I've just realised that there is no need to angst over one's DHW circuit:
between
1) large bore pipes with pumped 2nd circuit to keep it hot, and
2) a single uncirculated high-pressure microbore circuit.

One simply plumbs in the first, but makes the 2nd circuit returns out of microbore (as would probably be done anyway).

During periods of ample heat one can use the large primary with pumped 2nd circuit, and during periods when heat is short (& losses are expensive), one can turn off the pump and large primaries, and simply deliver via the microbore secondaries (possibly enabling a pressure boost pump).

Have I just re-invented common practice, or is this approach fairly novel?

For a brief synopsis of secondary DHW circuits see: http://www.megaflo-unvented.co.uk/secondary-circulation.php

It is not just hotels and commercial buildings, but also large domestic properties that can benefit.

In periods where the heat is ample & free such as summer (solar), but where time & water aren't, then a secondary circuit is useful. In periods where heat is more expensive such as winter, then one can use microbore, high pressure, and suffer the waste of water.

I've simply spotted that one can have both, and switch between them (twice a year).

I'd be interested to know if anyone else has also realised this, or has even got such a system - or come across one?

Posted By: Ed DaviesBut at the times of year when you don't have lots of free solar heat the “losses” from the circuit will contribute to your heating anyway. Maybe if it's wind powered heating…

Excellent point, but this applies in cases where the DHW circuits lose heat to the living space rather than elsewhere, e.g. loft-space (my case ).