Ventilation is the process of introducing outside fresh air into a building space. In an HVAC system, ventilation air is usually heated, cooled, and dehumidified, depending on the weather conditions [14]. As a result, ventilation air consumed a significant amount of HVAC energy usage. According to [15], maximum ventilation rates, or the amount of fresh air delivered by the Air Handling Unit (AHU) are proportional to the maximum design occupancy of the building. Even though the space is only partially occupied, the actual occupancy rarely reaches the maximum design occupancy. It is not uncommon for an AHU to continually operate at the maximum ventilation rate, and this issue frequently leads to excessive ventilation, resulting in higher than necessary energy consumption [16].
Building spaces do not always need to have 100% fresh air. The demand for fresh air should vary according to the number of people in a building space at any one time. When there are fewer people in a building, the need for fresh air may be reduced. According to [17], DCV is a way of introducing varied amounts of fresh air depending on actual occupancy patterns. The mechanism allows the rate of ventilation to be adjusted constantly and automatically. The control is essentially performed by the use of sensors that respond to changes in occupancy. The output of the sensor is fed into a control device that regulates the AHU damper, which controls the pace of outdoor airflow through the ventilation system to ensure consistent air quality.
People would continuously exhale CO2 during working, walking or even resting. The amount of CO2 produced would be increased proportionally to the number of persons in a space. According to [18], a high CO2 level in a room (> 1000 ppm) suggests insufficient ventilation and low levels of CO2 (< 600 ppm) according to [19] may indicate that the ventilation rate could be reduced while maintaining good IAQ and reducing energy consumption. Many studies on human perception have been conducted to determine the relationship between optimal CO2 levels and occupant comfort. [20] showed a significant deterioration in health performance corresponding to a CO2 level of more than 1000 ppm in their study. According to ASHRAE Standard 62–2001, Section 6.1.3, comfort criteria are likely to be met if the ventilation rate did not exceed 1,000 ppm of CO2 level.
ASHRAE 62, 2004 edition, revised Section 6.1.3 to include a 700-ppm difference in indoor and outdoor CO2 concentrations as an acceptable level of human bio-effluents based on a specific ventilation rate (15 cfm/person) and outdoor CO2 concentration of 300 ppm. In this regard, CO2 sensor plays a vital role and is essential for DCV. It measures the CO2 concentration in the room and outputs the command variable. DCV based on CO2 concentrations in a space could maintain the air quality and improve the energy efficiency of the HVAC system [21]. The traditional methods for controlling airflow using a damper at the fan outlet reduced total energy consumption, but they also reduced fan static pressure and waste fan power [22]. In view of this matter, ventilation is a cornerstone of healthy and energy-efficient building design, balancing the need for indoor air quality (IAQ) with energy conservation. In office environments, particularly those situated in tropical climates, this balance is crucial yet challenging due to the high humidity and temperature conditions inherent to these regions. While DCV systems have been recognized for their potential to optimize energy use and maintain IAQ by adjusting ventilation rates based on occupancy, the bulk of research on DCV has been conducted in temperate climates. These studies underscore the system's capability to significantly reduce energy consumption while ensuring indoor air remains within healthful parameters.
However, a comprehensive review of the existing literature reveals a conspicuous gap: there is a lack of research focusing specifically on the application and effectiveness of DCV systems in tropical office spaces. This oversight is notable, as the unique climatic conditions of tropical regions, characterized by their consistently high temperatures and humidity levels can influence the performance and efficiency of DCV systems in ways that differ markedly from temperate settings. The absence of detailed studies in this area leaves a critical void in our understanding of how DCV systems can be optimized for tropical climates, thus limiting the applicability of current knowledge to a significant portion of the global context.