If you're going to fit a heat bank to get the benefit of mains pressure hot
water, no tanks, etc. etc., what are the pros and cons of heating the
radiators from either the store with the necessary coil and pump or directly
from the condensing boiler?

I'm wondering if I should just treat the heat bank as a cylinder and connect
the rad circuit(s) directly via a zone valve or to feed them from the store

I have this suspicion that if you buffer the radiators via a heat bank you
may lose some of the benefit of a condensing boiler since the return
temperature will be greater than if you designed the system for radiators,
opting for a lower than usual return. Yes, I know it means departing from
BS, having bigger rads, adjusting for mean temperature etc. but so what if
it achieves the desired effect ?

I bet this has been discussed before but I'm taking the easy option

"Jeff" wrote in message
...

If you're going to fit a heat bank to get the benefit of mains pressure
hot
water, no tanks, etc. etc., what are the pros and cons of heating the
radiators from either the store with the necessary coil and pump or
directly
from the condensing boiler?

I'm wondering if I should just treat the heat bank as a cylinder and
connect
the rad circuit(s) directly via a zone valve or to feed them from the
store

I have this suspicion that if you buffer the radiators via a heat bank you
may lose some of the benefit of a condensing boiler since the return
temperature will be greater than if you designed the system for radiators,
opting for a lower than usual return. Yes, I know it means departing from
BS, having bigger rads, adjusting for mean temperature etc. but so what if
it achieves the desired effect ?

I bet this has been discussed before but I'm taking the easy option

Get a larger heat bank and run at the lowest temp you canget away with for
DHW. Take the rads off the heat banks and use a Grundfos Alpha pump on the
rad circuit.

Advantages of Heat-Banks

- Instant high pressure hot water - When the store has reached temperature
water is delivered instantly at the taps.

- Very high water flow-rate - The high-end heat-banks have a flow-rate up to
45 litres/min.

- Long efficient boiler burn - Reduces boiler on-off cycling increasing
efficiency, although inefficient boiler cycling is no longer a major problem
as it was with balanced flues.

- Maintains optimum boiler temperature range - using a blending valve the
flow/return of the boiler can be kept to optimum maintaining greater
efficiencies. The boiler operates at optimum performance.

- Combines the output of the stored water and the boiler

- Cylinder may be smaller for a similar performance - smaller cylinders than
unvented cylinders.

- Cylinder at low pressure - Unlike an unvented cylinder it does not store
water at high pressures.

- Fast cylinder recovery rate - When the boiler is connected directly to the
heat-bank, and not via an indirect coil, the recovery rate is rapid.
Although in some cases a boiler may heat the heat-bank via an indirect coil,
reducing the recovery rate.

- Legionella bacteria eliminated - The Legionella bacteria cannot survive in
the high temperature sealed conditions of a heat-bank.

- No scale build-up in heat-bank - Containing primary and not secondary
fresh water, there is no scale build-up inside the heat-bank.

- Cold water storage eliminated - No need for cold water storage tanks.

- Solar heating storage - Water heated via solar panels may be stored in the
heat-bank via a solar coil.

- Easy maintenance - If an external plate heat exchanger requires cleaning
or replacing it is a matter of draining down the heat-bank, or closing
isolating vales, and unscrewing the plate heat-exchanger. In some rare
instances plate heat-exchangers are fitted directly inside the heat-bank
preventing on-site maintenance.

- Easy to improve hot water flowrates - By simply adding additional plate
heat-exchangers in parallel, hot water flow rates may be improved. Retrofit
additions are possible if extra bathrooms or showers are installed.

- Stored water vessel need not be cylindrical - As no internal coil is used
for hot water heat transfer the stored water vessel may be any shape, as
opposed to a thermal store which has to be cylindrical for maximum
efficiency. This has advantages where space is limited.

- Rads warm up period only a few minutes - The store holds enough hot water
for all the rads, so rads instantly hot

- If all TVRs Close the Boiler is Not Affected - Flow is always through the
boiler

Disadvantages of Heat-Banks

- The store needs be near fully temperature to supply baths - Before any hot
water is drawn off, the store must be up to temperature. Many later
versions use a blending valve on the return to the boiler to ensure only up
to temperature water is pumped into the store by the boiler. This prevents
agitation of the stored water, and aiding heat stratification within the
store giving useful water at the top of the store within a shot time. The
water is heat only in one pass through the boiler.

- Lower water temperatures with fast flow-rates - As with Combi boilers,
fast flow-rates through the plate heat-exchanger results in lower water
temperatures. This is not so pronounced with heat-banks as with
thermal-stores.

- Rads may need to be larger - Rads operate at lower temp, so may be larger



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"Jeff" wrote in message
...
If you're going to fit a heat bank to get the benefit of mains pressure
hot
water, no tanks, etc. etc., what are the pros and cons of heating the
radiators from either the store with the necessary coil and pump or
directly
from the condensing boiler?

I'm wondering if I should just treat the heat bank as a cylinder and
connect
the rad circuit(s) directly via a zone valve or to feed them from the
store

I have this suspicion that if you buffer the radiators via a heat bank you
may lose some of the benefit of a condensing boiler

I don't think so - though my boiler isn't condensing. With a heat bank and
a programmable thermostat you could set the boiler to kick in and out at
whatever is optimal for the boiler, isolating it totally from requirements
like not make every radiator scalding hot or stone cold.

On Tue, 19 Apr 2005 18:52:20 +0100, "Jeff"
wrote:

If you're going to fit a heat bank to get the benefit of mains pressure hot
water, no tanks, etc. etc., what are the pros and cons of heating the
radiators from either the store with the necessary coil and pump or directly
from the condensing boiler?

I'm wondering if I should just treat the heat bank as a cylinder and connect
the rad circuit(s) directly via a zone valve or to feed them from the store

I have this suspicion that if you buffer the radiators via a heat bank you
may lose some of the benefit of a condensing boiler since the return
temperature will be greater than if you designed the system for radiators,
opting for a lower than usual return. Yes, I know it means departing from
BS, having bigger rads, adjusting for mean temperature etc. but so what if
it achieves the desired effect ?

I bet this has been discussed before but I'm taking the easy option



If you have a condensing boiler, then it will work optimally and more
efficiently at lower temperatures. Especially at this time of year and
in the autumn, you can run the radiators at lower temperatures and the
boiler will modulate down to match.

