Hot water

Quick question:
Anyone know of a supplier of fast recovery vented hot water cylinders of 250L capacity[4]?
Loads of unvented cylinder are available at about that size, but your common or garden type seems scarce...
The background (this is partly an exercise in thinking aloud!):
Just deciding if it is cost effective to make a heat bank...
The choices for main pressure HW production seems to come down to:
COTS Heatbank like DPS Pandora I got a quote from them, and a 250L one with all the trimmings, ready to install and go, with pump and 160kW PHE on the output, a 12kW indirect coil to heat, plus 28mm blending valve, 3kW immersion, scale reduction[2], looks like costing about 1900
DIY Heatbank The paraphernalia around the edges could come to say 450, so much depends on the cost of a suitable tank...
Unvented [1] anything from 500 - 900
(and no, I don't want a combi, so let's not go there!)
Now most of the killer applications of a heat bank don't really apply in my case. I won't be integrating solar[3], solid fuel, or biomass etc, and heat pumps are at best only likely to match mains gas for price. So the main attraction is that in a hard water area, any scaling is going to be limited to the PHE, its a low maintenance option, and the (minimal) risks from having a pressurised cylinder are avoided. Installation is slightly easier, since there is no need for a emergency drain connection.
[1] Yes I know it supposed to be installed by a G3 certified bod, but they all come under building regs these days, and how many people remember to do a BN for a hot water tank swap? If one were to DIY, this is quite a cheap option. Pay for someone to do it however would probably make it the most expensive.
[2] DPS seemed keen on fitting a HydroFlow HS38A electronic water conditioning widget... I enquired if they found this effective, and they seemed to think that it worked in this application.
[3] The ideal roof slope is littered with dormers and chimneys, so nowhere to put a decent sized panel. (plus I am trying to do this with minimum capital outlay!)
[4] Doing the sums and planning for future requirements (i.e. at some point will have two teenagers co-resident <shudder>), I reckon on needing 400L of final temperature water from one "charge"[5] of the store. That comes to about 230L of store temp (70 deg C) water required to achieve that (spreadsheet available if you want it).
[5] Best overall efficiency is going to be achieved with a weather compensating controller on the boiler. The modern integrated electronic jobbies also seem to take care of all sorts of little details like being able to programme a period of high flow temperature operation for water cylinder recharging, while running the rad zones at far more efficent and appropriate temperatures. This tends to suggest that the best mode of operation, is to recharge the store during a heating setback period, and not attempt to do it while running any heating zones. The logic for this being you don't interrupt your heating, and your rad flow temp won't have to run up to 70 all the time the HW is calling for heat.
The down side of this is that you can't really augment the size of the store by allowing for concurrent boiler recharging - hence it needs to be big enough to cope with most eventualities.
--
Cheers,

John.

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wibbled on Tuesday 13 October 2009 05:20

Hi John
I got mine from Newark Copper
http://www.newarkcoppercylinder.co.uk /
They will customise a cylinder for you - I chose a standard form factor, in my case 1500mm x 500mm then sent drawings of top and all 4 sides (N,E,S,W) showing positions I wanted tappings and what the tappings were (solar, 3/4" BSP, 22mm compression, 1/2" sensor, immersion boss or dry sensor well).
Came to 612 + VAT + 30 delivery though copper prices are volatile. I had 3 immersion bosses and loads of sensor pockets and tappings.
Mine is directly heated - I presume by "fast recovery" you want a coil?
They offer a choice of foam insulation depths too.
They were certainly very helpful to me and rang up to query when something looked like it wasn't going to work physically.
I had most dealings with Tom Sharpe.
Cheers
Tim
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Tim W wrote:

That's uncanny. Just as I posted that message the other night, I had half a dozen tabs left in firefox with copper cylinder makers loaded up ready to read - that was the next one on the list ;-)

That sounds like it would be getting on for 300L - or is that the size including the foam etc? Oh, and I suppose you lose a bit for the solar coil.

OK ta.
Have you costed and selected sources for those bits yet? (ok, scratch that - I just looked at the spreadsheet you sent me!)
What connections are on that mixing valve BTW? They look threaded from the piccie...

Yup, I am going to use a sealed system primary (I want the space back occupied by the header tanks, plus there is not really enough head to make a vented system work well (that and I don't like vented systems at the best of times!).
That leaves the option of a coil, another PHE and pump, or a tank in tank type of arrangement. PHE is nice in that it gives rapid recovery, top down heating, and good condensing efficiency, but at the expense of another (albeit small) PHE and pump. However since its not going to be easy to arrange "on demand" heating of the store, the full boiler capacity recovery is less essential. A coile would probably be ok if its big enough to keep inside the boilers modulation range for most of the reheat.

How much did you go for? (I want some leakage to keep the airing cupboard warm)

Ta for that...
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Cheers,

John.

