Daniel Addis, Jensen Ying, and Eui Song (John) Kim, Carnegie Mellon University
When considering the program for a laboratory complex on St. Croix, we immediately encountered a few factors that directly relate to sustainability and carbon footprint. From the beginning, we decided to stay off the grid; with the strength of the sun at 17.7° North latitude, we deemed solar power generation a viable solution for energy demands. Meeting the complex's potable water needs was the next challenge; St. Croix has a limited ground water supply, and the current practice (desalinization) is expensive and energy intensive. Furthermore, the island is riddled with failing septic systems that contribute to ground water contamination. With these factors considered, our priorities were to provide a design solution that would generate clean energy on site, self-supply all its potable water needs, and safely treat all wastewater generated. Aligning the campus axis to capture the prevailing winds from the east and southeast has created a low-pressure conditions within the courtyard to help exhaust hot air from the unconditioned spaces. This orientation maximizes northern and southern exposure, allowing for optimal solar power generation from the south and effective daylighting from the north.
Photovoltaic solar-thermal arrays on most of the buildings satisfy campus energy and domestic hot water demands. The laboratory air-conditioner uses a heat-pipe, which removes heat from the incoming air supply before it reaches the cooling coil and then reapplies that heat energy to the super-cooled conditioned air to bring it to a supply temperature of 62 degrees. This eliminates the need to mechanically reheat supply air and allows for up to a 15 percent reduction in electrical loads for the air-handling unit. This system, paired with our saltwater Sea-O-Thermal heat exchanger, allows for a smaller, more efficient chiller unit. In the laboratory building, where a deep-seawater inlet is required for specimen tanks, a closed-loop heat exchanger rejects heat from the air conditioner's condenser to the return seawater outlet pipe, significantly improving condenser performance and bringing return deep seawater to a more appropriate coastal deposit temperature.
The potable water needs for all buildings are satisfied through rooftop rainwater collection. The primary laboratory-grade water tank is attached to a purification unit that consists of a carbon filter and an ultraviolet light sanitizer. Excess rainwater is deposited into a central tank, where it goes through a similar cleansing process in order to provide potable water to the entire campus. Wastewater from the campus is collected and processed on site with an environmentally neutral waste management approach. The Green Machine is a black water filtration system that uses naturally occurring ecology to bring wastewater to near-potable levels without the use of hazardous chemicals or significant energy expenditures. This is done through wetland plants with high tolerances for pollutants and heavy metals. These plants, paired with aerobic and anaerobic bacteria, work through a number of stages to produce grey water for non-potable usage requirements. This system is integrated within the central courtyard and blends in as a planted feature.
The combination of strategies for environmental impact mitigation allows our laboratory to function with extreme efficiency and minimal environmental impact. The use of the seawater inlet as a heat exchanger combined with a heat-pipe energy recovery system allows for high performance from conventional air conditioning components. Similarly, implementations like the photovoltaic solar-thermal array and the Green Machine work together to generate huge amounts of energy with minimal environmental disturbance.