DESIGN, BUILD, AND ENGINEERING
LV switchroom was constructed, which is accessed directly off the main service yard, into which the main LV electricity supply from the 1 MVA sub-station feeds. He added: “We also have a 500 kVA standby LV generator from Power Electrics running on diesel oil fuel, which would support the facility in the event of a power outage.” The external plant compound also houses two air-cooled chillers. All the electrical services are run at high level on designed steelwork. John Davies continued: “The two 800 kW Daikin Applied chillers were selected for their efficiency, and feature stepless inverter-screw driven compressors, and dual refrigerating circuits, each with separate isolation. This combination of equipment gives the facility a great deal of resilience. Chilled water is key, not only for the air-conditioning, but also for the closed loop cooling circuit to the autoclave vacuum pump. Savings on mains cold water usage are in the order of around 400 litres per cycle. We also use chilled water to maintain the endoscopy RO circulation system at around 19˚C, as one part of the bacterial growth control measures. Water quality in endoscopy is paramount, with strict quality requirements.”
The plant in more detail Moving to discuss the first of the two above-ground plant floors, John Davies said: “These contain the main ventilation, water treatment plant, and the air compressors.” Electrical distribution and control panels are provided for all plant items, with dedicated panels fabricated for each individual system. Within this plant floor, steam to domestic hot water plate heat exchangers and buffer vessels are also in operation. The floor above contains heating and chilled circulation pumps, and
Softened cold water storage tanks.
the boiler feed tank. The boiler feedwater comprises returned hot condensate and RO water top-up to prolong their life and minimise corrosion.
John Davies explained: “We have input natural gas, mains water, and electricity, into a fully self-supporting unit with no shared plant. Back-up electrical resilience is via standby generators and UPS equipment. Should the unit experience a natural gas outage, then two of the washer-disinfectors are fitted with dual steam/electric coils, so we can continue operating without steam. A back-up electric steam boiler was also installed, is regularly exercised, and will support two autoclaves during any outage period. This degree of resilience was embedded so that in the event of a temporary
interruption to the gas or electricity supply, the facility could continue functioning, albeit at reduced capacity.”
The building’s height
I asked what the biggest overall practical challenge had been. John Davies said: “Probably the building’s height – not only in terms of services distribution, but also the fire safety considerations. For instance, we had to divide the unit into sub-compartments, which meant installing fire curtains, and any service penetrations were fire stopped or dampered. While that was
straightforward, we had to design them to be easily accessible for maintenance, and to consider how we would protect and monitor the sizeable void areas.” The solution chosen was a smoke aspiration system. John Davies elaborated: “This essentially comprises a network of perforated red plastic sensing tubing which feeds back to sensing and monitoring control panels and test tubing, all maintainable at ground floor level. The ground floor areas are protected by an addressable fire alarm system linked to the local fire brigade. The smoke aspiration system, firemen’s ventilation control panels, and all the plant control panels, link to the main fire alarm system. Gas safety and sensor circuits will trigger and shut down gas supply in the event of fire or gas detection.”
Building energy management system
The maintenance walkway/access to air-handling plant on the mezzanine floor. 48 Health Estate Journal August 2020
A Distech building energy management system was chosen both for its technologically advanced capabilities, and its ability to engage with Internet-of- Things devices. John Davies explained: “Our BMS provider, Carrob Controls and
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