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HVAC Preventive maintenance Presentation EVRaju

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HVAC Preventive maintenance Presentation EVRaju

  1. 1. PRESENTATION E VENKATA RAJU 1
  2. 2. HVAC Preventive Maintenance,Serviceand Troubleshooting The preventive maintenance programme can help in two ways 1. To anticipate failure. 2.To operate the plant at design efficiency and save energy. E VENKATA RAJU 2
  3. 3. HVAC Preventive Maintenance,Serviceand Troubleshooting Preventive maintenance program should include 1.Adherence to an effective planned schedule to keep the heat-transfer surfaces, air-filtering and air handling equipment clean, free of dust, scale and corrosion . This is because refrigeration , being a heat-transfer equipment , even a small amount of fouling of the heat transfer surfaces can reduce its and complete system’s capacity and increase power consumption. E VENKATA RAJU 3
  4. 4. HVAC Preventive Maintenance,Serviceand Troubleshooting Conti----- 2.The lubrication of moving parts at the right time and with quality lubricants . Too much of the lubricant is as bad as too little of it. 3. Checking operation of safety and operating controls periodically . It is imperative to verify that all safety controls are functioning properly to protect the equipment against abnormal working conditions. E VENKATA RAJU 4
  5. 5. HVAC Preventive Maintenance,Serviceand Troubleshooting Conti----- 4. Periodical checking of the system for refrigerant leaks . In addition to the refrigerants being very costly , a system running short of the refrigerant can get affected due to excessive cylinder head pressure . In hermetically – sealed units , this can also result in compressor motor burnt-out and system contamination. 5. Check for the development of vibration . Vibration is one major factor contributing to refrigerant leaks. E VENKATA RAJU 5
  6. 6. HVAC Preventive Maintenance,Serviceand Troubleshooting Conti----- 6. Maintenance of a properly recorded log of readings of the plant . A faithfully recorded log helps in trouble shoot a fault. 7. Seasonal periodical overhaul of components . It is important to carry out the recommended periodical overhaul of equipment . For example , if the estimated life of a bearing is 7000 running hours and it is replaced when the equipment has run for 7000 hours , it is a relatively simple and comparatively inexpensive job that can be planned and done. However if this is not done , crankshaft journals can get effected, necessitating costly and time – consuming repairs. E VENKATA RAJU 6
  7. 7. HVAC Preventive Maintenance,Serviceand Troubleshooting A partially –blocked condenser , water filter or cooling tower spray nozzles increases the discharge pressure/temp of the compressor , contributing to increased power consumption for much less cooling effect. This will see in the following table. E VENKATA RAJU 7 Condition Suction Temp C/F Condensing Temp C/F TR Bhp/TR % reduction in capacity % increase in Bhp Normal 7.2 (45) 40.6(105) 17 0.93 - - High condensing temp 7.2(45) 46.1(115) 16 1.12 8.2 20
  8. 8. HVAC Preventive Maintenance,Serviceand Troubleshooting The various factors , which affect the capacity and the power requirement of a compressor. Sub cooling Suction Pressure drop Affect of the liquid pressure in suction line capacity & Discharge Super heating Power Pressure of suction gas requirement of a compressor E VENKATA RAJU 8
  9. 9. HVAC Preventive Maintenance,Serviceand Troubleshooting The various factors , which affect the capacity and the power requirement of a compressor. 1. Sub-cooling of the liquid: When the compressor running at a constant speed , the pressures and superheating remaining the same , the power requirement of the compressor will not change , whether the liquid is sub- cooled or not . But by sub-cooling , the net refrigeration effect of the refrigerant increases and so the refrigeration capacity increases for the same horse power. Hence hp per ton comes down. Sub-cooling of the liquid is not accomplished by the compressor. Arrangements for sub-cooling the liquid are usually incorporated in the system. E VENKATA RAJU 9
