Mixer valves for thermal store?

[Doctor Drivel]

Use a Remaha Broag "dual temperature boiler with integrated weather compensation. The cheapest way of doing it.

[Doctor Drivel]

Using a 150kW plate heat exchanger will lower the store temperature 10C or more as it extracts far more heat from the supplied water - the return temperature will be far lower. This promotes condensing efficiency. You still have the option to raise to 80C if you wish.

Look on Ebay 150kW plates are available. Or maybe two 75kW plates in series if the two are cheaper than one 150kW.

[PCPaul]

I was hoping to use most of the existing stuff (a decent set of evacuated tubes and a fairly new 24kW condensing combi that can be configured as a system boiler instead - but can't take preheated input to use as a 'solar combi').

So - thermal stores - am I right in thinking it works by heating big lump of water/slate/whatever to a highish temperature then giving 'instant mains pressure DHW' by passing mains cold through a coil inside the heat store? Sort of like a conventional tank, but inverted?

[YAPH]

wiki.diqfaq.org.uk has an article on thermal stores and heat banks

[Doctor Drivel]

Avoid coils if you can.

John Stumbles has doen a peice on them here:

bity short on some points but as an overview OK.

[Tim S]

PCPaul coughed up some electrons that declared:

Yes - although the tap hot water can be done buy pumping water through an external plate exchanger (looks like a metal brick with two independant water circuits). This is what I'm doing, although a 100kW exchanger is more standard, and John aka YAPH used a 50kW on in his, which is well worth a read:

nicked all his ideas and a few from other sources :)

Cheers

Tim

[YAPH]

't say anything about inbuilt triacs - ?

And apart from the fittings it looks like the type that failed on a customer's Pandora :-/

Can't remember off the top of my head what I found good. I think that's about right. If it's not sensitive enough your hot will go cold when you're running a low flow from a mixer tap (especially if you've got aerators to reduce water consumption). Too sensitive, of course, and it switches on if you have a slight leak, but you won't have that anyway, will you? ;-)

[Tim S]

YAPH coughed up some electrons that declared:

"Material, Contact:Triac"

as opposed to ruthenium...

:-<

Ok-dokey. Seems like a good enough bet then. Thanks. I shall double check with some empirical measurements, but a litre/min seems pretty slow.

Newark called - made my cylinder already! It is however going to stay there because I don't want it for 3 weeks... Making too much brick dust right now. Ordered a GRP 27 litre F&E tank. 27l is on the low side for a system with about 350l of capacity (expect 10l of expansion under normal conditions) but space for tank is limited. Have to rig the tank so it's got no more than 10cm of water in it when it's cold, but that's doable. It'll have about 20cm when system is hot.

GRP because it's over my daughter's head, when she's asleep. Although it would take a double wrongside failure to boil over (two stats or stat plus boiler failure), it seemed a sensible precaution.

Cheers Tim

[YAPH]

D'oh!

Durr, on my planet triacs are for switching AC - wonder why the specs only mention DC currents[1]? And what the difference is between # Current, Contact DC:0.5A and # Current, Switching DC Max:3A ??

[1] leaving aside the oxymoron of AC or DC /voltages/

[Tim S]

YAPH coughed up some electrons that declared:

It's OK - Farnell's description is talking bollocks. The datasheet says 250V RMS and 3A.

It does appear that it is pretty much designed to direct switch a pump, or other low power mains equipment.

Cheers

Tim

[Dave Liquorice]

With mechanical switches it's down to arcing. With AC the power goes off twice per cycle and thus the arc dies. This doesn't happen with DC the arc burns until the gap is too big for the arc to be sustained.

How this applies to solid state switching I'm not sure unless it's down to power disipation in the junction.

[Doctor Drivel]

> Doesn't say anything about inbuilt triacs - ?

The fittings failed or the flow switch?

[PCPaul]

Thanks to all for the link. I skimmed the FAQ a while ago but I didn't know that was on there now..

I'm guessing there's enough cost saving in doing your own over buying a commercial thermal store (£1000+) to make it worth doing?

[Tim S]

PCPaul coughed up some electrons that declared:

More like 2000 quid for a commercial one :(

Give me a day and I'll put up some drawings of what I'm doing and the price of the cylinder...

[YAPH]

That and it's easier to get an empty cylinder and sundry bits & bobs upstairs or even into an attic than a humungous Pandora (BTDTGTTS - the rectangular panny in the thermal store article was up a flight of twisty stairs!)

[YAPH]

Triacs only switch off when the AC drops to zero so they're a chocolate teapot for switching DC :-))

[YAPH]

The switch: it simply refused to switch on. ISTR it went intermittent and seemed OK after I'd replaced it, so I kept it and used it on another project ... at which point it went on strike again :-(

[Tim S]

YAPH coughed up some electrons that declared:

For that you need a GTO (gate turn off) thyristor, which is what they use on trains (well, DC ones, sometimes...).

I suppose a GTO triac would be possible, but there's not much demand...

[Doctor Drivel]

That is about the most reliable make around. bad luck.

[Doctor Drivel]

Google on this group "DIY heat bank" in the topic.