solar hot water vs. scum factory

I recently read something that said that hot water in a tank is supposed to be kept at a temp of 120 or higher at all times.  The reasoning had something to do with certain bacterias and other micro organisms can thrive at lower temps. 

So this makes me wonder ... if you have a few cloudy days  ... and folks have skipped showers for a few days ...  are you gonna end up showering in some sort of pond scum?

That is a really good question!

I've never heard of anyone having problems with this. When the sun shines it should heat the water in the system up above 120. I suspect running really hot water through the system will clear out anything. In the winter when the sun doesn't heat the water so much I suspect running it through an on-demand propane heater would wipe out anything when it gets hot as well. City water that has been chlorinated probably wouldn't have problems anyway.

This is just my hunch. Either way, I don't think it would be like "pond scum" as there won't be any algae or plant life growing in it without sun actually hitting the water.

Anyone know more?

Dave

Well, I'm not sure what "it" might be.

But I do find the whole thing about keeping the temp above 120 interesting.  And that's for water tanks that have no sunlight either. 

In fact, I read something about how commercial buildings have a special mater-mixer-thing that lowers the temp to something like 110 (or less) after leaving the hot water tank. 

I just wonder .... what's up with that?  Should we try to work something into our designs to compensate for "it"?  Or was somebody just being a busy body? 

I found this to be interesting
http://www.safety-council.org/info/home/hotwater.html

And this one is just plain scary
http://www.osha.gov/dts/osta/otm/legionnaires/hotwater.html

Wow.

That builds a really good case for the instant heat at the sink. 

And it makes a good case for solar water heat to be supplemental to something else, rather than the whole thing.

Solar hot water tanks should only be for storage of hot water and heat exchangers should run through it.  The tank water should be a heat sink and not a resource you use.  Even if there's no sun for a few days, if you have a tank of water stored in the house it will be at room temperature and preheat any water that goes through the heat exchanger.  If your well water is 45 to 55 degrees and it's preheated by room temperature water you're helping save a lot of BTU's in supplemental heat reducing the load on your water heater.
Unfortunately unless you live in a southern climate there are times when you don't have the sun to heat the water so you need a water heater too.  On demand or solar storage types are good,  LP gas or natural gas are best.  A standard water heater with preheated water running to it works okay too.  On demand is the most efficient but they require very clean water to prevent clogging.
Wood heat can be used to heat the water tank on off days too.  Stored hot water that you will come in contact with does need to be 120 degrees or more and a mixing valve is recommended to prevent scalding.  There are many sizes and shapes.  Ask your plumber which type will work in your situation. 

Maybe a solar system has to work a whole different way. 

So not worrying about this thing will probably mean folks will probably be okay.  But if everybody did it this way, a lot of people would probably get really sick. 

Perhaps a solar water strategy on low tech systems would be that on cloudy days the system should be emptied and aired out?

The way I described it is the way it works.  It's how my own house is set up and has been since 1982.  Right now my water heater with the water jacket heat exchanger jacket on it is old and needs replacement but it is the tried and true way to do it.
Those mixing valves are installed in houses everywhere.  It's an old technology.  Heat exchangers are two.  The manufactured versions of them now have a double wall inside them to make extra sure there's no transfer between the active water from the panels and the water you touch.  It's over kill but required by code now if you have a plumber do the install.

There are passive systems that require a reservoir tank that's located higher than the panels to create a thermosiphon but they work best in areas where the out side temperature is moderate and doesn't freeze very often because the water has to go directly into the tank from the panels and would require way too much anitfreeze to protect it.

paul wheaton wrote:
I recently read something that said that hot water in a tank is supposed to be kept at a temp of 120 or higher at all times.

140°F -- not 120°F -- is the magic temperature according to the OSHA and Canada Safety Council links posted above.

So the idea is that you have a water heater where the water is kept at 140 all the time.  And then you have a solar panel and some logic so that when the stuff in the solar panel gets hot enough, some circulation starts to happen.  Then the sun is keeping your water at 140 instead of electricity or gas.  But at night, there is no solar. 

The solar stuff might get temp fluctuations and be loaded to the gills with all sorts of icky stuff, but that water never mixes with the water you wash your hands with, so no big deal.

Am I on the right track?

OSHA standards are for the workplace.  Upon reflection I realized that recommendations for businesses and commercial facilities are not necessarily optimum for the home environment.

