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Ecodan - Legionella Operation Time and Target Temperature

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(@richard24738)
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Hi. What's a realistic operation time for a legionaire cycle?

New system: Ecodan 11.2kw and Telford Tempest HP 250L tank.

Mine is set for two hours with a 60 degree target.

1st half hour the heat pump flow temp gradually ramps up and Tank temp goes from 20 > 49

2nd half hour the flow temp starts to drop and tank temp goes up by 1 to 50

3rd half hour the flow temp continues to drop and the tank temp goes from 50 > 56 (Immersion on)

4th half hour the flow temp continues to drop and the tank temp goes from 56 to eventually just reaches 59 on the 2 hour mark.

I guess if I extend the run to over 3 hours it might get to 60 but that seems an awfully long time to be without any heating next winter. 

Any thoughts?

This topic was modified 1 month ago by Mars

Install 13 April 2024 - 4 Bedroom Brick Detached - Ecodan 11.2kw R32 - 25L Buffer - 250L Telford Tempest HP DHW - All 16 radiators replaced - Auto Adapt - Octopus Tracker


   
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Mars
 Mars
(@editor)
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It appears that your current Legionella cycle is quite lengthy. Typically, achieving and maintaining a water temperature of at least 60°C for about 30 minutes is enough for Legionella prevention. Given that your system is struggling to reach this temperature within a reasonable time frame, some adjustments might be necessary.

Typically, in low temperature units (like ours) the heat pump gets us 50C, the immersion takes over and gets us to 60C relatively quickly. I’m not sure why your immersion is “struggling”.

There are a lot Ecodan users in the forums that can provide their insights.

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Abernyte
(@abernyte)
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Ecodan user here and I have disabled the Legionella cycle..it is just not necessary. Heating water to 50C is more than adequate to mitigate Legionella bacteria growth, and as nearly all domestic settings do not have dead legs and do not have aerosol producing equipment and will turn over the water capacity in the pipework regularly so the risk is negligible. 

I also have Solar Thermal which raises the stored DHW temperature to 60C in any case and as the DHW is heated via the Ecodan's AlfaLaval heat exchanger there is no stagnant usable water in the 40C-45C state.

The 60C hype is an abundance of caution.  Your mileage may vary!


   
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(@richard24738)
Trusted Member Member
309 kWhs
Joined: 4 months ago
Posts: 21
Topic starter  

@abernyte Thank you for your reply and I agree that it's debatable as to whether a legionaires cycle is necessary. However, we are classed as vulnerable so maybe better safe than sorry.

Regardless, this is a new system so, at this time, what I am doing is simply proving that the system can do it if required. Based on what I have seen so far, it would appear something is not quite right so I was seeking information on what timings are to be expected.

The decision as to whether I continue with a legionaires cycle or not will come later.

 

Install 13 April 2024 - 4 Bedroom Brick Detached - Ecodan 11.2kw R32 - 25L Buffer - 250L Telford Tempest HP DHW - All 16 radiators replaced - Auto Adapt - Octopus Tracker


   
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Abernyte
(@abernyte)
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Understood. My 14kW Ecodan does the DHW cycle from cold 25Cish to 52C in about 30 minutes. I am not sure what yours is dawdling around doing! Just checked this mornings report: it started heating DHW at 1006hrs with flow temp of 28C and tank temp of 28C and completed it at 1035hrs with flow temp of 62C  and tank temp of 52C. No solar gain due to 100% cloud cover.

This post was modified 1 month ago by Abernyte

   
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Mars
 Mars
(@editor)
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@richard24738 I think the issue with your system, which requires investigation, is why it's taking so long and not ultimately getting to 60C. Like @abernyte, our heat pump (18kW) takes about 30 minutes to get the hot water over 50C, and then the immersion takes over. Since your system is new, I'd call your installers and also speak to Mitsubishi as everything is still under warranty.

Buy Bodge Buster – Homeowner Air Source Heat Pump Installation Guide: https://amzn.to/3NVndlU
From Zero to Heat Pump Hero: https://amzn.to/4bWkPFb

Follow our sustainability journey at My Home Farm: https://myhomefarm.co.uk


   
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(@richard24738)
Trusted Member Member
309 kWhs
Joined: 4 months ago
Posts: 21
Topic starter  

@editor Thanks.

I, of course, thought something was wrong with the timings but wanted to be sure what is normal before contacting my installer or Mitsubishi.

Install 13 April 2024 - 4 Bedroom Brick Detached - Ecodan 11.2kw R32 - 25L Buffer - 250L Telford Tempest HP DHW - All 16 radiators replaced - Auto Adapt - Octopus Tracker


   
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