Doctor Drivel wrote:

Dribble seems to make it a matter of principle to adopt a contrary
view on everything. ;-)

Chav, I am a pro not an amateur. I look at thing logically, not what I
have fitted in my own house - which in your case is one combi.

let me guess, I should have fitted two?

(odd we have not had the pet solution for ages now, are you fed up with
it?, it used to get an outing several times a week)

--
Cheers,

John.

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Doctor Drivel wrote:

- acting as a buffer allowing the boiler to do longish burns heating
the store, while in turn it fed heat to the house at a slower rate.
While this is still the case, a modulating boiler can make a pretty
good stab at doing this all by itself these days.

A poor stab at it I'm afraid. Modern boilers are designed for the

And yet still exceed 90% SEDBUK rating... how much more will your store get?

The 90%+ SEDBUK ratings on modern boilers assume typical setups and
controls, so even if you can improve on the efficiency and squeeze few
% more out of the system, you need to assess if the extra hardware and
install costs of the store are going to give worthwhile returns.

A boiler can be running at over 100% if set up properly heating a store.

Oh free energy, interesting concept...

There is a fair chance that in financial terms alone they never will
unless you have huge gas bills.

Chav, you just made that up.

No, actually I did the sums. It an engineering activity you ought to try
once in a while. It can save you spending 1000's trimming £10 off you
gas bill.

So will you get improvements in comfort or functionality to make the
cost worthwhile?

Most certainly!

Heat Loss:

If a boiler is correctly sized for the heat loss at say -3C outside,
when -3 it should run flat out continuously. Few do as most are
oversized, then boiler cycling occurs.

A great thing about a thermal store is that doesn't care how large the
boiler is, as long as the flow and return pipes are sized correctly. If
a house requires say 15kW and a 30kW boiler is coupled to the store
cylinder, it will just heat up faster and still no cycling. A boiler
twice the size of CH requirements directly heating rads will cycle like
hell.

unless it modulates down to match the load... oh hang on a minute most
of them do.

Also having the CH and DHW off a thermal store 100% electric backup is
available to CH & DHW, and also a second cheap backup boiler can be
coupled directly to the store too. So, a cheapie B&Q job boiler can act
as a backup. It will last as it will only be used once in a blue moon -
so full cheap to run on gas, 100% backup. Or have both boilers on and
zippo re-heat. Great when there is multiple showers and baths going on.

Wahay! Two combis almost makes an appearance...

So let me get this straight, so far the shopping list for the system is:

two boilers, one accumulator, a thermal store, half a dozen time dual
channel time switches, about 15 pumps, half a mile of copper pipe, a
couple of blending valves, weather compensator, immersion heater... (did
I forget anything - been losing track)

spose you might get change from £4k and a MTBF comparable to you collar
size.


--
Cheers,

John.

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"John Rumm" wrote in message
...
Doctor Drivel wrote:

Dribble seems to make it a matter of principle to adopt a contrary view
on everything. ;-)

Chav, I am a pro not an amateur. I look at thing logically, not what I
have fitted in my own house - which in your case is one combi.

let me guess, I should have fitted two?

You are getting there.

"John Rumm" wrote in message
...
Doctor Drivel wrote:

- acting as a buffer allowing the boiler to do longish burns heating the
store, while in turn it fed heat to the house at a slower rate. While
this is still the case, a modulating boiler can make a pretty good stab
at doing this all by itself these days.

A poor stab at it I'm afraid. Modern boilers are designed for the

And yet still exceed 90% SEDBUK rating.

In a setup where the boiler set properly. Not the case in most systems.
Then the auto by-pass runs out of setting.

A boiler can be running at over 100% if set up properly heating a store.

Oh free energy, interesting concept...

You really don't know.

If a boiler is correctly sized for the heat loss at say -3C outside,
when -3 it should run flat out continuously. Few do as most are
oversized, then boiler cycling occurs.

A great thing about a thermal store is that doesn't care how large the
boiler is, as long as the flow and return pipes are sized correctly. If
a house requires say 15kW and a 30kW boiler is coupled to the store
cylinder, it will just heat up faster and still no cycling. A boiler
twice the size of CH requirements directly heating rads will cycle like
hell.

unless it modulates down to match the load...

None of them modulate low enough.

Also having the CH and DHW off a thermal store 100% electric backup is
available to CH & DHW, and also a second cheap backup boiler can be
coupled directly to the store too. So, a cheapie B&Q job boiler can act
as a backup. It will last as it will only be used once in a blue moon -
so full cheap to run on gas, 100% backup. Or have both boilers on and
zippo re-heat. Great when there is multiple showers and baths going on.

Wahay! Two combis almost makes an appearance...

You should fit two combis.

So let me get this straight, so far the shopping list for the system is:

two boilers, one accumulator, a thermal store, half a dozen time dual
channel time switches, about 15 pumps, half a mile of copper pipe, a
couple of blending valves, weather compensator, immersion heater... (did I
forget anything - been losing track)

That would be a good system indeed. Cost effective for the functionality.

Doctor Drivel wrote:

"John Rumm" wrote in message
...
Doctor Drivel wrote:

- acting as a buffer allowing the boiler to do longish burns heating
the store, while in turn it fed heat to the house at a slower rate.
While this is still the case, a modulating boiler can make a pretty
good stab at doing this all by itself these days.

A poor stab at it I'm afraid. Modern boilers are designed for the

And yet still exceed 90% SEDBUK rating.

In a setup where the boiler set properly. Not the case in most systems.
Then the auto by-pass runs out of setting.

Perhaps you could translate: "Then the auto by-pass runs out of
setting." into English.

A boiler can be running at over 100% if set up properly heating a store.

Oh free energy, interesting concept...

You really don't know.

I know you won't see a SEDBUK rating of over 100% since they are using
the gross calorific value in their calculations. So here in the real
world, with normal physics and all that, 100% is the maximum you can
possibly get - when all the energy from the fuel you put in, is captured
and put to good use.

