Instantaneous Water Heaters

Crowley said:
We tested the geysers this month on solar. We have three geysers but used two to test, one in the roof and one mounted outside.

The numbers fluctuate a lot due to usage patterns but with the inside geyser running on timers where it is on for 4 hours a day we used on average 13kWH. Keeping it on used an average of 11 kWH. Roughly the same numbers on the outside geyser although it was marginally higher.
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Yes but WHEN it gets used matters if you are on solar.

I don’t want my batteries pumping away at the geyser overnight when I could be Eskom free instead.

Also with a timer you can basically cap the usage to a static expectation because it can’t use more than kW (element size) x hours run.

So if mine runs 4 hours a day it will never be more than 12kWh daily etc and only be slightly imperceptibly cooler for it.
 
Benedict A55h0le not said:
I only switch the geyser on once per day for 30 mins. If I keep it on, especially in winter, it will be on a lot more than that. I think it will be on 3 to 4 times more if always on during winter.
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Exactly that.

It’s more about capping the usage than trying to make it more efficient.

If it’s not on it can’t use power.

Doesn’t work for everyone but if you patterns of use are fairly static it’s no problem.

With a family of 4 mine is max 9kWh average a day with a 3kW element and I shower in the morning and at night and that’s worst case in winter.

Peak of summer it’s 6,4 kWh.
 
Benedict A55h0le not said:
Do not listen to misinformation spreaders like Lupus. Gas is much cheaper for certain things like cooking. Gas is terrible as a room heater. But gas is cheaper than electricity for water heating, since it heats on demand. There is also the option of mini-geysers. But the best option besides a massive solar system, is to get a Geyserwise pv panel solar geyser.
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How goes your solar and gas install at your place? You seem to speak from experience here?
So tell me from your own install how much does it cost to heat water with gas vs electricity? Come on you've got this installed at your home and have an idea of how it all works right?
You know how quickly 48kg can go for a family of 4 vs it's costs and that of electricity.
 
SauRoNZA said:
Yes but WHEN it gets used matters if you are on solar.

I don’t want my batteries pumping away at the geyser overnight when I could be Eskom free instead.

Also with a timer you can basically cap the usage to a static expectation because it can’t use more than kW (element size) x hours run.

So if mine runs 4 hours a day it will never be more than 12kWh daily etc and only be slightly imperceptibly cooler for it.
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Our use case might be different because we have people showering at night and in the morning so for us it works out better to just keep it on.
 
wingnut771 said:
Repeat test with using no hotwater. Yes, you'll have to not shower for 2 days. :p

IMHO, timers are to either manage the load or to save ones batteries overnight. That is all.

The geyser in the cottage uses about 5kWh per day with no hotwater being used.
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Which is 5kWh wasted if it’s not actually in use do a timer based on occupancy would save hundreds of kilowatts.
 
Crowley said:
Our use case might be different because we have people showering at night and in the morning so for us it works out better to just keep it on.
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or get a second geyser and heat both up during the day.
 
Crowley said:
Our use case might be different because we have people showering at night and in the morning so for us it works out better to just keep it on.
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Mine runs for an hour in the morning from 7:00-08:00 and then comes on at 12:00-19:00 when the solar would be in full force most days.

That allows for two people to shower in the morning, two people to shower at night and the kids to bath.

If I’m out later it’s usually not an issue but I can see temperature remotely and turn it on when heading home if I have to.
 
wingnut771 said:
Repeat test with using no hotwater. Yes, you'll have to not shower for 2 days.

IMHO, timers are to either manage the load or to save ones batteries overnight. That is all.

The geyser in the cottage uses about 5kWh per day with no hotwater being used.
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There's an issue with that geyser or you've got it set to high. If no water is being drawn it should be minimal.
With a family of 4 we only use 8 units to warm the geyser up with showers.
 
Grant said:
i know precious little about them.
i'm under the impression they are fairly good in terms of electricity consumption as they are not constantly having to maintain 200L of water at 55degrees, 24 hrs a day - every day, every week.

i may be wrong on that
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You are wrong at that. We maintain 200L at 55 degrees for the sake of efficiency.
this is the problem with water.

Joule/second is kW. One hour of that is Eskom unit.

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Lupus said:
How goes your solar and gas install at your place? You seem to speak from experience here?
So tell me from your own install how much does it cost to heat water with gas vs electricity? Come on you've got this installed at your home and have an idea of how it all works right?
You know how quickly 48kg can go for a family of 4 vs it's costs and that of electricity.
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Gas is cheaper per kw, and there is also much less heat loss than an electric geyser. I did not mention convenience, of course gas is more inconvenient if used a lot. For cooking I am amazed how far 9kgs go, it is way cheaper than electricity and the inconvenience is a non-factor for a 9kg for cooking.
 
Lupus said:
There's an issue with that geyser or you've got it set to high. If no water is being drawn it should be minimal.
With a family of 4 we only use 8 units to warm the geyser up with showers.
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It is outside though. Maybe its less than 5, maybe 4 or 3 as I'm thumb sucking from a total.
 
Sinbad said:
Get gas.
You need bags of heating power if you want a decent flow rate. Electricity doesn't cut it.
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ha!!
ok, there are few things better than a shower with high flow / pressure.

so now im thinking retain the high pressure geyser serving upstairs.
heater for downstairs - very little hot water is used there.
retain geyser for sq/ guest room.

although now in retrospect, will probably abandon the idea - few things. makes less sense than trying to fix something that is not broken !
 
Tomtomtom said:
FOUR 18 kW heaters? And you are happy to trip power any time say, two hot taps are opened simultaneously?

Maybe your own electrical installation is up to it... then I would be worried about your municipal feed!

These things demonstrate a fun fact about water: it's got a very high heat capacity. It takes a lot of energy to raise its temperature. And to raise it quickly, you need insane power.

Let's say you shower at 10 L/minute. That's about 170 mL/second.
Let's say your water comes in at 15 °C and you want it at 40 °C.
You need 18 kJ/sec to heat that water at that flow rate.
And that is... 18 000 W.

So the full 18 kW just about manages one shower, assuming your inlet temperature is not too bad and you're happy with that flow rate.

If your water comes in any colder though your options are a colder shower, or a slower one.

I think these can make sense in a boost configuration, where there's already a solar heated tank at say 20-30 °C. It's more economical to heat the rest of the way on demand, and it's definitely more convenient than waiting an hour or so for a normal ac element to do the job.
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Yup my current gas boiler is 24kw.

The one we had in SA was 35kw - rated at 20lpm
 
Grant said:
ha!!
ok, there are few things better than a shower with high flow / pressure.

so now im thinking retain the high pressure geyser serving upstairs.
heater for downstairs - very little hot water is used there.
retain geyser for sq/ guest room.

although now in retrospect, will probably abandon the idea - few things. makes less sense than trying to fix something that is not broken !
Click to expand...
And then there is the extra cost of the new plumbing that would be required and probably re-tiling as well ...
 
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