Modelling and testing a passive night-sky radiation system

G.D. Joubert, R.T. Dobson


The as-built and tested passive night-sky radiation cooling/heating system considered in this investigation consists of a radiation panel, a cold water storage tank, a hot water storage tank, a room and the interconnecting pipework. The stored cold water can be used to cool a room during the day, particularly in summer. A theoretical time-dependent thermal performance model was also developed and compared with the experimental results and it is shown that the theoretical simulation model captures the experimental system performance to within a reasonable degree of accuracy. A natural circulation experimental set-up was constructed and subsequently used to show that under local (Stellenbosch, South Africa) conditions the typical heat-removal rate from the water in the tank is 55 W/m2 of radiating panel during the night; during the day the water in the hot water-storage tank was heated from 24 °C to 62 °C at a rate of 96 W/m2. The system was also able to cool the room at a rate of 120 W/m3. The results thus confirmed that it is entirely plausible to design an entirely passive system, that is, without the use of any moving mechanical equipment such as pumps and active controls, for both room-cooling and water-heating. It is thus concluded that a passive night-sky radiation cooling/heating system is a viable energy-saving option and that the theoretical simulation, as presented, can be used with confidence as an energy-saving system design and evaluation tool.


Keywords: passive cooling and heating, buoyancy-driven fluid flow, theoretical simulation, experimental verification



  • Passively driven renewable energy heating and cooling systems are considered.
  • Time-dependent mathematical simulation model is presented.
  • Experimental buoyancy-driven heating and cooling system built and tested.
  • Experimental results demonstrate the applicability of the theoretical simulation model.
  • Saving and evaluation design tool.


Night-sky radiation; passive cooling and heating; buoyancy-driven fluid flow

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Botha, F., Dobson, R.T. and Harms, T. 2013. Simulation of a syngas from a coal production plant cou-pled to a high temperature nuclear reactor. Journal of Energy in Southern Africa 24(2): 37–45.

Cengel, Y. and Ghajar, A. 2011. Heat and mass transfer: Fundamentals and applications. Fifth Edition. McGraw-Hill Education.

Dobson, R.T. 2005. Thermal modelling of a night sky radiation cooling system. Journal of Energy in Southern Africa 16(2): 20–31.

Givoni, B. 1977. Solar heating and night radiation cooling by a roof radiation trap. Energy and Buildings 1(2): 141–145.

Hollands, K. and Lightstone, M. 1989. A review of low-flow, stratified-tank solar water heating systems. So-lar Energy 43(2): 97–105.

Joubert, G. 2014 Investigation of a passive night-sky radiation system, MSc Eng Thesis, University of Stel-lenbosch, Stellenbosch, South Africa.

Loveday, D. and Taki, A. 1996. Convective heat transfer coefficients at a plane surface on a full-scale building facade. International Journal of Heat and Mass Transfer 39(8): 1729–1742.

Meir, M., Rekstad, J. and LØvvik, O. 2002. A study of a polymer-based radiative cooling system. Solar Energy 73(6): 403–417.

Milford, R. 2009. Greenhouse gas emission baselines and reduction potentials from buildings in South Africa, UNEP SBCI Sustainable Buildings & Climate Initiative, metadc226635/.

Mills, A. 2009. Heat transfer. Pearson Education.

Okoronkwo, C., Nwigwe, K., Ogueke, N., Anyanwu, E., Onyejekwe, D. and Ugwuoke, P. 2014. An experi-mental investigation of the passive cooling of a building using nighttime radiant cooling. Interna-tional Journal of Green Energy 11(10): 1072–1083.

Stellenbosch-weather. 2014 August. Available at:

Stine, B. and Geyer, M. 2001. Power from the sun, e-book,

Wang, Y., Cui, Y., Zhu, L. and Han, L. 2008. Experiments on novel solar heating and cooling system. Energy Conversion and Management 49(8): 2083–2089.

Winkler, H. 2005. Renewable energy policy in South Africa: Policy options for renewable electricity. Ener-gy Policy 33(1): 27–38.

Winkler, H. 2007. Energy policies for sustainable development in South Africa. Energy for sustainable De-velopment 11(1): 26–34.



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