Prescription for Energy Savings: Reducing cost and consumption with upgraded cooling tower fans

by Katie Daniel | May 11, 2015 10:38 am

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by Cheryl Higgins
The average hospital uses three times the energy of typical commercial buildings, and U.S. medical facilities spend $8.8 billion annually on energy. Between lighting, medical equipment, HVAC, and plumbing, energy consumption in medical facilities outpaces any other type of building. For large hospital systems, annual costs can reach into the tens of millions of dollars—no small amount in an industry of thin margins.

With these startling statistics it is no wonder hospitals are searching for ways to lessen their energy costs. Hospitals recognize energy conservation is a priority and also realize the benefits, both to their bottom line and the environment. One initiative that may be implemented is upgrading the fan motors in cooling towers to more efficient systems, reducing costs and maintenance.

Cooling a campus
Below a campus’ sidewalks and streets lies a vast network of interconnected pipes that carry chilled water to buildings. This water flows through the pipes seven days a week, 365 days a year, but is especially important during the hot and humid summer months, when it helps to keep a diverse array of campus buildings cool.

Larger buildings and multiple campuses usually use a chiller plant to provide cooling. In such systems, chilled water is centrally generated and then piped throughout the building to air-handling units (AHUs) serving individual tenant spaces, single floors, or several floors. Ductwork then runs from each air-handler to the zones that are served. Chilled water-based systems result in far less ductwork than all-air systems because chilled water piping is used to convey thermal energy from the point of generation to each point of use.

Having a chilling process centralized is easier and more sustainable to maintain and operate as opposed to air-conditioning units on each campus building.

The cooling tower’s primary function is to remove heat from the condenser water system transferred from the campus electric chillers. During the air-conditioning cycle, heat is removed from the campus buildings via the chilled water loop; that heat is then transferred to the condenser water system and ultimately removed by the cooling tower.

Efficiency, sustainability, and conservation are important considerations for all buildings, not just healthcare facilities. At the core of many utility operations are cooling requirements calling for the use of a cooling tower. If allowed to operate in an uncontrolled environment, the water and energy efficiencies for such additions can be costly. Further, an uncontrolled cooling tower puts the asset at risk for high repair costs and downtime for production operations. One thing is for certain, for any business the cooling tower is a significant source of capital and operational expenditures.

The cooling tower is responsible for rejecting unwanted heat from the condenser water loop to the air outside the building. Proper sizing and control of cooling towers is essential to efficient chiller operation.

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In spite of the impact on facilities, cooling towers are among the most neglected equipment. Maintenance and engineering managers might understand a cooling tower’s role, but they may not fully realize the importance of keeping them operating at peak performance levels.

Reducing costs
One of the areas where overhead can be contained or reduced is in the operation of the chilled-water systems that support air-conditioning throughout the campus or facility, specifically the cooling towers.

Mechanical-draft cooling towers consist of one or more mechanically driven fans. These fans usually have multiple blades ranging from 0.6 to 10 m (2 to 33 ft) in length. An electric motor runs the blades at relatively low speeds through reduction gearing so they move large volumetric flow rates at relatively low static pressures.

Although cooling towers are relatively inexpensive and normally consume around 10 percent of the whole system’s energy, their operation has significant effect on the energy consumption of other related subsystems. Optimizing cooling tower performance will not only increase the tower efficiencies, but also have a direct affect on other subsystems.

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A poorly operating cooling tower reduces chiller efficiency and eventually leads to system failures. Most chilled-water plants have excess capacity, so one or more cooling towers are not operating during low-load hours. To make the most of existing cooling towers, condenser water can be run over as many towers as possible, at the lowest possible fan speed, and as often as possible.

Cooling tower fan motors are a major source of electricity use, as well as a generator of significant noise. Most towers are installed with a single- or two-speed motor. However, as the load on the cooling tower decreases, the fans might operate at a speed not necessary for that load, hampering energy efficiency.

Much has happened in recent years to give managers tools to improve motor efficiency. The federal government has developed energy standards manufacturers must meet. Replacing standard-efficiency motors with high-efficiency ones will reduce the energy requirements for that motor by two to eight percent. While that might not seem like a major improvement, depending on the motor’s horsepower and the number of hours it operates annually, energy savings can be significant.

The development of high-efficiency motors was only the first step. Premium-efficiency motors now meet even higher energy-efficiency standards and can produce even greater savings. A side benefit for both energy-efficient and premium-efficiency motors is to meet the energy standards, they require higher-quality components and more exacting manufacturing processes, resulting in a better motor.

High-efficiency motors can not only save money, but they can also make money. Some utilities offer rebates for installing these motors in new or retrofit work. In many cases, an upgraded motor can pay for itself in less than a year.

Upgrading with high-efficiency motors is a major part of the U.S. Environmental Protection Agency’s (EPA’s) effort to improve energy efficiency. Many resources offer comprehensive information on state, local, utility, and federal incentives that promote renewable energy and energy efficiency. Whether in a new design or an existing application, upgraded motors offer numerous advantages when used in cooling towers.

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Government’s commitment
As part of the Obama administration’s effort to double energy productivity by 2030 and reduce carbon emissions in commercial buildings, the Department of Energy (DOE) recently announced $9 million to encourage investments in energy-saving technologies that can be tested and deployed in offices, shops, restaurants, hospitals, hotels, and other types of commercial buildings. The funding will facilitate the implementation of market-ready solutions across the United States to improve commercial building energy efficiency, with a goal of demonstrating upwards of 20 percent savings across various approaches.

Each year, the country spends $400 billion to power buildings—about half on commercial and industrial facilities—which is equal to half the energy in the U.S. economy. Reducing energy waste in these buildings—and doing so cost-effectively—will save more than $80 billion on energy bills annually.

The DOE’s Better Buildings Challenge, a cornerstone of the Climate Action Plan, is partnering with more than 200 organizations to shape aggressive goals to reduce energy intensity by at least 20 percent within 10 years.

Utility programs
Utility companies’ commercial rebate programs offer financial incentives for commercial, industrial, and agricultural customers to invest in energy-efficient technologies. Standard rebates are available for lighting, HVAC technologies, motors, and motor drives. Custom rebates may also be obtainable for other projects that will save energy, but do not fall into any easily identifiable category. Institutions, such as healthcare campuses, and business are eligible for rebates for virtually any project that can be demonstrated to consistently save energy.

A unique incentive program to Pacific Gas and Electric (PG&E) healthcare customers is the Healthcare Energy Efficiency Program (HEEP), administered through Willdan Energy Solutions. HEEP is an incentive program created to assist hospitals and other healthcare providers install energy-efficient equipment to reduce energy consumption and low operating costs.

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There is a wide range of energy-efficiency measures that qualify for HEEP incentives, including those associated with:

• lighting;
• HVAC;
• variable speed drives;
• motors;
• chillers;
• kitchen hoods;
• occupancy sensors; and
• energy management systems.

This is just one example of the countless incentive and rebate programs available to healthcare organizations to help in the investment of energy-efficient equipment that will lessen energy consumption and costs.

Cheryl Higgins is product marketing manager with Leeson Electric, a manufacturer of electric motors, mechanical and electrical motion controls, and power generation products serving markets throughout the world. She has more than 30 years of industry experience managing technical and applications teams. Higgins can be contacted by e-mail at cheryl.higgins@leeson.com.

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