vitodens-200wb2c: flow temperature sensor slow-update leads to overshoot

[mikec]

Hi,

I have a setup for heating-under-floor, solar-panel, DHW. See schematic "Vitodens200_schema_exemplu_6_Cristea.jpg"

Unfortunately, I observed always an overshooting at each start of the heating. In "smarthouse_HeatingUnderFloor2.png" - the values in RED represents the FLOW temperatures at the hydraulic distributors for underfloor-heating (ground and 1st floor). BLUE values represents return-flow temperatures.

You can see that there's about 5minutes "dead-time" due to overshooting. This happens each start. I have a schedule for 5 times within 24hours that start HVAC and stop when the return-flow of the heating-under-floor reaches a certain threshold.

This overshooting mean about 5*5=25minutes loss in energy and time for the entire system.

I tried to adjust the demand temperature (by control of slope 0.2, or level=17K).

I think that the problem might be due to a slow (each minute) reading of T2 (flow-temperature sensor placed in low-loss header) by the automation of vitodens. This leads that controller cannot slow-down at the right moment (only 1 minute later) ... 

I attach a movie that shows how the flow-temperature T2 from schematic (low-loss header) is updated slowly (once a minute).

Attached files available here: https://www.dropbox.com/sh/6ewnexpi8esb214/AAAlsjT7APeMTWOObKAXdG1da?dl=0

Let me know if you have a suggestion on how to fix this issue.

Thanks,

Mike

[Mick_Arnold]

Hello, where are you from?
In my opinion, a heating circuit mixer is missing in the underfloor heating system.

With kind regards °pg

[mikec]

Hi, we're in Romania.
We already have that circuit-mixer using a grundfos-alpha2 pump at each floor. I didn't put in the schematic details of the under-floor heating hydraulics.
The problem I have is that the control-loop goes overshoot too much -> that stops the vitodens. Then it takes a lot of time to come back to the normal temperature. We loose about 5minutes at each start-up. In my opinion, if I make the reading of that T2-sensor every 3 seconds - > the controller will be able to control fine and avoid the high overshoot.
Are you aware of this slow-update of the temperature sensor? Is there a "secret" built-in filter applied on that sensor? Or is a bug in vitodens automation?

Kind regards,
Mihai

[Stefan_Pfleging]

Hello Mihai,

the Boiler is maybe too large or the heat loss on the secondary side of the hydraulic switch is too small.

Please contact the sales office in Romania:
Reprezentantţa Viessmann în România | Viessmann.ro
Viessmann S.R.L.
DN 1, km 174 +941, nr.2
507075 Ghimbav (Braşov)
Phone: 0040 268 407 800
Fax: 0040 268 407 840
E-Mail: info-ro@viessmann.com

With kind regards °pg

[mikec]

thanks for info,
Viessmann Romania already knows the problem with overshooting. And they are quite good specialists (at least in choosing the proper hidraulic parts and setup).
The vitodens boiler can modulate fine the temperature around 45-50degC once it started properly (2nd start). This modulation works for 15min (as it is now, outside temp around 10degC in the night - heating underfloor reaches quickly the setpoint) - or it works for 1hour during hard winter. The heating under-floor would get around 43degC.

Anyone knows how to change the (electronic or software) filter on reading temperature sensor T2 of the low-loss header?

Kind regards,
Mihai