Schools Strive for Efficiency, Comfort
New HVAC Technologies Help Administrators Meet Indoor Environment Goals
Across the country, school administrators are realizing the importance of good IAQ and a comfortable indoor environment, which both contribute significantly to student success. In the following case studies, school administrators employ solutions like variable-refrigerant flow (VRF), thermal energy storage, energy recovery, and variable-speed technology to achieve energy efficiency while ensuring occupant comfort and health.
Brescia University College
Brescia University College’s newest residence hall and dining complex feature a state-of-the-art VRF system that looks good, provides occupant comfort, and makes Canada’s premier women’s university the first London, Ontario, Canada, building project to rack up an environmental rating of five Green Globes.
The university’s building officials worked with its design team to choose VRF, which makes the $31 million facility one of Ontario’s first major commercial projects featuring the technology as both the primary heating and cooling source. The facility’s VRF strategy played an important part in the total energy performance, which was 60 percent lower than Canada’s Model National Energy Code for Buildings (MNECB) standard.
VRF had other benefits for the 125,000-square-foot, 300-bed student residence, Clare Hall, and The Mercato at Brescia dining pavilion. “It offered the quietest and most energy-efficient HVAC system option for the resident rooms at reasonable equipment and maintenance costs,” said Derek Vakaras, professional engineer and principal at Chorley & Bisset in London, Ontario.
Vakaras led an HVAC design team that included Cornerstone Architecture, Mitsubishi Electric distributor Baymar Supply, refrigeration contractor Art Blake Refrigeration, and mechanical/plumbing contractor Besterd Mechanical, all of London, Ontario.
A major VRF system concern among engineers and architects is the fact that conventional line set insulation prematurely deteriorates due to birds and weather conditions. The result can cause thermal transfer degradation and copper piping leaks from formicary and pitting corrosion. To help prevent line set deterioration, Baymar Supply worked with Chorley & Bisset to specify the RD Series of line set protection duct by RectorSeal Corp. The corrosion- and scratch-resistant ZAM (zinc/aluminum/magnesium)-coated metal duct preserves line set insulation and its thermal transfer functions. It’s also a critical factor in presenting a clean, professional appearance, especially since there are rooftop sightlines from nearby campus buildings. “The appearance factor doesn’t always take precedence in all projects’ rooftop HVAC systems, but it should,” said Eric Shaw, refrigeration engineering technician, Baymar Supply.
Adding to the rooftop aesthetics is the rooftop VRF equipment — 34 Mitsubishi Electric City-Multi Series VRF condensers mounted on Big Foot Systems equipment mounts. The Mitsubishi City-Multi Series condensers supply 350 evaporators, of which the majority is model PFFY floor-mounted, concealed evaporators. Two 7,500 cfm, 100 percent outdoor air systems by Engineered Air, Calgary, Alberta, Canada, supply the common areas with fresh air, which is drawn into living quarters through bathroom exhaust fans. A third unit provides cooling and make-up air for the dining pavilion. Common area heating and cooling is handled by a combination of ducted and ductless Mitsubishi equipment.
Shaw said VRF is one of Canada’s fastest emerging HVAC technologies and that rooftop presentation has become equally important as performance function.
“As a result of a dedicated design team that paid as much attention to aesthetics as function, the rooftop HVAC condensers, equipment mounts, and line set protection ducting are one of the highlights of the project,” Shaw said.
The Brooks School
Two years ago, administrators of the Brooks School in North Andover, Massachusetts, were faced with having to replace both the dishwasher and the hot water heating system at the school. Instead of simply replacing the old boilers, administrators began looking into condensing tankless water heaters, which produce an endless supply of hot water on demand. For schools, which experience periods of high demand followed by periods of low or no demand for hot water, tankless water heaters can provide a logical solution to a water-heating problem.
