Solar energy use in buildings - Solar Energy Sciences and Engineering Applications - page 590

With high heat insulation standards and the heat recovery ventilation concept of
passive houses, a low limit of heat consumption has meanwhile been achieved, which
is around 10 times lower than today's average consumption values. A crucial factor
for the low consumption of passive buildings was the development of new glazing and
window technologies, which have enabled windows to become passive solar elements,
at the same time causing only low transmission heat losses. In buildings with low
heating requirements, other energy consumption in the form of electricity for lighting,
power and air conditioning, as well as warm water in residential buildings, is becoming
more and more dominant. In this area, renewable sources of energy, especially solar
energy, can make an important contribution to the supply of electricity and heat.
In warm climatic regions and in non-residential buildings with high internal loads,
cooling is the dominant energy requirement. Here, solar protection is the main issue
to reduce energy demand and high glazing fractions, which might be useful in cold
climates but which now cause problems for summer comfort.
The majority of the world's new buildings are constructed in Asia. The Asian
building sector today accounts for about 25% of final energy consumption and this is
expected to rise to 32% by 2030. A World Bank study showed that China and India
could cut their current energy consumption by 25% with cost-effective retrofitting of
lighting, air conditioning, boilers and heat recovery. The Chinese Ministry of Con-
struction states that 95% of all buildings are highly energy consuming and that energy
consumption is currently two to three times that of developed countries in achieving
the same comfort.
18.2 PASSIVE SOLAR GAINS IN COLD AND MODERATE
CLIMATIC REGIONS
Passive solar energy use contributes significantly to the heating energy demand of
every building. The main energy supply is via short-wave solar irradiance transmitted
by glazing, which provides daylight and is converted into heat by absorption on wall
surfaces. This form of energy transfer is described as passive and takes place solely by
solar irradiance absorption, thermal conduction, long-wave radiative exchange and
free convection; i.e. transfer is not line-bound and requires no auxiliary mechanical
energy for moving a heat carrier.
Solar irradiance is absorbed without transport losses directly by the building shell
or by means of internal storage. Besides windows and the associated internal stor-
age, the possibilities of passive use also include transparent thermal insulation on a
heat-conducting external wall. Despite having a lower solar efficiency compared to
windows, transparent thermal insulation in connection with a massive building com-
ponent enables a temporal phase shift between irradiance and utilization of heat. This
characteristic reduces overheating problems that can occur with large glazing.
Unheated winter gardens rank among the classical forms of passive solar use. As
elements placed in front of the building shell, they contribute to the insulation of the
building, but at the same time they reduce the amount of solar irradiance available to
the main building. Thus, the amount of both daylight and direct heat entry by solar
irradiance into the adjoining heated rooms are clearly reduced. Furthermore, indirect
heating of glazed conservatories by adjoining rooms often leads to an increase in the