MAPUA INSTITUTE OF TECHNOLOGY SCHOOL OF MECHANICAL ENGINEERING MURALLA ST., INTRAMUROS, MANILA
EXPERIMENT NO. 11 HEATING, VENTILATING, AND AIR CONDITIONING
Bautista, Dave G. 2007103408
Engr. Alberto Suralta INSTRUCTOR
I. OBJECTIVES At the end of this experiment, the student will be able to: 1. Operate an A/C system. 2. Determine factors affecting A/C system. 3. Know the heat load
II. THEORY Air conditioning is the cooling of indoor air for thermal comfort. In a broader sense, the term can refer to any form of cooling, heating, ventilation, or disinfection that modifies the condition of air. An air conditioner (often referred to as AC or air con.) is an appliance, system, or machine designed to stabilize the air temperature and humidity within an area (used for cooling as well as heating depending on the air properties at a given time), typically using a refrigeration cycle but sometimes using evaporation, commonly for comfort cooling in buildings and motor vehicles. An air conditioner is a device which uses a special type of substance which readily changes from its normal gas state to a liquid one. The gas is contained in a closed circuit of pipes connected to a pump. The pump compresses the gas so hard that the pressure is great enough for it to turn into a liquid. In doing this the gas/liquid has got hot (If you try to compress a gas, it will almost always get hot - think of a bike pump when you pump up a tyre (tire), the greater the pressure in the tyre, the hotter the pump gets). Now the hot liquid travels round a set of pipes which allow the heat to escape. Next the liquid under pressure passes through a valve into a pipe where the pressure is much lower, and the liquid evaporate back into its gas state. In doing this it needs to take in heat from its surroundings, thus making the pipes colder. The gas now gets back to the pump and the whole cycle starts again. The pipes are usually arranged so that there are fans to blow air over both the hot part of the pipes and the cold part. The hot part is frequently put outside the house, and the cold part inside. This is called either a 'split pack', or a 'twin pack' depending on which country you are in There are also portable versions which have both parts in the same box, with the cold air blowing out of the front, and the hot air blowing out of a flexible hose which you put put outside the room to allow the hot air to dissipate.
Air conditioners use the evaporation of coolants, such as Freon, a nonflammable fluorocarbon, to create cool air. The evaporation cycle in an air conditioner begins when the compression unit compresses cool Freon gas. The Freon is mixed with a small amount of oil, which
helps to lubricate the compressor. The compression of the Freon causes it to become a hot, highpressured gas. The gas is then propelled through a series of coils where it dissipates its heat and condenses into a liquid. Next, the Freon moves through an expansion valve where it becomes a cold, low-pressured gas. Then, the gas runs through another set of coils that allows the gas to absorb heat and cool down the air inside your home. Fans placed near these coils help to propel hot air outside and move cool air inside. Air conditioning into comfort and process.
engineers
broadly
divide
air
conditioning
applications
Comfort applications aim to provide a building indoor environment that remains relatively constant in a range preferred by humans despite changes in external weather conditions or in internal heat loads. Air conditioning makes deep plan buildings feasible, for otherwise they'd have to be built narrower or with light wells so that inner spaces receive sufficient outdoor air via natural ventilation. Air conditioning also allows buildings to be taller since wind speed increases significantly with altitude making natural ventilation impractical for very tall buildings. Comfort applications for various building types are quite different and may be categorized as
Low-Rise Residential buildings, including single family houses, duplexes, and small apartment buildings High-Rise Residential buildings, such as tall dormitories and apartment blocks Commercial buildings, which are built for commerce, including offices, malls, shopping centers, restaurants, etc. Institutional buildings, which includes hospitals, governmental, academic, and so on. Industrial spaces where thermal comfort of workers is desired.
Window and Split-system AC Units A window air conditioner unit implements a complete air conditioner in a small space. The units are made small enough to fit into a standard window frame. You close the window down on the unit, plug it in and turn it on to get cool air. If you take the cover off of an unplugged window unit, you'll find that it contains: A compressor An expansion valve A hot coil (on the outside) A chilled coil (on the inside) Two fans A control unit
The fans blow air over the coils to improve their ability to dissipate heat (to the outside air) and cold (to the room being cooled).
