A discussion in a separate thread has prompted me to look further at the
set up of my gas boiler.
I have a heating system designed & supplied by NuHeat ...... 17 zones,
all underfloor heating - no rads.

There is a thermal store (Energymaster) and if the stat on the store
(fitted on lower 1/3)is lower than 65C .. it requires heat .. zone
valve opens on primaries, pump starts and 220V sent to boiler.
Boiler runs until stat reaches 65C and opens.

The heating system us fed from a lower heat exchanger, and the DHW form
an a upper heat exchanger via a thermostatic valve.
There is no blending valve on loop circuit - design relies of store stat
limiting temp. ( I intend fitting a blending valve - but that id not
in current design)


Sketch of set up he http://tinyurl.com/ngeqfsy

Safety bypass and pressure vessels left out for clarity

The initial advice was to set boiler temp to Maxm .... but appreciate
this may not be optimum ....
I went back to NuHeat .. they advise
# Boiler stat should be set to 75C .....
# Diff between boiler F& return should not exceed 13C

Any suggestions on how to set this up ....... I have only the pump speed
and boiler temp setting to adjust.

Do I turn down boiler setting until it is at 75, then adjust pump for
13C difference ........ just not sure how to approach this.

On 09/11/2016 11:52, rick wrote:
A discussion in a separate thread has prompted me to look further at the
set up of my gas boiler.
I have a heating system designed & supplied by NuHeat ...... 17 zones,
all underfloor heating - no rads.

There is a thermal store (Energymaster) and if the stat on the store
(fitted on lower 1/3)is lower than 65C .. it requires heat .. zone
valve opens on primaries, pump starts and 220V sent to boiler.
Boiler runs until stat reaches 65C and opens.

The heating system us fed from a lower heat exchanger, and the DHW form
an a upper heat exchanger via a thermostatic valve.
There is no blending valve on loop circuit - design relies of store stat
limiting temp. ( I intend fitting a blending valve - but that id not
in current design)


Sketch of set up he http://tinyurl.com/ngeqfsy

Safety bypass and pressure vessels left out for clarity

The initial advice was to set boiler temp to Maxm .... but appreciate
this may not be optimum ....
I went back to NuHeat .. they advise
# Boiler stat should be set to 75C .....
# Diff between boiler F& return should not exceed 13C

Any suggestions on how to set this up ....... I have only the pump speed
and boiler temp setting to adjust.

Do I turn down boiler setting until it is at 75, then adjust pump for
13C difference ........ just not sure how to approach this.

It seems like you have a system optimised to get the best efficiency
possible from a conventional non condensing non modulating boiler. i.e.
Running the boiler at high output temperatures on high load in measured
bursts. Traditional boilers were not good at trickling heat into a
system at part load to match the heat loss of the building, and so the
thermal store made a good buffer. It is also a simple way of using
stratification to get a variety of output flow temperatures to suit
different applications such as DHW and UFH which have different
requirements.

So the first question is, what kind of boiler are you using?



--
Cheers,

John.

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On 09/11/2016 11:52, rick wrote:

A discussion in a separate thread has prompted me to look further at the
set up of my gas boiler.
I have a heating system designed & supplied by NuHeat ...... 17 zones,
all underfloor heating - no rads.

There is a thermal store (Energymaster) and if the stat on the store
(fitted on lower 1/3)is lower than 65C .. it requires heat .. zone
valve opens on primaries, pump starts and 220V sent to boiler.
Boiler runs until stat reaches 65C and opens.

The heating system us fed from a lower heat exchanger, and the DHW form
an a upper heat exchanger via a thermostatic valve.
There is no blending valve on loop circuit - design relies of store stat
limiting temp. ( I intend fitting a blending valve - but that id not
in current design)

Sketch of set up he http://tinyurl.com/ngeqfsy

Safety bypass and pressure vessels left out for clarity

The initial advice was to set boiler temp to Maxm .... but appreciate
this may not be optimum ....
I went back to NuHeat .. they advise
# Boiler stat should be set to 75C .....
# Diff between boiler F& return should not exceed 13C

Any suggestions on how to set this up ....... I have only the pump speed
and boiler temp setting to adjust.

The simplest empirical way is to monitor gas usage and daily min/max
outside temperature whilst making adjustments on a weekly basis. I doubt
if the boiler stat gets much of a look in compared to the thermal store
provided that the pump is actually running.

Do I turn down boiler setting until it is at 75, then adjust pump for
13C difference ........ just not sure how to approach this.

My instinct is that provided the pump is fast enough to avoid a 13C
temperature drop on the loop the overall efficiency won't be all that
much different. The only thing that might make a difference is if one of
the burner controllers is smart enough to determine the system thermal
inertia and loading to avoid overshooting the 65C target.

--
Regards,
Martin Brown

On 09/11/2016 13:59, John Rumm wrote:

requirements.

So the first question is, what kind of boiler are you using?



