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Legionnaires Disease An Issue With Reverse Indirects?
D107
Member Posts: 1,724
I'd like to verify what I've been told that Legionnaire's bacteria is not an issue with a reverse-indirect like Turbomax. This is supposedly because the domestic water is only within a coil that holds only a gallon or so. I have adjusted the Turbomax's aquastat to cut-out at 150 and cut-in at 135. The aquastat probe is positioned more than halfway down the tank, which likely means when it cuts out at 150, the water temp at the top of the tank could be 160. So assuming the aquastat is calibrated correctly--not a certitude by any means--the tank water fluctuates between 135 and 150 where the probe is, and a bit higher at top of the tank, and transfers X% of that heat to the actual DHW inside the coil. Perhaps the Turbomax engineers put the probe so low in the tank to simulate the actual temp of the water inside the dhw coil.
In order to cut down on the number of DHW calls during the day when there is little or no hot water usage, I'd like to lower the cut-in temp 5-10 degrees. (as long as this wider cut in-cutout spread, like a heating temp setback--does not waste more gas than it saves trying to make up the differential.)
As it is, tank water temp drops enough to force boiler to fire every 5 hours or so for about ten minutes. This and all other gas usage adds up to a therm a day, 3x my prior usage with stand alone hwh. I'm sure temp will drop less after I insulate the 1.25" steel and 3/4" copper pipes.
But if lowering that cut-in temp will increase risk of Legionnaires, I won't do it.
In order to cut down on the number of DHW calls during the day when there is little or no hot water usage, I'd like to lower the cut-in temp 5-10 degrees. (as long as this wider cut in-cutout spread, like a heating temp setback--does not waste more gas than it saves trying to make up the differential.)
As it is, tank water temp drops enough to force boiler to fire every 5 hours or so for about ten minutes. This and all other gas usage adds up to a therm a day, 3x my prior usage with stand alone hwh. I'm sure temp will drop less after I insulate the 1.25" steel and 3/4" copper pipes.
But if lowering that cut-in temp will increase risk of Legionnaires, I won't do it.
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Comments
ASHRAE now requires 140° as the minimum temp with 120° maximum at the faucet.
There's still a risk!
If boiler limit is 160°, Turbo Max limit is 155°.
15° on the diff.
120° at the mix.
As far as I know, they're all still kickin'. And if not, it wasn't from Legionnaires.
Any piping with temperatures lower have potential to harbor and grow bacteria in the slime or film inside the tubing or piping
One common protection method is to elevate and circulate the entire DHW piping circuit above 140 for an hour every day
Still you have short sections in supply tubes, dead end piping, etc that mag not get circulated at “kill” temperatures
There is no hard and fast, absolute anti legionella method or system I know of, even chemical treatment has some error potential
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
As for on-demand heaters, I found this quote from a manufacturer:
"A tankless water heater does not have the potential to contract and harbour Legionnaires Disease. A tankless completely flushes its system every time the hot water is turned on making it nearly impossible for Legionnaires Disease to repopulate the system."
Not sure about that. (?)
I would be surprised if your Turbomax keeps up with demand with lower settings that what you have now. No real upside to going much lower.
The sensor location conversation is interesting, I imagine that the tank stratifies considerable when the boiler pump turns off. Who knows what the internal temps are doing.
Albert Einstein
https://www.caleffi.com/usa/en-us/education/education#coffee-with-caleffitm
Another option is to install point of use mixers at sinks and two handle tub faucets and run the system at higher temperatures.
It's a catch 22 with DHW these days, especially in public facilities. Scald protection and prevention but also the need for elevated temperatures for bacteria control.
It could be you are more at risk walking past a water fountain or water feature in a park or building then you are with a home DHW system.
Hold your breath when near warm water vapors
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
As @hot_rod Bob suggests, we are faced with dropping the water temperatures to prevent scalding people while saving energy, but at the same time we're trying to prevent growth inside our systems. I suspect the lower the water temperature idea may be contributing to the problem.
I have no way to prove this, but we have worked at many apartment buildings (public and private) and many schools (public and private) over the years. Almost every one of the larger facilities had massive storage tanks (1000 to 5000 gallon) storage tanks that held dhw at 180 degrees or thereabouts. Most had an internal copper coil that was fed with low pressure steam or boiler water throughout the year. Most (but not all) had a mixing valve that was typically set to 140 degrees for the occupants. Some also had a high temperature dhw supply for slop sinks, mop buckets, laundry, etc. I suspect there were no or very few cases of Legionnaires at these buildings.
Today, we work on systems that store dhw somewhere between 120 and 140 degrees typically (to save energy and prevent scalding). The systems are sized appropriately
and preform well, however I am concerned there could be problems down the road.
I suppose on a new system were it was installed bacteria free and the tank or supply was always at elevated temperatures it would be less of a concern.
Older buildings with film or sediment in the piping could harbor bacteria and would need a zap of 140F plus to offer some thermal disinfection.
In a public building it would probably be wise to do occasional testing at various taps to assure it is bacteria free. Kevin indicated legionella testing is more readily available, and affordable now.
i do not think there will be a one solution that fits all buildings. thermal, chemical, UV, maybe a combination of all.
Starting to hear rumblings of legionella potential in cold water supply. Consider areas like Phoenix with public water supplies up to high 80F.
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
Yours, Larry
https://www.cdc.gov/legionella/wmp/overview/growth-and-spread.html
These levels are made worse when air born giving the bacteria direct access to the lungs. (you need to inhale it to get it)Showers, Water mists (Cooling Towers).
https://www.tapinto.net/towns/clark/articles/three-cases-of-legionnaires-disease-in-clark-22-in-union-county