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What electricity savings can be expected?

The electric geyser is the single biggest contributor to your monthly electricity bill and, on average, it will account for around 36% of your entire household electricity consumption [1]. It stands to reason, then, that the biggest single intervention a homeowner can implement to reduce her electricity bill lies with the geyser. The average household geyser consumes around 4259 kWh per year, or 355 KWh per month when controlled by its thermostat [2].
For a 150L geyser set at 70°C, the default setting for some geysers, around 76 kWh per month is expended by the geyser compensating for lost heat [3]. We call this usage standing losses. Left undisturbed, a geyser will lose around 2.5 kWh per day in this way. This accounts for around 21% of the total consumption of an average 150l geyser. These standing losses are affected by environmental conditions, efficiency, insulation, piping, geyser orientation and any number of other factors. Even with perfect scheduling and insulation, the homeowner is only reducing usage on 21% of the geyser’s total consumption.
The remaining 79% of usage is almost exclusively determined by how the homeowner uses hot water. Savings on this portion occur mostly from reducing the set temperature on the geyser as well as behaviour change. Every time hot water is used, the geyser gets refilled with cold water that needs to be heated to a set temperature, which is normally around 70°C. We call this a usage event. Without any form of control over the geyser, every time hot water is used, the geyser will heat back up to 70°C, which consumes a tremendous amount of electricity. [4]

Below, we explain the effect of reducing a geyser’s set temperature: [5]

From these calculations, we can see that:

  • Simply reducing the set temperature by 20°C can save you 40% on the user-dependent component. Because this component comprises 79% of total geyser usage, a 40% saving on this component correlates to a 6% (a) saving on the geyser’s total consumption.
  • Employing schedule control can save you even more by significantly reducing standing losses. An estimate is required here as this is dependent on so many environmental variables.
    • Suppose, for example, you are saving 50% of the standing losses (due to a lower set temperature and proper on/off scheduling), you would be saving around 38 kWh per month, an additional 7 % (b) off the total consumption
  • Thus, the total theoretical savings on electricity for your geyser could be as high as 3% (a+b) based on these calculations.

Question: “Why don’t I just set my thermostat to 50°C, why do I need your product to do that?”

Answer: There are a few reasons why our product

  1. People rarely make the mental jump to connect your electricity bill to the geyser and then associate the geyser usage with that of the thermostat set temperature. Some, if not most, people are simply unaware of the geyser’s electricity usage, the thermostat setting, or the potential savings from changing the set temperature.
  2. The next hurdle to overcome is actually to climb into your roof and do it – in SA most geysers are located in the roof space or high up on a wall. Then to get to the thermostat setting one would need to turn off the geyser at the mains, get all the equipment you need and a ladder, get into the roof, switch off the isolator switch, remove the faceplate of the geyser, turn the mechanical thermostat dial (with little precision) to a chosen temperature, then put everything back in place again. Now test the temperature on the next shower and possibly have to return to make an adjustment. It really is just a lot of effort to use the thermostat in this way.
  3. You can more easily and frequently change the temperature with our product.
    For example:
    – Someone might only want lukewarm water in the morning for a shave, but scalding hot water in the evening for a shower. Using the Geasy you can set multiple schedules with varying temperatures throughout the day or week.
    – Another person might have solar power which they want to take full advantage of, setting the geyser to maximum temperature throughout the sunniest part of the day, then store that heat until the next day. Using only your thermostat will result in your geyser heating to that temperature throughout the whole day, and not only when you can take advantage of solar power. This means the temperature will never be allowed to drop, thus heating at times when solar power isn’t available as well as increasing standing losses because of a higher temperature being maintained.

It bears mentioning that the savings on your geyser as a percentage of your total household electricity bill will vary drastically based on your total electricity consumption. Suppose a user saves R200 per month on their geyser usage. The % savings on the total electricity bill would be very different for a household with a monthly electricity bill of R500, compared to a household with a bill of R2 000 as an example:

Consider the recent real electricity rate for the City of Cape Town (which has increased more recently):

  • <600 kWh = R2.12/ kWh
  • >600 kWh = R2.92/ kWh

The average geyser, as mentioned above, uses around 355 kWh when controlled with a thermostat. Remaining on the conservative side and assuming a household uses less than 600 kWh/month. This means an average geyser would cost around R752.6/month. Assuming a household can save an arbitrary amount of 94.34 kWh on their geyser’s consumption, that would be equivalent to a monetary saving of R200 and a 26.57 % saving on their geyser’s usage – which research has shown to be entirely possible [6].

Household 1Household 2
Monthly electricity bill before Geyser ControllerR500R2 000
Monthly savings on Geyser only(R200)(R200)
Monthly electricity bill using Geyser ControllerR300R1 800
% saved on total monthly electricity bill40%10%

As we can see above, the same savings on a geyser’s electricity consumption will look very different based on the total consumption of a household. We are, however, confident that a 25% saving across household electricity usage is entirely possible when a home has few energy hungry appliances and multiple geysers.
Ultimately, the largest savings occur in the event of a leak or burst, when timeous action can prevent much larger water, electricity, and consequential losses bills.

References

  1. QS Catherine Effective Geyser Management through Intelligent Hot Water Usage Profiling Dissertation, Cape Peninsula University of Technology (2009) p.5; Harris, A, Kilfoil, M. & Uken, E-A. 2008. Options for residential water heating. Proceedings of the 16th Domestic Use of Energy Conference, Cape Town, Cape Peninsula University of Technology (2008) pp.141-148.
  2. QS Catherine Effective Geyser Management through Intelligent Hot Water Usage Profiling Dissertation, Cape Peninsula University of Technology (2009) p.5; Harris, A, Kilfoil, M. & Uken, E-A. 2008. Options for residential water heating. Proceedings of the 16th Domestic Use of Energy Conference, Cape Town, Cape Peninsula University of Technology (2008) pp.141-148.
  3. QS Catherine Effective Geyser Management through Intelligent Hot Water Usage Profiling Dissertation, Cape Peninsula University of Technology (2009) p.13
  4. A high setting of 65°C was chosen as research previously done by (Delport, 2005: 139-144) showed that 64.3°C is the average temperature setting of thermostat controlled geysers. QS Catherine Effective Geyser Management through Intelligent Hot Water Usage Profiling Dissertation, Cape Peninsula University of Technology (2009) p.53
  5. Calculations based on formula (1) in P.J.C.Nel, M.J.Booysen, B.van der Merwe “Energy perceptions in South Africa: An analysis of behaviour and understanding of electric water heaters*”* 32 Energy for Sustainable Development 62-70 at 65.
  6. Nel, P. J. C., Booysen, M. J. & Van Der Merwe, B. Saving on household electric water heating: what works best and by how much?. In IEEE Innovative Smart Grid Technologies – Asia (ISGT-Asia), 4-7 December 2017, Auckland, New Zealand, doi:10.1109/ISGT-Asia.2017.8378439.
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