Today, solar architecture is one of the most important methods to replace conventional energies and to reduce environment pollution. Passive use of solar energy, natural cooling and day lighting represent the wide spectrum of existing strategies for the implementation of solar energy in architecture.
Characteristic solar architectures are the ones in which absorption, storage and use of solar energy have been taken into account during the design phase;Buildings, in which means of ventilation, location of different functions, materials and arrangement of heat-losing boundary surfaces are taken into account and are optimally situated in the site with regard to natural solar supplies, so as to reduce the energy demands to the minimum possible and to maximize the use of solar supplies; Buildings, which correspond formally to the shadings of surrounding trees, geometry of the sun, direction of wind and water and other potential resources in the area.
Solar architecture is characteristically design oriented and found in particular buildings. It's been shown that it's possible to employ solar design techniques in a studied manner to create mild and well-tempered interiors in which inhabitants feel good.
A passive house is a building which is warmed by the sun, internal heat sources and recovered heat , therefore has no need for a separate active heating system. Passive house is a consequent development of low energy houses but consumes 80% less energy for heating.
Counting the heating oil, a passive house consumes less than 1.5 liters of oil per square meter per year. This sensational reduction in passive house energy demand is achieved through two basic principles: Avoiding heat losses and optimizing free heat gains.
A very well insulated building envelope with an insulation layer of 25 to 40 centimeters, as well as triple glazed heat saving windows with sealed frames help keep heat inside the house. Fresh air is supplied by a comfort ventilation with a heat recovery system. More than 75% of the sensible heat of the exhaust air is recovered to heat up the fresh air. So for instance, with an outside temperature of 0° C and an inside temperature of 20°C, the fresh air enters the house at 16°C, thanks to the heat recovery mechanism. Not only people with allergies and asthma appreciate the pollen-free and low dust air in passive houses.
Heat gains in a passive house are either solar, through windows, or internally produced by inhabitants and appliances. In summer, sensible shading, for instance by balconies or shades, prevents over-heating in rooms. In cold winter months, the incoming fresh air is warmed up in the ventilation system so as to eliminate the need for a separate heating system.
Through an effective insulation, all the inner walls and floors are equally warm, even when they are boundary surfaces, subject to the cold outside air. This results in a high level of comfort. Low air quality at nights, when windows are closed against noise or cold weather, never occurs in passive houses due to the comfort ventilation system.
Also mold growth is impossible, effective heat insulation and continued ventilation help prevent humidity and condensation in building elements even on the edges of glazing.
All building parts of the outside envelope need to be thoroughly insulated. Edges, corners, fixtures and connections have to be carefully designed to avoid heat bridges. All opaque elements of the outer envelope have to be so well insulated as to reach a heat transmission coefficient of below 0.15 W/m2K which means that by a temperature difference of 1 degree, and per square meter of outside surface, 0.15 Watt is lost. The more compactly a building envelope is constructed, the easier and cheaper it will be to achieve passive house standards.
Appropriate orientation, no shading from surrounding elements and reduced share of window frames are other conditions which allow „passive“ solar gains to be optimized and turn into a main heat supply. Particularly in single family dwelling, such considerations can help save extravagances in insulation to reach passive standards. In multistory buildings and other compact building forms passive house standards can be achieved even without south orientation.
Windows (glazing and frames combined) should not surpass a U-value of 0.80. As such, specific windows with good insulation are needed. The glazing has a g value of 50% (g value=total energy transmittance, share of the solar energy, available inside the room). Windows have to be installed within the insulation layer of the wall without any heat bridges.
Leakage through uncontrolled joints has to prove less than 0.6 times the volume of the room per hour through a blower door test with a pressure difference of 50 Pascal between inside and outside.
A better air proofing of the envelope helps improve heat demands.
Fresh air can be led into the house through an earth heat exchanger (ventilation canals buried in earth). Even in very cold winter days, fresh air is thus per-heated by a temperature of above 5°C. This is a sensible measure but not necessary in every passive house.
The comfort ventilation with heat recovery system primarily provides a good indoor air quality, secondly, it helps save energy. In passive houses, at least 75% of the heat of the exhaust air is transferred to the in coming fresh air over a heat exchanger. In order for this to happen, fresh air and exhaust air pass by each other in separate canals. So the heat transfer is done without mixing of the fresh and exhaust air. However, the electricity demands of the ventilation system does not surpass a minimal amount.
Domestic hot water is provided partly with regenerative energy sources to reduce fossil fuel consumption. This can be achieved partly or completely by solar collectors, wood boilers or heat pumps.
Optimizing the general concept, Saving on costs
To reach passive house standards all components have to be optimized and tuned with one another. Therefore a passive house projection packet (PHPP) is developed. PHPP is an excel based energy performance evaluation tool for heat demand and primary energy demand, which includes many additional calculations such as window U-values, impact of orientation and shading, building heat losses and summer time over heating. With this tool, the planner can effortlessly optimize main components of the passive house and figure out most cost efficient strategies.
Photos: Andreas Buchberger