Re: [GBlist] Legionella and Open Radiant Heat Systems - results (was: tankless heater (AKA Instanteous Water Heat)

["Dr. Carmine F. Vasile" <gfx-ch@email.msn.com>]

Dear Mr. Alden: I'm not laughing. Here's what the Austrian Energy Agency has
to say about Legionella:

"1.Use of optimal hot water temperature for a given DESWH capacity Depending
on the number of persons in a household, the hot water temperature of a
DESWH can be reduced to the optimal temperature to supply exactly the amount
of hot water needed, thereby reducing standing and distribution losses.
However, the reduction of temperatures to <50 °C should be avoided in order
to prevent potential serious health problems caused by Legionella (critical
temperature range 32-42 °C)." [Quote from: "Analysis of Energy Efficiency of
Domestic Electric Storage Water Heaters" (DESWH), Study for the Directorate
General for Energy (DGXVII) of the Commission of the European Communities,
Contract No. SAVE-4.1031/E/95-013, FINAL Report, FEBRUARY 1998, Contractor:
Energieverwertungsagentur (EVA) the Austrian Energy Agency Vienna, Austria
EC Project Manager: Paolo Bertoldi DGXVII.]
=====================================================
 Dr. Carmine Vasile, CEO
 WaterFilm Energy Inc.,
 P.O. Box 128
 Medford, NY 11763
 Voice: 631-758-6271 [Fax: 631-758-0438]
 Email: gfx-ch@msn.com Web: http://oikos.com/gfx/
=====================================================



----- Original Message -----
From: "Speireag Alden" <Joshua.M.Alden.91@alum.dartmouth.org>
To: <greenbuilding@crest.org>
Sent: Saturday, March 17, 2001 12:28 PM
Subject: [GBlist] Legionella and Open Radiant Heat Systems - results (was:
tankless heater (AKA Instanteous Water Heat)


Sgrìobh John Herbert:

>Don't operate your water heaters (tankless or otherwise) at water
>temperatures lower than 60 Deg C otherwise you provide an
>environment for the growth of Legionella in your system, possibly
>causing you or your family to contract Legionnaires disease.

     I'm sure that Carmine Vasile is laughing right now.  We went
'round and 'round on this for a bit a few months ago.  You can find
it in the archives by searching subject lines for "Legionella and
Open Radiant Heat Systems", because I made sure to label it well.

     I excerpt large portions of my final post below, and then I
explain what I've done in the meantime, and how it's working.

     One note:  I think that your assertion, above, is too broad.  You
don't want *standing* water at temperatures less than 60°C (140°F).
If you heat it temporarily to something less, and then use it
reasonably promptly, Legionella has no time to breed, even if it's
present in trace amounts in the system (which it often is).  This is
an important distinction, since most tank heaters, and most tankless
heaters, actually heat water to around 125°F (52°C).  They're pretty
safe even so.  In this respect, tankless win over tanked, because if
you leave your tank heater alone for a month and let it bake the
water at a steady 125°F, you may have a problem, whereas the tankless
heater at room temperature won't cause any problems at all.
Legionella doesn't breed significantly at room temperature.

     If you want to know more about Legionella, I found this:
<http://www.dhs.vic.gov.au/phd/9903047/index.htm>.  This gives design
and operation guidelines for preventing Legionella.  Note that you
don't get infected by drinking water with Legionella in it - you get
it only by breathing it in aerosol form, which makes showers the most
likely vector.

>PS : Using a domestic water heater for underfloor heating I have
>been told is a US building code violation in some states.

     I believe that it's a building code violation in some places to
have an "open" system like mine, but I'm not aware that anyone would
care if you had an isolated system with heater, loop, and pump, none
of which communicated with the drinking water system.  However, as
you'll see below, I addressed the Legionella issue in the original
design, and then improved the design drastically.  It won't be a
problem.

     Herewith, my original post, slightly edited, and further results.

---

Hello, all.

     A month or so ago we had a discussion on the GreenBuilding list
about Legionella (Legionnaire's Disease) and how to use one tankless
water heater safely to provide both radiant floor heat and hot tap
water.  The experts recommended using two pumps and a heat exchanger
so that the fluid in the heating loop would be totally isolated from
the water in the regular plumbing.  I pointed out that as long as you
flushed the heating loops regularly Legionella would not be a threat,
and the system would cost less because you would not lose efficiency
through the heat exchanger, and you would not need a heat exchanger
and an additional pump.  The experts felt that this was risky,
because Legionella would build up if someone forgot to flush the
loop, and we all know that we forget to do things.

     Well, I got to thinking.  A regular American water heater, with a
tank, is at least twenty gallons, and maintains the correct
temperature for Legionella all the time.  (Yes, boiler systems are
hotter, and yes, some people save energy by setting their tanks on
timers, but bear with me.)  Probably, I reasoned, Legionella is not a
threat in these systems because a lot of water drives through them,
and so the entire volume of that tank gets exchanged and driven
through the system pretty regularly.

     Okay, so how could we achieve the same thing with an open heating
system like mine?

     After a few minutes of thought and a diagram on the back of an
envelope, I had a way.  Display this in a monospaced font:


source
   |
   |  __________
   \__|Pressure|------------------------------- cold water taps
      |  Tank  |-----\
      ----------     |
                     |
  /--------------\   |
  |   ________   |   |
  |  |tankless|  |   |
  |  | Heater |--+->-+--pump>--\
  |   --------                |
  |      |                    |
  |      | hot                |
  |      | water              |
  |      | return             |
  |      |                    |
  |      +______________ Radiant Floor
  |                         Loop
hot
water
taps

     Note the ">" between the two T's on the hot water line, just
upstream of the pump.  That's a check valve (a one-way valve).

