York Ref SA Letter Head
1
GUIDELINES FOR CENTRIFUGAL CHILLERS
NON OPERATIONAL USAGE
Colin Hewetson
10 April 2008
1) General
In particular project circumstances, Centrifugal chillers may be delivered & or installed on site prior to the completion of associated civil, mechanical & electrical works. In other circumstances Centrifugal chillers may be installed but remain inoperative due a lack of load. In such cases the chillers require special protection whilst inoperative, or on standby or in storage on site, to avoid damage or general deterioration to the heat exchangers, motors, control panels, compressors, shaft seal & bearings.
Such protective measures are also essential to protect any outstanding portion of the owner's standard warranty, which is 12months from date of commissioning or 18months from date of shipment whichever is the earlier event, or if agreed any extended warranty.
2) Operational chillers on standby
2.1) Issues
Operational standby chillers may be subject to the following damage during idle periods, dependant upon the duration of non operation.
- Settlement of suspended solids in the heat exchanger tubes & bonnets
- Corrosion, under deposit corrosion, crevice corrosion or Biocidal attack to tubes, tube sheets & bonnets
- Air/Oxygen entrapment in the chilled + cooling water circuits
- Reduction in design ppm for water treatment chemicals or inhibitor dosage for corrosion & biocidal
prevention.
- Shaft seal lubrication loss
- Compressor oil sump heaters may be de-energised
- False brinelling of motor & compressor bearings
2.2) Resolution
Operational standby chillers must be subject to the following precautions
- Ensure compressor oil heaters remain energized at all times during standby, this will require a separate feed to the control panel so that when the main chiller isolator is off the control panel/oil heater power feed remains energized.
- Standby chillers must have automatic sequencing facilities, ideally to rotate chillers between duty & standby on a regular basis every 24hrs to ensure even operating hours.
- By default or design, the automatic sequencer may not regularly rotate the chillers for extended periods. In such case it is recommended the chilled + cooling water should be drained down to avoid settlement of suspended solids in the heat exchangers, or the pumps run every day to ensure water circulation & treatment chemicals are dosed at the design rate.
- Regular chiller leak check operations should be undertaken weekly using an electronic leak detector & any leaks found repaired immediately.
- The chiller should be started at least once per week to ensure that the shaft seal is lubricated & avoid false brinelling.
- Cooler + chilled water boxes must be removed & heat exchangers inspected & cleaned as necessary bi annually, to maintain the design fouling factor, & check for any corrosion. Every 3 years tubes
should be subject to an Eddy current test to check for tube corrosion.
- Routinely check compressor oil heaters are fully functional.
3) Extended Storage
Chillers which are to be stored or installed but remain inoperative for extended periods must be subject to the following requirements
- Be covered with suitable dust sheets.
- Have a power supply connected to the compressor oil heater/control panel to ensure the heater is energized at all times.
- The chiller should be charged with dry Nitrogen to a pressure of at least 15lbf/in2 & a gauge installed to regularly check the system pressure is holding.
- The motor/compressor should be rotated weekly 180degrees by hand, to ensure the motor & compressor bearings avoid false brinelling caused by vibration induced from other operational rotating equipment
- If motor heaters are fitted these should be energized to ensure the winding temperature is above the dew point temperature & vapour pressure of the air. Where heaters are not fitted such as may apply for ODP motors, moisture absorbing chemical bags should be installed in the air inlet/outlet ducts + electrical control panels & the ducts taped off to ensure insects, dust & moisture ingress is reduced.
- Prior to start up after extended storage the chiller must be evacuated, leak tested & commissioned in the normal manner as per the York IOM manual by a York service engineer. Motors should be subject to a resistance test using a Megger to check the windings are within the manufacturers stated parameters prior to start up.
- Cooler & chilled water water box nozzles should be capped or blinded & any drain or vent valves closed, to prevent moisture & dust ingress.