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.