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).


If it makes any difference, some of the specs from the boiler manual
a

Max heat o/p Qmax(80°/60°C) = 28KW
Min heat o/p Qmax(80°/60°C) = 5.6KW
Max heat o/p (50°/30°C) = 29.7KW
Min heat o/p (50°/30°C) =6.1KW
Working efficiency at max o/p (80°/60°C) = 97.6%
Working efficiency at max o/p (50°/30°C) = 103.5%
Working efficiency at 30% max o/p (Average T=50°C) = 107%
Working efficiency at min o/p (80°/60°C) = 98.2%
Working efficiency at min o/p (50°/30°C) = 107%
Max heating temp = 90°C
Min heating temp = 20°C


If analogue control means it has a manual control knob to adjust heat
o/p then it has one for heating and one for DHW.
It also came with an outside probe (which I'm assuming is the
mentioned weather compensator). It says this must be fitted for
maximun efficiency.

Yes, I did mean that the most efficient method to heat store was
direct first, then PHE and lastly coil. I see that you believe that
using a PHE uses about 95% of boiler's output. If it is assumed that
directly heating store uses 100%, looks like there is not much in it
from that point of view. DPS were quoting me £75 inc VAT for PHE. Then
pump on top.

"John Rumm" wrote in message
...
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.

Chav, what might they be?

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.

You can't? New to me. The heat load for the boiler is very predictable
indeed and the boiler runs in an ideal hydraulic environment.

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.

Which means it is very suitable for a heat bank indeed and will promote
condensing.

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".

...and well suited for modern condensing boilers too operating at lower
temperatures and wider delta Ts.

Hence you have a nice "rule of thumb" solution to a number of problems.

We do? Prey tell....

The whole situation is much less clear cut here.

It is...let us hear...

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.

7 kW is 25,000 btu/hr which is afair amount of heat injected into a heating
system that may only require 0.5kW (1,500 BTU/hr). This will result in
boiler cycling. And as most boioer only go to around 10 kW minimum the
problems is well...a big problem.

([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,

...good observation.

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.

...that mean a lower store setpoint and lower boiler return temperatures,
improving efficiency.

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,

...yes...and...

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).

You can do this with the store, have the DHW section at a higher temperature
than the CH section which can be controlled via an outside weather
compensator.

Taking the rads off the boiler direct with TVRs all around is a poor
substitute with great setbacks. As one rad needs to be controlled by a wall
stat and the auto by-pass will lower efficiency greatly by short circuiting
the boiler. The boiler needs to be complex and may have a short life
because of low flows through the heat exchanger (in a poor hydraulic
environment) and constant off switching when on part load (boiler cycling).

...and after I thought you were doing so well.

wrote:
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).


If it makes any difference, some of the specs from the boiler manual
a

Max heat o/p Qmax(80°/60°C) = 28KW
Min heat o/p Qmax(80°/60°C) = 5.6KW
Max heat o/p (50°/30°C) = 29.7KW
Min heat o/p (50°/30°C) =6.1KW

That is a nice wide modulation range, which is good. When you subtract
the heat loss of the house from the lower figure it probably means that
the boiler can run the rads from almost no nett input which is ideal.

Working efficiency at max o/p (80°/60°C) = 97.6%
Working efficiency at max o/p (50°/30°C) = 103.5%
Working efficiency at 30% max o/p (Average T=50°C) = 107%
Working efficiency at min o/p (80°/60°C) = 98.2%
Working efficiency at min o/p (50°/30°C) = 107%
Max heating temp = 90°C
Min heating temp = 20°C


If analogue control means it has a manual control knob to adjust heat
o/p then it has one for heating and one for DHW.

That will probably just be the flow temperature cut off stat....

I was thinking more along the lines of the type that can signal the
actual temperature to the boiler, rather than just a call for heat.

It also came with an outside probe (which I'm assuming is the
mentioned weather compensator). It says this must be fitted for
maximun efficiency.

Ah, now that probably does present you with a control that will allow
you to something useful, i.e. arranging a higher flow temperature when
replenishing the store, and usually lower for the rads.

Yes, I did mean that the most efficient method to heat store was
direct first, then PHE and lastly coil. I see that you believe that
using a PHE uses about 95% of boiler's output. If it is assumed that
directly heating store uses 100%, looks like there is not much in it
from that point of view. DPS were quoting me £75 inc VAT for PHE. Then
pump on top.

The efficiency loss with the PHE is only only one of recovery time since
the boiler can modulate...

--
Cheers,

John.

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

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


If it makes any difference, some of the specs from the boiler manual
a

Max heat o/p Qmax(80°/60°C) = 28KW
Min heat o/p Qmax(80°/60°C) = 5.6KW
Max heat o/p (50°/30°C) = 29.7KW
Min heat o/p (50°/30°C) =6.1KW

That is a nice wide modulation range, which is good. When you subtract the
heat loss of the house from the lower figure it probably means that the
boiler can run the rads from almost no nett input which is ideal.

5.6 to 6.1 kW is high when the house is up to temp and one TRV opens
slightly.

Working efficiency at max o/p (80°/60°C) = 97.6%
Working efficiency at max o/p (50°/30°C) = 103.5%
Working efficiency at 30% max o/p (Average T=50°C) = 107%
Working efficiency at min o/p (80°/60°C) = 98.2%
Working efficiency at min o/p (50°/30°C) = 107%
Max heating temp = 90°C
Min heating temp = 20°C


If analogue control means it has a manual control knob to adjust heat
o/p then it has one for heating and one for DHW.

That will probably just be the flow temperature cut off stat....

I was thinking more along the lines of the type that can signal the actual
temperature to the boiler, rather than just a call for heat.

It also came with an outside probe (which I'm assuming is the
mentioned weather compensator). It says this must be fitted for
maximun efficiency.

Ah, now that probably does present you with a control that will allow you
to something useful, i.e. arranging a higher flow temperature when
replenishing the store, and usually lower for the rads.

Yes, I did mean that the most efficient method to heat store was
direct first, then PHE and lastly coil. I see that you believe that
using a PHE uses about 95% of boiler's output. If it is assumed that
directly heating store uses 100%, looks like there is not much in it
from that point of view. DPS were quoting me £75 inc VAT for PHE. Then
pump on top.

The efficiency loss with the PHE is only only one of recovery time since
the boiler can modulate...

--
Cheers,

John.

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

wrote in message
...
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.

What makes and models are DPS using?

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.

What makes and models are DPS using?

According to their spec, Reliance Water Controls (RWC) Heatguard
see http://www.rwc.co.uk/Product.aspx?page=CAT1

If you load the Panex tool and go to the Designer then click on the
green help bar to the right of the "No GX Primary" option, it brings
up about the GX circuit. Last paragraph says about the mixers and if
you click on "valve Sizing", gives you a graph.In fact if you click on
any of the green bars and then click on the Next and Prev buttons at
the top left corner, it gives a good explaination of the Pandora and
GX systems.

Thinking about the whole argument of the rads off or not off the
store, I guess new condensing boilers are designed largely to run rads
direct from boiler so it wouldn't be wrong and should be efficient
enough. However, the it is possible that more efficiency may or may
not be obtained feeding from the store. I guess neither is wrong and
looking at the big picture, there probably isn't much difference in
efficiency.

wrote in message
...


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.

What makes and models are DPS using?

According to their spec, Reliance Water Controls (RWC) Heatguard
see http://www.rwc.co.uk/Product.aspx?page=CAT1

If you load the Panex tool and go to the Designer then click on the
green help bar to the right of the "No GX Primary" option, it brings
up about the GX circuit. Last paragraph says about the mixers and if
you click on "valve Sizing", gives you a graph.In fact if you click on
any of the green bars and then click on the Next and Prev buttons at
the top left corner, it gives a good explaination of the Pandora and
GX systems.

Thanks I had not looked into their latest additions.

Thinking about the whole argument
of the rads off or not off the
store, I guess new condensing boilers
are designed largely to run rads
direct from boiler so it wouldn't be
wrong and should be efficient
enough.

New boilers are primarily designed for the replacement market and to mate up
with a system designed for 80 flow 70 return, temperature difference. More
heat can be delivered with a higher flow/return temp' difference. So a
condensing boiler may just do it at lower temperatures. The idea of burner
modulation (more complexity) is also to get the best efficiency out of the
system. Keston condensing boilers, up to about 5 years ago, were the most
simple boilers on the market - of any type. No pcb, no modulation, Super
simple and reliable. When these when connected to thermal stores/heat banks
they were the ultimate.

However, the it is possible that more
efficiency may or may not be obtained
feeding from the store. I guess neither
is wrong and looking at the big picture,
there probably isn't much difference in
efficiency.

One is better than the other and that is CH from the store, especially when
zoning. There is no central wall room stat to screw up the heat distribution
to the rooms, and heat can be injected to the rads from 0kW to the max they
can take.

The problem when using TRVs all around is the auto by-pass, these really
drop the efficiency when the house reaches temperature. ....and that is when
they are set properly, which 90% plus are not. Also, they are responsible
for many heat exchangers burning out as when not set properly or when they
run out of setting with wear, as they may restrict flow through the heat
exchanger. Best avoid that situation entirely if you can .....and you
can!!!!!!

Having the boiler operate at the optimum efficiency when re-heating the
store, you should really aim for too. And having the boiler only heat the
store this can be achieved.

As you are implementing a heat bank it is best take the two CH zones off the
store, and get the best system available. The cost is minimal for little
outlay.

wrote:

not be obtained feeding from the store. I guess neither is wrong and
looking at the big picture, there probably isn't much difference in
efficiency.

Therein is the rub. Will that small difference pay for the extra
hardware required, and extra installation time taken to include the rads
fed from the store (assuming the difference is even working in your
favour)?

You also need to think about how you will include a boiler interlock (a
building regs requirement) that stops the boiler firing once the house
is to temperature. Monitoring the store temperature alone is unlikely to
do this well enough.

--
Cheers,

John.

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

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

not be obtained feeding from the store. I guess neither is wrong and
looking at the big picture, there probably isn't much difference in
efficiency.

