Adsorption ice water generator,
solar radiation, cooling
Michał TURSKI, Robert SEKRET*
EXPERIMENTAL TESTS OF AN ADSORPTION COOLING
SYSTEM SUPPLIED BY SOLAR RADIATION ENERGY
The article summarizes the results of experimental testing of a system utilizing solar radiation
energy for driving an adsorption ice water generator. A testing stand is presented, which is composed
of four modules, each of them being designed for: solar radiation energy generation, accumulation,
transfer and use, respectively. Ice water generator operation parameters, i.e. pressure, temperature,
refrigeration power, thermal power demand and the refrigeration Coefficient of Performance (COP)
as a function of time and the unit’s refrigeration power as a function of evaporator temperature, are
also provided.
Additionally, the effect of weather conditions variation on the operation of both the cooling unit
and the whole cooling system has also been considered.
1. SOLAR RADIATION POTENTIAL IN POLAND
Based on the analysis of many years’ surveys it has been observed that the
magnitudes of direct solar radiation in Poland are 600–800 W/m2, while the values of
total radiation are contained in the range of 1000–1100 W/m2 [1]. The quantities of
direct and scattered solar radiation in particular months are shown in Figure 1. By
analyzing the operation conditions of buildings as an energy system it can be stated
that the maximum demand for refrigeration occurs during the maximum gains of solar
radiation, i.e. in summertime. This relationship is given in Figure 2. It should be noted
here that this arises an interest in the possibility of utilizing this relationship for
building cooling purposes. Moreover, as has been shown by research [3], systems
utilizing solar radiation energy can be successfully used even in countries with a
moderate climate.
* Czestochowa University of Technology, Department of Heating, Ventilation and Air Protection,
ul. J. H. Dabrowskiego 71, 42-201 Czestochowa, Poland
Fig. 1. Amount of direct and scattered radiation,
respectively, in respective months in the
territory of Poland [2].
Fig. 2. Unit solar radiation gain and demand for
heat and refrigeration, as dependent on the
season, acc. to [2].
2. ADSORPTION COOLING SYSTEM TESTS
2.1. DESCRIPTION OF THE TESTING STAND
The testing stand consisted of four basic modules: a generation module, an
accumulation module, a transfer module and an energy use module. The generation
module was responsible for the efficiency of heat and refrigeration. It included a
battery of solar collectors, an additional heat source and an Adsorption Ice Water
Generator (AIWG). The accumulation module was made up of heat and refrigeration
reservoirs. The analysis of operation of the transfer and use modules allowed the
determination of refrigerating powers possible to be achieved. A general schematic of
the testing stand is shown in Figure 3. For cooling, an adsorption ice water generator
was employed, which was designed and made in the framework of the Promoter’s
Grant N N523 611039. The AIWG is composed of an evaporator, an adsorber and a
condenser. The adsorber and the condenser are additionally equipped with heating
and cooling circuits. As the working medium, water is used, while as the sorption
material – wide-pore silica gel. For testing purposes, heating medium temperatures
possible to be achieved using solar collectors were simulated, i.e. 60oC, 80oC and
95oC. Initial working medium temperatures were also varied to be, respectively, 20oC,
16oC and 12oC. Assuming, based on literature data, the adsorption (refrigeration) time
to be equal to the desorption time, measurements were taken for varying process
durations, i.e. 15/15 min, 30/30 min and 60/60 min., respectively. On account of the
assumed parameters of AIWG operation, 27 tests were set, with three replicates in
each test.
Fig. 3. A schematic of the adsorption cooling system driven by solar radiation energy [4].
2.2. ANALYSIS OF THE RESULTS
From the performed analysis of the obtained results, a number of relationships have
been derived, some of which being presented below. Figure 4 represents the
relationship of pressure and temperature as a function of time. The cooling process
was preceded by the regeneration of the adsorbent at a temperature of 95C. It has
been demonstrated that the cooling process intensity is dependent on the initial
temperature of the working medium in the evaporator. The cooling process runs most
efficiently at a higher working medium temperature, so at 20C the temperature drop
in the cooling process was 10.1C. While at the initial working medium temperature at
a level of 16C and 12C, the temperature decreased by 5.5C and 3.5C, respectively.
An important relationship is also the effect of adsorbent regeneration temperature
on the cooling process efficiency. The relationship of the AIWG refrigerating power
as a function of evaporator temperature, while considering different regeneration
temperatures, is represented in Figure 5. The higher adsorbent bed regeneration
temperature, the more efficiently the process runs. At a regeneration temperature of
95C, the unit achieved a refrigerating power of 0.27kW; at lower bed regeneration
temperatures of 80C and 60C, the refrigerating powers were, respectively, 0.26kW
and 0.19kW. The performed analysis of the results found that the optimal cooling time
in all measurements was about 10-15 min., while at a higher adsorbent bed
regeneration process temperature the effective cooling time is shorter and the process
itself is more intensive and takes about 10 min. At the same time, shortening the
cooling process results in a shortening of the desorption process duration, and so the
adsorbent bed regeneration time. These relationships are illustrated in Figure 6.
Comparison of the refrigerating power of the AIWG with its thermal power demand
for the regeneration process shows that after a maximum refrigerating power has been
reached, the thermal power demand continuously increases, while the refrigerating
power of the unit decreases. Such a relationship confirms the rightness of assuming
the cooling time from 10 min. to 15 min., as dependent on the preceding temperature
of sorbent bed regeneration. The values of the refrigeration Coefficient of
Performance (COP) of the AIWG, as presented in Figure 7, range from 0.4 to 0.68 for
measurements taken after regeneration at 95C and, respectively, from 0.5 to 0.65 and
from 0.4 to 0.5 for regeneration temperatures of 80C and 60C.
