5. Conclusions
This paper presented an active ventilation cooling system that can be suitable for newly built and retrofit applications. The system is a mechanical ventilation system which uses PCM thermal storage in the ventilation path and utilise night cool air for solidifying the PCM which in turn cools recirculated or external air during its melting phase. The two case-studies presented are both retrofit applications; a seminar computer room (with internal heat gains of 60W/m2) and an open plan office (with internal heat gains of 45W/m2). The system was installed in the existing plenum of the space with access to outside. Detailed monitoring of the spaces and thermal/CFD analysis indicated that the system can provide acceptable thermal comfort throughout at seating occupant level (0.7 m from the floor) in the moderate weather summer conditions of south and west England using adaptive thermal comfort limits.
A parametric analysis was carried out to investigate possible improved performance by an optimised control strategy. It was found through simulations that increasing air flow will keep internal temperatures more frequently within the set-point range without compromising thermal comfort and indoor air quality with a small electricity increase penalty. Considering the increase of night purge duration and charging in relation to room air temperatures, the maximum improvement to thermal comfort was obtained by increasing air flow rates with an extended night purge of 3 h and extended night charge mode with a night time internal space target temperature of 20 ◦C that runs through until the occupied period. This strategy achieved an improvement which is 3% less than the biggest reduction in the time spent over the upper thermal comfort limit achieved by the extended night charge with a target temperature of 18 ◦C. The control proposed also achieves smallest time spent below the lower thermal comfort limit, with 21% less time spent below the limit compared to the strategy of night charge to 18 ◦C.
