©2012 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 54, no. 2, February 2012
By Simi Hoque, Ph.D., Associate Member ASHRAE; James B. Webb, Ph.D.; and Andy J. Danylchuk, Ph.D.
About the Authors
Simi Hoque, Ph.D., is an assistant professor, James B. Webb, Ph.D., is a post-doctoral fellow, and Andy J. Danylchuk, Ph.D., is an assistant professor at the University of Massachusetts-Amherst.
Due to environmental degradation and declining capture fisheries, aquaculture now accounts for nearly 40% of the world’s total fisheries production. While per capita seafood consumption has already reached record levels in the U.S., recent USDA recommendations suggest more than twice this amount for a healthy lifestyle. Achieving this goal represents a significant challenge considering approximately 85% of U.S. seafood is imported and nearly half of this comes from overseas aquaculture production. The reliance on imported, cultured seafood problematizes issues of food security, product quality, carbon emissions, and the growing costs of transport and globalization.
Building integrated aquaculture (BIAq) involves taking advantage of the interdependencies between a small-scale indoor recirculating aquaculture system (RAS) and the environment maintained by the building to maximize energy efficiency and optimize operations. In a BIAq approach, gained efficiencies have the potential to offset the energy intensity of recirculating aquaculture and ultimately make local-scale aquaculture more viable. From the twin perspectives of increasing food and energy security, as well as reducing greenhouse gas emissions and environmental waste, the benefits of applying green building principles to meet the needs of aquaculture facilities are clear. We identify areas where a BIAq approach might increase efficiency and reduce operating costs. Our focus is on processes and design decisions that have the greatest potential for energy conservation in the heavily populated temperate regions of the world.
To maintain a “water quality environment” suitable for the culture of fish and other aquatic organisms, traditional aquaculture systems such as ponds and net-pens rely on ambient outdoor temperatures and environmental services. This severely restricts the locations in which aquaculture can succeed. Because it has no such restrictions, an RAS provides an opportunity for commercial aquaculture within the urban and suburban environments where fish demand is greatest. To maintain a suitable water quality environment, an RAS uses an array of technology and equipment that provide thermal stability and oxygen, while simultaneously processing metabolic wastes, such as undigested solids, ammonia, and carbon dioxide, and limiting the proliferation of pathogenic organisms and disease (Figure 1). In an RAS, commercial success relies on balancing the costs of water treatment with the value of fish production. The high costs of operating water filtration and temperature control equipment requires culturing fish at exceedingly high densities (e.g., greater than 100 kg of fish per cubic meter [~1 pound per gallon] of water). Fish vary considerably in their tolerance to such conditions. Considering the majority of species amenable to an RAS require warm water, the success of local-scale BIAq in temperate climates relies largely on reducing the annual cost of heating water to levels below that of transporting processed fish from warm water production sites to temperate consumer markets.
Integrating Energy and Climate Control
Energy demands for space heating and cooling, water heating, humidity control, lighting, and electricity greatly influence overall building energy profiles. Studies have shown that in the U.S. over 75% of the total energy demands are due to building operations. In aquaculture facilities, additional complexities must be addressed. The specific enthalpy of the indoor environment is high due to the evaporation of the water, which requires extensive dehumidification and air exchange. Relative humidity, air temperature, water temperature and air quality are all critical environmental control factors. In BIAq facilities, water heating and dehumidification costs are coupled. Given that a significant portion of annual energy costs originates from water surface evaporation losses, care must be taken to reduce the evaporation rate. The warmer the water used in indoor recirculating aquaculture facilities, the higher the evaporation rate. The lower the indoor environment’s dew point, the higher the evaporation rate. Energy and climate control in BIAq facilities must take into consideration humidity, airflow, and condensation risks.
Conventional aquaculture facilities do not typically control for humidity, and latent loads are simply allowed to “float” within the interior environment. While this may help to reduce the overall energy lost to evaporation, the greater than 80% relative humidity that inadvertently results poses a significant threat to the building’s envelope. Without proper humidity control, increased relative humidity can present a host of structural as well as occupational hazards. High relative humidity levels inside a building are well known for their destructive effects on building structure due to moisture intrusion and condensation within the building assembly. Condensation within the building assembly degrades the structure and thermal effectiveness of envelope materials. It rots wood, rusts steel, and causes freeze cracking of masonry. It also reduces the thermal resistance of insulation. Increased humidity and risk of condensation also promote the growth of mold and mildew, which can adversely impact the air quality. To ensure building durability as well as occupant comfort, the relative humidity in a typical indoor zone for human occupation should be maintained within a range of 50 to 60%.
Citation: ASHRAE Journal, vol. 54, no. 2, February 2012
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