NUMERICAL ESTIMATION OF THE SOLAR COPS PERFORMANCE OF A SINGLE-STAGE ABSORPTION REFRIGERATION MACHINE FOR AIR-CONDITIONING A BUILDING
This study numerically investigates a solar absorption chiller coupled with a cylindro-parabolic (parabolic-trough) collector to air-condition an amphitheater at Ibn Khaldoun University in Algeria’s High Plateaus, specifically the city of Tiaret, whose astronomical coordinates recorded by the Ain Bo...
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| author | Mokhtari Fatima , Z. Mokhtari Abderahman , M. Mekroussi , Saïd |
| author_facet | Mokhtari Fatima , Z. Mokhtari Abderahman , M. Mekroussi , Saïd |
| author_institution_txt_mv | [
{
"author": "Z. Mokhtari Fatima ",
"institution": "University of Science and Technology Mohamed Boudiaf (USTO), Oran, Algeria"
},
{
"author": "M. Mokhtari Abderahman ",
"institution": "University of Science and Technology Mohamed Boudiaf (USTO), Oran, Algeria"
},
{
"author": "Saïd Mekroussi ",
"institution": "Ibn Khaldoun University, Tiaret, Algeria"
}
] |
| author_sort | Mokhtari Fatima , Z. |
| baseUrl_str | https://ve.org.ua/index.php/journal/oai |
| collection | OJS |
| datestamp_date | 2026-07-18T06:32:24Z |
| description | This study numerically investigates a solar absorption chiller coupled with a cylindro-parabolic (parabolic-trough) collector to air-condition an amphitheater at Ibn Khaldoun University in Algeria’s High Plateaus, specifically the city of Tiaret, whose astronomical coordinates recorded by the Ain Bouchakif meteorological station are: 35.21° N latitude, 1.28° E longitude, and 1000 m altitude, for a summer day in July. The hourly evaluation of the chiller’s solar coefficient of performance (SCOP) over the summer day considered the region’s solar irradiance and the thermal characteristics of the solar collector, whose geometric and physical properties were selected for this purpose. The solar COP obtained for our system reached approximately 0.4736, a considerable and acceptable value. |
| doi_str_mv | 10.36296/1819-8058.2026.1(84).145-154 |
| first_indexed | 2026-03-31T01:00:06Z |
| format | Article |
| fulltext |
145
Відновлювана енергетика. № 1/2026 | Сонячна енергетика
6.24: 004.942 https://doi.org/10.36296/1819-8058.2026.1(84).145-154
NUMERICAL ESTIMATION OF THE SOLAR COPS PERFORMANCE OF A SINGLE-STAGE ABSORPTION
REFRIGERATION MACHINE FOR AIR-CONDITIONING A BUILDING
Received Jan. 21, 2026; accepted Mar. 23, 2026
Available online Mar. 31, 2026
Mokhtari Fatima Z.¹,
Mokhtari Abderahman M.², Mekroussi Saïd³
Author for correspondence: Mokhtari Fatima
e-mail: mokhtari_f19@yahoo.fr
Abstract. This study numerically investigates a solar absorption
chiller coupled with a cylindro-parabolic (parabolic-trough) col-
lector to air-condition an amphitheater at Ibn Khaldoun Univer-
sity in Algeria’s High Plateaus, specifically the city of Tiaret,
whose astronomical coordinates recorded by the Ain Bouchakif
meteorological station are: 35.21° N latitude, 1.28° E longitude,
and 1000 m altitude, for a summer day in July. The hourly evaluation of the chiller’s solar coefficient of perfor-
mance (SCOP) over the summer day considered the region’s solar irradiance and the thermal characteristics of the
solar collector, whose geometric and physical properties were selected for this purpose. The solar COP obtained
for our system reached approximately 0.4736, a considerable and acceptable value.
Key words: concentrator; thermal efficiency; absorption; solar radiation; cooling; cylindro-parabolic; COP; ab-
sorber; Capderou; heat transfer fluid.
ЧИСЕЛЬНА ОЦІНКА СОНЯЧНОГО КОЕФІЦІЄНТА ПРОДУКТИВНОСТІ (COPS)
ОДНОСТУПЕНЕВОЇ АБСОРБЦІЙНОЇ ХОЛОДИЛЬНІЙ МАШИНИ ДЛЯ КОНДИЦІЮВАННЯ БУДІВЛІ
Отримано 21 січ. 2026 р.; рекомендовано до публікації 23 бер. 2026 р.
Доступно онлайн 31 бер. 2026 р.
Мохтарі Фатіма З.¹, Мохтарі Абдерахман М.²,
Мекруссі Саїд³
Автор для кореспонденції: Балу Пандіан,
e-mail: balumitauto@gmail.com
Анотація. У цьому дослідженні здійснено чисельний ана-
ліз продуктивності сонячної абсорбційної холодильної ма-
шини, поєднаної з циліндропараболічним (параболоцилін-
дричним) колектором, для кондиціювання амфітеатру
Університету Ібн Хальдуна у регіоні Високих плато Ал-
жиру, а саме в місті Тіарет, астрономічні координати
якого, зафіксовані метеорологічною станцією Айн-Бу-
шакіф, становлять: 35,21° пн. ш., 1,28° сх. д., висота – 1000 м над рівнем моря, для літнього дня в липні.
