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Experimental study on vapor injection air source heat pump with internal heat exchanger for electric bus
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Energy Procedia 158 Energy Procedia 00(2019) (2017)4147–4153 000–000 www.elsevier.com/locate/procedia
10th International Conference on Applied Energy (ICAE2018), 22-25 August 2018, Hong Kong, 10th International Conference on Applied Energy China(ICAE2018), 22-25 August 2018, Hong Kong, China
Experimental study on vapor injection air source heat pump with Experimental study on vapor injection air source heat pump with The 15th International Symposium on District Heating and Cooling internal heat exchanger for electric bus internal heat exchanger for electric bus Assessing the feasibility of using the heat demand-outdoor temperature function heatTian demand forecast a a d Xinxin Hana,b,c , Huimingfor Zouaa *long-term , Hongbo Xudistrict , Changqing ,Wei Kang Xinxin Hana,b,c, Huiming Zoua * , Hongbo Xua, Changqing Tiana ,Wei Kangd I. Andrić *, A. Pina , P. Ferrão , J. Fournier ., B. Lacarrière , O. Le Corre
a,b,c a Technology anda Key Laboratory of Cryogenics, b c c Beijing Key Laboratory of Thermal Science and Technical Institute of Physics and Chemistry, a CAS,and Beijing 100190,China Beijing Key Laboratory of Thermal Science and Technology Key Laboratory of Cryogenics, Technical Institute of Physics and Chemistry, b a Polytechnic University, Jiaozuo CAS, Beijing 100190,China IN+ Center for Innovation, Technology Henan and Policy Research - Instituto Superior454000, Técnico,China Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal c b b University of Polytechnic Chinese Academy of Sciences, Beijing 100049, Henan University, Jiaozuo 454000, China Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520China Limay, France d c Changchun Railway Vehicles Co., Ltd, Changchun 130062, Jilin, China c CRRCÉnergétiques University ofetChinese Academy -ofIMT Sciences, Beijing 100049, Département Systèmes Environnement Atlantique, 4 rue AlfredChina Kastler, 44300 Nantes, France d CRRC Changchun Railway Vehicles Co., Ltd, Changchun 130062, Jilin, China a
Abstract Abstract Abstract InDistrict this paper, a vapor injection ASHP unit addressed is developed for electric is experimentally studied heating networks are commonly in the literaturebus as and one the of heating the mostperformance effective solutions for decreasing the In this paper, a vapor injection ASHP unit is developed for electric bus and the heating performance is experimentally with the adjustment of compressor frequency under different working conditions. The optimum compressor frequency depends greenhouse gas emissions from the building sector. These systems require high investments which are returned through studied the heat with adjustment of compressor frequency under working conditions. The optimum depends on thetheworking andclimate at higher inlet air temperature condenser the higher compressor frequency isfrequency better. the sales. Due to conditions the changed conditions anddifferent buildingof renovation policies, heat demandcompressor in the future couldUnder decrease, on the working and at higher inlet airoftemperature condenser the higher compressor frequency is better. Under working condition of -20/20℃ and 85 Hz, COP the ASHP of with vapor injection is 1.60 and improves by 14.5% against thatthe of prolonging the conditions investment return period. working condition -20/20℃ Hz,the COP of and the ASHP with injection 1.60 and improves 14.5% against thatThe of no-injection. Under working condition -20/5℃ 85 it is 2.22 decreases by 2.9% against by that of no-injection. The main scope ofofthe this paper isand to 85 assess feasibility of Hz, using thevapor heatand demand –isoutdoor temperature function for heat demand no-injection. Under the working condition -20/5℃ and 85 Hz, it is 2.22 and decreases by 2.9% against that of no-injection. The results show that the advantage of vapor injection is reflected in the conditions of higher temperature difference between the forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 results show that the in advantage of vapor is typology. reflected the conditions of more higher temperature between the evaporator and condenser. According to theinjection comparison of COPCin , vapor injectionscenarios is beneficial as thedifference heating can't buildings that vary both construction period and Three weather (low, medium, high) andcapacity three district more beneficial as the capacity evaporator and condenser. the comparison of COPdeep). meet the heating demand. C, vapor renovation scenarios wereAccording developedto(shallow, intermediate, Toinjection estimateis the error, obtained heatheating demand valuescan't were meet the heating demand. compared with results from a dynamic heat demand model, previously developed and validated by the authors. Copyright © 2018 Elsevier Ltd. only All rights reserved. The results showed that when weather change is considered, the margin of error could be acceptable for some applications © 2019 The Authors. Published by Elsevier Ltd. Copyright ©in2018 Elsevier Ltd. Allresponsibility rights than reserved. Selection and peer-review under of for the all scientific committee of the 10th International Conference onrenovation Applied (the error annual demand was lower 20% weather scenarios considered). However, after introducing This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) th International Conference on Applied Selection and peer-review under responsibility of the scientific committee of the 10 Energy (ICAE2018). scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). Peer-review under responsibility of the scientific committee of ICAE2018 – The 10th International Conference on Applied Energy. Energy (ICAE2018). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the Keywords: heathours pump;of electric bus; heating decrease vapor in theinjection; numberairofsource heating 22-139h during performance the heating season (depending on the combination of weather and Keywords: vapor injection; air source heat electrichand, bus; heating performance renovation scenarios considered). Onpump; the other function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. * Corresponding author. Tel.: +86-10-82543697.
