Energy Efficiency
Monday, 12 August 2013 10:18

Insulation for energy-efficient buildings

A building’s thermal insulation plays a key role in energy saving and therefore requires due consideration.

INSULATION IS THE MOST EFFECTIVE WAY TO IMPROVE THE ENERGY-EFFICIENCY OF A HOME. INSULATION OF THE BUILDING ENVELOPE HELPS TO KEEP HEAT IN DURING THE WINTER, BUT ALLOWS FOR HEAT REFLECTION DURING THE SUMMER.

Insulating a building can save 45–55% of heating and cooling energy.

The South African National Building Regulations introduced requirements for energy usage in buildings in 2011. All new buildings and extensions have to comply with the climate-specific regulations in the relevant occupancy classes.

The South African National Standard (SANS) 10400-XA Energy usage in buildings provides guidance to achieve the performance parameters to reduce energy usage in buildings.

South Africa has been divided into six climatic zones, as energy-efficiency is influenced by specific climatic conditions. Building design and construction materials should consider a region’s climate to ensure its efficiency.

The mandatory levels of insulation required vary according to the climatic conditions in the particular locations. The appropriate level of insulation intervention will depend on climate, building construction type, and whether auxiliary heating and/or cooling is used.

The Guide to Energy-Efficient Thermal Insulation in Buildings, published by the Thermal Insulation Association of Southern Africa (TIASA), states: “Insulation reduces heat flow and is essential to keep a building warm in winter and cool in summer. A well-insulated and well-designed building will provide year-round comfort, decreasing energy costs. This, in turn, will reduce greenhouse gas (GHG) emissions.”

Benefits of insulation

For an average house, installing insulation can reduce the total house heat loss significantly. Additionally, the reduction in heat movement results in a home that is warm in the winter and cool in the summer.

Apart from the obvious thermal benefits, insulation is also an excellent sound absorber, as it forces sound waves that travel through it to bounce off the insulation fibres.

Types of insulation Bulk insulation Materials of low thermal conductivity rely on pockets of trapped air or low conductive gasses within its structure. Its thermal resistance is essentially the same, regardless of the direction of heat flow through it, and is proportional to its thickness, density and upper temperature.

Types of bulk insulation

Batt, blanket and matt insulation:

• Cellulose loose-fill fibre.

• Glass fibre (glass wool).

• Mineral wool (slag/rock wool).

• Polyester fibre.

 

Rigid board insulation:

• Expanded polystyrene.

• Extruded polystyrene.

• Phenolic foam.

• Polyurethane and polyisocyanurate.

• Vermiculite.

 

Spray-foam insulation:

• Polyurethane foam.

 

Reflective foil insulation

Reflective foil insulation (radiant barrier) mainly resists radiant heat flow due to its reflectivity, low absorption and conduction and low emissivity.

Reflective insulation works by letting through a small percentage of the radiant heat it receives and reflecting the rest using a shiny surface. It relies on the presence of a defined air space next to the shiny surface, creating a layer of air, which is important for reducing heat flow.

Composite bulk insulation

Composite bulk insulation is a combination of bulk insulation and reflective foil insulation.

Examples include:

• Foil-backed blankets.

• Foil-backed batts.

• Foil-faced boards.

The type of insulation installed in a building will vary depending on the use of the building and the climate zone in which it is located.

The design and construction of a building will affect the specific types of insulation which can be used, and where the insulation can be installed.

 

Selecting thermal insulation

When selecting insulation, ensure that the material:

• Complies to product standards.

• Is appropriate for the intended occupancy class in accordance with SANS 10400 Part A.

• Complies with the fire safety requirements given in SANS 10400 Part T and SANS 428.

• Complies with the recommended R-value for the relevant climatic zones in accordance with SANS 10400 Part XA and SANS 204.

 

The ABC’s of thermal insulation

Absorption: The take-up of heat by a surface of mass or membrane barrier, which contributes to the heat gain and loss through a wall or roof construction.

Added R-value: The added R-value is the value of the insulating material added to achieve a certain value required.

Bulk insulation: Materials of low thermal conductivity that mainly resist the transfer of conducted heat, relying on pockets of trapped air or low conductive gasses within its structure.

Composite insulation: Two or more types of material combined to achieve a required level of performance.

Continuous insulation: Interior insulation that is continuous across all structural members without any thermal bridges, excluding fasteners and service openings.

Density: The mass of a substance per unit of volume. The SI unit of measure is kg/m³.

Direction of heat flow: Most significant heat flow at a given time. Heat flows from hot to cold environments and this is considered to be the direction of natural heat flow. Thus “upwards” implies heat flow from a conditioned space through the ceiling or roof and “downwards” implies the opposite. Likewise, horizontal flows can be described as inwards and outwards.

Energy labelling: A system of rating the energy performance of new and existing buildings. This may include a star rating system.

Energy performance of a building: Calculated or measured amount of energy actually used or estimated to meet the different needs associated with a standard use of the building, which may include energy use for heating, cooling, ventilation, domestic hot water and lighting.

Heat transfer: The temperature of energy induced by a temperature difference by conduction, convection, radiation or any combination.

Insulation: Material or a combination of materials that resist heat flow. Note: Insulation of the building envelope helps to keep heat in during the winter and out during the summer to improve comfort and save energy. A well-insulated and well-designed home or building will provide year-round comfort, cutting cooling and heating costs and reducing greenhouse emissions. Resistance to heat flow is achieved by the use of either bulk insulation or reflective insulation, which work in different ways.

Insulation R-value: All insulation materials are rated for their performance in restricting heat transfer. This is expressed as the R-value, which is the measure of the material’s resistance to heat transfer, alternatively known as thermal resistance. The higher the R-value, the greater is the insulation effect. It is the reciprocal of thermal conductance/transmittance.

Passive design: A design that does not require mechanical heating or cooling, for example, buildings that are designed to take advantage of natural energy flows to maintain thermal comfort.

Reflective insulation: Any material with a reflective surface such as a reflective foil laminate, reflective barrier or foil batt capable of reducing radiant heat flow, in combination with air spaces and low emissive surfaces.

R-value: The thermal resistance (m².K/W) of a component. It is the measurement of a material’s thermal resistance. This is the material’s ability to resist heat flow – the thermal resistance (m².K/W) of a component calculated by dividing its thickness by its thermal conductivity.

Thermal break: An element of low thermal conductivity placed in an assembly to reduce or prevent the flow of thermal energy (transfer of heat) from one component to another.

Thermal mass: The ability of building materials to store heat. The basic characteristic of materials with thermal mass is their ability to absorb heat, store it and at a later time release it. By adding thermal mass within the insulated building envelope, it helps to reduce the extremes in temperature experienced inside the home/building, making the average internal temperature more moderate year-round and the home/building more comfortable. Building materials, which are heavyweight, store a lot of heat and have a high thermal mass. Materials that are lightweight do not store much heat and have a low thermal mass.

The use of heavyweight construction materials with a high thermal mass (concrete slab on ground and insulated brick cavity walls) can reduce the total heating and cooling energy requirements compared to a home built of lightweight construction materials with a low thermal mass (brick veneer with a timber floor).

Total R-value: The sum of the R-values of all the individual component layers in a composite element, including the air space and associated surface resistances, measured in m².K/W.

Total U-value: The thermal transmittance (W/m².K) of the composite element, including the air space and associated surface transmittance.

Solar energy: Electromagnetic energy radiated from the sun. <Block End>

Full thanks and acknowledgement are given to “The Guide to Energy-Efficient Thermal Insulation in Buildings” by TIASA and the website www.tiasa.org.za.

GIL Africa 2017

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