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wibbled on Tuesday 13 October 2009 17:56

I think it's nearer 250l - the dimensions are the size of the copper (no foam) but of course include the domed top and bottom, so you do lose out there. There are other standard sizes of cylinder - look at their solar page so you can probably select exactly what you want. The solar coil is 15mm.

I went to visit DPS too. There stuff was nice, but they were fairly expensive as you found. And I decided I wanted more custom options on mine. I have:
Top, under dome + just above solar coil - boiler connections in direct 22mm compression (that's an option now, no need for 3/4" bosses).
About 1/3 and 2/3 height, 2 sets of 22mm - one for rads and one for UFH.
Solar coil is placed about 0 and 1/4 height.
Absolute top and bottom - expansion and feed/drain, dualling as DHW circuit.
4 IIRC 1/2" bosses for thermostats (2 tank stats, one up top for solar overheat and one in the middle of the coil for solar (or tank stat).
6 dry sensor wells evenly spaced from top to bottom which one day I hope to shove some Dallas 1-wire temp sensors in and make the controller more intelligent - I can measure the stratification.
Doing the drawing was a bastard. Sketchup was just too painful with cylinders. So I went old-skool and used 2D CAD and contruction lines to draw top down and 4 side projections by hand. You could just as well do it on paper - Newark re-CAD it anyway.

22mm compression. DPS seem to favour 28mm for extra flow. I decided to use a mixer for DHW and UFH and run the rads at tank temperature. I can of course set the tank stats and boiler temp to regulate this if the rads are too hot or cold.

I think Newark could make you the coil the way you want.

Ditto - so I went for 50mm. The can do 25mm or more than 50mm (though they say they hate doing really thick ones).

Cheers
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Tim W wrote:

250L would do me I think. I am only using it for HW and not heating. I reckon that 250L at 70 degree would blend down to about 400L of shower or bath temperature water.

One trick I did pick up from talking to them which I thought was quite cute was how they do their vent. They actually put an expansion vessel on it, but discharge the air side of it (I presume wither by removing the schrader valve or drilling the case). This means the store remains at atmospheric pressure, but you have an effective vapour barrier enclosing it. (probably looks better than sticking a rubber glove on the vent ;-)

A high as pos on the flat side. or right on top of the dome?

IIUC with the boiler I am considering it used a temperature sensor rather than a stat - so pockets for that would be handy. As you say, a few others to instrument the thing would be nice...
Wandering off at a side track, do you know of any good value data acquisition boards with to discrete and analogue inputs, and can run TCP/IP over ethernet?

Yup, I will draw it up a see what gives...

I am tempted to go that way as well - the price difference was not huge, and I can see a time that it will be running two showers at once plus incidental usage.

I am going to leave mine running under the control of the weather compensated output from the boiler. Split into a couple of zone with prog stat control for each (plus TRVs obviously).

Something that can shift at least 12kW most of the time would be good. That's well in the modulation range of the boiler.

I have visions someone with a bucket of foam and a bad attitude! ;-)
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Cheers,

John.

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They remove the shrader valve. They fit an anti-vacuum valve and vent with anti-evaporation protection. This could be a gravity (non-spring) check valve fitted vertically. If the pressures gets substantially above atmospheric then the check valve opens and allows out pressure. It take a bit of pressure to lift the valve from its seating. The anti-vacuum valve then steps in to allow air in if a vacuum occurs when cooling off. If the check valve fails and pressure builds up because, say check valve fails, the loose diaphragm will break.
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On Tue, 13 Oct 2009 23:16:49 +0100, John Rumm wrote:

Arduino?
http://www.arduino.cc/en/Guide/ArduinoEthernetShield
The Arduino can use 1-wire sensors.
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Dave Liquorice wrote:

Interesting ta...
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Cheers,

John.

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On Thu, 15 Oct 2009 00:15:43 +0100, John Rumm wrote:

Coo, didn't you guys know about the Arduino?
The big snag of course is the interface from nice friendly logic to big nasty mains required for valves, pumps, boilers etc. Those could well cost more than the entire Arduino setup.
My current 4 zone 2 pump 1 boiler with pump overrun CH/HW control system is done with wiring and relay logic. It's not 100% on the pump overrun but it works. If I was doing it again I'd go for a PLC with enough I/O then the logic would be correct on the pump overrun and would have half a dozen DPDT relays involved... I might look at something like an Arduino but that interface problem raises it's head, a PLC is just a large block with lots of mains rated I/O...
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Dave.




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wibbled on Thursday 15 October 2009 14:36

No ;->

This perhaps:
http://uk.farnell.com/finder/38-51-7-012-0050/relay-screw-term-6a-12vdc/dp/1169346
It's true they're not cheap (nigh on a tenner) but I reckon you could drive those directly from an AVR (14mA coil current at 12V). Or a cheaper relay and a transistor?

