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Featured Video - Breathing Buildings - 11th January 2018

Bracing the Storm

S 1500 Mushroom under 60mph wind and rain

Breathing Buildings is proud to have launched the passive roof terminal with the best weather performance for any ventilation cowl. The mushroom cowl design is now de facto the preferred choice by contractors and designers alike. When we launched the first product in 2011 we were asked to compare its performance with penthouse louvre design terminals, and the results were simply astounding. The R Series mushroom was tested at BRE under standard test conditions 13m/s wind speed and 75mm/h rainfall rate and the cowl did not allow any water ingress.

More recently we have been asked whether the ventilation cowl design can withstand storm conditions. We therefore set the testing labs a challenge: how to design a test for a ventilation cowl under more severe wind conditions. The test conditions selected were based on those given in PD CEN/TR 15601 Hygrothermal performance of buildings, Resistance to wind driven rain of roof coverings with discontinuously laid small elements. This standard, which is primarily intended for testing roof coverings includes three wind-rain conditions, but it is the test with the most severe wind speed which was used this time 25m/s (56mph) wind speed and 6mm/h rainfall rate.

The roof terminals were installed on the test rig mounted in position at the wind tunnel outlet. On the underside of the test rig was a Perspex box which enabled the wind driven rain penetrating through the roof terminals to be collected and visual observations to be made. The wind tunnel velocity was measured using a Pitot-static tube placed in the wind tunnel free stream. A calibrated micro manometer was connected to this Pitot-static tube, and monitored the wind tunnel velocity during the testing.

The tests were carried out with the roof terminals mounted at the exit of the Wind Tunnel so that the wind flow was directed perpendicular to the units. Two horizontal spray bars were mounted at the exit from the tunnel, so that water could be sprayed into, and mixed evenly with the air stream. Testing was carried out with the wind/rain blowing on to the two principal orthogonal faces of the roof terminals. The wind rain conditions were maintained for a period of 10 minutes for each test.

The test results showed that with the terminal aligned at 90 and 0 degrees for the S1500L and R Series roof cowls respectively, the total rain collected after 10 minutes was a mere 14g and 48g.

Discussion
The wind/rain conditions applied in all of the tests represents, on average, the worst-case conditions that would be expected in any 50-year period in Northern Europe. It therefore follows that in most wind storms where the mean wind speed is 25m/s, the rainfall rate will be lower than that applied in these tests and the rain leakage through the terminals will be proportionately lower.

To put these results in to context; a weather louvre tested under conditions of 13m/s wind speed, 75l/hr rainfall can be classified as Class A even if it allows ingress up to 0.75l/hr per square metre of louvre. This is equivalent to 0.0125 litres per minute. All of the mushroom tests for the most recent tests (25 m/s wind speed) admitted less ingress than this, with the S Series at 90 degrees orientation providing 9x as much protection (amount of ingress is 9 times less than a 1 square metre louvre which is just within the Class A classification definition). Check out the video to see one of the tests in action.

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