What is the
purpose of a flysheet in a tent? (Second function)
As I said
before, a flysheet in a tent is supposed to offer thermal isolation for the
users, but it is really hard to find a tent that has a flysheet capable to meet
this expected function.
The main
reason is that to make it possible to create a thermal isolation it is needed
to have a physical barrier between inner fabric, the body, and outer one, the
flysheet.
The purpose
is that the air surrounding the tent finds something between outer side and the
interior, capable of reducing the thermal transmission, in cold weather
avoiding inner air being as cold as outer one and in hot weather avoiding inner
air being as hot as outer one.
In
architecture and construction, in a simplified manner, there have been
historically three main ways to reach this goal: first very effective way was
to make a thick barrier, sometimes even one meter wide; second way adopted, not
so effectively, was to reduce this thick walls in order to save money in the
house building substituting it with lighter materials and using inner layers of
isolation materials and leaving some space for creating an air barrier, and
finally it was discovered that one third effective way to create a chamber of air
in movement, between inner air and outer air, keeping this air chamber between
two layers of material. This is the effect known as ‘ventilated façade’.
The
ventilated façade works as follows:
When the
sun shines, the air inside the chamber is heated and it starts to flow to upper
areas. As the hot air goes up, fresh air occupies the space abandoned by hot
air, bringing fresh air inside the air chamber, if the hot air has an escape
way to flow to the atmosphere, this movement becomes continuous and the flow of
air avoids the inner air inside the tent getting hotter.
The air
barrier between outer layer and inner layer creates a difference, a gradient,
of temperatures, keeping the interior fresh.
When the
weather is cold outside, the same effect is produced. But with some
differences: If the hottest air is not allowed to escape the air chamber, the
air inside the chamber maintains a higher temperature than interior and avoids
the interior to lose temperature. In this way, the air inside the chamber is a
barrier that avoids inner air to cool too much.
When we
analyze most tents in the market, we can easily find that the immense majority of
tents have a flabby flysheet (those which have one) that is not capable to be
tightly separated from inner body, even many of them commonly touch frequently
the inner layer. This kind of flysheets are not capable of keeping an air
chamber functioning.
To have a
real air chamber capable of producing thermal isolation it is needed to have
inner and outer layer permanently separated. Otherwise, the free circulation of
the air inside the chamber would be obstructed and the air chamber wouldn’t
work.
To have a
tight flysheet separated of the inner layer and to keep both layers stretched
permanently it is not an easy task. Ctents is a tent that shows that it is
possible to create a ventilated façade effect for a tent.
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