After many many years of waiting for the necessary cash it is time for
me to upgrade my heating.

I have a large 45Kw modulating boiler. OK so it is a bit over the
top, but it modulates down to 11kw of so and I have a large house, and
ther builder paid for it. BUT, currently with knackered (inadequate)
pipework and the old cylinder - it rarely gets used over about 25Kw.

I intend to loose the old hot tank, relocate to the garage and put a
small rad in the airing cupboard.

One of the problems I have at present, is that my boiler controls
insist on absolute hot water priority. With the current cylinder, I
then feel the heating go off for the 20 minutes it takes to reheat the
hot water cylinder.

Whatever solution I come up with, I want to continue to use the
modulating boiler controls (together with a classy programmable
thermostat) to allow the boiler to modulate all the way down to run
the rads in the evening.

OK - so choice time.

Originally I thought of using a very high efficiency unvented
cylinder. The Keston Spa (210l) has a very high efficiency primary
coil. The thinking being that if HW is to have priority - make it
last the shortest time.
I still think I might go that way, but am a little put off by the
thoughts of having a potential bomb in the garage, as well as the 3Bar
limit on pressure (reduced I assume as well by the TMV) as well as the
ongoing maintence costs.

Then there's the plethora of heat stores and thermal banks.

I'd appreciate help on the choice here, as there seems to be a lot of
discussion as well as entrenched positions.

I can figure stuff out, if I have data, but that appears to be hard to
get.

So - the questions a

Should I go for a heat store where the CH is run off the boiler and
the DHW off the heat store? [ Pandora arranged as S plan? ] If so -
what is the reheat time? Should I install the flow switch trick on
the bath and showers? [ Is this a safe thing to do anyway, as an
overheat condition could occur if flow was restricted, or the switch
failed. ] What size do I need.

Should I run both off one of the different kinds of integrated heat
store?

Do the plates in a plate heat exchanger get dangerously hot to the
touch?

Any coherent thoughts , or pointers to unbiased discussions/texts
welcome.

Peter

PS I currently have 1 bathroom, 2 showers and am about to install a
third barthroom. I have 6 bedrooms. I am changing to pressurised
CH, in order to add rads to the attic. Similarly, I need presurrised
DHW for the attic bathroom.

On 20 Mar 2007 02:54:03 -0700 someone who may be "Peter"
wrote this:-

I intend to loose the old hot tank, relocate to the garage and put a
small rad in the airing cupboard.

Hot water cylinders are best located near to where the water is used
and where the boiler is. Putting cylinders where there are long dead
legs increases water consumption as well as heat losses.

PS I currently have 1 bathroom, 2 showers and am about to install a
third barthroom.

Are they and the kitchen located close together, or are they
scattered all round the house? In the latter case there comes a
point where local generation of hot water is better. This may be by
instant heaters in some cases and smaller cylinders in other places.

I have 6 bedrooms. I am changing to pressurised
CH, in order to add rads to the attic. Similarly, I need presurrised
DHW for the attic bathroom.

It would be possible for the boiler to be connected to the shell of
the unpressurised thermal store and a heating coil provided (in
addition to the hot water coil) for pressurised heating. However,
this sort of arrangement works better with the lower temperatures of
underfloor heating.

Going for a pressurised store simply means having the same "bomb"
problems as an unvented cylinder If there really is no possibility
of a heating header tank in the attic above the radiators then you
may well be best advised to go for a pressurised heating system with
unvented hot water cylinder.

An alternative would be two boilers, one pressurised for the heating
and one unpressurised for the thermal store. In effect these would
be "winter" and "all year" boilers. The latter would be relatively
small, as it would just need to regenerate the store more quickly
than heat was drawn off. I would add solar heating of the store and
probably drive some towel rails off the shell of the store so they
would dry towels all year round. The attic towel rails would be
electric.





--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

On Tue, 20 Mar 2007 02:54:03 -0700, Peter wrote:

I have a large 45Kw modulating boiler.... it modulates down to 11kw

I intend to loose the old hot tank, relocate to the garage and put a
small rad in the airing cupboard.

Whatever solution I come up with, I want to continue to use the
modulating boiler controls (together with a classy programmable
thermostat) to allow the boiler to modulate all the way down to run
the rads in the evening.

What's the heat requirement of the house? There are a couple of
calculators at
http://wiki.diyfaq.org.uk/index.php?...Heating_Design (in the
section 'Heat requirements')

My guess is that, even modulating down all the way to 11kW your boiler
is going to cycle a lot heating your house most of the time so your
modulating boiler controls aren't going to help efficiency much.

