On Mon, 15 May 2006 21:48:54 +0000, John Stumbles wrote:

... A configuration that might
give better flow might be to combine the output of the thermal store
with the output of the combi via a thermostatic mixing valve: combi to hot
input and combi to cold input of the valve. Again you'd only want this
in-circuit when the store can't supply hot enough water.

Mains pressure
hot/warm water ---------
from thermal store | combi |
------------------+---| DHW |------
| --------- |
| -----
| | H |
| | TMV |-------
| | C |
| -----
| |
---------------------


... you might use a 2-port or 3-port motorised valve to
bypass the combi, controlled by a thermostat sensing the temperature of
the store.

Actually, thinking about it, the arrangement above may just work (or
Just Work (tm) :-)) without faffing about with thermostats, motorised
valves etc. As long as the temperature of water from the store is above
the TMV's set point it'll only draw water from its Cold inlet i.e.
directly from the store. Only when the water gets too cool will it draw
from its Hot inlet which should automatically kick in the combi.

Note that in this case the TMV is not limiting the temperature of DHW
which could possibly get dangerously high when the solar system is working
well, so you may want another TMV mixing the output with cold water from
the main.