Archive | 2007

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6:00 am
November 1, 2007
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Utilities Manager: Cutting Costs In Process Cooling

New to North America, this proven technology soon may change the way you approach process cooling in your operations.

Although some technologies are constantly changing, at least one has remained virtually unchanged for decades: cooling tower systems. New technology in this arena, however, has at last hit the United States—and it’s changing everything about the way many people approach process cooling. As a utility manager, you might find you want to change your approach, too.

1107_um_cooling_fig1Ecodry is a closed-loop, dry-cooling system that nearly eliminates wastewater problems and drastically lowers energy bills. It does so by completely eliminating traditional cooling towers and the typical hassles associated with them.

The current situation
For over 80 years, cooling towers have been at the center of industrial cooling despite the ongoing expense of water treatment, regular heat-exchanger cleaning, difficult cold-weather operation and substantial water and energy consumption. Traditional cooling towers rely on constant evaporation of water passing through the air, resulting in an ever-increasing concentration of contaminants and dissolved solids. Until recently, cooling tower maintenance professionals have accepted these problems as inevitable. This new system, from the Italian company Frigel, offers an alternative.

While new to North America, the Ecodry system has been proven in well over 5000 installations worldwide. The concept originated in Europe, where energy is more expensive and water quality has been a huge challenge, making the perfection of this technology imperative.

In place of a traditional cooling tower, the Ecodry features a closed-circuit fluid cooler. The water returning from the process is pumped into heat exchangers and cooled with ambient air flow. This process provides clean water at the right temperature to process machines year-round.

The closed-loop design keeps heat exchangers scale-free, minimizing the need for costly chemical consumption and disposal. The ultimate result is a modular, flexible, preengineered system that produces the lowest operating cost and highest reliability for installation anywhere.

1107_um_cooling_fig2Water savings
The endless water challenges related to cooling tower systems include high levels of consumption, chemical treating needs and disposal issues.

Over-consumption occurs as water either evaporates or is dumped down a drain. Both events are inevitable with traditional tower systems, whereas the new closedloop system described here never exposes water to the elements—making it possible to use the same clean water over and over again. The reduced water consumption, when compared to conventional cooling towers, is up to 95%.

Most facilities’ incoming process water is not what you would call ideal. That’s why, in an open cooling tower system, continuous water treatment becomes an expensive part of everyday operations. It’s common for a local chemical representative to visit a plant every couple of months to test and adjust the water. In closed-loop, dry cooling, adjustments are made up front if needed. The time and resources spent on regular testing and treating are completely eliminated.

Many facilities also are struggling with local government regulations on contaminated water disposal. These facilities face large dumping fees, fines or the need to call a service to haul away chemically treated wastewater.

This type of closed-loop system minimizes environmental impact by using the same clean water continuously and not disposing chemically treated water into the ground, lakes and streams. With evaporation virtually eliminated, the Ecodry’s technology poses the lowest risk of refrigerant gas emission into the atmosphere.

Energy savings
According to Frigel, the Ecodry system can reduce energy consumption significantly by eliminating big pump tanks and using efficient fans that only run when needed.

1107_um_cooling_fig3

One of the key energy-saving components is the advanced microprocessor featuring an easy-to-use, remote interface. It not only controls functions of the system but makes the adjustments needed for the system to run at optimum efficiency. Based on ambient temperature and process water temperature, the controller adjusts fan speed and initiates evaporative functions to generate the required cooling capacity in the most efficient way possible. The microprocessor also manages the pumping stations to save energy and boost equipment longevity by controlling water pressure and pump rotation.

To power the fans, the system uses highly efficient, brushless, variable-speed DC servo motors with individual automatic speed control. These maintenance-free motors are 30% more efficient than traditional motors, feature quiet operation (less than 57 dBa), allow any fan to be changed while the equipment is running and offer increased reliability and durability. Overall, the average annual energy consumption of this closed loop system is 0.05 kWh/ton.

How the system works
Besides continuous maintenance, chemical expenses and wasted water, cooling towers also fall short of optimum performance when ambient temperatures soar above 85 F or drop below freezing.

When ambient air reaches 85 F or above, the Ecodry system automatically switches into “adiabatic” mode. Air passes through an adiabatic chamber before reaching the heat exchanger. A fine mist of tap water is “pulsed” into the incoming air stream inside the chamber and humidified air drops the water temperature to, at or below 95 F—even with ambient temperatures as high as 120 F.

The pulsed water evaporates instantly, cooling the air before it impinges on the cooling coils that carry the process water. The coil fins remain dry, thus the term “dry cooling.” To ensure consistent cooling, an advanced control panel continuously adjusts the amount of water sprayed.

Units can deliver heat loads of 17 tons or can be daisychained to deliver capacity up to 3500 tons.

Avoiding freezing
What happens if ambient air dips below 32 F when the plant is not running or a power outage occurs? The Ecodry system’s copper pipes are automatically drained by gravity to protect the unit and avoid icing. Furthermore, it is done without the need for valves, antifreeze or any manual interaction with the system at all. The self-draining process provides completely safe operation in extreme weather conditions.

