Wet UFH Plumbing & Wiring

[vala]

Hi all,

 

After taking advice from members on this site as well as doing more research into my UFH project I've decided to included a buffer tank. I need a bit of help with the order and components to be used and was hoping I could get that from members of this forum.

The order of plumbing I have is a 22mm flow and return from my external oil fed combi boiler to the buffer tank which will be in the understairs cupboard which I also plan on insulating. This cupboard will also be the location for the ground floor UFH manifold system when we get round to refurbishing the ground floor.

From the buffer tank the 22mm flow would go to the first floor manifold via a heating recirculating pump and 2 port zone valve. I planned on putting the heating recirculating pump just after the buffer tank under the stairs, and the 2 port zone valve would be upstairs by the manifold. Approximate distance from the pump to the manifold looks like it will be 7-8m. I thought this would be best as when the ground floor UFH goes in, I can tee into the feed just after the pump and go to the 2 port zone valve for downstairs UFH.

After the 2 port valve the flow goes into the manifold and then the 22mm return back down from the manifold to the buffer tank.

I was planning on getting a 100L buffer tank from Newark Cylinders however I need to give them more details with regards to number/size/use of connections so the tank can be made up.

Heating circulating pump I was going to go with a Wilo Yonos Pico 25/1-8.

2 port zone valves I haven't found one yet, but a quick google brings up many options.

 

Does this sound correct with regards to the plumbing and components to be used?

[PeterW]

Got too many components in there. 
 

Just install two decent manifolds complete with blending valves and circulation pumps. Buffer can be a standard 2 port buffer that just is tee’d into the flow and return. Needs a thermostat on the buffer - if Newark are making from scratch then ask them to put pockets at 1/3rd and 2/3rds down the tank and you can sort the call for heat  

[vala]

The manifolds along with the entire UFH system is from Wunda, so the manifold has the blending valves and pumps on. I'm speccing the Wilo pumps.

If there is to be no circulation pump straight after the buffer, and just using the pump on the manifold, would it be wise to have 3 flow and return connections on the buffer tank? This would be the flow and return to the boiler, and then a flow and return to the upstairs manifold and one for the ground floor manifold (once we get round to installing this).

Then a connection fitted for the cylinder stat which will be wired to the boiler?

[PeterW]

blender pumps will pull 7m from a buffer. Just have 2 connections and use tees - the boiler pump will circulate as needed. When the manifolds are calling for heat you will get little flow through the buffer. 

[vala]

Just remeasured the approximate distance from buffer tank to the manifold and its more like 8.5-9m, so am I correct then in thinking I can't just rely on the manifold pump?

Am I right in now thinking I can utilise an additional circulating pump after the buffer, or maybe swap out the Wilo that comes with the Wunda manifold for something larger?

The reason I thought about using the circulating pump after the buffer was a response by @Nickfromwales in a thread I read which showed this diagram,

I thought I could substitute the GSHP for my oil fed combi boiler.

However if the alternative of swapping out the pump on the manifold for something that can circulate the flow from the boiler to the manifold I think I'd be more inclined to go that way.

 

With regards to the flow and return connections on the buffer tank, is there any negative to having the ground floor and first floor separate without having to insert a tee when the time comes?

[vala]

So I spoke to Wunda and Wilo and they confirmed my query with regards to the distance from the buffer to the manifold pump.

I'll be using the standard Wilo pump as specified on the Wunda manifold.

 

I think that's it plumbing wise so now onto what wiring I need to get done.

I've got a feed from my consumer unit to the wiring centre which has a spur inline.

I've looked into an S plan wiring centre however this is where I start the get confused with what wires to bring up.

As my boiler is external I want to get the required cables to their relevant location so I can go ahead and get closing up/plastering various areas.

I've done a crude drawing which shows my plumbing and wiring circuit but I would gladly accept any help with working out how and why to include this s plan wiring.

This is the drawing I've done

[RHayes]

18 hours ago, vala said:

 

From what you've drawn here looks like it will work with the boiler providing heat to the buffer tank controlled by the tank stat, in order to maintain a constant source of heat in the buffer, regarless of demand from the UFH.  Then the UFH will run standalone with pump, zone valve and actuators.  Seems okay.