E-mail address:author. [email protected]. * Corresponding Tel.: +86-10-82543697. Keywords: Heat demand; Forecast; Climate change E-mail address: [email protected]. 1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility the scientific 1876-6102 Copyright © 2018 Elsevier Ltd. All of rights reserved. committee of the 10th International Conference on Applied Energy (ICAE2018). Selection and peer-review under responsibility of the scientific committee of the 10th International Conference on Applied Energy (ICAE2018). 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of ICAE2018 – The 10th International Conference on Applied Energy. 10.1016/j.egypro.2019.01.817
Xinxin Han et al. / Energy Procedia 158 (2019) 4147–4153 Author name / Energy Procedia 00 (2018) 000–000
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1. Introduction In cold region the heating performance of conventional air source heat pump (ASHP) degrades sharply due to the increase of compression pressure ratio and compressor suction specific volume. Vapor injection is considered as an effective way to improve the heating performance and reliability of ASHP at extreme low ambient temperature [1-3]. There are two basic types of vapor injection ASHP, flash tank (FT) and internal heat exchanger (IHX). The researches show that although the efficiency of ASHP with IHX is not as good as that of ASHP with FT, the flexibility of its adjustment on intermediate pressure makes it more practical of applications [4-6]. The earlier researches mainly focus on vapor injection ASHP applied for building air conditioning system. In recent years there are many studies on its application for electric cars due to its quick development. Jung et al. [7] numerically studied the vapor injection ASHP for electric vehicle. The results showed that at -10℃ ambient temperature the COP of vapor injection heat pump with a single- and dual-injection ports compressor against that of the no-injection heat pump improve by 7.5% and 9.8%, respectively. Qin et al. tested a vapor injection ASHP with a refitted scroll compressor for electric vehicle [8-9]. The results showed that the heating capacity improves by 28.6% compared with the conventional system at -20℃ ambient temperature. The above studies all showed vapor injection heat pump is effective for electric vehicle application. However, they are mainly for electric car and there are limited literatures for electric bus. Except for some similar characters, such as movability and vibration, the heat pump for electric bus still has some differences. It is a packaged unit other than a split unit and it can use return air like residential heat pump. Therefore, the research and development of vapor injection ASHP is significative for the application of electric bus in cold region. In this paper a vapor injection ASHP for electric bus was developed and the heating performance was experimentally investigated at low ambient temperature. According to the practical heating demand, the effect of inlet air temperature of condenser and compressor frequency on the heating performance was studied. 2. Experimental bench setup The experimental test bench of vapor injection ASHP was shown in Fig. 1. The unit has two independent cycle systems and the two indoor heat exchangers are shared by these two systems. Thus, as one system is on defrosting mode, the supply air temperature can be kept by the other system operating on heating mode. Because the two independent systems were symmetrical and all the components were identical, the experiment measurement was just focus on one system. ·
P T P T
·
four-way reversing valve T
four-way reversing valve
T
comp. P T
P T
one-way valve
EXV1
outdoor HX
P T M
gas-liquid separator
HX
T
P
P
T
comp.
P T
outdoor HX
P T
T
P T P T
P T
one-way valve
EXV1 HX T
gas-liquid separator
T
T M T T P
pressure
T
temperature
M
mass flow rate
P T
EXV2
EXV2
·
indoor HX
P T
P T
·
T
T
P T
indoor HX
Fig. 1 The schematic diagram of the test system
The heating performance of the unit was measured in an enthalpy difference lab. The working fluid in the unit was R410a. Table 1 shows the experimental test conditions. The two electronic expansion valve (EEV) in main branch and vapor injection branch both have 500 steps. When the EEV in vapor injection branch is set to 0, no refrigerant could inject into the compressor. That is no-injection cycle. When it is set among 1~500, the heat pump
Xinxin Han et al. / Energy Procedia 158 (2019) 4147–4153 Author name / Energy Procedia 00 (2018) 000–000
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can operate in vapor injection mode. In the experiment the superheat of evaporator and internal heat exchanger can be adjusted by the two EEV. The temperature was measured by T-type thermocouple with uncertainty of ±0.5 °C. The pressure was measured by the pressure transducer with uncertainty of ±0.5%. The refrigerant mass flow rate was measured by Coriolis flow meter with uncertainty of ±0.2%. Table 1. Test conditions Outdoor dry temperature/℃
Indoor dry temperature/℃
Compressor frequency/Hz
Outdoor air flow rate/(m3/h)
Indoor air flow rate/(m3/h)
-5
20, 15, 10, 5
70
3500
2000
-20
20, 15, 10, 5
60, 70, 80, 85
3500
2600
3. Results and discussions 3.1 The effect of inlet air temperature of condenser Fig.2 shows the heating performance of the ASHP with vapor injection and no-injection under different inlet air temperature of condenser. Fig. 2 (a) and Fig. 2 (b) show that the supply air temperature tsup and the compressor discharge temperature tdis decrease with the dropping of inlet air temperature of condenser at ambient temperature -5℃ and -20℃. The discharge temperature of vapor injection is lower than that of no-injection but the supply air temperature is higher than that of no-injection. The decrease of discharge temperature is caused by injecting low temperature refrigerant into the compressor and the increase of supply air temperature is caused by the heating capacity improvement. 40
70
35
60
30
50
25
40
20
30
15
-5℃, 70Hz
5
10 15 Inlet air temperature of condenser (℃)
tsup no inj
tdis inj
20
20
80 70
60
25
50
20
40
15 5
COP inj
10 15 Inlet air temperature of condenser (℃)
Qh no inj
10
2.0
9
1.5 -5℃, 70Hz 5
10 15 Inlet air temperature of condenser (℃)
(c)
20
20
20
1.0
Qh inj
COP no inj
COP inj
7
3.0
6 2.5
5
COP
2.5
Heating capacity (kW)
3.0
11
7
30
-20℃, 70Hz
(b) COP no inj
12
8
tdis inj
30
10
COP
Heating capacity (kW)
Qh inj
tdis no inj
35
(a) Qh no inj
tsup inj
Discharge temp (℃)
tdis no inj
Supply air temp (℃)
tsup inj
Discharge temp (℃)
Supply air temp (℃)
tsup no inj
4
2.0
3
2
-20℃, 70Hz 5
10 15 Inlet air temperature of condenser (℃)
20
1.5
(d)
