Search

This paper presents an autonomous hierarchical control method for a direct expansion air conditioning system. The control objective is to maintain both thermal comfort and indoor air quality at required levels while reducing energy consumption and cost. This control method consists of two layers. The upper layer is an open loop controller that allows obtaining tradeoff steady states by optimizing the energy cost of the direct expansion air conditioning system and the value of predicted mean vote under the time-of-use price structure of electricity. On the other hand, the lower layer designs a model predictive controller, which is in charge of tracking the tradeoff steady states calculated by the upper layer. Control performance of the proposed control method is compared to a conventional control strategy. The results show that the proposed control strategy reduces the energy consumption and energy cost of the direct expansion air conditioning system by 31.38% and 33.85%, respectively, while maintaining both the thermal comfort and indoor air quality within acceptable ranges, which validate the proposed methodology in terms of both comfort and energy efficiency. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the effect of operating water mist system to enhance the energy efficiency of air-cooled chillers under various operating conditions. A thermodynamic model for an air-cooled chiller with twin refrigeration circuits coupled with a water mist system was developed and validated by measured operating data. The validated model was used to investigate how the thermal properties of the entering condenser air and the performance of the air-cooled chiller varied under different operating schemes with water mist pre-cooling. Under the conventional head pressure control (HPC) with a designed water mist generation rate, the coefficient of performance (COP) increased by up to 21.3%. The chiller performance could be improved further under variable condensing temperature control (CTC). Under CTC, chiller COP was increased up to 51.5% with optimal water mist generation rate. The potential energy savings of these chillers serving a representative office building in subtropical climate was evaluated, and CTC coupling with optimal water mist generation rate would reduce the annual total electricity consumption for cooling by 14.1%. The water consumption of the water mist system was comparatively small, comparing with the total water losses for an open-loop cooling tower system with equivalent heat rejection capacity. [Copyright &y& Elsevier]

Abstract: Because of their excellent performance in local thermal environmental control, task/ambient conditioning (TAC) systems have attracted increasingly more research attention. However, the current applications of TAC systems are mainly for daytime activities, but seldom for nighttime. In fact, TAC systems may be best applied to a sleeping environment, since the subjects to be served by a TAC system are immobile during sleep. Therefore, there is a strong need for studying the operational and energy saving performance of TAC systems when applied to sleeping environments. This paper reports on an experimental study on evaluating the operational and energy saving performance of a novel bed-based TAC system. The experimental results and their analysis demonstrated that the use of the novel bed-based TAC system can help achieve energy saving, compared with the use of a full volume air conditioning (FAC) system. Considering the experimental limitations, the energy saving potential of the novel bed-based TAC system if used in an actual bedroom was studied through a theoretical analysis. It demonstrated that the novel bed-based TAC system would help achieve significant energy saving when used in real buildings. [Copyright &y& Elsevier]

Abstract: This paper evaluates the performance of a personalized air-conditioning system, namely an innovative partition-type fan-coil unit (PFCU), against that of a central air-conditioning system, in terms of their thermal comfort provided and cooling energy consumed. For a cooling load given, it is found that the thermal comfort index (PMV) resulted from the personalized system is always lower than that from a central system. Also, the PMV-curve of the personalized system responds to the loads faster. The experimental results indicate that the personalized system, as compared to the central system, can shorten the operation time for the same level of thermal comfort required and save up to 45% of the energy consumed by the central system. As regards thermal comfort, the experiment with a thermal manikin substrates the PFCU design for its considerable reduction of the cold draft. [Copyright &y& Elsevier]