This function also allows the system to be used for applications where contact with glycol is not tolerated. For facilities in cold-weather climates, partial glycol supplement is an option if the user requests it. It’s not preferred, however, because pure water has the best heat-transfer properties.

1107_um_cooling_fig4For colder weather, Frigel’s technology includes builtin freeze protection that monitors ambient and return water temperatures. In a pure-water system, if the leaving water temperature drops below the setpoint, the controller halts the pumps circulating to the outdoor heat exchanger (made entirely of non-corrosive copper, aluminum, bronze and stainless steel) and the Ecodry automatically drains its water back to an indoor reservoir. The central system then circulates cool water from its indoor tank until it becomes sufficiently warmed to permit sending it outdoors again to the heat exchanger.

Central chiller replacement
The closed-loop system also can be used in conjunction with chiller/temperature control units (Microgels) for individual control of chilled or heated water at each process machine. A single set of uninsulated pipes supplies the process water without heat loss to the chiller/ temperature control unit at each machine. These units offer high flow, precise temperature control and a builtin valve that provides automatic “free cooling” when ambient temperatures are lower than process setpoint.

“This setup is really great. In the winter we get free cooling because we’re sending water outside to cool down to temperature,” said Steve Streff, president of SK Plastics, whose company uses Frigel’s technology (see sidebar below). “Sometimes, the compressors don’t even run because the water’s already cool enough. So, we’re saving money and energy on several fronts.”

Free cooling means using the closed-loop fluid cooler or other non-refrigeration cooling methods in place of the chiller/refrigeration method. The Ecodry can provide free cooling to a variety of processes/devices based on process setpoint and local ambient conditions. This can save up to 80% on energy costs and improve processes the water is serving because of the precise water temperature delivered at individual process machines. This can have quite a positive impact on productivity. UM

 

An SK Plastics Case Study

1107_um_cooling_pic1SK Plastics Molding Inc. in Monroe, WI, once had a conventional cooling tower system, as so many in the industry do. The company always was having trouble with contaminants in the water, dumping that chemically treated water into the environment and then needing to add more chemicals all over again. When it came time to look for a new system as part of plant expansion, company leaders were determined to consider alternatives.

“We’re in a rural area. The water’s terrible,” says Steve Streff, SK’s president. “There’s dust in it, lime, lily pads and dandelions. The water treatment people have to come in and bleed-off all the chemicals added to it. Our heat exchangers were getting plugged and our molds were starting to lime up.”

Streff met with representatives from Frigel North America to discuss their closed-loop, dry-cooling system. What he learned soon started to make sense for his operation. While he was at first skeptical about a system so different from the one to which he was accustomed, the fact that the Ecodry didn’t require constantly adding water and chemicals had significant appeal.

“We’re now running just one waterline into the new room that breaks off into chillers. And there’s no tower,” Streff notes. “We just have two little 500-gallon tanks out back. When we shut down, there’s nothing to drain. And the Ecodry looks like a big radiator; it’s not up on the roof, so it’s easy to service. Our maintenance guy loves it.”

Streff also points out that with the Ecodry system in place, SK Plastics even has eliminated checking or cleaning the hydraulic heat exchangers when the company conducts its annual maintenance teardowns.

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292

6:00 am
August 1, 2007
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Utilities Manager: Fanning Up Energy Savings With Adjustable Speed Drives

How you modulate or vary the flow of your fan systems may be hurting your bottom line. This author runs you through important calculations.

Fans are designed to be capable of meeting the maximum demand of the system in which they are installed. Quite often, though, the actual demand varies and may be much less than the designed capacity.

fan_fig1The centrifugal fan imparts energy into air by centrifugal force. This results in an increase in pressure and produces airflow at the outlet of the fan. An example of what a typical centrifugal fan can produce at its outlet at a given speed is shown by the curve in Fig. 1. This curve is a plot of outlet pressure in static inches of water versus the flow of air in cubic feet per minute (CFM). Standard fan curves usually will show a number of curves for different fan speeds and include fan efficiency and power requirements. These are useful for selecting the optimum fan for any application, and are required to predict fan operation and other parameters when the fan operation is changed.

fan_fig2The system curve in Fig. 2 shows requirements of the vent system on which the fan is used. A plot of “load” requirement independent of the fan, it indicates the pressure required from the fan to overcome system losses and produce airflow. The intersection of the fan and the system curve is the natural operating point. It is the actual pressure and flow that will occur at the fan outlet when this system is operated. Without external influences, the fan will operate at this point.

Many systems require operation at a wide variety of points. There are several methods used to modulate or vary the flow (or CFM) of a system to achieve the optimum points. These include:

  • Cycling (as done in home heating systems)—This produces erratic airflow and is unacceptable for commercial or industrial uses.
  • Outlet dampers (control louvers or dampers installed at the outlet of the fan)—To control airflow, they are turned to restrict the outlet, thus reducing airflow.
  • Variable inlet vanes—By modifying the physical characteristics of the air inlet, the fan’s operating curve is modified, which, in turn, changes airflow.
  • Variable frequency drives (VFDs)—By changing the actual fan speed, the performance of the fan changes, thus producing a different airflow.

