UFH + Sunamp + Combi

[Tiny]

Hi, Still trying to resolve my heating and DHW,  I would like the ability to have two thermostatic mixer showers running at the same time. Plus have UFH on the ground floor and small rads/towel rails upstairs. Hoping to re use the existing Gas combi boiler. Open to using a Sunamp. I have seen they have a new range just launched.

Question is how to connect everything and what to use to control it Would like to keep the boiler modulating, Also would like some remote control similar to the Heatmiser Neo set up if poss without blowing the budget 

Do I just turn down the temp at the boiler to ensure modulation? 

Will the Sunamp trigger the boiler

Is it a good/bad idea to run the DHW and the UFH from the Sunamp?

was hoping to have four zones downstairs and three upstairs

 

Set off looking at ways to utilise modulating room thermostats to modulate the boiler,  am I right to think the above method using a Sunamp will negate their need.

was going to use a manifold system for the rads

I presume each of the four proposed UFH zones will need a thermostat,  do these just open the actuator on the manifold? What makes the call for heat?

I can see that with the above method the Sunamp will remain charged to enable DHW on demand, I know it has low standing losses but seems wasteful. 

Most of the time there is only two of us in the house, so reverting to the combi makes sense, however when we have friends stay over or holiday rent the house I would like to run the Sunamp. Is this practical in real terms?

Apologies the all the questions, tried phoning Vallient earlier today to ask about their V Smart controls, would only discuss with a qualified engineer!

All the plumbers I have contacted so far have not heard of Sunamp and only one had heard of a modulating thermostat, so I am trying to learn myself.

My head is hurting with all the options and conflicting advice

 

[le-cerveau]

A lot there and I am sure @Nickfromwales will comment.

 

1. A combi boiler is designed to provide DHW or heating without a cylinder.
2. UFH and boilers don't play well together without a buffer tank (or equivalent).
3. UFH and radiators have different temperature requirements.
4. Switching between low and high occupancy is adding complication (if you are happy for that).

The traditional way to resolve this, UFH, Rads and DHW would be a TS, Low tappings for UFH, rads of higher tappings and the ability to charge different amounts depending on DHW demand, this would be supplied by a system boiler not a combi but you can probably set the combi as a system boiler.  You can do the same with a SunAmp UniQ as a TS, to provide the variable capacity you could separate it into two units, a UniQ 6 will support a single bath/shower a UniQ 9 one bath & up to 2 showers (SunAmp figures) so in theory you could use two UniQ6's just charge and use one normally and when you have guests use both (have to work out the details) (or a 6 and an additional 3).

 

UFH control is done at the manifold (you have to have one), each zone thermostat will open/close respective loops at the manifold, the TMV at the manifold will blend the water to the desired temperature but you still want only warm (45C max preferably less) at the manifold TMV.

 

Upstairs Rads/Towel rails I would run off a second manifold, again each room stat opening/closing the respective manifold valve.

 

CAll for heat will depend on the overall system setup, with a combi it is the thermostat that signals the boiler (one for the whole system usually) with a TS/SunAmp teh TS/SunAmp calls for heat from the boiler when it requires it.

 

If you holiday let the house I would want to make it as simple as possible and limit the tenants ability to 'bugger up the system'.

 

I wait for the professionals corrections to my thoughts.

 

[Nickfromwales]

14 hours ago, Tiny said:

I would like the ability to have two thermostatic mixer showers running at the same time.

That will typically require a 22mm water circuit and a 22mm inlet / outlet off whichever type of water heater you go for. 

 

7 minutes ago, le-cerveau said:

you can probably set the combi as a system boiler

Correct. The only issue is diverting the DHW output from the 15mm outlet to say the ensuite shower for low use, and then the other bathroom/s need to be from a cylinder / Sunamp / other which is mothballed. The lack of practicality and complexity of such a setup really make that a non-starter tbh.

The last exact same job I did where they had a brand new 40kW Baxi Duotec fitted by a tool a few months prior to us sorting things out ( 8 bedroom, 4 bathroom, 3 cloakroom, and laundry annex, plus granny annex in the garage roof! ) we re-used the combi and relocated it from the house to the laundry annex, piped via a trench. We used DHW off the combi for the laundry annex utility sink and cloakroom wash basin, and nowt else, via the 15mm outlet.  

The bulk DHW needs were then met from a TS set up on a W-plan ( DHW priority ) arrangement from the heating side of the boiler. That also did space heating via port 3 of the 3-port W-plan zone valve. When heating was required and the TS was depleted, the cylinder stat was allowed to take full priority off the boiler and reheat very quickly. Once hot, the boiler would revert back to space heating. The TS, coupled with a cold mains accumulator, would run 3 showers flat out simultaneously. 

 

The SA range start with the eHw which is iirc a 15mm piped unit up to 6kW, but at 9kW and upwards I would need to check if they go to 22mm. If not then your onto the eDual for space heating and DHW if the remit is for high flow DHW. 

14 hours ago, Tiny said:

Is it a good/bad idea to run the DHW and the UFH from the Sunamp?

First work out why you've considered SA. Do you have PV?

