Instantaneous Water Heaters

PCWARITM said:
Gas is cheaper than a battery. Apples with apples.
Also electricity costs up to R9 per kWh at certain times of the year. Playing that game is painful.
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Besides having to replace the gas every couple of months. 48kg is R1450 right now. 48 kg lasted 2 and half years for cooking and kettle boiling. On average, an hour with a 16l gas geyser would be 2.5kg.
So a family of 4 with just a 5 min shower a day, in a week would use 5.81kg of gas. Which is about 2 months of gas.
Which works out at roughly 240 units a month of electricity at my rate. Currently, a 5 minute shower uses just under 2 units of power, so electricity comes in less and cheaper. At my rate, plus on solar with the geyser only running during the day, I've paid nothing.
Switching to a heat pump, it'll be under a unit to heat the water back.
 
PCWARITM said:
You have an electric instant hot water system?
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Nope, though may look into it. But currently the heat pump makes more sense 1.2kw for equivalent of the 3.5kw element.
Instant hot water system will only heat the water for short period so it may be an instant 3 to 5kw but it'll only be for the draw time.
If you're having a 5 minute shower will be 0.46kWh. Yes it's the instant draw but the actual usage is low
 
PCWARITM said:
Both make sense in my situation. I have a traditional geyser that runs off batteries and solar most of the day, but in my kitchen, the run to the geyser is a bit long so an instant gas heater makes sense. If 3kw is enough I'd say fine, but with my 11kw inverter + 400Ah battery, I wouldn't want to deal with 6kw draw every time the tap is turned on, then I have to think about the oven, the traditional geysers, etc.
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The draw is only during it running. It isn't all the time.
6kw draw won't be for the entire hour, it'll be for the period of the instant hot water. So you run the tap for 2 minutes, that's the length of the draw.
Your geyser isn't running all the time either. So the chances of it being 6kw draw is rare. Mine has hit that around 11am, but panels are giving over 7 already.
 
PCWARITM said:
Both make sense in my situation. I have a traditional geyser that runs off batteries and solar most of the day,
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Move the traditional geyser to its own panels on a geyserwise or similar mppt if you want to free up inverter capacity.
 
Sinbad said:
A 6kw water heater will give you a lukewarm dribble, not a shower
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Yes I did the numbers earlier. At only 6 kW you'll get ~8 degrees of heating at 10L/Min.

Tomtomtom said:
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.
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PCWARITM said:
Overall consumption isn't as much an issue as peak demand.
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I think it's fair to say instant water heating is about as incompatible with solar power as it's possible for anything to be. It's just a fool's errand.

The traditional water tank meanwhile is a no-brainer for storing for solar energy. It's a ~7 kWh thermal battery that can be trickle-charged with DC.
 
PCWARITM said:
Gas is cheaper than a battery. Apples with apples.
Also electricity costs up to R9 per kWh at certain times of the year. Playing that game is painful.
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There a lot of regs with gas. We couldnt install one even if we wanted to because it cant be near drain, window, door or aircon (electrical source incase of spark).
 
PCWARITM said:
You have an electric instant hot water system? That's what this thread is about. There are situations where it makes sense. I have to waste at least 10-20l of water every time I want hot water in the kitchen sink. I have 25kl of stored water on site which is barely enough to make it through a year, so instant water heaters make absolute sense.
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Consider insulating the pipe between kitchen and geyser?
 
PCWARITM said:
Both make sense in my situation. I have a traditional geyser that runs off batteries and solar most of the day, but in my kitchen, the run to the geyser is a bit long so an instant gas heater makes sense. If 3kw is enough I'd say fine, but with my 11kw inverter + 400Ah battery, I wouldn't want to deal with 6kw draw every time the tap is turned on, then I have to think about the oven, the traditional geysers, etc.
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My wife pointed me here... Our kitchen has only one plug connected to grid plus the oven (which she rarely use!) Our geyser is in the laundry room seperate from the house - it also supplies a one-bedroom flat we're renting out. It is on a prepaid supply so the consumption is not our problem. While we were still using the flat it was not an issue to use hot water in the laundry room although we did it so rarely I switched the geyser off. To get hot water to the kitchen meant 5 litres of water going into the second basin for rinsing before the hot water arrives. This water is thus not wasted. Now the other basin is filled with hot water, roughly 8 litres. People forget that that 8 litres of hot water is actually 13 litres as the pipe is still full of hot water.