By changing the airflow or the fan speed, the system or fan curves are affected, resulting in a different natural operating point—and, possibly, a change in the fan’s efficiency and power requirements.

fan_fig3Outlet dampers
The outlet dampers affect the system curve by increasing the resistance to airflow. The system curve can be stated as:

P = Kx (CFM)2

Where:
P is pressure required to produce a given flow in the system
K is a function of the system that represents the resistance to airflow
CFM is the airflow desired

fan_fig4The outlet dampers affect the K portion of this formula. The diagram in Fig. 3 depicts several different system curves indicating different outlet damper positions. Note that the power requirements for the type of system shown in Fig. 3 gradually decrease as flow is decreased (as shown in the Fig. 4).

Variable inlet vanes
This method modifies the fan curve so that it intersects the system curve at a different point. A representation of the changes in the fan curve for different inlet vane settings is shown in Fig. 5. The power requirements for this method decrease as airflow decreases, and to a greater extent than the outlet damper (as shown in Fig. 6). Variable frequency drives (VFDs) The VFD method takes advantage of the change in the fan curve that occurs when the speed of the fan is changed. These changes can be quantified in a set of formulas called the affinity laws.

0807_fan_equation_2

fan_fig5Where:
N = Fan speed
Q = Flow (CFM)
P = Pressure (Static Inches of Water)
HP = Horsepower

Note that when the flow and pressure laws are combined, the result is a formula that matches the system curve formula – P = K x (CFM)2.

0807_um_fan_equation3

Substituting (Q2/Q1)2 for (N2/N1)2 in the first equation gives us:

0807_um_fan_equation4

fan_fig6The quantity P1/(Q1)2 coincides with the system constant, K. As depicted in Fig. 7, this means that the fan will follow the system curve when its speed is changed. As the fan speed is reduced, a significant reduction in power requirement is achieved (as shown in Fig. 8).

The variable speed method achieves flow control in a way that closely matches the system or load curve. This allows the fan to produce the desired results with the minimum of input power.

Energy savings
Clearly, not all methods for modulating or varying flow are appropriate for a given fan system. How can you be sure that the method you are using is the right one? More importantly, how can you be sure it is the most efficient? Whatever your chosen method is for modulating or varying flow, it may be easier than you thought to estimate its power consumption and associate a cost of operation with it. To accomplish this, an actual load profile and a fan curve are required (as shown in Figs. 9 and 10).

The following simple analysis of the variable speed method compared to the outlet damper method shows how energy savings are calculated.

Using the fan curve in Fig. 10, assume the selected fan is to be run at 300 RPM and that 100% CFM is to equal 100,000 CFM as shown on the chart. Assume the following load profile.

0807_um_fan_dutycycle

fan_fig7For each operating point, we can obtain a required horsepower from the fan curve. This horsepower is multiplied by the percent of time (divided by 100%) that the fan operates at this point. As shown in the following table for the outlet damper method, these calculations are then summed to produce a “weighted horsepower” that represents the average energy consumption of the fan.

0807_um_fan_outletdamper

fan_fig8Similar calculations are done to obtain a weighted horsepower for variable speed operation. However, the fan curve does not have enough information to read all the horsepower values for our operating points. To overcome this problem, we can use the formulas from the affinity laws.

The first point is obtained from the fan curve. 100% flow equals 100% speed equals 35 HP. The flow formula Q2/Q1 = N2/N1 can be substituted into the horsepower formula, HP2/HP1 = (N2/N1)3 to give us:

0807_um_fan_equation5

When Q1 = 100% and HP1 = 35 HP, Q2 and HP2 will have the following values:

0807_um_fan_equation6

fan_fig9

0807_um_fan_fig101

As shown in the following variable speed method table, we now have sufficient information to calculate the weighted horsepower. Comparing the results of the two methods of control indicates the difference in power consumption.

In order to obtain a dollar value of savings, the kilowatt-hours used must be known. To calculate this, multiply the horsepower by 0.746 and then multiply the result by the hours that the fan will operate in a period of time. This would typically be for a month. Your results would look like the following example table at the bottom of the page.

This simple example shows a cost saving of more than $700 per month by using a variable speed method. Note that the example is very basic and does not consider motor and drive efficiency. Still, many organizations would consider that amount of monthly energy savings on a single fan system—or anything close to it—to be significant. Would yours? UM

0807_um_fan_tables


Sharon James is an application engineer with Rockwell Automation. E-mail him directly at: sjames@ra.rockwell.com

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6:00 am
August 1, 2007
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Utilities Manager: Challenge The “Rear-View Mirror” Approach To Energy Management

christopher_russell1

Christopher Russell, Principal, South River Facility Management

We’re all familiar with the monthly budget review meeting. This is when the general manager sits down with department heads to compare the latest month’s financial results to the organization’s operating budget. A common, well-intentioned business habit, it also has the potential to be quite damaging. That’s because the actual-to-budget review process focuses on the past at the expense of the future. Much like trying to steer a car by looking in the rear-view mirror, it is a big reason why organizations often fail to take meaningful control of their energy costs.

While the organization as a whole attempts to make money, department directors are primarily concerned with spending money for materials, labor, utilities, support services and the like. The monthly budget review is a discussion of variances—particularly those instances where spending is on a pace to exhaust funds before the end of the fiscal year. Top management provides annual performance incentives that focus on this year’s budget outcomes, not those of future years. Thus, a preoccupation with this year’s budget may be at the expense of potential savings that can accrue for years to come.

