How Air Conditioning Work

Saturday, January 31, 2009

Bahagian - Bahagian Air Dryer

1. Auto Drain Trap
2. Strainer
3. Injap
4. Accumulator
5. Pemampat
6. Control Box
7. Condenser
8. kipas Penyejuk
9. Arah Pembuangan Udara
10. Paip Masukan Udara
11. Paip Keluaran Udara
12. Instrumen Panel
13. Penukar Suhu
14. Injap Bypass Gas Panas

4) Proses Pengeluaran Udara

- ini fasa terakhir
- ia adalah proses dimana udara yang sudah dimampatkan berada dipenghujung rotor. Pada bahagian ini udara akan disalurkan pula ke bahagian lain manakala udara lain akan disedut masuk.
- proses ini adalah berterusan sehingga alat ini dimatikan. (OFF)

3) Proses Kemasukan Minyak

- minyak akan dimasukkan setelah proses mampatan udara hampir selesai.
- ia bertujuan untuk penyejukan rotor.
- komponen rotor pada pemampat akan mengalami pemanasan apabila proses mampatan udara berlaku.
- medium minyak di perlukan untuk penyejukan rotor pemampat.
- medium minyak dapat melancarkan proses mampatan udara.
- minyak dapat meminimumkan haus pada bahagian lurah rotor pemampat.

2) Proses Pemampatan

- ia adalah proses yang amat penting sekali.
- udara yang masuk ke dalam rotor, akan bergerak melalui lurah rotor pemampat mengikut pusingan rotor yang dipusingkan oleh motor.
- kedudukan lurah rotor yang rapat akan menghasilkan mampatan pada udara yang melaluinya.

1) Proses Kemasukan

- ia adalah peringkat paling awal dalam proses pemampat udara. Didalam proses ini, udara yang disedut akan disalirkan kedalam lurah yang terdapat didalam rotor pemampat.

Proses Pemampatan Udara

Proses pemampatan udara didalam pemampat berlaku dari empat proses penting;
1)Proses Kemasukan
2)Proses Pemampatan
3)Proses Kemasukan Minyak
4)Proses Pengeluaran Udara

Thursday, January 29, 2009

Chiller

A chiller is a machine that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. A vapor-compression water chiller comprises the 4 major components of the vapor-compression refrigeration cycle (compressor, evaporator, condenser, and some form of metering device). These machines can implement a variety of refrigerants. Absorption chillers utilize water as the refrigerant and rely on the strong affinity between the water and a lithium bromide solution to achieve a refrigeration effect. Most often, pure water is chilled, but this water may also contain a percentage of glycol and/or corrosion inhibitors; other fluids such as thin oils can be chilled as well.

Chilled water is used to cool and dehumidify air in mid- to large-size commercial, industrial, and institutional (CII) facilities. Water chillers can be either water cooled, air-cooled, or evaporatively cooled. Water-cooled chillers incorporate the use of cooling towers which improve the chillers' thermodynamic effectiveness as compared to air-cooled chillers. This is due to heat rejection at or near the air's wet-bulb temperature rather than the higher, sometimes much higher, dry-bulb temperature. Evaporatively cooled chillers offer efficiencies better than air cooled, but lower than water cooled.


Water cooled chillers are typically intended for indoor installation and operation, and are cooled by a separate condenser water loop and connected to outdoor cooling towers to expel heat to the atmosphere.

Air Cooled and Evaporatively Cooled chillers are usually intended for outdoor installation and operation. Air cooled machines are directly cooled by ambient air being mechanically circulated directly through the machine's condenser coil to expel heat to the atmosphere. Evaporatively cooled machines are similar, except they implement a mist of water over the condenser coil to aid in condenser cooling, making the machine more efficient than a traditional air cooled machine. No remote cooling tower is typically required with either of these types of packaged air cooled or evaporatively cooled chillers.

Where available, cold water readily available in nearby water bodies might be used directly for cooling, or to replace or supplement cooling towers. The Deep Lake Water Cooling System in Toronto, Canada, is an example. It dispensed with the need for cooling towers, with a significant cut in carbon emissions and energy consumption. It uses cold lake water to cool the chillers, which in turn are used to cool city buildings via a district cooling system. The return water is used to warm the city's drinking water supply which is desirable in this cold climate. Whenever a chiller's heat rejection can be used for a productive purpose, in addition to the cooling function, very high thermal effectivenesses are possible.

