Konsep Tata Udara

KONSEP TATA UDARA

KONSEP TATA UDARA

Andriyanto Setyawan

MENGAPA TATA UDARA DIPERLUKAN?MENGAPA TATA UDARA DIPERLUKAN?

Masalah tata udara bermula dari “apa yang menjadi objek kenyamanan”, yakni tubuh manusia.

Tubuh manusia merupakan mesin ajaib yang berusaha menjaga kenyamanan jika menghadapi perubahan parameter lingkungan.

Manusia akan menghasilkan panas pada saat melakukan suatu aktivitas.

Tubuh akan mempertahankan kenyamanan dengan cara membuang panas ke lingkungan sesuai dengan besarnya panas yang dihasilkan.

Jadi, suhu tubuh akan konstan.

MENGAPA TATA UDARA DIPERLUKAN?MENGAPA TATA UDARA DIPERLUKAN?

FAKTOR YANG MEMPENGARUHI KENYAMANANFAKTOR YANG MEMPENGARUHI KENYAMANAN

Dry bulb temperature

Relative humidity

Air cleanliness

Odor level

Mean radiant temperature

MENGATUR KENYAMANANMENGATUR KENYAMANAN

Dengan semua variabel di atas, maka mengatur kenyamanan manusia akan sangat sulit.

Namun, pengaturan kenyamanan dapat dilakukan jika manusia berada dalam ruangan yang terisolasi dari lingkungan.

JENIS SISTEM TATA UDARAJENIS SISTEM TATA UDARA

Sistem tata udara:

1. all-air

2. all-water

3. air-water

4. direct refrigerant

ALL-AIR SYSTEMALL-AIR SYSTEM

During the cooling mode of operation, this system supplies cool dehumidified air to the space to absorb heat and moisture.

The space temperature is usually maintained around 24°C and 50% relative humidity.

Air entering the space is typically drier (less moisture content than the space) and is between 10°C and 13°C.


The supply air is made cool and dry (relative to the conditioned space) by passing through a coil whose surface temperature is colder than the air.

The coil both cools the air, and removes moisture from the air.

The moisture condenses out of the air onto the cold coil surface, and is then drained away.


The cold supply air is transmitted from the coil to the conditioned space through a supply air duct system.

The duct system is insulated to prevent ambient moisture from condensing on the cold duct surfaces.

Power required to move the air through the duct system is provided by a supply air fan.


The use of a supply air terminal is required to provide good air motion in the conditioned space.

Good air motion facilitates absorbing the space-cooling load, and prevents draughts or dumping of cold air on the occupant.

Proper selection and location of the supply air terminal is therefore essential in providing “comfort” within the conditioned space.


Since air has been pumped into the space by the supply air fan, a return air grill must be provided to relieve warm air from the space.

If this were not done, the pressure would build in the space. This in turn would cause the fan to deliver less and less air until eventually the supply of air to the space would cease.

Without the proper amount of cool supply air entering the space, the heat load could not be absorbed, and the space temperature and humidity would climb above the control point.


In order to return the air back to the coil where it can be cooled once again, a return air duct system is required.


For systems having a very long return air duct system, a return air fan (Figure 17) is sometimes used.

The return air fan helps the supply air fan to move the air around the system by assisting in overcoming the air frictional losses in the ductwork.

When the return air reaches the coil it is cooled once more and returned to the space. The air cycle thus completes itself.


Dirt particles and pollen are removed from the circulating air by installing filters in the system.

The filters are available in a variety of types - depending upon the degree of filtration efficiency required.

The filters, coil, and supply air fan are typically combined into a manufactured product called an air handling unit (AHU).

Odor removal is handled by introducing fresh outdoor air into the air handling unit. This air is mixed with return air before being treated at the coil.


Since a quantity of fresh outdoor air is being brought into the system, an equal quantity of stale return air must be exhausted.

Dampers control the amount of outdoor air entering and exhaust air leaving the system.

The dampers are usually mechanically linked to assure a balance between the two.

If no air was exhausted, pressures developed by the fan in the system would prevent any fresh outdoor air from entering.


The source of cooling for the coil in the air handling unit is usually some type of water chiller that operates on the refrigeration cycle.

The chiller provides chilled water that is circulated by a pump to the coil in the air handling unit. Heat thus flows from the coil to the refrigeration equipment.


The final stage of the air conditioning system is to reject the heat removed from the space to the outdoor air.

One of several types of heat rejection devices transfers heat from the refrigeration equipment to the outdoor air. A cooling tower - with condenser water piping and a pump – is usually used.

The system could also use an evaporative condenser or an air-cooled condenser.


To complete the all-air system a heating cycle could be added.

