Control optimization of R744 duo-temperature supermarket refrigeration system with multi-ejector

doi:10.11949/0438-1157.20191076

Abstract

Abstract:

In order to make the duo-temperature R744 supermarket refrigeration system operate at maximum efficiency in any ambient temperature, a multi-ejector circuit (including gas-gas ejector and gas-liquid ejector) is added to the R744 parallel compression refrigeration system to ensure that the system can still operate at higher efficiency in high ambient temperature, and automatically switch between parallel compression refrigeration mode and boost refrigeration with multi-ejector mode with the change of ambient temperature. The thermodynamic model of the system is established. The calculation results show that when the ambient temperature is lower than 17.32℃, the parallel compression refrigeration system mode is adopted; when the ambient temperature is higher than 17.32℃, the transcritical boost refrigeration system with multi-ejector mode is adopted. When the ambient temperature changes from 21.1℃ to 36℃, the COP of the multi-ejector refrigeration system is 15.91%—32.61% higher than that of the parallel refrigeration system.

Key words: carbon dioxide, optimal design, model, ejector, supermarket, transcritical refrigeration

摘要：

为了使R744双温超市制冷系统在任何环境温度下都能以最高效率运行，在R744平行压缩制冷系统中增加了一个多喷射器组回路（包括气气喷射器和气液喷射器），以确保系统在高温环境下仍能以较高的效率运行。并在环境温度变化的情况下，通过自动控制阀切换多喷射增压制冷模式和平行压缩制冷模式，为此建立了系统的热力学模型。计算结果表明，当环境温度低于17.32℃时，采用平行压缩制冷模式;当环境温度高于17.32℃时，采用多喷射增压制冷模式。当环境温度从21.1℃变化到36℃时，多喷射器制冷系统的COP比平行压缩制冷系统高15.91％~32.61％。

关键词: 二氧化碳, 优化设计, 模型, 喷射器, 超市, 跨临界制冷

CLC Number:

TB61⁺7

Wei CHEN, Meihong YU, Hongxia ZHAO. Control optimization of R744 duo-temperature supermarket refrigeration system with multi-ejector[J]. CIESC Journal, 2020, 71(7): 3266-3277.

陈威, 于梅红, 赵红霞. 优化控制R744多喷射器双温超市制冷系统[J]. 化工学报, 2020, 71(7): 3266-3277.

Figures/Tables 13

Fig.1 Schematic diagram and P-h diagram of PCR system

Fig.2 Schematic diagram and P-h diagram of MEBR system

Fig.3 Relationship of COP, ambient temperature and outlet pressure of gas cooler of PCR system

Fig.4 Relationship of COP, ambient temperature and outlet pressure of gas cooler of MEBR system

Table 1 Summary of some important correlations of Gas coolers/condensers

系统	关联式	应用范围
PCR系统	$P g c = 47.3 ? b a r$ (9)	$t a m b ≤ 2 ℃$
PCR系统	$P g c = P s a t t a m b + 10 ?$ (10)	$2 ℃ < t a m b < 21.1 ℃$
MEBR系统	$P g c = 29.2642 + 1.9678 t a m b + 0.0099 t a m b 2$ (12)	$t a m b ≥ 21.1 ℃$
	$P g c = 75 ? b a r$ (11)	$t a m b ≤ 21.1 ℃$
	$P g c = 24.8642 + 2.3441 t a m b + 0.00198 t a m b 2$ (13)	$t a m b > 21.1 ℃$
二氧化碳循环中温零售食品制冷系统的优化控制^[7]	$P g c ? = 44.97 ? b a r$	$t a m b < - 5 ℃$
	$P g c ? = 1.352 t a m b + 51.1$	$- 5 ℃ ≤ t a m b ≤ 15 ℃$
	$P g c ? =$ 72.05 $b a r$	$15 ℃ < t a m b < 17 ℃$ for subcritical
	$P g c ? =$ 80 $b a r$	$15 ℃ < t a m b < 17 ℃$ for transcritical
	$P g c ? =$ 80 $b a r$	$17 ℃ ≤ t a m b ≤ 29 ℃$
	$P g c ? = 2.558 t a m b + 5.792$	$t a m b > 29 ℃$
常规增压制冷系统^[34]	$t g c = 0.6429 t a m b + 13.571$ , $P g c = 1.6633 t g c + 26.763$	$18 ℃ ≤ t a m b ≤ 40 ℃$
二氧化碳的解决方案^[15]	$P g c = 43.92 ? b a r$	$t a m b < 4 ℃$
	$P g c = P s a t t a m b + 5$	$4 ℃ ≤ t a m b ≤ 17 ℃$
	$t g c = 0.9 t a m b + 4.7$ , $P g c = 1.6633 t g c + 26.763$	$17 ℃ < t a m b ≤ 27 ℃$
	$t g c = t a m b + 2$ , $75 ?? b a r ≤ P g c ≤ 110$ bar （optimized）	$t a m b > 27 ℃$
R744增压系统^[10]	$P g c = 45.02 ? b a r$	$t a m b < 0 ℃$
	$P g c = P s a t t a m b + 10 ?$	$0 ℃ ≤ t a m b ≤ 18 ℃$
	$P g c = 69 ? b a r$	$18 ℃ < t a m b < 22 ℃$
	$P g c = 75 ? b a r$	$22 ℃ ≤ t a m b ≤ 25 ℃$
	$P g c = 2.9211 + 0.10003 t a m b + 0.00254 t a m b 2$	$t a m b > 27 ℃$ for standard transcritical booster system
	$P g c = 2.2487 + 0.13516 t a m b + 0.0021 t a m b 2$	$t a m b > 27 ℃$ for transcritical booster system with bypass compressor
	$P g c = 0.362 + 0.25237 t a m b + 0.0004 t a m b 2$	$t a m b > 27 ℃$ for transcritical booster system with upstream expansion valve

