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The Characteristics of the Evaporator/Evaporator for Direct Expansion Solar Assisted Heat Pump System

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Mingyan Zhu
Mingyan Zhu
Mingyan Zhu
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Huanrong Xie
Huanrong Xie
Huanrong Xie
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Biao Zhang
Biao Zhang
Biao Zhang
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Xin Guan
Xin Guan
Xin Guan
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Abstract and Figures

Direct expansion solar assisted heat pump (DX-SAHP) technology is developed by combining solar energy heat utilization with heat pump energy saving technology. The experimental researches of the DX-SAHP hot water system are conducted in this paper, and overall performance of DX-SAHP is analyzed with three different structures of collectors/evaporators, namely a bare-plate collector, a glass-plate collector and double collectors/evaporators (a bare-plate collector and a glass-plate collector). The influence factors and overall performance are studied, which show that the overall performance of the system is mainly influenced by solar irradiation intensity and the collector area. Comparing with glass-plate collector in similar conditions, bare-plate collector system COP is higher. While increasing collector area is conducive to improve the system COP, but will reduce the collector efficiency and increase the workload of the compressor by comparing the bare-plate collector with double-plate collectors.
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Journal of Power and Energy Engineering, 2013, 1, 73-76
http://dx.doi.org/10.4236/jpee.2013.15012 Published Online October 2013 (http://www.scirp.org/journal/jpee)
Copyright © 2013 SciRes. JPEE
73
The Characteristics of the Evaporator/Evaporator for
Direct Expansion Solar Assisted Heat Pump System
Mingyan Zhu, Huanrong Xie, Biao Zhang, Xin Guan
Institute of Energy and Power Engineering, University of Shanghai for Science and Technology, Shanghai, China.
Email: zmy117060164@163.com
Received October 2013
ABSTRACT
Direct expansion solar assisted heat pump (DX-SAHP) technology is developed by combining solar energy heat utiliza-
tion with heat pump energy saving technology. The experimental researches of the DX-SAHP hot water system are
conducted in this paper, and overall performance of DX-SAHP is analyzed with three different structures of collec-
tors/evaporators, namely a bare-plate collector, a glass-plate collector and double collectors/evaporators (a bare-plate
collector and a glass-plate collector). The influence factors and overall performance are studied, which show that the
overall performance of the system is mainly influenced by solar irradiation intensity and the collector area. Comparing
with glass-plate collector in similar conditions, bare-plate collector system COP is higher. While increasing collector
area is conducive to improve the system COP, but will reduce the collector efficiency and increase the workload of the
compressor by comparing the bare-plate collector with double-plate collectors.
Keywords: Direct Expansion Solar Assisted Heat Pump; Collector/Evaporator; Experimental Research
1. Introduction
Energy sources are widely utilized in many aspects with
a high-speed human society development period. Solar
energy is known as the renewable and “free” energy
source, without doubt, it is the best choice to be a heat
source of heat pump like the air source. In order to im-
prove the heat pump COP, the idea of combining the heat
pump with solar energy application system has been
proposed and developed by many researchers around the
world, which is the direct expansion solar assisted heat
pump(DX-SAHP), the solar collector and the heat pump
evaporator are installed into a single unit (collector/eva-
porator), where the refrigerant is directly evaporated in
the solar collector-evaporator by absorbing the solar
energy (and/or ambient air energy) to undergo a phase
transition from liquid to vapor. The DX-SAHP concept
was first proposed by Sporm and Ambrose in 1955 [1].
Following their work, many theoretical and experimental
studies (thermodynamic analysis, numerical simulation
etc.) have been reported. Such as the United States Sporm
S.K, Chaturvedi, M.P.O ‘Dell, Australian G.L. Morrison,
Hawlader, Krakok and Lin in Japan, Huang BJ etc [1-8].
