HVAC Preventative Maintenance Basics Presented by Mike Crawley
Air Handlers/Package Units: Coils have to be clean! The main purpose of any coil is to absorb or reject heat If coils are dirty; air flow is restricted and minimal heat exchange is taking place Evaporator Coils Need to change filters on a quarterly basis Rule of thumb: 1.5 square foot of filter for each ton of capacity On a RTU refrigerating system poor heat exchange can lead to: freezing up, liquid flood back to compressor, and blocked air flow in which all can damage compressor 2
Air Handlers/Package Units: Condenser Coils Air cooled condenser units will set outside They need to be cleaned at least once a year depending on location Higher condenser temps can lead to hot gas entering metering device and evaporator. Over a long period of time, oil breakdown can occur. The lubricity becomes thinner as the oil heats up. The low viscosity can cause compressor failure Belts Belts need to be properly aligned with a straight edge or a string pulled tight on a multi-grooved variable pitch pulley Misalignment can be destructive to belts and pulleys wich can groove the pulley and wear out the belt 3
Air Handlers/Package Units: Belt tension is very important! Rule of thumb: Tension needs to be approximately 1/64 of an inch deflection for every inch from shaft center to shaft center Belt conversion Note 1: 4L belt to A belt = the length of the 4L belt - 2 = A belt Belt conversion Note 2: 5L belt to B belt = the length of the 5L belt 3 = B belt 4
Air Handlers/Package Units: Grease Motors and bearings all need grease or oil. Metal to metal contact is not good How much and what kind of grease? There is no rule of thumb for grease amount. Consulate bearing manufacturer. You can grease a ball bearing until you see a slight amount of grease around the seal Grease type: typically a NLGI2 (national lubricant grease institute) is recommended for roller bearings 5
Air Handlers/Package Units: Electrical All units have various forms of electricity from throw away relays and contactors to large serviceable starters Check for: corrosion, burnt wires, bubbled insulation, discoloration With electricity locked out tagged out, check for: snug (not Godzilla tight) fittings consult the manufacturer for torque values. Unlike conductors (ie:copper to aluminum) should have anti-oxidant compound Electrical also needs to be clean! Use dry nitrogen at low pressure Don t use a hose off the air compressor receiver tank. Moisture and oil may get into components Dust and grime can get in and cause over heating on starters Serviceable starter can be cleaned with contact cleaner Some pitting is okay and normal, needs to be monitored Large motors 20HP+ can be megged A megger is a hand-crank or push button DC volt generator. DC volts are used because it is easier to control 6
Air Handlers/Package Units: Drain Pans Cleaning will help deodorize most smells. Pan tabs and pads will help Debris can build up and block drainage Drain lines need to have correct fall P-traps need to be vented on the leaving side of the trap Pan seal can be used to coat older more rusted out pans Blow through coils - no need for trap Draw through coils - have to be trapped 7
Pumps Pumps are broken down into many categories. The HVAC industry generally deals with centrifugal pumps End suction pumps, close coupled pumps, and split case pumps dominate the industry Pumps have to be level Check pump coupling for wear Check for shaft seal leaks Pump alignment is important Pumps can be aligned by three methods: Feeler gauges and a straight edge A dial indicator rim and face method And laser alignment 8
Pumps Keep logs of pressures Head = PSI x 2.31 / specific gravity (specific gravity of water is = 1.0) You need to make sure you maintain a net positive head Exercise isolation valves Grease bearings Check starters Clean strainers on cooling tower applications 9
Chillers Chillers are a major investment for a facility and are costly to maintain. An in depth maintenance program can increase reliability Facilities with a thorough PM, have found for every dollar invested in maintenance they save $10 in operating cost Daily logs can help you trend pressures, temps, etc. Inspections can be set-up as three quarterly run inspections and one comprehensive e e annual inspection 10
