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Comment by cogman10 | Hacker News Reader

Yup. Heating and cooling are 2 things that can be delayed in most cases with little negative effects. A hot water tank set at 60C isn't going to be harmed if it's allowed to cool to 55C due to high power demand it also doesn't instantly empty out with usage.

The same is true about climate control. 1 or 2C from the desired temperature is still pretty comfortable but can make a huge difference in power savings, particularly if it's coordinated.

That said, I suspect that the even better route for power companies to go down is installing more grid batteries. Those can directly address and smooth out high demand. Put them at the various substations and you can shut off the main grid to the substation temporarily under high load.

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Aren't water tank set to a recommended minimum temperature to ensure no Legionella or comes in your pipes?

Of course. The likely scenario is that the water tank has a preset range of acceptable temperatures and uses demand forecast information to decide whether to heat to the upper end of the range or let it cool to the lower end. Nobody suggests that we let them cool to unsafe temperatures.

I'm not saying its impossible to achieve technically, just that there is a whole fleet of installed equipment and the comment I responded to made no mention of unsafe temperatures...

Unsafe temperatures happen at 42C. Pasteurization starts at 50C. A water heater that stays in the 60 to 55C range I mentioned never leaves the safe zone.

But further, once pasteurization has occurred (which takes 2 minutes at 60C), Abiogenesis doesn't happen. A water heater can safely go down to 36C after it's hit that 60C temperature. Not that it would.

So long as your water heater is hitting 60C once a day and stays above 42C, you have very little risk of developing dangerous levels of Legionella in the tank.

Remember the currently common margins account for the fact that you actually use some of the water every now and then. That water in the tank will regularly cross the merely transiently safe temperature range, by design.

Once silicon is in control (which is where responding grid requests to delay consumption is more or less necessarily heading) you could even achieve better (worst-case) safety margins at reduced (total) power consumption. Because the machinery no longer needs to be designed around two "dumb" thermo switches and do a little extra in case layers of varying temperature manifest after two or more spaced periods of consumption. With continuous monitoring in software, you can integrate the worst-case bacterial growth based on time elapsed outside the "practically safe" temperature ranges. Then the tank always knows what is needed, and can both operate on tighter margins and reliably know when reducing or delaying power draw is ok.

They have to be _brought_ to that temperature periodically, but they don't have to stay at it; if they did you'd never actually be able to use the water (as that tends to drop the tank temperature, dramatically).

Its ok if the tank is heated up to 60C once per week to avoid Legionella.

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