If a boiler is correctly sized for the heat loss at say -3C outside,
when -3 it should run flat out continuously. Few do as most are
oversized, then boiler cycling occurs.

A great thing about a thermal store is that doesn't care how large
the boiler is, as long as the flow and return pipes are sized
correctly. If a house requires say 15kW and a 30kW boiler is coupled
to the store cylinder, it will just heat up faster and still no
cycling. A boiler twice the size of CH requirements directly heating
rads will cycle like hell.

unless it modulates down to match the load...

None of them modulate low enough.

Think through the implications.

Say you have a boiler that modulates down to 6kW, and lets guess that
the OPs three storey stone built house loses heat at a rate of 4kW on a
moderate day. Now aside from the fact the boiler will probably be
running at its highest efficiency at this output, you will also note
that the nett contribution of power to the building is 2kW.

Now if you have ever used a nett input of 2kW from a fan heater to try
and heat any space of significant size (like an entire house for
example), you will realise that in real terms this is a very low rate of
heat input - and you will get very little cycling of the boiler on its
internal stat. What little you do get will have little effect on overall
seasonal efficiency.

So let me get this straight, so far the shopping list for the system is:

two boilers, one accumulator, a thermal store, half a dozen time dual
channel time switches, about 15 pumps, half a mile of copper pipe, a
couple of blending valves, weather compensator, immersion heater...
(did I forget anything - been losing track)

That would be a good system indeed. Cost effective for the functionality.

Well lets say it squeezed an extra 5% out of the boiler (which seems
unlikely - a SEDBUK efficiency around 90% usually corresponds to a
boiler efficiency of some 92% or more, so we would have to be pushing
97% recovery at the boiler to achieve that).

Your above "cost effective" system has added £2k - 3k to the install
cost. Lets say the gas usage for heating is pretty high at £500/year,
that extra saving could be as much as £25. So you could see a return on
your investment in as little as 80 years. (assuming you don't pay that
saving over for extra electricity to run all those pumps)

--
Cheers,

John.

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Frank here again.

Thanks for all the further input.

I think I know now how I want to manage the zones either with an HB or
a combi.

However, I suspect that the actual saving either way (HB or combi) are
fairly minimal. It's more a question of initial outlay, system
flexibility, ease of servicing and future proofing (ie electric
immersion back up or solar energy when the Russians cut off the gas).
Many of the boxes are ticked by a heat bank - perhaps a few more than
the combi. There is a greater outlay of time with the HB and although
the technology seems tried and tested actually building the heatbank
and commissioning it is something of an act of faith as they are not
an everyday domestic item.

So some more questions:

I need more info in the PHE please.
Who would you say make the most reliable units and what sort of size
am I looking for?
How do I predict the flow rate for a given temperature of HW?
What is the service life of a PHE likely to be?
Great help if you could point me in the direction of more technical
data of PHEs

I think it would be best in my setting to have two smaller cylinders.
One for the CH and one for the HW.

I could site them optimally for each use and have the benefit of
greater control of each cylinder than if I were trying to make one
cylinder do both jobs. Or am I barking?

I've looked at this schematic:

hxxp://aycu27.webshots.com/image/38786/2000028197462625313_rs.jpg

and taken on board DD's tweeks to the design. It looks very
buildable. My only concern would be pump noise and what *exactly* the
blending valve is designed to do in this cicuit. Presumably if I used
two cylinders I'd need another blending valve and they would be set at
different temps because (I assume) the CH cylinder is likely to be at
a lower temp setting that the HW one.

That's all for now. Thank you again for this thread.

Frank.

wrote:

However, I suspect that the actual saving either way (HB or combi) are
fairly minimal. It's more a question of initial outlay, system

Yup. It is the way you need to look at it, although DD will argue to the
contrary, you can't really claim that a HB solution will save much if
any money over directly driven rads with a modern boiler - the numbers
just don't support it. Hence it needs to come down to what else it buys
you, and is that something worth paying for.

flexibility, ease of servicing and future proofing (ie electric

Ease of servicing is partly down to what facilities you design in, and
how simple the system is in the first place.

immersion back up or solar energy when the Russians cut off the gas).
Many of the boxes are ticked by a heat bank - perhaps a few more than

Yup, a heatbank is handy when you want to aggregate different sources of
heat - especially if some of those are "low grade" heat.

the combi. There is a greater outlay of time with the HB and although
the technology seems tried and tested actually building the heatbank
and commissioning it is something of an act of faith as they are not
an everyday domestic item.

So some more questions:

I need more info in the PHE please.
Who would you say make the most reliable units and what sort of size
am I looking for?

I take it you are talking about a PHE used for on the fly HW heating
from the store rather than one used for isolating a vented store from a
sealed primary?

Size is the easier one, you can work that one back from your HW flow
rate requirements. So say you want 25 lpm of water at a final temp of 50
degrees, and this is to happen with the ground water at 5 degrees, you
need to shift 4200 x 45 x 25 = 4.7MJ / min or 78kJ/sec aka kW. So 80kW
or better would be required here.

How do I predict the flow rate for a given temperature of HW?

rearrange the above formula...

So for a given PHE power of P, a temperature rise of Td, you get a flow
rate F of:

P x 60
F = ---------
4200 x Td

will give a flow in kg/min or litres

What is the service life of a PHE likely to be?

How hard is your water?

Great help if you could point me in the direction of more technical
data of PHEs

GEA have a fair bit of info on their site:

http://www.gea-ecoflex.de/

I think it would be best in my setting to have two smaller cylinders.
One for the CH and one for the HW.

I could site them optimally for each use and have the benefit of
greater control of each cylinder than if I were trying to make one
cylinder do both jobs. Or am I barking?

You are running counter to your requirement for simplicity and
serviceability. The only particular advantage it addresses is location
close to point of use. Note that only really matters for HW production
- you probably are not going to care if the rads need another 20 secs to
get hot.


--
Cheers,

John.

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| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

"John Rumm" wrote in message
...
wrote:

However, I suspect that the actual saving either way (HB or combi) are
fairly minimal. It's more a question of initial outlay, system

Yup. It is the way you need to look at it, although DD will argue to the
contrary, you can't really claim that a HB solution will save much if any
money over directly driven rads with a modern boiler - the numbers just
don't support it.

