Heat recovery with low pressure loss for natural ventilation.

Heat recovery is difficult to implement in passive stack ventilation because the pressure loss is usually too high in conventional heat exchangers compared with the stack pressure. Laboratory investigation and computer simulation have been carried out on a low pressure-loss heat recovery device based on heat pipes which is suitable for application in passive stack systems and other systems where a low pressure loss is essential. It was found that heat recovery efficiency decreased with increasing air velocity. Heat recovery efficiency of close to 50% have been achieved using a single-bank plain-fin unit and the efficiency of a double bank unit was 40% higher than that of a single bank unit. It was also found that the pressure loss coefficient reduces as velocity increases but the reduction is around 10% over the entire range of common velocities in natural ventilation systems. The pressure loss across the plain fin unit is in the order of 1 Pa at a flow velocity of 1 m/s. The wire fin and plain fin type heat-pipe units are superior to other types investigated in this study.