Replace two existing mechanical HVAC systems from the 1960s that served critical areas of the hospital. Any downtime risk had to be carefully scheduled and managed. The existing equipment was buried in the second-floor mechanical space. A building column was located within the mechanical space needed for the new, replacement HVAC design.


The engineer coordinated closely with the owner to design around built-in-place, field-erected HVAC equipment. Two 65,000 CFM side-by-side air handling units were designed to replace the existing systems. Units are 100% outside air makeup air units. The units were carefully located for proper service access, future component replacement, and redundant airflow to the building spaces. A vertical building column was built into one of the units.


  • Owner – Catholic Health Services/Mercy Hospital (Abbott Road)
  • Design Consultant – M/E Engineering
  • Installing Mechanical Contractor – Quackenbush Company
  • ATC Provider – U&S Services
  • Equipment Provider – Air Enterprises SiteBilt AHUs/ R.L. Kistler

Points of Interest

Air handling unit construction materials and major components were constructed of all aluminum or stainless steel materials. This all-aluminum construction included the 2-1/2” panels system, the structural support base, and the AHU walking surfaces. Internal components consisted of three levels of filtration (HEPAs, carbon, pre-filtration, heat recovery, hot-water heating, chilled water cooling, steam humidification, and an 8-fan array).

A temporary rental system was supplied to risk-mitigate downtime concerns during mechanical room demolition and the field building of each new AHU. Each unit was field erected in place in less than three weeks.

Both units were field performance tested to ensure quantified performances were met. Units were air-leakage tested at 8” static pressure, allowing less than 1/2% air leakage.

One of the units was designed around an existing building column, carefully located within the AHU design to allow proper airflow and unit serviceability.