120°F is what my water heater is set at.  120°F is the temp my gas company suggests to save energy -- I don't think they'd suggest an unsafe temp (especially in California, land of lawsuits).

additional info I found on the subject:

Legionnaires' disease is a serious disease caused by Legionella bacteria, which thrive in stagnant, warm water. Outbreaks of this disease have been associated with cooling towers, evaporative condensers, showers, faucets, hot tubs/whirlpool spas, and other sources of aerosolized water. Legionella  bacteria favor a temperature of 25-42 C (77-108 F) for growth.
  . . .
People get Legionnaires' disease when they breathe in mist or vapor that has been contaminated with the bacteria.

[source: Centers for Disease Control and Prevention]

Although some manufacturers set water heater thermostats at 140ºF, most households usually only require them set at 120ºF. Water heated at 140ºF also poses a safety hazard—scalding. However, if you have a dishwasher without a booster heater, it may require a water temperature within a range of 130ºF to 140ºF for optimum cleaning.

Reducing your water temperature to 120ºF also slows mineral buildup and corrosion in your water heater and pipes. This helps your water heater last longer and operate at its maximum efficiency.

[source: U.S. Department of Energy]

Getting clean water, especially warm clean water, is complicated, and you can get sick if you overlook something.

(Ernie's more practical advice: Save energy by insulating the water tank better, instead of lowering the temperature.)

I'm not building my own hot water system, so I feel like speculating.
Here are some thoughts on appropriate technology for sustainable human lifestyles. 
(Ignore me if you're on a more practical project. )

How did our ancestors handle this?

In a lot of regions, it seems like there's some form of boiled beverage-of-choice: tea, coffee, soup, even just plain boiled hot water (the favored drink of old men in China, apparently).  Africa, Asia, the Andes, Britainnia, even hot places like Arabia have a tradition of drinking tea or boiled herbs together.  (Advanced civilizations quickly discover Irish coffee.)

Other places have traditions involving alchohol, or special drinks like fruit nectars, tonic waters, and other "treats" that are also hygenically treated and/or fermented. 
(Of course, one tribe's "hygenic" fermented chicha or yoghurt can still make a stranger pretty darn sick, especially if they start the ferment by spitting in it or souring it.)

Some places, they boil tap water before using it even in modern apartments, like you would out camping. 
My grandmother prefered to keep a little boiled water in a kettle, and offered it when I wanted a drink, possibly a leftover habit from early days on a farm.

Many places, there are springs or wells of deep water that are cherished and maintained by the community.  People walk for miles to get water, and the fuel to boil it.

You sure don't drink the bath water. 
Or dishwater.
Or what comes out of the irrigation hose.

Our clean, chlorinated city water supplies have allowed us to forget the basics of water: standing water is stagnant water, unsafe to drink.

If you leave clean tap water out for 24 hours, the chlorine is gone and it's safe to put in a fishtank. 
Thus, it's also less safe to drink: all the things chlorine kills, begin to grow in it again.  They can get there from dust, or someone's cough.  Less dangerous than untreated water, but still good to know.

If you like roughing it, and getting back to the land, it's a good idea to start building that mental distinction again: between "clean water" for fish, swimming, or sprinkler systems, and "safe drinking water" for people.

Tha alternative is to be all dirt-macho, and just drink any reasonable-looking water and hope your gut adapts.  In some areas this can work fine for years, and if there's a problem, then you test and de-contaminate.

In other areas you learn very quickly to treat or boil your food and drink.

You can save energy by using "dirty" or untreated water for other purposes:
sand-filtered rainwater is mostly safe to drink, provided you collect it in a food-safe way.  (But creating a hygenic roof is kinda tricky. ) 
Rainwater or creek water can be collected and used for washing and swimming; greywater is great for irrigation.

Hot water need not be plumbed into every corner of the house.  You can even have a separate tap for drinking or final rinse, and do all your dishes in creek water.  If there are children, suburban guests, or mentally impaired adults in a house, then some warnings and/or special tap keys might be needed, to prevent accidents.

A final note on DIY clean water:
If you do get some kind of gut-destabilizing parasite, and you don't trust the water, and you've got  diarrhoeia (and may also be puking) and you're getting dehydrated: 
   You still need water. 
   Now that you have dysentery, you need water more than ever.
  You will die without it.
So you are better off drinking the "bad" water than not drinking water.  Of course, use the best available filtering or treatment options, even strain it through cotton clothing, boil it if at all possible.

