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British Energy’s operational support centre at Barnwood in Gloucestershire operates the data centre for the company’s eight nuclear power stations. As part of its environmental strategy, British Energy has already converted all of the site’s systems from R22 to non ozone depleting replacements, but until recently was unable to find a suitable alternative to R22 for its flooded chillers. This had been a concern in view of the phase-out of the use of virgin R22 for service work, and the fact that replacing the chiller was likely to cost over £500,000.
British Energy had experimented with a number of R22 alternatives, such as R422D, but the chiller could not achieve the temperature difference across the evaporator that is an essential requirement.
The decision based on a cost-benefit analysis was taken to covert one its flooded chillers to RS-45 (from R422D).
Details:
PCX 700 chiller
Condenser number SEPX790
Screw Compressor Model 2515DHFIL00
Age 30 Years
Flooded Evaporator
Pilot Operated Thermostatic Expansion Valve + Partial Hand Expansion Valve
Heat Recovery circuit on Condenser
Recommended Charge 1,200 kgs R22
Charged with 1,200 kgs RS-45
Original oil Mineral Viscosity 170
Charged with POE Viscosity 170
The control system operates compressor un-loader system based on a number of inputs which include but are not limited to chilled water leaving temperature, suction pressure, discharge pressure, motor loading percentage. The following readings were taken:
Suction Pressure 74.32 psig
Discharge Pressure 188.30 psig
Motor amps 50 (Maximum setting 80, FLA 120)
Entering chilled water temperature 10.6 C
Leaving chilled water temperature 8.01 C (set point 80C)
Suction Temperature 5.50C
Evaporator Superheat 2.10C
Motor load % 55.62 %
Outside air Temperature 170C
Energy usage would appear to be lower with RS-45 with 50C achieved at 65 amps, against design of 5.5C at 108 amp. The system was operating up to 5.50 temperature difference on chilled water which was equal to design capacity. Before the initial conversion from R22 to R422D, the lubricant in the chiller had been changed from mineral oil to polyo ester. The superheat was very consistent and did respond to adjustments to the expansion devices.
John Bravery of Balfour Beatty oversaw the conversion of the chiller to RS-45 alongside A-Gas’s John Ormerod The changeover process was quite straightforward, and no problems have subsequently been encountered since the machine has been achieving the duty previously obtained when operating on R22.
“We have been planning to phase out R22 on this site before the cut-off date for using new R22 for service work kicks in at the end of 2009, but finding a refrigerant which can match the performance of R22 in the flooded chillers here had not been possible until the arrival of RS-45 (R434A),” says Geoff Benton, British Energy’s Site Engineer,
“The fact that using RS-45 to replace R22 in one of our flooded chillers has resulted in an identical performance to using R22 in this unit means that we will be converting the remaining flooded chiller on site, and thereby achieving our overall objective to be free of ozone depleting substances prior to the phase out date in Europe. Overall, we are very pleased with the performance of RS-45 in what I understand is one of the most difficult applications for R22 replacements.”