Vaillant AquaPlus flow rates

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Water Systems

Anyone have any experince of these combis? Vaillant say:

Vaillant has three ranges of standard efficiency boilers. The first is the pioneering new aquaPLUS combination boiler with integrated power store. Thanks to the 15-litre stainless steel store the boiler delivers outstanding bath filling and shower performance, supplying over 170 litres of hot water (delta T 35°C) in 10 minutes.

They say 15 litres/min, and it delivers 170 litres in 10 mins - that is 17 litres/min. There is a store of water in it. Does this run out? After how long?
 
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The boiler just keeps a tankfull of water at high temperature. On a demand, it delivers hot water using the stored heat at the same time as cranking up the boiler to deliver more hot water. Once the temperature of the heatstore falls close to HW setting, either the water temperature will drop or you will need to reduce the flow (to 15 l / min) to maintain the rated Delta-T. Once it's heating water at max output, the boiler will not have any reserve to reheat the store. Calculating when the heatstore 'runs out' is not straightforward - because it doesn't suddenly go from hot to cold. It makes less and less of a contribution as its temperature falls.
 
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croydoncorgi said:
The boiler just keeps a tankfull of water at high temperature. On a demand, it delivers hot water using the stored heat at the same time as cranking up the boiler to deliver more hot water. Once the temperature of the heatstore falls close to HW setting, either the water temperature will drop or you will need to reduce the flow (to 15 l / min) to maintain the rated Delta-T. Once it's heating water at max output, the boiler will not have any reserve to reheat the store. Calculating when the heatstore 'runs out' is not straightforward - because it doesn't suddenly go from hot to cold. It makes less and less of a contribution as its temperature falls.

Thanks. Any ideas of:

1. Size of store
2. Is the store primary or secondary water?

Is this boiler a condenser?
 
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Are you a troll or a prat?

The size of the store is 15l. This is part of the cut-and-paste from your own posting!!.

As any fule know, 15l is the legal max that a store can hold before it becomes an 'unvented system', with restrictions that would be inconvenient on a combi boiler.

The same webpage where you got your cut-and-paste would also have told you, had you bothered to read it, that it's a primary store, with a pump to circulate water to the DHW HX.

And finally, as your own posting also mentions, this is a STANDARD EFFICIENCY non-condensing boiler, so not of much practical use to the majority of real-world customers.

Why are you wasting valuable message-space?
 
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croydoncorgi said:
Are you a troll or a prat?

The size of the store is 15l. This is part of the cut-and-paste from your own posting!!.

Thanks missed that.

As any fule know, 15l is the legal max that a store can hold before it becomes an 'unvented system', with restrictions that would be inconvenient on a combi boiler.

Very true using secondary water.

The same webpage where you got your cut-and-paste would also have told you, had you bothered to read it, that it's a primary store, with a pump to circulate water to the DHW HX.

Primary water? Then 15 litres doesn't apply is an immersed coil is not used.

And finally, as your own posting also mentions, this is a STANDARD EFFICIENCY non-condensing boiler, so not of much practical use to the majority of real-world customers.

Is there a condensing version?

Why are you wasting valuable message-space?[/quote]

You got the 15 litres maximum wrong. You have been wasting space then.

Croydon? Such a horrid little town. Horrid.
 
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We used to fit a lot of these, mainly in the Croydon area, funnily enough.

They were dropped by Vaillant in early 2005 because, as stated they were not going to meet the new efficiency regs. If my memory serves correctly, they were a 637 thermoCOMPACT with a heatstore, making them a few inches deeper than the ordinary boiler.

Vaillant aim their hw output of the boiler at 42 degrees delta T, but like most manufacturers quote the standard 35 deg rate for comparison purposes, so actual flow output results may be less than the specs suggest.