If you have a heat bank in the middle, in order to heat the hot water,
you need to run it at 75 to 80 degrees. You can take heat out of it
to run the radiator, of course, but then the problem is that it will
have the effect of causing the boiler to run in bursts of full output
to replenish the store. This is not as efficient as letting it run
continuously or near continuously at lower power to match the radiator
requirement.

Heating the space with radiators and providing the hot water are two
different problems. WIth the space heating, you can achieve optimal
efficiency by driving the radiators directly from the boiler. For
water heating, the objective is to dump as much heat into the cylinder
as quickly as possible and with efficiency as less of a concern.

In my system design I have a condensing boiler with weather
compensator driving the radiators directly. THe radiator sizing has
been arranged such that at the nominal -3 degree outside temperature
used as part of UK heating designs, the flow temperature will be 70
degrees and return 50 degrees or less. I achieved exactly this in
practice during the winter. Now when just a little heat is required
in the evenings, the boiler modulates down to about 3-4 kW and the
flow temperature can be around 40 degrees or so.

However, when there is hot water demand, the boiler is switched over
to driving the cylinder (a fast recovery type) and winds up to full
power. The concept of this is to reheat the cylinder quickly and
then switch back to running the heating.

It works very well.




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"Andy Hall" wrote in message
...

If you have a heat bank in the middle,
in order to heat the hot water,
you need to run it at 75 to 80 degrees.

Using a heat bank, the temperature only be 10C above DHW temperature. IF
you want 50C at the taps, then 60C store temp will do. So a condensing
boiler with a 22C flow/return temp differential need only be running at 38C
return. Very economical. The store then needs to be larger.

You can take heat out of it
to run the radiator, of course,
but then the problem is that it will
have the effect of causing the boiler
to run in bursts of full output
to replenish the store.

Yes, economically so.



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Jeff wrote:

If you're going to fit a heat bank to get the benefit of mains pressure hot
water, no tanks, etc. etc., what are the pros and cons of heating the
radiators from either the store with the necessary coil and pump or directly
from the condensing boiler?

With a modern boiler (and hence sophisticated load compensating control
system), you will usually be better off letting it drive the rads
directly. (Thermal stores are good at improving efficiency on old "all
or nothing" boilers, but often just serve to cock up the closed loop
control system on modulating boilers)

I'm wondering if I should just treat the heat bank as a cylinder and connect
the rad circuit(s) directly via a zone valve or to feed them from the store

Personally I would connect the rads directly. However there is sure to
be someone along shortly to contradict that. ;-)

I have this suspicion that if you buffer the radiators via a heat bank you
may lose some of the benefit of a condensing boiler since the return
temperature will be greater than if you designed the system for radiators,

Yup, you can get round some of the problems with extra work (blending
valves etc), but it is usually far simpler to avoid creating the problem
in the first place than spending lots of money fixing it.

A modern modulating boiler will run at its most efficient when it can
reduce its output down to a steady low state to match the actual
radiator load. If you stick an extra sodding great energy store into the
equation then you are introducing extra complexity that will usually
prevent the most efficient mode of operating from being reached.

opting for a lower than usual return. Yes, I know it means departing from
BS, having bigger rads, adjusting for mean temperature etc. but so what if
it achieves the desired effect ?

Not sure I follow that bit?

I bet this has been discussed before but I'm taking the easy option

It has, to death ;-) Google will have loads.

One of the difficulties is that for many years the thermal store was
actually a "good thing" in radiator circuits since it improved boiler
efficiency by reducing short cycling etc. Modern boilers and control
systems have now rendered that common wisdom less relevant in many
cases. However some folks are not so easily separated from their old
ways ;-)


--
Cheers,

John.

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

"Doctor Evil" wrote in message
...

You can take heat out of it
to run the radiator, of course,
but then the problem is that it will
have the effect of causing the boiler
to run in bursts of full output
to replenish the store.

Yes, economically so.


OK, you covered all the pros and cons quite comprehensively, bearing in mind
I think a condensing oil boiler can only fire at the rated output, you are
saying it's likely to be quite economical to let it dump a load of heat into
the store and then let the rads draw it off?

"John Rumm" wrote in message
...

With a modern boiler (and hence
sophisticated load compensating control
system), you will usually be better off
letting it drive the rads directly.

The great thing about a thermal store/heat bank is that a simple none
complicated boiler need only be used. This adds reliability, and less
service changes as less to go wrong.

(Thermal stores are good at improving
efficiency on old "all or nothing" boilers,
but often just serve to cock up the closed loop
control system on modulating boilers)

Not so. Modulating boilers work wekll with heat banks.

snip misinformation

A modern modulating boiler will
run at its most efficient when it can
reduce its output down to a steady
low state to match the actual
radiator load.

He doesn't need a modulating boiler with sophisticated load compensation
control.

One of the difficulties is that for many years the thermal store was
actually a "good thing" in radiator circuits since it improved boiler
efficiency by reducing short cycling etc. Modern boilers and control
systems have now rendered that common wisdom less relevant in many
cases. However some folks are not so easily separated from their old
ways ;-)

Old ways? What a joke.Thermal stores never took off and obtained the status
it deserves because plumbers couldn't understand them and builders kept
putting in silly tanks and cylinders. It is also too new for many people, so
much for "old ways". They are becoming more popular now as people realise
they have more advantages than unvented cylinders which require annual
services.

The store is a superb neutral point separating, the boiler, rads, DHW, solar
input, etc.



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"Jeff" wrote in message
...

I should have mentioned - no gas here,
I'll (or probably someone else) will
be fitting a condensing oil boiler. AFAIK,
they don't modulate. I think it's firing or not firing.

Oil condensers are very expensive and don't offer great efficiencies over
non-condensers. Yep, just get a normal heat bank.

Possibly that would make me lean
towards taking the rads off the heat bank,
to reduce cycling.

Very wise. Get a heat bank with two cylinder stats

Otherwise, during not so cold weather
the boiler will be oversized and cycling regularly.
Would you agree?

Yep.

I can see the advantage
there but then I think that the heat bank
will get up to temperature and
take the return temp up above the optimum.
Pandora says the water in the
store is typically 75 degrees.

It can be higher. They want lower temps to get the best out of gas
condensers.

If the rads are off the boiler, I could
design the system for a suitable
return temperature to try and keep
it condensing. But then, that only
applies when the system is fully loaded,
and how often is that?

With a non-condensing oil boiler you don't want low temps.

Maybe I worry too much about this efficiency lark.

Just have two cylinder stats to prevent boiler cycling and lag the hell out
of all exposed pipes. You could fit a blending valve on the flow/return.
The likes of DPS would fit one for you.