While history typically provides useful insight, it also can obscure future potential. Consider the following “rear-view mirror” approach to moving forward.

Let’s say a facility has yet to adopt energy-efficient technologies, behaviors and procedures. This means that it habitually buys more energy than is actually needed, because waste is built into its operations. The budget account for energy, then, is inflated to accommodate these inefficiencies. For example, energy losses add up to about 40% of the total energy delivered to U.S. manufacturing facilities as a whole. Stated differently, the typical manufacturing facility must inflate its energy procurement budget by a factor approaching two-thirds to account for energy that is both used and wasted.

A possible solution
Break down annual energy expenses into two separate line items. One represents the value of energy that actually will be applied to perform useful work. The second line item represents energy that will be wasted. How do you allocate energy expenditures into these categories? The answer is to conduct an energy audit that thoroughly evaluates energy inputs, uses, losses and potential consumption improvements. While industry averages are generally helpful, the most reliable indication of any single facility’s energy flow depends on a proper energy audit—the more thorough the better. Without distinguishing between energy applied and energy wasted, department directors often conclude that they “don’t have the money for energy improvements.”

The account for energy waste (a budget artifact directly related to past performance) is, in reality, an account from which energy improvements should be budgeted. The energy waste line item also brings attention and urgency to the issue at each and every monthly budget review.

Managers can use the “energy waste” account to either MAKE energy savings or BUY energy that ends up being wasted. Dollars from the “energy waste” account are devoted to energy improvement projects when the cost to save a unit of energy is less than its purchase price per unit. This is one line item that actually forces managers to look forward, and not in the rear-view mirror, when planning energy consumption. UM


Updated weekly, Christopher Russell’s energy management blog can be found at http://energypathfinder.blogspot.com

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6:00 am
May 1, 2007
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Utilities Manager: Recognizing Energy As A Business Risk

christopher_russell1

Chrisopher Russell, Principal, South River Facility Management

Organizations should be prepared to manage a wide and growing variety of energy-related business risks. These include energy market volatility as well as rapidly evolving technologies and regulation. Solutions involve more than pursuing a “project”—such as capital investment in a big chunk of machinery. Another alternative involves changing the way that daily, energy-related decisions are made throughout an organization. Energy risk management will require input from a variety of departments and people:

Procurement, budgeting and finance people will be the first-line in dealing with electric utility deregulation. Companies need to develop strategies for making the best use of the many procurement options that are available in deregulated power markets.

Finance people will lead the pursuit of tax deductions and credits that apply to certain energy improvements such as lighting, heating, air conditioning, and building structural systems. Finance people also set the criteria for evaluating energy-related investments.

Engineers will monitor emerging technologies and standards. Companies will ask: What are these technologies? Which ones will provide value for me? How shall I evaluate them? Engineers will also design, commission, and monitor new energy-using equipment and systems.

Operations managers will rethink the dozens of staff decisions made each day, across plant floors or office spaces. Machine operators and office workers are largely unaware of how their everyday choices impact the energy bill. Solutions begin with increased staff awareness of their energy use.

Human resource professionals need to inventory their staff training needs, then seek appropriate training opportunities. Maintenance workers and machine operators need to learn “best practice” techniques that save money and boost reliability.

Environmental, health and safety professionals need to monitor emerging regulations. Compliance with these regulations puts many dollars at stake in the form of potential fines and penalties. Note that an energy management agenda will closely overlap safety and emissions compliance strategies.

Marketing and corporate strategy people need to understand the opportunities posed by “sustainable” business practices. Energy efficiency is a component of sustainable business practices. Sustainability is also the key to developing new products and services and winning new customers. Look at Wal-Mart: they force their suppliers to squeeze as much waste as possible from their production costs. Companies that sell their products to Wal-Mart (and many other like-minded firms) are aware of this trend and have a strategy ready for it. Failure to adapt to this trend is to risk losing business.

Needless to say, an organization needs to coordinate these many players so that they are not working at cross-purposes. This is essentially the role of an energy manager.

Forward-thinking companies respond to energy risk by changing they way they use energy. They often begin by rethinking their work habits and procedures. They quickly discover that energy use is as much a human issue as it is mechanical. To ignore the human component of energy cost-control is to invite business risk. A lack of awareness begets a lack of accountability. And without accountability, companies have no effective response to energy risk.

Christopher Russell is recognized by the Association of Energy Engineers both as a Certified Energy Manager and a Certified Energy Procurement Specialist. As the director of industrial programs at the Alliance to Save Energy from 1999-2006, he documented and evaluated energy management practices at dozens of facilities and today continues to advise end users and others on the planning and promotion of industrial energy programs. Updated weekly, his energy management blog can be found at http://energypathfinder.blogspot.com

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6:00 am
May 1, 2007
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Utilities Manager: Medical Center Cures Its Hot Water Pressure Woes

Its booster pump system simply could not keep pace with fluctuating demands for hot water. Turning to skid-mounted pumps with intelligent controls made the pain go away for this major healthcare facility.

