Remember the tremendous excitement a few years ago when the energy crunch was building up and office-building designers rediscovered windows that can be opened to relieve the strain on a building's cooling system?

Another old idea whose time may have returned is district heating. In use in the United States for more than 100 years, it consists basically of a central plant to heat water or make steam that is then delivered through pipes to customers. Several cities are planning such installations.

The advantages, including not only lower fuel usage but cleaner air, led the Washington-based Urban Land Institute to devote an entire recent issue of its montly publication Environmental Comment to the subject.

According to the institute report, the first commercial district heating operation began in 1877 at Lockport, N. Y. By 1879, steam service was offered in New York City and has been continuous ever since.

Today, Consolidated Edison of New York has the world's largest district heating operation, ULI said; in 1978, that utility sold 32 billion pounds of steam to 2,300 different customers -- 40 percent of all steam sales in the United States.

With the growth of the electricity industry, the real savings came about. Steam is produced in boilers to drive turbines that turn generators to make electricity. Exhaust steam from the turbines can be wasted -- or it can be put into pipes and sold to customers either for industrial use or for heating buildings. By 1909, about 150 companies throughout the country were selling steam from one form or another of that process -- a type of cogeneration.

The fuel efficiency of a simple electric generating plant is usually about one-third. With the addition of cogeneration district heating, that efficiency rises to about 60 percent.

Cheap, plentiful oil and gas whittled the district heating business down to insignificance during the middle decades of this century, both by competing directly with and by accelerating the growth of suburbs, where the scattering of houses made district heating less economical.

Today, however, the idea is being revived. Probably the largest current project is that of the Twin Cities -- Minneapolis-St. Paul, Minn. -- where the planned system will take 20 years to build at a cost of $750 million in 1980 dollars and, when completed, will provide 2,600 megawatts of energy. Other U.S. cities with active projects include Detroit and Piqua, Ohio.

Robert C. Embry Jr., then-assistant secretary of the Department of Housing and Urban Development, is quoted as saying, "District heating, if implemented in the United States now, could save 1 million to 2.5 million barrels of oil or natural gas equivalent a day by AD 2000."

In addition to economy, air purity is improved by having one large burner rather than many small ones. Emissions from a single burner can be monitored and controlled more effectively, while taller stacks better dissipate the emissions into the air.

Lowered fuel consumption is currently saving Stockholm, Sweden, $11 million a year. The city's district heating system serves nearly half its 700,000 population. In 1960, when the system began, Stockholm had an annual sulfur dioxide concentration of 200 micrograms per cubic meter; in 1980, it had fallen to 120 micrograms per cubic meter.

Several European countries, particularly the northern ones, adopted district heating programs after World War II. Today, about 40 percent of the households in Denmark are connected to district-heating pipes; Finland's capital, Helsinki, with some 500,000 people, meets about 65 percent of the demand for heat that way; and the Soviet Union leads the world, with more than 1,000 stations supplying heat and electricity to some 800 cities. Elsewhere, Japan and Canada have strong commitments to the system.

District heating is very minor in the Southland, although a spokesman said the Southern California Edison Co. is studying it intensively. At present, most of SoCal Edison's gas- and oil-fired plants condense and reuse the exhaust steam.

Most American plans contemplate distributing hot water, although Detroit, at least, expects to continue distributing steam as well, since is has an established group of customers.