Quote:
Originally Posted by Franziska
That's a different game. Home water cylinders are permanently attached to electricity and the heater kicks in when the water gets below a certain heat. |
Not necessarily.....
In Oz, we have an electrically heated HWS power supply colloquially called 'off peak hot water supply'.
Essentially, many years go, it was noticed that there was little demand for electricity over night, and so the generators had to run down, which was not good for them, so the 'authorities' came up with a plan to utilise the excess power being produced by the idling generators at night.
'Peak power' was when lots of demand was on the grid, 'off peak' when demand was low. So to better utlise the 'off peak' supply, they enabled a system whereby water heaters ran ONLY at night. This supply is separate to the 'main' supply, and can only be utilised by the water
heater, which is the only appliance legally allowed to be connected to it. The carrot was that such 'off-peak' power was one third the
price of the regular 'mains peak' supply cost.
So each house was fitted with a 'ripple switch' - which detected a
radio signal sent along the power lines by the power distributor, that then 'switched on' the "off peak hot water supply".
Now these ripple switches were only able to activate after 11.00pm and usually switched off before 7.00am.
The element in the
heater tank was also thermostatically controlled, so would turn itself off once water in the tank reached a set temperature. So an insulated tank might only switch on and run up to temp once per night.
This temperature was usually set at 60 deg C, as this was the optimum temp for killing Legionella but not scalding users.
In very recent times it has been mandated that such water heaters be now fitted with a compulsory tempering valve, to mix the 60 deg C water from the tank with cold water supply to reduce faucet/tap temperature to 45 deg C, as this is considered a 'non-scalding' temperature and is thus safer for babies, the elderly, and the idiots who jump into a hot bath and scald themselves. But the temp in the tank will still kill the Legionella.
The POINT is that once the tank reaches 60 deg C it cuts power to the element, so probably is only at 60 deg C for an hour or too, enough to kill the Legionella, apparently, and perhaps only once a night at best.
My conclusion from this practice - that demonstrably does not lead to legionella outbreaks - is that an occasional burst to 60 deg C is probably sufficient on a boat.
It is also my understanding (mate who works for Zip instant-boiler maker) that instantaneous hot water heaters are designed to kill Legionella, so even though of shorter duration (water heated to req temp for less time) it is done to an 'adequate' level.
I conclude there is nothing to worry about if you have a heater on the boat, *provided* it is cycled occasionally to kill any outbreaks that might have somehow survived the last
heating cycle.
Another point: that article on copper silver filtration linked to by Franziska is quite clear that carbon-activated filters are a *known* breeding ground for such parasites and clearly therefore require regular
cleaning and or
flushing to remove the biofilms that support the microbes. They actually stated that up to a month after the 'testing' process Legionella were still apparent in pretty regular concentrations in the effluent from the filters.
They concluded that, while it appeared from the results that combining the carbon and silver seemed to lead to a
reduction in Legionella bypassing the filter, compared to the non-silver carbon filtration, that it was not a 100%
removal, so could not conclude that using such a combo was advisable.
Ergo, reliance on any sort of carbon-filtration system might be risky, if Legionella, giardia or cryptosporidium were the targets. Fine for removing chlorine (what kills everything else) and other 'odours' but not so great for removing organisms.
Heat to 60 deg C kills the Legionella; mechanical filtration below 0.5 microns takes out the others.
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