Modeling and Dynamic Simulation of a Hybrid Liquid Desiccant System with Non-Adiabatic Falling-Film Air-Solution Contactors for Air Conditioning Applications in Buildings

Juan Prieto,Antonio Atienza-Márquez,Alberto Coronas

doi:10.3390/en14020505

Abstract

This paper presents an experimentally validated, dynamic model of a hybrid liquid desiccant system. For this purpose, we developed new components for the air-solution contactors, which are of the non-adiabatic falling-film type with horizontal tubes (made of improved polypropylene) and the solution tanks. We also provide new experimental correlations for both the tube-solution heat transfer coefficient and the mass transfer coefficient on the airside as a function of the air velocity. To validate the model, the results obtained from the dynamic simulations were compared with those obtained by monitoring a demonstration unit installed in a sports center in Taipei (Taiwan). Once validated, the model was used to perform a sensitivity analysis at different operational conditions, such as the inlet water temperatures in the air-solution contactors and the LiCl mass fraction at which the system operates. The results of the sensitivity analysis were used to optimize the seasonal performance in terms of comfort and energy required by the system. Compared with a conventional air-handling unit that controls air temperature and humidity, the annual energy savings of the liquid desiccant systems are 17%.

Highlights

Liquid desiccant systems (LDS) are interesting air conditioning systems (HVAC) when dehumidification has an important role in the thermal loads because they can achieve a low level of humidity and be driven by low-grade heat sources [1,2,3,4]
Cooling coil that cools below the dew and temperature, it requires two devices: a cooling coil that cools the air below dew and temperature, it requires two devices: a cooling coil that cools the air below the dew point to dehumidify it to the set-point supply air humidity ratio, and a heatingthe coil to point to dehumidify it to the set-point supply air humidity ratio, and a heating coil to point to dehumidify it to the set-point supply air humidity ratio, and a heating coil to achieve the set-point supply air temperature
A CS is less efficient than an hybrid liquid desiccant system (HLDS), which achieve the set-point supply air temperature

Summary

Introduction

Liquid desiccant systems (LDS) are interesting air conditioning systems (HVAC) when dehumidification has an important role in the thermal loads because they can achieve a low level of humidity and be driven by low-grade heat sources [1,2,3,4]. The main components of an LDS are the absorber and the regenerator, where the moist air is dehumidified, and the liquid desiccant is regenerated, respectively. Both processes take place by direct contact between the humid air and the liquid desiccant material. The combination of LDS with vapor compression refrigeration systems is called a hybrid liquid desiccant system (HLDS). HLDS handles the temperature and humidity control more efficiently than conventional HVAC systems [6] For all these reasons, it has been shown that HLDS has enhanced COP by between 23.1% and 73.8% and made energy savings of between 26% and 80% [7]

Methods

Results

Discussion

Conclusion