wrote in message
...

Funny you should mention that. The kitchen is a long way from the
boiler so I was going to bung a Santon in there with a feed to the
downstairs loo and probably the utility room.

You can have a DHW secondary circulation loop from the combi/heat bank.
Have the combi pre-heat the heat bank plate heat X. From the plate take a
loop back to the inlet side of the plate (between plate & combi). Have the
plate flow switch before the combi on the cold inlet. Have two check valves
where the loop tees between the plate and the combi to prevent back
circulation into the combi. The loop only circulates through the plate. Do
not have check valve on the circuit from heat bank to the plate. This is to
allow natural circulation through the plate. The loop then takes this heat
and heat the whole loop. A bronze pump on the loop where it tees between
the combi and plate. Draw it out.

Disadvantage: If a weather compensator has the heat bank temp as say 30C and
the combi gives 60C then dropping of DHW temp.

Worth at this stage reviewing the plus points and Neg points. My
proposed systemis:

Heatbank for CH with 3/4 pumped zones off it. HB cylinder VERY well
insulated

Heated by condensing combi

Via quick recovery coil or plate and pump (which may be cheaper than a quick
recovery coil and quicker too.

DHW preheated by PHE off Heatbank before going through Combi

Have the combi pre-heat the plate. Using a combi and a heat bank gives
backup if the combi or heat bank is down. If the heat produced by the combi
is not used by plate the heat is pumped into the heat bank.

Cold water to basins, WCs and baths from loft tanks with slow running
ball-cocks.

Basins can have mixers. Not required on bath.

Mains CW to shower and Kitchen.

Santon Aquaheat in in cellar under kitchen.

See above, DHW loop.

Advantages:
CH - very efficient use of boiler. Heat bank can be at optimum
temperature for CH and available for CH when combi heating DHW or off
(until HB run down)

Decent combi not much more than a decent vented system boiler.

True. Look at the Keston - may be open vented using a combi, ring makers.

Capital outlay of system kept under control

For low use of hot water (95% of time - two baths and a shower per
day) saves keeping HB hot.
During 5/12 when CH not on either no pre-heat of DHW or minimal
occasional warming of heatbank only necessary to take the edge off and
give good flow.

If house full for a weekend. Merely juice up the HB for good flow
through the combi Via the PHE.

Instant HW which never runs out even if the HB is exhausted or breaks
down.

DHW available via HB and immersion if boiler breaks down. Also some
CH though expensive.


Disadvantages:

Er... DD etal please fill in.

None really as you have backup. A heat bank only will give higher DHW
flowrates. The combi is not guaranteed high flowrates as the pre-heat
temperature is not guaranteed all year around. In summer the heat bank will
pre-heat a little. You could have solar panels heating the bank too, giving
free heat to pre-heat.

Thanks again for your excellent help with this project.

Thanks for that.

Keston say they don't do a combi that will work unvented but no
problem.

Most of the ones I've looked at seem to tolerate a high input
temperature for the CW supply eg 50C.

One thing that might spoil the party a bit would be a flow restrictor
in the boiler that couldn't be opened enough or was fixed. This might
limit the flow through the combi's own HE even when there was still
some slack in th Delta T.

I like the Keston Combi but don't need 36KW
Boderus we've mentioned as possible. I has an adjustable flow
regulator.

One thing I can't seem to get a straight answer from on the data
sheets is the extent or otherwise to which condensing combis condense
when they are in DHW mode.

Are some better that others in this respect.

Many thanks again,

Nearly there I think...

wrote in message
...
Thanks for that.

Keston say they don't do a combi that will work unvented but no
problem.

The Atmos may do. The Keston uses they same heat exchanger on the combi as
on the vented boilers, as does the Atmos. The combi version is packaged
with the pressure vessel etc.

Most of the ones I've looked at seem to tolerate a high input
temperature for the CW supply eg 50C.

One thing that might spoil the party a bit would be a flow restrictor
in the boiler that couldn't be opened enough or was fixed. This might
limit the flow through the combi's own HE even when there was still
some slack in th Delta T.

I like the Keston Combi but don't need 36KW
Boderus we've mentioned as possible. I has an adjustable flow
regulator.

One thing I can't seem to get a straight answer from on the data
sheets is the extent or otherwise to which condensing combis condense
when they are in DHW mode.