Wednesday, January 28, 2009

VENTILATION AND EXTRACT SYSTEMS


 

VENTILATION AND EXTRACT SYSTEMS


 

INTRODUCTION

The surrounding air enters the room whenever the door of the room is opened. The temperature and moisture content of this outside air have to be brought down to the room conditions. So this results in load on the system. The frequency of opening of the door/s is dependent upon the volume of the room.


 

VENTILATION

Ventilation is the process of supplying and removing air by natural or mechanical means to and from any space.

Ventilation air is part of the supplied air from outdoors plus any re-circulated air that has been cleaned or treated.

Inadequate ventilation can increase the effects of indoor air pollution.

Outdoor air in sufficient quantities must be brought inside to mix with and dilute the pollutant emissions and the indoor air must be vented to the outside to carry out pollutants.


 

RATE OF VENTILATION

The excess carbon dioxide water vapor, odors and air pollutants that accumulate in a building must be exhausted. At the same time an equal amount of fresh air must be introduced to replace the exhausted air. Where the polluted air in a room cannot be re-circulated to other areas, such as from kitchens and toilets, it is exhausted directly to the outdoor atmosphere. Such areas are 100% fresh air ventilated. Normally about 5 % to 25 % of the air circulated for cooling will be outdoor air.

Under certain circumstances much larger amounts of outdoor air are introduced. For example, the American Society for Heating Refrigeration and Air Conditioning Engineers (ASHRAE) recommends five times as much outside air for people who smoke than for nonsmokers (Table 6.2).

The number of air changes per hour (ACH) that a building will experience based on their appraisal of the building type, construction and use.    

To determine the required rate of ventilation, determine the cubic content of the area to be ventilated ( length x width x height ).

The next step is to determine the recommended air changes rate (Equation 6.1).


 


 


 


 


 


 


 

where,

        N    =    air changes rate (per hour)

        V    =    volume of required area to be ventilated (ft3)


 

For metric calculation use the equation below :


 


 


 


 


 


 


 

Table 6-1 : Required Rate of Ventilation

Application 

Air change rate (minute) 

Residential 

1 to 2 min 

Offices 

2 to 5 min 

Factories/warehouses 

3 to 6 min 


 

Solution :


 

The procedures to determine the air volume flow rate are :-

  1. Calculate the cubic content (40ft by 30ft by 8ft = 9600ft3).
  2. Refer to Table 6.1 which recommends a 1 to 2 min air change (an average of one air change every 1.5 minutes).
  3. Divide the air change rate (1.5) into 9600ft3 = 64000cfm.
  4. Select a fan size closest to the required cfm.

Table 6-2 : Minimum ventilation rates for different types of buildings

Type of building 

Air changes per hour 

Type of building 

Air changes per hour 

Schools

Classrooms

Assembly halls

Changing rooms

Dining rooms

Dormitories

Gymnasia

Common rooms

Staff rooms

Laboratories 


 

6

3

3

3

3

3

2

2

Operating theatres

X-ray rooms

Entrances

Lavatories and

Bathrooms 

10

6

3

Kitchens(varying according to volume of air required through canopy)

20-40 

Laundries

Boiler houses

Smoking rooms 

10-20

10-15

10-15 

Hospitals

Wards

Dormitories

Day rooms

Staff bedrooms

Corridors 


 

3

3

3

2

Note : For places of public entertainment such as cinemas, theatres, concert halls, assembly halls and dance halls the ventilation rate depends upon the Local Authorities Regulations, usually 28m3 per hour, per person.


 

VENTILATION SYSTEM FOR INTERNAL BATHROOMS AND TOILETS

Ventilation for these rooms should provide a minimum extract rate 20m3/hr from a toilet cubicle, or a bathroom without a water closet (W.C) and a minimum extract rate of 40m3/hr from a bathroom with a W.C. The ventilation system must be separate from any ventilation plant installed for any other purpose. In the common dust system the inlets from the bathrooms or W.C compartments should preferably be connected to the main vertical duct by a shunt duct at least 1m long This shunt duct will offer better sound attenuation between the dwellings and also tends to prevent the spread of smoke and fumes in the event of a fire.

The fans must be capable of extracting the total flow of air, plus an allowance on the fan static pressure to counteract wind pressures.

