exp: Northside Hospital Forsyth vertical expansion and central plant addition

Electrical, power; HVAC, mechanical; plumbing, piping.

By exp August 10, 2017

Engineering firm: exp

2017 MEP Giants rank: 11

Project: Northside Hospital Forsyth vertical expansion and central plant addition

Address: Cumming, Ga.

Building type: Hospital/health care facility

Project type: Addition to existing building

Engineering services: Electrical, power; HVAC, mechanical; plumbing, piping

Project timeline: February 2015 to December 2016

MEP/FP budget: $510,000


One of the main challenges of the project was enclosing the existing roof and converting it into a mechanical floor. This was complicated in several ways; for example, the existing rooftop air handling units (AHUs) had to be retrofitted to be able to handle the additional static pressure of ductwork on the outside air intakes.Since the floor was now enclosed, the “relief air” had to be dealt with as well.

Adding ductwork on the relief outlet of the AHUs would have added even more cost to the project. Additionally, existing exhaust fans on the old roof had to be relocated to the new roof and then adjusted to handle the additional static pressure of three additional floors of ductwork.


For the existing AHU retrofits, the return fans were modified to increase their horsepower and therefore assist with the intake of outside air through the new ductwork.

The relief didn’t need to be ducted because project leaders used the entire new mechanical floor as a “relief air plenum” with perforated walls to allow the floor to be positively pressurized. This reduced the cost of construction by eliminating the need for new ductwork on two existing and two new AHUs. Motor horsepower increases allowed the exhaust fans to deal with the additional static pressure.