Next-generation dedicated outdoor air cooling systems for low-energy buildings

Abstract

Building operations take up more than 40% of the overall energy consumption in the United States, among which cooling energy comprises an especially significant part in hot and humid climates. To achieve low-energy and low-carbon building communities, it is necessary to design high-performance building enclosures and develop energy-efficient cooling technologies and systems. High-level prescriptive code requirements for low-energy buildings are available but details of building envelope construction are missing in the literature. Previous studies have primarily focused on analyzing one type of new technology or its applications in a particular climate, while a systematic comparison is needed to address the prospects and limitations of each system. In this thesis, thermodynamic analysis has been performed on dedicated outdoor air cooling systems (DOAS).

Energy performances of next-generation DOAS cooling systems, namely those with desiccants and membranes, are compared with the industrial benchmark, the widely used chiller system based on vapor-compression cycle, on the basis of first-law and second-law efficiencies. Low-energy building prototypes have been constructed with specified design details to provide indoor cooling loads for the DOAS cooling systems, and the building energy performances are validated against the existing zero-energy buildings. Dynamic working conditions are simulated, and effects of cooling equipment designs on the energy performances are further examined. Integrations of passive cooling strategies are applied in different climates, and climate-specific solutions have been proposed to achieve best energy performances. Economic costs of each system are estimated, presented with payback period of replacing the existing chiller system.

The thesis reveals the principles of how to systematically organize cooling equipment to achieve potential energy savings from a thermodynamic point of view. Innovative cooling systems are proposed with next-generation cooling technologies. Significantly improved energy performance has been demonstrated through careful system design and integration, as well as energy recuperation. An automated and interactive workflow has been developed to thermodynamically analyze the cooling energy system performances.