Keep yourself hydrated, and get to clean water, and help, as fast as you can.
(From Peace Corps training my sister had in Morocco.)

Yours,
Erica

I read a bit or watched a bit about the water heaters made to heat water with water heated by the sun  and they were quite complicated and a man who put in such things could explain them better me but here a start on them as i understand them.
      As far as i remember they had endless input holes and out put holes because when the sun stopped shinning or in winter, the tank changes to being heated by electricity, so maybe the water does not get cold when theres no sun, another system just takes over.
 
    If you put solar water heater into youtube you get lots of videos of people making solar panels, the good site, the one i like is, "free solar heat "how its made" solar panel" colonella.
      They work like solar cooking, you make a box insulate it put in something that soaks up heat aluminium or copper painted black and have a glass on top so the heat does not get back out.
      You make the box put some insulating in the bottom and then aluminium foil and then a tube of copper that you bend to snake over the bottom of the box , some use  the back part of a fridge, the part that was tubes full of refrigerator liquid instead of copper tubes. On top of the tubes in your box you put a sheet of aluminium painted black. The professional water heater panels, get the aluminium or copper sheet placed on the copper tubing to hug round the tops of the tubes so the aluminum transfers more heat instead of laying flat on them.
    The end of your tubes come out of your box and down into your tank where they pass through the water in the tank heating it up and so the copper tubbing  goes round in the box and then is taken round the the the water tank. The water or liquid anti freeze is in a closed circuit.
      According to dirtbox the tubes with water running through them that heat the water in your tank  can't be set into the water you want to heat but have to run through an outside departmentin the tank, round the tank of water you are heating, not through the water your heating itself.

  Another great youtube address is "hydrogen home" you can see all the incredible ideas of mike strizki.

    -Free solar heat "how its made" solar panel-    colonella          youtube
      -DIY solar water heater-                                    ABTPlumbing    youtube
      -hydrogen home-                                            mike strizki        youtube
agri rose macaskie

Twice this year I got to gander at interesting solar hot water systems and hear the pitch for the hundredth time.  On the second time, the person had a very professional setup and might have been an installer.  There were about 20 of us gathered around and he was getting ready to tell us how awesome it was.  "we don't start for a couple of minutes ..."

So I asked "will you be talking about Legionnaires' disease?" and he said he wasn't familiar with it.  But the water often gets very hot and that would kill all bacteria.    And then I tried to paint a picture of the water not getting all that hot and the bacteria being a problem .... further, it seems some solar hot water systems are really simple and some are really complicated, and maybe the complexity had to do with this concern.  His response to that was that the complex stuff had to do with governments being to cautious. 

It was then time to start the presentation ...

I felt really weird. 

I guess I am really keen on the solar hot water, and I was hoping to hear something about "the reason why this system does not incubate legionnaires' disease is ...." as opposed to "I've never heard of it, so I'm sure we're safe" or "I've taken 100 showers with this and I'm not dead, so it must be fine."

It got me wondering about all sorts of things.  Maybe we don't have legionnaires' disease in our water here to begin with - so it isn't something to worry about.  There are lots of solar hot water setups all over - maybe the level of problems is so low that a person has a better chance of being hit by lightning, therefore it is kinda silly to worry about. 

I guess I would feel a lot better about all of this if the solar hot water folks were savvy to the whole legionnaires' disease thing and could explain why folks don't need to worry about it.

paul wheaton wrote:
Twice this year I got to gander at interesting solar hot water systems and hear the pitch for the hundredth time.   ...

I guess I would feel a lot better about all of this if the solar hot water folks were savvy to the whole legionnaires' disease thing and could explain why folks don't need to worry about it.

Of course you don't need to worry about it.  Why worry?

Either you prevent the problem- -
-- use a system designed to maintain safe temperatures, with back-up checks or extra heat or heat-exchangers with treated water or what-have-you; don't incubate known pathogens...

-- or use your sun-warmed water in a way that doesn't expose you to known pathogens (for example, taking a hot bath or sponge-bath would reduce the respiratory hazard of breathing droplets of lukewarm water compared to a shower...)

-- or heat water on demand, for example putting chlorinated "safety water" in a black plastic bag, to heat a solar shower for single use;

-- in any case, you don't breath or drink from warm shower-water unless you know it's been maintained as safe as possible;

-OR -

- you remain in blissful ignorance about the danger, until it actually happens to someone you know (they get deathly ill).