What numbers do you have? None at all. You are making this up.

flexibility, ease of servicing and future proofing (ie electric

Ease of servicing is partly down to what facilities you design in, and how
simple the system is in the first place.

A heat bank using a simple boiler, time clock in one location, Smart pumps
in one location for each zone is: simple, easy to maintain and cheap to run
and maintain.

immersion back up or solar energy when the Russians cut off the gas).
Many of the boxes are ticked by a heat bank - perhaps a few more than

Yup, a heatbank is handy when you want to aggregate different sources of
heat - especially if some of those are "low grade" heat.

the combi. There is a greater outlay of time with the HB and although
the technology seems tried and tested actually building the heatbank
and commissioning it is something of an act of faith as they are not
an everyday domestic item.

They are very common indeed, maybe not around your way though. Whole
estates are fitted with them.

So some more questions:

I need more info in the PHE please.
Who would you say make the most reliable units and what sort of size am I
looking for?

DPS sell them for approx £70. Gledhill can supply. Go to their site and
download the instructions on the Systemate and the the part No. is in their.
Ring a local agent and they will give a price, usually around £80. Or you
may know a local dealer who supplies them. Go for a long and thin plate of
100 kW. The Swep that Gledhill use is very good for efficiency. The Danfoss
double pass plates which are great but expensive.

What is the service life of a PHE likely to be?

How hard is your water?

Large plate resist scale as the plates flex, so scaling is not an issue wuth
them. Not the case on small plates used in many combis. Best use a 100kW
plate as the plates are larger. 20 years minimum should be the expect life
of a quality plate.

Great help if you could point me in the direction of more technical
data of PHEs

GEA have a fair bit of info on their site:

http://www.gea-ecoflex.de/

http://www.heatweb,com
have some details on plates too.

I think it would be best in my setting to have two smaller cylinders.
One for the CH and one for the HW.

I could site them optimally for each use and have the benefit of
greater control of each cylinder than if I were trying to make one
cylinder do both jobs. Or am I barking?

You are on the right track.

You are running counter to your requirement for simplicity and
serviceability.

He isn't at all. He is dividing and ruling, separating the functions and
optimising each. Easy to work on, maintain and greater efficiency. The ch
buffer will be completely off in the summer. With all the zones he has a ch
buffer is ideal, and acts as a large neutral point and header combined. A
dual temperature boiler with an integrated weather compensator will keep the
CH buffer at what the outside temperature dictates and rise to heat the DHW
heat bank. Have DHW priority in heating the cylinders, using a 3-way
"diverter" valve at the boiler. CH calling? Full boiler heat to the DHW
cylinder. DHW satisfied and CH calling? The weather compensator takes
control of cylinder temperature.

wrote in message
...
I've looked at this schematic:

hxxp://aycu27.webshots.com/image/38786/2000028197462625313_rs.jpg

and taken on board DD's tweeks to the design. It looks very
buildable. My only concern would be pump noise and what *exactly* the
blending valve is designed to do in this cicuit.

The blending valve's function is explained in this thread.

It guarantees the highest temperature set so only very hot water enters the
store at the top of the cylinder ready for use to give useful DHW, even
after 2 minutes of running from cold a sink can be filled. It also
guarantees the boiler is operating within its delta T (flow/return temp
difference) and maximises thermal expansion. It guarantees top down heating
of the store and the water is heater one pass of the boiler quickening the
re-heat - this can mean a smaller cylinder in many cases as the energy of
the boiler and cylinder are combined. It also increases boiler longevity as
the boiler is operating in an ideal hydraulic environment.

Presumably if I used two cylinders I'd need
another blending valve and they would be set at
different temps because (I assume) the CH
cylinder is likely to be at
a lower temp setting that the HW one.

No. Only one blending valve for DHW. The ch buffer cylinder doesn't need
it.

Frank here again.

Thanks to both JR and DD for their further comments. I'll get my head
round the PHE info later on.

One thing DD said though had me a bit foxed. The weather compensator
makes plenty of sense. CAn they be wired into any boiler - such as
the Glow Worm you suggested or do I have to be careful to get one that
will cope?

Also 'Dual temperature boiler'? I think I can imagine what that is
but clarification would help. Sounds good - do I have to be careful
what I choose or can they all be made to do it?

Thanks again,

Frank

wrote in message
...
Frank here again.

Thanks to both JR and DD for their further comments. I'll get my head
round the PHE info later on.

One thing DD said though had me a bit foxed. The weather compensator
makes plenty of sense. CAn they be wired into any boiler - such as
the Glow Worm you suggested or do I have to be careful to get one that
will cope?

A weather compensator can be a stand alone device. Danfoss used to make a
cheap one.

Many boilers now have them integrated. Keston, Atmos, even a cheapo BIASI
model too.

Also 'Dual temperature boiler'? I think
I can imagine what that is but clarification
would help. Sounds good - do I have to be careful
what I choose or can they all be made to do it?

There are a few a round. The MAN comes to mind as well. Even a Ravenheat
does this too - not sure if it has a compensator though.

The Keston Qudos is dual temperature.
http://tinyurl.com/257dae This is cheap for what it is.
The manual can be downloaded from,
http://www.keston.co.uk

The DHW sensor/stat is wired into the boiler. When DHW is called it runs up
to max temp (or what you select), when no DHW and CH called then it reverts
to weather compensator control

The Atmos Intergas has similar specs, except I don't think it is duel
temperature. This can usually be done by opening, or shorting the outside
sensor making the burner run full on. Then it can be used to reheat DHW
fast. Best see the makers on how get around it. Atmos are super reliable
and very well made
http://www.atmos.uk.com/product_grou...n=000200130003
The installation manual is also on line too.

Many of these boilers have a laptop interface so you can see how the boiler
is performing.

From Frank

A first look at the installation guide etc. for the Keston Kudos is
very promising. A whole load of functionality for around the same
price mark as other less handy looking machines. I like the wiring
being external and proper diagrams in the guide etc.

