hvac preventive maintenance presentation evraju

HVAC Preventive Maintenance,Serviceand Troubleshooting

PRESENTATION

E VENKATA RAJU 1

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


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


TroubleshootingConti-----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


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


TroubleshootingConti-----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


TroubleshootingA 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/FTR Bhp/TR

% reductio

n in capacity

% increase

in Bhp

Normal 7.2 (45) 40.6(105) 1

7 0.93 - -

High condensin

g temp7.2(45) 46.1(115) 1

6 1.12 8.2 20


TroubleshootingThe 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 compressorE VENKATA RAJU 8


TroubleshootingThe 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


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


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


TroubleshootingReduction of Volumetric efficiencyIf 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


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


TroubleshootingReasons 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


TroubleshootingConti-- Reasons for increase in Discharge pressure3.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


TroubleshootingConti-- Reasons for increase in Discharge

pressure4. Presence of non-condensable in the system5. 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


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

dischargePurging of By cleaning By draning By doing

pressure Non CT water &cleaning Bleed offCondensable strainers the CT tank daily fortnightly

E VENKATA RAJU 17


TroubleshootingPreventive 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


TroubleshootingConti-- Preventive steps to prevent an increase in

discharge pressure4.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


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 strainersCapacity compressors

E VENKATA RAJU 20


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


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

pipingE 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.


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


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 regularlyEvaporator efficiency

Brush water tubes in flooded chillers check and rectify oil increases

At least once in a year return problems

E VENKATA RAJU 24

METRO PROPERTY MANAGEMENT

By E Venkata Raju 20+ years experience in MEP installations

and facilities technical maintenance services

THANK YOUE VENKATA RAJU 25

hvac preventive maintenance presentation evraju

Documents