Performance of a Solar Air Composite Heat Source Heat Pump System

Renewable Energy xxx (2015) 1e6

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Renewable Energy

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Performance of a solar air composite heat source heat pump system

* Yin Liu a, , Jing Ma b, Guanghui Zhou a, Chao Zhang a, Wenlei Wan a a Zhongyuan University of Technology, Zhengzhou, Henan, China b Henan University of Technology, Zhengzhou, Henan, China article info abstract

Article history: For the shortcoming of air source heat pump in heating condition, a composite heat exchanger was Received 21 March 2015 designed which integrates ﬁn tube and tube heat exchanger, and it can achieve synchronous and Received in revised form composite heat exchange in one heat exchanger between working ﬂuids, gaseous and liquid heat source. 23 August 2015 With the above composite heat exchanger as the core component, the Solar Air Composite Heat Source Accepted 1 September 2015 Heat Pump System (SACHP) was developed which has three working modes, including single solar heat Available online xxx source mode, single air heat source mode and solar air dual heat sources mode. A SACHP experiment table was established and conducted a comprehensive experimental study of three working modes of Keywords: Heat pump this system in the standard enthalpy difference laboratory. The results show that when the ambient Composite system temperature was 15 C, compared to the single air heat source mode, the dual heat source mode Solar energy increased 62% in heat capacity and 59% in COP; when the temperature difference of combined heat Air source transfer was 5 C, compared to the single air heat source mode, the dual heat source mode increased 51% in heat capacity and 49% in COP. Experimental results demonstrate that the application of the solar air composite heat pump technology can accelerate the application process of the solar heat pump in air conditioners for buildings. © 2015 Elsevier Ltd. All rights reserved.

1. Introduction especially in winter when the evaporating temperature decreases with the temperature fall of outdoor air heat source, there will be a Solar energy is the most important and basic energy among a signiﬁcant drop in the ratio of heating capacity of heat pump and variety of renewable energy sources and it is a priority source used energy efﬁciency, or even a severe frosting, as a result, the machine as renewable resource because it is clean, inexhaustible, affordable, may fail to work properly [7]. and free from regional restriction and high quality [1]. Solar heat Since solar heat pump and air source heat pump had their pump is an effective way for air conditioning system to utilize solar respective advantages and disadvantages, the researchers com- energy, but in general, the researchers have found that solar energy bined the solar heat pump with the air source heat pump to is an intermittent energy which changes greatly depending on time develop a composite heat source heat pump system, in order to and weather, for this reason, supplementary heat source is required improve the reliability of the system. The current composite heat to ensure the continuous and reliable operation of solar heat pump source heat pump system is provided with multiple different heat [2,3]. exchangers to utilize different heat sources, involving more Since the advent of air source heat pump, it has become the complicated equipment, causing higher cost and other related is- research focus and has been rapidly popularized and applied, sues, and making it impossible to simultaneously utilize various owing to its unique advantages of energy conservation and envi- heat sources [8e14]. Badescu designed thermal energy storage ronment protection. Air heat source is gradually obtaining the device integrated into a solar assisted heat pump system for space largest market share in the application of building energy by virtue heating, established model and simulates the working character- of its unique advantages [4e6]. However, the application of single istic [15e17]. air source heat pump is also subject to weather conditions, and Aimed at the disadvantages of solar heat source heat pump, air source heat pump and composite heat source heat pump with multiple heat exchangers, a heat exchanger was designed that can

* Corresponding author. achieve synchronous composite utilization of solar heat source and E-mail address: [email protected] (Y. Liu). air heat source in one heat exchanger. With this heat exchanger as http://dx.doi.org/10.1016/j.renene.2015.09.001 0960-1481/© 2015 Elsevier Ltd. All rights reserved.