Are Kestons well thought of in terms of value and reliability?

Two other things at this stage I would like comments on please:

1) It looks as thought the pump sending HW to the PHE from the
cylinder is either on or off. When load on the DHW is light does this
not mean that quite hot water is sent back t the bottom of the
cylinder and disadvantageously admixed with the colder water there? I
presume that the flow switch in the mains supply is either on or off
and likewise the Grunfos.

2) Using a direct cylinder for the CH heatbank may be the most
efficient but risks grot from the rads getting into the boiler. Is
the magnaclean generally though to be adequate? I suppose one could
put a PHE between the boiler and the DHW cylinder but there comes a
point...

Thought please.

Frank

wrote in message
...
From Frank

A first look at the installation guide etc. for the Keston Kudos is
very promising. A whole load of functionality for around the same
price mark as other less handy looking machines. I like the wiring
being external and proper diagrams in the guide etc.

Are Kestons well thought of in terms of value and reliability?

They are generally fine. The Celsuis was a dog, but by the time they got rid
of the problems they dropped it. This appears a dropped down commercial
boiler with parts from other reliable boilers. It can also have 60 metres
of plastic flue pipe (normal drain pipe).

Two other things at this stage I would like comments on please:

1) It looks as thought the pump sending HW to the PHE from the
cylinder is either on or off. When load on the DHW is light does this
not mean that quite hot water is sent back t the bottom of the
cylinder and disadvantageously admixed with the colder water there? I
presume that the flow switch in the mains supply is either on or off
and likewise the Grunfos.

That is the case. Having spreader pipes prevents excessive disturbance of
stratification.

2) Using a direct cylinder for the CH heatbank may be the most
efficient but risks grot from the rads getting into the boiler. Is
the magnaclean generally though to be adequate?

Yes.

I suppose one could
put a PHE between the boiler and the DHW cylinder but there comes a
point...

Thought please.

The Magnaclean is all you need. And just re-dose the system every 4 years
with inhibitor.

wrote in message
...
From Frank

A first look at the installation guide etc. for the Keston Kudos is
very promising. A whole load of functionality for around the same
price mark as other less handy looking machines. I like the wiring
being external and proper diagrams in the guide etc.

Are Kestons well thought of in terms of value and reliability?

Two other things at this stage I would like comments on please:

There was a thread on the Keston a few weeks back.

Thanks for that DD.

You said 'That is the case. Having spreader pipes prevents excessive
disturbance of
stratification.'

As I understand it a spreader pipe in inserted through the lower
flange and has holes drilled below and to the sides. Presumably if
this is warmer than the water at the bottom it will pass up through it
and with it. So - if I am picturing this correctly - there must be
mixing and disruption of the stratification. How much of problem is
this to efficiency? Are there any other ways of reducing the mixing?
Or is it not a problem?

Waiting to hear back from the Gledhill rep how much for the PHE

I wonder what size the cylinders should be.

Look forward to hearing your further thoughts.

Frank

Doctor Drivel wrote:

However, I suspect that the actual saving either way (HB or combi) are
fairly minimal. It's more a question of initial outlay, system

Yup. It is the way you need to look at it, although DD will argue to
the contrary, you can't really claim that a HB solution will save much
if any money over directly driven rads with a modern boiler - the
numbers just don't support it.

What numbers do you have? None at all. You are making this up.

I already gave you an example.

If you look at the (externally verified and tested) specs of many modern
boilers, you will note they will run at about 92%+ efficiency into a
conventional radiator setup with room stat interlock and TMVs on the non
room stat rads. (SEDBUK values typically adjust this down to 90% taking
into account seasonal influences)

Note that this is a real efficiency figure calculated using the gross
energy content of the gas - none of your "make believe 106% no use to
man nor beast" style efficiencies. So any amount of extra complexity you
decide to glue between your boiler and radiators, is not going to be
able to raise the efficiency by more than 5% at best.

Back in the days of high water content fixed output boilers with dumb
controls, the store may have made a notable difference in efficiency,
and been well worth having on fuel consumption grounds alone. That is no
longer the case.

So by all means use a store if it gets you other facilities that you
desire, just don't be mislead into thinking it will save you any
significant money

--
Cheers,

John.

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\================================================= ================/

Frank Here again,

Most parts seem easy enough to get hold of but there are two items
I've little experience of.

Flow switch and blending valve.

Any recommendations of makes that have been found reliable and good
value by others?

Many thanks,

Frank

wrote:

Most parts seem easy enough to get hold of but there are two items
I've little experience of.

Flow switch and blending valve.

http://cpc.farnell.com/jsp/search/br...ow+switch&Ntx=

(the reed switch versions ought to be very reliable as long as you make
sure you don't overload the contacts)

Any recommendations of makes that have been found reliable and good
value by others?

Screwfix and BES both have blending valves. Can't tell you which is
better though.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Frank again,

Thanks for all that.

Should manage a proper schematic and costing of my proposed system in
the next day or two and then bound to have a few more questions.
Thanks again for all the above information.

Frank

wrote in message
...
Frank Here again,

Most parts seem easy enough to get hold of but there are two items
I've little experience of.

Flow switch and blending valve.

Any recommendations of makes that have been found reliable and good
value by others?


Here is how to do a DHW only heat bank and the parts...

Read http://www.heatweb.com for an explanation of how heat banks work.

1. Fit a Surrey type of flange in the top tapping of cylinder. 1" if you
can.

2. The plate heat exchanger connects to the Surrey flange port that is
immersed in the cylinder water. Drill a few holes in the protruding tube
that goes into the water to ensure heat is extracted from cylinders dome,
not being pumped to the bottom of the cylinder. The protruding tube has a
plate over the end to stop the water heat right to the bottom of the
cylinder.

3. The boiler flow is taken from the other connection of the Surrey flange
on the top of the cylinder. The return into the old cold feed tapping.

