2 hours ago, Gnome said:

(I mean there is a max obv, around 60℃ but these thermostats aren't exactly accurate).  I only turn it on for 30 minutes twice a day.

Yes the actual scale perhaps not. What I have measured is the power used by a 3kw element and found it to use as little as 200Watt which means it went up by just over 1 degree before it switched off again. This is without any water used from the previous switch on. Power measured with an electronic power meter which is quite accurate if compared with the munic meter.

10 minutes ago, Scorp007 said:

Yes the actual scale perhaps not. What I have measured is the power used by a 3kw element and found it to use as little as 200Watt which means it went up by just over 1 degree before it switched off again. This is without any water used from the previous switch on. Power measured with an electronic power meter which is quite accurate if compared with the munic meter.

If you measure it on the same day, yes it'll be great at getting to a temperature and generally keeping it there.  But in absolute terms it is garbage at keeping a set temperature.  It has drift over time.  Drift in a single day will not be significant so obviously looking at a single day is a bit like eye balling a measurement using your fingers, then calling it good.  When it says 60℃ on the dial it doesn't actually mean 60℃ because they are mass manufacturing these things.  There is no way they are trimming the contacts on every single one to bring it exactly into a tight tolerance.

They use large bi-metal contacts (IIRC).  Your drift and calibration on those is likely something like 10-15℃ degrees drift is acceptable within the product range.  Whereas something like a PT100 is 100 parts per million.  One device is laser trimmed, the other one is manufactured to within an "acceptable" tolerance with minimal testing.

TL;DR: I don't trust the setting on a geyser thermostat.  If I put at PT100 or PTC in there I'd have more confidence.  But at "60℃" on the thermostat it is whatever.  Probably somewhere between 55-75℃.  Water if f#ck hot when it comes out and I turn off the Astute, so my guess is closer to 70℃.

Edited February 8, 20224 yr by Gnome

On 2022/02/03 at 3:28 PM, Gnome said:

Just wanted to mention, even with a heat pump, you are looking at an efficiency of 3:1 (maybe 4:1 if you are lucky).  So 1 watt of energy = 3 watt of heat.

I would seriously consider those solar geyser if I were you.  In summer in SA you can probably go completely of grid in terms of heating that way.

Comparing to your electricity usage, I recently switched to a class B geyser + geyser blanket + pipe insulation and my monthly electricity consumption on that Geyser averages ~37kWh.  Sadly I have no idea what it was before because I only installed the measuring device afterward.  So insulation may help also.

Do you mean 37kWh with resistive heating or heat pump or in addition to solar? Because you can calculate how much water you can heat from 20°C to 40°C with 37kWh (assuming 0 losses) and easily verify how far off you are.

Edited February 8, 20224 yr by P1000

14 minutes ago, P1000 said:

Do you mean 37kWh with resistive heating or heat pump or in addition to solar? Because you can calculate how much water you can heat from 20°C to 40°C with 37kWh and easily verify how far off you are.

Resistive for me.

But the 50w figure is total nonsense.  It is a made up number that is totally irrelevant except to compare two products to each other.  You need a delta T to calculate heat loss.  They setup an experiment with two geysers and then the one lost 50w, the other 100w.  But that is as relevant to your geyser as your car's speed is to a random car driving in a highway somewhere in Europe.

Edited February 8, 20224 yr by Gnome

3 minutes ago, Gnome said:

Resistive for me.

But the 50w figure is total nonsense.  It is a made up number that is totally irrelevant except to compare two products to each other.  You need a delta T to calculate heat loss.  They calculated some arbitrary value based on what they think the temperature is of incoming water and outdoor temperature, took a value they felt was representative of "most" people and called it a day.  More reasons why that value is totally unusable is because it doesn't say anything about how much heat loss occurs in the pipes.  Any water heater loses significant heat from the pipes around the geyser.  They are copper and as we know other than diamonds, copper is nearly the best heat conductor out there.  So you have these huge heat pipes coming out of your geyser.  So how much of that is the 50w?  What temperature was the geyser set point?  (the higher that is the higher the losses).

Ok, I don't think you have nerd sniped anyone. Everyone is just confused about what you are arguing for or against. Yes, the losses on the geyser is not always representative for a specific situation, but they are measured in a standard way - with a standard T delta, and R1 lagging on all pipes for at least 5m from the geyser etc. So not quite a made up number, and definitely one you can use to compare geysers.

