Worcester Bosch Boiler flowrates vs Kw Output

[aj_newman]

1) In the WB literature, the WB Greenstar Hightflow has a max ouput o

29.2 Kw, and a max flowrate of 20 l/min with a increase in temp of 3 deg C. The 40 HE Plus can output 40Kw and only manage 16 l/min bu has an almost identical efficiency. Q - How is this possible?

2) Are manufacturers boiler statistics accurate?

3) Does WB performance degrade after 1 month / 1 year?

4) I have read that it is illegal to place a pump in an unvente system. Is this true? I wondering if a flow limited pump exists (an it legal) that I can put after my mains feed for cold water int kitchen. This would be able to boost the pressure through the maze of pipes i my house and ensure that the showers can operate at the maximum flo available. (Shower has 6body jets at uses about 18 l/min )

5) Is there such a thing as an unvented Cold Water tank with a expansion vessle inside? I was thinking that this would enable a shor term higher feed rate of the hot and cold water requirements of th house.

6) Are there any recent high flow combi boilers equivalent to the W Greenstar 440 that are Better that it terms of Continuous unlimite Flowrate. (Note: I am not looking for a multi boiler info, nor info o one that involves storing hot water when not in use, just continuous H supply)

Cheers, Anton

-- aj_newman

[Christian McArdle]

The Greenstar Highflow has an internal heatbank to store energy. It is not an instantaneous combi, like the 40HE Plus. This is why the Highflow is a large floor mounted appliance.

Yes, but for comparisons, always check the Delta-T. It should be 35C to be meaningful. Better still, just look at the kW for a condensing instantaneous combi.

No, provided you take precautions against scaling if you are in a hard water area.

No. It is illegal. For good reason. If you pump mains water, you reduce the pressure of the incoming mains. You may reduce the pressure below the ambient, which leads to any leaks in the water company's pipes to draw in contaminated ground water (very bad), rather than leak fresh water out (only a bit bad).

If the pressure is not good enough from the mains, then a mains pressure solution might not be appropriate.

Yes. It is called an accumulator. It can't fix problems with static pressure, but it can help with flow rates, at least for short periods. The following link is to a supplier of such systems. Not a recommendation as such, I've never used them.

6) Are there any recent high flow combi boilers equivalent to the WB

Then the Highflow is not for you, as it is a storage solution. You won't find many boilers larger than the 40kW WB, although there are some out there. However, don't be afraid of storage solutions. You may have had experience of a wanky 1970s storage cylinder that always goes cold for hours after a bath. A modern storage solution using rapid recovery coils, or direct circulation heat banks can maintain the same hot water output as a combi indefinitely (i.e. it will never run out even if you showered 24 hours a day). The only difference is that they can boost to many times the flow rate for a period of time, which is ideal for bath taking. You also don't have to wait for the genuinely instantaneous combi to fire before hot water is available.

Christian.

[Christian McArdle]

Just noticed your comment about a 18lpm shower. This would eventually run out. However, a bog standard 28kW system boiler and a 180L heat bank, like mine, would be capable of running this shower for 40 minutes before running out. In this time, it will have heated 720 litres of water to 40C, which is about the equivalent of 6 baths. If you actually ran such a shower for such a period on a regular basis, I'll personally nominate you for a "fat arsed american" environmental damage award. I'm not actually suggesting that you intend to, mind, just that such a storage solution would easily meet any sane needs for a domestic property. i.e. a 5 or 10 minute 18lpm shower won't trouble it at all. OTOH, even the largest genuinely instantaneous combis with no storage would struggle with a 18lpm body jet shower. You certainly couldn't turn on a tap elsewhere without problems.

Christian.

[Doctor Drivel]

instantaneous

It is a one-box solution though.

The ACV Heatmaster 35TC is a one box and has high flowrates - excellent product.

Gledhill Gulfstream also have high flow (35 litres/min) one-box solutions. They have 3 sizes.

[Doctor Drivel]

That is 18 litres/min "mixed" hot and cold. Some can cope OK and even have the odd tap turned on and not affect the performance.

[Mr Fizzion]

There is the MAN Micromat 76kw combi boiler from MHG-Heiztechnik based in Hamburg, Germany. (Formerly part of the volkwagen group).

am not sure what the current situation is but if you look back through the archives of this group, they used to be rebadged by Eco-hometec and MHS Boilers in the UK.

Officially you would need to upgrade your gas supply as all(?) domestic meters are U6/E6 by default which means they can supply 6 cubic metres/hour. The 76 kw model uses up to 7.6 cubic metres per hour according to the installation manual (which I could find only in German

Evil has previously asserted that you can run your gas meter at double capacity though not many people agreed with him! :-)

Mr F.

[Doctor Drivel]

)

I don't care if they agree with me or nopt, I have done it and they haven't. I used to design gas system and the U6 had a 100% overload. We would go up to around 300 to 350 cu foot per hour for 212 cu foot rated meter. Transco now probaly would not allow this as they want you to go the next size up and charge more.