Energy Efficiency in buildings
SANS 10400-XA: 2011
The application of the National Building Regulations – Part XA: Energy Usage
In 2011 the SANS 10400–XA ‘Energy Usage in Buildings’ Regulations were added to the National Building Regulations to improve the energy efficiency of our country’s buildings.
A considerable amount of the world’s electricity is consumed by residential and commercial buildings, with the building sector the single largest contributor to greenhouse gas emissions. Energy efficient buildings make an important contribution to reduce energy demand and greenhouse gas emissions.
A comfortable indoor climate can be achieved through building design that is appropriate for the local climate. Energy efficient buildings seek to maximise the effects of passive design to minimise the use and energy consumption of active systems e.g. lighting, heating, cooling and ventilation.
Municipalities are responsible for checking compliance with the NBR when they approve building applications. These standards for energy efficient design and construction and energy usage in buildings are part of NBR.
National Building Regulations (NBR) for Energy Usage in Buildings
The NBR for Energy Usage in buildings are based on the standards published by the South African Bureau of Standards (SABS) for energy efficiency in buildings, SANS 10400–XA, that must be adhered to in all new building and in major refurbishments of existing buildings.
The regulations permit different routes of achieving the standards;
The Prescriptive route are commonly used for houses and smaller buildings and requires that a set of minimum regulations be adhered to for water heating, insulation and glazed areas. Where owners have specific needs that require a Rational Design to enable compliance, Performance and Reference building routes offer greater freedom to achieve the energy efficiency targets, involving the modelling of the building and calculating its energy consumption. A Rational Design however requires a specialist Competent Person and is therefore generally more expensive.
Energy Efficiency through Passive Design – Guidelines
1 Energy Zones
The local climate plays the determining role in designing energy efficient buildings; the sun’s movement, prevailing wind direction, humidity level and the temperature difference between day and night. The standard defines seven energy zones in South Africa with different thermal requirements for buildings.
2 Orientation
Depending on orientation, rooms are warmer or colder. Although not a mandatory requirement, it is highly advisable that buildings face north where possible. In a north orientated home, living spaces should be arranged such that, rooms where people spend most of their time are located on the northern side of the building to make the best use of the heat of the sun in winter. Combined with the prescribed glazing and shading specifications to block the sun in summer, this can significantly enhance the thermal comfort of a home, without using excessive electricity.
If a building is not orientated to the best orientation and is east or west orientated, the design may be subject to a rational design.
3 Shading
The general requirement for all north orientated houses is for the northern windows to be provided with shading in the form of, for example, roof overhangs or fixed canopy. It is specifically during the summer period where shading must be provided to minimise sun rays and solar radiation. Should this not be possible, a higher specification of Solar Heat Gain Co-efficient is required of the glazing in the form of tinting or glass coating or through the use of external shading devices or screens.
4 External Walls
The two main categories of walls – masonry and non-masonry walls – have different requirements for the relevant climate zones and compliance. A masonry wall is defined as masonry units jointed together with mortar to form a structure, either made from fired clay or concrete units. Every other wall type is classified as a non-masonry wall and will have to comply with the minimum thermal resistance (R-value) values for north orientated homes.
5 Fenestration
The fenestration of a building is defined as any glazed opening including windows, doors and skylights, which comprises glazing and framing elements that are either fixed or movable. Fenestration may not exceed a certain percentage of the net floor area per storey, to comply with the minimum energy performance requirements, whilst window frames must comply with the required air leakage benchmark. If the fenestration area exceeds 20% (SANS10400-XA Ed2) of the net floor area, a rational design would be required to calculate the conductance (Cu) and solar heat gain (CSHGC) of the glazing. The fenestration manufacturer must provide proof of compliance, which includes the frames and its installation.
6 Roof Assembly
The roof assembly is defined as the building cover and it’s supporting structure, including any ceiling structure and additional components such as insulation. Some 70% of the heat losses and gains in an un-insulated structure occur via the roof. There is therefore a strong need for providing the necessary thermal resistance to the roof and insulation of the ceiling system.
7 Floors
Where an underfloor heating system is installed, the heating system must be insulated underneath the slab with insulation. Suspended floors are seen as exposed floors from which heat loss can readily occur, e.g. offices or residential accommodation built over ground floor parking, and are required to have insulation that will retain its thermal properties.
8 Building sealing
Much energy is lost because of poor sealing against air infiltration. In hot climates, warm humid unconditioned air infiltrates at the expense of cooler conditioned air whilst in cold seasons, the previously heated warm air is lost from buildings as cold air ingress takes place. Roofs, external walls, and floors that form the building envelope, including any opening such as windows and doors in the external fabric, shall be constructed to minimize air leakage.
9 Hot Water Supply
The functional regulations XA2 state that hot water systems need to comply with the requirements, with at least 50% (volume fraction) of the annual average hot water heating requirement to be provided by means other than electrical resistance heating. All hot water service pipes must be clad with insulation and collectors should be situated on the north facing roof slope. The hot water storage tank should be located as close to the main areas of hot water (bathroom and kitchen) as practically possible and solar collectors positioned as close to the storage tanks as possible.
All additional standards relating to solar water heating systems and installation must be adhered to with proof from the manufacturer to be obtained for the systems to show compliance.
10 Lighting
Both the energy demand and energy consumption of a house is required to be regulated. The usage of low energy lighting throughout recommended.
11 Air conditioning
HVAC systems should be designed in such a way that the temperature in different parts of the building can be regulated separately and switched off in parts not being used. There are different types of HVAC systems using air, water or a combination of water and air. Systems need to comply with the minimum required level of energy efficiency for unitary and packaged air-conditioning equipment.