Our dishwasher uses ~10 litres of water per (normal) cycle. Water-wise washing by hand or with the washer is thus a non-issue for a single wash. Electricity usage is the bigger issue. Our procedure for dinner dishes:
  • If there's something not suited for the washer we boil water in the kettle (battery energy), pour it in the basin, add cold water and wash it by hand.
  • The "normal" dishes we stack in the washer after rinsing them in the rinse water used previouly.
  • Weekday breakfast dishes are added to the washer after rinsing. (These are normally just plates, mugs, etc.)
  • The washer is (generally) set to start at 11 by which time there's more than enough solar energy to not use any battery power. This is simple to check on Accuweather or any of the solar forecast apps.
For showers we currently use gas water heaters. The bathrooms are too far apart to use one so we have two. The next step planned is the installation of either a heat pump or solar water heating for the bathrooms. I have two electric geysers (donated by a plumber friend) I can use to store hot water. The gas geysers will not be discared but just bypassed so they remain available as a standby.

Basic planning and gas water heating means our family of 4 currently uses a maximum of 100kWh of grid electricity per month for the house. The heat pump or solar water heating currently doesn't really make financial sense, but I prefer to invest in our independence from the council and Eskom..

The "issues" with the instant heaters is the cost. Yes, boiling water in a kettle is a bit of effort, but so be it.
 
PCWARITM said:
So it's inefficient in that department.
Overall consumption isn't as much an issue as peak demand.
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Nope, still efficient, ie, the energy you put in is the energy you get out.
It's demanding, but efficient - no heat is wasted.

Gas is much better for this application.
 
Ernabr said:
The next step planned is the installation of either a heat pump or solar water heating for the bathrooms. I have two electric geysers (donated by a plumber friend) I can use to store hot water. The gas geysers will not be discared but just bypassed so they remain available as a standby.
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Can you put the gas inline with the tank outlet to boost the tank water temperature when solar is low?

This is pretty much the energy mix that California runs off...
 
Tomtomtom said:
Can you put the gas inline with the tank outlet to boost the tank water temperature when solar is low?

This is pretty much the energy mix that California runs off...
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I had a solar geyser, feeding an Atlas 20lpm forced induction gas geyser. The atlas geyser had a set point output temperature, so it only used as much gas as was needed to boost the water to 50 degrees. If it came out of the solar geyser hotter than that, the gas geyser did next to nothing.
 
Sinbad said:
If it came out of the solar geyser hotter than that, the gas geyser did next to nothing.
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Sounds like the way to go. When you say "next to nothing" do you mean it came on and switched back off, or just ran its fan, or what? For several months of the year you could presumably have it completely disabled. Did it cause any noticeable pressure loss on top of the geyser's?
 
Tomtomtom said:
Sounds like the way to go. When you say "next to nothing" do you mean it came on and switched back off, or just ran its fan, or what? For several months of the year you could presumably have it completely disabled. Did it cause any noticeable pressure loss on top of the geyser's?
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it came on but at a very minimal level. There was a control for it inside next to the geyserwise display so you could manually turn it off if you knew the solar was really hot. I'm sure you can get even better ones now - this was installed over 10 years ago.
The atlas didn't have any effect on the pressure - my solar geyser was the bottleneck.
 
veniqe said:
What do we think of this 12kw instant water heater? It'd be for the bathroom. We don't need a full tub of water when we take a bath.

www.plumblink.co.za

ARISTON AURES 3 POINT MULTI FLOW INSTANT WATER HEATER 12KW 3195219 | Plumblink - Plumbing, Bathroom & Kitchenware

Plumblink is a specialist plumbing, bathroom and kitchenware merchant currently operating from over 100 branches strategically situated throughout South Africa.
www.plumblink.co.za www.plumblink.co.za
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How will you get 12kW of power to the bathroom?
 
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