In order to keep the system operating in the event of failure of a single fan, it is recommended that two fans and motors are installed, with an automatic change-over damper.

To replace air extracted from the rooms, air should be drawn from the entrance lobby through a wall grill or a 19mm gap left under the door of the room.


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 

Sunday, January 18, 2009

SUPPLY DEVICES AND ROOM AIR DISTRIBUTION


SUPPLY DEVICES AND ROOM AIR DISTRIBUTION

One way to condition air is to use a fan to move the air over the conditioning space. The components that make up the forced-air system are the blower (fan), the air supply system, the filter, the balancing damper, the return air system, grilles and registers where the circulated air enters the room and returns to the conditioning equipment.

TYPES OF FANS

The fan or blower as it is sometimes called, can be described as a device that produces airflow or movement. The fan provides the pressure difference to force the air into the duct system, through grilles and registers and into a room. Several different types of fans produce this movement such as propeller fan, axial-flow fans and centrifugal fans.


The propeller fan is used in exhaust-fan and condenser-fan applications. It will handle large volumes of air at low pressure differentials. The propeller fan can be cast iron, aluminum or stamped steel and is set into a housing called a venturi to encourage airflow in a straight line from one side of the fan to the other. The propeller fan makes more noise than the centrifugal fan so it is normally used where noise is not a factor.

The centrifugal fan has characteristics that make it desirable for duct work. It builds more pressure from the inlet to the outlet and moves more air against more pressure. This fan has a forward curved blade and a cutoff to shear the air spinning around the fan wheel. The centrifugal fan is very quiet when properly applied.

SUPPLY AIR DUCT SYSTEM

The supply duct system distributes air to the terminal units, registers or diffusers into the conditioned space. Starting at the fan outlet, the duct can be fastened to the fan housing directly or have a fireproof vibration eliminator between the fan and the ductwork. The duct system must be designed to allow air moving toward the conditioned space to move as freely as possible but the duct must not be oversized. Duct systems can be plenum, extended plenum, reducing plenum or perimeter loop.

Plenum System

It has an individual supply system that makes it well suited for a job in which the room outlets are all close to the unit. This system is economical from a first cost standpoint and can be installed easily with minimum experience. The supply diffusers are normally located on the inside walls and are used for heating system with very warm or hot air as the heating source. The return air system can be a single return located at the air handler which makes materials economical.

Extended Plenum System

This system can be applied to a long structure such as the ranch-style house. This system takes the plenum closer to the farthest point. The extended plenum is called the trunk duct and can be round, square or rectangular. The system uses small ducts called branches to complete the connection to the terminal units.

Reducing Plenum System

The reducing plenum system reduces the trunk duct size as branch ducts are added. This system has the advantage of saving materials and keeping the same pressure from one end of the duct system to the other when it is properly sized. This ensures that each branch duct has approximately the same pressure and velocity pushing air into its takeoff from the trunk duct.

Perimeter Loop System

The perimeter loop duct system is particularly well suited for installation in a concrete floor in a colder climate. The loop can be run under the slab close to the outer walls with the outlets next to the wall. The loop has a constant pressure around the system and provides the same pressure to all outlets.



RETURN AIR DUCT SYSTEM

The return air duct is constructed in much the same manner as the supply duct except that some installations are built with central returns instead of individual room returns. Individual return air systems have a return air grille in each room that has a supply diffuser. The individual return air system will give the most positive return air system, but they are expensive. The return air duct is normally sized at least slightly larger than the supply duct so there is less resistance to the airflow in the return system than in the supply system.

AIR FILTERS

The purpose of an air filter is to free the air of as much of the airborne contaminants as is practicable. The main types of filters are :


  1. Dry : in which the contaminants are collected in the filter medium
  2. Viscous or Impingement : in which the contaminants adhere to a special type of oil.
  3. Electrostatic : in which the contaminants are positively charged with electricity and collected on negative earthed plates.


Dry Filters

These use materials such as cotton wool, glass fiber, cotton fabric, treated paper, foamed polyurethane as the cleaning medium. The efficiency of the filter depends largely upon the area of medium offered to the air stream and for this reason the filter can be arranged in a 'V' formation which increases the area


In the case of an automatic roller type filter, when the filter is dirty, a pressure switch will switch on an electric motor which will turn the dirty spool and allow clean fabric to enter the filter chamber.




