Arrhenius and the mayor.
Our story starts with a politician taking a shower in a new home in Las Vegas in the mid 1990s and ends with tens of thousands of houses with leaks and litigation. Our story takes a detour to the Great War * and one of the most famous naval engagements that almost didn't take place and an underappreciated and much maligned national hero. Along the way we become reacquainted with one of the greatest minds of all time--so great that the physicists and chemists both claim him as one of their own.
Jan Laverty Jones buys a new house in Las Vegas and is incensed that it takes five minutes for hot water to get to her shower. She becomes furious when the builder says that he is not responsible and that's the way that it is. Unlike most new homeowners with a grudge, she happens to be the mayor (Photo 1). In a move that would make Boris Yeltsin proud, she decrees that all new houses must have hot water recirculation systems. OK, it wasn't a decree. It was a bylaw change. But, you get the idea. Never mind the energy implications of this decision. This was the 1990s. Who cared about energy back then? The implications of this decision haunt Vegas homeowners and home builders to this day.
What is the big deal about hot water recirculation systems? They have been around a long time. We know how they work. We know about the energy penalties. Well, Las Vegas is different, as we all know. But, the difference I am referring to is the water, not the other stuff. The water in Las Vegas, when coupled with hot water recirculation systems and the type of plumbing system that became common in the home building industry around then, makes for an interesting study of physics, chemistry, and unintended consequences.
Las Vegas has lots of sulfates and carbonates and a high pH in its water, along with lots of chlorides and fluoridates. The sulfates and carbonates and high pH come from nature; the chlorides and fluoridates come courtesy of the Las Vegas water department. And, for reasons not well-understood, Las Vegas water has lots of dissolved oxygen.
None of this is a surprise to folks who know and love water. It does not seem to be a problem with the folks living there since gangster Bugsy Siegel kicked Las Vegas into the big time in the late 1940s. But it has been, and continues to be, a huge problem with hot water heaters. Hot water heaters in Las Vegas fail faster than almost anywhere else--often in only three to five years.
The hot water heaters fail from the precipitation of those pesky carbonates in the water. Now, other places also have lots of carbonates, but not lots of dissolved oxygen, and not lots of other neat stuff in the water as in Las Vegas. The precipitation of the carbonates is much faster in Las Vegas hot water heaters than elsewhere. This results in the sort of unintended consequences that leave your head spinning. The water heaters are, in essence, pretty effective water-purifying systems, which take dissolved minerals out of the water. The minerals of interest happen to be calcium and magnesium. Remember this for later.
The problem of failed hot water heaters in Las Vegas is simply accepted. You move to Las Vegas, and live with the fact that you must replace your hot water heater every couple of years. It is annoying, but not a big deal. Everyone goes through it. The water heaters are all located in garages. They are easy to replace. There is no real collateral damage to worry about. Las Vegas lives with a system of disposable water heaters. Think of it as a "hot water tax" that is almost unique to Las Vegas.
Home builders, in their continuing efforts to reduce their costs and improve their production efficiencies, began to replace traditional copper-based piping systems with cross-linked polyethylene (PEX) water supply piping. PEX has a lot going for it. It does not corrode, is chlorine-resistant, it does not develop pinhole leaks, has fewer fittings, connections, and elbows. Did I mention the part about the fewer fittings, connections, and elbows? Home builders began to use PEX systems almost everywhere, including Las Vegas.
With PEX systems the fittings and couplings are almost universally brass. Brass, which is a metallurgist's dream, is a magnificent alloy of copper and zinc. But to the British Grand Fleet and its commander John Rushworth Jellicoe (Photo 2), admiral and hero of the British Empire, brass is a nightmare.
British dreadnoughts (Photo 3) used 70/30 brass tubes in their condensers. These brass tubes, 70% copper, 30% zinc, suffered from "dezincification," which is a process where the zinc is preferentially removed by corrosion. Zinc is a highly reactive metal with a weak atomic bond. The process is referred to by old sea dogs as "condenseritis." ([dagger]) Dezincification had more effect than German U-boats (Photo 4) and the Imperial German Navy's High Seas Fleet in knocking British ships out of action during World War I.
Because of condenseritis, Admiral Jellicoe almost didn't steam out of Scapa Flow ([double dagger]) to meet Vice-Admiral Scheer and their respective destinies at arguably the largest naval battle in history--the Battle of Jutland--the greatest clash of big-gun armored warships ever.
