Solar energy use in buildings - Solar Energy Sciences and Engineering Applications - page 609

The temperature field T ( x , t ) is related for illustration purposes to the amplitude of
the surface temperature fluctuation T sm . Even at just 5 cm component depth, the sur-
face amplitude of a concrete wall is reduced by 30%. The phase shift between the
maximum surface temperature and the temperature at a depth of 5 cm is 1.5 h. The
heat flow into a component with a periodic temperature boundary condition is again
calculated using Fourier's Law, from the temperature gradient at the surface. The heat
flow

Q/A is proportional to the surface temperature amplitude T sm .

18.10 SOLAR GAINS, SHADING STRATEGIES AND
AIR CONDITIONING OF BUILDINGS

Existing office and administrative buildings in cool or moderate climates have approx-
imately the same consumption of heat as residential buildings and most have a higher
electricity consumption. In warm climates, air conditioning needs dominate consump-
tion. Both heat and electricity consumption depend strongly on the building's use.
In terms of the specific costs, electricity almost always dominates.
More than half of the running costs are accounted for by energy and technical
services. A large part of the energy costs is due to ventilation and air conditioning.
Heat consumption in administrative buildings can be reduced without difficulty, by
improved thermal insulation, adoption of low-energy standards, which can reduce
consumption to a few kWh per square metre and year in a passive building. Related
to average consumption in the stock, a reduction to 5-10% is possible. Electricity
consumption dominates total energy consumption where the building shell is energy-
optimized. The measured electricity consumption for German office buildings was
between 30 and 130 kWh m − 2 a − 1 .
The detailed measurements shown in Figure 18.10.1 over several years in the first
passive office building in Germany (Weilheim/Teck), completed in 2000, illustrate
ways of energy optimization: the passive house standard is realizable at low additional
costs; hot water consumption is insignificant in office buildings; and the electrical
energy consumption for building services (ventilation, lighting, pumps) can be limited
to low target values ( < 15 kWh m − 2 a − 1 ). The main consumer of electric energy is office
equipment, which is responsible for more than 40% of the total energy consumption,
with a rising trend during the three measurement years even though energy-saving
equipment was used.
It is also possible to achieve the passive house standard through building rehabili-
tation. Detailed measurements at an office building in Tübingen, Germany (see Figure
18.10.2) show that a very low thermal heat consumption of less than 25 kWh m − 2 a − 1
can be achieved, although not all building elements, such as the ground floor, can be
well insulated due to the low ceiling heights.
Non-residential buildings often have high internal loads due to a high amount
of electrical equipment. About 50% of internal loads are caused by office equip-
ment such as computers, printers, photocopiers, etc., which leads to an area-related
load of about 10-15 W m − 2 . Modern office lighting has a typical connected load of
10-20 W m − 2 at a luminance level of 300 to 500 lx. The heat given off by people,
around 5 W m − 2 in an enclosed office or 7 W m − 2 in open-plan offices, is also not
negligible. Typical mid-range internal loads are around 30 W m − 2 , resulting in a daily