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

[Simon Haslam <simon_haslam@xxxxxxxxxxx>]

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!

--- On Tue, 14/9/10, Pete Church <yahoo@xxxxxxx> wrote:

From: Pete Church <yahoo@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, 6:50







=C2=A0



=20=20


=20=20=20=20
=20=20=20=20=20=20
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I think the 2 hours was implied in an earlier post - a c.200 Litre ta=
nk

needed about 6kWh of energy, which if heated with a 3kW immersion would
tak=
e

2 hours.  Now the variables in reality will be different - you may not be

heating from scratch and you may have a higher power heat source.  2 hours

would be a maximum in this scenario.



However the tank stat should turn off the demand for heat from the heat

source when the desired temperature is reached so even if the heat source
i=
s

live for 2 hours it will only run for as long as it is needed, so
additiona=
l

control shouldn't be needed  (sorry! ;-( )



Pete



_____=20=20



From: ukha_d@xxxxxxx [mailto:ukha_d@xxxxxxx] On Behalf Of

Vargster

Sent: 13 September 2010 19:35

To: ukha_d@xxxxxxx

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



Chaps,



Where does this magic "two hours" heating time come from?

I'd set it to an hour and see if you run out of hot water, then

increase/decrease as necessary.



I had mine set in steps for monthly periods, starting at 15 mins, going up

to an hour during January, never as high as two hours!



The solar h/w panel install over summer has spannered that s/w, so need to

write some more code to read the tank top temperature and apply so logic to

generate a minimum heating time (subject to SWMBO not being aware heating

times are being adjusted).



Lee



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