Fig. 2 The effect of inlet air temperature of condenser on heating performance
Fig. 2 (c) - (d) show the heating capacity and COP of the ASHP with vapor injection and no-injection. At ambient temperature -5℃ the heating capacity of vapor injection and no-injection at 5℃ inlet air temperature of condenser are 11.8% and 20.5% higher than that at 20℃ inlet air temperature of condenser. At -20℃ ambient
Xinxin Han et al. / Energy Procedia 158 (2019) 4147–4153 Author name / Energy Procedia 00 (2018) 000–000
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temperature they improve by 9.9% and 20.2%, respectively. The COP goes up with the dropping of inlet air temperature of condenser for the reduction of input power of compressor. At -20℃ ambient temperature the COP of vapor injection ASHP improves from 1.62 (at 20℃) to 2.37 (at 5℃) and the COP of no-injection ASHP improves from 1.52 (at 20℃) to 2.46 (at 5℃). Comparing to the no-injection condition, the heating capacity of vapor injection improves obviously. Under -5℃ ambient, the heating capacity at 20℃ and 5℃ inlet air temperature of condenser improve by 17.4% (at 20℃) and 8.9% (at 5 ℃ ), respectively. Under -20 ℃ ambient, they improve by 23.0% (at 20 ℃ ) and 12.4% (at 5 ℃ ), respectively. The COP of vapor injection is greater than that of no-injection at higher inlet air temperature of condenser while it is lower than that of no-injection at lower inlet air temperature of condenser. For example, at -20℃ ambient temperature the COP corresponding to inlet air temperature of condenser of 20℃ improves by 6.6%. However, the COP decreases by 3.4% for inlet air temperature of condenser of 5℃. The change trends of heating capacity and COP indicate the heating performance of vapor injection improves more obviously at higher inlet air temperature of condenser because of the higher compression pressure ratio. In order to analyse the heating performance further, the comprehensive coefficient of performance COPC is defined as follows [10]: 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 =
𝑄𝑄𝐿𝐿
𝑃𝑃𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 +𝑃𝑃𝑒𝑒
=
𝑄𝑄ℎ +𝑄𝑄𝑒𝑒
(1)
𝑃𝑃𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 +𝑃𝑃𝑒𝑒
where QL is the heating demand of the electric vehicle; Qh is the heating capacity of ASHP; Qe is the heating capacity of the electric heater; Pcomp and Pe are the input power of the heat pump and electric heater, respectively. COPC reflects the comprehensive efficiency of the heat pump and electric heater. At ambient temperature of -20℃ the heating demand of the electric bus is assumed as 12kW, 10.5 kW, 9 kW, 7.5 kW, respectively, corresponding to the inlet air temperature of condenser of 20℃, 15℃, 10℃, 5℃. The efficiency of electric heater is set as 0.95 and then COPC can be calculated. Fig. 3 shows the COPC of vapor injection at different inlet air temperature of condenser is greater than that of noinjection. This means as the heating capacity can't meet the heating demand, vapor injection mode is beneficial to improve the comprehensive efficiency. 2.0
2.00
inj
Heating loss (kW)
no inj
1.80
COPC
1.60 1.40 1.20
1.00
1.5 1.0 0.5 0.0
5
10
15
Inlet air tempreature of condenser (℃)
Fig. 3 The variation of COPC
20
y = 0.0907x - 1.2053 R² = 0.9625
22
24 26 28 30 Temp diff bt indoor and outdoor (℃)
32
Fig. 4 The heating loss to the ambient environment
3.2 Heating capacity loss Because the heat pump unit in the experiment is a packaged unit, the whole unit was placed in the outdoor environment chamber of the enthalpy difference lab and this will cause a large amount of heat loss at low ambient temperature. Therefore, an experimental study on heat loss was carried out. The test condition is ambient temperature -16℃, inlet air temperature of condenser 7-15℃. As shown in Fig. 4, the heating capacity loss increases linearly with the increasing of temperature difference between the ambient temperature and inlet air temperature of condenser. Base on this predicted formula, the heating capacity loss under the working condition of -20/20℃ reaches 2.42 kW, which is 34.1% of the total heating capacity. This means the loss heat of the packaged unit at
Xinxin Han et al. / Energy Procedia 158 (2019) 4147–4153 Author name / Energy Procedia 00 (2018) 000–000
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extreme low ambient temperature is very appreciable and the heating performance could be better if the unit gets more effective insulation. 3.3 The effect of compressor frequency Fig. 5 shows the effect of compressor frequency on heating capacity. It is measured at ambient temperature of -20℃ and inlet air temperature of condenser of 20℃, 15℃, 10℃, 5℃. The heating capacity increases with the increasing of compressor frequency under different working conditions. Under working condition -20/20 ℃, the heating capacity of vapor injection at 85 Hz improves by 60.4% against that at 60 Hz. Under working condition -20/5℃, it improves by 45.2%. The heating capacity of vapor injection is greater than no-injection at different compressor frequency. Under working condition -20/20℃, it improves by 26.0% (at 85 Hz ) and 22.0% (at 60 Hz). Under working condition -20/5℃, it improves by 18.1% (at 85 Hz ) and 11.9% (at 60 Hz). -20/20℃ inj
-20/15℃ no inj
6 4 2 0
60
65 70 75 80 Compressor frequency (Hz)
85
Heating capacity (kW)
Heating capacity (kW)
-20/20℃ no inj 8
8 6 4 2
60
65 70 75 80 Compressor frequency (Hz)
(a)
-20/10℃ inj
-20/5℃ no inj
10 8 6 4 2
60
85
(b)
65 70 75 80 Compressor frequency (Hz)
85
Heating capacity (kW)
Heating capacity (kW)
-20/10℃ no inj
-20/15℃ inj
10
-20/5℃ inj
10 8 6 4 2
60
65 70 75 80 Compressor frequency (Hz)
(c)
85
(d) Fig. 5 The effect of compressor frequency on heating capacity
Fig. 6 shows the effect of compressor frequency on COP. The optimum compressor frequency corresponding to the maximum COP is different under different working condition. For higher inlet air temperature of condenser the higher compressor frequency is better and for lower inlet air temperature of condenser the lower compressor frequency is better. Under the working condition -20/20℃, COP of the ASHP with vapor injection at different frequency is greater than that of no-injection. At 85 Hz, COP is 1.60 and improves by 14.5%. Under the working condition -20/5℃, COP of the ASHP with vapor injection at different frequency is lower than that of no-injection. At 85 Hz, COP is 2.22 and decreases by 2.9%. For working conditions of -20/15℃ and -20/10 ℃, COP of vapor injection is similar with that of no-injection. The experimental results indicate that the advantage of vapor injection is reflected in the conditions of higher temperature difference between the evaporator and the condenser.