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"Andy Hall" wrote in message
...
If you're going to fit a heat bank to get the benefit of mains pressure
hot
water, no tanks, etc. etc., what are the pros and cons of heating the
radiators from either the store with the necessary coil and pump or
directly
from the condensing boiler?

I'm wondering if I should just treat the heat bank as a cylinder and
connect
the rad circuit(s) directly via a zone valve or to feed them from the
store


If you have a condensing boiler, then it will work optimally and more
efficiently at lower temperatures. Especially at this time of year and
in the autumn, you can run the radiators at lower temperatures and the
boiler will modulate down to match.

Only if it's a modulating boiler surely. If it can only do full or nothing
I'd still suggest putting the heat bank in the middle is a better option.

"Jeff" wrote in message
...
I should have mentioned - no gas here, I'll (or probably someone else)
will
be fitting a condensing oil boiler. AFAIK, they don't modulate. I think
it's firing or not firing.

Yes

Possibly that would make me lean towards taking the rads off the heat
bank,
to reduce cycling. Otherwise, during not so cold weather the boiler will
be
oversized and cycling regularly. Would you agree?

Yes. The other problem with direct connection in not so cold weather is you
don't really take much heat from the boiler, but it is running flat out so
the boiler thermostat operates more often than the control thermostat and
you can actually feel the temperature of the radiators going down whilst
waiting for the boiler to come on again. A heat store will level out this
effect.


If the rads are off the boiler, I could design the system for a suitable
return temperature to try and keep it condensing. But then, that only
applies when the system is fully loaded, and how often is that?

You probably won't have the boiler ever fully loaded. Thus keeping it
optimal is impossible.


Maybe I worry too much about this efficiency lark.

No. Do worry about it. But for non-modulating boilers I think a heat store
is the best approach.

"Mike" wrote in message
...

"Jeff" wrote in message
...
I should have mentioned - no gas here, I'll (or probably someone else)
will
be fitting a condensing oil boiler. AFAIK, they don't modulate. I
think
it's firing or not firing.

Yes

Possibly that would make me lean towards taking the rads off the heat
bank,
to reduce cycling. Otherwise, during not so cold weather the boiler
will
be
oversized and cycling regularly. Would you agree?

Yes. The other problem with direct connection in not so cold weather is
you
don't really take much heat from the boiler, but it is running flat out so
the boiler thermostat operates more often than the control thermostat and
you can actually feel the temperature of the radiators going down whilst
waiting for the boiler to come on again. A heat store will level out this
effect.


If the rads are off the boiler, I could design the system for a suitable
return temperature to try and keep it condensing. But then, that only
applies when the system is fully loaded, and how often is that?

You probably won't have the boiler ever fully loaded. Thus keeping it
optimal is impossible.

If the boiler is connected directly to a store, it will be fully loaded when
reheating.

Maybe I worry too much about this efficiency lark.

No. Do worry about it. But for
non-modulating boilers I think a heat store
is the best approach.



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"Doctor Evil" wrote in message
...
If the rads are off the boiler, I could design the system for a
suitable
return temperature to try and keep it condensing. But then, that only
applies when the system is fully loaded, and how often is that?

You probably won't have the boiler ever fully loaded. Thus keeping it
optimal is impossible.

If the boiler is connected directly to a store, it will be fully loaded
when
reheating.

That's what I said in the paragraph after

On Tue, 19 Apr 2005 22:06:49 +0100, "Jeff"
wrote:


"Doctor Evil" wrote in message
...

You can take heat out of it
to run the radiator, of course,
but then the problem is that it will
have the effect of causing the boiler
to run in bursts of full output
to replenish the store.

Yes, economically so.


OK, you covered all the pros and cons quite comprehensively, bearing in mind
I think a condensing oil boiler can only fire at the rated output, you are
saying it's likely to be quite economical to let it dump a load of heat into
the store and then let the rads draw it off?



He may be saying that, but it isn't the case.

Most condensing boilers can modulate downwards to match the heating
load. If you connect a small load such as radiator space heating
during spring and autumn then the boiler can modulate down and operate
at lower temperatures which are more efficient for it as well as not
needing to fire on and off.

If you do this via a heatbank, then the boiler can never enter the
lower temperature ranges and probably won't modulate down either.

The technique of using a heatbank as intermediary for space heating is
useful in two scenarios:

- If you have a non-condensing boiler, it will provide a "smoothing"
action which will reduce the amount of cycling considerably and
improve its efficiency. The non-condensing boiler is designed to run
at high temperature anyway.

- If you have another source of heat such as solar and need to do
combining of some sort.



--

..andy

To email, substitute .nospam with .gl

On Tue, 19 Apr 2005 23:11:57 +0100, "Mike" wrote:


"Andy Hall" wrote in message
.. .
If you're going to fit a heat bank to get the benefit of mains pressure
hot
water, no tanks, etc. etc., what are the pros and cons of heating the
radiators from either the store with the necessary coil and pump or
directly
from the condensing boiler?

I'm wondering if I should just treat the heat bank as a cylinder and
connect
the rad circuit(s) directly via a zone valve or to feed them from the
store


If you have a condensing boiler, then it will work optimally and more
efficiently at lower temperatures. Especially at this time of year and
in the autumn, you can run the radiators at lower temperatures and the
boiler will modulate down to match.

Only if it's a modulating boiler surely. If it can only do full or nothing
I'd still suggest putting the heat bank in the middle is a better option.

Most new condensing boiler designs are modulating.

If it isn't then there could be an advantage in putting a heatbank in
the middle to reduce cycling.



--

..andy

To email, substitute .nospam with .gl

"Andy Hall" wrote in message
...
On Tue, 19 Apr 2005 22:06:49 +0100, "Jeff"
wrote:


"Doctor Evil" wrote in message
...

You can take heat out of it
to run the radiator, of course,
but then the problem is that it will
have the effect of causing the boiler
to run in bursts of full output
to replenish the store.

Yes, economically so.

OK, you covered all the pros and cons
quite comprehensively, bearing in mind
I think a condensing oil boiler can only
fire at the rated output, you are saying
it's likely to be quite economical to let it
dump a load of heat into the store and
then let the rads draw it off?

He may be saying that, but it isn't the case.

It is the case.

Most condensing boilers can modulate
downwards to match the heating
load.

Most cannot accurately enough. To do it properly you need a boiler can
modulate down very low and have load compensation control. They are
"expensive" to buy and have more to go wrong.

