Investigation of the aerodynamic and thermal performance of a Decentralised Air Handling Unit (DAHU) heat recovery using balls charge

Abstract

Decentralised ventilation solutions are applicable for both new and renovated buildings. This has a positive economic impact and helps ensure that there is sufficient fresh air even in limited indoor spaces. Unfortunately, there are no design guidelines for selecting wall-integrated decentralised air handling units (DAHUs) according to temperature, energy and aerodynamic requirements. The objective of this paper is to study the thermal and aerodynamic performance of an innovative DAHU using a regenerative thermal load. The analysis solves the main design issues and dimensions of the main and additional DAHU components: regenerative heat exchanger, fans, outdoor grille, indoor diffuser, grids and filters. Special attention is paid to the analysis of the thermal charge composed of balls using analytical and numerical methods. The pressure loss, the average heat transfer coefficient, the temperature of the airflow and the thermal charge of the heat exchanger are analysed. The numerical analysis is conducted using COMSOL Multiphysics to evaluate transient processes and the importance of the charge material. A comparison of analytical and numerical results shows that the heat transfer process of the regenerative heat exchanger charge can be estimated with sufficient accuracy in both cases, while differences in aerodynamic results are observed. In the case of the designed DAHU, the diameter of the elements is recommended to be 15 mm, taking into account the requirements for the pressure loss and, at the same time, to achieve a sufficiently efficient heat transfer process, the unit is designed with 60 m3/h fan that produces a pressure of 130 Pa. In general, this study contributes to the development of decentralised ventilation systems and the design of new ones.