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Assessment of Energy Use and Comfort in Buildings Utilizing Mixed-Mode Controls with Radiant Cooling

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Abstract

This thesis describes the background, execution and results of a study of the feasibility of mixed-mode building cooling strategies involving radiant systems in California’s 16 climate zones. Informed by case studies, building modeling and evaluation literature, detailed climate studies, and past experience, the research team created a parametric building simulation model in EnergyPlus. The simulation model was used in conjunction with Adaptive and Predicted Mean Vote occupant comfort models to evaluate the energy and comfort performance of mixed-mode buildings with radiant cooling by simulating a range of mechanical systems, control strategies, and physical building characteristics in each climate. Energy performance was quantified as kBtu/ft2-yr and comfort was quantified using the percentage of occupant hours with more than 20% of occupants predicted to be dissatisfied, also known as the exceedance percentage. The cooling strategies simulated performed particularly well in moderate coastal climates, but were also able to meet comfort criteria when gains were controlled through building shell improvements and efficient equipment operation. In several climates, the chilled mass of a floor slab charged overnight by water from a cooling tower was sufficient to preserve comfort throughout the day while using approximately 75% less pump, fan, and chiller energy than a comparable conventional HVAC system. In cases where a cooling tower was insufficient, a chiller was used to improve overnight cooling or to support the all day operation of the slab. The examination of model sensitivity to inputs, and the evaluation of discomfort predicted by the Adaptive Comfort model vs. the Predicted Mean Vote model indicate that site context and occupant expectations will play a significant role in determining the feasibility of mixed-mode cooling strategies. Results are presented graphically to allow comparisons across and within climates and in the form of regional maps that illustrate the geography of potential feasibility of mixed-mode cooling systems. 

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