دانلود رایگان مقاله انگلیسی تجزیه و تحلیل عملکرد عملیاتی سیستم تهویه مکانیکی خنک کننده با ذخیره سازی انرژی حرارتی پنهان - الزویر 2018

abstract

Latent Thermal Energy Storage (LTES) is a promising solution to reduce cooling energy consumption in buildings. Laboratory and computational studies have demonstrated its capabilities while commercial passive and active systems are available. This paper presents data and analysis of the performance of an active LTES ventilation system in two case-studies, a seminar room and an open plan office in the UK. Analysis using environmental data from the system’s control as well as additional space monitoring indicates that (a) internal temperature is maintained within adaptive thermal comfort limits, (b) acceptable Indoor Air Quality is also maintained (using metabolic CO2 as indicator) and (c) energy costs are low compared to air-conditioned buildings. Thermal and CFD computational studies indicate that purging and charging duration and associated set-points for room temperature as well as air flow rate are the important parameters for optimised performance for a given LTES design. These parameters should be optimised according to the use of the space and prevailing external conditions to maintain internal thermal comfort within upper (usually in the afternoon) and lower (usually in the morning) limits.

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.