Thermal performance analysis of a Carnot battery driven by waste heat from a liquid-cooled data center coupled with a heat pump and a transcritical CO2 power cycle

doi:10.19799/j.cnki.2095-4239.2024.0934

Abstract

Abstract:

To recover waste heat from liquid-cooled data centers and advance the development of green data centers utilizing renewable energy, this study proposes a Carnot battery system driven by waste heat from liquid-cooled data centers. The system consists of a heat pump and a transcritical CO₂ power cycle. A thermodynamic model is developed to evaluate the system's thermal performance under various operating conditions. The results indicate that under design conditions, with an energy storage capacity of 100 kW × 5 h and R245fa as the heat pump working fluid, the heat pump achieves a COP of 5.23. Additionally, the power generation efficiency based on heat pump heating reaches 13.28%, and the round-trip efficiency is 67.64%. The study further investigates the effects of key operating parameters—including heat pump evaporator superheat, high and low water tank temperatures, power generation cycle pump outlet pressure, and condensing temperature—on system performance. The findings reveal that round-trip efficiency increases with higher superheat in the heat pump evaporator but decreases as the power generation cycle's hot and cold water tank temperatures, pump outlet pressure, and condensing temperature rise. Notably, when the condensing temperature of the power generation cycle falls below 18 ℃, round-trip efficiency can exceed 100%. A sensitivity analysis of the system's operating parameters further highlights that the condensing temperature of the power generation cycle has the most substantial impact on round-trip efficiency.

Key words: Carnot battery, heat pump, transcritical CO₂ power generation, liquid-cooled data center, waste heat recovery

CLC Number:

TK 02

Yun TAN, Ruochen DING, Xiaoyu ZHOU, Xinxing LIN, Wen SU, Bo XU, Hong WU. Thermal performance analysis of a Carnot battery driven by waste heat from a liquid-cooled data center coupled with a heat pump and a transcritical CO₂ power cycle[J]. Energy Storage Science and Technology, 2025, 14(4): 1471-1480.

Figures/Tables 13

Fig. 1

Fig. 2

Table 1

Energy balance equations for the main components of the Carnot battery"

工况	部件名称	能量平衡方程
热泵循环	蒸发器1	$m f 1 = Q h 1 / (h 1 - h 4)$
	冷凝器1	$Q c o n d 1 = m f 1 ⋅ (h 2 - h 3) = m w 1 ⋅ (h h, w a t e r - h l, w a t e r)$
	压缩机	$W c o m = m f 1 ⋅ (h 2 - h 1) / η g / η m$
	压缩机	$η i s, c o m = (h 2 s - h 1) / (h 2 - h 1)$
	节流阀	$h 3 = h 4$

储热回路	加压水罐	$V w a t e r = t c h a r g e ⋅ m w 1 ⋅ 3600 = t d i s c h a r g e ⋅ m w 2 ⋅ 3600$
储热回路	加压水罐	$M w a t e r = t c h a r g e ⋅ m w 1 ⋅ 3600 = t d i s c h a r g e ⋅ m w 2 ⋅ 3600$

跨临界CO₂ 发电循环	泵	$η i s, p = (h 9 s - h 8) / (h 9 - h 8)$
	泵	$W p = m f 2 ⋅ (h 9 - h 8) / η g / η m$
	透平	$η i s, t u r = (h 5 - h 6) / (h 5 - h 6 s)$
	透平	$W t u r = m f 2 ⋅ (h 5 - h 6) ⋅ η g ⋅ η m$
	加热器1	$Q h 1 = m f 2 ⋅ (h 10 - h 9)$
	加热器2	$Q h 2 = m w 2 ⋅ (h h, w a t e r - h l, w a t e r) = m f 2 ⋅ (h 5 - h 10)$
	冷凝器2	$Q c o n d 2 = m f 2 ⋅ (h 6 - h 7)$

Table 1

Table 2

Fig. 3

Table 3

Table 4

Fig. 4

Fig. 5

Fig. 6

Fig. 7

Fig. 8

Table 5

References 22

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工况	运行参数	符号	数值
数据中心液冷循环	冷却液	—	YL-70
	冷却液进口温度	T_1′	60 ℃
	冷却液出口温度	T_4′	50 ℃
	冷却液压力	P_coolant	0.1 MPa

热泵循环	工质	—	R245fa
	蒸发器窄点温差	PPTD_evap	5 ℃
	蒸发器出口过热度	T_sup,evap	10 ℃
	蒸发器压损	∆P_evap	0.03 MPa
	压缩机等熵效率	η_is,com	85%
	冷凝器1窄点温差	PPTD_cond1	5 ℃
	冷凝器1热端端差	∆T_ht,cond1	10 ℃
	冷凝器1压损	∆P_cond1	0.04 MPa
	轴承机械效率	η_m	98%
	电机效率	η_g	98%

储热回路	高温水箱温度	T_h,water	100 ℃
	高温水箱温度损失	∆T_h,loss	1 ℃
	加压水压力	P_water	0.2 MPa
	低温水箱温度	T_l,water	60 ℃

跨临界CO₂ 发电循环	净发电量	W_net	100 kW
	放电时间	t_discharge	5 h
	冷凝温度	T_cond2	25 ℃
	冷凝器2出口温度	T₇	24 ℃
	泵出口压力	P₉	10 MPa
	加热器1压力损失	∆P_h1	0.05 MPa
	加热器2压力损失	∆P_h2	0.01 MPa
	泵等熵效率	η_is,p	90%
	透平等熵效率	η_is,tur	82%
	加热器1窄点温差	PPTD_h1	5 ℃
	加热器2窄点温差	PPTD_h2	10 ℃

冷却水循环	冷却水进口温度	T_7′	18 ℃
	冷却水出口温度	T_6′	22 ℃
	冷却水压力	P_cool	0.1 MPa

性能指标	单位	文献[22]	本工作所建模型	相对误差/%
热泵COP	—	4.96	4.94	0.34
动力循环热效率	%	10	10.27	2.70
系统往返效率	%	50	48.51	2.98

参数	数值
充电参数	304.31 kW×2.43 h
放电参数	100 kW×5 h
数据中心产热量/kW	1297.83
冷凝器1放热量/kW	1590.08
加热器2吸热量/kW	753.08
冷凝器2放热量/kW	1942.50
压缩机耗电功率/kW	304.31
透平输出功率/kW	152.96
泵耗电功率/kW	52.96
热泵COP	5.23
基于热泵供热的发电效率/%	13.28
基于吸热量的发电效率/%	4.88
储电效率/%	67.64
加压水总质量/t	82.81

运行参数	热泵COP		基于热泵供热的发电效率/%		基于吸热量的发电效率/%		往返效率/%
运行参数	范围	平均值	范围	平均值	范围	平均值	范围	平均值
热泵蒸发器过热度/℃	4.79~5.23	0.09	—	—	—	—	62.04~67.64	1.12
高温水箱温度/℃	5.35~5.01	-0.07	13.52~12.96	-0.11	4.83~4.94	0.02	70.41~63.42	-1.40
低温水箱温度/℃	5.23~5.04	-0.04	—	—	—	—	67.64~64.95	-0.54
发电循环冷凝温度/℃	—	—	27.18~13.28	-0.87	8.17~4.88	-0.21	138.44~67.64	-4.43

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Thermal performance analysis of a Carnot battery driven by waste heat from a liquid-cooled data center coupled with a heat pump and a transcritical CO₂ power cycle

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