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Tuning up cooling systems

As the cooling season creeps closer, technicians will be performing more A/C system tune-ups; a good place to start is with a list of check points and values.

By Ron Auvil

When the weather is warm outside, it is imperative to make sure that the mechanical cooling systems of a building are working at maximum efficiency. Since budgets are still tight, nobody wants high energy costs or, worse, equipment failure. Emergency maintenance is so much more expensive than routine maintenance, so the best way to avoid either of these scenarios is to perform a cooling-system tune-up. Following is a list of check points and values to help technicians get started.

Checks by equipment type
Since types of cooling equipment can vary widely, typical spring start-up checks are listed by equipment type—from water chillers to cooling towers, air-handlers and package cooling equipment (rooftops and heat pumps).

WATER CHILLERS

Note: Always review and follow manufacturer’s recommendations.

Electrical checks
• Use an insulation tester on oil pump motor and record readings;
• Use an insulation tester on compressor motor at the starter terminals. Record readings;
• Measure and record oil-pump voltage and amperage;
• Inspect the motor starter for signs of overheating, arcing, burns, etc.;
• Clean starter cabinet;
• Inspect starter and starter components for discoloration, burns, moisture, etc.;
• Inspect wires for discoloration and burns;
• Test accuracy of motor current (amp meter);
• Test tightness of terminal connections;
• Inspect contacts and change as necessary;
• Measure operating voltage and record;
• Check sensor readings for accuracy;
• Tighten terminal connections on the oil-pump motor;
• Verify operation of the oil heater; and
• Check starter contacts and change as necessary.

Oil and lubrication system
• Change oil and filter, test oil for acidity and check oil level;
• Clean purge drum and oil separator, change oil in purge pump and oil separator;
• Test oil again after startup for test lab analysis;
• Verify operation of oil-cooling system if applicable;
• Clean oil strainer and change oil filter once per year;
• Analyze compressor oil; and
• Check oil-pump heater and purge oil heater operation.

Miscellaneous
• Leak test system at piping flange connections, exterior refrigerant lines, etc.;
• Lubricate and check operation of purge unit;
• For centrifugals, inspect vane motor, shaft and fitting, and lubricate inlet vane linkage;
• Check water strainers and clean if needed;
• Start unit, log operating conditions after unit stabilizes;
• Use thermography to check for heat losses and bad insulation;
• Check operation of variable-speed drive; and
• Check water flow in branch piping.

COOLING TOWERS
• Remove debris from in and around unit, and flush as needed;
• Check and clean strainers, bleed, overflow, drain;
• Lubricate fan-motor bearings per manufacturer’s recommendations;
• Change oil in gear¬-reducer assembly per manufacturer’s recommendations;
• Check motor pulley, belts, motor mounts, and alignment, and replace or adjust as needed;
• Check motor operating conditions;
• Check operation of variable-speed drive on tower fans;
• Inspect electrical connections, contactors, relays, operating/safety controls;
• Clean make-up float valve assembly and check for proper operation;
• Check operating conditions, and adjust as needed; and
• Check temperature and flow sensors for accurate readings.

AIR HANDLERS
• Take pressure drop readings across filters; change when indicated;
• Check air flow with pitot tube or at flow measuring station;
• Check sensor readings at building control system, and calibrate if necessary;
• Check air flow at diffusers;
• Check indoor CO2 readings for IAQ and ventilation;
• Check economizer operation versus sequence of operation;
• Check and clean fan assembly;
• Lubricate fan bearings;
• Check belts and sheaves;
• Tighten all nuts and bolts;
• Check motor mounts and vibration pads;
• Check electrical conditions and motor operation;
• Lubricate and adjust associated dampers and linkage;
• Check fan operation;
• Clean outside air-intake screen;
• Check and clean drains and drain pans;
• Check and clean strainers, steam traps, and hand valves;
• Inspect and clean filters, coils, and humidifiers;
• Clean external surfaces as needed; and
• Measure and record voltage and current at fan motors.

PACKAGE COOLING EQUIPMENT (ROOFTOPS AND HEAT PUMPS)
• Check compressor evaporator and condenser pressures;
• Check operating voltage and current readings;
• Check filter pressure drop;
• Check thermostat accuracy with recording meter and temperature sensor;
• Check fan operation;
• Check reversing-valve operation for cooling switchover; and
• Check air flow and static pressure.

Doing some of the checks listed here will definitely pay off. Now is a great time to take the initiative to save energy and reduce excessive downtime.
Typical HVAC values
Note: Do not assume that these are laws—they are only typical values. Each specific HVAC system is different, and the values must be verified for each application.
Air movement 6 air changes/hour
Ventilation rate 25 cfm/person
Fan energy 1,000–1,500 cfm/hp
Chiller size 300–400 ft2/ton
Chilled water 2.4 gpm/ton (10°F rise)
Condenser water 3 gpm/ton (10°F rise)
Chiller input 7–0.8 KW/ton
Chillers, pumps, and towers 9–1.0 KW/ton
VAV 55°F cooling
10% box leakage flow
40%–50% minimum fan volume
People load 450 Btu/person/hour
    
Common HVAC equations
Sensible air-conditioning
Btu/hr = cfm x 60 min/hr x .075 lb/ft3 x 0.24 Btu/lb x DT
Btu/hr = 1.08 x cfm x DT
Latent air-conditioning
Btu/hr = 60 min/hr x .075 lb/ft3 x cfm x DH
Btu/hr = 4.5 x cfm x DH
Water heating and cooling
Btu/hr = gpm x 60 min/hr x 8.33 lb/gal x 1 Btu/Ib/°F x DT

Ron Auvil is a Senior Instructional Consultant for a major HVAC/controls manufacturer , specializes in staff and workforce performance issues. An author and curriculum developer, Auvil has provided custom training on how to improve the operations of their environmental systems. His clients have included NASA, the Pentagon, the University of South Carolina and many others.

For more information, visit www.fluke.com or contact Leah Friberg at leah.friberg@fluke.com.

 
 
 
 
 
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