Energy efficiency in buildings

Low, Passive, Zero and Plus Energy Buildings

Energy-efficient buildings are designed to use as little energy as possible. Buildings can be made energy-efficient by using quality building and insulation materials which help prevent heat loss and make the building airtight. High-quality design and craftsmanship are prerequisites in energy-efficient building. Minimising thermal bridges is the key.

Energy-efficient buildings are classified into four categories: Low Energy, Passive, Zero and Plus Energy buildings. Passive buildings are often the optimal solution when considering the lifecycle of a building.

Type 0 - Standard Building

A standard building is constructed to meet only minimum building standard energy efficiency requirements.

Type I - Low Energy Building

A low energy building consumes only half of the energy needed by a standard building. Energy efficiency is achieved by improved insulation and windows and a ventilation heat recovery system. To bring a building to a low energy level is not notably more expensive than building a standard house (0 - 5 %). Annual energy consumption for heating a low energy building is in the range of 50 – 60 kWh/m2.

Type II – Passive Energy Building

A passive building consumes less than a quarter of the energy used by a standard building. It stays warm by using energy generated in the building. It has no separate heating system apart from heat recovery ventilation.

The passive building definitions applied in different parts of Europe are based on the preliminary energy need requirements presented in the Promotion of European Passive Houses (PEP) and Passive-on studies of the Intelligent Energy Europe research programme.

The definition of a passive building is based on its energy need. The building’s total energy need is estimated in primary energy and it has limit values. For example, in Germany, a primary energy conversion factor of 2.7 is used for all electric energy bought from the grid. The energy conversion factors are agreed on the national basis.

Country  Space heating and cooling energy demand  Primary energy demand  Heating power demand  Air tightness 50 Pa 
  kWh/m2a  kWh/m2a  W/m2  exch/h
Finland 20 - 30  130 - 140   0.6 
Norway 15 + 3.5(T - 5)
T = annual temperature

Sweden South 45
North 55
Total purchased energy
  South 10
North 14
(0.3 l/sm2
Germany 15  120    0.6 
Southern Europe  15 + 15 = 30 120    0.6 

Energy efficiency is based on passive building envelope solutions: low U-values and particularly good airtightness. It has a very well insulated structure, quality windows and doors.

Building a passive house is only 5 – 10 % more expensive than building a standard house. However, the additional costs of the more solid structures are compensated for by not needing to install a heating system. No new technical skills, special equipment or materials are needed for passive building. Annual energy consumption for heating a passive building depends on the building’s location and varies from 15 kWh/m2 in Central Europe to 30 kWh/m2 in North Europe.

According to the Commission’s plans, passive houses are expected to become standard in new buildings in the EU by 2015.

Type III – Zero Energy Building

A zero energy building is a building with zero net energy consumption and zero carbon emissions annually. These buildings can be independent of the energy grid supply.

Type IV - Plus Energy Building

The plus energy concept is based on buildings having an energy efficiency level of a passive building and additional integrated active energy supply systems that exploit solar or wind energy. During the summer, the building sells excess amounts of electricity to the national grid and buys it back during the winter. The prerequisite for such a building is the existence of a national sales tariff, which is not yet the case in most countries. The current tariffs are heavily subsidised to promote the development of new technology.

An extra investment cost for a Plus Energy Building is at least 10 % compared to a standard building. Plus Energy Buildings are currently rare but are likely to become a new building trend in the near future.