Hi,

I'm trying to get the right design for a CH system as a complete replacement for the existing.

We are modernising and extending our house and in the process want to replace and update the heating and hot water systems.

It is going to have to be some sort of mains pressure HW system as the tank has to go. I've decided on the DPS Pandora, any body had experience of these?

The new bathroom and conservatory lack wall space, I though UFH may be the solution, but I'm unsure if, given the small areas that it will provide enough heat, any views?

I'm new to plumbing systems (I'm a electronics product designer) what are the differences, advantages, fallbacks of the Y and S plans, how do I decide which is right?

Its only a three bedroom house, with a dining room, large bathroom, lounge, kitchen and small conservatory. Is it sensible to still use multiple zones?

Is it sensible to zone the UFH (if used?) as I think it would be necessary to warm the conservatory on cold summer nights (to keep plants happy).

Any other suggestions?

Regards,
Jason.

Christain has one and swears by it. It apears DPS have hiked up the price. Try http://www.range-cylinders.co.uk They do an "integrated" thermal stopre/heat bank that does both CH and DHW. Get a "direct" version. Price one up.

S is better as Y has a mid-position valve which are more troublesome. Using an integrated heat bank, you don't need any of these plans. .[/quote]

Its only a three bedroom house, with a dining room, large bathroom, lounge, kitchen and small conservatory. Is it sensible to still use multiple zones?

More than two zones may be over top, but I would do upstairs and down as separate zones. Take both zones of a heat bank with a pump on each. The heat bank makers will install two flow and return tappings on the bottom of the heat bank for the two CH zones. The best way.

More than two zones may be over top, but I would do upstairs and down as
separate zones.

I would always put the conservatory on its own zone, even if conventionally
heated, rather than UFH. Like all zones, but specifically in this case, it
should have its own programmable thermostat, so that the conservatory is
only heated when it is needed.

Also, if you use a fan convector in the kitchen, they work better on their
own zone, as they can hog the heat even when off, otherwise.

Take both zones of a heat bank with a pump on each. The heat bank makers
will install two flow and return tappings on the bottom of the heat bank
for the two CH zones. The best way.

Although if the zones start to multiply, you can always share a tapping on a
pumped circuit, if you're careful.

Personally, if I was designing a system from scratch, I'd be tempted to have
one tapping, one pump, a "manifold" and an S-Plan system, rather than go
multiple pump, which can have issues with parasitic circulation (or noisy
valves to cure such) in some cases. Also, zone valves can be cheaper than
pumps, which may be an issue on multiple zone systems.

Finally, S-Plan-Plus allows long distance unzoned trunking, which can be
more efficient in pipework (and hence energy efficiency through primary
circuit losses). (i.e. you can have the zone valves near the point of
delivery and have a single trunk pipe snaking around the house, rather than
a pair of pipes for each zone, running alongside each other).

Christian.

A heat bank/thermal store, presents you with a wonderful neutral zone. Pumps are not expensive and are far more reliable than 2-port zone valves. You put a check valve on each CH zone to prevent back circulation. Each pump can have its speed set to the needs of the zone. There will be no parasitic circulation if each zone has its own flow and return tapping off the store.

This is another point of confusion for myself.

To take the CH and/or UFH from the store or the boiler circuit.
Obviously, to take it from the store means instant heating, but depletes our DHW source.
The other way means that we are 'steeling' heat from the input to the store, so it will take longer to replenish.

Any other factors in deciding which side the heating should come from?

The only thing I can think of is the need for more than one pump.

J.

Take it from the store. If the store is sized well enough it will not deplete the store. Also the CH flow and return are taken near the bottom, leaving the upper DHW untouched. You could have it a priority system. Wheh the DHW is called the CH pump(s) is switched off. The boiler operates independently heating the store of water to a pre-defined temperature. Have two stats on the heat bank so as to avoid boiler cycling. Have the klargest boioer you can afford. A therml store/heat bank is not fussy what sized boiler heats it. Make sure the flow and return pipes are 28mm.

Two CH zones: Either:

1. Two pumps (both directly off the store)
2. One pump and two 2-port valves. (only one pipe off the store)

Taking all zones directly off the store eliminates a balancing act between two zones.

This is another point of confusion for myself.

To take the CH and/or UFH from the store or the boiler circuit.
Obviously, to take it from the store means instant heating, but
depletes our DHW source.

But the boiler is capable of replenishing at a far greater rate than the
radiators extract heat, so there is no massive effect. Just make sure that
store isn't already marginal in size.

Any other factors in deciding which side the heating should come from?

Direct heating has a considerable advantage when running with a condensing
boiler capable of open venting. You lose the advantages of sealed
pressurised operation, such as easy refilling, but you get a more efficient
system. The heatbank is designed to be heated to 75C. With direct heating,
with no heat exchanger differential to maintain, this allows a 75C flow
temp, rather than 82-85C. It also frequently provides a low return
temperature, with a nice large differential. This provides good condensing
action in the boiler.

Christian.

Please explain what a check valve does - any weblinks with nice pictures?

I did a search and found lots of people trying to sell them, but I've still no idea why I would want one..

Doctor Evil wrote:

circulation. Each pump can have its speed set to the needs of the
zone. There will be no parasitic circulation if each zone has its own
flow and return tapping off the store.

except you don't want to be running your heating off the store with a
modern boiler....

--
Cheers,

John.

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

On Wed, 16 Feb 2005 06:08:37 +0000, John Rumm wrote:

Doctor Evil wrote:

circulation. Each pump can have its speed set to the needs of the zone.
There will be no parasitic circulation if each zone has its own flow and
return tapping off the store.

except you don't want to be running your heating off the store with a
modern boiler....

Hi John,

Why not - I thought thermal stores assisted the boiler by ensure long
efficient burns?

Tim

On Wed, 16 Feb 2005 08:00:10 +0000, Tim S wrote:

On Wed, 16 Feb 2005 06:08:37 +0000, John Rumm wrote:

Doctor Evil wrote:

circulation. Each pump can have its speed set to the needs of the zone.
There will be no parasitic circulation if each zone has its own flow and
return tapping off the store.

except you don't want to be running your heating off the store with a
modern boiler....

Hi John,

Why not - I thought thermal stores assisted the boiler by ensure long
efficient burns?

Tim

This depends on the type of boiler in use.


If you are talking about a conventional one operating at 82 degree
flow and 70 return, then there *could* be a benefit in the approach of
running the heating circuit from the store on the long efficient burn
argument.

However, with a condensing boiler, the greatest efficiencies occur
when the burner is modulated down rather than on/off and when the
operating temperature is lower.