  10. 10. HVAC Preventive Maintenance,Serviceand Troubleshooting Conti----- 2.Discharge pressure: If the discharge pressure goes up (for example when condenser surface gets fouled up) compression ratio too goes up , consequently the capacity of the compressor comes down due to the effect of clearance volume . However , more power will be required to compress the gas to a higher discharge pressure and thus Bhp per ton increases. 3.Suction pressure: As the suction pressure comes down , the compressor capacity drops . This is due to the effect of CR , the CV and decrease in the density of the vapour . Hence the hp per ton increases . E VENKATA RAJU 10
  11. 11. HVAC Preventive Maintenance,Serviceand Troubleshooting Conti----- 4. Superheating of suction gas : As the superheat increases , the compressor capacity drops due to reduction in the density of the gas . Then the hp per ton increases . 5. Pressure drop in suction line : This is due to a drop in suction pressure. E VENKATA RAJU 11
  12. 12. HVAC Preventive Maintenance,Serviceand Troubleshooting Reduction of Volumetric efficiency If the compression ratio increases , the volumetric efficiency of the compressor comes down , and so the compressor capacity gets affected . The compression ratio can increase if the discharge pressure increases or the suction pressure comes down or both happen together. E VENKATA RAJU 12
  13. 13. HVAC Preventive Maintenance,Serviceand Troubleshooting Reasons for increase in Discharge pressure Clogging of air Scale formation Over charge Increase cooled condenser in W.C condenser of refrigerant in discharge Fouling of tubes Presence of pressure in water cooled non condensable condenser E VENKATA RAJU 13
  14. 14. HVAC Preventive Maintenance,Serviceand Troubleshooting Reasons for increase in Discharge pressure 1. Clogging of air cooled condenser : The fins of the air- cooled condenser can get clogged with dust and lint . This can increase resistance to air flow thus reducing the air quantity for the condenser. The film of dust also decreases the heat-transfer efficiency . The result is increased discharge pressure. 2. Fouling of tubes in water cooled condenser: The cooling tower or pond being located out in the open collects lot of atmospheric dust and muck which end up in the condenser fouling the water tubes. The impeller passages in the condenser pump too can get chocked , there by reducing the water quantity through the condenser. The result of all these is increased discharge pressure. E VENKATA RAJU 14
  15. 15. HVAC Preventive Maintenance,Serviceand Troubleshooting Conti-- Reasons for increase in Discharge pressure 3.Scale formation in condenser water tubes : The impurities and salts contained in water precipitate as scale in the condenser water tubes . The scale formation is accelerated as the temperature of the tube surfaces increases . Few top tubes of the water cooled condenser are subjected to the highest temperature as the hot super heated discharge gas gets cooled on impinging on them . So scale formation in these tubes is faster and thicker . As scale offers more resistance to heat transfer , the heat exchange between the refrigerant and water in the tubes gets affected , resulting in higher condensing temperature / discharge pressure . E VENKATA RAJU 15
  16. 16. HVAC Preventive Maintenance,Serviceand Troubleshooting Conti-- Reasons for increase in Discharge pressure 4. Presence of non-condensable in the system 5. Overcharge of refrigerant in the system : The excess liquid refrigerant accumulates occupying more volume in the condenser thereby reducing the heat transfer area available for the high pressure refrigerant gas to be cooled and condensed. This causes the discharge pressure / the condensing temperature to rise , more the overcharge higher will be the rise in discharge pressure / condensing temperature . There will be a slight , but distinct temperature difference between the portion of the condenser where there is liquid and from the portion filled with vapour . This can be felt physically by slowly moving the hand over the shell of the water cooled condenser and by feeling the U bends of the air cooled condenser coil. E VENKATA RAJU 16
  17. 17. HVAC Preventive Maintenance,Serviceand Troubleshooting Preventive steps to prevent an increase in discharge pressure By cleaning the air By removing By cleaning& descaling Air cooled con’ser regularly excess refrigerant condenser water tubes periodically Reduction in high discharge Purging of By cleaning By draning By doing pressure Non CT water &cleaning Bleed off Condensable strainers the CT tank daily fortnightly E VENKATA RAJU 17