Located in the heart of Phoenix, AZ, St. Joseph’s Hospital and Medical Center is a 520-bed, not-forprofit hospital that provides a wide range of health, social and support services with special advocacy for the poor and underserved.

“St. Joe’s” is a nationally recognized center for quality tertiary care, medical education and research.

Founded in 1895 by the Sisters of Mercy, St. Joe’s was the first hospital in the Phoenix area. It has come a long way since it opened with 24 private rooms—each opening up onto a porch. With tens of thousands of annual admissions, emergency room visits and outpatient/inpatient surgeries—not to mention thousands of babies delivered each year—St. Joe’s water demands clearly are critical to its operations.

0507_um_whatshot1Specifically, this bustling institution requires an effi- cient way to maintain the availability of hot water pressure in its growing complex of buildings. Like all healthcare facilities, the system needs to be operational 24-hours-aday and downtime has to be kept to a minimum. That’s not always been easy.

As the hospital has expanded over the years, the water service for new facilities has simply been tied into the existing lines supplied by two outdated sets of pumps—one each for cold water and hot water service.

With its water service requirements increasing, the medical center began experiencing problems as a result of the hot water booster‘s inability to keep up with the cold water booster in terms of pressure. Depending on the varying needs during the day, the hot water system pressure fluctuated so much that it was causing damage on multiple showerheads and valves. In addition, maintenance on the existing pumps was becoming intolerable.

According to Michael Marquez, a technical sales representative for Quandna, Inc., a Phoenix-based fluidhandling solution provider and distributor for ITT, St. Joe’s was having to do quite a bit of maintenance on the old pumps. “The pumps have been rebuilt numerous times because they were constantly running overspeed and way off the curve,” he notes. “Additionally, the medical center maintenance people would sometimes have to be sent to the booster set to turn on another pump to maintain hot water pressure.”

Plug and play solution
It was clear that St. Joe’s really needed a booster pump system that could keep up the pressure for the hot water no matter what the facility requirements were. Quadna’s team of application specialists proposed a design—created specifically for the hospital—that would achieve these goals and serve as a drop-in replacement. The replacement system also needed to be functional quickly, as the medical center could not be without hot water for more than four hours.

To more effectively accommodate the hospital’s fast-paced growth, Quadna selected ITT’s Goulds Pumps brand SSV high-pressure, vertical multistage pumps combined with ITT’s PumpSmart® PS200 control system. Quadna manufactured a custom-designed booster pump skid to house the three pumps and their control systems. The pumps, which are combined to optimize their capabilities, offer the medical center optimal high pressure, in a mechanically friendly, space-saving design.

The new system also met St. Joe’s requirements to connect efficiently with the medical center’s existing piping system, as well as for elevator weight and the proper dimensions to pass through doorways. When the skid was installed in February 2007, the “plug and play” system became fully functional in just a couple of hours, minimizing the amount of time the hospital went without hot water. Other characteristics of this pump system include a design to handle variable pressure drops. The pressure set point can be modified for future system requirements and the intelligent pump controllers automatically adjust to changes in system conditions.

0507_um_whatshot2Low costs/high efficiency
Equipping each pump with the PumpSmart control system was done to meet the medical center’s concerns for a system with low total life-cycle costs. PumpSmart’s intelligent flow system works with any pump. The product utilizes a smart variable frequency drive (VFD) controller and proprietary control software to provide advanced process control, enhanced reliability through failure prevention, reduced life cycle costs and, according to the manufacturer, significantly lower energy costs—up to 65%.

“PumpSmart will provide the hospital with great energy savings,” says Marquez. “The medical center is on a strict budget. When you consider that it was running the old pumps at full speed, the savings provided by this type of intelligent control system will be significant.”

The PS200 model offers process control and pump protection in one easy-to-use package for virtually every industrial process. With preprogrammed applications such as pressure, flow and level control, setup is quick and easy. The PS200 is capable of coordinating efforts between other PS200 controllers as well as existing constant speed pumps.

“I am a big fan of these systems,” Marquez continues. “A skid, equipped with a PumpSmart system, allows the user to cut down on management and maintenance. Maintenance people don’t have to be sent out to the pumps to change the pressure—which is what has been done previously. This control system also has the ability to automatically rotate the pumps out as needed.”

One less headache
With its new reliable PumpSmartequipped pumps and their low life-cycle costs, St. Joe’s now can face future expansion plans and the varying demands of patient care with fewer things to worry about. There are enough headaches involved with operating a major medical center—trying to ensure adequate hot water service 24/7 should not be one of them.

ITT Goulds Pumps
Seneca Falls, NY

 

 

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6:00 am
May 1, 2007
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Utilities Manager: Maintenance Is Key To Green Roof Success

0507_um_greenroofs1

Much effort and attention has focused on educating people about the existence, significance and function of green roofs. What’s next in terms of maintenance is equally important to protect a green roof investment.

Do I really have to bring the lawn mower up to the roof?” asked the facility manager after his company had just installed a 4000 sq ft green roof.

The direct answer is “No.” But, regular maintenance is just as important to green roofs as to any other roofing system.