Gas condensing - Baxi Barcelona set for 1000,000 Btu/h (sorry meant to
add that in OP) it has been fully upgraded to 100HE spec

On 09/11/2016 14:25, Martin Brown wrote:

My instinct is that provided the pump is fast enough to avoid a 13C
temperature drop on the loop the overall efficiency won't be all that
much different. The only thing that might make a difference is if one of
the burner controllers is smart enough to determine the system thermal
inertia and loading to avoid overshooting the 65C target.


Just a little unsure of what I'm trying to set ....
NuHeat say 75C ....
Comments I have read elsewhere state that I have to get return no higher
than 55C to remain condensing ... that would be 13C difference



I can happily take temp readings - but not sure what I should be setting to.

On 09/11/2016 14:25, Martin Brown wrote:

My instinct is that provided the pump is fast enough to avoid a 13C
temperature drop on the loop the overall efficiency won't be all that
much different. The only thing that might make a difference is if one of
the burner controllers is smart enough to determine the system thermal
inertia and loading to avoid overshooting the 65C target.

Can anyone explain to me why it is desirable to avoid a temperature
difference of more than 13C ? That means when it starts up from cold,
with the inflow around say 15C that the outflow should be no more than
28C - which means the pump must send the same water around several times
before the outflow gets to 75C?

I don't understand why a boiler with a flame at several hundred Celsius
would be more efficient working like that than it it raised it right
away from say 15 to 75C.

--
Clive Page

On 09/11/2016 14:49, rick wrote:
On 09/11/2016 14:25, Martin Brown wrote:

My instinct is that provided the pump is fast enough to avoid a 13C
temperature drop on the loop the overall efficiency won't be all that
much different. The only thing that might make a difference is if one of
the burner controllers is smart enough to determine the system thermal
inertia and loading to avoid overshooting the 65C target.


Just a little unsure of what I'm trying to set ....
NuHeat say 75C ....
Comments I have read elsewhere state that I have to get return no higher
than 55C to remain condensing ... that would be 13C difference

You have a conflict of interests here really... Thermal stores work well
at high temperatures, and condensing boilers get bigger efficiency gains
at lower temperatures.

Even at return temps above 54 degrees (the dew point of the flue gasses)
the modern boiler will be more efficient than an older style one as a
result of its larger heat exchanger. The efficiency graph just gets a
bit steeper at that point.

With a condenser there is no real problem with a delta over 13 degrees -
that used to be a limitation of older boilers where you wanted to
prevent them from condensing (since there was no mechanism for
collecting and disposing of the condensate, all it was going to do it
accelerate corrosion in the boiler). Modern condensing systems are often
run at 20 degree delta or more.

I can happily take temp readings - but not sure what I should be setting
to.

I expect your best situation is to have the boiler flow temperature set
so that it can just satisfy the store stat in the coldest of conditions.

--
Cheers,

John.

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On 09/11/2016 17:44, John Rumm wrote:


I expect your best situation is to have the boiler flow temperature set
so that it can just satisfy the store stat in the coldest of conditions.



Did have a follow up email form Nuheat .. they stated manual advice was
based on old style boilers, not modern condensing .... but no other
advice on setup.

On 09/11/2016 17:44, John Rumm wrote:

You have a conflict of interests here really... Thermal stores work
well at high temperatures, and condensing boilers get bigger efficiency
gains at lower temperatures.

Even at return temps above 54 degrees (the dew point of the flue gasses)
the modern boiler will be more efficient than an older style one as a
result of its larger heat exchanger. The efficiency graph just gets a
bit steeper at that point.

Like this (reposted):
http://www.maxwell.myzen.co.uk/uk.d-i-y/AM3_fig2.6.gif

The design seems mad to me. Surely for optimum efficiency you want the
UFH running straight off the boiler primary, at the lowest feasible
temperature. Weather compensation would help here, by reducing the
temperature further in mild weather. Then use the store for DHW only
with appropriate controls to heat it to ~65 deg. a couple of times a
day, or as required, by running the boiler flat out into it for short
periods (i.e. HW priority control).

--
Andy

On 09/11/2016 23:46, Andy Wade wrote:
On 09/11/2016 17:44, John Rumm wrote:

You have a conflict of interests here really... Thermal stores work
well at high temperatures, and condensing boilers get bigger efficiency
gains at lower temperatures.

Even at return temps above 54 degrees (the dew point of the flue gasses)
the modern boiler will be more efficient than an older style one as a
result of its larger heat exchanger. The efficiency graph just gets a
bit steeper at that point.

Like this (reposted):
http://www.maxwell.myzen.co.uk/uk.d-i-y/AM3_fig2.6.gif

The design seems mad to me. Surely for optimum efficiency you want the

Not mad - but possibly from a different age! Its the kind of setup that
a previous regular of this group was fond of promoting. It made sense
with old clunker boilers.

UFH running straight off the boiler primary, at the lowest feasible
temperature. Weather compensation would help here, by reducing the
temperature further in mild weather. Then use the store for DHW only
with appropriate controls to heat it to ~65 deg. a couple of times a
day, or as required, by running the boiler flat out into it for short
periods (i.e. HW priority control).

Yup I think that is the way I would design it if given the same choice
of components (assuming the boiler can modulate low enough to run the
UFH directly - you may need a blending valve or two in there).