  18. 18. HVAC Preventive Maintenance,Serviceand Troubleshooting Preventive steps to prevent an increase in discharge pressure . 1. Clean the air–cooled condensers regularly with compressed air or an air blower . If the fins are badly choked , clean with a high-pressure water pump and cleaning solution. 2. Clean the CT water strainers daily and the strainers in the water system every week . When the strainers get very much clogged up , they can never be fully cleaned . They should be replaced . Drain and clean the CT tank periodically , say once in a fortnight . 3. Clean and descale condenser water tubes periodically. E VENKATA RAJU 18
  19. 19. HVAC Preventive Maintenance,Serviceand Troubleshooting Conti-- Preventive steps to prevent an increase in discharge pressure 4.Non condensables can find their way into the system when it is opened for repairs . Therefore whenever a system is opened it should be evacuated with a vacuum pump before charging the system again. The presence of noncondensables can be judged from the standing pressure of the system. Pump down the system and cool down the condenser to the outside temperature. In air cooled condensers run the condensers fan alone to achieve this. In water cooled condensers run the water pump to bring down the temp of the condenser to level of that water. 5. Remove excess refrigerant. E VENKATA RAJU 19
  20. 20. HVAC Preventive Maintenance,Serviceand Troubleshooting Reasons for Reduction in Suction pressure Fouling of evaporator Throttling devices Reduction of air quantity surface failure/improper adjustments over cooling coils Reduction in Suction Pressure Clogging suction Shortage of Clogged liquid-line Filters of high refrigerant strainers Capacity compressors E VENKATA RAJU 20
  21. 21. HVAC Preventive Maintenance,Serviceand Troubleshooting Preventive steps to prevent decrease in suction pressure Wash the all cooling coils Checking of Dampers checked periodically throttling devices for proper fixing and Increase properly free movement in suction Cleaning of Suction filters of Comp. Leak testing pressure Air filters periodically inspected for refrigerant leaks Once in a week checked E VENKATA RAJU 21
  22. 22. HVAC Preventive Maintenance,Serviceand Troubleshooting Reasons for Liquid flood back Improper adjustment of Dirty cooling coil/ Reduced air flow expansion valve chiller over cooling coils LIQUID FLOOD BACK Reduced water flow Temp. of crankcase Liquid draining by In chillers falling below cooling gravity due to improper coil temp layout of refrigerant piping E VENKATA RAJU 22 Liquid flood back : Liquid flood back to compressor in some times during operation from the evaporator to the compressor can dilute oil appreciably and cause damage to bearings. If liquid refrigerant enters compressor crankcase , it dilutes the oil resulting in poor lubrication of bearings.
  23. 23. HVAC Preventive Maintenance,Serviceand Troubleshooting SUCTION VAPOUR SUPERHEATING: Excessive suction gas superheat , in addition to reducing the compressor capacity to some extent ,cause excessive heating of the compressor body /head. Preventive steps The plant room should be shaft seals be lubricated well well ventilated Reduction in suction vapour superheating Oil and oil lines in compressor should be cleaned E VENKATA RAJU 23
  24. 24. HVAC Preventive Maintenance,Serviceand Troubleshooting Evaporator (Chiller) Efficiency: The leaving temperature difference (LTD) is the simplest of checking the evaporator performance. LTD = Outlet temperature of the fluid- Temp of the refrigerant in the evaporator(Saturation temperature of the refrigerant corresponding to the evaporator pressure) Steps for getting maximum efficiency from evaporator: Clean /wash the evaporator coils Clean strainers and filters in the periodically. Water system regularly Evaporator efficiency Brush water tubes in flooded chillers check and rectify oil increases At least once in a year return problems E VENKATA RAJU 24
  25. 25. METRO PROPERTY MANAGEMENT By E Venkata Raju 20+ years experience in MEP installations and facilities technical maintenance services THANK YOU E VENKATA RAJU 25

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