Seeking advice on UFH and weather compensation...

[dodgem]

Hi all,

This is my first post here, I've joined up to ask for advice about a new CH setup...

I don't want to hit you all with a wall of text, so I'll try and keep it short and sweet, although I've spent so long thinking about what I want to achieve that it's hard to get it into a few sentences! :wink5:

Basically, I've fitted UFH downstairs and am keeping 4 radiators upstairs. I've settled on a Vitodens 200 35kW combi boiler with VT200 weather compensator and sub-mounted mixer kit. I want to have to separate weather compensated feeds, one for the UFH and one for the radiators.

Now as I understand it, the boiler doesn't accept 'call for heat' signals when it's using the VT200 controller, so it seems that the Heatmiser system I've bought for the UFH won't work. I think I can get around this by using a low loss header and secondary pump, but it seems daft to be feeding just one circuit (the UFH) off of a LLH. So I was wondering whether I could simply connect the flow and return of the sub-mounted mixer directly to the UFH manifold and do away with the Heatmiser UFH1 controller, the manifold blending valve, the room stats, and the manifold valve actuators. Essentially just have the boiler pump water round the UFH loops continuously at a temperature that varies with outside so as to keep the rooms comfortable. I was also hoping that any differences in heat requirements between rooms (due to varying quality of insulation) could be sorted out by setting the flow rate for each loop at the manifold.

Please let me know your thoughts on this, i'm not sure if I've grasped how it's supposed to work or if I'm actually doing a good impression of a crazy person gibbering to himself!

Thanks in advance

Simon

 

[SimonJohns]

Will you get 60*c water for the ufh to run. When your weather compensation unit is modulating the flow temp down to 40*c?

 

[dodgem]

Will you get 60*c water for the ufh to run. When your weather compensation unit is modulating the flow temp down to 40*c?

No, but if the boiler is providing 40C water then that is because it's not freezing cold outside. I am expecting the flow temps for the UFH to vary between say 50C when it is -4C outside and 21C when it is 21C outside. I do expect it to take some experimentation to get it right though!

 

[SimonJohns]

I Would of thought that a compensated floor would require indifferent temp to a compensated rad

 

[dodgem]

"indifferent temp"? I'm not being funny, but do you mean that the radiators and floor would use the same temp water or different temp water? I'm planning to have two compensated circuits, the one for the rads being about 20C higher than the floor - again, i'll have to experiment.

 

[SimonJohns]

Sorry meant to say different

 

[dodgem]

An update for anyone interested:

I emailed Viessmann technical and asked a few questions. They have said that the circulating pump in the sub mixer will be able to pump the water round my ufh, so I can just connect the output of the mixer to the manifold and let the weather compensation do its thing

The only thing that concerns me is the possibility of accidentally setting the controls in such a way that water that is too hot for the floor gets sent to the manifold. To combat this I thought I would put a 3 port valve just after the flow from the boiler and have it send water to the ufh below say 50C, and straight back to the boiler return above 50C.

Rather than using a motorised 3 port valve with temp sensor etc, is there something like a thermostatic mixer valve that works instead as a diverter? I'd rather have that than adding more complexity...

 

[Gray0689]

You have to have some kind of mixing valve either way!!

 

[dodgem]

With respect, I don't think I do HAVE to have some kind of mixing valve...

What I would like though, is some kind of safety system to prevent excessively hot water reaching the floor.

Here is how I think I would achieve this:

(note that the only pump in the system is the boiler's integral circulation pump, and there is no mixer at the manifold, the water is supplied at the correct temperature by the boiler).



The 'Diverter' would be set to redirect the water straight back to the boiler, bypassing the ufh, if it exceeds a preset temperature. Can I simply use a thermostatic mixer valve plumbed in backwards? Or is there a specific device, and if so what is it called? I have tried looking for thermostatic diverter valves, but all that comes up is shower mixers

Thanks for looking.

Simon