Well I have finally implemented my DIY Heatbank system, using the
following as a very useful starting point.

http://www.wiki.diyfaq.org.uk/index....=DIY_Heat_Bank

I have a couple of things of which I am currently uncertain in the
fine tuning of my setup:

1) Currently I just have a single cylinder stat which is about 400mm
or so from the bottom of the tank. I have read elsewhere regarding
the use of 2 cylinder stats and a latching relay. I understand this
is to allow the tank to work within a temperature range before the
boiler re-fires to prevent cycling. I think I get far more cycling
from my CH than from the Heatbank though - which leads on to an
additional question below. But first: what height does the 2nd stat
go on the tank? How are the 2 stats wired together? Can you buy an
off the peg latching relay to do this? If not what components are
required? Is it worth doing?

2) The CH does not go via the heatbank; this is currently just for
DHW. I have a programmable Horstmann roomstat for the CH, but am very
dissapointed at how much cycling this causes. It switches in and out
very regularly. Can anyone recommend a better unit? I have seen the
Honeywell CM67 highly spoken of, but am not sure whether it is still
made; screwfix don't list it.

3) I am aware that CH can also be fed off a heatbank, but am not sure
exactly what additional plumbing I'd need to do - would I need new
tappings into the tank, or could I just tee of the existing output
from the top of the tank and use a flow valve after the CH arm of the
tee? Currently the flow from the boiler goes system pump 3port
valve - 1 leg to CH flow // 1 leg to top essex flange/diffuser on the
cyclinder .

4) One curious thing I have noticed whilst becoming more intimate with
my system is that when the system pump is running a trickle of water
is coming over into the FHE tank. The problem originally started when
I moved the boiler and pump from the cellar - the flue location did
not meet current building regs when the boiler was replaced, so no
option but to relocate to 1st floor. Now the pump is obviously much
closer to the FHE tank. There is no actual overflow, but hot water is
flowing round and back down the fill pipe, which isn't ideal as the
tank is acting as a small inefficient plastic radiator in the attic,
and causing condensation to boot!! The only way I can prevent it is
to close the valve on the fill pipe, once I'm sure the system is
devoid of air. This stops the flow around through the tank,
effectively making the enclosed, but not unvented as any expansion can
still occur up the overflow pipe towards the FHE tank. I don't think
running the pump on it's lowest setting is viable - it is a 4 storey
house. The boiler and pump (and the heatbank) are all on the 1st
floor and heat has to go down 2 storeys and up 1 storey and return
obviously, so the pump needs a bit of grunt. What on earth can I do
to prevent this occuring?

5) And finally what are the optimum flow and return temps of a
condensing boiler - I have a Worcester Bosch Greenstar 24Ri (24kW). I
have seen 70/50deg C, but the heatbank needs 75-80degC, so I'd need to
go a bit higher than this. If I set the boiler too high, it tends to
cut in and out too, even if the system pump is set high, so it's a
delicate balance I need to find.

=====

For background and if anyone is interested, the following specific
info may be a useful addition to what is on the DIY Heatbanks wiki:

- The first significant improvement I to the blueprint on the wiki was
using a 100kW PHE from GEA which was about £180 incl VAT.

- The second improvement is diffuser pipes within the cylinder. I
have a c200litre direct tank [1700x500(dia) mm] double insulated. I
had the tank made to spec to fit the space I have available with a
single top port - a standard BSP 1" male connector. The top connector
takes the flow to the PHE primary and is tee'd off to the FHE tank
overflow. I added 2 essex flanges myself through which I passed my
own diffuser tubes prior to assembley of the flanges into the tank.
The diffusers are 22mm copper tube with a yorkshire end stop soldered
on and between 30 and 40 (can't recall exactly now!) 6mm holes
carefully drilled and cleaned of swarf as much as poss. The diffuser
runs across the full width of the tank from the flange to just short
of the the opposite internal side of the cylinder. The bottom flange
is 100mm from the bottom of the tank and is tee'd to take the PHE and
boiler returns (they actually flow in different directions - check the
wiki if that confuses). The top flange is for the boiler flow and is
just below the top of the cylinder side, below the join with the dome
cap. The holes on the diffuser are oriented to aim sideways and
upwards from the top diffuser and sideways and downwards from the
bottom to diffuser to preserve stratification in the tank.

1) Currently I just have a single cylinder stat which is about 400mm
or so from the bottom of the tank. I have read elsewhere regarding
the use of 2 cylinder stats and a latching relay. I understand this
is to allow the tank to work within a temperature range before the
boiler re-fires to prevent cycling. I think I get far more cycling
from my CH than from the Heatbank though - which leads on to an
additional question below. But first: what height does the 2nd stat
go on the tank? How are the 2 stats wired together? Can you buy an
off the peg latching relay to do this? If not what components are
required? Is it worth doing?

To quote from Heatweb:

"With large or fixed output boilers it may not be desirable for the
boiler to fire up when only a very small amount of store water needs
heating, as the boiler may cycle. To overcome this we can fit a second
cylinder thermostat, which will hold off the boiler from firing up
until both thermostats are calling for heat. The boiler will then fire
until both are satisfied."

On Dec 12, 3:16 pm, " wrote:
1) Currently I just have a single cylinder stat which is about 400mm
or so from the bottom of the tank. I have read elsewhere regarding
the use of 2 cylinder stats and a latching relay. I understand this
is to allow the tank to work within a temperature range before the
boiler re-fires to prevent cycling. I think I get far more cycling
from my CH than from the Heatbank though - which leads on to an
additional question below. But first: what height does the 2nd stat
go on the tank? How are the 2 stats wired together? Can you buy an
off the peg latching relay to do this? If not what components are
required? Is it worth doing?

To quote from Heatweb:

"With large or fixed output boilers it may not be desirable for the
boiler to fire up when only a very small amount of store water needs
heating, as the boiler may cycle. To overcome this we can fit a second
cylinder thermostat, which will hold off the boiler from firing up
until both thermostats are calling for heat. The boiler will then fire
until both are satisfied."

Yes, I knew that!!! Read the question D'OH

In article
s.com, Mike Holmes writes
On Dec 12, 3:16 pm, " wrote:
1) Currently I just have a single cylinder stat which is about 400mm
or so from the bottom of the tank. I have read elsewhere regarding
the use of 2 cylinder stats and a latching relay. I understand this
is to allow the tank to work within a temperature range before the
boiler re-fires to prevent cycling. I think I get far more cycling
from my CH than from the Heatbank though - which leads on to an
additional question below. But first: what height does the 2nd stat
go on the tank? How are the 2 stats wired together? Can you buy an
off the peg latching relay to do this? If not what components are
required? Is it worth doing?

To quote from Heatweb:

"With large or fixed output boilers it may not be desirable for the
boiler to fire up when only a very small amount of store water needs
heating, as the boiler may cycle. To overcome this we can fit a second
cylinder thermostat, which will hold off the boiler from firing up
until both thermostats are calling for heat. The boiler will then fire
until both are satisfied."

Yes, I knew that!!! Read the question D'OH

LOL, I don't know if it is a good idea (the concept sounds ok) but if
you want to try it, here's how to do it:

No need for a latching relay, use a common double pole mains relay and
use the second contact to provide the latch electrically.

(Use a fixed width font)

___L
| RLY
| CONTACT A
| __- __-o
|----o' o------------------o' o---|
| LOW LVL STAT |
| __- |-----------------|
|----o' o---------|
HIGH LVL STAT |
_|_ ___L RLY
| | | CONTACT B
| | | __-o
| | |--o' o-----------
RLY |___| BOILER
COIL | CALL FOR HEAT
|
_|_ N

All contacts are shown in the no demand position, stat contacts open,
relay de-energised.

Control sequence:

1. Low level stat will close first but cannot energise the relay because
there is no direct connection to the coil.

2. High level stat closes, energising the relay and closing contacts A
and B. Contact B feeds demand to the boiler.

3. After some time heating the heat bank, the high level stat will drop
out but the relay will remain energised as it is now fed from the low
level stat via relay contact A.

4. When the low level stat drops out the relay de-energises and demand
is removed from the boiler.

Almost any 2 pole mains power relay will do the job, first one to hand
is from http://cpc.farnell.com/ , item code SW02489, 5.12 inc vat and a
screw terminal holder is code SW02484, 3.50 inc vat. Grab a plastic box
to mount it in while you're there.

It may be possible to use a single pole relay to do this job but it is
cleaner to separate the functions and 2 pole mains relays are cheap.

