condensers
in a normal air cooled condenser operating between 80F and 115F ambient, condensing pressures are sufficiently high. but in winter, condensing pressures can drop by...
100 psi or more. this can make it difficult for the expansion device to maintain control of liquid flow and causes erratic evaporator operation.
approximately _____ percent of the heat is removed heat
15%
approximately _____ percent of the heat is rejected during subcooling
5 percent
approximately _____ percent of heat is rejected through condensation
80 percent
low ambient control is...
a device used to allow proper condensing operation at low outdoor ambient temperature.
three types of condensers are used with HVAC/R systems:
air cooled , water cooled, evaporative, which is a combination of air and water cooled
packaged room coolers and through the wall air conditioners both use what kind of condensers?
air cooled, these units are manufactured in sizes ranging from 1/2 to 3 and 1/2 tons of cooling capacity. they are commonly used in houses, apartments, townhouses, condominiums, offices, schools, and motels.
improved metering devices that can regulate with very low pressure differential reduce the need for head pressure control and save energy by...
allowing the system to operate against lower head pressures
split systems consist of two parts:
an outdoor condensing unit, and an indoor blower coil. the condensing unit, located outside, includes the compressor, condenser, and condenser fan. the blower coil, located inside the building, includes the evaporator, metering device, blower, and an air filter. instead of a blower coil, an evaporator coil can be placed on top of a furnace and the furnace fan used as the air handler.
air cooled condensers can be part of a packaged system that contains all the refrigeration components in one cabinet; they can be part of a condensing unit that contains the...
compressor, condenser, and condenser fan in one unit located outside, or there can be a separate component in a location separate from all the other refrigeration components.
the condensing unit is a popular use of air cooled condensers. this unit includes the....
compressor, condenser, fan, and outdoor circuitry.
what are remote condensers?
condensers that are located by itself, in a different location from the compressor. with this arrangement, compressors can be placed inside away from the weather where it can last longer. the two lines going from the system to the condenser are the discharge line and the liquid line. they are both high pressure, high temperature lines and are normally not insulated. occasionally, the liquid line is insulated if it run a long distance through a very hot space.
the three most common constructions for air cooled condensers are...
copper tubing with aluminum fin sheets, aluminum tubing with aluminum spine fins that are wrapped around the tubing, and micro channel aluminum tubing with aluminum fins
describe the three changes refrigerant goes through in the condenser
de-superheating, condensing, and subcooling. the refrigerant enters the condenser superheated from the compressor, the removal of heat in the first part of the condenser causes the refrigerant temperature to drop until it is saturated, this is de-superheating. then additional heat is removed but does not cause the refrigerant temperature to change, instead it changes state (latent) from a gas to liquid. this is the condensing process. after all the refrigerant has condensed to liquid, further heat removal in the final part of the condenser causes the refrigerant to drop below the saturation temperature. this is sub cooling.
one common use of the air cooled condenser is for...
domestic refrigerators and upright freezers
the condenser removes the heat picked up in the ...
evaporator and in the compressor. c
forced draft condensers use a ______ to push air across the condenser
fan, the cup of the fan blade faces the condenser on a forced draft condenser
condensers are made of metal for...
fast and efficient heat transfer
dirty air cooled condenser coils result in...
high utility usage and less cooling
when it comes to air cooled condensers in packaged units,where are the condensers located?
in the lower part of the cabinet, and a small fan is used to pull rom air over the surface of the condenser coil, and exhaust it back out into the room. some refrigerators use a natural draft type condenser coil on the back of the cabinet.
due to changes in federal law regarding the minimum SEER and EER for air conditioning systems, manufacturers are being required to design higher efficiency condensers. there are several ways that an air cooled condenser can be made more efficient. three common methods are...
increase the coil size to increase the heat transfer area increase the airflow rate to remove more heat decrease the condenser tube size so that more tubing can be added which increases the heat transfer rate
air cooled condensers are made of tubing with fins added to the tubing to...