Погодинне оцінювання сонячної продуктивності холодильної машини (COP) протягом літнього дня здій-
снювали з урахуванням показників сонячного опромінення в регіоні та теплових характеристик соняч-
ного колектора, геометричні й фізичні параметри якого були обрані для цієї мети. Отримане для сис-
теми значення сонячного коефіцієнта продуктивності (COP) становило приблизно 0,4736, що є досить
значним і прийнятним показником.
Ключові слова: концентратор; теплова ефективність; абсорбція; сонячне опромінення; охолодження;
циліндропараболічний; COP; абсорбер; модель Капдеру; теплоносій.
1 студент ф-ту машинобудування
https://orcid.org/0009-0002-4388-9957
2 професор лабораторії матеріалів, ґрунтів
і теплотехніки, ф-т архітектури та цивільної
інженерії
https://orcid.org/0000-0002-9725-5995
3 Професор лабораторії промислових
технологій
https://orcid.org/0000-0001-8824-3960
1, 2 Університет науки і технологій імені
Мохамеда Будіафа (USTO), Оран, Алжир
3 Університет Ібн Хальдуна, Тіарет, Алжир
1 Student (Faculty of Mechanical Engineering)
https://orcid.org/0009-0002-4388-9957
2 Professor (Laboratory of Soil and Thermal
Materials, Faculty of Architecture and Civil
Engineering)
https://orcid.org/0000-0002-9725-5995
3 Professor (Laboratory of Industrial
Technologies)
https://orcid.org/0000-0001-8824-3960
1, 2 University of Science and Technology
Mohamed Boudiaf (USTO), Oran, Algeria
3 Ibn Khaldoun University, Tiaret, Algeria
146
Відновлювана енергетика. № 1/2026 | Сонячна енергетика
Abbreviations
𝐼𝑏 – Direct solar irradiation [ W m−2 ]
𝑇𝐿 – Linke turbidity factor
𝑞𝑢 – Useful energy transferred to the heat-transfer fluid
𝐹𝑅 – Heat-removal factor
𝐹′ – Collector efficiency factor
𝜂𝑜𝑝𝑡 – Optical efficiency of the concentrator
𝜂𝑡ℎ – Thermal efficiency of the concentrator
𝐴0 – Collector aperture area (m2)
𝐴𝑟 – Outer surface area of the absorber tube (m2)
𝐴𝑣 – Glass envelope surface area (m2)
𝐷𝑖 – Inner diameter of the absorber (m)
𝐷𝑜 – Outer diameter of the absorber (m)
𝜎 – Stefan–Boltzmann constant
5.66897 × 10−8 W m−2 K−4
𝜀𝑟 – Absorber emissivity
𝜀𝑣 – Glass emissivity
𝑇𝑎𝑚𝑏 – Ambient temperature (K)
𝑇𝑎𝑏 – Absorber temperature (K)
𝑇𝑖 – Inlet temperature of the heat-transfer fluid (oil) (K)
𝑇𝑣 – Glass temperature (K)
𝑃 – Pressure [ bar ]
𝑈𝐿 – Overall heat-loss coefficient [ W m−2 K−1 ]
ℎ𝑐 – Convective heat-transfer coefficient [ W m−2 K−1 ]
ℎ𝑟 – Radiative heat-transfer coefficient [ W m−2 K−1 ]
𝑄 – Heat transfer rate [ W ]
ℎ – Enthalpy [ J kg−1 ]
𝐾𝐹 – Thermal conductivity of the heat-transfer fluid
[ W m−1 K−1 ]
𝑉 – Wind speed (m s−1)
𝐶𝑝 – Specific heat at constant pressure [ J Kg−1 K−1 ]
𝑋 – Solution concentration
Introduction
Using solar energy for air-conditioning is a promising ap-
proach because peaks in cooling demand generally coincide
with maximum solar irradiance. Moreover, solar-thermal
air-conditioning systems reduce electricity consumption,
allow the use of environmentally friendly refrigerants, min-
imize noise, and simplify electrical infrastructure, particu-
larly in rural areas.
In December 2009, more than thirty 50 MW plants based
on cylindro-parabolic mirror technology and a 17 MW
tower plant (with 15 h of storage) were under construction
in Spain [1]. By 2017, Spain accounted for nearly half of
global capacity, at 2300 MW, making it the world leader in
deploying concentrating solar-thermal power plants. The
United States followed with 1740 MW [2]. The largest con-
centrating solar-thermal projects worldwide include the
“IVANPAH” solar facility (392 MW) in the United States,
which uses solar-tower technology, and the “MOJAVE SO-
LAR” project (354 MW) in the United States, which uses
parabolic-trough concentrators [2].