I'd be inclined to think of a f**k-off great heat bank buffering the
output of the boiler to supply both CH and DHW, connected to the boiler
directly in a vented system with a header tank - see
http://wiki.diyfaq.org.uk/index.php?...nf igurations
Being directly connected the boiler can dump its full output into the
heat bank quickly and then shut off.

It does mean the boiler will need to heat it to 70 or 80C so you won't
benefit from low return temperatures if it's a condensing boiler (you
don't say whether it is) in which case there's a question (which I can't
answer for you) of whether the gain from having it firing for very short
times rather than cycling outweighs the loss of efficiency at higher
return temps. If it's not condensing this doesn't apply.

PS I currently have 1 bathroom, 2 showers and am about to install a
third barthroom. I have 6 bedrooms. I am changing to pressurised CH,
in order to add rads to the attic. Similarly, I need pressurised
DHW for the attic bathroom.

With appropriate coils in the heat bank you can run all your rads as
a sealed system, plus UFH if you wanted that without needing a mixing
valve (just an extra pump and controls). If you're in a soft water
area or have a water softener you could have a DHW coil in the tank, but
if you have hard water you'd want an external PHE + pump + flow switch +
TMV arrangement (as shown in
http://wiki.diyfaq.org.uk/index.php?title=DIY_Heat_Bank
although these components are built-into thermal store products such as
the Pandora).

If you wanted to DIY parts of the system you could use an assembly (or
more than one) such as shown above to provide DHW closer to the points of
use instead of having a run all the way from the garage going cold between
uses. (If the primary heating water has gone cold it'll take a few seconds
for hotter water to get to your local PHE but you don't need to throw away
lots of cooled DHW to get hot water.)

Do the plates in a plate heat exchanger get dangerously hot to the
touch?

They'll be roughly as hot as the store and boiler flow pipes -
uncomfortably rather than burningly hot. I'm curious why you ask - do you
forsee a problem? You'd normally have the PHE tucked out of the way
somewhere, and preferably insulated.

On 20 Mar, 12:11, John Stumbles wrote:

(snip)

With appropriate coils in the heat bank you can run all your rads as
a sealed system, plus UFH if you wanted that without needing a mixing
valve (just an extra pump and controls). If you're in a soft water
area or have a water softener you could have a DHW coil in the tank, but
if you have hard water you'd want an external PHE + pump + flow switch +
TMV arrangement (as shown in
http://wiki.diyfaq.org.uk/index.php?title=DIY_Heat_Bank
although these components are built-into thermal store products such as
the Pandora).

If you wanted to DIY parts of the system you could use an assembly (or
more than one) such as shown above to provide DHW closer to the points of
use instead of having a run all the way from the garage going cold between
uses. (If the primary heating water has gone cold it'll take a few seconds
for hotter water to get to your local PHE but you don't need to throw away
lots of cooled DHW to get hot water.)

Do the plates in a plate heat exchanger get dangerously hot to the
touch?

They'll be roughly as hot as the store and boiler flow pipes -
uncomfortably rather than burningly hot. I'm curious why you ask - do you
forsee a problem? You'd normally have the PHE tucked out of the way
somewhere, and preferably insulated.

I've just had a look at the DIY Wiki page above and have a couple of
questions :

1 Why is the motorised valve 3 position when all it is doing is to
direct the flow either to the tank or the CH system ?

2 Is it acceptable to run the CH system at the 80 dec C that the
store is going to want.?

3 One of the comments somewhere else in the Wiki is that feeding the
PHE pump straight back into the tank can lead to de-structuring of the
stratification and suggests using a thermostatic valve in that part
of the circuit controlled by the DHW output to restrict the flow. Is
this not a preferable option to the tmv ?

4 I also do not like the triac - a round based relay from eg Maplin
is far more maintainable and easier for the average person to build
and replace ? (qualified and old electronic engineer!)

Sorry that's 4 questions !

Rob

Hot water cylinders are best located near to where the water is used
and where the boiler is. Putting cylinders where there are long dead
legs increases water consumption as well as heat losses.

PS I currently have 1 bathroom, 2 showers and am about to install a
third barthroom.

Are they and the kitchen located close together, or are they
scattered all round the house? In the latter case there comes a
point where local generation of hot water is better. This may be by
instant heaters in some cases and smaller cylinders in other places.


Amazingly, both showers, the kitchen and bathroom are all quite
close.


It would be possible for the boiler to be connected to the shell of
the unpressurised thermal store and a heating coil provided (in
addition to the hot water coil) for pressurised heating. However,
this sort of arrangement works better with the lower temperatures of
underfloor heating.

