CWCT FACETS

05.01 General

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Categories: Thermal Properties

Introduction
Buildings consume nearly half of the energy used in the UK (cfr CIBSE). Tangible benefits from energy efficiency which range from the individual to the national level are:

  • improved building design and operation
  • reduction of energy costs
  • better working environments
  • life-cycle cost savings
  • added market value of buildings
  • environmental: mainly through reduced emissions of carbon dioxide (CO2) and reduced consumption of finite fossil fuels



National energy use
The Commission of the European Communities (Thermie, 1993) estimated that 28% of primary energy use in the EC is associated with buildings. The consumption of energy for space heating accounts for about 20% of the EC primary energy consumption, but around 30% of this amount could be eliminated by better insulation of buildings. Further reductions are possible with the active and the passive use of solar energy.
 


Reduction of the energy bill
Energy efficient buildings need cost no more to build than conventional buildings. The integration of the fabric and services design can present opportunities to reduce capital cost. For example, minimising or avoiding air conditioning plant can offset the cost of external shading.

The energy bill for most existing commercial and public buildings could be reduced by at least 20% using measures regarded as cost effective by most common investment criteria. New buildings and major refurbishment represent even greater potential. New low-energy buildings consume 50% less energy than similar existing buildings and 20% less than typical new buildings.
 


Environmental issues
It is also important to reduce the production of CO2, SO2 and NOx gasses from combustion of energy sources which contributes to atmospheric pollution, resulting in a wide range of damage both to the environment and public health.
 


Legislation
There is an increasing level of legislation addressing energy and environmental issues. The 1994 Building Regulations for England and Wales include more stringent thermal performance measures for new and refurbished buildings, and new measures covering energy efficient heating and lighting controls. A further revision of the Regulations is under development to address the energy efficiency of air conditioning and mechanical ventilation in both new and refurbished buildings. More information about the Proposals for Amending the Energy Efficiency Provisions can be found at the following web site: http://www.construction.detr.gov.uk/consult/eep/index.htm.
 


Comfort
Recent work has indicated that buildings that are designed and managed in an energy efficient way can be more comfortable and their staff more productive, making investment in good energy efficient design and management even more cost effective to a client organisation. Examples of thermal discomfort are draughts and radiation from cold surfaces (thermal bridges, glass surface). Section 06.01 gives more information about comfort.
 


Condensation
Heat transfer and condensation risk are linked. The occurrence of surface condensation depends on the lowest temperature on the surface of a component and the relative humidity of the adjacent air. The temperature distribution within the component in turn depends on the heat transfer through the component.

Condensation poses three problems:

  • if condensation occurs on an exposed surface then it is visible, and visible condensation on a regular basis may lead to a perception of poor performance
  • condensation may lead to mould growth, staining or corrosion of surfaces on which it occurs, or onto which it runs - corrosion is a particular concern where it is unlikely to be seen until too late, whereas staining is a problem on visible exposed surfaces
  • condensation may lead to a breakdown or degradation of the performance of insulation systems.



Further information
More information about the mechanisms of heat transfer are explained in the following sections: