CONCEPTUAL DESIGN of the swimming pool - ETFE material

Outline design guidance

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General description


The Roofs consist of pneumatic cushions comprising of between 2 and 5 layers of a modified copolymer Ethylene Tetra Flouro Ethylene. The ETFE Foil is extruded into thin films and supported in an aluminium perimeter extrusion which is supported on the building frame.
The Cushions are inflated by a small inflation unit to approx. 220 Pa which gives the foil a structural stability and gives the roof high insulation properties.


Life


ETFE Foil is unaffected by UV light, atmospheric pollution and other forms of environmental weathering. The material has been extensively tested both in the laboratory and out in the field and no degradation or loss of strength is observed. The material has been in existence for over 36 years and does not become brittle or discolour over time. We have been building etfe enclosures for over 21 years and no signs of ageing em-brittlement discoloration or the like have been observed. It is anticipated that the material has a very long life.


Transparency


ETFE Foil is very transparent across the visible light region ( 380-780 nm ) having a light transparency of approx. 94-97% of total light. Transmission across the ultraviolet range ( 320- 380nm) is also very good ( 83-88%). It is also important to note that the Film has high absorption in the infra red range, a property that can be exploited to reduce buildings energy consumption.


Solar Control


Whilst the base material is very transparent, ETFE Foil can be treated in a number of different ways to manipulate its transparency and radiation transmission characteristics. The Foil can be over printed with a variety of surfaces to affect transmission, or printed with graphic patterns to reduce solar gain whilst retaining transparency, or can incorporate a white body tint to render the foil translucent. The degree of translucency can then be manipulated by adding additional layers of foil into the system. Alternatively cushions can be constructed with variable shading and reflectance by differentially pressurising air chambers in cushions to cause opaque graphics on intermediate layers to alternately cover or uncover each other.

Colour Rendering


Due to the good transmission characteristic colour rendering under an ETFE Foil roof is extremely good, being as daylight across the visible light range.


Insulation


A standard three layer cushion has a U value of 1.96 w/m²K . This is better than triple glazing when used horizontally (glazing manufacturers figures are for vertical glazing which considerably enhances the figures). The cushions insulative qualities can be further enhanced by the addition of further layers of foil which can in turn be treated with coatings.


Inflation units


The cushions are inflated by inflation units. The energy consumption used by the inflation units is minimal because the blower units only need to maintain pressure, they do not need to create air flow. A Roof is generally powered by one or several inflation units with each inflation unit maintaining pressure to approx. 1000 m² of roof . An inflation unit comprises two backward airfoil blowers powered by electric motors. The inflation unit operates approximately 50% of the on an average roof and uses a similar amount of power to a light bulb.


Air dryers


The inflation units can easily be fitted with dehumidifiers to dry air being fed to the cushions. We would recommend that this be considered for high humidity environments.


Power Failure


In the event that an area experiences a power failure, the ETFE Foil Roof will maintain pressure for approx. 4-8 hours due to the non return valves built into the inflation system. Should the power failure extend beyond 4-8 hours, no harm will come to the roof. However we would recommend that the roof is closely monitored particularly if it has a very shallow orientation. Should high winds also be experienced then the slack cushions can flog and make a load cracking sound. For this reason we recommend that if prolonged power failure is experienced a small generator is utilised to power the inflation units until power is returned to the grid.


Safety/Explosion risk


ETFE Foil is a flexible material which can take extremely high short term loading. This makes it an ideal material for use where there is a risk of explosion. Equally if there is a risk of vandalism ETFE Foil cushions do not break and fall out of their frames risking life below.


Replacement


Should an ETFE Foil cushion become damaged the panel can be easily replaced from outside with no internal access being required. Small repairs are easily effected to the Foil in situ, using a specially treated etfe foil.

Fire


ETFE Foil has low flammability and is self extinguishing. The cushions self vent in the event of fire as the hot plume causes the foil to shrink back from the source of the fire allowing the fire to vent to atmosphere. The quantity of material in the roof is insignificant in fire terms and one does not experience molten drips of Foil from the roof.


In many situations it is not possible to guarantee that the cushions will fail as one cannot be certain that the products of combustion reach 200 deg C. In these circumstances one can utilise Texlon SV our patented invention where we can cause the cushion to fail on demand.


Acoustics


A foil roof is acoustically relatively transparent. This means that the foil acts as an acoustic absorber for room acoustics, enhancing the internal perceived environment. Rain noise can be controlled with our patented rain suppressers.


Cleaning


Unlike fabric structures ETFE Foil is an extruded material . This means that the surface is extremely smooth . This smoothness coupled with ETFE Foils anti adhesive properties means that the surface does not attract dirt, and any dirt, such as bird droppings, is washed off whenever it rains. ETFE Foil roofs never need to be cleaned externally. Internally foil roofs are usually cleaned on a 5- 10 year cycle depending on the dirt in the internal atmosphere. This usually means that expensive internal access equipment is not required as the long cleaning cycles make rope access a cost effective solution.


Weight


ETFE Foil cushions are extremely light weight weighing only 2- 3.5 kg/m²


Cushion size


Cushions can be manufactured to any size and shape the only limit being the wind and snow loading. This in turn is effected by the cushions orientation ie is it horizontal or vertical.


As a general design guide for rectangular cushions the cushions will span 3.5m in one direction and as long as one requires in the other, ie cushions 3.5m x 30m are possible.


For triangular cushions where the foil is two way spanning the size can be increased.


Should the designer require larger cushion sizes then larger cushions can be manufactured by incorporating reinforcement into the internal and external foils of the cushion.


Warranties


We are happy to warranty our system as required. The maximum warranty we have offered to date is 15 years We generally advise that any warranty should be back to back with a maintenance agreement to ensure that the air pumps, plenums etc are well maintained.


Material Strength
For foil thickness 90-150 micron


 

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    General description The Roofs consist of pneumatic cushions comprising of between 2 and 5 layers of a modified copolymer Ethylene Tetra Flouro Ethylene. The ETFE Foil is extruded into thin films and supported in an aluminium perimeter extrusion which is supported on the building frame. The Cushions are inflated by a small inflation unit to approx. 220 Pa which gives the foil a structural stability and gives the roof high insulation properties. Life ETFE Foil is unaffected by UV light,...

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