Vitodens 100

Joe Mattiello

EtienneHancock

Vitodens 100 Modulation

How does this boiler decide to modulate. Assuming we're tying into a pump relay, not the 0-10vDC controler.
Is the fan speed regulated by system Delta T?

ALH_4

Modulation

The burner modulates to maintain a temperature setpoint. That works fine for low temperature systems, but isn't ideal if you have emitters that require 160°F+ fluid at design. Outdoor reset is the key to efficiency in higher temperature systems.

EtienneHancock

Thanks Andrew

What is determining what the temperature it maintains? If I simply hook it to a tsat/pump relay I assume it will try to hit the high limit setting on the dial? How does it modulate - Delta T?

This will lead to my next question: If I do hook it to say a Taco PC700, will I then be overshooting temp on the boiler or short cycling?

Joe Mattiello

Taco, put together a great resourse guide, called radiant made easy, available at;



For your reference I attached the outdoor reset document.

Mike T., Swampeast MO

Your second question is fairly simple to answer: The fan speed varies with input (e.g. modulation level). The more fuel is being consumed, the faster the fan will run as more fuel requires more combustion air. The Vitodens 200 is unique in its ability to constantly self-adjust the fan speed based on the conditions in and length of the flue itself. This is in addition to adjusting the fan speed based on the fuel input. I'm not positive but it looks like the Vitodens 100 lacks the ability to adjust the fan based on the flue. (It is after all a relatively inexpensive alternative to the flagship 200 series.)

As to how the Vitodens 100 modulates the flame, I can only give the goal of it (and essentially every other mod-con). A "target" boiler temperature is established and the boiler does its best to modulate the flame to just maintain the target during a call for heat.

The Vitodens 100 REQUIRES some form of external control. If such is merely a wall thermostat, I can only assume that the "target" temperature will be fixed at the "maximum temperature setting" that YOU make inside the boiler itself. Note that this is NOT the same as the "fixed high limit" that prevents the boiler from overheating.

More likely though you will use some form of reset controller to establish the target temperature. In this case the boiler will attempt to modulate to just maintain the temp established by the reset control. Such target is the PRIMARY (e.g. "boiler" temp) and it cannot assumed that secondary temperature will be the same. (This generally isn't a problem, but it's something that bears repeating since the Vitodens 200 with its integrated control will modulate to achieve target in the low-loss header itself.)

Exactly how it modulates to achieve the target temperature is immaterial. Some mod-cons start at high fire and work their way down; others start low and work their way up. If the boiler is firing a minimum input and the primary temperature still exceeds the target by some (presumably fixed) degree, the burner will cycle--just like any other.