Vitodens 200 mixing valve pump control

Mike T., Swampeast MO

Coding 099:001 = "Output signal for domestic hot water production active (ON))" Unfortunately I can't find anything else in the manuals and the schematics don't identify the connection. Viessmann can certainly help. I've been told "everything's in the manuals" but sometimes they're very hard to find...

Connections X13.19 and X13.20 provide 20VDC to the DHW diverting solenoid and there shouldn't be any problem adding a small relay coil to the circuit even though I'd still verify with Viessmann. Obviously, the diverter will only function during DHW production.

Given the way the Vitodens 200 produces DHW (by engaging a diverter solenoid for a different path through a different pair of pipes) I don't see any way to get away from DHW priority and don't recall anything mentioned in the manuals.

As to engaging the circulator on a call for heat, just use your thermostat wiring (Rh & ground) to power a relay coil.

Use the DHW production relay to interrupt Rh <I>before</I> the relay coil used to operate the circulator.

The circuitry in the Unico will keep the fan from running until the coil heats as well as the post purge.

Why do you want the circulator to operate in "fan" mode?

Tom Hopkins

constant circulation?

I'm in the midst of installing the mixing valve kit on a vitodens 200. The design is for that pump after the mixing valve to be constant circulation. The pump is hooked up to the mixing valve controller. Will this provide constant circulation? Should I be connecting the pump directly to power (through a switch) to ensure that? I couldn't find documentation that discusses how the pump works when connected to the mixing valve control.

Justme_8

Constant Circulation

You will get constant circ. as long as you are not in warm weather shut-down

Tom Hopkins

Thanks!

Could I be so bold as to have someone double-check my "coding"?

000:003 One heating circuit with mixing valve, system with domestic hot water heating.

011:001 External call for heat or external switching of heating program active at X4.1 – X4.2

014:001 Party button effective for heating circuit A and heating circuit B

027:001 External call for heat (for FHA circuit)

042:075 Boiler water temperature in heating mode: 75 (167) (is this only effective on external call for heat and weather responsive otherwise?)

0A7:070 Anti-legionnaire temperature 70 (158) (I have a thermostatic mixing valve to prevent scalding, set to 120. Any opinions on the value of this?)

0B8:002 Optimum DHW heating with anti-legionnaire function

0C5:010 Heating circuit pump on, mixing valve pump normal, mixing valve normal, dhw normal

0D5:001 Large display format

0D5:001 Temperature displayed in farenheit

Heating circuit B (mixing valve) Slope = 0.9, Shift = 0 (staple up, thermofin/thinfin, 3/4 strip oak over 3/4 subfloor.

Anything I'm missing?

Thanks in advance.

Paul Pollets

Mixing valve theory with Vitodens

you only need the mixing valve if you're using heating circuit "A" for a med to high temp application. If your radiant circuit is the only circuit connected to the LLH, circuit "A" may be used for the radiant low temp application. It will modulate with the LLH and the pump is on constant circulation by adding the expansion board to the pump control module (with the pump wired to the expansion board). It costs far less than adding the mixing valve and motor actuator. When 2 temps are required, so is the mixing valve.

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Mike T., Swampeast MO

Coding [seems] OK, but of course I can't see the system...

Am I correct to assume that "Heating Circuit A" is connected to a hydro-air unit(s) and you're using X4.1-X4.2 for connecting and on-off thermostat (or on-off controller if multiple hydro air units)?

If yes:

1) Be aware that's a form of subterfuge around the Comfortrol and the hydro-air will not be weather-responsive (e.g. no form of reset). With the external demand active, the boiler will fire to the temperature at address 0A2. Default value of 0A2 is 75C (167F). While I'm not positive, I believe this value trumps the one at 042 which establishes the max temp of "heating mode" which I interpret as "weather-responsive" operation.

Again, the boiler will attempt to fire to the 0A2 value whenever the external demand is active. I say attempt, because if the air handler(s) and the underfloor circuit (remember--it's still active and due to a lower supply temp will have effective "priority") are able to liberate full boiler output at less than this temp, the supply will never rise higher.

