1 and 2 New Ludgate
Article from the June 2015 edition of the CIBSE Journal written by Phil Thompson.
The strict noise requirements of Land Securities’ commercial development helped to determine the specification of the chillers for the project. Air conditioning manufacturer Carrier worked closely with the client, consultant and contractor, SRW, to develop a compact, energy efficient design that enabled the chillers to be located in a restricted space. As a result, the chillers could be mounted on the rooftop, rather than in the basement, which was where the plant was located in the original design. This gave Land Securities more usable commercial space.
The chiller manufacturer designed and built a custom package to enclose the chillers and reduce the amount of noise. The condensers are specifically configured to resist damage from hailstorms that can otherwise create significant, accumulating, impact damage to the coils, reducing their performance.
Air conditioning for the buildings is supplied by six 930 kW (nominal) chillers with variable speed drive (VSD)-controlled screw compressors, alongside six smaller chillers with scroll compressors. The project included a bespoke pump, control and chiller sequencing package.
"The software was programmed in-house and designed to maximise energy efficiency and air conditioning performance, as well as extend the working life of the chillers by careful run-time sequencing," says Danny Lear, specification and solutions manager at Carrier UK. "We were able to carry out full witness testing of working chillers at our facility in France, ensuring the solution met the specification fully."
After installation, Carrier’s service team will, under a full-maintenance contract, ensure the chillers are maintained at peak performance level. The six screw compressor chillers are supplied with integral control that combines variable-speed condenser fans with variable-speed screw compressors, enabling close matching of cooling output to current load conditions. The constant control of the onboard intelligent control system, claims Carrier, enables the chiller to operate with very good part-load efficiency.
With the ability to vary both condenser fan speed and compressor speed in response to constantly changing demand, the chiller can continue to operate in its ‘sweet spot’ in terms of performance and energy efficiency. Carrier asserts it delivers a full-load energy efficiency ratio (EER) of up to 3.4 and a European seasonal energy efficiency ratio (ESEER) up to 4.9. Through a control system, building owners can monitor log performance data from the chiller via a web browser.
Newly introduced software optimises the use of compressors, fans and cooling circuits by constantly calculating the most efficient fan speed and water-flow rate, based on the current load and ambient conditions, and controls them to main appropriate refrigerant operating pressures through continuous feedback and adjustment.
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