Xinxin Han et al. / Energy Procedia 158000–000 (2019) 4147–4153 Author name / Energy Procedia 00 (2018)
64152
-20/20℃ no inj
-20/20 inj
-20/15℃ no inj 2.2 2.0
1.6
COP
COP
1.8
1.4 1.2
1.8 1.6
60
65 70 75 80 Compressor frequency (Hz)
1.4
85
60
65 70 75 80 Compressor frequency (Hz)
(a)
-20/10℃ no inj
-20/10℃ inj
-20/5℃ no inj
-20/5℃ inj
2.6 COP
2.0 COP
85
(b)
2.2 1.8 1.6 1.4
-20/15℃ inj
60
65 70 75 80 Compressor frequency (Hz)
2.4 2.2 2.0
85
60
65 70 75 80 Compressor frequency (Hz)
(c)
85
(d) Fig. 6 The effect of compressor frequency on COP
3.4 Increasing frequency or opening injection valve Since increasing the compressor frequency or injection valve opening can both affect the heat capacity, their effects on the heating performance are shown in Fig. 7. Under the working condition of -20/20℃,the heating capacity of injection mode at 60 Hz is lower than that at 70 Hz no-injection mode. However, the results are different at 70 Hz and 80 Hz. For example, the heating capacity of injection mode at 70 Hz improves by 6.1% comparing to that of no-injection mode at 80 Hz. Fig. 7 (b) shows the COP of injection mode at lower frequency is greater than that of no-injection at higher frequency. The COP improvement is more obvious at higher frequency. Therefore, from the viewpoint of heating capacity and COP, the injection mode at lower frequency is better than no-injection mode at higher frequency under the working condition of -20/20℃. 1.65
7
-20/20℃
1.60
6
1.55
5
1.50
4
1.45 1.40
3
2
1.35
1
1.30
0
-20/20℃
COP
Heating capacity (kW)
8
60Hz 70Hz 60Hz 70Hz 80Hz 70Hz 80Hz 85Hz 80Hz no inj no inj inj no inj no inj inj no inj no inj inj
(a)
1.25
60Hz 70Hz 60Hz 70Hz 80Hz 70Hz 80Hz 85Hz 80Hz no inj no inj inj no inj no inj inj no inj no inj inj
(b)
Fig. 7 The comparison between increasing frequency and opening injection valve
Xinxin Han et al. / Energy Procedia 158 (2019) 4147–4153 Author name / Energy Procedia 00 (2018) 000–000
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4. Conclusions In this paper the heating performance of a vapor injection ASHP designed for electric bus is experimentally studied at different inlet air temperature of condenser with the compressor frequency varying from 60 Hz to 85 Hz. Based on the experimental results the following conclusions can be drawn: 1) The heating capacity and COP of the ASHP with vapor injection and no-injection increase with the dropping of inlet air temperature of condenser. Comparing to no-injection, the heating performance of vapor injection improves more obviously at higher inlet air temperature of condenser. 2) The heating capacity of ASHP with vapor injection at different compressor frequency is greater than that of no-injection. The maximum improvement rate reaches 26.0% at 85 Hz under the working condition of -20/20℃. The optimum compressor frequency corresponding to the maximum COP depends on the working conditions and at higher inlet air temperature of condenser the higher compressor frequency is better. 3) Under the working condition of -20/20℃ and 85 Hz, COP of the ASHP with vapor injection is 1.60 and improves by 14.5% against that of no-injection. Under the working condition -20/5℃ and 85 Hz, COP is 2.22 and decreases by 2.9%. At extreme low ambient temperature, like the working condition of -20/20℃, the heat loss reaches 34.1% of the total heating capacity. It is very necessary to improve the insulation of the unit to get better performance. 4) According to the comparison of COPC, vapor injection mode is beneficial to improve the comprehensive efficiency as the heating capacity can't meet the heating demand. Acknowledgements We would like to thank the support by the National Key Research and Development Program of China (No. 2017YFB0103801), the Natural Science Foundation of China (No. 51676201) and External Cooperation Program of BIC, Chinese Academy of Sciences (No. 1A1111KYSB20130032). References [1]
Ma G Y, Zhao H X. Experimental study of a heat pump system with flash-tank coupled with scroll compressor[J]. Energy & Buildings, 2008, 40(5):697-701. [2] Heo J, Min W J, Kim Y. Effects of flash tank vapor injection on the heating performance of an inverter-driven heat pump for cold regions[J]. International Journal of Refrigeration, 2010, 33(4):848-855. [3] Redón A, Navarro-Peris E, Pitarch M, et al. Analysis and optimization of subcritical two-stage vapor injection heat pump systems[J]. Applied Energy, 2014, 124(7):231-240. [4] Wang X, Hwang Y, Radermacher R. Two-stage heat pump system with vapor-injected scroll compressor using R410A as a refrigerant[J]. International Journal of Refrigeration, 2009, 32(6):1442-1451. [5] Xu X, Hwang Y, Radermacher R. Refrigerant injection for heat pumping/air conditioning systems: Literature review and challenges discussions[J]. International Journal of Refrigeration, 2011, 34(2):402-415. [6] Chul Woo Roh, Jin Woo Yoo, Min Soo Kim. Vapor refregerant injection techniques for heat pump systems: The latest literature review and discussion[J]. International Journal of Air-Conditioning and Refrigeration, 2014, 22(01):1-6. [7] Jung J, Jeon Y, Lee H, et al. Numerical study of the effects of injection-port design on the heating performance of an R134a heat pump with vapor injection used in electric vehicles[J]. Applied Thermal Engineering, 2017, 127: 800-811. [8] Qin F, Xue Q, Velez G M A, et al. Experimental investigation on heating performance of heat pump for electric vehicles at −20 °C ambient temperature[J]. Energy Conversion & Management, 2015, 102:39-49. [9] Qin F, Xue Q, Zhang G, et al. Experimental Investigation on Heat Pump for Electric Vehicles with different Refrigerant Injection Compressors [J]. Energy Procedia, 2015, 75(6):1490-1495. [10] Zhang Guiying, Zou Huiming, Qin Fei, Xue Qingfeng, Tian Changqing. Investigation on an improved heat pump AC system with the view of return air utilization and anti-fogging for electric vehicles[J]. Applied Thermal Engineering, 2017, 115 (25):726-735.