The boiler would need to be capable of (or be fooled into) split
temperature operation so that it could run an appropriate flow temp for
heating, but then use a much higher temp for store recharge.


--
Cheers,

John.

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On 09/11/2016 15:36, Clive Page wrote:
On 09/11/2016 14:25, Martin Brown wrote:

My instinct is that provided the pump is fast enough to avoid a 13C
temperature drop on the loop the overall efficiency won't be all that
much different. The only thing that might make a difference is if one of
the burner controllers is smart enough to determine the system thermal
inertia and loading to avoid overshooting the 65C target.

Can anyone explain to me why it is desirable to avoid a temperature
difference of more than 13C ?

Its advice that applied to old non modulating non condensing boilers. If
you designed for a delta of about 12 degrees, then you could be safe in
the knowledge that even if you dropped the flow temperature to 65, you
would still keep the return temperature above the point at which you
would get condensation of the flue gasses in the boiler (once it was all
up to temperature of course - you would still get some condensation at
startup - but that water could be boiled off soon after). This at the
time was a good thing since it stopped the boiler with its cast iron
lump HX from rusting away.

That means when it starts up from cold,
with the inflow around say 15C that the outflow should be no more than
28C - which means the pump must send the same water around several times
before the outflow gets to 75C?

With old boilers they just ran at a fixed output - the system balancing
combined with the boiler's internal stat would set the parameters. So it
would condense a bit at startup, and then run normally once up to
temperature.

I don't understand why a boiler with a flame at several hundred Celsius
would be more efficient working like that than it it raised it right
away from say 15 to 75C.

They don't have the power to lift that quantity of water to 75 in one pass.

The efficiency gain in the condenser comes from two factors. Firstly
being able to extract more heat from the combustion in the first place
(bigger more efficient HX), and secondly by condensing the water
produced during the combustion process, you can claw back the energy
tied up in the latent heat of vaporisation of the H2O manufactured when
you burn a hydrocarbon fuel.

--
Cheers,

John.

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

On 10/11/2016 01:32, John Rumm wrote:
On 09/11/2016 15:36, Clive Page wrote:
On 09/11/2016 14:25, Martin Brown wrote:




A bit of pushing back at NuHeat and they admit the commissioning notes
of setting to 75C and a 13c differential were actually based on old
style non-condensing boilers.

Even though my system was specifically to be used with a condensing
boiler. When asked what to set it to all they will advise is Boiler
must be set higher than store stat temp ... anything else is up to me.

So back to question ... do I set the boiler to run the water at 75C,
then what do I set the pump speed at.. on old system you would adjust
pump speed to to get correct differential ...
Or would I be better setting at lower temp ... boiler has option to
limit flow temp to 63C by a control board jumper setting.

This is what it is currently set to ... and pump is on max speed.


(If any of you have knowledge of Baxi's .. I have posted separate Post
on Baxi control board jumpers - welcome input)

On 10/11/2016 01:32, John Rumm wrote:

The efficiency gain in the condenser comes from two factors. Firstly
being able to extract more heat from the combustion in the first place
(bigger more efficient HX), and secondly by condensing the water
produced during the combustion process, you can claw back the energy
tied up in the latent heat of vaporisation of the H2O manufactured when
you burn a hydrocarbon fuel.

Thanks. I hadn't thought about the efficiency of the condensing stage.
I guess that is a large part of the explanation.


--
Clive Page

On 10/11/2016 01:22, John Rumm wrote:
[...]
Yup I think that is the way I would design it if given the same choice
of components (assuming the boiler can modulate low enough to run the
UFH directly - you may need a blending valve or two in there).

Er, if the heat demand is less than the minimum modulated output of the
boiler the boiler will just cycle on and off (PWM). If you force it not
to do that it will be delivering excess energy which has to go
somewhere. Either the house will overheat, or a room 'stat will perform
the PWM function instead. Unless weather compensation is employed that
will be the main control mechanism in any case.

[Re DHW:]

The boiler would need to be capable of (or be fooled into) split
temperature operation so that it could run an appropriate flow temp for
heating, but then use a much higher temp for store recharge.

True. Combis do this innately of course if you replace "store recharge"
with "provide hot water, but I dont know if there are any system boilers
that have two demand inputs like that. There should be though...

--
Andy

On 10/11/2016 20:26, rick wrote:
On 10/11/2016 01:32, John Rumm wrote:

So back to question ... do I set the boiler to run the water at 75C,
then what do I set the pump speed at.. on old system you would adjust
pump speed to to get correct differential

If efficiency is your aim I'd ignore that and set to the lowest boiler
temperature that gives you sufficiently hot water and adequate space
heating, with your system as-is. (Min. 60 deg. for HW to kill Legionella
of course.)

Or would I be better setting at lower temp ... boiler has option to
limit flow temp to 63C by a control board jumper setting.

Yes, try it and see,

.... and pump is on max speed.

Temperature differential is generally not critical over quite a wide
range. I'd aim for the lowest speed that gives adequate performance.
Preferably keep the return temp down in the low 50s (or less) to keep
the boiler in condensing mode.

