Abstract
The main objective of this study is to investigate the indoor air quality enhancement performance of two different liquid desiccant and evaporative cooling-assisted air conditioning systems, such as the variable air volume (VAV) system with the desiccant-enhanced evaporative (DEVap) cooler, and the liquid desiccant system with an indirect and direct evaporative cooling-assisted 100% outdoor air system (LD-IDECOAS), compared with the conventional VAV system. The transient simulations of concentration variations of carbon dioxide (CO2), coarse particles, and fine particles (PM10 and PM2.5) in a model office space served by each system were performed using validated system models that were found in the literature. Based on the hourly thermal loads of the model space predicted by the TRNSYS 18 program, each air conditioning system was operated virtually using a commercial equation solver program (EES). The results indicated that the LD-IDECOAS provided the lowest annual indoor CO2 concentration among all the systems considered in this research, while the VAV system with DEVap cooler exceeded the threshold concentration (i.e., 1000 ppm) during the cooling season (i.e., July, August, and September). For the indoor particulate contaminant concentrations, both liquid desiccant and evaporative cooling-assisted air conditioning systems indicated lower indoor PM2.5 and PM10 concentrations compared with the reference system. The LD-IDECOAS and the VAV with a DEVap cooler demonstrated 33.3% and 23.5% lower annual accumulated indoor PM10 concentrations than the reference system, respectively. Similarly, the annual accumulated indoor PM2.5 concentration was reduced by 16% using the LD-IDECOAS and 17.1% using the VAV with DEVap cooler.
Highlights
Liquid desiccant and evaporative cooling technologies are attracting particular interest for developing an alternative air conditioning as an alternative to conventional air conditioning systems that are based on the vapor compression refrigeration cycle [1,2]
This was because, in the desiccant-enhanced evaporative (DEVap) system, 30% of the dehumidified process air should be exhausted to the outside at the dew point indirect evaporative cooler (DP-IEC) before the conditioned zone; the occupants would experience a lack of ventilation
During the heating season, when the minimum required outdoor air was introduced in each air conditioning system, the indoor CO2 concentration was maintained below the threshold (i.e., 1000 pFpigmur)ein8. aInlldcoaosreCs,Oa2scsohnocewnntraintioFnigmuorneth8.ly box plot chart
Summary
Liquid desiccant and evaporative cooling technologies are attracting particular interest for developing an alternative air conditioning as an alternative to conventional air conditioning systems that are based on the vapor compression refrigeration cycle [1,2]. Lee et al [4] suggested a novel air handling system by integrating the desiccant-enhanced evaporative (DEVap) cooler developed by Kozubal et al [3] with the conventional variable air volume (VAV) system. They replaced the cooling coil of the VAV system with the DEVap cooler that consists of an internally cooled liquid desiccant (LD) dehumidifier and a dew point indirect evaporative cooler (DP-IEC). Lee et al suggested a desirable annual operation sequence of their proposed system, and demonstrated that their system could provide air conditioning to the conditioned zone without chiller operation, in addition to 2–3% of the primary energy reduction compared with the conventional VAV system. The LD-IDECOAS indicated 68% less annual operating energy consumption over the conventional VAV system
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