Chiller Performance: Testing, Inspection and Maintenance
Comprehensive chiller maintenance can extend the life of equipment, enhance its reliability, save scarce refrigerant, and reduce energy and other operating costs while buying you time to work out a long-range plan.
Testing and inspection
Youll need design specifications, equipment manuals and repair history for each part, and a cost history for buy, repairs and operation. Are some elements getting more repairs and costing more than others? Are annual energy costs increasing faster than rate increases? Have recent costs surpassed past costs? Are your costs higher than costs at other similar facilities? Are they higher than averages from your specialized association? Youll want to do this testing every year or two, so set up a recordkeeping system if you dont have one. Decide if you want to test in-house or use an inspection agency with the instrumentation and specialized know-how.
If you decide on a specialized, your maintenance staff will have to turn on and set the system for the inspector, change excursion ratios, add dampers if needed, replace worn parts, and show the inspector where panels and equipment are located. Tell your equipment vendor and consulting engineer about the inspection so they can provide design information about the original system.
Youll need to conduct air balance, water balance and sound testing. The elements tested are:
• air-moving equipment
• supply and exhaust fans
• diffusers and grilles
• water-balance elements
• circulating water pumps
• cooling towers
• air- and water-cooled condensers
A balance test on a packaged unit takes about a day; on built-up units, at the minimum two or three days or more for multi-zone or multi-unit systems. All testing instruments should be calibrated within six months of testing.
Youll need to do air-balance testing first because system air must be in balance for water-balance testing to proceed properly. Special tools and instrumentation used are:
• hot wire anemometer
• rotating vane anemometer
• self-timing speed counter
• pitot tubes 18-60 inches
• velocity meters
• clamp-on ammeter
• static tips
• several 8-inch stem thermometers
• motorized psychrometer
• hand sling psychrometer
• inclined gages 3-inch and 10-inch
• multi-point surface pyrometer
• combustion test sets
• electric drill motors
• balancing hoods
• recording thermometers
• smoke gun
• and two-way radios.
the time of action includes testing and adjusting blower rpm to design; motor actual vs. complete load amps; pitot tube traverse of supply ducts and design CFM of fans; system supply and exhaust static pressures; design vs. actual recirculating air; design CFM of outside air; entering wet and dry bulb air temperatures; exiting wet and dry bulb air temperatures; adjusting all supply and return air ducts and zones to design CFM; adjusting each diffuser grille and register to within plus or minus 10 percent of design requirements; FPM velocity at each diffuser, grille and register; and adjustments to minimize drafts. Also, all controls must be checked for proper calibration and settings.
Water-balance testing should be completed only after air-balance testing is complete and the air system is properly balanced. In addition to the before mentioned tools, youll need water-pressure gages, a differential gage set for reading orifice and venturi stations, and meter sets for reading velocity and flow. Youll also need vibration analyzers, and air and water pollution test equipment.
The water-balancing course of action includes:
• starting and setting all controls to proper settings
• removing and cleaning strainers
• examining water for proper treatment and cleaning
• checking pump rotation
• verifying that expansion tanks are charged and not air or water bound
• checking air vents at top of water system to ensure that they are installed and working
• setting temperature controls to complete cooling
• checking operating temperatures of chiller and boilers
• making sure that chilled water pumps are calibrated for proper GPM delivery
• checking existing and return water temperatures
• checking chiller water flow pressure
• monitoring water and balance temperatures at inlet side of cooling coils
• monitoring pressure drop by coils and flow rate
• monitoring pump operating suction and release pressures.
List all pump mechanical specifications, motor rated and running amps and water metering device readings.
Old systems loosen up, get misaligned or perhaps were not correctly sound insulated when installed. Thorough sound testing using decibel meters and vibration examination is a part of the testing and inspection. Sound tests include background sound level with equipment off, total sound level with equipment on, and correction of sound level to equipment only. Sound levels are compared with building specifications using readings in decibels. Equipment vibration absorbers and insulation are checked for effectiveness.
Before completing repairs, make sure youve complied with all safety precautions, such as wearing personal protective equipment and performing lockout and tagout procedures. The most shared repairs required as a consequence of test data are cleaning and minor adjustments. All systems need filter and duct cleaning on the air side at the minimum once a year. If the filters are tight and duct joints are properly sealed or taped, cleaning wont be a big job, and the air system will be more efficient. Water, oil and refrigerant sample tests indicate the equipments condition. If theres water in the refrigerant, seals should be replaced. If there is refrigerant, rusted metal or metal filings in the oil sample, inspect the seals, piping, bearings and rotary or reciprocating elements for use.
excursion gears, bearings, belts and couplings will last for years with a good PM plan. They should be checked at the minimum yearly, already if fluids dont indicate a problem. V-belt drives should be tight on the bottom and slack on top between the sheaves for more arc of contact and less slipping. If the sheave groove bottoms are bright, the V-belts are bottoming out and will slip. Either change the V-belts if theyre worn or change the sheaves if theyve been slipping and the V-grooves are worn. Worn sheaves will quickly ruin new V-belts.
