Comparative trials of ventilation systems for humidity control.

Three ventilation systems were installed in the EA Technology Ventilation Test House: passive stack ventilation (PSV), mechanical ventilation with heat recovery (MVHR) and extract fans. Humidifiers were used to simulate occupancy and the performance of the systems monitored over the winter of 1993/94. The aim was to assess the effectiveness of different ventilation systems in controlling indoor humidity at a level that will inhibit the growth of house dust mites. The PSV system produced low ventilation rates in typical winter weather; excessive ventilation loss in cold windy weather was prevented by the high standard of air tightness in the house. The MVHR system has the advantage of producing consistent ventilation in all weathers. Total energy consumption of the systems was similar. MVHR was the most effective in reducing indoor humidity and in coping with peaks of moisture production; this is to be expected given its greater ventilation rate. Extract fans dealt well with moisture peaks, but should continue to run after moisture production has finished. Detailed results are presented for the variation in humidity between rooms for each ventilation system.