Thesis (MEng) -- Stellenbosch University, 2014. / ENGLISH ABSTRACT: A passive night-sky radiation cooling system consists of a radiation panel and
a cold water storage tank. The stored cold water may be used to cool a room
during the day time, particularly in summer. In this thesis a theoretical and
mathematically sound simulation model is developed. An experimental set-up
was constructed and subsequently used to show that the theoretical model
effectively simulates the transient heating or cooling response of the system.
It is shown that under South African conditions the typical heat emitting rate
during the night is 55 W/m2. After the heat has been removed from the water,
it is stored in a cold water tank from where it is circulated through a natural
convector during the day time to absorb heat from the room. The experiment
extracted a minimum of 102 W/m3 of heat from a 1.87 m3 galvanized steel room
while a brick room with a volume of 120 m3 requires 22.7 W/m3. Additional
to cooling, the system during the day, absorbed an average of 362 W of energy
and heated 68 l of water from 24 °C to 62 °C within an 8-hour period. The
system achieved similar results during winter conditions and the experiment
confirms that the system is capable of operating without a control system.
Therefore it is recommended that renewable energy-conscious designers pay
more attention to the use of night-sky radiation cooling in future. / AFRIKKANSE OPSOMMING: en ’n koue water tenk. Die sisteem kan gebruik word om ’n vertrek gedurende
die dag te verkoel, veral in die somer, deur gebruik te maak van die gestoorde
verkoelde water. In hierdie tesis word ’n teoretiese en sinvolle wiskundige
simulasie model ontwikkel. ’n Eksperimentele stelsel is gebou en vervolgens
gebruik om te bewys dat die teoretiese model die veranderende verkoeling en
verwarming van die stelsel effektief simuleer.
Die tesis dui aan dat onder Suid Afrikaanse toestande daar ’n hitte vrystellings
tempo van 55 W/m2 is gedurende die nag. Nadat die water verkoel is, word
dit gestoor in die koue water tenk vanwaar dit deur ’n natuurlike konvektor
sirkuleer en gedurende die dag warmte vanuit die vertrek onttrek. Die eksperiment
het ’n minimum van 102 W/m3 warmte vanuit die galvaniseerde 1.87 m3
vertrek geabsorbeer, terwyl ’n baksteen vertrek van 120 m3, 22.7 W/m3 verkoeling
benodig. Bykomstig tot die verkoelingstelsel verhit die sisteem 68 l
water vanaf 24 °C to 62 °C gedurende ’n 8-uur periode in die dag, dus word
362Wenergie geabsorbeer. Die sisteem is ook getoets tydens winter toestande,
die resultate was dieselfde as wat in die somer verkry is. Verder is daar ook
bewys dat die sisteem sonder enige beheerstelsel kan funksioneer. Verder word
daar aanbeveel dat hernubare energie bewuste ontwerpers in die toekoms meer
aandag aan ruimte straling verkoeling skenk.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/95912 |
| Date | 12 1900 |
| Creators | Joubert, Gideon Daniel |
| Contributors | Dobson, R. T., Stellenbosch University. Faculty of Engineering. Department of Mechanical and Mechatronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xvi, 98 p. : ill. |
| Rights | Stellenbosch University |
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