Similarly, if the air handler(s) and underfloor circuit cannot liberate full boiler output at maximum temp, the burner will still modulate down to maintain the maximum temp. This situation can occur when you don't believe it should. How? If you're moving a lot (say much more than 130%) of the maximum boiler flow through the air handlers, the excess water short-circuits back to the supply in the low-loss header. Return temp to the boiler will rise (at least though you do have the underfloor to help keep it down somewhat). Since return water is now cooling the supply water in the low-loss header, the boiler has to maintain a higher internal temperature to maintain the desired temp in the LLH. While I [believe] the Vitodens 200 can operate at up to 180F internal temperature in such a situation, you can wind up internal temp maxed and the LLH temp below the desired fixed temp and the air handlers may not be properly supplied (especially during any setback recovery). It will look like a "not enough flow" problem to the air handlers, when the exact opposite is true. If you at all suspect this might happen, I would highly suggest installing a good metering valve in each air handler circuit. With proper adjustment you'll be able to hit the sweet spot where flow (and temperature) on both sides of the low-loss header are in reasonable agreement.

2) You do not mention the curve setting for Heating Circuit A. Even though you're using Heating Circuit A as a fixed temp circuit, it will still be active when there is no external demand for heat. Since the Comfortrol assumes that the mixing valve circuit operates at a lower (or technically equal) temperature, the curve for Circuit A should in your case be identical to Circuit B. At least this will allow the most efficient operation whenever the air handler(s) are not calling for heat.

3) While I don't know the design load or heat losses, a slope of 0.9 with 0 shift sounds a bit low for Thermofin Thinfin under 1 1/2" of wood. While only time will tell, I suspect that a lower ratio with positive shift (perhaps fairly high) will be required. Just don't forget to change the heating curve of Circuit A to match!

Tom Hopkins

> Coding [seems] OK, but of course I can't see the

> system...

>

> Am I correct to assume that "Heating

> Circuit A" is connected to a hydro-air unit(s)

> and you're using X4.1-X4.2 for connecting and

> on-off thermostat (or on-off controller if

> multiple hydro air units)?

>


Yes. Only one hydro-air unit - a Unico - controlled by an upstairs thermostat near the bedrooms.

> If yes:

>

> 1) Be

> aware that's a form of subterfuge around the

> Comfortrol and the hydro-air will not be

> weather-responsive (e.g. no form of reset). With

> the external demand active, the boiler will fire

> to the temperature at address 0A2. Default value

> of 0A2 is 75C (167F). While I'm not positive, I

> believe this value trumps the one at 042 which

> establishes the max temp of "heating mode" which

> I interpret as "weather-responsive"

> operation.

>


I don't expect the FHA to be weather responsive. The FHA was an in-between measure between the time of the crummy baseboard installation and the improved radiant installation. I will only have radiant on the first floor, and in the second floor baths. However, the FHA remains so far, and it remains to be seen how much it is used. If we need it too much to heat the bedrooms in the morning, I plan to install a European wall-mounted rad in each bedroom.

> Again, the boiler will attempt to

> fire to the 0A2 value whenever the external

> demand is active. I say attempt, because if the

> air handler(s) and the underfloor circuit

> (remember--it's still active and due to a lower

> supply temp will have effective "priority") are

> able to liberate full boiler output at less than

> this temp, the supply will never rise

> higher.

>

I'm not sure I understand this part. I was thinking that OA2 was going to be it, and the mixing valve would compensate (if not close entirely) to keep the underfloor circuit to the desired weather responsive temperature. The FHA will have no problem "liberating" the high temp... I usually see a delta of about 40 degrees on a cold day on that circuit.

