Just to let anyone who is interested know, I have just installed my DPS
Pandora heat bank. Possibly anyone considering a new hot water system might
be want to read on.
It is a 180 litre model with the standard plate exchanger and indirected
heated by coil. Except it isn't, because the new boiler hasn't been
installed yet and the old one is using a feed/expansion tank below the level
of the tappings so can't be plumbed into it. It is currently electrically
heated by 3kW immersion. The immersion thermostat is set to be identical to
the indirect coil thermostat, so performance should be similar.
It does work exactly as expected. It easily fills an entire bath up. Flow
rates are higher than my old gravity system into the bath (but not really a
patch on my parent's Megaflo or the pumped gravity system in my previous
house). However, at the top end of flow rate, the temperature does start to
drop a little. I still need to mix cold in though, even at full pelt.
However, you need to turn it down to half near the end to bring the
temperature up to the TMV's set point. (If you are anything like me, you'll
fill the bath with warm water, get accustomed to it and then pour in very
hot only to raise it up to just sub-scalding).
The performance on a shower is absolutely superb and totally comparable to
an unvented cylinder, as you would expect. Despite the much longer run to
the kitchen in the new layout, I also get hot water quicker due to the extra
pressure helping with the long 15mm run to that tap and the high pressure
only design (I bought the tap in anticipation of the mains pressure).
So all in all, for the same purchase cost as an unvented cylinder, you do
get a system that isn't much lower in performance in practice. Obviously,
there are benefits to it, such as the main vessel containing static
inhibited water that will eliminate scaling, the inherently greater safety
of using zero head pressure in a large heated vessel, and the fact that the
DHW itself is not stored and can be poured straight into the kettle or cup
(assuming no phosphate dosers or ion-exchange softeners).