Absolute Filters

These are of dry fabric type and are very efficient in moving even the smaller particles from the air. This high performance is obtained by close packing of a very large number of small diameter fibers but this unfortunately results in a high resistance to air passing through the filter.

Viscous Filters

These have a large dust-holding capacity and are therefore often used in industrial areas where there is a high degree of atmospheric pollution. The filter medium is coated with a non-inflammable, non-toxic and odorless oil, which the contaminants adhere to as they pass through the filter. There are two types of viscous filters such as cell type and automatic type

Electrostatic Filters

These types of filters have three main components : ionizer, metal collector and electrostatic power pack. The various air contaminants are given a positive electrostatic charge by an ionizer screen which is the first part of the filter. The screen consists of a series of fine wires possessing an electrostatic charge produced by a direct current potential of 13 kV. The wires are spaced alternatively with rods or tubes which are at earth potential.

The air containing these positively charged contaminants then passes through a metal collector, which consists of a series of parallel plates about 6mm apart, arranged alternatively so that one plate which is earthed, is next to a plate which is charged with a positive direct current potential of 6 kV. The positively charged air contaminants passing through the collector are repelled by the plates of similar polarity ( which are positive) and are attracted by the negative earthed plates.

BALANCING DAMPERS

A well-designed system will have balancing dampers in the branch ducts to balance the air in the various parts of the system. Balancing the air with dampers enables the technician to direct the correct volume of air to the correct run of duct for better room temperature control.


The dampers should be located as close as practical to the trunk line, with the damper handles uncovered if the duct is insulated. The place to balance the air is near the trunk so if there is any air velocity noise, it will be absorbed in the branch duct before it enters the room. A damper consists of a piece of metal shaped like the inside of the duct with a handle protruding through the side of the duct. The handle allows the damper to be turned at an angle to the air stream to slow the air down.

ROOM AIR DISTRIBUTION

The supply air enters a room either through a grille, register or diffuser. A supply grille has adjustable vanes for controlling the direction of the air entering a room. A register is a grille that also has a damper behind it so that the amount as well as the direction of the air entering a room can be controlled.

The location of supply air outlets is very important for the comfort of the occupants. The goal is to gently circulate all of the air in a room so that there are neither stagnant nor draftly areas. Make sure too that beams or other objects do not block the air supply from reaching all parts of a room. Where heating is the major problem, the outlets should be paced lower. However, to prevent short-circuiting of the air, do not place return openings right next to supply outlets. Also avoid floor return grilles because dirt and small objects fall into them.

DISTRIBUTION OF PRESSURE THROUGH A SYSTEM OF DUCT WORK


 

DISTRIBUTION OF PRESSURE THROUGH A SYSTEM OF DUCT WORK

INTRODUCTION

Air flowing through a duct exerts two types of pressure on its surroundings. The first is dynamic pressure due to its motion or kinetic energy; this is velocity pressure (VP). The second is the bursting pressure of the air trying to escape from the enclosure or of the surrounding air trying to enter the enclosing duct. This is static pressure (SP) and it acts in all directions. The sum of these two pressures is the total pressure (TP).

STATIC PRESSURE (SP)


 

Static pressure is the outward force of air within a duct. This pressure is measured in mm of water (mmH2O). The static pressure within a duct is similar to the pressure within an automobile tire. It is basically an inactive pressure.


 

VELOCITY PRESSURE (VP)


 

Velocity pressure is the forward-moving force of air within a duct. This pressure is measured in inches of water. The velocity of the air and the weight of the air create velocity pressure. The static pressures balance each other and the velocity pressure is the difference. The velocity pressure is comparable to the rush of air from a punctured tire.


 

TOTAL PRESSURE (TP)


 

Total pressure is the sum of velocity pressure and static pressure, otherwise known as impact pressure. This pressure is expressed in inches of water. The total pressure is associated directly with the sound level of the outlet. Therefore, anything that increases the total pressure, such as under sizing of outlets or increasing the speed of the blower will also increase the sound level. The total pressure of a duct can be measured with a manometer applied a little differently. Notice that the velocity component or probe of the manometer is positioned so that the air is directed into the end of the tube. This will register the static and velocity pressures.


