Is it really necessary to install a pump to provide power shower
performance? Terry Scaife, Technical Services Manager of Aqualisa, examines the
issues. The last two decades have seen steady growth in the demand for showers
is both the new build and the 'one-off' refurbishment sectors. In particular we
have seen significant growth in consumer demand for 'power showers'. The homeowner
has experienced high performance showers in hotels and on holidays abroad and
wants the same sensation of a high pressure, drencher shower at home.
Despite consumers' growing knowledge of shower products there remains a popular
misconception that a high performance shower equates to a 'power shower', ie one
with a pump. This is not always the case. Here at Aqualisa, we describe high performance
showers as having four key characteristics:
Temperature control
Thermostatic control is required to maintain water at a set temperature (with
acceptable variation) even when other taps in the house are turned on/off.
High flow rates
At increased pressures also emphasise the requirement for full fail-safe protection.
Should either supply fail the shower should shut-off immediately for total safety.
Flow rate: 15 litres/minute or more are needed to satisfy most people's perception
of the 'power' showering (drenching) experience.
Shower patterns
This is determined by showerhead design. Personal tastes will dictate preference
for an all-over spray or focused jet or small or large drops, simple or aerated.
Flow pressure
And so we come to the question, do I need a pump?
Whether or not apump is necessary is determined by the hot/cold
water system installed in the home. If it is a gravity storage system with a cold
water header tank located in the loft space, the likelihood is that the distance
from the base of the cold cistern to the showerhead may be only 1m resulting in
a relatively low pressure shower.
Therefore, installing a pump will make a dramatic difference. Unvented/mains
fed systems featuring a high-pressure cylinder a 2-3 bar and adequate pipe diameters
are capable of achieving high performance results.
What about Combi systems? While a standard 80,000 Btu/h (23kW)
Combi system can deliver non-stop hot water at some eight litres/minute, this
flow rate, together with a quantity of cold, will blend to provide a generous
enveloping shower. But this could not be described accurately as a 'power' shower.
The layman and occasionally the uninformed installer might think it would be possible
to install a pump to increase the flow rate. They would be wrong; it cannot be
done.
To increase the flow rate it is the Combi that requires upgrading to 100,000
or 120,000 Btu/h (28.75 to 34.5kW) to provide a flow of 11-14 litres/minute. Alternatively,
a more practical solution could be to install a storage system to be heated by
the Combi and which may then be pump boosted. As this 'dual system' leaves other
terminal fittings to be supplied separately by hot water generated by the Combi
there would be no sudden surprises in the shower cubicle when other hot or cold
taps are operated.
What of an electric/instantaneous shower? Modern electric showers
can be the obvious choice for many installations but even a powerful 10kW unit
will only deliver about 5-6 litres/minute - insufficient to satisfy the perception
of a 'power' shower.
In short, if the question were to be "Can I have a 'power' shower?"
the answer is yet another question, "Have you the right hot/cold water system?"
If you have a mains pressured system capable of supplying a minimum hot water
flow rate in the region of 12 - 15 litres/minute at as maintained temperature
of 55-60 C then the answer would most likely be "Yes." If the system
is gravity storage, a pump is necessary for a 'power' shower.
Finally, when installing a pump consider and check the following
Pump sizing
Do not fall into the trap of 'when is doubt buy a big one.' Installing too powerful
a pump is neither sensible nor energy efficient.
Pump siting
Regard a twin-ended pump as a 'pusher' not a 'puller'. The pump must be sited
close to the water cylinder.
Pipework sizing
At Aqualisa we always recommend the use of 22mm pipework for pumps for both the
inlets and outlets to ensure optimum performance. We would not endorse the use
of 15mm pipework when installing pumps capable of generating pressures in excess
of 1 bar.
Hot water cylinder capacity
We print an easy-to-read pump performance chart so that the installer can ensure
adequate hot and cold storage capacities. Remember the general rule that mixed
water at the showerhead is approximately 2/3rds hot and 1/3rd cold.
Hot water cylinder temperature control
Ensure that the cylinder is controlled to a maximum 65C. Water may boil in a kettle
at 100C but reduce the pressure on a liquid, as we do in the inlet or suction
side of a pump, and we correspondingly reduce the boiling point. If the pressure
is reduced to such an extent that pump inlet water is nearing its boiling point,
cavitation will occur resulting in poor showering performance and reduced pump
life.
