Basic AHU System Planning

Basic AHU System Planning

Basic Problems

The rapid development in various sectors of urban & industrial activities has a positive impact as well as a negative impact on environmental conditions. The negative impacts that arise are often realized only as temporary impacts from the development and development process, but in less than five years, it turns out that the environmental impacts in question have had a fairly large negative effect on various benchmarks of the quality of life of urban communities, which include the level of degradation of health and environmental comfort. The environment as a human habitation has a major influence on the behavior and habits of the people who live in it. Talking about environmental issues, then one of the things that can't be left behind is the issue of air.

In areas that are quite densely active, air is a big problem that is quite a concern for regional leaders, one of which is DKI Jakarta as the capital city of the country, with its location on the coast and with a population of almost 15 million people, it is not surprising that Jakarta has air conditions that are very good. not good (hot and dirty).

Good urban spatial planning can provide various comforts for its residents. Living a happy, healthy and able to develop themselves optimally is the result of this comfort. Good air conditions and able to cover all activities, both human activities and production activities will be able to make all activities more productive.

To achieve these conditions, air conditioning is needed. Air conditioning is the process of conditioning the air so that it reaches the ideal temperature and humidity. Air conditioning systems are generally divided into two main groups, namely air fresheners for work comfort and industrial air conditioners. Air conditioning is still a luxury today, but has become a necessity that must be met. Without this system, many activities cannot be carried out properly, especially activities carried out indoors, because the activities carried out in the room will certainly provide a heat load to the room itself. the air in the room becomes uncomfortable. Most air conditioning units are used for comfort (confort air conditioning), namely to create comfortable air conditions for people in the room. With this air refresher, it is hoped that the air will be fresh so that employees can work well, hospital patients will be more comfortable and residents will be more comfortable. While the refreshment system for industry is designed to obtain temperature, humidity and air distribution in accordance with those required by the process as well as production equipment or machinery used in a production process as well as for a place or room to store raw materials and products.

One of the industries that really need a refresher system or air conditioning system is the textile industry. In a textile industry, the production machines used function to process cotton into yarn and process yarn into cloth. During the process, many fine fibers from the cotton are flying in the air.

In the basic method of making textile materials such as yarn and cloth, a production area that has a certain humidity and temperature is needed, because the production in the form of yarn and cloth will have a certain quality when processed at a certain temperature and humidity, in addition to the water content in the air. too little will also cause dust or dirt to fly easily so that it can make the workers in the room uncomfortable. In addition, dust can also cause damage to production machines.

However, if the humidity in the room is too high, the threads will become too wet because they contain a lot of water which causes the threads to break easily, and will eventually interfere with production activities and reduce the quality of the production itself.

In addition, the demands of the increasingly fierce competition in the industrial world require producers to produce more and faster production, good quality and efficiency in production activities.

Therefore, here the author tries to design a system that is intended to regulate and control humidity in the production area. Here the author only limits the humidity setting because Air Condition is used for temperature regulation.

Schematic of Air Handling Unit System

Airflow Theory

The shape and airflow in the room can be divided into two types, namely one-way airflow (unidirectional) and random/turbulent airflow (non-directional). In certain applications, mixed flow is also used, which is a combination of the two types of airflow mentioned above.

1. One-way airflow

One-way airflow can be defined as airflow that moves with uniform velocity and forms parallel flow lines. The type of flow in which the streamlines are straight and parallel is the simplest plane flow. This type of flow is called uniform flow.

One-way airflow is divided into vertical and horizontal airflow. By using one-way airflow, all contaminant particles that are less than 15 m in size will be swept away and can be prevented from entering the air stream. Disturbance in the form of objects or movement of objects in the course of the air flow will cause turbulence.

2. Turmonth Flow

Turbulent flow is an air flow with different speeds at each point, with a Reynolds value above 2300. In turbulent air flow, air moves in random directions so that the number of particles contained in it is also more than the one-way flow.

3. Mixed air flow

Mixed airflow is a combination of one-way airflow and turbulent airflow in one room. One-way airflow is only used in certain areas in the room that are considered the most critical, while other areas use turbulent airflow. This air system is only used on workstations and curtain units.

Healthy & Comfortable Criteria

The human body is an organism that can adapt, even the human body is able to function in quite extreme thermal conditions. The diversity of temperature and humidity of the outside air is often beyond the limits of the body's adaptability, therefore a healthy and comfortable environment is needed.

Thermal Comfort

The human body continuously produces heat that must be channeled, it aims to keep the body temperature constant. The process of transferring heat from the human body to the surrounding space can occur by convection (carried by the surrounding air) and radiated (from the body to the surface of the environment with a lower temperature).

Air Quality

Air quality in a room is regulated by removing impurities inside and outside the room and then entering fresh or new air. Ventilation plays an important role in both processes of air circulation. Ventilation creates a significant burden on equipment or cooling.

