Reverse Return CH Piping

[cr0ft]

Hi all. Does anyone have a good reference with diagrams that explains how this works? Been asked to quote for a system which will require 2x 35KW System boilers and am wanting to install them both onto the same CH pipework. It will be a 3 zone system in a very large property.

Spoken with Viessmann and they have said the only special requirement is that they should be piped using a reverse return configuration. Can someone enlighten me? I have never installed more than one boiler in a property before.

Cheers!

 

[ShaunCorbs]

easier to look at pics, and it just balances the flow through the system

Insulation Outlook Magazine, your guide to industrial and commercial insulation

 

[stevetheplumber]

one ive never realy understood but the idea is you get the same resistance across each rad

 

[chris watkins]

Otherwise know as "first in - last out"

so if boiler one's flow is the first to connect to the pipe work then the return is the last.

Personally I would still use a low loss header even on a job like this.

 

[chris watkins]

View attachment Low Loss pipe work Drw 2.pdf
View attachment Low Loss pipe work Drw.pdf

These might help ?

 

[Masood]

Agree with Chris. Low loss header all the way...

 

[Scott_D]

Reverse return to the boilers or reverse return to the radiators ?

 

[tolly]

View attachment 24634
View attachment 24635

These might help ?

who did those drawings out of interest chris?

 

[tolly]

I think they would have meant only a reverse return on the boilers on primary side, so it still includes a LLH

 

[tolly]

 

[chris watkins]

who did those drawings out of interest chris?

Me if they are good, Me mate is not.

 

[cr0ft]

Thanks all. From some initial reading on low loss headers the diameter should be 3x the primary diameter. Is this accurate? I would be running 2x 35kw system boilers into 35mm primary pipework. I will reverse return connect the boilers to the primaries.

1x 300L unvented cylinder for hot water. Will be a 3 zone heating system.

Exact heating load for the property has been calculated at 63KW.

Happy with the plans on how to run these, this all makes sense. I'm happy with the pipe sizing stuff but how do I design my low loss header for the system?

The meter is a U16 meter and the gas pipe run is very short, around 4m.

This is new to me and I like a challenge and want to get it right!!

 

[tolly]

Thanks all. From some initial reading on low loss headers the diameter should be 3x the primary diameter. Is this accurate? I would be running 2x 35kw system boilers into 35mm primary pipework. I will reverse return connect the boilers to the primaries.

1x 300L unvented cylinder for hot water. Will be a 3 zone heating system.

Exact heating load for the property has been calculated at 63KW.

Happy with the plans on how to run these, this all makes sense. I'm happy with the pipe sizing stuff but how do I design my low loss header for the system?

The meter is a U16 meter and the gas pipe run is very short, around 4m.

This is new to me and I like a challenge and want to get it right!!

Why not speak to your viessmann rep Croft. They make their own range of LLH's so could poimt you in the right direction and help with controls etc.

 

[cr0ft]

Thanks will give them a call on Monday. Any more info helpful too. I get the impression these can be made of of large bore copper pipe easily enough though for systems this size?

 

[chris watkins]

Header basics

Try these they will make you one with the configuration you require & out of copper so no 42mm M/Irons ! etc & cheaper than the boiler manufacture ones.

You can take the 2 boilers into it on their own 22mm's if the runs are short as per my second drawing. Do the proposed boilers require / have their own circulators (shunt)?

Then on the other secondary side of the LLH you can choose to have either a single F&R with just one big circulator feeding each circuit or 3 individual pairs each with their own small circulator.

I prefer the latter as it makes the controls easier, the circulators can be sized & set for its own circuit rather than having one large going summer or winter trying to cover all eventualities.

 

[cr0ft]

Thanks Chris,

Will go with separate circulators (4 off) on the secondary side. The boilers are system boilers so have their own pumps.

Am going to see if I can design my own and make one using large bore copper pipe. More interesting and A chance to use my degree for once!

 

[chris watkins]

Honestly get a quote from VA I found it just wasn't worth doing it myself you get it all with silver soldered joints AAV, D/O & munson rings to fix it to the wall with all in its own presentation box.

 

[stevetheplumber]

just out of interest in the drawing chris put up the flow and return to the cylinder is tapped of pipework rather than having its own tapping on the LLH any reason for this ?

 

[chris watkins]

just out of interest in the drawing chris put up the flow and return to the cylinder is tapped of pipework rather than having its own tapping on the LLH any reason for this ?

These drawings were produced to show level 3 students a couple of different options after they had designed there own systems with twin boilers & LLH.

The one you are referring to steve is based on what most of the manufacturers were offering at the time i.e. 2 in, 2 out of the LLH with 40 FI con's, so there was no choice but to tee off of a larger F&R to feed the cylinder & heating. I don't know what is on offer now a days?

 

[cr0ft]

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.

 

[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