An experimental and a numerical investigation of HVAC system using thermosyphon heat exchangers for sub-tropical climates

•Enthalpy change across the CWC with THEs assist HVAC are higher than conventional system.•The precooling and reheat recovery increased at lower RH for all cases examined.•Reheat recovery rises with increasing the air velocity against increased fan power demands.•HVAC with THEs assist reducing energy saving to 5–35% and enhancing dehumidification 5–20%. Research has been undertaken on thermosyphon heat exchangers (THEs) for coolness recovery in sub-tropical climates conditions to explore the potential for energy savings and humidity control in HVAC systems through using THEs. This work includes an experimental and numerical model of THEs install in HVAC system. The performance of these individual systems was experimentally investigated throughout a wide range of outside design condition DBT (35–50)°C and RH (10–100)%. The outdoor tested parameters were the effect of RH, DBT, type of working fluid charged in THEs (Water, Methanol, Ethanol, Acetone, Butanol and R134a) and the air velocity. The experimental part involves a careful choose of the specification, design and construction of a THEs, an associates conventional chilled water coil, a fan and duct system, and a full range of properly calibrated sensors. The numerical model aims to develop a CFD model to define the flow characteristics (distribution of temperatures, moisture content and air velocity) for a THE in duct flow using momentum, turbulence model κ-ε, moisture content and energy equations in 3D by using FORTRAN code to reach the better results to simulate accurately the influence of adding one or more THEs to the existing HVAC system. This indicates the importance of fully integrating the design process right from the outset of the system design if THEs are to be installed into a HVAC system so as to give the maximum possible energy saving benefits in efficient air handling unit (AHU) designs. On the basis of this study, it is recommended that subtropical HVAC systems should be installed with THEs for dehumidification enhancement (5–20%) and energy saving (5–35%).