Are some better that others in this respect.

It depends on the DHW temp set at the combi, 45C condenses more than say
60C, the power of the combi and the incoming cold water temp. It may be
sending back to the main heat X from the combi plate heat X water temp that
is above dew-point (54C). I may be sending water back below 54C. If
pre-heated water is about 50C it will condense little. But the main heat X
is bigger than normal so it is more efficient than a non-condensing boiler.

Having the combi pre-heat the cold water running fast through the combi and
then into the heat bank DHW plate heat X, will mean it will be in condensing
most of the time as the water entering is cold and the water leaving the
combi is "warm" pre-heated water.

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

wrote in message
...
Thanks for that.

Keston say they don't do a combi that will work unvented but no
problem.

The Atmos may do. The Keston uses they same heat exchanger on the combi
as on the vented boilers, as does the Atmos. The combi version is
packaged with the pressure vessel etc.

Most of the ones I've looked at seem to tolerate a high input
temperature for the CW supply eg 50C.

One thing that might spoil the party a bit would be a flow restrictor
in the boiler that couldn't be opened enough or was fixed. This might
limit the flow through the combi's own HE even when there was still
some slack in th Delta T.

I like the Keston Combi but don't need 36KW
Boderus we've mentioned as possible. I has an adjustable flow
regulator.

One thing I can't seem to get a straight answer from on the data
sheets is the extent or otherwise to which condensing combis condense
when they are in DHW mode.

Are some better that others in this respect.

It depends on the DHW temp set at the combi, 45C condenses more than say
60C, the power of the combi and the incoming cold water temp. It may be
sending back to the main heat X from the combi plate heat X water temp
that is above dew-point (54C). I may be sending water back below 54C. If
pre-heated water is about 50C it will condense little. But the main heat
X is bigger than normal so it is more efficient than a non-condensing
boiler.

Having the combi pre-heat the cold water running fast through the combi
and then into the heat bank DHW plate heat X, will mean it will be in
condensing most of the time as the water entering is cold and the water
leaving the combi is "warm" pre-heated water.

Having the combi pre-heat cold water mean that temperature in the heat bank
may be lower, say 65C, as it has to do less work. This again promotes
condensing efficiency. If the heat bank is to be heated using a weather
compensator then this does not apply.

The heat bank, say set at 65C and supplying rads at 65C (size rads to suit
with delta T across the rads of 20C), will mean a cheaper non-weather
compensator boiler may be used and condensing efficiencies are guaranteed in
DHW and CH.

DD, Thanks for that.

Very useful information on condensing. Thanks.

Interesting to consider pre-heating the DHW in the combi and then up
to final temp using the Heat Bank.

I can see that would be better from a condensing point of view for the
reasons you've described.


As you know I intended doing it the other way round - take the edge
off with some energy from the HB and then a quick final blast in the
combi.

I can see your point though. Perhaps we are into a summer/winter
setting thing:

If the HB needs to be at 65C to do the CH - I was hoping it could be a
bit lower but I see it depends on radiator size and outside temp as
well as house heat loss - then it could do the bulk of the DHW temp
rise in the winter. In the summer either the HB does nothing if the
incoming water is warm enough or, if the flow is inadequate, then the
occasional warming of the HB just enough to raise the mains water up
say 10C should do the trick. I assume that if the HB is really well
insulated and the temp differential between the water inside and the
outside is small then it will stay warm enough to only require a quick
burst every couple of days.

Thanks again,

Frank

wrote in message
...
DD, Thanks for that.

Very useful information on condensing. Thanks.

Interesting to consider pre-heating
the DHW in the combi and then up
to final temp using the Heat Bank.

I can see that would be better from a
condensing point of view for the
reasons you've described.

As you know I intended doing it the
other way round - take the edge
off with some energy from the HB
and then a quick final blast in the
combi.

Draw out and think through both setups. List advantage and disadvantages.
It gets clearer when you do that. You could stage it, 1st stage, the
combi, 2nd the heat bank. The combi always cuts in. A two-port modulating
valve on the cold into the HB DHW plate . The two DHW outlets of the plate
and the combi combine . The DHW temp for the two-port valve is after the
tee. When all cold except the HB is charged, the taps is opened the HB cut
in as the valve is fully open, as does the combi. When the DHW temps say is
approaching 50C the valve closes and reduces the flow from the heat bank.
want high flows by opening the taps up and the valve opens up. low flows and
the valve close off. Flow regulators could be on each line: combi and HB
DHW plate, to ensure say 10 litres/min on each leg, giving say 20 max. It
may take a bit of setting to balance between the two.