We are told there is a condenser version on the way, which would be nice because currently there is only the worcester Highflow 440 at the quality end of the market. The Viessmann 333 will soon be back on the market and has a similar performance but is BIG.........but beautifully made. If you are solo installer you'll drop your boll***s getting it in.

Now I think of it, the aquaPLUS was a heavy bast**d to lift onto the wall and keep there.
 
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I should add that Croydon is a big town, and once applied for city status. I don't know about CroydonCorgi, but I was born and educated (!) there, and apart from the council or despite them it is a nice-ish place.

The heat store contains the actual hot water for the tap, in case there is any confusion over primary and secondary.
 
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simond said:
We used to fit a lot of these, mainly in the Croydon area, funnily enough.

They were dropped by Vaillant in early 2005 because, as stated they were not going to meet the new efficiency regs. If my memory serves correctly, they were a 637 thermoCOMPACT with a heatstore, making them a few inches deeper than the ordinary boiler.

Vaillant aim their hw output of the boiler at 42 degrees delta T, but like most manufacturers quote the standard 35 deg rate for comparison purposes, so actual flow output results may be less than the specs suggest.

We are told there is a condenser version on the way, which would be nice because currently there is only the worcester Highflow 440 at the quality end of the market. The Viessmann 333 will soon be back on the market and has a similar performance but is BIG.........but beautifully made. If you are solo installer you'll drop your boll***s getting it in.

Now I think of it, the aquaPLUS was a heavy bast**d to lift onto the wall and keep there.

Thanks. Vaillant don't have a high flow combi, and this was about the best.

Other floor mounted combis are: Powermax, Geminox, Gledhill Gulfstream, Ideal Istore, Vokera (the washing machine sized one), ACV HeatMaster. The Gledhill (certain versions) and ACV can do three bathrooms. I think Ariston still have their high flow combi (wall mounted). Alpha CD50 high flow combi is wall mounted too. I like the ACV and Viessmann. The ACV is a tank-in-tank design and always condenses.

All the above have stored water of some sort either primary or secondary. The best infinitely continuous wall mounted is the MAN from Germany (special order), which is around 76kW, your gas supply will need uprating as will cope with ~62kW max on a U6 meter.

Another option is a small CH system boiler for CH only and have a high flowrate Japanese Rinnai or Andrews multi-point water heater - these can be fitted outside on the wall (quite small too). If you have a body jet shower a larger unvented cylinder would be very expensive and take up space. These go outside and never run out of hot water, being highly cost effective. Have a small CH boiler and a Rinnai multi point and installation is simpler and more reliable with no zone valves, etc.
 
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simond said:
I should add that Croydon is a big town, and once applied for city status. I don't know about CroydonCorgi, but I was born and educated (!) there, and apart from the council or despite them it is a nice-ish place.

The heat store contains the actual hot water for the tap, in case there is any confusion over primary and secondary.

Thanks the pillock implied primary water.
 
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Can't understand WS' simultaneous (and conflicting / conflicted?) interests in storage combis, heatstores and (see other post) high efficiency condensing boilers. Different planets!

The 'efficiency' of a heatstore depends on how hot it is, hotter the better. If you heat it only to (say) 70 degrees, it will be difficult to get an acceptable flowrate of DHW at 55 degrees. Also, the store itself will need to be larger to store enough watts to be worthwhile.

On the other hand, if you have a smaller heatstore running at (say) 80 degrees or hotter, and connected to a condensing boiler, it's most unlikely that the boiler will ever run in condensing mode - so 5 to 8% of energy efficiency is lost straight away. Return water from the store will be hotter than 56 degrees all the time.

So decide what you want: energy efficiency or improved hot water response. Heatstores are not a way to achieve both.
 
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croydoncorgi said:
Can't understand WS' simultaneous (and conflicting / conflicted?) interests in storage combis, heatstores and (see other post) high efficiency condensing boilers. Different planets!

Do you mean people should only be interested in one thing?