Going for a pressurised store simply means having the same "bomb"
problems as an unvented cylinder If there really is no possibility
of a heating header tank in the attic above the radiators then you
may well be best advised to go for a pressurised heating system with
unvented hot water cylinder.


But here is the thing ..it only needs to be 1.5bar or so for th
pressurise CH, so not the same situation as a 3bar DHW cylinder.

Does a direct heat bank speced for 1.5bar exist?



An alternative would be two boilers, one pressurised for the heating
and one unpressurised for the thermal store. In effect these would
be "winter" and "all year" boilers. The latter would be relatively
small, as it would just need to regenerate the store more quickly
than heat was drawn off. I would add solar heating of the store and
probably drive some towel rails off the shell of the store so they
would dry towels all year round. The attic towel rails would be
electric.


Nice idea - but I cant accomadate a second one. Need to use what I've
got already.
--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

My guess is that, even modulating down all the way to 11kW your boiler
is going to cycle a lot heating your house most of the time so your
modulating boiler controls aren't going to help efficiency much.

Actualy, the calculators both say I am about a 12kW house, suggesting
boiler sizes of between 26 and 35kW.
And I really really like the radiators running at a lower temp
continuously when merely maintaining temp.


I'd be inclined to think of a f**k-off great heat bank buffering the
output of the boiler to supply both CH and DHW, connected to the boiler
directly in a vented system with a header tank - seehttp://wiki.diyfaq.org.uk/index.php?title=Thermal_Stores_and_Heat_Ban...
Being directly connected the boiler can dump its full output into the
heat bank quickly and then shut off.

Direct connection between boiler and heat store is a wonderful
concept.


It does mean the boiler will need to heat it to 70 or 80C so you won't
benefit from low return temperatures if it's a condensing boiler (you
don't say whether it is) in which case there's a question (which I can't
answer for you) of whether the gain from having it firing for very short
times rather than cycling outweighs the loss of efficiency at higher
return temps. If it's not condensing this doesn't apply.

PS I currently have 1 bathroom, 2 showers and am about to install a
third barthroom. I have 6 bedrooms. I am changing to pressurised CH,
in order to add rads to the attic. Similarly, I need pressurised
DHW for the attic bathroom.

With appropriate coils in the heat bank you can run all your rads as
a sealed system, plus UFH if you wanted that without needing a mixing
valve (just an extra pump and controls). If you're in a soft water
area or have a water softener you could have a DHW coil in the tank, but
if you have hard water you'd want an external PHE + pump + flow switch +
TMV arrangement (as shown in
http://wiki.diyfaq.org.uk/index.php?title=DIY_Heat_Bank
although these components are built-into thermal store products such as
the Pandora).

Is Pandora a direct or an indirect system? If indirect, what loading
is the primary coil?


If you wanted to DIY parts of the system you could use an assembly (or
more than one) such as shown above to provide DHW closer to the points of
use instead of having a run all the way from the garage going cold between
uses. (If the primary heating water has gone cold it'll take a few seconds
for hotter water to get to your local PHE but you don't need to throw away
lots of cooled DHW to get hot water.)

Do the plates in a plate heat exchanger get dangerously hot to the
touch?

They'll be roughly as hot as the store and boiler flow pipes -
uncomfortably rather than burningly hot. I'm curious why you ask - do you
forsee a problem? You'd normally have the PHE tucked out of the way
somewhere, and preferably insulated.


It will be in the garage, and in general I dont like the idea of very
hot things being below 3ft off the ground - for kids safety.

On Tue, 20 Mar 2007 05:46:55 -0700, robgraham wrote:

I've just had a look at the DIY Wiki page above and have a couple of
questions :

1 Why is the motorised valve 3 position when all it is doing is to
direct the flow either to the tank or the CH system ?

This system was a direct adaptation of an existing Y-plan system with a
conventional DHW system. I might have chosen a diverter valve if I were
building it from new.

2 Is it acceptable to run the CH system at the 80 dec C that the
store is going to want.?

Probably nearer 70C: because it's direct you don't have a temperature drop
between boiler and store so there's just the drop in the PHE. The reason
stored DHW is normally 60C is hygiene: you don't need or want DHW coming
out of the taps at 60C so the store can run cooler than that and still
give DHW that's plenty hot enough.


3 One of the comments somewhere else in the Wiki is that feeding the
PHE pump straight back into the tank can lead to de-structuring of the
stratification and suggests using a thermostatic valve in that part
of the circuit controlled by the DHW output to restrict the flow. Is
this not a preferable option to the tmv ?

What configuration are you referring to here? I don't think I've come
across that one.