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Energyonline Procedia 00 (2018) 000–000 Available onlineatat www.sciencedirect.com Available www.sciencedirect.com Energy Procedia 00 (2018) 000–000
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Energy Procedia 158 Energy Procedia 00(2019) (2017)4147–4153 000–000 www.elsevier.com/locate/procedia
10th International Conference on Applied Energy (ICAE2018), 22-25 August 2018, Hong Kong, 10th International Conference on Applied Energy China(ICAE2018), 22-25 August 2018, Hong Kong, China
Experimental study on vapor injection air source heat pump with Experimental study on vapor injection air source heat pump with The 15th International Symposium on District Heating and Cooling internal heat exchanger for electric bus internal heat exchanger for electric bus Assessing the feasibility of using the heat demand-outdoor temperature function heatTian demand forecast a a d Xinxin Hana,b,c , Huimingfor Zouaa *long-term , Hongbo Xudistrict , Changqing ,Wei Kang Xinxin Hana,b,c, Huiming Zoua * , Hongbo Xua, Changqing Tiana ,Wei Kangd I. Andrić *, A. Pina , P. Ferrão , J. Fournier ., B. Lacarrière , O. Le Corre
a,b,c a Technology anda Key Laboratory of Cryogenics, b c c Beijing Key Laboratory of Thermal Science and Technical Institute of Physics and Chemistry, a CAS,and Beijing 100190,China Beijing Key Laboratory of Thermal Science and Technology Key Laboratory of Cryogenics, Technical Institute of Physics and Chemistry, b a Polytechnic University, Jiaozuo CAS, Beijing 100190,China IN+ Center for Innovation, Technology Henan and Policy Research - Instituto Superior454000, Técnico,China Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal c b b University of Polytechnic Chinese Academy of Sciences, Beijing 100049, Henan University, Jiaozuo 454000, China Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520China Limay, France d c Changchun Railway Vehicles Co., Ltd, Changchun 130062, Jilin, China c CRRCÉnergétiques University ofetChinese Academy -ofIMT Sciences, Beijing 100049, Département Systèmes Environnement Atlantique, 4 rue AlfredChina Kastler, 44300 Nantes, France d CRRC Changchun Railway Vehicles Co., Ltd, Changchun 130062, Jilin, China a
Abstract Abstract Abstract InDistrict this paper, a vapor injection ASHP unit addressed is developed for electric is experimentally studied heating networks are commonly in the literaturebus as and one the of heating the mostperformance effective solutions for decreasing the In this paper, a vapor injection ASHP unit is developed for electric bus and the heating performance is experimentally with the adjustment of compressor frequency under different working conditions. The optimum compressor frequency depends greenhouse gas emissions from the building sector. These systems require high investments which are returned through studied the heat with adjustment of compressor frequency under working conditions. The optimum depends on thetheworking andclimate at higher inlet air temperature condenser the higher compressor frequency isfrequency better. the sales. Due to conditions the changed conditions anddifferent buildingof renovation policies, heat demandcompressor in the future couldUnder decrease, on the working and at higher inlet airoftemperature condenser the higher compressor frequency is better. Under working condition of -20/20℃ and 85 Hz, COP the ASHP of with vapor injection is 1.60 and improves by 14.5% against thatthe of prolonging the conditions investment return period. working condition -20/20℃ Hz,the COP of and the ASHP with injection 1.60 and improves 14.5% against thatThe of no-injection. Under working condition -20/5℃ 85 it is 2.22 decreases by 2.9% against by that of no-injection. The main scope ofofthe this paper isand to 85 assess feasibility of Hz, using thevapor heatand demand –isoutdoor temperature function for heat demand no-injection. Under the working condition -20/5℃ and 85 Hz, it is 2.22 and decreases by 2.9% against that of no-injection. The results show that the advantage of vapor injection is reflected in the conditions of higher temperature difference between the forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 results show that the in advantage of vapor is typology. reflected the conditions of more higher temperature between the evaporator and condenser. According to theinjection comparison of COPCin , vapor injectionscenarios is beneficial as thedifference heating can't buildings that vary both construction period and Three weather (low, medium, high) andcapacity three district more beneficial as the capacity evaporator and condenser. the comparison of COPdeep). meet the heating demand. C, vapor renovation scenarios wereAccording developedto(shallow, intermediate, Toinjection estimateis the error, obtained heatheating demand valuescan't were meet the heating demand. compared with results from a dynamic heat demand model, previously developed and validated by the authors. Copyright © 2018 Elsevier Ltd. only All rights reserved. The results showed that when weather change is considered, the margin of error could be acceptable for some applications © 2019 The Authors. Published by Elsevier Ltd. Copyright ©in2018 Elsevier Ltd. Allresponsibility rights than reserved. Selection and peer-review under of for the all scientific committee of the 10th International Conference onrenovation Applied (the error annual demand was lower 20% weather scenarios considered). However, after introducing This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) th International Conference on Applied Selection and peer-review under responsibility of the scientific committee of the 10 Energy (ICAE2018). scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). Peer-review under responsibility of the scientific committee of ICAE2018 – The 10th International Conference on Applied Energy. Energy (ICAE2018). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the Keywords: heathours pump;of electric bus; heating decrease vapor in theinjection; numberairofsource heating 22-139h during performance the heating season (depending on the combination of weather and Keywords: vapor injection; air source heat electrichand, bus; heating performance renovation scenarios considered). Onpump; the other function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. * Corresponding author. Tel.: +86-10-82543697.