Numerical studies and numerous experimental works have
addressed the coefficient of performance of refrigeration
equipment, particularly solar refrigeration. For example,
Cascales et al. [3] developed several models of LiBr/H₂O so-
lar absorption refrigeration equipment. O. Kizilkan et al. [4]
improved the cost-effectiveness of such equipment by es-
tablishing optimal standards. Romero et al. [5] conducted a
comparative performance study of a reversible absorption
heat-pump system using the mixtures (LiBr/H₂O) and (KOH
+ NaOH + CsOH). The results showed similar performance
for both mixtures and noted that the (KOH + NaOH + CsOH)
mixture operates over extended temperature ranges for
the condenser and absorber.
In this context, our work estimates the solar performance
of a single-stage absorption refrigeration machine driven
by thermal energy transferred from a cylindro-parabolic
collector with carefully selected geometric and optical
characteristics, under the climatic conditions of the Tiaret
region, Algeria, for a summer day in July.
Solar Modelling
In the literature, several authors have proposed empirical
relations linking meteorological variables to radiometric
parameters (global, diffuse, and direct illuminance). For the
present work, we adopt the Capderou model [6], which re-
lies on attenuation coefficients of solar radiation by atmos-
pheric constituents to compute the direct component of
solar irradiation received on an inclined plane under clear-
sky conditions.
𝐼𝑏 = 𝐼𝐶exp [−𝑇𝐿 (0.9 +
9.4
0.89𝑍
sin(ℎ))
−1
] cos(θ)
with 𝐼𝐶the Earth–Sun distance factor:
𝐼𝐶 = 𝐼0 [ 1 + 0.0033cos(
360
365
𝑛)]
𝐼0 is the solar constant = 1367.
cos(𝜃), the cosine of the incidence angle, varies with the
solar tracking mode. In our case, full solar tracking is used;
hence cos(𝜃) = 1 ⇒ 𝜃 = 0.
𝑇𝐿 is the Linke turbidity factor.
Thermal Modelling of a Parabolic-Trough Concentrator
(PTC)
The solar irradiance estimated in the previous section is
captured by an inclined cylindro-parabolic concentrator
equipped with a tracking system so that the incident rays
remain perpendicular to the concentrator’s aperture plane.
147
Відновлювана енергетика. № 1/2026 | Сонячна енергетика
We modelled this collector using heat-transfer equations
among the absorber’s components (Fig. 1). To simplify the
model, we adopt the following assumptions:
• The PTC has a tracking system that perfectly follows
the sun throughout the day.
• Transverse conduction within the absorber and within
the glass envelope is negligible.
• A vacuum is maintained between the absorber tube
and the glass envelope.
• Solar radiation is uniformly distributed within the ab-
sorber.
• Conduction heat exchange within the absorber and
within the glass envelope is negligible.
• The heat-transfer fluid is incompressible.
• The parabolic geometry is symmetric.
Fig. 1. Heat fluxes exchanged in the parabolic-trough collector (PTC) [7]
Thermal efficiency (𝜂th) [7,13] is the ratio between the use-
ful heat transferred to the heat-transfer fluid and the direct
solar power incident on the collector surface (PTC):
𝜂th =
𝑞𝑢
𝐴0 𝐼𝑏
The useful power gained by the fluid in the concentrator is
given by [8]:
𝑞𝑢 = 𝐹𝑅[𝜂opt 𝐴0 𝐼𝑏 − 𝑈𝐿 𝐴𝑟 (𝑇𝑖 − 𝑇𝑎𝑚𝑏)]
The heat removal factor 𝐹𝑅can be computed from [10,11]:
𝐹𝑅 =
𝑚̇𝐶𝑃
𝐴0𝑈𝐿
(1 − 𝑒
(
𝐴0𝑈𝐿𝐹′
𝑚̇𝐶𝑝
)
)
The optical efficiency 𝜂opof the concentrator is [8,12]:
𝜂op = 𝜌0 𝛼0 𝛾 𝐾
With the incidence-angle modifier 𝐾given by [7,9]:
𝐾 = 1 − 0.00384 (𝜃) − 0.000143 (𝜃)2
The overall heat-loss coefficient 𝑈𝐿 is calculated as [10,
11]:
𝑈𝐿 = [
𝐴𝑎𝑏
(ℎ𝑤 + ℎ𝑟,𝑣−𝑎𝑚𝑏) 𝐴𝑣
+
1
ℎ𝑟,𝑎𝑏−𝑣
]−1
Here, ℎ𝑤is the external convection coefficient between
the glass and ambient air, with wind speed 𝑉(m s-1), com-
puted as [10]:
ℎ𝑤 = 5.7 + 3.8 𝑉
The radiative exchange coefficient between the glass and
ambient air is [10, 11]:
ℎ𝑟,𝑣−𝑎𝑚𝑏 = 𝜀𝑎𝑏 𝜎 (𝑇𝑣 + 𝑇𝑎𝑚𝑏) (𝑇𝑣
2 + 𝑇𝑎𝑚𝑏
2 )
The radiative exchange coefficient between absorber and
glass is [10,11]:
ℎ𝑟.𝑎𝑏−𝑣 =
𝜎(𝑇𝑣+𝑇𝑎𝑏)(𝑇𝑣
2+𝑇𝑎𝑏
2 )
1
𝜀𝑎𝑏
+
𝐴𝑎𝑏
𝐴𝑣
(
1
𝜀𝑣
−1)
The mirror efficiency factor 𝐹′is determined as [10, 11]:
𝐹′ =
1
𝑈𝐿
1
𝑈𝐿
+
𝐷0
ℎ𝑓𝑖𝐷𝑖
+(
𝐷0
2𝐾𝐹
ln
𝐷0
𝐷𝑖
)
The internal convection coefficient of the absorber is [10]:
ℎ𝑓𝑖 =
𝑁𝑢 𝐾𝐹
𝐷𝑖
As shown schematically in Fig. 2(a), the parabolic-trough
concentrator is coupled to a single-stage H₂O–LiBr absorp-
tion chiller. Thermal energy is delivered via a circulating
heat-transfer fluid, driven by a pump, to ensure heat ex-
change in the generator between the H₂O–LiBr solution and
the heating water. The refrigeration cycle operates through
the chemical absorption of the H₂O/LiBr solution, governed
by the operating temperatures and pressures of each sub-
system component.
