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Issues in Air Conditioning and Mechanical Ventilation System Design
By Low Cheng Yee, Ow Chee Sheng, Abu Hashim Abd Ghani, Hazran Husain, Tan Chee Fai
Air-Conditioning and Mechanical Ventilation( ACMV) systems provide thermal comfort and acceptable indoor air quality to the occupants of a building. Such systems are important in the structural design of residential, commercial, leisure, healthcare and industrial buildings where safe and healthy building conditions are regulated with respect to temperature, humidity and the introduction of conditioned fresh air from the outdoors.
Air conditioning [ 1 ] is the process of controlling the temperature and humidity in a building typically to maintain a cool atmosphere to suit human comfort. It is a system that removes heat from the air inside an occupied space, thus lowering the air temperature. The cooling is typically achieved through a refrigeration cycle. Air conditioning is also intended to maintain air cleanliness through a filtering element as well as its distribution within the space.
Ventilation is the process of introducing and circulating fresh air in any space to provide high indoor air quality. This process involves temperature control, oxygen replenishment and removal of moisture, odours, smoke, heat, dust, airborne bacteria and carbon dioxide. In addition, ventilation includes both the exchange of air to the outside as well as circulation of air within the building. It is one of the most important factors for maintaining acceptable indoor air quality within buildings.
ACMV System & Design Process
There are various types of air conditioning systems. Table 1 lists these and their cooling capacity. A typical system installed in Malaysia is the Water-Cooled Chilled Water System. It is a large system with design capacity in most cases above 200 Tons of Refrigerant( TR). The system architecture is illustrated in Figure 1.
The basic equipment for Water-Cooled Chilled Water System includes a Chiller, a Chilled Water Pump, a Condenser Water Pump, a Cooling Tower, Air Handling Units( AHU) and Fan Coil Units( FCU). Heat exchange takes place between the Condenser Water Open Loop, Chilled Water Closed Loop, and as well as between the Chilled Water Closed Loop and Air Circulation.
Type |
Application |
Tons of Refrigerant( TR) |
Window Unit / Split Unit |
Small room / space |
< 5 |
Air-Cooled Package Unit |
Small room and difficult to get |
5-20 |
|
water supply |
|
Water-Cooled Package Unit |
Medium system |
20-40 |
Air-Cooled Chilled Water System |
Medium large system |
40-100 |
Water-Cooled Chilled Water System |
Large system |
> 100 |
District Cooling |
Large system |
> 2000 |
Source: JKR’ s Guideline on Air-Conditioning System Design [ 2 ] Table 1: Types of Air-Conditioning Systems
34 VOL 71 JULY- SEPTEMBER 2017