Solar water heating and combi boilers

[PeTe33]

:¬)

Likewise with "organic"

[Mary Fisher]

Not true.

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[Peter Parry]

If it proves popular what's the betting ownership of it will get taxed (indeed the mechanism for doing so has already been put in place by Nulabor) :-).

I'd be interested in seeing any. The only mentions I have found are unsubstantiated statements usually made by peddlers of solar fittings.

Both have bearing on the life of the "conventional" system and hence the economics of solar water heating. In many boilers the pumps and control valves are integrated within the boiler.

The boiler casing. It is a fairly common cause of terminal failure of room sealed boilers.

I snipped the bits about saving energy (which I agree is a far more sensible starting point and applicable no matter what system is used) but didn't see anything about how solar heating can save more gas than people think.

So will unsubstantiated and incorrect claims for solar water heating making economic sense. People may buy it for other reasons not all of which may be altogether objective and that is their free choice. What is wrong is to claim it makes _economic_ sense when quite plainly in the vast majority of cases it doesn't (which of course is exactly why the proponents of it always studiously avoid using figures).

For example the oft quoted solution of the solar powered motor pumped panels on the direct side of the water system makes great claims about the economic sense of doing this (saving the few watts an electric pump takes) but makes little or no mention of the fact that for most people living east of a line drawn roughly from Lincoln to Bristol you also need to install an ion exchange water softener otherwise the panel will quickly be ruined because of scale from the hard water.

[Mary Fisher]

You haven't given any evidence of your claims.

[John Rumm]

Well, let us get some...

How much did your solar system cost in total?

[Mary Fisher]

No, dear, he's supposed to be providing the 'evidence'.

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[Mary Fisher]

Why do you want to know?

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[John Rumm]

I will let him do that, but my question still stands if you don't mind me asking?

What did your system cost to have installed? And what does it consist of?

[John Rumm]

Because I am curious obviously!

Solar systems seem to vary from those essentially assembled from scrap (old radiators and yards of black MDPE pipe etc), to very high tech vacuum tube based collector systems run by sophisticated digital controllers. You have posted in the past about how your system performs, but that only gives us half the story without us also knowing what components it is made from, or what its capital cost was.

[Mary Fisher]

I have also given the url.

Far be it from me to be accused of advertising so I shan't do it again.

Most people seem to think that the payback time is the most important aspect of such installations. We don't (we don't consider the payback time on anything else we buy either) but for those people we've worked out that on present gas prices we'll recover the cost in ten years (if we live that long). I doubt that present gas prices won't stay what they are so nobody can determine what the payback time will be.

Nobody.

That includes you and Parry and all the other sceptics.

Mary

[Steve Firth]

FWIW, prices have been dropping fast recently. I've picked up a 300 litre

20 vacuum tube unit for the tractor shed/store at the farm. We're installing a bathroom/office at the back of the store and the only source of hot water will be solar. The total cost of the unit + installation is £700, cheaper than an LPG system.

[John Stumbles]

Mains pressure hot/warm water --------- from thermal store | combi | ------------------+->--| DHW |--->--- | --------- | | ----- | | H | | | TMV |---->--- | | C | | ----- | | ---------->-----------

Actually, thinking about it, the arrangement above may just work (or Just Work (tm) :-)) without faffing about with thermostats, motorised valves etc. As long as the temperature of water from the store is above the TMV's set point it'll only draw water from its Cold inlet i.e. directly from the store. Only when the water gets too cool will it draw from its Hot inlet which should automatically kick in the combi.

Note that in this case the TMV is not limiting the temperature of DHW which could possibly get dangerously high when the solar system is working well, so you may want another TMV mixing the output with cold water from the main.

[John Stumbles]

Hint: google for fisher and solartwin :-)

're about £1500 to buy.

[John Stumbles]

I'd have thought a (much cheaper) phosphor-dosing scale inhibitor would serve this purpose, as it does for other water-heating appliances such as combi boilers. Do you have some evidence to show that this is not the case?

[Mary Fisher]

You have to understand the limitations of some folk, they expect to be spoon fed :-)

Mary

[Chris Bacon]

If you're going to snip, and I commend you for this new departure, please do it properly. Some actual info. instead of simple trolling would be nice, too.

[Peter Parry]

That turning boilers off for weeks or months on end causes harm? Ask your local plumber. Failing that look at the pattern of repairs that one user of this group who fixes such things by the thousand has reported in the past - each autumn the spares consumption increases dramatically as boilers come on after summer and pumps, valves and PCB's fail.

If you want a more academic treatise Failure Modes Effects Analysis by Palady discuses failure modes effects and criticality. Shafts bind to bearings if not used - Machinerys Handbook (every edition since the beginning of the last century).

It is simple basic mechanics. There is ample evidence that lack of use shortens life and causes harm in devices such as boilers. There is none at all that not using them for some months every year does them good or extends their working life.

[Steve Firth]

Say what? The water in the panel should be recirculated and contain rust and scale inhibitors (as in a primary boiler circuit). The heat should be transferred to a separate hot water cylinder of exactly the same type as is used on non-solar systems.

[John Rumm]

Yup, found it ta...

(it does help when you have read the original post so that you know the name of the system to google for!)

[John Rumm]

Must have missed that...

The solartwin one?

OK I have downloaded and read through the installers manual....

Interesting system... the "direct" plumbing approach solves a number of the normal complications of similar systems (although introduces some as well).

What form of water softening do you use with it, or do you have soft water in your neck of the woods anyway?

Payback time is only one measure as you say (although in many cases the economic cost of an activity also has a good correlation with its environmental cost as well)

Have you made any estimate of its heating power on a sunny day?

Why do you call me a sceptic? The only scepticism that I expressed with regard to solar water heating, was when used with a combi boiler that does not also have some form of storage. For example the system you have would be of no practical benefit in this circumstance since the flow rate through the panel is far to low to do much in the way of either pre-heating the inlet water or directly blending with the output of a combi.