Assignment3: Recirculating Air Conditioning Unit
1.0
INTRODUCTION
1.1
Air Conditioning
Air Conditioning, which may be described as the control of the atmosphere so that a desired temperature, humidity, distribution and movement are achieved, is a rapidly expanding activity throughout throughout the world. Obvious applications for air conditioning are homes, hospitals, public meeting places, mines, shops, offices, factories, land, air and sea transport, t ransport, but there are numerous other applications in which human comfort is not the prime consideration. These include textile and printing industries, computers, laboratories, photographic and pharmaceutical industries, manufacture, inspection and storage of sensitive equipment, horticulture, animal husbandry, food storage and many others.
1.2
Recirculating Air Conditioning
The Recirculating Air Conditioning Trainer unit is related to the Air Conditioning Laboratory Unit and enables even more experimentation as it f eatures recirculation recirculation of the air stream. This unit provides provides for the study of a self-contained air air conditioning system, system, as you would find within a typical building. Air flow may be introduced introduc ed from outside or it may be recirculated for recycling recycling within the system. Thus it is able to simulate open loop or or closed loop systems. The student may simulate different types of environments and conditions within a circuit or a room type situation.
1.3
Types of Air Conditioning
1.3.1
Portable Air Conditioning
If you’ve ever lived in a small house or an apartment building, you’ve
probably used a PTAC – portable terminal air conditioner. Portable air conditioners are typically noisier and less efficient than central air conditioners and cool a much smaller area than central air conditioners. That said, if you have limited space or a limited budget, you won’t do much better than a portable air conditioner.
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Assignment3: Recirculating Air Conditioning Unit 1.3.2
Wall/Window Air Conditioning
A wall/window model is usually installed in a window or external wall, and can cool rooms and open-plan areas of up to 50 square meters. While smaller units can be plugged into a normal power point, larger ones may require additional wiring.
1.3.3
Central Air Conditioners
Central air conditioners can be broken down into two different types – split system and packaged air conditioners.
1.3.3.1
Split System Air Conditioners
The more common of the two types of central air conditioners, split system air conditioners have the compressor / condenser housed in a unit outdoors and the evaporator indoors. The primary benefit of split system air conditioners is that they keep the noisy part outside! Split system air conditioners connect into your existing ductwork, cooling your home evenly and quietly.
1.3.3.2
Packaged Central Air Conditioners
less common in homes than split system air conditioners, packaged air conditioners, as the name suggests, “package” the two
components in a single unit, usually mounted on the roof or, occasionally, on a wall. If you’ve ever seen an air conditioning unit on the top of a building, you’ve seen a packaged central air conditioner.
1.3.4
Ductless Air Conditioners
Air conditioners that you can hook up throughout your home without installing ductwork. Ductless air conditioners can be thought of as a combination of split system central air conditioners and portable air conditioners – basically you have an outdoor unit that connects to multiple small indoor units connected via smaller conduits instead of ducts.
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Assignment3: Recirculating Air Conditioning Unit 1.3.5
Evaporation Coolers
Also called swamp coolers, evaporation coolers pull hot air through damp pads, evaporating the water in the pads. They’re primarily used in
places like Arizona where the dry heat is almost unbearable. Once the air is pulled through the pad and cooled, it is circulated through the house by means of a large blower fan. It might not seem like it, but swamp coolers can bring the temperature of a house down by as much as 30 F.
1.3.6
Inverter Technology
With conventional air conditioners, the compressor is either on (working to 100% capacity) or off. Inverters can vary the compressor speed and maintain the set temperature within a narrow range. Manufacturers claim inverter models are more efficient and reduce running costs.
1.3.7
Cooling-only/Reverse Cycle
Reverse-cycle models only cost a bit more than cooling-only models, but you can also use them for heating in winter. While the purchase and installation costs can be high, reverse-cycle air conditioners are among the cheapest forms of heating to run. They cause less carbon dioxide to be produced in power plants burning fossil fuel than other kinds of electric heater
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Assignment3: Recirculating Air Conditioning Unit 2.0
OBJECTIVES
1.
Familiarization with an air conditioning system and its’ components
2.
Investigating the prime factors that can be controlled in a typical air conditioning system.
3.
To provide data for which a psychometric chart be plotted, heat transfer be explored, recirculation and “adiabatic” mixing be investigated, condensate be measured and
the effects of cooling and heating loads be observed. 4.
To study the process of humidification, pre-heating, and cooling and dehumidification.
5.
To investigate and calculate the energy and discrepancy of heat transfer in the preheater process.
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Assignment3: Recirculating Air Conditioning Unit 3.0
APPARATUS/EQUIPMENT
1. A771 Recirculating Air Conditioning Unit 2. Compressor 3. Condenser 4. Expansion Valve 5. Evaporator
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Assignment3: Recirculating Air Conditioning Unit 4.0
RESULT AND DISCUSSION
Condenser
A condenser is a device or unit used to condense a substance from gas to liquid. They are basically heat exchangers which have various designs and come in many sizes ranging from rather small (hand-held) to very large industrial-scale units used in plant processes. A condenser unit used in central air conditioning systems typically has a heat exchanger section to cool down and condense incoming refrigerant vapor into liquid, a compressor to raise the pressure of the refrigerant and move it along, and a fan for blowing outside air through the heat exchanger section to cool the refrigerant inside. A typical configuration of such a condenser unit is as follows: The heat exchanger section wraps around the sides of the unit with the compressor inside. In this heat exchanger section, the refrigerant goes through multiple tube passes, which are surrounded by heat transfer fins through which cooling air can move from outside to inside the unit. There is a motorized fan inside the condenser unit near the top, which is covered by some grating to keep any objects from accidentally falling inside on the fan. The fan is used to blow the outside cooling air in through the heat exchange section at the sides and out the top through the grating. These condenser units are located on the outside of the building they are trying to cool, with tubing between the unit and building, one for vapor refrigerant entering and another for liquid refrigerant leaving the unit. Of course, an electric power supply is needed for the compressor and fan inside the unit.
