Weather Compensation on Both Rads and UFH?

[Agile]

OOPS, i meant of course 1132 litres/hour, not per minute!

We always talk about litres per minute. That comes to 19 li/min.

That would need 48 kW of boiler power to provide it concurrently.

Of course the whole point of a domestic stored system is that its heated "off peak" and not just as its being used.

Tony

 

[ALEC1]

very definitely... Look at it this way, the flow temperature ramps up with weather compensation before the heat leaves the building...

in any event you can't/ shouldn't use manual mixing valves with variable temperature circuits...

Tony is right about boiler sizing, the issue is at the lower end...but vaillant and viessman controls both cope well with the low end, so its not really an issue at all..

I would however make sure you buy a twin coil cylinder and plumb them in series...cylinder manufactures are notoriously stingy when it comes to coil size..

Tony the programming looks after the difference in heat loss... one house 1 terraced house I installed the kit on has a heat curve for the screed floor of 0.4 and the house 1.8....

One last thing, avoid timber floors for UFH, its a good insulator...

 

[Onetap]

My questions is,[/b] Can this all be setup with the Vaillant weather compensation control? i.e. Can the weather compensation be used to control both the radiators and the ufh?

Yes, I think so, but I haven't installed one so you'd need to confirm that with Vaillant before committing money. I believe you'd need the VR61 and VRC430. The system would need two different flow temperatures for the UFH and radiators and so two separate weather compensation curves. I think these are HC1 and HC2 mentioned in the VR61 installation manual.

http://www.vaillant.co.uk/stepone2/data/downloads/4c/43/00/vr-61-installation-guide.pdf

The boiler obviously supplies the radiators directly, which should require the higher flow temperature. The radiators' flow temperature is controlled by modulating the boiler flow temperature, set by the HC1 parameters. When there is a HWS demand from the cylinder, the radiators stop whilst the boiler runs at the higher temperature required. This won't work if you have a big HW demand (B&B or similar), with long demands from the cylinder.

The UFH runs at a lower temperature achieved by a 3-port mixing valve and secondary pump, set by the HC2 parameters.

Check that with Vaillant, confirm which of the 4 hydraulic diagrams is applicable and ask for details of recommended installers in your area.

 

[GeorgeWBush]

With six adults I strongly recommend a 300 li cylinder! I also think that you are misinterpreting the cylinder figures.

Could you expand on this a little please...? I mean, with regards to the performance figures, how should they be read? 406 Litres in the first 10 minutes and a continuous flow of 1132 lit/hour - Is this not a true capability in reality? Is this not better than a 300 litre store that takes appx half an hour to reheat?
Thanks.

 

[Agile]

You can only get out what you put into a cylinder.

To get anywhere like those figures you would need the appropriate boiler power ( of 48 kW ).

Thats not sensible or practical either.

The cylinder makers often are a little naughty and sometimes quote reheat times for an elevated boiler flow temperature rather than the 70 C at which the boiler operates efficiently.

The also sometimes just quote the MAXIMUM heat input that it would adsorb when the contents are cold. That falls as it warms up.

Tony

 

[GeorgeWBush]

My questions is,[/b] Can this all be setup with the Vaillant weather compensation control? i.e. Can the weather compensation be used to control both the radiators and the ufh?

Yes, I think so, but I haven't installed one so you'd need to confirm that with Vaillant before committing money. I believe you'd need the VR61 and VRC430. The system would need two different flow temperatures for the UFH and radiators and so two separate weather compensation curves. I think these are HC1 and HC2 mentioned in the VR61 installation manual.

http://www.vaillant.co.uk/stepone2/data/downloads/4c/43/00/vr-61-installation-guide.pdf

The boiler obviously supplies the radiators directly, which should require the higher flow temperature. The radiators' flow temperature is controlled by modulating the boiler flow temperature, set by the HC1 parameters. When there is a HWS demand from the cylinder, the radiators stop whilst the boiler runs at the higher temperature required. This won't work if you have a big HW demand (B&B or similar), with long demands from the cylinder.

The UFH runs at a lower temperature achieved by a 3-port mixing valve and secondary pump, set by the HC2 parameters.

Check that with Vaillant, confirm which of the 4 hydraulic diagrams is applicable and ask for details of recommended installers in your area.

Thank you very much for your post.

Just phoned up Vaillant tech support asking if WC can be set up with rads and UFH and the response was their WC will not work wih UFH because UFH can not be linked to the ebus. "So your WC will only work with radiators?" Response was yes.

That can't be right can it!?

 

[ALEC1]

now you see what installers are up against..

I have installed UFH with the vr61 and it does work...very satisfactorily...

I have to say though thats why I use Viessmann though...there technical lines are fully competent and au fait with their technology

 

[GeorgeWBush]

You can only get out what you put into a cylinder.