Please cite this article in press as: Y. Liu, et al., Performance of a solar air composite heat source heat pump system, Renewable Energy (2015), http://dx.doi.org/10.1016/j.renene.2015.09.001 2 Y. Liu et al. / Renewable Energy xxx (2015) 1e6 the core component, SACHP was designed. Then, the experimental 3. Description of the solar-air composite heat source heat table of SACHP was established and the experimental study was pump system done in the standard enthalpy difference laboratory. The results of the experiment have indicated that the composite heat pump has SACHP comprises of two parts, one is the part of solar heat been obviously improved in cooling capacity and performance collection and heat accumulation, another is the composite heat compared with the single air source heat pump; the margin of source heat pump, among which the solar heat collection and heat increase was increasing with the decrease of outdoor ambient accumulation include solar collector, hot water accumulator, tank temperature. Under the ultra low temperature heating condition at for domestic water, heat exchange coil, circulating pump and con- the outdoor ambient temperature of 7 C specified in the national necting pipe and valves; the composite heat source heat pump standard, the heating capacity and performance of the composite includes compressor, composite heat exchanger, heat exchanger for heat pump both increased by over 50% than that of the single air user, combined throttle device, four way reversing valve, connect- heat source heat pump. ing pipe, valve, etc. It can be observed in Fig. 4. The dual heat source composite heat exchanger is the core 2. Meteorological and actinometrical data component of this system. Fig. 5 shows the schematic diagram of structure. According to the characteristics of fin tube heat According to the Meteorological Library of China Meteorological exchanger and tube heat exchanger, and based on fin tube heat Administration Meteorological Information Center [18], the average exchanger, this heat exchanger was made by inserting another heat sunshine of Zhengzhou is 2400 h/year, the total annual solar radi- exchanger tube into the heat exchanger tube of fin tube heat ation energy for 5771 MJ/(m2$a), the total heating season solar exchanger, forming three medium channels, including the cavity of radiation energy to 1740 MJ/m2. According to solar radiation data, inside tube working as the solar water channel, space between the Zhengzhou's daily sunshine is shown in Fig. 1, the total daily solar outer wall of inside tube and the inner wall of outside tube as the radiation shown in Fig. 2, a month solar radiation shown in Fig. 3. heat pump refrigerant channel and the space between the fins and Zhengzhou's daily average sunshine curve shows that the average outer surface of the outside tube as the air channel. of sunshine is 4.8e7.9 h year around. The average sunshine time is SACHP is provided with the composite heat source heat high from April to August, and it is about 8 h a day. In winter, exchanger that combines solar heat collection and heat accumu- however, the average sunshine time is 5 h a day. Annual daily lation with composite heat source heat pump in a scientific and average sunshine has little fluctuations. In comparison, Fig. 2 shows reasonable way. In summer, the part of solar heat collection and the solar irradiation day-by-day all year in Zhengzhou. The curve heat accumulation and composite heat pump system work indi- shows that solar irradiation day-by-day all year has the same trends vidually, and in winter, these two parts work together. The dual as the curve of monthly daily average sunshine in Zhengzhou. The heat source composite heat exchanger (as an evaporator) can use summer's daily solar irradiation is higher than other season. either or both air source and low solar heat as the heat pump heat However, the fluctuation of the solar irradiation day-by-day all year source, for this reason, the solar energy collected in the daytime can is not outstanding. be used by the heat pump at night, which contributes to solve The curve of the monthly average solar irradiation is shown in problems where solar energy is unavailable at night as an inter- Fig. 3. The solar irradiation ranges are from 11.724 MJ/(m2$day) to mittent energy, eliminate the effect of low temperature on air 18.504 MJ/(m2$day) when the solar collector installed tilted at source heat pump, greatly enhance the working efficiency of heat latitude. Where Ht is monthly averaged, daily total solar irradiation pump in winter and improve the reliability of heat pump system. on horizontal surface (MJ/m2$day), Hd is monthly averaged, daily diffuse solar irradiation on horizontal surface (MJ/m2$day), Hb is 4. Experimental study of the solar-air composite heat source monthly averaged, daily direct solar irradiation on horizontal sur- heat pump system face (MJ/m2$day), H is monthly averaged, daily total solar irradiation on surface tilted at latitude (MJ/m2$day), Ho is monthly 4.1. Description of experimental system averaged, daily total solar irradiation above the aerosphere (MJ/ m2$day). Solar air composite heat source heat pump system is equipped with a compressor with an air displacement of 16.7 ml/rev and has a cooling capacity of 2770 W under the standard air conditioning 10 conditions. Throttle device is a combined throttle device which comprises of two capillary tubes with a tube diameter of 2 mm and a 9 average minimum length of about 2 m for each one and one FD-4-type one-way valve 8 with a design flow of more than 3.2 L/min. Heat exchanger for user has wall-mounted fan coil, and the dual heat source composite heat ) r 7 u exchanger has heat exchanger tubes in single-row arrangement, o H ( 6 among which, the outside tube is rifled copper tube with a tube e n