--
Andy

On 11/11/2016 00:25, Andy Wade wrote:
On 10/11/2016 01:22, John Rumm wrote:
[...]
Yup I think that is the way I would design it if given the same choice
of components (assuming the boiler can modulate low enough to run the
UFH directly - you may need a blending valve or two in there).

Er, if the heat demand is less than the minimum modulated output of the
boiler the boiler will just cycle on and off (PWM). If you force it not
to do that it will be delivering excess energy which has to go
somewhere. Either the house will overheat, or a room 'stat will perform
the PWM function instead. Unless weather compensation is employed that
will be the main control mechanism in any case.

It will indeed.

The purpose of the blending valve in this case is to control the maximum
flow temperature into the UFH to prevent it being uncomfortably hot on
the feet, or distorting floor coverings etc.

The boiler will still need to cycle to only deliver the power level
actually needed.


[Re DHW:]

The boiler would need to be capable of (or be fooled into) split
temperature operation so that it could run an appropriate flow temp for
heating, but then use a much higher temp for store recharge.

True. Combis do this innately of course if you replace "store recharge"
with "provide hot water, but I dont know if there are any system boilers
that have two demand inputs like that. There should be though...

There are a few - I spent some time researching when looking for a
system boiler setup for my place. Some have it built in, others you can
add it or get the same effect with the right control system. Anything
that has weather compensation will normally include it.

Most of the Vaillant models seem to include separate temperature
controls on the boiler itself for the DHW and CH - even on the basic 400
series "heat only" vented range.

The posher weather compensating controls allow for the CH flow temp to
be slaved to the external temperature, modified via user selectable
response curves to model the thermal properties of the building, and
also to introduce an element of PID style control such that the current
target temperature in the building will be taken into account (i.e. girl
mode - if its well below the current set temperature it will turning it
up more for faster warm up ;-). The DHW then runs at a separate preset
maximum flow temp (with an optional weekly "anti legionella" cycle where
it recharges the DHW at a higher temperature).

Many weather compensators seem to use a NTC thermistor as their
temperature sensor. So a control system could obviously switch in
additional resistors to trick the system into running a different flow
temperature.


--
Cheers,

John.

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On 10/11/2016 20:26, rick wrote:
On 10/11/2016 01:32, John Rumm wrote:
On 09/11/2016 15:36, Clive Page wrote:
On 09/11/2016 14:25, Martin Brown wrote:




A bit of pushing back at NuHeat and they admit the commissioning notes
of setting to 75C and a 13c differential were actually based on old
style non-condensing boilers.

Even though my system was specifically to be used with a condensing
boiler. When asked what to set it to all they will advise is Boiler
must be set higher than store stat temp ... anything else is up to me.

So long as the flow temp is higher than the set temp on the store you
should be ok.

So back to question ... do I set the boiler to run the water at 75C,
then what do I set the pump speed at.. on old system you would adjust
pump speed to to get correct differential ...

With your boiler I would not worry about differentials particularly.
Just go for the lowest setting that does the job adequately (less system
pump noise that way)

Or would I be better setting at lower temp ... boiler has option to
limit flow temp to 63C by a control board jumper setting.

This is what it is currently set to ... and pump is on max speed.

The lower temp will give better efficiency but possibly at a slight
price of longer re-heat times on the store.

How is the store heated? (i.e. direct or indirect coil)

If its an indirect coil, then it might be worth checking what the
maximum transfer rate for the coil is specced at. If its an older diesgn
it may limit the maximum power to somewhat less than the boiler's full
output anyway.

(stores used for system buffers like that are often "direct" - i.e. they
are full of primary water heated by the boiler)

(If any of you have knowledge of Baxi's .. I have posted separate Post
on Baxi control board jumpers - welcome input)

Nope, nothing specific, although I probably have collection of manuals
for many of the older ones.

--
Cheers,

John.

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

On 11/11/2016 09:48, John Rumm wrote:


How is the store heated? (i.e. direct or indirect coil)

Direct - whole contents of store circulated around boiler
2 heat exchangers - lower for UFH
Upper for DHW (with Thermostatic mixing valve)

as per: http://tinyurl.com/ngeqfsy


The tank is set to 60 degrees .. to limit max temp of water that can get
to UFH circuits.
My plan is to install a Thermostatic Mixing Valve set to 50C and run
tank at higher temp (probably 70)

The store has a baffle - to help stratification, but as soon as you draw
any hot water it energises the pimp on primaries to 'stir' the store and
keep recharging heat exchanger.

On 11/11/2016 13:05, rick wrote:
On 11/11/2016 09:48, John Rumm wrote:


How is the store heated? (i.e. direct or indirect coil)

Direct - whole contents of store circulated around boiler
2 heat exchangers - lower for UFH
Upper for DHW (with Thermostatic mixing valve)

ok, so it can take the full boiler output which makes it a bit simpler.

as per: http://tinyurl.com/ngeqfsy

Yup saw that, was just not sure if there was no coil or you had omitted
it for simplicity.

