Numerical study on the thermal performance of earth-tube system in ningbo china

Abstract

Earth tube system (ETS), which capitalizes on the high soil thermal inertia, is gaining popularity in recent years as an alternative to conserve energy for space cooling/heating in buildings. This paper presents a numerical study of the thermal performance of the basic ETS in Ningbo, China, through Computational Fluid Dynamic (CFD) modeling and then assesses its corresponding energy saving potential in the local climate. The primary impact parameters, i.e. pipe diameter and inlet air velocity, are discussed in terms of their influences on the ETS thermal performance. It is found that (1) the outlet temperature increased as the inlet velocity was higher as a result of reduced contact time between soil and airflow; (2) the outlet temperature increased when the diameter of the pipe was larger due to more airflow was passed through in a unit time; (3) a balance between outlet temperature required and volumetric airflow rate stipulated by regulations needed to be established provincially; (4) the ETS was estimated being able to provide cooling of 1185kWh in summer period (i.e. 86% of the projected energy demand) in Ningbo and attained a COP of 3.3. The overall research indicated the ETS has the potential to become the effective energy saving technology in Ningbo buildings and thus could contribute to the related carbon emission reduction in China.