4 I also do not like the triac - a round based relay from eg Maplin
is far more maintainable and easier for the average person to build
and replace ? (qualified and old electronic engineer!)

Fair enough: I don't think Maplin had any suitable relays when I was
shopping for bits so I went with the triac solution. You could also go for
a flow switch which could switch the pump directly, as DPS do on the
Pandora.

On Tue, 20 Mar 2007 06:19:20 -0700, Peter wrote:


My guess is that, even modulating down all the way to 11kW your boiler
is going to cycle a lot heating your house most of the time so your
modulating boiler controls aren't going to help efficiency much.

Actualy, the calculators both say I am about a 12kW house, suggesting
boiler sizes of between 26 and 35kW.

Eh? If the heat loss of the house is 12k you'd add on maybe 2k for DHW,
plus extra rule-of-thumb chunks for a conservatory etc, but how do you get
the 26-35k figure?

And I really really like the radiators running at a lower temp
continuously when merely maintaining temp.

Direct connection between boiler and heat store is a wonderful
concept.

I don't see a simple way of having both: if you have the boiler drive the
CH directly, modulating down to low flow temperatures (if that's what it
does) and you want rads in the attic then you have to have a sealed
system. You could legally have a directly-coupled unvented heat bank
(according to Dr Drivel in a fairly recent post) but you have all the same
safety implications, AIUI it's just a loophole in the regs that it's not
covered under the same regs as unvented DHW cylinders.


Is Pandora a direct or an indirect system? If indirect, what loading is
the primary coil?

Indirect, fairly quick recovery I thik but nowhere near 45kW!
DPS do a direct heat bank (called GL or GX or GLX or something, I think)
but see above...

John Stumbles wrote:
On Tue, 20 Mar 2007 06:19:20 -0700, Peter wrote:

My guess is that, even modulating down all the way to 11kW your boiler
is going to cycle a lot heating your house most of the time so your
modulating boiler controls aren't going to help efficiency much.
Actualy, the calculators both say I am about a 12kW house, suggesting
boiler sizes of between 26 and 35kW.

Eh? If the heat loss of the house is 12k you'd add on maybe 2k for DHW,
plus extra rule-of-thumb chunks for a conservatory etc, but how do you get
the 26-35k figure?


warm up time.

A boiler that can only just keep paces with losses takes a very long
time to warm a house up.

On Tue, 20 Mar 2007 06:19:20 -0700, Peter wrote:


My guess is that, even modulating down all the way to 11kW your boiler
is going to cycle a lot heating your house most of the time so your
modulating boiler controls aren't going to help efficiency much.

Actualy, the calculators both say I am about a 12kW house, suggesting
boiler sizes of between 26 and 35kW.
And I really really like the radiators running at a lower temp
continuously when merely maintaining temp.


I'd be inclined to think of a f**k-off great heat bank buffering the
output of the boiler to supply both CH and DHW, connected to the boiler
directly in a vented system with a header tank - seehttp://wiki.diyfaq.org.uk/index.php?title=Thermal_Stores_and_Heat_Ban...
Being directly connected the boiler can dump its full output into the
heat bank quickly and then shut off.

Direct connection between boiler and heat store is a wonderful
concept.


It does mean the boiler will need to heat it to 70 or 80C so you won't
benefit from low return temperatures if it's a condensing boiler (you
don't say whether it is) in which case there's a question (which I can't
answer for you) of whether the gain from having it firing for very short
times rather than cycling outweighs the loss of efficiency at higher
return temps. If it's not condensing this doesn't apply.

PS I currently have 1 bathroom, 2 showers and am about to install a
third barthroom. I have 6 bedrooms. I am changing to pressurised CH,
in order to add rads to the attic. Similarly, I need pressurised
DHW for the attic bathroom.

With appropriate coils in the heat bank you can run all your rads as
a sealed system, plus UFH if you wanted that without needing a mixing
valve (just an extra pump and controls). If you're in a soft water
area or have a water softener you could have a DHW coil in the tank, but
if you have hard water you'd want an external PHE + pump + flow switch +
TMV arrangement (as shown in
http://wiki.diyfaq.org.uk/index.php?title=DIY_Heat_Bank
although these components are built-into thermal store products such as
the Pandora).

Is Pandora a direct or an indirect system? If indirect, what loading
is the primary coil?


If you wanted to DIY parts of the system you could use an assembly (or
more than one) such as shown above to provide DHW closer to the points of
use instead of having a run all the way from the garage going cold between
uses. (If the primary heating water has gone cold it'll take a few seconds
for hotter water to get to your local PHE but you don't need to throw away
lots of cooled DHW to get hot water.)