The tank is set to 60 degrees .. to limit max temp of water that can get
to UFH circuits.
My plan is to install a Thermostatic Mixing Valve set to 50C and run
tank at higher temp (probably 70)

It would store more energy in the tank, at a slight cost in boiler
efficiency (but probably only for the last few degrees of the reheat).

The store has a baffle - to help stratification, but as soon as you draw
any hot water it energises the pimp on primaries to 'stir' the store and
keep recharging heat exchanger.


--
Cheers,

John.

/================================================== ===============\
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| John Rumm - john(at)internode(dot)co(dot)uk |
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On 11/11/2016 23:46, John Rumm wrote:

ok, so it can take the full boiler output which makes it a bit simpler.


It would store more energy in the tank, at a slight cost in boiler
efficiency (but probably only for the last few degrees of the reheat).

Not easy trying to get information on how to best set up ........

GasSafe servce guys have no clue at all about Thermal stores, in fact
couldn't even advise on how to set up jumpers on control board.

NuHeat who designed & sold system - admit their commissioning notes are
based on non-condensing boilers - and when asked about what I should do
for a condensing boiler - advise just make sure flow temp is higher than
tank stat ... the greater the difference the quicker it will recover -
but other than that they say to contact boiler manufacture.

Baxi reply with "with the store needing to maintain a constant store
temperature of 60 degrees. You will need to follow the manufacturers
guidance, as it is their system that requires these temperatures to run
correctly, and unfortunately achieving a target 55 degree return
temperature doesn't sound possible."


At the moment the boiler control board is set to 100,00BTU/h and 83C
Turned down variable temp control (user front panel knob) to get 75C
and reduced pump to speed II
I'll try fitting a pair of thermometers and watch the F&R and see if I
can reduce speed further.
Maybe I can get a reasonable differential on F&R ... but Baxi don't
think I will not get 55C

rick wrote:

Baxi reply with "with the store needing to maintain a constant store
temperature of 60 degrees. You will need to follow the manufacturers
guidance, as it is their system that requires these temperatures to run
correctly, and unfortunately achieving a target 55 degree return
temperature doesn't sound possible."

Does the store really want to stay constant? I'd have thought with a
non-modulating boiler, firing in frequent short bursts would not be the
most efficient while the UFH is drawing out heat.

On 12/11/2016 10:56, rick wrote:
On 11/11/2016 23:46, John Rumm wrote:

ok, so it can take the full boiler output which makes it a bit simpler.


It would store more energy in the tank, at a slight cost in boiler
efficiency (but probably only for the last few degrees of the reheat).

Not easy trying to get information on how to best set up ........

GasSafe servce guys have no clue at all about Thermal stores, in fact
couldn't even advise on how to set up jumpers on control board.

NuHeat who designed & sold system - admit their commissioning notes are
based on non-condensing boilers - and when asked about what I should do
for a condensing boiler - advise just make sure flow temp is higher than
tank stat ... the greater the difference the quicker it will recover -
but other than that they say to contact boiler manufacture.

Baxi reply with "with the store needing to maintain a constant store
temperature of 60 degrees. You will need to follow the manufacturers
guidance, as it is their system that requires these temperatures to run
correctly, and unfortunately achieving a target 55 degree return
temperature doesn't sound possible."

I think there is a danger of over thinking this one! Beyond basic
requirements like making sure the flow is hot enough to get the store to
its set point, there are only a few variable to play with, and each has
pros and cons - so pick whichever is most important to you. None are
necessarily right or wrong.

You have a setup that was really conceived as a way of gaining
efficiency on systems with a demand for low flow temps (i.e. UFH) and a
fixed output non condensing boiler.

As addition benefits it allows high delivery rates of mains pressure DHW
without being limited to the instantaneous power available from your
gas/oil supply, and makes it easy to incorporate multiple sources of
heat into a system.

At the moment the boiler control board is set to 100,00BTU/h and 83C
Turned down variable temp control (user front panel knob) to get 75C and
reduced pump to speed II
I'll try fitting a pair of thermometers and watch the F&R and see if I
can reduce speed further.
Maybe I can get a reasonable differential on F&R ... but Baxi don't
think I will not get 55C

You will do if the store is nearly depleted, but obviously as it warms
up that will get harder. All that means is you will get a reduction in
boiler efficiency for the last phase of the reheat.


--
Cheers,

John.

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On Sat, 12 Nov 2016 13:00:32 +0000, John Rumm
wrote:

You have a setup that was really conceived as a way of gaining
efficiency on systems with a demand for low flow temps (i.e. UFH) and a
fixed output non condensing boiler.

As addition benefits it allows high delivery rates of mains pressure DHW
without being limited to the instantaneous power available from your
gas/oil supply, and makes it easy to incorporate multiple sources of
heat into a system.


Not being much good at plumbing but having some experience of thermal
stores:

My first point is that it's far better to store the energy as natural
gas and only convert it to heat as you need it.

So the OP's system has a heat store for the two reasons John has
discussed

1) to deliver more instantaneous hot water than the boiler can supply
from the top part of the thermal store that, I assume this goes
through a plate heat exchanger so returns to the bottom of the store
at near ambient? Water from the main tends to be around 10C here.

