Geyser on, geyser on. Does it save electricity?

[Annetta]

Hello all

Please advise me or guide me to an info portal where I can find out if switching my geyser on and off every day saves electricity.

Additionally, if a geyser is designed to maintain a steady temperature, does cooling and re-heating shorten it's structural integrity?

We will be re-locating in two years so installing solar will be in the next house.

Thank you.

[Justloadit]

Using a geyser timer does save electricity, but it also relies on the amount of usage.

There a number of types of solar water heating systems.
Evacuated tubes.
They supply enough tubes, to keep the price low, and also, that the water does not over heat during summer.
When winter comes, the sun radiance is a lot less, and the amount of hot water consumption goes up, forcing you to use electricity to heat up the water. They hide this by installing a controller which brings the water temperature up when the sun goes down. This defeats the object of having a solar water heating system to save money on electricity.
Installation also requires that a reticulation be pump installed, and water pipes have to be modified to suite the system.

PV Based system
I have a PV based system, which I have designed and selling, which uses the existing geyser geyser thermostat and element to heat water.
I turn my thermostat to maximum, and I have 65°C hot water every day, and hardly use electricity to heat my water except for the days that water is over used, or there is hardly any sun radiance.
Installation involves rerouting the wires from the element to the controller, and installing at least 1200watts of PV panels on your roof.

Since I installed my system for 2 geysers, I have saved over R500.00 a month on power bills, and have already clocked 2,000 KWHours of solar from November 2020 to July 2021. That's just over 8 KWhours a day.

[GCE]

Hello all

Please advise me or guide me to an info portal where I can find out if switching my geyser on and off every day saves electricity.

I was involved in testing geyser efficiency and we ran them leaving geysers off and switch on after a time period leaving geysers on all the time and allowing the thermostat to control them.

It made basically no difference to the electricity usage .

If you use 10 liters of hot water you have to heat 10 liter's of cold water , whether you do it at 12H00 or do it at 8H00 hours there is still the same amount of energy needed to heat it . If you take another 2 liter's whether on or off it is still the same amount of energy to heat 2 liter's independent of whether the geyser is at temperature or below temperature

I have pasted the formula below that illustrates the amount of energy needed -

Qs = (m Cp) T
Qs total heat capacity of the storage tank [kWh]
m volume of the storage tank [m³]
Cp heat capacity of water [1.16 kWh/m³K]
T temperature difference - hot water temperature and cold water temperature [K]

The only way to save electricity with a geyser is to reduce the high switch off temperature from 65 degrees downwards as this would reduce the temperature difference needed in the calculation.

[Justloadit]

I was involved in testing geyser efficiency and we ran them leaving geysers off and switch on after a time period leaving geysers on all the time and allowing the thermostat to control them.

It made basically no difference to the electricity usage .

If you use 10 liters of hot water you have to heat 10 liter's of cold water , whether you do it at 12H00 or do it at 8H00 hours there is still the same amount of energy needed to heat it . If you take another 2 liter's whether on or off it is still the same amount of energy to heat 2 liter's independent of whether the geyser is at temperature or below temperature

Where I think the difference comes is is as follows :-
Geyser is off from say 6AM to 5PM. I then switch the geyser on for 1 hour. If I have a 150L geyser with a3kWatt element, it will heat the water by a differential of 30°C. So if my initial temperature was 25 degrees, them after an hour I have 50°C, more than enough to have 2 showers. I then switch it on again at 5AM for 1 hour. Again the water temperature is approximately 50°C, more than enough temperature to have 2 showers. In fact any temperature above 42 degrees is sufficiently hot to have a comfortable shower.

So effectively 6kWH a day. After the solar installation, I found that I saved R500 worth of electricity a month. If at R2.30 it may be higher because of the consumption tier a kWH then it meant 217kWh a month or 7.2kWh a day. Close to my statement above.

What also contributes to the extra energy is a poorly insulated geyser. I have noted that the new geysers being sold, loose approximately 0.5°C per hour, as opposed to the earlier versions loosing 1.5 to 2°C per hour depending on the ambient temperature.

