It is straight physics that x amount of energy is needed to heat water from y temperature to z temperature. When you do that, does not affect the energy usage.
If a geyser is full and heated to set temperature, but no water drawn, the only energy that is used to keep the temp at that temperature, is that needed to replace the heat lost to the outside atmosphere. This heat loss speed is a function of the insulation and the difference between the temperature of the hot water and the temperature of the air around the geyser. Naturally the better the insulation the slower the heat loss and the lower the replacement energy. This is why insulation of a geyser is important. Any water drawn for usage will have to be heated by using a set amount of energy, no matter when during the day you do that, so that is why it does not figure here.
The graph of heat loss speed, with regards temperature difference between the water temperature and the air temperature are however not linear. The higher the set temperature, and thus the greater the difference between the two temperatures, the quicker heat loss will be, if all else stays the same. There will therefore be an energy saving by running your geyser at a lower temperature, as the heat loss over time will be slightly less. If this is big enough to bother, I cannot say, but do know that for only me and the wife, 60 Deg C works fine, but 50 deg mean we have to leave some time between showers to let the geyser catch up. For bigger families you might run out of hot water quicker at low temperatures if everybody want to shower one after the other, thus the need to stagger or use a higher temperature.
There is thus only two real ways by which energy could be saved with an existing geyser system and piping where a family occupy the house constantly. Better insulation and lower set temperatures. Ideally one should lag the pipes to the taps also, but special attention must be given to the 1 to 2 meters nearest the geyser, as that part of the piping does allow heat the leak out of the geyser, even with no water running. I have measured the loft temperature at the geyser during the day and most days it is in any case between 45 and 55 deg C (my situation), so very little loss to the air would occur and therefore very little or no heating is done by the geyser, so it make no sense switching off the geyser if it ain't going to work in any case.
Please note that the above does not address the question whether you should switch a geyser off when leaving on holiday or at what interval you will reach a break even point if you do.
If a geyser is full and heated to set temperature, but no water drawn, the only energy that is used to keep the temp at that temperature, is that needed to replace the heat lost to the outside atmosphere. This heat loss speed is a function of the insulation and the difference between the temperature of the hot water and the temperature of the air around the geyser. Naturally the better the insulation the slower the heat loss and the lower the replacement energy. This is why insulation of a geyser is important. Any water drawn for usage will have to be heated by using a set amount of energy, no matter when during the day you do that, so that is why it does not figure here.
The graph of heat loss speed, with regards temperature difference between the water temperature and the air temperature are however not linear. The higher the set temperature, and thus the greater the difference between the two temperatures, the quicker heat loss will be, if all else stays the same. There will therefore be an energy saving by running your geyser at a lower temperature, as the heat loss over time will be slightly less. If this is big enough to bother, I cannot say, but do know that for only me and the wife, 60 Deg C works fine, but 50 deg mean we have to leave some time between showers to let the geyser catch up. For bigger families you might run out of hot water quicker at low temperatures if everybody want to shower one after the other, thus the need to stagger or use a higher temperature.
There is thus only two real ways by which energy could be saved with an existing geyser system and piping where a family occupy the house constantly. Better insulation and lower set temperatures. Ideally one should lag the pipes to the taps also, but special attention must be given to the 1 to 2 meters nearest the geyser, as that part of the piping does allow heat the leak out of the geyser, even with no water running. I have measured the loft temperature at the geyser during the day and most days it is in any case between 45 and 55 deg C (my situation), so very little loss to the air would occur and therefore very little or no heating is done by the geyser, so it make no sense switching off the geyser if it ain't going to work in any case.
Please note that the above does not address the question whether you should switch a geyser off when leaving on holiday or at what interval you will reach a break even point if you do.
