Our current house has a solar water heating system put in by a previous
owner.

Or rather, it has half a system. We have 8 large evacuated tubes on the
side wall, a thermostatic mixer in the loft and a modulating combi
boiler..

...but there is *no* preheat cylinder.

As far as I can see, this means the only benefit we get is that when we
actually draw water the boiler gets really hot water from the underworked
tubes (temperature limited by the mixer valve). So, not much help at all,
really. No storage.

Has anyone else come across this setup? Is it worth fitting a dual coil
cylinder to add some storage to the system? If so, can it go in the loft?

I've looked at the installation manual for the boiler and it can be set
up to handle a cylinder as well as being used as a straight combi.

"PCPaul" wrote in message
om...
Our current house has a solar water heating system put in by a previous
owner.

Or rather, it has half a system. We have 8 large evacuated tubes on the
side wall, a thermostatic mixer in the loft and a modulating combi
boiler..

..but there is *no* preheat cylinder.

As far as I can see, this means the only benefit we get is that when we
actually draw water the boiler gets really hot water from the underworked
tubes (temperature limited by the mixer valve). So, not much help at all,
really. No storage.

Has anyone else come across this setup? Is it worth fitting a dual coil
cylinder to add some storage to the system? If so, can it go in the loft?

I've looked at the installation manual for the boiler and it can be set
up to handle a cylinder as well as being used as a straight combi.

Where is the cold water runing to? Through the panels?

Look at a heat bank thermal store - ideal.

Look at this.
http://www.heatweb.com/products/cyli...Operation.html

A drain down direct solar heat bank.
http://www.heatweb.com/solar/solargx.pdf

Many other companies do heat bank thermal stores, not just this one.

On Wed, 07 May 2008 17:00:24 GMT someone who may be PCPaul
wrote this:-

Our current house has a solar water heating system put in by a previous
owner.

Or rather, it has half a system. We have 8 large evacuated tubes on the
side wall, a thermostatic mixer in the loft and a modulating combi
boiler..

..but there is *no* preheat cylinder.

Presumably the tubes are the sort with over-temperature protection,
otherwise they would probably overheat.

As far as I can see, this means the only benefit we get is that when we
actually draw water the boiler gets really hot water from the underworked
tubes (temperature limited by the mixer valve). So, not much help at all,
really. No storage.

When the boiler is running for a shower or bath the tubes will soon
cool down, so they will not give much heat when needed most.

Is it worth fitting a dual coil cylinder to add some storage to the system?

A dual coil cylinder implies that it is to be heated by the boiler
as well as solar. Are you intending to re-arrange the hot water
supply for better performance? Perhaps the cylinder doing bathrooms
and the boiler a hot tap in the kitchen?

Where is the boiler? If it is nearby then a single coil cylinder may
be a better bet, with the water just heated by solar.

Depending on the tubes, do you have information on the make, type
and dimensions of the tubes, they may not be enough to heat a large
cylinder. The options would then be a small cylinder or more tubes
and a large cylinder.

If so, can it go in the loft?

It can, provided there is proper access. Note also that a
pressurised cylinder involves extra hassles and these can be avoided
by a thermal store, which would feed hot mains pressure water to the
boiler without these hassles.




--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

On 7 May, 18:00, PCPaul wrote:

Has anyone else come across this setup? Is it worth fitting a dual coil
cylinder to add some storage to the system? If so, can it go in the loft?

Designed by computers. Built by robots. Installed by an idiot.

It needs storage. What else might he have done wrong?

On 7 May, 18:00, PCPaul wrote:
Our current house has a solar water heating system put in by a previous
owner.

Or rather, it has half a system. We have 8 large evacuated tubes on the
side wall, a thermostatic mixer in the loft and a modulating combi
boiler..

..but there is *no* preheat cylinder.

As far as I can see, this means the only benefit we get is that when we
actually draw water the boiler gets really hot water from the underworked
tubes (temperature limited by the mixer valve). So, not much help at all,
really. No storage.