Chaturvedi conducted a theoretical analysis for several
types of collectors/evaporators in 1979 and found that
using the inexpensive bare-plate collector can have a
high COP and collector efficiency, whether the capacity
of the collector and the compressor capacity match or not,
which directly affect system performance, in order to
achieve higher COP and the collector efficiency, the col-
lector/evaporation temperature should keep greater than
ambient temperature at a range of 5˚C - 10˚C [3,4]. In
order to solve the reliability problems, Shanghai Jiaotong
University Guo Junjie studied two different evaporation
areas and found that system’s reliability has improved by
increasing the evaporation area in low-temperature con-
ditions [9].
2. Experimental System Device Introduction
In order to investigate influence of collectors/evaporators
on thermal performance of DX-SAHP, we set up the
DX-SAHP experimental equipment, which is shown in
Figure 1. It mainly contains the solar energy collector/
evaporator, compressor, condenser, heat storage water
tank, gas-liquid separator, filter drier and thermal expan-
sion valve parts, and the structural parameters of the
main components are as follows: 1) Solar collector/eva-
porator: Sampux “PYT/L2.0-3” tablets of finned tube
type collector/evaporator, two pieces of collectors/eva-
porators (one is a bare-plate collector, the other is a
glass-plate collector), both the collectors area are 2 m2,
the valid heating area 1.87 m2; 2) Compressor: NJ6226Z
type Hermetic reciprocating compressor, the rated power
of 735 W; 3) condenser: “BL14-20D” type plate heat
exchanger with heat transfer area of 0.35 m2; 4) heat sto-
The Characteristics of the Evaporator/Evaporator for Direct Expansion Solar Assisted Heat Pump System
Copyright © 2013 SciRes. JPEE
74
1, 2—Collector/evaporator; 3—Gas-liquid separator; 4—Compressor; 5—Condenser; 6—High pressure accumulator 7—Thermal expansion valve;
8—Circulating water pump; 9—Heat storage water tank.
Figure 1. Schematic diagram of the direct expansion type of the solar heat pump hot water system.
rage water tank pressure type 304 stainless steel tank
design, capacity of 150 L; 5) Throttling device: “TN 2”
type thermal expansion valve, the system refrigerant is
the pollution-free R134a; 6) Circulating water pump:
“HRS20/11-Z” type pump, the rated input power of 120
W, the rated head of 7.5 m and the rated flow of 0.55
m3/h;
In the direct expansion type solar heat pump system,
the operating temperature of the collector and the refri-
gerant evaporation temperature keeps consistent and in
low temperature range, which can obtain higher collec-
tion efficiency and avoid the solar energy heat pump af-
fected by the shortage of time and weather, the refrige-
rant is directly evaporated in the solar collector-evapo-
rator by absorbing the incident solar energy (and/or am-
bient air energy) to undergo a phase transition from liq-
uid to vapor, then the vaporized refrigerant passes through
the compressor and finally pumped into the condenser,
where it gets condensed by water as cooling medium
through a refrigerant-to-water heat exchanger out of the
water tank.
3. Running Performance of DX-SAHP
The performance of DX-SAHP is greatly influenced by
the environment parameter, in order to study it, we use
three kinds of collectors/evaporators operation mode
respectively, a set of experimental data are selected to
analyze the time-dependent performance of the DX-
SAHP system in different meteorological conditions. The
collectors/evaporators are a glass-plate collector (Ac = 2
m2), a bare-plate collector (Ac = 2 m2) and double-plate
collectors (Ac = 4 m2), where Ac is the collector area.
The solar irradiance ranges 143.12 W/m2 - 664.6 W/m2
and the system COP is 2.49 - 3.47. The following is the
comparative analysis on the collectors in similar condi-
tions.
From the data shown in Figures 2 and 3, with the
glass-plate collector (Ac = 2 m2) and a bare-plate collec-
tor (Ac = 2 m2), respectively, the DX-SAHP is affected
by external environment (solar irradiance, ambient tem-
perature, wind speed, etc.), during the experimental pe-
riod, the average value of the solar radiation and ambient
temperature are 602 W/m2, 30.2˚C and 604 W/m2, 29.4˚C
respectively, the COP of the glass-plate collector opera-
tion mode is 2.69 and the other is 3.25. The average val-
ue of the solar radiation is almost alike, however, the
instantaneous solar radiation varied with the effect of
cloud, thus unstable system operation thereby affecting
the heating power and compressor power consumption, it
was found that the system COP increases or reduces with
the solar irradiance increases or decreases at the begin-
ning of the system’ running, then, the system operation is
stable gradually with time, namely, although the system
is still affected by the instantaneous solar radiation,
which is not with a high fluctuation.