0507_um_greenroofs2With vegetated roofs having gained strong public interest in the United States over the last decade, there is widespread appreciation for the intricacies involved in building a green roof. Now, though, facility managers, engineers and others interested in and/ or involved with this emerging technology have new questions, including: “How do I maintain my green roof once it’s installed? “

Green roofs are living systems. Thus, regular and proper maintenance, on an ongoing basis, is vitally important in order for them to survive and succeed. This is especially crucial in the first two years after a green roof installation. In fact, green roofs must be attended to much more frequently in the first two years. Furthermore, because such a system is a roof environment, all safety precautions and OSHA regulations still need to be implemented.

The initial cost for installation of a green roof can be one-and-a-half to two times the cost of a traditional roof. With proper maintenance, however, a green roof can double the life expectancy of a roof. Add to that the cost savings for heating and cooling a green building and, amortized over the life of the roof, green ones—if properly maintained—come out on top economically.

Once installed, property management staff can be left a bit perplexed as to what to do, or who to hire to carry out the job of green roof maintenance safely and correctly. Green roof installers are often a good place to start. Some of them offer green roof maintenance as part of the recommended ongoing preventive maintenance that is imperative to the care of any roof system.

If your organization is considering a green roof for your facility—or if you’ve already installed one—here are some things you’ll want to keep in mind going forward.

0507_um_greenroofs3

Green roof maintenance 101
Types…

There are two basic types of green roofs—extensive and intensive.

Extensive green roofs are lightweight veneer systems with thin layers of drought-tolerant, self-seeding vegetated roof covers requiring little or no irrigation or fertilization after establishment. They are built when the primary desire is for an ecological roof cover with limited human access.

On extensive green roofs, vegetation should grow to cover the soil surface, usually within two years after it is installed. Extensive vegetated roofs generally have three to six inches of engineered growing media and are designed to be self-sustaining over time. Drought tolerant plants, usually succulents, are planted and grow quickly over the soil surface. Most of the succulents—Sedum—have adventitious roots, meaning they can form new roots at the stems and leaves. Cutting back healthy plant material, distributing across the bare areas of the roof and irrigating for a few weeks is an economical method of re-establishment.

Engineered growing media is comprised of lightweight aggregates and minimal amounts of organic matter. The growing media is designed to be lightweight, not decay over time, and needs little amending to provide adequate nutrients to plant material.

The vegetated system can be walked on from time to time, but should not be used in a highly recreational setting. Walkways made of pavers or gravel ballast may be installed to guide maintenance workers to mechanical equipment.

Many times, the primary reason extensive green roofs are integrated into the building is to capture storm water. Calculations are done on a project basis to satisfy local ordinances, or to apply for green building, such as LEED, incentives. In this instance, it is important for as much of the roof to be covered with vegetation as possible. Overall, green roofs can retain and detain 60-100% of rainfall.

Intensive green roofs are more elaborately designed roof landscapes, such as roof gardens and underground parking garage roofs that are intended for human interaction. The growing media starts from about 8-12″ and can range to 15′ or more, depending on the loading capacity of the roof and the architectural and plant features that the building owner desires. Maintenance will need to be more frequent, resembling the needs of a typical ground landscape.

Aesthetics and usage…
Visually, one should expect the green roof to behave similarly to the landscape of the surrounding area. For example, the plants will go dormant in the winter around the same time the tree canopy loses its leaves. Some plants will die back and others are evergreen, but colors change to dark reds and browns. In the spring, growth will resume with warm days and rain showers, and plants will bloom throughout the growing season.

One matter that should be resolved between the owner and the facility staff ahead of the planting of the green roof is the expectations of the vegetated roof, including usage (as in, who will be visiting the roof).

A roof system that is only visited by roofers and mechanical crews providing periodic maintenance will not need to be maintained as frequently for aesthetics as one that is viewed daily through office windows or entertains frequent visitors.

Extensive systems may be designed with a specific pattern, often achieved from a bird’s eye view. For example, representation of a theme for the building or client may be incorporated in the design. Many succulent plants are aggressive growers in this setting, and more frequent maintenance is imperative to achieve the desired aesthetic goals.

Irrigation…
A newly installed green roof should be maintained monthly, as necessary. Temporary irrigation should be available for the first few months, and should saturate the system at least two or three times a week. Thereafter, irrigation should be weaned, with the intent that the vegetation will remain self-sustaining within the first year.

During hot and dry spells, the system should receive water. While irrigation seems counter-intuitive in a roof designed to capture and detain stormwater, irrigation is mandatory in order to have a healthy and functioning green roof system long-term.

Plant and media concerns…
Initially planted and allowed to fill in over time, there is an opportunity for unwanted plants to germinate, grow and seed themselves on the roof. For projects in temperate climates, weed pressure begins in early spring and continues throughout the year, including winter. In small green roofs, hand weeding may be the fastest and most effective method of removal. However, for larger projects, protocols should be agreed upon for use of alternative weed management techniques or approved chemicals.

Approved growing media is comprised of approximately 20% organic matter. Over time, German green roofs have shown the organic content is reduced to 7%. Within the first several years, additional fertilizer should be applied. The FLL German standards, as well as ASTM, recommend a very low rate of application, using slow release fertilizers. Commercially available organic fertilizers are an option.

