e-mosty June 2017: Osman Gazi B. US Suspension. Hålogaland B. e-mosty June 2017: Suspension Bridges | Page 58
3.4 Plant Rooms
The plant rooms house the mechanical systems for
the development of a volume of stored dry air to be
injected into the cables. Each plant room was
required to be equipped with a desiccant wheel
dehumidifier, plate heat exchanger and supply fans.
The plant rooms were designed to function as
insulated plenum chambers for the dehumidified air.
This strategy allowed energy efficiency through
passive heat recovery, close control of temperature
and humidity and insulation against heat loss/heat
gain. Standard off-the-shelf equipment was used to
simplify future maintenance and reduce capital and
long-term operational costs (Figure 20).
modular construction such that all components could
fit through the existing anchorage access doors.
However, for the Eastbound Bridge, internal plant
rooms were not feasible due to the location of the
anchorages. Therefore, only one plant room was
specified and located under the bridge on the
approach-span deck truss.
This resulted in the plant room being exposed to
harsh marine conditions including high wind speeds,
solar gain, salt-laden marine air and low ambient
winter temperatures. As such, it was required to be
constructed of steel framework with twin-skinned
insulated and vapor sealed stainless steel wall panels.
To facilitate system commissioning, the contract
required the plant rooms and control systems to be
preassembled in the shop and tested prior to delivery
to the project (Figure 21).
Figure 20: Injection fans with HEPA filters
The contract specifications provided the performance
parameters for the plant rooms including the
management of relative humidity, dew point, and
internal pressure.
Moreover, to assist in reducing operational costs, the
systems were required to be developed such that
plant room relative humidity could be adjusted
upwards and injection pressures/flows reduced, once
the relative humidity at the exhaust points of the
main cables was sustained below the target threshold.
The ability to adjust the system over time reduces
energy consumption, electrical costs and long-term
wear-and-tear on the equipment.
For the Westbound Bridge, the contract required two
plant rooms, one in each of the concrete anchorages,
to shield them from the harsh external environment.
This provided the ability to specify lightweight
Figure 21: Eastbound Bridge plant room preassembly and shop
commissioning
Once the plant rooms and controls were witnessed by
the construction management team and deemed
functional, the contractor was authorized to ship
them to site.
The requirement for shop testing was implemented to
minimize field testing and troubleshooting, since the
work could prove to be challenging with the remote
location and limited access where the plant rooms
were to be installed.
2/2017