legionella-do I need hot recirc. loop?

Constantin

... I found that a recirculation loop is the best way to ensure that all the BTU's I harvest via the solar system get redistributed throughout the house via the recirc system. Part of that is due to my plumbers (not every pipe was insulated well), part of it is simple physics (i.e. a huge surface area). I am now looking into running the recirc only whenever someone steps into the bathroom.

I am also a bit unsure whether you can run a DHW system hot enough to allow recirculation at 140°F. I thought the max allowable exit temp at the tank was around 120°F per most codes... Even if it were allowed, a hot water system that runs at 140°F should entail a mixing valve at every distribution point (to prevent scalding). That's a lot of mixing valves to maintain but it can be done, I suppose.

Me, I'm OK with a tank at 140°F and the rest of the system at 110-115°F. Eventually, all water that was in the copper pipes is recirculated into the hot tank anyway. Some bacterial growth on the inside pipe walls is still possible, but the copper should limit that and a bacteria-free DHW or DCW system is a nearly-impossible-to-attain proposition anyway.

I do not run my recirc 24/7, which would be a good way to supplement your heating system in winter and tax both boiler and AC system in summer. Even when it is running, my recirc system is only 5 minutes on and 20 minutes off. The water stays plenty hot. I would experiment in your own home to see which on/off cycles yield usable hot water with a minimum of pumping.

HTH.

JimH

is this overkill?

Slowly, carefully working through questions I need answered
before I start taking bids for upgrading my ancient cast iron gravity system with Vitodens/Vitocel...

Okay, I've done some reading on legionella, and I'm totally
sold on keeping the indirect @ 140* (although if a few more
folks would chime in on my asse 1016/1017 valve thread saying "yeah, those things are as dependable as a Rolex" it would bring needed reassurance...).

So, according to what I've read, the current best practice
is to set up a recirculating loop to keep the water in the
lines too hot for the bacteria to grow and handicap them
by preventing stagnation.

What I haven't been able to determine is whether this is
truly necessary in a single family residence, or just something that needs to be done in hospitals and nursing
homes.

Does the fact that I'll be connected to a large, pretty well run municipal water supply change anything? How about the absence of plastic pipe, and the associated oxygen infiltration?

Is a dedicated return line mandatory? Does the circulator have to run 24/7? If so, is it possible to avoid thermal losses on a scale large enough to negate the efficiency improvement from going to the indirect?

Thanks for any insight on this subject...

-JimH

brucewo1b

Well I am not sure how dependable

a Rolex is but most tempering valves will operate for years with no problem, usually where there is a problem it is in system where they are attached to tankless coils in boilers where the temps are often times over 200 degrees, I have much better results with them when running 140 degree water through them.
Depending on how long your hot water runs are the recirc will be one of those things your wife will love you for just because.
The water supply has no bearing on the issue at hand.
Yes a dedicated return line is nesassary for recirc, you can run the circ on aquastat so it only fluxuates a few degrees but either way insulate those pipes.

Darrell

Now there's an idea...fire the recirc with a motion sensor switch in the bathroom or kitchen...timed on/off, hot water when you want it but not all night.

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Steve J_4

yes can someone show me how i could do that on motion start the recerc pump what would i need i can get a motion sensor. but what controls could i use with my buderus g115 with 2107

also with a small 80ft 1/2 copper loop how long would it take for a recerc pump to get hot water to the tap once the motion is tripped

thank you

Constantin

Credit goes to Lifebreath...

... Check out the Leviton Occupancy sensors for lighting applications. They are little round disks in the ceiling that can be adjusted for sensitivity, length of "on" after being disturbed and at what light levels they shut off (a feature none of us are interested in for this application).

With the occupancy sensor, you buy a powerpack. The power pack can power up to 3 sensors and also incorporates a 120VAC relay. I do not know if the relay can handle a pump start/stop... you may need a second relay... but if the relay is good, you have everything there to make the recirc pump "go" whenever you wish.

Now, if you want to get really fancy, consider getting a second controller that is preset to turn "on" for 5 minutes, then idle 25 minutes. That way, the recirculation system will not steal BTUs from the IDWH while people are showering. This is what I am working towards (once I have some free time again).

Steve J_4

very interesting Constantin please keep me updated on the 5min on 25min off control. i will do this in my own home :-)and not use the the buderus 2107 dhw recerc control timer

thank you

larry

Constantin,

At some point it's worth looking at a small automation controller from companies like HAI or Elk. You'll then have access to a wide range of PIR sensors, and can use their event driven programming model to create pretty much any kind of behavior you want. The systems are very capable and expandable with all sorts of inputs, outputs and relays, and can serve as a full security system as well. Visonic makes some very nice small PIR detectors that can be hidden inside the wall except for a hole coming through the size of a nickel which is flush with the wall surface (the Spy series). It makes for a nice subtle and nearly invisible automation installation. If your in the middle of construction or have access to joists, you can also implement stress sensors which operate by seeing the deflection of the joists when someone walks over an area.

Constantin

Neat stuff,

I'll have to look into it later. Just goes to show how many different ways one can skin a cat.... hee, hee, hopefully, Savannah didn't hear that! :-)

Phil Malone may or may not allow some event-driven programming via the WEL in the future. In theory, the 1-wire system supports that, the question is whether Phil would like to tackle the implementation.

Thanks again for the pointers!

JimH

recirc. primarily for convenience?

Constantin, are you running the recirculating loop more
for the convenience of having instant hot water, or to
suppress bacterial growth?

-JimH

Constantin

To limit water waste...

... which would fall under your convenience bracket?

JimH

My original question (which remains unanswered) is whether
one needs a recirculating loop to prevent amplification
of legionella bacteria in a single family residence. I've
scoured the internet looking for a definitive answer on
this and come up empty handed.

Water is abundant here, and no pipe to a point of use will
be more than about 20 feet long, so I don't think I really
need a loop for conservation or convenience.

-JimH

[Deleted User]

As with any hydronic heating question, there is only one answer.

It depends... Think about the ideal growing conditions for the amplification of legionella. They need warmth, stagnation, food and shelter and no natural antibiotics.

If you hold your storage tank at 140 and circ until you get 130 back to the tank, the heat will keep them at bay. If the mains and return are copper, it is a natural antibiotic and will keep the bugs at bay.

You could do as the Germans do and put a "Sanitization Cycle" on your system and flush extremely hot water through the system 2 times per week during the wee hours of the morning.

My present system is so short I don't need a circ return, and in my new home, I will be using copper for its natural killing ability.

So, in a nut shell, it depends...

ME

Dave Yates (GrandPAH)_2

some reading materials

www.cdc.gov

www.legionella.org/100960699-1.pdf

http://www.estechlab.com/Legionella-Friend or Foe.htm

http://www.contractormag.com/articles/column.cfm?columnid=98

http://www.contractormag.com/articles/column.cfm?columnid=22

http://www.contractormag.com/articles/column.cfm?columnid=17

http://www.contractormag.com/articles/column.cfm?columnid=162

http://www.contractormag.com/articles/column.cfm?columnid=168

http://www.contractormag.com/articles/column.cfm?columnid=193

www.scirus.com/srsapp/search?q=legionella&t=all&ds=bls&ds=ide&ds=mps&ds=cps&ds=sd&ds=nsc&q=%22community+acquired+pneumonia%22&t=all&g=r