[adrianh]

@Justloadit

Isn't it a bit silly for all of us to keep 100L of water hot all day in case one needs to use 50L - The whole thing just seems like a total waste.

Is it not more cost effective to develop a system that heats the water inline only when you need to - like those gas heaters?

Lets say one passes the water through some form of coiled pipe going through a microwave oven (of course everything will be designed with safety and efficiency in mind) - It just seems like such an obvious device to me if it is done properly. Imagine manufacturing small devices that go be installed close to the points where the hot water is needed eliminating the temperature losses though the pipes as well. This is of course only viable if the device can heat the water cost effectively.

[Justloadit]

@Justloadit

Isn't it a bit silly for all of us to keep 100L of water hot all day in case one needs to use 50L - The whole thing just seems like a total waste.

Is it not more cost effective to develop a system that heats the water inline only when you need to - like those gas heaters?

Lets say one passes the water through some form of coiled pipe going through a microwave oven (of course everything will be designed with safety and efficiency in mind) - It just seems like such an obvious device to me if it is done properly. Imagine manufacturing small devices that go be installed close to the points where the hot water is needed eliminating the temperature losses though the pipes as well. This is of course only viable if the device can heat the water cost effectively.

The major issue with using electricity to heat water as you use it, boils down to the amount of energy required instantaneously. For a decent flow of water where you have a low temperature water coming in, and you wish to have it at say 42 degrees, then you may need approximately 5 or 6KW. For a single phase system, it will be above 21Amps. In many cases the DB main breaker may not be large enough to carry the instant geyser load, and other loads simultaneously.

The other issue is that instantaneous heated hot water can not raise the temperature high enough to pour a bath, by the time the bath is at a suitable level, the temperature of the water will have dropped dramatically.

Yes, inline gas geysers work, after all the whole of Europe uses this concept, however the homes in Europe are built with heating efficiency in mind.

The geyser concept probably comes from the old days in which the old wood fired stoves would heat water while cooking and heating the home.
The other advantage of the geyser, is the low amount of instant energy to heat the water over time, it is just less load on the electrical system, since water retains the heat if the geyser is well insulated. The total amount of electricity per liter of water would be the same. The extra cost of geysers are the poor insulating properties of the old geysers, where the thermostat attempts to maintain a constant temperature.

[Blurock]

I shower every morning, turning the tap off while soaping or washing my hair.
So, using less water, a habit that formed when we had a severe drought in the 80's and water had to be recycled to flush the toilet.

In summer, we switch the geyser on every 2nd day as we need it just hot enough to be comfortable and to take the chill off.
Winter is another story, but we only switch on an hour or 2 before having a shower or just before we go to bed.
Because there is only the 2 of us, some lukewarm water remains and cost is not excessive.

[Annetta]

Thanks for all the info. We have fully insulated the geyser and the pipes and installed a solar pre-heater which ups the ambient feed.

[adrianh]

Ah...of course - the energy required to heat the water is the same so one trades low energy consumption over a long period for high energy consumption over a short period (everything else being equal)

So in essence using solar installations add energy to the system in a more cost effective manner (again provided that the solar system is not prohibitively expensive)

We looked at installing gas for cooking and heating water but the installation costs and running costs have a terrible return on investment - it would have taken us something like 8 years to break even.

[Justloadit]

Ah...of course - the energy required to heat the water is the same so one trades low energy consumption over a long period for high energy consumption over a short period (everything else being equal)

So in essence using solar installations add energy to the system in a more cost effective manner (again provided that the solar system is not prohibitively expensive)

We looked at installing gas for cooking and heating water but the installation costs and running costs have a terrible return on investment - it would have taken us something like 8 years to break even.

Yep.

Solar as an alternative to energy is a convenience, and can not be substantiated by ROI (Return On Investment)
When you have regular power loses as we have been experiencing in the last year or 2, let me tell you forget the ROI, but concentrate that I have an alternative source of energy besides my noisydiesel generator.