Transforming Fairfax County's Most Energy-Intensive Building into a High-Performance Facility
Located in Chantilly, Virginia, Cub Run Rec Center is operated by the Fairfax County Park Authority (FCPA). This unique 65,001 ft² facility features two indoor natatorium spaces, a fitness center, offices, and multipurpose rooms. In 2020, Fairfax County’s Office of Environmental and Energy Coordination (OEEC), in partnership with FCPA, engaged CMTA to perform energy audits and implement upgrades across County facilities under an energy savings performance contract. As part of this project, CMTA aimed to transform Cub Run from one of Fairfax County’s most energy-intensive buildings to one of its highest-performing recreation centers. By overhauling the facility’s central plant and heat recovery systems, the project significantly reduced energy usage and greenhouse gas emissions while creating a healthy and comfortable indoor environment for occupants.
Project At A Glance
Size: 65,001 Square Feet
Cost: $1,240,000
Guaranteed Savings: $95,949 Annually
Actual Savings: $203,179 Annually
Completed: 2022
Baseline Energy Use: 502 EUI
Post-Project Energy Use: 203 EUI
Carbon Reduction: 1,636 MTCO2e Annually
Awards
ASHRAE International Technology Award - First Place
The Challenges
Reduce energy usage by targeting the central plant and heat recovery systems
Maintain thermal comfort and adequate ventilation in challenging pool spaces
Align with Fairfax County's climate action goals to reduce greenhouse gas emissions
[This project is] a testament to the Park Authority’s commitment to sustainability. As stewards of public spaces, we prioritize energy efficiency not only to reduce environmental impact but also to ensure long-term operational savings.
Jai Cole
FCPA Executive Director
The Solutions
The $1.24 million project at Cub Run Rec Center was largely driven by Fairfax County’s climate action goals and the need for cost-effective infrastructure upgrades. To reduce energy consumption while maintaining thermal comfort and adequate ventilation, CMTA targeted Cub Run’s central plant and heat recovery systems. Despite challenges such as space constraints in the mechanical room and conducting upgrades while the facility remained operational, the team implemented innovative solutions. CMTA re-engineered the central plant to recover heat from mechanical dehumidification for space reheat and pool water heating, achieving a combined heating and cooling COP of 8.42 under part-load conditions with a Dedicated Heat Recovery Chiller (DHRC). This effort aligned with the County’s Operational Energy Strategy by shifting a significant portion of the heating load from fossil fuels to electricity.
To maximize DHRC efficiency, the team reduced the hot water supply temperature below 135°F while decoupling systems requiring higher temperatures, such as domestic water and spa heating, onto a dedicated boiler loop. This allowed the main heating loop to operate at lower temperatures, improving the performance of the new condensing boilers with a 15:1 turndown ratio and 93.7% thermal efficiency. The hydronic system was also converted to variable primary pumping, enhancing performance and reducing energy waste. Advanced central plant controls with updated Sequences of Operation (SOO) were implemented, including Direct Digital Control (DDC) sequences for temperature resets and differential pressure control, ensuring efficient pump operation and optimized water circulation.
Despite a 70% rise in energy costs during construction due to inflation, the system delivered significant financial benefits, avoiding $316,000 in costs during its first year and reducing the simple payback period to 3.9 years from an initially projected 13 years. A 30-year life-cycle cost analysis revealed a 27.8% cost reduction, equating to $7.4 million in savings compared to a baseline system. This project highlights the potential for strategic central plant design to achieve measurable environmental and economic benefits, setting a new standard for energy efficiency initiatives.
Optimal Indoor Air Quality
CMTA implemented strategic measures to enhance indoor air quality (IAQ) throughout the building, with a particular focus on the natatorium spaces. Through the retro-commissioning of airside equipment, CMTA effectively addressed the unique thermal challenges associated with natatorium environments, achieving optimal space conditions. The air temperature in the natatorium was precisely maintained just above the pool water temperature, while relative humidity levels were controlled between 50% and 60%. Ventilation rates were optimized to 0.48 cfm/ft², and the spectator area’s supply air rates were adjusted to ensure over 10 air changes per hour, guaranteeing effective air distribution and ventilation to the occupants’ breathing zone.
Additionally, an initial technical energy audit conducted in 2021 identified critical issues in the demand control ventilation (DCV) sequences, which were failing to maintain acceptable IAQ levels within the fitness center, office spaces, and multipurpose rooms. Notably, a faulty CO2 sensor returned a reading of -47 PPM compared to the air handling unit (AHU) CO2 setpoint of 5,000 PPM. To address these deficiencies, the project team repaired defective sensors and reprogrammed the system logic to appropriately modulate outdoor air dampers in response to elevated carbon dioxide levels. Leveraging the Building Automation System (BAS), the team implemented detailed tracking of critical variables, such as temperature, humidity, fan operations, and air/water temperatures, at 15-minute intervals. These comprehensive adjustments have resulted in marked improvements to thermal comfort and IAQ, with a significant decline in occupant complaints reported following the renovation.
System Reliability
For a recreation center operating 7 days a week and dependent on indoor pool rentals for revenue, system reliability was paramount. The upgraded central plant equipment and operational sequences were meticulously designed to ensure reliability, redundancy, and energy efficiency. A constant-flow design in the heat recovery chiller streamlined controls and minimized compressor trip risks, while motorized control valves enabled a single boiler in the heating loop to manage domestic water heating during faults, enhancing overall system resilience.
The Results
This project transformed Cub Run from Fairfax County’s most energy-intensive building, with an EUI of 502 kBTU/ft²/yr, into one of its best-performing recreation centers, now achieving an impressive EUI of 203 kBTU/ft²/yr. This 60% reduction in total energy use translated into approximately $316,000 in avoided costs during its first year of operation and a significant reduction of 1,636 tons of CO₂ equivalent emissions annually.
Furthermore, the project converted a large portion of the building’s heating load from onsite fossil fuel to electricity using the DHRC for base heating, while still reducing annual electric demand by 19%, easing strain on power systems during peak periods. By FY23, Fairfax County Government reported a 12% reduction in total natural gas use across its portfolio, with this award-winning project playing a key role. The success of Cub Run aligns with the County’s 2040 climate action goals, advancing efforts to cut building energy consumption by 50% and achieve carbon neutrality in operations.
