White Rust: What it is, and How to Protect Your Project

What is "white rust"? Well, while it is white, it really isn't 'rust' in the normal sense of iron-oxidization. White rust is instead a corrosion product of zinc oxidization that often strikes galvanized surfaces subjected to moisture. In our industry, the most common victims of this corrosion mechanism are cooling towers and fluid coolers. And in these products, white rust can cause thousands of dollars of damage in a relatively short period of time.

White rust damages equipment by allowing a rapid and localized corrosion of the protective zinc coating on galvanized surfaces. Normally, in a galvanized surface, the zinc protects the underlying steel by providing a sacrificial cathodic protection to small areas of exposed steel, and provides bulk protection by providing a durable protective inert zinc oxide coating to prevent exposure of the underlying steel.

In white rust, however, this normal oxidation of the zinc surface goes wrong, and instead of providing a durable dull-gray surface, a porous, powdery or waxy oxide is produced instead. This corrosion product allows a rapid removal of the protective zinc surface--made worse in that the corrosion is generally localized in 'cells' which cause a very quick penetration of the zinc surface, exposing the underlying steel in a pitting process.

In recent years, the incidence of white rust has increased dramatically, leading the industry to study the process in greater depth. The Association of Water Technologies has produced an informative paper (pdf) that investigates the reasons for this increase (essentially changes in the methods used to produce galvanized sheet metal and water treatment methods) and how to prevent its occurrence.

Generally, white rust is more prevalent in soft water areas, which makes it a big problem in the Pacific Northwest. Preventing it entails both design and operational considerations.

White Rust Cells in Basin of Tower

If galvanized surfaces are used in your tower, it is critical that the tower be subjected to a 'passivation' treatment. This is a temporary water treatment regimen in the first few weeks of tower operation that acts to ensure the development of a desirable zinc oxide surface. Evapco discusses this process in this engineering bulletin. If Evapco's non-chemical Pulse~Pure product is provided, passivation is be included in the first year service that is provided with all installations. It is critical that this be performed immediately upon filling the tower with water--if water is left in the tower untreated for a period of time before the passivation treatment begins, white rust cells can develop in the interim. This is a very common cause of white rust corrosion in otherwise well-treated towers.

The other method to avoid problems with white rust in your tower installations is simply to chose your materials of construction wisely. In cooling towers, the most critical portion of the system is the basin--white rust can cause a rapid pinhole leak through the basin of a galvanized basin that would require immediate refurbishment. Providing a 304 ss basin is a very economical way to avoid costly system renovation at a future date. For areas with high chlorides, or when using water treatment methods that operate at high cycles of concentration (thus increasing the low chloride content of the utility water to dangerous levels) 316 ss is also available. Of course, the entire tower can also be constructed from these corrosion-resistant materials if desired.

In fluid coolers, however, the coil is an additional problem area. White rust on this galvanized component can rapidly lead to perforation of the closed-loop side of the system causing loss of cooling water and/or glycol coolant into the open loop side of the system. This can be a triple-threat due to the economic loss of glycol and water, an increased threat of freeze up, and huge water-quality problems due to bacterial growth and plasticization due to glycol exposure in the open side of the cooler.

Plasticized Bacteria/Glycol Slime: Yuck

The coil in your fluid cooler is the single most expensive component in it, by a large margin. And replacing coils can be an extremely costly proposition, especially in coolers without easy access to the coil section.

Until recently, there hasn't been a lot of choice for protection of this critical component of the system. Other than selecting a tower, like Evapco's highly efficient ESWA fluid cooler, that provides easy coil access for coil replacement, the usual option was to ensure a thorough passivation program. However, Evapco has now introduced 304 SS fluid cooler coils to protect your project's investment in this costly and critical component.



White rust is a problem that can cause great economic losses for building owners and operators. Thus it is critical that designers and contractors are aware of the prudent requirements necessary to prevent this damage. But with simple precautions, namely requiring a passivation program or wisely selecting materials of construction, this problem can be avoided in your projects.

