Performance of heat recovery in passive stack ventilation systems.

The large heat loss from Passive-stack ventilation (PSV) systems quite often makes natural ventilation systems unattractive and it is therefore desirable to implement heat recovery in PSV stacks. As the stackpressure is usually about a few Pascal, it is crucial that the heat recoveryunit used in a PSV system produces even lower pressure loss, which is extremely difficult to achieve with the conventional plate heat exchangers. This work is concerned with an a low pressure-loss heat recovery device based on heat pipes. The heat pipe is a completely passive device without power consumption and its simple construction also means that it also has a low initial cost. Experimental investigation has been carried out using four types of heat pipe heat exchangers. Heat recovery efficiency of over 60% has been obtained using two banks of exchangers. It was also found that the efficiency decreases with increasing air velocity. Spine fin exchangers provided much lower efficiency than plain fin systems. Louver fined system produced the greatest efficiency but also the largest pressure loss. The wire-fin type produced a lower pressure loss than the plain fin type although its efficiency is also slightly lower. It was concluded that the wire fin type provided the optimum balance between the requirements for low pressure loss and high efficiency.