 

AIR MEASURING INSTRUMENTS FOR DUCT SYSTEMS


 

To establish the fan performance and to trouble-shoot air distribution systems faults it is necessary to measure static and velocity pressures in ducts and air systems. The pressure involved in air systems is very small, hence it is measured in terms of water gauge ( 704mm of water column represents one psi pressure). The water manometer has been mentioned as an air pressure measuring instrument. An instrument used to measure the actual air velocity is the velometer. This instrument actually measures how fast the air is moving past a particular point in the system. When the average velocity of the air (in m/s) passing a point in the duct can be determined by using instruments, the volume of the air can be determined by using the area of the duct in m2. These instruments should be used as the particular manufacturer suggests.A special device called a pitot tube was developed many years ago and is used with special manometers for checking duct air pressure at most pressure levels.


 

PRESSURE CHANGES AT FANS

    

The fan produces a rise of total pressure in the whole system. This rise is the fan total pressure (Pa). The fan total pressure rise is equal to the drop of total pressure due to friction in the ductwork system. The fan total pressure is calculated from the total pressure in the fan outlet duct minus the total pressure in the fan inlet duct.


 

The fan velocity pressure is defined as the velocity pressure in the discharge area from the fan. The fan static pressure is defined as fan total pressure minus fan velocity pressure. Note that this is not necessarily the same as the change in static pressure across the fan connections.

Saturday, January 17, 2009

AIR HUMIDIFICATION


 


 


 


 


 

AIR HUMIDIFICATION


 

TYPES OF HUMIDIFIERS


 

The plenum-mount humidifier is mounted in the supply plenum or the return air plenum. The furnace fan forces air through the media where it picks up moisture. The air and moisture are then distributed throughout the conditioned space . The under-duct humidifier is mounted on the underside of the supply duct so that the media is extending into the air flow where moisture is picked up in the air stream.


 

Atomizing humidifiers discharge tiny water droplets (mist) into the air, which evaporate very rapidly into the duct air stream or directly into the conditioned space. These humidifiers can be spray-nozzle or centrifugal types, but they should not be used with hard water because it contains minerals (lime, iron etc) that leave the water vapor as dust and will be distributed throughout the house or building. Eight to ten grains of water hardness is the maximum recommended for atomizing humidifiers.


 

The spray nozzle type sprays water through a metered bore of a nozzle into the duct air stream where it is distributed to the occupied space. Another type sprays the water onto an evaporative media where it is absorbed by the air stream as a vapor. They can be mounted in the plenum, under the duct or on the side of the duct.


 

The self-contained humidifiers may use the evaporative, atomizing or infrared processes. These units may include an electric heating device to heat the water or the water may be distributed over an evaporative media. A fan must be incorporated in the unit to distribute the moisture throughout the room or area.


 


 

HUMIDIFIER MEDIA


 

Humidifiers are available in several designs with various kinds of media. A type using disc screens are mounted on a rotating shaft, causing the slanted discs to pick up moisture from the reservoir. The moisture is then evaporated into the moving air stream. The discs are separated to prevent electrolysis, which causes

the minerals in the water to form on the media. The wobble from the discs mounted at an angle washes the minerals off and into the reservoir. The minerals then can be drained from the bottom of the reservoir.

Monday, January 12, 2009

TYPES OF HUMIDIFIERS

TYPES OF HUMIDIFIERS

Evaporative Humidifiers work on the principle of providing moisture on a surface called a media and exposing it to the dry air.
This is normally done by forcing the air through or around the media and picking up the moisture from the media as a vapor.

The by pass humidifiers relies on the difference in pressure between the supply (warm/inlet) side of the furnace and the return (cool) side.
It may be mounted on either the supply plenum or duct or the cold air return plenum or duct. Piping must be run from the plenum or duct where it is mounted to the other plenum or duct.
If mounted in the supply duct, it must be piped to the cold air return.
The difference in pressure between the two plenums draws some air through the humidifier to the return duct and is distributed throughout the house.

Sunday, January 11, 2009

AIR HUMIDIFICATION

INTRODUCTION

For comfort, the dried-out air should have its moisture replenished.
The recommended relative humidity for a home is between 40% and 60%.
When the relative humidity varies above the limits, studies have shown that bacteria, viruses, and other organisms become more active.
In conditioned spaces with lower relative humidity, the dry warm air draws moisture from carpets, furniture, plants and human.
With more humidity in the air, a person is more comfortable at a below temperature.
An efficient and effective equipment called humidifiers produce the moisture and make it available to the air by evaporation.