Seasonal issues
The growing media should be evaluated to ensure proper drainage throughout the green roof system, and off the roof. Yearly pH testing will tell when the growing media should be amended with lime. One sign that the green roof is too acidic is the presence of moss. It is up to the owner whether to keep the moss. It is probably harmless, and can create a lush green color in the cool season, but it may not be desired by the roof owner.

Spring responsibilities include broadcasting with a slow-release fertilizer. Removing leaves and branches is recommended, but not necessary. Periodic weeding in the summer season will keep weed pressure low. In preparation for winter, irrigation water lines on green roofs need to be drained and cleaned before a freeze. During a mild winter, weeds should be pulled before they are allowed to flower and set seed.

In summary
Green roof maintenance is as critical to the success of a green roof as plant selection, climate and other installation criteria. Without regard for the care or maintenance of a green roof once it has been installed, building and facility managers may not be adequately prepared to protect their building’s asset long term. Moreover, they may not be able to reap the inherent benefits associated with green roofs and the role they play in sustainability. UM


Angie Durham is a green roof specialist with Magco, Inc. For more information on green roofs, contact her directly through Tecta America Corp. Telephone: (866) 832-8259; or visit www.tectaamerica.com or www.greenroof.com

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6:00 am
January 1, 2007
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Utilities Manager: Energy Cost Control: How Much Will You Save?

The question that industrial decision-makers will most frequently ask about energy cost control is “How much can I save?” The question that really should be asked is, “How much am I likely to save?”

How much can I save?
The average industrial facility can expect to reduce its energy consumption somewhere within a range of 10% to 20%. Keep in mind that this describes an average range of expectations. Some facilities can capture more savings, some less. If you want a more precise number, you will need to conduct an energy audit—a facilitywide study of energy inputs, uses and losses.

Keep in mind that energy audits are a very human process, refl ecting the skills and experience of the team that conducts them. Ten different audit teams can examine the same facility—and develop 10 different sets of recommendations. Their findings may generally overlap, but each report will present different cost-benefit evaluations, suggested priorities or even unique findings. I say “10% to 20%” because of the following sources:

  1. Refer to the U.S Department of Energy fact sheet entitled “Save Energy Now in Your Motor Systems.” It includes comments about all potential sources of industrial energy savings, not just motors. According to this document, plants with an energy management program already in place can save an additional 10% to15% by using best practices, as recommended by the U.S. Department of Energy. Remember, that’s in addition to an existing energy management program.
  2. Refer to “Energy Loss Reduction and Recovery in Industrial Energy Systems.” This U.S. DOE document claims, on page 22, that industry’s overall energy consumption can be reduced by 24% through efficient technologies and practices. Several appendices in this report share industry-specific claims for energy savings potential. This cannot be overemphasized: no single industrial facility is “average.” Each facility features a unique design, purpose, product mix, operating schedule, maintenance history and work habits. Savings potential varies accordingly.

How much am I likely to save?
I wish more people would ask this question. My answer involves the following checklist. The more times you can answer with a “yes” to these questions, the more likely you are to achieve savings (or the higher you will be on that range of potential savings). 

0207_um_outsidethebox1Will you conduct an energy audit?

0207_um_outsidethebox1 Will your staff know the purpose of the audit and not be intimidated by it?

0207_um_outsidethebox1 Will your facility support energy cost control as an ongoing process rather than as a one-time project?

0207_um_outsidethebox1 Will your top management stand behind the goals and accountabilities set by an energy management plan, or ignore them after a year has passed? 

0207_um_outsidethebox1 Will your staff be responsive to energy awareness training?

0207_um_outsidethebox1 Will operations, maintenance and procurement be willing to change the way they do things by incorporating energy best practices into their work habits? Take heart. No one answers “yes” to all of these points. But, as you achieve more “yes” answers, the more you are likely to save.

crussell@energypathfinder.com

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239

6:00 am
January 1, 2007
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Utilities Manager: Cavitation Is Increasing Your Utility Cost

Show me a cavitating pump and I’ll show you an energy hog.

Most operating facilities in today’s marketplace are aware of the effects that cavitation has on mechanical pump reliability. Reduced rotor stability, shorter bearing life and the ever-popular premature mechanical seal failure are just a few of the more common manifestations. If, however, we were to look at the total cost of ownership for a cavitating pump, including its reduced efficiency and subsequent higher utility costs, we would see that this daily operating expense mounts up to a huge waste of both energy and money.

0207_um_pumpingefficiencies1Unraveling the issue
“Best in Class” companies evaluate the purchase of a pump based on Total Life Cycle Cost (TLCC). Pump efficiency will be one of the variables that weigh into this calculation. A specified margin for Net Positive Suction Head Required (NPSHR) and a range for Suction Specific Speed will be specified in their engineering guides. Again, these pump characteristics weigh into the purchasing decision, but can ultimately be overridden during the project development cycle due to delivery schedules and initial purchase price. The TLCC philosophy applies to new pumps being purchased today.

What about the large population of pumps in service today that are 20, 30 or even 40-plus years old. TLCC and pump reliability were not even on the map when these units were purchased and commissioned. Their inefficiencies and diminished reliability are further aggravated by being operated at off-design conditions resulting from process demand changes that occurred after the pump was installed.

