HVAC Preventive maintenance Presentation EVRaju

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

HVAC
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

HVAC
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

HVAC
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

HVAC
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

HVAC
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

HVAC
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

HVAC
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

HVAC
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

HVAC
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

HVAC
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

HVAC
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

HVAC
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

HVAC
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

HVAC
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

HVAC
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

HVAC
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

HVAC
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

HVAC
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

HVAC
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

HVAC
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.

HVAC
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

HVAC
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

METRO PROPERTY MANAGEMENT
By
E Venkata Raju
20+ years experience in MEP installations and
facilities technical maintenance services
THANK YOU
E VENKATA RAJU 25

HVAC Preventive maintenance Presentation EVRaju

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