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