"John Stumbles" wrote in message
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On Tue, 08 Aug 2006 12:58:35 +0100, Doctor Drivel wrote:


"John Stumbles" wrote in message
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On Mon, 07 Aug 2006 00:09:05 +0100, Doctor Drivel wrote:


"John Stumbles" wrote in message
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This works and provides excellent recovery but you do need a gravity
(not sealed/unvented) primary.

???

What do you mean '???' ?

If the primary is unvented you have an unvented hot water cylinder of
15l
requiring all the appropriate safety controls. This rapidly gets outside
DIY.

You missed it.

I don't think so ...

No, you never. We shall see.

Some quick recovery cylinders can be quite expensive. I gave a solution
which would outperform a quick recovery vented cylinder using a bronze
pump,
plate heat exchanger and cheap direct cylinder. The flow and return to
the
coil would just go into the plate heat exchanger. The plate and pump
replaces the quick recovery coil. The bronze pump is switched in at the
same time DHW is called. This will take all the output of a 40,50,60kW
boiler outperforming a quick recovery coil and cheaper in many cases.

Yes I got that but that wasn't what I was talking about.

Then I said if the mains pressure is good, using a flow switch and a
cheaper
pump a heat bank can be made from the same components. The cylinder will
be
vented at atmospheric pressure. The only high pressure is in one side of
the plate. All cheap and works a treat.

Yes, that was what I was responding to. I said that it gives excellent
recovery (which mine certainly does) but I pointed out that the primary
must be vented (which you didn't specifically mention in your earlier post
though you do above).

The primary does not have to be vented at all. The cylinder can be heated
via a coil and the primaries a part of a sealed unvented system. The only
time they require venting, is if the cylinder is being heated directly.

So are we agreed?

You never got it.

Vented primary + direct cylinder + pump + flow switch + PHE = DIY heat
bank/thermal store.

It doesn't have to be heated directly.

My only reservation is that with my cheap standard direct cylinder
("Screwfix Direct direct cylinder") the amount of hot water you get from
it off the electric immersion is probably only enough for a shower. I
think it really needs a larger cylinder, and/or maybe an immersion heater
mounted at the bottom of the cylinder to _reduce_ stratification when
heated electrically. Probably something like a large off-peak storage
cylinder would be more suitable.

A large thermal store is an advantage if electric only. But an eletric
boiler and pump will heat it up reasonably fast.