Fig. 4. Evaporator pressure and temperature as
a function of time.
Fig. 5. AIWG refrigerating power as a function
of temperature.
Fig. 6. AIWG refrigerating power and thermal
power demand as a function of time.
Fig. 7. AIWG refrigerating Coefficient of
Performance (COP) as a function of time.
3.2. UTILIZATION OF SOLAR RADIATION FOR COOLING PURPOSES
Adsorption cooling systems of high powers (above 50 kW) can efficiently operate
at a feeding medium temperature of 60–95oC, which makes them able to be supplied
by the most widespread (flat liquid) solar collectors, while attaining a COP value in
the range of 0.6–0.7 [2]. In addition, low-temperature waste heat can be utilized for
supplying them. There is also a possibility of their operation with the municipal heat
distribution network. The tests carried out have confirmed that the prototype AIWG
can effectively operate within the feeding medium temperature range of 60–95oC,
while attaining a refrigerating COP value from 0.4 to 0.65. For feeding the Ice Water
Generator tested, e.g. flat liquid solar collectors with an absorber area of 1.82 m2 and
an optical efficiency of 84% can be used in the number of 9 units, which will provide
a refrigerating power of 0.27kW at a feeding medium temperature of 95C and with a
total solar radiation magnitude of approx. 1000W/m2, which occurs in the territory of
Poland in the months June – July. With the total solar radiation magnitude at a level
of approx. 600W/m2, 14 solar collectors would be required in order to obtain the same
refrigerating power. By using the same solar collectors in the number of 7 units, a
refrigerating power of 0.19kW would be provided at a feeding medium temperature of
60C and with a total solar radiation value of approx. 600W/m2, which occurs in the
months April – September. It should be remembered that, notwithstanding the
uncertainty of supplies of renewable source energy, which includes solar radiation
energy, the demand for refrigeration occurs in the period of the largest solar radiation
gains. Therefore, by additionally using cold and heat stores in the form of buffer
tanks, the problems related to daily refrigeration demand and refrigeration process
heat demand will be eliminated.
3. SUMMARY
Adsorption ice water generators supplied by solar radiation energy can be used in
public facilities, single-family houses, sports facilities, as well as in energy-efficient
building. A basis for making the selection of a solar system is the demand for
regeneration heat. The design and use of a solar system in a manner appropriate to the
demand and weather conditions will enable the assumed energy and economic effects
to be achieved. Poland has relatively good conditions for the use of solar radiation
energy, provided that the type of systems and the properties of equipment using this
energy are adapted to the nature, structure and time distribution of solar radiation.
Due to the variation in the intensity of solar radiation energy in the daily cycle, a need
arises for the accumulation of refrigeration in buffer tanks.
REFERENCES
[1] BUDZYŃSKI K., NAROWSKI P.G., CZECHOWICZ J.: Przygotowanie zbiorów
zagregowanych danych klimatycznych dla potrzeb obliczeń energetycznych budynków.
Ministerstwo Infrastruktury, dane źródłowe Instytutu Meteorologii i Gospodarki Wodnej,
Warszawa, 2004
[2] KWIECIEŃ D.: Kolektory słoneczne w solarnych systemach klimatyzacyjnych. Materiały
konferencyjne, Forum Wentylacja, Salon Klimatyzacja, Warszawa, 18-19 marca, 2009
[3] RUBIK M. Klimatyzacja solarna – możliwości i tendencje rozwoju, Ciepłownictwo,
Ogrzewnictwo, Wentylacja nr 10/2006, 34 – 38.
[4] Materiał zawarty we wniosku o grant promotorski nr 83132, rysunek autorski.
[5] Projekt badawczy promotorski N N523 611039: Teoretyczne i eksperymentalne badania
adsorpcyjnych systemów klimatyzacji słonecznej, Politechnika Częstochowska, Wydział
Inżynierii i Ochrony Środowiska, Katedra Ogrzewnictwa, Wentylacji i Ochrony Atmosfery,
Częstochowa, 2011.
BADANIA DOŚWIADCZALNE ADSORPCYJNEGO SYSTEMU CHŁODZENIA
ZASILANEGO ENERGIĄ PROMIENIOWANIA SŁONECZNEGO
W artykule przedstawiono wyniki badań eksperymentalnych instalacji wykorzystującej energię
promieniowania słonecznego do napędu adsorpcyjnej wytwornicy wody lodowej. Zaprezentowano
stanowisko badawcze składające się z czterech modułów: wytwarzania, akumulacji, przesyłu i
wykorzystania energii promieniowania słonecznego. Przedstawiono również parametry pracy wytwornicy
wody lodowej, tj. ciśnienia, temperatury, moc chłodniczą, zapotrzebowanie na moc cieplną i
współczynnik wydajności chłodniczej COP w funkcji czasu oraz moc chłodniczą urządzenia w funkcji
temperatury w parowniku. Dodatkowo rozważony został wpływ zmienności warunków atmosferycznych
na pracę urządzenia chłodniczego, jak i całego systemu chłodzenia.
This scientific research has been financed from the MNiSW (Ministry of Science
and Higher Education) resources allocated for scientific development in the years
2010 – 2011, as Research Promoter’s Project No. N N523 611039.