If you do this via a heatbank, then
the boiler can never enter the
lower temperature ranges and probably
won't modulate down either.

You can have a weather compensator maintaining the bottom CH zone in the
heat bank. The boiler comes in to reheat the mass of water to the settings
of the compensator. Simple and effective. Cycling is vastly reduced as a
mass of water cools slowly.

The technique of using a heatbank
as intermediary for space heating is
useful in two scenarios:

Let's see what wisdom we have here...

- If you have a non-condensing boiler,
it will provide a "smoothing"
action which will reduce the
amount of cycling considerably and
improve its efficiency.

"Eliminate" cycling with another stat. The same also applies to condensing
boilers.

The non-condensing boiler is designed to run
at high temperature anyway.

Above condensing point. They run more efficiently when a flow/return
blending valve is set to maintian the return at 59C. At 11c delta T that is
70C flow temp.

- If you have another source of heat
such as solar and need to do
combining of some sort.




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"Andy Hall" wrote in message
...
On Tue, 19 Apr 2005 23:11:57 +0100, "Mike" wrote:


"Andy Hall" wrote in message
.. .
If you're going to fit a heat bank to get the benefit of mains
pressure
hot
water, no tanks, etc. etc., what are the pros and cons of heating the
radiators from either the store with the necessary coil and pump or
directly
from the condensing boiler?

I'm wondering if I should just treat the heat bank as a cylinder and
connect
the rad circuit(s) directly via a zone valve or to feed them from the
store


If you have a condensing boiler, then it will work optimally and more
efficiently at lower temperatures. Especially at this time of year and
in the autumn, you can run the radiators at lower temperatures and the
boiler will modulate down to match.

Only if it's a modulating boiler surely. If it can only do full or
nothing
I'd still suggest putting the heat bank in the middle is a better option.

Most new condensing boiler designs are modulating.

On temperature, not load.

If it isn't then there could be an
advantage in putting a heatbank in
the middle to reduce cycling.

Always an advantage.


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On Tue, 19 Apr 2005 21:55:37 +0100, "Jeff"
wrote:

I should have mentioned - no gas here, I'll (or probably someone else) will
be fitting a condensing oil boiler. AFAIK, they don't modulate. I think
it's firing or not firing.

Ah.... you didn't say that. I believe that there are modulating oil
boilers on the market, but most are not.


Possibly that would make me lean towards taking the rads off the heat bank,
to reduce cycling. Otherwise, during not so cold weather the boiler will be
oversized and cycling regularly. Would you agree?

If the boiler has fixed and high output in relation to the needs of
the radiators then yes.

I can see the advantage
there but then I think that the heat bank will get up to temperature and
take the return temp up above the optimum. Pandora says the water in the
store is typically 75 degrees.

Bear in mind that there will be a range of temperatures from top to
bottom. When you have just the radiator load, the return water
temperature into the store will probably not be as low as when you are
heating cold water and the return water is from the plate heat
exchanger.


If the rads are off the boiler, I could design the system for a suitable
return temperature to try and keep it condensing.

Remember that there isn't a Holy Grail that you get to when condensing
begins. In reality what happens (if you think of it as a graph) is
that efficiency increases with falling return temperature. Below the
dew point where condensing begins, the *rate* of efficiency
improvement increases. In other words at 53 degrees, it's not hugely
better than at 55 degrees. To achieve maximum efficiency, you would
need to arrange the temperature to be as low as possible.

The problem is that the scenario for the radiators is different to
that for the hot water.

For the radiators, you would ideally like to let the store get almost
cold and then fire up the boiler, simply because for most of the time
you are using heat at a lower rate than the boiler can provide. This
would result in the boiler firing up and reheating an almost cold
store, which, given a fixed output boiler, is the best that you are
going to get.

For the hot water, you really need to have the store as fully charged
for as much of the time as possible. This is because when you make a
sudden large demand such as a bath, you are using heat far faster than
the boiler can produce, but of course the store can keep up while its
heat lasts. If you allow the store to deplete to improve boiler
efficiency, then you lose the benefit of storage and the set up
becomes limited to boiler ability in terms of HW flow rates.

So really the two objectives don't coincide that well.

I suppose that one could put more sophisticated temperature sensors
and control systems around the store to detect load behaviour and (for
example) fire the boiler up sooner if the temperature drop is rapid,
but this is becoming complex to do and the return on investment may
not be there.


But then, that only
applies when the system is fully loaded, and how often is that?

Probably only when you are starting the store from cold or having a
large



Maybe I worry too much about this efficiency lark.




--

..andy

To email, substitute .nospam with .gl

On Wed, 20 Apr 2005 00:21:50 +0100, "Doctor Evil"
wrote:


"Andy Hall" wrote in message
.. .
On Tue, 19 Apr 2005 22:06:49 +0100, "Jeff"
wrote:


"Doctor Evil" wrote in message
...

You can take heat out of it
to run the radiator, of course,
but then the problem is that it will
have the effect of causing the boiler
to run in bursts of full output
to replenish the store.

Yes, economically so.

OK, you covered all the pros and cons
quite comprehensively, bearing in mind
I think a condensing oil boiler can only
fire at the rated output, you are saying
it's likely to be quite economical to let it
dump a load of heat into the store and
then let the rads draw it off?

He may be saying that, but it isn't the case.

It is the case.

It depends on the type of boiler.


Most condensing boilers can modulate
downwards to match the heating
load.

Most cannot accurately enough. To do it properly you need a boiler can
modulate down very low and have load compensation control. They are
"expensive" to buy and have more to go wrong.

"Accurately" is not an appropriate way to describe it. It is true
that some boilers are able to modulate over a greater range than
others, but that has to do with a number of factors. There are now
some relatively inexpensive ones able to cover a very wide range and
drop down to below 5kW.

It's a complete nonsense to suggest that a boiler with load
compensation control has more to go wrong than one without. There is
an additional temperature sensor outside and a more sophisticated
control algorithm used in the controller electronics. this does not
imply that there is more to go wrong.



If you do this via a heatbank, then
the boiler can never enter the
lower temperature ranges and probably
won't modulate down either.

You can have a weather compensator maintaining the bottom CH zone in the
heat bank. The boiler comes in to reheat the mass of water to the settings
of the compensator. Simple and effective. Cycling is vastly reduced as a
mass of water cools slowly.

You can, but it is still at variance to the required behaviour from
the store when heating the DHW. One doesn't really want the behaviour
of the hot water heating to change with the weather.



