Prospects of the low exergy cooling system motivated this study to explore the performance of such a design in practice for the tropical context. The objective of this study was to evaluate the performance of the low exergy systems in the tropics depicted as DDOAS (decentralized dedicated outdoor air system)-RCP (radiant ceiling panel) in terms of thermal comfort, indoor air quality, energy and exergy saving potentials. The low exergy concept in the tropics encourages using low valued exergy sources for building services in order to minimize exergy destruction of processes inside building. In particular, for air conditioning system, this means satisfying cooling load of space with
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chilled water closer to thermal comfort temperature range. This change from conventional air conditioning to DDOAS-RCP requires modification and customization of components to accommodate an effective implementation of the concept. The new conditioned space with DDOAS-RCP has different characteristics compared to the conventional all air system which needs to be determined. The second objective was to explore these characteristics and determine the perception of occupants toward these low exergy technologies as well as any possible indoor air quality concerns.
Thermal comfort is the status of human body when it gets into thermal equilibrium with environment without feeling dissatisfied. The main variables which influence the comfort status of human body include dry bulb temperature, mean radiant temperature, clothing level, metabolic rate, water vapour pressure and air velocity. In addition to these parameters, mental condition and well-being of occupants also play some roles which are beyond the scope of this PhD research. Thermal comfort needs to be investigated for the whole occupancy zone as well as for local discomfort concerns if there is considerable variation of environmental parameters in the space. Indoor air quality of the space also needs to meet some minimum requirements for the main pollutants provided by the local and the International guidelines and standards. This is to ensure the pollutant concentrations do not exceed the thresholds and there is no health risk for occupants. This research aimed to investigate the conformability of indoor air space conditioned by DDOAS-RCP with the local/International standards and thermal comfort models.
The main advantages of DDOAS coupled with radiant ceiling panel compared to the conventional all air system are less noise and better thermal
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comfort for occupants achieved by radiant heat transfer. In addition, this design can reduce the required floor to floor height in buildings and potentially it consumes less energy and exergy compared to the conventional system. On the other hand, the main concerns of this system for the tropics are the potential condensation risk on radiant panels and lower air movement compared to the conventional air conditioning systems in this climate. The latter issue is mostly relevant in the tropical context while in moderate and cold climates, lower air movement or less draft is mostly considered as a benefit. With high outdoor humidity levels all year round, dew point of the interior space has to be actively controlled to be well below the radiant panel surface temperature in order to avoid condensation. With this consideration, there would be some limitations regarding the contribution of radiant ceiling panel in total sensible heat removal of space. Overall, the operating condition of radiant ceiling panel should be optimized based on the sensible cooling load of the space. Developing a better understanding on the ratio of sensible cooling provided by radiant panel compared to sensible and latent cooling provided by decentralized air supply units is one of the main objectives of this research. The air movement in DDOAS-RCP is lower than that for the conventional all air system which may not satisfy the requirement of local standard SS 554 (in range of 0.1-0.3 m/s). Albeit, in DDOAS-RCP design, this lower air movement is compensated by lower mean radiant temperature in space, the response and adaptation of occupants in the tropics to this new indoor environment needs further investigation.
Computer aided engineering (CAE) is gaining more weight in the building related research and industry over time and the advanced simulation models are
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capable of predicting different aspects of building performance. Inside the buildings, CFD (computational fluid dynamics) can provide insights into indoor air characteristics, spatial distribution of environmental parameters and pollutants in the space. This study utilized CFD simulation to numerically determine indoor air characteristics and radiative/convective heat transfer mechanism around radiant panel and occupants. As a necessary step, it is required to validate the CFD simulation results with experimental data in order to be able to proceed with predictions of different scenarios. Providing a clear understanding on differences between indoor air characteristics of DDOAS- RCP with the all air system was one of the objectives of this thesis.
There is potential for integration of DDOAS-RCP with compatible technologies like low temperature lift chillers. These integrations can further enhance energy saving opportunities of the design. Higher operational efficiency of chiller can be achieved by deploying a separate low loft chiller for radiant cooling system. The level of improvement in COP of chiller is required to be quantified for the tropical context. The order of improvement would determine whether running two parallel chillers in DDOAS-RCP could be economically attractive to building managers.