Although there are several ways of heating the space, one typical means is to connect a boiler into the water piping serving the coil.

Heat thus flows from the water to the air, and from the air to the space.


All-air system components review

1. Central air handling unit

a. Coil

b. Filter

c. Fan

d. Outside air dampers

e. Return air dampers

2. Supply air ductwork

3. Supply air terminal

4. Return air grill

5. Return air duct

6. Possible return air fan

7. Refrigerant and/or water piping

8. Refrigerant equipment

9. Heat rejection equipment

10.Boiler


The problems associated with part-load control and heating or cooling with air have led to the development of several common all-air systems,

single-duct variable air volume,

dual conduit,

single-duct with reheat,

multizone,

double-duct constant volume

ALL-WATER SYSTEMALL-WATER SYSTEM

ILLUSTRATION

A 16 mm outside diameter water pipe is required to transfer 3.5 kW of cooling at 0.15 l/s, 1.8 m/s velocity, and 5.5 K water temperature rise.

To provide a similar 3.5 kW of cooling capacity with air, a 200 mm diameter round duct at 0.19 l/s, and 6.1 m/s velocity would be required. Or, a 125 mm diameter round duct at 0.19 l/s and 15.8 m/s velocity would be required.

Regardless of the velocity, the air duct requires more space.

This difference in space requirement is significant in multi-story buildings and retrofit type construction, and led to the development of all-water systems.


In an all-water system, water (the controllable fluid) is circulated to the space. Thus a special type of terminal unit (Figure 25) is required in the space.

Essentially each space requires a small air handling unit consisting of a coil, a fan and a filter.


Return air is drawn into the unit by the suction of the fan. The air is then filtered and passes on to the suction of the fan.

The fan blows the air across a coil, through which chilled water is flowing.

Common chilled water temperature ranges from 4.5°C to 7°C.

In passing through the coil, the air is cooled and dehumidified.

The grill in the top of the unit directs the cool air into the space and establishes the required room air motion.

The cool air mixes with the air in the space and absorbs the heat load. The cycle then repeats itself.


Heat removed from the space is then transferred to the refrigeration equipment through a network of chilled water pipes.

Heat rejection equipment then transfers the heat from the refrigeration equipment to the outdoors.

Heating is provided by activating a boiler and sending hot water instead of cold water to the coils in the terminal units.


Does the all-water system satisfy all the requirements for good comfort air conditioning?

Well, both space dry bulb temperature and relative humidity are treated at the terminal coil.

A degree of filtration is provided, however, owing to space constraints the quality of filtration cannot equal that available in a central station air handling unit.

Room air motion is provided by grilles located in the top of the terminal.

The only thing lacking is proper odor removal, because an all-water system circulates water, not air.

AIR-WATER SYSTEMAIR-WATER SYSTEM

The lack of odor removal leads us to the third basic system - the Air-Water System.

A separate air system is provided to supply fresh ventilation air to the space.

AIR-WATER SYSTEMAIR-WATER SYSTEM

The temperature of the air entering the space may be neutral (24°C) allowing the water system to handle all the heat entering the space.

Or, the temperature of the ventilation air may be lowered to 10-13°C and some of the space heat load can be absorbed by the ventilation air.

By doing this the water system can be smaller - handling the remainder of the space heat load.

DIRECT REFRIGERANT SYSTEMDIRECT REFRIGERANT SYSTEM

The most popular is window or through- the- wall packaged terminal air conditioners.

All external ductwork and piping are eliminated.

The single piece packaged unit incorporates an air handling unit, refrigeration cycle, and heat rejection equipment.

A typical two-position vent provides ventilation air.

Heating is either supplied as part of the unit (electric resistance), or a supplementary heating system such as baseboard heat is used.


As the size of the air conditioned space increases, maintaining proper room air motion with window or through-the-wall type units becomes difficult. The “rooftop” unit solves this problem.

The unit itself contains an air handling unit, refrigeration cycle, and heat rejection equipment.

A minimal external supply and return air duct system is required to complete the installation.


The external ductwork, supply air terminals, and return air grilles provide the flexibility in design required to meet the variety of building layouts encountered in larger commercial installations.

Rooftop units incorporate gas, electric resistance, or hot water heating as part of the unit design, or a separate supplementary heating system may be used, if desired.


When physically it is not possible to run ductwork through the roof to the conditioned spaces, the rooftop unit can be split into two separate units.

The outdoor unit, which may be mounted on the roof or alongside the building, contains the refrigeration cycle and heat rejection equipment.

The indoor unit is a small air handling unit and contains a fan, a coil, and filters.

Refrigerant piping connects the indoor coil of the air handling unit to the remainder of the refrigeration cycle located in the outdoor unit.

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Konsep Tata Udara