Environmental Engineering Reference
In-Depth Information
the bathroom basin hot supply, which is 54 °C. Likewise the basin cold tap delivered
at 21 °C (this was in May, so the water presumably reached house temperature
through the plumbing). The shower spray exit temperature I measured to be
38 °C. Consequently, the mixer delivers 2.5 l/min if the combi is just above cut-out
and 3.3 l/min if the combi is safely above cut-out. These results agree with measure-
ments of the actual fl ow rate. In fact I set the fl ow at a little more than 3.3 l/min
because the cold water supply is not good and can be affected by other users.
It is understandable that the industry should choose a normal minimum fl ow rate
conservatively in order to accommodate numerous manufacturers and to avoid risk.
Nevertheless, some mixers and fl ow limiters do refer to
maximum
values of 6 l/min.
I would recommend cautious experimentation by users with reducing fl ow rates. It
is not wise to operate regularly close to the limit where the combi will cut out, both
for comfort and for longevity of the combi.
Mixer Shower with Hot Water Tank
This system has the disadvantage of heat
loss from the permanently hot water in the tank, but it has the advantage that hot
water may be taken as slowly as one wishes. A notable example of a low-fl ow mixer
shower of which I had experience had the unusually low mixed water fl ow rate of
1.7 l/min. This was because its rose was clogged with limescale. The owner was
happy with it, probably because the fl ow had diminished gradually. It was gentle
and relaxing and I liked it too. Later the fl ow became too low and the rose was
cleaned, and the fl ow returned to its design value which was higher but still gentle
and economical.
Electric Shower
Electricity has, as noted in the 'Energy' subsection, a high energy
to CO
2
e conversion factor. (This factor will come down, relative to other sources of
energy, if in the future more electricity is generated from renewable sources.) In any
case, electric showers have some compensating advantages. Even apart from the
argument for continuing to use good equipment rather than change before its end of
life, there can be a case for installing a new electric shower. In the fi rst place, an
electric shower is virtually 100% energy effi cient. Almost all the energy is turned
into heat delivered at the shower rose. There are no burner or fl ue losses and virtu-
ally no transmission losses. (In effect, all of these occur before the energy is deliv-
ered at the household, which partly accounts for the high energy to CO
2
e conversion
factor.) The second advantage for the energy-conscious bather is exactly the reason
why the profl igate user dislikes electric showers - sometimes passionately, as Walsh
(
2004
) probably does, judging from the quotation earlier in this subsection. For
whilst a combi-heated shower cannot run very slowly, an electric shower cannot
produce heat at a great rate, and in late winter and early spring, when the incoming
mains water is cold, this limits the fl ow rate for an acceptable warmth of water. The
upper limit of power of an electric shower is limited by wiring and safety standards,
and the power available in the UK is in the range of 7.5-10.8 kW with the higher
powers heavily promoted and 7.5 kW showers now having very little profi le. I used
a 7.5 kW electric shower for many years. I did fi nd it adequate in cold weather, but
it did take some experience to use it correctly, mainly because of the heat capacity
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