The technique of using a heatbank
as intermediary for space heating is
useful in two scenarios:

Let's see what wisdom we have here...

- If you have a non-condensing boiler,
it will provide a "smoothing"
action which will reduce the
amount of cycling considerably and
improve its efficiency.

"Eliminate" cycling with another stat. The same also applies to condensing
boilers.

?????



The non-condensing boiler is designed to run
at high temperature anyway.

Above condensing point. They run more efficiently when a flow/return
blending valve is set to maintian the return at 59C. At 11c delta T that is
70C flow temp.

?????





- If you have another source of heat
such as solar and need to do
combining of some sort.




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--

..andy

To email, substitute .nospam with .gl

Jeff wrote:

I should have mentioned - no gas here, I'll (or probably someone else) will
be fitting a condensing oil boiler. AFAIK, they don't modulate. I think
it's firing or not firing.

Possibly that would make me lean towards taking the rads off the heat bank,
to reduce cycling. Otherwise, during not so cold weather the boiler will be
oversized and cycling regularly. Would you agree? I can see the
advantage

Yup if you don't have the modulation then you are back to cycling to
achieve less than the max effective output. So being able to consume the
maximum output in big lumps (i.e. with a store is better)

Many oil fired boilers are fixed output, although you can get some
modulating ones. Often the modulation range is not as wide as with gas
though. Misteral seem to do quite a number.

Grab a copy of the free SEDBUK database of boilers from SDA he

http://www.sda.co.uk/qsedbuk.htm

If the rads are off the boiler, I could design the system for a suitable
return temperature to try and keep it condensing. But then, that only
applies when the system is fully loaded, and how often is that?

It is unlikely to ever be fully loaded on heating alone. HW water is the
place you can sink big outputs in a short amount of time.

Remember however that efficiency is better when condensing, but it is not
a magic bullet - if you stop condensing there is not a big step change.
The condensing boiler will still be more efficient that its conventional
sibling simply by virtue of its better heat exchanger design.

Maybe I worry too much about this efficiency lark.

Possibly, I would focus more efforts on getting the type of system
performance you want first, and then the best economy within those
parameters second. Otherwise you will always be a bit dissatisfied with
the system, and knowing that "at least it is as cheap to run as
possible" may not offer much consolation.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
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\================================================= ================/

"Andy Hall" wrote in message
...

SNIP

He may be saying that, but it isn't the case.

Most condensing boilers can modulate downwards to match the heating
load. If you connect a small load such as radiator space heating
during spring and autumn then the boiler can modulate down and operate
at lower temperatures which are more efficient for it as well as not
needing to fire on and off.


Andy
Whilst the principles of your argument regarding the system are correct it
is not the case that the OPs intended "oil" fired condensing boiler can
modulate. To maintain good (efficient) combustion with small oil burners it
is neccessary to closely match the oil rate and atomisation through the
nozzle with the airflow rate. The economics and the practicalities are such
that turning up or down the oil rate will require adjustment of either the
oil nozzle hole size or oil pressure. The oil nozzle is a precision bored
unit and is effectively non adjustable. The alteration of the oil pressure
leads to alteration of the quality of atomisation. Again, alteration of the
airflow requires some considerable additional hardware and controls i.e.
servo operated air damper or fan speed but the fan is invariably mounted on
the same motor shaft as the oil pump (gear type).
On some larger (intermediate) oil burners a step modulation is employed by
installing twin nozzles in the burner head and a two stage (solenoid
operated hydraulic ram positioner) air shutter but these are only found in
burners of 100kW and above. I have seen only one progressively modulating
oil burner (serving a very large office building and made IIRC by Veissman)
but as it was so unusual out in the field I would anticipate its cost was
prohibitive.
These problems are most likely behind the reasoning to not require
condensing boiler installation for oil until 2007 at the present state of
affairs?

"John" wrote in message
...
These problems are most likely behind the reasoning to not require
condensing boiler installation for oil until 2007 at the present state of
affairs?


I think more likely was the fact that almost every oil boiler on the market
is 85% efficient so the 86% requirment of part L was a little silly.
Non-condensing gas boilers are more inefficient for reasons I'm sure
somebody here can explain.

This has been very interesting and helpful, thanks all contributors.

Trying to sort out the consistent themes and the most appropriate for me I'm
coming to the following conclusions:

(From the other thread) I don't need a bypass valve of any sort as long as I
have a water path at all times when pumping but I do need a zone with time
and temp control per 150 m2 max. 'Bypass' rads to have 2 lockshields.

An oil condensing boiler does not have the efficiency benefit over a
standard one, in comparison with gas models, and is also likely to be much
more expensive (checked out the efficiency on SEDBUK site)

A heat bank will usefully buffer the boiler output including for the rad
circuits particularly so for a non-condenser. A two-stat model will further
reduce cycling.

So I'm thinking I'll design for the 'normal' or higher temperature range of
boiler output, meaning I won't feel compelled to have slightly larger rads
(cost saving), I won't have to specify a condensing boiler so since I'll
probably be using an installer for the boiler and tank I should get
quotations competitivie with the installer's favoured models.


Now, how to size the boiler. Calculated heat loss over 2 floors plus a bit
for utility areas is around 29kW but it's unlikely we would ever want every
room up to design temperature. It's an old and poorly insulated property
but I'm hoping to significantly improve the main living rooms to a high
standard. No modulation, should I keep the boiler rating on the low side or
should I allow for the heat bank dhw load in addition?




"Jeff" wrote in message
...
If you're going to fit a heat bank to get the benefit of mains pressure
hot water, no tanks, etc. etc., what are the pros and cons of heating the
radiators from either the store with the necessary coil and pump or
directly from the condensing boiler?

I'm wondering if I should just treat the heat bank as a cylinder and
connect the rad circuit(s) directly via a zone valve or to feed them from
the store

I have this suspicion that if you buffer the radiators via a heat bank you
may lose some of the benefit of a condensing boiler since the return
temperature will be greater than if you designed the system for radiators,
opting for a lower than usual return. Yes, I know it means departing from
BS, having bigger rads, adjusting for mean temperature etc. but so what if
it achieves the desired effect ?

I bet this has been discussed before but I'm taking the easy option

"Jeff" wrote in message
...
This has been very interesting and helpful, thanks all contributors.

Trying to sort out the consistent themes and the most appropriate for me
I'm coming to the following conclusions:

(From the other thread) I don't need a bypass valve of any sort as long as
I have a water path at all times when pumping but I do need a zone with
time and temp control per 150 m2 max. 'Bypass' rads to have 2
lockshields.

