Energy Efficiency in Traditional Buildings - Dublin City Council

ENERGY EFFICIENCY IN TRADITIONAL BUILDINGS
WIND: SHELTERED OR EXPOSED
Ireland is an exposed island on the edge of a large
ocean with high maximum and average wind speeds
when compared to most other European countries.
Wind conditions vary from place to place with
pronounced differences on the coast and on high
ground. Winds are strongly influenced by local
topography: for example, rough terrain reduces wind
speed. Similarly trees, vegetation, hills, valleys and
water affect wind speed and, in consequence, the
amount of heat lost from any adjacent buildings.
When wind blows across the external envelope of a
building the rate of heat transfer to or from the
building’s surfaces increases. Wind can also affect heat
gains or losses by infiltration (draughts) due to
increased pressure or through defects in the building
fabric. The importance of achieving shelter from cold
and damp wind has traditionally been understood; the
traditional selection of a location for a dwelling was
often in the lee of a hill and, equally importantly, not in
a hollow prone to frost. Where natural features did not
provide sufficient protection, shelter belts of trees
were often provided.
SW prevaling wind
SW prevaling wind
Houses on Great Blasket Island in lee of the hill with
their gables turned towards the direction of the
prevailing wind
Creating shelter on a site can reduce heat loss by up to
15% and reduce the wind chill factor for people
outdoors. Notwithstanding any shading they may
confer, a permeable barrier such as a stand of trees is
efficient at reducing wind speed. According to The
Climatic Dwelling - an introduction to climate-responsive
residential architecture, protection by a stand of trees
(with 40-50% permeability) can provide protection for
up to seven or eight times the height of the trees.
Shelter belts with under-planting, positioned
perpendicular to the direction of the prevailing wind,
can offer protection for up to 25 times the height of
the trees provided that the shelter belt is at least 15
times as long as it is high. Interestingly, protection
from a shelter belt also extends upwind for some
distance, as the wind lifts up in advance of passing
In terms of orientation, the traditional response was
to orientate houses so that a gable faced the
direction of the prevailing wind, an optimum
arrangement (above). The least effective orientation
for a building, from a thermal efficiency point of
view, is when the main walls are at an angle of 45
degrees to the prevailing wind (below), this is
because the wind streams along the length of the
wall, thereby cooling it, rather than rising over it
over the obstacle ahead of it. In comparison, a solid
wall is only effective for a distance of four to five times
its height (from Green Design, Sustainable Building for
Ireland). Solid obstructions to the wind can also create
uncomfortable and disturbing turbulence whereas
permeable barriers allow some air to move through
the barrier and so create a smoother airflow pattern.
Where they exist, outbuildings can provide shelter to
the main house in addition to providing shelter to the
outdoor working or recreation areas. While it is true
that wind direction constantly changes so that no
single orientation provides a complete solution, when
the direction of the prevailing wind is taken into
account it allows an optimum orientation to be
identified.
All the above are approaches to modifying the
microclimate around a building, to the benefit of the
building users, both within and around the building.
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