The 11 grandchildren who are heirs to the Heurich real estate and brewery fortune have sold the Hertz Rent-a-Car garage at 1622 L St. NW for $9.3 million to Realinvest, which plans to demolish the structure and erect an office building.

James C. Martin, a real estate broker who is married to one of the grandchildren, Corinne Heurich, said it took six years of complex negotiations to complete the sale of the property.

"I had it 98 percent finished before I showed it to them," Martin said of the heirs. "By and large, we didn't have any problems."

In the end, Martin said he negotiated a deal under which Hertz has leased another garage property owned by the Heurich heirs, a facility at 11th Street and New York Avenue NW that most recently has been used as an Exxon gas station and parking lot.

John Blake, Hertz Corp.'s vice president of properties and facilities, said the firm has a 19-year lease on the New York Avenue property, the same length of time that was left on its L Street site. He said workers are renovating the garage and installing a rental office on the property, which is across the street from the D.C. Convention Center. It should be open by Dec. 1, he said.

In addition, he said Hertz will open a temporary downtown office at 1660 L St. NW in a building next to its longtime garage, and then eventually reopen a rental office in Realinvest's new building.

Pierre Tilmans, a Realinvest partner, said he hopes to start construction on the 180,000-square-foot office building in January. He said the $40 million structure should be finished in mid-1987.

The Heurich heirs are grandchildren of Christian Heurich, who died in 1945 at the age of 102. Their father, Christian Heurich Jr., died six years ago. The senior Heurich founded a brewery here in 1873 on 20th Street and later moved it to the site where the Kennedy Center now stands. The brewery closed in 1956, and later the junior Heurich and two sisters donated part of the brewery site for the construction of the Kennedy Center.

IN THE BUSINESS . . . The Fairfax County Redevelopment and Housing Authority has authorized the issuance of an $8.7 million multifamily housing revenue bond for the purchase and rehabilitation of the 266-unit Grand View Apartments at Columbia Pike and Carlyn Spring Road . . . The Federal Home Loan Mortgage Corp. (Freddie Mac) has started selling 15-year mortgage participation certificates on a daily basis, just as its 30-year certificates are sold. Since June 1984, Freddie Mac has sold $3.9 billion of the 15-year certificates . . . Commercial Real Estate Women is giving its first annual award for contributions to the real estate community and quality of life here to the Franklin Square Association for its efforts in revitalizing the area around the park of the same name.

PERSONNEL FILE . . . HBW Group, a Rockville-based commercial and industrial real estate firm, has named Thomas J. Bundy as its new president and chief executive officer . . . James L. Eichberg, president and director of Smithy Braedon Co., has been named 1985 Realtor of the Year by the Washington Board of Realtors . . . John M. Derrick Jr. of Potomac Electric Power Co. is the 1985-86 president of the Washington Building Congress . . . Bernard R. Shepherd has been named chief financial officer of J. E. Robert Co., a real estate management and marketing firm, while Mark E. Jessell has been named senior asset manager . . . Hadid Investment Group Inc. has named Stuart H. Gary vice president and general counsel . . .Kaempfer Co., a real estate development and management firm, has appointed John G. Tyers as marketing director . . . Cadillac Fairview Urban Development Inc. has named John G. Shoosan as a vice president and manager of its downtown D.C. office and David D. Fitch as vice president and manager of the firm's suburban projects . . . The Fairfax County Board of Supervisors recently presented its first annual Exceptional Design Awards to 20 designers, builders and developers. The honor awards went to Dewberry & Davis for the Times/Journal Co. headquarters and the state Division of Motor Vehicles express offices; to Kamstra, Dickerson & Associates Inc. for the Salvation Army Adult Rehabilitation Center, and to Donald, LeMay & Page for the concession and restroom complex at the Occoquan Regional Park . . . Harvey Rosendorf is the 1985-86 president of the Montgomery County Board of Realtors.