To get anywhere like those figures you would need the appropriate boiler power ( of 48 kW ).

Thats not sensible or practical either.

The cylinder makers often are a little naughty and sometimes quote reheat times for an elevated boiler flow temperature rather than the 70 C at which the boiler operates efficiently.

The also sometimes just quote the MAXIMUM heat input that it would adsorb when the contents are cold. That falls as it warms up.

Tony

That is naughty I agree! So if the ACV does not perform as detailed on their website in reality (unless you get a monster boiler to power it), theres really no benefit in going for one over a more conventional unvented cylinder (like the OSO Super S)?

 

[ALEC1]

go for a twin coil and plumb the two in series!

 

[GeorgeWBush]

go for a twin coil and plumb the two in series!

Something like this?
http://www.plumbingsupplyservices.co.uk/acatalog/Oso_Solarcyl_Twin_Coil_Cylinders.html
Is there a particular cylinder you would recommend?

Just to make sure I understand, twin coil cylinders are designed to be heated by a boiler plus solar, but you are suggestting connecting the 2 coils together so they can both be heated by the boiler, correct?

Is this something your average plumber can easily do i.e. connect the 2 coils together to act as one?

 

[Onetap]

That can't be right can it!?

I wouldn't have thought so, but I wouldn't spend any time in trying to decypher what they're saying. I've got a Vaillant and VRC 430 and I'm fairly certain that it could do as you described. The Vaillant e-bus protocol is inflexible and inappropriate for anything other than the plug-&-play applications in the Vaillant manuals.

Ask Viessmann similar questions and see where you get.

 

[Agile]

That is naughty I agree! So if the ACV does not perform as detailed on their website in reality (unless you get a monster boiler to power it), theres really no benefit in going for one over a more conventional unvented cylinder (like the OSO Super S)?

It is assumed that anyone looking at the specs is either a professional and will ( should ) see exactly what is being said. In reality the technical abilities of the average plumber are pretty dire and few would be able to understand them. Thats what will happen when you can become a plumber with three GCSEs ( or less ).

A high recovery cylinder with a powerful boiler would be used at a football club where 24 players want to use six showers in quick succession for example.

Almost all cylinders will be able to absorb most of the output from a 24 kW boiler most of the time at 70 C flow.

Rads under WC control are supplied with a flow of 30-75 C directly from the boiler. UFH needs 25-45 and so to be controlled for UFH needs as seperate adjustable temperature control instead of the simple thermostatic blending valve normally used for fixed temperature operation.

I think that Vaillant do supply the appropriate kit but this is a rather specialist area and it does not surprise me that their tech help may give you the wrong answer.

Most like Alex who only do WC installations stick to the Viessmann as their kit is designed with WC in mind as its required in their native Germany.

Vaillant oddly do not promote their WC very heavily in the UK and not all their products are marketed or supported here. We dont know why!

Tony

 

[ALEC1]

Sorry Tony UFH with weather comp and in screed supplies water down to about 25c....thats why you need the electronic mixing valve.

OP Yes plumb the two in series....

 

[D_Hailsham]

I've ran the program linked to above (thanks D_Hailsham!) and it has advised I need 23.44 KW. It's a lot lower than what I has previously been advised, is this a good approximation?

Yes. Presumably the figure includes 2kW for Domestic Hot Water allowance. This isn't strictly necessary if you have weather compensation as DHW will always be be given priority, i.e the CH will stop while the HW tank is reheated. This has to be done as the boiler temperature needs to be at max for HW heating but may be much lower for CH requirements.

However there's no harm installing, say, a 24kW boiler as it will heat the cylinder faster and provide for colder winter temperatures. The Ecotec 624 has a modulation range from 8.7 to 24KW, which means it be modulating for external temperatures between -1C and 13C, which is very good.

Have the radiators been sized to take account of the 20C temperature differential required by the boiler? Assuming the system is designed for a maximum flow temp of 70C and return of 50C (mean 60C) and a room temperature of 20C, giving a differential of 40C, you should use the page headed 40Δt of the Stelrad Elite Catalogue to select the correct size radiators.

The ACV has some very impressive performance figures hence my picking it - 406 litres at 40C in the first 10 minutes, continuous flow at 40C of 1132litres/min(hr?).

The hot water flow rate cannot be any faster than the incoming cold water flow rate! 1132 litres/hr = 18.32 l/min, which is nothing spectacular.

Don't forget that, if you have an unvented HW cylinder, fed directly from the mains, all hot and cold water is supplied from the incoming mains, so using the washing machine may have an effect on the flow rate from the bath tap or the shower. It will all depend on the water pressure and the incoming cold water flow rate. Have these been measured?

 

[Norcon]

ALEC wrote

...but wrong to choose honeywell controls as the honeywell controls that allow weather compensation are not available in the UK

Honeywell Smile. Climate center.