Carrier cuts cost of air-conditioning control at Stansted Airport

As part of this retrofit chiller installation at Stansted Airport, Carrier has installed its own controls system — saving tens of thousands of pounds compared with a customised approach.
integrated controls for an air-conditioning installation at Stansted Airport is said to have saved tens of thousands of pounds in customised software routings, wiring and additional controls. The recently completed controls elements of the installation cost £9000, compared with around £500 000 for the chillers, and ensure they operate at peak efficiency, even at low loads, and that compressors do not suffer excessive wear and tear from unnecessary stops and starts. In the cavernous plant rooms beneath the terminal, Carrier has two inverter-controlled centrifugal chillers providing 2.4 MW of cooling and two Global heat-reclaim water-cooled screw machines providing 1.2 MW of cooling. They supply chilled water to the air-handling system for the main arrivals and departures terminal. The installation of inverter control for the chillers from the outset of this retrofit installation ensured that this would always be an energy-efficient operation. The incorporation of the latest Carrier electronic controls system makes possible much greater savings from good management of the chillers according to seasonal demand and ambient conditions. It also ensures that load characteristics are optimised at all times. Under the supervision of Graham Easter of Carrier Service, a Chillervisor System Manager III was installed to control system temperature and sequencing for the chillers. It also provides summer/winter changeover duty based on calendar date. All ancillary equipment such as valves, pumps and gas-detection system are integrated through a Carrier Comfort controller. In summer mode, the Vacon inverter-driven centrifugal chillers take the lead in the system, with the condenser temperature set at 25°C, with the Global chillers acting as emergency back-up. In winter mode, the heat-reclaim Global chiller take the lead and the condenser circuit setpoint is raised to 38°C and low-grade reclaimed heat is incorporated. The centrifugal chillers provide backup. A modem link enables the facilities-management team to have knowledge of the system operation at all times and the Carrier Service team to run predetermined programmed maintenance routines.
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