E-mail address:author. [email protected]. * Corresponding Tel.: +86-10-82543697. Keywords: Heat demand; Forecast; Climate change E-mail address: [email protected]. 1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility the scientific 1876-6102 Copyright © 2018 Elsevier Ltd. All of rights reserved. committee of the 10th International Conference on Applied Energy (ICAE2018). Selection and peer-review under responsibility of the scientific committee of the 10th International Conference on Applied Energy (ICAE2018). 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of ICAE2018 – The 10th International Conference on Applied Energy. 10.1016/j.egypro.2019.01.817
Xinxin Han et al. / Energy Procedia 158 (2019) 4147–4153 Author name / Energy Procedia 00 (2018) 000–000
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1. Introduction In cold region the heating performance of conventional air source heat pump (ASHP) degrades sharply due to the increase of compression pressure ratio and compressor suction specific volume. Vapor injection is considered as an effective way to improve the heating performance and reliability of ASHP at extreme low ambient temperature [1-3]. There are two basic types of vapor injection ASHP, flash tank (FT) and internal heat exchanger (IHX). The researches show that although the efficiency of ASHP with IHX is not as good as that of ASHP with FT, the flexibility of its adjustment on intermediate pressure makes it more practical of applications [4-6]. The earlier researches mainly focus on vapor injection ASHP applied for building air conditioning system. In recent years there are many studies on its application for electric cars due to its quick development. Jung et al. [7] numerically studied the vapor injection ASHP for electric vehicle. The results showed that at -10℃ ambient temperature the COP of vapor injection heat pump with a single- and dual-injection ports compressor against that of the no-injection heat pump improve by 7.5% and 9.8%, respectively. Qin et al. tested a vapor injection ASHP with a refitted scroll compressor for electric vehicle [8-9]. The results showed that the heating capacity improves by 28.6% compared with the conventional system at -20℃ ambient temperature. The above studies all showed vapor injection heat pump is effective for electric vehicle application. However, they are mainly for electric car and there are limited literatures for electric bus. Except for some similar characters, such as movability and vibration, the heat pump for electric bus still has some differences. It is a packaged unit other than a split unit and it can use return air like residential heat pump. Therefore, the research and development of vapor injection ASHP is significative for the application of electric bus in cold region. In this paper a vapor injection ASHP for electric bus was developed and the heating performance was experimentally investigated at low ambient temperature. According to the practical heating demand, the effect of inlet air temperature of condenser and compressor frequency on the heating performance was studied. 2. Experimental bench setup The experimental test bench of vapor injection ASHP was shown in Fig. 1. The unit has two independent cycle systems and the two indoor heat exchangers are shared by these two systems. Thus, as one system is on defrosting mode, the supply air temperature can be kept by the other system operating on heating mode. Because the two independent systems were symmetrical and all the components were identical, the experiment measurement was just focus on one system. ·
P T P T
·
four-way reversing valve T
four-way reversing valve
T
comp. P T
P T
one-way valve
EXV1
outdoor HX
P T M
gas-liquid separator
HX
T
P
P
T
comp.
P T
outdoor HX
P T
T
P T P T
P T
one-way valve
EXV1 HX T
gas-liquid separator
T
T M T T P
pressure
T
temperature
M
mass flow rate
P T
EXV2
EXV2
·
indoor HX
P T
P T
·
T
T
P T
indoor HX
Fig. 1 The schematic diagram of the test system
The heating performance of the unit was measured in an enthalpy difference lab. The working fluid in the unit was R410a. Table 1 shows the experimental test conditions. The two electronic expansion valve (EEV) in main branch and vapor injection branch both have 500 steps. When the EEV in vapor injection branch is set to 0, no refrigerant could inject into the compressor. That is no-injection cycle. When it is set among 1~500, the heat pump
Xinxin Han et al. / Energy Procedia 158 (2019) 4147–4153 Author name / Energy Procedia 00 (2018) 000–000
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can operate in vapor injection mode. In the experiment the superheat of evaporator and internal heat exchanger can be adjusted by the two EEV. The temperature was measured by T-type thermocouple with uncertainty of ±0.5 °C. The pressure was measured by the pressure transducer with uncertainty of ±0.5%. The refrigerant mass flow rate was measured by Coriolis flow meter with uncertainty of ±0.2%. Table 1. Test conditions Outdoor dry temperature/℃
Indoor dry temperature/℃
Compressor frequency/Hz
Outdoor air flow rate/(m3/h)
Indoor air flow rate/(m3/h)
-5
20, 15, 10, 5
70
3500
2000
-20
20, 15, 10, 5
60, 70, 80, 85
3500
2600
3. Results and discussions 3.1 The effect of inlet air temperature of condenser Fig.2 shows the heating performance of the ASHP with vapor injection and no-injection under different inlet air temperature of condenser. Fig. 2 (a) and Fig. 2 (b) show that the supply air temperature tsup and the compressor discharge temperature tdis decrease with the dropping of inlet air temperature of condenser at ambient temperature -5℃ and -20℃. The discharge temperature of vapor injection is lower than that of no-injection but the supply air temperature is higher than that of no-injection. The decrease of discharge temperature is caused by injecting low temperature refrigerant into the compressor and the increase of supply air temperature is caused by the heating capacity improvement. 40