Has anyone else come across this setup? Is it worth fitting a dual coil
cylinder to add some storage to the system? If so, can it go in the loft?

Absolutely but keep in mind the weight of a cylinder - ten pounds
weight per gallon or 62.5 pounds wieght per cubic foot of water plus
the metalwork.

I've looked at the installation manual for the boiler and it can be set
up to handle a cylinder as well as being used as a straight combi.


The rate of solar absorbtion in the uk is simply insufficient to give
a throughflow system with the typical domestic size of panels.
To gain a worthwhile benefit you must have some means of energy (heat)
storage.
My system is happily churning away at the moment 10.00 am, with the
collector at 47 degrees and the bottom of my twin coil vented cylinder
at 39 degrees C, top at 52 residual from yesterday.
By early afternoon yesterday the collector was at 63 degrees and the
cylinder at 58 degrees all the way to the bottom.
In high summer the limit programmed for the cylinder is 65 degrees
which would stop pumped transfer of heat. When that happens the water
in the header of the panel would vapourise and the resultant steam
cause that part of the primary water volume to be pushed back into the
(20 litre) expansion vessel. The tubes are designed to look after
themselves.
When water is drawn and cold enters the bottom of the cylinder the
sensor detects this and the controller restarts the primary
circulation, cools the header and energy absorbtion resumes.
I bought mine as a kit (Panel assembly, sensors, controller, twin coil
cylinder) from an e-bay shop circa £1000 but the impetus was a need to
replace the old cylinder anyway.
If you already have an evacuated tube panel you are about 40% there
In your position I would install either an unvented twin coil cylinder
or a vented conventional system again with a twin coil cylinder. If
you go down the route of the vented cylinder you could retain the
combi hot water outlet for the shower supply

"cynic" wrote in message
...
On 7 May, 18:00, PCPaul wrote:
Our current house has a solar water heating system put in by a previous
owner.

Or rather, it has half a system. We have 8 large evacuated tubes on the
side wall, a thermostatic mixer in the loft and a modulating combi
boiler..

..but there is *no* preheat cylinder.

As far as I can see, this means the only benefit we get is that when we
actually draw water the boiler gets really hot water from the underworked
tubes (temperature limited by the mixer valve). So, not much help at all,
really. No storage.

Has anyone else come across this setup? Is it worth fitting a dual coil
cylinder to add some storage to the system? If so, can it go in the loft?

Absolutely but keep in mind the weight of a cylinder - ten pounds
weight per gallon or 62.5 pounds wieght per cubic foot of water plus
the metalwork.

I've looked at the installation manual for the boiler and it can be set
up to handle a cylinder as well as being used as a straight combi.


The rate of solar absorbtion in the uk is simply insufficient to give
a throughflow system with the typical domestic size of panels.
To gain a worthwhile benefit you must have some means of energy (heat)
storage.
My system is happily churning away at the moment 10.00 am, with the
collector at 47 degrees and the bottom of my twin coil vented cylinder
at 39 degrees C, top at 52 residual from yesterday.
By early afternoon yesterday the collector was at 63 degrees and the
cylinder at 58 degrees all the way to the bottom.
In high summer the limit programmed for the cylinder is 65 degrees
which would stop pumped transfer of heat.


Have it set to 90C and have a blending valve on gthe DHW outlet.


When that happens the water
in the header of the panel would vapourise and the resultant steam
cause that part of the primary water volume to be pushed back into the
(20 litre) expansion vessel. The tubes are designed to look after
themselves.
When water is drawn and cold enters the bottom of the cylinder the
sensor detects this and the controller restarts the primary
circulation, cools the header and energy absorbtion resumes.
I bought mine as a kit (Panel assembly, sensors, controller, twin coil
cylinder) from an e-bay shop circa £1000 but the impetus was a need to
replace the old cylinder anyway.
If you already have an evacuated tube panel you are about 40% there
In your position I would install either an unvented twin coil cylinder


Avoid unvented. It cannot be DIYed and costs an annual service each year.
Any economic solar gains are wiped out immediately. A heat bank thermal
store is the way.


or a vented conventional system again with a twin coil cylinder. If
you go down the route of the vented cylinder you could retain the
combi hot water outlet for the shower supply


He could install a pressurised thermal store (no G3 certificate needed) and
run the cold water through this. The outlet set to 30C by a blending valve,
so the combi will raise the water by 35C and give high flowrates. When cold
in winter the flow reduces, or have the combi heat the thermal store to
maintain the high flowrate. The thermal store can be as high as 90C.