British metallurgists eventually solved the problem with adding arsenic, which produced "admiralty brass" (1) So, that was pretty much it for brass for about a half a century.
The problem of dezincification of brass water fittings was first identified in the 1950s. (1) This type of dezincification is referred to as "meringue dezincification" where the corrosion product, zinc oxide residue, blocks the fitting (Photo 5). Although meringue dezincification was known since the 1950s, it was rare unless you had "aggressive water," which is water with high levels of oxygen, chloride ion and sulfate content. Hello, Las Vegas. Guess what happens when we begin to see lots of brass fittings and couplings in Las Vegas?
This leads us to Svante Arrhenius (Photo 6). Heat is needed for most chemical reactions to occur. Arrhenius gave us the quantitative relationship that governs these reactions. This is a big deal. Activation energy is his baby. Maxwell-Boltzmann distributions, Gibbs free energy, and Planck's constant all are intertwined with the Arrhenius equation. Engineers, being engineers, simplify the famous equation: for most chemical reactions the rate doubles for every 10 K rise in temperature. Guess what recirculation systems do? They make the hot water side of the piping systems hot all the time. Guess what this does to the rate of dezincification? Svante Arrhenius meet Jan Laverty Jones.
Most of the new houses in Las Vegas with PEX piping are undergoing repairs and the associated litigation is a nightmare for everyone. In new Las Vegas homes, the damage never appears on the cold side. Arrhenius again.
Las Vegas gives us some interesting twists. Remember earlier when I mentioned calcium and magnesium? These minerals typically form scale on brass fittings, protecting them from dezincification. Guess what? The water heaters take them out of the water accelerating the process. Even more interesting, the elevated pH of Las Vegas water keeps the zinc oxide corrosion product at the fittings, blocking the water flow. So the meringue doesn't get flushed out of the system.
So what to do? Take the zinc out of the brass. Of course, you can't take it all out because then we wouldn't have brass anymore. We would have copper. Unfortunately, we can't use copper because it is not as strong as brass. The good news is that we have different types of brass. The most common type is "yellow brass," which is 35% zinc. It is the problem child. Remember: yellow is bad. Another type of brass is "red brass," which is less than 15% zinc. Red brass seems to work. Remember: red is good.
The couplings are the easy part. The trouble is that it is difficult to find all red brass fixtures and faucets. And, when you do find them, not everyone likes the way they "look." We don't seem to have a lot of "designer red brass fixtures and faucets." Do you want to look good, but leak?
What about the casinos? We know about new homes, but what about the important stuff in Las Vegas? Well, the casinos treat their water, have copper piping and regularly replace their fixtures. They consider their regular fixture replacement much the way homeowners consider their regular hot water heater replacement.
Photo 6: Svante Arrhenius. The boy from Vik, Sweden, writes a doctoral dissertation that gets the thumbs down treatment from the establishment at the Physical Institute of the Swedish Academy of Sciences. He has the last laugh when the work gets him the Nobel Prize in Chemistry in 1903. He still gets no respect today. He is the father of the Greenhouse effect, not Al Gore. Arrhenius said this more than one hundred years ago, "If the quantity of carbonic acid increases in geometric progression, the augmentation of the temperature will increase in nearly arithmetic progression."
What else can you do? Well, you can move to Phoenix. Why? Well, by the time you get downstream on the Colorado River most of the problem disappears. So once again, pretty much what happens in Vegas stays in Vegas. So, is this the mayor's fault? It's an interesting question. You can make recirculation systems work with the right stuff even with bad water. But, as they say in this business--who knew?
(1.) The Hendrix Group, Materials and Corrosion Engineers. 2004. "Dezincification." www.hghouston.com/coppers/brass75.htm.
* This was before we started numbering them. The first World War was thought to be the war to end all wars.
([dagger]) The used steam from the engines is passed into salt-water cooled condensers, so that the feed water can be pumped back into the boilers. If the condensers leak, the salt water contaminates the feed water, affecting the generation of steam, damaging the turbines.
([double dagger]) Scapa Flow was the main base for the British Grand Fleet. It is a body of water in the Orkney Islands, Scotland, United Kingdom.
By Joseph W. Lstiburek, Ph.D., P.Eng., Fellow ASHRAE
Joseph W. Lstiburek, Ph.D., P.Eng., is a principal of Building Science Corporation, in Somerville, Mass. Visit www. buildingscience. com.
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|Title Annotation:||Building Sciences; Svante Arrhenius|
|Author:||Lstiburek, Joseph W.|
|Date:||May 1, 2009|
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