Designing with the sun — and keeping its heat out in time

The building itself becomes a tool

In passive solar design, building components perform functions that might otherwise require additional technology. Windows admit solar radiation, suitable surfaces absorb heat, and heavy building elements can release it again after a delay. The US Department of Energy describes the interplay of openings, absorption, thermal mass, heat distribution and the control or limitation of gains. These principles are not a ready-made construction manual for every location. Orientation, shading from neighbouring buildings and local weather conditions alter their effect. How rooms are used also matters: an office occupied during the day has different requirements from a bedroom. The aim is not to capture as much solar heat as possible. It is to enable useful gains without causing glare or overheating, and without increasing the loss of heat used for heating through unnecessarily large areas of glazing.

Thermal mass is no substitute for solar shading

Heavy building elements can moderate temperature fluctuations by absorbing heat and releasing it later. However, their effect is limited if more heat enters the building over an extended period than can be removed. The thermal mass then warms up too. It is therefore particularly important to limit unwanted solar radiation effectively. The position, geometry and controllability of shading must suit the façade. Suitable night-time ventilation can also remove stored heat, provided outdoor conditions, security and noise levels allow it. The design should explicitly examine these prerequisites. A theoretically effective strategy is of little help if windows have to remain closed at night because of traffic noise. Internal heat sources from people and equipment must also be included in the balance. Summer comfort results from the coordinated interaction of these factors, not from a single choice of material.

Lower cooling demand is a robust goal

The International Energy Agency points out that cooling is becoming increasingly significant for buildings' energy demand. Passive measures can help limit this demand before active cooling systems are sized. However, they do not guarantee consistently comfortable temperatures under all conditions. Long hot spells, high occupancy or particular uses may require additional cooling. What matters is a transparent assessment of the specific building. This should consider not only an average summer day, but also challenging conditions. For existing houses, gradual improvements are often an option, such as suitable shading and adjusted operating practices. In new buildings, orientation and layout can be incorporated early on. The greatest advantage of passive design lies in preventing unnecessary heat loads from arising wherever possible, rather than removing them later using energy-intensive methods.

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