An oil condensing boiler does not have the efficiency benefit over a
standard one, in comparison with gas models, and is also likely to be much
more expensive (checked out the efficiency on SEDBUK site)

There is an efficiency gain by using a condensing boiler but it becomes less
as the load modulates down and the boiler doesn't. You imply you have looked
at pricing so I guess you have made the decision?


A heat bank will usefully buffer the boiler output including for the rad
circuits particularly so for a non-condenser. A two-stat model will
further reduce cycling.

So I'm thinking I'll design for the 'normal' or higher temperature range
of boiler output, meaning I won't feel compelled to have slightly larger
rads (cost saving), I won't have to specify a condensing boiler so since
I'll probably be using an installer for the boiler and tank I should get
quotations competitivie with the installer's favoured models.

Personally I would oversize in line with a future swap to condensing and use
TRVs for room comfort. In terms of which model of boiler I have a distinct
penchant for Firebird non- condensing units. They have a very good build
quality and an economic price. The burners Firebird use can vary but I
suggest you specify Riello RDB (which is the usual model that comes with the
boiler). The boiler is available for balanced flue operation (about
under-worktop height) and/or conventional flueing. Both kitchen (white
cased) and boilerhouse models are available



Now, how to size the boiler. Calculated heat loss over 2 floors plus a
bit for utility areas is around 29kW but it's unlikely we would ever want
every room up to design temperature. It's an old and poorly insulated
property but I'm hoping to significantly improve the main living rooms to
a high standard. No modulation, should I keep the boiler rating on the
low side or should I allow for the heat bank dhw load in addition?

Allow for everything being on-line unless you are absolutely, definitely,
certain about not wanting all on at some stage in the future. Also make sure
your oil storage facility complies with OFTEC and Environment regulations.

"John" wrote in message
...

An oil condensing boiler does not have the efficiency benefit over a
standard one, in comparison with gas models, and is also likely to be
much more expensive (checked out the efficiency on SEDBUK site)

There is an efficiency gain by using a condensing boiler but it becomes
less as the load modulates down and the boiler doesn't. You imply you have
looked at pricing so I guess you have made the decision?


No, I haven't looked at pricing or made a decision yet - I could still go
either way. I don't have a nominated installer - my feeling was that if I
ask for quotations for a specific output of *any* or a small option list of
boilers I am likely to get a keener quotation; in my experience once you
start asking a given supplier for something that isn't on their 'preferred'
stock list it can work aginst you. Of course, I'll be examining what is
offered and making any necessary mental adjustments for perceived
differences in quality/list price. Or, I could source the boiler myself and
see if I can get someone to fit it. Or, fit it myself, but what
certification would I need and will someone actually certify my
installation? I've never fitted an oil boiler or the associated tank and
supply lines.


A heat bank will usefully buffer the boiler output including for the rad
circuits particularly so for a non-condenser. A two-stat model will
further reduce cycling.

So I'm thinking I'll design for the 'normal' or higher temperature range
of boiler output, meaning I won't feel compelled to have slightly larger
rads (cost saving), I won't have to specify a condensing boiler so since
I'll probably be using an installer for the boiler and tank I should get
quotations competitivie with the installer's favoured models.

Personally I would oversize in line with a future swap to condensing and
use TRVs for room comfort. In terms of which model of boiler I have a
distinct penchant for Firebird non- condensing units. They have a very
good build quality and an economic price. The burners Firebird use can
vary but I suggest you specify Riello RDB (which is the usual model that
comes with the boiler). The boiler is available for balanced flue
operation (about under-worktop height) and/or conventional flueing. Both
kitchen (white cased) and boilerhouse models are available


You mean oversize the rads anyway on the basis the next boiler change will
be condensing? I could do this. If so, I would adjust the rad size for the
reduced mean temperature if I changed to condensing per the manufacturers'
tables.



Now, how to size the boiler. Calculated heat loss over 2 floors plus a
bit for utility areas is around 29kW but it's unlikely we would ever want
every room up to design temperature. It's an old and poorly insulated
property but I'm hoping to significantly improve the main living rooms to
a high standard. No modulation, should I keep the boiler rating on the
low side or should I allow for the heat bank dhw load in addition?

Allow for everything being on-line unless you are absolutely, definitely,
certain about not wanting all on at some stage in the future. Also make
sure your oil storage facility complies with OFTEC and Environment
regulations.


So would it be say 29kW plus say 6kW (notional guess) for dhw and aim for a
35kW model?

In article ,
"John" writes:
Allow for everything being on-line unless you are absolutely, definitely,
certain about not wanting all on at some stage in the future.

If you are zoning with a view to not always having all the heating on
(whether by simple use of radiator valves, or by use of multiple
heating circuits and zoning valves), remember when doing your heat
loss calculations that an adjacent room (sideways, above or below)
might be cold, or you'll find you can't get a room up to temperature
without all those around it also being heated, defeating the object
of what you're aiming to do. (Heating just parts of a house can
cause other problems too, such as condensation.)
Also, you need some headroom in the boiler output to heat a place up
from cold without it taking ages to do so.

--
Andrew Gabriel

"Jeff" wrote in message
...

This has been very interesting and helpful, thanks all contributors.

Trying to sort out the consistent themes and
the most appropriate for me I'm
coming to the following conclusions:

(From the other thread) I don't need a
bypass valve of any sort as long as I
have a water path at all times when
pumping but I do need a zone with time
and temp control per 150 m2 max.
'Bypass' rads to have 2 lockshields.

You can use a Grundfoss Alpha modulating pumps and TRVs on all rads. take CH
off heat bank.

Over 150 m2 it requires to be split into zones with time control. If you
are zoning have the flow and return of each zone off the heat bank. They
then will be totally independent of each other coming off a neutral point.
Then no zone valves, just a couple of Alpha pumps on each zone.

An oil condensing boiler does not have the efficiency benefit over a
standard one, in comparison with gas models, and is also likely to be much
more expensive (checked out the efficiency on SEDBUK site)

Yep.

A heat bank will usefully buffer the boiler output including for the rad
circuits particularly so for a non-condenser. A two-stat model will
further
reduce cycling.

Yep.

So I'm thinking I'll design for the 'normal' or higher temperature range
of
boiler output, meaning I won't feel compelled to have slightly larger rads
(cost saving), I won't have to specify a condensing boiler so since I'll
probably be using an installer for the boiler and tank I should get
quotations competitivie with the installer's favoured models.

