Solar assisted natural ventilation with heat pipe heat recovery.

Natural passive stack ventilation (PSV) consumes no power and so produces no harmfulemissions, has no running cost, no noise of operation, requires little maintenance and becauseit involves no moving parts, operation is reliable. However, virtually all PSV systems aredesigned and constructed without incorporating heat recovery, leading to wasteful heat loss.The goal of the research reported here, is to develop a passive stack ventilation system withheat recovery for use in naturally ventilated buildings.The heat recovery unit is based on the heat-pipe principle. A recovery unit having asufficiently high efficiency and a very low pressure drop is aimed at. The drawback of anefficient heat recovery is, that it reduces the stack pressure by reducing the temperaturedifference between the supply and exhaust air flows, which can cause the ventilation system tofail. To avoid this problem, a solar chimney and a wind generator driven fan are integratedinto the system to assist the air flows and to maintain them on a sufficient level from theviewpoint of indoor air quality. On the other hand, for the air flows not to be too high, acontrol unit is added to the system. A pilot plant shall be constructed, where all abovementioned features are included and thjs plant shall be monitored for six months to find out itsperformance.Until now several versions of the heat recovery unit have been tested. The highest effectiveness has been around 55% with two banks of heat pipes and a flow velocity of 1 m/s. With the same velocity the pressure loss through a two bank section is 4.5 Pa. The solar chimney has been studied both theoretically and experimentally. According to computations, the performance of the chimney is not very sensitive to small changes in direction on bothsides of the south. Measurements indicate a 47 % increase in air flow compared to aconventional stack. The air flow control unit has been developed and tested. It works wellaccording to a control strategy specified for the PSV system. The work continues by designingand optimisation of the pilot plant.