Transcript HVACR415_L12_CondensorSubcooling

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Air Conditioning
Condensers
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Types of Condensers
• Two main types of condensers:
– Water Cooled
– Air Cooled
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Air Cooled Condensers
• Air conditioning primarily uses forced draft condensers
• Use fans and blowers to move the air through a coil.
• Fins are connected to condenser tubes to provide more
surface area for heat transfer.
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Air Cooled Condenser
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Air Cooled Condenser
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Air Cooled Condensers
• The normal temperature difference between the
condensing point of the refrigerant and the ambient air
is 20 to 30 degrees F.
• The condensing point of the refrigerant is found by
converting the pressure in the condenser to temperature.
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Air Cooled Condensers
• Sub-cooling takes place in the last few passes of the
condenser.
– To measure sub-cooling use the condensing point temperature
and subtract the temperature of the refrigerant leaving the
condenser.
– The temperature of the refrigerant is found by placing a
clamp-on thermometer on the liquid line at the condenser
outlet.
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Subcooling
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Water Cooled Condensers
• There are three main types of water cooled condensers:
– Tube-N-Tube
– Shell-N-Tube
– Shell-N-Coil
Tube – N - Tube
• A tube within a tube
• The outer tube carries the refrigerant
– This allows the refrigerant to be cooled by both water and air.
• The inner tube carries the water.
– The inner tube often has a fin spiraled around it to add
surface area.
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Tube – N - Tube
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Shell - N - Tube
• A large tube with a number of small tubes inside.
• The refrigerant is again circulated around the water
tube and cooled by the water and air.
Shell – N - Tube
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Shell – N - Tube
• Both the tube-n-tube and shell-n-tube condensers can
be cleaned by pushing or forcing a special brush
through the water tubes or by using a chemical.
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Shell – N - Coil
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A large shell or tank with a coil inside.
Water is pumped through the coil.
Refrigerant is outside in the tank.
The refrigerant is cooled by both the air and the coil.
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Shell – N - Coil
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Water Regulating valves
• Used with water cooled condensers to adjust the
amount of water through the condenser
maintaining the condensing pressure.
• Water regulating valves are needed with
condensers using “city water” (open loop).
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Water Regulating Valves
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Water Regulating Valves
• A bellows on the valves is connected to a high pressure
access port.
• As the refrigerant pressure increases on the high side it
pushes on the bellows and forces the valves open.
• This allows more water to flow through the condenser.
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Water Regulating Valves
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Water Regulating Valves
• As the head pressure decreases the pressure on the
bellows decreases and allows a spring to push the valve
closed.
• This valve modulates to maintain the correct head
pressure and reduces water consumption.
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Water Regulating Valves
• When the compressor stops the head pressure
drops and the water regulating valve will close.
• This prevents waste of the “street” or well water.
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Water Towers
• The other way to cool water cooled condensers is
the use of a water tower or cooling tower.
• This “tower” is used to cool water in the water
cooled condensers.
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Water Towers
• The water used by the condenser is stored in the tower
and pumped to the condenser when the system
compressor runs.
• The water returns to the top of the tower after
absorbing heat from the refrigerant in the condenser.
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Water Towers
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Water Towers
• The heated water falls through the tower over baffles
cooling through evaporation as it gets to the bottom.
• The cooled water collects in the sump (bottom) of the
tower and gets pumped back to the condenser.
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Water Towers
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Water Towers
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Water Towers
• Fans are used to aid the tower and speed up the cooling.
• The fans are controlled by the water temperature.
• The ability of the tower to cool is based on outdoor wet
bulb and humidity.
• Water must be able to evaporate.
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Water Towers
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Evaporative Condensers
• These look like water towers but the difference is that
the condenser tubes are in the tower.
• The water is pumped from the sump of the evaporative
condenser and sprayed on the condenser tubes.
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Evaporative Condenser
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Evaporative Condensers
• When the water hits the tubes it evaporates and cools
the refrigerant inside the condenser tubes.
• Fans are sometimes added to speed and aid the process.
• The fans are controlled by the head pressure.
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Water Treatment
• Water used in the water towers and evaporative
condensers can cause scaling and corrosion.
• Scale is caused by the mineral concentration that
increases as the water evaporates.
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Water Treatment
• The pH level also changes as the water evaporates.
• Conductivity is a way of measuring the scaling
potential and pH levels should be monitored.
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Water Treatment
• Chemicals can be added to adjust the pH levels.
• Allowing some water to be dumped during operation
causes fresh water to be constantly added by a make up
water float and valve.
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Water Treatment
• This make up water flushes out some of the water and
minerals.
• This constant flushing aids in maintaining low mineral
concentrations.
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Subcooling
Subcooling
• What is subcooling?
– A temperature of a liquid when it is cooled below its
condensing temperature.
– Subcooling is the sensible heat removed from the liquid
after the change of state has taken place.
– Subcooling is used to determine if the condenser has
proper level of refrigerant.
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Subcooling
• The complete condensing of refrigerant should
occur in the bottom quarter of the condenser.
– Any heat that is removed after this point is subcooling.
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Subcooling
• Subcooling is needed to maintain proper system
balance.
• Normal subcooling is between 15-20 degrees F.
– Depending on how efficient the condenser is subcooling
may be a little higher or lower.
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Subcooling
– If the subcooling is low
• Possible dirty condenser
• Check condenser fan operation
• Look for overcharged condition
– If the subcooling is high
• Low charge
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subcooling
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Subcooling
• Subcooling can be accomplished by placing the
liquid line and the suction line in direct contact
with each other.
• This is usually done in small or low temperature
units.
• This higher subcooling results in a more efficient
unit.
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Subcooling
• The liquid in the liquid line will be cooled below its
condensing temperature.
– Also the suction line may be warmed slightly to boil any
refrigerant which may be present before entering the
compressor.
• The lower the temperature in the liquid line, the
greater the heat removal capacity.
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Subcooling
• This greater subcooling can also be achieved by
one system cooling another so that the system
can more efficiently reach lower temperatures.
– This is known as a cascade system.
• Cascade systems are usually required for ultra-low
temperature operations.
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Measuring Subcooling
• Determine the condensing temperate.
– Use your gauges and convert the high side.
– This should be the ambient temperature plus 30-35
degrees for air cooled systems.
• Measure the condenser outlet or the liquid line
temperature.
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Measuring Subcooling
• Subtract the liquid line temperature from the
condensing temperature.
• The result is subcooling.
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Subcooling Example
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Common Accessories
• Sight Glass:
– Provides a way to see the refrigerant in the system.
– Contains a strip that shows moisture in the system.
– Do NOT charge with this as you should always charge
with gauges.
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Common Accessories
• Filter Dryer:
– Located on the liquid line and removes the
moisture and/or debris from the system.
– The drier material is made out of Silica gel or a
molecular sieve which both filter and absorb
moisture.
– The liquid line filter should be replaced any time
the system is opened.
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Common Accessories
• Filter Drier (cont)
– Special cleanup driers and suction line “core
type” driers are usually installed on systems
that are badly contaminated.
– Make sure you are aware of the direction of the
arrow on filter driers. Most are not bidirectional.
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Common Accessories
• Suction line filter drier:
– Provides additional cleanup on a system that has had a
compressor burn out. It is placed on the suction line
between the evaporator and the compressor.
– Usually changed a few weeks after the compressor
change out.
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