Enhancing the efficiency of a steam jet ejector chiller for chilled ceiling

Abstract

• Steam jet ejector chillers (SJECs) can be suitable for buildings with high solar gains. • SJEC was combined with radiant chilled ceiling instead of convective cooling terminal. • Increasing evaporation temperature by using chilled ceiling improved COP. • This allows lower generation temperature resulting in smaller solar collector areas. Steam jet ejector chillers (SJECs) can be a suitable cooling technology in buildings where solar heat gains constitute a significant part of the cooling load. In this study, an SJEC was combined with a radiant chilled ceiling (CC) instead of traditionally used convective cooling terminals in an effort to increase the coefficient of performance (COP) by increasing the supply water temperature to the terminal ( T water,sup ) and thus the evaporation temperature. Experiments were used to verify a mathematical model of SJEC. The model was combined with T water,sup obtained from heat transfer calculations in three types of CC performed by a verified software. The COP of the ejector cooling system was 0.25 and 0.38 for R718 (water) and R1233zd, respectively, at a generation temperature of 130 °C and T water,sup of 7 °C, assuming a fancoil. Increasing T water,sup to 9 °C, which was considered to be the lowest T water,sup theoretically possible for CC involving pipes underneath the surface, improved COP by up to 14% while providing a maximum cooling capacity of about 80 W per m 2 of room area. Further increasing T water,sup to 15 °C improved the COP by 50% compared to the fancoil, while covering cooling loads of at least 40 W per m 2 . The estimated reduction in generation temperatures due to increased COP was up to 12% ( T water,sup = 9 °C) and 37% ( T water,sup = 15 °C). This means a lower energy input needed for the cooling machine, which allows a smaller solar collector area.