Effect of Pipework Circuit Length on Run-Around Heat Recovery Systems Performance

The need for use of outside fresh air according to standard ASHRAE 62-1989 (1999) Ventilation for acceptable inside air quality، increases fresh air usage and heat load، thus system performance and equipment costs increase. Energy recovery studies such as run-around heat recovery is useful for optimization of energy consumption in HVAC systems. Several theoretical analyses on run-around heat recovery systems have been done by researchers، but generally heat losses from pipework circuit was ignored. The main purpose of this paper is to investigate the effect of pipework circuit length on runaround heat recovery systems performance by a precise model based on system hydraulic and thermodynamic relations. Simulation results showed that heat transfer coefficient is linearly decreased by increasing distance of hot and cold streams and pump power is increased too. If pipework circuit pipelines are insulated properly، effect of pipework circuit length on run-around heat recovery systems performance will be negligible.