What PLCs are worth looking at?
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On Thu, 15 Oct 2009 15:22:24 +0100, Tim W wrote:

to
could
Perzackerly 50 for the an Arduino with ethernet. Then in my system 4 valves, 2 x pumps and 1 x boiler 70 for the relays not to mention a rats nest of wiring.

It's a long time ago now but I looked at the Mitsubishi Alpha. Played with the PC software got it doing what I wanted without very much (if any) RTFM. B-)
http://www.mitsubishi-automation.com/products/microcontrollers_ALPHAXL .html
Not cheap but a neat one box solution with a display that could give friendly information about the system. Rather than having to use LEDs or neons on the real outputs (and all the extra wiring that entails).
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Dave Liquorice wrote:

Alas no. The vast majority of embedded systems I have done have usually been on someone else's bespoke designed hardware (and frequently the poorer for it!). There is a whole world of small cheap off the shelf controllers out there that it could be fun to get to play with.

It looks like it could sink enough current for reasonable sized relays.
(I once had to use a daft 8031 microcontroller based hybrid (i.e. device, plus IO and external memory all on a 27C257 sized EPROM), that could not even switch a conventional bi-polar transistor by itself! We had to use MOSFETs on the output line, just to have it be able to flash a LED!)

Indeed, although ultimately its usually just a bunch of relays and a processor of some description to drive them. Its the programming environment that can make them more accessible and/or frustrating though.
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John.

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wibbled on Thursday 15 October 2009 16:18

You'll like AVRs then, which the Arduino is based on (forgive egg suckage - I assume you've not come across them?...). The C is very clean and the worst bit is reading the data sheet to load the configuration registers to configure each IO pin to one of umpteen and submodes.
After that, driving the pin is pretty much doing an "=" in C or a bit set if you desire.
Even the interrupts play nicely. And AVRs come from 8 pin 50p jobbies to 40 pin ones like this:
http://uk.farnell.com/atmel/atmega1284p-pu/mcu-8bit-avr-128k-flash-40pdip/dp/1715481
(128k flash, 4k EEPROM, 16k RAM, 20MHz and loads of features on board)
Those will drive 40mA per pin upto a max of 200mA total for the package, so easily 10+ well chosen relays.
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wibbled on Wednesday 14 October 2009 23:02

That looks pretty cool and reasonably priced. AVR based too. You could use their programming environment or dump it and code in C, which works very nicely on the AVRs and gcc is the defacto compiler. Nicer to work with than PICs IMO.
http://www.coolcomponents.co.uk/catalog/index.php?cPathP&sort *&page=1
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DPS claim the Pandora Heat Bank needs no overflow. This is nonsense. If the plate heat exchanger becomes holed the cylinder will fill with mains pressure water. This means something has to blow. That will be the weakest point, the rubber diaphragm open to atmosphere. Which means water spurting all over the place.
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On Thu, 15 Oct 2009 09:17:08 +0100, Doctor Drivel wrote:

If /any/ mains-fed pipework or component becomes holed you'll have water spurting all over the place. Are PHEs especially liable to holing? Given the number of combis on my patch which I'd get called out to if such a thing happened (it hasn't) I think it must be improbable enough to discount. In other words I think DPS are at least as justified in discounting it as unvented cylinder manufacturers are in not calling for their products to be installed in blast-proof bunkers ;-)
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Men are from Mars, Women are from Venus and Pop Psychologists are from Uranus
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I have known plate heat Xs to have holed. Not a lot, only one. It can happen because Murphy's law says so. If it does water all over the place.
Unvented cylinders have safety devices. The Pandora does not. if the cylinder fills up the diaphragms will bust in the expansion vessel - the weakest link. The expansion vessel open to atmosphere is to prevent sludging and evaporation of water as it is not open to the atmosphere.
Geldhill's Sytemate could be filled via an F&E with no ballcock - filled by hose. The water evaporated so the customer needed to top up.
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You could screw a pipe into the top of the pressure vessel and run this to outside. Then if the plate does hole there is an overflow. But that defeats one of the advantages shouted from the rooftop by DPS - no overflow or pressure discharge pipes needed to atmosphere.
But, it can be run into a tundish and into an internal drain via a HepVo trap, so no building fabric penetrations.
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On Thu, 15 Oct 2009 12:08:27 +0100, Doctor Drivel wrote:

So you mean "I have known one PHE to have holed". With respect, John, that's a statistically insignificantly basis on which to diss DPS' design. One might equally well insist on doing all water pipework in double-walled tubing and god-knows what other belt-and-braces measures on the basis of the small number of holes which occur in copper tube, brass fittings etc.
At the end of the day it's only water: we want running water in our houses and the price is that occasionally we will have it in places we don't want.
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Eagles may soar, but weasels don't get sucked into jet engines.
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That sounds like the voice of someone who earns a living on the bleeding edge of technology.
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