Optimizing Steam Systems: Saving Energy and Money in Mexican Hotels

by David Jaber, Alliance to Save Energy

Proper energy management can often save hotels a significant amount of energy and thus, money. In addition to energy-saving opportunities in air-conditioning, lighting, and motors - steam systems are perhaps more important because their maintenance is often neglected. With increased maintenance care and the installation of equipment upgrades that pay for themselves in a few years, an untended steam system can often achieve a 30-40 percent efficiency gain. Since system improvements directly reduce costs, saving $5,000 a year can be equivalent to $10,000 or $15,000 in extra revenue from rented rooms on the overall hotel balance sheet.

Unfortunately, both maintenance staffs, who lack both awareness of efficiency opportunities and sufficient training to implement solutions, and hotel owners, who fail to recognize the importance of steam as a business process, commonly hinder steam energy efficiency. The result is wasted energy and money. By operating a more efficient steam system, not only can hoteliers save money through reduced fuel consumption, they can also achieve a more reliable laundry service, a higher quality cooking facility and a safer workplace.

Steam is still one of the best ways to transfer heat at a constant temperature. Common uses of steam in hotels, hospitals, and universities include:

• Laundry. Steam consumption rates may range above 300 lb/hr when flat iron workers, clothes washing, and drying tumblers or dry rooms are in use. Typical laundry operating pressure is 100 psig.
• Kitchens. Cooking equipment such as steam kettles may need up to 25 psig steam. Plate and dish warmers, as well as food preparation and washing use low-level steam.
• Hot Water. Showers and swimming pools may not use steam directly, however, heat exchangers are employed to generate warm water.
• Space Heating. As with many buildings, room heat is often provided with radiators. To offer occupants temperature control in each room, steam boilers are used to charge a hot water loop.

The Alliance to Save Energy estimates that 25 to 35 percent efficiency gains are a reasonable target for a typical steam system. Table 1 shows the specific areas in steam generation, operation and maintenance, and distribution where efficiency gains can be made. Generally, the majority of the improvement is after the steam is generated – in the operations and maintenance and the distribution systems. These areas have leaks and malfunctioning equipment where steam is being lost and also provide heat recovery opportunities through use of condensers, trap condensate return and heat exchangers.

Hotel boilers commonly run from 50 psig to over 100 psig (with the laundry running). Depending on a variety of factors, boilers in good repair and properly maintained operate at average efficiencies of 76 to 85 percent. These efficiency levels can be improved by 2 to 5 percent with boiler tune-ups and auxiliary equipment when economically justified. When the boiler system is too old to warrant an upgrade, it should be replaced with a more efficient boiler system that offers increased heating surface areas and improved controls for fuel and airflow over the range of load conditions.

Substantial energy losses in the boiler are caused by waste heat literally going "up the chimney," incomplete combustion and heat loss from exterior boiler surfaces. Together, these losses can reach 30 percent of the fuel input, thus hurting efficiency. The three basic strategies for minimizing stack gas heat loss are: (1) Minimize excess air in combustion, (2) Keep heat transfer surfaces clean, (3) Add flue gas heat recovery equipment where justified. Typically, boiler efficiency increases about 1.0 percent for each 15 percent reduction in excess air, 1.3 percent reduction in oxygen, or 40° F reduction of stack gas temperature.

• Always produce maximum steam from process-waste heat-recovery systems. Use waste heat to preheat boiler feedwater.

• Always apply steam to process use at the lowest possible pressure and temperature levels.

• Always expand steam from a higher pressure level to a lower pressure level through the most efficient means possible.

Paying attention to maintenance and operation is key. Improper procedures can wear down fuel handling equipment, throw burners and controls out of adjustment, result in inadequate treatment of boiler water and flue gases, and allow hot condensate to be wasted. In boilers that have not been maintained for two years, a 20 to 30 percent gain of efficiency is immediately possible. Examples of opportunities are listed below:

• Water Treatment. If water is not properly treated, scale build-up can reduce boiler efficiency by as much as 10 – 12 percent and can even result in plant damage.
• Condensate Return. An additional 15 to 18 percent of boiler energy from the steam system is needed to re-heat each pound of cold makeup water.
• Load Controls. Digital, computer-based distributed control systems provide accuracy and reliability and can extend boiler life. Multiple burner controls coupled with air trim controls can result in fuel savings of 3 to 5 percent.

• Check condensers and steam traps to ensure condensate is efficiently returned.

• Install meters and keep track of where the steam is going. Routinely get facility-wide and individual process-unit steam balances.

 

Taking care of the steam distribution system provides one of the best opportunities for savings. The cost of maintaining steam traps and checking piping flanges and valves for leaks requires little or no capital investment. Giving maintenance staff proper training and the time to thoroughly go through the steam distribution system is generally well worth the expenditure.

• Steam Leaks. In a neglected steam distribution system, leaks will be found in the piping, valves, process equipment, steam traps, flanges, or other connections. Fixing steam leaks is a simple, no cost to low cost opportunity to save energy and money.
• Steam Traps. In the absence of a steam trap maintenance program, it is common to find 15 to 20 percent of a plant’s steam traps to be malfunctioning at any given time.
• Insulation. Industrial plants audited under DOE’s Industrial Assessment Center program demonstrated a savings potential ranging from 3 percent to as high as 13 percent of total natural gas usage on average. Through insulation installation, one plant was able to cut steam usage by approximately 6,000 lbs./hour, eliminate the use of purchased fuel, reduce CO2 emissions by 6 percent, and achieve a 6-month payback on investment.

• Establish a program for regular steam trap inspection, testing, and repair. Maintenance and operational personnel should be adequately trained in trap testing techniques. Where ultrasonic testing is needed, specially trained personnel should be used.
• Check steam piping for leaks.
• Check operation of control valves.
• Routinely survey steam systems to identify seldom-used steam lines which could be removed from service

A good resource for more steam system information is the U.S. Department of Energy’s Best Practice Steam Challenge program. 

Contact the program’s information clearinghouse at (800) 862-2086 or  steamline@energy.wsu.edu. 
There is also a website at www.oit.doe.gov/steam.