‘Cool shacks’ to fight Cape Town summer heat

The shacks found in the informal settlements on Cape Town’s eastern periphery get extremely hot in the summer time because they are iron structures that absorb and retain heat for hours from mid-day until late afternoon. Extreme temperature rises in shacks have the potential to cause heat stress that will affect young children and especially those suffering from epilepsy.

To find affordable ways of reducing temperatures in shacks, UCT’s Environmental and Geographical Science Department has been testing materials and designs for heat reduction as part of the ‘Cool Shack’ project. The project began in 2014 as a World Capital Design initiative. In the first phase, the researchers tested various structures and materials using high-resolution sensors to capture temperature and humidity data. The results were sufficiently encouraging to proceed to the second phase. When a corrugated iron structure was covered with a white woven fabric made from recycled plastic bottles, peak temperatures inside these structure could be reduced by as much as 9oC.

In November 2014, UCT’s Environmental and Geographical Science Department, together with several partners and undergraduate students, built two shacks at scale (2 x 2.5 m) — one an experimental shack and the other a control — on the UCT campus with the purpose of testing the performance of the materials during warm summer conditions. The main aim was to find simple ways of reducing temperature in the experimental shack by 10oC, compared to the conventional shack, and at least 2oC below ambient temperatures using low cost materials that were readily accessible.

The control and an experimental shack were fitted with continuous high resolution monitoring sensors and set to capture conditions in each shack every three minutes along with ambient conditions. Temperature and humidity data were sent via a telemetry system on a website to enable real time observation. In this way the researchers could determine exactly how the materials and designs performed, and could track the impact of various adjustments. The information from the scientific experiment could provide new insights in improving the living conditions of thousands of people who live in shacks on the Cape Flats.

DATA GRAPHIC 29 JANUARY 2015
Graphic showing temperature of the ‘cool shack’ (red) and conventional shack (blue). The green line shows outdoor temperature conditions from 08.00 until 14.30 on Thursday 29 January, 2015.

In essence, on very warm days, it should be cooler and more comfortable inside the dwelling than outside. There are many reasons for making shacks cool. For instance, the graph above shows a comparison between the control (conventional) shack and the experimental shack. On the 29 January 2015, it shows that temperature rose by 15oC from 08.30 to 10.00. A rapid rise in temperature has potential to cause heat stress that will affect young children and especially those suffering from epilepsy. On Thursday 29 January, which was a warm day in Cape Town, the UCT experimental shack outperformed the control shack when indoor temperatures in the experiment were 10oC cooler and 3oC cooler than outside temperatures. This is a small breakthrough following weeks of experimentation. During the experiment, the maximum observed temperature in the conventional shack reached a staggering 47.7 oC, with ambient conditions reaching 36.6 oC.

The shack project has other benefits too. The pitched roof drains water into rain gardens that are columns of soil contained by car tyres. Runoff is reduced through infiltration in the column. These micro gardens also offer opportunities for harvesting productive edible vegetables. The shacks are also fitted with ‘litres of light’ bottles that distribute light into the home during the day. In addition the dwelling has a plumbed basin that enables the occupants to dispose greywater into an aerobic and anaerobic soakaway, which makes it safer to dispose of unwanted water especially at night time. Further benefits include a fire retardation chemical that is soaked into the woven fabric covering the structure. The cloth is inflammable although it does melt with intense heat. The advantage is that it may give occupants a few extra minutes in the event of fire in an informal settlement. Finally, the walls a plastered uses a mix of cement and sand, with the bulk of the fill being comprising newspaper strips that offers indoor insulation during cool winter conditions.

 

Dr Kevin Winter is a lecturer in the Department of Environmental and Geographical Science and a lead researcher in the Urban Water Management Research Unit at the University if Cape Town. His research interest is in the social and technical interactions involving water and the environment in an urban setting.

Main image: The control shack (left) made from corrugated iron and the experimental ‘cool shack’ (right) which is covered with a white woven fabric made from recycled materials.

 

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