I am shortly going to convert my conventional open vented DHW cylinder
into a Heat Bank following the design given at
http://wiki.diyfaq.org.uk/index.php?title=DIY_Heat_Bank

I am going to set the post-PHE TMV to distribute DHW at 55degC. What
I need to know is how I go about determining the required PHE
secondary output temperature. Say the PHE output is designed to be
60degC. If one shower is running, for example, the TMV will blend a
little cold water to achieve 55degC. That's easy. What I'm finding
difficult is how to be sure what happens when the 2nd shower is
switched on, and then perhaps the kitchen hot tap...

I have a very good supply from the rising main. It runs at ~8bar
(reduced to 5bar by a pressure reducing valve at entry into the house)
and delivers 30l/min at 8bar.

When additional outlets ae opened, will the secondary output
temperature will drop as the flow rate through the PHE increases? Or
perhaps it won't... perhaps the flow rate to each outlet will drop...
and the temp will stay the same...?

Basically what I don't quite understand is the dynamics between water
pressure, flow rate and number of outlets open.

Many thanks in advance for any info on this.

Mike