i diameter of 15.7 m and a thickness of 0.5 mm, and the inside tube is h

s 5

n copper tube with a tube diameter of 9.52 mm and a thickness of u

s 0.3 mm; these 16 tubes with a length of 600 mm for each tube are y

l 4 i

a split into two groups in symmetrical design from top to bottom, D 3 allowing for the counter flow heat exchanging between solar heat medium (ground water) and heat pump working medium (refrig- 2 erant). The fins are 0.115 mm-thick hydrophilic aluminum foil fi 1 corrugated ns with a spacing of 2 mm, a width of 32 mm and a 123456789101112 height of 608 mm. It has a design face velocity of 2 m/s, air volume of 3 Month 2500 m /h, input power of 45 W and pressure of 30 Pa. To meet the requirement for continuous testing, this system used hot water Fig. 1. Monthly daily sunshine in Zhengzhou China. accumulator to simulate solar heat source, and the hot water

30 ) 2 25 m / J

M 20 ( n o i

t 15 a i d

a 10 r r i

r 5 a l o

S 0 Jan 1 Feb 1 Mar 1 Apr 1 May 1 Jun 1 Jul 1 Aug 1 Sep 1 Oct 1 Nov 1 Dec 1 Date

Fig. 2. Solar irradiation day-by-day all year in Zhengzhou China.

enthalpy difference laboratory which had an indoor environment at 50 dry bulb temperature of 10～40 C and wet bulb temperature of 9～ Ht 35 C, and an outdoor environment at dry bulb temperature of 15～ Hd 55 C and wet bulb temperature of 16～45 C, and the temperature 40 Hb ± H control accuracy was 0.2 C. Fig. 6 shows the indoor section of solar .d) 2 Ho air composite heat source heat pump system; Fig. 7 shows the out- m /

J 30 door section of solar air composite heat source heat pump system. M ( n o i

t a i 4.2. Experimental conditions

d 20 a r r i

r In order to fully grasp the operating characteristics of SACHP and a l

o 10 make heat pump system meet the needs under different conditions S and achieve the optimal matching of heat resources, the experiment mainly considered the impact of two heat resources, solar 0 123456789101112 heat medium and air on the performance of system. With the reference of “ Performance Rating of Unitary Air-Conditioning & Month Air-Source Heat Pump Equipmeng” ANSI/AHRI Standard 210/ 240e2008 [19], “Room Air Conditioner” GB/T7725-2004 [20] and Fig. 3. Monthly solar irradiation in Zhengzhou. “Unitary air conditioners” GB/T17758-2010 [21], the author selected to conduct the experiment under rated heating operating accumulator with a volume of 0.6 m3 had two built-in 30kw-power conditions at high temperature, low temperature and ultra-low electric heaters, so that the heat of solar thermal medium can be temperature and the minimum heating operating conditions recovered quickly. To prevent the hot water from freezing when specified in above standards. In addition, the most important SACHP operates at low temperature, the hot water accumulator used characteristic of the heat pump system is that it can solve the glycol water solution with a volume concentration of 33.6% as solar problem of small heating capacity and low operating efficiency thermal medium. Agilent 34970A-type gatherer was applied for the when the air source heat pump system is running in the low collection of various temperatures and analog signals system data at temperature condition. Therefore, the author chose to conduct the 15 s intervals for data collection and connected to a computer for experiment at outdoor ambient temperature of 15 C and 10 C real-time recording of experimental data. as the low temperature condition. According to the design capacity The entire experimental study was carried out in the standard of the system, the solar heat medium flow is 0.6 m3/h.

Water tank Water tank Valve Combined throttle device

Valve

Solar collector Valve Indoor composite heat exchanger Air heat exchanger

Pump Pump Valve Valve Valve Four-way reversing valve

Compresser

Fig. 4. Schematic diagram of solar air composite heat source heat pump system.

Fin humidity of humid air in nozzle inlet. In equation (2) Solar water sffiffiffiffiffiffi ¼ PV G KCdA 0 (3) Vn Outside tube where K is coefficient and it is 1.414 [20], Cd is discharge coefficient of flow nozzle, A is area of nozzle, PV is static pressure difference Inside tube before and after the nozzle.