Firstly, the water temperature difference maintains a
constant basically, secondly, the compressor power con-
sumption rises all the time, which are the reasons that the
COP of the bare-plate collector has been declining. Even
though the compressor power consumption and the water
temperature difference are all higher than the glass-plate
The Characteristics of the Evaporator/Evaporator for Direct Expansion Solar Assisted Heat Pump System
Copyright © 2013 SciRes. JPEE
75
Figure 2. System COP and solar irradiance with different
operation mode.
Figure 3. Compressor power consumption and water tem-
perature difference with different operation mode.
collector, however, the COP of the bare-plate collector is
higher than that of the glass-plate collector along the
running process, by comparing the rise rate of the water
temperature difference with the rise rate of the compres-
sor power consumption, we can find that the proportion
of the bare-plate collector is higher.
As for the experimental data for the bare-plate collec-
tor/evaporator during the test, the average value of the
solar radiation, the average ambient temperature and the
average wind velocity are 602 W/m2, 29.1˚C and 1.0 m/s
respectively; And corresponding to the DX-SAHP sys-
tem with double plate collector/evaporator, which is
664.6 W/m2, 22.5˚C and 0.8 m/s.
It can be noted from data shown in Figure 4, double
collectors operational system ‘COP is higher than that of
the bare-plate Collector operational mode in the process
of system operation, by calculation, the former is 3.47
and the latter is 3.26; while the collection efficiency of
double collector is constant lower than that of the bare-
plate collection, when the external environmental para-
meters are under similar condition. With the increase of
Figure 4. Comparison with the collection efficiency and COP
between bare-plate collector and double-plate collectors.
heating area, the COP increases while the efficiency de-
creases oppositely. Firstly, this is because that the col-
lector area increases, the solar irradiation absorbed by the
evaporator increases, leading the refrigerant evaporation
temperature increases, finally improving the COP of DX-
SAHP; as the evaporation temperature increases, the heat
absorbed from the atmosphere in evaporator increased,
whereas the efficiency of the collector is decreased. While
the collector area further increases, the rate of increase of
the COP gradually decreases, and this is because when
the collector area increases to a certain extent，the further
increase in heat absorption, the superheat degree and com-
pressor suction superheat degree increase, causing the
exhaust temperature overtops and the compressor power
consumption increases, at last the system performance
deteriorates.
Under the similar external environment, as the heating
process progresses, the comparison with the exhaust tem-
perature of compressor and hot water temperature be-
tween bare-plate collector and double-plate collector is
shown in the Figure 5. Of course, we can note that the
larger the collector area is, the faster the rise rate of hot
water temperature is and the shorter the time for making
hot water is. In addition, the exhaust temperature of com-
pressor rises, which is owing to the increasing of collec-
tor area, then the solar irradiation absorbed by the eva-
porator increases, thus the refrigerant temperature en-
hances, under the condition of the throttle valve opening
degree invariable, the degree of superheat of the evapo-
rator outlet increases, leading to the compressor exhaust
temperature rise eventually.
To sum up, increasing collector area is conducive to
improving the system COP, but will reduce the collector
efficiency and increase the workload of the compressor,
thus increasing the system cost and installation space.
