Climatic region maps are key to efficient passive building design. Two recent innovations redefine and update existing climatic maps for South Africa, and provide support for design using innovative building technologies.
Optimal passive solar design responses are built on analysis and simulation using available climate data. However, it is not feasible to undertake in-depth building analysis on smaller building projects and so the guidelines of SANS 10400-XA set out prescriptions for energy efficiency that forego the requirement for sophisticated building modelling. Appropriate prescriptive routes are determined by the site location within the climatic zones defined by the standard. But, according to the Council for Scientific and Industrial Research (CSIR), there are limitations to the current map.
In a recent paper, The Creation of Cooling Degree (CDD) and Heating Degree Day (HDD) Climatic Maps for South Africa, Dirk Conradie, Tobias van Reenen and Sheldon Bole sum up the concerns: “[It] does not optimally support quantified design decisions within the built environment… because the map cannot be related to actual energy usage, nor can it be used to support passive design strategies such as solar heating, thermal mass and natural ventilation.”
Refining weather data
Following these observations, the team developed a new map using the Köppen-Geiger climatic classification system at a resolution of 1km2, says Peta de Jager, group research leader at the CSIR.
The resulting map rendered 14 climatic zones and highlighted some specific climatic areas that were misrepresented in the six-zone map, specifically:
- The very hot Limpopo River valley
- A tropical descender into the northern parts of KwaZulu-Natal
- Pretoria, which has three climatic zones
- The climatic staircase effect starting from humid Durban, moving into the KwaZulu-Natal midlands and eventually the Drakensberg Mountains
- The very cold Lesotho Highlands
- The cold, high-lying area around Sutherland
- The arid climatic region north of Cape Town, starting at Yzerfontein.
“Built environment professionals experience increasing pressure to improve the performance of their designs so that they are resilient to unknown futures, but have had difficulty in responding adequately to this pressure due to a lack of availability of suitably packaged information,” says De Jager.
The development of the Köppen-Geiger climatic map was the first step towards making suitably packaged information available and accessible for built environment professionals, she adds.
Mapping building energy needs
The next step was to create a map that would represent human comfort and building energy consumption. The team tested two methods of mapping. They used Standard Effective Temperature (SET) as proposed by Gagge to indicate comparative thermal comfort levels. However, when they verified the data through comparative notional building simulation, the results rendered weak to poor correlations between SET and the expected building heating and cooling energy demands.
Next they characterised the climatic zones according to heating degree days (HDD), cooling degree days (CDD), relative humidity during the warmest month (RH) and average temperature during the warmest month (Tdb). Each selected geographical area was corresponded to a certain climate zone categorised by energy needs for space heating, cooling and dehumidification. Depending on the average amount of annual HDD and CDD in each area, an energy demand characterisation could be determined from “low” to “very high”. Two maps were produced using 18oC as the base temperature. The classes were simplified into low, medium and high (LMH) energy demand for both heating and cooling. These were combined into a single total energy demand map. Combining two different measures of LMH energy demand resulted in seven zones for the South African context.
Support for innovative technology choices
The National Home Builders Registration Council (NHBRC) plans to use the initial 14-zone climatic map to meet another innovation aim. Tasked by a meeting of the Ministers and Members of Executive Councils (Minmec) to improve the uptake of Innovative Building Technologies (IBTs), they have been developing a process that will help provincial departments of human settlements and municipalities to improve selection at the procurement stage.
According to Dominique Geszler, architect specialist of the NHBRC, many IBTs that have achieved Agrément South Africa certification or NHBRC rational design approval don’t necessarily guarantee quality construction of the final building. “The first step was to establish a guideline for implementing IBTs, which amongst other criteria includes a dynamic database of approved NHBRC IBTs, but we needed to assess the as-built results of each IBT system. In order to do this, we developed the Condition Assessment Tool that would assess how built IBTs were performing on-site. IBTs wanting to register on our database have to first pass the rigors of this tool. Once approved, they go onto our IBT database,” says Geszler.
A second tool was developed to compare IBT performance in different climatic regions, namely the Decision Support Model (IBT Analyser) for IBTs. This software compares how IBTs and standard building technologies perform against various criteria, arranged into three sections. First, the systems are tested for thermal comfort in a site’s specific climate zone. Next they are assessed against qualitative performance derived from Agrément certificates, including acoustic, energy, condensation, and fire and durability performance metrics. Finally, construction supply chain management – including labour, distance from suppliers, economies of scale, accessibility from the road and lead time flexibility – is considered.
“Once a shortlist of IBT-systems has been determined, this tool can be used for comparing systems in the different climatic zones. The tool also includes two standard building systems, namely masonry and established steel frame systems, so the IBTs can be compared with technologies that the industry is familiar with. At the moment, the database only includes 25 IBTs, so we will be looking to expand the list. In the meantime, a similar product to the one being considered can be selected for comparison purposes when it is not already on the database,” says Geszler.
The guidelines for implementing IBTs is a framework that will help IBT housing programmes in government and complement the initiatives developed for the 60% of new social infrastructure projects. “Although initially institutional buildings and social housing for IBTs are targeted, the strategy for low-income subsidy housing projects should be approached with care. The intention with low-income housing is that it is a starter home onto which beneficiaries can build additions at a later stage. This makes IBTs risky for low-income housing as there may be unfamiliar construction requirements and the execution of the additions is beyond our control once the building is handed over to the beneficiary. Procurement guidelines that place emphasis on, but are not limited to, integrated development and rigorous maintenance and service plans thus become critical.”
Looking ahead, the CSIR has plenty in the pipeline. “The old SANS 204 map will be replaced with the new energy demand map. This, and a Köppen-Geiger climate map – also created by the team with support from GIZ – will be made freely available for access on the StepSA website. Next we will be working on weather files – for use in energy modelling software – to be made available on a subscription basis,” De Jager says.
By Peta Brom
See earthworks Issue 32, June-July 2016 for the full feature.