Do the plates in a plate heat exchanger get dangerously hot to the
touch?

They'll be roughly as hot as the store and boiler flow pipes -
uncomfortably rather than burningly hot. I'm curious why you ask - do you
forsee a problem? You'd normally have the PHE tucked out of the way
somewhere, and preferably insulated.


It will be in the garage, and in general I dont like the idea of very
hot things being below 3ft off the ground - for kids safety.


What is the boiler? It not a Keston C40 as that's 11-40kW.
It's a very large an expensive piece of kit which we obviously want to
keep unless it's very wrong.

You say it uses 25kW (does the boiler tell you this - must be something
really high end?) or did you deduce it from the gas meter or the rpm of
the premix fan?

My guess is that a 6 bed modern house would be needing around 25kW may be
a little more in the coldest weather. Anyway we will await you plugging
the numbers into a heat loss program/web-site.

A house of this size would do well to have division of the heating into
zones. Maybe the pipes will let you do this easily or maybe not. Once you
have done that then the controls are going to be extended S plan. If you
don't do heating zones (and the loft rads would surely be candidates for a
zone?) then you have the choice of using a diverter or Y-plan.

A diverter valve causing the occasional outages of the heating for up to
20 minutes should not be a problem. It only turns out to be a problem for
people who program the heating and HW on together in the morning at
the same time. You really need to set the HW timer earlier (or even 24/7)
so that the peak demands are not competing for the 6:30am show.

You could go for a secondary return loop for the DHW, this requires a
bronze circulator (£150) and very well insulated DHW pipes. There should
be a severe flow restriction on the loop return (but not the flow of
course!) and ideally a timer on the pump. This should let you put the HW
store in the attached garage. If detached think again.

200 litres sounds about right.

Before embarking on any sort of mains driven DHW system you need to
verify that you have the supply. Ideally 32mm MDPE and a
standing pressure of 2.5 bar min. Even then with so many baths/showers the
auxiliary draw effects could be noticeable. Unvented is more tolerant of
multiple outlets as the expansion vessel/volume tends to buffer the
changes in draw off rates.

BTW:
It's nice being able to throw my spanner in to the works on a subject
like this without it causing a great inferno.




--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

On 20 Mar, 14:31, John Stumbles wrote:
On Tue, 20 Mar 2007 05:46:55 -0700, robgraham wrote:

3 One of the comments somewhere else in the Wiki is that feeding the
PHE pump straight back into the tank can lead to de-structuring of the
stratification and suggests using a thermostatic valve in that part
of the circuit controlled by the DHW output to restrict the flow. Is
this not a preferable option to the tmv ?

What configuration are you referring to here? I don't think I've come
across that one.


The DIY Wiki on "Thermal Store and Banks" has a box on Stratification
which makes reference this towards the bottom of the box. The
suggestion is varying the pump speed to reduce the water flow and
hence control the temperature, or use a thermostatic valve as I've
mentioned.

Rob

What is the boiler? It not a Keston C40 as that's 11-40kW.
It's a very large an expensive piece of kit which we obviously want to
keep unless it's very wrong.


Ideal Imax45

You say it uses 25kW (does the boiler tell you this - must be something
really high end?) or did you deduce it from the gas meter or the rpm of
the premix fan?

What I meant to say whas that the calculators say I need about 13kW
steadstate and they recommend a boiler of 25kW.



A house of this size would do well to have division of the heating into
zones. Maybe the pipes will let you do this easily or maybe not. Once you
have done that then the controls are going to be extended S plan. If you
don't do heating zones (and the loft rads would surely be candidates for a
zone?) then you have the choice of using a diverter or Y-plan.


Yup - the plumbing is all ready for 2 zones downstairs, 1st floor and
attric (4 zones in total) - although I may not put
air thermostats on each.


A diverter valve causing the occasional outages of the heating for up to
20 minutes should not be a problem. It only turns out to be a problem for
people who program the heating and HW on together in the morning at
the same time. You really need to set the HW timer earlier (or even 24/7)
so that the peak demands are not competing for the 6:30am show.

Ah - but you see the issue is that with my programmer DHW is always
on.
Then, when at 6.30 people have DHW drawoff, the DHW priority feature
of the programmer
tries to replenish the hot tank - hence the CH issue.


You could go for a secondary return loop for the DHW, this requires a
bronze circulator (£150) and very well insulated DHW pipes. There should
be a severe flow restriction on the loop return (but not the flow of
course!) and ideally a timer on the pump. This should let you put the HW
store in the attached garage. If detached think again.

