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Green HVAC Design Helps School District Cut Utility Costs by 35% in New 30% Larger H.S.


Clark County (Kentucky) school's innovative hybrid HVAC design using geothermal, chilled beams, heat recovery and other technologies.

The new $60-million George Rogers Clark High School's (GRCHS) green design is helping record up to 35-percent less monthly utility costs while providing better indoor air quality and comfort than the 30-percent smaller conventional building it replaced.

One reason for the increased efficiency is a hybrid HVAC design featuring a geothermal well field that supplies active chilled beams, dual wheel outdoor air dehumidification systems and other cutting-edge technologies, according to Paul Christy, superintendent, Clark County Public Schools. Christy, the county schools' former director of operations, oversaw the 300,000-square-foot high school's HVAC design team that included engineer, Charles H. Wade, P.E., LEED AP, vice president, KTA Engineers, Lexington, Ky; Mark Saunier, B.S.E.E., LEED AP, CEM and president of energy company, Comfort & Process Solutions, Lexington; and engineers from SEMCO, a Columbia, Mo.-based manufacturer of chilled beams and heat recovery outdoor air equipment. D.W. Wilburn Construction Co., Somerset, Ky, oversaw the construction and HVAC installation.

Originally specified as a conventional 200-foot, 80-well geothermal field with just GSHPs, Christy opted for enhancing the design by replacing the proposed 350 heat pumps with 542 active chilled beams and six SEMCO Pinnacle Series dedicated outdoor air (DOAS) heat recovery systems. Christy's decision was based on visiting a similar system at Greenville, S.C.-based Furman University and reviewing an 18-page building energy simulation report prepared by SEMCO.

The report, which was completed by using the Carrier hourly analysis program (HAP) in conjunction with SEMCO's supplemental Pinnacle hourly energy analysis module, compared the estimated annual energy consumption of the high school's three most-likely HVAC approaches:

1) a DX-based outdoor air system, including a total energy recovery wheel and hot gas reheat capabilities preconditioning the outdoor air delivered directly to the classroom spaces served by individual GSHPs.

2) a dedicated outdoor air system (DOAS) incorporating both energy recovery and passive dehumidification wheels, served by a ground source heat pump to precondition outdoor air delivered directly to the classroom spaces served by individual GSHPs.

3) a DOAS and active chilled beams combination, all served by a GSHP chiller to condition the media center and all classrooms.

Based on an electric rate of $.07/Kwh, the estimated annual HVAC energy cost for each of the three systems was 1) $73,490 ($.53/square foot); 2) $56,670 ($.41/square foot); and 3) $45,175 or ($.33/square foot), respectively. Some of the greatest efficiency is attributed to a 50-percent air flow reduction that chilled beam technology offers versus conventional forced air distribution methods.

"The (GRCHS) mechanical system was installed for $19.5 per square foot, which is the same or less than water source heat pumps or VRV ground source systems currently in Kentucky," said Saunier, whose company offers building automation, HVAC service and energy efficiency products.

The old, 199,492-square-foot circa-1960's high school building, a four-pipe boiler/chiller system with fan coil units, was averaging annual utility costs of approximately $194,040 ($.97/square foot). "In the first four months of operation, the new building's preliminary utility bill figures were $41,800 less than our old building during the same period," said Christy, who oversees 11 county schools.

The savings comes primarily from better humidity control and subsequently higher set point temperatures with no trade-off of indoor air comfort. The system's comparably lower 43F dew point temperature allows for greatly reduced air volume due to the superior humidity control from dual-wheel dehumidifiers that control both latent and sensible humidity, according to Saunier, who helped convert the original design from conventional heat pumps to Christy's requested chilled beam concept.

Other Clark County schools with conventional HVAC systems typically operate at 70F amidst occasional "too warm" complaints in spring, summer and fall. GRCHS's temperature complaints have been few due to better humidity control, even though set points average five degrees warmer at 75F. "We've had to educate teachers that set point classroom temperatures they may have previously perceived as being too warm, are now a more comfortable temperature due to this building's superior humidity control," Christy said.

The IQHC chilled beams, which are supplied by a water-to-water GSHP by ClimaCool, Oklahoma City, Okla., have a 12-slot nozzle that's field-adjustable for areas with excessive solar gain or heat loss. CPS service department is training the GRCHS maintenance staff to adjust volume and up to a 45-degree angle directional airflow for hotspots with each chilled beams' easily-accessed hand-operated levers for the greatest air flow flexibility efficiency. The nozzle adjustment additionally provides a unilateral, disproportional or equal air volume from each side. It allows ideal room coverage and flexible distribution possibilities without relocating the device.

