Nocturnal Radiation: New Opportunity in Building Cooling

Abstract

Free cooling systems are gaining increased attention as air conditioners are responsible for a remarkable amount of the electric peak load in summer. Several studies have shown that night ventilation of buildings reduces peak loads of the following day. However, their effect can be increased by a free cooling system based on nocturnal long wave radiation, which cools the air below ambient temperature. A perforated, corrugated metal plate which is used in transpired solar air heaters, functions as a radiating shield in this case. The air can reach temperatures below ambient as it passes the plate further increasing the free cooling's potential. A mathematical model has been set up to describe the cooling process. Based on governing equations diagrams are developed to show the correlation between the transpired radiant plate's temperature drop, as well as its cooling rate as a function of the long wave radiant heat flux and the air flow rate. Four European capitals are chosen to illustrate the cooling potential of nocturnal radiative air cooling. Building simulation is carried out using RETScreen 4 Clean Energy Project Analysis software. Results show that locations with drier climate reach higher nocturnal cooling performance as the moisture content of the atmosphere influences the radiant heat transfer.

Freeze–thaw field exposure and testing the reliability of performance test temperature cycle for concrete scaling in presence of de-icing salts

“…At night-time, this absorbed energy can be transmitted to the surrounding area as part of thermal exchange; therefore concrete surface can be found colder than the surrounding air in many cases when some meteorological conditions are coupled, such as a high visibility and a low wind velocity, this was modelled in [18]. This phenomenon is known as nocturnal radiation [26,27]. Beside the great differences in the thermal amplitudes that are noticed between laboratory and real conditions, several phenomena are involved in the thermal response of exposed concrete.…”

Investigation of the thermal performance of a solar absorber and nocturnal radiator (SAANR) hybrid panel for summer and winter seasons

“…[ 26 ], which implies that it is predominantly dry and that theoretically would work to support successful nocturnal radiation cooling according to the findings of Bokor, et al. [ 25 ] & Yoshihiro and Masato [ 24 ]. Okoronkwo, et al.…”

“…For instance, increased humidity and cloud cover with strong ambient winds exceeding 3.6 m/s will suppress or delay cooling. Bokor, et al [25] developed a mathematical model to describe the nocturnal cooling process by carrying out building simulations using RETScreen 4 Clean Energy Project Analysis software. The study concluded that locations with drier climates reach higher nocturnal cooling performance since increased moisture content of the atmosphere hampers the radiant heat transfer.…”

“…The study concluded that locations with drier climates reach higher nocturnal cooling performance since increased moisture content of the atmosphere hampers the radiant heat transfer. The climate of Botswana is semi-arid according to Atekwana, et al [26], which implies that it is predominantly dry and that theoretically would work to support successful nocturnal radiation cooling according to the findings of Bokor, et al [25] & Yoshihiro and Masato [24]. Okoronkwo, et al [27] carried out experimental tests in Owerri, Nigeria to determine the feasibility of using nocturnally cooled water for space cooling.…”

Experimental investigation of a solar absorber and nocturnal radiator hybrid system for simultaneous water heating and cooling

“…It is widely reported that nocturnal radiation cooling is one of the most effective natural passive cooling technologies by infrared radiation exchange between earthly surfaces and the sky [1,2,3,4,5,6,7,8,9,10,11]. The sun radiates heat to the earth and warms it up during the day, but at night the warmer earth would radiate the heat to the then colder sky.…”