From a flow point of view
there are two main types of roof drainage system, gravity flow and full-bore flow (UV-)
systems. See figures 1 & 2.
In gravity flow systems downpipes are usually dimensioned with a fill-factor
of 1/5 - 1/3. Lateral pipework may be designed to have a flow factor of 0.70 - 1.0.
As a consequence the drainage capacity may be considered to be dependent upon
the gradient of the laterally installed pipework.
In UV-Systems, all pipework has a flow factor of 1.0 at dimensional rainfall
intensity and the pressure in the pipework differs from the prevailing atmospheric
pressure. The full difference in height (head) between the roof outlets and the
discharge point to the main drainage system at ground level is utilised when dimensioning
the UV-System pipework. As a result considerably reduced pipe dimensions (when compared
to gravity flow systems) are produced with consequent higher flow velocities in the pipework.
The basic principles established by Messrs. Ebeling & Sommerhein
together with more than 3 decades experience of practical
application are encapsulated in the UV-System Technical Manual,
UV-System Software, Computer Modeling Manual, and training courses all
UV-System partners and distributors undergo.
National Standards bodies, Local Authorities and independent certifying agencies
from various countries have examined and approved UV-System technology and outlets
during the years since its invention. For example the British Board of Agrement awarded
the original UV-System a BBA certificate in 1988. The current BBA certificate (07/4438)
was completed in 2011.
Benefits of UV-Systems - In Brief
The key advantage of UV-Systems is the minimising of downpipe provision.
Not only are downpipes reduced in number and diameter but the siting of
drain points is totally flexible (see figure 3).
The elimination of air from pipework, both vertical and horizontal, is achieved
firstly by the use of the extensively tested UV-System outlet which prevents air
entrainment. Secondly UV-System dimensioning software utilises the height of the
building as a hydraulic "head" balancing the friction and local losses in the pipe
configuration and reducing the pipe diameters to the minimum necessary to transport
the design volume of water. Hydraulic balance is achieved via computer by permutating
the lateral and vertical pipe cross-sections.
The resultant full-bore flow or siphonic action allows the routing of an internal,
high level, horizontally-installed collecting pipe system serving multiple roof outlet
points. Ultimately each UV-System discharges via a vertical downpipe into the ventilated
flow main drainage system.
Extensive experience of UV-System design and installation world-wide leads us
to believe that although traditional roof drainage methods have been used for
centuries, they are now being replaced by full-bore flow systems for the roof
drainage of many contemporary building projects. Conventional gravity flow drainage
systems cannot effectively dispose of the volumes of water precipitated on large
and/or complex roofs without costly multiple discharge points inserted throughout
the building. The sophistication of today's buildings and the rigours of architectural
and engineering criteria often make traditional roof drainage disposal impractical
and out-of-keeping with modern advanced building technologies.
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