Basics of Refrigeration
Blue Star Ltd
AC &R Projects- Customer Service
BANGALORE
What is “TR”
(“TR” - Ton of Refrigeration)
TR is defined as amount of HEAT absorbed to heat
2000 lb of ICE to 2000lb of WATER at 0 Deg C
within 24 hours
The simultaneous control of Temperature,
Humidity, Air purity and Air motion
CPAC/Basic AC/2
Are You Comfortable?
Too much
Too warm? smoke and dust?
Too cold? Too stuffy?
Too humid?
NO!
CPAC/Basic AC/1
Basic Refrigeration Cycle
Air-Cooled & Water Cooled screw Chiller
Screw Compressor Sectional View
Duct Cleaning Services
Instruments to measure IAQ
UVC Emitters
VFD Fundamentals
How does a Variable Frequency Drive
Operate ?
Variable Frequency drive (VFD)
A variable-frequency drive is an electronic controller that adjusts the speed
of an electric motor by modulating the power being delivered. Variable-
frequency drives provide continuous control, matching motor speed to the
specific demands of the work being performed. Variable-frequency drives
saves 20-30% energy and equipment maintenance
Applications
Pumps, fans & Blowers
Changing Frequency Changes
Motor Speed
n Speed of motor
f Frequency of supply
P no of poles in the motor
Converts AC to DC and then Back
to AC
AC DC AC
Rectifier Inverter
Frequency Controls Motor Speed
h ig h sp e e d
lo w sp e e d
Working principle of Variable Frequency Drives
The air conditioning equipment is designed to perform under worst case conditions
like maximum human load, maximum outside ambient temperature, maximum
equipment load, etc.
The air conditioning requirement (TR & cfm) is not constant at all working
hours due to following:
Outside temperature variations in a day (Ambient Temperature)
Changing weather conditions in a year
No. of persons inside the air conditioned area
Equipment diversity
The Air Handling Units are selected to work under extreme conditions.
Thus, AHUs keep on doing surplus (not required) work and consuming
costly electrical energy all the time.
Relationships:
Speed of motor (N) is directly proportional to frequency of AC power supply.
N∞f
Quantity of air flow (Q) in a blower is directly proportional speed of motor (N).
Q∞N
Power consumed (P) is directly proportional to cube of speed of motor (N3).
Q ∞ N3
Refrigeration
Basics of Refrigeration Cycle
Step 1 : IN THE EVAPORATOR - As the liquid refrigerant flows through
the evaporator, it absorbs heat from the indoor air and changes from
liquid state to a saturated vapour. The air in the room does get cooler
and the refrigerant gas gets warmer while leaving the evaporator
CPAC/REF CYC/1
Step 2 : IN THE COMPRESSOR : The saturated gas is
compressed into high pressure and high temperature gas.
CPAC/REF CYC/2
Step 3 : IN THE CONDENSER : The hot refrigerant gas at high
pressure rejects the heat to the surrounding when passing through the
air cooled condenser. This condenses the gas to liquid state with out
any pressure change.
CPAC/REF CYC/3
Step 4 : IN THE CAPILLARY : The refrigerant goes through the
process of throttling expansion by which the warm liquid refrigerant at
high pressure reduces to low pressure and temperature liquid.
CPAC/REF CYC/4
HVAC system Start up
Check voltage
Ensure all valves in the system are open
Check for oil trace
Check expansion tank
Check cooling tower
Check compressor heater
Start chilled water pump, then cond. Water pump
Start AHUs
Re-Check valves in the system are open
Start the compressor
HVAC system – Daily Checks
Cleaning of equipment
Check lubrication
Check operating pressure
Check for unusual noise & vibration
Check pump gland packing
Check CHW entering and Leaving temp. & Pressure
Check Cond. entering and Leaving temp. & Pressure (if applicable)
Check ambient temp. (especially between 2.00 – 4.00 pm)
Check water level in the sump
Check AHU for filter condition, drive set condition, vibration and noise
Check for refrigerant leak and oil trace
HVAC system – General Checks
Maintain Log books (Neat and clean)
Hourly reading in the log book
Mention reason for stopping plant ex. Voltage fluctuation, power
failure, servicing etc
Use calibrated tools for measurement & servicing
Check the system condition before taking over
Run time equalization to be ensured for all equipments
Check all electrical connection
Always Remember…..
Do it yourself is a good motto, but know your
limitations
When in doubt ask
Keep plant room , equipment neat & clean
Start Chilled water system 1&1/2 hrs prior to
occupancy
Everyday during startup give min. load to system &
gradually increase the load
Practicing - Trouble shooting skills
Identify the problem to be diagnosed
Gather all the data needed to find the cause of the problem
Analyse the data and through a process of elimination, find the exact
cause of the problem.
Make the necessary repairs or adjustment to correct the problem.
Check out the system to be certain that the problem has been
eliminated.
Check back to find the original cause or root of the problem and take
necessary steps to make certain the problem will not occur
The following systematic check out of a system should unearth any type of
discrepancy in the operation of refrigeration cycle.
Suction pressure Condenser air entry/air
Head pressure leaving temperature
Oil pressure Cooler water in/water out
Discharge temperature temperature/pressure.
Sight glass or liquid level Condenser water in/ water
Temperature entering out temperature/pressure
compressor Ambient temperature
Current drawn DB/WB.
Air entering leaving
evaporator.
Compressor – High Head Pressure
What are all of the things that could cause high head
pressure?
Lack of coolant, Not enough air or water is flowing through the
condenser to remove the heat properly, or perhaps, coolant
temperature is too high.
An overcharge of refrigerant reducing the effective area of
condenser and preventing discharge of latent heat.
Blocked, corroded or insulated condensing surfaces such as
dirt or lime on air cooled or scale and debris on water cooled
condensers
Compressor- High Head Pressure
A restricted flow some where in the liquid supply which causes liquid
refrigerant to back up into the condenser
Non condensable gases causing higher than normal condenser
pressures.
Higher than normal loads.
Mismatched components
A condenser too small for compressor or a compressor too large for
the condenser.
Mixed refrigerants.
Compressor- Low Head Pressure
Low refrigerant charge.
Low compressor output. Compressor suction reeds, rings or
gaskets are leaking. Unloaders holding in, rods piston and
bearings worn or broken, etc
Lower than normal suction pressure.
Higher than normal coolant flow , or lower than normal
coolant temperature
Mismatched components, over sized condenser or under
sized compressor.
Mixed refrigerants. A lower pressure refrigerant added to a
high pressure refrigerant.
Compressor- Low Suction Pressure
Low refrigerant charge .
Low load.
Over sized compressor. ( Mismatched to
evaporator and / or load )
Low head pressure.
Restricted liquid flow from condenser to evaporator
( (clogged drier, starving TXV etc).
In adequate air or water through evaporator.
Wrong refrigerant for compressor or metering
device.
Clogged suction strainer.
Compressor- High / Low Amperage
A low amps indicate low compressor
loading which could be caused by any of
the things which result in low suction
pressure and low head pressure.
High amps draw could by any of the things
related to high suction / high head.
It could also indicate tight bearings, low
voltage, internal shorts, etc in the electrical
components
Do’s……
Operate unit in correct volts
Check water level in expansion tank
Operate plant / equipment in valve open position.
Ensure all safety guards are in place
Use only calibrated tools
Ensure PM is carried out at right time
Check the service report for correctness before
signing
Don'ts…
Do not operate in under voltage
Do not service, grease the equipment in running
condition
Do not operate without safety guard
Do not start all equipment at the same time
Do not bypass any safety control
Do not short-cut any process to start the system
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