In the intended set up with a HW cylinder (or store for that matter),
the boiler, in HW mode, operates balls-out to replenish the cylinder
quickly and at high temperature. Although this is one long burn, it
is not in the most efficient operating range. The heating circuit is
intended to be connected directly to the boiler and the boiler will
modulate down as the load reduces when TRVs begin to close. Ideally,
the system should reach an equilibrium with boiler running
continuously at lowish power to match the radiator load. This avoids
cycling and runs the boiler in a more efficient temperature range.

If you insert a store in between boiler and radiators, you effectively
defeat this arrangement and force a cycling situation. The radiators
gradually drain heat from the store, and at a certain point the boiler
is brought on to replenish it using a high temperature burn as for hot
water.

There *may* be exceptions to this if you want to bring in additional
heat sources such as solar, or possibly if you want a source of lowish
temperature water for UFH (although that can be done with a blending
valve)

Other than that, it is better to keep the store for DHW and let the
boiler drive the radiators directly if it's a modulating condensing
model.







--

..andy

To email, substitute .nospam with .gl

"the-moog" wrote in message
...

Doctor Evil Wrote:
...You put a check valve on each CH zone to prevent back circulation.
Each pump can have its speed set to the needs of the zone. There will
be no parasitic circulation if each zone has its own flow and return
tapping off the store.

Please explain what a check valve does - any weblinks with nice
pictures?

I did a search and found lots of people trying to sell them, but I've
still no idea why I would want one..

A non-return valve. Flow can go one way but not the other.


_________________________________________
Usenet Zone Free Binaries Usenet Server
More than 120,000 groups
Unlimited download
http://www.usenetzone.com to open account

"Andy Hall" wrote in message
...
On Wed, 16 Feb 2005 08:00:10 +0000, Tim S wrote:

On Wed, 16 Feb 2005 06:08:37 +0000, John Rumm wrote:

Doctor Evil wrote:

circulation. Each pump can have its speed set to the needs of the
zone.
There will be no parasitic circulation if each zone has its own flow
and
return tapping off the store.

except you don't want to be running your heating off the store with a
modern boiler....

Hi John,

Why not - I thought thermal stores assisted the boiler by ensure long
efficient burns?

Tim

This depends on the type of boiler in use.


If you are talking about a conventional one operating at 82 degree
flow and 70 return, then there *could* be a benefit in the approach of
running the heating circuit from the store on the long efficient burn
argument.

However, with a condensing boiler, the greatest efficiencies occur
when the burner is modulated down

Many heat banks run at 75C and many condensing boilers have a flow/return
22C temp differential. If two stats are used to ensure no boiler cycling,
the stores water is quite cool when the boiler is called to re-heat. Most
of the burn the boiler will be operating very efficiently. The overall
operation is very efficient. There is also the simplicity of having the CH
zones off the store (a neutral point). One circuit does not interfer with
the other and are simple to balance. The CH flow & returns are taken off the
bottom of the cylinder where it is cooler.




_________________________________________
Usenet Zone Free Binaries Usenet Server
More than 120,000 groups
Unlimited download
http://www.usenetzone.com to open account

...You put a check valve on each CH zone to prevent back circulation.

Please explain what a check valve does - any weblinks with nice
pictures?

It's a one way valve. A standard check valve needs too high a pressure and
can be very noisy in this application. Instead, you need a much harder to
locate flap type valve, preferably unsprung.

Christian.

"Christian McArdle" wrote in message
. net...
...You put a check valve on each CH zone to prevent back circulation.

Please explain what a check valve does - any weblinks with nice
pictures?

It's a one way valve. A standard check valve needs too high a pressure and
can be very noisy in this application. Instead, you need a much harder to
locate flap type valve, preferably unsprung.

Christian.

Running two CH circuits from the store of water, there is no need for check
valves. Not all check valves buzz.


_________________________________________
Usenet Zone Free Binaries Usenet Server
More than 120,000 groups
Unlimited download
http://www.usenetzone.com to open account

On Wed, 16 Feb 2005 10:11:26 -0000, "Doctor Evil"
wrote:


"Andy Hall" wrote in message
.. .
On Wed, 16 Feb 2005 08:00:10 +0000, Tim S wrote:

On Wed, 16 Feb 2005 06:08:37 +0000, John Rumm wrote:

Doctor Evil wrote:

circulation. Each pump can have its speed set to the needs of the
zone.
There will be no parasitic circulation if each zone has its own flow
and
return tapping off the store.

except you don't want to be running your heating off the store with a
modern boiler....

Hi John,

Why not - I thought thermal stores assisted the boiler by ensure long
efficient burns?

Tim

This depends on the type of boiler in use.


If you are talking about a conventional one operating at 82 degree
flow and 70 return, then there *could* be a benefit in the approach of
running the heating circuit from the store on the long efficient burn
argument.

However, with a condensing boiler, the greatest efficiencies occur
when the burner is modulated down

Many heat banks run at 75C and many condensing boilers have a flow/return
22C temp differential. If two stats are used to ensure no boiler cycling,
the stores water is quite cool when the boiler is called to re-heat. Most
of the burn the boiler will be operating very efficiently. The overall
operation is very efficient. There is also the simplicity of having the CH
zones off the store (a neutral point). One circuit does not interfer with
the other and are simple to balance. The CH flow & returns are taken off the
bottom of the cylinder where it is cooler.


This implies that the boiler would be operating in its most efficient
range with 75 flow (and by your numbers) 53 return.

While the return temperature implies that condensing just about
begins, this is not the most efficient part of the range by a long
way.

That is achieved by operating the boiler as cool as possible and by
allowing it to match its output to the continuous requirement of the
radiators at as low a temperature as possible.

Putting a store in the middle, with however many thermostats simply
won't achieve this objective. The radiators (and UFH if used) will
cause heat to be extracted from it at a continuous rate lower than the
peak output of the boiler. The boiler will then come on in cycles at
full output and replenish the store. The principle is exactly the
same as would happen if a hot tap were left on a low flow rate.

While this method of working matches a conventional boiler quite well
and can be useful if heat is being introduced from another source,
perhaps at lower temperature, it is not at all suited for a modern,
modulating condensing boiler which will operate far more efficiently
if allowed to drive the heating loads directly and continuously at low
power.

The boiler will be switched over to heating the store (used for hot
water production only) at full output power when required.

It is a pointless and inefficient exercise to connect the radiators to
a thermal store when a modulating condensing boiler is in use.





--

..andy

To email, substitute .nospam with .gl

On Mon, 14 Feb 2005 21:43:11 +0000, Doctor Evil
wrote:


the-moog Wrote:
This is another point of confusion for myself.