Therein is the rub. Will that small difference pay for the extra hardware
required, and extra installation time taken to include the rads fed from
the store (assuming the difference is even working in your favour)?

Oh my God. The ramblings of an amateur. The difference is large. A modern
low capacity water content boiler connected to a TRV rad system is a
compromise. And it has serious setbacks too. Read what I write..it is much
easier that way.

You also need to think about how you will include a boiler interlock (a
building regs requirement) that stops the boiler firing once the house is
to temperature. Monitoring the store temperature alone is unlikely to do
this well enough.

He has TRVs all around. They close down when the house is up to temperature.
Then when the heat store is up to temp it switches out the boiler. The boier
is not firing when the hosue is up top temp. Got it? I doubt it.

Doctor Drivel wrote:

not be obtained feeding from the store. I guess neither is wrong and
looking at the big picture, there probably isn't much difference in
efficiency.

Therein is the rub. Will that small difference pay for the extra
hardware required, and extra installation time taken to include the
rads fed from the store (assuming the difference is even working in
your favour)?

Oh my God. The ramblings of an amateur.

Must you? oh go on then, ramble away...

The difference is large.

Would you care to define "large"? Given that we are talking about a
boiler with a SEDBUK rating in excess of 90% here - a rating that is
based on a model that includes seasonal adjustment, typical control and
usage patterns in a domestic environment, and many other "real world"
factors. The scope for "large" would seem to be only for very small
values of "large"

(remember that that 100%+ efficiency values you think you can get do not
actually happen with the physics we use in this world).

A modern low capacity water content boiler connected to a TRV rad system
is a compromise.

What, being used in the way it was designed to be operated?

Hmmm....

And it has serious setbacks too. Read what I
write..it is much easier that way.

Actually reading what you write is never easy. You border on functional
illiteracy much of the time, and much of the rest is parrot like
repetition of other cruft.

You also need to think about how you will include a boiler interlock
(a building regs requirement) that stops the boiler firing once the
house is to temperature. Monitoring the store temperature alone is
unlikely to do this well enough.

He has TRVs all around. They close down when the house is up to
temperature. Then when the heat store is up to temp it switches out the
boiler. The boier is not firing when the hosue is up top temp. Got it?

Even with the large phase lag you introduced with the store huh?

A non TMV equipped rad and a programmable thermostat (per zone) will do
a better job and make for more practical comfort.


--
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:

not be obtained feeding from the store. I guess neither is wrong and
looking at the big picture, there probably isn't much difference in
efficiency.

Therein is the rub. Will that small difference pay for the extra
hardware required, and extra installation time taken to include the rads
fed from the store (assuming the difference is even working in your
favour)?

Oh my God. The ramblings of an amateur.

Must you? oh go on then, ramble away...

The difference is large.

Would you care to define "large"? Given that we are talking about a boiler
with a SEDBUK rating in excess of 90% here - a rating that is based on a
model that includes seasonal adjustment, typical control and usage
patterns in a domestic environment, and many other "real world" factors.
The scope for "large" would seem to be only for very small values of
"large"

I have explained the difference enough re-read.

(remember that that 100%+ efficiency values you think you can get do not
actually happen with the physics we use in this world).

That does explain ignorance.

A modern low capacity water content boiler connected to a TRV rad system
is a compromise.

What, being used in the way it was designed to be operated?

Oh my God! He can't even get that either. A compromise in design and
application.

You also need to think about how you will include a boiler interlock (a
building regs requirement) that stops the boiler firing once the house
is to temperature. Monitoring the store temperature alone is unlikely to
do this well enough.

He has TRVs all around. They close down when the house is up to
temperature. Then when the heat store is up to temp it switches out the
boiler. The boier is not firing when the hosue is up top temp. Got it?

Even with the large phase lag you introduced with the store huh?

Nah! You didn't get it.

A non TMV equipped rad and a programmable thermostat (per zone) will do a
better job and make for more practical comfort.

You don't know waht you are prattling about!!!!! Never did.

"John Rumm" wrote in message
...

(remember that that 100%+ efficiency values you think you can get do not
actually happen with the physics we use in this world).

Chav, they happen in the heating world. From Mikrofill:

"This ETHOS; is a high efficiency, condensing, combination Boiler. Flues are
cooled below condensation point by a Spiranox heat exchanger made of
stainless steel. This produces an additional heat which will contribute to
the boiler
efficiency, which is in excess of 107%. The European calculation method
assumes 100% efficiency for appliances which do not condense and
efficiencies higher than 100% for condensing appliances. "

http://www.mikrofill.co.uk/images/PDF/54-technical.pdf

Chav, notice the 107%. Still to lecky sockets.

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

(remember that that 100%+ efficiency values you think you can get do
not actually happen with the physics we use in this world).

Chav, they happen in the heating world. From Mikrofill:

"This ETHOS; is a high efficiency, condensing, combination Boiler. Flues
are cooled below condensation point by a Spiranox heat exchanger made of
stainless steel. This produces an additional heat which will contribute
to the boiler
efficiency, which is in excess of 107%. The European calculation method
assumes 100% efficiency for appliances which do not condense and
efficiencies higher than 100% for condensing appliances. "

http://www.mikrofill.co.uk/images/PDF/54-technical.pdf

Chav, notice the 107%. Still to lecky sockets.

Yes I notice.

Did you notice the "The European calculation method
assumes 100% efficiency for appliances which do not condense and
efficiencies higher than 100% for condensing appliances."?

This tells you that the method of calculation is flawed, and it will
yield a nonsensical answer. If you deliberately under specify the energy
content of the fuel when performing the calculation, but accurately
measure the heat output, you may well get a calculated efficiency of
over 100%. This does not mean that actual efficiency is over 100%, just
you have demonstrated GIGO yet again.

Let me make this quite clear for you. No combi boiler, condensing or
otherwise is going to violate the laws of conservation of energy.


--
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
...

(remember that that 100%+ efficiency values you think you can get do not
actually happen with the physics we use in this world).

Chav, they happen in the heating world. From Mikrofill:

"This ETHOS; is a high efficiency, condensing, combination Boiler. Flues
are cooled below condensation point by a Spiranox heat exchanger made of
stainless steel. This produces an additional heat which will contribute
to the boiler efficiency, which is in excess of 107%. The European
calculation method assumes 100% efficiency for appliances which do not
condense and efficiencies higher than 100% for condensing appliances. "

http://www.mikrofill.co.uk/images/PDF/54-technical.pdf

Chav, notice the 107%. Stick to lecky sockets.

Yes I notice.

Did you notice the "The European calculation method
assumes 100% efficiency for appliances which do not condense and
efficiencies higher than 100% for condensing appliances."?

Chav, yes, I did.

This tells you that the method of calculation is flawed,

It isn't it is just a method.

and it will yield a nonsensical answer.

It doesn't.

If you deliberately under specify the energy content of the fuel when
performing the calculation, but accurately measure the heat output, you
may well get a calculated efficiency of over 100%. This does not mean that
actual efficiency is over 100%, just you have demonstrated GIGO yet again.

Let me make this quite clear for you. No combi boiler, condensing or
otherwise is going to violate the laws of conservation of energy.

None do.

I've not posted here before but have been following the discussion and
would like some advice.

A comment by Dr Drivel in the summer got me thinking:

'This is where a thermal store comes in. Take all the zones from the
water
store and the boiler only heats the store with one long efficient
burn.'

I'm renewing the boiler and propose to use a combi as a replacement.
For HW I'm happy with the flow rate this will give. We use modest
amounts of hot water don't need a big store in reserve.

The CH is another matter - it is where way most of the energy goes. I
want to zone each room because of the number we don't use all the time
and the variable use throughout the day: Guest rooms, second
bathrooms, daytime office, first floor lounge only used in the evening
and so on. Our use is pretty predictable so thermostat timers in the
rooms and valves on a central flow and return tree going up the middle
of the house will work fine I think

Now that could, of course, all be wired into the boiler as it is
modulating and has an adjustable bypass valve. But I wondered if it
might be better to have the boiler heating up a cylinder which could
be placed in a cupboard in the heart of the house (It's a three storey
terrace) where no boiler could ever go. Then use the cylinder as a
heat store to feed the central heating.

Separpate pump required of course but I'm attracted by:

Boiler has a very simple job to do and can be carefully controlled.
Nice clean water with no radiator bits going through the heat
exchanger
Pair of thermostats and a latching relay on they cylinder to widen the
on/off temperature to stop the boiler topping up the store too quickly
when the load is small
Possibility to time the heating of the store in, say, the morning
before a demand for DHW so that the CH continues to function when bath/
shower running.
Possibility of electric immersion back-up for limited CH if boiler
breaks down

Downsides (and this is where I hope folks will help me the most):

Might be needlessly complicated
More expensive
Maybe unfeasable or inefficient for reasons I haven't anticipated.
For instance I imagine using a conventional rapid recovery copper
cylinder of a suitable size with indirect connection to the boiler and
the CH flowing through the (vented) cylinder. But I've a feeling that
might be a little inefficient though necessary to get enough flow to
the radiators. Or am I straying badly off piste here?
I haven't complicated things further by considering the use of heat
exchangers as yet but would welcome suggestions.

I look forward to hearing folks views. I want to get this right and
good information is hard to find so please help as much as you can.

Regards,

Frank

wrote in message
...
I've not posted here before but have been following the discussion and
would like some advice.

A comment by Dr Drivel in the summer got me thinking:

'This is where a thermal store comes in. Take all the zones from the
water
store and the boiler only heats the store with one long efficient
burn.'

I'm renewing the boiler and propose to use a combi as a replacement.
For HW I'm happy with the flow rate this will give. We use modest
amounts of hot water don't need a big store in reserve.

The CH is another matter - it is where way most of the energy goes. I
want to zone each room because of the number we don't use all the time
and the variable use throughout the day: Guest rooms, second
bathrooms, daytime office, first floor lounge only used in the evening
and so on. Our use is pretty predictable so thermostat timers in the
rooms and valves on a central flow and return tree going up the middle
of the house will work fine I think

Now that could, of course, all be wired into the boiler as it is
modulating and has an adjustable bypass valve. But I wondered if it
might be better to have the boiler heating up a cylinder which could
be placed in a cupboard in the heart of the house (It's a three storey
terrace) where no boiler could ever go. Then use the cylinder as a
heat store to feed the central heating.

