Abstract

Abstract The adoption of highly efficient vapour-compression heating, ventilation, air conditioning and refrigeration (HVAC&R) systems is compulsory to achieve a low-carbon society. Expansion work recovery using a two-phase ejector is widely recognized as one of the most promising measures to improve the energy efficiency of HVAC&R units. This holds true for all operation conditions provided that an effective capacity control technique is implemented. In this work a thorough critical review on the current status of the presently available capacity control strategies for two-phase ejectors was carried out. In addition, their pros and cons as well as the comparison of their performance were reported. It was concluded that two-phase ejectors can be properly capacity controlled in large- and medium-scale vapour-compression units. However, a suitable capacity control mechanism for small-scale vapour-compression solutions still requires a major breakthrough and is being intensively discussed among experts in the field.

Highlights

  • Vapour-compression refrigeration, air conditioning and heat pump (RACHP) systems play a key role in modern life, being extensively employed for satisfying many fundamental human needs, such as food preservation, medicine storage, water heating and cooling/heating of living spaces

  • It was concluded that two-phase ejectors can be properly capacity controlled in large- and medium-scale vapour-compression units

  • The results indicated that low air conditioning (AC) loads can lead to poor pressure recovery ratios (PRRs), revealing the need for capacity control in order to keep the PRR at acceptable values over the whole range of AC demand

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Summary

Introduction

Vapour-compression refrigeration, air conditioning and heat pump (RACHP) systems play a key role in modern life, being extensively employed for satisfying many fundamental human needs, such as food preservation, medicine storage, water heating and cooling/heating of living spaces. Their massive use leads the RACHP sector to be dramatically energy intensive, contributing to global 6 warming significantly. A two-phase ejector used for expansion work recovery is well-recognized as a promising solution allowing for highly efficient vapour-compression RACHP systems (Elbel, 2011; Sarkar, 2012; Sumeru et al, 2012).

Capacity control techniques for two-phase ejectors
Adjustable needle-based capacity control technique
Air conditioning and refrigeration applications: performance and cooling
Heat pump applications
Proposed measures for adjustable needle-based capacity control technique
Multi-ejector based capacity control technique
Large-scale applications
Medium-scale applications
Adjustable vortex-based capacity control technique
Summary of the current status on the adjustable vortex-based capacity control
Comparison
Conclusions and future developments
Findings
*Declaration of Interest Statement
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