Duct work in Air Conditioning

Good Duct Design Increases Efficiency

                   Central heating and cooling systems use an airdistribution or duct system to circulate heated and/or cooled air to all the conditioned rooms in a house. Properly designed duct systems can maintain uniform temperatures throughout the house, efficiently and quietly.

Why Duct Design Is Important

                               The efficiency of air distribution systems has been found to be 60-75% or less in many houses because of insufficient and/or poorly installed duct insulation and leaks in the duct system. Properly designed and installed ductsystems can have efficiencies of 80% or more for little or no additional cost, potentially saving a homeowner $50-200 or more per year in heating and cooling costs. Moreover, efficient duct system designs can reduce equipment size, further saving money for new or replacement equipment.

                         Duct systems that leak and/or do not distribute air properly throughout the house may make some rooms too hot and others too cold. Leaky and unbalanced duct systems may force conditioned air outside and unconditioned air into the house. This increases heating and cooling costs and may also draw humidity, dust, mold spores, and other contaminants into a home from the attic, crawlspace, or garage and radon gas from the soil. In extreme cases, poorly designed and installed duct systems can induce backdrafting—spillage of flue gases from combustion appliances (e.g., furnace, water heater, fireplace) into the living space— primarily when atmospheric or natural-draft flues are used rather than powered combustion systems.

                        Duct systems that are undersized, are pinched, or have numerous bends and turns may lead to low air flow rates and high air velocities. Low air flow rates cause the heating and cooling equipment to operate inefficiently. High air velocities increase noise.

Compressor Parts

Method For Installation Of Split Type Air Conditioner

Installation a Split System Air Conditioner

                                   Most people hire a professional to install a split system air conditioner. However, if you have some experience with plumbing and electrical work, you can install the unit on your own. Each split system or ductless air conditioner is unique to its manufacturer, but this article explains the general instructions for installing a split system air conditioner.

a. Install Indoor Unit

b. Install Outdoor Unit

c. Complete Split Air Conditioner Installation

Install Indoor Unit

1 Select an unobstructed location on your interior wall to mount the indoor air conditioning unit.

• Avoid direct sunlight and heat sources.
• Avoid locations where gas may leak or where oil mist or sulphur exists.
• The indoor unit requires at least 6" (15 cm) of open space surrounding its top and sides. The unit should also be mounted at least 7 feet (2.13 m) above the ground.
• Install the unit at least 3.3 feet (1 m) away from antenna, power or connecting lines that are used for television, radio, home security systems, intercoms or telephones. The electrical noise from these sources could cause operational problems for your air conditioner.
• The wall should be strong enough to hold the unit's weight. You may need to construct a wood or metal frame to provide added support.

 2 Secure the mounting plate to the interior wall.

Indoor unit holder

• Hold the mounting plate against the wall where you want to install the indoor unit.
• Use a level to make sure the plate is both horizontally and vertically square.
• Drill holes into the wall at the appropriate spots to affix the plate to the wall.
• Insert plastic anchors into the holes. Secure the plate to the wall with tapping screws.

 3 Create a hole in the wall to fit the piping.

Making hole in wall for piping

• Find the best spot for the hole to the exterior based on the opening in the mounting bracket. You should also consider the length of the pipe and the distance that it needs to travel to reach the outside unit.
• Drill a hole that is 3" (7.5 cm) in diameter through the wall. The hole should slope downward toward the exterior to ensure adequate drainage.
• Insert a flexible flange into the hole.

4 Check the electrical connections.

• Lift the unit’s front panel and remove the cover.
• Be sure the cable wires are connected to the screw terminals. Also, make sure that they match the diagram that comes with the unit.

5 Connect the pipes.

• Run the piping from the indoor unit toward the hole drilled through the wall. Minimize bending to ensure that the unit performs well.
• Cut a length of PVC pipe 1/4" (6 millimeters) shorter than the length between your interior and exterior wall surfaces.
• Place the pipe cap on the interior end of the PVC pipe. Insert the pipe into the hole in the wall.
• Bind the copper pipes, the power cables and the drain pipe together with electrical tape. Place the drain pipe on the bottom to ensure a free flow of water.
• Secure the pipe to the indoor unit. Use 2 wrenches, working in opposite directions, to tighten the connection.
• Join the water drainage pipe to the indoor unit’s base.
• Run the bound pipes and cables through the hole in the wall. Make sure that the drainage pipe allows water to drain in an appropriate place.