Separpate pump required of course but I'm attracted by:

Boiler has a very simple job to do and can be carefully controlled.
Nice clean water with no radiator bits going through the heat
exchanger
Pair of thermostats and a latching relay on they cylinder to widen the
on/off temperature to stop the boiler topping up the store too quickly
when the load is small
Possibility to time the heating of the store in, say, the morning
before a demand for DHW so that the CH continues to function when bath/
shower running.
Possibility of electric immersion back-up for limited CH if boiler
breaks down

Downsides (and this is where I hope folks will help me the most):

Might be needlessly complicated
More expensive
Maybe unfeasable or inefficient for reasons I haven't anticipated.
For instance I imagine using a conventional rapid recovery copper
cylinder of a suitable size with indirect connection to the boiler and
the CH flowing through the (vented) cylinder. But I've a feeling that
might be a little inefficient though necessary to get enough flow to
the radiators. Or am I straying badly off piste here?
I haven't complicated things further by considering the use of heat
exchangers as yet but would welcome suggestions.

I look forward to hearing folks views. I want to get this right and
good information is hard to find so please help as much as you can.

Regards,

A snippet. Yes, a CH buffer is the best way. For each room have a Wilo
Smart pump at £44 from Screwfix instead of zone valves. Simpler, more
reliable and better flow. A whole bank of them neatly on the wall. Have a
header off the cylinder of 28mm pipe and take all the pumps off this. Or if
possible two headers, upstairs and downstairs.

A boiler can go inside the house not on an outside wall. Look at the Keston
which can have 60 foot of cheap plastic waste pipe for the flue.

Frank, a bit late so I will get back to you tomorrow. You appear a bright
man.

On 12 Jan, 01:15, "Doctor Drivel" wrote:
wrote in message

...



I've not posted here before but have been following the discussion and
would like some advice.

A comment by Dr Drivel in the summer got me thinking:

'This is where a thermal store comes in. Take all the zones from the
water
store and the boiler only heats the store with one long efficient
burn.'

I'm renewing the boiler and propose to use a combi as a replacement.
For HW I'm happy with the flow rate this will give. We use modest
amounts of hot water don't need a big store in reserve.

The CH is another matter - it is where way most of the energy goes. I
want to zone each room because of the number we don't use all the time
and the variable use throughout the day: Guest rooms, second
bathrooms, daytime office, first floor lounge only used in the evening
and so on. Our use is pretty predictable so thermostat timers in the
rooms and valves on a central flow and return tree going up the middle
of the house will work fine I think

Now that could, of course, all be wired into the boiler as it is
modulating and has an adjustable bypass valve. But I wondered if it
might be better to have the boiler heating up acylinderwhich could
be placed in a cupboard in the heart of the house (It's a three storey
terrace) where no boiler could ever go. Then use thecylinderas a
heatstore to feed the central heating.

Separpate pump required of course but I'm attracted by:

Boiler has a very simple job to do and can be carefully controlled.
Nice clean water with no radiator bits going through theheat
exchanger
Pair of thermostats and a latching relay on theycylinderto widen the
on/off temperature to stop the boiler topping up the store too quickly
when the load is small
Possibility to time the heating of the store in, say, the morning
before a demand for DHW so that the CH continues to function when bath/
shower running.
Possibility of electric immersion back-up for limited CH if boiler
breaks down

Downsides (and this is where I hope folks will help me the most):

Might be needlessly complicated
More expensive
Maybe unfeasable or inefficient for reasons I haven't anticipated.
For instance I imagine using a conventional rapid recovery copper
cylinderof a suitable size with indirect connection to the boiler and
the CH flowing through the (vented)cylinder. But I've a feeling that
might be a little inefficient though necessary to get enough flow to
the radiators. Or am I straying badly off piste here?
I haven't complicated things further by considering the use ofheat
exchangers as yet but would welcome suggestions.

I look forward to hearing folks views. I want to get this right and
good information is hard to find so please help as much as you can.

Regards,

A snippet. Yes, a CH buffer is the best way. For each room have a Wilo
Smart pump at £44 from Screwfix instead of zone valves. Simpler, more
reliable and better flow. A wholebankof them neatly on the wall. Have a
header off thecylinderof 28mm pipe and take all the pumps off this. Or if
possible two headers, upstairs and downstairs.

A boiler can go inside the house not on an outside wall. Look at the Keston
which can have 60 foot of cheap plastic waste pipe for the flue.

Frank, a bit late so I will get back to you tomorrow. You appear a bright
man.

Dr Drivel

Thank you for getting back. Very encouraging.

I want to end up with a system that is as low on wasted energy as is
compatible with a high level of convenience and flexibility. (So no
surprise there then.) Of course this has to be balanced by an
increase capital outlay and time (my time so 'free' ha ha) for
installing. I can swallow a bit of a capital hit as the present set
up seems designed for maximum inefficiency. I hope to make good
savings.

I'll try to describe what I plan as fully as possible to help you make
further suggestions.

The house is a stone terraced mid Victorian thing on three floors in
Edinburgh. There is a central stairwell going the full height in the
middle. The foot-print isn't huge but I reckon ten zones:
G/F
1) Stairwell - full height so thermostat placement will be in
interesting one.
2) My office (I work from home),
3) Kitchen & main living area inc. D/S loo and utility room (I thought
of putting the utility on a trv as it will need to be on all the time
that Zone 3 is but not as warm).

F/F
4) Master bedroom
5) Child's room
6) Lounge
7) Bathroom

T/F
8) Guest Room
9) Bathroom plus small second guest room on TRV
10) Wife's study

Every one of the is Zones is justified by need according to the
criteria of 1) need to be on at different and nearly always predicable
times during the day/week and/or 2) benefit form individual
temperature control.

Of course all this assumes that he doors are kept closed and the inter-
room insulation is reasonable. This is the case I think except
possibly for Junior's bedroom door... (Nurse! the electrodes please.)


I plan to put the boiler on the second floor (in a cupboard off the
small guest room/store) where it is well placed for flue exit and
access. This location is directly above the first floor bathroom and
almost adjacent to the second floor bathroom so good for HW delivery.
The run from the boiler to the CH cylinder would also be fine from
here with plenty of space for good insulation of the flow and
return. the compact nature of the dwelling means that no zone is
very far from the central nest of control valves or pumps as you
suggest.

Okay a few specifics.

I'm thinking in favour of the Vaillant 937 boiler. As I'm sure you
know this had the 15l heatstore in it and blends the outflow to
produce rapid HW in at high pressure in good quanities. We don't use
much HW so what we do use must be instant and plentiful. The extra
cost of the heatstore thing in the Vaillant can be reduced by having
smallish timed windows when it is got up to and kept at running
temperatuire by the boiler. It is well insulated and blends even when
it has cooled down a bit so if it is poised and ready to go twice a
day for about an hour to coincide with morning ablutions and long-hot-
soaks I think we should be fine. Experience will tell if this has to
be altered much when we have guests.
It's a 28kw boiler I think so not over large but quite big enough to
run the CH via a heat store.
My expectation is that the extra cost of keeping the heatstore hot
will be almost irrelevant due to the low amount of HW used and the far
greater expense of the CH. The 937 is about 1K trade so is not cheap
for a modest sized combi. I think the benefits are worth the outlay.
Once again other folks experience here would be appreciated.

The roof is well insulated with Tri-Iso and I intend having a generous
CW storage tank. Whilst the CW to the shower mixer will have to be
from the mains the CW to the baths, basins and loos can be from the
tank. As I see it the advantages a
Warmer cold water so bigger bath for your money; more comfortable when
washing hands etc; loo cystern won't drip condensate. Added to this
if the tank is a reasonable size then it ca be set to refill quite
slowly and thus reduce thepressure drop of incoming mains at a time
when that might be most needed. If the tank refills slowly there
should be no chance of a tedious whistling of the pipes.


I wonder in no particular order:

1) What type and size of cylinder I should use for the CH heat store
and exactly how it should be configured. I'm not sure putting the
return in at the base is best as quiet warm water would hit cold water
and so total mixing rather that stratifying w
2) Whether to use the wilo smart pumps or valves for the zoning.
Pump noise would drive me bonkers. Obviously if I use the valves
there will be at least one pump. Certainly the valves are likely to
break down and need replacing earlier but they are a bit cheaper.
Wilos are supposed to be very quiet though...
I'll probably need to try one and see. They could be carefully
mounted and vibration insulated. Some of the zones are only be one
radiator and mostly microbore. Whooshing we don't need. Will the
lowest speed be low enough? The pumps will have valves either side
for servicing so the flow cold be restricted but then that puts the
pump under more strain. I'd be interested to know what people think
about this.

Finally - For now - thre is an anomaly in the system. The Kitchen is
about as far as it can get from the boiler. The Vaillant boasts about
15l per min flow. in 15mm pipe allowing a but for resistance I reckon
on better than a meter per second. It's 18m to the kitchen. Do I
want to wait 15-18s for HW? I think I might put a small Santon 10l
mains pressure electric aquaflow under the sink. Bigger outlay but
could be on a timer to warm once or twice a day and mains pressure HW
would be there instantly in the small quantities needed without waking
the boiler up. Amazing how much less HW we use at the sink once a
dishwasher is dong it's thing.
As an aside I tend to plumb DW and washing machine in with just a cold
supply.
The under sink Santon could easily be retrofitted if HW from the
boiler was found to be unsatisfactory.

Okay. Thanks for reading. I look forward to Dr Drivel and other
folk's comments and suggestions.

Regards to all,

Frank

wrote in message
...

The house is a stone terraced mid Victorian
thing on three floors in Edinburgh. There is a
central stairwell going the full height in the
middle. The foot-print isn't huge but I reckon
ten zones:

G/F
1) Stairwell - full height so thermostat placement
will be in interesting one.
2) My office (I work from home),
3) Kitchen & main living area inc. D/S loo and
utility room (I thought of putting the utility on a
trv as it will need to be on all the time that Zone 3
is but not as warm).

