Decarbonizing Defense: Modernizing Mission-Critical Infrastructure with a 4-Pipe HVAC Conversion

Project Overview

Constructed in 1991, Building X was originally equipped with a two-pipe system that required seasonal switchover, providing either heating in the winter or cooling in the summer, but never both at the same time. This created challenges, especially during the shoulder seasons when parts of the building required heat and others needed cooling.

The new four-pipe system resolves these issues by enabling automated, simultaneous heating and cooling, dramatically improving flexibility and efficiency. Chapman Construction/Design partnered with the client and design team to develop a multi-year roadmap for the conversion, which also included HVAC upgrades in Building Y and integration with the campus’s central utility plant. All this work was completed while Building X remained fully occupied and operational.

Existing System Overview

Before the upgrade, Building X’s HVAC system was built around a dual-temperature loop that delivered either hot or chilled water, but not both simultaneously. While a dedicated secondary chilled water loop kept critical IT spaces cool year-round, the rest of the facility relied on six rooftop air handling units and over 250 two-pipe fan coil units. These units lacked the flexibility to deliver simultaneous heating and cooling, forcing the building to undergo seasonal switchover procedures. The manual changeover process was time-consuming, inefficient, and often led to occupant complaints.

New System Overview

The upgraded four-pipe HVAC system features dedicated hot and chilled water piping, enabling year-round comfort and improved load balancing. As part of the project, we installed new hot water pumps and piping from the central utility plant to Building X, ran new vertical risers and distribution loops on each floor, and replaced all the old two-pipe fan coil units with more efficient four-pipe ones. We also replaced all six rooftop units to support separate heating and cooling coils, and integrated updated controls to enhance zoning and energy management. The system was designed with future decarbonization in mind; hot water coils are sized to work well with lower-temperature systems, such as ground-source heat pumps, providing the campus with flexibility to adapt over time.

Challenges

Working in an occupied facility always adds a layer of complexity, and this project was no exception. Cooling had to remain online at all times for mission-critical spaces such as IT rooms and data centers, requiring meticulous planning of system cutovers, the use of temporary equipment, and carefully scheduled after-hours work. Installing new piping in tight, congested utility corridors demanded creative problem-solving and close coordination among trades.

Beyond the immediate project challenges, the client faced broader pressures familiar to many organizations: aging infrastructure, escalating energy costs, and increasing carbon-reduction requirements. By aligning this HVAC upgrade with other planned capital improvements, they not only streamlined the work and minimized disruption but also positioned themselves ahead of future regulatory penalties, turning a necessary replacement into a strategic investment.

Advantages to the Client

The HVAC conversion delivers a range of significant benefits. Energy use is lower thanks to more responsive and efficient equipment, particularly during spring and fall when temperatures fluctuate. Occupants now enjoy improved comfort and precise zone control, which directly supports productivity and satisfaction.

The new system is also more resilient, with redundant piping and advanced controls that reduce the risk of downtime. On the sustainability front, the project positions the campus firmly on track to meet net-zero targets aligned with federal carbon-reduction goals for 2045. Cost savings extend beyond energy, with reduced maintenance requirements, longer-lasting components, and smarter building operations overall. Perhaps most importantly, the infrastructure is now ready to support future upgrades, such as electrified heating and cooling, as well as renewable energy systems.

Summary

This project shows what’s possible when thoughtful design, a committed client, and an experienced general contractor work in sync. By aligning the HVAC conversion with other planned capital improvements, the client maximized the investment’s value while minimizing disruptions to daily operations. Careful planning, smart phasing, and disciplined safety oversight ensured the project was delivered on time, on budget, and with the flexibility to adapt as future needs evolve.

By investing in resilient, low-carbon infrastructure now, the organization has taken a proactive step toward long-term resilience, cost efficiency, and regulatory compliance. It’s a strong example of how strategic infrastructure investment can deliver immediate benefits while laying the foundation for decades of sustainable growth.