Therefore, the solar Collector/evaporator is required to
carry out a reasonable selection technically and econom-
-10 010 20 30 40 50 60 70 80 90 100
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740 solar ir radiation(glass -plate collector )
solar ir radiation(bare-pl ate collector)
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compressor power consumpt ion (bare-plate col lector)
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water temperatur e difference(bare- plate collector)
Time(min)
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collecti on efficiency(doubl e-plate collector)
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collection efficiency
The Characteristics of the Evaporator/Evaporator for Direct Expansion Solar Assisted Heat Pump System
Copyright © 2013 SciRes. JPEE
76
Figure 5. The comparison with the exhaust temperature of
compressor and hot water temperature between bare-plate
collector and double-plate collectors.
ically.
4. Conclusions
1) The overall performance of DX-SAHP is researched
with three different structures of collectors/evaporators;
2) Under the similar external conditions, in compari-
son with the glass-plate collector, the bare-plate collector
system COP is higher with better irradiation and higher
environment temperature; increasing collector area is con-
ducive to improving the system COP, but will reduce the
collector efficiency and increase the workload of the
compressor;
3) Adopt bare-plate collector at summer with better ir-
radiation and higher environment temperature, in winter,
at the opposite case, using the glass-plate collector, whe-
reas the circulation water temperature is not reached the
requirement, double-plate collectors are needed;
4) If the irradiance is higher, the water temperature
rise rate will accelerate, the COP will increase and the
evaporation pressure (temperature) will rise, but the com-
pressor suction superheat and power will increase, which
impact the performance, so the superheat degree control
in a certain range is key to improve the direct expansion
type solar heat pump system performance.
REFERENCES
[1] P. Sporm and E. R. Ambrose, “The Heat Pump and Solar
Energy,” Proceedings of the World Symposium on Ap-
plied Solar Energy.
[2] S. I. C. Chaturvedi, A. S. Roberts and V. Mei, “Solar
Collector as Heat Pump Evaporator,” Proceedings of 13th
Intersociety Energy Conversion Conference, 2000, pp.
286-297.
[3] S. K. Chaturvedi and A. S. Roberts, “Analysis of Two-
Phase Flow Solar Collectors with Application to Heat
Pumps,” Journal of Solar Energy Engineering, Vol. 104,
1982, pp. 359-365. http://dx.doi.org/10.1115/1.3266330
[4] M. P. O’Dell, J. W. Mitchell and W. A. Beckman, “Solar
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[5] G. L. Morrison, “Simulation of Packaged Solar Heat-
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http://dx.doi.org/10.1016/0038-092X(94)90631-9
[6] M. N. A. Hawlader, S. K. Chou and M. Z. Ullah, “The
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http://dx.doi.org/10.1016/S1359-4311(00)00105-8
[7] K. L. Krakow and S. A. Lin, “Solar Source Heat Pump
with Refrigerant-Cooled Solar Collectors for Cold Cli-
mates,” Trans ASHRAE, Vol. 88, 1982, pp. 417-439.
[8] B. J. Huang and J. P. Chyng, “Performance Characteristic
of Integral Type Solar-Assisted Heat Pump,” Solar Ener-
gy, Vol. 71, 2001, pp. 403-414.
http://dx.doi.org/10.1016/S0038-092X(01)00076-7
[9] J. J. Guo, J. Y. Wu, M. L. Jiang and R. Z. Wang, “Air
Source Heat Pump Water Heater Evaporator Matching
Characteristics Research,” The Chinese Society of Engi-
neering Thermophysics. Engineering Thermodynamics and
Energy Conversion Conference, 2006, pp. 668-672.
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exhaust temperature(double-plate collector)
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hot water temperature(double-plate collector)
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)
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5
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Article
  • May 2020
This work presents the performance of a direct-expansion solar-assisted heat pump (DX-SAHP) to supply 60 L per day of domestic hot water. The operating values in tests, such as refrigerant pressure and temperature, were taken in a built prototype every five minutes. The weather data measurements were obtained with a WS-1201 meteorological weather station and a CMP3 pyranometer. Boiling took place in a bare flat-plate solar collector using ambient temperature and the solar radiation intensity, with an emissivity value of 0.10. The system used a photovoltaic panel to turn on a variable speed compressor with 95 W of maximum power at 3600 rpm using R134a as working fluid. The measured condensation average temperature was 41.2 °C, meanwhile boiling temperature was 5.5 °C, gaining 252.8 W in the collector/evaporator and allowing releasing 335.8 W in the condenser while water reached a maximum temperature of 39.7 °C. In Test 1, when solar radiation had an average daily value of 607.5 W/m2 with an average ambient temperature of 25.5 °C, water raised its temperature from 17.5 to 39.3 °C in 35 min. The maximum coefficient of performance (COP) of the system was 5.75 under rainy conditions in Test 2. Results showed that while the solar radiation intensity or ambient temperature were increased, the water heating time decreased. The environmental study also showed that by the implementation of the DX-SAHP, it could stop emitting 1065.6 kg of CO2 per year due to the system using renewable energy for its working.
