COOLING | EVAPORATIVE SYSTEMS Figure 1: Schematic of hybrid device working in DEC mode of regenerative evaporative cooling for air conditioning purposes. This work considered a prototype of a dual-mode evaporative cooler (a two-in-one device) that can operate in either direct or regenerative mode, depending on the seasonal climatic condition. The paper reports on exergy and economic analyses that were performed to check the suitability of both modes of operation, direct and regenerative, for cities that are indicative of five international climate zones. The dualmode cooler works in either REC or DEC mode, depending on the outside condition. There is a reversible-flow wet air column used in both DEC and REC mode, and a dry air column only employed for REC mode the flow arrangement being dependent on the positions of the two vanes and actuation of secondary air exhaust fan, as shown in Figure 1 and Figure 2. In DEC mode, the air is cooled and humidified by passing only through the wet channel (with the secondary exhaust fan off). In REC mode, the outdoor air is cooled sensibly. A proportion of this cooled dry air is sent to provide space cooling and the remaining fraction of the air is drawn by the exhaust fan through the wet channel, where it is humidified and further cooled and discharged to atmosphere. The dual-mode evaporative cooler can be switched from DEC mode to REC mode and vice versa as the outdoor air conditions change. Sketch psychrometric processes for both modes of operation are shown in Figure 3. The month-by-month analysis indicated that the cooling energy in the DEC mode is higher than REC, so the direct mode may Figure 2: Schematic of hybrid device working in REC mode be more suitable for places with high sensible heat loads where the increase in moisture content is not an issue such direct evaporation methods are often used in applications such as data centres. The exergy efficiency for REC mode is higher than DEC mode and independent of the climatic zone. However, the annual cost of operating the REC mode is always higher, being significantly affected by electricity charges. The paper shows that, with automated switching operation (based on incoming air wet-bulb temperatures) to select between the DEC or REC mode, significant operational savings can be made, particularly in a composite climate zone, as across large parts of mid-northern India. CJ The full paper Energy, exergy and economic assessments of the dual-mode evaporative cooler for various international climate zones by Sarvesh Kashyap et al of the Indian Institute of Technology (BHU), Varanasi, India, may be seen in BSER&T at bit.ly/CJMar22BSERT TIM DWYER is CIBSE Journal technical editor and BSER&T managing editor References: 1 Mahmood M et al, Overview of the Maisotsenko cycle A way towards dew point evaporative cooling, Renewable and Sustainable Energy Reviews, Volume 66, December 2016, pages 537-555. Figure 3: Sketch psychrometry of DEC and REC processes 40 March 2022 www.cibsejournal.com CIBSE March 22 pp39-40 Evaporative cooling.indd 40 25/02/2022 15:20