Solar heating cylinder

[Odsox]

Can anyone explain to me why you need a new cylinder for evacuated tube heating set up ?
I am seriously thinking of installing a 20 tube panel and as far as the costs are concerned it is just about do-able, until you see the part about needing a brand new stainless steel cylinder costing well over a thousand pounds/euros.

Is this sort of system pressurised and if so why ?
I can see no mention on the sites that sell you these systems as to why you need such an expensive piece of kit.

[MKG]

I have no direct knowledge of solar heating, but here's a straightforward engineering viewpoint. Evacuated tubes are a very efficient method of heating water (and it can get very hot, so you may need a method of dealing with excess heat - but that has nothing to do with the storage tank). I'd be willing to bet that most solar heating applications involve a heat exchanger coil within the hot water tank - so the tubes themselves are a closed system and so, once again, have nothing to do with the storage tank. The storage tank is simply somewhere to put hot water - it doesn't know whether that heat comes from an immersion heater, solar heating, a back boiler etc. and, what's more, doesn't care. You may well need a stainless steel tank for a pressurised heating system, but there is no great reason why a solar heating system should necessarily be connected to a pressurised tank.

In general, then, I can see no argument for evacuated tubes having to be connected to a stainless steel tank, and I'd be very interested to read the source of your information - just who was it who said it was necessary?

[Odsox]

Thanks MKG. I have no knowledge of pressurised water systems although I know some central heating systems are pressurised.
I have seen various sites that say you need a "special" hot water cylinder, but the only one that I could find for reference is http://www.kbf.ie/solar/cylinders.htm which links directly from their solar panel page.

I realise that you need a secondary coil for heat exchanging although I have seen a direct system quoted on another thread.
A heat dump is no problem I think, just a 2 port valve and a radiator somewhere. I just wondered what the significance of a stainless steel cylinder over a copper one for half the price was.

[MKG]

Well, after a little more searching, it becomes very apparent that a stainless steel tank is in no way necessary for solar heating. They come, generally, with lifetime guarantees as opposed to the more normal 10 years or so for copper tanks (but I've never, ever, had to replace a copper tank, nor do I know anyone who has had to) and are, generally, twice as expensive as copper. Make of that what you will as far as a commercial proposition might go.

[Big Al]

From what i've gleamed and it is by no means the be all and end all of it but there is a coil in the tanks. What you might want to look for is a coil for each type of heating you plan to do. I will be using a solar system and a wood burning stove with back boiler. Also there will be the normal combi heater. Therefore what i am [ at present anyway] looking for is a cylinder with three coils in it. The bottom one is for the solar heating, the second is for the wood burner and the third is the combi boiler. I was going to do away with the combi boiler as it's 16 yrs old and runsd on gas which I want to get away from the reliance on the energy companies but I was told i could just cap off the water [taps] part and use the otherside of the comi as an aditional source to heat the water if wanted. I guess it's belts and braces etc as to have the combi bit kick in it would need to be a very dull day [ no solar] with no wood to burn [stove] and then the combi would be used. This is not going to happen but belts and braces etc.

As for pressurised system I believe it is called a vented and non vented system. The idea behind a non vented system is that you can use mains pressure water so the taps is a lot faster and you can fill a bath in 3 to 4 minutes because the mains pressure goes through a coil and the water is heated in the coil by the hot water in the cylinder. Some coils have a mass of fins on so they heat the water faster and hence the abillity to fill a bath with hot water. I haven't at the moment got my head around the use of a wood stove / boiler on a non vented system as the water will need to expand and contract. How this will work in a sealed system I am not totally sure.

I'm still in a quandry as to how the CH will work although I think it will be using the hot water direct in the cylinder so you fill the cH system from the cylinder and then this water is heated by one or more of the coils from the heat sources.

If I'm making sense then hope that helps....

[Odsox]

My system, if I do it, would just be a simple system.
A panel of tubes on the roof with a small pump controlled by a thermostat pumping the heated water through the secondary coil of my copper cylinder ... full stop.
I don't need any other coils as the back up for cloudy days would be an immersion heater.

I also think that a system that I've seen with the pump being driven by a small PV panel ought to be a good idea too. After all, if there's no sun to generate electricity then there's no point in running the pump.

Big Al, I don't think the pressurised system that you describe applies to me anyway. Our "mains" water is a private supply from a mountain spring through about a mile of alkathene pipe ... the pressure is totally dependant on how much (or little) rainfall we have had.
I think for your pressurised non-vented system you need an expansion vessel to take care of the expansion/contraction in the pipework. It's similar to a small gas bottle full of air connected to your pipework, it works because air can be compressed where a liquid cannot.

[Odsox]

Just thinking about what I wrote on the above post, I might have answered my own original query.

If I have a solar panel on the roof, how do I get a header tank above the panel ?
If it was a pressurised system it wouldn't be a problem ... hence maybe the need for a more robust cylinder ?
Does that make sense ?

Should this be a problem then at least I have the option of mounting the panel at ground level, with the added benefit that I ought to be able to pipe it for thermo-syphon system and do away with the pump and controller.
The disadvantage of ground mounted panel is that I have 3 grandchildren here that play like children do ... kicking footballs, playing cricket and practising with a hurley.

[BDT]

I am thinking about heating my existing hot water cylinder with solar and back boiler sources then supplying a new non vented system with the pre heated water from the existing hot water system. Any thoughts?

[Odsox]

This is the kind of thing that is designed to confuse !
Taken from this site .. http://www.ashgrove.ie/solar-panels-schematic.htm
According to them you need not one, but TWO cylinders, presumably both stainless steel ones.
I can see how this might be an advantage if you intend to run central heating this way, but there is no explanation on the site. Also I'm amused that there is no water feed or expansion provision for the solar loop.
I hope I eventually get to grips with this solar panel idea.

[MKG]

Very pretty diagram. Highly inefficient. Complete crap.

You'd get an immediate payback by losing the two cylinders and replacing them with a single cylinder with two exchanger coils.

[contadino]

Very pretty diagram. Highly inefficient. Complete crap.

Ha! You're not wrong there. It's another example of an overpriced, over-engineered, overly complicated system.

[snapdragon]

http://www.firesonline.co.uk/acatalog/D ... ystem.html

This is a device to join two forms of water heating, a small additional cylinder that links heating systems

[Big Al]

Some interesting sites....


http://www.gledhill.net/building-produc ... ar-dia.pdf

http://www.gasapplianceguide.co.uk/torrent_indirect.htm

http://www.gledhill.net/building-products/bp-index.htm

http://www.greensystemsuk.com/solar_hot_water.php

[sunnybp]

The price for end user may be a little high. As far as I know, the price of solar water heater with 20 vacuume tubes is about USD400. For the delivery cost, custom tax and retailer profit, the price will higher.

[xone]

You can retrofit your current tank if you don't use your immersion.

Go here >> http://www.futureenergysystems.org.uk/solar-hot-water for more information.