2) To allow a blending valve to take water from the top of the thermal
store but under the part reserved for DHW, mix it with water going
around the under floor circuit and then return is at around 25C to
the bottom of the tank.

The need is always to return water below about 40C to the boiler to
keep it in condensing mode?

My thoughts are on how well the thermal store remains stratified or is
the flow too great such that it induces a lot of turbulence?

If it remains stratified then why can the boiler not be set to burn if
the DHW reserve falls below a high set temperature, whilst still
drawing cool water from the bottom of the tank?


The demand for underfloor heating then being sensed when the blender
valve input from the thermal store falls below the set underfloor
temperature it can maintain?


The boiler then heats the whole of the tank until it starts drawing
water above 40 C from the bottom of the tank?

The system I used to service a pellet boiler on in a block of flats in
Brixton failed to maintain stratification because the flows where so
high they constantly mixed the store's contents. I advocated a
possible solution but the german makers of the thermal store would not
countenance it.

AJH

wrote:
On Sat, 12 Nov 2016 13:00:32 +0000, John Rumm
wrote:

You have a setup that was really conceived as a way of gaining
efficiency on systems with a demand for low flow temps (i.e. UFH) and a
fixed output non condensing boiler.

As addition benefits it allows high delivery rates of mains pressure DHW
without being limited to the instantaneous power available from your
gas/oil supply, and makes it easy to incorporate multiple sources of
heat into a system.


Not being much good at plumbing but having some experience of thermal
stores:

My first point is that it's far better to store the energy as natural
gas and only convert it to heat as you need it.

So the OP's system has a heat store for the two reasons John has
discussed

1) to deliver more instantaneous hot water than the boiler can supply
from the top part of the thermal store that, I assume this goes
through a plate heat exchanger so returns to the bottom of the store
at near ambient? Water from the main tends to be around 10C here.

2) To allow a blending valve to take water from the top of the thermal
store but under the part reserved for DHW, mix it with water going
around the under floor circuit and then return is at around 25C to
the bottom of the tank.

The need is always to return water below about 40C to the boiler to
keep it in condensing mode?

My thoughts are on how well the thermal store remains stratified or is
the flow too great such that it induces a lot of turbulence?

If it remains stratified then why can the boiler not be set to burn if
the DHW reserve falls below a high set temperature, whilst still
drawing cool water from the bottom of the tank?


The demand for underfloor heating then being sensed when the blender
valve input from the thermal store falls below the set underfloor
temperature it can maintain?


The boiler then heats the whole of the tank until it starts drawing
water above 40 C from the bottom of the tank?

The system I used to service a pellet boiler on in a block of flats in
Brixton failed to maintain stratification because the flows where so
high they constantly mixed the store's contents. I advocated a
possible solution but the german makers of the thermal store would not
countenance it.


It seems an awfully complicated way of meeting two very different demands.

Wouldn't two boilers be simpler/cheaper? Condensing multipoint for HW and
standard condensing boiler for CH?

Tim

--
Please don't feed the trolls

On Sat, 12 Nov 2016 15:15:46 -0000 (UTC), Tim+
wrote:

It seems an awfully complicated way of meeting two very different demands.

Why it's just a matter of changing where the thermostats that trigger
the burner are placed except on the underfloor system a different
stat triggers on from the one that turns off the boiler?

Wouldn't two boilers be simpler/cheaper? Condensing multipoint for HW and
standard condensing boiler for CH?

At over £700 each?

AJH

On 12/11/2016 14:46, wrote:
On Sat, 12 Nov 2016 13:00:32 +0000, John Rumm
wrote:

You have a setup that was really conceived as a way of gaining
efficiency on systems with a demand for low flow temps (i.e. UFH) and a
fixed output non condensing boiler.

As addition benefits it allows high delivery rates of mains pressure DHW
without being limited to the instantaneous power available from your
gas/oil supply, and makes it easy to incorporate multiple sources of
heat into a system.


Not being much good at plumbing but having some experience of thermal
stores:

My first point is that it's far better to store the energy as natural
gas and only convert it to heat as you need it.

The problem there is that with a domestic supply you are going to be
limited to about 50kW which is only about 17 lpm at a 40 degree
temperature rise. The thermal store with a large plate HX will be able
to heat the water on demand at well over double that rate.

So the OP's system has a heat store for the two reasons John has
discussed

1) to deliver more instantaneous hot water than the boiler can supply
from the top part of the thermal store that, I assume this goes
through a plate heat exchanger so returns to the bottom of the store
at near ambient? Water from the main tends to be around 10C here.

2) To allow a blending valve to take water from the top of the thermal
store but under the part reserved for DHW, mix it with water going
around the under floor circuit and then return is at around 25C to
the bottom of the tank.

The need is always to return water below about 40C to the boiler to
keep it in condensing mode?

Below 54 is ideal...

My thoughts are on how well the thermal store remains stratified or is
the flow too great such that it induces a lot of turbulence?

If it remains stratified then why can the boiler not be set to burn if
the DHW reserve falls below a high set temperature, whilst still
drawing cool water from the bottom of the tank?