Further confusion is added by the term NPSHR. Keep in mind that the design goal of a pump manufacturer is to design a pump that meets the broadest range of operating conditions possible rather than designing a pump to meet your specific hydraulic needs.

A manufacturer’s certified performance curve will list the NPSHR for the pump. This curve is not the point at which incipient cavitation occurs in the pump. Rather, it is the point at which cavitation is significant enough that the pump head is reduced by 3%. This is determined by testing the performance of the pump with the suction fully fl ooded. The pump is later retested at known fl ow rates and the suction valve is pinched off. The NPSHR curve is then plotted once the head meets a 3% reduction at the target fl ows. This is accepted in industry because the 3% condition is typically repeatable independent of process conditions (fl uid, temperature, etc.). Consequently, many pumps in service today are being operated within the prescribed NPSHR margin, yet cavitation still exists-as evidenced by the damage found on their impellers during a pump repair.

Reliability teams fight to keep the pump available, but rarely get the opportunity to affect real change, since the cost of a design modification is thought to be too high. Pumps are pulled for maintenance. Cavitation is evident, as seen in Fig. 1. The affected area of the impeller is weld-repaired or, occasionally, the impeller is replaced with a more cavitationresistant metallurgy. The pump is reassembled and placed back in service. If a design change is considered, it usually is dismissed due to price-without the energy savings ever having been considered.

0207_um_pumpingefficiencies2

This is cavitation
The published or known efficiency of the pump includes the hydraulic inefficiencies that are sufficient to cause this kind of mechanical damage to the impeller. As the fl uid being pumped drops below the fl uid’s vapor pressure, it rapidly fl ashes from a liquid to a gas and back to a liquid. This is cavitation. The subsequent shock waves carry enough energy to literally rip a minute piece of metal from the impeller vane. Over the course of operating, these minute pieces of removed metal compound upon each other, leading to the damage shown in Fig. 1. Additionally, the vibration associated with these shock waves is transmitted down the shaft and its cumulative effect wipes out the mechanical seals and bearings. This is well known and discussed. One common solution is to install larger diameter or stiffer shafts with bigger bearings to try to extend the mean time between repairs (MTBR). API-610 has taken this approach in the last few revisions, which places a greater emphasis on the L/D ratios and other shaft stiffness design criteria.

Dealing with hydraulic inefficiencies
What we often fail to recognize is that hydraulic inefficiency from cavitation is costing us horsepower (HP) every time the pump is placed in service. In other words, pump users often are literally paying to tear up their equipment. With the availability of Computational Fluid Mechanics (CFM) and Computation Fluid Dynamics (CFD), the existing inherent inefficiency in a pump’s hydraulic development can be reduced-and in many cases eliminated.

CFM and CFD allows a qualified individual to evaluate the suction characteristics of the impeller before any manufacturing takes place. Adjustments can be made to the inlet eye diameter and/or the inlet vane angles that can dramatically improve these characteristics. Multiple modeling runs can be examined to optimize the impeller geometry around your specific desired hydraulic condition.

There are many different ways to calculate the annual savings, but for this discussion we will use the following equation:

Assigning some values to the above variables, we can use a typical pump efficiency of 69% and assume a modest 4% efficiency increase. Let’s say that we have a 200 HP motor with a rate load of 175 HP. Using a unit availability of 96% will give us 8,410 hours of operation. From the Energy Information Administration [Ref. 1], we find that in October 2006, the average retail price of electricity for an industrial user in the United States was 6.12¢ per kilowatt hour. Thus, the annual utility savings would be $6,098. By itself, for a single pump, that’s a nice piece of change. Think, though, what this type of savings could add up to for operations with multiple pumps.

What to do with about your hogs
If you have a cavitating pump, don’t just upgrade the metallurgy, stiffen the shaft and move on. Instead, eliminate or minimize the cavitation by redesigning the suction characteristics of the impeller. 0207_um_pumpingefficiencies3The savings detailed in this article are strictly a reduction in the cost of plant utilities for one pump. They do not take into account the overhead to maintain additional HP consumption. If the impeller needs to be replaced because of cavitation damage, then that cost should be removed from the incremental cost of a design modification. Once you couple in the increased MTBR and reduction in the maintenance budget, the total savings often make design changes practical.

Reference

  1. Energy Information Administration ( http:// www.eia.doe.gov/cneaf/electricity/epm/ table5_6_a.html )

Richard E. Martinez is vice president of operations with Standard Alloys, in Port Arthur, TX, a company he joined in 1989 as director of engineering, following several years working with the Lower Colorado River Authority (LCRA). Under his direction, Standard Alloys developed the capacity to perform custom design of impellers, volutes/diffusers and return guide vanes. Promoted to his current position in 2006, he now is responsible for operation of Standard Alloys Engineering, Pattern Shop, Foundry and Machine Shop/Repair Center. Martinez, who holds a B.S.M.E. from Lamar University, has published a number of articles related to pump performance, modifications and enhancements. For more information, telephone: (800) 231-8240 x 312; e-mail: richardm@standardalloys. com; Internet: www.standardalloys.com

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