When you get into larger air-conditioning applications its time to start looking at splitsystem units. A split-system air conditioner splits the hot side from the cold side of the system, as in the diagram below. The cold side, consisting of the expansion valve and the cold coil, is generally placed into a furnace or some other air handler. The air handler blows air through the coil and routes the air throughout the building using a series of ducts. The hot side, known as the condensing unit, lives outside the building. The unit consists of a long, spiral coil shaped like a cylinder. Inside the coil is a fan, to blow air through the coil, along with a weather-resistant compressor and some control logic. This approach has evolved over the years because it's low-cost, and also because it normally results in reduced noise inside the house (at the expense of increased noise outside the house). Other than the fact that the hot and cold sides are split apart and the capacity is higher (making the coils and compressor larger), there's no difference between a split-system and a window air conditioner. In warehouses, large business offices, malls, big department stores and other sizeable buildings, the condensing unit normally lives on the roof and can be quite massive. Alternatively, there may be many smaller units on the roof, each attached inside to a small air handler that cools a specific zone in the building. In larger buildings and particularly in multi-story buildings, the split-system approach begins to run into problems. Either running the pipe between the condenser and the air handler exceeds distance limitations (runs that are too long start to cause lubrication difficulties in the compressor), or the amount of duct work and the length of ducts becomes unmanageable. At this point, it's time to think about a chilled-water system. REFRIGERANTS
Air conditioning has to use refrigerants and although there are many types of refrigerants, including air and water, it is necessary to use chemicals for reasons of efficiency and ultimately to conserve energy. Types of Refrigerants ODP - The ODP or Ozone Depletion Potential, is the potential for a single molecule of the refrigerant to destroy the Ozone Layer. All of the refrigerants use R11 as a datum reference and thus R11 has an ODP of 1.0. The less the value of the ODP the better the refrigerant is for the ozone layer and therefore the environment. GWP - The GWP, or Global Warming Potential, is a measurement of how much effect the given refrigerant will have on Global Warming in relation to Carbon Dioxide, where CO2 has a GWP of 1. This is usually measured over a 100-year period. In this case the lower the value of GWP the better the refrigerant is for the environment.
R11 is a single chlorofluorocarbon or CFC compound. It has a high chlorine content and ozone depletion potential (ODP) and high global warming potential (GWP). The use and manufacture of R11 and similar CFC refrigerants is now banned within the European Union even for servicing. ODP = 1, GWP = 4000
R22 is a single hydro chlorofluorocarbon or HCFC compound. It has low chlorine content and ozone depletion potential and only a modest global warming potential. R22 can still be used in small heat pump systems, but no more new systems can be manufactured for use in the EU after late 2003. From 2010 only recycled or saved stocks of R22 can be used, as it will no longer be manufactured. ODP = 0.05, GWP = 1700 R134A is a single hydro fluorocarbon or HFC compound. It has no chlorine content, no ozone depletion potential, and only a modest global warming potential. - ODP = 0, GWP = 1300 R407C is a ternary blend of hydro fluorocarbon or HFC compounds, comprising 23% of R32, 25% of R125 and 52% of R134a. It has no chlorine content, no ozone depletion potential, and only a modest direct global warming potential. - ODP = 0, GWP = 1610 R410A is a binary blend of hydro fluorocarbon or HFC compounds, comprising 50% of R32 and 50% of R125) it has no chlorine content, no ozone depletion potential, and only a modest global warming potential. ODP = 0, GWP 1890 R417A is the zero ODP replacement for R22 suitable for new equipment and as a drop-in replacement for existing systems.