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... ARINZE et al. used dynamic numerical model to study the heat transfer performance of flat plate collector with glass cover [10].FIJITAF et al. studied the performance of the heat pump system with cover plate collector / evaporator by experiments [11].Bare flat plate collector has been widely studied because it can absorb solar energy and air energy at the same time.ZHU et al. compared the heat pump system with cover plate collector and bare flat plate collector, and concluded that the performance of bare flat plate collector is better [12].ITO et al. carried out experimental research on the relationship between evaporation temperature and system performance of bare flat plate collector [13].CHATA et al. studied the effect of refrigerant on the performance of bare flat plate collector heat pump system [14].HAWLADER et al. used experiments to analyze the impact of bare plate collector area on system performance [15].KONG et al. analyzed the annual operating characteristics of the bare flat plate collector heat pump system by establishing a dynamic numerical model, and analyzed the influence of different environmental parameters on the performance of the bare flat plate collector [16]. ...
Heating Performance of Solar Heat Pump Heating System with Aluminum Tube Collector (November 2021)
Article
Full-text available
  • Feb 2021
A solar heat pump heating system with an aluminum tubular collector is proposed in this paper. Mathematical models are established for solar energy absorption and air energy absorption of the aluminum tubular collector, as well as the heat-absorption coefficient of the working substance. The electronic expansion valve is controlled via the fuzzy PID method to adjust the working substance flow rate, as well as to control the evaporator overheating and set the indoor heating temperature. TRNSYS is used to analyze the effects of the wind speed, solar radiation amount, environment temperature, and working substance flow rate on the heat transfer performance of the aluminum tubular collector. The results indicate that the heat transfer performance of the aluminum tubular collector is significantly affected not only by the solar radiation but also the wind speed. For wind speed > 2 m/s, the absorbed power of the collector increases rapidly with an increase in the wind speed; when the working-medium flow rate reaches 4 m/s, the collector absorption power tends to be saturated. Subsequently, an experimental heating system with a heating area of 170 m2 is constructed. Experiments revealed that the maximum coefficient of performance (COP) of the heating system is 4.46, and the average COP value is 3.95, indicating good heating effect.
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... En los últimos años se ha incrementado el estudio de la BCAES-ED como tecnología de calentamiento de agua, varios estudios analíticos, numéricos y experimentales han sido desarrollados por investigadores con la finalidad de caracterizar el coeficiente de desempeño y la eficiencia exergética de una BCAES-ED buscando mejorar el rendimiento térmico. El coeficiente de operación del sistema ( está en función de parámetros meteorológicos como la temperatura ambiental, radiación solar y también de parámetros operacionales como la velocidad de rotación del compresor [4].La influencia del área del panel evaporador/colector solar en el rendimiento térmico del sistema ha sido identificada por Zhu et al. [5], los cuales manifiestan que al incrementar el área del colector solar mejora el del sistema pero se reduce la eficiencia del colector solar y se incrementa la carga de trabajo del compresor. Siendo necesario analizar la influencia de las variables meteorológicas conjuntamente con los parámetros de operación para caracterizar el funcionamiento de esta tecnología y potenciar la introducción de la misma en climas tropicales y húmedos. ...
