Solar water but missing cylinder..

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.
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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/cylinders/gxv/operation/GXOperation.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.
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On Wed, 07 May 2008 17:00:24 GMT someone who may be PCPaul

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

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.

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.

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.
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David Hansen, Edinburgh
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Designed by computers. Built by robots. Installed by an idiot.
It needs storage. What else might he have done wrong?
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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.

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
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wrote:

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.

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_pressure/thermaflow/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.
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PCPaul wrote:

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
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On 8 May, 13:06, snipped-for-privacy@care2.com wrote:

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?
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