 

I know I have joined this thread a little late, but I'd like to ask why the buffer tank with a boiler?  In my view the buffer tank connected to a boiler is an extra source of heat loss from the system and unncessary load on the boiler as the buffer tank will cool down, causing the boiler to come on even when there is no demand from the underfloor heating.  Most underfloor heating wiring centres have a boiler enable switch so that the boiler comes on only when the underfloor heating needs it to and then the blender valves control the amount of heat fed to the floor.  This way the boiler only runs when needed and only heats the water needed instead of the whole of the buffer.

 

As opposed to an a GSHP in the original diagram where heat pumps are, in short, much more sensative than boilers and need the larger body of water and a 'buffer' potentiailly between supply and demand.

 

Welcome anyones thoughts to advise if I am missing something.

[vala]

Reason for the buffer tank is to reduce short cycling of the oil fed combi boiler, as these run either off or at 100%.

 

Where I'm a bit lost is how an S plan wiring would fit in. From my research at present into them it appears all the connections I could make direct to the Wunda wiring centre, I would now have to go through an S plan wiring centre first.

 

The next zone for the heating in the house will be the ground floor UFH which I'll get onto next year but again that will have its own Wunda wiring centre so again this confuses me with introducing the S plan wiring centre.

[RHayes]

21 hours ago, vala said:

The next zone for the heating in the house will be the ground floor UFH which I'll get onto next year but again that will have its own Wunda wiring centre so again this confuses me with introducing the S plan wiring centre.

I'm guessing that you have an S plan system currently, right?  

 

If you are planning on haveing underfloorh heating throughout with the Wunda wiring centres, (and by the way one thing that has been left off your drawing is any thermostats and the cable runs from them to the Wunda wiring centre) and as there isn't a direc link to the boiler (boiler simply maintains the buffer temperture) then there isn't a need for an S plan wiring centre.  That said, how is your hot water heated?

[vala]

Tbh at present I don't believe I have currently a s plan wiring. Cables from my boiler go to a receiver for the wireless thermostat. There's only 1 thermostat currently for the whole house. Also I can't see a zone valve anywhere.

 

thermostats for the UFH are all Wunda smart ones which pair with the wiring centre so no cables between them.

 

boiler is an oil fed external combi boiler so DHW water comes straight from that and the temp is set on the control panel on the boiler.

[Nickfromwales]

2 hours ago, RHayes said:

I'm guessing that you have an S plan system currently, right?  

 

If you are planning on haveing underfloorh heating throughout with the Wunda wiring centres, (and by the way one thing that has been left off your drawing is any thermostats and the cable runs from them to the Wunda wiring centre) and as there isn't a direc link to the boiler (boiler simply maintains the buffer temperture) then there isn't a need for an S plan wiring centre.  That said, how is your hot water heated?

The call for heat from the UFH will energise the cylinder stat on the buffer. That will tell the boiler to fire upon demand only. During the summer the buffer will remain cold. 
S plan is 100% needed. 

[PeterW]

On 17/08/2021 at 08:51, RHayes said:

This way the boiler only runs when needed and only heats the water needed instead of the whole of the buffer.

That isn’t correct as a boiler even fully modulated down will produce far more heat than the UFH can absorb with a single zone open and calling for heat. 
 

On 14/08/2021 at 19:08, vala said:

Am I right in now thinking I can utilise an additional circulating pump after the buffer, or maybe swap out the Wilo that comes with the Wunda manifold for something larger?

That’s not going to work as the buffer pump will be pushing against closing valves and will cause issues. You may want to move that pump to between the boiler and the buffer unless it has a built in pump 

[vala]

2 hours ago, Nickfromwales said:

The call for heat from the UFH will energise the cylinder stat on the buffer. That will tell the boiler to fire upon demand only. During the summer the buffer will remain cold. 
S plan is 100% needed. 

This is exactly what I was concerned about after speaking to my electrician yesterday.

in the summer months the buffer will continue to heat, and cool down even though there's no demand from the UFH.