F/F
4) Master bedroom
5) Child's room
6) Lounge
7) Bathroom

T/F
8) Guest Room
9) Bathroom plus small second guest room on TRV
10) Wife's study

Every one of the is Zones is justified
by need according to the criteria of
1) need to be on at different and nearly
always predicable times during the
day/week and/or 2) benefit form individual
temperature control.

I plan to put the boiler on the second
floor (in a cupboard off the small guest
room/store) where it is well placed for
flue exit and access. This location is
directly above the first floor bathroom and
almost adjacent to the second floor bathroom
so good for HW delivery. The run from the
boiler to the CH cylinder would also be fine from
here with plenty of space for good insulation
of the flow and return. the compact nature
of the dwelling means that no zone is
very far from the central nest of control valves
or pumps as you suggest.

Okay a few specifics.

I'm thinking in favour of the Vaillant 937 boiler.
As I'm sure you know this had the 15l heatstore
in it and blends the outflow to produce rapid
HW in at high pressure in good quanities. We don't use
much HW

Frank,

The first approach I would look at is a heat bank/thermal store heated by a
Glow Worm HXi vented "heating" boiler, not a combi.
http://tinyurl.com/2p279m
The 24 kW version is £638.03 Including VAT at 17.5% Made by Vaillant. It
is small in size. A set speed pump is needed to heat the heat bank
cylinder.

This give a CH buffer and instant mains presure DHW.
Look at:
http://www.rangecylinders.co.uk/prod...dels/cylinder/
The 200 litre model.

As the cylidner is central in the house with rads above it, an F&E tank must
go inthe loft.

Your zones.

You can have simple cheap timeclocks in bank in a central location, saving
on clock/stats, so all the rooms can be set and switched on or off without
running around the house. And have one master time clock to switch all of
the system off, so the 10 timeclocks are slaves. to the master clock. Have
TRVs on each rad then. No wall stats needed. The Wilo Smart pump will
automatically run up and down speed depending on pressure. If all TRVs on
one zone are closed, or near closed, it runs down. Most of the time the
pump is at reduced speed saving power and reduced noise. If all are fully
off the pump is off, well runs very slowly. They are quiet. They have
three settings, probably setting 1 is fine for all but one zone. If one rom
only need 0.25 kW of heat the Smart pump just gently injects it into the
rad(s). Get good quality full bore rad valves, then no restriction.

Cost per zone using a Smart pump, TRV and simple time clock is about the
same as a clock/stat and 2-port zone valve (only use "good" quality zone
valves and they are not cheap).

Pump/zone headers:

Off the heat bank cylinder have a 28mm header pipe out of the flow tapping
and tee off all zone pumps from this. A check valve after each pump. The
same for the return, a 28mm return header with all return pipes teed into
this. I would put a full bore 12/4 turn isolating valve here so the whole
zone can be isolated and drained to avoid a full drain down.

Have a Magnaclean filter on the return to thye cylinder. Make sure enough
inhibitor is in the system.

So you have:

- one heat bank cylinder giving DHW and CH buffer.
- one simple vented boiler
- centralised time control (you can have the odd one local in a room if
neede be).
- No by-pass needed.
- small boiler. The 937 is the size of a washing machine.
- more reliable temperature control
- more reliable zoning using a pump.
- more reliable simple boiler.
- buffering of CH.
- no Boiler cycling.
- reduced size boiler as a thermal storage system only needs the boiler to
be sized for avearge use, not peak use.

In the morning when CH come in, not all zones at the same time it appears,
the rads are heated instantly as the water is dumped into the rads from the
cylinder. The boiler comes in re-heats at full belt. The rads then do not
require full heat from the cylinder and DHW can be served quite easily.

wrote:

I'll try to describe what I plan as fully as possible to help you make
further suggestions.

The house is a stone terraced mid Victorian thing on three floors in
Edinburgh. There is a central stairwell going the full height in the
middle. The foot-print isn't huge but I reckon ten zones:
G/F
1) Stairwell - full height so thermostat placement will be in
interesting one.
2) My office (I work from home),

What sort of equipment do you have in here, other than you?

3) Kitchen & main living area inc. D/S loo and utility room (I thought
of putting the utility on a trv as it will need to be on all the time
that Zone 3 is but not as warm).

F/F
4) Master bedroom
5) Child's room
6) Lounge
7) Bathroom

T/F
8) Guest Room
9) Bathroom plus small second guest room on TRV
10) Wife's study

Every one of the is Zones is justified by need according to the
criteria of 1) need to be on at different and nearly always predicable
times during the day/week and/or 2) benefit form individual
temperature control.

I would question whether you will ever reap any return on the cost and
complexity of system required to support this number of zones. Remember
that individual temperature control in a room can be achieved via its TRV.

Before going much further in this you need to do some detailed heat loss
calculations for the building. Once these are done you can factor in the
effect of leaving particular rooms unheated, and see how that changes
the overall heat loss picture (and hence running costs).

I expect you will find that the difference between 10 zones and say
three (e.g. "all day" spaces, evening spaces, sleeping spaces), will be
negligible in terms of difference in running costs and day to day comfort.

I plan to put the boiler on the second floor (in a cupboard off the
small guest room/store) where it is well placed for flue exit and
access. This location is directly above the first floor bathroom and
almost adjacent to the second floor bathroom so good for HW delivery.
The run from the boiler to the CH cylinder would also be fine from
here with plenty of space for good insulation of the flow and
return. the compact nature of the dwelling means that no zone is
very far from the central nest of control valves or pumps as you
suggest.

Have you thought about what your hot water requirements are? i.e.
showers, baths, one or two at a time?

Have you established if your mains supply is capable of meeting your hot
water requirements on demand without any storage facility?


Okay a few specifics.

I'm thinking in favour of the Vaillant 937 boiler. As I'm sure you
know this had the 15l heatstore in it and blends the outflow to
produce rapid HW in at high pressure in good quanities. We don't use
much HW so what we do use must be instant and plentiful. The extra

"Don't user much", and must be "plentiful" sound like contradictory
requirements. Could you clarify?

The roof is well insulated with Tri-Iso and I intend having a generous

That's the multi foil stuff?

CW storage tank. Whilst the CW to the shower mixer will have to be
from the mains the CW to the baths, basins and loos can be from the
tank. As I see it the advantages a

Why mains to the shower mixer if you are planning to run gravity hot?

Warmer cold water so bigger bath for your money; more comfortable when

Not really... where does the heat come from that warms the cold water?
You pay for it all in the end.


1) What type and size of cylinder I should use for the CH heat store
and exactly how it should be configured. I'm not sure putting the
return in at the base is best as quiet warm water would hit cold water
and so total mixing rather that stratifying w

You need to do the heatloss calcs first to have any idea.

Finally - For now - thre is an anomaly in the system. The Kitchen is
about as far as it can get from the boiler. The Vaillant boasts about
15l per min flow. in 15mm pipe allowing a but for resistance I reckon
on better than a meter per second. It's 18m to the kitchen. Do I
want to wait 15-18s for HW? I think I might put a small Santon 10l
mains pressure electric aquaflow under the sink. Bigger outlay but
could be on a timer to warm once or twice a day and mains pressure HW
would be there instantly in the small quantities needed without waking
the boiler up. Amazing how much less HW we use at the sink once a
dishwasher is dong it's thing.

If you are going for HW from a thermal store then it would be simple to
implement a secondary circulation loop for the sink. That would ensure
instant hot water there.


--
Cheers,

John.

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

"John Rumm" wrote in message
...

Why mains to the shower mixer if you are planning to run gravity hot?

He is not running gravity hot.

Warmer cold water so bigger bath for your money; more comfortable when

Not really... where does the heat come from that warms the cold water? You
pay for it all in the end.

Solar gain the loft can make an effect.

If you are going for HW from a thermal store then it would be simple to
implement a secondary circulation loop for the sink. That would ensure
instant hot water there.

Some sense here at last.

Thanks for the above posts. I appreciate the effort.

I take on board what Dr Drivel and JR have to say.

I like the idea of using a more basic boiler and a vented system. All
very doable and simple to fix when it goes wrong.

Not sure I fancy paying Range or a similar company that much for
putting a PHE inside a copper cylinder.

Is there any reason why an external PHE with a circulating pump and
flow switch could not be fitted for those things that demand mains
pressure HW? This would be a shower and possibly the top floor
bathroom. I've seen some designs elsewhere for a diy set up and folk
saying that a 100kw PHE can be had for a bout £100.
Of course I would be demanding a lot from the cylinder. It would have
to be a thermal store (rather than a heat bank if I have understood
the nomenclature correctly) for the CH as well as for HW via gravity
or the PHE.

I assume the cylinder would be heated indirectly by the boiler and the
PHE take off would be at the very top with the CH flow and return
lower down. I can see that there might be issues with loss of
stratification when the CH is cranking away but perhaps with clever
timing of the initial CH burst in the morning to a limited number of
zones and then a re-heat to prepare for ablutions the set up would
cope fine. The CH has a fair amount of inertia in it and the cylinder
could be of the rapid recovery type.

Modest sized indirect copper cylinders can be had reasonably cheaply
still so perhaps two smaller ones would be better with CH in one and
HW in the other. Would have a choice of direct/indirect in the HW one
then.

The other major expense is controlling all the zones. TRV + single
channel timer + pump(or valve) is going to be about £90 per zone.
There might be some scope for reducing the number of zones but it soon
gets wasteful.

On other thing. A heat store for the HW does mean that water is being
heated up that won't always be used. Not a problem so much in the
winter as the CH will be doing it's thing but in the summer it might
be wasteful though perhaps not much. One of the attractions of a
combi I suppose.

I am very interested to know what Dr Drivel and John Rumm as well as
anyone else has to say to these ideas.

In response to some of the other points:

1) Equipment in office making heat? Only a couple of laptops.
2) Mains flow/pressu Inlet from street is lead into 15mm pipe.
15mm to top of house. At top of house is 4bar
Flow rate:
13lpm at 3.3bar
17lpm at 2.5bar
20lpm at 2.0bar

3) hot water demand? might be a shower and bath at same time now and
then.