increase the surface area in contact with the air . this is done to help accelerate the heat transfer rate out of the tubes when cooling the refrigerant. by adding tight fitting aluminum fins to the refrigerant circuits tubes, the air side surface and heat transfer can be greatly increased.
even though the subcooling account for only a small amount of the total heat rejection, it is important for two reasons:
it ensures that a solid stream of liquid will enter the metering device it adds to the cooling capacity of the system at a rate of about 0.5 percent of the total cooling capacity per degree of subcooling. for example: with 10F of subcooling, 5 percent additional capacity is added to the system (0.5%/F•10F=5%)
the condenser coil is usually a part of the unit containing the compressor for residential and...
light commercial, this combination of compressor and condenser coil is referred to as a condensing unit
one solution to the problem of low ambient operation is to...
maintain a minimum head pressure to ensure proper feeding of refrigerant to the evaporator. There are several ways of doing this. the most common are fan cycling (cycles the condenser fan on and off to regulate condenser pressure), fan speed control (varies the condenser fan to regulate condenser pressure), damper control (mechanism that controls damper position in an air distribution system), condenser flooding (backing up the liquid into the condenser.
natural draft condensers have no fan and rely entirely on...
natural convection and radiation
the airflow across an air cooled condenser can be...
natural draft, forced draft, or induced draft
is air a good conductor of heat ?
no
at outdoor temperature of 65F and lower, systems with fixed restrictions and no head pressure control cannot...
operate reliably. even systems with standard thermal expansion valves can adjust only so far.
air cooled condensers give off heat to the air and are normally located where?
outdoors. however, the condenser is part of the appliance on small systems like refrigerators and some medium-sized commercial refrigeration systems. these systems expel the heat to the air surrounding them. At normal peak load conditions, the temperature of the refrigerant. in the condenser is 25F - 30F higher than ambient temperature. this means that on a 95F day, the condensing temperature is between 120F and 125F.
induced draft condensers use a fan to...
pull air across the condenser. the cup of the fan on an induced draft condenser faces away from the coil
operating an aircooled condenser at low ambient temperatures can drastically ______ the system high side pressure
reduce. if the pressure drop is too severe, the metering device will not feed. low ambient temperature can also cause a decrease in system capacity
a condenser is basically a heat exchanger, it exchanges heat between the...
refrigerant and a cooling medium, such as air or water. it removes heat from the refrigerant inside the condenser coil and sends that heat into the air or water outside the condenser coil.
the purpose of a condenser coil is to...
reject heat (desuperheat) from a refrigeration or aie conditioninh system. it does this by condensing the high pressure high temperature gas to a liquid.
air cooled condensing units use ambient air to ....
remove heat from the condenser. they're available residential and commercial applications
low ambient control is essential in places like...
restaurants, computer labs, hospitals, and office buildings, they all have excessive indoor heat loads and they require cooling even in cold weather.
SERVICE TIP: dirt builds up on air cooled condenser coils, be sure to keep them clean seasonally.
the coil must be cleaned with an appropriate solution to remove the dirt and debris. an appropriate solution manufacturer approved. extremely dirty air cooled condenser coils can result in very high head pressures. if the head pressure and temperature get too high, the refrigerant can decompose, forming acids.
the two refrigerant lines are...
the high pressure liquid line, which carrie's liquid from the condensing unit to the metering device inside, and a low pressure suction line, which carries low pressure gas from the evaporator to the condensing unit as a whole.
most metering devices will feed too little refrigerant when the pressure drop across the metering device is lower than...
the system design pressure differential.
systems with fixed restriction type metering devices are most affected by low head pressure because...
they have no means of adjusting to changing conditions. when the pressure difference falls, the flow of refrigerant is severely reduced.
when it comes to energy efficient condensers, they are usually larger than lower efficiency ones.
this should be considered when replacing
air cooled coil construction
tube and fin spin fin microchannel
low ambient temperature can cause thermal expansion valves to...
underfeed