 

So going off the wiring diagram off Wunda which most matches my set up

 

Does this mean the 3 core from the boiler still goes into the s plan wiring centre and then the cylinder stat from the buffer vessel also goes into the boiler?

and from Wunda's wiring diagram I can omit the rad stat.

so when there's a call for heat from the UFH, the draw will be from the buffer vessel (via the zone valve opening and the circulating pump on the manifold also being live), and only if there's a call for heat AND the buffer vessel stat is low will the boiler kick in?

[vala]

2 hours ago, PeterW said:

That’s not going to work as the buffer pump will be pushing against closing valves and will cause issues. You may want to move that pump to between the boiler and the buffer unless it has a built in pump 

I spoke to Wunda and Wilo about this and they confirmed for my application the Wilo pump they spec will draw the flow over the 8.5-9m run of pipe work I have between buffer and manifold, as the vertical distance doesn't exceed 6.2m.

[RHayes]

19 hours ago, vala said:

 

 

Does this mean the 3 core from the boiler still goes into the s plan wiring centre and then the cylinder stat from the buffer vessel also goes into the boiler?

and from Wunda's wiring diagram I can omit the rad stat.

so when there's a call for heat from the UFH, the draw will be from the buffer vessel (via the zone valve opening and the circulating pump on the manifold also being live), and only if there's a call for heat AND the buffer vessel stat is low will the boiler kick in?

Ok, so terminal 4 on the S plan wiring diagram above is ultimatly the call for heat from your underfloor heating and in the fulness of time I assume you'll have 2 zone valves wired in to this, ground and first floor UFH.

 

Then from terminal 4, this needs to go do the buffer vessel stat, then from the buffer vessel stat on to the boiler.  This is the basics of it, see below.  

 

Edited August 19, 2021 by RHayes

[vala]

1 hour ago, RHayes said:

Ok, so terminal 4 on the S plan wiring diagram above is ultimatly the call for heat from your underfloor heating and in the fulness of time I assume you'll have 2 zone valves wired in to this, ground and first floor UFH.

 

Then from terminal 4, this needs to go do the buffer vessel stat, then from the buffer vessel stat on to the boiler.  This is the basics of it, see below.  

 

I was under the impression when I come to install the ground floor UFH, this would have its on S plan wiring centre along with its own Wunda wiring centre etc???

 

not wanting to contradict your diagram as its extremely helpful however I came across this page from Wunda whilst looking more at the diagram I previously posted,

 

it shows the common and 1 (call for heat?) going into numbers 6 and 10.

is this what you've suggested just amended to suit the combi boiler wiring diagram I posted up, as I don't have any timers etc for HW?

[RHayes]

 

4 hours ago, vala said:

 

 

 

 

I have to confess I did read the drawing incorrectly.  My diagram should have been to terminal 10 instead of 4 to match the S plan diagram.  You will only have 1 S plan wiring centre and the two underfloor heating manifolds would connect in to it.  One as shown above, in terminals 1 and 9, and the other one in to 1 and 5 (in place of the radiator stat).  The hot water part (terminals 6 & 8) is not needed.

 

An S plan wiring centre is simply a fancy name for a multi terminal junction box as far as I am aware.  The terminalso 1 to 10 are simply means of joining the right wires together and the numbers are to make it easy for anyone to do.  It doesn't matter which number of terminal you use for what. so long as the correct wires are joined so as to follow the switching sequence.

 

I call it a switching sequence as the flow of 230v power (demand) has to go through the right components and in the righ order.  A convential system would be Power supplied from the consumer unit/spur, to timer, on to thermostat, on to valve, on to boiler and/or pump.  Therefore the switching sequence is time control, temperature control, open the valve, then run the boiler/pump.

 

As you say you don't have the hot water part of the above diagram and the thermostats are wireless, (although if you have the option to run wires in (I strongly recomend it) and go for a wired thermostat then you won't have to change batteries and won't be depending on the weak RF signal from them.) therefore the power goes to the Wunda wiring centre.  (This then switches its own local pump at the manifold).  You then have the demand live coming from the wiring centre to the zone valve (Brown).  The Grey on the zone valve is permanent live and the orange becomes a switch live to the buffer stat, which is then passed on to the boiler if the buffer is not warm enough.

 

Hope this helps explain and simplify the 'S plan wiring centre' or 'fancy junction box.

