In message , John
Rumm writes
On 14/03/2011 10:06, harry wrote:

Precisely. These are all things one needs to consider. In my case, a
conventional gravity fed storage system won't hack it - no space for the
header tank and not enough head. Combi (alone) won't hack it either -
not enough peak delivery. Hence mains pressure storage system, or large
heatbank with substantial HE and possibly a combi as well is what fits
the bill.

What is the point of a combi AND a hot water store? None I would say.

Its one possible solution that would tick most of the right boxes.

Ultimate design will have two baths, three showers. Peak flow
requirements are high. Mains water flow rate and pressure availability
are high. There is a large airing cupboard available for a substantial
size of cylinder, and no loft space at all. Airing cupboard is right
next to downstairs shower room, and right under main bathroom, which is
right next the en-suite - all nicely concentrated in the middle of the
house. Kitchen and utility room are at least 40' of pipe away at the
back of the house.

Heating needs three zones in total, two heating with independent
programmable room stats, and one for water. Split temperature operation
is required for cylinder recharge, and full weather compensation with
external sensor.

So a system boiler plus unvented cylinder, or heatbank with flowswitch,
pump, and large PHE could adequately provide the required peak flow for
baths / showers. However there would be (as now) a significant dead leg
to get hot water to the kitchen. So given there is little difference in
price, or complexity between a system boiler and a combi, one could use
the latter, and have it HW output feed just the kitchen and utility
room - in which it would be located. You could also then set it to
provide hotter water there than that set on the main blending valve on
the output of the cylinder, and you would also get pottable hot water.

Fit an under sink heater? It solved similar issues for us. I actually
fed it from the hot supply to take advantage of softened water.

A bit of nifty work with some isolation valves would also allow for a
bit of two way backup. If the combi part failed, you could route
cylinder water to the kitchen, and if there was a cylinder problem you
could route combi water to the baths/showers. If the boiler goes
totally unserviceable, then a couple of immersion heaters in the
cylinder can take over.

Can you suggest a better solution?

What me?

regards


--
Tim Lamb