Efficient Shower Simulation

We wanted to get an idea of what sort of electricity savings are possible using an efficient shower nozzle.

We used the new PowerProphet consumption modelling tool to compare the expected electricity consumed heating water when a conventional shower nozzle is used, in comparison to an efficient shower nozzle (that typically restricts the flow to about half of normal).

The assumptions used to construct the simulation are listed at the bottom of the page.

Daily Results

The bar chart below shows the half-hourly kWh values (just like your meter would record) for the two scenarios over a typical summer day.  The conventional shower head results are shown in blue while the more efficient shower head’s results are in red.

shower_kwhacc_summerday

You can see the two main heating periods, where cold water flowing into the geyser was heated.  The blue bars representing the conventional shower head, show the element was on longer than in the case of the efficient shower head.  You can also see the periodic reheating spikes (assumed to be 10 minutes every 4 hours) between the main heating events.

The same chart for a typical winter day is shown below.

shower_kwh_winterday

You can see the heating element is on much longer during winter.

It is useful to view the same data represented on an accumulated basis, because that is what you pay for (i.e. all the energy you consume added up over any period).

The charts below show the accumulated energy consumption using the same data as above.

shower_kwh_summerday

You can see that on a typical summer day you would consume about 7.6kWh heating water for showers using a conventional shower head, while an efficient shower head would only result in 5.1kWh consumed (a saving of approx. 33%, which compares well with our own tests conducted previously).

The accumulated energy consumption graph for winter is shown below:

shower_kwhacc_winterday

The extra energy required to heat colder water, as well as the additional hot water used during longer showers is evident.  In this case we estimate 11.9 kWh for a conventional shower, vs 7.2 kWh for an efficient head.  A saving of 39%!

Monthly Results

We extended the period of calculation to a calendar month.  In addition, we showed monetary values rather than engineering values, to get a sense of what sort of monthly amounts we would be paying to heat water for showers in each case.

The summer accumulated energy graph (showing costs in Rand) is shown below:

shower_kwhacc_summermonth

The graph predicts a cost of R278.01 per month to heat water for a conventional shower head in summer, vs R186.56 for an efficient head.  A saving of R91.45 per month.

While the winter results are shown in the graph below:

shower_kwhacc_wintermonth

In this case the costs to heat water for showering in winter are R435.30 per month for the conventional head, and R263.38 for the efficient head.  A saving of R171.92 per month.

If you assume all winter months are the same, and the same for are all summer months, and that there are only three winter months in the year, then annual savings expected are:

9 x R91.45 + 3 x R171.92 = R 1,338.81 (an average of R111.57 per month)

Which is not bad for a relatively low cost device!  This represents a payback period of no more than a few months in most cases, depending on the cost of the efficient shower nozzle.

Bare in mind this only takes into account the energy savings expected, but you will also be saving on water costs which will be an additional amount to that above..

 Assumptions Used

  • Two showers daily, one at 07:00 and the other at 21:00.
  • In summer each shower lasts for 5 minutes.  But in winter people tend to shower for a bit longer, so we chose a time of 7.5 minutes.
  • We assumed a 150L geyser using a 3kW heating element was used to heat the water with a set point temperature of 55C.
  • We then simulated two different scenario’s; one using a conventional shower head flowing at 20L/min, vs an efficient shower head flowing at 10L/min.
  • In both cases we assumed that the thermostat would reheat the water for ten minutes every four hours between main cold water heating events, to replace heat lost via the geyser insulation.  So the only difference between the two scenarios would be the length of time required to heat cold water after a shower.  We looked up those times in the hot water heating calculations on the PowerProphet site.
  • The PowerProphet water heating calculations assume that the cold water temperature in summer was 20C, while in winter it was 15C.
  • We used the current Ekurhuleni residential tariff of R1.18/kWh to estimate the monetary savings.

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