“In 2012, Brooks was looking to make its entrance into energy-efficiency projects,” said Brian Palm, director of sustainability and teacher of environmental science at The Brooks School. “This was an area that had previously been taken on only when a piece of equipment was no longer working. As it happened, two separate departments — dining and facilities — were dealing with issues that were inextricably linked; the dining services director was having repair concerns with the dishwasher, and the director of facilities was concerned about an aging hot water heating system in the basement of the building that provided the kitchen and dishwasher with hot water.”
After receiving proposals for replacing both the dishwasher and the hot water heating system, the operation team at The Brooks School projected that upgrading to tankless water heaters would provide more than $23,000 in savings on an annual basis. “We calculated the project would have a payback of 2.3 years,” Palm said.
That assessment moved the school to replace two 400,000-Btu boilers and a 300-gallon storage tank with three Navien NPE-240A tankless water heaters.
“A year later, the AP Environmental Science class took on the challenge of quantifying first-year savings,” Palm said. “As they found, the opportunity to calculate this return on investment (ROI) provided the chance to combine their understanding of water use and energy use in a real-world application. The project demonstrated the value of this type of investment.”
Bob Avila, owner of Avila Plumbing and Heating, Lawrence, Massachusetts, recommended and installed the Navien units, which include built-in ComfortFlow™ technology that incorporates a buffer tank and pump inside of the casing, eliminating the need for the installing contractor to purchase and plumb in a pump and recirculating line. Avila has installed hundreds of Navien’s NPE units around the Boston area and is a fan of the corrosion-resistant dual stainless steel heat exchangers. “The school’s previous boiler’s stainless steel venting system had pit holes in it and had rotted over time,” he said.
For the Brooks School, the redundancy of the three step-fired Navien NPE units over one replacement boiler and hot water tank was an important and obvious choice, especially since the school had a history of “blowing through” hot water tanks on a regular basis.
Falmouth Elementary School
Built in 1963, the 75,778-square-foot Falmouth Elementary School in Fredericksburg, Virginia, was in urgent need of renovation by 2010. The Stafford County Public Schools Division (SCPS) had begun a shift towards sustainable building practices, including an emphasis on LEED (Leadership in Energy and Environmental Design) philosophies and participating in the Go Green Virginia Green Public Schools Challenge. SCPS decided Falmouth should be renovated with energy reduction as a top priority.
One of the critical challenges to the energy-efficiency renovation for Falmouth was the selection of a new cooling and heating system. The existing through-wall unit ventilators on a two-pipe system did not have proper dehumidification capacity (the cooling coils were not deep enough), and there were no dehumidification cycle controls, which contributed to poor IAQ and a constant battle with mold. The school also maintained a building housing the central boiler and an adjacent chiller garden that was inconveniently located in the school’s parking lot, which made student drop-off and pick-up complicated. Lastly, the system was inefficient. Records show that Falmouth Elementary was operating at 90,000 Btu per square foot, per year, before the renovation — 30 percent higher than the average for educational facilities in that climate area.
Scott Horan, SCPS assistant superintendent for facilities, recognized the school’s very complicated, pre-stressed, precast plank structure meant there was little room for ductwork or piping above a suspended ceiling. Using a traditional variable air volume (VAV) air-handling system would not be the most viable method for this project, he said.
The team included b2E Consulting Engineers (b2E), Leesburg, Virginia, to help them find a solution. “We wanted a design team with a track record of bringing huge energy savings to outdated school buildings,” Horan said. “b2E is known in the area for applying the latest technology to reduce energy consumption in buildings with optimal results.”
b2E and SCPS decided on a new mechanical system that included a VRF zoning system from Mitsubishi Electric US Cooling & Heat-
ing Division. “As a result of installing the Mitsubishi Electric VRF zoning system, we were able to keep the original ceiling heights. Planned suspended ceiling heights improve lighting levels, reduce sound levels in classrooms to NC [Noise Criterion] 30 or quieter, and improve occupant comfort,” said Bruce E. Beddow, professional engineer and founder, b2E.
