Green Buildings: Passive Houses and Plus Energy Buildings

Prof. Dr. Peter Heck,
Managing Director of IfaS
M.Sc. Thomas Anton,
Head of Department for Renewable Energies and Energy Efficiency
M.Sc. Patrick Huwig,
Team Member of Department for Renewable Energies and Energy Efficiency
University for applied Sciences Trier, Environmental Campus Birkenfeld Institute for Material Flow Management (IfaS) - Birkenfeld / Germany

Saved energy is the best energy. According to this principle, the goal of energy efficient buildings is to be operated with the least possible amount of cooling or heat energy. Besides heating or cooling energy, the sector of electricity offers great potential for identifying savings, compared to conventional devices and lighting.

While in Europe thermal heat for building airconditioning requires the largest share on the final energy consumption (average temperature in Germany: approx. 0.3°C in Winter and approx. 16.5°C in summer), the largest share on the final energy consumption on the Arabian peninsula is required for building cooling (average temperature in Dubai: approx. 20°C in Winter and approx. 33°C in summer). As shown in the progress of this article, building air-conditioning (heating and cooling) can take place in a renewable manner while simultaneously being competitive or even cheaper in comparison to conventional technologies.

Especially photovoltaic and solar thermal plants are being in operation million fold in Europe since over a decade (the installed PV-capacity within the EU amounts up to around 80 Gigawatt), even though the solar irradiation yields in Central Europe are on a relatively low level, compared to sunny countries. For comparison: the solar irradiation yields in Europe with around 800 to 1,300 kWh/kWp is much lower than on the Arabian Peninsula with around 1,600 to 2,200 kWh/kWp. Therefore, the specific costs in Central Europe are much higher compared to the costs on the Arabian Peninsula.

Passive Houses and Plus Energy Buildings

The passive house institute Darmstadt calculates and certifies passive houses according to the following definition: „A passive house is a building, in which thermal comfort can be achieved and guaranteed alone through reheating or re-cooling of the fresh air flow, which is required for a sufficient air quality without the need for additional usage of circulating air.”1. The passive house standard in residential construction is deemed to have been achieved, if a specific thermal heat demand of 15kWh/ (m²*a) and a specific primary energy demand of 120 kWh/ (m²*a) is not exceeded (requirement for a certification).

An even more ambitious version of the passive or zero heat energy houses is the plus energy house. Instead of using even small quantities of energy for heating and operating of the building from external sources, plus energy houses produce, financially, more energy than it consumes on its own. Here again official definitions exist, on which basis the buildings are evaluated: “The plus energy house level is achieved, if a negative annual primary energy demand (ΣQp < 0 kWh/(m²a)) as well as a negative annual final energy demand (ΣQe< 0 kWh/ (m²a)) exist.”2. To achieve the plus-energy building standard, the usage of renewable energies in terms of solar thermal and photovoltaic systemsis necessary. When building passive or plus-energy buildings in hot climate zones, the following points need to be considered:

  • Massive structures with thick walls and heavy building materials (e.g. 40 cm thick clay walls) Preferably white washed roofs and shaded windows
  • Air tight construction (low air change during the day and intensive ventilation during the night)
  • Utilization of storage mass of the soil → floor slab on the soil and preferably without cellar
  • Multi-storey constructions → in relation less roof area and therefore lower cooling load

Regenerative Building Air-Conditioning

For hot regions with high cooling demands and solar irradiation, two regenerative air-conditioning possibilities on a solar basis can be provided, especially for larger buildings. For electricitybased air-conditioning reversible operating heat pumps (heating and cooling) or conventional compression refrigeration machines, in combination with photovoltaic plants, can be operated. The photovoltaic system is used, to supply the cooling systems with regenerative electricity. It needs to be considered, that the higher the temperature spread between outside temperature (e.g. 40°C) and the desired indoor temperature (e.g. 20°C), the more inefficient compression cooling machines become. The efficiency of cooling systems is described with the performance factor, which mirrors the relation between input energy (e.g. electricity or heat) and the usable energy (cooling energy). While in temperate climate zones a temperature spread of around 10°C accompanies with a performance factor between 3 and 4, the performance factor decreased with temperature spreads between 20 and 25°C to around 1.5 and 2. Therefore, more electricity has to be spent on air-conditioning.

While compression technologies own an electrically driven compressor, absorption technologies operate with thermal compressors. These compressors can be operated with, for instance, solar thermal plants while the solar heat is used as a propulsion medium. Through thermodynamic and physical effects (evaporation, condensation, compression, absorption) the absorption technology can provide regenerative cooling energy from solar heat.

