Case study: Design-assist approach allows for expedited project delivery
After Allegheny Health Network (AHN) identified a need for diverse options focused on coordinated wellness in the western Pennsylvania marketplace, they sought to create a first-of-its-kind transformational health care facility that would raise the bar on patient convenience, care coordination, quality, and service excellence. Eager to bring this powerful health facility to market as soon as possible, AHN needed an accelerated delivery method that could enhance the certainty of outcome while ensuring a high-quality result.
With a focus on innovation and time to market, and to bring trade contractors on earlier than otherwise could be possible in the traditional design-bid-build process, the design team developed basis-of-design performance documents. The documents included performance narratives and an schematic design/design development-level building information model. The narratives defined the scope of work and provided a general description of a plan and strategy that would deliver a fully code-compliant and operational facility within the target budget. Further, the narratives described the overarching mechanical, electrical, and plumbing (MEP) system concepts and defined major equipment types and system capacities, such as:
- Chilled-water distribution equipment and two 400-ton rotary screw, air-cooled chillers.
- Hot-water distribution equipment and three 4,000-MBH, direct-vent, condensing, modular boilers.
- Eight variable air volume (VAV) air handling units with capacities ranging from 2,000 to 40,000 cfm.
- Building automation system requirements.
- A 4,000-amp, 277/480 V, 3-phase, 4-wire main electrical service entrance.
- A 1,500-kW, 277/480 V, 3-phase, 4-wire diesel emergency generator.
- A 125-kVA uninterruptible power supply (UPS) with 480 V, 3-phase input and a 120/208 V 3-phase-output UPS system.
- Four 100-gal, 199,000-Btu/h input, 230-gph recovery, gas-fired, direct-vent domestic-water heaters.
- Medical gas systems consisting of vacuum, air, oxygen, nitrogen, nitrous oxide, and carbon dioxide provided in accordance with NFPA 99: Health Care Facilities Code.
The early BIM provided a basis of understanding of physical equipment geometry and major infrastructure distribution and routing. This culminated in a bid package of sufficient scope definition to competitively bid the MEP trades and enable subcontractors to join the design team.
The engineering design team continued to advance the MEP system design to a point where the trade contractors that were now on board could develop a guaranteed maximum price (GMP) based on a 50% construction documents/100% scope design package. The design/construction teams met regularly as the process continued to discuss design options and project approach.
MEP system design guidelines were developed to become the basis for the trade contractors to complete the design from the 50% level while working in the BIM environment. Examples of relevant design guidelines include:
- HVAC zoning requirements (VAV box zoning).
- Air-balance requirements (space pressurization).
- Ductwork design standards (maximum velocity and pressure drop).
- Duct material standards (see Figure 1).
- Hydronic piping design standards (maximum velocity and pressure drop).
- Electrical maximum circuits per feeder.
- Panel schedule criteria.
- Lighting-power density requirements.
- Reflected ceiling plan prototypical layouts (for lighting symmetry).
- Domestic-water distribution branch piping—maximum length and flow velocity.
This design criteria provided the subcontractors with the information needed to assist in the completion of the documents, saving the engineering team from detailing better suited to the trade contractors’ expertise. As the subcontractors became engaged, they worked very closely with the engineering team to complete the deliverables, reinforcing a constructible solution that accurately represented the design intent. (See Figure 2)
The benefit of having the MEP engineers and subcontractors at the table together became clear as the respective trade contractors further developed the design model to a coordinated, interdisciplinary model, and ultimately to their shop drawing/fabrication model. This increased efficiency in the submittal and shop drawing review phase allowed for a detailed 3-D construction-coordination process to ensure that building components, assemblies, and systems properly fit in their “to-be-installed” condition without interferences with other building assemblies—all while maintaining the engineering team’s design intent. The design engineer maintained the responsibility as EOR.
This process allowed the design engineers to focus on what they do best—developing high-performance building systems concepts—and enabled engineers and subcontractors to partner and develop design and construction packages collaboratively, essentially combining the completion of construction documents with the shop drawing phase. The project was delivered in an aggressive 22-month design and construction schedule, with construction completed in 18 months.
Daniel Fagan and Robert Ward are lead mechanical engineers and office engineering leaders at their respective offices for CannonDesign. Each has more than 30 years of experience in the construction industry and has worked on numerous projects including commercial, institutional, health care, and education facilities. Management of more than $100 million worth of construction annually has provided them with knowledge of a variety of project approaches and delivery strategies.