Energy Demand of Buildings - Low Energy Cooling for Sustainable Buildings - page 4

1.1 Residential Buildings

1.1.1 Heating Energy

Due to the wide geographical extent of the European Union covering nearly 35 ◦ of
geographical latitude (from 36 ◦ in Greece to 70 ◦ in northern Scandinavia), a wide
range of climatic boundary conditions are covered. In Helsinki (60.3 ◦ N), average
exterior air temperatures reach 6 ◦ C in January, when southern cities such as Athens

at 40 ◦ N latitude still have averages of

−

10 ◦ C. Consequently, building construction
practice varies widely: whereas average heat transfer coefficients ( U -values) for
detached houses are about 1 W m − 2 K − 1 in Italy, they are 0.4 W m − 2 K − 1 in Finland
(see Table 1.1). The heating energy demand calculated from monthly energy bala-
nces (according to European Standard EN 832) is comparable in both cases at about
50 kWh m − 2 a − 1 .
If existing building standards are improved to the so-called passive building stan-
dard, heating energy consumption can be lowered to less than 20 kWh m − 2 a − 1 . Studies
in Switzerland showed that additional investment costs for passive residential buildings
are about 14% (Minergie P label). For buildings with a low energy standard (reaching
the Swiss Minergie label) investment costs were about 6 to 9% higher (Binz, 2006).
Depending on the assumptions made for energy price increases, the additional invest-
ment costs can be compensated by lower energy costs during operation. In Germany
with its high number of passive building projects, additional investment costs for the
high standard are only 3 to 5%.
Since the implementation of the European Building Performance Directive in 2003,
nearly all European countries have significantly increased the requirements to reduce
transmission heat losses. The European Performance Directive asks for the establish-
ment of a calculation methodology for energy demand and an energy certification
process, whereas limits on energy demand are regulated by national laws.
Average U -values for new buildings are about 25% lower than in 2003. The re-
quired U -values to achieve passive building standards are listed in Table 1.1 for some
cities from different European climates. For these insulation standards, heating en-
ergy consumption is between 15 and 20 kWh m − 2 a − 1 . By comparison, today's resi-
dential buildings in Germany with low energy standards have annual heating energy

+

Table 1.1 U -values for residential passive buildings (Truschel, 2002)

U -values Rome Helsinki Stockholm

Wm − 2 K − 1

Wall 0.13 0.08 0.08

Window 1.40 0.70 0.70

Roof 0.13 0.08 0.08

Ground 0.23 0.08 0.1

Mean 0.33 0.16 0.17

U -value