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Legionnaires' Disease & Home Hot Water: Understanding Risks and Prevention

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(@derek-m)
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Posted by: @transparent

Two further points:

1: Legionella  is a Notifiable Disease to UK Health Security Agency. Any infection is subject to an investigation which must identify the source.

I've posed the question as to why a potential risk isn't notifiable.
Prevention would seem to be the better option!

 

2: The DESNZ Public Consultation on Delivering a smart and secure electricity system (closing date is tomorrow 21st June) contains a number of questions in Section-1 on their proposals to include Heat-Pumps within the corpus of devices subject to DSR controls (Demand Side Response).

In short that means they intend to legislate to allow Service Providers to switch off your heat-pump during times of high grid demand. This would work in similar fashion to smart EV chargers being controlled by your electricity supplier.

That comes with the risk that your heat-pump might've been switched off during a period when the anti-legionella cycle would normally have run. It also means that the DHW tank temperature is more likely to have dropped to a temperature where growth of legionella bacteria would be increased.

If that were so, how would a homeowner know that the anti-legionella cycle hadn't occurred?
Is it reported somewhere?
Can a heat-pump be requested to report the last time the cycle had run?

Given the dearth of site-specific information and instruction given to homeowners, how many are likely to know how to start an anti-legionella cycle manually, even if they realised that it hadn't occurred to a programmed schedule?

If my understanding is correct, for most, if not all, heat pump controllers to respond to a stop and start signal from a Smart meter then this functionality would have to be enabled within the heat pump controller. How many consumers do you think would allow this function to be enabled?

 


   
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Transparent
(@transparent)
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@derek-m  DESNZ isn't proposing to route DSR controls via Smart Meters.
They intending using the internet.
It's another 'blunt instrument' which will take no account of local/regional conditions or tariff schedules.

There are two different DSR payment methods being trialed by NGED/SSEN which reward homeowners for participating in their heat-pump (and other Energy Smart Appliances) being switched on/off remotely. There are also two different control methods.

See an overview of the Equinox Project trials here, and the details in this presentation from autumn'23 in particular.

I've written to the Innovation Team a few hours ago to ask if they're aware of the risks of Legionnaires Disease when Heat-pumps are turned off remotely.

Save energy... recycle electrons!


   
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MikeFl
(@mikefl)
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@transparent Just read through the Equinox presentation, which does mention that any impact must not affect end-user safety, which concerns you've raised obviously could. I'm hoping they don't draw too much from the "high level of compliance and adherence" seen in the trials, as I'd expect anyone participating in such a trial to be an atypical user (as I guess any HP owner would be of the general population, by and large). As an EDF customer, they have run several "lower your consumption during these times" cashback schemes to encourage lower usage during peak times, and I wonder if the results of that are being similarly examined to enable trends to be seen? Of course, there's a massive difference between trials/short-term schemes, and enforced remote-control of consumer energy consumption.

Grant Aerona 3 10kW


   
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Transparent
(@transparent)
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Let's note that the Equinox Trial is being run by competent engineers from DNOs.
They're not heat pump experts.

What we can do here is to provide them with background knowledge of what happens when power to heat-pump is cut.

If a Power-outage extends over a time period when an anti-legionella cycle would've occurred, are HP controllers 'aware' of that?
When power is restored, does it provide any indication that the cycle has been omitted?
Does any HP run an anti-legionella cycle as a precaution when power is applied?

Does any HP take action if it's sensors detect that the temperature in the DHW cylinder has fallen within the danger zone for legionella?

 

DESNZ's Public Consultation is asking if there should be a Directive to Manufacturers to make HP models such that they have particular features to better suit them for DSR operation. [Q.26]

The Consultation asks specifically about whether HPs should be able to modulate their output in response to Explicit-DSR commands? [Q.11]

And they want us to comment on whether DESNZ should set a max limit on how long a heat-pump should be switched off due to Explicity-DSR commands. [Q.17]

Save energy... recycle electrons!


   
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