The 'efficiency' of a heatstore depends on how hot it is, hotter the better. If you heat it only to (say) 70 degrees, it will be difficult to get an acceptable flowrate of DHW at 55 degrees.

Wrong. The efficiency for DHW purposes is how efficient the heat exchanger is. Plate heat exchangers are highly efficient. A store of 70C can produce DHW at 60C, which coils cannot match.

Also, the store itself will need to be larger to store enough watts to be worthwhile.

Not so, if it is larger it is marginal. Thermals stores (using coils) and Heat Banks (using plate heat exchangers) are different, with the heat bank more efficient and giving much higher flowrates.

On the other hand, if you have a smaller heatstore running at (say) 80 degrees or hotter, and connected to a condensing boiler, it's most unlikely that the boiler will ever run in condensing mode - so 5 to 8% of energy efficiency is lost straight away. Return water from the store will be hotter than 56 degrees all the time.

Not so. Using a TMV on the flow and return of the boiler will ensure return water below dew point for most of the re-heat period. From cold the water only enters the store at store setpoint and heats the store top down. The temp at the top may be 75C and yet a few inches down in the cylinder 30C – a line of say 70 to 75C will just work its way down the cylinder with the water at the bottom very cool indeed. Also the energy in the store and the boiler can be combined to give greater flows, or drop the store size or have tall thin cylinder giving high condensing efficiencies – the scope is there. Few heat banks are at 80C store temp these days. Most are at 70C to 75C. I know one DHW only heat bank set to 65C and gives 55C at the taps. Efficiency is guaranteed.

Heat banks tend to be taller and thinner to take advantage of stratification ensuring that water at the bottom (the return to the boiler) is cool and forces condensing of the boiler. The TMV ensures heat only at setpoint enters the top of the cylinder and the bottom remains cool. It also ensures the delta-T of the boiler is maintained too. A boiler can only gives certain temp rise, say 35C. If the store is 25C at the bottom then it can only deliver a flow of 60C. The TMV ensures 70 to 75C (depending on how it is set) enters the top of the cylinder. All falls into place.

The ACV HeatMaster Thermal store/boiler (well an unvented cylinder/thermal store hybrid) condenses at all times. I “think” their web site has the instruction manual to download. Have a look.

Having a hybrid of a DHW coil at the bottom of the cylinder and a plate heat exchanger, will ensure at the bottom of the cylinder, near the return take off to the boiler will always be cool water. The cold mains cools the water here and ensures condensing in the boiler. Then from the coil, which pre-heats the cold mains water, to the high efficiency plate heat exchanger. This gives: high flowrates, low store setpoint temperatures, maximum condensing efficiency.

In a test using a standard direct cylinder, I rigged up a second plate heat exchanger on the boiler return, with mains water running through cooling the return temp - this was in place of the coil at the bottom of the cylinder, as described above. Cool water from the bottom of the store entered the plate which was cooled further by incoming cold mains water. Worked very well indeed ensuring the boiler was working at max condensing efficiencies. The plate like a coil was entirely passive. A small coil at the bottom of the cylinder would have less main pressure restrictions, especially if made of stainless steel.

So decide what you want: energy efficiency or improved hot water response. Heatstores are not a way to achieve both.

You need to understand heat stores better and don’t go on old wives tales. Look at http://www.heatweb.com for an introduction - I have no connection with this company. Read carefully what I have written and how the ACV HeatMster works too. Understand all. Things have moved on a hell of a lot since the old coiled thermal stores.
 
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This is amazing, Water Systems abuses all of us and then asks a question that he would be expected to be able to read from the manufacturers instructions.

When you tell him the obvious he continues to abuse you!

I dont know why you all bothered to reply.

He is retired, not CORGI registered, and is not fitting any boilers but just takes a vicarious interest, often completely misunderstanding the MI.

Remember when he argued against me saying that combi boilers dont modulate on DHW. You would have thought that he would have realised that I do know a little about boilers!

Tony
 

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