Analysis of performance of CO2 transcritical heat pump system with mechanical subcooling and ejector

doi:10.16085/j.issn.1000-6613.2020-2077

Abstract

Abstract:

The use of ejector can reduce energy loss and improve the performance of cycle in heat pump. The ejector was integrated with the existing cycle,CO₂ transcritical heat pump system with mechanical subcooling that major cycle with ejector and auxiliary cycle with ejector were proposed respectively. A thermodynamic model was developed to analyze the performance of system when using three different terminals, traditional designed radiator (TDR), floor-coil radiator (FCR) and small temperature difference fan-coil unit (STD-FCU). The new systems were compared with CO₂ basic system (BASE) and CO₂ mechanical subcooling heat pump system (MSHPS). Four typical climate cities were selected in China and heating seasonal performance factor (HSPF) were discussed during the heating season. The results indicated that a maximum coefficient of performance (COP) exists at optimum major discharge pressure, auxiliary discharge pressure and subcooler outlet temperature in mechanical subcooling system. The system with STD-FCU as the terminal has the highest COP. Compared with the COP of BASE system under rated condition, MSHPS (AWE) and MSHPS (MWE) can increase by up to 21.18% and 26.66% respectively. And compared with the COP of MSHPS, the new system can increase by about 2.62% and 9.53% respectively. MSHPS (MWE) has better performance improvement effect. MSHPS (MWE) can still operate under severely cold conditions. The system with ejector has higher HSPF in different temperature regions. The HSPF improvement effect of the cold regions represented by Harbin is most obvious. The system with TDR as the terminal is more suitable for the cold region of high latitude, and the system with STD-FCU as the terminal is more suitable for the area of low latitude. In addition, refrigerants used in auxiliary cycle affect the overall performance of the system. CO₂ achieves the best effect in MSHPS (AWE) and R717 achieves the best effect in MSHPS (MWE).The system can reach higher COP when R32/R1234yf is employed in auxiliary cycle but can’t achieve the best effect.

Key words: CO₂ heat pump, ejector, mechanical subcooling, terminal, coefficient of performance(COP), heating seasonal performance factor(HSPF)

摘要：

热泵循环中引射器的使用能减少能量损失，改善循环性能。在已有机械过冷循环的基础上加入引射器，本文提出主循环带引射器［MSHPS（MWE）］和辅循环带引射器［MSHPS（AWE）］的跨临界CO₂机械过冷热泵系统。通过建立热力学模型，对系统使用散热片（TDR）、地盘管（FCR）和小温差风机盘管（STD-FCU）3类不同末端的性能进行分析。将该系统与CO₂基本系统（BASE）、CO₂机械过冷系统（MSHPS）进行了对比，并选取了我国4个典型气候城市，对其供暖期间的运行进行了季节供热性能系数（HSPF）分析。结果表明，在额定工况下，机械过冷系统均存在最优主、辅循环排气压力和最优过冷器出口温度，使系统性能系数（COP）最高；其中以STD-FCU为末端的系统具有最高COP。通过与已有系统的对比，表明在额定工况下，MSHPS（AWE）和MSHPS（MWE）较BASE系统的COP最高分别能提升约21.18%和26.66%，较MSHPS最高能分别提升约2.62%和9.53%，MSHPS（MWE）具有更好的性能提升效果。MSHPS（MWE）系统在严寒工况下仍能运行，带引射器的系统在不同温区均具有更高的HSPF。以哈尔滨为代表的严寒地区的HSPF改善效果最明显，以TDR为末端的系统更适用于高纬度的严寒地区，以STD-FCU为末端的系统更适用于低纬度的地区。此外，辅循环工质的种类会影响系统的整体性能，MSHPS（AWE）中使用CO₂的提升效果最好, MSHPS（MWE）中使用R717的提升效果最好。使用混合工质R32/R1234yf的系统具有更高的COP，但提升效果并非最优。

关键词: CO₂热泵, 引射器, 机械过冷, 散热末端, 性能系数, 季节供热性能系数

CLC Number:

TK124

DONG Liwei, LI Minxia, YAO Liang, MA Yitai, ZHAN Haomiao. Analysis of performance of CO₂ transcritical heat pump system with mechanical subcooling and ejector[J]. Chemical Industry and Engineering Progress, 2021, 40(10): 5431-5440.

董丽玮, 李敏霞, 姚良, 马一太, 詹浩淼. 带引射器的跨临界CO₂机械过冷热泵系统性能分析[J]. 化工进展, 2021, 40(10): 5431-5440.

Figures/Tables 13

References 26

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末端	散热末端形式	供水温度/℃	回水温度/℃
1	TDR^［14］	65	40
2	FCR^［14］	40	35
3	STD-FCU^［15］	35	30

末端	散热末端形式	供水温度/℃	回水温度/℃
1	TDR^［14］	65	40
2	FCR^［14］	40	35
3	STD-FCU^［15］	35	30

参数	城市
参数	哈尔滨	北京	西安	上海
纬度位置^［14］	45°45ˊN	39°48ˊN	34°81ˊN	31°18ˊN
供热室外设计温度^［14］/℃	-24.2	-7.6	-3.4	-0.3
供热设计负荷^［19］/W·m^-2	66.6	61.8	63.1	89.8
除霜损失系数^［20-21］	1	0.965	0.955	0.89

参数	城市
参数	哈尔滨	北京	西安	上海
纬度位置^［14］	45°45ˊN	39°48ˊN	34°81ˊN	31°18ˊN
供热室外设计温度^［14］/℃	-24.2	-7.6	-3.4	-0.3
供热设计负荷^［19］/W·m^-2	66.6	61.8	63.1	89.8
除霜损失系数^［20-21］	1	0.965	0.955	0.89

末端	BASE	MSHPS		MSHPS（AWE）			MSHPS（MWE）
末端	COP	COP	COP增量（BASE）/%	COP	COP增量（BASE）/%	COP增量（MSHPS）/%	COP	COP增量（BASE）/%	COP增量（MSHPS）/%
TDR	2.001	2.375	18.691	2.432	21.539	2.400	2.542	27.036	7.032
FCR	2.229	2.619	17.497	2.682	20.323	2.405	2.829	26.918	8.018
STD-FCU	2.539	2.937	15.675	3.014	18.708	2.622	3.217	26.703	9.534

Analysis of performance of CO₂ transcritical heat pump system with mechanical subcooling and ejector

带引射器的跨临界CO₂机械过冷热泵系统性能分析

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