determines the best stage delay based on the operation of the system.
BOILER MASS
The BOIL MASS setting allows the installer to adjust the control to the thermal mass of the type of heat sources used in the application. The BOIL MASS setting also adjusts the minimum
Lo (1)
The Lo setting is selected if the boiler(s) that is used has a low thermal mass. This means that the boiler(s) has a very small water content and has very little metal in the heat exchanger. A boiler that has a low thermal mass comes up to temperature quite rapidly when fired. This is typical of many copper
Med (2)
The Med setting is selected if the boiler(s) that is used has a medium thermal mass. This means that the boiler(s) either has a large water content and a low metal content or a low water content and a high metal content. This is typical of many modern residential cast iron boilers or steel tube boil- ers. The Med MASS setting stages on additional boilers at a slower rate than the Lo MASS setting.
Hi (3)
The Hi setting is selected if the boiler(s) that is used has a high thermal mass. This means that the boiler(s) has both a large water content and a large metal content. A boiler that has a high thermal mass is relatively slow in coming up to temperature. This is typical of many commercial cast iron and steel tube boilers. The HI MASS setting stages on additional boilers at the slowest rate.
DIFFERENTIAL
An on / off heat source must be operated with a differential to prevent short cycling. With the control, either a fixed or an auto differential may be selected. The boiler differential is divided around the boiler target temperature. The first stage contact closes when the supply water temperature is
½of the differential setting below the boiler target tempera- ture. Additional stages operate if the first stage is unable to bring the supply water temperature up to the boiler target temperature at a reasonable rate. As the supply tempera- ture reaches ½ of the differential above the boiler target temperature, stages are staged off.
Fixed Differential
If the user desires to have a fixed differential, this is set using the BOIL DIFF setting in the ADJUST menu (FIG. 11).
Auto Differential
If the Auto Differential is selected, the control automatically determines the best differential as the load changes. This reduces potential short cycling during light load conditions (FIG. 11).
FIG. 11 |
SECTION C: PUMP OPERATION
SECTION C1: PUMP OPERATION
PRIMARY PUMP OPERATION
The primary pump operates under the following conditions:
•The control receives a boiler demand and is not in warm weather shut down (WWSD).
•The control receives a DHW demand when DHW MODE is set to 3 or 4.
•The control receives a set point demand and set point MODE is set to 3.
Primary Pump Purge
After a demand is removed, the control continues to operate the primary pump for a period of time. The maximum length of time that the primary pump continues to run is adjustable using the Purge setting. The primary pump continues to run until either the purging time has elapsed or the boiler supply temperature drops more than a differential below the boiler minimum setting, see Figure 12.
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