Now, how to size the boiler. Calculated heat loss over 2 floors plus a
bit
for utility areas is around 29kW but it's unlikely we would ever want
every
room up to design temperature. It's an old and poorly insulated property
but I'm hoping to significantly improve the main living rooms to a high
standard. No modulation, should I keep the boiler rating on the low side
or
should I allow for the heat bank dhw load in addition?

If the boiler is connected directly to the heat bank, not via a coil, then,
as long as the flow and return pipes are sized properly, minimum 28mm, you
can have a very large boiler. Size doesn't matter as the boiler is
disconnected from the DHW and CH functions. The larger the boiler the
quicker the re-heat and still no cycling. Some larger boilers are cheaper
than smaller models because of volume sales. This is certainly the case
with gas boilers.

If your house is very large, then it may be worth your while having two
smaller boilers heat the heat bank. The beauty of a heat bank is that
boilers can independently heat with their own flow and return from the heat
bank. Then you have back up if one is down. The two re-heat pretty quickly
and no cycling. Price up two boilers, you may be pleasantly surprised.



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"Jeff" wrote in message
...

"Doctor Evil" wrote in message
...

You can take heat out of it
to run the radiator, of course,
but then the problem is that it will
have the effect of causing the boiler
to run in bursts of full output
to replenish the store.

Yes, economically so.


OK, you covered all the pros and cons quite comprehensively, bearing in
mind
I think a condensing oil boiler can only fire at the rated output, you are
saying it's likely to be quite economical to let it dump a load of heat
into
the store and then let the rads draw it off?

Yep.



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"Andy Hall" wrote in message
...

If you do this via a heatbank, then
the boiler can never enter the
lower temperature ranges and probably
won't modulate down either.

You can have a weather compensator
maintaining the bottom CH zone in the
heat bank. The boiler comes in to reheat
the mass of water to the settings
of the compensator. Simple and effective.
Cycling is vastly reduced as a mass of
water cools slowly.

You can, but it is still at variance to
the required behaviour from
the store when heating the DHW.
One doesn't really want the behaviour
of the hot water heating to change with
the weather.

Read what I wrote. The bottom CH zone. This will be at a different
temperature to the hotter upper DHW zone. The DHW zone is priority in that
if it calls for heat, say 75-80C then the boiler only sends heat to that
upper zone. then it reverts to weather compensator control of the lower CH
zone. All the same body of water.

The technique of using a heatbank
as intermediary for space heating is
useful in two scenarios:

Let's see what wisdom we have here...

- If you have a non-condensing boiler,
it will provide a "smoothing"
action which will reduce the
amount of cycling considerably and
improve its efficiency.

"Eliminate" cycling with another stat.
The same also applies to condensing
boilers.

?????

Quite clear.

The non-condensing boiler is designed to run
at high temperature anyway.

Above condensing point. They run more efficiently when a flow/return
blending valve is set to maintian the return at 59C. At 11c delta T that
is
70C flow temp.

?????

Quite clear.


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"Jeff" wrote in message
...
This has been very interesting and helpful, thanks all contributors.

Trying to sort out the consistent themes and the most appropriate for me
I'm
coming to the following conclusions:

(From the other thread) I don't need a bypass valve of any sort as long as
I
have a water path at all times when pumping but I do need a zone with time
and temp control per 150 m2 max. 'Bypass' rads to have 2 lockshields.

An oil condensing boiler does not have the efficiency benefit over a
standard one, in comparison with gas models, and is also likely to be much
more expensive (checked out the efficiency on SEDBUK site)

A heat bank will usefully buffer the boiler output including for the rad
circuits particularly so for a non-condenser. A two-stat model will
further
reduce cycling.

So I'm thinking I'll design for the 'normal' or higher temperature range
of
boiler output, meaning I won't feel compelled to have slightly larger rads
(cost saving), I won't have to specify a condensing boiler so since I'll
probably be using an installer for the boiler and tank I should get
quotations competitivie with the installer's favoured models.


Now, how to size the boiler. Calculated heat loss over 2 floors plus a
bit
for utility areas is around 29kW but it's unlikely we would ever want
every
room up to design temperature. It's an old and poorly insulated property
but I'm hoping to significantly improve the main living rooms to a high
standard. No modulation, should I keep the boiler rating on the low side
or
should I allow for the heat bank dhw load in addition?

I'd go for one with the Riello RDB 90 burner - Grant Euroflame boiler house
is the one I chose - which can be easily jetted down if you find you need
less poke.

As you say, with a non-condensing oil boiler you can run the radiators
hotter and so have smaller sizes. This is especially useful in older houses
where the easiest place to put the rad isn't always the biggest.

And as you say - insulate. Then insulate some more. From the calculations
our house as we bought it was unheatable - unless we bought a commercial
boiler anyway - whereas several lorryloads of Kingspan/Celotex later we used
under 1000 litres this winter.

"Doctor Evil" wrote in message
...

......

If your house is very large, then it may be worth your while having two
smaller boilers heat the heat bank.

You were doing well until this. Remember it's oil, not gas. Oil boilers
get better with size. Small ones are inefficient, big ones are much better.
And really big ones can put out serious amounts of poke efficiently if you
have something like a heat bank to actually take the energy and store it for
later use.

"Mike" wrote in message
...

"Jeff" wrote in message
...
This has been very interesting and helpful, thanks all contributors.

Trying to sort out the consistent themes and the most appropriate for me
I'm
coming to the following conclusions:

(From the other thread) I don't need a bypass valve of any sort as long
as
I
have a water path at all times when pumping but I do need a zone with
time
and temp control per 150 m2 max. 'Bypass' rads to have 2 lockshields.

An oil condensing boiler does not have the efficiency benefit over a
standard one, in comparison with gas models, and is also likely to be
much
more expensive (checked out the efficiency on SEDBUK site)

A heat bank will usefully buffer the boiler output including for the rad
circuits particularly so for a non-condenser. A two-stat model will
further
reduce cycling.

So I'm thinking I'll design for the 'normal' or higher temperature range
of
boiler output, meaning I won't feel compelled to have slightly larger
rads
(cost saving), I won't have to specify a condensing boiler so since I'll
probably be using an installer for the boiler and tank I should get
quotations competitivie with the installer's favoured models.


Now, how to size the boiler. Calculated heat loss over 2 floors plus a
bit
for utility areas is around 29kW but it's unlikely we would ever want
every
room up to design temperature. It's an old and poorly insulated
property
but I'm hoping to significantly improve the main living rooms to a high
standard. No modulation, should I keep the boiler rating on the low
side
or
should I allow for the heat bank dhw load in addition?