If belt plies are separated, change the belts. If theyre loose enough so that pressing them in the center between the sheaves moves them more than one thickness of the belt, realign them with a straight edge; then tighten them. Loosen the motor keep up in a place bolts, back the motor away from the pushed sheave by turning the motor frame adjusting screw under the motor until the belts are properly tensioned.
Bearings and gears protected with the right amount and kind of clean lubricant can run hotter than you can touch — more than 110 degrees — for years without problems. already new lubricant is not perfectly clean, so in-line oil filters are a good investment. Regular filter inspection and change will uncover problems before they become serious. Pillow block bearings should not be greased too often. Usually, a few shots once every three to six months is adequate. Seals can be damaged by overlubrication. Remove the relief plug before adding grease, and allow the bearing to run awhile to release the excess. Check the color and texture for signs of rust, metal, water or other contamination. Rubber gloves and safety glasses or complete confront protection should be worn where acidic refrigerant might be present.
Regular PM safety and electrical checks are an important part of your annual test and inspection course of action. Your system documentation will show:
• where these devices are located
• what checks to perform
• how to perform them, and how often
• what tools you need.
Start by talking to the requester or tenant to get a description of the problem. For example, if the problem is in a package heating and A/C unit, find out if its a cooling or heating problem, or both. Always start with the obvious:
• Is strength getting to the system?
• Are the fuses and fused switch contacts good?
• Are circuit breaker contacts clean and tight?
If the heating works but the cooling doesnt, this probably eliminates the heating circuit controls. Observe operation to confirm this. When youve narrowed the possibilities, hop-scotch the electrical circuit in the area of the problem with a voltmeter, set to the circuits voltage range. Keep the circuit diagram handy — usually inside the electrical panel door or in the operating and service manual. Sometimes a microswitch or relay sticks open. If you find an open switch — no voltage where a voltage should be present — which should be closed when the circuit is energized, tap it a few times with an insulated screwdriver manager. If this causes the system to begin again operation, turn off the system, turn it back on, and repeat the test.
If this proves that the switch is faulty, replace it. Then try the system again to make sure its the only problem, and that the substitute was done properly. When using a tester, its good practice to use an alligator clip on one rule. Only one hand is needed to do the testing with the other probe.
Many trouble calls from improper temperature are from too high a temperature in the duct or temperature time lag. Too high a temperature may be due to delivering mixed air at, say, 62 degrees, when it should be 54-58 degrees. Temperature time lag is too long a time to cool the air during the modulating period resulting in a feeling of discomfort. As much as 35 percent of monthly operating costs can be due to compensation for leakage. To correct this problem and lower your operating costs at the same time, check the zone mixing dampers for leakage. Soft foam plastic on the leading edges of blades seals them better when they are closed. Leaking dampers also increase the noise level.
Manual dampers should be installed off the confront of multi-zone units; itll provide exact adjustment of total flow. Diffuser, side wall or automatic dampers are only meant for fine adjustment. Check their linkages and range of motion. You cannot field air balance your system without the right number of dampers in the right place.
Routine PM for most frequently used chillers — electric centrifugal, electric reciprocating and absorption — includes annual lube oil, oil filter component and refrigerant filter-dryer cartridge changes. Oil sampling and inspection for bearing or gear use particles is done in addition as checking magnetic plugs in the oil reservoir.
Rust particles originate in the condenser and indicate air and moisture in the refrigerant system. Chemical examination of both the refrigerant and oil provide valuable information about the presence and source of contaminants. Fluid leak tests are made twice a year, unless low fluid levels indicate the need to test more frequently. Leaks in the refrigerant system of air and non-condensable gases are best handled by regular purges. Clean tubes after every season and inspect for corrosion, erosion, stress corrosion and fatigue caused by thermal stress. Always use a water treatment specialist for initial charging of a new system and for continuous monitoring. Current testing instruments can detect tube fractures early; replace the tubes as soon as theyre discovered.
The water solution of lithium bromide used as a refrigerant in absorption chillers is very corrosive. It attacks steel, copper and copper alloys in 300 F air or higher. Use corrosion inhibitors in the manufacturer-recommended range; check it twice a season. Also check alkalinity and presence of ammonia, copper or iron which may be present in small (parts per million) quantities. Water strainers and traps should be checked, cleaned and modificated yearly.
Vibration examination of rotating equipment at the bearings should be completed during operation to check for bearing and gear use, bent shafts, imbalance in fan and blower blades, and coupling or other misalignment in air handling equipment, water pumps, chillers and motors. Infrared scanning of electrical switches, circuit breakers, motors and gear boxes will detect overheating conditions and help clarify loose or corroded electrical contacts, hot motor windings, bad bearings and gears and low oil levels. These predictive maintenance inspections should be done at the minimum yearly after establishing a baseline or normal reading at each point — and do them before the major shutdowns so findings can be analyzed in time to decide what repairs are required. This approach allows rule time for obtaining spares, special tools and equipment and planning the work.
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