Robert D. Campbell Junior High School, Winchester, Ky.
School representatives agreed to replace circa- 1970s unit ventilators with chilled beams and dedicated outdoor air systems (DOAS)—but with a new twist. The 43-year-old junior high is the world’s first known building to use smart, plug-and-play controllable chilled-beam pump modules (CCBPM). The CCBPMs combine chilledbeam pinpoint indoor air comfort temperature and humidity control with energy efficiency.
Performance Services Inc.’s (PSI’s) CCBPM specification enabled the reuse of 100 percent of the existing two-pipe loop’s piping, pumps, and the relatively new replacement chiller and boiler installed in the 1990s and 2003, respectively. Another advantage is that CCBPMs eliminate the need for heat exchangers.
A CCBPM, which includes a powered integrated direct digital controller, chilled- and hot-water connections, valves, variable-speed electronically commutated motor pumps and smart sensors, is superior in temperature and humidity control to the original unit ventilator design, especially during season changes. The plug-and-play CCBPMs eliminate the guesswork associated with chilled-beam system specification, installation, balancing and commissioning. As with most two-pipe designs, the many wildly fluctuating temperatures of spring and fall days previously resulted in uncomfortable indoor temperatures because of the extensively long periods required to switch from heating to cooling modes.
Conversely, Robert D. Campbell Junior High School’s design provides pinpoint tempered conditions within a 1-degree tolerance, regardless of the season, because its control is based on outdoor dew point, not temperature. If the OA dew point is less than or equal to 45 F, the space latent load is satisfied by DOAS ventilation air, which is distributed through each chilled beam and controlled via its respective CCBPM. When the dew point surpasses 45 F, the chiller is needed to maintain space conditions.
Donahue Mechanical executed PSI’s design of reusing all hydronic trunk lines and the former unit ventilator taps for the first floor but needed to extend the second floor unit ventilator taps to the ceiling for CCBPM and chilled-beam connection. Most CCBPMs are mounted above each level’s classroom zone’s 18-inch-high T-bar drop ceilings and typically control four ceiling flush-mounted chilled beams ranging from 2- by 2- to 2- by 8-foot sizes. Each CCBPM was centrally positioned in each zone to limit chilled-beam piping circuitry and allow its front panel to swing down through a removed 2- by 2-foot ceiling tile for easy access.
“Our project is best described as a three-loop system—the original pipe loop from the central plant, the take-off loop to and from each CCBPM, and the loop that connects a series of four to eight chilled beams to its respective CCBPM,” explains Gary Sprague, PSI’s energy management specialist.
The third loop is a “game-changer,” according to Sprague because the CCBPM blends and recirculates its return water within its zone to convert typical 42 F (cooling) and 140 F (heating) primary loop supply water temperatures to optimal 58 F(cooling) or 100 F (heating) chilled-beam discharge temperatures, respectively. This prevents cooling-mode condensation and heating-season heat stratification.
A building management system monitors the CCBPM via Ethernet with the BACnet protocol and sends outdoor temperature/humidity information. Sprague receives alarms and periodically reviews real-time and historical data from the BMS to spotlight trends and calibrate energy-efficiency improvements.
The project also reused the building’s two 125-ton air-cooled RTAA-Series chillers manufactured by Trane and three 3-million BTU/h modulating boilers by Thermal Solutions.
Clark County School District Superintendent Paul Christy likes the decibel reduction of chilled-beam induction versus the disruptive operational noise of unit ventilator fans for classroom environments. “The two-pipe conventional unit ventilators that preceded the retrofit were noticeably loud and distracting, whereas now I walk into classrooms with the chilled beams and I can’t hear any sound from the HVAC system,” Christy says.
Using CCBPMs in the school’s two-phase HVAC retrofit saved the district $147,000 in labor installation costs versus another system that was considered. The chilled beam/DOAS combination also saves $33,000 annually versus the school’s former unit ventilator system. The energy savings will lower capital dollars spent on the project by $500,000, which is guaranteed by a performance contract with PSI.
Photo: SEMCO LLC