The chilled beams never develop condensation because five rooftop DOAS units ranging from 3,700 to 14,500-cfm supply them with semi-neutral, super dry air. There is one 7,000-cfm DOAS that resides in a mechanical room. Some areas with high ceilings that aren't ideal for chilled beams, such as the cafeteria and gym, use their own DOAS to distribute cooling and heating via the GSHP loop.

 

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The DOAS units feature variable frequency drives (VFD), integrated GSHPs and dew point discharge control that are all interfaced with the school's building automation system by, Delta Controls, Surrey, B.C. The control system runs through each DOAS unit's wintertime supply temperature control stages that use the enthalpy wheels' heat recovery to minimize the onboard mechanical heat pump's runtimes. The system also saves energy by maintaining humidity with a recirculation mode during unoccupied periods, which lessens ramp up time heating or cooling when the school opens each day.

Besides energy savings, GRCHS also received the following benefits from the HVAC system:

saved 2,000-square-feet of storage space that would have been consumed by heat pumps in two mechanical rooms that are now used for storage and other uses;

reduced maintenance because chilled beams require no filters and moving parts, thus eliminating any periodic classroom interrupting maintenance tasks;

less piping because only two of every classroom's four chilled beams were four-piped. Additionally, chilled beam piping diameters are considerably smaller than the original configuration of piping heat pumps to each classroom;

reduced ductwork because chilled beams require only six-inch-supply take-offs and half the air volume of a traditional system;

quieter classroom environments because chilled beams are approximately 10 to 15-db quieter than heat pumps;

better temperature and humidity control by independently controlling each load;

"We like the idea of constant air movement at low velocities from a comfort and a noise perspective," said Ron Murrell Jr., AIA, LEED AP, principal at Rosstarrant Architects, Lexington, an architect firm that designs educational facilities exclusively. Chilled beams provide a quieter learning atmosphere as opposed to the considerably noisier method of mechanical units cycling on and off in or near the classroom."

"When we told a state education representative that our outdoor air system wouldn't shut off because it actually drives the chilled beams, he was excited because some conventional Kentucky school buildings suffer poor IAQ when school operators shut off outdoor air to eliminate high indoor humidity," said Saunier.

The building qualifies on the energy requirements for LEED platinum certification, however the school district chose to instead use the application money for educational programs, according to Saunier.

Besides the HVAC, the building design also contributes greatly to energy efficiency. Rosstarrant designed the facility with a variety of efficient techniques and materials, such as orienting the rectangular, three-story building to its site by exposing the long axis to the north and partially integrating the south side into a steep grade the plat offered naturally.

windows are one-inch, insulated glazing with a low-E coating by Guardian, Auburn Hills, Mich.;

an aluminum sun shade by Peachtree Protective Covers, Hiram, Ga., shields exterior windows from solar heat gain;

building envelope features a closed cell spray polyurethane foam insulation manufactured by BASF, Houston, Texas, in the load-bearing cavity masonry wall construction;

The roof consists of light insulated concrete by Siplast, Irving, Texas, and white PVC cool roof membrane by Sika Sarnafil, Canton, Mass;

T-5 fluorescent lighting throughout and 148 tubular solar lights in the top floor classrooms help cut utility bills;

Christy also boasts of .53-percent student attendance increases the first five months of operation in the 2013 Fall Semester versus the same period the previous year, which he attributed partially to superior indoor air quality (IAQ) and humidity control.
The success of the project has led the school district's design team to consider chilled beams and DOAS in an upcoming school retrofit. "Because of space restrictions in a retrofit, we see chilled beams as a space-saving and an air comfort solution," said Christy.

About SEMCO: Since its founding in 1963 as a sheet metal fabrication company with five employees, SEMCO has built a reputation as a worldwide product innovator in the science of air movement, noise abatement, energy efficiency and indoor air quality with more than 300 employees and more than 300 manufacturer's representatives. Major product lines include spiral metal HVAC duct, energy recovery equipment, chilled beams, and acoustics equipment. SEMCO is a Fläktwoods company based in Columbia, Mo. SEMCO operates three manufacturing facilities in Morrilton, Ark., Petit Jean, Ark., and Roanoke, Va. SEMCO also operates an ASHRAE 84-compliant research and development facility dedicated to the innovation of new products for the 21st Century and beyond. For more information, please visit www.SEMCOhvac.com; email sales.SEMCO@flaktwoods.com; or call 1-888-473-6264.


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