DHW Tank - Sterilisation

[richo106]

Good Evening

 

I have an ASHP and 300L DHW tanks, I was just looking at a few things tonight regarding energy and realised the weekly sterilisation cycle on my tank uses around 48kwh of electricity 

 

The current sterilisation set up is 1am Monday morning, the sterilisation temperature is 60 degrees for 1 hour is this normal? Can the duration be reduced to say 30 minutes? 
 

My normal set point of the water tank is 52 degrees

 

Any advice/suggestions welcome, many thanks 

[marshian]

That's a hefty wack of energy on a weekly basis

 

I do a legionaires cycle once a week to coincide with Mrs BC's Friday bath - I heat the 114 litre tank to 60 deg instead of the normal 50 and the energy used is between 3.6 and 4.5 kWh depending on tank temp at the start. I heat it 1 hr before it's needed so the tank sits at 60 deg for that time

 

I do have a vented system but have no concerns about storing water at 52 degrees - if Mrs BC didn't want a Friday bath I wuldn't bother to do a sterilising cycle - we use pretty much all the HW on a daily basis

 

Some good articles here

 

https://www.heatgeek.com/hot-water-temperature-scalding-and-legionella/

 

 

[JohnMo]

7 hours ago, richo106 said:

weekly sterilisation cycle on my tank uses around 48kwh of electricity 

Not sure it can you are only adding around 3kWh to the water to get from 52 to 60 degs.

 

Where are you getting this usage figure from?

 

I suspect to get to 52 degrees every day the immersion is kicking in more frequently than you think. Have you checked?

 

Do yourself a favour and read the details of legionella. We store at 50, within 2 hrs 80-90% of legionella is dead - if it was there in the first place. We do not do a legionella cycle.

[richo106]

Hi 

 

I have attached some pictures of my energy monitor

 

As you can see I normally use around 4kwh per day except on the day my sterilisation where its above 40, it was 47.2 kwh last week

 

Is this normal? Or do i need to speak to my installer about this? It just seems high to me

 

Many Thanks  

[Alan Ambrose]

It does seem odd - generally a quick temperature rise should be proportional to energy input. I would guess the correct number should be 5 or 6. What temperature does it get to in both cases and what was the inlet temperature? Could it be this is unvented and the pressure increase causes a bunch of hot water to exit via the tundish? 40 kwh in the small space where a tank is normally kept would have the room at unbearable temperature. How long is it meant to stay at top temperature?

[ProDave]

I would question what that meter is actually reading and is it true?

 

for a sanity check, I would read the dial on your electricity meter (not any in home display if you have a smart meter).  If you know the time of the sterilisation cycle you can read your meter before and after the cycle and see how much electricity it is really using.  Try and not use any other big loads in the house during that time to get an accurate reading.

[marshian]

3 hours ago, ProDave said:

I would question what that meter is actually reading and is it true?

 

for a sanity check, I would read the dial on your electricity meter (not any in home display if you have a smart meter).  If you know the time of the sterilisation cycle you can read your meter before and after the cycle and see how much electricity it is really using.  Try and not use any other big loads in the house during that time to get an accurate reading.

I'd definately do that.....

 

I'd also be seeing if

 

1. Store temp was actually 52 or something much lower

2. What temp it was heating the store to on the legionaires cycle

 

Quick on line math ignoring the COP of the heat pump from here

 

https://www.omnicalculator.com/physics/water-heating

 

Store temp 50 at start

Store temp 60 at end

Volume of water 300 L

Energy required 3.5 kWh

 

So 41.6 kWh is bonkers

 

[Dave Jones]

have any solar ?

 

We have our ASHP set to 45C the eddi than dumps solar into it until it hits 65C, doesnt take very long this time of year. 

 

Never run a dedicated cycle, cant see the need.

[John Carroll]

On 20/08/2024 at 21:38, richo106 said:

Hi 

 

I have attached some pictures of my energy monitor

 

As you can see I normally use around 4kwh per day except on the day my sterilisation where its above 40, it was 47.2 kwh last week

 

Is this normal? Or do i need to speak to my installer about this? It just seems high to me

 

Many Thanks  

Change the sterilisation day and see does the consumption follow it.

Edited August 23 by John Carroll

[marshian]

Any update @richo106?

[richo106]

On 12/09/2024 at 11:03, marshian said:

Any update @richo106?

I am pretty sure it’s an error on the ASHP energy monitor, it doesn’t seem to tie up with the smart meter I have just installed. I have set a reminder in my phone to make sure I read my meter before and after