There are currently no restrictions on equipment or use of the following refrigerants: R134A, R407C, R410A, and R417A. Alternative Refrigerants R290 - Pure propane, a hydrocarbon (HC) an efficient naturally occurring refrigerant with similar properties to R22, but have no ozone depletion potential and an extremely low global warming potential. Whilst it is environmentally safe, it is also highly flammable and must only be used after careful consideration is given to safety. - ODP = 0, GWP = 3. Ammonia - A highly efficient refrigerant, which has been used in industrial applications for many years and with success. It is however; highly toxic and very careful consideration must be given to any design or application.
III. LIST OF APPARATUS 1. AMATROL T7082 2. AMATROL T7083 3. ANEMOMETER
IV. PROCEDURE Modify the air movement components on a thermal system and evaluate the change in the air flow path. Option 1: Open all ducts, maximum heat load Option 2: Open all ducts, minimum heat load Option 3: Open supply ducts, 25% return air, maximum heat load How to turn on the Air Conditioning System (Cooling Mode) Step 1: Open the “turn on” button Step 2: Set to “F” for the Fahrenheit unit Step 3: Press “Set” and select 55 OF Step 4: Press “Set” and select -10 Step 5: Press “Set” and select “C1” for Cooling Mode
Skills:
1. Close the ventilation without attic insulation, open all heat load, open all ducts. Heat Loads: Bright Light Attic Heater Ceiling Fan Attic Fan
2. Open ventilation with attic insulation, off all loads 3. Open heat loads, close ventilation with attic insulation, 25% return air
V. SET – UP OF APPARATUS
VI. DISCUSSION This experiment is all about the air – conditioning system. Here, the students were able to see the process of a thermal system and how it works. The students discussed the process of heating and cooling of the thermal system individually. The parts of the thermal system were also discussed.
VII. CONCLUSION After the experiment that we have done, I can say that we were able to operate an A/C system. We were able to have the knowledge about its basic component, function, operation and its application. Factors affecting the A/C system were also determined. Lastly, we were able to the heat load of the refrigerant 134A.
VIII. QUESTIONS AND ANSWERS 1. What is a refrigerant? A refrigerant is a substance used in a heat cycle usually including, for enhanced efficiency, a reversible phase change from a gas to a liquid.
2. What is Air Conditioning? It controls the properties of air so that the air will be suitable for its intended use.
3. What are the functions of Air Conditioning?
Control the temperature Control the humidity Control the purity, that is, removal of dust and other impurities Control of air movement or circulation
IX. PROBLEMS AND SOLUTIONS 1. A room being air conditioned is being held at 25°C dry bulb and 50% relative humidity. A flow rate of 5 m 3/s of supply air at 15°C dry bulb and 80% relative humidity is being delivered to the room to maintain that steady condition. What is the sensible heat absorbed from the room air in kw? Solution: PV = mRT 100(5) = m(0.287)(15 + 273) m = 6.049 kg/s Qs = sensible heat = mCp(t2 – t1) = 6.049(1.003)(25-15) = 60.8 kW
2. What is the enthalpy of the air – vapor mixture at 65% relative humidity and 34°C when the barometric pressure is 101.3 kPa? Given: Psat at 34°C = 5.318 kPa hg at 34°C = 2563.6 kJ/kg Solution: Pv = RH x Psat = 0.65 x 5.318 = 3.4567 kPa W = 0.622
= 0.622 (
) = 0.022 kg/kg
h = Cpt + Whg = 1.0(34) + 0.022(2563.6) = 90.4 kJ/kg
3. A mechanical draft dry cooling tower cools the cooling water from 60°C to 25°C at the rate of some 149.4 giga grams per hour. Atmospheric air enters the tower at 20°C and leaves at 35°C. The fan is driven by a 7460 kw motor. What is the mass flow rate of the air into the cooling water in kg per second? Solution: mw =
= 41, 500 kg/s
heat loss by water = heat gain by air (mCpΔt)water = (mCpΔt)air 41,500(4.187)(60-25) = ma(1.006)(35-20) ms = 403, 023 kg/s
X. REFERENCES
http://en.wikipedia.org/wiki/Refrigerant
Mechanical Engineering Formulas 2 nd Edition, by Jas Tordillo