Thermal Switch Blow

Contoh thermal switch ialah 2A 250V 150 darjah celsious untuk kipas angin (stand) di rumah, pastikan soldering dalam keadaan betul, jangan bersentuh dengan coil kipas angin.

SAFETY FACTOR

SAFETY FACTOR

An addition of 5% on Room Sensible heat (RSH) is taken as a safety factor and this also covers items such as heat gain by the supply duct, leaks, etc.

INTERNAL HEAT GAIN

Appliances

Some appliances give off both sensible and latent heats; the latent heat being given off directly or as a result of their function such as cooking, drying, etc. Refer to the data provided by manufacturers of the appliances or in design tables, for arriving at the sensible heat contributed by the appliances. In bigger installations such as hotels, exhaust hoods with positive exhaust are provided which remove considerable amount of sensible heat and moisture. Also, all the appliances may not be functional at the same time. So the diversity factors have to be judiciously arrived at for such applications.

Saturday, January 10, 2009

INTERNAL HEAT GAIN

2. Lights

Fluorescent light = number of lamp x total watts x 1.25

and

Incandescent light = number of lamp x total watts

INTERNAL HEAT GAIN

1. People

Heat is generated within the human body by the process of metabolism.

The metabolic rate for women is about 85% and for children it is 75%.

The metabolic rate varies with the type of activity of the individual.

Design tables provide the sensible and latent heat generated per person.

Multiply the sensible and latent heat per person by the number of persons to get the sensible heat gain due to occupancy.

Equation for find people factor:
People : factor of sensible and latent heat x number of people x number of
hours

2.4 HEAT TRANSMISSION THROUGH GLASS AND PARTITIONS

In addition solar gain through the glass, there is a heat gain by transmission through the glass because of the temperature difference between the surroundings and the conditioned space. Also heat gain occurs through the partition walls between the non-conditioned and the conditioned space.

Heat gain = A x U x TD

AIR CHANGE LOAD

Once the number of air changes per 24 hours has been determined from a given table, the total air change volume per 24 hours is found by multiplying the inside volume in cubic feet by the number of air changes.
To calculate the air change load in BTU per 24 hours, multiply the total air change volume by the standard air density to convert to pounds per hour and then by the difference in enthalpy between the outdoor and indoor air (ho – hi).

Formula,
Air change load = (inside volume)(air changes)(0.075) (ho – hi)

Thursday, January 8, 2009

AIR CHANGE LOAD

AIR CHANGE LOAD

The air changes occurring in the space are brought about almost entirely by infiltration through door openings.

The quantity of outside air entering a space through door openings in a 24 hour period depends on the
(1) number,
(2) size and,
(3) location of the door or doors;
on the frequency and duration of the door openings; and on the densities of the inside and outside air.

Since the combined effect of all these factors varies with the individual installation and is difficult to predict with reasonable accuracy, it is general practice to estimate the air change quantity on the basis of experience with similar applications.
Experience has shown that, as a general rule, the frequency and duration of door openings and hence, the air change quantity, depend on the inside volume of the cooler and the type of usage.

WALL GAIN LOAD

WALL GAIN LOAD

In determining the wall gain load, the heat gain through all the walls, including the floor and the ceiling, should be taken into account. When several walls or parts of walls are of different construction and have different U factors, the heat leakage through the different parts is computed separately.

Walls having identical U factors may be considered together, provided that the temperature differential across the walls is the same.

Where the difference in the value of U is slight and or the wall area involved is small, the difference in the U factor can be ignored and the walls or parts of walls can be grouped together for computation.

Wall gain load = A x U x TD

Where, A = outside surface area
U = wall gain factor
TD = temperature difference between the surroundings and the conditioned space.

Wednesday, January 7, 2009

HEATING AND COOLING LOADS OF A ROOM

INTRODUCTION

For summer air conditioning, the air conditioned space is maintained at a temperature lower than the surrounding temperature. The moisture content may also have to be maintained at a level lower than the atmospheric level. So there has to be transfer of heat as well as ingression of moisture from the surroundings to the air conditioned space. Further, we have to take into account the heat generated by occupants, electric lights, fans and other appliances.