You can tweak these things by selecting where you sense the temperature
of the store. You can also use two stats some distance apart to increase
the hysteresis and hence boiler run time to get larger more efficient
recharges.

The demand for underfloor heating then being sensed when the blender
valve input from the thermal store falls below the set underfloor
temperature it can maintain?


The boiler then heats the whole of the tank until it starts drawing
water above 40 C from the bottom of the tank?

The system I used to service a pellet boiler on in a block of flats in
Brixton failed to maintain stratification because the flows where so
high they constantly mixed the store's contents. I advocated a
possible solution but the german makers of the thermal store would not
countenance it.

What was your suggested solution?


--
Cheers,

John.

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

On 12/11/2016 15:15, Tim+ wrote:
wrote:
On Sat, 12 Nov 2016 13:00:32 +0000, John Rumm
wrote:

You have a setup that was really conceived as a way of gaining
efficiency on systems with a demand for low flow temps (i.e. UFH) and a
fixed output non condensing boiler.

As addition benefits it allows high delivery rates of mains pressure DHW
without being limited to the instantaneous power available from your
gas/oil supply, and makes it easy to incorporate multiple sources of
heat into a system.


Not being much good at plumbing but having some experience of thermal
stores:

My first point is that it's far better to store the energy as natural
gas and only convert it to heat as you need it.

So the OP's system has a heat store for the two reasons John has
discussed

1) to deliver more instantaneous hot water than the boiler can supply
from the top part of the thermal store that, I assume this goes
through a plate heat exchanger so returns to the bottom of the store
at near ambient? Water from the main tends to be around 10C here.

2) To allow a blending valve to take water from the top of the thermal
store but under the part reserved for DHW, mix it with water going
around the under floor circuit and then return is at around 25C to
the bottom of the tank.

The need is always to return water below about 40C to the boiler to
keep it in condensing mode?

My thoughts are on how well the thermal store remains stratified or is
the flow too great such that it induces a lot of turbulence?

If it remains stratified then why can the boiler not be set to burn if
the DHW reserve falls below a high set temperature, whilst still
drawing cool water from the bottom of the tank?


The demand for underfloor heating then being sensed when the blender
valve input from the thermal store falls below the set underfloor
temperature it can maintain?


The boiler then heats the whole of the tank until it starts drawing
water above 40 C from the bottom of the tank?

The system I used to service a pellet boiler on in a block of flats in
Brixton failed to maintain stratification because the flows where so
high they constantly mixed the store's contents. I advocated a
possible solution but the german makers of the thermal store would not
countenance it.


It seems an awfully complicated way of meeting two very different demands.

Wouldn't two boilers be simpler/cheaper? Condensing multipoint for HW and
standard condensing boiler for CH?

Only if you like hot water dribbling from the taps ;-)

An alternative would be to drive the UFH from a modern boiler directly
with blending valves. The devote the store to just giving you DHW.

No real advantages over a unvented hot water cylinder though it has to
be said.


--
Cheers,

John.

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

John Rumm wrote:
On 12/11/2016 15:15, Tim+ wrote:
wrote:
On Sat, 12 Nov 2016 13:00:32 +0000, John Rumm
wrote:

You have a setup that was really conceived as a way of gaining
efficiency on systems with a demand for low flow temps (i.e. UFH) and a
fixed output non condensing boiler.

As addition benefits it allows high delivery rates of mains pressure DHW
without being limited to the instantaneous power available from your
gas/oil supply, and makes it easy to incorporate multiple sources of
heat into a system.


Not being much good at plumbing but having some experience of thermal
stores:

My first point is that it's far better to store the energy as natural
gas and only convert it to heat as you need it.

So the OP's system has a heat store for the two reasons John has
discussed

1) to deliver more instantaneous hot water than the boiler can supply
from the top part of the thermal store that, I assume this goes
through a plate heat exchanger so returns to the bottom of the store
at near ambient? Water from the main tends to be around 10C here.

2) To allow a blending valve to take water from the top of the thermal
store but under the part reserved for DHW, mix it with water going
around the under floor circuit and then return is at around 25C to
the bottom of the tank.

The need is always to return water below about 40C to the boiler to
keep it in condensing mode?

My thoughts are on how well the thermal store remains stratified or is
the flow too great such that it induces a lot of turbulence?

If it remains stratified then why can the boiler not be set to burn if
the DHW reserve falls below a high set temperature, whilst still
drawing cool water from the bottom of the tank?


The demand for underfloor heating then being sensed when the blender
valve input from the thermal store falls below the set underfloor
temperature it can maintain?


The boiler then heats the whole of the tank until it starts drawing
water above 40 C from the bottom of the tank?

The system I used to service a pellet boiler on in a block of flats in
Brixton failed to maintain stratification because the flows where so
high they constantly mixed the store's contents. I advocated a
possible solution but the german makers of the thermal store would not
countenance it.


It seems an awfully complicated way of meeting two very different demands.

Wouldn't two boilers be simpler/cheaper? Condensing multipoint for HW and
standard condensing boiler for CH?

