2 boilers - will we need seperate cover for each?

Waterways_2

Cardew wrote: »

It is relevant to point out that the pre-heating of the thermal store to some extent means that is is slightly less economical than a combi heating the water directly as there will be losses from the store.

That is true, however modern insulated cylinders and stores have little heat loss worth worrying about.

Agreed they might not claim that the 440 can deliver 20L/min indefinately, on the other had they don't qualify the claim of 20L/min!!

The info is all there in the brochure
http://www.worcester-bosch.co.uk/cache/file/259/technical-and-specification-information.pdf

However I would agree with you that such a boiler would comfortably meet the needs of most housholds.

The 550 clearly is a two bathroom job and the 440 will cope too.. W-Bosch are behind in their control systems. The Continental protocol standard is OpenTherm which is not implemented, but I believe it is to be introduced. Integrated weather compensation control would be superb. This would really drop the gas bills.

As the chart shows temperature change(and not temperature) what is the relevance of quoting the input water temperature as 10C?

The average in London is 10C. It rarely gets below this. The ground temperatures is reasonably stable. The same in many towns and cities. If it is 5C then @ 35C temp rise you get 40C at the taps. To get a higher deliver temperature the flow has to be reduced - by turning down the taps. Conversely if the cold water mains temperature is higher then a higher flowrate can be had.

Alpha FlowSmart

The Alpha FlowSmart that was mentioned on this thread. This is a two stage flowrate combi, similar to the HighFlow in operation. The thermals store is remote rather than inthe same box. This is a 35kW combi with a thermal store assist to raise the flow rate. It delivers 18 litres/min for 30 minutes. That is 540 litres in 30 minutes and 5 - 7 minutes reheat. It reverts to around 16 litres/min as the combi is a 35kW model. An economic advantage is that the thermal store can be turned off in summer if only showers are used, and switched on if high water usage at any time. Or, kept off all the time and only switched on when high flows are needed like a few showers or a bath. It takes around 5 -7 minutes to reheat so not a problem. If a few people are in two bathrooms just hit the switch and higher flowrates in a few minutes. Very economical.

The W-Bosch 550 is around £2k, about the same as the FlowSmart with the GasSaver, which is from around £2k to £2.3k. The great thing about the FlowSmart is that the combi can be fitted and space left for the thermal store at a later date if say an extension is planned.

It also has a backup electric immersion heater boss.

Combi Boost Thermal Store

The Alpha 35c combi is around £900, maybe cheaper. It can be coupled to one of these pressurised 80 litre combi boost thermal stores, which is cheaper than the dedicated Alpha store and will deliver for longer too as it holds 80 litres. Boosting combi flows is not new.
http://www.copperform.co.uk/mains_pressure/thermaflow/index.htm

The blending valve can be turned up to say 40 or 45C to improve flowrate as the Combi Boosts has an 80 litres store, not a 50 litres as in the Flow Smart.

The Combi Boost cylinder can also have a backup electric immersion heater installed too.

The whole lot can be put together for well under £2K I would reckon and outperform any unvented cylinder in DHW delivery and outperform the FlowSmart too. Just have the combi over the Combi Boost cylinder as does the FlowSmart.

Just copy the Alpha using the Combi Boost, using the Alpha manual and the 35C combi:
http://www.alpha-boilers.co.uk/products/downloads/flowsmart/alpha_FlowSmart_installation_and_servicing_instructions.pdf

Simple to do. And any combi that can take heated water into its cold inlet and have the inlet throttle opened up, can be used to have its flow output boosted.

Waterways_2

I have just been informed that Copperform have taken off the market the Combi Boost, even though it is on their web site. A rather dumb thing to do when the Alpha Flow Smart is selling.