[vala]

@RHayes thank you for this. I'm trying to get it noted down in the order of 1-10 and noting what will go to where. Getting a bit lost as the Wunda wiring diagram I have for the smart connection box doesn't have a switch relay, so although I can put the live into 1, I only have a neutral and an earth left (for 2 and 3).

This is the diagram for the Wunda wiring centre I'll be getting?

 

I have a feeling maybe the folder of wiring diagrams for different systems they supply may well be for there non smart wiring centres??

With regards to the thermostats the smart ones that Wunda supply are all wireless. There's a 'HubSwitch' which connects to my router in my AV cupboard which will over wifi pair with the smart connection box.

I do feel I'm getting closer to understanding all this, just am a bit concerned with the amount of cabling I'll have to feed down various conduits etc, as if there's to be just 1 S plan wiring centre I'll have to install this downstairs where the ground floor UFH manifold etc will be. So I'm hoping the zone valve cabling can be extended.

Or that I could have a S plan wiring centre for each of the manifolds.

Edited August 19, 2021 by vala

[PeterW]

Heating source on the right is the pair you need to the buffer thermostat then on to the boiler. May need a live feed if the boiler requires power to switch on. 
 

 

[vala]

1 hour ago, PeterW said:

Heating source on the right is the pair you need to the buffer thermostat then on to the boiler. May need a live feed if the boiler requires power to switch on. 
 

 

 

According to the Wunda page the heating source is also for the boiler/zone valve. I'm assuming this is where the need for a S plan wiring centre comes into play.

I could run a pair of cables from here to 1 and 10 on the S plan so its the same as the grey and orange as the zone valve?

And then a pair of cables from the S plan (from 1 and 10) goes to the buffer stat?

So this way I connect the zone valve, buffer stat and boiler together?

Edited August 19, 2021 by vala

[PeterW]

Ok - any reason for zone valves ..? All of your UFH zones have valves on them. 
 

You are making this much more complicated than it needs to be. 

[vala]

6 hours ago, PeterW said:

Ok - any reason for zone valves ..? All of your UFH zones have valves on them. 
 

You are making this much more complicated than it needs to be. 

I'm just going off the wiring diagram from them and trying to adapt it to suit my project. On that it includes zone valves.

also next year when the ground floor UFH goes in, then the zone valves will be needed to ensure the flow only goes round which ever circuit is calling for heat?

Its also never been mentioned in any of the previous posts to not have them hence why I continued with having them.

Edited August 20, 2021 by vala

[PeterW]

They are using Zone valves to potentially stop thermosyphoning but with a decent manifold they really aren’t required if you’re going all in on UFH. 
 

Where they are needed is between buffer and boiler, and DHW and boiler which is standard S Plan wiring. The variation is where you add the buffer thermostat and the call for heat from the manifold(s) in place of the room stat, and let the UFH control when the boiler fires based on the buffer temperature. 
 

The only downside to this is you need to align the timers (or put the buffer zone on constant) as there is no direct interlock between UFH time controls and the boiler controls. 

[RHayes]

Typically I would recomend puting in zone valves before underfloor heaing manifolds as it helps extend the life of the actuators on the manifold (prevents let by), however in this system as we only have the manifold/mixing pump sets and no other pump between the buffer tank and manifold there isn't really the need, it is just another component to go wrong, (and there is one particular make of zone valves that is notorious for that).

 

As PeterW has confirmed, wire 1 and 10 on the S plan wiring centre to 1 and 2 on the Wunda wiring centre.  Then from 10 in the S plan will need to go to the buffer tank stat and then on to the boiler switch live.  I think you mentioned that the boiler is a combi so no need for any zone valves.  If there is a timer at the boiler or buffer then I'd also advise putting these on constant and let the control be from the Wunda thermostats, otherwise you will be depending on both timers being on to get any heat.

[vala]

Thank you both for all this extra information.

having no zone valve at the manifold will definitely simplify things for me and will make 1 less cable to get through to where the downstairs UFH/buffer and s plan wiring centre will be.

 

i'm going to draw up a schematic for my system with regards to the S plan and I'll post that up. Hopefully it'll be correct or require little amendments!

 

I'm definitely understanding more and more with regards to this so thank you all!