4) Circulation loop to the kitchen. Thanks for that suggestion. What
factors would reduce heat loss other than lagging?

5) Warming up the cold water in tanks in the loft. Don't reckon I can
ever make the loft as cold as the incoming water temp in winter so I
hope to cash in on some of the inevitable heat loss from house into
this space. Warmer in summer of course.

Would be fun to think of a way of 'preheating' the mains water going
to the HW supply up here as well.
A degree or two would make all the difference would it not?

I sometimes wonder if the bath/shower waste couldn't be made to warm
up the incoming cold water on it's way to the street.

I look forward to further helpful comments and suggestions from one
and all. May I say again how much I appreciate the trouble Dr Drivel
and JR are taking?

Thanks

Frank

wrote:

I like the idea of using a more basic boiler and a vented system. All
very doable and simple to fix when it goes wrong.

"basic" in the context of a modern boiler is a bit of a oxymoron. None
are exactly simple, and even the simplest will have extensive
electronics controlling its operation.

Is there any reason why an external PHE with a circulating pump and
flow switch could not be fitted for those things that demand mains
pressure HW? This would be a shower and possibly the top floor
bathroom.

No, not at all. Why would you want the HW supplied any other way?

I assume the cylinder would be heated indirectly by the boiler and the

If have a vented primary circuit then you could heat it directly or
indirectly. Personally I favour a sealed primary, and hence would opt
for indirect heating of the store.

PHE take off would be at the very top with the CH flow and return
lower down. I can see that there might be issues with loss of
stratification when the CH is cranking away but perhaps with clever
timing of the initial CH burst in the morning to a limited number of
zones and then a re-heat to prepare for ablutions the set up would
cope fine. The CH has a fair amount of inertia in it and the cylinder
could be of the rapid recovery type.

Modest sized indirect copper cylinders can be had reasonably cheaply
still so perhaps two smaller ones would be better with CH in one and
HW in the other. Would have a choice of direct/indirect in the HW one
then.

Or cut the complexity, go for a boiler with a decent modulation range,
and let the boiler drive the rads directly.

(dribble prefers his one size fits all solution using the store for
everything, as you can probably judge from the previous messages)

The other major expense is controlling all the zones. TRV + single
channel timer + pump(or valve) is going to be about £90 per zone.
There might be some scope for reducing the number of zones but it soon
gets wasteful.

I think when you do the heatloss calcs your will find there is little to
be gained by going beyond a handful of zones. If you leave a room
unheated then you just increase losses from the rooms that surround it,
and it ends up being heated indirectly anyway. You also would need to
work out how to plumb it. With lots of zones controlled from a central
location you are going to have masses of pipework, which aside from
being expensive to purchase, will require lots of install time and lots
of hacking about of the house.

If you really want lots of zones you may be better with a pair of
largish primary "backbone" pipes providing flow and return points for
each floor, and then teeing off them for the individual rooms / zones.
The zones could be enabled by valves (or pumps if you prefer) locally -
even if you take the control back to a central location.

On other thing. A heat store for the HW does mean that water is being
heated up that won't always be used. Not a problem so much in the
winter as the CH will be doing it's thing but in the summer it might
be wasteful though perhaps not much. One of the attractions of a
combi I suppose.

If the store is well insulated it will make little difference. In the
winter any heat it looses will pass beneficially into the house anyway.

In response to some of the other points:

1) Equipment in office making heat? Only a couple of laptops.

OK, not huge then. I tend to find that a couple of PCs running 24/7 is
usually enough extra heat to require very little input from the heating.

2) Mains flow/pressu Inlet from street is lead into 15mm pipe.
15mm to top of house. At top of house is 4bar
Flow rate:
13lpm at 3.3bar
17lpm at 2.5bar
20lpm at 2.0bar

So is 20 lpm the best flow rate you can get?

If so this negates some of the advantages of having a thermal store
arrangement for HW production since the supply would not be able to keep
up with multiple simultaneous users of the water even if the store could.

3) hot water demand? might be a shower and bath at same time now and
then.

You may find a combi with its HW output feeding the shower, and a fast
recovery indirect cylinder on a zone on the heating side of the boiler
would meet that requirement better. Fast flow rate for the bath from the
cylinder, and high pressure for the shower from the mains, but without
over stretching the mains supply. (you could throttle the cold tank
replenishment rate if you have a largish tank)

4) Circulation loop to the kitchen. Thanks for that suggestion. What
factors would reduce heat loss other than lagging?

If you can predict likely times for use, having a timer control on the
loop ought to achieve that. (you just need to accept that you will need
to run off some cold water and wait a bit should you use the tap at
other times). Failing that, if you do use a combi, then perhaps it can
supply the kitchen tap if not too far away.

5) Warming up the cold water in tanks in the loft. Don't reckon I can
ever make the loft as cold as the incoming water temp in winter so I
hope to cash in on some of the inevitable heat loss from house into
this space. Warmer in summer of course.

Just take care not to insulate under them - you need a little heat loss
to stop them freezing.

Would be fun to think of a way of 'preheating' the mains water going
to the HW supply up here as well.
A degree or two would make all the difference would it not?

All the difference to what?

I sometimes wonder if the bath/shower waste couldn't be made to warm
up the incoming cold water on it's way to the street.

Can be done - there is another thread running in the group on that at
the moment. It has also been discussed before.


--
Cheers,

John.

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| John Rumm - john(at)internode(dot)co(dot)uk |
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Just got round to measuring flow rate and opening all cold taps at
once and measuring total quantity of water in 1 minute, it looks like
I have a flow rate of about 37L/min. Hopefully, that is pretty good.
As to pressure, don't have a guage for this but believe it to be very
strong. can't hold thumb over tap without water still spurting out
quite forcefully. (Very scientific I know but seem to remember someone
suggesting that once!)

Also checked existing pipework and as I currently have a combi,
pipework to bath is in 15mm. Is it necessary to upgrade it 22mm? Would
be bit of a pain if need to as bathroom all tiled etc. Would mean a
long route of going downstairs then back up again.

wrote in message
...
Thanks for the above posts. I appreciate the effort.

I take on board what Dr Drivel and JR have to say.

I like the idea of using a more basic boiler and a vented system. All
very doable and simple to fix when it goes wrong.

The HXIs are simple enough and well made.

Not sure I fancy paying Range or a
similar company that much for
putting a PHE inside a copper cylinder.

It is outside, but follow the thread and you can make one yourself . I gave
instructions on how to do it. I will try to dig them out.

Is there any reason why an external PHE
with a circulating pump and flow switch could
not be fitted for those things that demand mains
pressure HW? This would be a shower and
possibly the top floor bathroom.

You can do. What is wrong with putting the whole DHW on the plate heat X?

I've seen some
designs elsewhere for a diy set up and folk
saying that a 100kw PHE can be had for a bout £100.

About £70 from DPS I hear. Gledhill will supply them as standard
replacement parts too, for around £80

Of course I would be demanding a lot from
the cylinder. It would have to be a thermal
store (rather than a heat bank if I have understood
the nomenclature correctly) for the CH as well
as for HW via gravity or the PHE.

No. If you have a house that needs 24 to 27 kW for CH a 200 litre cylinder
will do CH and DHW. Find out the Kw requirements of the house (heat loss)

I assume the cylinder would be heated
indirectly by the boiler

No, directly

and the PHE take off would be at the very
top with the CH flow and return lower down.

Yep.

I can see that there might be issues with loss of
stratification when the CH is cranking away
but perhaps with clever timing of the initial
CH burst in the morning to a limited number of
zones and then a re-heat to prepare for ablutions
the set up would cope fine.

Install spreader pipes.

The CH has a fair
amount of inertia in it and the cylinder
could be of the rapid recovery type.

Keep the cylinder direct it is more efficient.

Modest sized indirect copper cylinders
can be had reasonably cheaply
still so perhaps two smaller ones would be
better with CH in one and HW in the other.
Would have a choice of direct/indirect in the HW one
then.

The two could be heated directly by the one boiler. Two pumps or one pumps
and a 3-way "diverter valve. DHW has priority. When DHW calls its cylinder
gets all the boilers heat. Then it drop back to heating the CH cylinder.

The other major expense is controlling
all the zones. TRV + single
channel timer + pump(or valve) is going
to be about £90 per zone. There might be
some scope for reducing the number of zones but it soon
gets wasteful.

The more zones the more money - simple.

On other thing. A heat store for the HW
does mean that water is being
heated up that won't always be used.
Not a problem so much in the
winter as the CH will be doing it's thing
but in the summer it might be wasteful
though perhaps not much. One of the
attractions of a combi I suppose.

You could get a combi to match your DHW needs and then have a CH buffer
heated by the boiler using a fast recovery coil.

In response to some of the other points:

1) Equipment in office making heat? Only a couple of laptops.
2) Mains flow/pressu Inlet from street is lead into 15mm pipe.
15mm to top of house. At top of house is 4bar
Flow rate:
13lpm at 3.3bar
17lpm at 2.5bar
20lpm at 2.0bar

Not startling at all.

3) hot water demand? might be a
shower and bath at same time now and
then.

You might want to consider an accumulator tank and a combi. The accumulator
is simple to fit - a tee into the mains pipe, anywhere on the cold water
mains. . Then high pressure and adequate flow and stored water backup if
water is off from street.

4) Circulation loop to the kitchen. Thanks
for that suggestion. What factors would
reduce heat loss other than lagging?

A time clock and a pipe stat.

5) Warming up the cold water in tanks
in the loft. Don't reckon I can ever make
the loft as cold as the incoming water temp
in winter so I hope to cash in on some of
the inevitable heat loss from house into
this space. Warmer in summer of course.

Would be fun to think of a way of 'preheating'
the mains water going to the HW supply up here as well.
A degree or two would make all the difference would it not?

Just have an adequate combi or heat bank.

I sometimes wonder if the bath/shower
waste couldn't be made to warm
up the incoming cold water on it's way to the street.