> Similarly, if the air handler(s) and

> underfloor circuit cannot liberate full boiler

> output at maximum temp, the burner will still

> modulate down to maintain the maximum temp. This

> situation can occur when you don't believe it

> should. How? If you're moving a lot (say much

> more than 130%) of the maximum _I_boiler_/I_ flow

> through the air handlers, the excess water

> short-circuits back to the supply in the low-loss

> header. Return temp to the boiler will rise (at

> least though you do have the underfloor to help

> keep it down somewhat). Since return water is

> now cooling the supply water in the low-loss

> header, the boiler has to maintain a higher

> _I_internal_/I_ temperature to maintain the

> desired temp in the LLH. While I [believe] the

> Vitodens 200 can operate at up to 180F

> _I_internal_/I_ temperature in such a situation,

> you can wind up internal temp maxed and the LLH

> temp below the desired fixed temp and the air

> handlers may not be properly supplied (especially

> during any setback recovery). It will look like

> a "not enough flow" problem to the air handlers,

> when the exact opposite is true. If you at all

> suspect this might happen, I would highly suggest

> installing a good metering valve in each air

> handler circuit. With proper adjustment you'll

> be able to hit the sweet spot where flow (and

> temperature) on both sides of the low-loss header

> are in reasonable agreement.

>


I've been told I'm currently undersized to the air handler (a unico) at 1/2"... I was going to increase this to 3/4" to a manifold in the attic, and to feed the bedroom rads if needed (I have a feeling this will be the case).

> 2) You do not

> mention the curve setting for Heating Circuit A.

> Even though you're using Heating Circuit A as a

> fixed temp circuit, it will still be active when

> there is no external demand for heat. Since the

> Comfortrol assumes that the mixing valve circuit

> operates at a lower (or technically equal)

> temperature, the curve for Circuit A should in

> your case be identical to Circuit B. At least

> this will allow the most efficient operation

> whenever the air handler(s) are _I_not_/I_

> calling for heat.

>


Hmmm. This is a good point. I was planning a steeper curve to have a higher max temp on the FHA circuit. I had a few thoughts related to this. If there is no call for heat on the FHA, the vitodens will modulate down. I also thought I could put the FHA circuit on a setback for all except the morning hours. If the curve is identical, won't this limit the high-temp of the FHA to about 125 degrees?

> 3) While I don't know the

> design load or heat losses, a slope of 0.9 with 0

> shift sounds a bit low for Thermofin Thinfin

> under 1 1/2" of wood. While only time will tell,

> I suspect that a lower ratio with positive shift

> (perhaps fairly high) will be required. Just

> don't forget to change the heating curve of

> Circuit A to match!




Thanks! Your detailed reply is very much appreciated.

Mike T., Swampeast MO

I'm not sure I understand this part. I was thinking that OA2 was going to be it, and the mixing valve would compensate (if not close entirely) to keep the underfloor circuit to the desired weather responsive temperature. The FHA will have no problem "liberating" the high temp... I usually see a delta of about 40 degrees on a cold day on that circuit.

Yes, during the external call for heat the boiler will attempt to fire to maintain the temp at 0A2 in the low-loss header. Your 0C5:010 setting will keep the mixing valve active with weather-responsive control for Circuit B. What I was saying is that if the sum output of the emitters exceeds the maximum boiler output that supply temperature may not the fixed maximum.

Hmmm. This is a good point. I was planning a steeper curve to have a higher max temp on the FHA circuit. I had a few thoughts related to this. If there is no call for heat on the FHA, the vitodens will modulate down. I also thought I could put the FHA circuit on a setback for all except the morning hours. If the curve is identical, won't this limit the high-temp of the FHA to about 125 degrees?

Once you apply the external demand, the boiler will fire to the 0A2 temp (as closely as possible) while retaining weather-responsive operation in the mixing valve circuit. Without the external demand, the boiler will fire to maintain Heating Circuit A. The mixing valve circuit is a slave to Circuit A, so the Circuit A curve must be at least as high as Circuit B. Since you're using the external demand, Circuit A will be under its control--NOT the Circuit A heating curve.

