Running Out of Steam

As facilities age, school districts and other educational institutions are paying the price for having poorly maintained facilities and systems. Many buildings that contain 20- to 30-year-old mechanical systems are inefficient, need significant repairs and may even produce safety concerns.

In general, buildings constructed between 1950 and 1980 use boiler-generated steam heat. At the time those schools were built, boilers were the cost-effective, energy-efficient choice most frequently specified. Now, more energy-efficient systems are available.

Schools that performed the recommended maintenance over the years have systems that may still be reasonably effective. But many schools have historically lacked the staff and operating funds to adequately maintain their equipment. In those cases, preventive maintenance has been limited or non-existent, and repairs piecemeal at best.

How do you know if your system has problems? How do you determine whether to repair or replace it? What preventive maintenance would help keep your system working longer and more efficiently? Here are some answers.

Symptoms of deterioration Have your heating bills increased over the past few years-with increases that you can't link to additional building space, rate increases or other reasons? If so, that may be an indication your heating system is faulty.

A walk through your buildings can quickly identify some of the more obvious problems. Many you can easily see or hear, including:

-Manual boiler controls not functioning.

-Dripping or corroded pipes.

-Worn-out insulation.

-Hot floors (over under-the-floor distribution systems).

-Steam leaks.

-Condensate pumps not running constantly.

-Inordinate amount of untreated makeup water usage.

The maintenance crew or a local consulting engineer may help identify other trouble spots, such as malfunctioning steam traps, leaky flanges or corrosion within the boiler or boiler shell.

Repair or replace? In general, steam heating systems have a useful life of 20 to 30 years. Repair parts are rarely available for systems older than 30 years, so you should probably replace systems at that point. However, spare parts should be readily available for systems purchased since 1980, so these are worth evaluating.

Consider three main areas when deciding whether to repair or replace: the source (the boiler), the terminal equipment (the air-handling unit, heat exchanger, radiator, steam convectors or unit heaters-whichever your facility has) and the distribution system connecting them.

-Boiler. Deciding whether to repair or replace a boiler entails considering both safety and efficiency. It is fair to assume that when you installed your boiler it operated correctly and met the certification standards of the American Society of Mechanical Engineers (ASME). However, without proper maintenance, that certification may have lapsed, and the system may pose a danger. High temperatures and rising pressures could cause explosions.

Among the most common problems is corrosion within the heat exchanger. This occurs when water has not been softened properly. Insufficiently softened water also can cause solids to build up and limit flow. This taxes the system's efficiency.

Some recommendations for common boiler problems:

-If boiler tube sheets are warped or contain holes, replace.

-If boiler tubes leak or are filled, repair; if many are leaking, replace.

-If the heat exchanger leaks, repair; if cracked, replace.

-If the fuel-oil/gas train contains leaks, repair; if it does not meet code or operates questionably, replace.

-If operating and safety controls are questionable, replace.

-If safety valves leak, replace.

-Distribution system. The distribution system consists of supply piping and condensate piping. As a general rule, if less than 20 percent of the system is leaking, repair is probably appropriate; if more than 20 percent, particularly on old systems, replacement may be the better alternative.

Two types of connections (flanged and welded) are typical in steam distribution systems. In flanged systems, both gaskets and valves are potential points of leakage. Leaking gaskets need replacement.

Evaluation of a leaky valve could show that a seat inside the valve can be replaced or that the entire valve needs replacing.

Welded pipe is less likely to leak than flanged. If the pipe is adequately thick, welds that go bad can probably be re-welded. If the pipe is too thin, you must replace it.

Most schools use low-pressure steam (under 15 pounds per square inch) for heating. Consequently, they have gravity-flow systems, where condensate drops rather than rises. For this reason, many distribution systems were placed in crawl spaces below floor level. The maintenance staff or a consulting engineer will need to evaluate whether there is enough room to repair the distribution system.

If you cannot repair the system, you will need to evaluate it further to determine other options. For instance, if ceilings are high enough, you could run distribution piping along them. You could use either exposed or enclosed piping. Burying preinsulated piping outside, in tunnels or in the ground with access manholes for valves is another option.

Ceiling-mounted supply piping requires greater pumping capacity than a gravity-fed system. But absorbing the added cost allows you to avoid the expense and disruption of having to remove your floors to replace the system.

If your system is old enough to have asbestos in the insulation, replace it. The most likely route to take is to encapsulate the old piping and place the distribution piping elsewhere. If you even suspect the presence of asbestos, contact an engineering firm that specializes in asbestos abatement.

-Terminal equipment. To determine the adequacy of terminal equipment, observe how it is functioning. Repair or replace leaky steam coils in air-handling equipment. Repair leaks in radiators or convectors. Check traps for proper operation; if steam is being bypassed, repair or replace them as necessary. Also inspect control valves, strainers and traps. Generally, clogged strainers may cause control valves to have inadequate pressure and flow rates. In radiators, convectors and unit heaters, strainers play an important role. Cleaning these weekly should prevent flow problems.

East St. Louis (Ill.) School District 189 is an urban school district with 26 buildings ranging in age from 10 to 60 years old. Like many districts, most major maintenance repairs occurred only when critical and when funding was available.

Three schools are particularly illustrative of the district's situation. Floor temperatures at Lansdowne Middle School approached 140 degrees F, and floor tile was rising from the heat. The leaky, under-the-floor steam supply system was the cause. District personnel added 700 gallons of untreated makeup water daily. Since supply piping was in a tight crawl space, putting new piping under the floor would have been prohibitively expensive. The solution? Replacement piping runs along classroom and corridor ceilings.

Only one boiler served Dunbar Elementary School. Now two boilers, each half the original's capacity, serve more efficiently. One operates alone until outside temperatures drop to about 30 degrees F; the second provides additional capacity at lower temperatures. Lower natural-gas usage and increased boiler life should result from the higher-efficiency boilers and alternating boiler usage.

Asbestos insulation complicated replacement of deteriorated steam-supply and condensate-return lines at Lincoln Junior High School. Ceiling-mounted supply lines replacedcrawl-space piping; condensate lines now run about six inches above the floor, served by new, easily accessible and maintainable condensate return pumps. Although only one of five zones leaked, all exhibited deterioration. Therefore, one new, exposed main will soon serve the entire building.

TAGS: Energy HVAC
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