(3) Coefﬁcient of performance

Refrigerant Q Q COP ¼ ¼ (4) W U $I $cos f þ U $I $cos f þ U $I $cos f Ambient air 1 1 1 2 2 2 3 3 3

Fig. 5. Schematic diagram of dual heat source composite heat exchanger. 5. Experimental results and discussions

4.3. Computer analysis 5.1. System heating capacity

(1) Power dissipation Fig. 8 shows the comparison of SACHP's heating capacities in the single air heat source mode, the solar air heat source mode and the The system power dissipation includes compressor, indoor fan single solar heat medium heat source mode. The data in the ﬁgure and outdoor fan, and it is computed by voltage, current and power below shows the heating capacity in the solar and air heat source factor. mode is greater than that both in the single air heat source mode and the single solar heat medium heat source mode, and the ¼ $ $ f þ $ $ f þ $ $ f W U1 I1 cos 1 U2 I2 cos 2 U3 I3 cos 3 (1) margin of increase gets greater with the decrease of ambient temperature. When the ambient temperature is 15 C, the heating f where W is system power dissipation, U1, I1 and cos 1 are the capacity in the solar and air heat source mode increases by 62% f voltage, current and power factor of compressor, U2, I2 and cos 2 compared with that in the single air heat source mode. If the are the voltage, current and power factor of indoor fan, and U3, I3 temperature difference of combined heat transfer is 5 C, the f and cos 3 are the voltage, current and power factor of outdoor fan. heating capacity in the solar and air heat source mode increases by 51% than that in the single air heat source mode. When the ambient (2) Heating capacity temperature is 5 C, the heating capacity in the solar-air heat source mode can reach the heating capacity under rated heating (high temperature) condition (at ambient temperature of 7 C) in ð Þ the single air heating source mode. ¼ G h2 h1 Q 0 ð Þ (2) Vn 1 Wn 5.2. System COP where Q is heating capacity, G is indoor air output of fan and it measured by nozzle, h1 and h2 are air enthalpy of air supply and Fig. 9 shows the COP of SACHP in the single air source mode, the 0 ﬁ return, Vn is wet air speci c volume in nozzle inlet and Wn is solar-air source mode and the single solar heat medium heat source

Fig. 6. Indoor section of solar air composite heat source heat pump system.

Fig. 7. Outdoor section of solar-air composite heat source heat pump system. mode. The data in the ﬁgure below shows the COP in the single transfer is 5 C, the COP in the single solar heat medium heat source solar heat medium heat source mode is larger than the COP in the mode increases by 61% than that in the single air heat source mode; solar and air heat source mode under different conditions; the COP the COP in the solar-air heat source mode increases by 49% than in the air-solar heat source mode is larger than the COP in the single that in the single air heat source mode. If the ambient temperature air heat source mode, and increases with the decrease of ambient is 5 C and the solar heat medium temperature is about 0 C, the temperature. The COP in the single solar heat medium heat source COP in the solar-air heat source mode is up to the COP in the single mode shows a continuous increase distribution with the increase of air heat mode under rated heating (high temperature) conditions solar heat medium temperature; it is mainly unaffected by the (at ambient temperature of 7 C). If the ambient temperature ambient temperature condition. Impacted by temperatures of the is 10 C and the solar heat medium temperature is 4 C, the COP solar heat medium and air heat medium, the COP in the solar-air in the single solar heat medium heat source mode can reach the heat source mode shows a leaping linear distribution in different COP in the single air heat source mode under rated heating (high environmental conditions with the increase of the solar heat me- temperature) conditions (at ambient temperature of 7 C). dium temperature. When the ambient temperature is 15 C, the COP in the single solar heat medium heat source mode increases by 6. Conclusions 76% compared with that in single air heat source mode; the COP in the solar-air heat source mode increases by 59% than that in the air The study has shown that the solar air composite heat pump heat source mode. If the temperature difference of combined heat

Fig. 8. Heating capacity comparison. Fig. 9. COP comparison.