An absorption system, Fig. 2(b), comprises first the set
(condenser, expansion valve, evaporator) through which
only the pure refrigerant circulates. This set is connected to
the chemical section of the process, which alters the state
of the evaporated refrigerant so that it becomes condensa-
ble at the temperature of the environment.
148
Відновлювана енергетика. № 1/2026 | Сонячна енергетика
а) b)
Fig. 2. (a) Schematic of a solar absorption refrigeration system coupled with a solar collector. (b) Pressure–temperature
diagram for the refrigeration cycle
Two balances – mass and solute concentration – can be
written at the absorber (Fig. 3):
𝑚𝑓 +𝑚𝑔 −𝑚𝑎 = 0(overall H2O-LiBr–solution balance),
𝑚𝑔 𝑋𝑐 −𝑚𝑎 𝑋𝑑 = 0(LiBr balance),
where 𝑋𝑐is the mass fraction (title) of the concentrated so-
lution leaving the generator and entering the absorber, and
𝑋𝑑 is the mass fraction of the binary mixture, rich in refrig-
erant, leaving the absorber and entering the generator.
Fig. 3. Absorber balances
Enthalpy balances for each component
• Condenser: 𝑄𝑐 = 𝑚𝑓 (ℎ8 − ℎ7)
• Evaporator: 𝑄𝑒 = 𝑚𝑓 (ℎ10 − ℎ9)
• Generator: 𝑄𝑔 = 𝑚𝑓 ℎ7 +𝑚𝑔 ℎ4 −𝑚𝑎 ℎ3
• Absorber: 𝑄𝑎 = 𝑚𝑔 ℎ6 +𝑚𝑓 ℎ10 −𝑚𝑎 ℎ1
• Pump: 𝑊 = 𝑚𝑎 (ℎ2 − ℎ1)
Flow ratio
The Flow ratio 𝐹𝑅(specific flow rate of the H2O-LiBr solu-
tion) is defined as
𝐹𝑅 =
𝑋𝑐
𝑋𝑐 − 𝑋𝑑
=
𝑋6
𝑋6 − 𝑋1
Coefficient of performance (COP)
The COP of the absorption machine is then
𝐶𝑂𝑃 =
𝑄𝑒
𝑄𝑔 +𝑊𝑃
=
(ℎ10 − ℎ9)
ℎ7 + (𝐹𝑅 − 1)ℎ4 − 𝐹𝑅(ℎ3 + ℎ1 − ℎ2)
Thermophysical property calculations (𝑯𝟐O–LiBr)
To evaluate performance, the thermodynamic properties
(pressure, enthalpy, concentration) of the H2O-LiBr pair at
each cycle state point were computed from the thermody-
namic relations derived from the analytical Gibbs-energy
formulation, as follows.
