More space, more people, more conventions.

The expansion of the Salt Palace convention center is certain to bring more dollars to Utah, convention officials say.

Backing that argument are new projections commissioned by the Salt Lake Convention & Visitors Bureau, showing an expanded Salt Palace will increase direct visitor spending to $229 million annually, up from $189 million today.

On Tuesday, sketches of the larger convention center were unveiled to members of the Salt Lake Convention & Visitors Bureau board of trustees and the Salt Lake Chamber's board of governors.

Already, four major bookings have resulted since expansion plans were announced:

• American Chemical Society, March 2009, 14,000 people.

• Society of Toxicology, March 2010, 5,000 people.

• American Society for Mass Spectrometry, May 2010, 6,000 people.

• Rotary International, June 2011, 21,000 people.

In addition, the twice-yearly Outdoor Retailer, Salt Lake's biggest trade show drawing 35,000 visitors annually, announced in August a renewed five-year contract to hold its show in Salt Lake City based in large part on the Salt Palace expansion plans.

"If our facilities are not competitive today for the future we'll miss those bookings," said Dianne Nelson Binger, chief executive of the bureau. "With the expanded meeting space we could book about another $40 million worth of direct visitor spending annually."

Kelly Matthews, economist for Wells Fargo and chairman of the Salt Lake Convention & Visitors Bureau, called the expansion an engine of economic growth for the state.

The indirect spending brought in by conventions, Matthews said, is at least double direct spending figures, amounting to hundreds of millions of dollars multiplying through the economy.

Construction is under way on an underground Salt Palace parking facility that will add 400 stalls — accessible by 300 West — to the existing 600 stalls off 200 South. The expanded underground parking structure will enlarge a plaza area floor slab to the west of the convention center. The first phase, which will cost $15 million and is funded by Salt Lake County, will be complete this summer.

The remaining phase — estimated to cost $58 million — will add 80,000 square feet of new meeting space, a 145,000-square-foot exhibit area and more loading docks.

Just who will pay for the second phase is uncertain.

It is anticipated that the Legislature will be asked to increase hotel and restaurant taxes to fund the project. However, Alan Dayton, a consultant to Salt Lake County, said no legislation yet exists to raise taxes.