Weather Compensation on Both Rads and UFH?

[GeorgeWBush]

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.

Does this mean the boiler will struggle if temperature falls below -1C?

Have the radiators been sized to take account of the 20C temperature differential required by the boiler?

No. I take it I just take the size from the catalog 40 Delta t section, no need to oversize?

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..

True, but after the 406 litres in the first 10 minutes it sounded good to me. It's not so impressive now that I understand that it can only be achieved with a 48KW boiler!

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?

We had a lead supply pipe which was measured, can't remember the figures. But, it is being replaced with a 32mm mdpe which is awaiting connection by Thames Water. Plumber has said to me not to worry, flow and pressuure will be good and adequate for a pressurised system.

Thanks for posting

 

[ALEC1]

smile is a possibility but its prohibitively expensive or was when I installed it on an Atag q solar......and not as good as viessmann or vaillants weather compensation system

but you can't use it on a vaillant boiler as the smile uses OT (or something special) and viessman use ebus and vaillant km bus...

acv would be a good cylinder but really you should go with the viessmann as they operate on a pretty well infinite delta T

 

[D_Hailsham]

Does this mean the boiler will struggle if temperature falls below -1C?

No. The Weather Compensation will run the boiler at higher temperatures when the temperature is below -1C, so the rad outputs will increase.
If the temperatures are 75C/55C the rad output will increase by 18% and if they are 80C/60C by 36%, which is sufficient for approx -9C. On the few occasions the boiler is running with a return above 55C it will not be condensing, but the efficiency will still be about 90%.

I take it I just take the size from the catalog 40 Delta t section, no need to oversize?

That's correct. You will see that the outputs on the 40 Delta T page are lower than those on the 50 Delta T, so you just have to select rads which give the required heat from the "40" table and the oversizing is automatically included.

 

[GeorgeWBush]

very definitely... Look at it this way, the flow
One last thing, avoid timber floors for UFH, its a good insulator...

I was going to put down engineered wood flooring which I understand is OK.

 

[ALEC1]

well carpets and wood both higher resistivity than screed, ceramics or stones...it will work at lower temperatures with these materials

e.g. the other day two viessmann systems with weather compensation:

with wood convering 36c, with stone 28c....both at the same outside temperatures

 

[Andygasman2010]

I recently quoted a customer for a job very similar to yours. It was a first for me so I did the research you're doing now. I got some great advice for some of the guys in here, particularly Alec (cheers!)

I too was told by Vaillant tech DO NOT use there controls with UFH as you WILL get problems. I phoned up on three occasions speaking to 3 different guys and got the same response. No where in the VR61 manual does it mention UFH, it only talks about a VT circuit with an electronic mixer valve so one has to assume it means radiators only.

Bottom line is... if you used Vaillant controls to do something they say it can't do, you could end up in a sticky situation.

If you're using manifold pumps/mixers for you underfloor heating then forget it anyway, just use on/off controls.

 

[Andygasman2010]

Alec...

When you've used the VR61 with UFH, rads and WC (electronic mixer) before how have you limited the flow temp in the UFH to 45c? Can it be done with the VRC430?

I assume this is the problem that Vaillant are referring to if used in this way.

 

[ALEC1]

Screen c11 for max flow temp, my ufh was hc2 and towel rails the hc1....

 

[GeorgeWBush]

I recently quoted a customer for a job very similar to yours. It was a first for me so I did the research you're doing now. I got some great advice for some of the guys in here, particularly Alec (cheers!)

I too was told by Vaillant tech DO NOT use there controls with UFH as you WILL get problems. I phoned up on three occasions speaking to 3 different guys and got the same response. No where in the VR61 manual does it mention UFH, it only talks about a VT circuit with an electronic mixer valve so one has to assume it means radiators only.

Bottom line is... if you used Vaillant controls to do something they say it can't do, you could end up in a sticky situation.

If you're using manifold pumps/mixers for you underfloor heating then forget it anyway, just use on/off controls.

OK, so say I forget the WC on the UFH, will the WC work on the radiators if they are set up as 2 zones (One rad zone upstairs and one rad zone downstairs)?

 

[Andygasman2010]

Screen c11 for max flow temp, my ufh was hc2 and towel rails the hc1....

So with the VR61 does the WC in the VRC430 apply to both circuits? Or can this be selected? I mean, you don't want the towel rads to be weather comp'd...?

 

[Andygasman2010]

A Viessmann Vitodens 200-W with weather compensation plus a Sub mounting kit with mixer is perfect for this job. Add in a Vitocell cylinder and you don't need a 2 port valve on the cyl primaries.

The boiler gives the correct flow temp for the rads by burner modulation at variable temperature, and the mixer supplies the lower variable temp for the underfloor. These circuits plus the dhw are all on separate 7 day electronic control [and a second mixed circuit can be controlled as well] with all controls in the boiler. Wireless remote control and off-site remote control are available.

This is all plug-and-play, and if your Installer has been on a [free] training course, he can give you an unlimited five year warranty.

I've not used Viessman before so can't really advise but this does sound good. It doesn't look like Vaillant can do exactly what you want here. Especially seeing as Vaillant themselves say you can't use there controls with UFH!

OP... How are you plumbing in the UFH? Have you got pump/mixer sets for each manifold or are you using electronic mixers? Or... have you not decided yet?

 

[Andygasman2010]

Zone 1 Radiators - upstairs 4 beds, bath and landing
Zone 2 radiators - Downstairs, 1/2 hallway, reception room, shower/wc room
Zone 3 UFH - Kitchen
Zone 4 UFH - 1/2 Hallway and living room
Zone 5 Cylinder (not sure if this is sep zone?)

To use Vaillant you'd have to group zones 1 and 2 together, and group zones 3 and 4 together too.

Use the VR61 with VRC430 and VR81. You'd have to use the WH40 low loss header too.

This would mean going against Vaillants advice not to use there controls with UFH.

 

[ALEC1]

in fact viessman and vaillant have pretty similar approaches, but the technical hlep line at viessmann is light years ahead for this type of install...


I wouldn't bother with the viessmann viocell 200 cylinders they are specifically for the UK, they are not sold in Germany ... i think that a vitocell 300 is the one to go for...but you might as well stick with the ACV

 

[ALEC1]

Why so many zones George?

 

[Andygasman2010]

Alec... If using the VR61 with rads, UFH and hot water would it be best to put any towel heaters on the hot water circuit? I mean you wouldn't want to have them WC'd... I know this would effect cylinder recovery time but not too much surely.