Análisis energético y exergético de una bomba de calor de expansión directa con energía solar
Article
Full-text available
  • Apr 2020
A direct expansion solar assisted heat pump (BCAES-ED) is a water heating technology with great potential in countries located in tropical and humid areas, so it is important to conduct energy and exergy-based analyzes that allow characterization its operation and promote its application in industrial processes. The present study used meteorological parameters that influence an experimental installation located in Portoviejo-Ecuador for a collector / evaporator of 3 and 1.5 m2 and compressor rotation speeds of 400 and 600 rpm. The energy analysis reported a coefficient of performance of the system between 3.5 and 4.5. The compressor obtained the highest value of exergy destruction, followed by the solar collector, the condenser and the expansion valve. The exergy efficiency of the system reached the value of 70%. The feasibility and advantages of using this technology in tropical countries are demonstrated.
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... The results suggested that a high COP is feasible using bare collectors and that a higher collector area improves performance, presenting a COP 1.5 to 2 times higher than a conventional fancoil heat exchanger heat pump. Zhu et al. [15] suggests that in order to maximize COP a bare collector should be used during the summer when high ambient temperatures and high radiation conditions are present and that a glass-plated collector should be used during the winter to minimize the performance drop. Anderson et al. [16] evaluated the performance of these devices as water heating systems. ...
Thermal Capacity: Additional Relative Efficiency to Assess the Overall Performance of Heat Pump-Based Heating Systems
Article
  • May 2019
  • APPL THERM ENG
The present analytical study is carried out to introduce the thermal capacity, a relative efficiency based on a different approach, to assess the performance of heat pump-based systems. Through the first law of thermodynamics and the universal heat transfer coefficient, the heat yielded by the heat pump and the thermal load demanded by the product are quantified respectively, consequently determining the heat transfer capabilities of the system. This performance metric was tested using experimental data published on different researches using four distinct setups, working under various geographical and climatological conditions and for both indoor air conditioning and water heating purposes. Since the parameter introduced was developed as a complement to the already existing relative efficiencies, when combined with the coefficient of performance, COP, a region of minimum required performance is created, where the heat pump is expected to operate, being able to fulfill the energy demand of the product while maintaining an acceptable performance. Finally, the information provided by the thermal capacity was found to be useful regarding the design and operation of these systems due to its conditional nature, enabling the operator or decision maker to assess categorically the performance and to propose modifications to the heat pump system accordingly.
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... Al panel colector/evaporador se lo clasifica como colectores solares planos con y sin capa de vidrio; los parámetros investigados en los colectores solares son: eficiencia del colector, área del colector, condiciones ambientales, propiedades de los refrigerantes, temperatura del agua, temperatura de evaporación de diferentes refrigerantes, entre otros. Zhu et al. [23] comparan los colectores planos de una o dos cubiertas de vidrio en similares condiciones con los colectores desnudos, encuentran que a mayor radiación solar y temperatura ambiental una BECAES-ED que utiliza colectores planos sin capa de vidrio tienen mejor desempeño que los colectores con una o dos capas de vidrio. Garg et al. [24] comparan experimentalmente dos colectores solares, uno con y otro sin capa de vidrio relacionándolos con el desempeño térmico de una BCAES-ED. ...
Actualidad y perspectivas de una bomba de calor de expansión directa con energía solar Current and future perspectives of direct expansion solar assisted heat pumps
Article
Full-text available
  • Jan 2016
La bomba de calor de expansión directa con asistencia de energía solar se utiliza en el modo de calefacción para diversas aplicaciones entre las que podemos citar, calentamiento de agua, calentamiento de aire para climatizar edificios, desalinización de agua, secado solar entre otras. El presente trabajo revisa las principales investigaciones sobre esta tecnología enfocando sus aplicaciones para el calentamiento de agua, para lograr este objetivo se describen en detalle la configuración básica y avanzada con la finalidad de caracterizar el coeficiente de desempeño de cada una de estas configuraciones; también es oportuno analizar esta tecnología de acuerdo a la segunda ley de la termodinámica para identificar bajos desempeños en los componentes del sistema. Esta revisión bibliográfica apunta a desarrollar esta tecnología para calentamiento de agua en un rango de 60-90 °C, ideal para aplicaciones industriales. Palabras claves: Bomba de calor, energía solar, expansión directa, aplicaciones a alta temperatura. Abstract Direct expansion solar assisted heat pumps have been used in the heating mode for several applications among them we may cite, water heating, heating space for building, water desalination system, solar drying, amongst other. The present work review the most important research about this technology approaching their applications for water heating, to reach this goal the basic and advanced configuration model are describe in details with the purpose of characterize the coefficient of thermal performance; is relevant too, analyze this technology according to the second law of thermodynamics to point out slow performance in the components of the system. This review rightly point out to develop this technology for heating water in a 60-90 °C range, ideally suited for industrial applications.
