Our client purchased an existing 728,520 SF distribution center shell building as the location for its new food production, cold storage warehouse, and distribution facility.
The building, constructed using tilt-up construction, was completely unfinished on the interior and lacked essential features such as cooling systems, refrigeration panels, and other necessary components for a food storage property.
This paper describes how we addressed the challenges of retrofitting an existing shell building to create a complex cold storage facility with multiple refrigeration zones that meets USDA requirements, on a strict 180-day schedule.
Retrofitting an Existing Distribution Center Shell into a Cold Storage
Our client purchased an existing 728,520 SF distribution center shell building as the location for its new cold storage warehouse and distribution facility.
The building, constructed using tilt-up construction, was completely unfinished on the interior and lacked essential features such as cooling systems, refrigeration panels, and other necessary components for a food storage property.
Construction required a complete retrofit of the existing building to transform an empty shell building that had never been occupied into a highly complex distribution center, cold storage facility, and office.
Specifically, the new cold storage warehouse would house six independent temperature zones, including:
- 5,000 SF –20° ice cream room;
- 78,000 SF 0° freezer with 21,000 SF cold dock;
- 168,800 SF 34° refrigerated area;
- 122,000 SF 65° conditioned storage area;
- 264,200 SF dry storage area for non-refrigerated foods and products and future freezer space;
- 23,247 SF Ready-To-Eat / Cheese Packaging and Processing Area – A temperature- and ventilation-controlled area with insulated metal panel walls and ceilings that houses 13 separate rooms for the preparing and packaging of cheese and ready-to-eat items. Flooring in this area would have to be sloped with multiple drains to meet USDA requirements.
The refrigeration would be controlled at the various levels with an extensive industrial ammonia refrigeration system and insulated metal panel walls and ceilings. Plans called for an underfloor glycol warming system beneath the freezer areas to prevent the ground from freezing
The specific requirements for this building were complicated by the fact that we were starting with a shell building; in a typical ground-up construction project, the various internal features would be planned and built as part of the overall development of the structure. With the shell building in place, however, we had to develop and engineer new approaches to meet the specific requirements of a food storage and handling facility.
The Challenges of Retrofitting an Existing Distribution Center
The North Texas Cold Storage Warehouse presented several unique challenges.
Retrofitting.
Perhaps the greatest challenge of this project was that it involved a complete reengineering and retrofit of an existing warehouse facility, rather than a “ground-up” new building project.
Had the project been a new building, incorporating all the unique features and requirements of the freezers would have been integrated into the slab and shell production. With the walls, slab, and roof in place, however, we were forced to make substantial structural changes to the existing building so we could create the freezer zones.
As a result, we performed extensive demolition and earthwork in the confined space of an existing building. Over 150,000 SF of 6” slab on grade and at all the freezer areas had to be saw-cut, demolished, and hauled off. More than 6,500 cubic yards of select fill from under the existing slab had to be removed and exported to allow for the installation of the underfloor glycol system (pictured above right), six inches of floor insulation, and a seven-inch floor slab (pictured right) because this work took place in an enclosed space, all equipment operating inside the building required exhaust scrubbers.
The fact that we were retrofitting an existing building also drove us to design an innovative approach for creating the freezers.
The initial plans called for a box-in-a-box freezer setup that used insulated metal panel (IMP) walls and ceilings to create a tight vapor barrier.
Unfortunately, due to the existing clear heights and fire sprinkler requirements under the IMP ceiling, this approach limited the maximum height of the freezer area to only 27 feet.
During the design conceptualization phase, we developed a distinct approach to building the freezers. We abandoned the box-in-a-box approach in favor of creating an independent structure for the 83,000 SF 0°F Freezer and to facility the 58,700 SF future freezer.
The process to create this independent structure included the following steps:
- installing 33 double columns on newly constructed footings at the freezer perimeter;
- installing new girders for the newly added columns;
- Cutting existing angles from the girders to the old columns and adding new angle steel from the girders to the new columns;
- breaking the roof deck;
- Cutting 42 existing columns;
- lifting the existing columns and inserting column blocks on the interior freezer columns; and
- For the 0°F Freezer, installing five-inch R-42 IMP walls from the floor through the roof deck and tying the IMP to the roof membrane.