1. Saturation pressure of water (high and low), Dupré
formula [14]
𝑃𝑒𝑞 = 𝑃𝑐𝑒𝑥𝑝(
𝑇𝑐
𝑇𝑘
∑𝛼)
With
• 𝛼 =
𝑇𝑐
𝑇𝑘
(−7.85823 𝑇0 + 1.83991 𝑇0
1.5 − 11.7811 𝑇0
3 − 22.6705 𝑇0
3.5 − 15.9393 𝑇0
4 + 1.77516 𝑇0
7.5)
𝑇0 = 1 −
Tk
Tc
• Tc = 647.14𝐶°
• Tk = 𝑇 + 273.15
• Pc = 22064𝐾𝑝𝑎
• Enthalpy of water (refrigerant) as a fun
149
Відновлювана енергетика. № 1/2026 | Сонячна енергетика
• ction of temperature, 𝒉(𝑻)
• Liquid enthalpy ℎliq[15]
hliq(T) = CP. T
Where Cp = 4.185 2 (Kj/Kg °C)
• Saturated-vapor enthalpy ℎvap(𝑇)[16]
ℎvap(𝑇) = −125397 × 10−8 𝑇2 + 1.88060937 𝑇 + 2500.55
• Superheated-vapor enthalpy ℎsurch(𝑇, 𝑃)[17]
ℎsurch(𝑇) =
(ℎ𝑠ℎ2 − ℎ𝑠ℎ1) 𝑇
100
+ ℎ𝑠ℎ1
Equilibrium pressure of the H2O/LiBr mixture 𝑷(𝑻, 𝑿)[17]
log𝑃 = 𝐶 +
𝐷
𝑇𝑟 + 273.15
+
𝐸
(𝑇𝑟 + 273.15)2
with, 𝐶 = 7.05, 𝐷 = −1596.49, 𝐸 = −104095.5, and
• Tr =
−2E
(D+[D2−4E(C log P)]0.5)−273.15
• 𝑇sol = ∑𝐵 + 𝑇𝑟∑𝐴
Mixture enthalpy 𝒉(𝑻,𝑿)for H2O/LiBr [17]
• For 0% < 𝑋 < 40%:
ℎ = [𝐴0𝑋
0 + 𝐴1𝑋
1 + 𝐴2𝑋
2 + 𝐶𝑇 (𝐵0𝑋
0 + 𝐵1𝑋
1 + 𝐵2𝑋
2)] × 3.326
where , 𝐶𝑇 = (
9
5
𝑇) + 32
• For 40% < 𝑋 < 70%:
ℎ = ∑𝐴 + 𝑇∑𝐵 + 𝑇2∑𝐶
Mixture density 𝒅LiBr(𝑻,𝑿)[18]
𝑑LiBr =
1145.36 + 470.84𝑋 + 1374.79 𝑋2
1000
− (33.3393 + 0.51749 𝑋)
𝑇 + 273.15
100000
Results and Discussion
The thermal and dynamic calculations for our system were
performed using a computational code implemented in
MATLAB. The geometric and optical characteristics of the
collector were carefully selected from the parabolic-
trough (CCP/PTC) data provided by Sandia National Labor-
atories (SNL) and are reported in Table [7].
Table. Optical and geometric characteristics of the stud-
ied solar concentrator
Characteristic Value
Mirror length 𝐿(mm) 7800
Mirror width 𝑙(mm) 5000
Absorber outer diameter 𝐷𝑜(mm) 70
Absorber inner diameter 𝐷𝑖(mm) 66
Glass envelope outer diameter 𝐷𝑉𝑜(mm) 115
Glass envelope inner diameter 𝐷𝑉𝑖(mm) 109
Absorber-tube emissivity 0.14
Glass-envelope emissivity 0.89
Intercept factor 𝛾 0.92
Mirror reflectance 𝜌𝑚 0.92
Glass transmittance 𝜀𝑣 0.95
Absorber absorptance 𝛼𝑎𝑏 0.904
Fig. 4 shows the evolution of solar irradiance from sunrise
to sunset on 3 July 2025. Solar irradiance was computed us-
ing the Capderou model [6], which is the reference model
most commonly used in the Algerian atlas. As indicated in
the figure, at noon the global solar irradiance reaches 1100
W·m⁻², while the direct component attains 975 W·m⁻²; by
19:00, irradiance drops to 2 W·m⁻². Overall, the calculations
yield satisfactory radiative results, supporting the design
and deployment of a solar-collector field sized as needed
for the study area.
The optical efficiency of the solar collector is directly deter-
mined by the concentrator’s geometric and optical proper-
ties. As shown by the thermal-efficiency formulation, sev-
eral terms act directly on the parabolic-trough’s optical
efficiency. Some are intrinsic to design and manufacture—
most notably the intercept factor 𝜸, which sets the fraction
of direct solar radiation captured by the absorber tube and
is on the order of 95%. Mirror reflectance 𝝆𝒎is likewise
high (≈ 95%) and depends on mirror cleanliness. The glass-
envelope transmittance 𝝉 for solar radiation is also around
95%, while the absorber absorptance 𝜶𝒂𝒃 governs the por-
tion of direct solar input actually absorbed. These values do
not account for additional influences with immediate im-
pact, including environmental soiling (dust), alignment or
assembly errors, and related factors.
150
Відновлювана енергетика. № 1/2026 | Сонячна енергетика
0 5 10 15 20 25
0
200
400
600
800
1000
1200
S
o
la
r
ra
d
ia
ti
o
n
(
W
/m
2
)
Time (hour)
global radiation
direct radiation
diffuse radiation
Fig. 4. Solar irradiance profile for 3 July 2025
From Fig. 5, the optical efficiency 𝜂optreaches 77.52%, the
highest value obtained by the collector, and remains essen-
tially stable over the day owing to continuous solar track-
ing. The maximum thermal efficiency 𝜂thattains 65.27% at
12:30, corresponding to the peak of useful energy delivered
by the concentrator.
