Apollo Energy Control, Inc., based in North Palm Beach, Fla., and represented in this area by Dewey W. Chapman in Fairfax, will demonstrate a working model of a solar energy domestic hot water and pool heating system at the Tysons Corner Shopping Mall, beginning Monday through May 7. Slides and tapes of solar installations in other parts of the nation will be used in the demonstration, which also will be in the National Housing Show scheduled to begin May 10 at the Sheraton Park Hotel.

Freeman W. Williams, executive vice president of Ambric Testing and Engineering of Virginia, has been elected president of the Washington Area Council of Engineering Laboratories.

Margaret D. Martin, a realtor associated with Jack Foley Realty, Inc., has been promoted to sales manager of the firm's office in Silver Spring.

The Community Associations Institute, based in the District, has elected William Don Sally of Chicago as president of the group, which is concerned with homeowner association management. Francis B. Francois, a member of the Prince George's City Council, was elected a vice president of Home Federal Savings & Loan Association here, was elected treasurer of the national organization.

Wellborn Management, Inc., a real estate firm based in Reston, has been granted a home improvement contracting license in Fairfax County.

Standard Court, East and West, a new office-warehouse-distribution center, now is under construction in the Oakland Ridge Industrial Center at Columbia. Standard Medial Systems, Inc., is the developer and Glen Arm Development Construction Co. is the builder of the facility designed by Thomas M. Nichols.

The fifth annual Takoma Park House and Garden Tour will be held Sunday, May 1, from 1:30 to 5 p.m. Turn-of-the-century houses will be featured and minibus service will be provided. Tickets are $2.50. The tour will begin at the municipal building at 7500 Maple Ave.

Snider Bros., Inc., announced that it has leased the landmark Takoma Theater at 4th and Butternut streets NW to KB Theaters, which has remodeled and reopened the theater to feature Spanish-speaking films. In 1970, the Snider firm handled the sale of the property from RKO-Stanley Warner Theaters to the current owner, William Walowitz.

J. Edwards Co., Inc., a residential realtor firm in Alexandria, has joined ERA, a nationwide network of brokers offering an electronic phot listing service to clients. Sandra Lenthan is president of the Edwards firm.

Jeanne Hester has been named sales manager of the home building division of the Ryland Group's Columbia operation. She is the first woman to be named a divisional sales manager by Ryland, which she joined a 14 months ago as a sales agent.

The Northern Virginia Board of Realtors and the Arlington Distributive Education Service are offering courses in various aspects of real estate in evening courses. For information, call 558-2581.

The Chas H. Tompkins Co. announced that it is the only local general contractor to receive the Master Builders' Association annual safety award for outstanding safety achievement in 1975.

International Developers, Inc., and MAP Construction Co. are developing 90 houses in the Oakton area of Virginia. The subdivision is called Cob Hill. Prices begin in the $90,000s.

E. Gaye Gaummitz has been named manager of the new office of Century 21/Preferred Properties in Annandale.

A day-long seminar on rehabilitation of apartments will be held May 18 at the Ramada Inn in Lanham by Chapter 8 of the Institute of Real Estate Management. Loren M. Simkowitz will be seminar leader. For information, call 474-6207.

Thomas J. Bertke has been named vice president and sales manager of the new office of Ingham and Associates, Inc., at 7702 Norfolk Ave., Bethesda.

Walker & Dunlop, a Washington mortgage banking firm, arranged a $700,000 loan for the 1111 N. Capitol Street building with North American Life Assurance Co. The four-story office-warehouse building had 175,000 square feet of space leased to GSA for the Smithsonian Institution. Jack Stone is the owner of the building located six blocks north of the Capitol.

Barnes, Morris & Pardoe, Inc., handled the sale of the Duke Street Shopping Center in Alexandria to Davis Memorial Goodwill Industries. Federal Realty Investment Trust sold the shopping center, in which Goodwill will be a principal tenant, for $320,000.