HVAC

Case study: Hospital HVAC system benefits from IPD

A new and existing hospital building were delivered using IPD.
By Laurence V. Wilson, PE, ASHRAE HFDP, LEED AP, CDT October 31, 2018

Lakeland Medical Center in St. Joseph, Mich., is building a new 250,000-sq-ft clinical pavilion addition that includes a new surgical suite, an intensive care unit suite, a central sterile suite, a set of imaging suites, a conference center, and an atrium. In addition, the project includes almost 80,000 sq ft of renovation. All phases of the project will be delivered using integrated project delivery (IPD).

The HVAC system is comprised of five custom air handling units (AHUs) housed in a single large fan room toward the top of the 5-story building. The fan room contains two identical (the “twins”) AHUs that service the operating rooms and three identical AHUs (the “triplets”) that service the remainder of the newly constructed building. These AHUs form the heart of the HVAC system for the building addition and were designed and documented in an extremely collaborative manner between the owner, engineers, and contractors.

Decisions had to be made early to meet strict design criteria, such as indoor dry-bulb temperatures, indoor relative humidities, supply-airflow rates, and outdoor-airflow rates, given the hot-dry, hot-humid, and cold-dry outdoor conditions. Other decisions needed to be made related to airspeed criteria through the AHUs, draw-through versus blow-through cooling-coil configurations, air filter/cleaning subsystems, and acoustical concerns. On top of all this, the team had to decide what level of safety factor, firm capacity, and quality would be necessary/appropriate. All this, plus so many more details-like trap heights, catwalks, etc.-needed to be rolled up into the myriad collaboration sessions held at the trailer; this sort of work flow is the essence of IPD.

The design and documentation of the AHUs turned out to be one of the most complex tasks on the project. Close coordination was required between the owner, mechanical and electrical engineers, contractors, and many other design professionals and specialty contractors.

As the engineers focused on calculations, the contractors focused on how to arrange the AHUs. Trying to minimize the enormous amount of sheet metal required while at the same simplifying ongoing operations and maintenance led the contractors to push for systems that did not include airside economizers. The engineers agreed with this approach, especially considering using airside economizers in a building that would be humidified would lead to excessive energy consumption.

In order to provide the energy conservation features required by ASHRAE Standard 90.1: Energy Standard for Building Except Low-Rise Residential Buildings, the engineers and contractors looked at the technical and economic feasibility of using either waterside economizers or heat-recovery chillers. The heat-recovery chiller solution was shown to be more beneficial; the chillers would be used year-round to satisfy the process cooling loads while using the rejected heat for preheating domestic hot.

There was an intense amount of work done with the vendors to optimize component selection, analyze acoustics, and work on layout. Structural steel, space for maintenance, catwalks for the double-decker AHUs, installation, future removal/replacement, and many other issues had to be hammered out. This work was completed so that the five AHUs could be pre-purchased before the final design phase was complete. This helped improve the overall schedule for the project.


Laurence V. Wilson, PE, ASHRAE HFDP, LEED AP, CDT
Author Bio: Laurence V. Wilson is a principal at SmithGroup. He has more than 3 decades of experience in the field of building system engineering, including analysis, planning, design, and construction administration.