Ping Andy Hall re flowswitches

[mike ring]

Andy Hall wrote in news: [e-mail]:

Many thanks for your link to heatweb, Andy, and all the other gen.

My barf is in fact 1600 mm overall length and I figure 120L will fill it more than adequately, and there is absolutely no room for a bigger one. And my present elderly 96L one seems to work.

(I very rarely use the bath, I'd have to take the coal out first)

I think you are right about tank sizes, I might go for a 120L indirect or perhaps an 80L superduty type (thanks to IMM for another source of quick recovery tanks!), but I think 120L is safer.

I get adequate flow from the bath tap and the washbasin, so might settle for a booster for the kitchen sink; maybe just a shower pump.

Anyhow I can now find the necessary bits and do some sums, and felt much better informed on what's what.

Sorry about provoking the discussion with IMM, but I learnt something from that, so it wasn't all wasted - I bet that makes you feel better!

Regards

mike

[Andy Hall]

If you are going to cut and paste, then quote the complete text.

Their definition for recovery assumes going from 20 to 60 degrees. The 20 degree starting point will only happen in the summer.

They don't say what the results will be with 5 degree or even 10 degree mains cold water because that makes the figures look a great deal worse.

With 5 degrees as the starting point, the recovery time would be more like 11 minutes and the production rate 245 litres/hour.

More importantly, they also neglect to mention that even under these idealised conditions, the water would be delivered as 7.5 45 litre lots. This is not the same as the equivalent for the 80 or 120 litre cylinders which will be able to deliver a good bath load with a bit to spare.

This isn't to say that fast recovery cylinders aren't a great invention - they are. However, the reality is being stretched here.

?????

It's irrelevant anyway because it's a red herring.

It demonstrably is unless the requirements are downgraded to the point that taps have to be mucked around with to reduce flow and juggling with hot and cold has to happen.

ROTFLMAO.

Err.... let me see now. What's the principle of physics behind all of this? Energy = mass x specific heat x temperature rise.

Hmmm...... sounds like thermodynamics to me.

Could it be that engineering has to abide by the laws of physics?

Well there's a turn up for the books.

as long as you don't have expectations of filling a bath to any useful depth quickly without messing around with the taps and waiting around.

.andy

To email, substitute .nospam with .gl

[Andy Hall]

You're only talking about 900 high (albeit 450mm) rather than 750 (at

400mm) so it isn't a big deal unless you are very tight on space.

Is the issue that the pipe run is longish to the kitchen? You could possibly improve the flow by running some of it in 22mm. The trouble is that it then takes longer for the hot to come through which is probably not what you want.

A shower pump would help. They do need careful siting though. It should really be at the floor level of the cylinder, not in the loft. Also, they like to push not pull the water so need to be nearer the tank and cylinder than the taps.

.andy

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[Andy Hall]

Yawn.....

.andy

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[IMM]

80 litres quick recovery will do your requirements. No need for bigger. Don't take any notice of people with no experience of these matters reading from school physics books.

[IMM]

< snip Andy and he doesn't know what he is on about >

[IMM]

You don't know anything about engineering. It is not in your schule physics book.

[Andy Hall]

Well... in fact I have an engineering degree, but don't let that fact confuse what you wanted to say.

.andy

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[IMM]

You do engineering and never have.

[Andy Hall]

NMI..... time for a reboot.....

.andy

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[mike ring]

Andy Hall wrote in news: [e-mail]:

Yes, and it's diameter that's the bind; the present cylinder is 400, 450 would be ok, I think, 530 is not on, as it won't go through the door. (No, I'm not removing the frame). but of course, shorter would also have been better - another shelf in the inadequate airing cupboard.

Also I have to allow for pipes, pumps etc., and my plumbing skills.

I'm considering - just - a preplumbed one, in spite of the cost, but I don't think it has a prayer of having the bits in the right place. And I might like to try S plan, (I think it was you suggested that way back when I was horrified at the titchy holes in a 3port valve). But it all depended on finding ou what's about, what's feasible, and reasonably efficient. I didn't get a flood of answers saying "superduty 45L - transformed my bathtimes".