To take the CH and/or UFH from the store or the boiler circuit.
Obviously, to take it from the store means instant heating, but
depletes our DHW source.
The other way means that we are 'steeling' heat from the input to the
store, so it will take longer to replenish.

Any other factors in deciding which side the heating should come from?

The only thing I can think of is the need for more than one pump.

J.

Take it from the store. If the store is sized well enough it will not
deplete the store. Also the CH flow and return are taken near the
bottom, leaving the upper DHW untouched. You could have it a priority
system. Wheh the DHW is called the CH pump(s) is switched off. The
boiler operates independently heating the store of water to a
pre-defined temperature. Have two stats on the heat bank so as to
avoid boiler cycling. Have the klargest boioer you can afford. A
therml store/heat bank is not fussy what sized boiler heats it. Make
sure the flow and return pipes are 28mm.

Two CH zones: Either:

1. Two pumps (both directly off the store)
2. One pump and two 2-port valves. (only one pipe off the store)

Taking all zones directly off the store eliminates a balancing act
between two zones.

This is misinformation if a modulating condensing boiler is used.





--

..andy

To email, substitute .nospam with .gl

On Mon, 14 Feb 2005 17:54:26 +0000, Doctor Evil
wrote:


Christian McArdle Wrote:


Doctor Evil Wrote:

Take both zones of a heat bank with a
pump on each. The heat bank makers
will install two flow and return tappings on
the bottom of the heat bank
for the two CH zones. The best way.


Although if the zones start to multiply, you can always share a
tapping on a
pumped circuit, if you're careful.

Personally, if I was designing a system from scratch, I'd be tempted
to have
one tapping, one pump, a "manifold" and an S-Plan system, rather than
go
multiple pump, which can have issues with parasitic circulation (or
noisy
valves to cure such) in some cases. Also, zone valves can be cheaper
than
pumps, which may be an issue on multiple zone systems.


A heat bank/thermal store, presents you with a wonderful neutral zone.
Pumps are not expensive and are far more reliable than 2-port zone
valves. You put a check valve on each CH zone to prevent back
circulation. Each pump can have its speed set to the needs of the
zone. There will be no parasitic circulation if each zone has its own
flow and return tapping off the store.


This is only true if a conventional boiler is used or if there is a
need to introduce heat from another source such as solar or possibly
some form of stove.

It is not an appropriate technique to use if a modulating, condensing
boiler is the primary or sole heat source since the boiler will not be
allowed to ever operate in its most efficient temperature range.




--

..andy

To email, substitute .nospam with .gl

"Andy Hall" wrote in message
...
On Wed, 16 Feb 2005 10:11:26 -0000, "Doctor Evil"
wrote:


"Andy Hall" wrote in message
.. .
On Wed, 16 Feb 2005 08:00:10 +0000, Tim S wrote:

On Wed, 16 Feb 2005 06:08:37 +0000, John Rumm wrote:

Doctor Evil wrote:

circulation. Each pump can have its speed set to the needs of the
zone.
There will be no parasitic circulation if each zone has its own
flow
and
return tapping off the store.

except you don't want to be running your heating off the store with
a
modern boiler....

Hi John,

Why not - I thought thermal stores assisted the boiler by ensure long
efficient burns?

Tim

This depends on the type of boiler in use.


If you are talking about a conventional one operating at 82 degree
flow and 70 return, then there *could* be a benefit in the approach of
running the heating circuit from the store on the long efficient burn
argument.

However, with a condensing boiler, the greatest efficiencies occur
when the burner is modulated down

Many heat banks run at 75C and many condensing boilers have a flow/return
22C temp differential. If two stats are used to ensure no boiler
cycling,
the stores water is quite cool when the boiler is called to re-heat.
Most
of the burn the boiler will be operating very efficiently. The overall
operation is very efficient. There is also the simplicity of having the
CH
zones off the store (a neutral point). One circuit does not interfer with
the other and are simple to balance. The CH flow & returns are taken off
the
bottom of the cylinder where it is cooler.


This implies that the boiler would be operating in its most efficient
range with 75 flow (and by your numbers) 53 return.

No. When the store calls for heat the bottom will be very cool. This is the
return temp, which is makes the boiler very effcient. Whhe the store warm
sup this will gradually rise. So, for most of the re-heat time the boiler is
operating effciently.

snip


_________________________________________
Usenet Zone Free Binaries Usenet Server
More than 120,000 groups
Unlimited download
http://www.usenetzone.com to open account

"Andy Hall" wrote in message
...
On Mon, 14 Feb 2005 21:43:11 +0000, Doctor Evil
wrote:


the-moog Wrote:
This is another point of confusion for myself.

To take the CH and/or UFH from the store or the boiler circuit.
Obviously, to take it from the store means instant heating, but
depletes our DHW source.
The other way means that we are 'steeling' heat from the input to the
store, so it will take longer to replenish.

Any other factors in deciding which side the heating should come from?

The only thing I can think of is the need for more than one pump.

J.

Take it from the store. If the store is sized well enough it will not
deplete the store. Also the CH flow and return are taken near the
bottom, leaving the upper DHW untouched. You could have it a priority
system. Wheh the DHW is called the CH pump(s) is switched off. The
boiler operates independently heating the store of water to a
pre-defined temperature. Have two stats on the heat bank so as to
avoid boiler cycling. Have the largest boiler you can afford. A
therml store/heat bank is not fussy what sized boiler heats it. Make
sure the flow and return pipes are 28mm.

Two CH zones: Either:

1. Two pumps (both directly off the store)
2. One pump and two 2-port valves. (only one pipe off the store)

Taking all zones directly off the store eliminates a balancing act
between two zones.

This is misinformation if a modulating condensing boiler is used.

Not in the least. Many modulate on the flow temp (maintain a constant flow
temp). Those that modulate on load compensation will modulate down when the
return and flow temps narrow down.




_________________________________________
Usenet Zone Free Binaries Usenet Server
More than 120,000 groups
Unlimited download
http://www.usenetzone.com to open account

On Wed, 16 Feb 2005 16:15:07 +0000, Andy Hall wrote:

On Mon, 14 Feb 2005 17:54:26 +0000, Doctor Evil
wrote:


Christian McArdle Wrote:


Doctor Evil Wrote:

Take both zones of a heat bank with a pump on each. The heat bank
makers
will install two flow and return tappings on the bottom of the heat
bank
for the two CH zones. The best way.


Although if the zones start to multiply, you can always share a tapping
on a
pumped circuit, if you're careful.

Personally, if I was designing a system from scratch, I'd be tempted to
have
one tapping, one pump, a "manifold" and an S-Plan system, rather than
go
multiple pump, which can have issues with parasitic circulation (or
noisy
valves to cure such) in some cases. Also, zone valves can be cheaper
than
pumps, which may be an issue on multiple zone systems.


