Nocturnal Radiation Cooling Tests

Pan

Building Services Engineering Research and Technology

et al. 2016

The importance of atmospheric down-welling radiation in studying building thermal environments and energy performance has been well identified, and empirical formulae to evaluate atmospheric down-welling radiation values developed with their inadequacies. In this paper, a study of developing an alternative general method for evaluating atmospheric down-welling radiation values to the water pond-based empirical formula by Clark and Allen is reported. The validity of the alternative general method has been demonstrated by comparing the atmospheric down-welling radiation values evaluated using the alternative general method and that using the Clark and Allen’s formula. Since the alternative general method developed is based on a building roof system, and no water is involved, the alternative general method developed in this paper appears to have more advantages. On one hand, this could eliminate any potential impacts on prediction accuracy when water is used in different climates. On the other hand, the application of the alternative general method is relatively easier as only a suitable existing roof system is required. Therefore, the use of alternative general method can provide a more reliable and economic alternative in evaluating atmospheric down-welling radiation, when compared to using Clark and Allen’s empirical formula. Practical application The alternative general method developed for evaluating atmospheric down-welling radiation values in this paper could be used as an alternative to the empirical formula proposed by Clark and Allen and is valid for all climate conditions and easy to be implemented to evaluate alternative general method values. It can be used when evaluating building night sky cooling, building passive cooling system, etc.

Section: Introductionmentioning

confidence: 89%

An alternative general method to evaluate the atmospheric down-welling radiation

Pan

Building Services Engineering Research and Technology

et al. 2016

“…By using perfect mathematical model, the active thermal performance of the system during summer climate is calculated, based on the heat transferred to the ambient air from the air inside the radiator. Hollick in Nocturnal radiation cooling tests has summarized that the sun and earth radiate heat to earth and sky in the day and night, respectively. The solar radiation gains by the roofs at day time, and on the other hand, at night time, earth radiates heat to the sky, and due to this heat loss has the facility to cool air as roofs can occur at a temperature decrease from 2 to 12 °C below surrounding temperature.…”

Section: Literature Reviewmentioning

confidence: 99%

Comparative Study of Experimental and Theoretical Evaluation of Nocturnal Cooling System for Room Cooling for Clear and Cloudy Sky Climate

Mulik

Kapale²,

Kamble

2019

Global Challenges

Nocturnal radiation is one of the effective passive cooling technologies by infrared radiation exchange between earthly surfaces and the sky. Heating ventilation and air conditioning (HVAC) systems are highly energy‐demanding and there is a need to develop alternative low‐energy means to achieve comfort. Radiative cooling reduces the electricity requirements, which normally is generated through fossil fuels, in order to run active cooling systems. During the day, this is offset by solar radiation gains on the roof; however, at night, this heat loss has the ability to cool air, as roofs can experience a temperature drop of 2–12 °C below ambient. The experimental investigation of the aluminum material and their surface colors on nocturnal cooling is presented for clear and cloudy sky conditions. The material of aluminum and black color coating are considered. Results obtained reveal that the plates' performances greatly depend on the presence of clouds in the night. The best results are obtained in a clear sky summer climate condition than in the cloudy sky condition. The net cooling rate of night sky radiation system for without and with coating on aluminum of mass flow rate 0.05 kg s−1 is near about 72.30–80.99 W m−2 for clear sky and 48.75–53.25 W m−2 for cloudy sky condition.

Building Services Engineering Research and Technology

“…Their results showed that the surface temperature can be decreased by 1 C to 6 C below the ambient temperature under both clear and cloudy skies; however, the temperature of the roof radiator is quite close to the surrounding air under a rainy sky. The transpired solar collector was proposed by Hollick 10 for the application of nocturnal radiative cooling, in which the temperature of the ambient air used for cooling the building can be reduced by 4.7 C on a clear night. Although nocturnal radiative cooling has energy-saving potential for building applications, its potential is limited at nighttime due to the mismatch between diurnal radiative cooling and solar radiation.…”

Section: Introductionmentioning

confidence: 99%

Analysis of the impact of a novel cool roof on cooling performance for a low-rise prefabricated building in China

Zhang

Chen

et al. 2020

The recently proposed scalable-manufactured randomized glass-polymer hybrid metamaterial (i.e. metamaterial film) exhibits good energy-saving potential for building applications. The most convenient way to employ this metamaterial film-based radiative cooling is to integrate it with buildings as cool roofs. However, metamaterial film-based radiative cooling is more suitable for buildings with higher roof area to floor area ratios, as this accounts for its relative lower cooling power of 110 W/m2 on a daily average. The prefabricated buildings in China are commonly less than two floors, which are preferable for the application of this metamaterial film-based radiative cooling. To clearly reveal the cooling performance of the metamaterial film-based cool roof (MFCR), a single-floor prefabricated building is modelled in this study, and the energy-saving potential and economic feasibility of the application of the MFCR on the prefabricated building are discussed in detail. When comparing the model in this study with buildings that have the more commonly used shingle roofs or typical white roofs, the annual cooling electricity consumption is reduced by 28.9%–43.0% and 7.8%–12.9%, respectively, for buildings with MFCRs located in five cities in China, each in a different climate zone. Furthermore, the simple payback period for the buildings with MFCRs located in all five climate zones is less than three years compared to the buildings with shingle roofs. Practical application: A recently proposed metamaterial film exhibits good energy-saving potential for building applications. This paper explores the application of this metamaterial film as a cool roof on a low-rise prefabricated building. The analysis of the cooling performance and economic value of this low-rise prefabricated building located in all five climate zones in China provides guiding significance for the application of MFCR.