The cooling potential of sky radiation with variations in system parameters

[+] Author and Article Information
M. Adrienne Parsons

University of Louisville, Louisville, KY, USA

M. Keith Sharp

University of Louisville, Louisville, KY, USA

1Corresponding author.

ASME doi:10.1115/1.4042453 History: Received September 26, 2017; Revised December 20, 2018


A heat pipe augmented sky radiator system was simulated by a thermal network, including a thin polyethylene cover with and without condensation, white (ZnO) painted radiator plate, condenser and evaporator ends of the heat pipe, thermal storage fluid (water), tank wall, room, sky and ambient air. Nodal temperatures were simultaneously solved as functions of time using Typical Meteorological Year (TMY3) weather data for Louisville, KY. Auxiliary cooling was added as needed to limit room temperature to a maximum of 23.9°C. Effects of radiator orientation, thermal storage capacity and cooling load to radiator area ratio, LRR. Results were compared to a baseline with LRR = 10 W/m2K, horizontal radiator and one cover, which provided an annual sky fraction (fraction of cooling load provided by sky radiation) of 0.855. A decrease to 0.852 was found for an increase in radiator slope to 20°, and a drop to 0.832 for 53° slope (latitude + 15°, a typical slope for solar heating). These drops were associated with increases in average radiator temperature by 0.73°C for 20° and 1.99°C for 53°. A 30% decrease in storage capacity decreased sky fraction to 0.843. Sky fractions were 0.720 and 0.959 for LRR of 20 and 5, respectively. LRR and thermal storage capacity had strong effects on performance. Radiator slope had a surprisingly small impact, considering that the view factor to the sky at 53° tilt is less than 0.5.

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