HTH
--
fred
Plusnet - I hope you like vanilla

Mike Holmes wrote:

1) Currently I just have a single cylinder stat which is about 400mm
or so from the bottom of the tank. I have read elsewhere regarding
the use of 2 cylinder stats and a latching relay. I understand this
is to allow the tank to work within a temperature range before the
boiler re-fires to prevent cycling. I think I get far more cycling
from my CH than from the Heatbank though - which leads on to an
additional question below. But first: what height does the 2nd stat
go on the tank? How are the 2 stats wired together? Can you buy an
off the peg latching relay to do this? If not what components are
required? Is it worth doing?

Doing it will increase the hysteresis of the stat a bit, and delay the
recovery of the heat bank. Depending on how close you get to depleting
the heat bank this may or may not be desirable.

2) The CH does not go via the heatbank; this is currently just for
DHW. I have a programmable Horstmann roomstat for the CH, but am very
dissapointed at how much cycling this causes. It switches in and out
very regularly. Can anyone recommend a better unit? I have seen the
Honeywell CM67 highly spoken of, but am not sure whether it is still
made; screwfix don't list it.

The cycle rate of the state is more an indication of the rate of change
of temperature in its current location. Is your in a draft?

(I have a Horstmann Centaur stat 7 day programmable jobbie, and don't
find that it cycles particularly quickly).

3) I am aware that CH can also be fed off a heatbank, but am not sure
exactly what additional plumbing I'd need to do - would I need new
tappings into the tank, or could I just tee of the existing output
from the top of the tank and use a flow valve after the CH arm of the
tee? Currently the flow from the boiler goes system pump 3port
valve - 1 leg to CH flow // 1 leg to top essex flange/diffuser on the
cyclinder .

If you used the existing ones, your would in effect run you rads at a
fairly high temperature - a lower top tapping would drop the rad temp a
bit and might give more even room temps with less overshoot. This will
be at the expense of a slightly longer warm up time from cold.

IIUC, your boiler is non modulating, so imposing the heatbank between
rads and boiler may reduce cycling a little. (with a boiler that
modulates over a wide range this is less desirable since it just
complicates the boiler ability to load balance)

4) One curious thing I have noticed whilst becoming more intimate with
my system is that when the system pump is running a trickle of water
is coming over into the FHE tank. The problem originally started when

"over into" from where? Up the Feed and Expansion pipe, or falling out
of the vent pipe?

5) And finally what are the optimum flow and return temps of a
condensing boiler - I have a Worcester Bosch Greenstar 24Ri (24kW). I
have seen 70/50deg C, but the heatbank needs 75-80degC, so I'd need to
go a bit higher than this. If I set the boiler too high, it tends to
cut in and out too, even if the system pump is set high, so it's a
delicate balance I need to find.

Lower return temps are more efficient for the boiler, but you are
restricted there by the desire to get sufficient energy into the store.
I would have thought with a direct tank, it ought to keep the return
temperature reasonably down for a fair proportion of the heating time.

Some sticky tape (as a target) and an IR thermometer is handy for tuning
here so you can see what is happening with the various pipe temperatures.



--
Cheers,

John.

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

"Mike Holmes" wrote in message
...

Well I have finally implemented my
DIY Heatbank system, using the
following as a very useful starting point.

http://www.wiki.diyfaq.org.uk/index....=DIY_Heat_Bank

I explained a better approach, but you used this one. Ignore the ridiculous
electronics. The heat web site has the circuitry of the latching relay. The
circuit has been given anyhow on this thread.

Can anyone recommend a better unit?

The Drayton electronic is fine.

3) I am aware that CH can also be
fed off a heatbank, but am not sure
exactly what additional plumbing I'd
need to do - would I need new
tappings into the tank, or could I just tee
of the existing output from the top of the
tank and use a flow valve after the CH arm
of the tee? Currently the flow from the boiler
goes system pump 3port valve - 1 leg to
CH flow // 1 leg to top essex flange/diffuser
on the cylinder .

Study the heatweb site. You can use a Surrey flange in the cylinder top and
take the CH off the immersed pipe. Best to extend the inner pipe of the
flange to the centre of the cylinder. The Ch return to the bottom on the
cylinder. The room stat controls the Ch pump. The 3-way valve can go and
the boiler "only heats the cylinder directly".

4) One curious thing I have noticed
whilst becoming more intimate with
my system is that when the system
pump is running a trickle of water
is coming over into the FHE tank.

Take the cold feed to the DHW port away from the boiler flow influences. One
of the reason why I recommended not to use this drawing.

5) And finally what are the optimum
flow and return temps of a condensing boiler
- I have a Worcester Bosch Greenstar 24Ri (24kW). I
have seen 70/50deg C, but the heatbank needs
75-80degC, so I'd need to go a bit higher than this.

A DHW only heat bank can operate at 65C, depending on cylinder size. Plate
heat exchangers are so efficient at heat transfer.

=====

For background and if anyone is interested,
the following specific info may be a useful
addition to what is on the DIY Heatbanks wiki:

- The first significant improvement I to
the blueprint on the wiki was using a
100kW PHE from GEA which was
about £180 incl VAT.

These can be got for £80 to £100. Get a Gledhill one for a Systemate from a
dealer. DPS sell them cheaper than that too.

The bottom flange is 100mm from the
bottom of the tank and is tee'd to take
the PHE and boiler returns (they actually
flow in different directions - check the
wiki if that confuses).

Best to have the boiler and PHE returns in separate tapings. A 200 litre
cylinder will just about do CH and DHW.

It may be worth having circuitry that brings in the boiler immediately when
DHW is called (the flow switch activated) and CH is called. This eliminates
the lag. When DHW is being called this can be switched out.

John,

Many thanks for the detailed relies - further comments/clarifications
below:

The cycle rate of the state is more an indication of the rate of change
of temperature in its current location. Is your in a draft?

Well I hadn't thought so - didn't appreciate it would be so
sensitive. It is on the side of the stairs with open ballustrades
(where the old room stat was originally), so I guess there may be a
slight draft coming down off the edge of the stairs and causing it to
cycle

(I have a Horstmann Centaur stat 7 day programmable jobbie, and don't
find that it cycles particularly quickly).

This is exactly the model I have, so that's reassuring that it works
well for you. Will have to relocate mine I think.

IIUC, your boiler is non modulating,

No it's fully modulating - here is the spec:

http://www.worcester-bosch.co.uk/ind...on_id=12370 2

(with a boiler that
modulates over a wide range this is less desirable since it just
complicates the boiler ability to load balance)

Why is that? I'm thinking that because the boiler fully modulates
that there shoudln't be a problem with having the boiler set high for
the DHW, meaning the return temp would be higher than ideal from the
CH, if the boiler DIDN'T modulate. However as my boiler DOES modulate
does this mean that even if it's on 100% (which equals 24kW and max
flow temp of 82degC) that it will actually modulate down to achieve
the ideal return temperature?

I think perhaps the problem of my system cutting in and out is
possibly purely down to the poor placement of my room stat.


4) One curious thing I have noticed whilst becoming more intimate with
my system is that when the system pump is running a trickle of water
is coming over into the FHE tank.

"over into" from where? Up the Feed and Expansion pipe, or falling out
of the vent pipe?

I thought the feed pipe and the expansion pipe were different things
and that the expansion is synonymous with the vent pipe. Anyway in
your terminology, it is flowing out of the vent pipe and back down the
Feed and Expansion pipe. As I said there is no net overflow or actual
filling from the mains going on - just a flow through the FHE tank
that shouldn't be happening.

If I set the boiler too high, it tends to
cut in and out too, even if the system pump is set high, so it's a
delicate balance I need to find.

I would have thought with a direct tank, it ought to keep the return
temperature reasonably down for a fair proportion of the heating time.


It's OK on the DHW demand as you say, but I'm thinking the CH return
will end up being too high, unless the boiler's ability to modulate
down gets round this even though the boiler output is set way up.

Some sticky tape (as a target) and an IR thermometer is handy for tuning
here so you can see what is happening with the various pipe temperatures.

The IR thermometer was a bit pricey, so I got a digital one with a
probe from screwfix and some thermal paste from maplin to conduct
efficiently.

Thanks again

Mike

DD - thanks for the suggestions esp clarification of plumbing
electrics mods to operate the CH off the heatbank too.

Take the cold feed to the DHW port away from the boiler flow influences. One
of the reason why I recommended not to use this drawing.

This occurred well before I rigged the heatbank - as explained in the
OP.

A DHW only heat bank can operate at 65C, depending on cylinder size. Plate
heat exchangers are so efficient at heat transfer.