     So, in this system, water circulates through the loop when the
pump drives it, and that moving water activates the heater.  So you
have floor heat, working as usual.

     However, when you turn on a hot water tap, the water has to go
through the heating loop before it hits the heater.  That means that
any time you use hot water, you are exchanging water in the heating
loop.  And, I might add, it's very linear; unlike a tank, where the
new water mixes with the old and you need a lot of flow before you
can consider the water to be completely changed, the new water
completely replaces the old very quickly.

     I have a very simple system, with one heating loop for the entire
house, about 500 feet long.  I used 1/2-inch tube.  500 feet of
1/2-inch tube holds about five gallons, which is much less than the
tank in a conventional water heater.

     So, in this system the water in the loop is completely exchanged
any time anyone takes a bath, or a shower more than a couple of
minutes long, or runs a load of laundry with hot or warm water, or
runs a dishwasher a few times.  Not only safe, but safer than a
standard residential system.  And it's automatic, so there's nothing
for the homeowner to remember.

     When the floor loop has been used recently to heat the house, the
first five gallons of water out of the hot water taps will be hot
even if you demand a higher flow than usual, because your heater has
pre-heated the water a few minutes earlier.

     Using the hot water taps will inject cold water into the floor,
yes, but if you're running the heat you don't care, because the
heater is heating it up.  You don't lose any energy, because the
small amount extra you're putting into the floor is offset by the
small amount less you use to heat up the water for the tap.  Not only
that, but during the summer, when you never put hot water back into
the loop, you'll get a very mild cooling effect because the cold
water supply is travelling through the loop before it hits the
heater.  The heater will run a little hotter or provide a little more
volume, because the water reaching it is slightly pre-heated.

---

     Now, I had planned to implement this plan this coming summer,
when I could take my time because I wouldn't have to worry about
disassembling the hot water system.  Unfortunately, circumstances
forced me to act earlier:  I flushed my earlier system once each week
through a long, buried line which empties into a pond.  The bottom
end of that line froze shut, under a layer of snow and under frozen
ground.  There was no easy way to get to it until spring, and no easy
way to empty the heating loop thoroughly.  So, rather than cross my
fingers and hope for the best, I tore down the heart of my plumbing
system and re-built it, in accordance with the diagram above.

     Note that the diagram is simplified for conceptual simplicity;
there are more details, like a tempering valve and the drain to the
pond.  Also, you have to take care that there are no "dead end"
sections longer than eighteen inches, which is a standard
specification on fire sprinkler systems.  Stagnant water would permit
bacteria to breed.  That means you need to use a little more pipe in
order to get your junctions spaced properly.  In a fire sprinkler
system, if you have a sprinkler 'way off in a corner, you must run
the supply pipe to within eighteen inches of the sprinkler and then
back again to the tap.  That way, when someone runs the tap, the
entire system is flushed.  I was careful to do that with mine,
bringing the pipe to the junctions.  Finally, I installed a lot more
thermometers so I could tell exactly what was going on.

     I'd love to provide a detailed diagram, but it's beyond my "ASCII
art" capabilities.  I have a handwritten diagram, and it's on my list
of things to do to make it available on the web, along with many
other building details for my house.  However, it won't be coming
soon.

     Verdict:  works great.  A single bath flushes the floor loop
several times over.  Run a hot water tap and cold water enters the
heating loop, even with the circulating pump running, which is as it
should be.  The only potential problem is the reduced pressure at the
hot water taps because of the 500 feet of additional half-inch pipe
which all of the hot water has to go through.  However, flow is still
adequate, and more than the standard flow regulators in the fixtures
will permit anyway, so it's not a problem.

     The only difficulty arises from the heater's flow
characteristics.  The Myson generally puts out water at 125°F or so.
However, sometimes it can peak as high as 160°F for short periods,
and with two small children I decided to put a tempering valve on the
whole system, just after the heater.  Alas, the only valve I had has
a highest setting of 120°F.  That means that even at normal output,
the heater isn't running at full, and sometimes the tempering valve
chokes things down to where the heater turns off.  The result down
the line is lukewarm water from the hot water tap.  The lesson to
learn here is that your tankless heater's set point should be less
than your tempering valve's set point.  I can't adjust my Myson's set
point, so I'll have to get a new tempering valve and set it to 130°,
which will still be reasonably safe but will permit the system to
work a lot better (and be adequate to re-fresh a cool bathtub, which
120°F isn't).

     But that's got nothing to do with the Legionella protection.  The
system works great.  If you're going to have an open system, with one
tankless heater supplying floor heat and hot tap water, you can still
have a system safer than a standard residential system.

     If anyone would like more details, I'd be happy to supply them.

-Speireag.
--
Speireag Alden, aka Joshua Macdonald Alden
Usually found somewhere in the wilds of New Hampshire.

______________________________________________________________________
This greenbuilding dialogue is sponsored by REPP/CREST, creator of
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______________________________________________________________________




______________________________________________________________________
This greenbuilding dialogue is sponsored by REPP/CREST, creator of
Solstice http://www.crest.org, and BuildingGreen, Inc., publisher of
Environmental Building News and GreenSpec http://www.BuildingGreen.com
______________________________________________________________________