70
35
60
30
50
25
40
20
30
15
-5℃, 70Hz
5
10 15 Inlet air temperature of condenser (℃)
tsup no inj
tdis inj
20
20
80 70
60
25
50
20
40
15 5
COP inj
10 15 Inlet air temperature of condenser (℃)
Qh no inj
10
2.0
9
1.5 -5℃, 70Hz 5
10 15 Inlet air temperature of condenser (℃)
(c)
20
20
20
1.0
Qh inj
COP no inj
COP inj
7
3.0
6 2.5
5
COP
2.5
Heating capacity (kW)
3.0
11
7
30
-20℃, 70Hz
(b) COP no inj
12
8
tdis inj
30
10
COP
Heating capacity (kW)
Qh inj
tdis no inj
35
(a) Qh no inj
tsup inj
Discharge temp (℃)
tdis no inj
Supply air temp (℃)
tsup inj
Discharge temp (℃)
Supply air temp (℃)
tsup no inj
4
2.0
3
2
-20℃, 70Hz 5
10 15 Inlet air temperature of condenser (℃)
20
1.5
(d)
Fig. 2 The effect of inlet air temperature of condenser on heating performance
Fig. 2 (c) - (d) show the heating capacity and COP of the ASHP with vapor injection and no-injection. At ambient temperature -5℃ the heating capacity of vapor injection and no-injection at 5℃ inlet air temperature of condenser are 11.8% and 20.5% higher than that at 20℃ inlet air temperature of condenser. At -20℃ ambient
Xinxin Han et al. / Energy Procedia 158 (2019) 4147–4153 Author name / Energy Procedia 00 (2018) 000–000
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temperature they improve by 9.9% and 20.2%, respectively. The COP goes up with the dropping of inlet air temperature of condenser for the reduction of input power of compressor. At -20℃ ambient temperature the COP of vapor injection ASHP improves from 1.62 (at 20℃) to 2.37 (at 5℃) and the COP of no-injection ASHP improves from 1.52 (at 20℃) to 2.46 (at 5℃). Comparing to the no-injection condition, the heating capacity of vapor injection improves obviously. Under -5℃ ambient, the heating capacity at 20℃ and 5℃ inlet air temperature of condenser improve by 17.4% (at 20℃) and 8.9% (at 5 ℃ ), respectively. Under -20 ℃ ambient, they improve by 23.0% (at 20 ℃ ) and 12.4% (at 5 ℃ ), respectively. The COP of vapor injection is greater than that of no-injection at higher inlet air temperature of condenser while it is lower than that of no-injection at lower inlet air temperature of condenser. For example, at -20℃ ambient temperature the COP corresponding to inlet air temperature of condenser of 20℃ improves by 6.6%. However, the COP decreases by 3.4% for inlet air temperature of condenser of 5℃. The change trends of heating capacity and COP indicate the heating performance of vapor injection improves more obviously at higher inlet air temperature of condenser because of the higher compression pressure ratio. In order to analyse the heating performance further, the comprehensive coefficient of performance COPC is defined as follows [10]: 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 =
𝑄𝑄𝐿𝐿
𝑃𝑃𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 +𝑃𝑃𝑒𝑒
=
𝑄𝑄ℎ +𝑄𝑄𝑒𝑒
(1)
𝑃𝑃𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 +𝑃𝑃𝑒𝑒
where QL is the heating demand of the electric vehicle; Qh is the heating capacity of ASHP; Qe is the heating capacity of the electric heater; Pcomp and Pe are the input power of the heat pump and electric heater, respectively. COPC reflects the comprehensive efficiency of the heat pump and electric heater. At ambient temperature of -20℃ the heating demand of the electric bus is assumed as 12kW, 10.5 kW, 9 kW, 7.5 kW, respectively, corresponding to the inlet air temperature of condenser of 20℃, 15℃, 10℃, 5℃. The efficiency of electric heater is set as 0.95 and then COPC can be calculated. Fig. 3 shows the COPC of vapor injection at different inlet air temperature of condenser is greater than that of noinjection. This means as the heating capacity can't meet the heating demand, vapor injection mode is beneficial to improve the comprehensive efficiency. 2.0
2.00
inj
Heating loss (kW)
no inj
1.80
COPC
1.60 1.40 1.20
1.00
1.5 1.0 0.5 0.0
5
10
15
Inlet air tempreature of condenser (℃)
Fig. 3 The variation of COPC
20
y = 0.0907x - 1.2053 R² = 0.9625
22
24 26 28 30 Temp diff bt indoor and outdoor (℃)
32
Fig. 4 The heating loss to the ambient environment
3.2 Heating capacity loss Because the heat pump unit in the experiment is a packaged unit, the whole unit was placed in the outdoor environment chamber of the enthalpy difference lab and this will cause a large amount of heat loss at low ambient temperature. Therefore, an experimental study on heat loss was carried out. The test condition is ambient temperature -16℃, inlet air temperature of condenser 7-15℃. As shown in Fig. 4, the heating capacity loss increases linearly with the increasing of temperature difference between the ambient temperature and inlet air temperature of condenser. Base on this predicted formula, the heating capacity loss under the working condition of -20/20℃ reaches 2.42 kW, which is 34.1% of the total heating capacity. This means the loss heat of the packaged unit at
Xinxin Han et al. / Energy Procedia 158 (2019) 4147–4153 Author name / Energy Procedia 00 (2018) 000–000
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extreme low ambient temperature is very appreciable and the heating performance could be better if the unit gets more effective insulation. 3.3 The effect of compressor frequency Fig. 5 shows the effect of compressor frequency on heating capacity. It is measured at ambient temperature of -20℃ and inlet air temperature of condenser of 20℃, 15℃, 10℃, 5℃. The heating capacity increases with the increasing of compressor frequency under different working conditions. Under working condition -20/20 ℃, the heating capacity of vapor injection at 85 Hz improves by 60.4% against that at 60 Hz. Under working condition -20/5℃, it improves by 45.2%. The heating capacity of vapor injection is greater than no-injection at different compressor frequency. Under working condition -20/20℃, it improves by 26.0% (at 85 Hz ) and 22.0% (at 60 Hz). Under working condition -20/5℃, it improves by 18.1% (at 85 Hz ) and 11.9% (at 60 Hz). -20/20℃ inj
