Education institutions at all levels have the unique opportunity of informing tomorrow’s energy stewards. For this reason, schools and universities should invest not only in their students, but also in the facilities where their students learn.
On a more practical level, investing in sustainable technologies today can help buffer current and future fossil and electrical fuel costs, reducing energy and operational expenditures. Here’s a look at a few sustainable (and renewable) technologies that can be used today and tomorrow in K-12 and university facilities, and the benefits and drawbacks to each:
Mechanical Systems
Because of the high heating and cooling loads K-12 and university buildings typically have during the school year, any reduction in HVAC system expenditure will minimize the school’s carbon footprint and increase operational savings. The most viable mechanical system strategies for schools include chilled beams, water-source heat pumps and variable refrigerant flow systems.
•Chilled beams. A chilled-beam system provides heating and cooling all year to spaces using a combination of water and air. The system works by using primary air from either a dedicated outside-air system or a traditional air-handling unit and mixing it with induced air from the space. The chilled beam then conditions this mixed air to the desired temperature and releases it into the space.
The system gains efficiency by using water to transport cooling and heating around the building (water has a higher capacity to store energy than air), while also saving on fan horsepower by moving less air through the ductwork, as part of the conditioned air comes from the space itself.
Although chilled-beam systems are ideal for dry climates, they are less so for climates with high humidity, where condensation from operable windows can be a conflict. For this reason, chilled beams may not be the best fit for K-12 schools with densely occupied classrooms equipped with operable windows, but can be ideal for university facilities that typically don’t have operable windows and are less dense.
•Water-source heat pumps. These function like a window air-conditioning unit, conditioning the air in the space and dumping the opposite outside via water. They are reversible, however, and can condition the space with either hot or cold air.
Each space is fitted with an individual water-source heat pump to control the local temperature, making it ideal for K-12 schools or a university’s administrative offices where there are rows of rooms. Similar to the chilled beam, this system can be more efficient than traditional air-handling units because the heating and cooling transportation energy is low, and the heating efficiency of water can be several times greater than that of gas.
When employed in temperate climates, water-source heat pumps can eliminate the need for a central heating system; in cold climates, a supplementary source of heat (like a hot-water boiler or electric reheat system) is necessary.
Because the pumps condition each space locally, the amount of ductwork can be reduced greatly and therefore, floor-to-floor heights can be reduced by as much as a foot each. Potential disadvantages include a high first-cost of equipment, and noise and maintenance disruptions because the units are situated in the actual classrooms.
•Variant refrigerant flow system. Taking the concept of the first two systems one step further, a variant refrigerant flow (VRF) system uses refrigerant to move energy around a building in small pipes (2 inches or less). The VRF system uses compressors on the roof and fans and filters typically situated locally, which can occupy even less space than chilled beams or water-source heat pumps, making it ideal for urban schools where old buildings don’t allow for ductwork or where hot-water boilers may not already exist.
Downsides include the high cost of the VRF system and the potential risk that refrigerant could leak into occupied spaces.
Electrical Systems
Some notes about lighting and electrical systems:
•LEDs vs. fluorescents. There is a progression toward LEDs, and they are ideal for spaces where dimming is required, such as auditoriums, conference rooms or classrooms where daylighting is employed. Other examples are gymnasiums where it is difficult for maintenance personnel to change bulbs, and instant-on applications where occupancy sensors are used. However, fluorescents are competitive in other areas compared with LEDs, including first-cost, longevity and energy. In fact, it’s still possible to meet and even beat current energy codes using a well-designed fluorescent layout. Long-life fluorescents will last almost as long as LEDs and are ideal for classrooms; they are less expensive and more standardized, which makes updates and changes easier.
•Switching/Sensors. The National Electric Code requires classroom lights to be zoned, so they can be turned off as necessary via an automatic time-of-day control or occupancy sensors. Occupancy sensors are the least expensive way to meet this requirement, but can be problematic if they are not designed or commissioned properly, because lights could turn on and off at undesired times. Dual-technology sensors that include passive infrared and ultrasonic technologies tend to be less problematic.
The automatic time-of-day control may be more costly for smaller spaces compared with occupancy sensors, but it gives occupants more control over lighting levels. Otherwise known as a central lighting control system, the time-of-day control also can provide dimming, zoning and multiple program options. Although the time clock may be more difficult to justify on a K-12 budget, it usually is a good fit for a university where more control is desired and larger spaces require more flexibility and varied schedules.
•Solar renewables. Schools talk so much about employing renewable energy that it seems like a given to specify some type of renewable source. However, a cost-benefit analysis is imperative to determine if a school’s budget will justify the often longer-than-desired payback that still plagues many renewable energy generation sources.
Although the sun is the most accessible source of renewable energy, the following solar options will require a significant amount of roof space to produce even a small percentage of a school’s total energy expenditure. All are viable for both K-12 and university applications:
-Solar hot water. This option uses solar radiation to heat water and can even produce energy during the winter in colder climates. The more water used, the quicker the payback, making this renewable ideal for a locker room, for example, where water demand is high.
-Solar ventilation panels. Using solar radiation to preheat ventilation air, solar ventilation panels are made of triangle-shaped, black corrugated metal with holes. They are viable even in colder climates, but need a significant amount of roof or wall area for proper application.
-Photovoltaics. The most popular of the solar renewables, photovoltaics are great for demonstrating a school’s commitment to sustainable energy and carbon footprint reduction. But they have a long return on investment. Even as the price of photovoltaics drops, and government subsidies continue, most climates will still experience a 20-year payback on installations.
Brooks, PE, is a partner at McGuire Engineers, Chicago. He has been designing sustainable technologies in schools and universities for 18 years.