RE: 24/7 versus limited on and off time for water heating

[Simon Haslam <simon_haslam@xxxxxxxxxxx>]

Interesting - yes, mine's the same and I've also boxed in 3 sides with
25mm=
PIR board and rockwool. Once I got the 1-wire sensors hooked up though it'=
s quite clear - they're very sensitive - you can see from the middle
sensor=
when a just bowl of hot water has been run! We're currently using the imme=
rsion (as the boiler and solar aren't yet hooked up) so the obvious side
ef=
fect is that if you leave it at 50C without heating the water is too cold
t=
o shower a day later.

My suspicion is much of the loss is from the pipes at the top of the
cylind=
er - lagged in climaflex but probably not far enough. Apart from
convection=
from the copper, it could well be that little thermo-syphons are being set=
up in the vertical pipes taking heat out of the cylinder and radiating it =
up the pipe into the room above. Of course all of this is relatively small
=
beer (even at several kWh a day) compared to space heating.

Not quite sure how I got us so far off the HA topic ;-)

S

--- On Tue, 14/9/10, Dave McLaughlin <dave_mclaughlin@xxxxxxx> wrote:

From: Dave McLaughlin <dave_mclaughlin@xxxxxxx>
Subject: RE: [ukha_d] 24/7 versus limited on and off time for water heating
To: ukha_d@xxxxxxx
Date: Tuesday, 14 September, 2010, 13:22







=C2=A0



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The element on my water tank is inserted from the bottom. As an aside=
, the tank itself seems to well insulated as there is a metal cover on the
=
outside and it hardly gets warm when the water is at the max temperature.

=20

Reference your PS. I see nothing wrong with this. You are into HA are you
n=
ot? SWMBO=E2=80=99s the world over will never understand us=E2=80=A6

=20

=20

From: ukha_d@xxxxxxx [mailto:ukha_d@xxxxxxx] On Behalf Of S=
imon Haslam

Sent: 14 September 2010 14:28

To: ukha_d@xxxxxxx

Subject: RE: [ukha_d] 24/7 versus limited on and off time for water heating

=20

=20=20

Agreed - the thermostat will turn the element off after the preset temp is
=
reached (it should 60C to kill Legionella bacteria).



One other consideration though is where the heating element is placed: if
i=
t is at the top of the cylinder, diagonally pointing down (the traditional
=
design) then the top, say, quarter of the cylinder is heated quickly - I
us=
ed to find that a relatively short burst would be enough for a quick
shower=
. Larger tanks may have the immersion element horizontally mounted about
ha=
lf-way down - in this case you have to heat half the tank to the
temperatur=
e you want at the top - I can't quite work out why they do it like that
(pe=
rhaps it puts less thermal stress on the element?).=20



One thing I am finding is that heat loss, even from a modern insulated
cyli=
nder, is significant - currently about 1C an hour for me - so for maximum
e=
fficiency you don't want to heat it for much more than you use. Of course
i=
t might not be so bad in the tropics ;-)



Simon

PS. I've got my 1-wire sensors on my new cylinder and think I might be=20

turning into a DHW bore! SWMBO is not convinced that you should have to=20

look at a graph on the kitchen computer to judge if the water is hot=20

enough for a shower!



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