Gfx a thread is already on this:
http://gfxtechnology.com/

Try just having a cylinder as a CH buffer heated by a combi via a fast
recovery coil, or a plate heat exchanger and pump. The plate & pump and
direct cylinder may work out cheaper than a fast recovery coil, and it
operates far better too.

Have a combi suited to your DHW needs and fit an accumulator tank. Then no
open tanks in the loft, except one F&E tank supplying the CH buffer
cylinder. Look at:
Replaceable Membrane Potable at:
http://www.rwc.co.uk/Product.aspx?page=CAT6

If you need 100 litres of cold water storage, then get a 200 litres model.
The membranes are replaceable. Pump up with car pump.

wrote in message
...

Just got round to measuring flow rate and opening all cold taps at
once and measuring total quantity of water in 1 minute, it looks like
I have a flow rate of about 37L/min. Hopefully, that is pretty good.
As to pressure, don't have a guage for this but believe it to be very
strong. can't hold thumb over tap without water still spurting out
quite forcefully. (Very scientific I know but seem to remember someone
suggesting that once!)

Also checked existing pipework and as I currently have a combi,
pipework to bath is in 15mm. Is it necessary to upgrade it 22mm? Would
be bit of a pain if need to as bathroom all tiled etc. Would mean a
long route of going downstairs then back up again.

37L is quite good. If one 15mm pipe and all cold appliances teed off inc
combi then a no. no. If you have to go back to the stoptap, do it in 22mm
only for the combi.

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

If have a vented primary circuit then you could heat it directly or
indirectly. Personally I favour a sealed primary, and hence would opt for
indirect heating of the store.

Please stop guessing. Best have direct all the way and elimate heat
exchangers and improve efficiency.

Or cut the complexity, go for a boiler with a decent modulation range, and
let the boiler drive the rads directly.

Which is an expensive more complex boiler and non modulate down low enough
and an auto by-pas has to be used reducing efficiency on part load. You need
to understand buffering. Big in Germany. Fitting one combi does not make
you a heating engineer.

(dribble prefers his one size fits all solution using the store for
everything, as you can probably judge from the previous messages)

.....an amateur heating man speaks

If you really want lots of zones you may be better with a pair of largish
primary "backbone" pipes providing flow and return points for each floor,
and then teeing off them for the individual rooms / zones.

Pumps under the floors? Shishhhhh. Best have all controls in one place.
This pipe will just return back to the boiler raising the return temp
lowering efficiency.

You may find a combi with its HW output feeding the shower, and a fast
recovery indirect cylinder on a zone on the heating side of the boiler
would meet that requirement better.

Er no..... Best have a cold water accumuator.

wrote:

Just got round to measuring flow rate and opening all cold taps at
once and measuring total quantity of water in 1 minute, it looks like
I have a flow rate of about 37L/min. Hopefully, that is pretty good.

Yup, that is very good.

As to pressure, don't have a guage for this but believe it to be very
strong. can't hold thumb over tap without water still spurting out
quite forcefully. (Very scientific I know but seem to remember someone
suggesting that once!)

It does not take much static pressure to defeat the thumb over the end
gambit ;-) 1.5 bar would do it.

Also checked existing pipework and as I currently have a combi,
pipework to bath is in 15mm. Is it necessary to upgrade it 22mm? Would
be bit of a pain if need to as bathroom all tiled etc. Would mean a
long route of going downstairs then back up again.

At mains pressure that will probably be fine.


--
Cheers,

John.

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|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

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

Just got round to measuring flow rate and opening all cold taps at
once and measuring total quantity of water in 1 minute, it looks like
I have a flow rate of about 37L/min. Hopefully, that is pretty good.

Yup, that is very good.

As to pressure, don't have a guage for this but believe it to be very
strong. can't hold thumb over tap without water still spurting out
quite forcefully. (Very scientific I know but seem to remember someone
suggesting that once!)

It does not take much static pressure to defeat the thumb over the end
gambit ;-) 1.5 bar would do it.

Also checked existing pipework and as I currently have a combi,
pipework to bath is in 15mm. Is it necessary to upgrade it 22mm? Would
be bit of a pain if need to as bathroom all tiled etc. Would mean a
long route of going downstairs then back up again.

At mains pressure that will probably be fine.

Until another taps is turned on.

Doctor Drivel wrote:

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

If have a vented primary circuit then you could heat it directly or
indirectly. Personally I favour a sealed primary, and hence would opt
for indirect heating of the store.

Please stop guessing. Best have direct all the way and elimate heat
exchangers and improve efficiency.

As you have said yourself on many occasions, the efficiency of a plate
heat exchange is very good. Sealed systems are generally preferable when
they can be used.

Or cut the complexity, go for a boiler with a decent modulation range,
and let the boiler drive the rads directly.

Which is an expensive more complex boiler and non modulate down low

More hand waving dribble? How much more complex?

Answer - very little difference. Different gas valve perhaps, but these
rarely fail anyway. Still has much the same burner layout, electronic
controls, ignition, forced induction, condensate collection and disposal
etc. Price difference? hundred perhaps. Hardly figures in the grand
scheme of things does it?

enough and an auto by-pas has to be used reducing efficiency on part
load. You need to understand buffering. Big in Germany. Fitting one
combi does not make you a heating engineer.

Posting ill thought through "solutions" on usenet does not make you one
either. Neither does you inability to maintain any grip on capital cost
of your projects.

If you really want lots of zones you may be better with a pair of
largish primary "backbone" pipes providing flow and return points for
each floor, and then teeing off them for the individual rooms / zones.

Pumps under the floors? Shishhhhh.

Who suggested under the floor? You it seems. You are right though, daft
idea.

Best have all controls in one place.

With a boatload of pipe running to and from each zone...

This pipe will just return back to the boiler raising the return temp
lowering efficiency.

Which pipe?

I think you will find flow and return pipes with rads strung across them
is pretty much how most heating systems work (if you ignore old single
pipe systems). Perhaps you should read up on the background a little.

You may find a combi with its HW output feeding the shower, and a fast
recovery indirect cylinder on a zone on the heating side of the boiler
would meet that requirement better.

Er no..... Best have a cold water accumuator.

Ah right, and how much does that cost?

20 lpm while not a huge supply rate is not dire, and more than adequate
for a shower.

Note also if you go back to the OPs requirements: "I'm renewing the
boiler and propose to use a combi as a replacement. For HW I'm happy
with the flow rate this will give. We use modest amounts of hot water
don't need a big store in reserve."

Its funny how you flipflop between "a combi is ideal because there is no
room for tanks in small British houses", to "Oh just slap in a 300L
accumulator alongside the heatbank" depending on which way it suits your
argument.

(not suggesting an accumulator is a bad idea in general - it has a place
in some installations. Just entertained how your solutions run on and on
sucking in ever more hardware to get yourself out of corners you have
designed yourself into, with no concept of capital cost)


--
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
...
wrote:

If have a vented primary circuit then you could heat it directly or
indirectly. Personally I favour a sealed primary, and hence would opt
for indirect heating of the store.

Please stop guessing. Best have direct all the way and elimate heat
exchangers and improve efficiency.

As you have said yourself on many occasions, the efficiency of a plate
heat exchange is very good.

But not better than direct which eliminated them completely.

Sealed systems are generally preferable when they can be used.

Are they? New on me. Since when?

Or cut the complexity, go for a boiler with a decent modulation range,
and let the boiler drive the rads directly.

Which is an expensive more complex boiler and does not modulate down low
enough.

More hand waving dribble? How much more complex?

A lot. Look at a Glow Worm HXi inside. Not much there at all.

Answer - very little difference.

Says the amateur.

Price difference? hundred perhaps. Hardly figures in the grand scheme of
things does it?

A top quality boiler that modulates low, none go low enough, with decent
control is north of £1K more like £1.5k

enough and an auto by-pas has to be used reducing efficiency on part
load. You need to understand buffering. Big in Germany. Fitting one
combi does not make you a heating engineer.

Posting ill thought through "solutions" on usenet does not make you one
either.

I am one. That is obvious as you learnt a lot from me :-)

Neither does you inability to maintain any grip on capital cost of your
projects.

How many projects have you undertaken? Mmmm...none!! Apart form fitting
your own combi.

If you really want lots of zones you may be better with a pair of
largish primary "backbone" pipes providing flow and return points for
each floor, and then teeing off them for the individual rooms / zones.

Pumps under the floors? Shishhhhh.

Who suggested under the floor? You it seems. You are right though, daft
idea.

Local control from loop pipe means local equipment in odd places, usually
under the floor.

Best have all controls in one place.

With a boatload of pipe running to and from each zone...

.....and ease of fitting, maintenace and setting up. The pipe to rads can be
microbore. The heat bank/buffer is in a central location. The OP stated
that.

This pipe will just return back to the boiler raising the return temp
lowering efficiency.

Which pipe?

This loop you are on about. What other pipe were you on about?

I think you will find flow and return pipes with rads strung across them
is pretty much how most heating systems work (if you ignore old single
pipe systems). Perhaps you should read up on the background a little.

You were advocating a loop, which is a glorified header around the house
giving off heat where not needed.

You may find a combi with its HW output feeding the shower, and a fast
recovery indirect cylinder on a zone on the heating side of the boiler
would meet that requirement better.

Er no..... Best have a cold water accumuator.

Ah right, and how much does that cost?

£300 to £400. A Stuart Turner pump for one shower is around £250, more for
higher pressures, then the fittings on top...and the noise too. This does
"all" of the house and stores cold water too. I have put a number in to
great success. Very impressive. They work well with heat banks and high
flow combis.

20 lpm while not a huge supply rate is not dire, and more than adequate
for a shower.

Note also if you go back to the OPs requirements: "I'm renewing the boiler
and propose to use a combi as a replacement. For HW I'm happy with the
flow rate this will give. We use modest amounts of hot water don't need a
big store in reserve."

Its funny how you flipflop between "a combi is ideal because there is no
room for tanks in small British houses", to "Oh just slap in a 300L
accumulator alongside the heatbank" depending on which way it suits your
argument.

