Hi Lawrence,
we were told to built our tunnel with the axis running E-W but decided
that in our windswept area that did not make sense. The main winds and
storms come from the SW/W. By orientating the axis N-S (i.e. broadside
E-W) the wind does not hit the front head on but can sweep over the
curve of the sides. I have been very happy with light intensity and heat
in the tunnel. Productivity has been good. And the 3-year plastic lasted
for 6 years (there is also a shelterbelt to the West). Having said that
I don't have hard data on the difference it makes in terms of light
intensity and heat.