HVAC

Solutions for tight spaces in HVAC design

An historic university building had tough mechanical space requirements. Here’s how these challenges were met.
By Lincoln Pearce, PE, LEED AP, BEAP, IMEG Corp, Des Moines, Iowa January 30, 2019

The mechanical systems employed in the Marston Hall at Iowa State University (ISU) in Ames renovation provided more than the energy efficiency being sought for the project. The chilled beam/radiant heat with dedicated outside air system (DOAS) and associated mechanical infrastructure also met the goal of physically integrating 21st century systems within a facility that was not intended to house them—and still retain as much of the original building architecture as possible.

Specifically, the chilled water and steam piping and the ducting of the DOAS unit required much less space for transferring the cooling and heating energy compared to that required for a traditional central AHU system relying on air for heating, cooling, and ventilating. The reduced space requirements of the chosen systems were a perfect fit for Marston Hall.

Figure 5: Marston Hall’s DOAS unit provides the minimum ventilation air required by code. To the right—above and below the walkway—is the location of the former hot deck/cold deck tunnel. Courtesy: IMEG Corp.

Figure 6: This pre-renovation photo shows Marston Hall’s existing tunnel stub looking west. Courtesy: IMEG Corp.

The early 20th century, Second Empire-style building structure was characterized by low floor-to-floor heights, tall windows, and an original masonry system that integrated air supply and relief shafts within thick corridor walls. A hot deck/cold deck tunnel (split top/bottom) ran under the ground floor central corridor and fed a series of vertical masonry shafts within the structural walls that served individual upper spaces throughout the building’s four floors. The original mechanical design—a pneumatically controlled multizone system—was impressive for a 1903 building.

A similar utility distribution strategy was employed in the renovation to bring the modern and energy-efficient systems into the building. The hot deck/cold deck tunnel below the ground floor hallway was cleared out to create a walkable service corridor. A majority of the mechanical, electrical, and plumbing (MEP) ducts, pipes, and associated services, which originate from central mechanical rooms in the basement, are distributed in this lower level to five main vertical chase locations throughout the floor plate. This allowed the horizontal distribution on each occupied floor to be minimized and contained within small zones on each floor. This allowed ceiling heights to remain higher than if larger utilities had been piped and ducted across the floor plate on each occupied level (see Figure 7). Cutouts within the steel beams for utility routing further enabled maintaining higher ceilings.

Figure 7: The Marston Hall mechanical system schematic is shown. Courtesy: IMEG Corp.

The DOAS unit also required much less space compared to bringing in a much larger central air handling unit (AHU). Even so, to get the new DOAS unit into the basement, the team designed and installed a new, precisely sized opening in the existing exterior wall—with clearances down to the inch.

Another important space-fitting solution was required to maintain the architectural integrity in the east and west vestibules, where substantial amounts of outside air entering the building precluded the practicality of using chilled beams. Instead of chilled beams, the engineering team employed fan coil units in these areas; however, there was not sufficient room for ducting the supply air over the vestibule entry doors.

Figure 8: To get the new DOAS unit into Marston Hall’s basement, the team designed and installed a new, precisely sized opening in the existing exterior wall. Courtesy: IMEG Corp.

To solve this problem, the team custom-designed a supply louver/service door (referred to on the project as an SLS door) to solve the supply air distribution challenge and provide excellent service access to the equipment. In each vestibule, the fan coil unit was housed directly behind a full-size, architecturally compatible hinged access door. A louver in the door acts as the supply grill, with a small duct plenum on the back side of the door that mates up with the supply duct from the fan coil unit when the door is closed. Return air is then ducted in the wall cavity to the floor landing above.

Allowing space for access to the mechanical systems for operation and maintenance also was integral to the Marston Hall design:

  • The DOAS unit, main mechanical pumps, and heat exchangers are all located in the mechanical space in the building’s reconfigured basement. Exterior access is available through the new door built for the DOAS installation, and interior access available via the mechanical room elevator and stair. Adequate space is provided for coil pulls, filter changes, and regular maintenance.
  • The air handler serving the auditorium is located in a mechanical room adjacent to the auditorium, on floor level off of the central corridor.
  • Fan-powered variable air volume (VAV) boxes are located above accessible ceilings for filter changes.
  • Chilled beams and perimeter radiant convectors only require periodic cleaning and are accessible throughout the building.
  • During the construction of the project, the design team, contractors, and owner worked together to place and map isolation valves and control valves for optimized access and clearance. The isolation, control, and drain valves serving the perimeter heating system in the auditorium are located behind an access panel at floor level, as opposed to above the high auditorium ceiling.

Figure 9: An underfloor air displacement system for cooling and ventilation is employed in Marston Hall’s large auditorium, where chilled beams would not be practical. Courtesy: IMEG Corp.


Lincoln Pearce, PE, LEED AP, BEAP, IMEG Corp, Des Moines, Iowa
Author Bio: Lincoln Pearce is a senior principal and client executive for IMEG Corp. where he leads the firm’s commissioning team. He has been with IMEG his entire career, serving as project executive, project manager, systems concept engineer, and lead mechanical engineer for many of the firm's large, complex, and unique projects.