What KW rating of standard cylinder coil?

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Without wanting to start a watersystems style flame war.

Say I were to heat the bulk store of a combi cylinder and instantly heat water via the coil what flow rate would this equate to? Would one get a 24kw conversion for insatnce?

Or is it always necessary to use two pumps and a plate heat exchanger for instant mains pressure dhw from an open vented thermal store?

Secondly, what if I just use the coil as a preheat for a 35kw combi? which I would expect to boost performance considerably to say 20 litres, but for more sustainability than what is available in the modern storage combi.
It's for a pub, failed system is a Sime super 4, which cannot really provide sufficient water for the pub kitchen bar sink and two rest rooms.

I expect the other quoters will go with a Worcester Hiflow.

I have in mind an unvented cylinder and system boiler, or a combi boosted by a thermal store, both ways would allow for some water via immersion heaters should the boiler or the gas supply fail.

Another consideration in mind is two combis in series for water, parallel for heating.

The gas meter is in the same room.
 
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I think even a Highflow would struggle.....people have a misconception of them that they deliver 18-20litres per minute, indefinatly. the dont and the flow rate drops after about 5-6 mins to a fairly average 11 litres per minute.

This is why i alwys rate a highout putr combi that can delivers 16litres+ indefinatly.


In this instance I think the best choice would a traditional tanks and boiler be it open or unvented.

Combi or Combis in series are not really going to suffice as a tap is likely to be used every few mins not really giving heating a fighting chance of doing its side of things.
 
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Powermax 150HEi

150lt stored mains water

18-20 min reheat

Immersion back up
 
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I didn't mention it heats the pub, so Andrews won't do.

I wasn't aware of that Potterton product. That looks really impressive, and should be the easiest option from the point of view of an installer.

Yes I take the point that with so many areas that hot water could be called from the heating will be cancelled many times. This could be overcome with a blend valve on the output of combi 1 which allows first water drawn to go straight to the taps, but in the event of too much flow being expected and water cooling diverts flow through combi 2. Combi 2 would therefore be available for heating most of the time. Yet in the event of a break down there would remain hot water at the flow rate of one combi and heating.

I have a nursing home on a tandem heating system, and a hostel, but in both cases when they call me for a breakdown both boilers have finally broken down. They don't even notice when the first one goes down. I have tried to educate them to check the boilers at least once a week. In both cases however I have been able to get one boiler going while I order parts for the second. Even if it's both fans, at least one of them usually gets going with lubrication long enough to get the new fan. Of course these things only seem to happen at 11pm on a Friday night and the clients in these sort of applications are as happy about no heating and hot water for a whole weekend as my wife is about the day before her period.
 
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There are two smaller versions of the Powermax the '115' and '85' (soon to be a '90') don't be tempted as they may deplete too quickly.
Never had a complaint of a 150 running out of hot water.
Doddle to install.
 
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How about a pair of CD50's.
If the HW outputs are separated and CH shared, someone notices if one goes down. A couple of lever valves can then cross connect the HW if required.
Have done a few similar - people lurve the redundancy.
 
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Paul Barker wrote

This could be overcome with a blend valve on the output of combi 1

A blend valve has three ports. Cold inlet - Hot inlet and Blended outlet.



which allows first water drawn to go straight to the taps, but in the event of too much flow being expected and water cooling diverts flow through combi 2.
Do you mean a thermostaticaly controlled three port divertor.

Combi 2 would therefore be available for heating most of the time. Yet in the event of a break down there would remain hot water at the flow rate of one combi and heating.

It sounds good if I knew what you were talking about, a diagram would be good.
 
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I was refering to the Alpha part, it takes the output from the 90ltre solar store and diverts it through a suitable combi as required. Substitute solar for combi 1.
 
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Bigburn said:
It sounds good if I knew what you were talking about, a diagram would be good.

The heating outputs of both boilers are in parallel, the hot water output of one boiler is sent to the Alpha patented blend valve, which sends the output of combi one straight to the tap until the temperature drops below 60 degrees cenbtigrade whereupon it sends all the output through combi 2. Finaly tmv's at sensetive outlets.

For the use of the Alpha blend valve on any combi check first with the manufacturer that A/ the combi can takeup to 60 degrees incoming and B/ that the warranty is not affected. Yes these conditions are met with Alpha boilers. But should also be achievable with many others.
 
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I think my solution would be to use TWO cheap combis.

First mainly as a kitchen/bar hot water source and No 2 heating boiler.

Second as heating No 1 boiler and DHW to washrooms with auto off DHW taps fitted there.

Both boilers would be manually switchable to perform either function!

Probably suggest two Vizos as the best value! And as they are condensing very economical !

My installation would be so simple and easy and my price would undercut you significantly and I would have 100% spares in stock.

Tony
 
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Dualcombi3.jpg


Like this Paul.
Problem is the thermostatic sensor senses cold water initally, so the flow passes through the second combi until the sensor senses heat and shuts off the flow through the second combi .
 
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I can't see a 24 kW combi satistying a kitchen/bar area. Only one tap working at a time as usual :( ? Nah!
 
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Bigburn said:
Dualcombi3.jpg


Like this Paul.
Problem is the thermostatic sensor senses cold water initally, so the flow passes through the second combi until the sensor senses heat and shuts off the flow through the second combi .

Yes it is true that there is a small head of cold water which causes the second combi to fire briefly but in practice the delivery is very smooth.

Tony, I might be carrying Biasi spares soon too. OOPs sorry Viso is Heatline. I've approached them also, as I am told reliably that they pay better and give you shed loads of spares.
 
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It now occurs to me that if you put the dhw temp of first combi to max, and second combi to slightly below max, it will only kick in on an as required basis.

Moreover if you set the first combi on dhw only and the second on heating and hot water, the client will be aware if the second combi breaks, and just switch over. Non return valve on both CH flows to prevent back flow of output from combi one into combi 2.

I'll leave two spare diaphragms inside the boilers.

The Potterton product looks great, but in all honesty I would be more attracted to unvented cylinder to be used as a complement to a pair of combis as above, saving 300 or more to make up for the extra installation costs but with amaising back up options.

I have now used 4 different makes of UV cylinder, but am very attracted to the ACV method, not the least because the unvented kit is prejigged and mounts very easily on top as a whole, with obvious space benefits and hight of discharge pipework starting point benefits.. which in this case, as th einstallation is half in and half out of a cellar I may make use of, though I may in anycase have to sump and pump it, together with the condensate.
 

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