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Solar Building Design

Solar and energy-efficient architecture – building envelope and system technology

Solar and  energy-efficient architecture deal with the use of renewable energy  and  a reduction of energy  consumption in the construction and operation of buildings. In Germany, 46 % of final energy  consumption occurs  in buildings. 90 % of this is accounted for by low temperature heat (< 80°C), chiefly used  in heating. Renovation of old buildings  has shown  that  it is possible  to save 70 % of final energy  consumption using currently available technologies. In newly built homes it has been possible  to reduce consumption by over 80 % using  the available standard technologies.

Many different  concepts are available:
•   3-liter home
•   Passive solar home
•   Zero energy  home
•   Plus-energy  home

Architects and  their clients thus have a wide range of options to choose from when  design- ing a solar energy  building. For new residential buildings, the three-litre standard is currently the advanced standard; here,  the house  is designed so that  residents can make do with 3 litres of heating oil per square  meter per annum.

Passive homes are a further  development that includes  a ventilation system  with heat  recovery. Both of these  methods primarily attempt to reduce heat  loss. Zero energy  homes have also proven successful in practice, though they have not  been produced in such numbers to make them generally  affordable. However,  a proper marketing strategy could  increase  sales of such homes enormously in the next  few years.

In office buildings, integrated total  energy concepts (heating, cooling, electricity,  light) and the use of passive systems  (such as cooling with night  ventilation or heat-storing materials) can achieve  a 50 % reduction in energy consumption – for the most  part  without adding greatly  to the cost of construction.

 

Research and  development requirements

R&D should  aim to conserve energy  in buildings and  increase  the share of renewables used  while simultaneously offering the same  or higher standards of comfort. The tasks of research and development can be divided  into system technologies and  technological/ conceptual improvements to the  building envelope.

The building envelope is the  interface  with the environment, influencing heat  flows through windows and  walls. Loss can be reduced through good insulation, heat  can be gained through transparent thermal insulation, and daylighting can be used.  It is a functional and design  element into which  new technologies from the  field of renewable energy sources  can be integrated (such  as photovoltaics, facade collectors).

In the  past  few years, the  development of highly insulating vacuum panels  has been an important step  in the  optimization of building envelopes. Such panels  offer the  same installation as conventional insulating layers that  are some  five to ten  times thicker.  In particular, research is required for the optimization of service life and  the  integration of systems  in buildings and  the construction process.

While opaque walls ensure  very low thermal conductivity (K value), windows are still thermal weak points  in the  building envelope – unless we take account of solar energy gains. Double  or complex triple glazing  provides  for values below  0.5 W/(m2K).

Vacuum glazing  represents an interesting option. Here, the  space  between the  panes  is evacuated down to below  10-3  mbar, which almost  completely eliminates thermal conductivity. HVAC systems  used  play a decisive role in a building's energy efficiency (heaters, control  systems,  and  use of the  overall system).

A focal point  of research is the  replacement of high-performance, active systems  based on fossil fuels by systems  that  use heat  sources  and heat  sinks in the  environment, such as in the ground, ambient air, or groundwater (low exergy  systems  or “LowEx” for short).  For instance, the  heat  storage capacity  of light- weight construction can be improved to the level of heavy construction if phase-change materials  (PCMs) can be used  inside. Rooms would  then  heat  up much less. The heat  stored during the  day in the  PCMs could  then  be released again  at night, when  the  outdoor area is cooler.  If such systems  are properly designed no other  cooling  technologies will be aditionally necessary anymore.

Natural  and  artificial lighting in indoor  meeting points  also provide  practical  visual ambience.

At the  same  time,  building illumination must also be included in the  calculation of the  build- ing’s overall energy consumption. Researchers have developed a number of planning instruments that  allow for natural  and  artificial illumination concepts to be created and optimized. Entire facades  can be designed to optimize energy consumption for illumination, and  tests can be conducted to determine how these  facades  affect the  energy demand for lighting.

In addition to the  further  development of materials  and  encapsulation procedures, system development plays an important role today. Furthermore, robust overall concepts need to be developed so that  new components and systems  can work together smoothly without a reduction in building comfort. Current approaches utilize simulation-based building management concepts, some  of which  even take into account weather forecasts  and  user response.