Please cite this article in press as: Y. Liu, et al., Performance of a solar air composite heat source heat pump system, Renewable Energy (2015), http://dx.doi.org/10.1016/j.renene.2015.09.001 6 Y. Liu et al. / Renewable Energy xxx (2015) 1e6 system can well achieve the organic integration of solar collection technology adoption in residential reference buildings, Renew. Energy 60 e technology and air source heat pump technology, and the com- (2013) 615 624. [6] P. Moreno, C. Sole, A. Castell, L.F. Cabeza, The use of phase change materials in bined utilization of two renewable heat sources of solar power and domestic heat pump and air-conditioning systems for short term storage: a air. A SACHP experiment table was established and conducted a review, Renew. Sustain. Energy Rev. 39 (2014) 1e13. comprehensive experimental study of three working modes of this [7] T. Changqing, S. Wenxing, S. Wang, Research on two-stage compression variable frequency air source heat pump in cold regions, Acta Energiae Solaris system in the standard enthalpy difference laboratory. The results Sin. 25 (2004) 388e393. of the experiment have indicated that the composite heat pump has [8] Z.M. Amin, M.N.A. Hawlader, A review on solar assisted heat pump systems in been obviously improved in cooling capacity and performance Singapore, Renew. Sustain. Energy Rev. 26 (2013) 286e293. [9] L. Zhu, J. Yu, M. Zhou, X. Wang, Performance analysis of a novel dual-nozzle compared with the single air source heat pump; the margin of ejector enhanced cycle for solar assisted air-source heat pump systems, increase was increasing with the decrease of outdoor ambient Renew. Energy 63 (2014) 735e740. temperature. Under the ultra low temperature heating condition at [10] J. Jie, C. Jingyong, H. Wenzhu, F. Yan, Experimental study on the performance ﬁ of solar-assisted multi-functional heat pump based on enthalpy difference lab the outdoor ambient temperature of 7 C speci ed in the national with solar simulator, Renew. Energy 75 (2015) 381e388. standard, the heating capacity and performance of the composite [11] S. Odeh, S. Nijmeh, B. Akash, Performance evaluation of solar-assisted double- heat pump both increased by over 50% than that of the single air tube evaporator heat pump system, Int. Commun. Heat Mass Transf. 31 (2004) e heat source heat pump. Therefore, the application of the solar-air 191 201. [12] O. Ozgener, A. Hepbasli, Performance analysis of a solar-assisted ground- source composite heat pump technology can solve the source heat pump system for greenhouse heating: an experimental study, outstanding problems of the single heat source heat pump, further Build. Environ. 40 (2005) 1040e1050. expand the heat supply and application range of the air source heat [13] J. Ji, G. Pei, T. Chow, W. He, A. Zhang, J. Dong, et al., Performance of multi- functional domestic heat-pump system, Appl. Energy 80 (2005) 307e326. pump in winder and accelerate the application process of the solar [14] M. Karagiorgas, K. Galatis, M. Tsagouri, T. Tsoutsos, A. Botzios-Valaskakis, Solar heat pump in air conditioners for buildings. assisted heat pump on air collectors: a simulation tool, Sol. Energy 84 (2010) 66e78. [15] V. Badescu, Model of a solar-assisted heat-pump system for space heating Acknowledgment integrating a thermal energy storage unit, Energy Build. 34 (2002) 715e726. [16] V. Badescu, Model of a space heating system integrating a heat pump, pho- This research was supported by Young Key Teachers Subsidy tothermal collectors and solar cells, Renew. Energy 27 (2002) 489e505. [17] V. Badescu, Model of a thermal energy storage device integrated into a solar Scheme of Colleges and Universities in Henan (2011GGJS-115), and assisted heat pump system for space heating, Energy Convers. Manag. 44 by the Ministry of Education of Henan (14A480005) and the Min- (2003) 1589e1604. istry of Science and Technology of Zhengzhou (20130653). [18] Meteorological Library of China Meteorological Administration Meteorolog- ical Information Center, Tsinghua University Department of Building Science, Meteorological Data of China Building Thermal Environmental Analysis, China References Construction Industry Press, Peking, 2005. [19] Air-conditioning, Heating, and Refrigeration Institute, Performance Rating of [1] D. Chwieduk, Solar Energy in Buildings, Academic Press, Oxford, 2014. Unitary Air-conditioning & Air-source Heat Pump Equipmeng, ANSI/AHRI [2] J.R.S. Brownson, Solar Energy Conversion Systems, Academic Press, Boston, Standard 210/240, 2008 (Arlington, VA: USA). 2014. [20] The state administration of quality supervision, Inspection and Quarantine of [3] S.A. Kalogirou, Solar Energy Engineering, second ed., Academic Press, Boston, the People's Republic of China, China National Standardization Management 2014. Committee, Peking: China, 2004. Room Air Conditioner, GB/T7725. [4] S.P. Lohani, D. Schmidt, Comparison of energy and energy analysis of fossil [21] The state administration of quality supervision, Inspection and Quarantine plant, ground and air source heat pump building heating system, Renew. of the People's Republic of China, China National Standardization Man- Energy 35 (2010) 1275e1282. agement Committee, Peking: China, 2010. Unitary air conditioners, GB/ [5] N. Aste, R.S. Adhikari, M. Manfren, Cost optimal analysis of heat pump T17758.

Please cite this article in press as: Y. Liu, et al., Performance of a solar air composite heat source heat pump system, Renewable Energy (2015), http://dx.doi.org/10.1016/j.renene.2015.09.001