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Watkins Mill High School HVAC Retrofit

Gaithersburg, MD

General Contractor:  Shapiro & Duncan, Inc.
Construction Manager:  Keller CM
Engineer/Architect:  Building Dynamics, LLC
Contract Amount:  $1,031,300.00
Start Date:  6/20/16 Completion Date:  8/12/16

Challenge

Shapiro & Duncan went to “summer school” between mid-June and mid-August 2016, when our project team completed the final phase of the HVAC Renovation at Watkins Mill High School in Gaithersburg, MD.  The original HVAC system in this 301,579-sq. ft. Montgomery County Public School dated to 1989, when the school opened. This eight-week project started June 18, 2016 and was completed on August 12, 2016. 

The most challenging part of the scope of work required removing 73 Trane fan coil units on the upper level of the school building and replacing them with 69 Dakin floor-mounted fan coil units and 4 Dakin ceiling-mounted fan coil units. Specifically, we were challenged to maximize the efficiency of coordinating, prefabricating, delivering, staging and installing such a large number of fan coil packages. In order to do this, our team and subcontractor partners had to choreograph a repetitive process that could be easily replicated on the job site.

But there was a lot more to this job than just the fan coil units. The scope of work also included:

  • Removing 2 Trane rooftop units and replacing them with 2 AAON self-contained package rooftop units with custom built curb adapters;
  • Adding 17 hydronic heating hot water duct-mounted coils to the second floor existing/to remain ductwork;
  • Replacing 2 chilled water pumps with 2 Bell & Gossett chill water base-mounted circulation pumps located in the lower level pump room;
  • Adding 2 new chilled water pump ABB variable frequency drives;
  • Replacing the existing fan coil unit pneumatic control system with a new electronic direct digital control system;
  • Replacing air distribution sheet metal and registers, grills and diffusers, ductwork and piping thermal insulation;
  • Upgrading electrical service to the fan coil units, rooftop units, pumps and variable frequency drives;
  • Performing air and water testing;
  • Adjusting and balancing of HVAC components and systems; and
  • Equipment rigging.

Solution

Coordination and prefabrication were the key elements of our team’s solution. Our coordination process began by getting all the trades together and working through the step-by-step process of building a fan coil package. With that process established, we set up a four-at-a-time installation sequence.

First, our Virtual Design Coordination (VDC) team prepared 3-D digital models of the needed piping. Next, piping assemblies for all 69 fan coil units were prefabbed at Shapiro & Duncan’s 51,000-square-foot fabrication shop in Landover, Md.  To get as much of the needed prefabrication done ahead of time, our subcontractors even came to our fab shop to insulate piping, install electrical controls and pre-wire the units.

The prefabricated fan coil units were then delivered to the site in several shipments. Each truckload contained pallets loaded with a pod of four units per pallet. The pallets were rolled on dollies through the front of the school to the back elevator, then distributed throughout the upper-level classrooms starting at the furthest point in the rear of the school and working to the front. Once the pods of prefabbed units were set in place, the final piping, electrical and control terminations were made – four units at a time.

Meanwhile, the two chilled water pumps were also prefabbed in the fab shop. The two pumps were shipped to the site on skates in one piece, rolled through the school and set on the modified existing house-keeping pads and bolted to the slip-on flanges. Then the suction diffusers, flex connectors, piping and valves were also bolted to the pumps. Installing the pumps in this fashion minimized the number of field welds and expedited installation.

Prefabrication was also part of the solution when it came to the ductwork to the two self-contained package rooftop units. Our subcontractor measured the drops and had them delivered to the site prior to setting the units. Both units were removed, ducted and set in one day.

Results

Thanks to the superb coordination between all of our project team members and subcontractors, Shapiro & Duncan “aced” the Watkins Mill High School summer school assignment with a smooth retrofitting of the school’s aging HVAC system. By making smart use of prefabrication and carefully sequencing field installation of new equipment, we were able to complete the project comfortably within the eight-week period of performance. When it comes to innovative, time-saving mechanical solutions in schools and universities, Shapiro & Duncan is at the head of the class.