- Adding 2’ x 2’ x 32’ pilasters with newly drilled piers to support the tiltwall panels that were no longer supported by the joists and deck, which allowed the tiltwall to remain and provided a uniform wall type.
Through the creative use of this independent structure approach, we were able to increase the allowable storage space inside the freezer by approximately 20%. The new approach for building the freezers in the existing building was a key reason why we were selected to perform this project, and the approach worked flawlessly to deliver the temperature-controlled spaces as intended.
The roof of the existing distribution center also presented a unique challenge. In the months leading up to North Texas’s acquisition of the distribution center, the existing roof had sustained hail damage and required replacement. Further, the insulation on the existing roof was insufficient; it needed to be upgraded to maintain the desired temperatures in the warehouse.
We value-engineered a solution in which the existing 45 mil TPO membrane was demolished, but the 1.5-inch ISO roof insulation was left in place, and additional insulation was added to achieve the desired R-values: R-50 at areas below 32°F (190,000 SF); R-37 at areas between 35°F and 65°F (316,000 SF) and R-27 at the unconditioned area (218,000 SF).
To combat future hail damage, we proposed a top-of-the-line 135-mil roof system comprised of 80-mil TPO and 55-mil fleece-back adhered with Flexible Fast Adhesive. In sub-freezing areas, the roof membrane was connected to the insulated metal panels and foam-in-place insulation to create a vapor barrier. Additionally, in sub-freezing areas, the top layer of insulation was fully adhered to create a more effective vapor barrier.
To make the floor functional for a refrigeration facility, we needed to install a system that would prevent the ground beneath the slab from freezing and creating instability.
To address this concern, we designed an underfloor glycol warming system. After the demolition and excavation of the slab in the 83,000 SF freezer and 58,700 SF future freezer areas, we installed the warming system. The glycol piping is encased in a three-inch mud slab, which is located below six inches of insulation and the seven-inch slab. The system ensures that the ground beneath the freezers remains unfrozen, regardless of the temperatures in the building on the other side of the slab.
Schedule.
The difficulties of retrofitting were not the only challenges faced during this project.
Another challenge with the construction of this project arose from the client’s aggressive schedule for facility occupancy. The initial contract was based on a schedule of 110 days of design followed by 180 days for construction. The client adjusted the schedule to 180 days to complete both phases.
To accommodate the compressed schedule, we collaborated with the city to develop a strategy for obtaining five separate permits for demolition, site work, and underfloor work, allowing us to commence construction prior to the submission of the complete design. These multiple permits allowed us to begin demolition only seven days after the project was awarded, for example.
The schedule below shows the permitting process we were able to coordinate with the city:
- Awarded: 4/2
- Demo Permit from City: 4/9
- Executed Contract: 5/3
- Site Work Permit: 6/13
- Underfloor Permit: 6/13
- Certificate of Occupancy for Temporary Cooler: 6/21
- Maintenance Building Permit: 6/24
- Complete Building Permit from City: 8/01
- Temporary Certificate of Occupancy: 12/23
The compressed schedule also forced us to maximize the overlapping of trades. Throughout the project, our jobsite would have as many as 250 workers from 18 different contractors performing pier drilling, steel work, roofing, concrete work, EMP, dirt work, and finish-out all at the same time. Our site superintendents were required to manage more activities and more subcontractor employees simultaneously than a less-demanding schedule would have necessitated.
Another aspect of the schedule involved creating a temporary warehouse space for the client to use early in the construction process. Upon award in April 2014, the client requested the construction of a 51,000-square-foot temporary warehouse space, refrigerated to 40 Degrees, at the facility. Their lease at the other facility had expired, and they needed the temporary warehouse to be operational by June 24.
In response, we designed, obtained permits for, and constructed this temporary space in under 60 days.
This required special effort and close coordination with subcontractors and suppliers to ensure that items with high lead times were in place on time. For example, the lead time for refrigeration equipment is typically 8-10 weeks from approved submittals. We needed the equipment on site two weeks prior to occupancy to allow for installation and for the space to cool. The refrigeration equipment vendor initially offered a June 21 delivery date, which meant the space wouldn’t be operational until July 8. We worked directly with the equipment vendor and coordinated with the subcontractor to expedite the equipment’s arrival on site, then worked in shifts around the clock to install it.
