Domestic Hot water Tank - Bacteria issue
Domestic Hot water Tank - Bacteria issue
(OP)
Hi all,
I'm designing a solar hot water system similar to the below layout.
http ://www.sol arforce.co m/files/45 -0147_MSTR _large.jpg
The storage tank is large - 1000gal and is supposed to store domestic hot water at 120-140F. Should I be concerned about any bacterial growth in the tank, though the stored hot water is constantly being drawn for domestic needs and new water being introduced daily? Is there any CODE guideline on this? Any information on bacterial growth in storage tanks would be very helpful. Thank you
bplwithu
NY, USA
I'm designing a solar hot water system similar to the below layout.
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The storage tank is large - 1000gal and is supposed to store domestic hot water at 120-140F. Should I be concerned about any bacterial growth in the tank, though the stored hot water is constantly being drawn for domestic needs and new water being introduced daily? Is there any CODE guideline on this? Any information on bacterial growth in storage tanks would be very helpful. Thank you
bplwithu
NY, USA





RE: Domestic Hot water Tank - Bacteria issue
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Are you using chlorinated water?
RE: Domestic Hot water Tank - Bacteria issue
But my advice would be to store your water at 140. Anything much less than that and you have the potential to have Legionella in your system.
Use master mixing valve to reduce temperature to 120 in the hot water loop or circulate 140 water and use point of use thermostatic mixing valves at faucets and showers.
RE: Domestic Hot water Tank - Bacteria issue
Try a google search using search terms {legionella, plumbing, "hot water"}.
RE: Domestic Hot water Tank - Bacteria issue
http://virtualpipeline.spaces.msn.com
"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain
RE: Domestic Hot water Tank - Bacteria issue
Thank you PEDARRIN2, UNCLESYD and DAVEFITZ for the replies. Very helpful.
Wikipedia has more info. on different temperature ranges that affect the survival of the bacteria.
http://en.wikipedia.org/wiki/Legionella
RE: Domestic Hot water Tank - Bacteria issue
Since this is a solar system, the temperature in the tank varies depending on the weather - lowest would be around 120 during winter months. Glad to hear that 120F is a safe number. Most part of the year, my tank temp. would be above 140F.
RE: Domestic Hot water Tank - Bacteria issue
http://virtualpipeline.spaces.msn.com
"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain
RE: Domestic Hot water Tank - Bacteria issue
RE: Domestic Hot water Tank - Bacteria issue
Therefore, be VERY careful about since you are in the 140+ range. You will be required to have thermostatic mixing valves (whether a central or local will depend on your use and AHJ requirements).
RE: Domestic Hot water Tank - Bacteria issue
http://virtualpipeline.spaces.msn.com
"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain
RE: Domestic Hot water Tank - Bacteria issue
I just don't want any bacterial infection on the potable HW tank and cause diarrhea to all the people in the 5-storey building :o
RE: Domestic Hot water Tank - Bacteria issue
Temperature affects the survival of Legionellae as follows:
70 to 80°C (158 to 176°F)-Disinfection range
At 66°C (151°F)-Legionellae die within 2 min
At 60°C (140°F)-Legionellae die within 32 min
At 55°C (131°F)-Legionellae die within 5-6 hr
50 to 55°C (122 to 131°F)-They can survive but do not multiply
20 to 50°C (68 to 122°F)-Legionellae growth range
35 to 46°C (95 to 115°F)-Ideal growth range
Below 20°C (68°F)- Legionellae can survive but are dormant
RE: Domestic Hot water Tank - Bacteria issue
Hopefully you are using a thermostatic valve and not a pressure balancing valve. With temperatures as high as you will have, the thermostatic valves are a must especially for domestic use.
RE: Domestic Hot water Tank - Bacteria issue
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Just curious, anybody worked with large size HW storage tanks for domestic or radiant-heat usages? I assume radiant systems run often into bacterial problems because of their operating range ~ 110F, especially when the system is stagnant during summer.
Thank you everyone for your inputs.
RE: Domestic Hot water Tank - Bacteria issue
"Open" systems such as yours, heating water that will be used for bathing and washing cooking utensils etc.- such systems have much more risk of causing harm to people.
I don't know if there are any NSF or other standards on this or not. Typical domestic hot water systems don't have the residence time that yours will due to the volume you need to store. You are right to be concerned, and others here are right to point out that higher temperatures minimize the bacteriological concern while raising others (ie. scalding etc.)