Alpha do an off the shelf system. It is cheaper to do it yourself using a
combi booster by copperform:
http://www.copperform.co.uk/mains_pr...flow/index.htm

The Alpha Flowsmart:
http://www.alpha-boilers.co.uk/products/?id=7
http://www.alpha-boilers.co.uk/products/downloads/flowsmart_50/alpha_FlowSmart_service_guide.pdf

Also these combi boost thermal stores can have electric backup too. They
can be very small too. Copperform will add a solar coil for you.

PCPaul wrote:
Our current house has a solar water heating system put in by a previous
owner.

Or rather, it has half a system. We have 8 large evacuated tubes on the
side wall, a thermostatic mixer in the loft and a modulating combi
boiler..

..but there is *no* preheat cylinder.

As far as I can see, this means the only benefit we get is that when we
actually draw water the boiler gets really hot water from the underworked
tubes (temperature limited by the mixer valve). So, not much help at all,
really. No storage.

Has anyone else come across this setup? Is it worth fitting a dual coil
cylinder to add some storage to the system? If so, can it go in the loft?

I've looked at the installation manual for the boiler and it can be set
up to handle a cylinder as well as being used as a straight combi.

If there's no storage anywhere then presumably the CW feed is
running thru the tubes. This is not ideal, as scale usually occurs,
which with solar panels hits performance. At least it doesnt affect
vac tubes as much as flat panels. Theres also the risk of freezing
in winter, which would shatter the glass tubes.


NT

On 8 May, 13:06, wrote:
PCPaul wrote:
Our current house has a solar water heating system put in by a previous
owner.

Or rather, it has half a system. We have 8 large evacuated tubes on the
side wall, a thermostatic mixer in the loft and a modulating combi
boiler..

..but there is *no* preheat cylinder.

As far as I can see, this means the only benefit we get is that when we
actually draw water the boiler gets really hot water from the underworked
tubes (temperature limited by the mixer valve). So, not much help at all,
really. No storage.

Has anyone else come across this setup? Is it worth fitting a dual coil
cylinder to add some storage to the system? If so, can it go in the loft?

I've looked at the installation manual for the boiler and it can be set
up to handle a cylinder as well as being used as a straight combi.

If there's no storage anywhere then presumably the CW feed is
running thru the tubes. This is not ideal, as scale usually occurs,
which with solar panels hits performance. At least it doesnt affect
vac tubes as much as flat panels. Theres also the risk of freezing
in winter, which would shatter the glass tubes.

NT- Hide quoted text -

- Show quoted text -

I've not yet come across any evacuated tube systems which could pass
tapwater through the tube in the manner you describe. The "evacuated"
part is a twin walled glass tube enclosing a black sealed copper tube
containing a low boiling point liquid under reduced pressure. Light
energy (heat) passes through the glass and is absorbed by the black
surface, heating the liquid within and this vaporises, the vapour
rises up the tube to the capped top end. This top end is in thermal
contact with a horizontal manifold across the top which contains the
cylinder primary heating fluid. Heat is transferred, the vapour cools
and condenses, to be replaced by more heated vapour from below. It
would be possible to pass the tapwater through the manifold but you
would be lucky to get more than a degree or so of temperature
elevation in use. Under no flow conditions however a bubble of steam
would form and may scald users.

As you said - "not ideal"!

I have seen catalogued a panel which had a horizontal cylindrical
header abut 300mm dia, containing secondary tap water which is heated
more or less directly by the tops of the evacuated tubes. To the OP
does this sound more like your system?