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

[Speireag Alden <Joshua.M.Alden.91@alum.dartmouth.org>]

Sgrìobh Dr. Carmine F. Vasile:

>I'm not laughing.

     Okay.  Up to you.  I thought you'd be amused that the topic has 
come around yet again, regardless of which side of the argument you 
sit on, but I guess not.  I was not suggesting that Legionella is 
anything other than a serious topic.  Re-reading my post, I don't 
think that I was particularly unclear, but I'll try to do better in 
the future.

>  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)."

     Okay.  I was relying on the Australian paper I referred everyone 
to, but that's all right, because they say much the same thing. 
Here's the Australians:

"Bacteria in the genus Legionella are widely distributed natural 
inhabitants of waters. They have been found in lakes, rivers, creeks 
and other bodies of water ranging in temperature up to 60°C. However, 
significant multiplication of these bacteria is generally restricted 
to temperatures of 20°C to 45°C and particularly to the range 35°C to 
43°C (Figure 1). Systems with waters of this temperature range 
facilitate proliferation (Figure 2)."

     For those of us who use the silly American system rather than the 
metric system, here's a dictionary:

45°F = 7°C
70°F = 20°C
90°F = 32°C
100°F = 38°C
120°F = 49°C
125°F = 52°C

60°C = 140°F
50°C = 122°F
45°C = 113°F
42°C = 110°F
42°C = 108°F
35°C = 95°F
32°C = 90°F
20°C = 68°F

---

     Now, my well water comes out of the ground at about 7°C.  It sits 
in the pipes and the pressure tank, where it warms gradually to the 
interior temperature of the house, like all water in all domestic 
systems.  However, at least in the case of the pressure tank and the 
cold water line up to the manifold, it seldom actually gets as high 
as 20°C, because we use what's there and more comes in behind, at the 
colder groundwater temperature.

     So the cold water system would seem to be pretty safe.

     Now, when I turn on a hot water tap, the cold water travels 
through a bunch of pipe and goes into the heater.  There it gets 
heated to about 52°C.  Although this temperature is within the 
"danger zone" of 20°C to 45°C, it's a bit higher than the "critical 
temperature range" of 32-42°C or 35-43°C (depending on whether you're 
Austrian or Australian).  And, it stays at that temperature for 
perhaps a few seconds at the longest, and then it goes out the tap 
and gets used or put down the drain.  The remaining water in the hot 
water lines gradually cools to the interior temperature of the house 
(but gradually; those lines are insulated).  That temperature is at 
the extreme low end of the "danger zone", and sometimes lower.  If 
Legionella is present at all, it will breed slowly or not at all. 
Since we live in this house and use the taps, it will get flushed 
constantly.  This is the normal condition for residential plumbing.

     So far, so good.  Legionella is not so prolific that it go from 
almost nothing to a dangerous concentration in a few seconds.  I hope 
you will agree that there is no difficulty so far.

     Now we come to the heat loop.

     If we turn on the circulating pump, it drives water through the 
heater and back through the floor loop.  The water gets heated to 
about 52°C in the heater, and it cools to anywhere between 30°C and 
38°C as it goes through the floor.  Then it gets cranked back up to 
52°C in the heater.  The entire loop circulates every five minutes or 
so.

     That water is in the "critical temperature range".  However, that 
doesn't make it immediately lethal, even if Legionella is present. 
It has to stay at those temperatures for a while so that Legionella 
can breed.  How long?  Well, the Design Guidelines document I'm 
quoting recommends that in systems where water is STORED at 42°C, you 
flush the taps for fifteen seconds once a week.  You can bet that 
they built a margin of error into that guideline, so it takes 
Legionella over a week to attain dangerous levels, even when 
temperatures are optimal for its growth.

     Even in midwinter, when we're running the heat most often, our 
floor cools to ambient temperature frequently over the course of the 
day.  The house is well-insulated, and doesn't require lots of 
supplemental heat.  So if there's any Legionella in the system, 
conditions aren't generally optimal for rapid growth, and it's going 
to take significantly more than a week to be a problem.  That's why I 
was flushing the loop once a week, minimum, even before I re-plumbed 
our system.

     In the new system, the only way for water to get to the heater is 
through the floor loop.  That's how water goes from the pressure tank 
to the heater.  So every time any hot water tap runs, anywhere, it 
flushes the floor loop.  Five gallons of use flushes the floor loop 
completely.  We use more than five gallons by far in a bath, and even 
if we didn't take baths daily, the combination of washing the dishes, 
washing the clothes, and washing our hands would use five gallons 
daily, and then some.

     So, in the worst possible situation, Legionella takes over a week 
to reach dangerous levels.

     We flush our system more than once a day.

     We put chlorine through the system once a year, and every time I 
modify the plumbing.

     Where is the problem?

-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
Solstice http://www.crest.org, and BuildingGreen, Inc., publisher of
Environmental Building News and GreenSpec http://www.BuildingGreen.com
______________________________________________________________________