The main  goals of solar architecture include:

•   High-quality building  outer  shell with especially good heat  insulation, consistent avoidance of heat  exchangers, and  airtight design.
•   Compact structures to reduce heat-exchanging components in order  to lower costs and reduce energy  consumption.
•   Solar-optimised windows with switchable transmission properties leading  to a positive total  annual  energy  balance whilst at the same  time preventing overheating in the summer months and  allowing  extensive use of daylight, especially in office buildings (improved thermal insulating layers with high  solar transmission, electrochromic and gas-chromic glazing,  microstructured types of glazing  in order  to redirect daylight  and give shading from the sun).
•   Solar-active  opaque facade  elements to store solar heat  in the exterior  walls. In principle, transparent thermal insulationoffers great potential for use if technological systems  can be successfully developed for simple practical  application.
•   Other  very elegant approaches include  sys- tems  that  allow a variable amount of energy to pass through them so that  solar heat  can be used  effectively in the winter  even as a shade  is provided in the summer (switchable insulation) as well as systems  that  combine the functions of heat  and  cold storage and the use of daylight  by integrating phase-change materials  in light-permissible components.´
•   Daylight  systems  for the interior  lighting of buildings, systems  for the redirection and distribution of daylight with implemented switchable transmission properties. They allow a better use of natural radiation for lighting, achieving greater lighting  comfort and  a reduction in the cooling  load.
•   Examples include  optical  fibres with low losses and  great  colour  trueness, highly reflective light tubes, and  sunscreen systems backed cast shade  effectively even though they are transparent.
•   New approaches in construction planning that  allow for passive cooling  in buildings not  used  for residential  purposes, including concepts for nightly  ventilation, for instance, and  building-integrated water  circulation  for heat  removal.  Furthermore, with flat heat storage elements with great  energy  density should  be developed for implementation in walls and  ceilings (such as phase-change materials). 
•   Functional  materials  with low thermal emissivity can considerably lower the amount of energy  that  enters  buildings through heat  radiation in the summer. Such layers are therefore being  optimized and means of application, such as woven  glass fibres and  materials for use in textile architecture, are being  developed. The implementation of efficient technologies for passive cooling,  such as radiative cooling, poses another challenge.
•   New  approaches for the development of the multifunctional facades.  This field covers the function of energy  generation and  storage, shading, noise and  heat  insulation, visual protection and  daylighting, ventilation, and design  aspects. Examples include  building- integrated photovoltaics facades  that combine the use of daylight, provide shading and  visual protection, and  generate electricity.
•   Interesting overlapping occurs  here,  such as when  photovoltaics facades  are combined with window blinds.  Window  blinds that react automatically to the amount of daylight or weather conditions also represent attractive, inexpensive architectural solutions that  can be further  optimized. Automatic thermohydraulic drives are also an interesting form of this combination.
•   System management in buildings is the key to the effective integration of innovative technologies. Future system  management concepts intelligently take account of current user behaviour and  external conditions when computing controls  for individual compo- nents. The development and  implementation of such concepts is a crucial challenge in future  research and  development. 
•   Generally,  high-quality energy  carriers, generally  fossil fuels, are used  to heat  and cool rooms. New developments aim to use the potential of the energy, called “exergy”, sparingly.  Keeping  system  temperatures  down  is one  step  towards that  end.  Therefore, innovative  systems  run with very small temperature differences between the heating/cooling medium and  the target room temperature. In this way, renewable sources  of energy  can be used  very effectively, such as thermal solar for heating and  the natural cool of subsoil for cooling. Taking account of and  optimizing exergy flows in buildings can help identify potential for additional increases  in efficiency. 
•   The energy certificates  for buildings that  have been recently  launched require  the determination under standardized conditions of the energy  demand of the planned new buildings  or existing  buildings  if no consumption  values are available.  Parameters and tools that  are suitable  for our planning and consulting have to be developed so that values can be confirmed, feasibility studies undertaken, and  properties optimized. Such tools must  be further  developed in order  to fulfil the requirements of current building codes  (such as DIN V 18599 for the assessment of a building’s overall energy efficiency) and  of future  standards.

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