I can see your point though. Perhaps we are into a summer/winter
setting thing:

If the HB needs to be at 65C to do the CH
- I was hoping it could be a
bit lower but I see it depends on radiator
size and outside temp as well as house
heat loss - then it could do the bulk of
the DHW temp rise in the winter.

Try and size the rads 60-40, and balance them to suit. Then a 60C HB temp.

In the summer either the HB does nothing if the
incoming water is warm enough or, if the flow
is inadequate,

It depends on what temp you set it to. If coming in at 18C and you need 30
C to supplement the combi to run off a bath, then the HB will need heating
to 35 to 40C.

If the combi pre-heats, and the DHW tap temp is set to say 47C, then the HB
would need to be 52ishC in summer, maybe less. If low flows because a
basin is on the combi will that and just sent DHW up to temp through the HB
plate.

The DHW secondary loop with three or four 15 litre electric storage heaters
on the loop may solve many things. Gives enough flow, electric backup if all
on and the combi, it could give say an extra 12kW supplementing say 38kW of
the combi. If large volume of water are needed of course, say like when
visitors are in and are in the showers at the same time. This maintains DHW
temps throughout summer and winter and gives 45 to 60 litres of DHW storage,
that the combi automatically tops up.

Then the cylinder is only a simple CH buffer with electric backup. 9kW
immersions are available.

then the occasional warming of
the HB just enough to raise the mains water up
say 10C should do the trick.

I assume that if the
HB is really well insulated and the temp differential
between the water inside and the outside is
small then it will stay warm enough to only require a quick
burst every couple of days.

Yep.

DD

Plenty more to think about. Thanks.

I'll get back once I've got it all straight.

Thanks again.

Frank.

wrote:

One thing I can't seem to get a straight answer from on the data
sheets is the extent or otherwise to which condensing combis condense
when they are in DHW mode.

That is because many don't, and also this is something not included in
the sedbuk rating. The ones that do often make a point of talking about
in the blurb.

Are some better that others in this respect.

Yup.

--
Cheers,

John.

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

Thanks JR,

I'll check that out. Have you any makes/models in mind.

Frank.

wrote:
Thanks JR,

I'll check that out. Have you any makes/models in mind.

Don't think you can split by make... for example there are some
superficially similar WB models like the CDi and the Si where IIRC one
of the differences was that one did condense on HW production and the
other not.

Some are listed in the second table he

http://wiki.diyfaq.org.uk/index.php?...iler_Evolution


--
Cheers,

John.

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

Thanks for that further JR,

I am closely investigating the various boiler options.

DD: you mentioned 'two port modulating valve' I assume this is just
a normal two ort valve with a suitable thermostat strapped to the pipe
as suggested and connected together appropriately.

Or is it a special bit of kit.

Also several times suggested 'bronze pumps' I see they cost more ++.
What exactly are the benefits?

Service life I assume but anything else?

Thanks again,

Frank

wrote in message
...
Thanks for that further JR,

I am closely investigating the various boiler options.

DD: you mentioned 'two port modulating valve' I assume this is just
a normal two ort valve with a suitable thermostat strapped to the pipe
as suggested and connected together appropriately.

Or is it a special bit of kit.

It is specialist. Usually with remote temp pipe sensor and a valve that
"modulates". Danfoss make them.

Also several times suggested 'bronze pumps' I see they cost more ++.
What exactly are the benefits?

They operate on fresh water, otherwise the same. Ebay sell them cheaper.

Hi again DD & JR from Frank.

Been away. Thanks for the further info. I've searched for the
Danfoss modulating two port valve but have had no luck. If someone
had a URL that would handy.

I see about the bronze pump now. No rust inhibitor in fresh water so
needs to be made of non-ferrous material.

Thanks again.

Soon be time to p**s or get off the pot on this project. I'll let you
know what level of complexity/flexibility/expense I am going to opt
for.