4. From the Surrey to the plate and then to the pump then to a spring loaded
check valve and back into the bottom cylinder port. Make a diffuser by
inserting 22mm pipe into the bottom cylinder port and drilling holes in and
stopping up the end with an internal pipe stop (available from BES). File
down the inside of a brass compression fitting that screws to the cylinder
port, removing the pipe stop so the pipe can go straight through. This will
spread the returning water mainly down, so it will not upset stratification
in the cylinder.

5. Two cylinder stats can be used to give a long efficient boiler recovery
burn. One stat about half way up and the other about 25% of the way up the
cylinder. Set bottom say to 70-80C, set top say to 60-65C. The stats must be
latched in with a relay.

6. The cold mains direct from the cold mains stoptap with no tee offs. Take
into the flow switch then into the bottom connection of the plate heat
exchanger and then to the DHW blending valve.

7. Have thermostatic shower mixers and take the hot supply for these
directly off the plate heat exchanger "before the TMV (blending valve). No
need to run DHW through two thermostatic mixers.

8. Install a phosphor de-scaler, or other de-scaler, on the incoming mains
pipe.

9. Install isolation valves on heavy usage appliances such as the washing
machine, and throttle back so it will not rob showers and baths of hot
water.

10. Have the F&E tank top up at the bottom of the cylinder and vent at the
top. You may want to vent from the boiler flow pipe.

11. Fill with inhibitor - about 1% of total system volume. An average system
is approx 100 litres, so a system has one 1 litre can. If say 150 litre
cylinder then two cans for the cylinder alone, which is three.

12. Fit a Magnaclean filter on the rads return pipe to the boiler.

The performance is brilliant and you will be delighted with the mains fed
showers and no vibrating power shower pump noise. High pressure mixers can
be on all appliances.

Gledhill will supply a Plate Heat X. The model for the 145 litre Systemate
will do. If you can get another cheaper source then try them. A 100kW plate
heat exchanger is needed

http://www.bes.co.uk or Screwfix will supply most of the fittings. They
don't do the plate heat exchangers.

Farnell will supply the flow switch http://www.farnell.co.uk Farnell
number: 1006771 with 22mm compression joints.

Flow Switch, makers site: The FS06
http://www.gentechsensors.com/produc...asp?ProdId=113
This flow switch is about the best - very good.

If the boiler requires to be in a sealed system then have a cylinder with a
quick recovery coil, the boiler heats this ASAP. Most boilers can be fitted
to an open vented system. Best have open vented.

wrote in message
...
Frank Here again,

Most parts seem easy enough to get hold of but there are two items
I've little experience of.

Flow switch and blending valve.

Any recommendations of makes that have been found reliable and good
value by others?

The boiler flow/return blending valve? Reliance 28mm. I think onepost
gives the model number.

"John Rumm" wrote in message
...
Doctor Drivel wrote:

However, I suspect that the actual saving either way (HB or combi) are
fairly minimal. It's more a question of initial outlay, system

Yup. It is the way you need to look at it, although DD will argue to the
contrary, you can't really claim that a HB solution will save much if
any money over directly driven rads with a modern boiler - the numbers
just don't support it.

What numbers do you have? None at all. You are making this up.

I already gave you an example.

In short, none at all.

Back in the days of high water content fixed output boilers with dumb
controls, the store may have made a notable difference in efficiency, and
been well worth having on fuel consumption grounds alone. That is no
longer the case.

Once again no figures given. You must stop making things up.

If making a heat bank it is rather foolish not to take the CH off the store
as it gives a great CH buffer and the befits have been explained in other
posts. It is clear you can't see this, so please be quiet as a person here
wants sound advice, not the ramblings of an amateur whose only experience is
fitting a combi.

As to the efficiencies of these boilers that directly heat the rads. The
system is balanced properly and by-pass valve set correctly (few are set
correctly). At the weekend I was in a friends house - a big house. He said
the system warms up evenly enough around the house then one side of the
house is hotter than the other as the rads on one side are hotter.

I looked and found that the by-pass valve opened too early (all too common)
and much of the flow went back to the boiler. The flow which never went to
the rads on one side of the house. This reduced the condensing efficiency
of the boiler and efficiency went right down. I adjusted the by-pass and all
was well. With many boilers the by-pass has to open early as they require a
minimum flow through the boiler which may be quite high.

Take SEDBUK with a pinch of salt - a guide only. Efficiencies can be
bettered by engineering the system.

wrote in message
...
Thanks for that DD.

You said 'That is the case. Having spreader
pipes prevents excessive disturbance of
stratification.'

As I understand it a spreader pipe in inserted through the lower
flange and has holes drilled below and to the sides. Presumably if
this is warmer than the water at the bottom it will pass up through it
and with it. So - if I am picturing this correctly - there must be
mixing and disruption of the stratification. How much of problem is
this to efficiency? Are there any other ways of reducing the mixing?
Or is it not a problem?

The disturbance is minimal when using spreaders. Also, the heat is not
wasted it is put back where is came from - the cylinder. Once the DHW pump
is off the hotter water rises and stratification occurs naturally as the
cylinder settles again.

Waiting to hear back from the
Gledhill rep how much for the PHE

I wonder what size the cylinders should be.

I'll be back on that.

Doctor Drivel wrote:

What numbers do you have? None at all. You are making this up.

I already gave you an example.

In short, none at all.

The sums are quite easy to do. Even for you.

Back in the days of high water content fixed output boilers with dumb
controls, the store may have made a notable difference in efficiency,
and been well worth having on fuel consumption grounds alone. That is
no longer the case.

Once again no figures given. You must stop making things up.

Well if you can explain how you can pay for all this out of a maximum of
5% efficiency gain then be my guest.

If making a heat bank it is rather foolish not to take the CH off the
store as it gives a great CH buffer and the befits have been explained
in other posts. It is clear you can't see this, so please be quiet as a

I can't see it because it is wrong. Alas you can't see it as it is too
firmly entrenched in your mind along with various other old wife's tales.