DESIGN CONSIDERATIONS

The air-conditioning plant is designed to maintain the specific internal air temperature and humidity when the expected heat gain and losses occur. The cooling load on refrigerating equipment seldom results from any one single source of heat. Rather, it is the summation of the heat that usually evolves from several different sources. Some of the more common sources of heat that supply the load on refrigerating equipment are as follows :-

-heat that leaks into the refrigerated space from the outside by conduction through the insulated walls.
-heat that enters the space by direct radiation through glass or other transparent materials.
-heat that is brought into the space by warm outside air entering the space through open doors or through cracks around windows and doors.
-heat given off by warm product as its temperature is lowered to the desired level.
-heat given off by people occupying the refrigerated space.
-heat given off by any heat-producing equipment located inside the space, such as electric motors, lights, electronic equipment, steam tables and materials handling equipment.

COOLING TOWERS

- Cooling towers is a equipment that passes air over the water to remove the system heat from the water.
- Cooling towers are broadly divided into two type:

(1) The natural-draft or atmospheric tower, in which the air movement through the tower depends upon natural wind movement.
(b) The mechanical-draft tower through which air is drawn by fans.

Natural-Draft

-It's designed to cool water by means of air moving through the tower at the low velocities usually existing in open spaces.
-For this reason the roof of a building is an excellent location.
-These cooling towers should be so located that sufficient space is available all around the tower for free movement of air.
-Water returning from the condenser is sprayed down the tower through nozzles.
-The heat transfer from water to air is dependent upon the surface of water exposed to the air stream.
-Therefore for a good spray pattern, to produce as many fine droplets of water as possible, it is essential for good performance of the cooling tower.
-So clean nozzles are a must.
-Worn-out nozzles, scale or dirt in nozzles and piping, clogged strainers and pump impellers, all these can cause a reduction in the capacity of the cooling tower.

Mechanical-Draft

-The difference between this tower and the atmospheric type is that the draft in the mechanical-draft cooling tower is mechanically created by a fan.
-These are further classified as forced-draft or induced-draft towers.
-In the forced-draft, a fan forces the air up through the tower, while in the induced-draft type, a fan sucks the air through the tower.
-The return water from a condenser is fed into trough/troughs at the top of the cooling tower.
-Water is spread over the cooling tower area through orifices on the trough.
- Spray nozzles are seldom used.
- The towers are generally filled with a network of staggered wooden slats, to break the fall of the water over a larger surface.
-This provides more intimate contact with the air that is forced up through the cooling tower.
-The condenser water is cooled while the air is warmed and its vapor content is increased.
- The air leaves the tower in a nearly saturated condition.
-Eliminators have to be used to minimize the carry-over of entrained water in the air stream.

Monday, January 5, 2009

type of condenser

1. Air-Cooled Condensers
There are two types under this category :
a. Natural Convection.
b. Forced-Air Type.

(a) Natural Convection

Air movement over the surface of condenser tubes is by natural convection. As air comes in contact with the warm-condenser tubes, it absorbs heat from the refrigerant and thus the temperature of the air increases. Warm air being lighter, rises and in its place cooler air from below rises to take away the heat from the condenser. This cycle goes on.

(b) Forced-Air Circulation

This type employs a fan or blower to move air over the condenser coil at a certain velocity. The condenser coil is of the finned type. Fins in such coils are closely spaced (ringing between 8 and 17 fin per inch). The space between the fins get choked with dirt and lint. Therefore to obtain optimum capacity, the fins should be kept clean. To circulate air over the condenser, fans are mounted on the shaft/pulley of the compressor motor. For bigger-capacity plants a separate motor is used to drive the fan or blower. This also applies to the hermetic-compressor units.


2. Water Cooled Condensers

There are three types of condensers which fall under this category: -

(a) Double Tube Condensers

The double tube condenser consists of two tubes so arranged that one is inside the other.Water is piped through the inner tube while the refrigerant flows in the opposite direction in the space between the inner and outer tubes. With this arrangement, some air-cooling of the refrigerant is provided in addition to the water cooling.

(b) Shell-And-Coil Condenser

The shell and coil condenser is made up of one or more bare-tube or finned-tube coils enclosed in a welded steel shell. The condensing water circulates through the coils while the refrigerant is contained in the shell surrounding the coils. Hot refrigerant vapor enters at the top of the shell and condenses as it comes in contact with the water coils. The condensed liquid drains off the coils into the bottom of the shell, which often serves also as the receiver tank. As a general rule, shell and coil condensers are used only for small installations up to approximately 10 tons capacity.

