Principles of energy conversion and noise characterization in air ventilation ducts exposed to solar radiation

Abstract

The aim of this paper is to present a design tool with its guiding principles for energy conversion and noise characterization of an exterior rectangular duct often installed on building envelopes for pre-conditioning of fresh air. The energy conversion in an exterior rectangular duct is a function of solar irradiation, air gap width, mass flow rate and pressure, wall and air temperatures. A generalized two dimensional thermal analysis of an outdoor duct is presented by placement of surface and air nodes into two adjacent stacks of control volumes representing outer and inner walls of duct. A matrix solution procedure is adopted by constituting conjugate heat exchange of conduction, convection, radiation and ventilation heat transport. The rectangular duct model is built by a metallic exterior wall exposed to a steady heat flux generation due to solar heat gain and a well-insulated back panel as its counterpart wall. The model improves the results of traditional thermal models for the cases where: (i) there are sections of conjugate heat exchange; and (ii) stack effect due to thermal buoyancy necessitates 2-D nodal analysis for distant composite nodes. The design tool is supported with some numerical and experimental results of an airflow window with a photovoltaic (PV) solar wall installed in an outdoor test-room. Furthermore, some examples of noise characterization calculations are illustrated using devised noise measurement equations.