6 8 10 12 14 16 18 20
0,0
0,2
0,4
0,6
0,8
thermal efficiencie
optical efficiencie
E
ff
ic
ie
n
c
ie
Time (hour)
Fig. 5. Diurnal evolution of the parabolic-trough collector’s (PTC) optical and thermal efficiencies on 3 July 2025
Fig. 6 shows the time evolution of the heat-removal factor
𝐹𝑅and the collector efficiency factor 𝐹′over the study day,
from sunrise to sunset. The coefficient 𝐹′is defined as the
thermal resistance between the absorber and the ambient
relative to the resistance between the fluid and the ambi-
ent. In this study, 𝐹′was 0.6471 at sunrise, 0.5399 at mid-
day, and 0.6506 at sunset.
Regarding 𝐹𝑅, it is presented here as the mirror efficiency
factor, expressing the ratio of the actual energy transfer to
the maximum possible transfer. It is known that 𝐹𝑅varies
with two parameters—𝐹′ and the overall loss coefficient
𝑈𝐿 . According to Figure 6, 𝐹𝑅 and 𝐹′evolve in parallel,
although 𝐹′shows the larger relative variation. We observe
𝐹𝑅 = 0.6421at sunrise, a minimum of 0.5287 at mid-day,
and 0.6450 at sunset.
Coating the absorber tube with a transparent surface re-
duces heat loss between the absorber and the glass enve-
lope. It retains more of the incident solar radiation and lim-
its dissipation to ambient air by radiation and thermal
convection, since the glass is opaque to the long-wave
emission from the absorber. To further limit these losses,
one may use a selective surface on the absorber tube or
create an evacuated annulus between the absorber and the
glass envelope to suppress convection and conduction.
Solar radiation -inclined at 30°- July 3, 2025
151
Відновлювана енергетика. № 1/2026 | Сонячна енергетика
6 8 10 12 14 16 18 20
0,52
0,54
0,56
0,58
0,60
0,62
0,64
0,66
FR
F'
F
R
e
t
F
’
Time (hour)
Fig. 6. Evaluation of the heat-removal factor (FR) and the mirror efficiency factor (F′)
As shown in Fig. 7, the overall thermal loss coefficient
𝑈𝐿peaks at 7.513 W/m²·K at 12:30, and decreases to 4.352
W/m²·K at the beginning and end of the day. This is signifi-
cant; mitigation requires assessing direct solar irradiance,
outdoor air temperature, and wind speed. These drivers are
necessary to improve collector performance and efficiency.
6 8 10 12 14 16 18 20
4,5
5,0
5,5
6,0
6,5
7,0
7,5
8,0
U
L
(
W
/m
2
.K
)
Time ( hour)
Fig. 7. Evaluation of the overall heat-loss coefficient (𝑈𝐿) as a function of time
To validate our single-stage H₂O–LiBr absorption chiller
model, we compared our computed COP (Fig. 8) with the
results reported by Romero et al. [5]. The selected operat-
ing temperatures are:
• Generator temperature 𝑇𝑔: 65–90 °C
• Condenser temperature 𝑇𝑐: 43 °C
• Absorber temperature 𝑇𝑎: 40 °C
• Evaporator temperature 𝑇𝑒: 7–10 °C
• Heat-exchanger effectiveness: 𝜂 = 0.70
The agreement between our calculations and the literature val-
ues is good, supporting the fidelity of the implemented model.
Fig. 9 shows how the coefficient of performance (COP)
varies with generator temperature 𝑇𝑔, for 𝑇𝑎 = 40∘C,
𝑇𝑐 = 43∘C, 𝑇𝑒 = 7∘C, and heat-exchanger effectiveness
= 0.70. The COP increases roughly linearly between 80
and 90 °C. From about 95 °C, it tends to level off and
reaches a stable value of 0.71 once 𝑇𝑔 > 105∘C. Near 110
°C, crystallization (“gelling”) begins as solids form and
block fluid circulation. To prevent this, control the salt
concentration, use efficient pumps and heat exchangers,
and keep both temperature and flow rate within their
safe operating ranges.
152
Відновлювана енергетика. № 1/2026 | Сонячна енергетика
65 70 75 80 85 90
0,45
0,50
0,55
0,60
0,65
0,70
0,75
Romero et al [5]
Nos calcul (Te=2°C) C
O
P
Tg (°C)
Fig. 8. Comparison of our results with those of Romero and al. [5]. Conditions: 𝑇𝑎 = 30∘𝐶, 𝑇𝑐 = 30∘𝐶, 𝑇𝑒 = 2∘𝐶, heat-
exchanger effectiveness (𝐸𝐹𝐹) = 0%
85 90 95 100 105 110
0,40
0,45
0,50
0,55
0,60
0,65
0,70
C
O
P
Tg (°C)
COP
Fig. 9. COP versus generator temperature
Fig. 10 shows the variation of the coefficient of perfor-
mance (COP) with evaporator temperature 𝑇𝑒for differ-
ent generator temperatures 𝑇𝑔. COP increases as the
evaporation temperature rises. In addition, higher gen-
erator temperatures yield a higher COP for the ma-
chine.