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But what if it's too late, and you already have white rust on your tower? Well, there are an array of options, including attempting to re-passivate the galvanized surfaces or a full refurbishment of the basin using a polymer coating like Evapco's Evapliner. The helpful people at Fluid-Tek would be happy to help you determine the best course of action for your project.

LEED™ and Pulsed-Power Water Treatment

Pulsed-power water treatment offers many advantages to designers of sustainable systems.

First, it eliminates the use of industrially produced chemicals and their subsequent release into the environment. Secondly, it provides superior control of scale and biological growth, both of which negatively affect the efficiency of systems utilizing treated condenser water. Pulsed-power water treatment also allows safe operation at high cycles of concentration in the condenser water which acts to reduce the use of our limited water resources.

But there are other ways in which Pulsed-power water treatment can contribute to the sustainability of your project--and these can often lead to opportunities to gain LEED™ points.

Evapco has developed their Pulse~Pure pulsed-power water treatment system in an effort to minimize the impact of our engineered systems on the environment. They have also provided a handy guide to attaining credit for this reduced impact through attaining points through the LEED™ program:



If you are considering a sustainable project where condenser water systems are to be used, it is well worth the effort to see if pulsed-power water treatment fits into your goals.

Open House: Where, When and How

THURSDAY, OCTOBER 16th!

Details:


Where: 2001 22nd Ave S, Seattle WA, 10:00 AM to 6:00 PM

The open house will be located just down the street from the JB offices, about 5 blocks south of I-90, just off of Rainier Avenue in Seattle.

(click for active map, or click HERE)

Directions: Directions from your location can be found by clicking on on the active map above, then right-clicking on the open house location, selecting "Directions to" and typing in your starting address in the box provided! Parking is available.

Transit: Plan your trip Here (Use "2001 22nd Ave S" as the destination)

What:


Schedule of Presentations:

• 10:30 AM: Non-Chemical Water Treatment Case Studies. John Junk, Fluid-Tek
  
• 12:30 PM: Aggressive Building Energy Performance: Getting to 50 and Beyond. Mark Frankel, New Buildings Institute
• 1:45 PM: PSE/SCL Energy incentive updates
• 2:30 PM: Introduction to Variable-Refrigerant Flow Systems. Kim Olson, Sanyo
• 3:30 PM: Introduction to Active Chilled Beams. Rand Conger, Johnson-Barrow

Lunch provided at 11:30 AM to 1:30 PM

Refreshments provided 4:00 PM to 6:00 PM


Featured Products on site for your inpsection:

Climate Craft Matrix Air Handler

Evapco AT cooling tower with Super Low Sound Fan

Evapco Pulse~Pure non-chemical water treatment

Sanyo Mini-Splits

Dadanco Active Chilled Beams

Cerus Starters

And even MORE!

How:

Come throughout the day. Visit for as long or as short as you like

If you do plan to come, we would appreciate some feedback on when you think you will be here.

Please visit HERE to give us a quick RSVP. Thanks! (We'll still let you in if you don't)

Saving Water in Evaporatively Cooled Systems

Water is a limited resource, just like energy. Engineers are very aware of the need to save energy in their designs, and one of the best ways to do this is to take advantage of evaporative heat rejection for their cooling systems. The traditional cooling tower is an extremely effective way to reduce energy use at the compressors in a traditional cooling system. But introducing a cooling tower introduces a need for water to the system. It would be advantageous if this water use could be kept to an absolute minimum.

Especially since, in Seattle, water is expensive. As of this posting, the water utility rate per thousand gallons is $4.48 (summer) and the Sewer costs tack on an additional $9.96. When you consider that a cooling tower consumes a minimum of 1.8gph/ton (evaporation required to reject that heat), you can see that over a 1900 hour cooling season, these costs can really add up for a reasonably-sized cooling tower.



Earlier, I posted an article that highlighted ways to reduce water use in traditional cooling tower systems. For the most part, these recommendations address keeping the actual water use as close to the theoretical 1.8gph/ton evaporation figure as possible. Reducing the water use any further requires reducing the load on the tower, since evaporation is the only way a cooling tower can reject heat.

