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]

Due to the increased expectations on human thermal comfort in sleeping environments at a low energy consumption, task/ambient air condition system (TAC) can be the best air conditioning method when considering the immobility of a sleeping person. Previously, convection-based TAC systems for sleeping environments were developed, with an obvious inadequacy of cold-draft problem. Therefore, a new radiation-based TAC system (R-TAC) was previously developed and experimentally studied at a set of fixed design parameter for its radiant panel. Therefore, a follow-up numerical study on the effects of varying design/operating parameters of the radiant panel on indoor thermal comfort and energy saving performances has been carried out, and the study results reported in this paper. Firstly, a geometry model based on the experimental bedroom used in the previous experimental study, boundary conditions and numerical study cases are detailed. Secondly, the results of validating the numerical method using the previous experimental data are reported. Thirdly, the numerical results on indoor thermal comfort, energy saving and draft risk at different surface temperature and emissivity, area of the radiant panel, and the distance between the radiant panel and a bed are presented. The numerical results demonstrated that all the four design/operating parameters of the radiant panel can significantly affect thermal comfort and energy saving performances in the bedroom when using the R-TAC system: increasing surface temperature can lead to a higher PMV value and a higher EUC value; increasing surface emissivity and area of the radiant panel a lower PMV value and a lower EUC value; reducing the distance between the bed and the panel a lower PMV value and a higher EUC value. Finally, the DR values were at a very low level in all the study cases, indicating the cold draft problem encountered when using a convective heat transfer based TAC system for a sleeping environment can be effectively resolved when using the R-TAC system. [ABSTRACT FROM AUTHOR]

This paper systematically reviews literature on passive heating and cooling of buildings using roof ponds. The main aims were to gain a detailed understanding of different roof pond configurations and their performance, compare effectiveness of different roof pond variants, evaluate performance of different roof pond variants relative to other passive design techniques, explore effects of climatic conditions and various design configurations on the performance of roof ponds, and identify gaps in knowledge and data. Overall, 19 roof pond cooling and 4 roof pond heating systems were identified. This review suggests that, in some cases, roof ponds can provide year-round thermal comfort while reducing demand for active heating and cooling systems. Therefore, they can be utilized in efforts towards the goal of carbon–neutral design. Roof ponds with wet gunny bags, shaded roof ponds, ventilated roof ponds, and roof ponds with movable insulation proved to be more effective relative to other variants of roof pond cooling systems. Comparing performance relative to other passive strategies showed that, in many cases, roof pond cooling systems are about equally effective in maintaining indoor thermal comfort. Meteorological conditions, water depth, roof deck material, and thickness of the insulating panel are the main factors affecting performance of roof ponds. Several areas of weakness in the literature are identified. Future research should, among other things, provide more detailed knowledge on performance of all roof pond variants, further explore suitability of roof ponds relative to other passive design measures, examine effectiveness of roof ponds when combined with other passive design measures, analyze life-cycle costs of roof ponds, and provide more knowledge on their real-world application. [ABSTRACT FROM AUTHOR]

A bed-based TAC system applied to sleeping environments has been developed and its performances experimentally and numerically studied, and the study results are reported in this paper. Firstly, a detailed description of an experimental rig for the bed-based TAC system at two settings is presented with a return air inlet on the wall (Setting 1) and with a return air plenum and inlet placed under the bed (Setting 2). Secondly, the experimental results on the operating performances of the bed-based TAC system at the two settings in terms of thermal environmental control and energy saving are analyzed and reported. Thirdly, to supplement the experimental study for a more detailed analysis on air temperature and flow fields, a follow-up numerical study was carried out and is reported. Both the experimental and numerical study results suggested that the bed-based TAC system at Setting 2 performed better in controlling thermal environment in an occupied zone but with a relatively poorer energy saving performance, as compared to that at Setting 1. [ABSTRACT FROM AUTHOR]

Abstract: In the museum environment, the temporal stability and the spatial uniformity of the indoor microclimatic parameters are necessary primarily for the correct artwork conservation and then for the occupant thermal comfort. Therefore, a HVAC system is usually necessary. This paper above all emphasizes the integration of Building Energy Performance Simulation (BEPS) and Computational Fluid Dynamics (CFD) codes. This coupled numerical approach can provide accurate information about both the HVAC system energy request and the indoor microclimatic control (temporal and spatial distribution of the parameters). Then, a case study concerning a typical museum exhibition room is examined. The annual energy request for three types of all-air system, as well as the temporal variation of indoor temperature and relative humidity, is evaluated by means of a BEPS code. Energy savings can be obtained using a system with desiccant wheel (11%) or enthalpy wheel (9%), compared to the base system. As regards indoor relative humidity control, this is more critical for summer conditions, and the best performance is obtained by the system with desiccant wheel. Then, the spatial microclimatic control is analyzed by means of a CFD analysis, for various thermal load conditions and different air diffusion xequipments. The best performances are obtained by using the swirling (vortex) diffusers; also the perimetrical stripes of slot diffusers show satisfactory performances. Finally, in order to evaluate the ability of air diffusion equipments to assure good ventilation effectiveness, an analysis of the mean age of air is carried out too. [Copyright &y& Elsevier]

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]

• The potential of energy saving by using adaptive setpoint temperatures. • The influence of thermostats according to their accuracy: 0.1, 0.5, and 1 °C. • The analysis of two case studies in the current scenarios, 2050 and 2100. • The 0.5 and 1 °C thermostats achieved energy savings of more than 40%. Building energy performance should be improved to reduce the impact of climate change. The energy saving potential has been recently proved with adaptive setpoint temperatures. However, the accuracy of thermostats hinders the achievement of the energy saving obtained in previous studies. For this reason, this paper studies the influence of three types of thermostats according to their configuration accuracy: 0.1, 0.5, and 1 °C. Two case studies (with and without retrofitting) were analysed in three cities in the current scenario, in 2050, and in 2100. The results showed that the implementation of adaptive setpoint temperatures in thermostats of 0.1 °C virtually obtains the same savings as the direct application of thermal comfort limits. Nevertheless, obtaining considerable energy savings in the other two thermostats depends on the type of energy consumption, climate, and the category of the thermal comfort model. The application of adaptive setpoint temperatures in air conditioning systems obtains energy savings greater than 40%, regardless of the type of thermostat and category, whereas in heating systems, only the category III obtains energy savings with old thermostats. [ABSTRACT FROM AUTHOR]