Environmental Engineering Reference
In-Depth Information
of the water in the shower's heating tank, which meant that one had to make fl ow
adjustments slightly and wait to see it if was right.
The relation between fl ow rate and power is simple:
Flow rate l per
power
/
in
( 7.2 )
14 3
.
/
kW
/
temperature increase
/
C
and a graph of this relationship may be found on p 8 of Mira (
2006
). As noted in the
subsection on Energy, Zenex Energy (
undated
) states that 'in winter the [incoming
mains water] temperature may fall as low as 4 °C'. I believe this is an extreme. I
have lived several decades in East Anglia and I believe that the incoming mains
water has never been that cold. Nevertheless, accepting this worst case and the stan-
dard temperature of 38 °C for the warmed water and power of 7.5 kW, one fi nds the
fl ow rate to be 3.2 l/min. This will clearly give an economical shower. The canonical
5 min would use 16 l of water and 0.63 kWh of electrical energy. Is it acceptable?
Certainly it does require an adequately heated bathroom for comfort. Beyond that,
there is no objective answer to the question. It depends on the person. Those, how-
ever, who answer with an emphatic 'no' and use a power shower at 16 l/min should
be confronted with the larger implications of their lifestyle.
The electric shower I used had a medium power setting which I measured to be
approximately 4.5 kW. I was able, due to the warmer incoming water, to use the
shower on the medium power setting from sometime in May to mid-November.
Through the year the fl ow when I showered was about 4 l/min in cold weather, 5 l/
min in cool weather with power = maximum and about 2.6 l/min in mild weather
with power = medium. The temperature rise versus fl ow rate graph (for 7.5 kW)
shown in Mira (
2006
) covers fl ow rates from 2 to 11 l/min. I think that 2 l/min is
indeed a lowest fl ow rate for a 7.5 kW electric shower, for reasons of safety. At
lower fl ow rates, a small reduction of fl ow rate could lead to a dangerous increase of
water temperature. On medium power, 4.5 kW, a lower fl ow rate could be used. One
can understand, within the currently dominant culture, why electric showers are
disliked by many and also why the trend with electric showers is to ever higher pow-
ers, the fl ow for a given temperature rise being proportional to the power. Still, the
ecological issue will not go away and a change to sustainable values is literally vital.
7.2
Bath
The mantra 'take a shower instead of a bath', endlessly repeated over many years
and continued still (e.g. see Royal Borough of Kensington and Chelsea
2012
), is
misleading in three ways: (1) shower and bath are not equivalents, (2) it leaves
'basin/bowl' unspoken and (3) many people now take a daily shower, whereas few
(other than children) take a daily bath. In Sect.
7.3
I will return to point (2) and in
Sect.
7.4
I will return to point (3). Concerning (1), a bath is not an alternative to a
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