I'd go for one with the Riello RDB 90 burner - Grant Euroflame boiler
house
is the one I chose - which can be easily jetted down if you find you need
less poke.

Coupling the boiler "directly" to a heat bank, the size doesn't matter. You
can't oversize a boiler, as long as the flow and return pipes are sized up
properly, You can oversize a boiler if it is coupled directly onto a rad
circuit; it will cycle far too much, be inefficient and wear out the
controls pronto.

As you say, with a non-condensing oil boiler you can run the radiators
hotter and so have smaller sizes. This is especially useful in older
houses
where the easiest place to put the rad isn't always the biggest.

And as you say - insulate. Then insulate some more. From the
calculations
our house as we bought it was unheatable - unless we bought a commercial
boiler anyway - whereas several lorryloads of Kingspan/Celotex later we
used
under 1000 litres this winter.



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"Mike" wrote in message
...

"Doctor Evil" wrote in message
...

.....

If your house is very large, then it
may be worth your while having two
smaller boilers heat the heat bank.

You were doing well until this.

As I know more about this field than anyone here and I aways do well. I
don't know the size of his house. He could get a better deal with two
boilers (buy two at a discount) than buying one big one.

I know one v country large house had a large Viessmann installed. It broke
down, occasionally they do. the whole place was freezing until repaired.
They Viessmann because it was the best and reliable, etc. Two mid priced
boilers would have been a far better way.

Remember it's oil, not gas. Oil boilers
get better with size. Small ones are
inefficient, big ones are much better.
And really big ones can put out serious
amounts of poke efficiently if you
have something like a heat bank to
actually take the energy and store it for
later use.

Look at sedbuk. You will find that is not the case in small v large =
efficiency.


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On Wed, 20 Apr 2005 07:46:48 +0000 (UTC), "John"
wrote:


"Andy Hall" wrote in message
.. .

SNIP

He may be saying that, but it isn't the case.

Most condensing boilers can modulate downwards to match the heating
load. If you connect a small load such as radiator space heating
during spring and autumn then the boiler can modulate down and operate
at lower temperatures which are more efficient for it as well as not
needing to fire on and off.


Andy
Whilst the principles of your argument regarding the system are correct it
is not the case that the OPs intended "oil" fired condensing boiler can
modulate. To maintain good (efficient) combustion with small oil burners it
is neccessary to closely match the oil rate and atomisation through the
nozzle with the airflow rate. The economics and the practicalities are such
that turning up or down the oil rate will require adjustment of either the
oil nozzle hole size or oil pressure. The oil nozzle is a precision bored
unit and is effectively non adjustable. The alteration of the oil pressure
leads to alteration of the quality of atomisation. Again, alteration of the
airflow requires some considerable additional hardware and controls i.e.
servo operated air damper or fan speed but the fan is invariably mounted on
the same motor shaft as the oil pump (gear type).
On some larger (intermediate) oil burners a step modulation is employed by
installing twin nozzles in the burner head and a two stage (solenoid
operated hydraulic ram positioner) air shutter but these are only found in
burners of 100kW and above. I have seen only one progressively modulating
oil burner (serving a very large office building and made IIRC by Veissman)
but as it was so unusual out in the field I would anticipate its cost was
prohibitive.
These problems are most likely behind the reasoning to not require
condensing boiler installation for oil until 2007 at the present state of
affairs?


Point taken. In the first post we didn't know that it was oil or that
it was (probably by implication) non modulating, though, John.

--

..andy

To email, substitute .nospam with .gl

On Wed, 20 Apr 2005 12:09:13 +0100, "Doctor Evil"
wrote:


"Andy Hall" wrote in message
.. .

If you do this via a heatbank, then
the boiler can never enter the
lower temperature ranges and probably
won't modulate down either.

You can have a weather compensator
maintaining the bottom CH zone in the
heat bank. The boiler comes in to reheat
the mass of water to the settings
of the compensator. Simple and effective.
Cycling is vastly reduced as a mass of
water cools slowly.

You can, but it is still at variance to
the required behaviour from
the store when heating the DHW.
One doesn't really want the behaviour
of the hot water heating to change with
the weather.

Read what I wrote. The bottom CH zone. This will be at a different
temperature to the hotter upper DHW zone. The DHW zone is priority in that
if it calls for heat, say 75-80C then the boiler only sends heat to that
upper zone. then it reverts to weather compensator control of the lower CH
zone. All the same body of water.

This sounds like waffle.

Are you suggesting thermostats on different heights on the cylinder,
or more than one indirect coil or what?



The technique of using a heatbank
as intermediary for space heating is
useful in two scenarios:

Let's see what wisdom we have here...

- If you have a non-condensing boiler,
it will provide a "smoothing"
action which will reduce the
amount of cycling considerably and
improve its efficiency.

"Eliminate" cycling with another stat.
The same also applies to condensing
boilers.

?????

Quite clear.

Come on, it's waffle and you know it.



The non-condensing boiler is designed to run
at high temperature anyway.

Above condensing point. They run more efficiently when a flow/return
blending valve is set to maintian the return at 59C. At 11c delta T that
is
70C flow temp.

?????

Quite clear.


70-59 = 11 is clear, as is 59 degrees being above the dew point.
However, what was the point that you were trying to make?



--

..andy

To email, substitute .nospam with .gl

"Doctor Evil" wrote in message
...
Remember it's oil, not gas. Oil boilers
get better with size. Small ones are
inefficient, big ones are much better.
And really big ones can put out serious
amounts of poke efficiently if you
have something like a heat bank to
actually take the energy and store it for
later use.

Look at sedbuk. You will find that is not the case in small v large =
efficiency.

That's a somewhat biased test I'm afraid. Bit like urban mpg figures for
cars. In real life a bigger oil boiler operating for a shorter time will
always be more efficient.

"Mike" wrote in message
...

"Doctor Evil" wrote in message
...
Remember it's oil, not gas. Oil boilers
get better with size. Small ones are
inefficient, big ones are much better.
And really big ones can put out serious
amounts of poke efficiently if you
have something like a heat bank to
actually take the energy and store it for
later use.

Look at sedbuk. You will find that is not the case in small v large =
efficiency.

That's a somewhat biased test I'm afraid. Bit like urban mpg figures for
cars. In real life a bigger oil boiler operating for a shorter time will
always be more efficient.

I would have agreed with you 20 years ago.



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