 

BTW, you cannot heat the entire contents of your geyser in 30m, so you will only be partially heating the water (ie top half is hot, bottom is cold). That is fine, as long as you do a sterilization run once a week (like 70°C for 1h, look up the legionella tables). If you only use it in that fashion, while absolutely optimal, is not safe.

1 minute ago, P1000 said:

BTW, you cannot heat the entire contents of your geyser in 30m, so you will only be partially heating the water (ie top half is hot, bottom is cold). That is fine, as long as you do a sterilization run once a week (like 70°C for 1h, look up the legionella tables). If you only use it in that fashion, while absolutely optimal, is not safe.

Yeah Sundays.

1 minute ago, P1000 said:

Yes, the losses on the geyser is not always representative for a specific situation, but they are measured in a standard way - with a standard T delta, and R1 lagging on all pipes for at least 5m from the geyser etc. So not quite a made up number, and definitely one you can use to compare geysers

Where do they give the exact experiment.  Then I can contrast.  But again, I'm running it again, so let's see what happens?  I reset it, I have an accurate timestamp now and I can contrast after 30 days.

3 hours ago, Gnome said:

Where do they give the exact experiment.  Then I can contrast.  But again, I'm running it again, so let's see what happens?  I reset it, I have an accurate timestamp now and I can contrast after 30 days.

The 50w/hr might be irrelevant to our real world situation but surely an indication of possible minimum standing losses. In another thread on this forum a figure of 1.16wh per litre per °c of water heated is used.

Not knowing your inlet water temp or max water temp - let's take an arbitrary 20°c inlet and 60°c max for a 40 degree delta T.

Your 37,000wh per month / 1.16/40 = +-800 litres per month. Approx 26 litres per day of hot water useage.

That is without any losses whatsoever - No standing losses in geyser or pipes etc

Two days in.  Washed dishes today so not surprised by the higher usage.  Also when I took a shower, water was hot, I don't even turn it to full hot on faucet 🤷‍♂️

Temperature inside my geyser cupboard

 

 

Edited February 8, 20224 yr by Gnome

On 2022/01/27 at 10:52 AM, JonB said:

Hi all,  I didn't want to hijack Friendly Toast's awesome thread, so I thought I'd wade in separately.
 

Some Background:

I recently bought an old house with 5 (yes 5) geysers. 
No way to consolidate them, the place is stretched out and cavernous, aside from telling some family to suck it up and just not shower or shutting off water to the kitchen and outbuildings, it's just not feasible.

Then we had a 15 day power outage... so my wife gave me that look that said "fix this, now!

 

I am on prepaid.  Monthly bill is R6k. +- 2040 kWh monthly.  She's a hungry house.
I added sonoff switches to measure geyser consumption. Daily load is around 34kWh.
3 of the geysers have non-working heatpumps. 

Option 1 is to fix at cost of R12K (for the 3 total) and reduce load to 1.4kWh per unit.
Option 2 is to take the geysers off power onto PV completely (R60K)
Option 3 is to integrate it using option 1 into by solar PV setup.

House has 5 db boards.  COC issued but she's going to need some work to wire as kitchens / geysers all run of secondary db's

I've had a couple of installers in - everyone's got a product and varying degrees of pricing, but i'd appreciate advice from users

I've been quoted / recommended  a 8kWh backup solution + 10kWh Li batteries and 20  +-400w panels to power it

That's not enough power to take the house off-grid, i know, but it's a start and can keep the lights on in a 15 day power outage and take care of loadshedding so an oke can work and run a few essential geysers.

 

WHAT ARE MY BEST OPTIONS?:

1. Should I separate my geysers from my PV solution and run them independently as has been suggested by one contractor?  Maybe add one or two on the PV and take the non-essentials offline or put them on separate power?

2. Should i spend the money instead on just bulking up my PV to the home and include the geysers in the PV system?

3. Something else?

 

Thanks!

Excellent options have been tabled but the immediate "the look" solution  has not been proposed! I will put on my hardhat for this one and run after.... I small genie (+-ZAR 9,000) is your friend, to tide you over this initial phase of tidying up you DBs, rationalising what loads will be essential, planning the hotwater solution and finally deciding what your first (rev A) of your solar solution will be!
The boss wants lights, TV, internet and possibly the kettle working now! granted the genie will get parked eventually but as a stop gap measure it cannot be beat! It worked for me and even now when we get eskom's special extended loadshedding events after the scheduled events and mother nature adds rain and cloudy weather for a few days on a trot, I have rolled the gennie out to get past the worst of the outages!