A heat bank/thermal store, presents you with a wonderful neutral zone.
Pumps are not expensive and are far more reliable than 2-port zone
valves. You put a check valve on each CH zone to prevent back
circulation. Each pump can have its speed set to the needs of the zone.
There will be no parasitic circulation if each zone has its own flow and
return tapping off the store.


This is only true if a conventional boiler is used or if there is a need
to introduce heat from another source such as solar or possibly some form
of stove.

It is not an appropriate technique to use if a modulating, condensing
boiler is the primary or sole heat source since the boiler will not be
allowed to ever operate in its most efficient temperature range.

I can think of other reasons to operate a heatbank - mains pressure hot
water without using a combi for one.

Perhaps a good reason not to bother with a condensing boiler then (yes, I
know about the supposed law mandating them, more b*ll*cks interference in
my home by the government blah blah...)

Tim

"Andy Hall" wrote in message
...
On Mon, 14 Feb 2005 17:54:26 +0000, Doctor Evil
wrote:


Christian McArdle Wrote:


Doctor Evil Wrote:

Take both zones of a heat bank with a
pump on each. The heat bank makers
will install two flow and return tappings on
the bottom of the heat bank
for the two CH zones. The best way.


Although if the zones start to multiply, you can always share a
tapping on a
pumped circuit, if you're careful.

Personally, if I was designing a system from scratch, I'd be tempted
to have
one tapping, one pump, a "manifold" and an S-Plan system, rather than
go
multiple pump, which can have issues with parasitic circulation (or
noisy
valves to cure such) in some cases. Also, zone valves can be cheaper
than
pumps, which may be an issue on multiple zone systems.


A heat bank/thermal store, presents you with a wonderful neutral zone.
Pumps are not expensive and are far more reliable than 2-port zone
valves. You put a check valve on each CH zone to prevent back
circulation. Each pump can have its speed set to the needs of the
zone. There will be no parasitic circulation if each zone has its own
flow and return tapping off the store.


This is only true if a conventional
boiler is used or if there is a
need to introduce heat from another
source such as solar or possibly
some form of stove.

Not so.

It is not an appropriate technique to use if a modulating, condensing
boiler is the primary or sole heat source since the boiler will not be
allowed to ever operate in its most efficient temperature range.

Not so. Any boiler will operate efficiently on a thermal store. It must be
able to maintain a constant flow temperature.




_________________________________________
Usenet Zone Free Binaries Usenet Server
More than 120,000 groups
Unlimited download
http://www.usenetzone.com to open account

Non modulating condensing boilers are available. Boilers which modulate to
maintain a flow temp, are perfectly suitable: W-B Greestar, Glow Worm. Condensing boilers are more efficient than non-condesning, even at high temperatures.

On Wed, 16 Feb 2005 16:48:05 -0000, "Doctor Evil"
wrote:



No. When the store calls for heat the bottom will be very cool. This is the
return temp, which is makes the boiler very effcient. Whhe the store warm
sup this will gradually rise. So, for most of the re-heat time the boiler is
operating effciently.



You've missed the point. While the boiler drives the radiators
directly, the return can always be cool except in the depths of
winter.

Your approach cycles the boiler in the same way as if the boiler is
running a DHW cycle

This is not the most efficient operating mode for a modulating and
condensing boiler.

Continuous, lower output will be more efficient than cycling into a
store or cylinder even if the return temperature is low.




--

..andy

To email, substitute .nospam with .gl

On Wed, 16 Feb 2005 16:52:31 +0000, Tim S wrote:



I can think of other reasons to operate a heatbank - mains pressure hot
water without using a combi for one.

Yes of course and I didn't suggest otherwise. My point was
specifically in regard to modulating, condensing boilers. If you were
to use a conventional one then a long run is sensible.



Perhaps a good reason not to bother with a condensing boiler then (yes, I
know about the supposed law mandating them, more b*ll*cks interference in
my home by the government blah blah...)


I think that this is one case where it is worth doing something
despite silly government meddling I've certainly saved considerably
on gas consumption using a condensing boiler.



Tim


--

..andy

To email, substitute .nospam with .gl

On Wed, 16 Feb 2005 16:57:20 -0000, "Doctor Evil"
wrote:


A heat bank/thermal store, presents you with a wonderful neutral zone.
Pumps are not expensive and are far more reliable than 2-port zone
valves. You put a check valve on each CH zone to prevent back
circulation. Each pump can have its speed set to the needs of the
zone. There will be no parasitic circulation if each zone has its own
flow and return tapping off the store.


This is only true if a conventional
boiler is used or if there is a
need to introduce heat from another
source such as solar or possibly
some form of stove.

Not so.

My point was very specific and is correct.


It is not an appropriate technique to use if a modulating, condensing
boiler is the primary or sole heat source since the boiler will not be
allowed to ever operate in its most efficient temperature range.

Not so. Any boiler will operate efficiently on a thermal store. It must be
able to maintain a constant flow temperature.

The point was clear and correct for a modulating condensing boiler.

I didn't say that it wouldn't work with a store and indeed with
respect to hot water production makes good sense.

My point was purely about putting a store between boiler and heating
load when the boiler is a modulating and condensing type. In that
scenario, the boiler will not be operating in its most efficient way
when just driving the radiators. THe effect of the store would be to
cause cycling, and even if the return is cool will still be less
efficient than running the boiler continuously at lower output.

There are two reasons for this:

- THe boiler won't have the possibility of operating at the lowest end
of its temperature range

- It will be cycling (albeit occasionally) which is not as efficient
as a continuous low power burn.







--

..andy

To email, substitute .nospam with .gl

On Wed, 16 Feb 2005 16:50:58 -0000, "Doctor Evil"
wrote:



Not in the least. Many modulate on the flow temp (maintain a constant flow
temp). Those that modulate on load compensation will modulate down when the
return and flow temps narrow down.


It will still not have the opportunity to operate at the low
temperatures possible with a direct connection to the radiator load
and it will also cycle.

I've made the point, it is correct for the scenario described
(modulating, condensing boiler) and I am not going to repeat it.




--

..andy

To email, substitute .nospam with .gl

"Andy Hall" wrote in message
...
On Wed, 16 Feb 2005 16:48:05 -0000, "Doctor Evil"
wrote:



No. When the store calls for heat the bottom will be very cool. This is
the
return temp, which is makes the boiler very effcient. Whhe the store
warm
sup this will gradually rise. So, for most of the re-heat time the boiler
is
operating effciently.