Chillers Heat exchangers Air cooled chillers condensing coils should be cleaned regularly Water cooled chillers tubes should be brushed annually Note:.002 of fowling will reduce efficiency by 20% Anodes should be changed annually or depending on condition Eddy Current analysis should be performed every 3 years or as needed to both condenser bundles and evaporator bundle 11
Chillers Oil testing can be performed on an annual basis on large centrifugal and screw chillers Oil testing is a useful tool in determining internal conditions of a compressor Reciprocating and scroll compressors generally require a field acid test Oil filters changed manufacturers specifications Leak checking chillers All chillers should be leak checked annually Water flow must be maintained through the barrels Low/High water flow=poor heat exchange Purge Units low pressure chillers Monitor pump out minutes Check for proper operation Change filters annually 12
Chillers Starters Electrical must be tight and clean Contact points must be inspected and cleaned annually Change the VFD or SSS coolant on manufacturers recommendations Motor terminals must be secure in a dry environment Motors should be megged annually 13
Chillers Panels Safeties should be tested annually Sensors and transducers should be tested and calibrated on each visit Wiring should be neat and secure Flow switch operation should be checked annually Parameters need to be logged and maintained Refrigerant and oil circuit should be logged and maintained Predictive maintenance for chillers Vibration analysis Infra red testing Open rotor bar test Oil analysis Eddy current testing 14
Cooling Towers Water treatment is very important with towers To prevent scale corrosion sludge and biological growth Conductivity should be high Monitor blow down solenoid Blow down is used to re-circulate water to drain dissolved solids Make up water valve Ensure proper water level is in tower basin (3 to 4 inches below overflow pipe) Tower fans can be either belt driven or gear box driven Grease bearings Inspect belts and sheaves Inspect gear box oil level change annually Oil samples and vibration analysis can be performed on the gear boxes Keep tower inlet screens clean Inspect hot deck and spray headers 15
Cooling Towers Towers should be cleaned annually and inspected on a daily basis as well as a quarterly Inspect all electrical connections and disconnects Have motors tested Freeze protection Basin heaters maintained Exposed piping should be insulated with heat trace Make up water line should also be insulated with heat trace Tower by-pass must be checked in seasonal weather 16
Pneumatics Heart of pneumatics is the air compressor Air compressor has five components: Motors Pumps Receiver Tank PE switches Alternating Relays on duplex machine 17
Pneumatics Inspections: Intake filter; monthly Change filter annually or sooner depending on environment Piping Check for air leaks Relief valve Check for proper operation Oil llevell Change oil twice a year Note: any 30 weight non detergent oil will work, do not use synthetic Verify belt condition, alignment, and grease motor bearings 18
Pneumatics Inspect electrical Starters, PE switches, and alternating relays for proper operations and condition Blow down Important to verify moisture and oil removal from tank Inspect coalescing oil removal filter Inspect bypass Air dryer Ensure condensers are clean and compressor is operating Check the operation of the dryer every six months Maintain a main air pressure of 20 PSI 19
Pneumatics Thermostats and VAV boxes All Pneumatic thermostats are different Thermostats are sensitive, if adjusted to much calibration will be thrown off Fan power boxes can be inspected each season PE switches, heat strips, return fan motors should all be checked Equation for percent run time; see attachment 20
VFD Notations Common to most HVAC equipment Keep a copy of all start-up parameters Important to note any changes that are made Once every six months VFDs should be shut down so that the electrical can be inspected, tightened, and the drive blown out with air in a can or by dry nitrogen under low pressure Check the cooling fan for operation VFDs can damage older non-inverter rated motors Inverter rated motors can handle higher voltage spikes (from VFD) and run at lower speeds which h can overheat older motors damaging bearing etc Bearing fluting is not a myth Occurs when Eddy Currents from the drive operations take a path to ground on the bearings Some ways to counter this are to make sure drive is installed and grounded properly a grounding brush can also be installed in the motor to shield unwanted currents 21