Merely worrying about it does no good at all.

Let us know if you ever meet a solar hot-water builder who's familiar with legionaire's disease and other pathogens, and can describe prevention strategies.

Maybe the copper pipes actually help reduce pathogenicity?

-Erica

So the innards of a $100 electric water heater probably have a helluva lot more going on inside than one might think.  There's probably stuff in there to not just keep the water over 120, but to make sure that there aren't any cool pockets where bacteria can fester. 

I know very little about the legionnaire's bacteria.  But I would guess that building a good population would be a key ingredient.  And it would probably take at least three days to do that. 

So if a solar hot water system goes unused for three cool, cloudy days, that might be just enough - right?  The highest temp in one corner of the tank might be 105.  And the bacteria just have a great time reproducing. 

Hmmmm .... so if you are in a house, and you leave for a week and then come back .... and then drink water from the tap - that would be a similar problem because the water might be at 70 for a long time.  But it would be not a problem with the legionnaire's bacteria because for that to be a problem you have to breathe it in, right? 

Posts here seem pretty well-informed, so I don't know how much I can add from my own experience. We had a solar hot water system installed in our Seattle home in June 2008 and noted an immediate drop in our gas bill of 80%. We were so happy with this that we didn't think at all about any possible health problems.
With five or six people taking showers daily or semi-daily we have noted no problems of the kind mentioned here. Our system was professionally designed and installed, and definitely separates the fluid that gets heated from the water that goes to our conventional water heater. Perhaps that's why we've had no problems with it.

Heard of this concern for the first time at the permaculture convergence.  Did some research and it would appear that the problem is more conceptual than practical unless people are using stored water improperly.   A domestic electric, gas or wood fired water heater can suffer the same challenge; same goes for a well pressure tank or rain water capture tank. 

Home Power Magazine has this to say about the issue.   Other sources of info were basically describing best practices of using hot water heated at 120+F.

The system we saw at the convergence was a simple batch heater from China and billed as good because it was low cost.  Even if the presenter knew of this issue or not, the device was presented as a non-potable water solution.  Although not required, using potable water for cooking, bathing and cleaning is not a bad idea.  Swimming or bathing in a creek, pond or lake exposes us to a whole host of bacteria.  Or using creek or rain water collected from potentially toxic surfaces to bathe with can also be an issue.  Our immunity helps mitigate this stuff.

For domestic solar hot water systems,  it is recommended to refer to the  SRCC for performance tests and other info.  And it is always best to use a closed loop setup.  In fact, closed loop may be code in some states.

Home Power has a good primer on system design.

Storage tanks that contain the solar heated water feed into either a electric or gas water heating device (tank or on demand) that provide a consistent 120F+ water.  When the storage tank contains water that is over 120F, a tempering valve is required to be in the system to ensure scalding won't occur.

With my storage tank, I deal with water that is in the 60s - 90sF most of the winter unless the sun is really shining.  In the summer, the water temp is limited to 150F.  And for over four years, go days without using the water.  I think I have more risk driving on I5 than inhaling the steam from my shower.   For the sake of argument, anyone on a well system with a pressure tank can also grow bacteria.  So, in the big picture, there are all kinds of vectors, not just solar hot water systems.

If a person is significantly worried about bacterial contamination, put a UV filter on the output from the final point of use (assuming the bulb is rated to deal with 120-130F temps).  In the end, if the problem were so that the use of solar hot water storage tanks themselves were causing problems (outside of other known vectors), it would be well known given the decades of deployment in the US and even more so given the wide spread deployment and use around the world.  Having seen the roof tops in southern Germany (seems like 20%) hosting evacuated tubes, if the problem were as serious as made out, susceptible people would be getting sick a lot. 

Hope this helps. 

Your first link had a link that seemed to have more info:  http://www.nlm.nih.gov/medlineplus/ency/article/000616.htm

It sounds like one of those things where we're still low on info.  At the same time, it sounds like we probably don't need to worry - just because not many people have reported problems.

OTOH:  I suppose people that have died of it are not likely to report on it. 

I guess my feeling is that Legionnaire's disease is the toughest problem - so if there is a thorough understanding of it and the risk is mitigated, then all of the lessor problems will be gone too. 

(why do I get nutty about this sort of thing .... my spidey sense is tingling ....)

