A hybrid indirect evaporative cooling-mechanical vapor compression process for energy-efficient air conditioning

Qian Chen,M Kum Ja,Muhammad Burhan,Faheem Hassan Akhtar,Muhammad Wakil Shahzad,Doskhan Ybyraiymkul,Kim Choon Ng

doi:10.1016/j.enconman.2021.114798

Qian Chen, M Kum Ja + Show 5 more

Open Access

https://doi.org/10.1016/j.enconman.2021.114798

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Abstract

The indirect evaporative cooler (IEC) is deemed an effective and sustainable alternative to existing mechanical vapor compression (MVC) chillers in cooling applications. However, IEC is a passive cooler that has no effective control over the supply air temperature and humidity. Also, the performance of IEC degrades severely when the humidity of the air is high. To overcome these limitations, we investigate a hybrid process that connects IEC and MVC in tandem. The outdoor air is firstly pre-cooled in the IEC by recovering energy from the room exhaust air, and then it is further processed to the desired condition using MVC. Such a hybrid IEC-MVC process benefits from IEC’s high energy efficiency and MVC’s capability of humidity and temperature control. A pilot IEC unit with the cross-flow configuration is firstly constructed and tested under assorted outdoor air conditions. Employing the room exhaust air as the working air in the wet channels, the IEC simultaneously cools and dehumidifies the outdoor air. Under the operating conditions considered, the outdoor air temperature can be reduced by 6–15 °C, and the humidity ratio drops by 0.5–4 g/kg. The coefficient of performance (COP) for IEC is 6–16, leading to an overall COP of 4.96–6.05 for the hybrid IEC-MVC process. Compared with a standalone MVC, the electricity consumption can be reduced by 19–135%.

Highlights

With the increase of global energy consumption for air conditioning (AC) [1,2], searching for energy-efficient and environmentally-friendly cooling technologies is becoming more and more critical
In addition to coefficient of performance (COP), we evaluate the percentage of cooling load that can be provided by the indirect evaporative cooler (IEC) unit, as it helps to quantify the energysaving potential of using IEC as the pre-cooler
The wet channel is supplied with room air, which has a temperature of 23 ± 1 ◦C and a humidity ratio of 11 ± 1 g/kg

Summary

Introduction

With the increase of global energy consumption for air conditioning (AC) [1,2], searching for energy-efficient and environmentally-friendly cooling technologies is becoming more and more critical. The indirect evaporative cooler (IEC) is an effective and sustainable alternative to existing mechanical vapor compression (MVC) systems in cooling ap plications [3]. It uses the evaporation of water as a natural driving force, and the energy consumption is very low [4]. One important research direction for IEC is the development of mathematical models for performance prediction and optimization. Dizaji et al [5] presented a novel mathematical model for a regenerative IEC based on the wet-surface theory. Cui et al [8] developed a modified log mean temperature difference (LMTD) method, and it allows for quick evaluation of IEC performance. The discrepancy between the predicted temperature drop and the experiment measurement was 5%

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