High Efficiency Fill

Posted by: Jim Smith | General

Why an owner might not choose the highest efficiency fill for a repack

This is a scenario we walk through on a regular basis with many of our customers. We also perform a lot of thermal runs using our STAR program to model towers and compare the benefits of using a cross-fluted fill or an offset-fluted fill. When we present a STAR analysis and customers see that a certain high-efficiency fill might be able to provide slightly colder water for their process, it’s hard sometimes not to jump to the conclusion that that’s the best fill for the application. However, when we come to that point, we need to discuss water quality and the process being served by the cooling tower system.

While initial thermal performance is certainly appealing, that performance is only accurate as long as the tower remains in new condition. What happens when the fill begins to foul (which will happen no matter how good your water treatment program is)? For high efficiency cross-fluted fills, while lower water velocity through the packs provides the increased heat transfer that is good for tower performance, it also reduces shear stresses and allows a more hospitable environment for biological growth in the fill packs. When these characteristics start to yield fouling, that is when our customers start to realize that the super high-efficiency fill doesn’t necessarily look so super anymore.

Brentwood’s R&D lab has done thermal testing of new products for decades, and more recently, in conjunction with the Brentwood fouling chamber, they have been testing biofouled fill products. This allows them to see the impact that biofouling and weight gain have on a product’s thermal performance since most of the product’s serviceable life will not be in an “as-new” state but in some state of degradation from “new.” This is important for owners to know so they can get a good idea of the true performance after the tower is no longer “new.”

Based on testing, they have seen that the thermal performance of a high-efficiency cross-fluted fill can readily fall below that of an offset-fluted product by significant percentages in overall tower performance. The loss in tower performance of a fouled cross-fluted fill, as compared to an offset-fluted product under the same conditions, shows that while a cross-fluted fill may show a slight increase in performance when new, as the tower ages and the fill begins to foul, the tower performance can fall well below that of a more fouling resistant offset-fluted product. This is important to keep in mind. Additionally, if the tower has over 5 ft. of fill, the offset-fluted product may actually perform better than the cross-fluted product from the beginning.

They are committed to continuing this type of testing so that they can share these insights with the industry. In fact, Brentwood will be presenting a paper that includes some of this research at the 2017 Cooling Technology Institute (CTI) Annual Conference in New Orleans next week! If you can’t join us, you can also purchase it from CTI – Paper# TP17-05, “A Study on the Bio-Fouling Characteristics of Contemporary Trickle and Modular Splash Fills.”

 

Engineering Corner: Effects of Fouling on Tower Performance

Just what are the effects of fouling on a fill, and what does it mean for overall tower performance? This is a question that Brentwood has been researching for a few years. As film fills have evolved and tower owner/operators have paid tuition to the “school of hard knocks,” it has become apparent that one of the keys to proper fill choice is choosing a fill that lasts for years so that you can get a positive return on your investment.

The balance scale that weighs fill performance vs. fouling resistance means that, generally, in order to gain fouling resistance you have to give up cooling performance. The design of low-fouling fills incorporates this fact into their design. As fill designers coming up with a lower-fouling fill, we sacrifice some initial cooling capability with the intent that as the fill fouls, it will be able to maintain roughly the same level of cooling capability over the long haul.

Example Tower Capability Loss Overview

What this means is that if a tower is designed around a low-fouling fill, it will either be larger and/or require more airflow (i.e. fan power if it is not a natural draft tower) than a tower designed around a high efficiency fill in order to achieve the same design duty. Generally, this means that the initial expense of a low-fouling fill tower will be higher than a comparably designed high efficiency fill tower. While that may make sense from a capital expenditure perspective, the recurring yearly expenses may skyrocket due to lost production capabilities or other factors if the tower loses 15% of its cooling capability in only 5 years.

Based on testing at Brentwood’s R&D facilities, we have compared the impact that fouling has had on both film fills and newer “wire-frame” style products. Our goal was to compare both the fouling characteristics and the effects that the fouling has on the overall cooling capabilities of different products simultaneously. Thus, for an equal time of residence in a given circulating water condition, how much fouling and sediment buildup would accumulate, and what would that do to the “as new” fill’s capacity to cool?

Product Spotlight

The new Brentwood CFUltra counterflow drift eliminator is a refined/upgraded version of the CF80MAx that leads the industry in performance, taking drift reduction to the next level. The CFUltra has been independently tested by a CTI-licensed testing agency, and the results show that it is capable of producing drift rates from 0.0004%, down to 0.00025%, of circulating water flow. These third-party-verified rates are applicable when the product is utilized in accordance with Brentwood’s installation and operating procedures.

The CFUltra achieves this level of performance without adding additional air resistance over the industry-standard CF80MAx product, making it a perfect drop-in upgrade for existing installations and a must-have for new towers. When cooling tower emissions are a concern for permitting or if drift is causing increased maintenance costs due to premature corrosion of gears, fans, and motors, a simple upgrade to CFUltra can reduce your tower’s drift by 20-50%.