On June 24, the temperature in the temporary warehouse space had dropped to 40 degrees, and we had obtained a certificate of occupancy.
The fact that the client needed to use a portion of the interior space as a temporary refrigerated distribution center meant that their employees – including fork lift operators, IT staff, management and delivery truck drivers – were operating continuously inside the building and in the parking lot where our equipment/materials were staged and in use throughout the entire construction process. From a safety perspective, this significantly increased the difficulty of our operations.
Through the effective use of strong project management and oversight, the selection of an excellent team of designers and subcontractors, and close coordination with city and client representatives, we successfully met the project milestones on schedule.
Other Challenges.
Finally, the North Texas Cold Storage Warehouse project addressed the typical challenges inherent in the needs of a food manufacturing and storage facility.
- To meet USDA requirements in the Cheese / Ready-To-Eat Processing Area, over 17,000 SF of slab was demolished and poured back with a vapor barrier and proper sloping to 28 floor drains for drainage, and coated with a ¼” Dur-A-Flex Poly-Crete® floor coating to withstand extreme temperatures.
- Due to the various temperature-controlled zones, we installed over 40 evaporators on the roof-level structural steel. The existing structure was insufficient to support the weight of the evaporators and required more than 40 tons of structural steel reinforcement for the roof.
- The existing building had no refrigeration system, so our work in this regard was essentially starting from scratch. We engineered and constructed a central plant ammonia refrigeration system to serve food processing and storage areas, housed in a new 3,500-square-foot building constructed adjacent to the distribution center. The new system includes:
- 52 evaporators, one outside air unit designed to deliver a 38°F leaving air temperature,
- One energy-saving under-floor hot gas ammonia to glycol heat exchanger and
- Five compressors, including one VFD drive compressor for each suction level. Room temperatures range from -15°F to +65°F, and system suction temperatures at the evaporators range from -25°F to +33°F.
- 1,456 tons of ammonia with extra capacity for future growth.
- The energy-efficient control system features hot gas defrost, variable frequency drive compressors, condenser and evaporator fans, fan cycling, and a control package for the ammonia pump recirculator.
- The majority of the approximately 12,000 feet of refrigeration piping is located primarily on the distribution center’s roof, and all piping inside the occupied areas is continuously welded to minimize the possibility of leaks.
- To meet the owner’s deadline for starting product movement through the facility, temporary halocarbon systems were ordered and installed within 50 days. To reduce overall construction costs, the hot gas defrost evaporators were engineered and constructed for dual duty, serving first the halocarbon direct expansion system and later the ammonia recirculation system.
- At the dock openings, the owner requested a total of 118 dock levelers. To deliver this request, we cut in and poured back dock pits for the dock levelers. In conditioned areas, the lip size was increased by four inches, and foam-in-place insulation was installed to combat condensation.
- The shell distribution center had no facilities to support the trucks that transport products to and from the location. As part of this project, we constructed a standalone 6,100-square-foot truck maintenance building with three service bays. We also added two 12,000-gallon diesel tanks with pumping and overhead canopy features, creating a refueling station that can service two trucks simultaneously. To support the dozens of trucks that park and navigate around the building every day, we added 264,558 square feet of new paving to the parking lot.
Conclusion
Through creative design, value engineering, and close management of subcontractors, we successfully developed the North Texas Cold Storage Warehouse, which serves as a showcase example of a facility featuring refrigeration systems and industrial finish-out.
The refrigeration systems are working flawlessly to cool the various zones to their respective levels. Our innovative approach to building the freezer section has delivered a controlled environment for 0°F storage with 20% more space than other contractors had been able to provide.
Overall, the interior is well designed to meet the diverse needs of clients’ different food warehousing operations. The 13-room Ready-To-Eat / Cheese Packaging and Processing Area is properly equipped with sinks, sloped floors, and overhead air compressors to support the work performed in this area of the building.
To support the green energy warehouse equipment, the new facility features three separate battery rooms equipped with the necessary power and racking to maintain a fleet of warehouse equipment running on clean power suitable for food storage and handling. Finer details, such as the continuously welded refrigeration piping, reflect an attention to quality and detail as well.
