Weather Comp+ UFH

[Chablais]

Trying to get my head around what I need to install UFH and four towel radiators and three small aluminium panel radiators. Been in touch with Wunda, asked about Wilo pumps and they said no longer supply, asked about a lower temp range blending valve and they said 35 is the min. So I started looking around at other suppliers. Came across Emmetti, and they do a mixed rail manifold M3V that has a hot side for rads and a cool side for UFH. Or is this just overcomplicating matters.

 

Has anyone used their weather comp controls? They have a modulating blending valve connected to their weather comp, as I am feeding all the heating from a buffer tank, I presume I cannot weather comp the boiler, as it only gets a call for heat from the buffer stat, or the DHW stat in the main tank.

My UFH is sitting in 55mm Cemfloor screed, sat on top of a concrete beam and block floor, with 300mm sprayed insulation on the underside, so it will be slow to respond. I was originally looking at Heatmiser Neo stats and multiple zones, but now thinking that due to the slow response, that the whole ground floor, circa 100m2 will eventually even out temp wise, and may be better controlled via weather comp and the modulating mixer valve. Has anyone any real life experience of this set up?

 

It's a big learning curve for us, our project has gone from an estimate of six months to over 18 months in now, and we are keen to get the floor screeds in and heating going before winter.

 

thanks

 

Andy

[Nickfromwales]

The FMU3 is ample tbh. The combination control group is a bit OTT imo, but it is a relatively neat solution too. Ultimately you can do all this 'conventionally' and spend a bit less, depending on how you want to control the rads eg rads linear to heat requirement via TRV's on the rads, or ON / OFF via room stats and manifold actuators. In bedrooms I think I'd still prefer TRV's in each room, so maybe consider 'smart' TRV's from a control package supplier that does the whole family of products as a finished system solution. 

The biggest focus here should be on room stats with at most a 0.5oC hysteresis so you then don't actually need W-Comp. I've fitted Vailllants W-Comp and it was a huge ball-ache with many return visits to try and get it to work nicely. Ended up removing it IIRC and just going back to the boiler stat vs TRV's which worked perfectly well ( client simply turned the boiler temp up slightly in the bitter part of the winter and vice / versa ).

 

I 'recently' fitted the Honeywell EVO system and am quite impressed with the range of products and the simplistic stat-per-zone for temps plus a central hub for the 'thinking' side of things. Pretty much plug and play so a nice easy handover  

 

If you're feeding everything from a buffer ( have you already spec'd and bought this, and what is heating this and to what stored temp ? ) then you'll need one tapping for rads and another for UFH, ideally with a 2-port zone valve on each leg. Pointless in having the extremely expensive M3V in this instance, as the secondary manifold will deffo need its own pump ( as you're going to be hydraulically separated from the pump of the heat source because of the buffer ). The images shown in the Emmetti literature expect a 6m pump to be on the primary side of the UFH manifold to force water around those loops, and you'll be missing that unless you buy and install it. Personally I'd try and do away with the second primary pump and just use pumps on manifolds to feed both rads and UFH as these should pull heated water from the buffer without any further help ( as long as they are on separate tappings or Tee'd off away from each other immediately at the buffer ( eg with a 28mm x 22mm x 22mm tee ).

 

Also, Vaillant stated that they did not have a W-Comp solution for 2x heating circuits + DHW eg triple S-Plan  but that was a few years back.

Edited August 3, 2020 by Nickfromwales

[Chablais]

Hi Nick

Thanks for the reply, very helpful. The tank i am thinking of using is this https://www.ebay.co.uk/itm/OSO-Optima-ECPI-Heat-pump-cylinder-c-w-internal-buffer-store/113741035093?hash=item1a7b7e7655:g:70sAAOSwYkRc0rwF 

What do you think? I need to buy a new gas system boiler to power it.  Was thinking the upper coil would give a faster re heat time, and both tanks have immersion elements in as back up and as somewhere for me to dump the 4Kw of PV to.

 

I am struggling to 'design' the pipework to make it all work, not sure what needs to go where. 

So presume the boiler pump will supply to both upper and lower tanks, so a zone valve on each feed?

Boiler controlled by stats in each tank

Will I need a pump to pump to the UFh and Rads manifold( rads manifold on first floor) or will the pump on the manfold pull the water from the buffer, so a manifold pump on the rads manifold as well. Presume this one will not need a mixing valve.

Going to duel fuel the towel rads, so electric in summer, or could divert PV to buffer immersion?

Do I need some sort of bypass or non return valves in the system

 

I have piped up all the potable stuff on a Hep20 manifold, and pressure tested with mains supply and it all works, so far so good.

So now about to start piping for the towel rads and rads in 10mm Hep20

Do you have any recommendation for towel rails, was going to use stainless steel, seen these https://www.towelradiator.co.uk/stainless-steel-towel-rails

Sorry for all the =uestions, trying to push on but wary of making errors in spec

Found the forum to be very useful and insightful

[Chablais]

Hi Everyone,

 

Can anyone offer any advice as to if the cylinder I showed is going to be suitable to use with a system boiler and UFH and three small rads. It is attractive as it keeps the two tanks in a single unit, and also has an immersion in each section. Is the fact that it is designed for a heat pump an issue? 

[joth]

It's a cleaver idea and I was tempted by it myself, in the end I've opted for the Delta Geocoil (and a separate low loss header), as that one is Erp=A rated (vs B for the Optima), and my top priority is reducing heat loss in summer (both to maximize PV self consumption across cloudy days, and avoid the tank losses overheating the house) when the buffer tank is going to be unused and in effect is unhelpfully increasing the volume of heated water that contributes to those heat losses. In a lower efficiency house where the heating is on more of the time the balance may shift.

[Caveat: not yet installed so I'll withhold final judgement until ~next year]

 

To your specific question I can't help, but I ran loads of technical Qs via their UK sales email address and got fast and helpful responses: sales.uk@oso-hotwater.co.uk

 

 

[Chablais]

Hi Joth

Thanks for the advice, I am also tempted by the A rated Delta Geocoil cylinders, as there are still a few on E bay at 395.00. I am a little put off by the heating coils being a smaller surface area than many other makes, which I guess only matters if a fast reheat time is needed.  Also the Optima makes piping up easier and takes less space in our utility.  I don't anticipate the buffer tank becoming hot in the summer months,  as no heating demand. My challenge is piping it all up correctly. 

 

[joth]

 yup makes sense

 

1 hour ago, Chablais said:

I don't anticipate the buffer tank becoming hot in the summer months,  as no heating demand.

OK my thinking is, there's no insulation between the hot tank and the buffer, so if the hot tank is hot it surely will slowly heat up the buffer area too (diluting the temperature of the hot tank as it does). The impact of this would depend largely on the overall usage patterns.