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Revisión del estado del arte de sistemas DX-SAHP para la obtención de agua caliente sanitaria
Article
Full-text available
  • Apr 2020
El objetivo del presente artículo es revisar de forma detallada las distintas investigaciones realizadas con sistemas de bombas de calor de expansión directa asistidas por energía solar (DX-SAHP) utilizadas para el calentamiento de agua en los últimos años. El creciente consumo energético, el uso de refrigerantes que debilitan la capa de ozono, la emisión de gases de efecto invernadero a la atmósfera y los efectos en el calentamiento global, son los principales problemas que presentan los sistemas convencionales de calentamiento de agua. El uso de hidrocarburos como refrigerantes representa una reducción en la contaminación, además de ser una de las mejores opciones para reemplazar a los clorofluorocarbonos e hidroclorofluorocarbonos por sus valores de potencial de calentamiento global y potencial de destrucción de la capa de ozono cercanos a 0. Un sistema DX-SAHP aprovecha la energía solar térmica directamente, empleando un colector solar de placa plana sin cubierta. Esos sistemas proporcionan agua caliente sanitaria a más de 50 °C, calentando volúmenes de agua de hasta 200 litros, alcanzando valores de COP superiores a 4. La energía solar y el uso de refrigerantes alternativos de bajo impacto ambiental son propuestos para alcanzar este propósito.
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THERMAL PERFORMANCE OF REFRIGERANT COOLED SOLAR COLLECTORS IN A SOLAR SOURCE HEAT PUMP SYSTEM.
Article
Solar Collectors cooled directly with Refrigerant 12 and acting as the evaporator of a solar source heat pump system has been experimentally investigated. The refrigerant cooled solar collector may be operated at an evaporation temperature lower than its ambient temperature and thus has an efficiency higher than that of the flat plate solar collectors in conventional systems.
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Simulation of packaged solar heat-pump water heaters
Article
  • Sep 1994
  • SOL ENERGY
The performance of heat-pump water heaters with solar boosted evaporators is investigated experimentally, and a simulation model in the TRNSYS package is developed for assessing annual performance. A packaged heat-pump system with a passive evaporator and condenser in the one unit, which eliminates parasitic energy consumption of the usual circulating pump and fan-coil unit, is assessed for a range of climatic conditions.
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Analysis of Two-Phase Flow Solar Collectors With Application to Heat Pumps
Article
  • Nov 1982
A thermodynamic model is developed to analyze the thermal performance of twophase solar collectors. The well-known equilibrium homogeneous theory is used to model the two-phase flow in the solar collectors. The resultant set of coupled ordinary differential equations for saturated pressure and quality of working fluid in the collector tubes are solved by an iterative procedure using a fourth-order RungeKutta method. The results are then applied to determine the thermal performance of a solar assisted heat pump which uses two-phase flow collectors as the evaporator. The results indicate that even with the use of less expensive bare solar collectors as evaporator for the heat pump, the heating coefficient of performance (COP /SUB H/) as high as 6 can be obtained under realistic ambient conditions provided a proper matching exists between the collector's evaporative capacity and the compressor's pumping capacity.