You've missed the point. While the boiler drives the radiators
directly, the return can always be cool except in the depths of
winter.

Your approach cycles the boiler in the same way as if the boiler is
running a DHW cycle

This is not the most efficient operating mode for a modulating and
condensing boiler.

Continuous, lower output will be more efficient than cycling into a
store or cylinder even if the return temperature is low.

A tall cylinder can have wide stratification. The bottom of the cylinder can
be very cool indeed, especially when the store calls for the boiler. There
is no inefficient boiler cycling either.

You can also have a section at the bottom of the thermal store that is kept
to the temperature dictated by an outside weather compensator. Once again no
inefficient boiler cycling and the boiler operating at very low efficient
return temperatures.



_________________________________________
Usenet Zone Free Binaries Usenet Server
More than 120,000 groups
Unlimited download
http://www.usenetzone.com to open account

"Andy Hall" wrote in message
...
On Wed, 16 Feb 2005 16:50:58 -0000, "Doctor Evil"
wrote:



Not in the least. Many modulate on the flow temp (maintain a constant
flow
temp). Those that modulate on load compensation will modulate down when
the
return and flow temps narrow down.


It will still not have the opportunity to operate at the low
temperatures possible with a direct connection to the radiator load
and it will also cycle.

I've made the point, it is correct for the scenario described
(modulating, condensing boiler) and I am not going to repeat it.

That's good, it is wrong.


_________________________________________
Usenet Zone Free Binaries Usenet Server
More than 120,000 groups
Unlimited download
http://www.usenetzone.com to open account

"Andy Hall" wrote in message
...
On Wed, 16 Feb 2005 16:57:20 -0000, "Doctor Evil"
wrote:


A heat bank/thermal store, presents you with a wonderful neutral zone.
Pumps are not expensive and are far more reliable than 2-port zone
valves. You put a check valve on each CH zone to prevent back
circulation. Each pump can have its speed set to the needs of the
zone. There will be no parasitic circulation if each zone has its own
flow and return tapping off the store.


This is only true if a conventional
boiler is used or if there is a
need to introduce heat from another
source such as solar or possibly
some form of stove.

Not so.

My point was very specific and is correct.

Not so.

It is not an appropriate technique to use if a modulating, condensing
boiler is the primary or sole heat source since the boiler will not be
allowed to ever operate in its most efficient temperature range.

Not so. Any boiler will operate efficiently on a thermal store. It must
be
able to maintain a constant flow temperature.

The point was clear and correct for a modulating condensing boiler.

Nor so.

I didn't say that it wouldn't work with a store and indeed with
respect to hot water production makes good sense.

My point was purely about putting a
store between boiler and heating
load when the boiler is a modulating
and condensing type.

A store of water between (a buffer) is the best thing as it eliminates
boiler cycling.

THe effect of the store would be to
cause cycling,

Not so, cycling eliminated

- THe boiler won't have the possibility of operating at the lowest end
of its temperature range

It will if an outside weather compensator dictates the temperature of the
bottom of the store.

- It will be cycling (albeit occasionally) which is not as efficient
as a continuous low power burn.

Not so. Boiler cycling eliminated as the thermal store (buffer) prevents
boiler cycling. Boiler directly connected to the rads cycle once the heat
demand is below the lowest boiler output.



_________________________________________
Usenet Zone Free Binaries Usenet Server
More than 120,000 groups
Unlimited download
http://www.usenetzone.com to open account

On Wed, 16 Feb 2005 17:17:14 +0000, Andy Hall wrote:

On Wed, 16 Feb 2005 16:52:31 +0000, Tim S wrote:



I can think of other reasons to operate a heatbank - mains pressure hot
water without using a combi for one.

Yes of course and I didn't suggest otherwise. My point was
specifically in regard to modulating, condensing boilers. If you were to
use a conventional one then a long run is sensible.


Ah, my apologies. "Modulating" condensing boilers is a new one to me.


Perhaps a good reason not to bother with a condensing boiler then (yes, I
know about the supposed law mandating them, more b*ll*cks interference in
my home by the government blah blah...)


I think that this is one case where it is worth doing something despite
silly government meddling I've certainly saved considerably on gas
consumption using a condensing boiler.


I'll probably get a significant gain just by fixing the roof
insulation(!). Which is slightly non-trivial as a dormer conversion is
involved and I don;t want to do anything to bung up the already limited
airflow between roof and upper ceiling. Still thinking about that.

Tim

On Thu, 17 Feb 2005 08:06:19 +0000, Tim S wrote:

On Wed, 16 Feb 2005 17:17:14 +0000, Andy Hall wrote:

On Wed, 16 Feb 2005 16:52:31 +0000, Tim S wrote:



I can think of other reasons to operate a heatbank - mains pressure hot
water without using a combi for one.

Yes of course and I didn't suggest otherwise. My point was
specifically in regard to modulating, condensing boilers. If you were to
use a conventional one then a long run is sensible.


Ah, my apologies. "Modulating" condensing boilers is a new one to me.

Most of the newer ones do do this, and the general mode of working is
that when they do a hot water cycle (i.e. reheat the cylinder or
store) that they go to full power - the philosophy being to get the
maximum amount of heat as quickly as possible into the cylinder.

However, condensing boilers operate more efficiently the lower the
return temperature. When below the dew point (at which condensation
actually begins to take place) they become even more efficient
(although realise that there is not a sudden Nirvana). In effect
what happens is that the rate of change of efficiency increases below
the dew point. Therefore the lower the return temperature the
better. One aspect of this of course is that the lower the operating
temperature, the lower the flue gas temperatures and hence less heat
simply going out with the flue gases.
The other aspect is that there is always an inefficiency involved with
starting the burner whatever the type of boiler. Therefore the less
times it goes on and off the better.

All of this takes you to the point that it is most efficient to run
this type of boiler continuously at lower temperature than to force it
into a situation of reheating a cylinder in bursts. For the hot
water, you have to do this, but for the space heating you don't.

If this type of boiler is connected directly to the radiators and you
have TRVs, as the room temperature reaches the set point, you have
effectively balanced the building heat loss with the radiator outputs.
THe TRVs will begin to close. If the boiler is directly connected to
them, it is able to sense the reduced heat demand and modulate down
accordingly. Thus, in the typical UK autumn/spring situation, which
is a lot of days of the year, and you need *some* heat, then you can
have the boiler operating in this equilibrium mode at low temperature.

If you put a store in the way, you will be emptying it at a low
continuous rate of (e.g.) 8kW, but then when most of the energy has
been used, replenishing it in bursts of perhaps 25kW - all controlled
by a thermostat on the cylinder. Therefore you prevent the boiler
behaving as it was intended to do - you force it to run at the high
temperature end and even though it will probably be one continuous
burn to replenish, there will still be more of those than if the
boiler had been left running continuously at lower output.