As to the efficiencies of these boilers that directly heat the rads. The
system is balanced properly and by-pass valve set correctly (few are set

Woa there boy, you seem to have a bit of a fixation on bypass valves.
Are these like plastic plumbing were you claim the whole system does not
work properly based on your hacksaw escapades?

With room stat controlled zones, that have rad without a TMV there is no
need for a bypass valve within any of the zones. The only time you may
need a bypass outside of the zones is to allow pump overrun (which
occurs when the burner is not firing and hence loses no efficiency).

If you are paranoid about your ability to set this correctly, then place
your bypass on a three way diversion valve such that the flow path only
exists where there is no call for heat from any zone.

correctly). At the weekend I was in a friends house - a big house. He

They let you out at weekends do they?

Take SEDBUK with a pinch of salt - a guide only. Efficiencies can be
bettered by engineering the system.

Agreed, but not by enough to make all the titting about cost effective.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 2008-01-21 12:54:17 +0000, John Rumm said:

Doctor Drivel wrote:

correctly). At the weekend I was in a friends house - a big house. He

They let you out at weekends do they?

"Big House" being a slang term (principally American I believe) for
prison........

"Andy Hall" wrote in message news:4794e3b8@qaanaaq...

"Big House" being a slang term (principally American I believe) for
prison........

Matt, have you been a big house?

Frank here again.

Glad to sat Gledhill very co-operative. GT017 PHE for £74 plus vat
and carriage.

The flow switch looks fine too.

I was wondering about a compromise system. Please tell me what you
think.

What led me to thinking about heat banks in the first place was the
slow flow rate of DHW from 28-30kw combis and the desire to get a long
life out of a boiler by using a HB for the CH.

Instead of HB for both DHW and CH I wonder if a reasonable alternative
might be to slightly preheat the incoming mains water (7C at the
moment) to say 20-25 degrees by running it through a PHE connected to
a suitable part of the CH heatbank cylinder and then putting it
through a combi.

What would the result be of putting this through a combi rated to
give, lets say 12lts per minute at a rise of 35C if we expected it
only to give a rise of 25 or 30 degrees.

Would this be a good way of getting 15ltrs/min plus of water at 50-55C
out of a modest sized Combi?

Or one could take the whole 35C rise at slower rate and mix it down to
a safer temp with a blender.

When the CH is off the incoming mains water is warmer. At the moment
the flow rate from anything but a really big combi is going to be
little more than a dribble. Anything 13ltrs/min and up of 50 - 55C
water is fine for me . Mixes down to about 44 for a nice shower and
hot enough to give a hot shot into a cooling bath to re-invigourate
it.

We don't use much DHW but it would be good to have decent delivery
when we do. I know the full HB thing will do that but this is a kind
of Lite version.

Just wondering what the drawbacks of this idea are and how it might by
improved or why it should be discarded.

Thanks again,

Frank

wrote:

What led me to thinking about heat banks in the first place was the
slow flow rate of DHW from 28-30kw combis and the desire to get a long
life out of a boiler by using a HB for the CH.

Instead of HB for both DHW and CH I wonder if a reasonable alternative
might be to slightly preheat the incoming mains water (7C at the
moment) to say 20-25 degrees by running it through a PHE connected to
a suitable part of the CH heatbank cylinder and then putting it
through a combi.

You can, with provisos. You would need to check the specs on the combi
carefully to see if it has a maximum input water temperature - some
don't like hot water up em.

You might be able to get enough preheating without a PHE - just by using
a indirect cylinder and running the cold feed through the coil. A bog
standard indirect cylinder may add 5kW that way - a fast recovery could
add 20+.

Having said that, you are throwing away the best advantage of the
heatbank - i.e. the ability to get decent flow rates of mains pressure
water.

What would the result be of putting this through a combi rated to
give, lets say 12lts per minute at a rise of 35C if we expected it
only to give a rise of 25 or 30 degrees.

Well take the given spec and convert that to energy terms:

12 x 4200 x 35 = 1.764MJ / min

So, lets say you want water at 40, and the incoming main is preheated to 20:

1.764x10^3
New flow rate = -----------------
4200 x (40 - 20)


= 21 lpm of 40 degree water.

Would this be a good way of getting 15ltrs/min plus of water at 50-55C
out of a modest sized Combi?

Not especially unless you have the PHE and heatbank do most of the heavy
lifting. In which case why bother with the combi.

(its a workable way of making use of low grade heat from other sources
like solar thermal etc)

Or one could take the whole 35C rise at slower rate and mix it down to
a safer temp with a blender.

Or just take the preheated water into the cold side of a blending valve
and the combi output into the hot.

When the CH is off the incoming mains water is warmer. At the moment
the flow rate from anything but a really big combi is going to be
little more than a dribble. Anything 13ltrs/min and up of 50 - 55C
water is fine for me . Mixes down to about 44 for a nice shower and
hot enough to give a hot shot into a cooling bath to re-invigourate
it.

So you need about 45.5kW of heating power available to archive this in
the winter.

We don't use much DHW but it would be good to have decent delivery
when we do. I know the full HB thing will do that but this is a kind
of Lite version.

If you want the lite version just leave the rads off the HB and use it
just for HW.

Just wondering what the drawbacks of this idea are and how it might by
improved or why it should be discarded.

cue dribble's two combis suggestion

;-)



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

wrote in message
...
Frank here again.

Glad to sat Gledhill very co-operative.
GT017 PHE for £74 plus vat and carriage.

Good price. The Swep is great plate Heat exchanger for DHW as it is long and
thin, rather than short and fat.

Instead of HB for both DHW and CH
I wonder if a reasonable alternative
might be to slightly preheat the incoming
mains water (7C at the moment) to say
20-25 degrees by running it through a
PHE connected to a suitable part of the
CH heatbank cylinder and then putting it
through a combi.

What is the point of this when the Heat bank can deliver high flowrates all
by itself and uses a cheaper simpler boiler that will not cycle? You will
gain nothing.

When the CH is off the incoming
mains water is warmer.

At the moment the flow rate from
anything but a really big combi is
going to be little more than a dribble.