There are two ways to reduce load on a cooling tower--Reducing the total building load, or rejecting heat through some other method other than the cooling tower. Assuming the first option has already been exhausted through good engineering practices, the only other option is the second.

This is the approach taken by Aaon in their evaporative condenser systems. They essentially use a dry finned coil as the first stage of cooling before the refrigerant is cooled by evaporative methods. This essentially allows the system to reject as much heat as possible through a non-evaporative method before water is used. Every btuh that is rejected in this manner means less water used in the system.


This idea could be borrowed and applied to an open cooling tower by the use of a dry-cooler as a pre-cooler before a cooling tower. This way, the system rejects as much heat as possible in a dry fashion, and only uses water for what the dry-cooler can't do. This system gets to take advantage of the strengths of both methods of heat rejection--the water conserving function of a dry-cooler, and the lower water temperatures and more efficient heat rejection provided by a cooling tower.

Evapco has capitalized on this approach by creating a new, water-saving fluid cooler called the WDW:


This unit is a hybrid between a dry-cooler and an evaporative fluid cooler. It is provided with a control panel that controls both wet and dry sides of the unit, varying fan speeds with a VFD and determining when to run the evaporative pumps to optimize both water efficiency and fan energy.

Cutaway of an Evapco WDW unit

In practice, the evaporative system is only used for a small portion of the year, only when the design condenser water temperatures cannot be met by the dry-cooler side alone. What you see is a major reduction in water use compared to the same system served by a fully evaporative system:


Other advantages of this approach besides reduced water use are reduced chance of tower plume (since there are far fewer hours in which water is being evaporated, and when this does occur, it occurs in warmer temperatures) and the ability to provide some cooling even if city water is lost due to a service disruption.

But since a dry-cooler uses more fan energy per ton of cooling than a cooling tower, this system will inevitably use more energy to save water. Does this approach pay off?

An example from a real project might help demonstrate the economies involved. Below are the utility cost calculations from a project utilizing a 240 ton WDW installed in Seattle on a heat pump system with a portion of the load serving a 24/7 cooling application:



Note that even with the reduced water cost (to approximate the effective cost of using a deduct meter to avoid being charged wastewater charges for evaporated water) the hybrid system saves about 18% of the annual operational utility costs compared to a fully evaporative system. This affords a relatively quick payback for the added equipment costs associated with the hybrid system.

Your Next Energy Conservation Measure May be a Quiet Fan

It might sound strange, but a super low sound axial cooling tower fan is an energy-saving device--But not because it uses less energy than the fan it replaces, because it doesn't. The reason is a little more complicated than that.

But first it makes sense to review a few basics about cooling towers.

The Basics

There are two major types of cooling towers and fluid coolers: Induced Draft and Forced Draft.


Forced-Draft towers utilize centrifugal fans to blow air through the tower. The air is forced into a pressurized plenum inside the tower and then through the fill. This means that access into these towers is limited, since doors must be able to resist pressure without leakage and tend to be small and difficult to use. This also makes it difficult to observe the basin of these towers while operating in order to troubleshoot problems if necessary.



Induced draft towers use an axial fan to pull air through the tower, creating a negative pressure within the tower. This allows the unit to be built in an open configuration, making access and observation far easier. In general, induced draft towers cost less, are easier to maintain and, importantly, require about half the fan horsepower to do the same cooling as a forced draft unit.

In fact, there are only a few reasons why you wouldn't use an induced draft tower in preference to a forced draft tower:
1. Height restrictions
2. Static pressure capacity for ducted installations
3. Noise Control

If you project requires an extremely short cooling tower or needs a tower to be installed indoors with ducted inlets and/or outlets, there is a good chance you will need to use the less efficient forced-draft tower. And, until recently, it used to be that the same was true of sound-critical installations. But not any more.

The acoustical benefit of forced draft units are twofold: First, they are quieter than induced draft units right out of the box. (Low-profile forced-draft units are especially quiet.) And, secondly, they can easily accept sound attenuators to make their already quiet performance even quieter. The price you pay, of course, is fan energy and dollars. Attenuators require that you expend even more money and fan energy than the already more expensive and less efficient bare forced draft unit.