7 8 9 10 11 12
0,56
0,58
0,60
0,62
0,64
0,66
0,68
0,70
0,72
0,74
0,76
Tg=85 °C
Tg=90 °C
Tg=95 °C
Tg=100 °C
Tg=105 °C
Tg=110 °C
C
O
P
Te (°C)
Fig. 10. COP versus 𝑇𝑒for different 𝑇𝑔values. Conditions: 𝑇𝑎 = 40∘𝐶, 𝑇𝑐 = 42∘𝐶, heat-exchanger effectiveness = 0.70
153
Відновлювана енергетика. № 1/2026 | Сонячна енергетика
Fig. 11 illustrates the performance of the solar absorption re-
frigerator over a July summer day. The solar coefficient of per-
formance (SCOP) peaks at 0.4736 at noon, when irradiance is
highest, and falls to zero at sunrise and sunset. This pattern
underscores the system’s dependence on the intensity of solar
radiation intercepted by the concentrator throughout the day.
6 8 10 12 14 16 18 20
0,0
0,1
0,2
0,3
0,4
0,5
COPS
C
O
P
S
Time (hour)
Fig. 11. Time profile of SCOP on 3 July 2025
Conclusion
This study develops a dynamic simulation of a single-stage
solar absorption cooling system using the water–lithium
bromide (H₂O–LiBr) pair to cool a conference room sched-
uled for the summer day 03/07/2025. We first formulated
a mathematical model for the cylindro-parabolic collector
and another for the cooling subsystem. Balance equations
were written for every component in both units, and a
MATLAB program was implemented to simulate system be-
haviour under the site’s specific climatic conditions. We
then examined diurnal variations in solar irradiance, the
collector’s thermal efficiency 𝜂𝑡ℎ, the heat-removal factor
𝐹𝑅, the collector efficiency factor 𝐹′, and the overall heat-
loss coefficient 𝑈𝐿 . Finally, we validated the computed co-
efficient of performance (COP) by analysing its sensitivity to
generator and evaporator temperatures, with the aim of
characterising the time evolution of the solar coefficient of
performance over the study day.
Findings:
• The global solar irradiance 𝐼𝐺 reached a daytime maxi-
mum of ≈ 1100 W·m⁻².
• The collector’s maximum thermal efficiency 𝜂𝑡ℎwas
65.27%, and the optical efficiency 𝜂𝑜𝑝was 77.52%.
• The heat-removal factor 𝐹𝑟and the collector efficiency
factor 𝐹′evolved in parallel; the maximum 𝐹′was
0.6506 early in the day, while at noon it was 0.5399.
• The overall heat-loss coefficient 𝑈𝐿peaked at ≈ 7.513
W·m⁻²·K-1.
• The calculated COP values agree with Romero et al.;
the maximum COP was 0.71.
• As evaporator temperature increases, COP increases;
higher generator temperatures further enhance per-
formance.
• The highest solar performance (SCOP) at noon was
0.4736.
• The maximum solar performance (SCOP) attained by
the system was 0.4736.
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|
| id | veorgua-article-602 |
| institution | Vidnovluvana energetika |
| keywords_txt_mv | keywords |
| language | English |
| last_indexed | 2026-07-19T01:18:39Z |
| publishDate | 2026 |
| publisher | Institute of Renewable Energy National Academy of Sciences of Ukraine |
| record_format | ojs |
| resource_txt_mv | veorgua/b9/cd3a3cd1764dbcd546333c78c54b24b9.pdf |
| spelling | veorgua-article-6022026-07-18T06:32:24Z NUMERICAL ESTIMATION OF THE SOLAR COPS PERFORMANCE OF A SINGLE-STAGE ABSORPTION REFRIGERATION MACHINE FOR AIR-CONDITIONING A BUILDING ЧИСЕЛЬНА ОЦІНКА СОНЯЧНОГО КОЕФІЦІЄНТА ПРОДУКТИВНОСТІ (COPS) ОДНОСТУПЕНЕВОЇ АБСОРБЦІЙНОЇ ХОЛОДИЛЬНІЙ МАШИНИ ДЛЯ КОНДИЦІЮВАННЯ БУДІВЛІ Mokhtari Fatima , Z. Mokhtari Abderahman , M. Mekroussi , Saïd concentrator; thermal efficiency; absorption; solar radiation; cooling; cylindro-parabolic; COP; absorber; Capderou; heat transfer fluid. концентратор; теплова ефективність; абсорбція; сонячне опромінення; охолодження; циліндропараболічний; COP; абсорбер; модель Капдеру; теплоносій. This study numerically investigates a solar absorption chiller coupled with a cylindro-parabolic (parabolic-trough) collector to air-condition an amphitheater at Ibn Khaldoun University in Algeria’s High Plateaus, specifically the city of Tiaret, whose astronomical coordinates recorded by the Ain Bouchakif meteorological station are: 35.21° N latitude, 1.28° E longitude, and 1000 m