Table 1 Summary of some important correlations of Gas coolers/condensers

系统	关联式	应用范围
PCR系统	$P g c = 47.3 ? b a r$ (9)	$t a m b ≤ 2 ℃$
PCR系统	$P g c = P s a t t a m b + 10 ?$ (10)	$2 ℃ < t a m b < 21.1 ℃$
MEBR系统	$P g c = 29.2642 + 1.9678 t a m b + 0.0099 t a m b 2$ (12)	$t a m b ≥ 21.1 ℃$
	$P g c = 75 ? b a r$ (11)	$t a m b ≤ 21.1 ℃$
	$P g c = 24.8642 + 2.3441 t a m b + 0.00198 t a m b 2$ (13)	$t a m b > 21.1 ℃$
二氧化碳循环中温零售食品制冷系统的优化控制^[7]	$P g c ? = 44.97 ? b a r$	$t a m b < - 5 ℃$
	$P g c ? = 1.352 t a m b + 51.1$	$- 5 ℃ ≤ t a m b ≤ 15 ℃$
	$P g c ? =$ 72.05 $b a r$	$15 ℃ < t a m b < 17 ℃$ for subcritical
	$P g c ? =$ 80 $b a r$	$15 ℃ < t a m b < 17 ℃$ for transcritical
	$P g c ? =$ 80 $b a r$	$17 ℃ ≤ t a m b ≤ 29 ℃$
	$P g c ? = 2.558 t a m b + 5.792$	$t a m b > 29 ℃$
常规增压制冷系统^[34]	$t g c = 0.6429 t a m b + 13.571$ , $P g c = 1.6633 t g c + 26.763$	$18 ℃ ≤ t a m b ≤ 40 ℃$
二氧化碳的解决方案^[15]	$P g c = 43.92 ? b a r$	$t a m b < 4 ℃$
	$P g c = P s a t t a m b + 5$	$4 ℃ ≤ t a m b ≤ 17 ℃$
	$t g c = 0.9 t a m b + 4.7$ , $P g c = 1.6633 t g c + 26.763$	$17 ℃ < t a m b ≤ 27 ℃$
	$t g c = t a m b + 2$ , $75 ?? b a r ≤ P g c ≤ 110$ bar （optimized）	$t a m b > 27 ℃$
R744增压系统^[10]	$P g c = 45.02 ? b a r$	$t a m b < 0 ℃$
	$P g c = P s a t t a m b + 10 ?$	$0 ℃ ≤ t a m b ≤ 18 ℃$
	$P g c = 69 ? b a r$	$18 ℃ < t a m b < 22 ℃$
	$P g c = 75 ? b a r$	$22 ℃ ≤ t a m b ≤ 25 ℃$
	$P g c = 2.9211 + 0.10003 t a m b + 0.00254 t a m b 2$	$t a m b > 27 ℃$ for standard transcritical booster system
	$P g c = 2.2487 + 0.13516 t a m b + 0.0021 t a m b 2$	$t a m b > 27 ℃$ for transcritical booster system with bypass compressor
	$P g c = 0.362 + 0.25237 t a m b + 0.0004 t a m b 2$	$t a m b > 27 ℃$ for transcritical booster system with upstream expansion valve

Fig.5 Relationship between compressor mass flow and ambient temperature

Fig.6 Relationship between compressor power consumption and ambient temperature

Fig.7 Relationship between intermediate throttling pressure and ambient temperature in PCR system

Fig.8 Performance index of ejector

Fig.9 Relationship of ejector outlet pressure, efficiency and ambient temperature

Fig.10 Relationship of COP of PCR system and MEBR system and ambient temperature

Fig.11 Schematic diagram of OCMER system

Fig.12 Analysis of the average annual COP of four typical cities in China

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