Most smaller combis deliver 10 to 12 litres/min. Middle range 13 to 16, top
end 15 litres plus. There are the odd tiny 9 litres/min jobs still about,
however combi performance has increased dramatically in the past 5 years, to
the point they must be the first consideration in the average British home.
They are highly cost effective, even the top end quality models.

Thank you very much for those comments.

Of course combis don't do vented as far as I know for the CH so if I
used a HB off a combi for the CH presumably it would need to be heated
via indirect coil or another PHE. Is that correct?

Thanks again,

Frank.

On 2008-01-23 01:09:52 +0000, "Doctor Drivel" said:


wrote in message
...
Frank

here again.

Glad to sat Gledhill very co-operative.
GT017 PHE for £74 plus vat and carriage.

Good price. The Swep is great plate Heat exchanger for DHW as it is
long and thin, rather than short and fat.

Instead of HB for both DHW and CH
I wonder if a reasonable alternative
might be to slightly preheat the incoming
mains water (7C at the moment) to say
20-25 degrees by running it through a
PHE connected to a suitable part of the
CH heatbank cylinder and then putting it
through a combi.

What is the point of this when the Heat bank can deliver high flowrates
all by itself and uses a cheaper simpler boiler that will not cycle?
You will gain nothing.

When the CH is off the incoming
mains water is warmer.

At the moment the flow rate from
anything but a really big combi is
going to be little more than a dribble.

Most smaller combis deliver 10 to 12 litres/min. Middle range 13 to
16, top end 15 litres plus. There are the odd tiny 9 litres/min jobs
still about, however combi performance has increased dramatically in
the past 5 years, to the point they must be the first consideration in
the average British home. They are highly cost effective, even the top
end quality models.

They even defy physics these days.

"Andy Hall" wrote in message news:479706e3@qaanaaq...
On 2008-01-23 01:09:52 +0000, "Doctor Drivel" said:


wrote in message
...
Frank

here again.

Glad to sat Gledhill very co-operative.
GT017 PHE for £74 plus vat and carriage.

Good price. The Swep is great plate Heat exchanger for DHW as it is long
and thin, rather than short and fat.

Instead of HB for both DHW and CH
I wonder if a reasonable alternative
might be to slightly preheat the incoming
mains water (7C at the moment) to say
20-25 degrees by running it through a
PHE connected to a suitable part of the
CH heatbank cylinder and then putting it
through a combi.

What is the point of this when the Heat bank can deliver high flowrates
all by itself and uses a cheaper simpler boiler that will not cycle? You
will gain nothing.

When the CH is off the incoming
mains water is warmer.

At the moment the flow rate from
anything but a really big combi is
going to be little more than a dribble.

Most smaller combis deliver 10 to 12 litres/min. Middle range 13 to 16,
top end 15 litres plus. There are the odd tiny 9 litres/min jobs still
about, however combi performance has increased dramatically in the past 5
years, to the point they must be the first consideration in the average
British home. They are highly cost effective, even the top end quality
models.

They even defy physics these days.

Matt, have you been drinking this time of the morning?

wrote in message
...
Thank you very much for those comments.

Of course combis don't do vented as far as I know for the CH so if I
used a HB off a combi for the CH presumably it would need to be heated
via indirect coil or another PHE. Is that correct?

Frank, I think you mean a CH buffer heated via the combi and use the combi
for DHW only. Yes, you would need a fast recovery indirect cylinder or a
pump and plate heat exchanger to heat the CH buffer cylinder.

"Doctor Drivel" wrote in message
reenews.net...

wrote in message
...
Thank you very much for those comments.

Of course combis don't do vented as far as I know for the CH so if I
used a HB off a combi for the CH presumably it would need to be heated
via indirect coil or another PHE. Is that correct?

Frank, I think you mean a CH buffer heated via the combi and use the combi
for DHW only. Yes, you would need a fast recovery indirect cylinder or a
pump and plate heat exchanger to heat the CH buffer cylinder.

If using a combi and a CH buffer, then the cylinder size must be the total
system volume plus 25%. This means in the morning a full cylinder of hot
water is waiting to be dumped into the rads giving instant CH heat up. If
the combi is used for DHW the 25% extra will buffer the heating untill the
combi reverts to re-heating the cylidner.

Thanks for that.

I can't find any ready reckoner for radiator volume. Without doing a
drain down at this stage. If we take an average radiator of 600x1000
double convector multiply by 13 and add the volume in the combi and a
bit for pipe work what sort of figure will I end up with?

Now they really tricky bit. Which boiler?

Given that I want this thing to last for as long as possible I suppose
the best thing is to be prepared to pay a bit of a premium to get a
make with a good track record, decent reputation for spares supply and
ease of service and repair.

Boderus looks a possible or should I avoid the non SS heat exchanger?

Any thoughts?

Thanks again,

Frank
Particular makes to avoid?

wrote in message
...
Thanks for that.

I can't find any ready reckoner for radiator volume. Without doing a
drain down at this stage. If we take an average radiator of 600x1000
double convector multiply by 13 and add the volume in the combi and a
bit for pipe work what sort of figure will I end up with?

The average modern system is 80 to 100 litres

Now they really tricky bit. Which boiler?

Given that I want this thing to last for as long as possible I suppose
the best thing is to be prepared to pay a bit of a premium to get a
make with a good track record, decent reputation for spares supply and
ease of service and repair.

Boderus looks a possible or should I avoid the non SS heat exchanger?

If heating a heat bank "directly" then I would go for SS - and use a Glow
Worm HXi or Vaillant equivalent open vented boiler. If indirectly, I then
any open vented, SS or alum'. If having CH off the cylinder then have a
Magnaclean filter on the CH return to the cylinder.

The Buderus 600 range is v good. Buderus is owned by Bosch and
Worcester-Bosch service people attend, so no problems there. Buderus is a
large outfit on the Continent, much larger than Worcester. Eventually the
name Bosch may replace Worcester and Buderus.

Thanks for the info.