Google leads me to http://en.wikipedia.org/wiki/Legionellosis

"an estimated 8,000 to 18,000 people get legionellosis in the United States each year." and "The fatality rate of Legionnaires' disease has ranged from 5% to 30% during various outbreaks."  My reading so far suggests that if you are a one time case, your chances of survival are worse.  Because when there is an outbreak, the medical people are looking for folks with symptoms.  Whereas, most of us with a bit of a cough just wait for it to go away. 

"this disease usually occurs as single, isolated cases not associated with any recognized outbreak."

"Potential sources of such contaminated water include [...] hot water systems, showers [...]"

Wow - speaking of UV light:  "Legionella bacteria itself can be inactivated by UV-C-Light. However Legionella bacteria that grow and reproduce in amoebae or that are sheltered in corrosion particles cannot be killed by UV-light alone. An innovative way is the combination of ultrasonics' and UV-C-light. This uses a two stage process, where ultrasonic cavitation disrupts the amoebae or corrosion particles and leaves the Legionella bacteria exposed for UV radiation. Such combined system are used for example in hot water systems in sensitive areas, such as hospitals, where the inhabitants are more vulnerable than in normal environments"

So, I wonder about a disconnect between folks getting LD and using solar showers. 

Maybe I'm just being a nervous nelly about this.  But I would sure like to hear a bottom line about how this is properly mitigated in a solar hot water system.  Something where the designs are aware of the concern and what happens to make sure there is no problem. 

Mitigation is by heating the water, as simple as that.  Just like any other water heating/storage device.  That is the purpose of the existing domestic water heather, to heat the water to a constant temp.  

Do you have a well on your property?  Does it have a pressure tank?  If so, what techniques are you using to mitigate?  The legionnaires bacteria comes from the well.  It gets into the pressure tank.  It gets into your hot water heater.  Now what?  How are you mitigating your current situation?  There is potable hot water in your home, right?

In my system it goes like this:  well -> pressure tank -> solar hot water tank -> electric hot water tank -> me.

Looking at the % of the US population, 18,000 out of 300,000,000 is?  And of the 18,000, what percentage engaged with a domestic solar hot water system?  This is like worrying about getting AIDS from sitting on a toilet seat in a public restroom, even with the paper gasket between the bum and lid. 

You raise some significant personal concerns.  Given these concerns, I don't think you would be a good candidate to own or use a domestic solar hot water system.  No one will really be able to give you a mitigation design outside of just keeping the water hot; just like you do today in your current hot water heater.   

Cheers,
Jeff

Having the solar hot water pre-heat sounds very wise.

Supposing out of 18,000, 400 have to do with solar hot water only the connection has not been made.  How many solar hot water setups are there in the US?  Maybe 200,000? 

Supposing 400 out of 200,000 would be 0.2%

So if a person uses solar hot water for 20 years, they have a 4% chance of getting LD.  If you have four people in a home, then you have a 16% chance that one of them will get it. 

Of course, this is entirely based on made up numbers, so maybe it isn't nearly that bad.  Or maybe it is much worse. 

Up until recently I never thought there was any problem with solar hot water.  And then I hear about this and I think:  well, surely somebody has figured out why this isn't a problem for solar hot water ... 

I'm not saying there has to be a big study or anything.  All I'm saying is that a little understanding of the problem space may be wise.

Curious, how do you mitigate this today?  You realize you are at risk; that your current water heater is a breeding ground, right? 

My current hot water is kept at 130 all the time.  So I guess I'm safe.

Exactly! 

Safe as you would be if there were a pre-heat storage tank containing water heated by a solar collector in the loop.  Remember in a solar setup it is:  water source -> pre-heat tank -> point of use water heater. 

As you see, the there is just another tank in the loop.  The 'mitigation' is at the point of use, which in your case is your water heater regardless of what fuel it uses to keep the temp at 130F or where the water came from to fill it. 

It is impractical and relatively useless to operate a solar hot water collector storage tank as the only storage of hot water.  The water is either way too hot or far too cold to be used on our skin in the manner we're accustomed to. 

There will always be a device at point of use that heats the water to 120F+.  Whether that device is a tank or tank-less heating apparatus, it is used at the point of use to mitigate the problem. 

Make sense?

Well, rather than "totally useless" I would say "there are significant disadvantages".

Oh!  And as to my earlier thing about "16%" - I guess the mission might be to try to reduce that to "0.16%" or even "0.0016%" due to thinking things through a wee bit.