Any further comments very welcome.

Frank

wrote in message
...
Hi again DD & JR from Frank.

Been away. Thanks for the further info. I've searched for the
Danfoss modulating two port valve but have had no luck. If someone
had a URL that would handy.

Look at:
http://heating.danfoss.com/Content/adb19c5f-8aec-4552-a913-d5e21ac5f6c5_MNU17402280_SIT54.html

I see about the bronze pump now. No rust inhibitor in fresh water so
needs to be made of non-ferrous material.

Thanks again.

Soon be time to p**s or get off the pot on this project. I'll let you
know what level of complexity/flexibility/expense I am going to opt
for.

Any further comments very welcome.

Frank

Thanks for the URL above. Very helpful diagrams.

Looking at the UK site:

http://danfoss-randall.co.uk/xxTypex...04_SIT313.html

http://danfoss-randall.co.uk/xxTypex...03_SIT313.html


it seems that the nearest equivalent is a VMT (two way seated valve)
22mm plus a RAVK (self acting thermoststic element (25-65C). These
together plus vat and carriage come to £149:00 via city plumbing. So
not totally out of the question for setting the DHW temp out of the
PHE. The valve goes on the inlet to the Heatbank side of the PHE and
the sensor on the DHW outflow from the PHE. Okay there will be a bit
of a control lag due to the water in the PHE at any given time but I
suspect the volume of water held in the PHE is very small by nature
of the design of the device.

Using this I could ensure that the water entering the combi to have
it's heat topped up can be kept at a reasonably constant temperature
anywhere in the range up to the temp of the HB. Imagine the HB will
be about 65 perhaps less and the water temp into the combi about 30C
all year. Limiting factor will be how fast a 30kw Glowworm can shove
the water through with -say- a 20C temperature rise.

Any guesses? Quoted Lpm @ DT of 35C is 12.3 so for a DT of 20/25...
I know this won't be very efficient from a condensing POV but it is
the CH that will take the vast majority of the energy and that will be
very efficient.

Result? Good flow from the combi whatever the season without having
to have the HB temp higher than needed for the CH. In the summer the
HB only needs to be topped up occasionally to a very modest
temperature every couple of days (approx 30C) to ensure good DHW flow.

Seems a good compromise on complexity/flexibility/expense graph.

BTW Danfoss want to know if I want a Kvs of 5 or 2.3 on the VMT. I
don't know what this is though it might be maximum flow rate as it is
cubic m/H

Comments please.

Thanks again,

Frank

wrote in message
...
Thanks for the URL above. Very helpful diagrams.

Looking at the UK site:

http://danfoss-randall.co.uk/xxTypex...04_SIT313.html

http://danfoss-randall.co.uk/xxTypex...03_SIT313.html


it seems that the nearest equivalent is a VMT (two way seated valve)
22mm plus a RAVK (self acting thermoststic element (25-65C). These
together plus vat and carriage come to £149:00 via city plumbing. So
not totally out of the question for setting the DHW temp out of the
PHE. The valve goes on the inlet to the Heatbank side of the PHE


Do you mean the cold mains inlet?


and the sensor on the DHW outflow from the PHE. Okay there will be a bit
of a control lag due to the water in the PHE at any given time but I
suspect the volume of water held in the PHE is very small by nature
of the design of the device.

Using this I could ensure that the water entering the combi to have
it's heat topped up can be kept at a reasonably constant temperature
anywhere in the range up to the temp of the HB. Imagine the HB will
be about 65 perhaps less and the water temp into the combi about 30C
all year. Limiting factor will be how fast a 30kW Glowworm can shove
the water through with -say- a 20C temperature rise.


The valve can take 10 bar so fine on the mains - check this with Danfoss.
How about having the 2-port valve on the cold feed to the Plate heat X,
which feeds the combi and have the temperature sensor on the DHW outlet of
the combi. Some testing would be needed, but it is a simple task of moving
the temp sensor between the plate and combi if the flow and temperature on
the outlet fluctuates.


Any guesses? Quoted Lpm @ DT of 35C is 12.3 so for a DT of 20/25...
I know this won't be very efficient from a condensing POV but it is
the CH that will take the vast majority of the energy and that will be
very efficient.


at 20C temp rise about 15/16 litres/min.