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Assignment3: Recirculating Air Conditioning Unit Compressor
Air conditioner compressors are the heart of the system because they pump the refrigerant through the system in a closed cycle in much the same way as the heart pumps blood through the body’s system. The othe r main function of the air conditioner compressor
is to compress low pressure refrigerant gas from the evaporator converting it to a hot, high pressure gas. In doing this the compressor also removes vapor from the evaporator to help it maintain a constant temperature. Generally,refrigerant enters an air conditioner compressor as a low-pressure gas and decreases in size so the fluid molecules will compact and increase in energy and temperature. The refrigerant then leaves the compressor and enters the condenser, which cools it and changes it to a high-pressure liquid to cool the air that enters your home or car. The compressor is needed to pumping refrigerant. There are pistons inside a compressor motor, which move up and down. Refrigerant is drawn into the compressor
on
the
down
strokes
and
compresses
on
the
up
strokes.
Besides that, compressor also needed to adjust temperature. Compressing a gas causes its temperature to rise. The refrigerant enters an air conditioner compressor at a low temperature and moves to the exiting side of the compressor at a higher temperature before it enters the condenser. A compressor removes vapor from the evaporator, which will draw the humidity out of the air before it blows.
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Assignment3: Recirculating Air Conditioning Unit Expansion valve
The expansion device is one of major component in air conditioner units. It is also known as meter devices. Air conditioner expansion valve is the divided point between the low side and the high side of the air conditioner units. The meter device is located indoor (air handler) units with the evaporator coils. It’s small and hard to see, unless you open the
evaporator compartment. The function of expansion valve to removes pressure from the liquid refrigerant to allow expansion or change of state from a liquid to a vapor in the evaporator. The high-pressure liquid refrigerant entering the expansion valve is quite warm. This may be verified by feeling the liquid line at its connection to the expansion valve. The liquid refrigerant leaving the expansion valve is quite cold. The orifice within the valve does not remove heat, but only reduces pressure. Heat molecules contained in the liquid refrigerant are thus allowed to spread as the refrigerant moves out of the orifice. Under a greatly reduced pressure the liquid refrigerant is at its coldest as it leaves the expansion valve and enters the evaporator. Pressures at the inlet and outlet of the expansion valve will closely approximate gauge pressures at the inlet and outlet of the compressor in most systems. The similarity of pressures is caused by the closeness of the components to each other. The slight variation in pressure readings of a very few pounds is due to resistance, causing a pressure drop in the lines and coils of the evaporator and condenser.
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Assignment3: Recirculating Air Conditioning Unit Evaporator
Air conditioning evaporator works by absorb heat from the area (medium) that need to be cooled. It does that by maintaining the evaporator coil at low temperature and pressure than the surrounding air. Since, the AC evaporator coil contains refrigerant that absorbs heat from the surrounding air, the refrigerant temperature must be lower than the air. The expansion device provides a pressure reduces between the high side and the low side of the system, the saturation temperature of the refrigerant entering the air conditioning evaporator is lower than the medium to be cooled. One of the characteristic of a ac refrigerant is that as the pressure is reduced the boiling point is also reduced. Therefore, as the pressure is reduced through the expansion device so is the point at which it will boil and become a vapor. As the warm air from the space passes over the evaporator coil, it gives up its heat to the lower temperature liquid/vapor mixture passing through the evaporator. As the liquid refrigerant absorbs this heat it boils changing from the liquid state to the vapor state. The amount of heat the air conditioner evaporator absorbs must equal the amount of heat it lost For instance, if the air conditioning evaporator gives up 100 Btu’s of heat to the surrounding hot air, then the refrigerant within the air conditioning evaporator coil must gain 100 Btu’s of heat. The amount of liquid entering the evaporator must be enough, so by the time it reaches the end of the evaporator. It will be completely boiled to the vapor state.There must be enough air flows across the AC evaporator coil to provides heat to the refrigerant in the evaporator coil. This is just a safety way to ensure the air conditioner compressor doesn’t
have the liquid refrigerant entering it.
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Assignment3: Recirculating Air Conditioning Unit
5.0
CONCLUSION
As a conclusion, the Recirculating Air conditioning unit may used to demonstrate and evaluate most of the processes found in practical air conditioning plant, such as heating, cooling, humidification, dehumidification air stream. Sometime two or more of these process are needed to bring air to desired temperature and humidity level. Various air conditioning processes appear as horizontal line on this chart since moisture content of the air remains constant during this processes. Air is commonly heated and humidified in winter and cooled and dehumidified in summer. . 6.0
REFERENCES
1. Hilton
P.A,
(1994),
Experimental
operating
and
maintenance
manual
(Reciculating air conditioning unit A771), P.A Hilton limited Hampshire, England. 2. SOLDEQ, Air Conditioning Laboratory Unit, Equipment For Engineering Education & Research Solution Engineering Holdings Berhad,Puchong. Selangor Darul Ehsan. 3. http://oee.nrcan.gc.ca/equipment/cooling-ventilation/5503 4. http://www.brighthub.com/engineering/mechanical/articles/897.aspx 5. http://www.aelag.com.au/air-conditioning-types 6. http://www.michaelbonsbyhvac.com/blog/types-of-air-conditioners/
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Assignment3: Recirculating Air Conditioning Unit
7.0
APPENDIX’S
Figure1
Figure3
Figure2
Figure4
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Assignment3: Recirculating Air Conditioning Unit
Figure5
Figure6
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