Perhaps I should try dropping the temperature and see how it performs


These can be got for £80 to £100. Get a Gledhill one for a Systemate from a
dealer. DPS sell them cheaper than that too.

I can't vouch for the Gledhill PHEs, but I quizzed GEA about the DPS
PHE, which you may or may not have realised they supply. Personally,
what I could find out wasn't conclusive, but I wouldn't trust the data
quoted for the PHE on the DPS website. I don't pretend to fully
understand the ins and outs of the PHE head load/output calcs, but for
the input params I gave GEA their model equivalent to the one
marketted through DPS was definitely not 100kW, but needed a bigger
beast - the one I now have. Sorry to be a bit vague, I don't have the
model no and calculation sheets with me at the moment, so I can't
check and include full details. Suffice to say that my PHE is
definitely 100kW working under the conditions I supplied GEA. I
decided I'd rather spend a bit more and get a PHE that definitely did
the job rather than having to upgrade and waste money later on.


The bottom flange is 100mm from the
bottom of the tank and is tee'd to take
the PHE and boiler returns (they actually
flow in different directions - check the
wiki if that confuses).

Best to have the boiler and PHE returns in separate tapings. A 200 litre
cylinder will just about do CH and DHW.

I don't see any advantage in this - it works fine. When there is a
demand for DHW from the PHE primary pump and boiler has demand (ie the
system pump is running) the return from the PHE just cariies on
straight down the boiler return rather than going through the tank
(give or take any differences between the respective pump flows
generated - the return tapping into the bottom of the tank will
balance the flow at the tee in this scenario, to prevent any resultant
presure diffs).


It may be worth having circuitry that brings in the boiler immediately when
DHW is called (the flow switch activated) and CH is called. This eliminates
the lag. When DHW is being called this can be switched out.

Mike Holmes wrote:

Many thanks for the detailed relies - further comments/clarifications
below:

The cycle rate of the state is more an indication of the rate of change
of temperature in its current location. Is your in a draft?

Well I hadn't thought so - didn't appreciate it would be so
sensitive. It is on the side of the stairs with open ballustrades
(where the old room stat was originally), so I guess there may be a
slight draft coming down off the edge of the stairs and causing it to
cycle

Pretty much the same place I have mine by the sounds of it.

(I have a Horstmann Centaur stat 7 day programmable jobbie, and don't
find that it cycles particularly quickly).

This is exactly the model I have, so that's reassuring that it works
well for you. Will have to relocate mine I think.

IIUC, your boiler is non modulating,

No it's fully modulating - here is the spec:

http://www.worcester-bosch.co.uk/ind...on_id=12370 2

ah ok, the sedbuk database has it wrong then!

(with a boiler that
modulates over a wide range this is less desirable since it just
complicates the boiler ability to load balance)

Why is that? I'm thinking that because the boiler fully modulates
that there shoudln't be a problem with having the boiler set high for
the DHW, meaning the return temp would be higher than ideal from the
CH, if the boiler DIDN'T modulate. However as my boiler DOES modulate
does this mean that even if it's on 100% (which equals 24kW and max
flow temp of 82degC) that it will actually modulate down to achieve
the ideal return temperature?

OK, with a modulating boiler that changes things. Usually you set the
desired flow temperature, and the boiler will adjust the power input to
achieve its desired return temperature, so it should run closer to
maximum efficiency for longer.

If you stuck the thermal store between boiler and rads then you
introduce a big energy store and damper into your closed loop control
system. The effect of which will vary depending on the details. It may
still work fine, or you might find there is enough phase lag in the
control feedback that you get erratic temperature variations.

So unless you have a very well insulated house that usually requires
significantly less than the minimum 8kW output of the boiler, you will
usually get better results letting the boiler drive the rads directly.
Note that 8kW is relatively high, so you would expect some cycling
whatever you do once the house is up to temperature.

I think perhaps the problem of my system cutting in and out is
possibly purely down to the poor placement of my room stat.

It could well be. How is the temperature control in the rest of the
house? Depending on the answer, you might want to play with the balance
of the uncontrolled rad in the same room as the stat.

I noticed when upgrading from a fixed output boiler with a conventional
stat, to a modulating one with prog stat the general level of comfort
and consistency in the house improved. The boiler runs for longer
periods at low output and there is less temperature swing in the house.

4) One curious thing I have noticed whilst becoming more intimate with
my system is that when the system pump is running a trickle of water
is coming over into the FHE tank.
"over into" from where? Up the Feed and Expansion pipe, or falling out
of the vent pipe?

I thought the feed pipe and the expansion pipe were different things
and that the expansion is synonymous with the vent pipe. Anyway in

No, you have a Feed and Expansion pipe - this will be fed from under the
water line in the header tank. It will allow water to feed into the
system, as well as allowing expansion to push water back into the tank
as the system heats up.

In addition to that you have a vent pipe that dispenses back into the
top of the tank, and it serves as a safety feature to prevent dangerous
pressure build up. Normally nothing should flow from this pipe.

It is also possible to have both these pipes combined. In this case the
vent runs as it currently does, and the F&E pipe tees into it a couple
of feet above the highest part of the system pipework.

your terminology, it is flowing out of the vent pipe and back down the
Feed and Expansion pipe. As I said there is no net overflow or actual
filling from the mains going on - just a flow through the FHE tank
that shouldn't be happening.

That is pump over, and you are right, it is not good. Not only will the
tank contents get very hot, you will also be introducing fresh air into
the water which will accelerate corrosion in the system

If I set the boiler too high, it tends to
cut in and out too, even if the system pump is set high, so it's a
delicate balance I need to find.

I would have thought with a direct tank, it ought to keep the return
temperature reasonably down for a fair proportion of the heating time.


It's OK on the DHW demand as you say, but I'm thinking the CH return
will end up being too high, unless the boiler's ability to modulate
down gets round this even though the boiler output is set way up.

The modulation ought to help, but once the house is warm and the TRVs on
the rads start to close, the return temp will start to rise. There will
come a point where the boiler will have to cycle off on its own internal
stat since it won't be able to maintain the output temperature below
your selected maximum while still heating at 8kW. Usually in this case
the boiler will keep running its pump and then just kick in when the
return shows a drop again (assuming the prog stat is still calling for
heat).

Note that this type of cycling does not have the same inefficiency
drawbacks as you would get with an old high water content boiler with
external controls and pump. There each time the boiler cycled off the
retained heat would end up being lost from the flue. On yours it should
keep most of the heat in the primary circuit, and not much is lost from
the boiler anyway.

Some sticky tape (as a target) and an IR thermometer is handy for tuning
here so you can see what is happening with the various pipe temperatures.

The IR thermometer was a bit pricey, so I got a digital one with a
probe from screwfix and some thermal paste from maplin to conduct
efficiently.

Yup, that should do it...

--
Cheers,

John.

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

On Thu, 13 Dec 2007 03:47:38 +0000, John Rumm wrote:

It switches in and out very regularly.

The cycle rate of the state is more an indication of the rate of change
of temperature in its current location.

Or possibly, with a programmable stat, proportional control feature. This
is feature where the stat tries to balance the heat loss with heat input
from the boiler by pulse width modulating the firing of the boiler. The
effect is of "very regular" firing. Not recommended on systems with
motorised valves as they have to cycle far more frequently than a
traditional bang/bang system.

--
Cheers
Dave. pam is missing e-mail

Fred

Many thanks for the guidance on the latching relay circuitry - looks
pretty straightforward now I've had a chance to study it a bit.

Can anyone recommend approximate placements of the low and high stats
on the tank itself

Cheers

Mike

On 13 Dec, 12:35, Mike Holmes wrote:
John,

Many thanks for the detailed relies - further comments/clarifications
below:

The cycle rate of the state is more an indication of the rate of change
of temperature in its current location. Is your in a draft?

Well I hadn't thought so - didn't appreciate it would be so
sensitive. It is on the side of the stairs with open ballustrades
(where the old room stat was originally), so I guess there may be a
slight draft coming down off the edge of the stairs and causing it to
cycle

(I have a Horstmann Centaur stat 7 day programmable jobbie, and don't
find that it cycles particularly quickly).

This is exactly the model I have, so that's reassuring that it works
well for you. Will have to relocate mine I think.

IIUC, your boiler is non modulating,

No it's fully modulating - here is the spec:

http://www.worcester-bosch.co.uk/ind...roduct.techdat...

(with a boiler that
modulates over a wide range this is less desirable since it just
complicates the boiler ability to load balance)

Why is that? I'm thinking that because the boiler fully modulates
that there shoudln't be a problem with having the boiler set high for
the DHW, meaning the return temp would be higher than ideal from the
CH, if the boiler DIDN'T modulate. However as my boiler DOES modulate
does this mean that even if it's on 100% (which equals 24kW and max
flow temp of 82degC) that it will actually modulate down to achieve
the ideal return temperature?

I think perhaps the problem of my system cutting in and out is
possibly purely down to the poor placement of my room stat.



4) One curious thing I have noticed whilst becoming more intimate with
my system is that when the system pump is running a trickle of water
is coming over into the FHE tank.

"over into" from where? Up the Feed and Expansion pipe, or falling out
of the vent pipe?

I thought the feed pipe and the expansion pipe were different things
and that the expansion is synonymous with the vent pipe. Anyway in
your terminology, it is flowing out of the vent pipe and back down the
Feed and Expansion pipe. As I said there is no net overflow or actual
filling from the mains going on - just a flow through the FHE tank
that shouldn't be happening.

If I set the boiler too high, it tends to
cut in and out too, even if the system pump is set high, so it's a
delicate balance I need to find.
I would have thought with a direct tank, it ought to keep the return
temperature reasonably down for a fair proportion of the heating time.

It's OK on the DHW demand as you say, but I'm thinking the CH return
will end up being too high, unless the boiler's ability to modulate
down gets round this even though the boiler output is set way up.

Some sticky tape (as a target) and an IR thermometer is handy for tuning
here so you can see what is happening with the various pipe temperatures.

The IR thermometer was a bit pricey, so I got a digital one with a
probe from screwfix and some thermal paste from maplin to conduct
efficiently.

Thanks again

Mike

You didn't try Ebay then for your IR Thermometer ? A tenner (from
HK !!) and seems excellent.

Rob

- The second improvement is diffuser pipes within the cylinder. *I
have a c200litre direct tank [1700x500(dia) mm] double insulated. *I
had the tank made to spec to fit the space I have available with a
single top port - a standard BSP 1" male connector. *The top connector
takes the flow to the PHE primary and is tee'd off to the FHE tank
overflow. *I added 2 essex flanges myself through which I passed my
own diffuser tubes prior to assembley of the flanges into the tank.


Hi, very interested in this thread. As wanted to build my own heatbank
too.

Latest diagram I came up with was:
http://aycu27.webshots.com/image/387...2625313_rs.jpg

..but it still comes in expensive!!

If you have plenty of time on your hands, you can read my thread at
http://www.screwfix.com/talk/thread.jspa?threadID=63364

Couple of questions,
1.Where did you get your cylinder from and approx what price?
2. Where the essex flanges straight forward enough to fit?
3. What cylinder stats did you use and where these external or pocket
type?
4.Have you or do you intend to run Ch from heatbank or leave as is?

Cheers

Ian

wrote in message
...
- The second improvement is diffuser pipes within the cylinder. I
have a c200litre direct tank [1700x500(dia) mm] double insulated. I
had the tank made to spec to fit the space I have available with a
single top port - a standard BSP 1" male connector. The top connector
takes the flow to the PHE primary and is tee'd off to the FHE tank
overflow. I added 2 essex flanges myself through which I passed my
own diffuser tubes prior to assembley of the flanges into the tank.


Hi, very interested in this thread. As wanted to build my own heatbank
too.

Latest diagram I came up with was:
http://aycu27.webshots.com/image/387...2625313_rs.jpg


Nice!!!

Have the open vent to the F&E tank separate to the flow to the Plate heat
exchnmager or use a Surrey flange at this point.

On Jan 1, 11:52*pm, "Doctor Drivel" wrote:
wrote in message

...
- The second improvement is diffuser pipes within the cylinder. I

have a c200litre direct tank [1700x500(dia) mm] double insulated. I
had the tank made to spec to fit the space I have available with a
single top port - a standard BSP 1" male connector. The top connector
takes the flow to the PHE primary and is tee'd off to the FHE tank
overflow. I added 2 essex flanges myself through which I passed my
own diffuser tubes prior to assembley of the flanges into the tank.

Hi, very interested in this thread. As wanted to build my ownheatbank
too.

Latest diagram I came up with was:http://aycu27.webshots.com/image/387...2625313_rs.jpg


Nice!!!

Have the open vent to the F&E tank separate to the flow to the Plate heat
exchnmager or use a Surrey flange at this point.

That is supposed to be a surrey flange on top, forgot to indicate.

Think you were part of the original screwfix thread and provided a
great deal of input so credit mainly to you!!

Just need to source a cheap 200L direct cylinder and find out if it is
straight forward enough to fit essex flanges. (I generally fit basic
kitchens and bathroom suites for housing associations so basic
plumbing OK. Used Surrey flanges before but never Essex which
obviously means cutting a hole in new cylinder!

wrote in message
...
- The second improvement is diffuser pipes within the cylinder. I
have a c200litre direct tank [1700x500(dia) mm] double insulated. I
had the tank made to spec to fit the space I have available with a
single top port - a standard BSP 1" male connector. The top connector
takes the flow to the PHE primary and is tee'd off to the FHE tank
overflow. I added 2 essex flanges myself through which I passed my
own diffuser tubes prior to assembley of the flanges into the tank.


Hi, very interested in this thread. As wanted to build my own heatbank
too.

Latest diagram I came up with was:
http://aycu27.webshots.com/image/387...2625313_rs.jpg


Put the check valves on the CH circuits "after" the pumps.

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

wrote in message
...
- The second improvement is diffuser pipes within the cylinder. I
have a c200litre direct tank [1700x500(dia) mm] double insulated. I
had the tank made to spec to fit the space I have available with a
single top port - a standard BSP 1" male connector. The top connector
takes the flow to the PHE primary and is tee'd off to the FHE tank
overflow. I added 2 essex flanges myself through which I passed my
own diffuser tubes prior to assembley of the flanges into the tank.


Hi, very interested in this thread. As wanted to build my own heatbank
too.

Latest diagram I came up with was:
http://aycu27.webshots.com/image/387...2625313_rs.jpg



Also interested as it seems an excellent post-fix to a system with a newish
boiler.

Advantages over (say) a combi would seem to be flow rate but the biggest
combi advantage is infinite capacity (at whatever flow rate one can argue
they deliver).

Web sites for thermal stores don't seem to quote capacity of drawn off hot
water. Let's say (hypothetically) one has a thermal store with a tank of
water of 300l at 80degC and a plate heat exchanger set to deliver DHW at
65degC. At a flow rate of (say) 30l/min, how long does the hot water last
(at that flow rate, boiler heating will be too slow to be significant). Or,
in non scientific units, how many full baths can you run one after the
other? I should be able to work it out,from the physics I guess, but someone
should know!!


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

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

wrote in message
...
- The second improvement is diffuser pipes within the cylinder. I
have a c200litre direct tank [1700x500(dia) mm] double insulated. I
had the tank made to spec to fit the space I have available with a
single top port - a standard BSP 1" male connector. The top connector
takes the flow to the PHE primary and is tee'd off to the FHE tank
overflow. I added 2 essex flanges myself through which I passed my
own diffuser tubes prior to assembley of the flanges into the tank.


Hi, very interested in this thread. As wanted to build my own heatbank
too.

Latest diagram I came up with was:

http://aycu27.webshots.com/image/387...2625313_rs.jpg



Also interested as it seems an excellent post-fix to a system with a
newish boiler.

Advantages over (say) a combi would seem to be flow rate but the biggest
combi advantage is infinite capacity (at whatever flow rate one can argue
they deliver).

This heat bank system has many advantages.

Look at the flow pipe from the boiler into the cylidner. Take this pipe
inside the cylinder and bend it up towarads the DHW draw-off at the top,
terminating inside the dome pointing up. The flow would be sucked into the
plate heat X by the DHW pump. When the store is exhausted of heat the flow
rate will revert to what the boiler can give, which will be a good shower at
least and "never" run out of hot water. This principle is applied to stored
water combis which are two stage: high flow using stored water and low rate
using only the ouput of the boilers burner.

You could use the flow switch to always bring in the boiler always when DHW
is called. This "combines" the output of the boiler and the heat of the
stored water, giving greater capacity - or the cyldiner culd be dopwnsized
using this method. A high limit stat would need to be on the cylinder to cut
out the boiler if the temperature was above 95C.

The diagram uses two CH zones off the store using Wilo Smart pumps. This is
a great advantage, as only 0.5 kW will be drawn-off if need be. All rads
can then have TRVs on them. This increases comfort conditions.