Only if you like hot water dribbling from the taps ;-)

A bit unfair on instantaneous water heaters. For sure not going to match
the best output of a stored water solution but more than adequate for many
folk who don't run a bath too often.

Tim


--
Please don't feed the trolls

On Sat, 12 Nov 2016 19:20:14 +0000, John Rumm
wrote:

What was your suggested solution?

Return the cold water tangentially to prevent the mixing, the colder
water then inducing a slight vortex and falling to the bottom, any
warmer water at the same level would be less dense so would rise and
not tend to move past the denser colder layer from centrifugal effects
as long as there was little turbulence. Hot take offs were already
from the centre of the 3000litre cylindrical tanks.

AJH

On 12/11/2016 20:36, Tim+ wrote:
John Rumm wrote:
On 12/11/2016 15:15, Tim+ wrote:
wrote:
On Sat, 12 Nov 2016 13:00:32 +0000, John Rumm
wrote:

You have a setup that was really conceived as a way of gaining
efficiency on systems with a demand for low flow temps (i.e. UFH) and a
fixed output non condensing boiler.

As addition benefits it allows high delivery rates of mains pressure DHW
without being limited to the instantaneous power available from your
gas/oil supply, and makes it easy to incorporate multiple sources of
heat into a system.


Not being much good at plumbing but having some experience of thermal
stores:

My first point is that it's far better to store the energy as natural
gas and only convert it to heat as you need it.

So the OP's system has a heat store for the two reasons John has
discussed

1) to deliver more instantaneous hot water than the boiler can supply
from the top part of the thermal store that, I assume this goes
through a plate heat exchanger so returns to the bottom of the store
at near ambient? Water from the main tends to be around 10C here.

2) To allow a blending valve to take water from the top of the thermal
store but under the part reserved for DHW, mix it with water going
around the under floor circuit and then return is at around 25C to
the bottom of the tank.

The need is always to return water below about 40C to the boiler to
keep it in condensing mode?

My thoughts are on how well the thermal store remains stratified or is
the flow too great such that it induces a lot of turbulence?

If it remains stratified then why can the boiler not be set to burn if
the DHW reserve falls below a high set temperature, whilst still
drawing cool water from the bottom of the tank?


The demand for underfloor heating then being sensed when the blender
valve input from the thermal store falls below the set underfloor
temperature it can maintain?


The boiler then heats the whole of the tank until it starts drawing
water above 40 C from the bottom of the tank?

The system I used to service a pellet boiler on in a block of flats in
Brixton failed to maintain stratification because the flows where so
high they constantly mixed the store's contents. I advocated a
possible solution but the german makers of the thermal store would not
countenance it.


It seems an awfully complicated way of meeting two very different demands.

Wouldn't two boilers be simpler/cheaper? Condensing multipoint for HW and
standard condensing boiler for CH?

Only if you like hot water dribbling from the taps ;-)

A bit unfair on instantaneous water heaters. For sure not going to match
the best output of a stored water solution but more than adequate for many
folk who don't run a bath too often.

Yup fair point, It was intended more of a "in comparison to what the
thermal store can deliver", rather than in absolute terms.

Many multipoints are only about 24kW though - so 9 lpm of hot water.


--
Cheers,

John.

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

John Rumm wrote:
On 12/11/2016 20:36, Tim+ wrote:


A bit unfair on instantaneous water heaters. For sure not going to match
the best output of a stored water solution but more than adequate for many
folk who don't run a bath too often.

Yup fair point, It was intended more of a "in comparison to what the
thermal store can deliver", rather than in absolute terms.

Many multipoints are only about 24kW though - so 9 lpm of hot water.



Okay, not a multipoint then, just a big combi. ;-)

Tim

--
Please don't feed the trolls

On 12/11/2016 15:15, Tim+ wrote:

It seems an awfully complicated way of meeting two very different demands.

Wouldn't two boilers be simpler/cheaper? Condensing multipoint for HW and
standard condensing boiler for CH?

Tim
Certianly not in may case

Certainly not in may case as single boiler already installed...
In general the store is not particularly expensive .. and in my case I
also dump all spare electrically generated power form my Solar PV array
.... very easy to mix any heat source as the store is just a storage
battery. It also provides a very large buffer - so if tehre is demand
for a lot of heat for heating or DHW .... don't have to wait ... it's
there and immediate.

On 12/11/2016 19:20, John Rumm wrote:

The need is always to return water below about 40C to the boiler to
keep it in condensing mode?

Below 54 is ideal...

My thoughts are on how well the thermal store remains stratified or is
the flow too great such that it induces a lot of turbulence?

If it remains stratified then why can the boiler not be set to burn if
the DHW reserve falls below a high set temperature, whilst still
drawing cool water from the bottom of the tank?

You can tweak these things by selecting where you sense the temperature
of the store. You can also use two stats some distance apart to increase
the hysteresis and hence boiler run time to get larger more efficient
recharges.


The issue is the stratification is there with the horizontal baffle in
the store .. but once you start running DHW the pump on the primaries is
operated to 'stir the store' ondoing any stratification.
I have 'improved' things with a delay .. DHW has to be running for
45sec before pump will start ...... which prevent lots of small runs.