In your case where you only plan on infrequent use of the air handler, I believe this is actually a good use of the External Call. Why? Because if you wanted to use the air handler in a weather-responsive manner, the curve would certainly be higher than for the underfloor and the boiler would constantly have to operate at the higher temperature curve--regardless of whether or not the air handler is calling for heat. The way you plan however allows the boiler to operate at the minimum possible temperature whenever the air handler is not calling.

1/2" is awfully small for any air handler, BUT the present 40F delta-t sounds good. As long as the present supply temp is very near that of the Vitodens during an external call and you're not trying to move an insane amount through the 1/2" piping, all might be well...

Don't forget that the Vitodens 200 uses full DHW priority so if the indirect has to be refreshed when you're "recovering" via the air handler, the DHW will win and the air handler will blow cold air unless it has control to shut down the fan when supply temp drops too low.

Tom Hopkins

Thanks again... I think I'm heading in the right direction now. I just need to make sure I program everything as planned.

With respect to blowing cold air, I'm planning on adding a relay (already bought and tried it out... 3.50 + shipping :-) on #30 to lock out the fan when the DHW solenoid is enabled. I had to pick up an extra SR501, and the unused SR504 will probably land on e-bay. It would be nice if there was something built-in to provide that... One of the codes seems to imply you can get an external signal, but I couldn't find anything else about it. My electrical plan is attached.

In reviewing the vitodens manual yet again last night, it did seem that I could give the FHA heating circuit priority over the DHW, but I think I prefer my approach.

Tom Hopkins

Tom Hopkins

Thanks so much for your reply. I think I'm on the right track.

WRT blowing cold air :-) I'm planning to add a relay to #30 so I know when the vitodens is making hot water. I've already tested the relay, and know it will both work and not interfere with the operation of the solenoid. Attached is my control diagram. I've got most of it working, except cutting off the fan when making hot water, and enabling the HCA pump on a call for fan (as well as call for heat). We don't want no cold air.

I recall seeing something in the coding section of the manual that indicated it was possible to get a signal indicating when DHW was being made, but I couldn't find anything else. I also saw something that indicated I could have given heating priority, so it wouldn't make hot water while there was a call for heat, but I'd rather not run out of hot water.

Sometimes I feel like this is overkill, but comfort is important to us.

Tom Hopkins

I'll have to look again to see what it is I thought I found about heating priority. I'll get back to you on that.

As far as engaging the circulator, I have the expansion board, so I figured that would do the job of running the circulator during the call for heat, and add freeze protection (since the unico is in an unheated, not well insulated, attic space).

Why operate the circulator in fan mode? We will occasionally run the fan in the winter, when there isn't a call for heat, to simply filter the air. We have UV and an additional filter on the unico. I'd like to find a thermostat that will run a fan cycle (know of any?) without heat or cool, in addition to the traditional 4 cycles per day. Anyway, the purpose of running the circulator is to keep the hydronics at least at the weather responsive temperature offered to the radiant, following the "We will blow no cold air in winter" directive :-)

Tom Hopkins

Here it is: 003:000 DHW Tank Without priority switching over heating circuit pump(s). No idea if it means what I thought it meant.

Justme_9

Coding

What size of Vitodens 200 are we dealing with?

042:075 Boiler water temperature in heating mode: 75 (167) (is this only effective on external call for heat and weather responsive otherwise?) **only for weather responsive**

0C5:010 Heating circuit pump on, mixing valve pump normal, mixing valve normal, dhw normal **this is fine DHW tank will be recieving boiler water temp as per coding address 0A2**

003:000 this address will allow the DHW pump and HTG circuit pump to run at the same time. "no priority". The disadvantage of this, is that if the HTG circ. set-point is lower than DHW setpoint you can suck heat from the DHW tank.
**
099:000 dhw re-circ pump operates as per recirc schedule
099:001 dhw re-circ pump operates whenever there is a call for DHW
0A2:075 during external call for heat boiler will produce this water temp.
**

External call for heat takes priority over everything!!!