THe two exceptions that I made were a) if it's a conventional or
non-modulating boiler - there you would make an improvement by having
it recharge the cylinder once as opposed to driving the radiators
directly and cycling to match effective power output to load; or b) if
you want to introduce other sources of energy such as solar. Since
these change the economics, it may be that the overall equation works
better by having a store in the middle.





Perhaps a good reason not to bother with a condensing boiler then (yes, I
know about the supposed law mandating them, more b*ll*cks interference in
my home by the government blah blah...)


I think that this is one case where it is worth doing something despite
silly government meddling I've certainly saved considerably on gas
consumption using a condensing boiler.


I'll probably get a significant gain just by fixing the roof
insulation(!). Which is slightly non-trivial as a dormer conversion is
involved and I don;t want to do anything to bung up the already limited
airflow between roof and upper ceiling. Still thinking about that.


The roof is generally the biggest loser of heat in a house and usually
the easiest and cheapest to fix. However, it's worth doing the heat
loss calculations. For example, if you already have 100-150mm of
insulation in a roof space and nothing in the walls, you will probably
get a better result from doing something about the walls than adding
another 100mm in the roof. As you say, definitely avoid doing
anything that reduces ventilation. This is asking for trouble.

If you are tight for space, you could consider sliding sheets of
Celotex into the awkward spaces. It comes in various thicknesses and
has about four times the insulating property for a given thickness
than glass fibre mats.







Tim


--

..andy

To email, substitute .nospam with .gl

"Andy Hall" wrote in message
...

All of this takes you to the point that it is most efficient to run
this type of boiler continuously at lower temperature than to force it
into a situation of reheating a cylinder in bursts.

Which is exactly what it will do when heat demand is les than the minimum
output of the boiler. Most of them it is around 8 kW, some go down to 5 kW.
You will get cycling.

If this type of boiler is connected directly
to the radiators and you have TRVs, as
the room temperature reaches the set point, you have
effectively balanced the building heat loss with
the radiator outputs.
THe TRVs will begin to close. If the boiler is directly connected to
them, it is able to sense the reduced heat
demand and modulate down accordingly.

But not enough and inefficient boiler cycling occurs.

If you put a store in the way, you
will be emptying it at a low
continuous rate of (e.g.) 8kW,
but then when most of the energy has
been used, replenishing it in bursts of
perhaps 25kW - all controlled
by a thermostat on the cylinder.

Putting a thermal store between the boiler and the rads with the temperature
controlled by an outside weather compensator will eliminate boiler cycling
and operate at very low return temperatures promoting efficiency.

When house only requires 1kW of heat, it can just take this from the thermal
store at the exact temperature dictated by an outside weather compensator.
The boiler stays off until the store water drops below what the outside
weather compensator dictates. Then it comes in to reheat to the required
temperature in one long low temperature efficient burn.

THe two exceptions that I made were a) if it's a conventional or
non-modulating boiler - there you would make an improvement by having
it recharge the cylinder once as opposed to driving the radiators
directly and cycling to match effective power output to load;

Most modulating boiler modulate to maintain a flow temperature. These are
perfectly suitable for a thermal store. Even those modulating on load
compensation operate quite well too. Best to buy:

a) A condensing non-modulating boiler
b) A condensing modulating to maintain a flow temperature.

These generally are cheaper and less sophisticated and less to go wrong.
Keep it simple.



_________________________________________
Usenet Zone Free Binaries Usenet Server
More than 120,000 groups
Unlimited download
http://www.usenetzone.com to open account

On Thu, 17 Feb 2005 09:55:45 +0000, Andy Hall wrote:

On Thu, 17 Feb 2005 08:06:19 +0000, Tim S wrote:


Ah, my apologies. "Modulating" condensing boilers is a new one to me.


snip
If this type of boiler is connected directly to the radiators and you
have TRVs, as the room temperature reaches the set point, you have
effectively balanced the building heat loss with the radiator outputs.
THe TRVs will begin to close. If the boiler is directly connected to
them, it is able to sense the reduced heat demand and modulate down
accordingly. Thus, in the typical UK autumn/spring situation, which is
a lot of days of the year, and you need *some* heat, then you can have
the boiler operating in this equilibrium mode at low temperature.

If you put a store in the way, you will be emptying it at a low
continuous rate of (e.g.) 8kW, but then when most of the energy has been
used, replenishing it in bursts of perhaps 25kW - all controlled by a
thermostat on the cylinder. Therefore you prevent the boiler behaving
as it was intended to do - you force it to run at the high temperature
end and even though it will probably be one continuous burn to
replenish, there will still be more of those than if the boiler had been
left running continuously at lower output.

Hi Andy

Yes - thanks for the excellent explanation.

It makes sense - though I have an overriding reason to use a heat bank in
my setup. Not a problem as we already have a not-very-old back boiler
which should be good for 20 years.

Do they make condensing back boilers?

I suppose that it would be possible to have an intelligent controller
between the heatbank and boiler, that would "learn" the characteristics of
the bank and based on various measurables (rate of temp drop at various
vertical points for one) and could make a decision to run the boiler at
partial output. Be quite a nice little project with a PC, then turn it
into a micro-controller package.

If modulating condensors are indeed becoming the norm, I'm sure that one
of the more advanced controller manufacturers will think of doing this.

Tim

"Tim S" wrote in message
news
On Thu, 17 Feb 2005 09:55:45 +0000, Andy Hall wrote:

On Thu, 17 Feb 2005 08:06:19 +0000, Tim S wrote:


Ah, my apologies. "Modulating" condensing boilers is a new one to me.

snip

Hi Andy

Yes - thanks for the excellent explanation.

It is not.

It makes sense -

It doesn't, as it is incorrect. See my post on this.

though I have an overriding reason to use a heat bank in
my setup. Not a problem as we already have a
not-very-old back boiler
which should be good for 20 years.

Do they make condensing back boilers?

I suppose that it would be possible to have an intelligent controller
between the heatbank and boiler, that would "learn" the characteristics of
the bank and based on various measurables (rate of temp drop at various
vertical points for one) and could make a decision to run the boiler at
partial output. Be quite a nice little project with a PC, then turn it
into a micro-controller package.

Yep. Try the Gledhill range. They have "smart" thermal stores with a large
pcb controlling all. It learn the characteristics of your boiloer and knows
whe to bring it in. I have one. Try a BoilerMate on your back boiler - have
the CH run off the store. Leave the back boiler temp full on an the store
does everything else. No clicking on and off noises in your living room.
It will reduce fuel bills.