The boiler only heats the store so running without cycling and to maximum
effciency and flow throught it at all times. One of the big problems with
boilers fitted these days, is that the auto-by-pass is incorrectly set,
allowing too much flow through a condensing boiler reducing its efficiency
or in many cases too little flow and reducing the lifespan of the heat
exchanger. A boiler heating a store has no such problems and will outlast
boilers coupled directly to rads with TRVs on the rads. Also a simple,
cheaper, more reliable non-modulating boiler can be fitted.

Web sites for thermal stores don't seem to quote capacity of drawn off hot
water. Let's say (hypothetically) one has a thermal store with a tank of
water of 300l at 80degC and a plate heat exchanger set to deliver DHW at
65degC. At a flow rate of (say) 30l/min, how long does the hot water last
(at that flow rate, boiler heating will be too slow to be significant).
Or, in non scientific units, how many full baths can you run one after the
other? I should be able to work it out,from the physics I guess, but
someone should know!!

Later...

Bob Mannix wrote:

Latest diagram I came up with was:
http://aycu27.webshots.com/image/387...2625313_rs.jpg



Also interested as it seems an excellent post-fix to a system with a newish
boiler.

Depending on the sophistication of the boiler and control systems you
may get better results with the rads driven directly rather than from
the store.

Advantages over (say) a combi would seem to be flow rate but the biggest
combi advantage is infinite capacity (at whatever flow rate one can argue
they deliver).

That is not really any different with a store - at some point once you
have used any stored heat, the rate at which you can draw further heat
from it will be governed by how fast the boiler can replenish it.
However this will equate to a significant drop in delivery rate since
you can draw energy from the store at a rate well above that which you
can get from your gas supply.

Web sites for thermal stores don't seem to quote capacity of drawn off hot
water. Let's say (hypothetically) one has a thermal store with a tank of
water of 300l at 80degC and a plate heat exchanger set to deliver DHW at
65degC. At a flow rate of (say) 30l/min, how long does the hot water last

Say you are drawing 30lpm of water at 60 deg that is being heated from
(say) 5 deg, you require a heating power of (60 - 5) x 4200 x 30 / 60 =
115.5 kW

(at that flow rate, boiler heating will be too slow to be significant). Or,

Not necessarily... if the boiler is kicked in by a flow switch at the
start of the draw off, a 20kW boiler would be replacing a 5th of the
energy used in real time. So you reduce the effective energy transfer
rate from the store to 95.5 kW

in non scientific units, how many full baths can you run one after the
other? I should be able to work it out,from the physics I guess, but someone
should know!!

Lets say you want 200L of 45 deg water for the bath, that means you want
145 l of hot water. It will take 4.8 mins to fill the bath. You have had
33.5MJ out of the store, so at say 20kW (1.2 MJ/min) input it will take
about half an hour to replenish fully. So you can have baths every half
hour indefinitely, or faster for a limited time. Obviously smaller
baths and more powerful boilers can change that picture dramatically.


--
Cheers,

John.

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

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

Latest diagram I came up with was:
http://aycu27.webshots.com/image/387...2625313_rs.jpg



Also interested as it seems an excellent post-fix to a system with a
newish boiler.

Depending on the sophistication of the boiler and control systems you may
get better results with the rads driven directly rather than from the
store.

Advantages over (say) a combi would seem to be flow rate but the biggest
combi advantage is infinite capacity (at whatever flow rate one can argue
they deliver).

That is not really any different with a store - at some point once you
have used any stored heat, the rate at which you can draw further heat
from it will be governed by how fast the boiler can replenish it. However
this will equate to a significant drop in delivery rate since you can draw
energy from the store at a rate well above that which you can get from
your gas supply.

Web sites for thermal stores don't seem to quote capacity of drawn off
hot water. Let's say (hypothetically) one has a thermal store with a tank
of water of 300l at 80degC and a plate heat exchanger set to deliver DHW
at 65degC. At a flow rate of (say) 30l/min, how long does the hot water
last

Say you are drawing 30lpm of water at 60 deg that is being heated from
(say) 5 deg, you require a heating power of (60 - 5) x 4200 x 30 / 60 =
115.5 kW

(at that flow rate, boiler heating will be too slow to be significant).
Or,

Not necessarily... if the boiler is kicked in by a flow switch at the
start of the draw off, a 20kW boiler would be replacing a 5th of the
energy used in real time. So you reduce the effective energy transfer rate
from the store to 95.5 kW

in non scientific units, how many full baths can you run one after the
other? I should be able to work it out,from the physics I guess, but
someone should know!!

Lets say you want 200L of 45 deg water for the bath, that means you want
145 l of hot water. It will take 4.8 mins to fill the bath. You have had
33.5MJ out of the store, so at say 20kW (1.2 MJ/min) input it will take
about half an hour to replenish fully. So you can have baths every half
hour indefinitely, or faster for a limited time. Obviously smaller baths
and more powerful boilers can change that picture dramatically.

Thanks for the calcs- surely it may be slightly better than that though. The
requirement for 145l of hot water might be met twice over by a store
(depending on its size) so one might get 2 baths then wait an hour, which
is, of course the same on average, but practically may be a lot better! It
was the gearing between the size of the store and DHW run-off I was looking
for. Looking at the websites on the PHE, for 80degC store, it would seem
that 150l flow of hot water out of the PHE would need about 100l of water
from the store flowing into it - a 210l or above store would then give two
baths (roughly) before the system is cold (ie not able to perform at full
spec). Does this sound right?


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

Bob Mannix wrote:

in non scientific units, how many full baths can you run one after the
other? I should be able to work it out,from the physics I guess, but
someone should know!!
Lets say you want 200L of 45 deg water for the bath, that means you want
145 l of hot water. It will take 4.8 mins to fill the bath. You have had
33.5MJ out of the store, so at say 20kW (1.2 MJ/min) input it will take
about half an hour to replenish fully. So you can have baths every half
hour indefinitely, or faster for a limited time. Obviously smaller baths
and more powerful boilers can change that picture dramatically.

Thanks for the calcs- surely it may be slightly better than that though. The
requirement for 145l of hot water might be met twice over by a store
(depending on its size) so one might get 2 baths then wait an hour, which
is, of course the same on average, but practically may be a lot better! It

Yup, that is what I meant by "every half hour indefinitely, or faster
for a limited time" ;-)

Although looking again at the figures - you probably can't draw that
much energy out of the store without it impacting the final water temp a
little toward the end...

that 33.5MJ would represent a 26.5 degree store temperature drop without
any replenishment. With 20kW going back in that would be a 22 degree
drop. So the last bit of the bath fill would start to cool very
slightly. If you were sticking 35kW back in then you would only see a 16
degree drop in the store and output temp would be unaffected.

was the gearing between the size of the store and DHW run-off I was looking
for. Looking at the websites on the PHE, for 80degC store, it would seem

Well if you allow a couple of degrees from loss on the PHE, then that
18 degree difference represents (so 300 * 4200 * 18 = 22.7MJ) of energy.
Once you have drawn that and without any replenishment then the output
temp from the PHE will start to fall below 60. That equates to about
100l of drawn water.

that 150l flow of hot water out of the PHE would need about 100l of water
from the store flowing into it - a 210l or above store would then give two
baths (roughly) before the system is cold (ie not able to perform at full
spec). Does this sound right?

Not quite - you can't usefully get all of the energy out of the store
unless you can accept a lower final water temperature. If you say that
the minimum useful temperature of the store water is 50 degrees (to
allow draw off at say 48 deg), and the maximum store temp is 80, then
you have 30 x 4200 x 300 = 37.8 MJ for water heating with a 300l store.

With ground water at 5 degs (i.e. worst case in the winter) and a bath
at 45 final temperature, that gives you no more than 300 / 40 x 30 = 225
l of hot water without replenishment. So with the boiler running, you
can probably just squeeze two deep baths in quick succession out of the
store. You would also need to adjust taps from time to time to allow for
the falling hot water temperature.


--
Cheers,

John.

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

But surely as the boiler is supplying to the top of the cylinder
rather than further down, (and perhaps boiler is better connected
using a surrey flange at top of cylinder), the output of the boiler is
mainly going straight to the PHE. Therefore, although flow rate may
have to be adjusted, you could continue to fill baths infinitely. This
would act like a combi so would just take a bit longer to fill.

On the point of........
"Depending on the sophistication of the boiler and control systems
you
may get better results with the rads driven directly rather than from
the store"

This is something I'm struggling with as boiler is new condensing.

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

Latest diagram I came up with was:
http://aycu27.webshots.com/image/387...2625313_rs.jpg



Also interested as it seems an excellent post-fix to a system with a
newish boiler.

