That's the conclusion I was getting to..
PVC pipe *can* take 180F temperatures or 12 bar pressure - but not both at the same time.
So it's a non starter. Oh well.
Do *you* know why a dual coil cylinder costs four times what a single coil one does, Ed?
On Sun, 13 Jul 2008 22:16:46 GMT someone who may be PCPaul wrote this:-
I was replying to, "Why do you need dual cylinder? I would take mains in into tank, heat with solar, then through combi. If the water is preheated the combi should just heat it less."
That was about using a single coil cylinder.
On Mon, 14 Jul 2008 00:07:53 +0100 someone who may be "dennis@home" wrote this:-
Boiler coils are short, even rapid recovery ones. They work on a large temperature difference and so don't need to be long. The extreme case is the primary in a large calorifier heated by steam or high temperature hot water.
Solar coils are much longer, in order to extract the maximum amount of heat from the primary.
On Mon, 14 Jul 2008 11:28:42 +0100 someone who may be Rod wrote this:-
Water in waste pipes doesn't remain hot for very long. Very different to the proposed use.
Total waste of money. Just slow the flow through them. You only need a trickle to collect the heat from a few sq meters and slowing the flow rate allows the heat to be transferred in a shorter coil. Sounds like solar coils are marketing BS to me.
On Tue, 15 Jul 2008 10:02:26 +0100 someone who may be "dennis@home" wrote this:-
Ah, proof by assertion.
Introducing artificial restrictions in the solar circuit increases the electricity consumed in the pump.
It also means that heat may not be removed from the collector quickly enough.
Ah, proof by assertion.
Have you got these on function keys?
A special pale green set down the side of the keyboard... ;-)
Ah, I see.
I've never seen a pure-solar cylinder, only dual coil versions.
marketing, the manufacturers+suppliers will charge what they can get for one. Probably worth shopping around.
I have a suspicion that Solar and unvented are not permitted, solid fuel and unvented are not allowed that's for sure.
A heat bank is by far the better idea, maybe cheaper and avoid regulatory hassles.
Ah. Green issues...
Why is that? Efficiency reasons? safety?
I'll have to read around them more. I thought heat banks were tons of slate buried underground in superinsulated pits... obviously I've missed a trick somewhere.
Going back to the idea of preheating the input to the combi, there can't be *that* many bits made of low temperature plastic on the cold inlet side of a boiler, can there? Could they be replaced?
No this wouldn't be at all ideal. The hot water would collect in the top tank and the overall efficiency would be much lower.
OK... I thought I understood this but now I'm not so sure...
With side-by-side, you'd be drawing water from the top of either the boiler heated or solar heated cylinder. If we optimistically assume the water has settled out first then we have say half the tank to draw before we get into the cold, or the turbulent water from the other tank.
If the solar tank is underneath and the boiler fed above, then the top tank should be at max-solar to full boiler temperature while the solar tank is from cold to full solar. If we draw off the top tank we get a full tank before touching cooler water.
What am I missing? If side by side works better, why do we have tall upright cylinders not long flat ones?
No, you'll have nominally an equal amount of hot water in each cylinder, irrespective of which heating coil is active. You'll be drawing off water equally from each.
Even the tallest upright cyclinder has it's coil at the bottom!
For one, when the top cylinder is hot, how's the coil inside that one going to heat the cold water in the bottom one?
Ah, denial by assertion.
Reducing the current to the pump reduces the flow and uses less electricity.
Just how sunny do you think it gets?
That is a statement of fact, no proof required. There can be no argument about it unless you have some machine for seeing what I think.
There isn't a coil inside the other.. the idea is that the boiler heats the upper coil and as hot water rises it doesn't heat the lower part.. the solar coil heats the bottom.. the cold water comes in at the bottom and displaces the solar preheated water upwards where it is heated by the boiler.
With two cylinders you just connect them in series, water into solar heated one and then into boiler heated one.
The heating circuits are independent.
A twin coil system has the advantage that the solar coil will heat the entire cylinder if you turn the boiler off (and its sunny enough).
On Tue, 15 Jul 2008 21:36:29 +0100 someone who may be "dennis@home" wrote this:-
For a given pump, the options to reduce the current are limited. Assuming it is on the lowest setting, for solar most are, the only option is a variable speed controller. One could change the pump, but most will reduce the flow rate by introducing an artificial restriction.
Stagnation temperatures are well over 150C with vacuum tubes.
When a system is running properly the collector temperature will sit at around the temperature difference above cylinder temperature. If it rises much more than this then heat is not being removed from the collector fast enough.
The bulb of a vacuum tube left in the sun will get too hot to touch within 20 minutes (don't try this at home). That is why the tubes are the last thing to be installed, after the rest of the system is working.
On Tue, 15 Jul 2008 16:59:22 +0000 (UTC) someone who may be Ed Sirett wrote this:-
They are allowed, though with the usual bureaucracy involved with "large" pressure vessels.
In fact most solar circuits are "unvented" themselves. It gives a higher flash margin, amongst other advantages.
And/or a bypass, so the resistance is less. No point in working the pump more than necessary.
Irrelevant.
On a system without a speed controller on the pump.. not a chance.
On Wed, 16 Jul 2008 13:13:02 +0100 someone who may be "dennis@home" wrote this:-
Ah, proof by assertion. In fact it confirms the point I made at the start of this part of the discussion. Heat must be removed from the collector quickly enough.
Ah, proof by assertion again. What I described is how the systems I am most familiar with spend large parts of the summer.
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