Viessmann 200 with Weather Compensation.

[Willewonte]

Evening,

I've recently had a new boiler (19kW Viessmann 200W)and DHW tank (Vitocell 150) installed, to replace the old boiler. I decided to also go with weather compensation (Vitotronic 200 HO1B controller) and the fully modulating pump.

I'm really pleased with it, keeping the house warm in the recent cold spell, but I have a question that I hope someone might help with.

From what I understand, the temperature in house is 'sensed' by the temperature of the return water (no room sensor, or provision for it), in relation to the outside air temp. I've set 20C, and it achieves that well and evenly. The setback temperature I've set is 16C (during the day in the week, when everyone is out and at night) I don't understand how that works, as the pump also goes off during the setback time.

Anybody deciphered the Viessmann manuals, and perhaps give an explanation? It'd be appreciated.

 

[Agile]

The principle of weather compensation is to measure the temperature OUTDOORS and then use programmed calculations to heat the rads to the required temperature which will give the desired room temperature indoors.

I would be surprised if the pump switches right off. Being a modulating pump are you sure its not just turning slowly?

 

[Willewonte]

Thanks for the clarification, shame they did not go for room influence on top of the weather compensation as well!

I checked the status of the system during the setback periods, and it states that the pump (and burner) is off.

I'm not massively concerned, but I was under the impression that the pump would run constantly during setback, and part of the decision to go for the modulating pump. It's just a case of me wanting the system set up properly and correctly, so that it can perform optimally.

Viessmann UK are 10 miles up the road, but the small exposure I've had to their tech dept (via the installer of the system) has left me hoping that the more experienced viessmann might be able to clarify this for me.

 

[Agile]

The Worcester W/C controller checking inside and outside temps and you can set it to take whatever proportion of the temps you like.

Nevertheless the Viesmann does seem to work well. But of course it does not know if you have left the windows open! The installer should have explained everything to you. I expect he ticked the box to say that he has!

You could always call Viessmann and ask for Hugh and I am sure he will pop round and sort you out!

Tony

 

[Willewonte]

The installer did not get the chance to clarify how the system works, as Viessmann had to come and sort the boiler out as it died half-way through commissioning! It appeared to have been built with a friday-afternoon fan unit, which died, taking out the main pcb. This at 5pm as well. Still, these things happen.

Viessmann sent around an in-house engineer next day who sorted it out, and finished the commissioning.

On the windows front, I've got the wife and kids trained well - close the TRV and then you can open the window

 

[ALEC1]

no its not sensed by the return water, it cant as there is no return sensor on this boiler.

The controller appears to measure the amount of heat going into the house. It uses some sort of averaging of the outside temperature to optimise the flow temp...

It works a dream, but viessmann are not very helpful in explainig how it works in their training to installers..

You could ring the technical help line...they are very helpful...

 

[mysteryman]

They assume that you are not trying to heat the house in winter with the windows open!

All the weather comp needs to know is the actual outside temperature and the desired indoor temperature. Assuming it is set up properly, it then knows what the radiator temperature needs to be to maintain comfort. The pump will be stopped when the outside temperature is equal to or higher than the set indoor temperature. This can easily happen in night setback if that is set low, even in winter. This and many other parameters can be altered to suit particular circumstances.

Energy savings result from accurate matching of heat input to the house with current heat losses, and more so as it automatically keeps the boiler in condensing mode for as much of the heating season as possible.

 

[Agile]

The Worcester unit on the other hand can take into account open windows as it senses inside temps.

This can occur when smokers open windows for example.

Tony

 

[ALEC1]

Only in the room with the sensor Tony..surely...

all theses systems are "world class" the real issue that should concern installers and the public alike are that training about them is scant...


All boiler manufacturers are guilty of "dumbing down" to avoid having to train installers and the public..

The reason is the undemanding low standard of the building regulations when it comes to heating regulations, coupled with a pretty undemanding public... the latter is changing of course a bit, but the regs who knows?

 

[Willewonte]

Energy savings result from accurate matching of heat input to the house with current heat losses, and more so as it automatically keeps the boiler in condensing mode for as much of the heating season as possible.

A nice description of the heating aspect (heat balance) of my day job, although I tend to spec heating systems and controls on a larger scale than my house!

In our old house, I had a Vaillant ecotec 824 installed, but used to manually adjust the flow temp to the rads depending on the season (higher in the winter, lower in the autumn and spring), and tweak this when we had weather extremes. Come May 1st, the heating went off until October at the earliest. Compared to running the ancient Apollo Thorn boiler we had, I ended up saving about 33% in gas consumption.

I'm expecting to achieve similar savings over the coming year with this new system, what with the weather comp, and the modulating pump, being able to dynamically match the outside conditions rather than wait for me to twiddle the knob, as it were.

On the pump stop, I'm using it similar to a BMS pump stop, and have it set for 16C OAT to shut down heating. Have the curve at 1.9 and will be dropping that as soon as I sort out some issues with draughts/heat leaks, caused by the remnants of the original warm air heating system from when the house was originally built.

Still, thanks for everyone's replies, they are appreciated.

 

[Willewonte]

Thanks for the tip on the room sensing.

I've had a good look through the codings in the service manual, and as you say, there are settings for room influence on the weather compensation. It also appears that the control can be set for weather comp with room influence during the day, and room temperature for setback.

I think I need a vitotrol 200 or 300 remote control unit to gain this extra functionality?