-20/15℃ no inj
6 4 2 0
60
65 70 75 80 Compressor frequency (Hz)
85
Heating capacity (kW)
Heating capacity (kW)
-20/20℃ no inj 8
8 6 4 2
60
65 70 75 80 Compressor frequency (Hz)
(a)
-20/10℃ inj
-20/5℃ no inj
10 8 6 4 2
60
85
(b)
65 70 75 80 Compressor frequency (Hz)
85
Heating capacity (kW)
Heating capacity (kW)
-20/10℃ no inj
-20/15℃ inj
10
-20/5℃ inj
10 8 6 4 2
60
65 70 75 80 Compressor frequency (Hz)
(c)
85
(d) Fig. 5 The effect of compressor frequency on heating capacity
Fig. 6 shows the effect of compressor frequency on COP. The optimum compressor frequency corresponding to the maximum COP is different under different working condition. For higher inlet air temperature of condenser the higher compressor frequency is better and for lower inlet air temperature of condenser the lower compressor frequency is better. Under the working condition -20/20℃, COP of the ASHP with vapor injection at different frequency is greater than that of no-injection. At 85 Hz, COP is 1.60 and improves by 14.5%. Under the working condition -20/5℃, COP of the ASHP with vapor injection at different frequency is lower than that of no-injection. At 85 Hz, COP is 2.22 and decreases by 2.9%. For working conditions of -20/15℃ and -20/10 ℃, COP of vapor injection is similar with that of no-injection. The experimental results indicate that the advantage of vapor injection is reflected in the conditions of higher temperature difference between the evaporator and the condenser.
Xinxin Han et al. / Energy Procedia 158000–000 (2019) 4147–4153 Author name / Energy Procedia 00 (2018)
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-20/20℃ no inj
-20/20 inj
-20/15℃ no inj 2.2 2.0
1.6
COP
COP
1.8
1.4 1.2
1.8 1.6
60
65 70 75 80 Compressor frequency (Hz)
1.4
85
60
65 70 75 80 Compressor frequency (Hz)
(a)
-20/10℃ no inj
-20/10℃ inj
-20/5℃ no inj
-20/5℃ inj
2.6 COP
2.0 COP
85
(b)
2.2 1.8 1.6 1.4
-20/15℃ inj
60
65 70 75 80 Compressor frequency (Hz)
2.4 2.2 2.0
85
60
65 70 75 80 Compressor frequency (Hz)
(c)
85
(d) Fig. 6 The effect of compressor frequency on COP
3.4 Increasing frequency or opening injection valve Since increasing the compressor frequency or injection valve opening can both affect the heat capacity, their effects on the heating performance are shown in Fig. 7. Under the working condition of -20/20℃,the heating capacity of injection mode at 60 Hz is lower than that at 70 Hz no-injection mode. However, the results are different at 70 Hz and 80 Hz. For example, the heating capacity of injection mode at 70 Hz improves by 6.1% comparing to that of no-injection mode at 80 Hz. Fig. 7 (b) shows the COP of injection mode at lower frequency is greater than that of no-injection at higher frequency. The COP improvement is more obvious at higher frequency. Therefore, from the viewpoint of heating capacity and COP, the injection mode at lower frequency is better than no-injection mode at higher frequency under the working condition of -20/20℃. 1.65
7
-20/20℃
1.60
6
1.55
5
1.50
4
1.45 1.40
3
2
1.35
1
1.30
0
-20/20℃
COP
Heating capacity (kW)
8
60Hz 70Hz 60Hz 70Hz 80Hz 70Hz 80Hz 85Hz 80Hz no inj no inj inj no inj no inj inj no inj no inj inj
(a)
1.25
60Hz 70Hz 60Hz 70Hz 80Hz 70Hz 80Hz 85Hz 80Hz no inj no inj inj no inj no inj inj no inj no inj inj
(b)
Fig. 7 The comparison between increasing frequency and opening injection valve
Xinxin Han et al. / Energy Procedia 158 (2019) 4147–4153 Author name / Energy Procedia 00 (2018) 000–000
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4. Conclusions In this paper the heating performance of a vapor injection ASHP designed for electric bus is experimentally studied at different inlet air temperature of condenser with the compressor frequency varying from 60 Hz to 85 Hz. Based on the experimental results the following conclusions can be drawn: 1) The heating capacity and COP of the ASHP with vapor injection and no-injection increase with the dropping of inlet air temperature of condenser. Comparing to no-injection, the heating performance of vapor injection improves more obviously at higher inlet air temperature of condenser. 2) The heating capacity of ASHP with vapor injection at different compressor frequency is greater than that of no-injection. The maximum improvement rate reaches 26.0% at 85 Hz under the working condition of -20/20℃. The optimum compressor frequency corresponding to the maximum COP depends on the working conditions and at higher inlet air temperature of condenser the higher compressor frequency is better. 3) Under the working condition of -20/20℃ and 85 Hz, COP of the ASHP with vapor injection is 1.60 and improves by 14.5% against that of no-injection. Under the working condition -20/5℃ and 85 Hz, COP is 2.22 and decreases by 2.9%. At extreme low ambient temperature, like the working condition of -20/20℃, the heat loss reaches 34.1% of the total heating capacity. It is very necessary to improve the insulation of the unit to get better performance. 4) According to the comparison of COPC, vapor injection mode is beneficial to improve the comprehensive efficiency as the heating capacity can't meet the heating demand. Acknowledgements We would like to thank the support by the National Key Research and Development Program of China (No. 2017YFB0103801), the Natural Science Foundation of China (No. 51676201) and External Cooperation Program of BIC, Chinese Academy of Sciences (No. 1A1111KYSB20130032). References [1]
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