Report: Analysis and documentation of experiments on cool roofs and walls in KwaZulu-Natal

The South African - German Energy Partnership undertook an independent analysis of the experiments on cool roofs and walls in KwaZulu-Natal. Through this project, the Energy Partnership supported its partner South African National Energy Development Institute (SANEDI) in analysing and documenting the experiments on cool roofs and walls done in KwaZulu-Natal at Genkem’s Umhlanga premises and at the Saint Lucia Ecolodge along the St Lucia Estuary.The gained results can be used for further project development and roll-out of cool roof/cool surface technology in South Africa.

For the St. Lucia experiment the monthly energy consumption driver could not be determined from the utility bills and occupancy as per the methodology that had initially been anticipated in the Terms of Reference (ToR), thus an adapted approach was chosen involving isolated controlled experimental metering. This proved to be successful in determining the effect of the technology by allowing the specific electricity requirement for both the coated and uncoated environment to be recorded. From this, over the examined 24-hours period in a controlled environment, a reduction of 1.3 kWh or 5 % was observed under given ambient conditions. A high-level extrapolation to a year using cooling degrees for St. Lucia indicates a potential reduction of cooling energy consumption in the order of 600 and 670 kWh, translating to cost reduction of between R 1,200 and R 1,340.

There seem to be issues with lichen growth on the coated surfaces. In order to determine the definite reason for that growth, further analysis of the matter would be required and is not covered within this report. It might be appearing due to insufficient preparation of the surface before applying the paint (explanation of the coating manufacturer) or due to specific climate conditions in the experimental area. The latter could be addressed by utilising different colours of cool coatings. This will however reduce the emissivity and thereby impact on the overall efficacy of the cool coating and thus may be worth investigating in more detail.

Based on the objectives of the study, both the maximum temperature and the average temperature were selected in the Genkem experiment for analysing the impact of the cool coating technology in reducing indoor temperature, energy consumption and demand. The maximum temperatures are a suitable measure for assessing the efficacy of cool coating in terms of reducing electric peak loads i.e. electricity demand; and the average temperatures are a good indication for the impact of the technology on HVAC energy consumption. Additionally, maximum, minimum and average temperatures have a clear impact on thermal comfort.

The container experiment has shown the efficacy of the cool coating technology by highlighting consistent differences of both average and maximum air temperature profiles between the coated and uncoated containers. Mean average daily temperatures differ by 1.9°C and mean maximum temperatures differ by 7°C. The efficacy of the technology could thus be demonstrated successfully and shows significant potential specifically for reducing electricity demand for cooling and improving thermal comfort during periods of high temperatures in warm coastal climatic conditions. Results are however very dependent on the location and climatic conditions of the application.

Based on this work and other studies referenced here, it can be seen that there is local capacity and capability in South Africa, which can be leveraged to demonstrate the applicability of this technology and support the wide spread application of cool coating in various sectors and building types.