I'm attracted by Buderus because they look well made and as if id
would be straightforward to replace components. S you say, a big
outfit so parts should be okay to fnd at reasonable prices. For
instance I think I read somewhere that the HX was about £125 and came
out on releasing some screw-clips. You mentioned the 600 range but
assume your comments go for the 500 range as well.

On another tack: I've fitted half a dozen boilers and CH systems in
the last decade to my own properties. I've done everything myself and
got a chap to certify the gas.

Never had any problems (Vokera mostly) but have always assumed that
because I'm not Corgi somehow my workmanship would magically be deemed
defective and no warranty honoured.

Am I right in continuing to assume this or do you have a cunning work-
round?

If you've time:

I've never had reason to use blending valves before so don't know what
to expect. One possible (ironic) problem with my proposed system for
pre-heating the cold (often 6-8C) mains water going to the combi - to,
say, 20C - is that it might easily heat much higher. Are blending
valves reliable enough to set one down stream of the PHE on the mains
supply to the boiler to mix in more cold and always send the water to
the combi @ 20C +/- a degree or two?

Not sure what it would do to the combi long term to send it anything
much above what it might have to cope with on a hot day in Spain for
instance - say, 25C or a bit more. My expectation is that the combi
won't like just topping the heat up say 15 degrees (If it comes in
from the PHE at 35C) without waste or perhaps damage.

If it won't mind then all well and good. Very flexible system.

Comments much appreciated as usual.

Thanks again,

Frank

wrote in message
...
Thanks for the info.

I'm attracted by Buderus because they look well made and as if id
would be straightforward to replace components. S you say, a big
outfit so parts should be okay to fnd at reasonable prices. For
instance I think I read somewhere that the HX was about £125 and came
out on releasing some screw-clips. You mentioned the 600 range but
assume your comments go for the 500 range as well.


Yep a clip in Heat exchanger. Brilliant. The 600 range is better. I think
they do an open vent model;. Check.


On another tack: I've fitted half a dozen boilers and CH systems in
the last decade to my own properties. I've done everything myself and
got a chap to certify the gas.

Never had any problems (Vokera mostly) but have always assumed that
because I'm not Corgi somehow my workmanship would magically be deemed
defective and no warranty honoured.

Am I right in continuing to assume this or do you have a cunning work-
round?


It is legal to DIY. The makers need to honour the guarantee, as it is legal
if fitted properly. A way around is fit it and get a landlords certificate.


I've never had reason to use blending valves before so don't know what
to expect. One possible (ironic) problem with my proposed system for
pre-heating the cold (often 6-8C) mains water going to the combi - to,
say, 20C - is that it might easily heat much higher. Are blending
valves reliable enough to set one down stream of the PHE on the mains
supply to the boiler to mix in more cold and always send the water to
the combi @ 20C +/- a degree or two?


Should be fine. But I can't see the reason to pre-heat when the heat bank
doing DHW will do it far better than a combi. By pre-heating you are not
getting anything for nothing, as you still have to pay for the heat that
pre-heats.


Not sure what it would do to the combi long term to send it anything
much above what it might have to cope with on a hot day in Spain for
instance - say, 25C or a bit more. My expectation is that the combi
won't like just topping the heat up say 15 degrees (If it comes in
from the PHE at 35C) without waste or perhaps damage.


Some combis can accept pre-heated water at 60C and above.

wrote in message
...

I've never had reason to use blending valves before so don't know what
to expect. One possible (ironic) problem with my proposed system for
pre-heating the cold (often 6-8C) mains water going to the combi - to,
say, 20C - is that it might easily heat much higher. Are blending
valves reliable enough to set one down stream of the PHE on the mains
supply to the boiler to mix in more cold and always send the water to
the combi @ 20C +/- a degree or two?


One way to improve combi performance is to forma secondary circulation loop
around the taps to give instant DHW at he taps. Not new and Ethos have a
kit for this for their combi. They can be made up for most combis using a
bronze pump, a few check valves and a pipe stat.

A only give instant DHW at the taps. The way to improve flow rate
performance and give electric backup is have a number 15 litre mains
pressure electric water heaters in the loop. One under the sink, under
basins, etc. They are unvented and because they under not over 15 litres
they can be DIYed. So having 3 of them giving 45 litres of storage
distributed around the house, assisted by the combi will fill a bath up
pretty fast. When say the bath tap or shower is on, hot water is drawn out
of the DHW secondary circulation loop. this will cool and a pipe stat will
bring in the combi which will be re-heating the loop as the DHW is being
drawn off.

When exhausted of heat the combi will still operate to heat them back up via
the bronze pump. If the combi is down turn them on and electric backup. So
for around £300, you can have instant DHW at the taps, no dead-leg pipe,
fast flowrates and electric backup. No big expensive cylinder as the DHW
storage is distributed around the house.

Funny you should mention that. The kitchen is a long way from the
boiler so I was going to bung a Santon in there with a feed to the
downstairs loo and probably the utility room.


Worth at this stage reviewing the plus points and Neg points. My
proposed systemis:

Heatbank for CH with 3/4 pumped zones off it. HB cylinder VERY well
insulated

Heated by condensing combi

DHW preheated by PHE off Heatbank before going through Combi

Cold water to basins, WCs and baths from loft tanks with slow running
ball-cocks.

Mains CW to shower and Kitchen.

Santon Aquaheat in in cellar under kitchen.

Advantages:
CH - very efficient use of boiler. Heat bank can be at optimum
temperature for CH and available for CH when combi heating DHW or off
(until HB run down)

Decent combi not much more than a decent vented system boiler.

Capital outlay of system kept under control

For low use of hot water (95% of time - two baths and a shower per
day) saves keeping HB hot.
During 5/12 when CH not on either no pre-heat of DHW or minimal
occasional warming of heatbank only necessary to take the edge off and
give good flow.

If house full for a weekend. Merely juice up the HB for good flow
through the combi Via the PHE.

Instant HW which never runs out even if the HB is exhausted or breaks
down.

DHW available via HB and immersion if boiler breaks down. Also some
CH though expensive.


Disadvantages:

Er... DD etal please fill in.


Thanks again for your excellent help with this project.

Frank