WE BEGAN LOOKING into the issues associated with combination, open-loop, hydronic space-heating systems last month ( A matter of grave concern). While these systems have been around for about as long as water has been inside pipe, the methodology of piping water has changed rapidly over the past few years.
Prior to the introduction of copper, galvanized iron pipe was the standard, and even it had issues of corrosion that caused its life expectancy to be less than desirable under certain operating conditions. I've watched some systems degrade to the point of failure in less than two years.
Enter copper. Many people don't realize it, but copper has some interesting characteristics that allow it to be antibacterial. Copper sulphate is commonly used to control algae in water systems. It suppresses the growth of the bio-slime necessary to support bacterial growth.
Many water heater manufacturers have had combination space and domestic hot water systems on the market for many years. The majority of these systems used copper as the primary water piping media. These systems had to be maintained at an elevated temperature to guarantee space-heating performance, so the chances of contracting any kind of a waterborne disease were fairly slim.
Then came the advent of hydronic radiant floor-heating systems. These fantastic new heating systems no longer utilize copper to transport heat. A minute part of the system may be piped in copper, but most efficient plumbing and heating contractors have turned to flexible plastic tubing for mains distribution as well as radiant panel installations.
This creates a whole new set of conditions under which the omnipresent bacteria can manifest itself, and can actually propagate and increase its bacterial count to the point of becoming dangerous. This is referred to by the Centers for Disease Control and Prevention as bacterial amplification. Remember, the bacteria I'm talking about here is Legionella Pneumophila, the same bug responsible for Legionnaires' disease. Many other waterborne bacteria are running through these systems, but if you protect yourself against the LD bug, you will also address its nasty cousins.
The conditions necessary for bacterial amplification are as follows:
- A stable, wet environment with a temperature between 68° and 120° F;
- Existence of bio-film to feed and shelter the bacteria;
- Oxygen to allow the bacteria to breath;
- The absence of any material, such as copper, that could suppress bacterial growth; and
- A pH between 5.5 and 9.2
Unfortunately, through the introduction of plastic tubing as a water transport media, one critical control component — copper — has inadvertently been eliminated from this process. So, in a nutshell, we have given the bacteria the perfect environment for bacterial amplification. These combination open loop space/domestic hot water heating systems provide all the key ingredients necessary to ensure an increased level of exposure to everyone who uses them.
Bio-film is a naturally occurring material that occurs on the inside of virtually all potable water piping systems. Where you have water, you have biofilm. This is the food and shelter that harbors and feeds the LD bacterium.
At water temperatures less than 68?F, the bacteria are consumed by naturally occurring amoeba that live within the water. At water temperatures higher than 120?F, the bacteria are cooked to death and amplification is drastically reduced. Legionella can survive temperatures as high as 180?F, as found in hospital DHW systems that are maintained at 180?F for the specific reason of reducing bacteria, but the bacteria cannot readily reproduce under those conditions.
Oxygen needed to sustain bacterial growth is either readily available from the incoming water source, or, in the case of plastic potable water piping, drawn directly through the wall of the pipe. The normally acceptable range of pH in potable water piping is in the range of 6.5 to 8.5, the perfect growing conditions for the bacteria.
So, as you can see, we have inadvertently allowed our state-of-the-art plumbing systems to become the ideal home for bacterial amplification. Is everyone using these systems going to get LD? Probably not. Only those people who are elderly, have depressed immune systems, or who smoke or abuse alcohol. These people have a much higher risk factor for contracting this deadly disease.
I am, however, living proof that there are exceptions to every rule. I'm not considered elderly, I don't smoke, I don't drink to excess and, to the best of my knowledge, my immune system has not been compromised, yet I contracted this deadly disease and almost became a casualty.
Tune in next month as we continue our journey to the center of this issue. Until then, stay healthy and, remember, even you can contract Legionella Pneumophila.
Mark Eatherton is a Denver-based hydronics contractor. He can be reached via e-mail at [email protected] or by phone at 303/778-7772.