Low-energy and passive houses

by silvia in Energy efficiency, Modern Architecture, Passive houses | 0 comments

Low-energy and passive houses are well sounding concepts but it’s not always entirely clear for non-professionals what lies behind them. Under the EU law, all new buildings after 2020 must have net energy consumption for heating, near zero without using fossil energy. So let’s clarify what is behind these concepts.

Low-energy building is the one that needs 30 to 70 kWh of energy for heating or cooling per square meter of the usable area per year. This is equivalent to 3 to 7 liters of liquid fuel or 3 to 7m3 of natural gas.

A passive building is one that needs max 15kWh of energy per square meter of usable area to maintain internal microclimate.

According to Passive House Institute, the criteria for a passive house are:

  1. The consumption of energy or heating and cooling per year is 15 kWh per square meter of the usable area of the building.
  2. The energy needed for heating, ventilation, heating water, household appliances and lighting should be maximum 120 kWh per square meter of usable area of the building.
  3. Air permeability
  4. Temperature comfort – all the hours a year in which the average ambient temperature exceeds 25°C should not be more than 10%

Those criteria can be achieved by design that includes:

  • Minimal thermal bridges in construction
  • High quality windows
  • Ventilation/Heat exchanger system
  • Quality insulation
  • Airtight construction

Under the law of conservation of energy, the sum of the heat loss must equal the sum of all heat gains. Therefore the ventilation and heat transfer losses that cannot be compensated by solar energy and internal heat gains, should be compensated by a heating system or by the accumulated energy provided by occupancy of the building (human warmth, cooking, lighting, electrical appliances etc.) also accumulating solar power (appropriate location, solar systems).

To reduce heat and energy losses of the building a number of other factors like: ambient temperature, available renewable energy sources, area and color of the outer surface of the building, area of the windows and doors, lighting should be considered. The best combination of methods and materials ensures the optimal microclimate and comfort of the dwellers. All elements of the house, even the smallest details, are designed in virtual space. The information of the entire project is linked in a common database, which allows to find the best solution for the specific situation.

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