6 Secure the indoor unit to the mounting plate by pressing the unit against the mounting plate.

Install Outdoor Unit

1

Choose the best place to install the outdoor unit.

• The outdoor unit’s location needs to be away from any heavily trafficked, dusty or hot areas.
• The outdoor unit needs 12" of space surrounding its perimeter to ensure proper functioning.

 2 Lay the concrete pad on the ground and make sure that it is level.

The pad should be high enough so that the condenser will sit above the level of winter snows.

• Set the outdoor condenser on top of the pad. Use rubber cushioning under the unit's feet to minimize vibration.
• Make sure that no antenna of a radio or television is within 10 feet (3 meters) of the outdoor condenser.

 3 Connect the electrical wires.

• Remove the cover.
• Refer to the unit’s wiring diagram and make sure the cable wires are connected as the diagram suggests. Following the manufacturer's instructions for wiring is crucial.
• Fasten the cables with a cable clamp and replace the cover.

 4 Secure the pipes’ flare nuts to the corresponding pipes on the outdoor unit.

Complete Split Air Conditioner Installation

1 Bleed the air and humidity from the refrigerant circuit.

• Remove the caps from the 2-way and 3-way valves and from the service port.
• Connect a vacuum pump hose to the service port.
• Turn the vacuum on until it reaches an absolute vacuum of 10mm Hg.
• Close the low pressure knob and then turn off the vacuum.
• Test all of the valves and joints for leaks.
• Disconnect the vacuum. Replace the service port and caps.

2 Wrap the joints of the piping with insulating covering and insulating tape.

3 Affix the piping to the wall with clamps.

4 Seal up the hole in the wall using expanding polyurethane foam.

Warning

Follow all municipal codes for electrical wiring and other aspects of installation.

• Some split system air conditioner manufacturers void the unit’s warranty if it is not installed by a licensed tradesman.
• Do not allow any wiring to touch the compressor, refrigerant tubing or any moving fan parts.

Things That You'll Need

• • Level
  • Drill with drill bits
  • Plastic anchors
  • Tapping screws
  • Reciprocating saw or hole saw
  • Electrical tape
  • 2 wrenches
  • Cable clamp
  • Vacuum pump
  • Insulating covering and tape
  • Clamps
  • Expanding polyurethane foam

Absorption Refrigeration

How Absorption Works

                                         Like the compressor in an electric vapor compression cycle, the absorption system uses its "thermal" compressor (consisting of the generator, absorber, pump and heat exchanger) to boil water vapor (refrigerant) out of a lithium bromide/water solution and compress the refrigerant vapor to a higher pressure.  Increasing the refrigerant pressure also increases its condensing temperature.  The refrigerant vapor condenses to a liquid at this higher pressure and temperature.  Because this condensing temperature is hotter than the ambient temperature, heat moves from the condenser to the ambient air and is rejected.  The high-pressure liquid then passes through a throttling valve that reduces its pressure.   Reducing its pressure also reduces its boiling point temperature.  The low-pressure liquid then passes into the evaporator and is boiled at this lower temperature and pressure.  Because the boiling temperature is now lower than the temperature of the conditioned air, heat moves from the conditioned air stream into the evaporator and causes this liquid to boil.  Removing heat from the air in this manner causes the air to be cooled.

                                       The refrigerant vapor then passes into the absorber where it returns to a liquid state as it is pulled into the lithium bromide solution (the absorption process).  The diluted lithium bromide solution is pumped back to the generator.   Because lithium bromide (the absorbent) does not boil, water (the refrigerant) is easily separated by adding heat.  The resultant water vapor passes into the condenser, the absorbent solution returns to the absorber, and the process repeats.

                                        Although the process is similar to conventional electric vapor compression systems, absorption cooling substitutes a generator and absorber, called a thermal compressor, for an electric compressor.  Efficiency and lower operating costs are achieved through the use of a pump rather  than a compressor and a heat exchanger to recover and supply heat to the generator.   Double-effect absorption cooling adds a second generator and condenser to increase the refrigerant flow, and therefore the cooling effect, for a fraction of the heat input of a single-effect system.

