THE DEVELOPMENT OF AN AIR-COOLED ABSORPTION CHILLER CONCEPT AND ITS INTEGRATION IN CHP SYSTEMS

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2004

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This dissertation focuses on the feasibility, crystallization issues, and the integration of LiBr-H2O air-cooled absorption chillers into Cooling, Heating and Power (CHP) systems. The concept of an air-cooled system is attractive because the cooling tower and the associated installation and maintenance issues can be avoided. However, crystallization of the LiBr-H2O solution then becomes the main issue in the operation of the unit, since the air-cooled absorber tends to operate hotter than the water-cooled absorber due to the relative heat transfer characteristics of the coolant leading to crystallization of the working fluid. Differently from the conventional approaches to air-cooled absorption chillers, novel temperature control strategies in conjunction with a specialized application is proposed. This prevents crystallization but presents unique system integration challenges and opportunities. A model to accurately reflect the thermodynamic characteristics of air-cooled absorption chillers and to facilitate control is developed as part of this research, and field experiments that simulate air-cooled conditions with a water-cooled absorption chiller, which was driven by the waste heat of a microturbine, were conducted to validate the feasibility of the air-cooled concept and the accuracy of computer model. While CHP provides a good opportunity for the application of air-cooled absorption chillers, system integration issues need to be investigated. The capital cost of CHP equipment and the load fluctuation of a commercial building restrict the advantage of designing a unit sized for peak load. Therefore, the conventional Heating Ventilation and Air Conditioning (HVAC) system is needed to pick up the residual loads. Thus, the result of an extensive system integration analysis is that CHP should be arranged in series with the HVAC system to ensure obtaining more operating hours at its full capacity, so that the cost savings achieved through the recovery of waste heat are fully realized to repay its higher initial capital cost. The primary energy savings are presented for all potential configurations. As a part of this research a fully integrated CHP system has been installed and instrumented at the Chesapeake Building. It is a commercial office building on the University of Maryland campus. The experimental setup, data processing, and experience gained are detailed here. Based on the computer simulation, extensive experiments, first hand installation, operation and maintenance experience, valuable guidelines on the integration of an air-cooled absorption chiller in CHP are developed. All the guidelines are also applicable to water-cooled absorption chillers.

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