A novel hybrid radiative and ventilative cooling system integrated with latent heat storage for buildings in hot-arid climates

Zein Elabdein, Rami (2019) A novel hybrid radiative and ventilative cooling system integrated with latent heat storage for buildings in hot-arid climates. PhD thesis, University of Nottingham.

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Abstract

The use of phase change material (PCM) as potential energy storage for cooling of buildings using night low-temperature air is one of the promising sustainable strategies referred to as “the free cooling of buildings”. Application of this strategy in hot climates is not exploited, and most of the published work has been carried out in moderate and continental climates. Moreover, the free cooling potential is insufficient under extreme summer conditions, owing to the small temperature difference between the PCM and the ambient air in addition to the limited available charging time. Therefore, with the aim of sustaining and enhancing the free cooling potential in such disadvantageous conditions, an innovative hybrid nocturnal radiative and ventilative cooling system using latent heat storage (NRV-LHS) has been proposed in this study. Such a combined system has not been adduced in previous studies.

In this research, the nocturnal radiative and free cooling potential in hot-arid regions is assessed. According to the local climate and thermal comfort conditions of the case study, a paraffin-based RT28HC PCM of a transition temperature range of 27-29 °C was considered. Thermal energy storage (TES) system comprising a number of PCM panels has been proposed and assessed using transient computational fluid dynamics modelling to optimise the geometrical configuration under various inlet air conditions. The proposed PCM storage system has been investigated experimentally to evaluate the charging and discharging behaviour of the PCM for a range of PCM modules arrangements. The operational performance of the hybrid NRV-LHS system has been evaluated experimentally under hot and moderate summer conditions of hot-arid climate for various scenarios of free and radiative cooling operation modes.

The parametric study results have shown that a compact TES system design made of thin PCM modules and narrow air flow channels is more effective in accelerating the PCM charging process. The difference between the PCM transition temperature and the inlet air temperature, along with the air flow rate play a significant role in the heat transfer rate during both transformation phases.

The findings have indicated that the proposed NRV-LHS system has a great potential to operate satisfactorily under the severe summer conditions in hot-arid regions. The system can improve the thermal performance of the free cooling systems by extending the charging period beyond the free cooling range. The system also enhances the heat transfer rate and minimises the effect of PCM supercooling, which contributes positively to the charging effectiveness. For the summer period (May-October), the system could fulfil up to 57% of the cooling load. The estimated COP of the system varied between 5.82 and 9.01. This performance could allow the system to maintain the thermal comfort, leading to substantial energy savings up to 76% compared to conventional air conditioning systems. The outcomes of this research would be beneficial to introduce an appropriate design of PCM-air heat exchangers combined with an air-based nocturnal radiative cooling system, applicable for real implementation in buildings, especially in hot-arid regions.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Omer, Siddig
Gan, Guohui
Keywords: Free cooling; Radiative cooling; Thermal Energy Storage; Phase change material; Hot-arid
Subjects: T Technology > TH Building construction > TH7005 Heating and ventilation. Air conditioning
Faculties/Schools: UK Campuses > Faculty of Engineering > Built Environment
Item ID: 55966
Depositing User: Zein Elabdein, Rami
Date Deposited: 19 Jul 2019 12:35
Last Modified: 07 May 2020 11:45
URI: http://eprints.nottingham.ac.uk/id/eprint/55966

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