altitude, for a summer day in July. The hourly evaluation of the chiller’s solar coefficient of performance (SCOP) over the summer day considered the region’s solar irradiance and the thermal characteristics of the solar collector, whose geometric and physical properties were selected for this purpose. The solar COP obtained for our system reached approximately 0.4736, a considerable and acceptable value. У цьому дослідженні здійснено чисельний аналіз продуктивності сонячної абсорбційної холодильної машини, поєднаної з циліндропараболічним (параболоциліндричним) колектором, для кондиціювання амфітеатру Університету Ібн Хальдуна у регіоні Високих плато Алжиру, а саме в місті Тіарет, астрономічні координати якого, зафіксовані метеорологічною станцією Айн-Бушакіф, становлять: 35,21° пн. ш., 1,28° сх. д., висота – 1000 м над рівнем моря, для літнього дня в липні. Погодинне оцінювання сонячної продуктивності холодильної машини (COP) протягом літнього дня здійснювали з урахуванням показників сонячного опромінення в регіоні та теплових характеристик сонячного колектора, геометричні й фізичні параметри якого були обрані для цієї мети. Отримане для системи значення сонячного коефіцієнта продуктивності (COP) становило приблизно 0,4736, що є досить значним і прийнятним показником. Institute of Renewable Energy National Academy of Sciences of Ukraine 2026-03-28 Article Article application/pdf https://ve.org.ua/index.php/journal/article/view/602 10.36296/1819-8058.2026.1(84).145-154 Vidnovluvana energetika ; No. 1(84) (2026): Scientific and applied Journal renewable energy ; 145-154 Возобновляемая энергетика; ##issue.no## 1(84) (2026): Scientific and applied Journal renewable energy ; 145-154 Відновлювана енергетика; № 1(84) (2026): Науково-прикладний журнал Відновлювана енергетика; 145-154 2664-8172 1819-8058 10.36296/1819-8058.2026.1(84) en https://ve.org.ua/index.php/journal/article/view/602/513 Copyright (c) 2026 Z. Mokhtari Fatima , M. Mokhtari Abderahman , Saïd Mekroussi https://creativecommons.org/licenses/by-nc-nd/4.0 |
| spellingShingle | concentrator thermal efficiency absorption solar radiation cooling cylindro-parabolic COP absorber Capderou heat transfer fluid. Mokhtari Fatima , Z. Mokhtari Abderahman , M. Mekroussi , Saïd NUMERICAL ESTIMATION OF THE SOLAR COPS PERFORMANCE OF A SINGLE-STAGE ABSORPTION REFRIGERATION MACHINE FOR AIR-CONDITIONING A BUILDING |
| title | NUMERICAL ESTIMATION OF THE SOLAR COPS PERFORMANCE OF A SINGLE-STAGE ABSORPTION REFRIGERATION MACHINE FOR AIR-CONDITIONING A BUILDING |
| title_alt | ЧИСЕЛЬНА ОЦІНКА СОНЯЧНОГО КОЕФІЦІЄНТА ПРОДУКТИВНОСТІ (COPS) ОДНОСТУПЕНЕВОЇ АБСОРБЦІЙНОЇ ХОЛОДИЛЬНІЙ МАШИНИ ДЛЯ КОНДИЦІЮВАННЯ БУДІВЛІ |
| title_full | NUMERICAL ESTIMATION OF THE SOLAR COPS PERFORMANCE OF A SINGLE-STAGE ABSORPTION REFRIGERATION MACHINE FOR AIR-CONDITIONING A BUILDING |
| title_fullStr | NUMERICAL ESTIMATION OF THE SOLAR COPS PERFORMANCE OF A SINGLE-STAGE ABSORPTION REFRIGERATION MACHINE FOR AIR-CONDITIONING A BUILDING |
| title_full_unstemmed | NUMERICAL ESTIMATION OF THE SOLAR COPS PERFORMANCE OF A SINGLE-STAGE ABSORPTION REFRIGERATION MACHINE FOR AIR-CONDITIONING A BUILDING |
| title_short | NUMERICAL ESTIMATION OF THE SOLAR COPS PERFORMANCE OF A SINGLE-STAGE ABSORPTION REFRIGERATION MACHINE FOR AIR-CONDITIONING A BUILDING |
| title_sort | numerical estimation of the solar cops performance of a single-stage absorption refrigeration machine for air-conditioning a building |
| topic | concentrator thermal efficiency absorption solar radiation cooling cylindro-parabolic COP absorber Capderou heat transfer fluid. |
| topic_facet | concentrator thermal efficiency absorption solar radiation cooling cylindro-parabolic COP absorber Capderou heat transfer fluid. концентратор теплова ефективність абсорбція сонячне опромінення охолодження циліндропараболічний COP абсорбер модель Капдеру теплоносій. |
| url | https://ve.org.ua/index.php/journal/article/view/602 |
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