One basic problem is that the system has almost certainly add-ons to the original coal fired back boiler with gravity h/w. and no-ones improved the core piping etc. I keep coming back to 15mm pipes grafted on to 1" fittings.

True, that's the real bugbear. I think the main prob is the posh monobloc mixer tap with 10mm tails and a 2mm spout in a one hole fitting (in a Franke Granit sink, no option to go to two good oldfashioned taps without rebuiding kitchen)

Thanks, I was considering siting under the sink!

Thanks again, good luck with the skirmish with IMM

Regards

mike

[IMM]

No luck in it, he doesn't stand a chance.

[Andy Hall]

You can get them customised. It's possible that Albion or Telford etc. might do this.

You can get S-plan zone valves with a rotating paddle that gives a fair proportion of the bore rather than the rotating rubber ball arrangement used in others.

.andy

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[Mike Tomlinson]

In article , Andy Hall writes

Doesn't it rather depend on whether Archimedes habitually eats at McDoodles or is a stick insect? :)

[David]

In article , IMM writes

John, reading this thread I can only conclude that after all this time you are just a troll, surely no real person can really be as stupid as this

[IMM]

Bertie, you are still confused.

< snip babble >

[David]

In article , IMM writes

Sometimes certainly, but still not as stupid as you appear to be, I don't know why you do it, is your life really that sad? sat here night after night typing out drivel

[IMM]

Bertie, you are confused all the time.

< cut babble >

[Matt Beard]

{{senses a trap, but steps in anyway}}

OK, let's see, assume that this bungalow (which is so small that a standard sized cylinder cannot be accomodated) has a 30kW boiler (a tad large wouldn't you think?) and that this 30kW boiler combined with a quick-recovery cylider can magically give the same performance for "continuous hot water" as a combi (wow where did all those losses go?) then you could expect a 12l/min flow to give a rise of about 35C.

Assuming an incoming water temp of 5C and also assuming that the maximum possible use is made of this temperature rise (heating ONLY cold water, not attempting to heat any of the hot/warm water still in the top half of the cylinder) you could get 45l of "hot" water (at original tank temp, say 60C) plus a quantity of water that has been heated from 5C to

40C.

At 12l/min this would take 3mins 45s to transfer the 60C water to the bath, then in the next 1min 15s you would get 15l of 40C water. Total water from the hot tap = 60l at an average temperature of 55C. Great, except that to get the quoted 100l bath filled in 5 minutes you would also need to have the cold tap running at a rate to add an extra 40l of water at 5C giving a total of 100l at 35C (whoa! chilly half-full bath!!).

This is an over simplified model, but the errors in the model should all make the calculated temperature HIGHER than an accurate model.

Conclusion: Unless this method of heating water is considerably more efficient than using a combi there is no way you are going to get a bath filled with 100l of water at a decent temperature in 5 minutes.

[IMM]

No. But do go on.

No magic in it.

Yes.

What losses?

The other way around. 35C rise of about 12 l/min.

It is.

For your understanding:

Alpha CB50 combi with integral 57 litre unvented cylinder heated via a quick recovery coil. Output to water 28kW. Time to raise water store 50C: 8 mins Reheat time for 70% of store: (boiler ON): 3.5 mins (boiler OFF): 5 mins Outlet water temp: 65C.

This combi has an auto flow regulator, so that when the cylinder temperature is low the flow is restricted so the burner only is heating the water at a usable temperature. A two stage flow rate combi that never runs out of hot water. Neat eh?

Having 30kW output to water and a smaller quick recovery coil cylinder will give somewhere near the same performance. The Alpha easily fills a bath of

100 litres with hot water to spare.

If a heat bank was used and a two stage controller to maintain the DHW setpoint, the performance would be very good. When hot water is called for, the burners is always full on, well modulates up to max burner rate. Then if the flow rate is higher, like filling a bath, the second stage of the controller brings in the heat from the thermals store modulating the speed of a pump. This way the stored hot water assists the burners, not the other way around as other stored water combi's do. The Output of the two heat sources (burner and heat in the store) is combined at all times. A burner is

1st stage, store energy in the water is preserved. Performance then would be much better all around, extending the high flowrate time.