Depending on the sophistication of the boiler and control systems you may
get better results with the rads driven directly rather than from the
store.

Chav, please be quiet and do not comment on things you know sweet FA about.

wrote in message
...

But surely as the boiler is supplying to the top of the cylinder
rather than further down, (and perhaps boiler is better connected
using a surrey flange at top of cylinder), the output of the boiler is
mainly going straight to the PHE. Therefore, although flow rate may
have to be adjusted, you could continue to fill baths infinitely. This
would act like a combi so would just take a bit longer to fill.

On the point of........
"Depending on the sophistication of
the boiler and control systems
you may get better results with the rads
driven directly rather than from the store"

This is something I'm struggling with as boiler is new condensing.

Not a problem. The bottom of the store will be quite cool and condensing
will occur most of boiler run time. Most boilers only modulate to about 7
to 8 kW minimum. Lower than that and boioer cycling occurs. Taking the CH
off the store means that only 0.5 kW can be drawn off the store and no
boiler cycling. Then no auto-by -passes that can affect the boiler,
centralised room stats that cut out the boiler when some rooms may need
heat, etc.

When a boiler is heating rads directly with all rads except one with TRVs
and an auto by-pass fitted, when all or most TRVs close up the auto by-pass
opens up and hot water flows back to the boiler, then the boioer efficiency
drops like a stone.

wrote:
But surely as the boiler is supplying to the top of the cylinder
rather than further down, (and perhaps boiler is better connected
using a surrey flange at top of cylinder), the output of the boiler is
mainly going straight to the PHE. Therefore, although flow rate may
have to be adjusted, you could continue to fill baths infinitely. This
would act like a combi so would just take a bit longer to fill.

Of a sort, yes. However the drop in performance from a 115kW combi to a
(say) a 20kW one will make a dramatic difference in performance: 30 lpm
of 60 degree water down to 9 lpm of 40 degree water. So you could fill
that last bath slowly, but someone expecting shower at the same time is
in for a bit of a shock.

On the point of........
"Depending on the sophistication of the boiler and control systems
you
may get better results with the rads driven directly rather than from
the store"

This is something I'm struggling with as boiler is new condensing.

I note on your schematic you had a blending valve on the boilers return.
Presumably to maintain a minimum return temperature. While this is
common practice where one wants to prevent an older design of boiler
from seeing excessive periods of low return temperatures, it would be
counter productive on a condensing boiler since there is no requirement
to maintain a minimum return temperature. Artificially raising the
apparent return temperature when cooler water is available would just
lower the boilers condensing efficiency. It also adds an extra tapping
to the top of the tank and associated pipework.

If you have a high end "smart" boiler with analogue room temp sensing or
external weather compensation, then you would loose the ability to run
very low flow temperatures through the rads during the milder parts of
the year.

The presence of a big energy store between the boiler and rads can also
affect the performance of the boilers control system since it introduces
a big damping and delaying effect - possibly leading to unexpected
fluctuation of the store temp in response to changing heating loads, and
hence reduction in performance on hot water delivery. You also incur the
cost of the two extra pumps for these circuits.

You need to balance the cost and complexity of all the hardware against
what gains you get (both in performance terms and also running and
maintenance costs). You may well find a decent boiler with a simpler S
Plan+ system driving the rads directly and the store as another zone
would work equally well or better.


--
Cheers,

John.

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

Doctor Drivel wrote:

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

Latest diagram I came up with was:
http://aycu27.webshots.com/image/387...2625313_rs.jpg



Also interested as it seems an excellent post-fix to a system with a
newish boiler.

Depending on the sophistication of the boiler and control systems you
may get better results with the rads driven directly rather than from
the store.

Chav, please be quiet and do not comment on things you know sweet FA about.

LOL!, one could suggest you do the same. You have demonstrated many
times that your lack of grasp of control theory, surpasses even your
famously poor grasp of basic physics.



--
Cheers,

John.

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

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

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

Latest diagram I came up with was:
http://aycu27.webshots.com/image/387...2625313_rs.jpg



Also interested as it seems an excellent post-fix to a system with a
newish boiler.

Depending on the sophistication of the boiler and control systems you
may get better results with the rads driven directly rather than from
the store.

Chav, please be quiet and do not comment on things you know sweet FA
about.

LOL!,

Chav, the man has come here for advice. There are people here who know this
field backwards and their experience does not entail fitting one combi.
Please be quiet and do not comment on things you know sweet FA about.

"John Rumm" wrote in message

This is what happened when know-it-alls think they do actually know
something.

I note on your schematic you had a blending valve on the boilers return.
Presumably to maintain a minimum return temperature. While this is common
practice where one wants to prevent an older design of boiler from seeing
excessive periods of low return temperatures,

Chav, it is to maintain a high flow temperature into the thermal store for
DHW purposes. The CH section of the cylinder need not have the return
blending valve on the flow/return. It also keeps the boiler within its delta
T ensuring correct operation and longevity of the heat exchanger..

it would be counter productive on a condensing boiler since there is no
requirement to maintain a minimum return temperature.

There is a requirement to maintain a Deta T on all boilers

Artificially raising the apparent return temperature when cooler water is
available would just lower the boilers condensing efficiency.

DHW has to be....well hot. And there is no getting away from the fact that
the return temp will rise to create DHW. The Blending valve may be set to
50C with a boiler giving a 25C temperature rise. Many stores may run at 70C
comfortably as plate Heat Xs are so efficient. That is a return temp of 45C,
which is very efficient.

If you have a high end "smart" boiler with analogue room temp sensing or
external weather compensation, then you would loose the ability to run
very low flow temperatures through the rads during the milder parts of the
year.

No boiler modulates very low and they all cycle. He can fit a weather
compensator to the CH section of the cylinder and lower and raise that water
body to maintain outside weather influence and this will result in very low
return boiler temperatures being created.

snip a load of ill-informed crap!!!

Doctor Drivel wrote:

a load of ill-informed crap!!!

Par for the course...


--
Cheers,

John.

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

I note on your schematic you had a blending valve on the boilers return.
Presumably to maintain a minimum return temperature. While this is
common practice where one wants to prevent an older design of boiler
from seeing excessive periods of low return temperatures, it would be
counter productive on a condensing boiler since there is no requirement
to maintain a minimum return temperature. Artificially raising the
apparent return temperature when cooler water is available would just
lower the boilers condensing efficiency. *It also adds an extra tapping
to the top of the tank and associated pipework.

Blending valve added as it was suggested on the original thread that
the temperature difference between the boiler flow and return should
be around the 20 deg mark to allow optimum condensing. To be fair,
when I asked DPS for a quote, they included a blending valve too on
their spec. In fact they said it should be a 28mm version for boilers
of 20KW as the internal parts on a 22mm were too small.



If you have a high end "smart" boiler with analogue room temp sensing or
external weather compensation, then you would loose the ability to run
very low flow temperatures through the rads during the milder parts of
the year.

The presence of a big energy store between the boiler and rads can also
affect the performance of the boilers control system since it introduces
a big damping and delaying effect - possibly leading to unexpected
fluctuation of the store temp in response to changing heating loads, and
hence reduction in performance on hot water delivery. You also incur the
cost of the two extra pumps for these circuits.

It was considered better to use pumps rather than zoning valves due to
reliability.


In all honesty, I just want a good mains presure system that will
supply enough hot water for 2 showers running at once, where I don't
have to wait 30min+ to refill a bath and that ideally gives me 2
zones(upstairs and downstairs). I have a new 28KW condensing system
boiler and now need a cylinder. Don't want to pay £1300+ from DPS for
same design as you see here (and that's kit form and no metal casing
round the copper cylinder to make it look pretty either !) and don't
want an unvented. Had liked the idea of CH off the store but really
only due to the fact that the contents of the store could be dumped
into the rads for instant heat.If I could get something for around
£800 I think I'd be happy!!!

wrote:
I note on your schematic you had a blending valve on the boilers return.
Presumably to maintain a minimum return temperature. While this is
common practice where one wants to prevent an older design of boiler
from seeing excessive periods of low return temperatures, it would be
counter productive on a condensing boiler since there is no requirement
to maintain a minimum return temperature. Artificially raising the
apparent return temperature when cooler water is available would just
lower the boilers condensing efficiency. It also adds an extra tapping
to the top of the tank and associated pipework.

Blending valve added as it was suggested on the original thread that
the temperature difference between the boiler flow and return should
be around the 20 deg mark to allow optimum condensing. To be fair,
when I asked DPS for a quote, they included a blending valve too on
their spec. In fact they said it should be a 28mm version for boilers
of 20KW as the internal parts on a 22mm were too small.

