Reverse Return CH Piping

[tolly]

Ok folks. Would appreciate more experienced eyes looking at this to see if I have missed anything important: -

2x 35KW Viessman System Boilers connecting into a 35mm primary flow/return to the LLH. Boilers connected in reverse return configuration. 22mm magnetic filters fitted to return pipework to both boilers. Obviously being system boilers they will have their own pumps in there to push water to LLH.

LLH, 67mm diameter, height to suit so that there is a gap of 400mm min. between each flow and return. Flows at the top, returns at the bottom. Drain cock on bottom of LLH, air vent on top.

Outputs from LLH - 22mm hot water flow and return, pumped from a normal domestic CH circulating pump.

CH flow/return risers - 35mm initially dropping to 28 then 22mm as it tees off to each floor. Total of 6 CH zones each under 100m2, one of these is a 35m2 underfloor heating circuit in the kitchen by the plant room. CH circuit pumped by a 10m head pump which switches on with the boilers as soon as any of the zone valves open up. Each zone plumbed without reverse return and balanced accordingly on completion of work.

Central heating zones all controlled by one programmer with each zone having it's own room thermostat. UFH obviously controlled by it's own programmer/thermostat. TRVs fitted to all radiators. 22mm Automatic bypass valve fitted at top of riser, is this necessary if both boilers have a bypass valve anyway??

Is there anything else really obvious I am missing, obviously aware of the need for blending valves and manifold for underfloor heating.

The primary side between boiler and LLH doesn't need bypass as the LLH acts as a bypass anyway, but the secondary side should have a bypass, im not familiar with Viessmann but I know Vaillant don't require an ABV if you use a LLH as the auxiliary pump switches off with the 2 ports, only the primary pump has an overrun if you use there controls.

Good luck with everything

 

[chris watkins]

2x 35KW Viessman System Boilers connecting into a 35mm primary flow/return to the LLH. Boilers connected in reverse return configuration. 22mm magnetic filters fitted to return pipework to both boilers. Obviously being system boilers they will have their own pumps in there to push water to LLH.

35mm primary's might be a tad on the small size my quick pipe size has its max at 20degC being 62kW.
Don't forget if using a common pipe, each boiler will need to have a non-return valve to stop unwanted circulation if one is on & the other is off.

If it is a new system I wouldn't worry about the filters, it is one of the benefits of a LLH it will act as a dirt separator. (thats why they have the drain off at the bottom if installed in the vertical)

I know the boilers have their own vessels but I would strongly recommend fitting additional off of the LLH as it is such a large system the boilers will not be enough.

 

[chris watkins]

Outputs from LLH - 22mm hot water flow and return, pumped from a normal domestic CH circulating pump.
CH flow/return risers - 35mm initially dropping to 28 then 22mm as it tees off to each floor. Total of 6 CH zones each under 100m2, one of these is a 35m2 underfloor heating circuit in the kitchen by the plant room. CH circuit pumped by a 10m head pump which switches on with the boilers as soon as any of the zone valves open up. Each zone plumbed without reverse return and balanced accordingly on completion of work.

Central heating zones all controlled by one programmer with each zone having it's own room thermostat. UFH obviously controlled by it's own programmer/thermostat. TRVs fitted to all radiators. 22mm Automatic bypass valve fitted at top of riser, is this necessary if both boilers have a bypass valve anyway??
.

A domestic circulator should be OK for the domestic hot water but you will need a zone valve to signal the boiler/s and if unvented for the energy cut out.

With the controls the starting point is how are you going to control the boilers, are they going to work individually or as a cascading pair ?
Whats the load on the hot water for instants? if it is just one cylinder then do you want both boilers on to supply what could be managed by one? Same with some of the heating, the UF is likely to want to be on longer than the other circuits so again two would be firing when one would do.
Speak to Viessmann or others about the boiler controls & I am sure others on here will be abler to suggest something suitable.

You will need to size the heating pump/s properly most unlikely that just popping a 10m head in without checking suitable flow rates will do.

 

[Chalked]

Expansion vessels
Auto top up

 

[chris watkins]

Central heating zones all controlled by one programmer with each zone having it's own room thermostat. UFH obviously controlled by it's own programmer/thermostat. TRVs fitted to all radiators. 22mm Automatic bypass valve fitted at top of riser, is this necessary if both boilers have a bypass valve anyway??

Is there anything else really obvious I am missing, obviously aware of the need for blending valves and manifold for underfloor heating.

You need to have a look a Part L1a as my understanding is that both individual time & temp control is required at least between the bedrooms & living areas.
Auto bypass not normally required as new circulators alter speed to suit system demands & pump stops with close of last zone valve / no more demand.
How are all your heating zones going to turn the heating pump on & off ?

 

[cr0ft]

Hi Chris. The plan would be that SL from the thermostats will fire the zone valves (S-Plan) accordingly and if any of the 5 heating zone valves are sending 230v to orange wire then the pump will fire.

I am planning to run both boilers at once as much as possible ideally and share the heating load equally. I understand that you could run one boiler some of the time and some at others but will speak to Viessmann technical to sort out these details. Am going to size the exact pump size required if I get the job to be honest as it looks like it takes a wee bit of time to do the calcs on a system this size. Don't want to waste any more time if I don't get it.

Quote for everything has come in at £25k including VAT supplied and fitted. She has got the quote and has said she will look at it tonight and get back to me once her kids are off to bed! Seemed incredibly expensive but the fact she's acknowledged it so quickly means it's not ruled out.

Chris will probably ask to pick your brains if I get this and PM you on here, you seem like you know your stuff regarding larger heating systems. Would that be ok?

Will also read L1a in more detail if I get the job too! Spent 4 hours already designing the system and the controls can be sorted if I get the job. May bung in programmable room stats for each zone all wired in. Will keep you posted.

Cylinder is an 18KW 300L rapid recovery cylinder.

 

[missplumb]

dont forget the pressurisation unit for systems over 45kw

 

[chris watkins]

dont forget the pressurisation unit for systems over 45kw

Why is one required for +45kW?

 

[missplumb]

local water authority regs, may be different elsewhere, but yorkshire water and northumbria water require automatic filling units with flood protection on all systems over 45kw.

 

[Gray0689]

Can you not put all radiators on there own manifolds and room stats in every room instead of zoning each floor