Th super low sound fan (SLSF) changes the playing field. The addition of the SLSF on an Evapco induced draft cooling tower does not affect the efficiency at all--the performance is the same with and without the quieter fan. And since the fan knocks 9-15 dBa off of the sound power of the tower, suddenly induced draft fans are competitive in sound level with a forced-draft unit. Generally speaking (and each application is different) a SLSF induced draft unit is just about as quiet (if not quieter) than a forced-draft unit of the same capacity--and very competitive in first cost. And further sound abatement is available to shave a few more dB off of the sound level.

This development makes it very possible to meet demanding noise criteria and still retain the sizable energy benefits of the axial fan. And with innovative products like the Evapco ESWA, the lowest-sound option can even be the energy leader!

Hearing is believing, so Evapco has provided a few video clips to help you get an idea of how significant this sound improvement is [videos may require Internet Explorer to work properly]:

Video 1
Video 2

More information on low-sound options is also available here (pdf).

Reducing Ground-Loop First Costs

Ground-Loop heat pump systems perhaps have the greatest potential for reducing energy use in the built environment than any other space-conditioning technology now in use. This potential has been long recognized by the EPA and the DOE, and represents a great opportunity for owners and designers attempting to create systems that out-perform those that are commonly built in this region.

They also have a reputation for being expensive--very expensive.

And with drilling costs in this region historically being quoted as high as $15/lineal foot, this reputation is well deserved. These prices usually put this technology out of the range of economic justification for typical projects.

So what can a designer do to minimize costs, yet still provide the energy benefits of this technology?

Add a cooling tower.

Hybrid Systems

To understand how adding a cooling tower to a ground loop saves costs, first you have to understand a simple concept about closed ground-loop systems. While the ground loop is often referred to as a "heat exchanger", the ground-loop (and the ground it occupies) acts more as a leaky heat storage battery. Unless there is sufficient ground-water movement through the well-field, most of the heat that is rejected into the ground remains there throughout the year unless it is later removed by the ground loop itself.

That means that over time, if the heat added is not balanced by heat removed, the ground temperature will continually increase over the seasons, increasing loop temperatures and decreasing system efficiency.

(graph showing increase in temperature over time for imbalanced loop of differing bore hole numbers. From here)

The best situation for a designer is when the heat added to the ground over the course of the year (by the process of cooling the building) is balanced by the amount of heat removed from the loop (by the process of heating the building). But a heat-pump does not just move heat from one source to another. Because a compressor is needed to perform this work, a heat pump always adds the heat of compression to the equation. This is a benefit in heating, since the heat of compression is added to the amount of heat moved from the loop to the building. This is a hindrance in cooling, since this compressor heat is added to the heat moved from the building to the loop. In practice, about 1.2 to 1.8 tons of heating are needed to balance out 1 ton of cooling. This means that many ground loops will see an imbalance where more heat is rejected to the loop than is removed from the loop over the course of a year. This effect can be significantly compounded (or mitigated) by the configuration and use of the building served--buildings with significant yearly cooling loads will be more affected than by buildings dominated by heating loads.

A ground-loop designer typically combats this effect by increasing the volume of the well field by increasing the number wells to a point where the relatively small amount of heat-leakage out of the well-field and added volume is enough to account for the imbalance of the system and minimize the heat gain. Thus ground loop well-fields are often sized due to the minimum requirements of either heating or cooling demand for the building. Cooling-dominated well-fields are more common throughout the US, especially in the southern portion of the country.

If the designer could correct for this imbalance and build the loop to the smaller size required by the heating load of the building, then fewer wells would be needed, and thus the overall cost of the loop would come down. One of the most cost-effective ways to provide extra cooling to balance out the loop on such a system is by way of a cooling tower or fluid cooler. When a cooling tower is used in conjunction with a ground loop, you have what is called a hybrid system.

