STRATEGIES TO IMPROVE INDOOR AIR QUALITY AND AIR CONDITIONING SYSTEM EFFICIENCY

Abstract

Indoor Air Quality (IAQ) has gained significant traction since the COVID-19 pandemic. Building owners and Facility Managers (FM) are facing pressures from building occupants and authorities to deliver an optimal IAQ that not only preserves the health and well-being of the occupants but also reduces the transmission risk and spread of infectious disease in the indoor environment. On the other hand, there is also an aggressive push towards energy conservation and reduction of carbon emission in the built environment sector. In this aspect, the authorities have aggressively raised the energy efficiency standards through the Green Mark 2021 certification. This created a conundrum because of the conflicting natures between IAQ and energy conservation. The conventional approach to achieve an optimal IAQ is through introducing additional outdoor air to dilute the carbon dioxide C02 and contaminant levels within the indoor environment. However, doing so will create the undesirable outcome of incurring additional energy to cool the outdoor air. ASHRAE 241 has reshaped this mindset by introducing the concept of equivalent clean airflow which comprises of both outdoor air and treated recirculated air. This allows building owners and FM to rely not only on the outdoor air, but also the treated recirculated air, which requires less energy to cool, to deliver an acceptable IAQ to the occupants. ASHRAE 241 has also further defined the additional requirements for an acceptable IAQ, which is to reduce the transmission risk and spread of infectious disease within the indoor environment. The study seeks to develop the framework for assessing the energy efficiency for delivering an acceptable IAQ, which is defined to the requirements of ASHRAE 62.2 and the additional requirements of ASHRAE 241. It applies actual data from an existing modern office building to calculate the energy efficiency of its air-conditioning system based on this framework and also explores the various strategies to drive further improvements to the energy efficiency. This includes efficient air distribution based on actual occupancy patterns so that cooling and equivalent clean airflow are delivered to the appropriate areas and at the appropriate time to the occupants. This minimizes cooling “over-provisions” and inefficiencies. The second strategy is to optimize the composition of the outdoor air so that it is just sufficient achieve the acceptable IAQ and keep the C02 limit to 700 ppm below outdoor ambient level. By relying less outdoor air and more treated recirculated air to deliver the equivalent clean air, less energy is incurred for cooling. The third strategy is the efficient treatment of the recirculated air by exploring the efficiency of other air filtration technologies other than the conventional mechanical fibrous MERV filters. This study aims to develop the concepts for energy efficiency for an acceptable IAQ and through this, provide building owners and FM the framework to evaluate and develop targeted solutions to enhance the energy efficiency performance of the air-conditioning system in this aspect.