Healthcare Domestic Hot Water - Legionella 1

[JDphxdg]

Hey guys. When designing healthcare domestic hot water re-circulation systems, how do you use temperature to control the growth of legionella? 160°F is an instant 100% kill, 140°F is a 2 minute 90% kill, and 120°F is a 2 hour 90% kill.

From what I'm reading, it seems as if you want to send water out at a minimum of 122°F, however not exceed 120°F to reduce chances of scalding. This is obviously a contradiction. In the past, we have sized our systems to generate 140°F and mix down to 120°F for distribution, with a return temperatures greater than 110°F.

Also, when using instantaneous heaters with master mixing valves immediately downstream of the heaters, it seems pointless to heat water up to 140°F rather than 120°F.

I believe that ASHRAE is getting ready to release new guidelines regarding this (188). Anyone have any comments? Thanks.

 

[PEDARRIN2]

ASHRAE has been "ready" to release the standard for years. The issue is there is no consensus between the "legionella" group, the "scalding" group and the various other parties with vested interest.

The issue with heating is, if it is present, the Legionella is in the cold water as well. So you kill it (or wound it) in the hot system and mix fresh back in with the cold. Also, heating it generally does nothing for the water in all the dead legs in the system and for the bioslime in the pipes.

That being said, I specify storage heaters for 140 F so that the majority of the hot water will be "free" of the bacteria.

From my perspective, the current "best" method of the meeting all the agendas is to have a non heat system, like chlorine dioxide, a Cu/Ag system, or even an ozonation system. This typically will require some form of onsite/contracted operator licensed by the EPA, which is an expense, but it solves the scalding and the cold water issue. A lot of hospitals do not want to add this unless forced, because the ASHRAE standard would not be binding unless the healthcare boards, which hospitals have to comply with, require it.

We have been trying to work with local hospitals in our area and most of them say that they will comply when they are told to comply - sort of like putting their heads in the sand.

 

[urgross]

Attached might be useful guidance:

http://www.va.gov/vhapublications/ViewPublication.asp?pub_ID=3033