CFD ANALYSIS OF DISPERSION OF CO2 IN OCCUPIED SPACE: EFFECT OF SENSOR POSITION

Open Access
Author:
Pei, Gen
Graduate Program:
Architectural Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
June 15, 2018
Committee Members:
  • Donghyun Rim, Thesis Advisor
  • William P Bahnfleth, Committee Member
  • Gregory Scott Pavlak, Committee Member
Keywords:
  • CFD
  • IAQ
  • Sensor position
  • CO2-based DCV
Abstract:
Demand-controlled ventilation (DCV) becomes more attractive to building system designers due to its potential to save energy while maintaining acceptable indoor air quality (IAQ). One of the most widely used DCV systems is based on the measurement of carbon dioxide (CO2) concentration. In a CO2-based DCV system, the supply airflow rate varies according to the signals from CO2 sensors. However, limited information is available for the relationships between building environmental factors and the CO2 dispersion in rooms as well as the performance of sensors positioned at various locations. This paper presents a numerically based study focusing on the effect of sensor position in rooms that are ventilated with CO2-based DCV systems. A total of eight realistic scenarios were examined using experimentally validated Computational Fluid dynamic (CFD) models. The parametric analysis results revealed the impacts of three major parameters: 1) ventilation strategy (mixing vs. displacement), 2) air change rate, and 3) number of occupants on the CO2 distribution and sensor performance. The results show that the CO2 transport and the sensor readings notably vary with the ventilation strategy, air change rate and number of occupants. The CO2 sensors placed at the exhaust show good performance for a DCV system with mixing ventilation while showing less accuracy with displacement ventilation. The results also suggest that sensors situated at wall at the breathing height (e.g., 1.2 m) can improve the measurement accuracy in displacement ventilation system compared to sensors located at the exhaust. The results indicate that the performance of the sensors placed on the office desk varies significantly with indoor airflow conditions and a careful prediction of the performance should be conducted before using them.