An important consideration for a school system is the automatic control system. The VRF zoning system comes on line at startup and does not need to have the energy management system (EMS) tested and commissioned prior to opening the school. The EMS allows the equipment to be controlled from a remote off-site location via the Internet.
Timm Guyer, project manager for Acme Mechanical Contractors of Virginia Inc., Manassas, Virginia, installed the system. “The Mitsubishi Electric VRF zoning system was a perfect fit for the Falmouth installation,” he said. “It was easy for us to install, is super efficient, and we have had zero warranty issues.”
From a utility bill comparison, Horan estimates a 25-30 percent average reduction in energy use. “This is impressive when you consider we increased the building area by about 20 percent, or 13,000 square feet.”
St. Lucie County School District
The air-cooled chillers at several St. Lucie County School District sites were reaching the end of their useful lives. In addition, utility rates that included both energy usage and demand charges were high. With air conditioning representing one of their largest energy use items, the school district sought more efficient HVAC solutions but knew that with the poor economy, getting budget approval to move forward with the needed renovations would be difficult. They also knew that with the hot, humid climate in South Florida, reliable air conditioning was a must.
The St. Lucie County School District put together an energy advisory board consisting of vendors, engineers, district staff, utility company personnel, architects, engineers, school board members, and others to address ways to reduce utility costs. Rather than just considering individual schools with immediate needs, the group outlined a long-term plan for replacing entire systems districtwide over a span of five, 10, and 15 years. The group evaluated its replacement-versus-repair options, taking into account maintenance expenses, the age of the chillers, and replacement chiller life cycle costs. Thermal energy storage was suggested as a sustainable solution for the district.
Pleased with its long-term relationship with Trane, which, according to school officials, included excellent equipment performance, superior service, and training for its technicians, board members asked Trane to bid on its HVAC upgrades. Trane presented a chiller plant upgrade with thermal energy storage using energy savings and utility rebates to offset the cost of the chiller investment.
After feasibility studies and school board approval, Centennial High School was selected as the first site for a Trane chiller plant upgrade with thermal energy storage. The project reduced the high school’s annual electric bill by more than 50 percent. Based on this success, the district moved forward with plans to upgrade 13 district locations.
The chiller plants were designed with highly reliable Trane air- and water-cooled chillers, ranging 600-1,200 tons, to accommodate the varying needs of the sites. Running at cooler temperatures, the chiller plants provide better dehumidification — an important benefit in the humid Florida climate — and operate more efficiently with less pumping and fewer fans.
After comparing options, the district selected the superior design and operation of the CALMAC IceBank® energy storage tanks for the plants. The ice-enhanced water- and air-cooled chiller plants build ice at night during off-peak hours when the cooling and power load is low, allowing the schools to take advantage of lower-cost electricity rates. Using full- and partial-load shifting helps the district manage peak electrical demand and avoid costly substation upgrades.
The chiller plants at three schools located in close proximity of each other were replaced with a centralized chiller plant built between them. The centralized plant, which includes more than two miles of underground piping to connect the schools to the plant, allowed the district to reduce chiller capacity by 300 ton. So as not to interfere with school operations, the centralized plant was installed during the summer with piping and interconnections being completed after school startup on weekends and holidays.
“A few years ago, our utility costs were about $12 million,” said Marty Sanders, director of growth management, maintenance, and facilities, St. Lucie School District. “We’re now under $7 million.”
Using the thermal energy storage to shift load from peak to non-peak hours has also reduced demand charges, and resulted in rebate incentives from Florida Power & Light and a three- to five-year payback on the project.
“If we reduce our demand during the peak daytime hours, the utility company doesn’t have to build as many power plants, and it also helps reduce brown outs,” said Sean Murray, energy manager, St. Lucie School District. “Being part of the solution is good.”
“We were ranked 60th of 67 counties in energy usage, and we’ve been able to reduce that to 18th in the state. By reducing our operational costs, we are, in essence, saving teachers’ jobs,” Sanders said. “This helped us save about 100 jobs.”
Publication date: 8/4/2014