Yup, that I what I thought it looked like they were trying to do... It
makes good sense on a fixed output boiler, and especially on a non
condenser. Not so sure it adds much with a condenser that will modulate
to lower return temperatures, and will give best condensing performance
with the lowest return temperature available....

As an aside, have you considered using a indirect store with a fast
recovery coil carrying the primary heating water? That would allow the
use of a sealed system primary to drive the rads and the store. Would do
away with the header tank as well. You could then have a quite simple
system that would also provide the hot water performance you want
without needing an unvented cylinder.

It was considered better to use pumps rather than zoning valves due to
reliability.

Simple two port valves seem quite reliable if exercised from time to
time during the summer...

In all honesty, I just want a good mains presure system that will
supply enough hot water for 2 showers running at once, where I don't
have to wait 30min+ to refill a bath and that ideally gives me 2
zones(upstairs and downstairs). I have a new 28KW condensing system

Yup, makes sense. Since you have the modern boiler, and I take it you
have enough cold mains flow rate available, I would be inclined to leave
the rads driven directly by the boiler (in their own zones). With a prog
stat per zone and TMVs on the rads you are going to end up with pretty
good efficiency and performance anyway on the space heating. Even if the
boiler does cycle a little when the house is warmed up, that is far less
of an issue with modern low water content boilers.

boiler and now need a cylinder. Don't want to pay £1300+ from DPS for
same design as you see here (and that's kit form and no metal casing
round the copper cylinder to make it look pretty either !) and don't
want an unvented. Had liked the idea of CH off the store but really
only due to the fact that the contents of the store could be dumped
into the rads for instant heat.If I could get something for around
£800 I think I'd be happy!!!

Its easy to end up adding more and more complexity to these solutions
and before long the parts bill alone is scary (something you have to
watch with Dr. Dribble's designs - they soon end up with half the
contents of the BES catalogue used in there somewhere!)

--
Cheers,

John.

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

As an aside, have you considered using a indirect store with a fast
recovery coil carrying the primary heating water? That would allow the
use of a sealed system primary to drive the rads and the store.

I have considered using another PHE to heat the store(particularly as
my boiler is ideally supposed to work on sealled systems but will
apparently work on vented if pressure sensor is disconnected). Thought
this better than coil as can be cleaned easily if necessary. Also I
assume order of efficiency is coil,PHE and best is heat store direct.


Would do
away with the header tank as well. You could then have a quite simple
system that would also provide the hot water performance you want
without needing an unvented cylinder.


Wouldn't I still need the tank as
a) stored water will still expand
b) stored water will need topping up from time to time?

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

Yup, that I what I thought it looked like they were trying to do... It
makes good sense on a fixed output boiler, and especially on a non
condenser. Not so sure it adds much with a condenser that will modulate to
lower return temperatures,

Chav, you really haven't a clue, even after an explanation. It guarantees
the highest temperature set so only very hot water enters the store at the
top of the cylinder ready for use to give useful DHW, even after 2 minutes
of running from cold a sink can be filled. It also guarantees the boiler is
operating within its delta T and maximises thermal expansion. It guarantees
top down heating of the store and the water is heater one pass of the boiler
quickening the re-heat. It also increases boiler longevity as the boiler is
operating in an ideal hydraulic environment.

snip ill-informed tripe

It was considered better to use pumps rather than zoning valves due to
reliability.

Simple two port valves seem quite reliable if exercised from time to time
during the summer...

Again the ignorance abounds. Having the two pumps means the CH zones are
fully independent (one has no effect on the other which is not the case when
using one pumps and zone valves) of each other as they both go back to the
neutral point - the store - which means superior balancing of rads and that
two smart pumps may be used using TRVs on "all" rads. Also the pumps can
inject even 0.25 kW into their respective CH zones, increasing comfort.

In all honesty, I just want a good mains presure system that will
supply enough hot water for 2 showers running at once, where I don't
have to wait 30min+ to refill a bath and that ideally gives me 2
zones(upstairs and downstairs). I have a new 28KW condensing system

Yup, makes sense. Since you have the modern boiler, and I take it you have
enough cold mains flow rate available, I would be inclined to leave the
rads driven directly by the boiler (in their own zones).

That is because you know sweet FA about thermal storage and heating systems.

With a prog stat per zone and TMVs on the rads you are going to end up
with pretty good efficiency and performance anyway on the space heating.
Even if the boiler does cycle a little when the house is warmed up, that
is far less of an issue with modern low water content boilers.

The boiler still cycles, and the auto by-pass will eventually restrict flow
through the boiler as it wears or open up too early and elinminates
condensing as a direct short cut is created.

boiler and now need a cylinder. Don't want to pay £1300+ from DPS for
same design as you see here (and that's kit form and no metal casing
round the copper cylinder to make it look pretty either !) and don't
want an unvented. Had liked the idea of CH off the store but really
only due to the fact that the contents of the store could be dumped
into the rads for instant heat.If I could get something for around
£800 I think I'd be happy!!!

Having the CH zones off the store is a great bonus. Having the boiler only
heat the heat bank cylinder is great bonus.

The store is a great neutral point. Each function of the system can be
isolated and optimised and one does not influence the other. The boiler is
de-coupled and optimised for performance. As are the CH zones, as is the DHW
take off too. The boiler can be optimised for condensing efficiency - heat
bank setpoint of 70C and return temperature of 45C. This means the boiler
condenses the vast majority of run time and operates in an ideal hydraulic
environment.

Forget all this tripe that a modulating boiler is the best option coupled to
rads. It may be if it modulates from 0kW to 27kW and no TRVs on the rads.
As no boiler goes down to 0kW that will not happen. The auto by-pass screws
up efficiency performance and the cycling reduces reliability putting
heavier demand on controls. The auto by-pass can screw up the heat exchanger
is not enough flow is allowed through the rad.

Most of the time a boiler is on part load, and this means a lot of the time
the auto by-pass valve is open eliminating condensing competely with
efficiency dropping like a stone.

snip ill-informed tripe by Chav!

wrote in message
...

I have considered using another
PHE to heat the store (particularly as
my boiler is ideally supposed to work
on sealled systems but will apparently
work on vented if pressure sensor is
disconnected).

I assume you mean the low pressure sensor. See this:
http://www.copperform.co.uk/mains_pr...flow/index.htm

This is a pressurised store running at 2.5 bar, so the boiler will operate
fine. Can be DIYed using plate heat Xs. They may make one to order without
the coil and insert the tapping where you want.

Thought this better than coil as can be
cleaned easily if necessary. Also I
assume order of efficiency is coil,PHE
and best is heat store direct.

I think you mean in reverse order. The coil is way less efficient than a
plate heat X. Direct is the ultimate.

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

Yup, that I what I thought it looked like they were trying to do... It
makes good sense on a fixed output boiler, and especially on a non
condenser. Not so sure it adds much with a condenser that will modulate
to lower return temperatures,

Chav, you really haven't a clue, even after an explanation. It guarantees
the highest temperature set so only very hot water enters the store at the
top of the cylinder ready for use to give useful DHW, even after 2 minutes
of running from cold a sink can be filled. It also guarantees the boiler
is operating within its delta T and maximises thermal expansion. It
guarantees top down heating of the store and the water is heater one pass
of the boiler quickening the re-heat. It also increases boiler longevity
as the boiler is operating in an ideal hydraulic environment.


["Chav" is a stupid and judgemental term and I do not wish to be asscoiated
with it.] On the other hand, DD's explanation for the blending valve seems
plain common sense and was part of my assumption. Also these thermal store
systems only work well (high hot water flow) if the primary side of the PHE
(and hence the store itself) is at a very high temperature (75-90degC). This
can only be achieved by subtracting the boiler's maximum delta-T from the
desired temperature and ensuring the answer is used as the set point for the
return water. The condensing efficiency argument is irrelevant as the whole
system won't work without the higher than normal return temperature.


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

wrote:
As an aside, have you considered using a indirect store with a fast
recovery coil carrying the primary heating water? That would allow the
use of a sealed system primary to drive the rads and the store.

I have considered using another PHE to heat the store(particularly as
my boiler is ideally supposed to work on sealled systems but will
apparently work on vented if pressure sensor is disconnected). Thought
this better than coil as can be cleaned easily if necessary. Also I
assume order of efficiency is coil,PHE and best is heat store direct.

Another PHE would do the trick quite nicely. While these are not cheap,
you would not need such a large one for this application since the
boiler power is the limiting factor here. You may even save equal or
more money by not needing an expensive cylinder with fast recovery coil.
(any direct tank could be used). Water to water PHEs are quite efficient
so you would not loose much if anything over pumping the primary through
a direct store.