His house is big. He explained that. The accumulator can go in a garage,
loft, garage loft (where I have put them) or just about anywhere. He has
the choice of open cold tanks or an accumulator which will give superb mains
cold water flow and pressure, eliminating pumps

If he had no space then a high flow combi and a new mains pipe to the street
is the way.

(not suggesting an accumulator is a bad idea in general - it has a place
in some installations. Just entertained how your solutions run on and on
sucking in ever more hardware to get yourse

They change to what the OP responds as he releases more info. I can't mind
read. If I was him I would make up a DHW/CH buffer heat bank and fit an
accumulator. First I would see what the cost and difficulties are to get
the mains pipe upgraded. Even if it costs £500 then I would have a new
mains pipe and drop the accumulator. The accumulator is a get out of jail
solution to poor mains pressure problems, although a brilliant one. It
stores cold water, gives it at high flow and pressure eliminating pumps,
enables the use of mixer taps all around with aerated heads to use less
water, no pump noise, electricity used, etc.

Hi Folks Frank here again.

Just to say thanks again for all the input.

I have been through the whole thread now and found DD's description of
how to
convert a cylinder from August 2007.

Also a couple of useful schematics.

Just getting my head round the responses overnight and today.

I'll try to come back with some thought out final system options that
suit my pocket/ability/temperament and some sensible points for
clarification later on.

I think this house is pretty leaky/poor u values. there is more to do
in the draught exclusion dept. The IDHEE calculator said I needed a
28kw boiler. It is a mid row terrace with partial DG and good loft/
basement insulation but stone with plaster and lathe dry lining
against quite a few external walls. Certainly some rooms cool down
pretty fast.

Is there a good heat loss calculator for rooms I could use? It has
been mentioned several times. How should I apply the info?

More later.

Thanks again.

Frank Front

A bit more...

If 25lpm @ 2.0bar 25lpm @ 1.5bar might be a problem as you seem to
suggest (measured at top of house) would it help to replace the 15mm
from the stop cock at ground level with 22mm pipe?
I think the lead inside diameter is more than 15mm but less than
22mm. It's about 7m of vertical pipe to get to the boiler if I put it
on the top floor as I propose. (Rooms about 3.5m high on ground and
first floors).

(Doing my best to give you all the relevant info without writing a
book.)

Frank

wrote:

I think this house is pretty leaky/poor u values. there is more to do

That was the point I was making to dribble about modulating boilers. The
fact that the boiler can't modulate from 0kW to full output is
generally neither here nor there since the house will still have some
heat losses. Even a reasonably well insulated place is going to leak a
few kW - so a boiler that modulated from say 6kW will be able to run
giving a nett contribution of only a couple of kW upwards. This will
allow efficient running with relatively little cycling even without the
thermal store.

One thing a store does very well, is allow very high flow rates of hot
water at mains pressure - but this is something you have said you are
not that fussed about. They were also very good in the days when boilers
only ran at high fixed outputs - acting as a buffer allowing the boiler
to do longish burns heating the store, while in turn it fed heat to the
house at a slower rate. While this is still the case, a modulating
boiler can make a pretty good stab at doing this all by itself these
days. So, IMO, the advantages are far less significant. The 90%+ SEDBUK
ratings on modern boilers assume typical setups and controls, so even if
you can improve on the efficiency and squeeze few % more out of the
system, you need to assess if the extra hardware and install costs of
the store are going to give worthwhile returns. There is a fair chance
that in financial terms alone they never will unless you have huge gas
bills. So will you get improvements in comfort or functionality to make
the cost worthwhile?

in the draught exclusion dept. The IDHEE calculator said I needed a
28kw boiler. It is a mid row terrace with partial DG and good loft/

If you genuinely are leaking 20+ kW then you need to spend money on
insulation and draft proofing as a matter of urgency! Having said that
many of these heat loss calculators tend to overestimate. You can
probably get a much better feel for the actual numbers if you just do it
with a spreadsheet.

(I have an example sheet if you want a copy - but see the end of this
email for a worked example).

I found on my place (5 bed semi, three storey, 9" solid wall + render,
dg all round, and top storey insulated to modern standards) that worst
cases losses (i.e. -3 degrees C outside) were about 8.6kW. With the
outside temp at a more typical 10 degrees, that falls to 3.5kW.

basement insulation but stone with plaster and lathe dry lining
against quite a few external walls. Certainly some rooms cool down
pretty fast.

Is there a good heat loss calculator for rooms I could use? It has
been mentioned several times. How should I apply the info?

There is a Myson one that is not bad - used to be available on their web
site but IIRC is not currently. Andy Hall may be able to lob you a copy
if you email him. Failing that, a spreadsheet, some u-values, surface
areas, and air change estimates will mean you can DIY.

Heat loss for a room:

you need to compute the area (in m^2) of each of the main surfaces. You
need to know the target temperature for your rooms, make a gustimate at
the likely air changes per hour, and know something of the construction
of the walls etc.

[fixed width font will help here]

Typical room parameters

Room type Room temp Air Changes
Lounge 21 1
Dining Room 21 2
Bedroom 18 0.5
Hall and Landing16 1.5
Bathroom 22 2
Kitchen 18 2


Material parameters:

Materials u-Value

Wall - outer 9" solid brick 2.2
Wall - internal plaster over 4" block 1.2
Wall - internal PB over stud 1.8
Floor (ground) - solid concrete 0.8
Floor - PB + joist + FB flow up 1.9
Floor - PB + joist + FB flow down 1.5
Roof pitched with felt + 100* insulation 0.3
Window - wood DG 2.9
Window - wood - low E 1.7
Door single glaze 3
Wall Insulated 0.6

* insulation assumed to be high performance foiled PIR foam

Example room:

Room Surface Area Tdelta u-value Loss AirC Vol

Lounge Front Wall 4.40 24 2.2 232 1.00 31
Window 4.80 24 2.9 334
Party Wall 8.40 0 2.2 0
Hall Wall 8.40 5 1.2 50
Rear Wall 6.90 0 1.2 0
Floor 13.45 24 1.9 613
Ceiling 13.45 3 1.9 77

Total 1307 267 1574

So in this example you can see there is 4.4m^2 of outside wall (and
4.8m^2 of window). The temperature difference is 24 degrees (assuming -3
outside). That means you lose 232W (area x TDelta x u-value) through the
wall, and 334W through the window. If you look at another wall - say the
party wall, the nett loss is zero since I am assuming next door's lounge
will be at least as hot as ours. Add all the losses (some of which may
be negative - i.e gains from an adjacent rooms) and you get 1.3kW. Next
deal with the air changes.

You compute room volume (31m^3 in this case, the floor area x the room
height). That is 0.36 x TDelta x Num air changes per hour x volume. (the
0.36 being constant based on the heat capacity of the air). This figure
will be a bit pessimistic since it assumes all the air changes are
happening with your nice heated air and cold outside air.

Add the two together and you get a total for this room of a tad under
1.6kW. That lets you size the rad for the room, as well as being part of
the answer for the house as a whole.



--
Cheers,

John.

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| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Thank you very much for that John.

I think losses can't be as bad as the calculation I gave you and I've
a feeling that included hot water needs. If that makes a difference.

The radiators in the rooms aren't huge and they do okay without the
existing very ancient Potterton kingfisher ll being cranked up to more
than just over half on the temperature knob. It seems to be about
28Kw.

In the rooms where the chimney losses are controlled and the shutters
get closed things are fine. However when the rads go off on a
particularly cold evening it becomes apparent pretty quickly.

On a slightly different tack I would be very interested in what the
inefficiencies/short-comings you and DD reckon would result from the
following (as it would help me to compare better with the outcome of
the heat bank method).

So considering CH only now:

Using a boiler for the CH complete the usual frills - weather sensor,
modulation, user adjustable bypass valve. What exactly are the
efficiency short-comings going to be if I zone that output (I've
manged to crunch down from ten zones to seven) using simple room stats
linked to centrally placed timers and conveniently located valves?

It would be very easy in my set up to pop a simple thermostat into
every zone with out any making good necessary.

In the bumf for most boilers it seems to assume one is going to just
fit TRV's to all the radiators and have a thermostat in the kitchen by
way of interlock block. This would be wasteful and inconvenient for
the way we use our house. (Though I do take your point about a cool
room sinking heat from a warm one.)

With the set-up I've outlined above I am not sure how to create the
interlock block. A 'master' stat might spoil it for some other part
of the house if it switches off. I imagine a secondary circuit
linking all the room stats in parallel would be needed so that when
none of them are calling for water the boiler stops. Is that right?

Incidentally taking our lounge for an example the floor area is about
26msq with one external wall with a DG bay window. The radiators
(against the external wall) I inherited are a total of about 1.6kw and
are fine if the shutters are closed and it isn't really bitter out.
To my shame I have to report that a) a sofa is pressed hard up against
the largest one, b) the chimney is partially open.

Thanks again to you and DD for your time and insights. I look forward
to your responses to the above.

Frank.

wrote:

I think losses can't be as bad as the calculation I gave you and I've
a feeling that included hot water needs. If that makes a difference.

They probably do... whether you need to depends on the type of water
system you have and your usage:

Traditionally they would add on say 5kW for HW and assume use of a mid
position valve that would allow the HW to be heated at the same time as
the rads. The cylinder coil would have been limited to approx 5kW
transfer anyway (which would give slow recovery times), so it made sense
to add the HW load to the heating one and run them together.

With a storage system that has fast recovery, it may well be able to
take all (or a sizeable part) of the boilers output, hence the
configuration that assigns priority to the water heating. Get the HW
reheated quick and then switch back to the CH after.

With a combi, then you can ignore the CH side altogether in most cases
and just size it for the HW requirements. Again it assigns priority to
the HW in that it can only heat one at a time.

The radiators in the rooms aren't huge and they do okay without the
existing very ancient Potterton kingfisher ll being cranked up to more
than just over half on the temperature knob. It seems to be about
28Kw.

If you have any marginally sized rads, then now would be a good time to
change them. Allowing for use of lower flow temps is also a good idea.
In many cases swapping single panel to double or ones without fins to
finned ones can let you do this with relatively little upheaval.