Estimated Heat Loss and Gain

In designing a system, we must take into account the type of material to be used, the geometric factor of the building and the climatic factor. Calculation of heat loss and gain is useful for calculating the capacity required in various heating and air conditioning equipment to maintain comfortable indoor conditions.

Design Conditions

Design conditions that need to be considered in calculating the air load include air humidity and also the intensity of sunlight. To calculate the maximum cooling load, it is necessary to know the geographical location and direction of the room to be calculated. The heat load received by a room depends on the orientation of the room, for example for a room facing east it can occur at 8 am, while for a room in the west, the maximum load will occur at 4 pm. Peak loads from the sun's heat for south-facing rooms will occur more in winter for northern latitudes, than in summer.

Dry Bulb Temperatur

Dry bulb temperature is the temperature value that is read on the thermometer used at the actual temperature in that place. For example, if the thermometer shows the number 28 °C, it means that the temperature in the room is 28 °C.

Wet Bulb Temperatur

Wet bulb temperature is the temperature value that is read on the thermometer used at the temperature where the bulb on the thermometer is wrapped in a wet cloth. Usually the wet bulb measurement is used to calculate the room humidity value at the actual value by comparing the wet bulb temperature with the dry bulb temperature assisted by the humidity table, so the actual humidity value will be found.

Dew Point Temperatur

The temperature at which the air containing water vapor begins to condense and the water vapor separates and collects somewhere to be then discharged or channeled to the disposal site so that the compressed air becomes dry (dry air).

Definition & Working Principle of Air Handling Unit

Air conditioning system or commonly known as "Air Handling Unit" is a system designed to condition the air in a room based on the air load and heat in the room. One of the goals of this air conditioning system is to create comfort and also the needs of the conditioned room.

Air conditioning systems currently receive special attention in their use in terms of efficiency, both in terms of cost, energy and time.

This time I will use two phases in this system which are divided into two different rooms in one system, namely:

1. Air Filter Room, the air returning from the room is drawn by one or more fans. The air from the room is dirty air that contains dust and various types of impurities left over from the production process. In this room, the return air is filtered from all dust and dirt and then the dirt will be accommodated into a container. The clean air will then be discharged out or flow back to the next phase according to the command from the control system.

2. Air Washer Room, the air that has flowed from the Air Filter Room and has been cleaned of dust and dirt is then combined with fresh air from outside the room. Once mixed, the two air will enter into the Air Washer Unit, here the air will be processed to adjust the temperature and humidity according to the conditions to be achieved.

Air Handling Unit Components

1. Fan/Blower
2. Filters
3. Pump
4. Damper/air valve
5. Washer unit
6. Cooling tower
7. Chiller units
8. Ducting
9. Piping
10. Sensor & control system

Fundamentals of Design Calculation

1. Fan Selection

Motor power

P = (Q x Total Pressure)  / (ƞ x 10)

Des : P   : Motor power (Watt)

         Q  : Airflow capacity (m3/h)

          ƞ  : Motor efficiency (safe limit between 75-85%)

2. Filter Size

A = (Q / 3600) / v

Des : A   : Filter surface area (m2)

         Q  : Airflow capacity (m3/h)

          v  : Air flow speed (average 4 - 6 m/s)

3. Pump Power

H = ha + Dhp + hl + (v2/2g)

Des : H      : Pump total head (m)

         ha     : Total static head (m)

         Dhp  : The difference in the pressure head acting on the two water surfaces (m)

         hl      : Various head losses in pipes, valves, turns, joints, etc.

        v2/2g : Head out speed (m)

4. Damper Size

A = (Q / 3600) / v

Des : A   : Damper cross-sectional area (m2)

         Q  : Airflow capacity (m3/h)

          v  : Air flow speed (average 4 - 6 m/s)

5. Ducting Size

A = √Q / (3600 x v)

Des : A   : Cross-sectional area of ducting (m2)

         Q  : Airflow capacity (m3/h)

          v  : Air flow speed (average 4 - 6 m/s)

6. Pipe Diameter

D = √(4/π) x (Q/v)

Des : D   : Pipe diameter (m)

         Q   : Airflow capacity (m3/h)

          v  : Air flow speed (average 4 - 6 m/s)

7. Cooling Load

Q = 0.59 x V x I x E

Des : Q   : Cooling load (btu/h)

         V   : Room volume (m3)

          I   : Use 10, if the room is isolated / on the ground floor / next to another room

                 Use 18, if the room is not insulated / on the top floor

          E  : Use 16, if the longest wall is facing north

                 Use 17, if the longest wall faces east

                 Use 18, if the longest wall faces south

                 Use 20, if the longest wall faces west

8. AC Unit Electric Power

P = (Q/9000) x 746 x 1.3

Des : P    : Electrical power (watt)

         Q   : Cooling loadn (btu/h)

Thus a few basic knowledge & calculations in planning an AHU (air handling unit) system. May be useful.