Result? Good flow from the combi whatever the season without having
to have the HB temp higher than needed for the CH. In the summer the
HB only needs to be topped up occasionally to a very modest
temperature every couple of days (approx 30C) to ensure good DHW flow.

Seems a good compromise on complexity/flexibility/expense graph.

BTW Danfoss want to know if I want a Kvs of 5 or 2.3 on the VMT. I
don't know what this is though it might be maximum flow rate as it is
cubic m/H


That is so. Look at the Danfoss tables.

Just a normal DHW blending valve can be used. On the DHW outlet of the
plate as per usual. Set this to the max the combi will take on the inlet,
say 50C. So 50C DHW is delivered to the combi inlet in winter. The combi is
set to say 55C, it tops up the 5C. In summer the heat bank is at 30C. The
blending valve is fully open as setpoint is 50C, the combi tops up the 25C
to maintain a DHW at the taps of 55C. Cheaper and no adjustment for
winter/summer.

From Frank,

DD thanks for that further. Yes I see that a normal DHW blending
valve would work fine thanks. With the VMT/RAVK set up I was aiming
at being able to adjust the flow through the PHE so that the water
going back into the bottom of the HB was cooler and likely flowing
slower than if the PHE was supplied from the HB by a pump either being
on or off. Perhaps irrationally I was trying to avoid shoving too
warm water back in the bottom of they HB unnecessarily fast and
disturbing the layers. Though of course the CH return will be fairly
vigorous at the times of most DHW demand so I'm probably wasting my
time with pointless (expensive) frills.

On the other hand I was anticipating teeing off the HW from the top of
the HB to the CH flow and PHE respectively. I hope that by regulating
the flow to the PHE I would not need to stop the CH pump/shut a valve
when there was a demand for DHW.

Or would I be wise to?

On a related topic... Will I need to use a surrey flange on the top
of the HB cylinder? If so I'm not exactly clear what the advantages
are. I think is is to do with air at the top on the cylinder but
can't understand why that won't get taken round until it finds the
vent pipe.

Explanation greatly appreciated. I suspect a bad place for the vent
pipe would be off the top of the cylinder as under extreme
circumstances there might be venturi problems. (Perhaps I've just
answered my own question Surrey flange)

Question: Given the above where is the best place to take the vent
from on the system I am proposing?

Thanks again to all who are/have assisted with this,

Frank.

wrote in message
...
From Frank,

DD thanks for that further. Yes I see that a normal DHW blending
valve would work fine thanks. With the VMT/RAVK set up I was aiming
at being able to adjust the flow through the PHE so that the water
going back into the bottom of the HB was cooler and likely flowing
slower than if the PHE was supplied from the HB by a pump either being
on or off. Perhaps irrationally I was trying to avoid shoving too
warm water back in the bottom of they HB unnecessarily fast and
disturbing the layers. Though of course the CH return will be fairly
vigorous at the times of most DHW demand so I'm probably wasting my
time with pointless (expensive) frills.

On the other hand I was anticipating teeing off the HW from the top of
the HB to the CH flow and PHE respectively.

Use a Surrey flange.

I hope that by regulating
the flow to the PHE I would not need to stop the CH pump/shut a valve
when there was a demand for DHW.

Or would I be wise to?

As it is only for pre-heat probbely not worth it. This control aspect can
always be added.

On a related topic... Will I need to use a surrey flange on the top
of the HB cylinder? If so I'm not exactly clear what the advantages
are. I think is is to do with air at the top on the cylinder but
can't understand why that won't get taken round until it finds the
vent pipe.

The Surrey flange make one port into two. Also the centre part protrudes
into the cylinders.

Explanation greatly appreciated. I suspect a bad place for the vent
pipe would be off the top of the cylinder as under extreme
circumstances there might be venturi problems. (Perhaps I've just
answered my own question Surrey flange)

Question: Given the above where is the best place to take the vent
from on the system I am proposing?

Usually the top draw-off pipe, if the F&E tank is high enough. If not then
off the shower tapping 3/4 of the way up and have an auto air vent in the
top.

Thanks again to all who are/have assisted with this,

Frank.

Thanks again DD for that further help.

I'll try to post a diagram soon and a parts list as I'm sure this
thread will be helpful to others.

More soon,

Thanks,

Frank