Mira Showers looks at the essential differences between ‘electric’ and ‘thermostatic electric’ showers, and why they provide a premium opportunity to upsell.
What sells an electric shower; price, looks, size, easy replacement or speciﬁcation? In reality, as with the short list above, the speciﬁcation often appears way too far down the decision-making process; especially as the purchaser may not fully understand what they mean and pick a product that may not be the best choice for their application.
Most will plainly know how an electric shower works, yet this overview will explain the differences in design and leave you in a stronger position to recommend a ‘thermostatic electric shower’ for ordinary use and particular demanding applications, such as when dealing with vulnerable people like the elderly.
Electric showers are essentially a type of continuous ﬂow water heater: heating up water, for immediate use. As such, there will be a number of supply variables that could, and in fact, will change the shower temperature, either decreasing it, which is not really a problem, or – and this is to be avoided at extremes – increasing it. The supply variables are: inlet water temperature, inlet pressure and supply voltage. There are others such as the room temperature and the user’s differing desired temperature which cannot be controlled by the shower.
“To make a product thermostatic there needs to be a device that senses changes in the shower temperature to which it reacts at the correct speed and movement…”
The inlet water temperature has a seasonal variation, and a property ‘dead leg’ variation – being generally consistent after a few minutes, and for the duration of a shower. The ‘dead leg’ is the dedicated supply pipe to the shower in which the water could have reached the room temperature, and temperatures along which the pipe runs. With some showers, the user may need to adjust the shower temperature if it has not been used for a week or so. Variations in inlet water temperatures will change the shower temperature of non-thermostatic showers.
The inlet water pressure will deﬁnitely vary during the use of the shower, this being caused by other water usages in the property or nearby properties. Basic electric showers are ﬁtted with a form of ‘elastomer ﬂow stabiliser’ which, depending on its control abilities, should keep the ﬂow constant. Some are better than others. A non-controlled variable ﬂow rate results in shower temperature changes. The supply voltage is likely to vary whilst showering; and a variable supply voltage will result in shower temperature changes for non-thermostatic electrics.
To make a product thermostatic there needs to be a device that senses changes in the shower temperature to which it reacts at the correct speed and movement – too slow or too fast and the temperature will go unstable. The reaction of a non-electronic device will be a movement, rotary, linear or indeed a change in its strength – with the important ability of returning to its original state or position.
Development and test work ruled out the use of wax capsule thermostats for this demanding application. Instead, a material whose strength changes with temperature was investigated and after much design using sophisticated Computational Fluid Dynamics (CFD) technology, the material Shape Memory Alloy (SMA) was chosen.
In this context, Mira uses the characteristics of SMA to accurately control the shower temperature. The coiled device, about 15mm in diameter and 25mm long, is situated in the top of a heater tank, near the outlet so that the water leaving the heater tank ﬂows over it. Its response to temperature changes is to vary its strength, and in so doing adjust the opening of a second cold feed into the heater tank.
The effect of this is to set the correct total ﬂow of water through the heater tank. The clever bit is that there is a set minimum ﬂow and the SMA system additionally varies the cold ﬂow which is evenly distributed throughout the entire length of the heater tank through a cylindrical, centrally positioned multi-outlet sparge pipe.
The result of this is that there is a very quick response to changes in the supply conditions as the incoming cold water is evenly distributed throughout the heater tank.
Computer technology has reached some leading proprietary electric showers where sensors measure variations in conditions and the data being sent to the CPU. This results in corrections to ﬂow and heating element combinations, some being applied at up to 84 times per second. Temperature control and safety has now been taken to a new high.
All very clever: yet what are the beneﬁts of a thermostatic electric shower over basic entry level non-thermostatic versions still marketed?
A well-speciﬁed thermostatic shower, used within the manufacturer’s published speciﬁcations, will accommodate the variable inlet variations explained above, delivering, for the user, an easy to use product with maintained shower temperatures.
Avoiding pulses or even blasts of minimally controlled water temperatures may not be easy with some entry level products.
The main advantage is that there is little need to change the angular position of the temperature control to account for external variations, explained earlier – especially good for younger and older users – and, importantly, the sudden surprises of hot or cold blasts, an occurrence of some lower speciﬁed units, will be prevented.