Would do
away with the header tank as well. You could then have a quite simple
system that would also provide the hot water performance you want
without needing an unvented cylinder.


Wouldn't I still need the tank as
a) stored water will still expand

Your system boiler will already include an expansion vessel designed to
cope with the expansion of the primary circuit. The water in the store
itself will also expand and contract, but this does not need to be
hermetically sealed and can have a small expansion gap at the top
(assuming your pumped PHE connections are via side tappings on Essex
flanges).

b) stored water will need topping up from time to time?

It can be filled from a hose (or suitably positioned fixed pipework and
tap of some sort). The only route of water loss from it will be via
evaporation.

--
Cheers,

John.

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

"Bob Mannix" wrote in message
...

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

Yup, that I what I thought it looked like they were trying to do... It
makes good sense on a fixed output boiler, and especially on a non
condenser. Not so sure it adds much with a condenser that will modulate
to lower return temperatures,

Chav, you really haven't a clue, even after an explanation. It
guarantees the highest temperature set so only very hot water enters the
store at the top of the cylinder ready for use to give useful DHW, even
after 2 minutes of running from cold a sink can be filled. It also
guarantees the boiler is operating within its delta T and maximises
thermal expansion. It guarantees top down heating of the store and the
water is heater one pass of the boiler quickening the re-heat. It also
increases boiler longevity as the boiler is operating in an ideal
hydraulic environment.


["Chav" is a stupid and judgemental term and I do not wish to be
asscoiated with it.]

A Chav is a Chav and he is one. And like you I want nothing to do with
them. All those tattoos and heavy jewellery!

On the other hand, DD's explanation for the blending valve seems plain
common sense and was part of my assumption. Also these thermal store
systems only work well (high hot water flow) if the primary side of the
PHE (and hence the store itself) is at a very high temperature
(75-90degC).

Nope. Plate heat exchangers are so efficient (and some are better than
others, like the Danfoss two-pass and the Swep used by Gledhill), that a
store temperature of 65C can be set and they will give more than adequate
DHW. The higher the temperature the more energy stored and the smaller the
cylinder, the lower the temp the larger the water store.

The condensing efficiency argument is irrelevant as the whole system won't
work without the higher than normal return temperature.

More old wives tales. A longish cylinder ensures that the bottom of the
cylinder has "very" low temperatures - superior stratification. Plate heat
Xs are so efficient at extracting heat the return temperature from them will
be 30C and below.

Thermal stores using an immersed coil DHW take off require higher
temperatures because the coils are so inefficient to a plate heat OX.

A well designed CH & DHW heat bank knocks cobs off a direct to the rads
boiler CH system. They are very efficient and highly reliable.

The design presented is a good one. If the points I suggested to improve
are implemented and the CH section heated direct not via a return blending
valve (a 3-way diverter valve is needed) a weather compensator controlling
in the water temperature in the CH section of the store the efficiency will
be "very" high.

Heat bank - plate heat X DHW
thermals store = immersed coil DHW

"John Rumm" wrote in message
...
wrote:
As an aside, have you considered using a indirect store with a fast
recovery coil carrying the primary heating water? That would allow the
use of a sealed system primary to drive the rads and the store.

I have considered using another PHE to heat the store(particularly as
my boiler is ideally supposed to work on sealled systems but will
apparently work on vented if pressure sensor is disconnected). Thought
this better than coil as can be cleaned easily if necessary. Also I
assume order of efficiency is coil,PHE and best is heat store direct.

Another PHE would do the trick quite nicely. While these are not cheap,
you would not need such a large one for this application since the boiler
power is the limiting factor here. You may even save equal or more money
by not needing an expensive cylinder with fast recovery coil. (any direct
tank could be used). Water to water PHEs are quite efficient so you would
not loose much if anything over pumping the primary through a direct
store.

It is cheaper, far more efficient in economy, and far quicker using a plate
heat X and bronze pump heating up a large direct cylinder. 95% plus of the
boilers heat is extracted via the plate and put into the fresh water in the
cylinder.

Here is an off-the-shelf model:
http://www.mcdonald-engineers.com/products/plateflow.htm

Would do
away with the header tank as well. You could then have a quite simple
system that would also provide the hot water performance you want
without needing an unvented cylinder.


Wouldn't I still need the tank as
a) stored water will still expand

Your system boiler will already include an expansion vessel designed to
cope with the expansion of the primary circuit. The water in the store
itself will also expand and contract, but this does not need to be
hermetically sealed and can have a small expansion gap at the top
(assuming your pumped PHE connections are via side tappings on Essex
flanges).

b) stored water will need topping up from time to time?

It can be filled from a hose (or suitably positioned fixed pipework and
tap of some sort). The only route of water loss from it will be via
evaporation.

You are describing a DPS Pandora. They have a few safety controls on that
and a deflated expansion vessel on the top of the cylinder.

Bob Mannix wrote:

On the other hand, DD's explanation for the blending valve seems
plain common sense and was part of my assumption. Also these thermal store
systems only work well (high hot water flow) if the primary side of the PHE
(and hence the store itself) is at a very high temperature (75-90degC). This
can only be achieved by subtracting the boiler's maximum delta-T from the
desired temperature and ensuring the answer is used as the set point for the
return water. The condensing efficiency argument is irrelevant as the whole
system won't work without the higher than normal return temperature.

The blending valve will indeed keep the boiler flow hotter (at least in
the early recovery stages after heavy demands have been made on the
store, and assuming you have very well controlled stratification in the
store), but there are many interacting variables and trade-offs here.
These are at their most complex with a directly heated store since you
can't control the heating load presented to the boiler as easily. It is
worth bearing in mind that this design is being proposed for use with a
modern modulating, condensing boiler that supports wide temperature
deltas. The whole "thermal store with everything hung off it" design
concept is very well suited to older boiler designs where long burns,
reduced cycling, high flow temps (and maintained above a threshold
return temps) are all "good things". Hence you have a nice "rule of
thumb" solution to a number of problems. The whole situation is much
less clear cut here.

Dribble is right that running rads from the store will let them run at
low powers, which was a big gain when the alternative was 20kW or
nothing and a mechanical stat overseeing the outer loop control. When
the choice is anything from 7[1] to 28kW or nothing and tighter outer
loop control, you are not going to notice much difference in a typical
house with a few kW of heat losses.

([1] number picked at random - I don't know how low the OPs boiler will
modulate).

Higher store temps are obviously good from an overall energy density
point of view, but less good from a condensing efficiency one. The
temperature you set for your hot water take off also has a big impact
since it dictates how much headroom you have under the store
temperature, and when falling store temperature will start to impact on
the HW temperature. Opting for water at a temperature close to that of
final use, and with less mixing at the point of use, will give more
consistent water temperature output form the store with less worries
about maintaining high and well stratified store temperatures.

With the modern boiler, the most efficient way to get the high flow temp
is to take advantage of a bigger delta T. If your boiler supports
analogue control, then even better. You can select higher temps for
replenishing the store, and much lower ones for running the heating
(which is where you will probably spend most of your money - and so
efficiency is of greatest importance).



--
Cheers,

John.

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

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

"John Rumm" wrote in message
...
wrote:
As an aside, have you considered using a indirect store with a fast
recovery coil carrying the primary heating water? That would allow the
use of a sealed system primary to drive the rads and the store.

I have considered using another PHE to heat the store(particularly as
my boiler is ideally supposed to work on sealled systems but will
apparently work on vented if pressure sensor is disconnected). Thought
this better than coil as can be cleaned easily if necessary. Also I
assume order of efficiency is coil,PHE and best is heat store direct.

Another PHE would do the trick quite nicely. While these are not cheap,
you would not need such a large one for this application since the boiler
power is the limiting factor here. You may even save equal or more money
by not needing an expensive cylinder with fast recovery coil. (any direct
tank could be used). Water to water PHEs are quite efficient so you would
not loose much if anything over pumping the primary through a direct
store.

It is cheaper, far more efficient in economy, and far quicker using a
plate heat X and bronze pump heating up a large direct cylinder. 95% plus
of the boilers heat is extracted via the plate and put into the fresh
water in the cylinder.

Here is an off-the-shelf model:
http://www.mcdonald-engineers.com/products/plateflow.htm

This also is a two-stage DHW delivery too. If he cylinder is exhausted of
heat it reverts to what the boiler gives like a combi. If no draw-off it
just re-heats the cylinder. So, even better performance from using a plate
rather than a coil.