Dont think this is the problem.


200 litres sounds about right.

Before embarking on any sort of mains driven DHW system you need to
verify that you have the supply. Ideally 32mm MDPE and a
standing pressure of 2.5 bar min.

I've got 25mm and about 5bar - as I seem to remember.
Don't suppose anybody has celer ideas how to measure the pressure
without expensive kit?

Even then with so many baths/showers the
auxiliary draw effects could be noticeable. Unvented is more tolerant of
multiple outlets as the expansion vessel/volume tends to buffer the
changes in draw off rates.

BTW:
It's nice being able to throw my spanner in to the works on a subject
like this without it causing a great inferno.


Spanners are fine - they are tools. I like tools.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is athttp://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQhttp://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQhttp://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs hehttp://www.makewrite.demon.co.uk/GasFittingStandards- Hide quoted text -

- Show quoted text -

On Tue, 20 Mar 2007 15:53:12 -0700, Peter wrote:




Ideal Imax45

You say it uses 25kW (does the boiler tell you this - must be something
really high end?) or did you deduce it from the gas meter or the rpm of
the premix fan?

What I meant to say whas that the calculators say I need about 13kW
steadstate and they recommend a boiler of 25kW.

This is a modern very well insulated and/or fairly small, 6 bed house, I
suppose.
Who is the 'they' in 'they recommend ... 25kW'. Either the requirement is
13kW or it's nearer 25kW. Some allowance for DHW should be made. I've
forgotten just why and how much but not more than 3-4 kW, and maybe
some for future proofing and/or insurance.

Really if the requirement is only 13kW then the boiler should be replaced
there are plenty of smaller (and very much cheaper) models to choose from.





A house of this size would do well to have division of the heating into
zones. Maybe the pipes will let you do this easily or maybe not. Once you
have done that then the controls are going to be extended S plan. If you
don't do heating zones (and the loft rads would surely be candidates for a
zone?) then you have the choice of using a diverter or Y-plan.


Yup - the plumbing is all ready for 2 zones downstairs, 1st floor and
attric (4 zones in total) - although I may not put
air thermostats on each.

Why have the zones then? Control each zone with a programmable thermostat.
I'd also have a master CH timer over all the CH zones as well.




A diverter valve causing the occasional outages of the heating for up to
20 minutes should not be a problem. It only turns out to be a problem for
people who program the heating and HW on together in the morning at
the same time. You really need to set the HW timer earlier (or even 24/7)
so that the peak demands are not competing for the 6:30am show.

Ah - but you see the issue is that with my programmer DHW is always
on.
Then, when at 6.30 people have DHW drawoff, the DHW priority feature
of the programmer
tries to replenish the hot tank - hence the CH issue.

Set the CH to have got the radiators warm before the bathroom scramble.
It must take the 45kW boiler all of about 5 minutes to get the rads to
temp.




You could go for a secondary return loop for the DHW, this requires a
bronze circulator (£150) and very well insulated DHW pipes. There should
be a severe flow restriction on the loop return (but not the flow of
course!) and ideally a timer on the pump. This should let you put the HW
store in the attached garage. If detached think again.

Dont think this is the problem.


200 litres sounds about right.

Before embarking on any sort of mains driven DHW system you need to
verify that you have the supply. Ideally 32mm MDPE and a
standing pressure of 2.5 bar min.

I've got 25mm and about 5bar - as I seem to remember.
Don't suppose anybody has celer ideas how to measure the pressure
without expensive kit?

You should be able to get something to do the job for under a tenner.
It only has to work a few times for you.

5 bar and 25mm should be OK, but this advice comes with no warranty.
If you absolutely had a disaster on your hands then a few hundred quid on
some accumulators will probably rescue you.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

Peter wrote:

But here is the thing ..it only needs to be 1.5bar or so for th
pressurise CH, so not the same situation as a 3bar DHW cylinder.

Does a direct heat bank speced for 1.5bar exist?

I would have thought that if you are using a direct cylinder[1] in this
way they it would have to be rated for operation at pressure at least as
great as the setting on the pressure blow off valve on the sealed
primary. Otherwise you could get a cascade failure, if for example your
expansion vessel failed that could cause the primary pressure to rise to
3 bar+. Ideally one would want the pressure release valve to operate
before explosion of the cylinder

[1] Even with an indirect cylinder you still have to allow for the
possibility a leak within the primary heating coil, undesirable at the
best of times, but particularly so if the cylinder is not vented.


--
Cheers,

John.

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

Ed Sirett wrote:

BTW:
It's nice being able to throw my spanner in to the works on a subject
like this without it causing a great inferno.

