Indoor Air Quality Improvement Effectiveness of Air-side Economizer using Air Quality Index

Abstract

The object of this paper is to find a relationship between Indoor Air Quality (IAQ) and air-side economizer. When air-side economizer is operated, all outdoor air come into the space. However, if outdoor air quality exceeds IAQ standard, occupants will feel uncomfortable and even have a chance to develop following diseases: cardiac disorder, respiratory disease, etc. This paper supposes a method that reduces contaminants coming into the space when air-side economizer is operated. The main idea is to adopt Air Quality Index (AQI) as a constraint condition. AQI is determined by the most adverse influence factor to air quality among PM10, PM2.5, Ozone, Nitrogen dioxide and Sulfur dioxide. AQI from zero to fifty indicate good state and from fifty-one to one-hundred indicate moderate state. For example, if AQI exceeds certain level of harming human being, air-side economizer stops operation in spite of good temperature and humidity condition for air-side economizer operation. Simulation was developed using Energy Plus, Open Studio and Excel programs. This study selected two big cities: Seoul, South Korea and Shanghai, China. Simulation results of Shanghai showed PM2.5 concentration over 75 ㎍/㎥ (China’s grade II 24 average PM2.5 standard) was about 1028 hours/year and 879 hours/year when operating differential enthalpy economizer and differential enthalpy economizer restricted AQI respectively. HVAC energy consumption increased about 2.10% when operating differential enthalpy economizer restricted AQI. It was found that PM2.5 concentration over 75 ㎍ /㎥ period was reduced by 2.83% when operating differential enthalpy economizer restricted AQI.