Hybrid systems can be extremely effective at bringing down first costs of ground loop systems. A study by Kevin Rafferty of the Oregon Institute of Technology found that hybrid systems can reduce the cost of a ground loop by as much as half for some systems:


But can we expect similar reductions in first cost for the Puget Sound region, where we have a generally cool climate and a long heating season? For some systems, it appears the answer is yes. A presentation by Scott Hackel of the University of Wisconsin at the ASHRAE 2007 summer meeting investigated the cost savings possible using hybrid systems throughout the country. His study showed very significant reductions in ground heat exchanger (GHX) loop lengths for school, retail and office applications in the Seattle region:

(Click for larger image)

Hybrid loops may just make the next ground loop you consider pencil out.

Advanced Tower Nozzle Design Eliminates Clogging

Anyone who has operated cooling towers for any significant amount of time knows that a common maintenance point is clearing clogged water distribution nozzles. This is especially a problem for gravity-fed cross-flow towers, where there is very little pressure to force debris through the nozzle orifice, and debris such as leaves, paper and ferrous 'throw' from the pipes can clog the nozzle. This reduces the effectiveness of the water distribution, and in turn the efficiency of the cooling tower.

Typical cross-flow tower gravity distribution pan

Pressurized distribution systems, as are found on Evapco counter-flow towers, eliminate a lot of clogging problems by utilizing pressurized large-orifice nozzles which use the force of the water pressure to keep the nozzles clear. But even these types of systems can clog periodically.

So that is why Evapco developed the Evapjet nozzle.



That's a nozzle?

Yes, it is, but probably the best way to appreciate it is by watching the video of it in action: Evapjet Video (may require Microsoft Internet Explorer to view).

(Pretty cool, huh?)

Importantly, this nozzle can pass a 1" ball, and reduces the total number of nozzles required for a tower by 66%! So you have a much reduced chance of clogging, and many fewer nozzles to maintain.

This nozzle is provided on new Evapco cooling towers, and is available for retrofit on many existing towers of most major manufacturers. If you are interested in retrofit, call Fluid-Tek for a quote!

UPDATE: 9/23/07

Don't be discouraged if you have a fluid cooler and not a cooling tower. Evapco offers their unique ZM (Zero Maintenance) nozzles (pdf) with similar anti-clogging properties as the Evapjet--they just don't make for as cool a video!

Read more about spray header and nozzle replacements here.

Evapco ESWA: The Most Efficient Fluid Cooler on the Market

Recently, Evapco introduced a new fluid cooler design that blows away other traditional units in efficiency and sound performance.

The secret? They re-thought how to design a fluid cooler.

In their testing, they found that the most efficient heat transfer occurred in a fluid cooler coil when the coil was completely flooded with water. However, in a traditional fluid cooler design, this condition could not be attained because air flow was needed over the coil in order to evaporate a portion of the spray water pouring over it.

Traditional Fluid Cooler Design

A little out-of-the box thinking led their engineers to realize that there were two heat transfer processes that really mattered in a fluid cooler:

1. The spray water cooling the fluid in the coil by conduction
2. The air cooling the spray water water by evaporation

Both of these processes were optimized in different conditions. So they decided to separate the two processes from each other:

New ESWA Design

The new ESWA cools the spray water with conventional cooling tower fill and then, only after the water is cool, floods the coil for optimal heat transfer.

The result? A fluid cooler that uses 30%-50% less energy than a traditional induced draft cooler, and up to 80% less than a forced draft tower!

And there are other benefits, too. Since the water basin is completely enclosed, the splash noise from the basin is attenuated, making the ESWA one of the quietest fluid coolers on the market. The basin is also accessible, making the ESWA coil extremely easy to inspect and clean. And since the air inlets are above the coil, very little 'stack' effect is created, making the heat loss from a standard ESWA in heating season less than that of a traditional fluid cooler equipped with positive closure dampers!

Evapco Hits the Big Time

Funny things happen when you type "Evapco" in to the search box at Youtube:



No, I don't understand it either

Cool Ways to Conserve Water

A few years back, I had an article published in the April 2005 issue of Plumbing Systems and Design Magazine that highlighted the many ways to optimize the water saving performance Cooling towers.



You can read that article right here.