Especially the water heating by solar thermal plants is of great advantage for hot regions, since a high load of solar thermal plants and therefore low costs for water heating can be ensured.

(Picture-Source: Florentine Visser - Architect)

Extreme-Example 1: Passive house in hot climatic zones (Aqaba, Jordan)

The architectural design is adapted to the local climate and makes use of the following design elements to improve the energy performance: building orientation, compact building mass, floor plan layout (individual rooms on the north side; circulation space as buffer-zone to the south side), shading for windows, facades and roofs, roof garden, improved natural ventilation, recessed windows, evaporative cooling, and thermal mass for heat.

accumulation and solar gain in the winter Windows are recessed in the thick walls and have Venetian shutters to allow shading and ventilation.

The building is built along an east-west axis to minimise solar gains in summer and maximise solar gains in winter. The building is oriented with bedrooms towards north and east to protect the interior rooms from summer afternoon heat. The zones towards the west side are buffer areas with a short term use; as corridors and bathrooms. The living room, is located on the ground floor, placed at the southernmost tip of the house, and is protected to the west by the garage and storeroom. The southern side offers a unique location where the low sun can heat it during the cool winter days, while the high sun can be easily shaded off during the hot summer days.

The building's structural design is aimed at upgrading conventional wall sections and experimenting with new ideas, keeping in mind the use of locally produced materials as much as possible. The structure is heavy with high thermal capacity combined with an insulation layer of 50 mm insulation (mineral wool and polystyrene) in the cavity walls of the envelope. The U-values for the wall systems range between 0.4 – 0.5 W/m²K. The windows are made of steady steel frames with good weather stripping and double glazing. Extra effort has been put into high-quality construction detailing and execution to prevent air leakage.

A solar-driven adsorption cooling system was installed on the top roof. The solar hot water matrix has been designed to deliver domestic hot-water, heating and energy for the adsorption chiller, which after some time of experimenting did not deliver the required cooling. With current feed-in tariff in Jordan, most efficient split units solar powered by Photo-Voltaics, could be the most cost efficient solution.

(Sources: - Your Guide to Energy Efficiency in Buildings, Dr. TareqEmtairah, Florentine Visser - Architect)

(Picture Source: © 2012 Engadin St. Moritz Mountains - GianGiovanoli /

Extreme-example 2: First plus-energy hotel in the Alp region with cold mountain climate (Engadin St. Moritz, Suisse)

While the previously shown extreme example shows a passive house in desert regions, this example is meant to provide another extreme example from cold regions. The Mountain Dining Romantic Hotel MuottasMuragl (16 double bed rooms) is located at an altitude of 2,456 meters above sea level and was refurbished in 2010 as a plus-energy hotel. Even that the heated useful area was increased by around 50%, the energy consumption could be reduced by 60% through refurbishment measures and the maximization of solar yields (passive and active). A solar thermal plant is used for water heating as well as serving as a supplementary heating system. The building heating is provided by a heat pump, which is supplied with ambient heat by a ground probe field with 16 probes (á 200 m). Additionally, waste heat from cooling plants as well as waste heat from the cable railway drive is used. The electrical energy is covered with a 64 kWp photovoltaic plant. Below the line, the hotel is producing more energy than it consumes.

(Source: Fanzun AG / Engadin St. Moritz Mountains AG)


As shown in the best-practice examples, the future of high efficiency buildings lies in a proper insulation of the building shell as well as in the active and passive usage of solar energy and avoidance of solar gains respectively for heat protection in hotter regions. In temperate climate zones, it is therefore of importance, to optimize the usage of solar energy during Winter, for instance through building orientation and window surface arrangements, letting as much solar energy enter the building as possible and through that save heating energy. In hotter climate zones on the other hand, it is important to minimize the solar entry to buildings by accordingly orienting the building and minimizing shading measures, to save as much cooling energy as possible.

From an ecological perspective, fossil CO2- emissions are avoided, the primary energy demand can be lowered to a minimum, integrating renewable energies (especially solar energy for heating and cooling with absorption-cold as well as electricity production from photovoltaics).

Another possibility to reduce the heat and cooling demand respectively is the use of greenery roofs or facades. The greening naturally serves as a protection against cold through the soil formation as well as a protection against overheating through absorption of sunlight by plants. In summer, the buildingand city climate additionally benefits from the cooling produced during evaporation by plants and rainwater. Furthermore, the roof greening improves the life span of the roof membrane, since the soil formation is a natural protection against UV-light as well as wind and rain.

(Picture sources: OPTIGRÜN,

Further information to the different topics is available here:
Passive houses: and
Roof and façade greening:
Absorption cooling:

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