1 Service (continued)
ModBus
When BMS is set to ACTIVE (see BMS Active / Inactive) and the boiler is being controlled through ModBus, set ModBus parameter to ACTIVE. Otherwise, set the ModBus parameter to INACTIVE. Note that the boiler can still be monitored by ModBus with this parameter set to INACTIVE. The default value is INACTIVE.
ModBus T/O
The amount of time the unit controls will wait to receive a communication string from the BMS controller before reverting back to its own internal parameters. This parameter is adjustable by the installer by accessing the ModBus T/O parameter. The adjustment range of this parameter is 5 seconds to 2 minutes. The default value is 10 seconds.
Cascade Address
The boiler designated as the Leader needs to be programmed with address 0. All the Member boilers require addresses from 1 to 7, and the addresses must be different for each Member. The addresses can be in any order, regardless of the order in which the units are wired together. This parameter is adjustable by the installer by accessing the Cascade Address parameter. The outdoor air (if used) and system supply sensor must be connected to the Leader boiler. The default address is 1.
If installing the boilers in an existing system, the new boilers should be programmed as the Leader and/or the higher number addresses.
Cascade Type (L/L / EFF)
There are two (2) options for the way a Cascade divides the load between its heaters. The first is Lead/Lag, designated as L/L in the menu. This method is used when it is desired to have the least amount of total flow through the boilers. This method will modulate the last two (2) boilers. This provides for smooth transitions when a boiler turns on or off. When the last boiler reaches 100% and the calculated load is still increasing, it will start the next boiler at 20% and reduce the previous boiler to 80%, thus eliminating the sudden jump in total output of the Cascade. When the calculated load is decreasing and the last boiler gets down to 20% fire, it will hold it there and start lowering the firing rate on the next-to-last boiler. When the next-to-last boiler reaches 20%, it will turn the last boiler off and raise the rate of the next-to-last boiler to 40%, thus eliminating the sudden drop in total output of the Cascade.
The other Cascade divider method is Efficiency Optimization, designated as EFF in the menu. This method is used, as the name implies, when it is desired to have the most efficient system. When the first boiler reaches a certain rate (default = 90%), it lowers its rate to 45% and turns on the next boiler at 45%. The two (2) boilers then modulate at the same rate.
Service Manual
As the calculated load increases further and both boilers ramp up to 90%, it lowers the rate of the first two (2) boilers to 60% and brings the next boiler on at 60%. The three (3) boilers then modulate together. As the calculated load decreases, the boilers will reach a lower threshold (default = 30%), at which time the last boiler (the third in our example) will turn off and the Cascade will increase the rates of the remaining boilers to provide the equivalent total output as before ((3 x 30%) / 2 = 45% in our example).
Maximum Cascade Set Point
This parameter determines the set point used by the individual boilers in a Cascade. When a boiler is commanded to fire by the Leader boiler, it will attempt to achieve this temperature at its outlet. The Leader boiler will limit the modulation of the last boiler to fire in order to hold the temperature at the system supply sensor to the user set point. If any of the boiler outlet temperatures reach the maximum cascade set point, the boiler will then modulate down on its own in order to keep its outlet temperature within the maximum cascade set point. Therefore, this parameter can be used to limit the outlet temperatures of all the boilers in a Cascade. Note that this parameter does not apply when the boiler is heating an indirect DHW tank. This parameter is adjustable by the installer by accessing the Maximum Cascade Set Point parameter. The temperature range of this parameter is 32° (0°C) to 190°F (88°C). The default maximum cascade set point is 185°F (85°C).
Cascade Offset
This parameter determines how much the temperature must go above set point before the lead boiler will turn off. This parameter can be adjusted by the installer by accessing the Cascade Offset parameter. The temperature range of this parameter is 0° to 20°F (11°C) The default value is 10°F (6°C).
Cascade Differential
This parameter determines how much the temperature must go below the turn off temperature (Set point + Offset) before the lead boiler turns on. This parameter can be adjusted by the installer by accessing the Cascade Differential parameter. The temperature range of this parameter is 0°F to 60°F (33°C) The default value is 20°F (11°C).
Minimum On/Off Time
In order to prevent units in a Cascade from short cycling, this parameter defines the minimum ON and OFF time for each unit. The installer can adjust this time by accessing the Minimum On/Off Time parameter. The minimum setting is 0 seconds and the maximum setting is 10 minutes. The default is 30 seconds.
Minimum Next On Time
In order to reduce the risk of temperature overshoot with a Cascade, this parameter defines the minimum time delay from starting one unit until the next unit may be started. The installer can adjust this time delay by accessing the Minimum Next On Time parameter. The minimum setting is 0 minutes and the maximum setting is 10 minutes. The default is 60 seconds.
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