Forums

Forums
Renewable Heating
Air Source Heat Pum...
Legionnaires and he...
 
Notifications
Clear all

Legionnaires and heat pumps

 
Air Source Heat Pumps (ASHPs)
Last Post by prjohn 2 years ago
4 Posts
4 Users
2 Likes
2,305 Views
RSS
 Justin
(@justinsb)
Reputable Member Member
48 kWhs
Joined: 3 years ago
Posts: 100
Topic starter 10/12/2021 5:54 pm  

I'd like to find out what people think about the Anti-Legionnaires settings on the Ecodans (& probably other ASHP's too). Look at @rv3's power usage graph a few posts back. Look at the orange DHW (Hot Water) readings. Every 15 days, look at the Anti-Legionnaires peak. I'm not advising anyone to do anything that might pose a health risk, but I am interested in an honest discussion about it. Particularly since the insulation on those tanks means that it keeps heat in beautifully. Does anyone know how long & at what temp we have to keep it to be safe? Also, how often?


   
Quote
 Kev M
(@kev-m)
Famed Member Moderator
5561 kWhs
Joined: 3 years ago
Posts: 1299
10/12/2021 8:54 pm  

Good topic.

I think the risk of catching Legionnaires from an ASHP heating/DHW system is very, very small. It's primarily an airborne pathogen and since most ASHP systems are unvented, it's hard to see how it would get into the water.  It could concievably enter at the water treatment plant but these are quite sterile environments and a lot of our water has stuff added to it that is likely to kill off any nasties. 

If any make it into your DHW, they won't be very happy.  This from Wikipedia.

Temperature affects the survival of Legionella as follows:[3]

  • Above 70 °C (158 °F) – Legionella dies almost instantly
  • At 60 °C (140 °F) – 90% die in 2 minutes (Decimal reduction time (D) = 2 minutes)
  • At 50 °C (122 °F) – 90% die in 80–124 minutes, depending on strain (D = 80–124 minutes)
  • 48 to 50 °C (118 to 122 °F) – can survive but do not multiply
  • 32 to 42 °C (90 to 108 °F) – ideal growth range
  • 25 to 45 °C (77 to 113 °F) – growth range
  • Below 20 °C (68 °F) – can survive, even below freezing, but are dormant

So the Legionnaires cycle decreases the risk from very, very small to vanishingly small.  If your DHW is at 50C constantly anyway, 60C for 3 hours once a week isn't going make a lot of difference. 

Should you do it/keep doing it? 

Only you can decide.    😉 

 

 

This post was modified 2 years ago 2 times by Kev M

   
ReplyQuote
Mars
 Mars
(@editor)
Illustrious Member Admin
16863 kWhs
Veteran
Joined: 3 years ago
Posts: 2334
10/12/2021 10:08 pm  

@kev-m, that’s all bang on. I didn’t realise Legionnaires died so quickly at over 60C. Interesting.

Our DHW is set to 44C. The heat pump was set to take it to 60C for a least an hour once a week. I changed that to 10 days. We have an iBoost that heats our hot water to over 60C using excess solar - today we produced loads of solar so the ASHP system has reset its 10 day countdown.

The likelihood of getting Legionnaires via your tank is slim, but I still keep our settings activated and let the iBoost do its thing, as we’d rather be safe than sorry. In a world that’s going more and more bonkers with each passing day, we’ve opted to be cautious.

Buy Bodge Buster – Homeowner Air Source Heat Pump Installation Guide: https://amzn.to/3NVndlU

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


   
ReplyQuote
 prjohn
(@prjohn)
Reputable Member Member
553 kWhs
Joined: 3 years ago
Posts: 124
11/12/2021 8:54 am  

The risk is very very small in catching legionella, in the whole of England and wales for 2016 there were 208 cases (most recent data found)


   
Mars and Mars reacted
ReplyQuote
Forum Jump:
  Previous Topic
Next Topic  



Share:

Join Us!

Latest Posts

Heat Pump Humour

x Powerful Protection for WordPress, from Shield Security
This Site Is Protected By
Shield Security →