_________________________________________
Usenet Zone Free Binaries Usenet Server
More than 120,000 groups
Unlimited download
http://www.usenetzone.com to open account

On Thu, 17 Feb 2005 09:55:45 +0000, Andy Hall wrote:

On Thu, 17 Feb 2005 08:06:19 +0000, Tim S wrote:

I'll probably get a significant gain just by fixing the roof
insulation(!). Which is slightly non-trivial as a dormer conversion is
involved and I don;t want to do anything to bung up the already limited
airflow between roof and upper ceiling. Still thinking about that.


snip

The roof is generally the biggest loser of heat in a house and usually the
easiest and cheapest to fix. However, it's worth doing the heat loss
calculations. For example, if you already have 100-150mm of insulation
in a roof space and nothing in the walls, you will probably get a better
result from doing something about the walls than adding another 100mm in
the roof. As you say, definitely avoid doing anything that reduces
ventilation. This is asking for trouble.

If you are tight for space, you could consider sliding sheets of Celotex
into the awkward spaces. It comes in various thicknesses and has about
four times the insulating property for a given thickness than glass fibre
mats.

(Changes topic)

I was looking at Celotex/Kingspan with some interest. I know that "reject"
panels can be obtained at lower cost.

Now my quandry: Bungalow with pitched roof + later (20 years ago) added
dormer conversion. 4" roof timbers, space between roof and plasterboard
assumed to be stuffed with glass wool. Dormer roofs themselves are approx
6" timbers(!) with a miserable 4" of glass fibre (noted when facias
replaced). Remaining roof voids outside of the upstairs floor area have a
mixture of knackered wool on the underside of the roof and bits of crap on
the floor.

I don't really want to have all the plasterboard off, so I'm proposing to
redo the voids first. Getting rid of the crap on the floor would be good
as it's nasty to route cables through - I would like the voids to be
reasonably clean for storage purposes.

I was considering either:

a) Put 50mm celotex on battens to leave 2" gap between tiles and celotex
but this would add complications with adding soffit vents everywhere, and
I'm not sure if doing so would impede the already dubious circulation of
air to the bits of the roof which are packed with glass wool and then have
plasterboard underneath for the dormer ceilings.

b) Replace 4" glass wool under the tiles and use breathable membrane to
contain dust. Ditto: not sure if this would affect airflow, seems that it
would.

I don;t believe there are much in the way of ridge vents, but the timbers
(that I can see) seem fine and when the dormer felt was replaced last
year, the builers found no evidence of rot.

The aim here is not to spend a huge amount of time and money to do it
"right", but to merely improve on the useless crap that's there now in teh
most practical way. Surprisingly it's actually quite warm up there already
and the gas bills are sane.

Next time the roof needs re-tiling, then I'll consider adding insulation
between the tiles and top of rafters.

Any ideas gratefully received.

Tim

On Thu, 17 Feb 2005 10:48:22 -0000, "Doctor Evil"
wrote:


"Andy Hall" wrote in message
.. .

All of this takes you to the point that it is most efficient to run
this type of boiler continuously at lower temperature than to force it
into a situation of reheating a cylinder in bursts.

Which is exactly what it will do when heat demand is les than the minimum
output of the boiler. Most of them it is around 8 kW, some go down to 5 kW.
You will get cycling.

There are a number of models now going down to around 4kW.

One also has to look at the amount of heat required, the number of
days in the year and times of day as well. For the large proportion
of days and the UK climate the heat load is likely to be at or above
the boiler minimum and continuous operation will result.

With your approach the boiler will *always* be forced to do high power
burns into the store so there will never be an opportunity for it to
operate in its most efficient range.



If this type of boiler is connected directly
to the radiators and you have TRVs, as
the room temperature reaches the set point, you have
effectively balanced the building heat loss with
the radiator outputs.
THe TRVs will begin to close. If the boiler is directly connected to
them, it is able to sense the reduced heat
demand and modulate down accordingly.

But not enough and inefficient boiler cycling occurs.

This of course is untrue.



If you put a store in the way, you
will be emptying it at a low
continuous rate of (e.g.) 8kW,
but then when most of the energy has
been used, replenishing it in bursts of
perhaps 25kW - all controlled
by a thermostat on the cylinder.

Putting a thermal store between the boiler and the rads with the temperature
controlled by an outside weather compensator will eliminate boiler cycling
and operate at very low return temperatures promoting efficiency.

This is nonsense under the conditions described which are more typical
of the real world.



When house only requires 1kW of heat, it can just take this from the thermal
store at the exact temperature dictated by an outside weather compensator.
The boiler stays off until the store water drops below what the outside
weather compensator dictates. Then it comes in to reheat to the required
temperature in one long low temperature efficient burn.

This is an attempt at obfuscation.


THe two exceptions that I made were a) if it's a conventional or
non-modulating boiler - there you would make an improvement by having
it recharge the cylinder once as opposed to driving the radiators
directly and cycling to match effective power output to load;

Most modulating boiler modulate to maintain a flow temperature. These are
perfectly suitable for a thermal store. Even those modulating on load
compensation operate quite well too. Best to buy:

a) A condensing non-modulating boiler
b) A condensing modulating to maintain a flow temperature.

These generally are cheaper and less sophisticated and less to go wrong.
Keep it simple.

This is an attempt to alter the agenda.



_________________________________________
Usenet Zone Free Binaries Usenet Server
More than 120,000 groups
Unlimited download
http://www.usenetzone.com to open account


--

..andy

To email, substitute .nospam with .gl

On Thu, 17 Feb 2005 10:57:18 +0000, Tim S wrote:

On Thu, 17 Feb 2005 09:55:45 +0000, Andy Hall wrote:

On Thu, 17 Feb 2005 08:06:19 +0000, Tim S wrote:


Ah, my apologies. "Modulating" condensing boilers is a new one to me.


snip
If this type of boiler is connected directly to the radiators and you
have TRVs, as the room temperature reaches the set point, you have
effectively balanced the building heat loss with the radiator outputs.
THe TRVs will begin to close. If the boiler is directly connected to
them, it is able to sense the reduced heat demand and modulate down
accordingly. Thus, in the typical UK autumn/spring situation, which is
a lot of days of the year, and you need *some* heat, then you can have
the boiler operating in this equilibrium mode at low temperature.

If you put a store in the way, you will be emptying it at a low
continuous rate of (e.g.) 8kW, but then when most of the energy has been
used, replenishing it in bursts of perhaps 25kW - all controlled by a
thermostat on the cylinder. Therefore you prevent the boiler behaving
as it was intended to do - you force it to run at the high temperature
end and even though it will probably be one continuous burn to
replenish, there will still be more of those than if the boiler had been
left running continuously at lower output.

