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Control options with Vitodens 200 WB2B (Vitotronic 200 + Vitotrol 300)
I'm planning to have a WB2B-19 installed, with only one circuit - heating through steel panel radiators.
In terms of heat control, I understand that ODR + constant/permanent recirculation is beneficial and will offer a true 'cruise control' to a hydronic system. On the other hand, I am aware that due to technological constraints, the mod/con boiler cannot 'modulate down' too much (to comply with the reset curves and to consume only the minimum volume of gas necessary to satisfy the ODR model). I gues s for reasons as simple as too weak and un-stable flame.
Thus, an ODR-driven control would suffer of some "wrong impedance matching" problem at relatively warm outdoor temps. And I'm thinking that we could compensate for this "weak point" of ODR by using a room thermostat. Which would serve only the role of "high temp limiter", and with no setback.
The main goal is not to mess with the ODR (Vitotronic 200 + Vitotrol 300) logic at relatively low temps. But to help the system being more efficient (i.e. cut the gas off and the recirc pump completely) when the ODR cannot anticipate properly unusual gains of heat in the house (sun or simply the speed at which the heat leaves the house is much slower).
So, what I would like to to is to have a "bang-bang controller" such as Room Thermostat, which should turn the stuff off when the temp is too high (since the boiler cannot modulate too low, it will attempt to burn at a min rate and which is not optimal for the current demand and such too much gas will be consumed).
I was reading through numerous posts (especially those from Chris), and still I failed to understand how the Vitotrol 300 really works. It does have a temp sensor and we know also that it helps the Vitotronic 200 downstairs to get an internal temp feedback and shift the currently selected heating curve up or down. BUT the main question is: is Vitotrol 300 really capable of telling the boiler to come to complete stop? Does it have also a bang-bang type of control (on/off)?
The other questions would be:
-What is that Plug 143 (pins 2+3) meant for ("external blocking"). Chris is repeatedly explaining that it's not meant to be a TT. I understand that the other pairs of pins (1+2) serves a more complex purpose ("external demand" i.e. snow melting and forcing the boiler to be in "slave" mode and comply to some min water temp, and turn off some pumps, but only of a limited time). What about the "external blocking". Why can't it be used to tell the boiler to "stand by"? Also what kind of thermostat would be compatible with those pins? Is dry contacts expected or it's something that has power inherently?
-The same question about the mysterious Plug 96. Is that a reminiscence from the Vitodens 100 - used for line voltage thermostats from Europe (230V)? In our case 110V? Could that be used as a TT?
-Also, Chris was mentioning that it's possible to impose an upper limit to the modulation rate of the boiler (i.e. when you are oversizing the boiler for certain reasons, i.e. in his case his total heat loss was in the 40KBTU/h range but he wanted to have good DHW heating). In my case, I won't have DHW, only one primary heating circuit, and with a total heat load of 30-35KBTU/h (3.0/3.5gpm max flow rate). Maybe from a fuel cost savings perspective it would be nice to tell the boiler up-front not to goo too high with the gas valve? Is there a "Coding Level 2" setting for that?
-Are there any North-American standard, low-voltage thermostats compatible with Viessmann Vitodens 200 / Vitotronic 200? There are some which can offer also a pair of dry contacts, such as the eco-bee. It would be interesting to be able to drive both the heating (for Viessmann) and A/C (for a standard A/C system from North-America) via the same RT.
My main goal is to try to avoid using the Grundfos Alpha dP pump (which will be the only pump in the system) running when not necessary and also to have the boiler not firing unless the bang-bang 'controller' validates that the rooms do need heat.I wish to save energy overall. It seems a bit strange at first to try to marry an ODR principle with a RT (on a 1st view seems like 2 conflicting interests), or also trying an ODR + electronic TRV (i.e Danfoss Living ECO) scenario.
I appreciate your insights.