In the rooms where the chimney losses are controlled and the shutters
get closed things are fine. However when the rads go off on a
particularly cold evening it becomes apparent pretty quickly.

Which sounds like you have quite high rates of air change in these
rooms. Sometimes just fixing drafts from windows etc can make a
difference even if you leave a chimney open since it prevents a through
draft.

On a slightly different tack I would be very interested in what the
inefficiencies/short-comings you and DD reckon would result from the
following (as it would help me to compare better with the outcome of
the heat bank method).

So considering CH only now:

Using a boiler for the CH complete the usual frills - weather sensor,
modulation, user adjustable bypass valve. What exactly are the
efficiency short-comings going to be if I zone that output (I've
manged to crunch down from ten zones to seven) using simple room stats
linked to centrally placed timers and conveniently located valves?

I would be surprised if you could not loose a few more zones by lumping
together some rooms that have roughly similar usage even if not identical.

You may want to consider using a prog stat in place of a conventional
one and timer. Not only do they tend to be more accurate stats than the
bog standard mechanical ones, they allow much better control of
temperature to suit your usage.

It would be very easy in my set up to pop a simple thermostat into
every zone with out any making good necessary.

Yup, if you choose the room in the zone to be the one that is hardest to
heat, and stick TMVs on the other rads in the zone.

In the bumf for most boilers it seems to assume one is going to just
fit TRV's to all the radiators and have a thermostat in the kitchen by
way of interlock block. This would be wasteful and inconvenient for
the way we use our house. (Though I do take your point about a cool
room sinking heat from a warm one.)

Well you can do similar - but with a stat per zone etc.

With the set-up I've outlined above I am not sure how to create the
interlock block. A 'master' stat might spoil it for some other part

If you have a stat for every zone then that achieves the goal. Once the
house is to temperature, there will be no call for heat from any of the
stats.

of the house if it switches off. I imagine a secondary circuit
linking all the room stats in parallel would be needed so that when
none of them are calling for water the boiler stops. Is that right?

They can in effect be wired in parallel to generate a call for heat.
When they are all satisfied there will be no call. (you may choose to
implement this using the switches on the zone valves rather than the
signal directly from the stat. A neon can also then wired up for each
valve to give you a handy "valve failed" indication by lighting up when
volts are applied to one side of its switch from the stat, but the
switch remains open)


--
Cheers,

John.

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"John Rumm" wrote in message
...

On a slightly different tack I would be very interested in what the
inefficiencies/short-comings you and DD reckon would result from the
following (as it would help me to compare better with the outcome of
the heat bank method).

So considering CH only now:

Using a boiler for the CH complete the usual frills - weather sensor,
modulation, user adjustable bypass valve. What exactly are the
efficiency short-comings going to be if I zone that output (I've
manged to crunch down from ten zones to seven) using simple room stats
linked to centrally placed timers and conveniently located valves?

Efficiency shortgains are that by-pass opens on part load to create a direct
shortcut to the boiler raising the return temp far too high. That is if it
is set properly, which most are not, and even then they can run out of
setting in time. They can also restrict flow through the boiler too,
causing heat exchanger damage. When heating a thermal store cylinder
directly there is always full flow through the boiler. The boiler is
operating in an ideal hydraulic environment, which means it will last longer
and be more efficient.

You may want to consider using a prog stat in place of a conventional one
and timer. Not only do they tend to be more accurate stats than the bog
standard mechanical ones, they allow much better control of temperature to
suit your usage.

But no central control.

It would be very easy in my set up to pop a simple thermostat into
every zone with out any making good necessary.

Yup, if you choose the room in the zone to be the one that is hardest to
heat, and stick TMVs on the other rads in the zone.

Best have TRVs all around and no stat to cut out when some rooms require
heat.

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

I think this house is pretty leaky/poor
u values. there is more to do

That was the point I was making to dribble about modulating boilers. The
fact that the boiler can't modulate from 0kW to full output is generally
neither here nor there since the house will still have some heat losses.

Oh my God, Chav, you really haven't a clue. Most boiler don't go below 8Kw
when up to temp the house will be calling for less than 8kW and then
inefficient boiler cycling occurs with the by-pass valve opening and then
efficiency drops like a stone.

A heat bank/thermals store can trickle kWs into a heating system and no
impair boiler performance, efficiency and longevity either.

One thing a store does very well, is allow very high flow rates of hot
water at mains pressure

Cha, you are getting it.

They were also very good in the days when boilers only ran at high fixed
outputs

They are still very, very good, nothing has changed.

- acting as a buffer allowing the boiler to do longish burns heating the
store, while in turn it fed heat to the house at a slower rate. While
this is still the case, a modulating boiler can make a pretty good stab at
doing this all by itself these days.

A poor stab at it I'm afraid. Modern boilers are designed for the
replacement boioer market, where rads were designed to run at 82C, hence
modulation which is not that effective a sthe boiler makers tells us. Then
TRVs on all rads makes matters worse for the boioetr. When having TRVs all
around best have them fed froma buffer cylinder (thermal store)

The 90%+ SEDBUK ratings on modern boilers assume typical setups and
controls, so even if you can improve on the efficiency and squeeze few %
more out of the system, you need to assess if the extra hardware and
install costs of the store are going to give worthwhile returns.

A boiler can be running at over 100% if set up properly heating a store.

There is a fair chance that in financial terms alone they never will
unless you have huge gas bills.

Chav, you just made that up.

So will you get improvements in comfort or functionality to make the cost
worthwhile?

Most certainly!

Heat Loss:

If a boiler is correctly sized for the heat loss at say -3C outside, when -3
it should run flat out continuously. Few do as most are oversized, then
boiler cycling occurs.

A great thing about a thermal store is that doesn't care how large the
boiler is, as long as the flow and return pipes are sized correctly. If a
house requires say 15kW and a 30kW boiler is coupled to the store cylinder,
it will just heat up faster and still no cycling. A boiler twice the size
of CH requirements directly heating rads will cycle like hell.

Also having the CH and DHW off a thermal store 100% electric backup is
available to CH & DHW, and also a second cheap backup boiler can be coupled
directly to the store too. So, a cheapie B&Q job boiler can act as a backup.
It will last as it will only be used once in a blue moon - so full cheap to
run on gas, 100% backup. Or have both boilers on and zippo re-heat. Great
when there is multiple showers and baths going on.

John thanks for that. All grist to the mill. I'm hoping we'll hear
some more from Dr Drivel soon.
In the mean time I take your point about prog stats however my
thinking was to keep the cost of zoning down by using basic analogue
stats which are cheap and have bimetallic strips so (I imagine) have a
wider hysteresis that digital so would reduce activity at the valves.
If I used centrally placed timers for the zones - as DD pointed out
less running around - they could be basic two channel timers normally
used for CH and HW but on this occasion two zones. The CH channel
will likely have a 'boost' facility which could be given to the most
deserving of the two zones controlled. This is the cheapest way of
zoning I could think of.

As you say TRVs on the secondary radiators on any given zone.

I like the idea of the neons for the valves. Nothing like a steady
red light for comfort.

Hope to hear more from Dr Drivel soon as you both seen to have
different and very informative views on the same things.

More thought required by me on the best overall approach and
specifically which way to jump on the HW provision - combi or HB...

Regards,

Frank.

wrote:

John thanks for that. All grist to the mill. I'm hoping we'll hear
some more from Dr Drivel soon.

Not often you read that in this group ;-)

In the mean time I take your point about prog stats however my
thinking was to keep the cost of zoning down by using basic analogue

Horstman prog stats are only about £24 in screwfix.

stats which are cheap and have bimetallic strips so (I imagine) have a
wider hysteresis that digital so would reduce activity at the valves.

at the expense of bigger swings in temperature - the prog ones do make a
noticeable difference to comfort.

If I used centrally placed timers for the zones - as DD pointed out
less running around - they could be basic two channel timers normally
used for CH and HW but on this occasion two zones. The CH channel
will likely have a 'boost' facility which could be given to the most
deserving of the two zones controlled. This is the cheapest way of
zoning I could think of.

It looses the ability to have the temperature of the zone vary over the
day though - this is one of the big wins with a prog stat. In a bedroom
for example to have it warmer as you wake and go to bed, but then
setback overnight and during the day etc.

As you say TRVs on the secondary radiators on any given zone.

I like the idea of the neons for the valves. Nothing like a steady
red light for comfort.

Would be easiest to wire so that they only come on when a valve has a
demand, that has not been satisfied... but yes in general a cheap LED or
neon can make a massive difference to the ability to diagnose problems
quickly.

Hope to hear more from Dr Drivel soon as you both seen to have
different and very informative views on the same things.

Dribble seems to make it a matter of principle to adopt a contrary view
on everything. ;-)

More thought required by me on the best overall approach and
specifically which way to jump on the HW provision - combi or HB...

The choice is yours... ;-)

--
Cheers,

John.

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

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

John thanks for that. All grist to the mill. I'm hoping we'll hear
some more from Dr Drivel soon.

Not often you read that in this group ;-)

You tend to get this:
http://tinyurl.com/2wdd25


The Elson Coral ST thermal store. All Elson "Coral" products are square
thermal stores that can be easily packaged in high positions or under
worktops. They have about 3 variations. They may be able to make one to
your specific size, call them.

You absolute God. The Coral Si is perfect,
though they may even be able to
do better, because for a small cost.


If I used centrally placed timers for the zones - as DD pointed out
less running around - they could be basic two channel timers normally
used for CH and HW but on this occasion two zones. The CH channel
will likely have a 'boost' facility which could be given to the most
deserving of the two zones controlled. This is the cheapest way of
zoning I could think of.

It looses the ability to have the temperature of the zone vary over the
day though - this is one of the big wins with a prog stat. In a bedroom
for example to have it warmer as you wake and go to bed, but then setback
overnight and during the day etc.

He could just have the timer switch on the bedrooms evening and morning.
Simple.

Hope to hear more from Dr Drivel soon as you both seen to have
different and very informative views on the same things.

Dribble seems to make it a matter of principle to adopt a contrary view on
everything. ;-)

Chav, I am a pro not an amateur. I look at thing logically, not what I have
fitted in my own house - which in your case is one combi.