Mills River, NC
- Elementary or Middle School
Henderson County Public School
Hillandale and Mills River Elementary Schools share a common design built on two different sites in Henderson County, North Carolina. Opening in August 2009, the two schools provide learning space for up to 722 students each, with core spaces sized to accommodate as many as 800 students through future classroom additions. Designed by Moseley Architects with 32 classrooms, a gymnasium, media center, art room and cafeteria, the two schools are the first facilities in Henderson County to earn LEED and ENERGY STAR certifications.
94 School House Rd. , Mills River, NC
Typical Number of Permanent Occupants
GENERAL FLOOR AREATotal Gross Floor Area 80,713 ft²
DATE OF OCCUPANCY/COMPLETION August 2009
ARCHITECTURAL MEASURE USED TO MEET A HIGH-LEVEL OF ENERGY PERFORMANCE
As daylighting relies on a complex interaction of many different components, Moseley Architects’ designers undertook significant steps to bring these parts together in the right way. Large windows and tubular skylights are utilized to provide high quality natural daylight throughout each school, with clerestory glazing added to high volume spaces such as the dining and multi-purpose rooms. As a key component of passive solar design, exterior sunscreens were installed at each south-facing window and sized to block out the direct summer sun, while allowing in sunlight during the winter months for free heating. Interior light shelves are also present to reflect light deeper into each space.
Most importantly, perhaps, the overall orientation of each building follows an east-west (E-W) axis to allow all classrooms to face north or south.
Daylight sensors are linked to classroom lighting controls to reduce energy use through on/off switching. Through conversations between HCPS and the project’s engineering team, Optima Engineering, the school district also agreed to a 35 footcandle illumination level for classroom lighting, which provides a substantial savings in lighting energy compared to the 50 footcandles often targeted by other school districts.
In many ways, the widespread participation of school staff in these efforts and the friendly competition between different schools in the district has fostered a culture of conservation at Hillandale and Mills River. Mills River’s Principal Todd Murphy concurs. “These are brand new facilities that we’re proud of and we obviously want to take care of them. We look at them as our homes. With our facilities being green schools, we work on incorporating that theme into the classroom as well.”
Estimated payback time of any investment in measures needed to reach zero net energy
Henderson County Public Schools’ primary energy goal for the design of Mills River was to minimize utility costs while obtaining a reasonable payback period on any investment made to achieve an improved performance. The county’s total investment in energy efficiency features in Mills River and Hillandale combined amounted to roughly 2.4 percent of their total construction cost, representing a total of only $3.87 per square foot. Based on the savings already accumulated in the first three years of operation, it is anticipated that the payback on this investment will be realized in less than five years.
Today, Mills River is saving $60,000 to $70,000 per year in energy costs over a normal design.
To promote reductions in energy use, Optima Engineering utilized a combination of Demand-controlled Ventilation (DCV) and Dedicated Outside Air Systems (DOAS) in conjunction with the schools’ water source heat pumps. In spaces with variable occupancy loads, such as the schools’ dining areas and gymnasia, DCV saves energy by restricting the amount of ventilation air (and thus the need for heating and cooling) when fewer people are occupying a space.
DOAS is most effective in spaces that are either full or empty throughout the typical occupied period, such as classrooms and media centers. Total energy wheels were used in the design to capture energy from the schools’ exhaust air stream. This use of energy recovery cuts down on installed tonnage and hence the operating energy of the DOAS. Because much of the school year occurs during the “shoulder seasons” of spring and fall, the DOAS unit is often able to satisfy space conditions without energizing the heating or cooling mode of individual heat pumps.
Building Envelope Thermal Performance and Mechanical Systems
Mills River's daylighting design, includes enlarged windows, exterior sunscreens to prevent too much solar heat gain in the cooling season, and interior light shelves that redirect visible light deep into each room and prevent glare. Powered lighting is programmed to dim based on how much natural light is available.
Mills River utilizes a solar hot water heating system, where the solar system heats the incoming water supply to 124 degrees. Natural gas boilers then heat the water to the desired temperature, for domestic hot water uses and the condensing boilers that feed the hot water loop for the schools’ water source heat pumps.