DESIGN, BUILD, AND ENGINEERING
had to design and construct a system of three drainage pods, sunk six metres into the ground, with a large cofferdam surrounded by sheet piles and a hydraulic bracing system. The three pods formed a duplex macerator station; two holding tanks combined into one chamber to provide storage of some 20,000 litres of waste and effluent water, and the third pod contained three lift pumps. John Davies explained: “The three pumps are sized so that only one is required at any one time. There are three separate pumped 100 mm diameter discharge lines which route back into the main sewer. The pods were fabricated offsite from polypropylene, and finished on site with steelwork and permanent shuttering, before being lowered into each cofferdam and being encased in concrete.”
Ribbed system
Moving to discuss the new building’s structure, he explained: “We utilised a composite floor decking system for the mezzanine, with the concrete poured in sections with a powerfloat finish. Once the concrete had cured, plinths were formed for the new plant, and we began lifting the new air-handling equipment, vessels, and pumps, onto the mezzanine floors. Once these operations were complete, this released the areas for the partitioning contractor to commence the wall erection. The metal frame system we used proved extremely successful. All the partitions and wall systems we used were formed using the Middas M100 demountable modular partition system. This was our first use of the system – which afforded considerable benefits in terms of speed and quality, while the boards are removable without affecting ceiling or floor finishes.” As part of the design process, the CFES design team undertook the facility design in 3D. Middas was able to take the 3D model and develop fabrication drawings alongside CFES MEP engineers, which detailed all electrical accessories and services penetration locations for preforming in the factory. John Davies explained: “Once we signed off on the fabrication drawings, Middas manufactured the panels with the cut- outs incorporated, while the framing system was erected, and first-fix MEP services were being installed, on site. The panels were then delivered to site fully protected, and the Middas team quickly assembled and installed these, allowing the MEP teams to then complete second fix.”
Two plant floors required
John Davies explained that the majority of spaces within the new decontamination facility are fully fresh air ventilated. He elaborated: “Most of the spaces are process areas. Our design team basically
46 Health Estate Journal August 2020
Supporting all the services Another ‘challenge’ on the project, John Davies explained, was how to effectively support and distribute all of the MEP services efficiently and independently of
Domestic hot water heat exchangers and pipework.
sub-divided the building into five zones for ventilation – the ISO Class 8 inspection and packing cleanrooms; the main wash and contaminated returns area; a sterile unload and ‘produced product’ area; the Endoscopy wash and dry pack area, and the Administration block – the latter provided with tempered air, with local heating and cooling provided by a mixture of fan coil units and radiant ceiling panels.”
I asked how complex designing the plant to ensure the correct air conditions and sterility etc. for the various decontamination activities had been. He said: “A facility like this is process engineering-driven, which we thrive on. We have to take all factors, such as equipment heat loads, contamination, chemical use, and aerosol dispersal, into consideration, as well as running thermal modelling, considering staff comfort, and complying with minimum air change rates, as stipulated within HBN 13 and HTM 03-01. We use similar principles to those employed when we are designing operating theatres, whereby we produce air flow regime drawings and consider door protection and pressure cascade between spaces. The former warehouse within which we constructed the new facility was, by its nature, quite ‘leaky’; thus we constructed a ‘box within a box’, making the design and specification of the building products used critical. Using wall and ceilings systems that could be fully sealed between joints and junctions, and easily fire stopped and maintained, was key to ensuring that the building was as airtight as possible.”
the main portal frame. He said: “Needing to ensure that our plant and services load was supported from the slab, and not t he building’s portal, we designed a secondary support system which was integrated into the Middas M100 partitioning system.”
He next turned to discuss the plant on the ground and two mezzanine floors. He said: “On the ground floor we have a main boiler room, with two natural gas- fired Cochran ST18 three-pass wetback horizontal steam boilers – a low NOx version, each rated at some 4,000 kg per hour at 8 bar, and distributing steam throughout the facility at that pressure. We selected the Dunphy package of a fully modulating burner and the corresponding touchscreen controls package with energy management software. The boiler package was specified with the inclusion of flue gas economisers, and recovery of the condensate within the system.”
Softened water storage
Adjacent to the ground floor boiler room is main softened water storage, with some 32,000 litres stored across two internal water storage tanks, for maximum resilience in the event of mains water outage. John Davies said: “We also have three Avidity Science water softeners – having selected the company both for the water softening equipment, and the reverse osmosis plant for the washer- disinfectors, sterilisers, and endoscope reprocessors, because it offered both the best technical and ongoing service support.” Each water softener provides around 12,000 litres per hour, replenishing the storage tanks. The water is delivered to the facility’s plant, equipment, and sanitaryware, via a triplex water booster set.
John Davies explained that a dedicated
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