New Central Library

Des Moines Library East viewDes Moines LibraryLibrary North View

Name : New Central Library

Location : Des Moines, Iowa

Architect : Herbert Lewis Kruse Blunck Architecture

Award Won : 2006 ABC of Iowa Excellence in Construction Award

This project presented challenges right from the beginning. The heart of the HVAC system consists of 3 large Custom Air Handling Units that are installed in two mechanical rooms below grade. These units weighed a total of 128,520 lbs and came in 10 sections.

AHU #1 (the largest of the three) weighs 71,000 lbs alone, and has a footprint covering 905 square feet. Due to the size of these units, it was impossible to get them through any of the openings that would remain once constructed. They were also too large to span with shoring, so the structural floor could be poured above them after they were in position.

After much consideration, we devised a plan that solved many problems. We would wait till the east section of first floor was poured, cured and re-shored; then set the units into the open section to the west of the lower level. We then used 16 custom made dollies to roll the units underneath the finished pour to the east. Once the entire floor was poured, and all shoring removed, we once again moved the units to their final location and assembled the sections.

This project specified that the supply ductwork have an air leakage test performed. With around 1,300 feet of supply duct running through the unconditioned parking garage, you want to make sure you are not wasting energy by leaking it outdoors. Once we were done testing the supply air ducts, we had a total leakage of 1,415 CFM, which, at first, sounds like a lot. However, when you are working with a total delivery of 100,250 CFM, that’s just 1.4% and 25% less than specified.

The solution came through teamwork. Install a row of legs, then a run of duct, and repeat the process. Cooperation between the flooring contractor and us was critical for both parties to complete their work. The perimeter of the building has 2,200-feet of continuous aluminum floor grille with mitered corners with a separate supply plenum fed from fan coils to treat the exterior glass walls. The shape of this building made it impossible have the corners of the grilles factory cut, so we ordered the parts longer than needed, and cut the miters in our shop to fit the building perfectly.