Hmm, quiet innit! ;-)

(wonder if he is on holls, or has croaked?)

--
Cheers,

John.

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

On 2007-03-21 01:15:03 +0000, John Rumm said:

Ed Sirett wrote:

BTW:
It's nice being able to throw my spanner in to the works on a subject
like this without it causing a great inferno.

Hmm, quiet innit! ;-)

(wonder if he is on holls, or has croaked?)

Eyebyeza, with puffy anorak courtesy of boiler manufacturer sales promotions

On 20 Mar 2007 15:53:12 -0700 someone who may be "Peter"
wrote this:-

Yup - the plumbing is all ready for 2 zones downstairs, 1st floor and
attric

Often vertical zones are better, as they allow for solar gains on
one side of the house. North/south and a core area for example.

You could go for a secondary return loop for the DHW, this requires a
bronze circulator (£150) and very well insulated DHW pipes. There should
be a severe flow restriction on the loop return (but not the flow of
course!) and ideally a timer on the pump. This should let you put the HW
store in the attached garage. If detached think again.

Dont think this is the problem.

It isn't a problem, it is a suggested solution.

I've got 25mm and about 5bar - as I seem to remember.
Don't suppose anybody has celer ideas how to measure the pressure
without expensive kit?

Pressure gauge that fits on washing machine connection. Screwfix
sell them for less than 20 pounds.



--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

On Tue, 20 Mar 2007 23:35:04 +0000 (UTC) someone who may be Ed
Sirett wrote this:-

This is a modern very well insulated and/or fairly small, 6 bed house, I
suppose.

It does sound like it. Or perhaps the windows and ventilation losses
have been ignored and the figure has been fudged upwards.

Some allowance for DHW should be made. I've
forgotten just why and how much but not more than 3-4 kW,

Depends how large a cylinder is to be heated and how quickly it is
to be reheated after draw off. This is also related to maximum
demand and is still something of a black art. 3-4kW should be fine
for most houses.

and maybe some for future proofing and/or insurance.

Now that modulating boilers are common this is perhaps sensible. In
Ye Olden Days it was best avoided as it just encouraged short
cycling.



--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

On Tue, 20 Mar 2007 15:19:03 -0700, robgraham wrote:

The DIY Wiki on "Thermal Store and Banks" has a box on Stratification
which makes reference this towards the bottom of the box. The
suggestion is varying the pump speed to reduce the water flow and
hence control the temperature, or use a thermostatic valve as I've
mentioned.

OK I was thinking TMV not TRV(-type).

(Should have known: I wrote that bit on the wiki!)

However if you've got blindingly fast recovery (like 45kW boiler direct
into heat bank) it doesn't really matter.

On Wed, 21 Mar 2007 07:36:17 +0000, David Hansen wrote:

On Tue, 20 Mar 2007 23:35:04 +0000 (UTC) someone who may be Ed
Sirett wrote this:-

This is a modern very well insulated and/or fairly small, 6 bed house, I
suppose.

It does sound like it. Or perhaps the windows and ventilation losses
have been ignored and the figure has been fudged upwards.

Some allowance for DHW should be made. I've
forgotten just why and how much but not more than 3-4 kW,

Depends how large a cylinder is to be heated and how quickly it is
to be reheated after draw off. This is also related to maximum
demand and is still something of a black art. 3-4kW should be fine
for most houses.

and maybe some for future proofing and/or insurance.

Now that modulating boilers are common this is perhaps sensible. In
Ye Olden Days it was best avoided as it just encouraged short
cycling.

If you follow 'the book' then my 'insurance extra' is off limits even with
modern boilers.




--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

On Wed, 21 Mar 2007 01:15:03 +0000, John Rumm wrote:

Ed Sirett wrote:

BTW:
It's nice being able to throw my spanner in to the works on a subject
like this without it causing a great inferno.

Hmm, quiet innit! ;-)

(wonder if he is on holls, or has croaked?)

It's like low level noise pollution you don't really notice it when it's
there but it's a nice surprise when it goes.




--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

On Wed, 21 Mar 2007 01:35:43 +0000, Andy Hall wrote:

On 2007-03-21 01:15:03 +0000, John Rumm said:

Ed Sirett wrote:

BTW:
It's nice being able to throw my spanner in to the works on a subject
like this without it causing a great inferno.

Hmm, quiet innit! ;-)

(wonder if he is on holls, or has croaked?)

Eyebyeza, with puffy anorak courtesy of boiler manufacturer sales promotions

With Alpha logo?