(c) Shell And Tube Condensers

The shell and tube condenser consists of a cylindrical steel shell in which a number of straight tubes are arranged in parallel and held in place at the ends by tube sheets. Construction is almost identical to that of the flooded-type shell and tube liquid chiller. The condensing water is circulated through the tubes, which may be either steel or copper, bare or extended surface. The refrigerant is contained in the steel shell between the tube sheets. Shell and tube condensers are available in capacities ranging from 2 tons up to several hundred tons or more.

Sunday, January 4, 2009

REFRIGERATION SYSTEM COMPONENTS_PART C

1. TYPE OF CONDENSERS
There are three types of condensers such as air-cooled, water-cooled and evaporative. As their names imply, air-cooled condensers use air as the cooling medium, water-cooled condensers use water as the cooling medium and the evaporative condenser is a combination of the above, i.e uses both water and air

REFRIGERATION SYSTEM COMPONENTS_PART B

1. CONDENSERS INTRODUCTION

The functions of the condenser are to de-superheat the high pressure gas, condense it and also sub-cool the liquid. Heat from the hot refrigerant gas is rejected in the condenser to the condensing medium-air or water. Air and water are chosen because they are naturally available. Their normal temperature range is satisfactory for condensing refrigerants.

REFRIGERATION SYSTEM COMPONENTS_PART A

COMPRESSORS

To reclaim the refrigerant vapor leaving the evaporator, it must be compressed to the pressure corresponding to a saturation temperature higher than the temperature of the naturally available air or water. A compressor is used for this purpose. The compressor also circulates the refrigerant through the system and its capacity determines the capacity of the refrigerating system as a whole.

Types of refrigeration compressors used are;

a) reciprocating
reciprocating compressors are available in sizes ranging from 1/8hp (approximately 9W input ) in small domestic units up to 250 tons or more in large industrial installations.

b) rotary
the displacement and compression of the refrigerant vapor is achieved in a rotary compressor by its circular or rotary motion, instead of a reciprocating motion.

c) screw
is a positive-displacement compressor. It consists of two meshing multi-start helically grooved rotors with very close tolerance clearances within a housing. Suction and discharge ports are provided at the either ends of the housing. The rotor whose shaft is connected to the motor is called the male rotor, and the other is the female rotor. When the male rotor rotates, the female rotor rotates in the opposite direction.

d) centrifugal
sometimes called ‘turbo-compressors’, are members of a family of turbo-machines that includes fans, propellers and turbines. These machines continuously exchange angular momentum between a rotating mechanical element and a steadily flowing fluid. For effective momentum exchange, their rotative speeds must be higher, but little vibration or wear results because of the steadiness of the motion and the absence of contacting parts. Centrifugal compressors are used in a variety of refrigeration and air-conditioning installations. Suction flow rates of compressors range between 60cfm and 30,000cfm, with rotational speeds between 1800rpm and 90,000rpm. As many as ten stages can be installed in a single casing. Side loads can be introduced between stages so that one compressor performs several functions at several temperature levels.

Friday, January 2, 2009

Thursday, January 1, 2009

Sample For Cooling Centralization System at PTSB (Kulim Polythecnic), Malaysia

figure 1.0: inlet/outlet water pipe

figure 1.1: Outdoor Unit for Split Unit

figure 1.2: distribution board


figure 1.3: Chiled Water Pump

Lighting Control System

Lighting Control System
- consists of a device,
- typically an embedded processor or industrial computer,
- that controls electric lights for a building or residence.
- Lighting control systems usually include one or more keypads interfaces.

These interfaces allow users the ability to toggle power to lights and fans, and dim lights.
A major advantage of a lighting control system over conventional lighting is the ability to control any device from any interface.
For example, a master touch panel might allow the user the ability to control all lights in a building, not just a single room. In fact, any lighting might be controlled from any location.
In addition, lighting control systems provide the ability to automatically power a device based on programming events such as:

1. Chronological time
-Chronological time is a time of day or offset from a time
2. Astronomical time
-Astronomical times includes sunrise, sunset, a day, or specific days in a month or year.
3. Room occupancy
-Room occupancy might be determined with motion detectors.
4. Alarm conditions
-Alarm conditions might include a door opening or motion detected in a protected area.
5. Program logic
-Program logic can tie all of the above elements together using constructs such as if-then-else statements and logical operators.

DIY Ductwork Installation

Typical Leak Search and Repair on Commercial A/C - Part I