Junior high achieves national first with innovative HVAC design
Photo courtesy of SEMCO
In the wake of its 3-year-old high school's nationally renowned sustainability design, Clark County (Ky.) Public Schools has improved upon its chilled beam energy-saving model with the recent HVAC retrofit of a 43-year-old school building.
Robert D. Campbell Junior High School was retrofitted in 2015 from 1970's unit ventilators to chilled beams and dedicated outdoor air systems (DOAS), but with a new twist.
Chilled beams and DOAS aren't new, but Campbell is the world's first known building to use smart, plug-and-play controllable chilled beam pump modules (CCBPM), according to SEMCO, manufacturer of the modules.
The pump modules helped save hundreds of thousands of dollars in capital equipment and labor/installation costs. They also combine chilled beam pinpoint indoor air comfort temperature and humidity control with energy efficiency.
Using pump modules in Campbell's two-phase HVAC retrofit saved the school district $147,000 in labor installation costs versus the alternative of variable refrigerant flow (VRF) technology. 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 the Lexington, Ky., branch of Indianapolis-based Performance Services Inc. (PSI), an integrated design and delivery engineering contractor that led the project.
PSI's pump modules specification enabled the reuse of all of the existing two-pipe loop's piping, the pumps and the relatively new replacement chiller and boiler installed in the 1990's and 2003, respectively. Another advantage is that pump modules eliminate the need for heat exchangers, according to SEMCO.
A pump module, which includes a powered integrated direct digital controller (ddc), chilled and hot water connections, valves, variable-speed electronically commutated (EC) 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 pump modules eliminate guesswork associated with chilled beam system specification, installation, balancing and commissioning.
As with most two-pipe designs, the fluctuating temperatures of spring and fall resulted previously with uncomfortable indoor temperatures, because of the extensively long periods required to switch from heating to cooling modes.
Chilled beams in school retrofits offer superior air comfort and lower costs compared to its nearest methodology competitor, VRF systems, said Gary Sprague, PSI's energy management specialist and Campbell project manager. Furthermore, Clark County School District Superintendent Paul Christy preferred a hydronic-based system versus VRF systems, because of its potential for refrigeration leaks from line sets and evaporators into classrooms and the environment. Chilled beams have three times the lifecycle expectancy of VRF technology and lower maintenance costs because there are no fans or condensate drain lines.
Donahue Mechanical, the project's sheet metal and piping contractor, 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 pump modules and chilled beam connection. Most pump modules 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-foot to 2 by 8-foot sizes.
Each module was centrally positioned in each zone to limit chilled beam piping circuitry and allow its front panel to swing down through a removed 2 x 2-foot ceiling tile for easy access.
The facility uses a building management system that monitors the modules 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 management system to spotlight trends and calibrate energy-efficiency improvements.
Cooling season condensation is prevented with the DOAS ducts that supply six-inch-round intakes on each chilled beam with conditioned, dehumidified air above dew point and satisfies outdoor air codes. The ducts easily fit into the restricted ceiling space, which was another impetus for using chilled beams versus other technologies requiring larger outdoor air ductwork.
The project also reused the building's two 125-ton air-cooled chillers and three 3-million BTU/h modulating boilers.
Christy, the catalyst for getting chilled beams specified with geothermal and DOAS in the district's sustainable award-winning new George Rogers Clark High School, also likes the decibel (dB) 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," she said.
After the project, the new high school's attendance numbers climbed, something Christy partially attributes to the comfortable learning environment created by the HVAC.
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