ROFL.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

On 2007-03-21 20:36:01 +0000, Ed Sirett said:

On Wed, 21 Mar 2007 01:35:43 +0000, Andy Hall wrote:

On 2007-03-21 01:15:03 +0000, John Rumm said:

Ed Sirett wrote:

BTW:
It's nice being able to throw my spanner in to the works on a subject
like this without it causing a great inferno.

Hmm, quiet innit! ;-)

(wonder if he is on holls, or has croaked?)

Eyebyeza, with puffy anorak courtesy of boiler manufacturer sales promotions

With Alpha logo?

ROFL.

Dunno.

Who's offering the best deals at the moment?

Mind you, with two combis and one of those magnetic sludge grabbing
things per customer, it's pretty easy to be the sales star.

On 21 Mar, 19:24, John Stumbles wrote:
On Tue, 20 Mar 2007 15:19:03 -0700, robgraham wrote:
The DIY Wiki on "Thermal Store and Banks" has a box on Stratification
which makes reference this towards the bottom of the box. The
suggestion is varying the pump speed to reduce the water flow and
hence control the temperature, or use a thermostatic valve as I've
mentioned.

OK I was thinking TMV not TRV(-type).

(Should have known: I wrote that bit on the wiki!)

However if you've got blindingly fast recovery (like 45kW boiler direct
into heat bank) it doesn't really matter.

Hi John - yes I thought it a little odd when you denied your own
writings !!

What if the boiler is somewhat more modest - mine for instance is
17kW. Would the same principle apply if it is a direct feed on the
basis that even with the smaller heat source, the ratio of boiler
capacity to DHW allowance of say 3kW is such that the re-heat rate
would be pretty fast, though not 'blindingly'. My mansion is a
somewhat more modest than Peter's (the OP) and with only two of us,
DHW demand is not great.

Rob

On Wed, 21 Mar 2007 16:02:01 -0700, robgraham wrote:

What if the boiler is somewhat more modest - mine for instance is
17kW. Would the same principle apply if it is a direct feed on the
basis that even with the smaller heat source, the ratio of boiler
capacity to DHW allowance of say 3kW is such that the re-heat rate
would be pretty fast, though not 'blindingly'. My mansion is a
somewhat more modest than Peter's (the OP) and with only two of us,
DHW demand is not great.

With my own setup on the few occasions that we've run the bank cold (which
is inevitably when you've got into a half-full bath and the hot's run
cold) it takes just a few minutes to get a reasonable stream of hot water
out again. With the non-rapid-recovery conventional cylinder we had before
you could, if you were patient, get a trickle of hot water out after a
quarter of an hour or so.

Apart from the equivalence of a directly-coupled arrangement to an
infinitely rapid-recovery coil I think there's also the factor that even
the fastest coil is heating the top half or so of the cylinder by
convection whereas in the direct heat bank the hot flow from the boiler is
probably getting sucked directly out of the top of the cylinder by the DHW
pump. Connecting the boiler flow to the top, rather than side tapping of
the cylinder, might help further but I haven't tried it. (If you saw the
state of the attic^H^H^H^HSWMBO's junkyard you'd appreciate why :-)

Well - everybody has certaily been giving me food for thought.

It seems to me that a directly heated heat bank with "blindingly fast"
recovery is the way to go.

So - I now have 3 further - and related questions:

1. With blindingly fast recovery .. how do I figure out how small the
heat store can be?
I mean normally, you'd use the calculator for #baths, singks,
showers etc. But with my arrangement what I've got is
more like a very large water content combi! [ Standard calculator on
heatweb suggests 230ishlitres ]

2. I already have, existing, 4 pipe runs to the attic. It is
difficult - though not impossible to add more.

If I go for a fully direct system (Rads off heat store as well), then
I need a header and expanstion tank in attic.
So that means I need pipes: Flow, returm, Cold feed, Vent, Mains
Cold. Thats five!
So - my quesiton is .... what are the dos and donts about the header
tank feeding into the return line?
[ If I did this, I get back to 4 pipes again ]
I know normally you do it just after an air seperator and just before
the pump - but I dont understand why.

3. Alternative to the idea in (2) is to run the rads off a seperate
heat exchanges off the heatstore and pressurise just the rads.
Anybody got any thoughts about the pros and cons. Ones I can think of
a
Yet another pump (would not be up to 4)
Not quite as fast heatup
separate boiler/heatstore water from rad water (a good thing i think)

Again - very grateful for all the ideas and discussion.



Peter

PS Amazing how ones thoughts change - I realsie that none of the
above options leaves me with my rads running off the clever modulating
controller - something which earlier on in the disucssion I said was a
must-have. Now it just doesn't seem so important.