Thermodynamics

                      The field of science, which deals with the energies possessed by gases and vapours, is known as Thermodynamics. It also includes the conversion of these energies in terms of heat and mechanical work and their relationship with properties of the system. A machine, which converts heat into mechanical work or vice versa, is known as Heat Engine. The field of engineering science, which deals with the applications of Thermodynamics and its laws of work producing and work absorbing devices in order to understand their function and improve their performance, is known as Thermal Engineering.(modern refrigeration)

The Refrigeration Cycle

The word cycle, as applied here, means a series of operation in which heat is first absorbed by the refrigerant, changing it from liquid to a gas, then the gas is compressed by the circulating air, thus bringing the refrigerant back to its original or liquid state. The cycle of operation onsists of the following steps:

1. The compressor pumps refrigerant through the entire system. It draws cool refrigerant gas in through the suction line from the evaporator freezer coils. At the same time, it compresses the gas and pumps it into the discharge line. The compressed gas sharply rises in temperature and enters the condenser.
2. The condenser performs a function similar to that of the radiator in an automobile, that is, the condenser is the cooling coil for the hot refrigerant gas. In the condenser, the heat is expelled into the room air outside the cabinet. During this process, the refrigerant gas gives up the heat it removed from inside the cabinet and changes into a liquid state.
3. As the hot refrigerant liquid leaves the condenser to enter the capillary tube, a drier - strainer removes any moisture or impurities.
4. The capillary tube is carefully calibrated in length and inside diameter to meter the exact amount of liquid refrigerant flow required for each unit. A predetermined length of the capillary tube is usually soldered along the exterior of the suction line, forming a heat exchanger which helps to cool the hot liquid refrigerant in the capillary tube. The capillary tube then connects to the larger diameter tubing of the evaporator.
5. As the refrigerant leaves the capillary tube and enters the larger tubing of the humid plate and evaporator, the sudden increase in tubing diameter forms a low pressure area, and the temperature of the refrigerant drops rapidly as it changes to a mixture of liquid and gas. In the process of passing through the evaporator, the refrigerant absorbs heat from the storage area and is gradually changed from a liquid and gas mixture to a gas.
6. The low pressure refrigerant gas leaving the evaporator coil now enters the accumulator. The accumulator is a large cylinder designed to trap any refrigerant liquid which may not have changed to gas in the evaporator. Since it is impossible to compress a liquid, the accumulator prevents any liquid from returning to the compressor.
7. As the refrigerant gas leaving the accumulator, it returns to the compressor through the suction line which is part of the heat exchanger, thus completing the cycle.

Heat Transmission

                           In refrigeration, the trasmission of heat may be accomplished in three ways;

1. By Conduction

2. By Convection

3. By Radiation

                                                      Conduction

                           This is the transference of heat by molecular impact from one particle to another in contact. For instance, if the end of a bar of iron is heated in the fire, some of the heat will pass through the bar to the cooler portion. Heat trevelling in a body, or from one body to another where the  two are in intimate contact, is termed conduction. Metal are usually splendid heat conductors. Each and every material has a conduction value, some good like the metals, other mediocre, and a few very poor. For instance, heat will quickly pass through a piece of copper but will have consideration difficulty in passing through a piece of cork. The material that have very low heat conductivities are termed heat insulators. Even the very poorest conductors, or insulation material, allow a certain amount of heat to pass through. There is no material which offers a perfect barrier or resistance to the passage of heat.

                                                      Convection

                              Convection is the principle used in hot-air heating. Air that is free to circulate, such as in any air body of appreciable size, will be set into motion where a difference of temperature occurs, for it will be absorb heat from the warmer wall, become heated, expand and become lighter The heated portion of the air eventually moves over to the colder wall, and the heat flows from the air to the colder object. Thus, any body of air capable of motion will transmit heat by convection. Hot-air and hot-water heating system work on the convection principle. They convey heat by bodily moving the heated substances from one place to another.

                                                      Radiation

                                Heat energy transmitted through air in the same way light is sent out by a lighted lamp, a radiant heater, or the sun, is called radiated energy. Large cold storage, warehouse, auditoriums, theaters, and homes are built with consideration of the heat evolved through radiant energy of the sun. Small household appliance rarely have to consider any radiant heat factor, for they are used in existing structures without any change in building design and are sheltered from direct heat.