Environmental Engineering Reference
In-Depth Information
3
Utilisation of Passive Solar Energy
The term "Utilisation of Passive Solar Energy" was first introduced in the seven-
ties of the last century. At that time, the criterion of "adding auxiliary energy" was
used to clearly distinguish between active solar energy applications. When auxil-
iary units (such as fans) were used, the systems were referred to as hybrid sys-
tems. However, the delimitation between passive and active systems remained
fluid: for a window equipped with automatic shading devices is both passive and
hybrid. Only recently, the term "Passive Solar Energy Utilisation" has been de-
fined in a more realistic and precise manner. According to the new definitions
passive solar systems convert solar radiation into heat by means of the building
structure itself, i.e. by the transparent building envelope and solid storage ele-
ments. Utilisation of passive solar energy (often also referred to as passive solar
architecture) is thus characterised by the use of the building envelope as absorber
and the building structure as heat store. In most cases, solar energy is transferred
without any intermediate heat transfer devices. However, also this definition does
not always allow for a clear differentiation of active and passive solar utilisation.
3.1
Principles
In a building, several energy flows can be observed (see Fig. 3.1). Energy is pri-
marily supplied by means of space heating systems, secondly, heat is created by
people, lighting and household appliances (so-called internal heat gain), and
thirdly, there are passive solar heat gains, such as heat created by transparent sur-
faces (so-called passive solar energy utilisation). Heat losses or heat gains (de-
pending on the ambient temperature) are due to the heat conductivity of the build-
ing envelope (i.e. transmission). Further heat losses are attributable to ventilation
and infiltration, generally required to maintain a certain air quality and to prevent
the system from exceeding the prescribed levels of carbon dioxide (CO
2
) and
other harmful substances, air humidity and certain odours. Within the building,
additional energy can either be absorbed or re-radiated by the available thermal
mass in the form of absorbed solar radiation. Thermal mass is also capable of
absorbing and intermediately storing heat in case of overheating. Heat is only
released if the thermal mass becomes warmer than the room temperature. The
following explanations focus entirely on the utilisation of passive solar energy,
and thus only apply to one of the energy flows in a building.
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