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Solar heat pump systems with refrigerant-filled collectors
Article
  • Jan 1983
The heat pump system with a refrigerant-filled evaporator consists of a standard air-to-air or air-to-liquid heat pump that utilizes a solar panel as the evaporator. A combination of solar energy and convection heat transfer acts as the ''free'' energy absorbed by the collector/evaporator. In this paper, the seasonal performance of such systems for industrial applications will be presented. Performance of collector/evaporator heat pumps will be compared with alternative heat pump and solar systems. The benefits of covered and coverless collector/evaporators will be discussed. Results to date have shown that refrigerant-filled collector heat pumps do not perform as well as conventional heat pumps at small collector areas but have as much as 15% performance improvement over conventional heat pumps at an appropriate collector area.
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The performance of a solar assisted heat pump water heating system
Article
  • Jul 2001
  • APPL THERM ENG
Analytical and experimental studies were performed on a solar assisted heat pump water heating system, where unglazed, flat plate solar collectors acted as an evaporator for the refrigerant R-134a. The system was designed and fabricated locally, and operated under meteorological conditions of Singapore. The results obtained from simulation are used for the optimum design of the system and enable determination of compressor work, solar fraction and auxiliary energy required for a particular application. To ensure proper matching between the collector/evaporator load and compressor capacity, a variable speed compressor was used. Due to high ambient temperature in Singapore, evaporator can be operated at a higher temperature, without exceeding the desired design pressure limit of the compressor, resulting in an improved thermal performance of the system. Results show that, when water temperature in the condenser tank increases with time, the condensing temperature, also, increases, and the corresponding COP and collector efficiency values decline. Average values of COP ranged from about 4 to 9 and solar collector efficiency was found to vary between 40% and 75% for water temperatures in the condenser tank varying between 30°C and 50°C. A simulation model has been developed to analyse the thermal performance of the system. A series of numerical experiments have been performed to identify important variables. These results are compared with experimental values and a good agreement between predicted and experimental results has been found. Results indicate that the performance of the system is influenced significantly by collector area, speed of the compressor, and solar irradiation. An economic analysis indicates a minimum payback period of about two years for the system.
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Performance characteristic of integral type solar-assisted heat pump
Article
  • Dec 2001
  • SOL ENERGY
The characteristic of an integral type solar-assisted heat pump water heater (ISAHP) is investigated in the present study. The ISAHP consists of a Rankine refrigeration cycle and a thermosyphon loop that are integrated together to form a package heater. Both solar and ambient air energies are absorbed at the collector/evaporator and pumped to the storage tank via a Rankine refrigeration cycle and a thermosyphon heat exchanger. The condenser releases condensing heat of the refrigerant to the water side of the thermosyphon heat exchanger for producing a natural-circulation flow in the thermosyphon loop. A 105-liter ISAHP using a bare collector and a small R134a reciprocating-type compressor with rated input power 250 W was built and tested in the present study. The ISAHP was designed to operate at an evaporating temperature lower than the ambient temperature and a matched condition (near saturated vapor compression cycle and compressor exhaust temperature <100°C). A performance model is derived and found to be able to fit the experimental data very well for the ISAHP. The COP for the ISAHP built in the present study lies in the range 2.5–3.7 at water temperature between 61 and 25°C.
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Solar Collector as Heat Pump Evaporator
  • Jan 2000
  • 286-297
  • S I C Chaturvedi
  • A S Roberts
  • V Mei
S. I. C. Chaturvedi, A. S. Roberts and V. Mei, "Solar Collector as Heat Pump Evaporator," Proceedings of 13th Intersociety Energy Conversion Conference, 2000, pp. 286-297.
Air Source Heat Pump Water Heater Evaporator Matching Characteristics Research
  • Jan 2006
  • 668-672
  • J J Guo
  • J Y Wu
  • M L Jiang
  • R Z Wang
J. J. Guo, J. Y. Wu, M. L. Jiang and R. Z. Wang, "Air Source Heat Pump Water Heater Evaporator Matching Characteristics Research," The Chinese Society of Engineering Thermophysics. Engineering Thermodynamics and Energy Conversion Conference, 2006, pp. 668-672.