Sustainable Construction & Design

The majority of current commercial building stock in the UK has been built with little consideration of sustainable construction or design. Yet, a combination of systematic energy efficient building design and energy efficient building use can have a significant beneficial impact on overall energy consumption and overall building costs.

Increasingly, there exist a raft of low energy solutions that can be incorporated into a building’s design. Very often these methods will entail no extra capital costs, provided they are decided upon early in the design stage. Often labelled sustainable design, this approach includes the use of renewable materials and - often - an attempt to limit the embodied energy used in a building’s construction. Embodied energy is an attempt to account for the total energy used - from the raw material extraction, to transport, manufacturing, assembly, installation as well as the capital and other costs of a specific material – as well as a material’s disassembly, deconstruction and/or decomposition.

Energy efficient design, which forms a significant part of sustainable design, is an integrated approach to orientation, ventilation, solar gain, day-lighting, thermal mass, heating and control systems.

In tandem, sustainable site development remains important, as consideration and referencing of a building’s position relative to the environmentand in particular to potential sources of renewable energy prior to its construction should be a key green objective. The existence of potential sources of naturally occurring energy are numerous and it is important to give thought to how to maximise a building’s potential benefits from them.

The principle sustainable design and technology solutions that currently exist for reducing energy consumption are detailed below. Many of these technologies are subject to financial incentives to encourage their take-up, such as eligibility for an Enhanced Capital Allowance or exemption from the Climate Change Levy:

• Combined Heat and Power (CHP) - According to the BRE, up to 70% of a standard commercial office building’s energy use is consumed by its heating and hot water systems. The installation of a typical CHP unit can immediately lead to a 35% reduction in energy use. CHP is a fuel-efficient energy technology that, unlike conventional forms of power generation, puts to use the by-product heat that is normally wasted to the environment. CHP produces up to 30% fewer emissions than conventional power generation.



• Air-conditioning – Air-conditioning (A/C) refers to the cooling and dehumidification of indoor air for thermal comfort. Cooling and ventilation systems typically account for around 5% a commercial offices energy consumption, although this varies markedly by the type of A/C system. There are five generic A/C types:
  
  
  • Chilled Ceilings or Beams (passive and active systems)
  
  
  • All-Air (variable air volume (VAV) and constant volume (CV) systems)
  
  
  • Fancoils (2-pipe and 4-pipe systems)
  
  
  • Split DX (cooling only, 2-pipe inverter and reverse cycle systems)
  
  
  • 3-pipe VRF/VRV (direct expansion systems with the ability to simultaneously heat and cool).
  
  

Of these, split DX and fancoil A/C systems are generally regarded as the least energy efficient, and chilled ceiling systems the most energy efficient. Chilled ceiling systems, circulate air using the principles of natural heat convection, avoiding the need for ductwork and air handlers. Such systems are chilled by an external source such as recirculated water.

The design and construction of the building envelope - principally its thermal insulation, airtightness, thermal mass, glazed area and shading devices – will clearly affect the heating and cooling loads of the building when used. Alternatives to traditional air-conditioning systems include natural ventilation, alternative refrigerants and displacement ventilation.

• Natural ventilation– there are two types of natural ventilation occurring in vuildings – wind driven ventilation and stack ventilation. The most efficient design for a natural ventilation building should implement both types of ventilation.
  
• Alternative refrigerants – there are four principal alternatives to CFCs and HCFCs (chloroflurocarbons and hydrochloroflurocarbons) – water, ammonia, hydrocarbons and HFCs (hydroflurocarbons). Yet according to the Government’s Climate Change Programme, HFCs are seen as the least sustainable alternative for the long-term.
  
• Displacement ventilation is essentially a buoyancy driven "displacement" process, with ‘fresh’ ventilation air being introduced at low velocity and at low-level into the occupied zone at a temperature typically around 19°C, slightly cooler than the design room air temperature. Air is extracted at ceiling level.

• Energy efficient lighting – a standard building’s lighting system accounts for approximately 13% of its energy use. A building with a fully integrated, intelligent and efficient lighting system automatically compensates for daylight levels and occupancy, controlling each light separately. Such a system could incorporate fluorescent technology, which is significantly more energy efficient than equivalent incandescent light due to a greater proportion of the power being converted to usable light and a smaller proportion converted to heat.



• Photovoltaic (PV) systems – PV systems convert solar radiation into electricity. It is best known as a method for generating solar power by using solar cells packaged in photovoltaic modules, often electrically connected in multiples as solar photovoltaic arrays to convert energy from the sun into electricity. The Direct Current (DC) electricity generated can either be stored in batteries for future use, or converted to Alternating Current (AC) via an inverter for use on-site or export to the electricity grid.



• Building-integrated photovoltaics (BIPV) – BIPVs can be retro-fitted as well as incorporated into new domestic and industrial buildings as a principal or ancillary source of electrical power. The photovoltaic modules that make up a BIPV system can be designed to form a building element such as a roof tile, roof membrane or facade panel then incorporated into the roof or walls of a building by standard construction methods (with additional electrical connections required).



• Renewable systems such as ground source heat pumps (GSHP) – GSHPs use a buried ground loop which transfers heat from the ground into a building. Heat collecting pipes in a closed loop, containing water (plus antifreeze) are used to extract this latent energy, which can then be used to provide heating and hot water. The efficiency of a GSHP is measured by the coefficient of performance (CoP). This is the ratio of units of heat output for each unit of electricity used to drive the compressor and pump for the ground loop. Average CoP is around 3-4 although some systems may produce a greater rate of efficiency. This means that for every unit of electricity used to pump the heat, 3-4 units of heat are produced.



• Wind turbine – a wind turbine is a mechanism for converting kinetic energy into mechanical energy. Mechanical energy can then be converted in to electricity.



• Rain-water harvesting– is the collection and storage of precipitation from roofs or a surface catchment for future use (such as landscaping, toilet flushing etc.). In addition to rainwater harvesting, other forms of water efficiency include the treatment and reuse of greywater (otherwise known as sullage) which is non-industrial wastewater, as well as low flow fixtures and fittings and closed loop systems.