New S Plan Plus to be installed... contains 3D drawing... must be viewed :)

[mozilla19]

Hello All,

First Time Poster on this forum and would appreciate some advice on a new S Plan Plus System Im looking to have installed next week.

Im an engineer by profession, however not a heating engineer or plumber, but have picked up a few things here and there and from reading textbooks. Before anyone has a rant, I am going to get a professional heating engineer to install my system based on good, sound engineering practice rather than on my own limited experiences.

Heres what I am looking to achieve:

2 Heating Zones:
Upstairs is 17 KW load across 7 radiators
Downstairs is 17.6 KW Load across 6 radiators

1 DHW Zone comprising of a 170 Litre Megaflow Cylinder... It takes 24KW Boiler Output to get the DHW from 15degC to 60degC in 22 minutes

... A typical S Plan Plus System....

Boiler to be sourced is a 40KW Worcester Bosch CDi Regular Boiler. I can only run it as a 2oo3 system due to the high demands so both heating circuits will have to come on together (if required) at different times to the DHW Circuit.

Based on Rads and pipework that have been installed, I have worked out my required flow rates and pipe resistances (pressure losses which includes plenty of margin) and have decided to go for a Magna1 25-60 pump.

My required head and flow rates are somewhere in the mid range of this Magna1 25-60 variable speed pump (PP2) as opposed to the upper range on a smaller Grundfos Alpha 2L 15-60 or 25-60. I figured the Magna1 pump wont be working as hard, therefore it will last longer.

Calculated index circuit Head came out as 2.5m Head and 1.8m3/hr Flow rate and like I stated previously, does includes lots of margin... I added a 100 percent to the final pipe lengths to account for pressure losses from pipe fittings in order to get my overall system losses. A bit OTT perhaps, but I figured with the possible addition of non-return valves on return circuits, this excess margin I included would account for it... I think one 28mm Check valve has the same resistance as 5 metres of 28mm pipe so the 100% excess I have allowed for in the calculation should be enough.

Calculated expansion vessel size came out to be 28 Litres with 1 bar charge pressure... purchased a 35 Litre just to be on the safe side... dont want the boiler going pop.

Now... Ive attached a 3D drawing that I quickly put together on what I think the system will look like in the small raised timber plinth boiler room I have built and this is where I have some important questions relating to industry practice. There are a couple of things that may not look right which Im hoping you'll point out.


The F in the Return Pipe work is a 28mm Spirotech Magnabooster2 Filter... P is obviously the Pump and is pumping downwards. Advice from Grundfos Technical Department said this was acceptable provided there was an air vent just before it... I believe theres also one inside this Worcester boiler aswell. I contacted Wilo Pumps just to make sure I wasnt being lied to and they said pumping downwards was also acceptable... with an air vent.

Now, hopefully the drawing Ive attached explains itself... Ive tried to incorporate 3 zones using mostly 28mm pipe work and reducing down to 22mm for the Megaflow Cylinder. My big worry was reverse circulation so Ive put in some non return valves on the return sides. Is this acceptable or should I definitely be observing the 3 Tees Rule? I realise the non return valves are adding in a lot of pressure loss, but the variable speed pump will easily eat it up. Please let me know your thoughts...

Ive added a shunt circuit which is the bathroom towel rad (700 Watt)... I figured as its a damp room this should always be heating up regardless of what the system demand is and in the event of a faulty zone valve this circuit will prove to be a life saver. Let me know if you think this is ok... Thought about Auto Bypass Valves but I still think this shunt circuit is a better solution. Ive also heard these Auto Bypass Valves are high failure items aswell... Again let me know your thoughts and why you agree or disagree.


Thats it really... Have a good look and if something dosen't smell right then please do let me know why.

 

[Reg Man]

Not sure about all these non return valves. Can't see why you need them on a properly designed system. They will restrict the flow and give no benefit.

 

[albatross]

Hello mozilla,
Picture resolution is poor!
You are correct mostly, you have gone a bit in depth though but no harm there!
I wouldn't bother with an extra AAV as they tend to leak and there is one in the boiler.
No need for check valves if its piped up right using 3T's rule. They will only rattle and stick in the future. Even without 3t's reverse circulation is rare on a S plan.
Your rad sizes average 3kw each, thats seems unusually high. If the house is so big I'd expect a bigger cylinder too?
Building regs state you should have an auto bypass which you will need as your towel rail should be after a zone valve. You also need TRV's on all rads apart from the two rooms that have room thermostats in .

 

[Howsie]

If I were you, id get a heating engineer to look over your requirments and specify accordingly.

You don't know what you don't know and reading a couple of textbooks is only going you an appreciation.

That's all from me, I've got a little project at the end of my garden that isn't going too well.

 

[SimonG]

35kw heating load. Big house or no windows?

 

[mozilla19]

Hello All,

Thanks for the replies... they were very useful.

The house is a large 5 bed built in the 1900s... rooms are big, i.e. living rooms of which there are 3 are as follows:

Living Room 1: 6m x 5m x 3.5m(H)
Living Room 2 : 6m x 4.5m x 3.5m(H)
Living Room 3: 10m x 4m x 3m (H)

All have large double glazed windows which must be atleast 15 year old... so as per SimonG's comment, might aswell be "no windows".

But yes, I agree, the radiators are oversized, but better to be over then under I say... and living in the north east of england, the average temperatures are much colder than in the south.

In Spring 2014, I will be installing external insulation to improve the thermal efficiency of the house, which will hopefully mean the 40KW boiler wont be working as hard in Winter 2014. The rads will definitely be oversized by then and TRVs will be used more frequently.


Thanks for the advice regarding the non return valves.... 3 Tees are definitely the way to go.

Regarding the following statement by albatross:

Building regs state you should have an auto bypass which you will need as your towel rail should be after a zone valve. You also need TRV's on all rads apart from the two rooms that have room thermostats in .

I agree and accept this regulation, however, what if, lets say...

The Zone Valve for upstairs Heating fails when it has been called for AND the Auto Bypass fails or to a lesser extent some little 5 year old lunatic decides to close all the TRVs... how else will the heat circulate?

In this situation would it not be better to have what is effectively a non-zoned bathroom radiator circuit to cover all disastrous scenarios. The pump overrun facility in most boilers will circulate the heat nicely around this circuit without flow restriction. I should mention, this shunt rad will not have an easy means for adjusting the flow just in case the 5 year old nutter decides to shut it off.

Please let me know what you think... and Im grateful for any advice / clarifications recieved.

 

[mozilla19]

Forgot to respond back to the comment from albatross:

your rad sizes average 3kw each, thats seems unusually high. If the house is so big I'd expect a bigger cylinder too?


House has 1 bathroom and 1 shower room which according to Heatrae Sadia, 170 Litre is sufficient... At the time I was debating whether to go up to the 210 Litre version... and yes, rad sizes are oversized... see my previous post.

 

[AWheating]

forget the non returns, dont need a magnetic filter, you will need an auto bypass, your cylinder seems small compared to the amount of heating you require for a large house. I would imagine your pipe sizing is over the top. your drawing is hard to read.

id get 3 quotes from local engineers and see what they recommend.

 

[Ermintrude]

No filter ? Tut tut.

 

[AWheating]

why do you need a filter on a new system? if fitted and flushed correcty then there will be no corrosion to be removed so a waste of £100.

 

[SimonG]

why do you need a filter on a new system? if fitted and flushed correcty then there will be no corrosion to be removed so a waste of £100.

He's an engineer, chance for a lot of 'playing' after installation.

Seriously though I would be fitting a filter.

I always wondered about filling a heating system with a light grade oil rather than water, but I digress.

 

[AWheating]

most filter on work on magnetic corrosion which there is little to non even in a poorly installed new system. If i was to fit a filter on a new system i would fit an mb3 as it filters small debris well. but a good flush a a few bottles of inhibitor should stop any corrosion from forming needing a filter.

i suppose it depends on the customers knowledge and needs.

 

[diamondgas]

What are your domestic hot water draw-off lengths mozilla19? It may pay to incorporate a secondary circulation around the house for your domestic hot water. It'll give you a better supply and less waste IMHO ...

 

[TBServices]

Stopped reading at engineer

 

[SimonG]

most filter on work on magnetic corrosion which there is little to non even in a poorly installed new system. If i was to fit a filter on a new system i would fit an mb3 as it filters small debris well. but a good flush a a few bottles of inhibitor should stop any corrosion from forming needing a filter.

i suppose it depends on the customers knowledge and needs.

I'm back on the trappex centramag. What makes the mb3?

 

[gassafe]

A magnet filter is a future investment... If he's spending 4k on equipment another 100 pound for belts & braces would not hurt to protect it all! There may be some old rads on system too...

All the sludged up systems we see everyday were new once too, look at em now!!

Inhibitor is good, but over the years it gets drained and does not get replaced!

 

[village idiot]

Stopped reading at engineer

Got in not long ago. Saw the post and its at page TWO now, so I decided to give OP a read. But after seeing the lengths to which he had gone to plan his installation in detail, I reckon he should just install it himself. He has the knowledge and technical ability to contact boiler and pump manufacturers to ensure he is not being lied to, so It's my opinion that anyone stupid enough to take on the job will have endless grief from the Engineer OP.
I'm all for customers having a good knowledge of their system or for a system they want installed. But this, I'll leave it at that. I'm out

 

[Ermintrude]

Know the feeling just been told this afternoon by a ships cat (fitter on a dive boat) that I should pipe all his hot and cold in 28mm to aid flow rate and minimise drop. 40kw combi. He's gonna run off about 30l before water gets hot!

 

[Killy Bing]

*grins*
a correctly designed system has no need for non return valves.
good job you included them.

you've forgotten the all important secondery return for your hot water

oh and you need a cylinder with an aditional two coils for when you add solar and an air source heat pump.

all properly designed systems have them you see!

 

[Ermintrude]

It's only a real system when there is a certain tank in tank UVHC with the ability to act as a LLH for mutipul heat inputs.

 

[doitmyself]

The house is a large 5 bed built in the 1900s

I had a large 5 bed 1905 semi, but it didn't need a 40kW boiler, only a 24kW one!

How were the boiler and rads sized?

I suggest you use Whole House Boiler Size Calculator to find out what size boiler you really need?

I agree, the radiators are oversized, but better to be over then under I say.

But you only need to size the boiler for the heat loss. Larger rads will mean that the boiler can run at a lower temperature, so it can be running in condensing mode more often.

 

[happyflyer]

AW hell what's the cost of a filter, £70 and can you guarantee that the dosing will stay in there and be replaced if it gets drained down,
better safe than sorry AW, I would like to see a better drawing before making a comment.