 

They're typically for storage so with gas you'll only really be looking at volume for DHW storage if you want to keep the combi. Space heating should be via a buffer ( minimal volume required ) so either a TS or the SA eDual would be typical for this scenario.

Options;

An UVC for DHW via 22mm tappings, plus small buffer tank to input boiler heat and glean differing value space heating as required. 

A TS with multiple tappings for DHW ( via a 22mm instantaneous coil ) and boiler / space heating as required. Made bespoke to suit the install.

A SA unit. The eDual has 1x non-potable 22mm heat exchanger ( heat energy in or out ) and 1x potable WRAS approved heat exchanger for DHW. 

 

The only one above thats energy efficient and does not require annual inspection / maintenance is the SA unit. Its also around a 1/3rd of the equivalent physical size for the same UVC volume. You could daisy chain 2x SA eDuals and mothball the first for low DHW demand, and then fire up the first when you need much more. Cheapest way would be good old UVC, lower capital cost, but then you have the G3 to pay for every year. As you have gas maybe just a small uplift in cost, ( if you choose a gas agent who has their G3 and can do 2 birds 1 stone at each gas service interval ).

Theres no easy or cheap way to select between high / low DHW demand, and as you have gas and mixed temp space heating thats not straightforward either. With a TS you can choose dual cylinder stats and just heat the top 1/3 for low DHW and then the whole TS for high DHW demand, and when requiring space heating it'll be fully heated regardless, a setup that we refer to as summer / winter normally but a slightly different spin where you can heat the full TS ( high DHW ) but not draw heating from it ( heating zone valves remain closed ).

Standing losses from the TS will be much higher than the SA unit, but probably less than the UVC + Buffer option ( UVC is all or nothing and must be sized for the high DHW needs ) so decide what your criteria actually is and consider the options from there. It can be made to work either way, by design, and each have pros and cons. Cons with the SA is they're not cheap to buy but pros are its lifespan and no cost to service / no moving parts / no pressure reducing valves / prv / G3 etc etc. 

 

Manifolds necessary for UFH and RADS. You'll need a low loss header at the very least, if not fitting a TS or other form of buffer, to create a common rail for those to feed from, otherwise the pumps will be able to 'see' each other and be fighting one another all the time.  

 

Why make the stats so complex? @JSHarris fitted a bog-standard room stat with 0.1oC hysteresis which is more than ample. Ive also never heard of modulating room stats and they must be manufacturer specific OEM units, like vaillants weather compensation kit, which just was nigh-on impossible to get to work properly. Even their tech guys got fed up in the end and sent a service agent out. He blamed me for the outside unit being in the wrong place after the pricks told me where to put it over the phone! Then they said the units weren't communicating because I has fitted the receiver in the boiler chassis ( where the bastard thing is MEANT TO GO ), again blaming me and stating to the customer that they never fit them there as the boiler acts as a Faraday cage and blocks the wireless signal. FFS!!!! Your making unnecessary work for yourself there, just dont overthink things and save a few £.

 

If its a holiday let ( as I dont know exactly what it is you want to do yet so that doesn't make it any easier ! ) then I'd go TS or SA. TS gives nigh-on constant, instant, high flow DHW. Remember you can have a 1000L hot water cylinder that can run 10 showers, but if your incoming cold main will only support one then your only ever going to get one shower  

Many questions to answer first and we need to know the mains pressure and flow rates too. 

Make your mind up as to what its to be and design for that, otherwise its "how long is a piece of string"  

 

 

   

 

 

 

 

 

 

 

[Nickfromwales]

NOTE : Just asked the question, and any size Uniq Sunamp unit will have 22mm inlets and outlets.

[Tiny]

Hi Nick

Thanks for the comprehensive reply. It is a full house renovation with extension, three bedrooms, two with ensuite showers, plus a ground floor shower in a utility room. All existing pipe work is being removed and the boiler needs to move also.

Our mains flow rate is circa 17 Lts per min, not sure of pressure need to acquire a pressure gauge and will report back. Just trying to have a system that is efficient and effective. 

UFH is appealing as one floor is open plan, not much wall space for rads 

I only thought about zones as some rooms will be unused for long periods, so do not need to be at 21deg. As it is a refurb I am pretty sure we will not achieve the level of airtightness and insulation that others on the forum have achieved with new builds. It will not be for 

lack of trying!

I only mentioned the Sunamp as thought it would save having a large TS or UVC, which apart from taking up loads of space appear to have larger standing losses, and the extra service cost if UVC

So as I am effectively starting from scratch, more than happy to take your advice on the best way forward, the thoughts I had mentioned where as a result of reading other posts and trying to do the donkey work myself.

same with the combi, will buy another boiler if required, but thought if I could utilise what we already have it is £1000-1500 to spend on something else.

So if I drop the requirement for simultaneous showers, does that make it easier. I hear what you are saying about keep it simple.

thanks for taking the time to reply, really appreciated, I have so many plates I am trying to keep spinning, I could do with bottoming some out!

thanks

[Tiny]

Hi

i have managed to borrow a pressure gauge and the water pressure measured at 5.1bar.

the flow rate was 17lts min

Boiler is a Vallient Ecotec Plus 824

Look forward to being able to move it forward

Edited July 19, 2018 by Tiny
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