Hi Andy

Yes - thanks for the excellent explanation.

It makes sense - though I have an overriding reason to use a heat bank in
my setup. Not a problem as we already have a not-very-old back boiler
which should be good for 20 years.

Do they make condensing back boilers?

I haven't seen any.

Your scenario is a good reason to put in some thermal buffering.



I suppose that it would be possible to have an intelligent controller
between the heatbank and boiler, that would "learn" the characteristics of
the bank and based on various measurables (rate of temp drop at various
vertical points for one) and could make a decision to run the boiler at
partial output. Be quite a nice little project with a PC, then turn it
into a micro-controller package.

That could be worth doing, although I fear that you might have
relatively little control over the boiler behaviour. Really it has to
be hot or off. Nevertheless I think that you could probably do some
predictive stuff to make it more responsive in anticipation of demand
and to turn it off in good time rather than overheating the store.
I presume that you are going to fully pump it. That will also give
you some good opportunities for control by timing the pump on off
ahead and after the burner.

Given what you have, I think it's definitely worth a go.


If modulating condensors are indeed becoming the norm, I'm sure that one
of the more advanced controller manufacturers will think of doing this.

Tim


--

..andy

To email, substitute .nospam with .gl

Dr Evil / Andy Hall.

I seem to have caused a bit of a storm with this one!!

Rather than dealing with hypothetical situations, lets deal with actualities. Perhaps that way I can add something to the argument that solves the riddle.

The Boiler WILL be a Condensing boiler, a Vaillent EcoMAX635E. Partly because this boiler is available under the local council money back scheme, but also because its one of two that meet the power output requirements for a low enough install cost.

The existing house is very lossy, its old and looses a lot of heat. We won't install injected cavity insulation as all the similar houses in the area that have had that done now have major damp problems. Though we are replacing the loft insulation.

We WILL have to use UFH as there is no room in at least three spaces for radiators.

I don't know if the UFH will run of the radiator circuit, but I expect it will.

At least one of the UFH circuits will have to be on its own zone as its a conservatory and may require independent heating.

Other spaces (three bedrooms) may run off UFH if its suitable, otherwise these spaces and the rest of the house, will run off radiators. It would be impossible to install wet UFH on the ground floor without digging out a LOT of soil.

The final and main reason for the heat store is to allow mains pressure hot water without using a combi as combis always suffer from severe temperature drop as the flow rate increases.

If I side with Andy, then it seems I need to run the radiators off the boiler, together with any UFH zones that are connected to CH circuits and the conventional UFH and HW off the thermal store, this seems to mean two separate S plan heating systems.

If I side with Dr Evil, then it looks much simpler; a manifold on an S plan direct from the store with as many zones as I can afford.

Is there a sensible solution?

Jason.

"Andy Hall" wrote in message
...
On Thu, 17 Feb 2005 10:48:22 -0000, "Doctor Evil"
wrote:


"Andy Hall" wrote in message
.. .

All of this takes you to the point that it is most efficient to run
this type of boiler continuously at lower temperature than to force it
into a situation of reheating a cylinder in bursts.

Which is exactly what it will do when
heat demand is les than the minimum
output of the boiler. Most of them it is
around 8 kW, some go down to 5 kW.
You will get cycling.

There are a number of models now going down to around 4kW.

With your approach the boiler will *always* be forced to do high power
burns into the store so there will never be an opportunity for it to
operate in its most efficient range.

Not so. Wghenthe temperature of the store is ciontrolled by an outside
weather compensator the return temp will always be cool. A boiler raises
the temperature of water a certain degree rate. If an outside weather
compensator operating on the lowest part of a store It may be setting ity to
say 45C. when the store gets below this the compensator tells the boiler to
re-heat. As the return temp will be below this the operation is very
efficient because the return temp is low. The store of water prevents
boioer cycling. Best have the water volume about the same as the heating
circuit, so when the heating demands heat all the rads are up to temp
immediately, the the boiler comes in to re-heat in one long efficfient burn.

If this type of boiler is connected directly
to the radiators and you have TRVs, as
the room temperature reaches the set point, you have
effectively balanced the building heat loss with
the radiator outputs.
THe TRVs will begin to close. If the boiler is directly connected to
them, it is able to sense the reduced heat
demand and modulate down accordingly.

But not enough and inefficient boiler cycling occurs.

This of course is untrue.

'fraid it is true.

If you put a store in the way, you
will be emptying it at a low
continuous rate of (e.g.) 8kW,
but then when most of the energy has
been used, replenishing it in bursts of
perhaps 25kW - all controlled
by a thermostat on the cylinder.

Putting a thermal store between the
boiler and the rads with the temperature
controlled by an outside weather compensator
will eliminate boiler cycling
and operate at very low return temperatures
promoting efficiency.

This is nonsense

'fraid it is not nonsense at all.

When a house only requires 1kW of heat,
it can just take this from the thermal
store at the exact temperature dictated
by an outside weather compensator.
The boiler stays off until the stored water
drops below what the outside
weather compensator dictates. Then
it comes in to reheat to the required
temperature in one long low temperature
efficient burn.

This is an attempt at obfuscation.

It appears you don't undertsand. It is very clear.

THe two exceptions that I made were a) if it's a conventional or
non-modulating boiler - there you would make an improvement by having
it recharge the cylinder once as opposed to driving the radiators
directly and cycling to match effective power output to load;

Most modulating boiler modulate to maintain a flow temperature. These are
perfectly suitable for a thermal store. Even those modulating on load
compensation operate quite well too. Best to buy:

a) A condensing non-modulating boiler
b) A condensing modulating to maintain a flow temperature.

These generally are cheaper and less sophisticated and less to go wrong.
Keep it simple.

This is an attempt to alter the agenda.

I'm afraid you are confused.

Best system:

1. Heat bank with a dedicated flow and return from the boiler for the top
half DHW set to 75C. Have two cyl stats in this section precvent boiler
cycling.

Bottom heating section with a dedicated flow and return from the boiler.
Temperature of botom section controlled by an outside weather compensator
for heating. This could be set to a very low temperaure by the compensator.

This gives two separate temp zones in one cylinder. The DHW takes priority.
If DHW calls, all the boilers heat is directed to the top half for quick DHW
recovery. When the DHW is satisfied the boiler is controled by the outside
weather compensator and only keep the bottom section to what the compensator
dictates.

2. A cheaper simpler, more reliable, non-modulating condensing boiler.




_________________________________________
Usenet Zone Free Binaries Usenet Server
More than 120,000 groups
Unlimited download
http://www.usenetzone.com to open account