Multi-factor coupling optimization of heat recovery effectiveness in a transcritical CO₂ heat pump

In the background of energy shortage and climate change, transcritical CO₂ heat pump(HTP) technology has attracted lots of attention because of its energy-saving and environmentally friendly advantages. In this research, an experimentally verified simulation model of transcritical CO₂ HTP is established to investigate multi-factor coupling optimization of heat recovery effectiveness(η_IHX). First, the coupling optimization mechanism of η_IHX and discharge pressure(p_dis) is analyzed. Moreover, this research explores the influence of η_IHX on heating capacity, power consumption, discharge temperature(t_dis), and internal heat exchanger(IHX) cost, and further proposes a comprehensive heat recovery index to optimize the above factors. Based on this index the optimal heat recovery effectiveness(η_IHX,opt) for each operating condition is obtained. Also, a failure boundary for the coupling optimization of the η_IHX is also indicated. In addition, the optimal discharge pressure(p_dis,opt) prediction correlation for different η_IHXs is proposed, which can be used for heat recovery effectiveness collaborative optimization control. Finally, a general method for evaluating IHX is provided. Taking Xi'an as an example, the optimal heat recovery area(A_IHX,opt) of this HTP system is 0.42m², with which the optimized HTP system operates safely at extreme operating conditions, resulting in an annual lucre of 1,211 CNY.