Wiring help!

[osmononame]

Good evening all,

 

We are in the final stages of running the cables for our build and it occurs to me that I have yet to run the cabling for the UFH control. 

 

I have been looking at schematics this evening:

 

Am I correct in thinking that I need 5 core cables running from the wiring centres (there will be 3 in total - 1 on each floor) to the motorised valves which are going to be located in the attic? At the same time I think I have to run a twin and earth cable from each wiring centre to where the boiler is going to be located (also in the loft)?

 

Truth be told its probably a question for my sparky and plumber but they are not back on site until end Jan so thought I would ask here so I can get on with things while I am off work over Christmas/New Year!!

[PeterW]

Does each wiring centre and manifold have its own pump ..? I would have the pump, wiring Centre and zone valve all at the manifold, and then have the buffer tank thermostat running to the boiler for the call for heat. 
 

In this scenario, the UFH zone calls for heat, the zone valve opens and when it’s fully open the manifold pump starts. As this draws hot water from the buffer then the buffer thermostat will trigger the boiler. This keeps it all very simple with each floor managing its own part of the system. 
 

Depending on distance you may need secondary pumps to draw the heat to the manifolds, alternate to this is you blend leaving the buffer and do not have TMVs on the manifolds but that does mean some zones may suffer with lower levels of heat being supplied. 
 

Who’s designed the system ..??
 

 

 

[osmononame]

48 minutes ago, PeterW said:

Does each wiring centre and manifold have its own pump ..? I would have the pump, wiring Centre and zone valve all at the manifold, and then have the buffer tank thermostat running to the boiler for the call for heat. 
 

In this scenario, the UFH zone calls for heat, the zone valve opens and when it’s fully open the manifold pump starts. As this draws hot water from the buffer then the buffer thermostat will trigger the boiler. This keeps it all very simple with each floor managing its own part of the system. 
 

Depending on distance you may need secondary pumps to draw the heat to the manifolds, alternate to this is you blend leaving the buffer and do not have TMVs on the manifolds but that does mean some zones may suffer with lower levels of heat being supplied. 
 

Who’s designed the system ..??
 

 

 

 

Yes - each manifold has its own pump - I guess the valve could be located at the manifold end but we won't have a buffer - its a gas boiler we are going with which modulates well (1:20 modulation) which should work well with ufh - or thats the plan at least! It's something we could look to add later should we feel it is required.

 

System was designed by the Underfloor Heating Store but they now closed until next year (and i am happy to deviate if theres a better way).

 

How would the wiring work without a buffer - I guess we would wire all the wiring centres to be able to trigger the boiler when required? 

 

 

[Gav_P]

If your not sure at the moment, bang some conduit in with a bit of cord to pull wires though later. Allows you to add more cable later if things change. 

[PeterW]

I would out the buffer in now... it will not modulate down far enough, and you will have issues. Look at your heat loss for a single room, then see if the boiler can modulate to lower than the heat input requirement - very very unlikely. 
 

Without this you need a relay module - each wiring centre will call for heat and trigger the relay with the NO contacts connecting to the boiler call for heat. You could try and use the zone valve micro switch but that’s better used to run the pumps. 
 

What boiler has been specced..? Internal circulation pump ..?
 

 

[ProDave]

I will just add to the thread the question, WHAT is the heat source?

 

I only ask because if it is an ASHP they can sometimes be a bit more complicated and need extra wiring.

 

My philosophy was to install the cables you know you need, and then one spare bit of 3 core & earth between each location for the bits you might have forgotten or add later.

[PeterW]

1 minute ago, ProDave said:

I will just add to the thread the question, WHAT is the heat source?

 

 

10 hours ago, osmononame said:

its a gas boiler

?

[osmononame]

We had thought about a buffer tank before - I think trying to keep a slim budget we discounted for that reason.

 

I guess i could reconsider the decision - we do have space in the plant room for it - the guys who designed the UFH system couldn't tell us what size we needed so i would need to do those calcs then find the cost for what size i need and costs etc. I did try looking online for this before but most guidance i could find was for ASHP / non-gas boiler set ups.

 

The boiler modulates down to 1.6kw which will exceed a single rooms heat demand.

 

p.s. and this is probably a stupid question but if the boiler only runs when one of the stat calls for heat what purpose does the motorised valve do?

[PeterW]

Ok so that 1.6kW is the output at 55°C which is 20°C more than you need for UFH, so you may as well say that’s possibly double what need at standard UFH temperatures. What are the design temperatures for the system by the designer ..?

 

I was assuming the plumber has requested the zone valves ..? Have all manifolds got a full set of actuators, blending valve and pump each ..? 
 

Are all floors timber with spreader plates or are there a mix of solid and timber floors ..? What are the final floor coverings ..??

 

 

[osmononame]

I will need to check with the designer about the temp... Can't seem to see the designed temp on the papers I have. 

 

It's 16mm pipe at 150 ctrs on gf in 80mm of screed and spreader plates at 250 ctrs on first and second floors.  

 

Will be timber floor on the gf and carpets FF and SF. 

[osmononame]

It was the designer/under floor heating store who specced the zone valves. But each manifold location does have its own pump/blender/actuators... Does that mean we might be able to do without the zone valves?

[PeterW]

Ok so the first and second floors doesn’t make any sense ..!! With no screed and the low heat capacity, along with the insulating capability of the carpet you are more likely to need closer than 250mm pipe spacing. 
 

These are all going to need to run for different times and at different temperatures - more than ever I would be putting a buffer into this as you are going to need to do some clever controls. 
 

Please tell me you’re not using Heatmiser stats in every room ..???

[osmononame]

So on GF it was meant to be different spacing but we decided to go closer to make the option of retrofitting an ashp in the future a possibility. I have a very old inefficient self build with ufh I am staying in now and heating demand is close to nil upstairs on all but the coldest of days. I think the calcs showed the same for us at the new place so I am.not too concerned about the spacing (and too late now anyway to do anything about it!). 

 

As far as heatmiser in each room - that's a debate I am having with the Mrs. I was thinking a thermostat per floor but she wanted independent control as it's the same as what we have. If you have any advice that might convince her I'm all ears. 

[PeterW]

9 minutes ago, osmononame said:

As far as heatmiser in each room - that's a debate I am having with the Mrs. I was thinking a thermostat per floor but she wanted independent control as it's the same as what we have. If you have any advice that might convince her I'm all ears. 

Give her the £1000 you save to spend on the bathroom.... 

[osmononame]

Tell me about it - between that and knowing that she will have windows open fully in the height of winter to 'air' the house out despite having a mvhr I have my work cut out!

 

I've checked the cost of a buffer tank and think I can go with one of those if I then chose a cheaper boiler that doesn't have as good as good a modulating range (1:10). 

[PeterW]

Before you do anything I would be getting the heat output for the floors and then ensure you have a decent programming and control method sorted. Have you got space on the ground floor for the buffer ..??

 

 

[osmononame]

I will check with the designer to see what he says - I am a little out my comfort zone here. 

 

I have space in the plant room but that's in the attic (I know it's a bit upside down!). 

 

What do you think about the zone valves - having a quick Google I don't think I need them on the back of each zone having an actuator?