We have extensively modelled residential properties in the Eastern Cape climate zone with interesting results – what ‘works’ in Cape Town does not necessarily work in the milder Eastern Cape climate in Port Elizabeth, Cape St Francis or Plettenberg Bay, etc.
Every property will respond differently of course dependent on orientation, internal volume, effectiveness of shading, etc, but as a general rule of thumb the following are some base-case construction technologies that produce good energy efficiency in this region:
- Single-glazed clear glass – this actually proves most favourable as it enables low altitude winter sun to penetrate properties in a ‘cold climate’ and assist with free passive heating which proves to substantially reduce heating requirements and costs (as long as sufficient shading is in place to protect against high altitude summer sun heat gain).
- Cavity wall construction – cavity wall construction is a requirement in this high condensation risk climate zone but sometimes adding just 25mm XPS closed-cell extruded polystyrene to the cavities substantially increases the thermal performance of properties increasing energy efficiency.
- Energy efficient hot water – heat pumps or solar hot water with gas backup (rather than electrical backup) work well in this region. Heat pumps have a lower average CoP Coefficient of Performance in reality in a cooler climate so one needs to be very careful to ensure that these are adequately sized to suit their specific demand requirements. If not then their efficiency can easily drop and in essence be no more efficient or effective than a traditional electrical hot water tank. The reduced efficiency of heat pumps, with their lower contribution on energy efficiency, must be competently considered in any rational design assessment.
- Perimeter foundation insulation – XPS extruded polystyrene can do wonders for keeping properties warm under-foot, enhancing levels of thermal comfort, and minimising heat loss & cold ingress. On larger properties it may be prudent to insulate the outer couple of meters to the perimeter of the dwelling underslab.
- Roof insulation – adequate insulation of any pitched roof proves to be critical anywhere in South Africa and there is common misunderstanding about how to use/detail sisalation in pitched roofs by architects (it MUST have a clear air space below it in order for the low emissivity surface to work).
- Adequate winter space heating – the Eastern Cape has long cold winters and hot dry summers with scorching Berg winds so adequate thought must be given to how buildings will be kept warm in winter (SANS 10400XA gives little consideration to efficient winter warming energy consumption).
The mid-year energy loads can clearly been seen on this graph below that indicates the carbon cost of heating (substantially) and cooling (hardly) a property in a predominantly cold winter location…